29.2 Intraoral Occlusal Assessment

2. Intraoral Occlusal Examination

Intraoral Occlusal Analysis Dimensions
  │
  ├── Sagittal Plane
  │     ├── Incisor Relationship (BSI 4418 Classification: Class I, II/1, II/2, III)
  │     ├── Overjet Measurement (Normal: 2–4 mm; increased vs reverse)
  │     └── Canine & Molar Relationships (Angle's Class I, II, III)
  │
  ├── Transverse Plane
  │     ├── Posterior Crossbites (Unilateral with displacement vs Bilateral)
  │     ├── Buccal vs Lingual Crossbite (Scissors / Brodie bite)
  │     └── Centreline Concordance (Upper & lower dental midlines to facial midline)
  │
  └── Vertical Plane
        ├── Overbite Depth (Normal: 1/3 to 1/2 overlap; 2–3 mm)
        ├── Overbite Completeness (Complete to tooth/soft tissue vs Incomplete)
        ├── Traumatic Deep Overbite (Palatal stripping vs Labial stripping)
        └── Anterior Open Bite (AOB: Digit habit vs Skeletal vertical excess)

Incisor Relationship: British Standards Institute (BSI 4418)

In the United Kingdom, incisor relationships must be classified according to the British Standards Institute system (BS 4418). Unlike Angle's molar classification, the BSI classification is based strictly on the relationship of the mandibular incisor incisal edges to the cingulum plateau of the maxillary central incisors:

[!IMPORTANT] The BSI Class II Division 2 Diagnostic Triad: BSI Class II division 2 is defined strictly by the retroclined maxillary central incisors with the lower incisor edges lying posterior to the cingulum plateau. It is frequently accompanied by proclined or mesio-labially rotated maxillary lateral incisors overlapping the central incisors, an increased interincisal angle ($> 140^\circ$), and a deep, complete overbite that often impinges traumatically onto the palatal or labial gingiva.

Canine and Molar Relationships (Angle's Classification)

• Canine Relationship:
  • Class I: The maxillary permanent canine occludes directly into the interdental embrasure between the mandibular canine and the mandibular first premolar.
  • Class II: The maxillary canine occludes anterior to the embrasure between the mandibular canine and first premolar (full unit = occluding between mandibular canine and lateral incisor).
  • Class III: The maxillary canine occludes posterior to the embrasure between the mandibular canine and first premolar.
• Molar Relationship:
  • Class I (Neutro-occlusion): The mesiobuccal cusp of the maxillary first permanent molar occludes in the buccal groove of the mandibular first permanent molar.
  • Class II (Disto-occlusion): The mesiobuccal cusp of the maxillary first permanent molar occludes anterior to the buccal groove of the mandibular first permanent molar.
  • Class III (Mesio-occlusion): The mesiobuccal cusp of the maxillary first permanent molar occludes posterior to the buccal groove of the mandibular first permanent molar.

Transverse Discrepancies and Posterior Crossbites

A crossbite represents an abnormal buccolingual relationship between opposing teeth.

• Buccal Crossbite (Standard Crossbite): The buccal cusps of the maxillary posterior teeth occlude lingual to the buccal cusps of the mandibular posterior teeth.
• Lingual Crossbite (Scissors Bite / Brodie Bite): The lingual cusps of the maxillary posterior teeth occlude completely buccal to the buccal surfaces of the mandibular posterior teeth (total failure of occlusal contact).
• Unilateral Posterior Crossbite with Mandibular Displacement (Shift):
  • The most critical transverse entity in the mixed dentition.
  • Aetiology: Symmetrical bilateral constriction of the maxillary arch.
  • Pathomechanics: When the child closes into the initial contact (retruded contact position - RCP), premature cuspal interferences prevent stable intercuspation. To achieve functional intercuspation, the patient reflexively deflects (shifts) the mandible laterally to one side into maximum intercuspation (intercuspal position - ICP).
  • Clinical Signs: Unilateral posterior crossbite on the side of displacement; dental centerlines coincident in RCP but lower centerline displaced towards the crossbite side in ICP; facial asymmetry evident in ICP but disappears when the mandible is guided into RCP.
  • Management: Immediate interceptive maxillary expansion (e.g. quadhelix appliance or rapid maxillary expansion - RME) in the mixed dentition. Failure to eliminate the displacement allows asymmetrical condylar adaptation and permanent skeletal facial asymmetry.
• Bilateral Posterior Crossbite without Displacement: Represents a severe, true skeletal transverse maxillary deficiency. Centerlines are coincident with no RCP-ICP slide.

Vertical Discrepancies: Overbite and Open Bite

• Overbite: The vertical overlap of the maxillary central incisors over the mandibular central incisors. Normal overbite is 2 to 3 mm (covering one-third to one-half of the mandibular central incisor crown height).
• Complete Overbite: The mandibular incisal edges contact the palatal surfaces of the maxillary incisors or the palatal mucosa.
• Incomplete Overbite: The mandibular incisal edges do not contact any opposing tooth or mucosal surface when the posterior teeth are in full occlusion.
• Traumatic Deep Overbite: The lower incisors directly traumatize the palatal mucosa (stripping palatal gingiva behind upper incisors), or the upper incisors bite onto the lower labial gingiva (causing labial gingival stripping and periodontal attachment loss). Mandates treatment.
• Anterior Open Bite (AOB): Total absence of vertical overlap between maxillary and mandibular incisors when posterior teeth are in full occlusion.
  • Digit Sucking Habit: Typically asymmetrical open bite; localized to the side of finger insertion; associated with localized maxillary arch constriction and proclined upper / retroclined lower incisors.
  • Skeletal High-Angle Pattern: Symmetrical open bite extending posteriorly into the premolar region; associated with increased LAFH, obtuse gonial angle, and steep MMPA.

A complete intraoral orthodontic assessment is recorded in a fixed order so that nothing is omitted: teeth present, absent and of poor prognosis; the condition of the teeth and oral hygiene; crowding or spacing in each arch; the inclination of the labial segments; the canine and molar relationships on each side; the overjet and overbite; the centrelines and any displacement on closure; and finally any crossbites, open bites or functional shifts. Recording the assessment in this sequence makes the diagnostic statement straightforward to write and ensures that an asymmetry or a displacement is identified rather than discovered later.