Good morning

MIDLINE DISCREPANCIES

Anusha Yaragani

PG student

Dept. of orthodontics

SIDS

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Contents Introduction Definitions Etiology Database for diagnosis Diagnosis Types of midline discrepancies Treatment Conclusion

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Introduction o Midline coordination and relative symmetry are basic to an

appreciation of facial harmony and balance.

o Although a subtle asymmetry of the midlines is within normal limits, significant midline discrepancies can be quite detrimental to dentofacial esthetics.

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o Of all occlusal asymmetries, midline discrepancies are the most obvious from the patients‘ perspective.

o Midline discrepancies maybe isolated, or may occur in concert with other occlusal asymmetries, particularly molar occlusion asymmetry, or the angle subdivision malocclusions.

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Definitions

o Woo in 1931 found that the human skull could be markedly asymmetrical.

o According to Lundstrom.A, these asymmetries are embryonically rooted and are associated with asymmetry in the central nervous system.

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o Dorland’s Medical dictionary defines symmetry as

“The similar arrangement in form and relationships of parts around a common axis or on each side of a plane of the body”.

o W.Schmid/Mongini mentioned two types of asymmetry

1. True Structural Asymmetry

2. Displacement Asymmetry

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We, orthodontists are often preoccupied with the lateral facial aspect of the patient, where as the general public tend to judge, beauty, symmetry & harmony from a frontal projection.

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Washburn in 1946, reported the effects of paralysis of facial muscles after unilateral sectioning of the facial nerve.

Bjork and Bjork in 1964 noted that compensatory asymmetric growth of maxilla and mandible can occur when the cranial base develops asymmetry at an early age.

Mulick in 1965 concluded that asymmetry of the face can be related to the functional demands of the masticatory apparatus and musculoskeletal system.

Sharad Shah and M.R. Joshi in 1978 observed that pleasing and apparently symmetrical faces do exhibit skeletal asymmetry, suggesting that the soft tissue of the face attempts to minimize the underlying skeletal asymmetry

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Etiology

1. Genetic alterations

2. Glenoid fossa position-growth of cranial base.

3. Moulding of parietal and facial bones due to intrauterine pressure.

4. Trauma/infection of TMJ

5. Pathological conditions- osteochondroma of condyle.

6. Local/environmental factors

7. Habits

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Etiology contd..

Genetics :

1. Clefts of the lip or palate2. Hemifacial microsomia 3. Hemifacial Hypertrophy 4. Congenital muscular torticollis 5. Postural Scoliosis

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Etiology contd.. Intra-Uterine pressure during pregnancy and significant pressure

at the birth canal during parturition can have observable effects on the bones of the fetal skull.

Molding of the parietal and facial bones from these pressures can result in facial asymmetry. These effects are generally transient with rapid restoration of the normal relationships of the skull within a few weeks to several month

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ENVIRONMENTAL FACTORS

a. sucking habits

b. asymmetrical chewing habits caused by dental caries, extractions, and trauma.

FUNCTIONAL DEVIATION.

Due to any premature contact.

LOCALISED PATHOLOGY

a.Osteochondroma of the mandibular condyle

b.condylar hyoplasia,hyperplasia

c.irradiation

d.lymphangioma

e.fibrous dysplasia etc.

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Etiology contd.. Trauma and infection must also be considered when encountering facial asymmetry. Untreated fractures of the mandible can display varying degrees of facial disfigurement.

Brodie concluded injury to the condylar region results in growth arrest, and consequently, a characteristic distortion of the mandibular form.

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Etiology contd..

Condylar fracture is not always followed by deviant growth of the mandible however, and many of the cases may remain undiagnosed as shown by Proffit et al.

It has been found that mandibular fracture may affect the growth of the middle facial area. The occurrence of maxillary midline shift towards the fractured site and the degree of the deformity are related to the site of the fracture of the mandible.

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Etiology contd..

o An increased incidence of crossbite and scissor bite is seen in children with enlarged adenoids, tonsils and impaired nasal breathing.

o Unilateral crossbite can be also associated with persistent intensive finger or dummy sucking habits.

