DSP I and II Resources 2015_SECURED.pdf

DENT 1005 and DENT 2005

School of Dentistry

Dental Science and Practice I and II Resources

DENTAL SCIENCE AND PRACTICE I & II RESOURCES

Prepared by

PROFESSOR GC TOWNSEND

and

ASSOCIATE PROFESSOR TA WINNING

Design, layout and format by the Sharjah Project

School of Dentistry The University of Adelaide

Updated 2014

Contents

Introduction

Recommended Reading ............................................................................. 1

History of Dentistry (Dr J McIntyre) ............................................................. 5

Section I Dental Anthropology

Evolutionary Changes in Skull Form .......................................................... 9

Comparative Anatomy of the Masticatory System ..................................... 13

Genetics and Crown Morphology ............................................................... 18

Genetics and Tooth Size ........................................................................... 22

Forensic Odontology (Dr KA Brown) ........................................................... 24

Bibliography ............................................................................................... 33

Section II Topics in Oral Anatomy

Functions of the Masticatory System I ....................................................... 37

Surface Anatomy of the Oral Cavity ........................................................... 38

Structure of Oral and Dental Tissues ......................................................... 48

Age Changes in Oral Tissues .................................................................... 59

Tooth Identification .................................................................................... 63

Identification of Permanent Teeth ............................................................... 64

Tooth Morphology ...................................................................................... 73

Permanent Dentition ........................................................................... 74

Primary (Deciduous) Dentition ............................................................ 118

Pulpal Anatomy .......................................................................................... 128

Timing and Sequence of Tooth Calcification ............................................. 132

Tooth Eruption and Emergence ................................................................. 138

Anatomy of the Skull .................................................................................. 142

Radiographic Anatomy ............................................................................... 146

Dental Diseases ......................................................................................... 151

Preventive Dentistry ................................................................................... 159

Bibliography ....................................................................................... 165

Section III Occlusion

Morphology of the Dental Arches ............................................................... 169

Concepts of Occlusion ............................................................................... 172

Occlusal Curvatures and Axial Alignment .................................................. 174

Opposing Tooth Contacts in Intercuspal Position ...................................... 179

Mandibular Movements and Positions ....................................................... 185

Functions of the Masticatory System II ...................................................... 191

Glossary

Introduction

This manual presents material related to oral anatomy which is mainly in the Dental Science and Practice stream during the first and second year of the Bachelor of Dental Surgery.

The topics covered in these two years relate to the functional anatomy of the dentition and associated structures, including the following:

evolutionary changes in skull form comparative anatomy of the masticatory system genetics of tooth size and morphology oral surface features the morphology of primary and permanent teeth pulp cavities timing and sequence of tooth calcification and emergence radiographic anatomy dental diseases dental occlusion

Recommended Reading The following books are recommended as sources of additional information to supplement the information presented in this manual.

1 Nelson SJ (2010) Wheelers dental anatomy, physiology and occlusion. 9th ed. WB Saunders, Philadelphia. BSL: 611.314 W56.9 (Main)

2 Ash GM and Nelson SJ (2003) Wheelers dental anatomy, physiology and occlusion. 8th ed. WB Saunders, Philadelphia. BSL: 611.314 W56.8 (Main)

3 Ash GM (1993) Wheelers dental anatomy, physiology and occlusion. 7th ed. WB Saunders, Philadelphia. BSL: 611.314 W56.7 (Joint)

4 Ash MM (1984) Wheelers atlas of tooth form. 5th ed. WB Saunders, Philadelphia. BSL: 611.314 W56a (Main)

5 Ash MM and Nelson SJ (2003) Dental anatomy, physiology, and occlusion. 8th ed. WB Saunders, Philadelphia. (BSL: 611.314 W56.8 (Main)

Introduction

1

6 Bath-Balogh M and Fehrenbah MJ (2006) Illustrated dental embryology, histology and anatomy. 2nd ed. WB Saunders, St Louis. BSB: 611.314 B332i.2 (Reserve and main)

7 Bath-Balogh M and Fehrenbah MJ (1997) Illustrated dental embryology, histology and anatomy. WB Saunders, Philadelphia. BSB: 611.314 B332i (Reserve and main)

8 Berkovitz BKB, Holland GR and Moxham BJ (1992) A color atlas and textbook of oral anatomy, histology and embryology. Wolfe Medical Publications, London. BSL: 611.314 B512c.2 (Main)

9 Berkovitz BB, Moxham BJ and Holland GR (2002). Oral anatomy, embryology and histology. 3rd ed. Mosby, Edinburgh. BSL: 611.314 B512o.3 (Main)

10 Brand RW, Isselhard DE and Satin E (2003)

Anatomy of orofacial structures. 7th ed. Mosby, St. Louis. BSL: 611.31 B817a.7 (Main)

11 Brand RW and Isselhard DE (1998) Anatomy of orofacial structures. 6th ed. Mosby, St. Louis. BSL: 611.31 B817a.6 (Main)

12 Carlsen O (1987) Dental morphology Munksgaard, Copenhagen. BSL: 611.31 C284d (Main)

13 Dixon AD (1986)

Anatomy for students of dentistry. 5th ed. Churchill Livingstone, Edinburgh. BSL: 611.00246176 D619a (Main)

14 Harris NO, Garcia-Godoy F and Nathe CN (2009) Primary preventive dentistry. 7th ed. Pearson, Upper Saddle River, New Jersey. BSL: 617.601 H315p.7 (Main)

15 Harris NO and Garcia-Godoy F (2004) Primary preventive dentistry. 6th ed. Appleton and Lange, Norwalk, Conn. BSL: 617.601 H315p.6 (Main and Reserve)

Introduction 2

16 Harty FJ and Ogston R (1987) Concise illustrated dental dictionary Wright, Bristol. BSL: 617.6003 H337c (Main)

17 Jordan RE and Abrams L (1991) Kraus dental anatomy and occlusion. Mosby Year Book, St. Louis. BSL: 611.314 K91.2 (Main)

18 Kasle MJ (1989) An atlas of dental radiographic anatomy. 3rd ed. WB Saunders, Philadelphia. BSL: 617.607572 K193a.3 (Main)

19 Mitchell DA and Mitchell L (2005) Oxford Handbook of Clinical Dentistry. 4th ed. Oxford University Press, Oxford. BSL: 617.6 M681o.4 (Main)

20 Mitchell L and Mitchell DA (1999) Oxford Handbook of Clinical Dentistry Oxford University Press, Oxford. BSL: 617.6 M681o.3 (Main and Reserve)

21 Mount GJ and Hume WR (2005) Preservation and restoration of tooth structure Knowledge Books and Software, Brighton, Qld. BSL: 617.6059 M928p.3 (Main and reserve)

22 Mount GJ and Hume WR (1998) Preservation and restoration of tooth structure Mosby, London. BSL: 617.6059 M928p (Main)

23 Okeson JP (2003) Management of temporomandibular disorders and occlusion. 5th ed.

Mosby, St Louis. BSL: 617.643 041m.5 (Reserve and Main)

24 Osborn JW (1982) A Companion to Dental Studies (Ed. Rowe, RHR and Johns, RB) Vol 1 Book 2. Dental anatomy and embryology. Blackwell Scientific Publications, Oxford. BSL: 617.6 C737 (Main)

25 Posselt U (1968) Physiology of occlusion and rehabilitation. Blackwell Scientific, Oxford. BSL: 617.623 P856.2 (Main)

Introduction 3

26 Ash MM and Ramfjord SP (1995) Occlusion. 4th ed. WB Saunders, Philadelphia. BSL: 617.643 R1720.4 (Main)

27 Scott, JH and Symons, NB (1982) Introduction to dental anatomy. 9th ed. Churchill Livingstone, Edinburgh. BSL: 611.314 S42i.9 (Main)

28 Teaching Research: A Division of the Oregon State System of Higher Education (1982) Dental anatomy: A self-instructional program. 9th ed. Appleton-Century-Crofts, Norwalk BSL: 611.314 O663d.9 (Main)

29 Thomson H (1990) Occlusion. 2nd ed. Wright, London. BSL: 617.643 T482o.2 (Main and reserve)

30 Van Beek GC (1983) Dental Morphology: an illustrated guide. 2nd ed. Wright, Bristol. BSL: 611.314 V218d (Main)

31 Woelfel JB and Scheid RC (1997) Dental anatomy: its relevance to dentistry. 5th ed.

Williams and Wilkins, Baltimore. BSL: 611.314 W842d (Reserve and Main)

32 Woelfel JB and Scheid RC (2002) Dental anatomy: its relevance to dentistry. 6th ed. Lippincott Williams and Wilkins, Philapdelphia.

