Removable PARTIAL DENTURE THEORY AND PRACTICE

5/30/2018 Removable PARTIAL DENTURE THEORY AND PRACTICE

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Removable PARTIAL

DENTURE THEORY AND

PRACTICE

Mostafa FayadLecturer of Removable Prosthodontic

Faculty Of Dental Medicine

Al-Azhar University

Cairo- Egypt

2011

2nd ed


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Table of contents

Subjects

1 OBJECTIVES AND CLASSIFICATION

2 BIOMICHANICS OF RPD

3 PARTIAL DENTURE DESIGN

4 DENTAL SURVEYOR

5 Denture base

6 RESTS AND REST SEATS

7 CONNECTORS

8 attachment

9 Direct retainers

10 INDIRECT RETAINERS

11 Stress breaker

12 ARTIFICIAL TEETH

13 LABORATORY PROCEDURES

14 Diagnosis of pd patients

15 PREPARATION OF MOUTH

16 IMPRESSIONS FOR REMOVABLEPD

17 ESTABLISHING OCCLUSAL RELATIONSHIPS

18 trial denture stage of treatment

19 Delivery of the RPD fayad

20 POST INSERTION COMPLAINTS RPD

21 MAINTENANCE AND REPAIRE OF RPD

22 Damaging effect

23 PERIODONTAL CONSIDERATIONS

24 Esthetic solutions in RPD

25 Phonitecs in RPD

26 Other Forms of the RPD

27 Swing lock

28 Removable Partial Overdenture

29 Rotational path

30 Temporary RPD

31 RPD in maxillofacial prosthesis

32 C.D opposing P.D

33 MS.ACTIVETY &P D


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OBJECTIVES AND CLASSIFICATION 1RPD THEORY AND PRACTICE

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OBJECTIVES AND CLASSIFICATION OF PARTIAL DENTURES

TERMINOLOGY

Prosthesis: Is an artificial replacement of an absent part of the human body.

Prosthetics: The art and science of supplying an artificial replacement for missing

parts of the human body.

Appliance used only for device worn by patient in course of treatment. e.g.

orthodontic appliance and splint

Prosthodontics: The branch of dentistry pertaining to the restoration and

maintenance of oral functions, comfort, appearance, and health of the patient by

the restoration of natural teeth and/or the replacement of missing teeth and

contiguous oral and maxillofacial tissue with an artificial substitute.

Dentulous Patients: Patients having a complete set of natural teeth.

Edentulous Patients: Patients having all their teeth missing.

Partially Edentulous Patient: Patients having one or more but not their entire

natural teeth missing.

Removable Partial Denture (RPD): An appliance that restores one or more but

not all of the missing natural teeth and associated oral structures for partially

edentulous patients.

Abutment: A tooth, a portion of a tooth, or that portion of a dental implant that

serves to support and/or retain prosthesis.

Free End Edentulous Area (Distal extension edentulous area): An edentulous

area, which has an abutment tooth on one side only.

Bounded Edentulous Area: An edentulous area, which has an abutment tooth on

each end.

Dental cast: a positive life size reproduction of a part or parts of the oral cavity.

The word cast is preferable than word model which used only for demonstration

Andrews Bridge : The combination of a fixed dental prosthesis incorporating a

bar with a removable dental prosthesis that replaces teeth with the bar area,

usually used for edentulous anterior spaces. The vertical walls of the bar may

provide retention for the removable component. By James Andrews.


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Gillett Bridge: Eponym for a partial removable dental prosthesis utilizing a

Gillett clasp system, which was composed of an occlusal rest notched deeply into

the occlusal axial surface with a gingivally placed groove and a circumferential

clasp for retention. The occlusal rest was custom made in a cast restoration.

MORA Device : Acronym for mandibular orthopedic repositioning appliance,

a type of removable dental prosthesis with a modification to the occlusal surfaces

used with the goal of repositioning.

Angle of Gingival Convergence : According to Schneider, the angle of gingival

convergence is located apical to the height of contour on the abutment tooth. It

can be identified by viewing the angle formed by the tooth surfaces gingival to the

survey line and the analyzing rod or undercut gauge in a surveyor as it contacts

the height of contour.

Continuous Gum Denture : An artificial denture consisting of porcelain teeth

and tinted porcelain denture base material fused to a platinum base.

Fulcrum Line : It is an imaginary line, connecting occlusal rests, around which a

partial removable dental prosthesis tend to rotate under masticatory forces. The

determinants for the fulcrum line are usually the cross arch occlusal rests located

adjacent to the tissue borne components.

Semi precision Rest : A rigid metallic extension of a fixed or removable dental

prosthesis that fits into an intracoronal preparation in a cast restoration.

Nesbit Prosthesis : Eponym for a unilateral partial removable dental prosthesis

design, that De. Nesbit introduced in 1918.

Resilient Attachments : An attachment designed to give a tooth borne/soft tissue

borne removable dental prosthesis sufficient mechanical flexion, to withstand the

variations in seating of the prosthesis due to deformation of the mucosa and

underlying tissues without placing excessive stress on the abutments.


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Partial Dentures:

Partial dentures are appliances restoring one or more but not the whole set of

natural teeth . These Appliances maybe in form of:

I- Fixed partial prosthesis ( bridge ):

An appliance which restores one or more missing teeth it is cemented to the

neighboring natural teeth and cannot be removed by the patient.

II- Removable partial prosthesis:

An appliance which restores missing teeth and the associated oral structures

for a partially edentulous patient " it can be removed by the patient .

Removable partial dentures may restore :

(a) Bounded edentulous area : which has an abutment tooth on each end.

(b) Free end edentulous area : which has an abutment tooth on one side

only . They are called distal- extension partial dentures.

III- Partial over dentures :

Partial over dentures are removable partial dentures that are constructed to overly

and gain additional support from either :

i. Natural teeth that are reduced in height and contour or :

ii. Implants inserted in the edentulous areas .

IV- Removable partial Dentures for Maxillo facial Defects :

These are removable prostheses restoring tissue defects which are either

developmentally or traumatically acquired. They are usually retained by clasps

on the remaining natural teeth.

Types of removable partial dentures :

( 1 ) Unilateral partial dentures : Partial dentures which restore teeth on one side of

the arch without being extended to the opposite side

( 2 ) Bilateral partial dentures : partial dentures restoring missing teeth and

extended on both sides of dental arch .

According to retention to natural teeth

a- Extra coronal retention

b- Intracranial retention

According to material

-Metallic - acrylic -flexible


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CONSEQUENCES OF TOOTH LOSS

1- A loss of ridge volumeboth height and widthcan be expected

Bone loss is greater in the mandible than the maxilla, more pronounced

posteriorly than anteriorly, and it produces a broader mandibular arch while

constricting the maxillary arch.

2- Alteration in the oral mucosa

The attached gingiva of the alveolar bone can be replaced with less keratinized

oral mucosa, which is more readily traumatized.

3- Aesthetic impact

Facial features can change Secondary to altered lip support and/or reduced

facial height as a result of a reduction in occlusal vertical dimension.

4- Reduction in masticatory efficiency

It is the ability to reduce food to a certain size in a given time frame. It has

been shown that there is a strong correlation between masticatory efficiency

and the number of occluding teeth in dentate individuals.

5.T.M.J.dysfunction

6. Tipping, migration, rotation and superimposition of remaining teeth.

7.Altered speech

OBJECTIVES OF REMOVABLE PARTIAL DENTURES

1- Preservation of the Remaining Tissues:

A- Preservation of the health of the remaining teeth.

The loss of teeth leads to migration, tilting or drifting of the remaining

natural teeth into the edentulous spaces, such movements leads to

unequal distribution of load on the remaining teeth.

B- Prevention of muscles and TMJ Dysfunction. Absence or movements of

posterior teeth may cause:

Changes in the pattern of mandibular closure. Change in maxillomandibular relations of the mandible and maxilla.

Consequently muscles and TMJ Dysfunction may arise.

Preservation of the residual ridge. By preventing rapid bone

resorption which may happen due to lack of function.