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THERE ARE THREE MAIN CAUSES OF FACIAL ASYMMETRY AND DENTAL MIDLINE IRREGULARITIES:

A. True skeletal asymmetries of the facial structures including the mandible and/or maxilla

B. Dental asymmetries in one or both arches and

C. Functional shifts of the mandible during closure or opening.

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Database for diagnosiso Detailed facial and intraoral examination.o Intra- and extraoral photographs/video.o Dental modelso Occlusogramo Lateral cephalogramo P-A cephalogramo 45o cephalogramo Panoramic radiographo Submental vertex radiograph.

@ Ravindra Nanda, SO 1996

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Diagnosiso A diagnostic protocol, which includes systemic evaluation of

1. The soft tissue – clinical and photographic examination.

2. The dentofacial skeleton – PA cephalogram, submentovertex view, TM Joint imaging.

3. The dentition – study model casts (model analysis), occlusograms, OPG’s and occlusal x-rays

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IDEAL FCIAL PROPORTION

TRANSEVERSE FACIAL PROPORTION

Rule of fifth describe the ideal transverse relationship of the face.

The face is sagittally divided in to five

equal parts from helix to helix of outer

ear.Each of the segments should be one

eye distance in width

A-THE CENTRAL FIFTH OF THE FACE

B- THE MEDIAL TWO FIFTH

C- THE OUTER TWO FITTH

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oVERTICAL FACIAL RELATION- THE FACIAL ONE THIRDS

oface is vertically divided in to equal

thirds by horizontal lines,

1. hairline to midbrow,

2. midbrow to subnasale,

3. subnasale to soft tissue menton.

oThe thirds are within a range of 55 to 65 mm,

vertically.

oThe appearance of the landmarks (incisor

exposure, interlabial gap) within the lower third

are more important in assessing balance than

are the equality of the middle and the lower

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Facial level: With the patient in natural head posture, the pupils are used as the horizontal reference line .

Structures compared with the pupil line are

1.upper canine level

2.lower canine level, and

3.chin and jaw level.

o Mandibular deviations commonly

have upper and lower occlusal cants

with chin and jaw line canting associated

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Clinically,facial midline

1. Intercanthus point

2. Nasal base

3. Nasal tip

4. Philtrum

5. Chin midpoint

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o In normal face, the profile is oriented to the vertical by horizontal positioning of paired symmetrical features (rims of lower eyelid, insertion point of the alae, direction of labial fissure, and upper border of eyebrows) .

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The composites of two left sides and two right sides display two different individuals.

Original

Right Left

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CEPHALOMETRIC EVALUATION

Most of the PA cephalometric analysis are quantitative and they evaluate the craniofacial skeleton by means of linear absolute measurements of

a.width or height,

b.Angles,

c.Ratios and

d.Volumetric comparison.

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o An angle finder can be used to confirm whether the required position has been achieved and also head position checking device can be used.

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PA Cephalograms and refined diagnostic tools, such as computerized tomographic images and stereophotography, allow 3 – dimensional analysis of the craniofacial complex

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Midlines

1. Facial midline

2. Skeletal midline

3. Maxillary apicalbase midline

4. Mandibular apicalbase midline

5. Maxillary dental midline

6. Mandibular dental midline

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PA cephalogram

o centric relation

@ The primary indication for obtaining a PA view is the presence of facial asymmetry (Proffit 1991).

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Various methods of analysis: Ricketts et al, 1972. Hewitt 1975. Svanholt and Solo 1977. Grayson et al, 1983. Chierici 1983. Grummons and Kappeyne Van de Coppello 1987.

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RICKETTS ANALYSIS

Construction of midsagittal plane.

A transverse plane is constructed by connecting the center of the zygomatic arches, then a perpendicular is constructred to the transverse plane through the top of the nasal septum or crista galli.

Skeletal asymmetry is evaluated

by relating the point ANS and

pogonion to this mid sagittal plane.

Denture Assymetry can be evaluated

by relating the upper and lower incisor

roots to the midsagittal plane.