BSL: 611.314 W842.6 (Reserve and Main)

Introduction 4

History of Dentistry Although it is uncertain when dentistry was first practised, it is most likely that some form of attention has been given to teeth since ancient times. There are references from as far back as 2700BC from both Egypt and China concerning remedies for toothache. Hippocrates, known as the Father of Medicine, wrote about dental ailments, and also invented crude dental instruments around 430BC.

Pierre Fauchard (1678-1761) has been referred to as the Founder of Modern Dentistry. The first recorded full-time, self-trained dentists began to appear around the end of the 18th Century. During the beginning of the 19th Century the first formal dental training courses commenced in Europe and North America, but progress in the first hundred years was slow. However, by the beginning of the present century, Victoria and NSW had only just established formal dental training courses. In Adelaide, the Faculty of Dentistry came into being in 1921.

The early practice of dentistry was understandably very different from that of the present time. Away from the cities, itinerant dentists would visit communities with portable barber chairs and set these up as required, usually for the extraction of an aching tooth. Although dentists were first involved in the use of general anaesthetics (Dr H Wells, 1844; Dr T Morton, 1846), local anaesthesia did not come into common use until the beginning of the 20th Century, and then only for the extraction of teeth.

With the relatively crude restorative and other equipment, a considerable amount of pain, and thus fear, was associated with dentistry. It is only in the last few decades that this has begun to change. The advent of better anaesthetics or analgesic solutions, the high speed drill for restorative procedures, and a marked emphasis on the prevention of caries and periodontal disease before teeth or gums become too damaged, have helped alleviate this situation.

For further reading concerning the history of dentistry, the following articles are available:

Levine S (1978) Australian dentists and dentistry around 1900. Australian Dental Journal 23(1):14.

Bremner MDK (1964) The Story of Dentistry. Henry Kimptons Medical House London. (Barr Smith

Lib. Ref. No. 617.609. B83.3)

Introduction 5

Introduction 6

Evolutionary Changes in Skull Form

Classification of primates Humans are members of the order Primates, which can be divided into two subgroups:

1. the lower primates (prosimians)

2. the higher primates (anthropoids).

The lower primates consist of 12 species, including lemurs, tree shrews and tarsiers. The higher primates (Anthropoidea) include New World Monkeys (Ceboids), e.g. squirrel monkeys, marmosets and tamarins of South America; Old World Monkeys (Cercopithecoids) which include macaques and baboons; and Hominoidae (Anthropoid apes). The latter group consists of three families of Pongidae, e.g. gorillas, chimps and orangutans; Hylobatidae (gibbons); and Hominidae (humans) which includes the Australopithecus genus and Homo genus. The Homo family includes various species, e.g. H. erectus (fossil), H. neanderthalensis (fossil), H. habilis (fossil) and H. sapiens, which is the only living species remaining.

Trends in primate evolution Early prosimians were arboreal, i.e. they lived in trees. They had prehensile digits, adapted to an arboreal existence, assisting escape from ground predators. Tree life resulted in a number of adaptations, such as opposability of the thumbs and big toes. The hind limbs became important for balance and support. The forelimbs were used for exploring. There was a tendency to sit upright and perch in trees when not moving. Hands were used for taking and putting food in the mouth. Coupled with a freeing of the forelimbs as now these were used to gain access to food, there was a corresponding reduction in the size of the snout as this was no longer the major site of first contact with the environment as was the case when walking on all fours. There was a reduced need for fine olfaction and there was a tendency for more acute vision, with the eyes positioned more anteriorly for stereoscopic vision.

Evolution of higher primates Monkeys became adapted for life in trees such that they developed brachiating (swinging through trees) habits, prehensile tails and the eyes became located in a more anterior position for stereoscopic vision which enabled judging of distances/depth.

Hominoid adaptations followed and are seen in all hominoids, i.e. Pongids, Hylobatids and Hominids, but the changes are more advanced in humans. The probable initial changes involved attainment of an upright posture and bipedal gait (3-4 x 106 years ago) which was accompanied by many changes to both the bones of the trunk and lower limbs as well as the head and neck region. Changes in the vertebrae involved alterations in the shape of the vertebrae and vertebral column with the development of an 'S' shaped curve and loss of tails. Changes in the pelvic girdle were required to transmit the weight of the entire body to the legs as well as assist in supporting the weight of the thoracic and abdominal viscera, such that the pelvic girdle developed with time into a bowl shape, with extensions of bone (sacrum) and ligaments across the birth canal.

Alterations in the head position and balance and/or musculature were needed to allow for the head to be held in a horizontal position. In Pongids this is evident in the extensive musculature and attachments on the posterior aspect of the skull, associated with large prominences (nuchal crest), while in Hominids there was a change in the balance of the head with the foramen magnum in a more inferior position, such that the head became more centred on the vertebrae.

Section I Dental Anthropology 9

This change in balance of the head is evident in the Hominid fossil record. By comparison with other mammals, primates' eyes faced forwards and were closer together, which was accompanied by a reduction in the simultaneous field of vision; however, this forward movement of the eyes enabled the development of specialised vision, i.e. stereoscopic vision. In humans, the loss of simultaneous field of vision was offset by the development of the ability of the head to rotate, mirrored by the development of large sternocleidomastoid muscles which in turn lead to an increased size of the mastoid process. The altered position of the eyes was accompanied by a change in the orbital walls, with the formation of a more complete bony eye socket by the development of a post orbital bar which lead to separation of the orbital cavity from the infratemporal fossa.

Concomitant with the further reduction in snout and removal of the head from the site of first contact with the environment (food and enemies), there was also a reduction in size of jaws and teeth (used for eating and fighting in lower primates, only used for eating in higher primates, e.g. canines decreased in size as they were no longer needed for killing). The forelimbs became the major implement for exploring, under the control of the brain and eyes. This development probably closely paralleled the expansion of the brain, in particular the cerebrum, because of this greater opportunity of exploration offered by the hands and improved vision. The brain assumed a globular shape and the face came to lie below the expanding forebrain. Approximately 2 x 106 years ago a developing social and cultural pattern was evident, with grouping of individuals into families and the development of tools respectively.

Main trends in evolution of skull form Many of these changes occurred concurrently due to various pressures that developed with the attainment of an upright posture. As already noted, there was enlargement of the brain which was more globular, recession of the snout such that the face was positioned below the forehead. The eyes were rotated forward with an orbital ring of bone enclosing the orbit. The foramen magnum became located inferiorly, associated with alteration in balance of the head. There was a reduction in muscularity. (Apes have massive trapezius muscles with extensive nuchal crests to hold the head as they are semi-erect.) The brow ridges, sagittal crest, temporal lines and occipital protuberances all decreased in size, although in humans today there is some sexual dimorphism in these characteristics.

Alterations associated with the dentition and supporting bones included changes in the shape of the arch, from U-shape (e.g. Pongids) to a more parabolic shape which was associated with decrease in the size of the snout. Other changes associated with the loss of the snout involved a reduction in size of the alveolar arches with less alveolar prognathism and overall reduction in jaw size. This resulted in the tendency of the brain and eyes being positioned over the teeth, i.e. orthognathism.

In addition, there has been a reduction in tooth number (mammals - 44 teeth, Prosimians and New World Monkeys (> 25 x 106 years ago) - 36 teeth, Old World monkeys and Anthropoids apes (< 25 x 106 years ago) - 32 teeth) and size with a reduction in importance of teeth for survival, i.e. with respect to killing food and fighting. For example, canines became less important for fighting and canine size reduced markedly (compare canines of pongids and hominids).

One of the more recent changes (approximately 75,000 years ago) associated with the reduction in size of the bones of the jaws, was the development of a chin. It is probable that rather than the development of a bony protuberance as a chin, the marked reduction in alveolar prognathism over time resulted in greater prominence of the anterior portion of the mandible. Development of the chin also may have been associated with the proposed evolution of speech, such that with a decrease in the simian shelf enabling increased movement of the tongue, increased strength for the mandible anteriorly was provided by a chin.


Trends in dentition of primates The general mammalian formula is:

I33 C

11 P

44 M

33 = 44

Prosimians incisors tend to be elongated and procumbent. By comparison with the general mammalian formula, they lose the third incisor and fourth premolar, so their dental formula is:

I22 C

11 P

33 M

33 = 36

New World Monkeys do not have such long snouts as prosimians. They have spatulate incisors, big canines and a diastema between the incisors and canines. Their dental formula is the same as prosimians.