Preservation of the tongue contour and space.


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2 Restore the Continuity of the Dental Arch to Improve Masticatory Function:

A reduction of the number of teeth leads to a decrease in the chewing

efficiency and greater effort on the digestive organs leading to digestive

disorders, accordingly replacing lost teeth will greatly improve the chewing

capability of the patients, distribute the load over the entire arch and improve

the balance over the whole masticatory system.

3- Improvement of Esthetics, and Providing Support to Lips and Cheeks:

Teeth and the alveolar ridge give support to the musculature of the lips and

cheeks. Non-replacement of the missing teeth gives the patient a senile

appearance characterized by nose-chin approximation and wrinkles around the

lips. Missing teeth can be replaced with predictable results using partial

denture.

4- Restoration of Impaired speech:

Anterior teeth play an essential role in phonetics, particularly in the production

of labio and linguo-dental sound. Loss or wrong position of anterior teeth and

subsequent alveolar ridge resorption can result in phonetic impairment.

Proper replacement of artificial teeth in relation to the lip, tongue and alveolar

ridge, also the proper contouring of dentures help in restoration of speech

defects.

5- Enhance psychological comfort:

Partial dentures should restore and correct the appearance for the

psychological benefits of the patient, by providing socially acceptable

esthetics. A comfortable prosthesis will encourage and help in patient

rehabilitation .

There is no perfect removable appliance, so "best possible" is defined as meeting, as

closely as we can, the following criteria:

It restores the lost occlusal function caused by the patient's missing teeth,

it minimizes the stress placed on abutment teeth to ensure their longevity,

it minimizes the trauma to the supporting and surrounding tissue and bone,

it's self-cleaning and does not produce food entrapment areas,

it's comfortable for the patient to use and wear, and

it meets the particular esthetic needs of your patient.


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Indications for removable partial dentures

1. No abutment tooth posterior to edentulous space (Free end edentulous area)).

2.After recent extraction, to improve esthetics, or for patient satisfaction.

3.Long edentulous bounded span, too extensive for fixed restoration.

4.Periodontally weak teeth not sufficiently sound to support fixed- partial denture.

5. With excessive loss of residual bone, using of labial flange to restore lost tissues.

6. Need of bilateral bracing (cross arch stabilization).after periodontal diseases

treatment, fixed prosthesis provide only antero-posterior stabilization(not

mediolateral) .

7. Enhancing esthetics in anterior region, by the use of translucent artificial teeth

instead of dull fixed partial denture pontic.

8. Young age (less than 17 years).

9. Geriatric patients

10. Immediate replacement.

11.Economic considerations,attitude and desire of the patient.

12.Physical problems.

13. Unfavorable maxillo-mandibular relation.

Contraindication

1- Large tongue. 2- Mentally retarded.

3 Poor oral hygiene.Advantages of removable partial denture over fixed partial denture:

1- They can be constructed for any case whilst fixed P.D. are confined to short

spans bounded by healthy teeth and with a normal occlusion.

2- Cheaper than fixed partial denture.

3- They are more easily cleaned.

4- They are more easily repaired.

5- No tooth reduction is required.

Disadvantages of a removable partial denture:

1- It can cause caries: by harboring food debris in close contact with the natural

teeth a partial denture may promote caries. This will depend on several factors:

a) The age of the patient, up to the age of 25 years caries susceptibility is

greatest, there after it tends to decrease.

b) The oral hygiene of the patient.


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c) The design of the denture: well designed dentures will cause for less

damage to the mouth than those of through less design.

2- It can damage the supporting tissues of the teeth and gum margins by:

a) Fitting too closely into the gingival tissues: through and causing mechanical

injury to it.

b) Allowing food to pack down between the denture and the teeth.

3- It may loosen the natural teeth by leverage: clasps which grip the teeth too

tightly or indirect retainers which are badly placed may cause excessive stresses to

be induced in the natural teeth .

4- It can cause traumatic damage to the palate.

5. Clasps can be unesthetic, particularly if placed on visible tooth surfaces.

HAZARDS OF IMPROPERLY DESIGNED PARTIAL DENTURE See damaging effect

1- Stagnation of food around component parts of partial denture in contact with

tooth surfaces that are not readily cleanedcauses tooth decay .

2- Induce stresses . If these stresses exceed the physiologic limits of tissue

tolerance, pathologic and destructive changes may occur:

a) Excessive stresses on abutment teeth cause periodontal membrane

destruction, pocket formation, mobility, and even loss of these teeth.

b)Inflammation, ulceration and gingival recession may occur due to excessive

stresses and undue coverage of tissues with the restoration. Inadequate support

causes displacement of denture towards the tissues causing gum stripping.

c) Stresses may also cause bone resorption and loss of the bony foundation

necessary to support the prosthesis.

3- Improper occlusion or presence of premature contact may cause T.M.J. disorders.

Phases of partial denture service1- Education of patient: the process of informing a patient about a health matter to

secure informed consent, patient cooperation, and a high level of patient compliance.

Patient education should begin at the initial contact with the patient and continue

throughout treatment.

2- Diagnosis, treatment planning, design, treatment sequencing, and mouth preparation.

3- Support for Distal Extension Denture Bases.

4- Establishment and Verification of Occlusal Relations and Tooth Arrangements.

5- Initial Placement Procedures.

6- Periodic Recall.


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REASONS FOR FAILURE OF CLASP-RETAINED P.D.

Diagnosis and treatment planning

1. Inadequate diagnosis

2. Failure to use a surveyor or to use a surveyor properly during treatment planning

Mouth preparation procedures

1. Failure to properly sequence mouth preparation procedures

2. Inadequate mouth preparations,

3. Failure to return supporting tissue to optimum health before impression procedures

4. Inadequate impressions of hard and soft tissue

Design of the framework

1. Failure to use properly located and sized rests

2. Flexible or incorrectly located major and minor connectors

3. Incorrect use of clasp designs

4. Use of cast clasps that have too little flexibility, are too broad in tooth coverage, and

have too little consideration for esthetics

Laboratory procedures

1. Problems in master cast preparation

a. Inaccurate impression

b. Poor cast-forming procedures

c. Incompatible impression materials and gypsum products

2. Failure to provide the technician with a specific design and necessary information .

3. Failure of the technician to follow the design and written instructions

Support for denture bases

1. Inadequate coverage of basal seat tissue

2. Failure to record basal seat tissue in a supporting form

Occlusion

1. Failure to develop a harmonious occlusion

2. Failure to use compatible materials for opposing occlusal surfaces

Patient-dentist relationship

1. Failure of the dentist to provide adequate dental health care information, including

care and use of prosthesis

2. Failure of the dentist to provide recall opportunities on a periodic basis

3. Failure of the patient to exercise a dental health care regimen and respond to recall


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CLASSIFICATION OF PARTIALLY EDENTULOUS ARCHES

Need for classification:

1- To differentiate between different partial denture.

2- It facilities writing or speaking about partial denture designs and referral orprescription writing to the laboratory thus facilitating communication.

3- To formulate good treatment plane.

4- To anticipate difficulties commonly to occur for each class.

Requirements of an Acceptable Classification:

Classifications are importantto facilitate communicationbetween the dentist and the

laboratory technician. Acceptable classification should satisfy the following

requirements:

1.Permit immediate visualization of the type of partially edentulous arch.

2.Permit immediate differentiationbetween bounded and free extension PD.

3. It should be universally accepted.

4. Serve as guide to design used.

Classifications

a- Classification according to the extent of the RPD:

1- Unilateral RPD (Removable Bridge): which restore missing teeth on one side of

the arch without being extended to the other side. This unilateral design provides

least amount of tooth preparation and least amount of tooth and soft tissue contact.

For unilateral removable partial denture to be successful:

1. Clinical crown of abutment tooth must be long enough to

resist rotational forces.

2. The buccal and lingual surfaces of the abutment tooth must be

parallel to resist tipping forces.