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Using the MSR plane Various transverse and vertical reference planes are constructed to measure the

Nasal cavity width,

Mandibular width,

Maxillary width,

Intermolar and intercuspid width

SVANHOLT AND SOLOW -

This method aims to analyze one aspect of transverse cranio-facial development, namely the relationship between the midlines of the jaws and the dental arches

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GRUMMONS ANALYSIS

This a comparative and quantitative PA analysis. The analysis consist of different components including

1.A midsagittal reference line.

2. Horizontal reference line,

3. Mandibular morphology analysis

4 Volumetric analysis.

5. Maxillo mandibular comparison of asymmetry.

6. Linear asymmetry assessment.

7. Maxillomandibular relation.

8. Frontal vertical proportion analysis

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The midsagittal reference line is Constructed from crista galli through ANS to the chin point.

oMSR plane is constructed from the midpoint of the z plane through ANS is used as a reference midsagittal plane .

Horizontal reference lines are

1.Z line,

2.ZA line,

3.J line.

4.One parallel to the z plane

through menton

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oMandibular morphology analysis Triangle are formed by connecting the head of the condyle,the antegonial notch and the menton and the triangles on either side is are compared .

Volumetric analysis o polygon is formed by connecting Condylion, antegonial notch, menton and a perpendicular from MSR and the right and left side polygon are compared.

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Maxillo mandibular comparison of asymmetry

Four lines are constructed perpendicular

to MSR from Ag and from J bilaterally.

Line connecting cg and J and lines from

Cg to Ag are also drawn.

Two pairs of triangles are formed in this

way, and each pair is bisected by MSR.

If symmetry present, the constructed

lines also form two triangles namely

J – Cg – J and Ag – Cg – Ag.

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Linear asymmetry assesement

Perpendicular projection are drawn from

the MSR to CO, NC, J, Ag and Me.

the linear distance from MSR

Frontal vertical proportion analysis

Ratios of skeletal and dental measurements

are made with respect to MSR and those

ratios can be compared with common facial

esthetic ratios and measurements

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GRAYSON ANALYSIS

Landmarks are identified on different

frontal planes at selected depth of the

craniofacial complex and subsequent

skeletal midlines are constructed.

In this way the analysis enables

visualization of midlines and midpoints

in the third (sagittal) dimension.

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HEWIT ANALYSIS

•Analysis of craniofacial asmmetry

is performed by dividing the

craniofacial complex into constructed

so called traingulation of face.

•The different angles, triangles and

component areas can be compared for

both the left and right side.

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LIMITATIONS OF PA CEPHALOGRAM:

1. Chances that apparent distances will be affected by a tilt of the head in the head holder. Because of this angular measurements can be influenced in an uncontrolled manner.

2. Precise measurements of the structures are difficult.

3. The conventional use of two ear rods to stabilize the head in radiographic cephalometry is based on the assumption that the transmeatal axis of humans is perpendicular to the midsagittal plane.

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o Thereby, the attempt to determine facial asymmetry of a patient generally results in a compromise rather than as an exact definition.

HOW TO OVERCOME THIS?o Any one ear rod should be used.o The other ear rod should be merely placed against

any part of the ear, or replaced by a small soft rubber cup

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3. Evaluation of the dentition, by means of study model casts (model analysis), occlusograms, OPG’s and occlusal x- rays;

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OCCLUSION EVALUATION

A. FUNCTIONAL EVALUATION: compatibility between centric occlusion (CO) and centric relation (CR) and to assess tooth wear. Since many Class II and asymmetric individuals have "habitual occlusions,”.

• Failure to appreciate meaningful inconsistency in CO and CR may result in significant errors in both treatment planning and in surgery.

B. STATIC EVALUATION : anatomically oriented models

1. intraarch analysis,

2. interarch analysis

3. tooth mass evaluation

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INTRAARCH ANALYSIS - MAXILLARY ARCH

oArch should be analysed for both transverse and AP symmetry

oAP reference plane is constructed using mid palatal raphae

othe tuberosity plane(drawn perpendicular to AP plane) is used as a transverse reference plane.

oCross section of the second palatal

Rugae

omid point between the paired

foveolae

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INTRAARCH ANALYSIS-MANDIBULAR ARCH

•The anterior point can be precisely

Marked using mental spine or

by using the lingual frenum

•The posterior point is determined by

a perpendicular, which runs from the

posterior edge of the MPR from the

maxillary to the mandibular cast

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Asymmetry in the dental arch can be assessed by placing a transparent ruled grid over the dental cast so that the grid axis is on the median palatal raphe.