Old World Monkeys have only two premolars in each quadrant. The molar teeth are more specialised with an increase in size of the molar teeth from M1 to M3. The lower third molar has 5 cusps, but molars generally have 4 cusps connected by transverse ridges. They have a specialised lower first premolar (sectorial, i.e. blade-like tooth) with two roots and a posteriorly tilted crown, leaving space for the upper canine when the teeth are in occlusion. This sectorial tooth is probably of major importance in the maintenance of a knife - like posterior edge of the upper canine. Their dental formula is:

I22 C

11 P

22 M

33 = 32

Anthropoid apes have the same dental formula as humans. They have a massive mandible with immense alveolar processes and no chin. The mandible has a shallow sigmoid notch and a simian shelf instead of genial tubercles. The dental arches are U-shaped and the permanent teeth are larger than human teeth. The incisors develop an edge-to-edge bite and canines are big and display sexual dimorphism, such that the canines in the male are particularly large. There is a diastema between upper lateral incisor and canine. The upper premolars have three roots while lower premolars have two roots. The cusps of molars and premolars are more pointed than humans and the lower first premolar is a specialised canine-like tooth (i.e. is single cusped). All cheek teeth have short crowns relative to the total height of the teeth (brachydont). Upper molars have four cusps, while lower molars all have five cusps.

Hominid evolution It seems that Hominidae (the human being phylogenetic line) became separated from the anthropoid apes at about the beginning of the Miocene period (approximately 14 x 106).

Ramapithecus may be representative of human beings' earliest ancestor. Ramapithecus is considered to have evolved approximately 14 x 106 years ago and existed to around 9 x 106 years ago. The fossil was found in India. Characteristics of the dentition included a parabolic dental arch (i.e. not U-shaped), anterior teeth were small compared with molars, the palate was arched and the morphology of teeth was more like human teeth than ape teeth.


Australopithecus is believed to have existed approximately 5-1 x 106 years ago. A number of species have been identified (A. afarensis, A. africanus, A. robustus, A. bosei). Australopithecines almost certainly walked upright but were still ape-like in some respects. They had heavy brow ridges, a relatively small brain (450-650cc), the occipital condyles more anteriorly placed than those of apes, but were not as anterior as those of modern humans, and they possessed a small but typically human mastoid process. They had a massive mandible but no chin, a parabolic dental arch rather than a U-shaped one, the teeth were large and human like but there was an increase in size from M1 to M3.

The various species of the Homo genus, including H. habilis, H. erectus, H. neanderthalensis and H. sapiens, probably diverged from the Australopithecines approximately 2-5 x 106 years ago. H. habilis existed alongside A. afarensis in Africa approximately 2 x 106 years ago. H. habilis had a larger brain capacity (680cc compared with 440cc) and possessed large but human-like teeth. H. erectus existed during the period of approximately 1.5 - 0.5 x 106 years ago. The first fossil of H. erectus was found in Java and others have been found, e.g. a fossil found in China known as Peking man. More human traits were present in H. erectus, e.g. they walked completely upright, the head was better balanced on the vertebral column, the foramen magnum was more forward and mastoid processes were prominent. The mandible was rugged, there was no chin and the teeth were like those of H. sapiens. There also was evidence of a rudimentary culture as various artefacts have been found.

H. neanderthalensis is believed to have evolved approximately 75,000 years ago. H. neanderthalensis demonstrates a large variation in the degree of various characteristics, e.g. there is a range from heavy brow ridges, flat nose, flaring zygomatic arches to more human-like (H. sapiens) forms.

Modern humans (H. sapiens) can be dated to approximately 30,000 to 40,000 years ago, with more archaic forms being identified to have existed more than 100, 000 years ago (e.g. H. neanderthalensis).

Major changes between H. sapiens and H. erectus were:

a further increase in cranial capacity (1300c compared with 850-1050cc) a reduction in the size of the jaws and teeth an increase in height and reduction in antero-posterior length of the skull.

Today there are minor variations in the teeth and skull morphology evident between modern ethnic groups (refer to section on Genetics and Crown Morphology).


Comparative Anatomy of the Masticatory System

Classification of vertebrates Vertebrates possess a vertebral column. Fish (three classes), amphibians, reptiles, birds and mammals belong to the subphylum Vertebrata. Mammals can be divided into primitive and modern forms. Modern mammals include:

monotremes (subclass Protheria), i.e. egg-laying mammals that are only found in Australia, such as the spiny ant eater (echidna) and platypus

marsupials (subclass Metatheria), i.e. opossum (found in South America) and Australian marsupials such as the kangaroo, wombat, koala and Tasmanian tiger (Thylacine wolf)

placental mammals (subclass Eutheria), e.g. o primates - shrews, lemurs, monkeys, apes and humans (refer to Evolutionary

changes in skull form)

o carnivores - cats, dogs, bears, seals and sea lions o rodents - rats, mice, squirrels and guinea pigs o ungulates - horses (odd-toed) and pigs, sheep and cows (even-toed) o cetacean - whales, porpoises, dolphins.

General characteristics of vertebrate dentitions Most fish have teeth, although some have horny keratinised epidermal structures (lamprey) rather than true calcified teeth and some are toothless (sturgeon). The method of attachment of teeth varies from a fibrous attachment in elasmobranchs (sharks and rays) to either a fibrous or ankylosed junction in bony fish. Teeth are usually small and conical (i.e. haplodont - simple cusp shaped), although some bony fish have different shaped teeth (i.e. heterodont as opposed to homodont when all teeth are the same shape). Generally, teeth are continually replaced with successional teeth, i.e. the dentition is polyphyodont (fish have many sets of teeth); however, some fish have a limited number of replacement dentitions. The major function of teeth in fish is to seize or grasp prey.

Amphibians have conical (i.e. haplodont) teeth, which are all the same (i.e. homodont) and are ankylosed and continually replaced (i.e. polyphyodont). Some amphibians do not possess teeth, e.g. toads.

Reptiles typically have a row of only conical or only tricuspid teeth which are similar in shape (homodont) but may vary in size, are ankylosed, simple rooted and are continually replaced.

Some reptiles have a more complex dentition, e.g. the crocodile and alligator have a periodontal membrane, i.e. the teeth are not fused to bone but are in sockets and are attached to bone by fibres, while in some snakes certain teeth are modified to form poison fangs that contain a canal or groove for venom, similar to a hypodermic needle. It is probable that the primitive mammalian dentition was derived from reptilian dentition.

No living birds have teeth, although, fossils show that they may have had teeth in former times.

Primitive mammals existed as early as 150 x 106 years ago. Different classes of teeth were evident, namely incisors, canines and premolars which were all of a simple pattern while the upper molars consisted of a triangular shaped trigon with a buccal amphicone (base of triangle) and lingual protocone. The lower molars consisted of a triangular shaped trigonid (the ending 'id' is used for terms describing lower molars), with a buccal protoconid and two lingual cusps (mesiolingual = paraconid; distolingual = metaconid). The lower molar also possessed a talonid


which was attached to the distal of the triangular trigonid. It is believed that the modern mammalian dentition evolved from this primitive form. The Cope-Osborne tritubercular theory suggests that molars evolved as follows:

Upper molars Amphicone developed two cusps, referred to as the paracone (mesial) and metacone (distal). Together these formed a triangle (trigon), with the protocone (palatal). A talon (heel) with one cusp, called the hypocone, developed on the distal of the trigon, resulting in a four-cusped upper molar. It is this portion of the tooth that shows the greatest variability.

Lower molars A trigonid similar to the trigon of the upper molars developed, with a buccal protoconid, mesiolingual paraconid and distolingual metaconid. A talonid with three cusps, called the hypoconid (buccal), hypoconulid (distal) and entoconid (lingual), developed on the distal of the trigonid. This resulted in a six cusped lower molar tooth. During evolution this six-cusped form evolved to a five-cusped form by loss of the paraconid from the mesiolingual, such that the metaconid became the mesiolingual cusp. In human lower second molars, the hypoconulid (distal cusp) is missing, resulting in a four-cusped tooth.

The complexity of the dentition in modern mammals is partly due to the fact that they have developed the function of chewing food to a high degree. This has resulted from the requirement to thoroughly process food because they rely on the energy produced by their bodies from ingested food to maintain the high rate of metabolism needed to keep warm, i.e. they are homothermic. This enables them to survive in a range of climates, which is in contrast to reptiles that obtain heat from the environment (e.g. the sun) and become inactive when the temperature drops. Small mammals have relatively larger surface areas compared with their volume of muscle by comparison with larger mammals; therefore they take in relatively larger quantities of food.

In contrast to other vertebrates, mammals have flexible (muscular) lips and cheeks which are important in the picking up of food and the positioning of food in the mouth optimal for chewing.

The development of the soft palate allows separation of the mouth and nasal cavities to enable breathing while chewing. In reptiles, these two passages cannot be totally separated, necessitating minimal holding and manipulation of food in the reptilian mouth. Strong muscles of mastication and temporomandibular joints developed from the previous hinge joint, enabling greater movement of the lower jaw and greater bite force.

The eutherian dentition is typically heterodont, i.e. teeth vary in form in different parts of the mouth.