3. Retentive undercuts should be available on both the buccal

and lingual surfaces of each abutment.Unilateral removable partial denture should be used with caution. as the chance of

the denture becoming dislodged and aspirated is too great.

Bilateral RPD: which restore missing teeth and extended on both sides of the

dental arch.


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B- Cummer's classification :

This classification mainly based upon various the position of the

direct retainer of the finished restoration .

The direct retainer may be diagonally, diametric, unilaterally or

multilaterally placed.

It describes the restored rather than the unrestored arch, so it

is of line value because it follows denture design .

C - Bailyn classification :

It is based on the support afforded to the denture :

o Tissue born prosthesis : the denture is enterily supported by the

mucosa and the underlying bone .

o Tooth born prosthesis : the denture is entirely supported by

abutment teeth .

o Tooth tissue supported prosthesis : the denture is supported bu

both abutment teeth and moucosa.

D- Fridman's classification :

Fridman classified partial dentures in to :

Group A for anterior restoration

Group B- For bounded posterior restoration

Group C- For posterior free end restoration (c= cantilever) .

E - Osborne and Lammie (1974)

Class I: Denture supported by mucosa and underlying bone

Class II: Denture supported by teeth

Class III: Denture supported by a combination of mucosa and tooth.

Class IV: Denture supported by implants.

F.Beckett and WilsonClass I: Bounded saddle and the abutment cant support the saddle

Class II: Free end saddle

A. Tooth and tissue support

B. Tissue support

Class III: Bounded saddle and the abutment can support the saddle


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Skinner's Classification

He introduced the classification in 1959. He said that about 1,31,072

combinations of partially edentulous arches are possible.

His classification is based on the relation of the edentulous arches to the

abutment teeth.

Class I: Abutment teeth are present anterior and posterior to the edentulous

space. It may be unilateral or bilateral.

Class II: All the teeth are present posterior to the denture base which

functions as a partial denture unit. It may be unilateral or bilateral.

Class III: All abutment teeth are anterior to the denture base which

functions as a partial denture unit. It may be unilateral or bilateral.

Class IV: Denture bases are located anterior and posterior to the remaining

teeth, and these may be unilateral or bilateral.

Class V: Abutment teeth are unilateral in relation to the denture base, and

these may be unilateral or bilateral.

H- Kennedy's Classification:

Dr. Edward Kennedy proposed this classification in 1923. This is the most

popular classification. It is based on locations and number of edentulous areas.

Class I: Bilateral edentulous areas (free-end saddles) located posterior to the

remaining natural teeth.72%

Class II: A unilateral edentulous area (free-end saddle) located posterior to the

remaining natural teeth.14%

Class III: A unilateral edentulous area with natural teeth remaining both

anterior and posterior to it.8,5%

Class IV: A single, but bilateral (crossing the midline ), edentulous area

located anterior to the remaining natural teeth.3%

Applegate later added two classes

Class V: A unilateral edentulous area with natural teeth remaining both anterior

and posterior to it but the anterior abutment is not suitable for support.

Class VI: A unilateral edentulous area with natural teeth remaining both anterior

and posterior to it with abutments capable for total support.


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FISET'S ADDITIONS

Class VII A partially edentulous situation in which all remaining natural

teeth are located on one side of the arch, or of the median line

Class VIII A partially edentulous situation in which all remaining natural

teeth are located in one anterior corner of the arch

Class IX A partially edentulous situation in which functional and

cosmetic requirements or the magnitude of the interocclusal distance

require the use of a telescoped prosthesis (partial or complete).The

remaining teeth are capable of total or partial support for the prosthesis.

Class X A partially edentulous situation in which the remaining teeth are

incapable of providing any support. If the teeth are kept to maintain

alveolus integrity, the arch must be restored with an OVERDENTURE

which is a complete denture supported primarily by the denture

foundation area

The numeric sequence of the classification system is based on the frequency

of occurrence of each class. Class I being the most common While class IV is the

least common. This classification was then modified by Applegate .

Why a unilateral edentulous area is considered as class II?

Because it include features of both class I and class III especially if

modification is present.

Advantages

1- It is the most widely used method of classification of the partially

edentulous arches.

2- It is simple and can be easily applied to nearly all partially edentulous

bases.

3- It permits immediate visualization of the partially edentulous arch and

permits a logical approach to the problems of design.


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Applegate's Rules for Applying the Kennedy Classification:

Applegate has provided the following eight rules governing the application of

the Kennedy system.

Rule (1) : Classification should follow rather than precede any extraction of

teeth that might alter the original classification.

Rule (2) : If the third molar is missing and not to be replaced, it is not

considered in the classification.

Rule (3) : If a third molar is present and is to be used as an abutment, it is

considered in the classification.

Rule (4) : If a second molar is missing and is not to be replaced (that is, the

opposing second molar is also missing and is not to be replaced ), it is not considered

in the classification.

Rule (5) : The most posterior edentulous area or areas always determine the

classification.

Rule (6) : Edentulous areas other than those determining the classification are

referred to as modification spaces and are designated by their number.

Rule (7) : The extent of the modification is not considered, only the number of

additional edentulous areas.

Rule (8) : There can be no modification areas in Class IV arches. Any

edentulous area lying posterior to the "single bilateral area crossing the midline"

would instead determine the classification.

Class IV Partial dentures especially those having long edentulous areas are

considered mesial extension bases. They require the same denture design principles as

class I partial dentures.


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ACP classification system for partial edentulism J Prosthodont 2002;11:181-193.Prosthodontic Diagnostic Index ( PDI )

The American College of Prosthodontists (ACP) has developed a classification

system for partial edentulism based on diagnostic findings. Four categories of partial

edentulism are defined, Class I to Class IV, with Class I representing anuncomplicated clinical situation and class IV representing a complex clinical

situation. Each class is differentiated by specific diagnostic criteria.

Diagnostic Criteria

1. Location and extent of the edentulous area(s)

2. Condition of abutments

3. Occlusion

4. Residual ridge characteristics.

Class I

It is characterized by ideal or minimal compromise in the location and

extent of edentulous area (which is confined to a single arch), abutment

conditions, occlusal characteristics, and residual ridge conditions. All 4 of the

diagnostic criteria are favorable.

1. The location and extent of the edentulous area are ideal or minimally

compromised:

The edentulous area is confined to a single arch.

The edentulous area does not compromise the physiologic support of the

abutments.

The edentulous area may include any anterior maxillary span that does

not exceed 2 incisors, any anterior mandibular span that does not exceed

4 missing incisors, or any posterior span that does not exceed 2 premolars

or 1 premolar and 1 molar.

2. The abutment condition is ideal or minimally compromised, with no need for

preprosthetic therapy.

3. The occlusion is ideal or minimally compromised, with no need for

preprosthetic therapy; maxillomandibular relationship: Class I molar and jaw

relationships.

4. Residual ridge morphology conforms to the Class I complete edentulism

description.


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Class II

This class is characterized by moderately compromised location and extent

of edentulous areas in both arches, abutment conditions requiring localized

adjunctive therapy, occlusal characteristics requiring localized adjunctive

therapy, and residual ridge conditions.

1. The location and extent of the edentulous area are moderately

compromised:

Edentulous areas may exist in 1 or both arches The edentulous areas

do not compromise the physiologic support of the abutments.

Edentulous areas may include any anterior maxillary span that does

not exceed 2 incisors, any anterior mandibular span that does not exceed

4 incisors, any posterior span (maxillary or mandibular) that does not

exceed 2 premolars, or 1 premolar and 1 molar or any missing canine

(maxillary or mandibular).

2. Condition of the abutments is moderately compromised:

Abutments in 1 or 2 sextants have insufficient tooth structure to retain

or support intracoronal or extracoronal restorations.

Abutments in 1 or 2 sextants require localized adjunctive therapy.

3. Occlusion is moderately compromised:

Occlusal correction requires localized adjunctive therapy.

Maxillomandibular relationship: Class I molar and jaw relationships.

4. Residual ridge morphology conforms to the Class II complete edentulism

description.

