Diagnosis and treatment planning in Orthognathic Surgery

DIAGNOSIS AND TREATMENT PLANNING IN ORTHOGNATHIC

SURGERY

Dr.N.R.K.Anil Kumar,II MDS,

Department of oral and maxillofacial surgery.

ContentsIntroduction History Diagnosis and Treatment Planning

Clinical evaluationCephalometric evaluation

Introduction Malocclusion can be due to many possible

reasons but they can be treated by:-1. Modification of growth2. Orthodontic camouflage which produces a

dental compensation for the skeletal compensation.

3. Surgical repositioning of the jaws and/or dentoalveolar segments

The term orthognathic originates from the words orthos and gnathos (Gr. orthos = straight; gnathos = jaw). Orthognathic surgery refers to surgical procedures designed to correct jaw deformities.

HISTORY

Hullihen is regarded as the first surgeon to describe a mandibular orthognathic surgical procedure. In 1849, he reported an anterior subapical osteotomy.

Jaboulay and Berard (1898), Kostecka (1931) performed operations on condylar neck and upper part of ramus by closed blind approach.

Surgical treatment for mandibular prognathism started in early 19th century.

In 1959, Trauner and obwegeser introduced sagittal split osteotomy as the beginning of a new era of orthognathic surgery.

American surgeons modify the technique for maxillary surgery that has been developed in europe

Epker, bell and wolford developed lefort-1 maxillary downward fracture ,so that we can keep the maxilla stable in all 3 planes of spaces.

By 1980 progress has reached such an extent to reposition either or both the jaws to move chin in all 3 planes of spaces.

Rigid internal fixation made it possible for comfort and better immobilization was achieved.

Envelope of discrepancy

Envelope of discrepancy shows how much of change can be produced by various treatment modalities.

3 5 252

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7 12 15

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INDICATIONS Severe skeletal class II &class III casesSkeletal open bite and deep bite casesDeep over bite in non growing individualsExtreme vertical excess or deficiency in

maxilla or mandibleSevere dentoalveolar problemExtemely compromised periodontal

situationSkeletal asymmetry

DIAGNOSIS AND TREATMENT PLANNING

There is no use of using a single diagnostic tool to implicate appropriate treatment as edward angle once hoped

Untill recently, hard tissues of the facial skeleton were the focus of diagnosis and treatment planning

It is now clear that the soft tissues are the limiting factor in the changes that can be produced in treatment and obtaining appropriate soft tissue proportions is the primary goal of treatment

Patient evaluation

Patient concerns or chief complaints,

Clinical examination,

Radiographic imaging and analysis,

Dental model analysis.

PATIENT’S CONCERNS

What are your concerns or problems?/what do you think is

wrong

Have you had previous treatment for this condition,

and what was the outcome?

Why do you want treatment?

What do you expect from treatment?

History taking

Personal information

Chief complaint - Motivation questionnaires

Medical history

Dental and orthodontic history

Pre-surgical growth assessment

Evaluation Esthetic facial evaluation - frontal facial analysis - profile analysis - intra oral evaluationCephalometric evaluationPanaromic / full mouth peripaical evaluationMasticatory muscle and TM joint evaluation

Photographs

Frontal view

Assessment of facial proportions and symmetry.

The ideal face in both males and females is vertically divided into equal thirds by horizontal lines at the hairline, the nasal base, and the menton

0.30

0.35

0.35

1 : 1.16 : 1.16

Fronto temporal point ( 0.65 )

Zygion ( 0.75 )

Gonion ( 0.66 )

6 – 8 yrs of age

Symmetry of canthiEyelids – ptosis, entropion, ectropionSclera, ocular imbalanceScleral show – mid facial defieciencyEyelid laxity – snap test

NOSEBoth males & females show more growth in

vertical ht than anteroposterior projection of nose but downward growth is greater in males

Form and symmetryLocation of deformityAlar base width (34 + / - 4 mm)A dorsal hump in the nose develops when class I & II malocclusion is present & is more pronounced in boys

• Alar width / nasion to pronasale = 3/5

• Cheek prominence • 8 – 12 mm laterally• 10 – 20 mm inferior to lateral canthus

•Ears• Upper 1/3rds just above the canthal level.