The typical mammalian dentition is:

I33 C

11 P

44 M

33

However, there is considerable variation. Teeth have roots attached by a periodontal ligament to the bony socket. Usually, there are only two sets of dentitions (diphyodont as opposed to polyphyodont), such that successional teeth or permanent teeth replace deciduous teeth. There are also accessional teeth, e.g. molars that emerge posterior to the deciduous dentition. The teeth usually consist of enamel, dentine and cement and the cheek teeth are normally multirooted. Teeth are specialised for function, e.g. fighting and defence (e.g. large canines) and mastication such that teeth interdigitate and occlude. Associated with this latter function are complex crown patterns of molars.


Specific examples of dentition of modern mammals Marsupials show a range of dentition which may resemble carnivores, rodents and ungulates. The adult kangaroo dental formula is:

I31 C

00 P

11 M

55

In young kangaroos the cheek teeth series consists of six teeth on each side, the second is a deciduous molar. This tooth and the one in front of it are replaced by a more distal molar, reducing the cheek series to five molars. In older kangaroos, the cheek teeth continue to be shed from the front and the molars move forward. Sometimes there is only one molar left on each side. This process of replacement of teeth from behind is called horizontal succession. Horizontal succession enables maximum stress to fall on those teeth below the zygomatic arch, so that as teeth wear, they move forward. The lower incisors project forward in line with the body of the mandible (procumbent). These teeth have pointed tips with sharp mesial and distal edges. The cheek teeth have transverse ridges and are well-adapted for an herbivorous diet. The medial pterygoid muscles are well-developed and attach to a deep hollowed-out fossa on the inner angle of the mandible.

In the Eutherian subclass, the elephant also displays horizontal succession in that generally only one molar in a quadrant is in function at any time. There is a limited number (3) of replacement molars, such that the elephants life span is restricted by this, each molar lasting approximately 20 years of function. The dentition of pigs also shows mesial migration and this feature is present in humans to a limited degree.

Dentitions of some members of the Eutherian subclass Primates have many features of the dentition in common, e.g. incisors are spatulate, canines are well-formed and the dentitions are diphyodont. The glenoid fossae and eminences generally are poorly developed except in apes and humans.

Carnivores have a wide range of dentitions ranging from flesh-eaters (cats) through more omnivorous, i.e. plant and animal eaters (dogs) to fish-eaters (seals and sea-lions). A characteristic feature of flesh-eaters in particular is specialisation of one cheek tooth in each quadrant, called carnassial teeth. These teeth consist of a blade-like upper that slices against the buccal of the opposing lower tooth to produce a scissor-like action. These animals also tend to have large canines. The upper lip is divided to provide mobility and possesses special sensory hairs called vibrissae. The temporomandibular joints are purely hinge joints, i.e. only opening and closing movements are possible.

The dental formula for the dog is:

I33 C

11 P

44 M

23

The incisors have a high central cusp with mesial and distal lobes adapted for holding and tearing, the canines are long and strong, while the upper fourth premolar and lower first molars are adapted as carnassial teeth.


The dental formula for the cat is:

I33 C

11 P

32 M

11

The incisors are similar to the dog but the canines are longer and stronger and the premolars and molars are reduced in number.

Rodents have a fairly constant type of dentition. They have chisel-shaped, continually erupting incisor teeth with a diastema between anterior and posterior teeth. There are no canines. The muscles of mastication are complex, especially the masseter muscles which as well as closing the jaws, work with the pterygoids and the temporalis to move the jaw back and forward. The palatal rugae are well-developed and the upper lip is divided.

The dental formula of the rat is:

I11 C

00 P

00 M

33

They only have one dentition, although the incisor teeth continually erupt. The labial surface of the incisors in covered with enamel, which is pigmented due to incorporation of an iron derivative (yellow/orange), while the lingual surface is covered with cementum.

The dental formula for the hamster is:

I11 C

00 P

00 M

33

Hamsters have large buccal pouches that extend along the side of head and neck and open into the oral cavity in the region of the diastema. The pouches are used for storing food.

Ungulates (hoofed animals) consist of two orders: the perissodactyls (odd-toed ungulates) including horses and rhinoceros, and the artiodactyls (even-toed ungulates) including sheep, cattle, pigs, hippopotamus, oxen and deer.

The dental formula of the sheep is:

I03 C

01 P

33 M

33

The upper incisors and canines are absent while the lower incisors and canines are shovel-shaped with sharp incisive edges. The lower incisors bite against a dense pad of mucous membrane in the upper jaw. Behind the lower anteriors there is a diastema separating the anterior teeth from the cheek teeth. The cheek teeth are termed selenodont since the unworn cusps are crescent-shaped.

The teeth also have high crowns which are described as hypsodont. The teeth are well-adapted for a vegetable diet because grass has a high silica content and is very destructive of tooth substance.

The dental formula for the horse is:

I33 C

11 P

44 M

33


16

The crowns of the incisors are columnar and covered by a thin layer of cement. When they first emerge they show a central pit surrounded by an elevated rim, but with wear the enamel of the rim is worn, leaving a central pit, then a circle of dentine, then enamel. The incisors develop an edge-to-edge bite for efficient chewing. In the female horse, the canines are rudimentary or may be absent, but they are small teeth in males. The premolars and molars are all similar in form.

The cheek teeth are hypsodont, i.e. cusps that are greatly elongated. The areas between the cusps are filled in with cement. As the tooth wears, the various dental hard tissues, which wear at different rates, are exposed. The glenoid fossae are flattened with no articular eminence. The capsule of the joint is strong but somewhat lax, which allows a wide range of movements such that extensive side-to-side movements are possible.

Cetaceans include whales, dolphins and porpoises. These are mammals that have returned to life in the sea. The dentitions have undergone a specialised reversion towards a simpler dentition, which is usually conical and homodont. The teeth may be lost altogether. In those members with no teeth, a series of baleen plates suspended from the upper jaw develop. These act as sieves for catching vegetable matter and plankton. Baleen (whalebone) represents exaggerated rugae, i.e. derived from the epithelium of the hard palate.


Genetics and Crown Morphology

When discussing the crown morphology of teeth, consideration should be given to their size and shape and the number of cusps, grooves, ridges etc. There are certain basic features of each tooth which indicate that it belongs to a certain class, but there is also tremendous variability between teeth of the same class. Some of these differences are difficult to define, but many others can be quantified either by measurement (metric characters, e.g. mesiodistal diameter, buccolingual diameter) and scoring (non-metric characters, i.e. the presence/absence or degree of expression of a trait).

For metric characters, we can consider normal and abnormal variation in terms of variation about mean values, i.e. 95% of values for normally distributed characters will fall within two standard deviations of the mean. For non-metric characters, the concept of normality and abnormality can be related to how frequently a character is observed. Characters which only occur in a very small percentage of individuals may be thought of as abnormal. The crown morphology of teeth, whether quantified in metric or non-metric terms, seems to have a reasonably strong genetic basis. It is most likely that a polygenic system is involved in the inheritance of crown morphology.

Studies of crown morphology are useful in many fields, including:

anthropology and genetics, where differences within and between populations are examined

forensic areas to determine the nature and timing of developmental disturbances,

and are relevant to clinical dentistry, e.g. assessment of the likelihood of caries. (Various morphological crown characters are discussed in more detail later in the following pages.)

Shovel shape trait This trait occurs on incisors and canines. It is characterised by prominent marginal ridges and a concave lingual surface, resulting in a shovel-like appearance of the teeth. It is prevalent in

Mongoloid ethnic groups; however, the degree of shovelling varies within populations. Shovelling tends to be more marked on upper teeth than lower teeth and is more often evident in the permanent dentition by comparison with the deciduous dentition. This trait has been noted in both recent and early humans. Males tend to show more pronounced degrees of shovelling. Ridging also may be found on the labial, producing a double shovelling appearance.


Lingual tubercles These tubercules occur on the lingual surface of canines and incisors. They may be single, double or multiple protuberances arising from the cingulum and they may be long pointed projections (more common on permanent teeth) or more rounded. Occasionally, on lower canines the lingual surface may have a double fold produced by an accessory ridge on the lingual and separated from the distal marginal ridge by a groove.

Carabelli trait This trait occurs on the lingual surface of the mesiolingual cusp of the upper first permanent molar and upper second deciduous molar. It is rarely found on other molars. The expression of the trait ranges from a pit, through a groove or double groove to a slight protuberance, small cusp or large cusp. There is a fairly high incidence of this trait in Caucasians (up to 90%) with a lower incidence in Mongoloid races. It is usually expressed bilaterally and appears to have a polygenic mode of inheritance.


Occlusal groove pattern Different groove patterns may be found on lower first permanent molars and lower second deciduous molars. Generally, five cusps can be identified but the groove pattern may vary from a Y to a + or X pattern. The Y form is sometimes called the Dryopithecus pattern because it is characteristic of early hominoid forms.

Protostylid The protostylid is found on the buccal surface of the mesiobuccal cusp of lower first permanent molar and lower second deciduous molar. It is rarely found on other molars. The trait may vary in expression from a groove to cusp. It is common in Mongoloid ethnic groups. The term paramolar cusp has been used to refer to all anomalous cusps on the buccal surface of both upper and lower molars, with the protostylids representing a subgroup of this general classification.


