Remember, without an accurate understanding and diagnosis it will be hard to answer a concerned teenagers questions! 

What is the Ideal Occlusion?

Andrews 6 Keys of an Ideal Occlusion are: 

• Class 1 Molar relationship 
• Flat occlusal plane (curve of spee) 
• No rotation 
• No spaces 
• Correct tipping of teeth 
• Correct inclination of teeth 

Confident Orthodontic Assessments Require an Understanding of Aetiology:

General Factors leading to Malocclusion: 

Skeletal:  

• Anteroposterior (AP): Maxillary relationships with the mandible, e.g. 
  • Mandibular retrognathia (Class II)  
  • Maxillary Protrusion can occur but rare (Class II) 
  • Maxillary retrusion (Class III) 
  • Mandibular protrusion jaw bone growth (Class III) 
  • Cranial Base development: length and angle (produce Class II OR Class III) 

Important to note: With favourable S/T conditions, Dento-alveolar compensation can occur, resulting in the Intra-oral malocclusion being less significant than the skeletal pattern. Example: proclination of lower incisors in a class II skeletal pattern.  

• Vertical Dimension (VD): (Mainly Lower Anterior Face Height) 
  • Affects: Lower Incisal incline, Overbite, Lip competency, Lower Lip Line, and AP position of chin point. 

• Growth: Producing, Long or short faces: 
  • Clockwise rotations: Backwards growth of the Mandible 
  • Anticlockwise rotations: Forwards growth of the Mandible 
  • Excess Maxillary Growth can increase facial height, leading to a retruded chip point because the mandible is rotated downwards and backwards. 

• Transverse: Ideally, the maxilla should be wider than the mandible.
  • Normal Buccal overjet = 2-4mm (1)
  • A small maxilla in all dimensions can be called: Absolute Transverse Maxillary Deficiency.
  • A normal width of maxilla, but with an anteroposterior discrepancy leading to malocclusion in the transverse plane (the width of the face) can be called: Relative Transverse Maxillary Deficiency.

Soft Tissues (the delicate muscular balance and equilibrium theory): 

Lips: 

• Lips: The Fullness and Tone can affect malocclusions e.g. “Strap-like lips” can cause Incisal retrusion 
• The lower lip line should cover 1/3-1/2 of the Upper centrals (1)
• Lip competency allows for an anterior oral seal.
• Adaptive Swallowing can affect anterior inclination. 

Tongue: 

• Size of the tongue: 
  • Macroglossia can lead to: Incisor proclination, Impede eruption, Open Bites, Abnormal swallow. 
• Endogenous tongue thrust. 
  • Can lead to anterior open bite or protruding incisors.
• Adenoids: enlarged – creating open mouth, leading to the Dahl affect. Causes an anterior open bite.
• Muscular Pathologies: 
  • Dystrophies: Lack of tone allows increases in growth and therefore increasing facial height. 

Local Factors leading to Malocclusion: 

The Teeth: 

• The number of teeth in the mouth will affect occlusions: 
  • Hypodontia/Supernumerary/Early loss of deciduous/Loss of 6s/Trauma. 
• The size of teeth can make a difference:  
  • Macrodontia = Crowding 
  • Microdontia: U2s associated with impacted 3s.  
  • General Dento-alveolar discrepancy 
  • Bolton discrepancy: How well teeth interdigitate due to a mismatch in size. 
• The position of teeth clearly has an impact:  
  • Infra-occlusion 
  • Impacted teeth
  • Transpositioned teeth (when erupt into the wrong place)
  • Failed or partial eruption   

S/T: 

• Frenal Attachments can cause:
  • Diastemas & Recession (Note: alveolar cleft present if blanching of the palatal occurs when the frenum is stretched). 
• Tongue thrusting can also cause anterior open bites/incisor proclination.

Habits: 

• Digit Sucking is the main habit.
  • If this habit continues as the child's anterior incisors are erupting (6/7 years old) this can have a significant affect on the occlusion:
    • Anterior Open Bite 
    • Increased Overjet 
    • Transverse posterior crossbite and posterior arch narrowing
• Fun Fact: It only takes 6hrs a day of force application to cause orthodontic changes!

Class 1 Malocclusion

Skeletal Pattern: The mandible is correctly positioned to the mid-facial skeleton (MD 2-3mm behind MX) 

Incisor relationship: The lower incisors occlude onto/just below the cingulum plateau of the upper incisors.  

Canine Relationship:  the maxillary canine tip falls directly between the mandubular canine and first premolar.  

Molar Relationship: the mesio-buccal cusp of the maxillary 6 occludes into the mesiobuccal groove of the mandibular 6.(= full intercuspation) 

Class 2 Malocclusion

Skeletal Pattern: The mandible is in a retruded position (behind)  in relation to the mid-facial skeleton (primarily maxilla). 

Incisor relationship: the lower incisors occlude behind the cingulum plateau of the upper incisors +  

• Div 1: the upper incisors are proclined 
• Div 2: the upper incisors are retroclined 

Canine Relationship: the maxillary canine tip falls in front of the gap  between the mandubular canine and first premolar.  

Molar Relationship: the mesio-buccal cusp of the maxillary 6 lies in front of the mesi-buccal groove of the mandibular 6, by the width of a premolar. (this leads to full intercuspation as it falls in the gap of the L5 and L6) 

• ½ unit Class II: The upper molars occlude in front of the lower molars by the width of half a premolar. (This leads to a cusp-to-cusp relationship). 

Class 3 Malocclusion 

Skeletal Pattern: The mandible is more prominent (in front of/ahead of) than the mid-facial skeleton.  

Incisor relationship: the lower incisors occlude in front of the cingulum plateau of the upper incisors. 

Canine Relationship: the maxillary canine tip falls behind the gap between the mandubular canine and first premolar.  

Molar Relationship: the mesiobuccal cusp of the maxillary 6 lies behind the mesio-buccal groove of the mandibular 6 by one premolar width. (this leads to full intercuspation as it falls in the gap between L6 nad L7). 

• ½ unit Class III: the upper molars occlude behind the lower molars by the width of half a premolar (this leads to a cusp-to-cusp relationship).