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MASTICATORY MUSCLE EXAMINATION .

The masticatory muscle examination has two primary functions.

First, to identify any painful and / or trigger points.

Second, to identify the deficient masticatory muscle mass that often exists in patients who have sustained trauma to this area or who have undergone previous orthognathic surgery.

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o MANDIBULAR MOVEMENTS

oThe normal interincisal opening is about 50mm.

ominimum normal protrusive and excursive movements are approximately 6mm.

oIf deviations of greater than 2 to 4 mm occur during opening, they are noted and recorded.

oIf opening is reduced or deviations exist, it is important to determine if this caused by true temporomandibular joint abnormalities or masticatory muscle problems

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TMJ EXAMINATION

TMJ is palpated, auscultated and examined for any pain, clicking sounds

and for normal position and movements of condyle.

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Evaluation of dental midlines should be done in mouth open, in centric relation, at initial contact, and in centric occlusion.

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Classification

Asymmetries

Quantitative Qualitative

@ Lundstorm A., Amer. Jrnl of Ortho, 1961.

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o Anders Lundstrom: in 1961o Qualitative asymmetry

Number of teeth. - oligodontia

- supernumerary teeth.

Cleft Palate

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Oligodontia

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Quantitative asymmetry:1. Size of the teeth

1. Microdontia

2. Macrodontia

2. Location of the teeth in dental arch.

1. Antero-posterior plane

2. Transverse plane.

3. Vertical plane.

3. Location of dental arches in the head.

1. Rotation in horizontal plane

2. Rotation in frontal plane

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Antero-posterior position: Posterior segment.

Ex - Class II sub div or Class III sub div

o This type of dental relation is seen in early/delayed exfoliation of deciduous teeth.

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Anterior segment:

Upper/ lower anterior midline can be deviated because

1. early exfoliation of deciduous canine,

2. ectopic eruption or missing upper/ lower permanent lateral incisors

3. peg shaped upper lateral incisors which might lead to abnormal canine as well as incisor relationship.

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Transverse plane: Dental asymmetry in the transverse plane can be due to

constricted maxillary/mandibular arch because of

1. digit sucking or mouth breathing habit

2. abnormal posture of the tongue.

3. Asymmetric chewing habits

4. Extraction of deciduous/permanent teeth

5. trauma

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Model analysis like Bolton’s should be considered in correction of midlines.

The tooth size discrepancy can be corrected either by restoring (build up) of small sized teeth or interproximal reduction of larger teeth.

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Vertical plane: Vertical discrepancy in

the arches can lead to a cant in the occlusal plane.

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Midline discrepancy

Skeletal

maxillary

mandibular

Dentoalveolar

Soft tissue

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Skeletal

1. Maxilla

2. Mandible

3. Combination of both

Maxillao Constriction of basal arch- posterior crossbiteo Rotational changes relative to cranial base-asymmetric

occlusiono Congenital anomalies-clefts

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Mandibular o Abnormal growth of cranial base-position of glenoid fossao Congenital

o Hemifacial microsomiao Trauma to mandibular condyle- scarring, fibrosiso Unilateral condylar hypertrophyo Infections – ankylosiso Rheumatoid arthritis-destruction of TMJ & disc.

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Muscular asymmetrieso Hemifacial atrophyo Cerebral palsyo Soft tissue-masseter muscle hypertrophy

Functional problemso Occlusal intrerferenceso Malposed tootho TMJ disorders- ant. Disc displacement without reduction

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MIDLINE DIASTEMA Midline diastema refers to anterior midline spacing between

the two central incisors. ETIOLOGY

1.NORMAL DEVELOPING DENTITION

Physiologic median diastema/ ugly duckling stage

Ethnic and familial

Imperfect fusion of midline of premaxilla

2. TOOTH MATERIAL DEFICIENCYMicrodontiaMacrognathiaMissing lateralPeg lateralsExtracted tooth2 nov 2011

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3. PHYSICAL IMPEDIMENTRetained deciduous MesiodensAbnormal labial frenumMidline pathologyDeep bite

4. HABITSThumb suckingTongue thrustingFrenum thrusting

5. ARTIFICIAL CAUSESRapid maxillary expansionMilwaukee braces

6. RACIAL PREDISPOSITION

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It is a transient or self correcting malocclusion which is seen in the maxillary incisor region between 8-9 years. It is particularly seen during the eruption of the permanent canines.