Accessory cusps The lower first permanent molar and lower second deciduous molar may show extra cusps. The sixth accessory cusp, C6, may be found on the distal aspect of the crown of these teeth between the distal cusp and the distolingual cusp. The seventh accessory cusp, C7, occurs between the two lingual cusps of these teeth.

The frequencies of the above characters vary between ethnic groups; therefore, they may be useful in forensic and anthropologic studies. The shovel shape has a high frequency in Mongoloids but a low frequency in Negroid and Caucasoid groups. The Carabelli trait has a low frequency in Mongoloid and Negroid groups but a high frequency in Caucasoids. The protostylids are similar in frequency to the shovel shape trait of anterior teeth, i.e a high frequency in Mongoloids but low frequency in Negroid and Caucasoid groups.

Other characters that also may be useful include:

missing 8s which have a high frequency in Mongoloids and a very low frequency in Negroids and Caucasoids respectively

supernumerary teeth are low in frequency in Mongoloid and Caucasoids but high in frequency in Negroids

abnormal crown morphology that is evident in various disorders such as: - ectodermal dysplasia, which is an X linked recessive disorder in which missing teeth

and cone-shaped teeth are common

- Down syndrome (trisomy 21) which is characterised by small teeth, a high frequency of crown abnormalities and missing teeth

- mental retardation, which may be associated with abnormal crown morphology.


Genetics and Tooth Size

Odontometry Odontometry is the term given to the measurement of teeth. It is of importance in many areas, such as clinical dentistry, human evolution, comparative and forensic odontology and genetic studies. Tooth measurements may be obtained either directly in the clinical situation, which is satisfactory for anterior teeth but difficult for posterior teeth, or indirectly using either radiographs or dental casts.

In clinical dentistry (e.g. orthodontics) measurements of tooth size are often made to predict whether there may be crowding in the arches. A mixed dentition analysis may be performed. The combined mesiodistal diameters of the lower canine, first and second deciduous molars are about 1.7mm greater than combined diameters of lower permanent canine and premolars.

Similarly, the mesiodistal diameters of the upper deciduous canine and molars exceed the permanent successor teeth by about 0.9mm. These differences in space occupied by the deciduous and permanent teeth are called leeway space. In endodontics, the lengths of teeth must be accurately estimated to enable satisfactory completion of a root canal filling.

In human evolution there has been a general reduction in tooth size over the last 100,000 years. Professor Loring Brace has proposed that reduction in tooth size has followed the introduction of a knife and fork culture, with less demands being placed on the dentition. It is likely that reductions in tooth size are secondary to an overall decrease in facial morphology.

In comparative odontology, comparisons of tooth size differences between modern populations have been applied in micro-evolutionary studies, while in forensic odontology tooth size variation may be useful in sex determination.

Genetics In studies of the genetic basis of various morphological features, teeth have a number of advantages. For example, their final size is determined early in life (most crowns are complete by about 7 years of age, refer to Timing and sequence of tooth calcification), they are virtually indestructible, and they can be studied from dental casts. Comparisons can be made between tooth groups, arches, sides etc. Tooth size is a metric character, and shows a continuous range of variability that is normally distributed. The mesiodistal and buccolingual dimensions are commonly used.

Twin and family studies suggest a polygenic mode of inheritance for tooth size. Heritability estimates of about 60% have been determined, i.e. 60% of the total phenotypic variability in tooth size is due to genetic differences between individuals in a population. There is some evidence that the sex chromosomes may influence tooth size, e.g. XYY males have larger teeth than normal.

Whilst genetic factors are important, environmental influences also play a role. This has been demonstrated in animal studies where fluoride incorporated during tooth formation tends to decrease tooth size and also affects tooth morphology: namely, fissure depth and cusp height are reduced. Decreased vitamin A and increased phosphate intake also have been associated with reduced tooth size. Human studies also indicate that environmental influences are important, e.g. low birth weight is associated with smaller teeth, as is maternal hypertension.

Maternal hypothyroidism and diabetes have been associated with large tooth size in offspring.

There is also evidence for an interaction between developing tooth germs influencing tooth size.


Variability Dahlberg has modified the concepts of Butler, resulting in the concept of a morphogenetic field for the dentition, i.e. each tooth class is thought to represent a distinct morphogenetic field under genetic control. Within each field the key tooth is under the strongest genetic control and tends to be most stable with respect to size, shape, timing of emergence and presence or absence. The key tooth is the most mesial tooth in each class, except for the lower incisors where the lateral incisor is the key tooth. The more distal teeth frequently show greater variability.

There is no evidence of directional asymmetry in the dentition, i.e. teeth on one side are not consistently larger than those on the other. There are, however, random, non-directional differences in tooth size between sides, termed fluctuating asymmetry. Experimental evidence indicates that the degree of fluctuating asymmetry is related to stress.

Other factors that influence variability are sex and ethnicity. On average, males tend to have larger teeth than females. This is referred to as sexual dimorphism, the lower canines showing the greatest sexual dimorphism. There also are differences in tooth size between different ethnic groups, e.g. Australian Aborigines have large teeth.


Forensic Odontology

Forensic Odontology may be defined as the application of dental science to the administration of the law and the furtherance of justice. It is the branch of dentistry that deals with the correct professional handling, examination, interpretation, and presentation of dental and oral evidence which may come before the legal authorities.

There are five areas in which forensic odontology has particular application.

1. Identification of living and deceased persons

2. Assessment of age

3. Bite-mark identification

4. Lip-print comparison

5. Assessment of dental injuries

In the performance of these functions, the forensic odontologist works in close cooperation with other members of the investigation team, including police officers, pathologists and technicians.

Evidence revealed by the teeth and mouth Information that may provide important evidence can often be obtained by the careful examination of the dental and oral structures and may indicate or assist in establishing the following:

1. Race

2. Sex

3. Age

4. Occupation

5. Dental treatment

6. Oral hygiene habits

7. Certain systemic diseases

8. Certain forms of treatment of systemic disease

9. Smoking habits

10. Behaviour habits

11. Diet


Age assessment Chronological age assessment may be an important factor in establishing the identity of a living or deceased person. It may also be a critical factor in certain legal proceedings when a specific charge for a particular offence may depend on whether the alleged offender is a juvenile, as, for example, in cases involving refugees or illegal immigrants. The procedures for age determination are complex and involve the consideration of many factors which include:

eruption and emergence times of teeth resorption of roots attrition oral pathology root transparency.

The accuracy of age assessment decreases after eruption of the permanent dentition has been completed.

Identification of dead bodies The legal events consequent upon death are complex and have far-reaching implications. These include:

the settlement of estates and the relief of dependants and relatives the succession of property payment of pensions settlement of life assurance claims remarriage of surviving spouse.

There are also humanitarian factors such as the performance of religious rites in association with the disposal of the remains and the emotional reactions of surviving relations. These events cannot proceed legally until a burial or cremation order is made by the Coroner and a Certificate of

Registration of Death has been issued by the Registrar of Births, Deaths and Marriages. A delay in the issue of these documents, therefore, can cause considerable hardship and distress for relatives and dependants. Correct personal identification is thus of considerable community importance.

Methods of identification Personal identification may be carried out by traditional or scientific methods, as follows:

Traditional

1. Visual recognition by a person to whom the deceased is known well.

2. Personal property comprising identifiable items found on or about the deceased.


Scientific 1. Fingerprints

2. Medical evidence

3. Dental evidence

Limitations of identification methods Any of the above methods may be limited by the circumstances surrounding the death. Post mortem changes to features, as the result of severe mutilation and fragmentation of the face and head, fire damage or decomposition, may alter or destroy the facial features. Personal property is readily transferable and is unreliable. Fingerprints are limited by the availability of a fingerprint record, and by the survival of the skin of the fingers.

Medical identification Medical evidence includes information about race, sex, blood group, height, weight, certain systemic diseases, radiographs and surgical operations.

Dental identification Dental identification depends on the following factors.

1. A comparison of the dental status of the deceased with dental treatment records of a person when identity is known.

2. The unique morphological characteristics of human teeth and dental restorations.

3. The resistance of teeth to environmental changes.

4. The availability of routine dental treatment records.

5. Denture identification: identification marks on dentures.

Dental records The dental records that may prove useful for identification include the following:

1. Charts and treatment records

2. Radiographs

3. Plaster casts of impressions

4. Wax bite records

5. Photographs

Procedures uses in dental identification

1. Proper collection and preservation of post mortem material and other evidence at the scene.

2. Laboratory examinations of post mortem material, including photography, radiography and post mortem impressions.


3. Reconstruction of oral tissues.

4. Collection and interpretation of ante-mortem data (dental records).

5. Comparison of post-mortem and ante-mortem material.

6. Photographic cranio-facial superimposition (if necessary).

7. Correct preparation of reports for Coroner and/or Counsel.

8. Presentation of evidence in court.

Disaster victim identification National disasters include earthquakes, tornadoes, hurricanes, cyclones, floods and fires (forest and bush fires). Artificial disasters include transportation accidents (road, rail, sea and aircraft), explosions and fires in buildings. The potential for loss of life is very great and the existing resources for handling all the consequences are severely taxed. Classification of a minor or major disaster depends upon the number of victims (including deceased, injured survivors and missing).