CheeksMalar prominences

LipsWidth of lips equal

to interpupillary distance

If asymmetry exists- Cleft lip- Facial nerve

dysfunction- Dental skeletal

deformityGull wing upper lip

has to be differentiated from vertical maxillary excess.

Normal patient 3 3 3 3 3 3

Vertical maxillary excess

6 6 6 6 6 6

Gull wing deformity

2 4 6 6 4 2

LIPS

The height of center part of upper lip trails behind the vertical height of the lower face in childhood & then catches up during & after adolescence.

Lip incompetence is common in childrenWhat looks like incompetent lips in childhood or early

adolescence is merely a reflection of incomplete soft tissue growth

Lip height Females : Upper lip - till 14Lower lip - continues to grow up to the age of 16Males : growth of both upper & lower lip continues into

late teens

Lip thickness is maximum during the conclusion of adolescent growth spurt & then decreases during late teens.

Smile evaluation

A balanced smile is achieved by appropriately positioning the teeth and

gingiva in the area that is displayed by lip animation during smiling

(dynamic display zone). The amount of incisor and gingival display

The transverse dimension / broadness of the smile

The smile arc

Buccal corridor

Negetive space

Incisor and gingival display

The difference between social and enjoyment smile is not the activity of orbicularis oris musculature but of orbicularis oculi.

Chin Tapered / squarishPinch test – semiquantitative assessment of

subcutaneous fatSub platysmal and supra platysmal fat -

differentiated

PROFILE VIEWFore headSlopes anteriorlyAccentuated at supra orbital rimFrontal bossingSupra orbital hypoplasia

Glabellar angleGl- N to N – prs132 + / - 15 degrees

Soft tissue proportions: profile view.

The prominent part of the forehead (glabella) should be approximately the same as the base of the nose, and the forehead should slope gently posteriorly.

The radix (the depth of the concavity at the base of the forehead) should be prominent to obscure the eyelash on the opposite side.

Lateral orbital rims – 8 to12 mm behind the anterior projection of globe.Infra orbital rim – 2mm anterior to the globe.

Cheek bone contour

The contour of the alae from the base of the nose to its tip should be well defined to form a "scroll".

The bridge of the nose (nasal dorsum) should then be a straight line from the base of the radix to the nasal tip cartilage, and there should be a slight prominence of the tip relative to the bridge.

Naso labial angle – 90 to 110 degrees

2

• Alar base has to be supported by skeletal nasal bone.• Nasal bridge – 5 – 8 mm ant to globes• Nasal tip ( prn ) – subnasale : subnasale – alar base crease = 2:1• If values of 1: 1 – maxillary defeciency

Clinical facial examination - Profile view

Mandibular area

Lower lip prominence

Soft tissue pogonion

prominence

Neck – chin angle – 110

Throat length contour – 50

mm

Overjet

Labiomental foldThe labiomental sulcus should form a

shallow S curve, with the upper and lower portions similarly shaped. The prominence of the chin should be slightly less than the prominence of the lower lip.

The angle between the lower lip, chin, and deepest point along the chin-neck contour should be approximately 90 degrees

Cervico mental areaMandibular angle- Inferior border defenition - well defined in profile - skin laxity, cervical facial lipomatosis, high

mandibular plane angle are conditions – obscure the defenition.

Neck – chin angle and length - normally 110 degrees - PoG – neck chin angle : distance is 50

mm.

TMJ Examination

• The range of movements

• Deviation from normal

movements

• Any pain during movement

• The joint sounds.

Intra-oral examinationSoft tissues

General periodontal condition

Tongue size, position and activity

Mentalis muscle activity

Finger or thumb sucking

Hard tissue

Dental assessment

Periodontal evaluation

Adequate attached gingiva

Maintain bone around the necks of each of the

teeth at the interdental osteotomy sites

Intra oral examination

Dentition

Vertical Overbite Plane of occlusion Curve of spee

Horizontal Anatomical variation Crowding / spacing Overjet

Transverse Crossbites

Maxillary retrusion

Mandibular retrusion

Clockwise mandibular rotation

Upper and lower denture base retrusion

Overjet increase

Canting of bilateral structures, specially

the lips and the dentition.