Class III

This class is characterized by substantially compromised location and extent

of edentulous areas in both arches, abutment condition requiring substantial

localized adjunctive therapy, occlusal characteristics requiring reestablishment of

the entire occlusion without a change in the occlusal vertical dimension, and

residual ridge condition.

1. The location and extent of the edentulous areas are substantially

compromised:

Edentulous areas may be present in 1 or both arches.

Edentulous areas compromise the physiologic support of the abutments.


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Edentulous areas may include any posterior maxillary or mandibular

edentulous area greater than 3 teeth or 2 molars, or anterior and posterior

edentulous areas of 3 or more teeth.

2. The condition of the abutments is moderately compromised:

Abutments in 3 sextants have insufficient tooth structure to retain or

support intracoronal or extracoronal restorations.

Abutments in 3 sextants require more substantial localized adjunctive

therapy (ie, periodontal, endodontic or orthodontic procedures).

Abutments have a fair prognosis.

3. Occlusion is substantially compromised:

Requires reestablishment of the entire occlusal scheme without an

accompanying change in the occlusal vertical dimension.

Maxillomandibular relationship: Class II molar and jaw relationships.

4. Residual ridge morphology conforms to the Class III complete edentulism

description.

Class IV

This class is characterized by severely compromised location and extent of

edentulous areas with guarded prognosis, abutments requiring extensive therapy,

occlusion characteristics requiring reestablishment of the occlusion with a change

in the occlusal vertical dimension, and residual ridge conditions.

1. The location and extent of the edentulous areas results in severe occlusal

compromise:

Edentulous areas may be extensive and may occur in both arches.

Edentulous areas compromise the physiologic support of the abutment

teeth to create a guarded prognosis.

Edentulous areas include acquired or congenital maxillofacial defects.

At least 1 edentulous area has a guarded prognosis.

2. Abutments are severely compromised:

Abutments in 4 or more sextants have insufficient tooth structure to retain

or support intracoronal or extracoronal restorations.

Abutments in 4 or more sextants require extensive localized adjunctive

therapy.

Abutments have a guarded prognosis.


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3. Occlusion is severely compromised:

Reestablishment of the entire occlusal scheme, including changes in the

occlusal vertical dimension, is necessary.

Maxillomandibular relationship: class II division 2 or Class III molar and

jaw relationships.

4. Residual ridge morphology conforms to the class IV complete edentulism

description.

Other characteristics include severe manifestations of local or systemic

disease, including sequelae from oncologic treatment, maxillomandibular

dyskinesia and/or ataxia, and refractory patient (a patient who presents with

chronic complaints following appropriate therapy).


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Implant-Corrected Kennedy (ICK) Classification System for Partially

Edentulous Arches Journal of Prosthodontics 17 (2008) 5025

Guidelines for the new classification system

The new classification system will follow the Kennedy method with the

following guidelines:

(1) No edentulous space will be included in the classification if it will be restored

with an implant-supported fixed prosthesis.

(2) To avoid confusion, the maxillary arch is drawn as half circle facing up and

the mandibular arch as half circle facing down. The drawing will appear as if

looking directly at the patient; the right and left quadrants are reversed.

(3) The classification will always begin with the phrase "Implant-Corrected

Kennedy (class)," followed by the description of the classification. It can be

abbreviated as follows:

(i) ICK I, for Kennedy class I situations,

(ii) ICK II, for Kennedy class II situations,

(iii) ICK III, for Kennedy class III situations, and

(iv) ICK IV, for Kennedy class IV situations.

(4) The abbreviation max for maxillary and man for mandibular can precede

the classification. The word modification can be abbreviated as mod.

(5) Roman numerals will be used for the classification, and Arabic numerals will

be used for the number of modification spaces and implants.

(6) The tooth number using the American Dental Association (ADA) system is

used to give the number and exact position of the implant in the arch. (Note: other

tooth numbering systems such as Federation Dentaire Internationale [FDI] can

be used, as can the tooth name. The ADA system was used by the authors because

of familiarity).


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Universal numbering system table

Permanent Teeth

upper right upper left

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

lower right lower left

(7) The classification of any situation will be according to the following order:

main classification first,

then the number of modification spaces,

followed by the number of implants in parentheses according to their position

in the arch preceded by the number sign (#).

(8) The classification can be used either after implant placement to describe any

situation of RPD with implants, or before implant placement to indicate the number

and position of future implants with an RPD.

(9) A different name, ICK Classification System, is given to this classification

system to be differentiated from other partially edentulous arch classification systems.


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ICK I (#2, 15).

ICK I (#2).

ICK I mod 3 (#18, 22, 28, 31).

ICK II mod 1 (#21, 26, 30).

ICK III mod 3 (#23, 26).

ICK IV (#6, 11)

ICK II (#2).


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Component Parts of removable partial dentures

Denture bases.

Artificial teeth .

Supporting rests.

Connectors: Major connectors

Minor connectors

Retainers : Direct retainers

Indirect retainers

These components may provide one or more of the following functions:

1-Support:

a. The resistance of a denture to tissue ward movement.

b. Adequate and wide distribution of the load to the teeth and mucosa.

2- Retention: The resistance of a denture to vertical displacement force (to move

away from its tissue foundation)).

3- Indirect retention: The resistance of denture rotationaway from the tissues about

an axis.

4- Bracing: The resistance of a denture to lateral forces.

5- Reciprocation: The resistance of lateral forces on the abutment during insertion

and removal of the removable partial denture .

Reciprocation is required as the denture is being displaced occlusally whilst

thebracingfunction, comes into play when the denture is fully seated.

6- Stability: The resistance of a denture to tipping movement.

Tipping movement: Vertical rotation around a line parallel to ridge crest

(twisting of the denture base)


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RPD THEORY AND PRACTICE Denture Base 2

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COMPONENT PARTS OF RPD

Components of metallic removable partial dentures are all rigid, with the

exception of the flexible retentive clasp arm located in an undercut area for retaining

the restoration against dislodging forces.

The components of removable partial denture are:

1. One or More Denture Bases.

2. Artificial teeth.

3. Supporting rests.

4. Major connectors.

5. Minor connectors.

6. Direct retainers.

7. Indirect retainers.

These Components May Provide One or More of the Following Functions:

1-Support: The resistance of a denture to tissue ward movement.

2- Retention: The resistance of a denture to vertical displacement force (to move away

from its tissue foundation).

3- Indirect retention: The resistance of denture rotation away from the tissues about an

axis.

4- Bracing: The resistance of a denture to lateral forces.

5- Reciprocation: The resistance of lateral forces on the abutment during insertion and

removal of the removable partial denture.

Reciprocation is required as the denture is being displaced occlusally whilst the bracing

function, comes into play when the denture is fully seated.

6- Stability: The resistance of a denture to tipping movement.

Tipping movement: Vertical rotation around a line parallel to ridge crest (twisting of

the denture base)


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Denture Base

The denture base is the part of the denture, which rests on the foundation tissues

and to which artificial teeth are attached. The denture base helps in transferring occlusal

stresses to the supporting oral structures.

Types of Denture Bases

1- Bounded partial denture bases

It covers an edentulous span between two abutment teeth.

2- Free-end partial denture bases (distal-extension base)

The base bounded by a natural tooth only on one side, while the other side is free.

This type is sometimes called distal extension base.

3- Bar type saddle

In case of posterior bounded saddle, where esthetic is not important, a bar of metal

is attached directly to the connector to form occlusal surface and no mucosal

contact .

Functions of the Denture Base

1. Carries the artificial teeth.

2. Transfers occlusal stresses to the supporting oral structures.

3. Providessupport in distal-extension and long span bounded dentures.

The snowshoe principle, which suggests that broad coverage furnishes the best support

with the least load per unit area, is the principle of choice for providing maximum support.

Therefore support should be the primary consideration in selecting, designing, and

fabricating a distal extension partial denture base.

4. Provides dentureretention for distal-extension dentures by physical means.

5. Provides denture bracing against horizontal movement when extended to cover lateral

borders of the ridge for distal-extension dentures.