There are six distinct steps to be carried out in dealing with the victims' remains in a mass disaster:

1. Recovery of the bodies from the site.

2. Identification.

3. Documentation.

4. Repatriation.

5. Disposal of the remains according to the wishes of the relatives and local authorities.

6. Recovery and disposal of victim's property.

Each step must be completed with scrupulous concern for detail, and carried out by the most experienced and competent experts available.

The identification team The identification team includes police officers, forensic pathologists, forensic odontologists and forensic photographers. Mutual trust among the team members is essential. It is important that a forensic odontologist is included in the field team.

Organisation of the identification team There should be two expert teams to work in liaison:

1. a field team (for recovery)

2. a team to collect, evaluate and transcribe the incoming data or dental records.

Standardisation of odontograms The standard notation system is the two digit FDI system.


Comparison of PM and AM data Depending on the number of victims to be identified, the comparison of the post-mortem and ante-mortem data may be made by personal visual comparison of the two odontograms, either by superimposing odontograms on transparencies or by computer programs.

Aircraft accidents Aircraft accidents present special problems. In these situations the identification of victims, in particular the air crew, and also the cause of their deaths, are vital to the investigation of the accident and the prevention of further similar accidents.

Questions to be answered include:

1. How many bodies are there?

2. Who are they?

3. What is their relationship to the accident?

The forensic dentist's role in aircraft accidents

1. Assisting in the recovery of deceased victims and significant identification material.

2. Charting the dentitions.

3. Examination of the oro-facial tissues.

4. Description of head injuries.

5. Interpretation of observations.

6. Making identifications.

Reasons for not identifying victims

1. Bodies not recovered due to:

(a) fire

(b) disintegration

(c) lost at sea.

2. Local difficulties, e.g. terrain, unsuitable facilities, limitation of time under pressure from authorities.

3. Lack of information, e.g. lack of availability of ante-mortem records.

The two golden rules

1. Use all available means of identification.

2. Do not release any of the bodies for burial until all the bodies have been identified as far as is humanly possible.


Bite-marks The investigation of bite-marks, which may be produced in both sexual and non-sexual assaults,

homicide, and also in non-biological materials and objects left at crime scenes, requires the employment of specialised techniques of photography, impression taking and electric microscopy.

In all these procedures the proper collection and handling of the material to ensure the security of the chain of evidence to comply with legal requirements for its acceptability as evidence in a court of law, must be understood and observed. Great care must be exercised in the interpretation of the evidence.

Classification of bite-marks of possible forensic significance

Non-human (animals). Human:

In foodstuffs (e.g. in part-eaten foodstuffs abandoned by offenders at scene of crime).

On non-biological objects (e.g. pencils, pipe-stems, detonators etc).

In human skin: Non-criminal (love-bites).

Criminal (malicious assaults, rape, etc).

These may be:

offensive (upon victim by assailant), or defensive (upon assailant by victim).

Bite-mark sites Bite-marks may be inflicted on almost any area of human skin. Some sites, however, seem more vulnerable than others. Table 1 shows the frequency of occurrence of bite marks in specific areas in a selection of 74 cases reported in Great Britain.

Table 1 Sites of 74 bite-marks in cases reported in Great Britain

Site Number %

Face and/or head 12 16.0

Ear 1 1.4

Nose 1 1.4

Neck 1 1.4

Shoulder 6 8.1

Breast 23 31.0

Arm 5 6.8


Hand and/or finger 5 6.8

Abdomen 10 13.5

Buttocks 3 4.1

Female genitals 2 2.8

Male genitals 1 1.4

Leg 1 1.4

Food 3 4.1

Appearance of bite-marks in foodstuff and skin The appearance of bite-marks in foodstuff varies considerably according to the nature and consistency of the type of food bitten. The tooth marks usually extend through the substance, leaving a sliding appearance. The margins of the surface are therefore often well defined.

The appearance of bite-marks in skin may vary from a faint bruise, or series of bruises, to a well-defined pattern of heavy bruising and even lacerations, in the general shape of the dental arches.

Unlike the marks produced in foodstuff, teeth merely leave impression marks in skin or slight penetration of the epithelium.

The pattern of the bite-mark bears a direct relationship to the shape and arrangement of the teeth and associated structures (lips and tongue) that produced the injury. The bruising is produced by the escape of blood from the subcutaneous capillaries and veins. The colour of the bruise is related to the depth of the injured vessels, the amount of blood released, and the time since the injury was inflicted.

The morphological changes in the skin produced by the forceful application of teeth are permanent if death of the victim occurs at about the time of injury. Because of the elasticity of the skin, in living victims, the morphological changes vanish within about 30 minutes, but sometimes may last longer. It is important, therefore, to begin the examination as soon as possible after the injury is inflicted.

Forensic significance of bite-marks Because of the direct casual relationship between teeth and the marks they inflict on human skin, it may be possible to establish that:

1. a particular lesion was produced by human or animal teeth

2. the marks were produced by a particular tooth or teeth of a suspect.

It may also be possible to exclude a suspect on the basis of the bite-mark evidence.

It may be possible to indicate the force with which the bite was inflicted. This kind of evidence may well be important corroboration in cases of sexual assault.

There is good reason to believe that many bite-marks may not be recognised as such. Some of these may have important significance as evidence in court.


Procedures used in the investigation of bite-marks The examination, investigation and interpretation of bite-marks in skin should be carried out by an experienced forensic odontologist.

The procedures used on victims and suspects and the procedures carried out by the dental laboratory are outlined below.

Victim 1. Visual examination

2. Photographs - colour and black and white

3. Swab for saliva

4. Impressions of skin surface

Suspects 1. Written consent for examination 2. Clinical examination of mouth

3. Saliva swab

4. Photographs - full face and intra oral

5. Full impressions - upper and lower teeth

6. Occlusal registrations in all mandibular positions

Dental Laboratory 1. Make casts of impressions 2. Articulate casts on adjustable anatomical articulator

3. Construct transparent overlays showing occlusal contacts of teeth in various mandibular positions

4. Compare overlays with photographs of bite marks on skin

5. Make stereo-photographic comparison of casts made from impression from skin and casts of teeth of suspects

Recording of bite-marks Records of bite marks are necessary for studying the marks and comparing them with the teeth that produced the marks.

Saliva swabs Saliva swabs should be taken prior to the impressions. These may assist in determining the serotype of the person who produced the mark. Current research into the typing of micro-organism in the saliva transmitted during a bite may provide a further means of comparison in establishing/confirming the identity of the person who produced the bite mark.


Photographs Photographs should be taken in both black and white and colour, and care should be exercised when using a flash which might wash out a faint bruise. Low angled light is important if the marks are deep, and the camera angle should be at 90 with the surface on which the marks appear.

Calibrated adhesive tape or a tape measure should be applied to the surface adjacent to the bite-mark and within the field of the view of the camera. An adhesive identification label, showing date, time and name or reference code, should also be placed on the skin in the field area. Follow-up examination, with photographs, should be made at intervals of one or two days to observe the changing pattern of the bruising until the bite-mark fades.

Impressions Impressions are made directly onto the skin using special micro-replication impression material, e.g. Xantopren and Optosil. The impression should be taken by the person who is to interpret the bite-mark (a forensic odontologist). The impression may be cast to give a positive likeness of the surface of the skin. In the case of living victims, because the marks fade relatively quickly due to the elasticity of the skin, it is important that the impression is taken as soon as possible. The impression should be labelled with the name and date and its orientation properly marked. This should be photographed in situ. After it is set, it should be placed in a labelled plastic bag and taken to the dental laboratory for casting.

Preservation of bite-marks in other materials such as foodstuffs Foodstuffs containing bite-marks are sometimes left at the scene of a crime, and the forensic significance of this evidence is obvious. Preservation of the material with a bite-mark is essential.

The following methods may be used according to the circumstances:

1. Freeze in an air-tight bag in a refrigerator. 2. Preserving fluid - equal parts of glacial acetic acid and alcohol. (Some shrinkage may occur with both of these methods.)

Records of a suspects teeth Consent must be obtained for the clinical dental examination and impressions. If consent is refused, and the suspect is arrested, Section 81 of the Police Offences Act applies (in South Australia). A forensic odontologist is not a medically qualified practitioner as is required by this Act, and one will have to be called to make the examination with the odontologist assisting. A full clinical examination of the suspects mouth should be carried out, and full impressions taken of the upper and lower dentitions. Casts are then made and articulated using bite records obtained from the suspects mouth.