As the permanent canines erupt they displace the roots of the lateral incisors mesially.

This causes a divergence of the crowns of the two central incisors causing a midline spacing.

This was described by Broadbent as the ugly duckling stage as children tend to look ugly during this phase of development. So it also known as Broadbent phenomenon.

It is a self correcting anomaly.

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Treatment plan1. Selection of treatment midline.

2. Apical base discrepancy is 2mm- ass. with molar occlusion- U/L midline which is closest to facial

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Treatment mechanics

1. bracket placement: in apicalbase discrepancy, incisal brackets are angulated- results in tipping.

2. Cantilevers – uprighting tipped incisors.

3. Asymmetric extractions

4. Varying time of extraction

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SKELETAL ASYMMETRY:

Antero-posterior Vertical Transverse

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A-P Skeletal Asymmetry

Age of the patient.

Growing individual with mild asymmetry – Growth modulation using Hybrid appliances .

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Functional shift of the mandible due to maxillary constriction:

Treatment Expansion of maxilla. Unilateral Fixed Functional Appliances –

Jasper Jumper, Churro’s or Fielo’s appliance.

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Moderate to severe asymmetries → Distraction osteogenesis

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Orthognathic Surgery

Guidelines – o More concern about transverse than vertical asymmetryo More concern about chin position than mandibular angleso Maxillary midline more critical than mandibular midline

o If nose and jaw are deviated to the same side, both should be corrected

o Asymmetry of higher structures - infra-orbital rims, Zygomatic arch – onlay grafts should be considered

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Transverse skeletal asymmetries

o Unilateral or bilateral constriction of the upper arch/lower arch in conjunction with a functional shift of the mandible.

o Sutural patency o Conventional rapid palatal expansion o Surgical assisted palatal expansion

A mandibular bilateral constriction can be corrected →oIn growing individuals: expansion appliances (tooth-borne appliances) can be used.oSympyseal distraction (bone-borne).oOrthognathic surgical procedure .

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DENTAL ASYMMETRIES

Dental asymmetries can exist in solo or in combination with a skeletal problem; but, the rectification strategies remain the same.

Asymmetric Midlines ( Antero-posterior / transverse plane): 1. In Begg Appliance

o placing uprighting springs on the side to which the midline is shifted along with Class II elastics or Class I elastics on the opposite side.

o Diagonal elastics can also be used.

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In PAE:

oMidline shift because of tipping of the incisors can be corrected by ligating figure of 8 ligature wire, which causes tipping of the engaged teeth.

oMidline corrections by bodily movement can be achieved using PAE brackets with a combination of open loop and a closed loop design in a rectangular S.S wire or by using a fixed functional appliances .

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TREATMENT OF CROSS BITE

factors to be considered

1.Age and growth potential of the individual

2.Type of cross bite- dental or skeletal

3.Anterior or posterior

APPLIANCES USED

REMOVEABLE APPLIANCE-includes catlans appliance posterior bite plane with Z spring

BANDED APPLIANCE -lingual arch, quad helix

MYOFUNCTIONAL APPLIANCE face mask for maxillary retrusion reverese activator, FR III and chin cap for excessive mandibular growth

EXPANSION SDREWS- slow and rapid palatal expansion screws

FIXED APPLIANCE-asymmectrically expanded arch wire and cross elastics

OCCLUSAL GRINDING- if the asymmetry is due to any occlusal interferences

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Conclusion Although some amount of discrepancy is treated as normal,….

Correction of midline discrepancies and asymmetric molar relationships need a careful diagnosis, treatment plan and biomechanical plan in order to achieve predictable results.

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thankyou2 nov 2011