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6. Provides stabilization against tipping of the distal-extension dentures (On the contra-

lateral side).

7. The denture base and the artificial teeth serve to prevent migration and over eruption

of the remaining teeth.

8. Provide stimulation by massage of the underlying tissues of the residual ridge. Oral

tissues placed under functional stress within their physiological tolerance maintain their

form and tone better than similar tissues suffering from disuse.

9. A the tooth-supported partial denturebase that replaces anterior teeth must perform

the following functions:

(1) Provide desirable esthetics;

(2) Support and retain the artificial teeth in such a way that they provide

masticatory efficiency and assist in transferring occlusal forces directly to

abutment teeth through rests;

(3) prevent vertical and horizontal migration of remaining natural teeth;

(4) Eliminate undesirable food traps (oral cleanliness);

(5) Stimulate the underlying tissue.

Requirements of an Ideal Denture Base Material

1- Accuracy of adaptation to the tissues, with minimal dimensional changes.

2- Sufficient strength in order to resist fracture and distortion.

3- Low specific gravity, i.e. light in weight in the mouth.

4- Biological acceptability, non-allergic and non-irritating surface capable of

receiving and maintaining a good finish

5- Allow thermal conductivity necessary for tissue stimulation.

6- Can easily be kept clean.

7- Esthetic acceptability.

8- Potential for future relining.

9- Low initial cost.


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FACTORS DETERMINING THE SELECTION OF DENTURE BASES

A. NEED TO RELINE.

1. Tooth-mucosa borne partial dentures direct functional forces as

pressure to the mucoosseous tissues. When resorptive changes occur, the base

requires relining to maintain optimum support. Resin bases are easily relined.

1. In tooth borne partial dentures with long span bases, the base may

require periodic relining to compensate for idiopathic or pressure induced

resorptive changes

B. NEED TO RESTORE MISSING TISSUES. A resin base may be shaped and

shaded to restore anatomic contour and esthetics.

C. LIMITED VERTICAL SPACE. When vertical space is limited, the minimal

space may require a stronger metal base.

D. MAGNITUDE OF APPLIED FORCES. The anticipated occlusal forces may

influence the choice of materials.

E. EASE OF ADJUSTMENT. Resin bases are more easily adjusted than metal

bases.

In tooth mucosa born PD:

The rotational movements of the RPD during function may excessively load

underlying mucosal tissues. Resin bases are easily adjusted to eliminate the

impingement.

F. LENGTH OF SPAN.

1.Long span bases. Denture base resin on metal framework.

a.Facilitates esthetic restoration of lost tissue contours.

b.Allows periodic relining to compensate for idiopathic or pressure induced

resorptive changes.

c.Facilitates adjustment if required.


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2.Short span bases. Metal base.

a.Provides maximum strength with mmimum bulk.

b.Esthetics may limit use in anterior regions.

c.Adjustment more difficult jf required,

G. INTERARCH DISTANCE. Limited interarch distance may indicate the use of

a metal base.

H. ANTICIPATED LOSS OF AN ABUTMENT TOOTH. A resin-metal base

facilitates the addition of an artificial tooth to the denture base.

Denture Base Material

I- Metallic denture bases

Metallic denture bases are generally used in thinner sections than resin bases.

They are made in the form of metal plates having metal posts that allow for

mechanical attachment with the acrylic resin layer holding the artificial teeth.

Metal such as chrome cobalt alloy, gold, or stainless steel is used. Chrome cobalt

alloy is the most commonly used alloy the material is used in cast form only. It

provides the needed rigidity for removable partial dentures even in thin section. It

has low specific gravity which is nearly half that of gold and provides high

resistance to corrosion.

Advantages of Metal bases as compared to resin bases:

1- Accuracy and Permanence of Form

Denture bases fit more accurately to the underlying tissues. Accurate metalcastings are not subject to distortion by the release of internal strains as are

acrylic denture resins.

The metal base provides an intimacy of contact that contributes

considerably to the retention of denture prosthesis. (called interfacial

surface tension).


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Additional posterior palatal seal may be eliminated entirely when a cast

palate is used for a complete denture, as compared with the need for a

definite post-dam when the palate is made of acrylic resin.

Permanence of form of the cast base is also ensured because of its resistance

to abrasion from denture cleaning agents.

2- Comparative Tissue Response

o Cast metal base contributes to the health of oral tissue when compared with

an acrylic resin base. Perhaps some of the reasons for this are the greater

density and the bacteriostatic activity contributed by ionization and

oxidation of the metal base.

o Acrylic resin bases tend to accumulate mucinous deposits containing food

particles and calcareous deposits.

3- Thermal Conductivity

Cast metal base has Greater thermal conductivity, while denture acrylic

resins have insulating properties.

4- Weight and Bulk

Metal alloy may be cast much thinner than acrylic resin and still have

adequate strength and rigidity. Cast gold must be given slightly more bulk

to provide the same amount of rigidity but may still be made with less

thickness than acrylic. less weight and bulk are possible when the denture

bases are made of chrome or titanium alloys.

an acrylic resin base may be preferable to the thinner metal base in (1)

extreme loss of residual alveolar bone may make it necessary to add fullness

to the denture base to restore normal facial contours and (2) to fill out the

buccal vestibule to prevent food from being trapped in the vestibule beneath

the denture.(3) Denture base contours for functional tongue and cheek

contact can best be accomplished with acrylic resin.(4) acrylic resin bases

may be contoured to provide ideal polished surfaces that contribute to the


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retention of the denture, restoration of facial contours, and prevention of the

accumulation of food at denture borders.

5- More hygienic as the fitting surface is polished and non-porous with less

tendency for food accumulation.

6- Stimulation to the underlying tissue so prevents some alveolar atrophy that

would otherwise occur under a resin base and thereby would prolong the health

of the tissue that it contacts.

Disadvantages of Metal Bases

1. Metal bases are difficult to rebase or reline when ridge resorption occurs.

2. They are difficult to repair.

3. The color of metal bases does not simulate the natural appearance or oral

tissues.

Retentive post used with metal base.

Indication: 1- short span posterior tooth born 2- when maximum strength is required

3- vertical height limited 4- significance anterior overlap

The choice of alloy is based on several factors:

(1) weighed advantages or disadvantages of the physical properties of the alloy;

(2) The dimensional accuracy with which the alloy can be cast and finished;

(3) The availability of the alloy;

(4) The versatility of the alloy; and

(5) The individual clinical observation and experiences with alloys in respect to quality

control and service to the patient.


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A-Chrome cobalt alloy:

It is used in cast form only, needs special investments and special casting and

polishing machine and high casting temperature (2400 f).

Advantages:

Accurate and rigid even in thin sections.

Low specific gravity 7-9 gram/cm3 nearly 1/2 of that of gold.

Highly polished surface.

High resistance to corrosion and abrasion.

Low density (weight), high modulus of elasticity (stiffness),

Cheaper than gold..

A low-fusing, chrome-cobalt alloy or gold alloy can be cast to wrought

wire, and wrought-wire components may be soldered to either gold or

chrome-cobalt alloys

B-Gold (type 4)

properties:

1-Heavier than chrome cobalt (specific gravity 15 gm/ cm3).

2- More rigid than acrylic resin but less than chrome cobalt. Modiolus of rigidity

14106 P.S.I

3- More expensive.

4- more specific gravity : Some times used for lower partial denture to help in

retention due to more specific gravity (weight).

5- Gold alloys have a modulus of elasticity approximately one half of that for

chromium-cobalt alloys for similar uses. The modulus of elasticity refers to

stiffness of an alloy.

6- It has been observed that gold frameworks for removable partial dentures are

more prone to produce uncomfortable galvanic shocks to abutment teeth restored

with silver amalgam than frameworks made of chromium-cobalt alloy.


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The greater stiffness of chromium-cobalt alloy is advantageous but at the

same time offers disadvantages.