Bibliography Berkovitz BB, Moxham BJ and Holland GR (2002) Oral anatomy, embryology and histology, 3rd ed. Mosby, Edinburgh.

Hillson, S (1996) Dental Anthropology, Cambridge University Press, Cambridge.

Jordan RE and Abrams L (1992) Kraus dental anatomy and occlusion. Mosby Year Book, St Louis.

Osborn, JW (1982) A companion to dental studies. Vol. 1, Book 2. Dental anatomy and embryology. Blackwell Scientific Publications, Oxford. Chapter 11, pp 357-398.

Scott JH and Symons NB (1982) Introduction to dental anatomy. 9th ed. Churchill Livingstone, Edinburgh.

Townsend GC (1978) Genetics of tooth size. Australian Orthodontic Journal 5(4):142-147

Townsend GC (1981) Fluctuating asymmetry in the deciduous dentition of Australian Aboriginals. Journal of Dental Research 60:1849-1857

Townsend GC (1992) Anthropological aspects of dental morphology with special reference to tropical populations. In Oral Diseases in the Tropics ed. Prabhu SR, Wilson DF, Daftary DK and Johnson NW. Oxford University Press, Oxford. Pp 45-58

Townsend GC and Brown T (1981) The Carabelli trait in Australian Aboriginal dentition. Archives of Oral Biology 26:809-814

Townsend GC, Yamade H and Smith P (1990) Expression of the entoconulid (sixth cusp) on mandibular molar teeth of an Australian Aboriginal population. American Journal of Physical Anthropology 82:267-274

Turner CG (1986) Dentochronological separation estimates for Pacific Rim populations. Science 232:1140-1142


Section II Topics in Oral Anatomy

Functions of the Masticatory System I

The masticatory system is involved in incision, mastication and swallowing. Respiration and provision of lip seal, speech and facial expression also involve the teeth.

Mastication Masticatory movements involve movements of the mandible, lips, tongue and cheeks. The reflexes involved in cyclic jaw movements are learned early in life and are refined as teeth emerge. Motor impulses are directed to the masticatory muscles from the brain. Sensory receptors in the TMJs, muscles, periodontium and oral mucosa provide feedback.

Patterns of mastication differ considerably from person to person, although for each individual they are reasonably constant. Other factors influencing the form of the masticatory cycle include: disease, prostheses, ageing and social customs. Generally, a typical chewing pattern consists of a few cycles on one side, then the bolus (food) is moved to the other side by the tongue and cheeks, followed by more chewing. There must be muscle coordination for correct positioning of the food bolus.

Deglutition (swallowing) This process is often divided into four stages:

1. Preparation of the food bolus

2. The passage of the bolus from the mouth to the pharynx

3. The passage of the bolus in the pharynx

4. The passage of the bolus in the oesophagus

The teeth are used to stabilise the mandible in the second stage. This is called somatic swallowing. The teeth come together in the intercuspal position (teeth interdigitate and there is maximal contact). If the tongue is used to stabilise the mandible, e.g. before teeth erupt or in the edentulous person, it is called an infantile or visceral swallow.

Respiration In natural respiration the mandible is generally in the rest position with the lips together. This lip seal helps keep the mouth moist, with breathing occurring through the nose.

Speech Correct positioning of teeth is important in speech. The term closest speaking space is sometimes used because while the incisors are very close when S-sounds are made, they do not generally touch. When dentures are being made, patients are asked to say S-sounds to check on the positioning of teeth.

Facial expression The position of anterior teeth is important in determining facial expression.

Section II Topics in Oral Anatomy 37

Surface Anatomy of the Oral Cavity

It is extremely important to be completely familiar with the surface anatomy of the oral cavity, to be aware of the wide variability in normal appearances, and to be able to distinguish between normal and pathological appearance.

Examinations of the oral cavity should be carried out in a systematic manner and include both soft tissues and hard tissues. Refer to the computer module Tour of the Mouth (available in the Health Sciences Faculty Computer Suite Room) for examples of clinical pictures of the various regions of the oral cavity. You will have an opportunity to work through the module in class. The structure and function of the tissues of the oral cavity will be discussed in more detail in Dental and Health Science II. The anatomy of the underlying regions of the oral cavity will be covered in detail in the Structure and Function Stream, in Second Year.

General structure The oral cavity lies between the hard palate above (roof of mouth) and the floor of the mouth below. Anteriorly it is bounded by the lips and teeth and posteriorly it is continuous with the pharynx through the fauces. The soft palate, at the back of the mouth, and the epiglottis, project into the oropharynx.

The oral cavity can be divided into:

an outer, smaller part called the vestibule (Figs 1a and b) an inner, larger part called the oral cavity proper (Figs 1a and b)

Fig. 1a. Diagrammatic representation of a sagittal section through the head and neck


Fig. 1b. Diagrammatic representation of a coronal section through

the oral cavity The oral vestibule is the slit-like space bounded externally by the lips and cheeks and internally by the alveolar tissues and teeth. It communicates with the exterior through the oral fissure (opening between the lips) and its lateral wall is formed by the buccinator muscle lying deep to the mucous membrane lining of the cheek. The oral cavity proper is bounded laterally and in front by the alveolar arches and teeth. Posteriorly, it communicates with the pharynx through an aperture called the oropharyngeal isthmus (i.e. the interval between the palatoglossal folds, bound superiorly by the soft palate and inferiorly by the posterior third of the tongue). The fauces is the region between the palatoglossal and palatopharyngeal folds. The floor of the mouth is formed by the mylohyoid muscle. The oral cavity proper contains the tongue which is attached to the mandible and the hyoid bone. Lips The lips contain the orbicularis oris muscle and associated elevator and depressor muscles. They are covered externally by skin and internally by mucous membrane. Externally, the nasolabial grooves separate the upper lip and cheeks. They run downwards and laterally from the outer aspect of the nose, lateral to the nostrils, ending near the corners of the mouth (Fig. 2). The philtrum is the medial depression of the upper lip extending from the base of the nose to the vermilion border of the upper lip (Fig. 2). The location of the oral fissure when the lips are resting together generally lies opposite the incisal edges of the upper incisors. Laterally, the lips are connected by the labial commissures at the angles (corners) of the mouth. With the lips at rest, the commissures are normally located in front of the first premolar tooth (Fig. 2). The mucous membrane of the lips is thin and translucent with small mucous glands. The area where the skin and mucous membrane meet, is the vermilion zone (red zone) and consists of modified skin without hair follicles with few sebaceous glands. (The skin contains hair follicles, sebaceous glands and sweat glands.)


Fig. 2 Nose and mouth region

Cheeks The cheeks form a large part of the sides of the face. They are composed mainly of the buccinator muscle, covered externally with skin and internally with mucous membrane that lines the vestibule. They contain mucous and mixed salivary glands that open into the vestibule and fat. The opening of the parotid duct is visible at the parotid papilla, located opposite the upper second molars (Fig 3).

Oral vestibule The oral vestibule, as mentioned previously, is the space between the alveolar tissues and teeth on the inside and the lips and cheeks on the outside (Figs 1a, 1b and 4). Various features of the mucous membrane lining the oral vestibule can be identified. The upper and lower fornices (sulci) are regions of reflection of the mucous membrane from the covering of the alveolus to the covering of the lips and cheeks (Figs 3 and 4). The alveolar mucosa near the fornix is dark red, mobile and non-stippled. The gingivae near the teeth are immobile, pale pink and stippled. The mucogingival junction is the line at the junction of alveolar and gingival mucosa (Fig 4).

The oral vestibule is marked by epithelial folds called frena or frenula. In the midline are the anterior superior and anterior inferior labial frena. There are also lateral frenula (Fig 4). The parotid duct opening (already mentioned) is located in the cheek opposite the maxillary second molars (Fig 3). The maxillary tuberosity is the rounded prominence of bone behind the last upper molar tooth. The region behind the posterior mandibular molar is referred to as the retromolar area or triangle (Fig 3).

Vermilion zone


Fig 3. Intraoral view of the buccal vestibule and cheek

Fig 4. Intraoral view of the vestibule


Gingiva The gingiva can be divided into free and attached gingiva. The free gingiva is the gingiva that is associated with the gingival sulcus, while the attached gingiva is attached to both the tooth and bone.

Between adjacent teeth, the gingiva that is triangular in shape, is referred to as the interdental papilla and may consist of both free and attached gingiva (Figs 5 and 13). Between the labial and lingual interdental papilla is the region of the interdental col, whose surface lining consists of junctional epithelium. In health, the shape of the col follows the contour of the contact point, i.e. it has a concave surface between the interdental papilla. There is a gingival crevice or sulcus surrounding every tooth which in health is about 0.5-2mm deep (Figs 5 and 13). Healthy gingivae attach to the tooth in the region of the cementoenamel junction (Figs 5 and 13) and are pink, firm, well contoured and stippled. In contrast, inflamed gingivae are red, swollen, puffy, non-stippled and bleed readily.

