Open Bite

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					                                             OPEN BITE
                                                                                    Week 11, 4/5/00
                                                                                        Dr. Chris Ho
1.0 DEFINITION
       1.1 Open Bite
                Absence of incisal overlap & / or
                Absence of occlusal overlap


       1.2 Incomplete Open Bite
                Incisal overlap is present, no occlusal overlap, i.e. no contact between anteriors


       1.3 Types of Open bite
           1. Dentoalveolar
                  No other associated extra oral skeletal features
           2. Skeletal
                  Open bite is due to underlying skeletal malformation


2.0 PREVALENCE
       2.1 Population distribution
                0.6% US population
                4% Caucasians
                16.3% Negro


       2.2 Age distribution
                highest occurrence in infants
                decreases rapidly in preschool age
                decreases more slowly through mixed dentition age
                levels out in adolescence


3.0 OPEN BITE CLASSIFICATIONS
       3.1 Transitional / Developmental
                OB evident in mixed dentition, or only at certain stages of development
                Usually spontaneous resolution
                Comprises most simple AOB cases
3.2 Habit Induced
      Usually due to digit sucking habit (non nutritive sucking)
      Major cause of simple AOB in children with good proportions
      Development of OB dependent on
       i.    Duration
       ii.   Intensity
             of the habit
      Duration of habit
        if discontinued after ~ 5yo, usually no problems develop
        persistence through mixed dentition may lead to problems
      Effect of Habit
       i.    inhibits vertical eruption of teeth
       ii.   prevents vertical dentoalveolar development, esp. in anterior section
       iii. anterior disclusion allows posterior over eruption
       iv. generated -ve pressures may lead to uni or bilateral crossbite development
      To Stop Habit
            Compliance is required to stop the habit
            Discuss the implications of the habit with the patient
             i.    5 – 6 yo
                        a. difficult to reason with
                        b. difficult for them to understand the implications
             ii.   7 & above
                        c.   can be reasoned with more easily
                        d. better appreciation of implications of the habit
            Non treatment options
             i.    paint bad tasting substances on fingers, e.g. chilli
             ii.   sew pajama arm holes closed
             iii. strap rolled up towel on elbow to prevent it bending
            Treatment Options
             o     URA or FA
                        e. Loops or spikes incorporated to prevent insertion of finger
                        f.   Can combine with palatal expansion where required
             o     URA – requires more compliant patient
             o     FA
                        g. reduced requirement for compliance
                        h. leave in maximum of 6 months
                        i.   design with rests on D’s
3.3 Primary Failure of Eruption
      aetiology is not understood
      due to a failure of the eruption mechanism
        i.e. tooth does not erupt spontaneosly
      usually limited to first permanent molars
      can occur in 3’s and 4’s
      unusual
      teeth will become ankylosed but don’t start out that way
      treatment
       i.    surgery to move teeth and close the open bite
       ii.   prosthetic overlay


3.4 Pathological Open bite
      OB caused by pathology
      Local Pathology examples
       i.    Supernumerary
       ii.   Cysts
       iii. Dilacerations
       iv. ankylosis
       v.    Cleft lip and palate
      Systemic pathology examples
       i.    Condylar hypo & hyperplasia
       ii.   Down’s syndrome
       iii. Cleidocranial dysostosis
      Management and treatment of the pathology may / may not allow normal
       eruption and closure of OB
      Nasal airway obstruction
            May result in OB
            Tongue rests against lower incisors
             i.    Inhibits anterior vertical development
             ii.   Allows over eruption of posteriors
            Difficult to assign cause and effect
             o     % of time mouth breathing difficult to determine
3.5 Soft Tissue Induced Open Bite
      tongue thrust
            may or may not be associated with OB
            2 types
             i.    endogenous tongue thrust
                       j.   difficult to prevent
                       k.   may lead to OB development
                       l.   treatment of OB will often relapse as tongue continues to act on
                            teeth post treatment
             ii.   Exogenous tongue thrust
                       m. Tongue thrust may be present to achieve oral seal where open
                            bite already existed
                       n. Correction of the OB should lead to discontinuation of the tongue
                            thrust
            Difficult to differentiate between endogenous & exogenous tongue thrust
            Treatment
             o     Correct the OB with ortho
            Relapse
             o     usually infers an endogenous tongue thrust
             o     difficult to prevent if endogenous tongue thrust
      large tongue