The hardness of chromium-cobalt alloys presents advantages when Greater

rigidity can be obtained with the chromium-cobalt alloy in reduced sections in

which cross-arch stabilization is required, thereby eliminating an appreciable bulk

of the framework. Its greater rigidity is also an advantage when the greatest

undercut that can be found on an abutment tooth is in the nature of 0. 05 inch. A

gold retentive element would not be as efficient in retaining the restoration under

such conditions as would the chromium-cobalt clasp arm.

The hardness of chromium-cobalt alloys presents a disadvantage when a

component of the framework, such as a rest, is opposed by a natural tooth or by

one that has been restored due to wear of natural teeth opposed by some of the

various chromium-cobalt alloys as contrasted to the Type IV gold alloys.

A high yield strength and a low modulus of elasticity produce higher flexibility.

The gold alloys are approximately twice as flexible as the chromium cobalt alloys,

which is a distinctadvantage in the optimum location of retentive elements of the

framework in many instances. The greater flexibility of the gold alloys usually

permits location of the tips of retainer arms in the gingival third of the abutment

tooth.

The stiffness of the chromium-cobalt alloys can be overcome by

1- Including wrought-wire retentive elements in the framework.

2- The bulk of a retentive clasp arm for a removable partial denture is often reduced

for greater flexibility when chromium-cobalt alloys are used as opposed to gold

alloys. This, however, is inadvisable because the grain size of the chromium-cobalt

alloys is usually larger and is associated with a lower proportional limit, and so a

decrease in the bulk of chromium-cobalt cast clasps increases the likelihood of

fracture or permanent deformation.

The retentive clasp arms for both alloys should be approximately the same size,

but the depth of undercut used for retention must be reduced by one half when

chromium-cobalt is the choice of alloys.


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c- Stainless steel:

It is used mainly in swaged form.

The disadvantages of this type are;

1- Less accurate than chrome cobalt or gold

2- Less commonly used.

d- TI/AL/vanadiaum / e- Commercial pure titanium

Commercially pure (CP) titanium and titanium in alloys containing aluminum

and vanadium, or palladium (Ti-0 Pd), should be considered potential future

materials for removable partial denture frameworks.

Currently, when CP titanium is cast under dental conditions, the material

properties change dramatically. During the casting procedure, the high affinity

of the liquid metal for elements such as oxygen, nitrogen, and hydrogen results

in their incorporation from the atmosphere.

The typical Young's modulus of elasticity of titanium alloy is half that of

chromium-cobalt and just slightly higher than type IV gold alloys. This would

require a different approach to clasp design than with chromium-cobalt alloys

and present some advantages. Wrought titanium alloy


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II- Non-metallic, acrylic resin denture bases

Acrylic removable partial dentures are considered as temporary partial dentures. It is made

of acrylic denture base, artificial teeth and wrought wire clasps.

Advantages:

1. Esthetically acrylic resin is satisfactory and looks better in the mouth due to its pink

colour.

2- Acrylic bases are light in weight.

3- The material is easy to reline, rebase or repair.

4- Needs simple processing procedures.

Disadvantages of resin base:

1. Resin bases are weak, brittle and are liable to fracture.

2. In order to attain enough strength, resin bases are made bulky

3. Acrylic bases have low thermal conductivity.

4. The fitting surface is porous and not polished which may lead to retention of soft

food particles and plaque causing bad oral hygiene, bad odour and inflammation

of the tissues.

Indications of Acrylic removable partial dentures:

1- When age and time factors may prohibit the construction of the definitive

prosthesis.

2- During the healing process after extraction until the permanent restoration is made.

3- Cases with extreme bone loss. The presence of acrylic resin is necessary to restore

the original contour of the ridge, giving more satisfactory results than metal bases.

4- When cost is a prime requisite.

5- Acrylic bases of temporary acrylic removable partial dentures.

6- Immediate denture

7- Transitional and interim denture

8- Only few isolated teeth remaining.


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Contraindications:

1. Single tooth edentulous spaces.

2. Where protrusive or lateral occlusal guidance will be on the prosthetic teeth.

Types of resin.

a.Polymethylmethacrylatc. (PMMA) (Most commonly used.)

b.Grafted polymethylmethacrylate.

c. 4-meta (4-methacryloxyethyl trimellitate anhydride) containing PMMA.

Potential to chemically bond to alloys capable of oxidation so it reduce

microleakage at metal-resin interface.

d. Polyvinyl.

e. Composite resin.

III- Combined Metallic and Acrylic Resin Bases:

Acrylic resin bases attached to metallic denture framework through metallic

minor connectors.

Metal resin interface exhibits a potential space which may enlarge during thermo

cycling and permit the entrance of microorganisms and fluids. This may lead to

discoloration, plaque accumulation and resin deterioration at the interface.

They are used in the following conditions:

1. Free-end saddle cases as in Kennedy class I, II and IV and in class III cases having

long edentulous spans to facilitate future relining. Relining is required to

compensate for bone resorption, which frequently occur in these cases.

2. Patients vulnerable to an increased rate of bone loss as diabetic patients or patients

on steroid therapy.

3. Cases with extreme bone loss. The presence of acrylic resin is necessary to restore

the original contour of the ridge giving more satisfactory results than metal bases.

4. Long span cases.

5. Recent extraction cases which will need early relining.

6. Cases with bone resorption prognosis as diabetic patients.

7. Class IV for appearance.


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Methods of Attaching Denture Bases

Denture Base Retention (Grid-work) minor Connector

Acrylic resin bases are attached to metallic denture framework by means of a

minor connector designed so that a space exists between it and the underlying

tissues of the residual ridge. (Relief of at least a 20-gauge thickness over the basal

seat areas of the master cast is used to create a raised platform on the investment

cast on which the pattern for the retentive frame is formed)

The minor connectors are either made in the form of

a) Lattice work construction.

b) Mesh construction.

c) Bead, wire, or nail-head minor connectors (used with a metal base).

Retentive mesh and retentive lattice are used when a plastic denture base will contact the

edentulous ridge.

Loops, beads, and posts are used with a metal base to which prosthetic teeth are attached

with processed plastic.

This type of minor connector must be

strong enough to anchor the denture base securely;

rigid enough to resist breakage or flexing,

Must not interfere as possible with arrangement of the artificial teeth.

Extension:

In the maxillary arch if the denture base is a distal extension base (no tooth

posterior to the edentulous space), the minor connector must extend the entire

length of the residual ridge to cover the tuberosities.

When a distal extension ridge in the mandibular arch is being treated, the minor

connector should extend two-thirds the length of the edentulous ridge.


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1- An open latticework (ladder-like pattern).

The latticework consists oftwo struts of metal, pieces of 12- or

14-gauge half-round wax and 18-gauge round wax are used to form a

ladder like framework., extending longitudinally along the edentulous

ridge.

A longitudinal strut should not be positioned along the ridge crest as it may act as a

wedge in the resin and may cause resin fracture.

In the mandibular arch one strut should be positioned buccal to the crest of the

ridge and the other lingual to the ridge crest.

In the maxillary arch one strut is positioned buccal to the ridge crest, and the border

of the major connector acts as the second strut.

Smaller struts, usually 16 gauge thick, connect the two struts and form the

latticework. These connecting struts run over the crest of the ridge and should be

positioned to interfere as little as possible with arrangement of the artificial teeth.

Generally, one cross strut between each of the teeth to be replaced should be satisfactory.

The latticework minor connector can be used whenever multiple teeth are to be

replaced. It provides the strongest attachment of the acrylic resin denture base to the

removable partial denture. It is also the easiest of the denture base retainers to reline if this

becomes necessary because of ridge resorption.

In construction, wax forms of the struts are positioned on the refractory

(investment) cast, which is duplicated from the master cast.

It is necessary to provide a relief space over the dentulous ridges for both the

latticework and the mesh minor connector so that there will be a space between the

struts or mesh and the underlying ridge.

It is in this space and around the struts or mesh that the acrylic resin denture base will

be formed. The locking of the acrylic resin around and through the latticework

provides the retention of the denture base.