The transition of the gingiva to the alveolar mucosa is demarcated by the mucogingival junction.

Fig 5. Anterior and cross-sectional view of gingiva


Palate The palate is composed of the hard palate and soft palate. The hard palate consists of the palatal processes of the maxillae and the horizontal plates of the palatine bones. It is covered by dense mucous membrane. The soft palate is a mobile muscular attachment at the posterior border of the hard palate. Located on the surface of the palatal mucosa are various anatomical features, including:

the oval or pear-shaped incisive papilla situated behind the incisors (Fig 6) palatine raphe which extends back from the papilla and forms a midline ridge (Fig 6) rugae (transverse palatal folds) which are located anteriorly. They form transverse

ridges on the hard palate and are more developed in carnivorous animals (Fig 6).

Other features associated with the palate are the hamular notch, which is located between the maxilla and the pterygoid plate of the sphenoid bone. The hamular process is the process from the medial pterygoid plate, which can be palpated posterior to hamular notch. The pterygomandibular fold is the fold of mucosa produced by a raphe running from the hamular process to the posterior part of the mylohyoid line on the mandible.

Fig 6a. The hard palate

Fig.6b. Diagrammatic representation of the hard palate.


Fauces The fauces or oropharyngealisthmus is the area or space between the palatoglossal (from palate to tongue) and palatopharyngeal (from palate to pharynx) arches (folds) located laterally and the soft palate superiorly and base of the tongue interiorly. It separates the oral cavity proper from the oropharynx (Fig 7). The folds are formed by muscles (with the same names) located underneath the mucosa. The palatine tonsil lies in the tonsillar fossa located between the pillars (Fig 7). The uvula hangs down at the back of the soft palate (Fig 7) and is continuous laterally with the folds that bound the fauces.

Fig 7. Diagrammatic representation of an open mouth

Pharynx The pharynx constitutes the area behind the nasal and oral cavities and larynx. It is the superior portion of the gastrointestinal tract which connects inferiorly with the oesophagus (Fig 8). It is involved in the passage of food to the oesophagus and air from the nose/mouth through to the larynx and to the lungs. Usually the pharynx is divided into three parts: nasopharynx, oropharynx, laryngopharynx, i.e. those parts lying behind the nasal cavity, oral cavity and larynx respectively (Fig 8).


Fig 8. Diagrammatic representation of a sagittal section through the head and

neck region

Tongue The tongue is a muscular organ with both intrinsic (contained within the tongue) and extrinsic muscles (extensions of muscles outside the tongue, attaching to various bones and soft tissue structures). Openings of minor salivary glands are located posteriorly on the dorsal surface. It can be divided into an anterior 2/3 and a posterior 1/3 by the V-shaped sulcus terminalis (Fig 9). These parts of the tongue have different embryological origins and different nerve supplies. The apex of the sulcus terminalis faces posteriorly and is marked by a pit, the foramen caecum (Fig 9). A shallow median groove extends from the tip of the tongue to foramen caecum. The top/superior surface of the tongue is referred to as the dorsal surface (Fig 9). The ventral (inferior) surface of the tongue is discussed below. The anterior 2/3 of the dorsal surface of the tongue is covered by small projections called papillae, while the posterior 1/3 contains lymphoid tissue.

There are four types of papillae found on the dorsal surface of the tongue:

1. Circumvallate or vallate, which are located immediately anterior to the sulcus terminalis, are 8-12 in number. They are mushroom-shaped, surrounded by deep troughs and taste buds are found on the lateral borders (Fig 9).

2. Fungiform, which are smaller and more numerous, are bright red spots located on the tip and margins of the tongue and carry taste buds (Fig 9).

3. Filiform are minute pointed projections, arranged in rows and covering the dorsal surface of the tongue. Filiform papilla impart the velvety texture of the tongue (Fig 9).

4. Foliate are approximately five short vertical folds on the sides of the tongue near the junction of the anterior 2/3 and posterior 1/3. They also possess taste buds (Fig 9).


Fig 9a. Part of the dorsum of the tongue

Fig 9b. Diagrammatic representation of the dorsal surface of the tongue

Floor of the mouth This includes two areas:

1. Sublingual sulcus, which lies between the tongue and the inner surface of the lower teeth. The position and shape of the sulcus constantly changes with movement of the tongue.

2. Inferior (ventral) surface of the tongue.

Various features of the ventral surface of the tongue can be identified. The lingual frenum, located in the midline, is a crescentic fold of mucous membrane connecting the under-surface of the anterior part of the tongue to the floor of the mouth (Fig 10). The fimbriated folds are fringed folds of mucous membrane on either side of the lingual frenum (Fig 10). Deep lingual veins are located medial to the fimbriated folds. They are bluish in colour and follow a tortuous path (Fig 10).

Prominent features of the sublingual sulcus include the sublingual glands that bulge on either side of the floor of the mouth. On top of each bulge is a delicate fold called the sublingual fold which contains the duct of the submandibular gland. The fold ends medially close to the lingual frenum in a small papilla that is referred to as the sublingual papilla. The submandibular duct opens at the sublingual papilla (Fig 10). Deep to the mucosa in the floor of the mouth is a muscular sling formed by the mylohyoid muscle.


Fig 10. Ventral surface of the tongue and the anterior floor of the mouth

Fig. 10b. Diagrammatic representation of the ventral surface of the tongue

Teeth - These will be described in detail in the following sections.


Structure of Oral and Dental Tissues

This section contains some more detailed information about the histological appearance of the oral and dental tissues. During First Year you are expected to have a good understanding of the basic histological structure of the oral hard and soft tissues. To assist in developing your understanding of this area, refer to histology texts from the Human Biology stream, or refer to oral histology texts, e.g. Avery JK (1992) Essentials of oral histology and embryology. The more detailed aspects of cell types in epithelium and connective tissue will be discussed further next year. Nevertheless, you might like to read about them now!

Oral mucosa Oral mucosa lines the oral cavity. It consists of a covering of stratified squamous epithelium and underlying connective tissue. It is important in protecting the underlying structures from damage such as trauma, bacteria and noxious substances.

Oral mucosa can be divided according to the type of epithelial covering in the various parts of the oral cavity:

Lining mucosa, which has a non- keratinised epithelial covering and is found on the cheeks, lips, soft palate, floor of mouth and ventral surface of tongue.

Masticatory mucosa, which has a keratinised epithelial covering and is distributed over the hard palate and gingiva.

Specialised mucosa, which is a mix of keratinised and non-keratinised epithelium and is located on the tongue (papilla have keratinised epithelium and intervening areas are covered with non-keratinised epithelium) and vermilion border of lip.

Epithelium The epithelial covering of the oral mucosa consists of layers of epithelial cells and can be divided into various layers or strata depending on the morphological and functional characteristics of the cells. The deepest layers of cells of the different types of epithelium have similar properties, while the more superficial cell layers differ. These differences depend on the differentiation pathway of these cells, i.e. non-keratinising or keratinising. Other non-epithelial cells that are found in the epithelium include Langerhans cells, lymphocytes, Merkel cells and melanocytes.

The epithelium of lining mucosa is non-keratinised; therefore, it is less able to resist damage but is capable of distension. The basal layer (stratum basale) is the layer/s of cells closest to the underlying connective tissue. These cells are the least differentiated of the epithelial cells. They are the smallest cells and are cuboidal or columnar in shape. This stratum is the site of cell division and production.

The spinous/prickle layer (stratum spinosum) is the next layer and these cells are larger cells by comparison with the cells in the basal layer. Cells in the prickle cell layer are polyhedral in shape. Cell junctions (i.e. desmosomes) are prominent in this layer. Keratin proteins, in the form of tonofilaments, become evident in this layer. The next layer is the intermediate layer, in which the cells become flattened and there is an increasing percentage of tonofilaments. The last layer of cells forms the superficial layer. These cells demonstrate membrane thickening. The permeability barrier develops in this layer of cells. There are decreased desmosomes between the cells and the nuclei persist. In this layer the cells are desquamated, i.e. they are shed from the surface.

The epithelial covering of the masticatory mucosa is keratinised and, therefore, is mechanically tough. The basal layer is similar to lining mucosa. The next layer is also called the spinous layer. In this layer there is an increase in tonofilaments, increased desmosomes and increased cell volume. The granular layer (stratum granulosum) is so-called because of the presence of basophilic keratohyalin granules. The cells in this layer are flattened cells and there is a decrease in the size of the nucleus. Membrane-coating granules increase in number in this layer. They contribute to the permeability barrier that is found in the adjacent superficial layer, the keratinised layer. In the keratinised layer (stratum corneum)

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