CEPHALOMETRIC EVALUATION

Burstone's Analysis (COGS)

Burstone, Randal, Legan, Murphy & Norton(1978)

ANATOMIC LANDMARKS Sella (S)

Nasion (N)

Rhinion (Rh)

Glabella (G)

Orbitale ( O )

Articulare (Ar)

Pterygomaxillary fissure (PTM)

Posterior nasal spine (PNS)

ANATOMIC LANDMARKS

Prosthion (P)

Anterior nasal spine (ANS)

Subspinale (A)

Menton (Me)

Gnathion (Gn)

Pogonion (Pg)

Mandibular plane (MP)

ANATOMIC LANDMARKS

Infradentale ( I )

Supramentale (B)

Condylion (C )

Pronasale (P )

The COGS appraisal describes Dental,SkeletalSoft tissue variations.

CRANIAL BASE

HORIZONTAL PLANE (HP), which is a surrogate Frankfort plane,constructed by drawing a line 7 o from the line S to N.

Ar- PTM :The greater the

distance between Ar-PTM, the more the mandible will lie posterior to the maxilla, assuming that all other facial dimensions are normal.

Therefore, one factor for prognathism or retrognathism can be evaluated by this measurement of cranial base.

HORIZONTAL SKELETAL PROFILE

N-A –Pg (Angle): gives an indication of the overall facial convexity. A positive (+) angle of convexity denotes a convex face; a negative (-) angle denotes a concave face.

N-A :

N-B:

N-Pog

VERTICAL SKELETAL AND DENTAL

Middle third facial height : Distance from N to ANS

Posterior maxillary height : PNS-N

Lower third facial height : ANS – GN

Divergence of mandible posteriorly : M.P-H.P angle(clockwise or counter - clockwise rotations of the maxilla and mandible)

U1 to NF: Anterior maxillary dental height

L1 to MP: Anterior mandibular dental height

These two measurements define how far the incisors have erupted in relation to NF and MP respectively.

Max. molar to NF : Posterior maxillary dental height

Mand. Molar to MP: Post mandibular dental height

MAX-MAND. RELATION

ANS-PNS: This measurement along with the N-ANS and PNS– N gives a quantitative description of the maxilla in the skull complex.

Ar - Go : Length of Mandibular ramus

Go - Pg : Length of Mandibular body

Ar - Go - Gn Angle : Gonial angle that represents the relationship between ramal plane and MP. Vertical /Horizontal growth

B - Pg : Distance from B point to line perpendicular to MP through Pg describes chin prominence.

DENTAL

OP- upper HP:

AB – OP:

U1 to NF angle & L1 to MP angle: These angulations determine the procumbency or recumbency of the incisors.

BURSTONE’S ANALYSISCHARLS .J.BURSTON ET AL: JOS,VOL 36 , PG 269-277

STEINER’S ANALYSIS

S.No

Measurement Mean

1. SNA 820

2. SNB 800

3. ANB 20

4. SND 760

5. M.P to SN 320

6. U1 to N-A 4mm

7. U1 to N-A (angle) 220

8. L1 to N-B 4mm

9. L1 to N-B (angle) 250

10.

Interincisal angle 1300

11.

Occ. Plane to S-N (angle) 140

S-line: Upper lip: 0mm Lower lip: 0mm

WITS APPRAISALAO is 2mm ahead of BO - skeletal class I

SCHWARZ ANALYSISLength of Mean

Anterior cranial base

Mandibular base ACB + 3mm

Maxillary base mmRamus length mm

Ramus width mm

HOLDAWAY’S SOFT TISSUE ANALYSISMeasurement Mean

Facial angle 90-920

Upper lip curvature 1.5-4mm (2.5)

Skeletal convexity at point A

-2 to +2

H-line angle 7-150

Nose tip to H-line Upto 12mm

Upper sulcus depth 3-7mm

Upper lip thickness 15mm

Upper lip strain Same as ULS

Lower lip to H-line 0mm -1to +2mm

Lower sulcus depth 5mm

Soft tissue to chin thickness

10-12mm

GRUMMONS ANALYSIS

The first horizontal plane connects the medial aspects of the zygomaticofrontal sutures.