Relief under the grid-work should not be started immediately adjacent to the abutment

tooth but should begin 1.5 - 2 mm from the abutment tooth.


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The junction of grid works to the major connector should be in the form of a butt joint

with a slight undercut in the metal.

The grid work on a mandibular distal extension should extend about 2/3 of the way

from abutment tooth to retromolar pad but not on the ascending portion of the ridge

mesial to the pad. It should has a tissue stop at their posterior limit to provide direct

contact with the ridge.

Maxillary distal extension grid-works should extend at least

2/3 of the length of the ridge to the hamular notch.

However, the junction or finishing line of the maxillary

major connector should extend fully to point to the hamular

notch area so that the acrylic resin base can be extended

into this area and provide a smooth transition from the

connector to the base.

2- in a closed meshwork configuration (plastic mesh pattern).

The mesh type of minor connector consists ofa thin sheet of

metal with multiple small holes that extends over the crest of

the residual ridge to the same buccal, lingual, and posterior

limits as does the latticework minor connector.

It can be used whenever multiple teeth are to be replaced.

The mesh pattern is less satisfactory as the space available for incorporatingacrylic resin between metallic strips is narrow so it makes it more difficult to pack

the acrylic resin dough because more pressure is needed against the resin to force it

through the small holes and not allow for enough bulk of resin which become weak

and may detached from the metal base. It also does not provide as strong an

attachment for the denture base.

The major difference between retentive mesh and retentive lattice is the size of the

openings. Retentive mesh has small openings while retentive lattice has much

larger openings.

The mesh type tends to be flatter, with more potential rigidity, but may provide less

retention for the acrylic if the openings are insufficiently large.

The lattice type has superior retentive potential, but can interfere with the setting of

teeth, if the struts are made too thick or poorly positioned.

Both types are acceptable if correctly designed.


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3- Metal denture bases

Posts, loops, beads , nail head, wire loop retention or metal stop may be used to for

retention of the resin. with metal denture base, which is cast so that it fits directly

against the edentulous ridge; no relief is provided beneath the minor connector.

The retention is gained by the projection of metal on this surface. These projections may be

beads (made by placing beads of acrylic resin polymer in the waxed denture base

and investing, burning out, and casting these beads);

wires that project from the metal base,

In the form of nail-head.

This form of denture base is hygienic because of better soft tissue response to metal

than acrylic resin. But it can not be relined adequately in the event that ridge resorption

takes place.

This type should be used on tooth-supported, well-healed ridges and when inter

arch space is limited and the available vertical space is so limited that an acrylic resin base

would be thin and weak. Because relining is not possible metal bases are generally not

indicated for extension RPDs.

Minor connectors forming mandibular distal extension bases extend posteriorly

about two-thirds the length of the edentulous ridge. They should be slightly extended onto

the buccal and lingual surfaces of the ridge. This design adds strength to the acrylic denture

base and helps to minimize-distortion of cured resin bases, which occurs due to the release

of strains after processing. However, minor connectors for maxillary distal extension

bases may sometimes be extended to cover the entire length of the residual ridge.


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Minor connectors forming denture bases should include tissue stops and finishing line:

Tissue stops:(tissue foot)

It is a foot included in the fitting surface of minor connector designed for retaining

acrylic base.

Tissue stops are integral parts of minor connectors. Tissue stops prevent settling of

the framework downwards, and elevate the minor connectors by a space equal to the

thickness of acrylic base.

They provide stability to the framework during the stages of transfer and processing.

They are particularly useful in preventing distortion of the framework during acrylic

resin processing procedures.

Altered cast impression procedures often necessitate that tissue stops be augmented

subsequent to the development of the altered cast. This can be readily accomplished

with the addition of autopolymerizing acrylic resin.

Tissue stops are essential parts in the fitting surface of minor connectors. They are

usually two or three in number that contact the cast.

Tissue stops stabilize the framework on the master cast

during processing as acrylic resin is packed in theretention spaces.

Tissue stops elevate the minor connectors, forming the

denture base, from the ridge, by a space equal to the thickness

of acrylic bases.

They are formed by making holes 22 mm in the relief wax

placed over the ridge during preparation of the master cast before duplication.

Finishing index tissue stop:

It is located distal to the terminal abutment and is a

continuation of the minor connector contacting the guiding

plane. Its purpose is to facilitate finishing of the denture base

resin at the region of the terminal abutment after processing.


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Finishing Lines:

Finishing lines are butt joints created at the junction of major connectors with the

denture bases.

Finish lines must be provided on all partial denture frameworks wherever denture

base resin and the metal join.

A finish line allows the resin to terminate in a butt joint to produce a smooth

surface.

In distal extension bases, these butt joint finishing lines, are made on both the

external and internal surfaces of the major connector where acrylic resin is

processed, while in short bounded metallic bases, the butt joint is required only on

the external surface where acrylic resin is packed, for the attachment of teeth.

External finish lines-:

An external finish line is located on the polished surface of a partial denture and is

formed in the wax pattern.

a. External finish lines are formed during the formation of the wax pattern by carving

a sharp definite angle in the wax pattern at the junction between the major

connector and the minor connectors forming the denture base.

b. This angle should be less than 90 degrees to lock the acrylic resin securely to the

minor connectors and for the acrylic base to blend smoothly and evenly with the

major connector.

c. External finish line is positioned just far enough lingual to the ridge crest to

position the artificial teeth.

d. External finish line fades into minor connectors or proximal plates as it approaches

the occlusal surfaces of the contacting teeth.

e. The external finish line should never be placed directly over the internal finish line.

It should be placed superiorly to the internal finish line so that a minimum amount

of denture base resin is used on the lingual aspect of the teeth.


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For maxillary RPDs. the palatal finish line should be located so that it allows for

proper positioning of the artificial teeth while still maintaining normal tissue contours and

a smooth transition from metal to plastic. It should be located 2 mm medial from an

imaginary line that would contacts lingual surfaces of missing posterior teeth.

For a mandibular distal extension RPD, the external finish line begins at the

distolingual aspect of the terminal tooth and angles posteriorly as it progresses toward the

floor of the mouth. The lingual finish line for a mandibular tooth-supported RPD should be

located just far enough lingually to allow for setting of the artificial teeth. If it is placed too

far lingually (and thus inferiorly), the major connector will be weakened.

Internal finish lines:

An internal finish line is located on the internal or tissue surface and is formedwhile blocking out the master cast.

If the resin ends in a thin edge, saliva and debris will accumulate between the

denture base resin and the metal. The resin will also fracture if left too thin in this area.

a. Internal finish lines are formed by carving the relief wax used to create space for

packing acrylic resin under mesh minor connector. This relief wax is applied on the

master cast before duplication.

b. In tooth-mucosa borne RPD the internal finishing line (IFL), it is placed approximately

at the junction of the vertical and horizontal planes of the palate to permit proper

relining since resorption of bone occurs all the way up to this level. While in case of

maxillary tooth borne PD, the IFL is slightly palatal to the EFL.

c. The internal finish line is located on the tissue surface side of the framework. It is

formed by the 24- to 26-gauge relief wax placed on the master cast prior to

duplication.

d. The internal finish line is normally placed farther from the abutment tooth or residual

ridge than the external finish line.

e. Internal finish line should be located to allow resin to cover mueo-osseous areas

where resorptive changes are anticipated. This permits the base to be relined to

reestablish mueo-osseous support.


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f. Internal finish line should be located 3-4 mm from the natural teeth. This allows a

highly polished metal surface to be placed adjacent to the free gingival margins.

g. Internal finish line should form a well defined butt joint with the denture base resin.

h. Internal line angle of the internal and external finish lines should be less than 90

degrees to provide mechanical retention for the denture base resin.

i. Internal and external finish lines should not be superimposed. A staggered (offset)

relationship maintains framework strength.

j. The palatal extension of the internal finish line is determined primarily by the need

to reline the partial denture to compensate for anticipated bone resorption.