3.6 Skeletal
   A. Ceph Features
       i.    Skeletal pattern
             o     Can be Class I, II or III
       ii.   Maxilla
             o     Downwards cant (slant) in posterior maxilla
             o     Upwards cant in anterior maxilla
             o     Increased posterior height between occlusal plane and palatal plate
             o     Dentoalveolar process in posterior maxilla is overdeveloped
       iii. Mandible
             o     Obtuse gonial angle
             o     Gonial notch
             o     Short ramus
       iv. Relationships
             o   Post’r face height (Sella – Gonion) : Ant’r Face height (nasion to menton)
                                                     2:5
             o   anterior face height
                     o. Nasion – ANS : ANS – Menton
                     p. Usually 0.8 : 1
                     q. OB 0.7 : 1
       v.    Glenoid fossa is more superiorly located than usual
       vi. Posterior maxillary dentoalveolar process development greater then ramus
             development
                     r.   Anterior open bite


   B. Clinical
            Lips often incompetent
            Circumoral musculature weak
            May have nasal airway obstruction
            Muscles of mastication
             o   Oblique muscle fibres often more developed than vertical muscle fibres


3.7 Iatrogenic Open Bite
      may be due to treatment , e.g. anterior bite plane may
       i.    allow over erupton of posterior teeth
       ii.   inhibit eruption of anterior teeth
       iii. limit vertical development of anterior dentoalveolar process
4.0 TREATMENT
       4.1 Interception
               May be possible with
                i.    Digit sucking
                ii.   Tongue thrust
       4.2 Ortho treatment
               possibilities
                i.    Vertical elastics between maxillary and mandibular incisors
                ii.   In Class II Div 1
                         Rectrocline anterior teeth
                         Extract premolars
       4.3 Orthognathic Surgery
               Impact posterior maxilla
                         Allows mandible to rotate closed further and close open bite
       4.4 Orthopaedic treatment
               Aim is to modify the growth of the maxilla
               Patient must be growing for treatment to be effective
               High pull head gear
                         Inhibits growth of posterior maxilla


5.0 RELAPSE
       1. habit induced
               if habit is ceased low relapse
       2. skeletal discrepancy
                a. if closed with ortho treatment
                         relapse is low if no unfavourable growth occurs
                b. if closed with orthognathic surgery
                         prone to relapse
          very difficult to correct severe OB without relapse
                     often soft tissue are a component in aetiology
                     action continues post treatment
          “the greater the skeletal elements contribute to the aetiology the poorer the
           prognosis”
FURTHER NOTES FROM SEMINAR
6.0 POSSIBLE CLINICAL FEATURES
       1. Lip incompetence
       2. Excess gingival and tooth display
       3. Tongue thrust swallow
       4. UI proclination
       5. LI retroclination
       6. High palatal arch


7.0 CEPHALOMETRIC FEATURES
       1. Increased AFH
       2. Steep mandibular plane
       3. Vertical maxillary excess
       4. Rotation of mandible


8.0 PROBLEMS
       1. Mastication
       2. Facial aesthetics
       3. Speech
       4. Tooth wear
       5. TMD


9.0 TREATMENT / MANAGEMENT
          Dependent on aetiology
       1. No treatment
                  80% 7 – 12 yo spontaneously resolve
       2. simple habit control
                  cribs, chemicals, gloves
       3. orthodontic treatment
                  intrusion, extraction, Md rotation
       4. orthognathic surgery

				
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