The second horizontal plane connects the center of the zygomatic arches.

The third horizontal plane connects the jugal processes.

A fourth horizontal plane runs through the menton and is parallel to the first plane.

Grummons article JCO 1987

Zygomaticofrontal sutural plane

Zygomatic arch plane

Jugal plane

Z plane through menton

Mandibular morphologyVolumetric comparison

Maxillo mandibular comparison of assymetry

MSR-J maxillary width

MSR-Ag mandibular width

MSR-NC width of NCNasal septum deviation

MSR-Co Asymmetry in condyle

MSR-Me Mandibular symmetry

LINEAR ASYMMETRYMAXILLARY MANDIBULAR COMPONENTS

VALIDITY OF CEPHALOMETRICS

Errors in cephalometric measurements

Radiographic cephalometry is a two dimensional representation of three dimensional object.

a)Radiographic projection errorMagnificationDistortion

b)Errors within measuring system

c)Errors in landmark identification

Quality of radiographic imagePrecision of landmark definition Reproducibility of landmark locationThe operator and registration procedure

Limitations of cephalometric radiographic analysis

1)Growth pattern not taken into consideration

2)Mean values are based on different population

3)Two dimensional representation of three dimensional object

4)Form and functions not taken into consideration

A combination of various cephalometric norms and variables should be compiled to arrive at a proper diagnosis.Although innumerable controversies exist in the field of cephalometrics, it is still a very significant & effective diagnostic tool.

Conclusion:

Methods of model surgery:

Simple method.

Anatomically oriented model surgery.

Anatomically oriented model surgery.

In complex cases, especially where multiple bimaxillary movements are required, it is essential to use a more refined technique such as the following variant of a popular “North American method”

In this technique, in addition to the impressions and sqash bite, a face-bow recording is taken.

1. The working models are anatomically trimmed and articulated on the semi adjustable articulator using the face-bow recording and then the standard squash bite.

Technique:

2. Horizontal and vertical reference lines are drawn on the mounting plaster to register the post-operative position of each maxillary and mandibular segments before surgery.

Two sets of parallel horizontal lines A/A and B/B are drawn on the upper and lower models. These are easily done by rotating the detached model with the felt pen.The B lines should be just clear of the apices of the teeth, and not less than 15mm from the A lines. These lines will be used to plan the vertical movements.

3. Three vertical lines VC, VB, VM are drawn from upper base line (A) to the lower baseline (A) on each buccal segment.

These will help to indicate the anteroposterior movements achieved by the model surgery.Upper and lower midlines are also drawn.

Marked models with the recorded distances.

4. The vertical distances from the buccal cusp tips of the three reference teeth to their A base lines are recorded to help calculate any vertical movements.

Transverse changes are recorded by the inter-canine and inter-molar distances measured across the palate and recorded by taking reference points on the canine tips and the mesiobuccal cusp of the first molars.

Cuspal reference points are used for transverse changes.

When all the reference lines have been drawn and the measurements completed, the osteotomy lines are drawn between A and B lines to correspond with the bone cuts.

The plaster mounting assembly is then sectioned at the osteotomy sites with a saw or large abrasive disc and the whole arch or segments are repositioned in the planned post-operative position.

Interrupted line is the proposed osteotomy site.

Maxilla is reassembled with the wax after the osteotomy cuts. Mandible closes in to the intermediate occusal relationship.

Intermediate wafer is made at this stage.

Lower segmental set-down of 3mm is carried out with the forward slide of 5mm to correct the interarch occlusal relationship.

Anterior view: models showing the upper midline split to widen the intercanine width and the lower anterior set-down.

THANK YOU

Diagnosis and treatment planning in Orthognathic Surgery

Health & Medicine

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