For tooth borne partial dentures, the internal finish lines should be placed

slightly palatal to the external finish lines. This staggered relationship

contributes to increased framework strength and an adequate thickness of

resin between the finish lines. Placement of the internal finish line more

palatally is usually not indicated, since minimal resorptive changes occur.

For tooth-mucosa borne partial dentures, the internal finish lines in the

edentulous regions should be placed close to where the vertical and horizontal

planes of the palate meet. This position is approximately 10 mm lingual to the

previous position of the lingual gingival margins of the missing teeth. This

permits proper relining, since bone resorption may occur up to this level. The

horizontal portion of the hard palate is relatively resistant to pressure-

induced resorptive changes.

1: black arrow indicates the external finishing line(EFL) in tooth-mucosa borne RPD. 2:. a case

of maxillary tooth-mucosa borne RPD. arrow (A) indicates The internal finishing line(IFL), it is

placed approximately at the junction of the vertical and horizontal planes of the palate to permit

relining. Arrow (B) indicates the EFL 3: in case of maxillary tooth borne PD, the IFL is slightly

palatal to the EFL


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External finish lines: junction of major

connector and minor connectors at palatal

finishing line should be located 2 mm medial

from an imaginary line that would contacts

lingual surfaces of missing posterior teeth.

Denture base extension

Maximum coverage of the edentulous ridge is always desirable to allow greatest

area of bone to share in resisting the occlusal stresses exerted during mastication. This

helps in decreasing the force per unit area and keeping the forces within the physiologic

tissue tolerance.

a) Antero-posterior extension

- In bounded spaces: It is determined by the abutment teeth.

- In free-end spaces: The base extends to cover the retromolar pad in the

lower arch and hamular notches and tuberosity in the upper .

b) Buccally: The flange should extend to the mucosal reflection. The labial flange is

sometimes omitted for esthetic reasons.

c) Lingually: The flange of the lower denture base should extend to the full depth of the

lingual sulcus as permitted by muscle function.

Lingual surfaces usually are made concave except in the distal palatal area. Buccal

surfaces are made convex at gingival margins, over root prominences, and at the border to

fill the area recorded in the impression. Between the border and the gingival contours, the

base can be made convex to aid in retention and to facilitate the return of the food bolus to

the occlusal table during mastication. Such contours prevent food from being entrapped inthe cheek and from working under the denture.

Occasionally, the path of insertion can cause the denture flanges to impinge on the

mucosa above undercut portions of the residual ridge, when the partial denture is being

seated. In these instances, it is usually preferable to shorten the flange, rather than

relieving the internal surface. If the internal surface is relieved significantly, a space will


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exist between the denture base and the tissues when the denture is fully seated. Food may

become trapped in the space and work its way under the partial denture.

Relationship of denture base to abutment

The ideal relationship between the denture base carrying the artificial teeth and the

adjacent abutment should either be:

1- Close contact between the denture and the proximal surface of the abutment. In this

condition relieving the gingival margin is necessary to avoid its traumatization.

2- Open Contact between artificial teeth carried by the denture base and the abutment

above the contact point allowing enough space between them to create a cleansable area.

On the other hand improper contact between the denture and the abutment tooth leaving

only a small space between the neck of the abutment tooth and the artificial tooth is

undesirable. This small space is difficult to clean predisposing to caries, gingivitis and

pocket formation.

Ideal base/abutment tooth relationship

1-Close contact between the denture and the proximal surface of the abutment

2- Open Contact. Enough spaces are self-cleansing.


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AESTHETICS OF RPD IN RELATION TO THE LABIAL FLANGE:

A. LONG ANTERIOR SADDLE

The natural appearance presented by the labial and buccal flange is depend upon:

The shaping of the gingival papillae,

The shaping of the gingival margins,

The overall contouring of the flange as a whole, and

Coloring and shading.

In shaping the gingival papillae, the space between the teeth should be filled. The

resin representing the papilla may then be lightly polished to give a surface, which is

readily self-cleansing.

The shape of the entire gingival margin is usually more sharply curved if the neck of

the tooth is not prominent, but is higher and straighter if the neck is prominent. A

more vigorous expression may be obtained by emphasizing the convexity of the

gingival margin. The whole area of the gingival margin should be polished highly to

avoid food debris accumulating round the necks of the teeth.

In ageing, both the interdental papilla and the gingival margin require modification.

The papilla is positioned higher on the neck of the tooth, and the gingival margin

regresses up the root of the tooth and a pointed rather than a curved form should be

used, especially at the neck of a prominent tooth such as the canine.

Contouring of the labial flange should be carried out to simulate the development of

bony prominences over the roots of teeth and Interdental depressions. Stippling of the

attached gingiva, as well as giving a pleasing natural appearance, has been found to

restrict lip movement in some cases. The lateral margins of labial flanges must be

reduced to wafer thinness and extended over the root eminences of the abutment teeth.

The thin edge allows the colour of the flange to blend more naturally with the

mucosa. Coloring and shading of labial flanges must be considered to blend

harmoniously with the natural tissues of the patient. Many manufacturers supply

acrylic materials containing colored fibers, to which may be added additional stain and

shaded polymers.


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B. SHORT ANTERIOR SADDLE

The general principles discussed in relation to long anterior saddles apply equally

to shorter ones:

The artificial papilla must be shaped to match the natural closest papilla.

The shape and contour of the gingival margin must be similar to that of the natural

teeth.

The junction between artificial and natural gum tissue as mixed together as

possible.

The margins of the flanges must be reduced to water thinness, and whenever

possible, extended over the eminences of the abutment teeth. Such thin edges not onlyblend inconspicuously with the natural tissues, but also allow their colour to show through.

It will be necessary to employ a path of insertion that will allow the thin acrylic to pass

over the eminence.

2. A gum-fit can be done by using a longer tooth than is really indicated which is

unsightly when the necks of the teeth are revealed by the patient. Usually it is better to use

a small flange if possible since this can be very thin and discreet and nearly undetectable at

normal distances. The use of a flange also increases the saddle area which is desirable

whenever possible. Fitting to the gum is recommended in some cases where the first

premolar has to be replaced and the canine is still standing.

The ridge just posterior to the canine is often quite prominent and the tooth

angulations will be better if no flange is used. In addition, a flange in this area is often

noticeable when the patient smiles.


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RESTS AND REST SEATS 3RPD THEORY AND PRACTICE

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RESTS AND REST SEATS

Definitions

Rests: Are rigid extensions of a partial denture, fitted into rest seats, which

are prepared on either the occlusal, lingual surfaces or incisal edges of the

teeth, providing support to the partial denture.

Support: The quality of the prosthesis to resist displacement towards

denture supporting structures.

Rest seat: The prepared recess in a tooth or restoration created to receive

occlusal, incisal, or lingual rest.

Types of Rests:

A- EXTRACRONAL (EXTERNAL) REST: which used with an extracronal

clasp assembly-type direct retainer although it is primarily within the contours of the

abutment tooth.

According to their shape and location on the tooth surface they may be

classified as:

1- Occlusal rest.

(1) Proximal occlusal (conventional),

(2)Interproximal

(3) Transocclusal (embrasure).

(4) Extended

2- Incisal rest.

3- Lingual rest.

4- Embrasure Hooks

5- Rest Recess

B- INTRACRONAL (INTRENAL) RESTS fit into rest preparations within

the contours of an abutment tooth crown. It is used with many precision and

semiprecision attachments.

PRECISION RESTS consists of two metal components manufactured to fit

together precisely. One component is a box type rest seat, keyway or matrix which is

incorporated into the crown of an abutment tooth. The other component is a rigid metal

extension (patrix) which fits the matrix precisely and is incorporated into the RPD.


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RESTS AND REST SEATS 3RPD THEORY AND PRACTICE

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A SEMIPRECISION REST is a box-type rest seat, keyway or

matrix which is fabricated in the dental laboratory by incorporating a

preformed plastic pattern into the wax pattern for the crown of the

abutment tooth, or by waxing the crown pattern around a special

mandrel in the dental sur

Removable PARTIAL DENTURE THEORY AND PRACTICE

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