Chapter 6: Occlusion

Occlusion

Contact relationship between the maxillary and mandibular teeth when the jaws are in a fully closed position; as well as the relationship of the teeth within the same arch

• Habitual way

Inter-arch

Between the two arches 

Intra-arch 

Within one arch 

Occlusal trauma

A result of occlusal disharmony and/or injury resulting from excessive occlusal forces

• Why we need orthodontists 

Range of Movement

Many patterns of tooth contact and variety of range of movement partially due to temporomandibular joint (TMJ) 

Occlusion Development

• Occlusion develops in a child as the primary teeth erupt

• Occlusion of erupting permanent dentition is dependent on primary teeth

Properly aligned teeth

When in proper alignment = self-cleansing by action of the cheek and lip musculature with the neutralizing flow of saliva over the smooth surfaces 

When teeth are aligned, the dental arch shape is…

parabolic (parabola)

Misaligned Teeth

• When teeth in detention are not aligned properly, there are imbalances or habits present = they lose the ability to self cleanse 

• May not be able to perform the functions in which they are designed

Centric occlusion

• Position when jaws are closed

  • Habitual way the teeth come together

  • Position that allows the greatest interdigitation of the teeth 

  • Related to the tooth occlusion 

  • Tooth-to-tooth relationship

  • Determined by the way the teeth fit together 

Other names for centric occlusion:

• Habitual occlusion 

• Intercuspal position 

• Acquired occlusion 

• Convenience occlusion

Centric occlusion importance:

• Creates proximal contact between neighboring teeth 

• Protects interdental papillae 

• Stabilizes each tooth in the arch 

• If contacts are open food gets impacted or “stuck” in between which can lead to trauma or irritation to dental papillae

During Centric occlusion - Since maxillary arch naturally overhangs the mandibular arch:

Each tooth in one arch is in occlusion with two others in the opposing arch 

During Centric occlusion - Antagonists:

each tooth in one arch is in occlusion with two others in the opposing arch

*2 places that there is 1 antagonist

*mandibular central incisors and the maxillary third molars

In centric occlusion, he lingual cusps of maxillary molars and premolars rest in…

the occlusal fossa of the mandibular molars and premolars 

• The working cusps of maxillary arch

In centric occlusion, the buccal cusps of the mandibular molars and premolars rest in…

the occlusal fossa of the maxillary molars and premolars 

• The working cusps of the mandibular arch

**Supporting/centric/working cusps are the…

• Buccal cusps of mandibular teeth 

• Lingual cusps of maxillary teeth 

• Incisal edges of mandibular anterior teeth

Guiding/non-centric/nonworking cusps are the…

opposite of the working cusps

• Lingual cusps of mandibular teeth

• Buccal cusps of maxillary teeth 

Centric Relation is the…

• Relationship of the mandible to the maxilla in which healthy muscles and bony contours comfortably guide the mandible into its most posterior position 

  • Occurs during strong muscle contractions such as swallowing 

• When mandible is in the most retruted position to which it can be carried by the muscles and ligaments 

  • Most stable and most posterior position 

• Repeatable/ reproducible 

• Jaw to jaw relationship

• Muscle guided, not tooth guided relationship 

Occlusal plane 

Imaginary plane placed on the masticatory surfaces of each dental arch

*Curve of Spee

The curved alignment of all teeth when viewing occlusal plane of the mandibular posterior teeth from the buccal 

• Know definition and what it looks like (viewed from buccal)

*Curve of Wilson 

• The occlusal curve that exists for the posterior teeth from right to left 

  • Know definition and what it looks like (viewed from anterior)

When a patient is closing in centric occlusion we will be looking for:

The horizontal overlap of the incisors and vertical overlap of the incisors

Overjet

• How far out are the maxillary central incisors from mandibular central incisors 

• Horizontal overlap

• *Only recorded if 4mm or more 

  • If not then N/A

Over bite 

• Vertical overlap of anterior teeth 

• If maxillary and mandibular teeth do not touch but are widely separated when in centric occlusion 

  • How much maxillary central incisors overlap the mandibular central incisors 

How to measure over bite:

• Have patient open 

• Measure entire mandibular incisor tooth length from the CEJ (CEJ does not change)

• Have patient close 

• Measure how much of mandibular incisor is visible 

Two types of overbite:

 anterior open bite or posterior open bite 

Anterior open bite

when person brings teeth together and only posterior teeth touching and anterior teeth are not, there is open space

Posterior open bite 

when person brings teeth together and only anterior teeth touching and posterior are not there is an open space

Overbite causes:

Most often thumb-sucking, mouth breathing, sleeping with a bottle 

• There can be other causes

Edge-to-edge

• When a person brings teeth together and anterior teeth of the maxilla do not overlap the anterior teeth of the mandibular arch but they meet and touch

  • An occlusion which the incisal edges of the maxillary incisors meet the incisal edges of the mandibular incisors when teeth are in centric occlusion 

• Edge-to-edge = anterior teeth 

End-to-end 

• Posterior teeth 

• (cusp to cusp)

Crossbite

• Malocclusion in which one or more teeth in the mandibular arch are located facial (or buccal) to their maxillary counterparts

  • Anterior or posterior 

  • Unilateral or bilateral 

  • Ex.) 3-30

Occlusal classifications can be ______ or ______

skeletal or dental

Skeletal

• Relationship of none to the maxilla to the bone of the mandible 

  • orthognathic/mesognathic, retrognathic, prognathic

Dental

• Relationship of the teeth of the mandible to the teeth of the maxilla 

  • Class I, II, III

Orthognathic/ Mesognathic

The upper jaw is in an approx. vertical relationship to the profile of the facial skeleton

Retrognathic

Mandible is posterior to its normal relationship with other facial structures

Prognathic

Mandible is anterior to its normal relationship with the other facial structures

Angles classification (dental)

• Most popular classification system 

• Based on the relationship of the molars to each other 

• Basis of classification 

  • 1st molars 

  • Canines 

    • Can be used if molars are not present (crowned or in crossbite)

Class I (1) 

• The mesiobuccal cusp of the maxillary first molar is directly in line with the buccal groove of the mandibular first molar 

• Canine (if molars are not present) 

  • Distal of mandibular canine within 1 premolar width of the mesial surface of maxillary canine

Class II (2)

Buccal groove of the mandibular first permanent molar is distal to the mesibuccal cusp of the maxillary first premolar by at least the width of a premolar 

• Canine 

  • Distal surface of the mandibular canine is distal to the mesial surface of maxillary canine by at least the width of 1 premolar

Class II (2) has 2 divisions:

• Division 1: anterior teeth are in alignment, may also include overjet

• Division 2: anterior teeth are not in alignment 

  • Max cent incisors are crowded, retruded, and inclined 

  • Deep overbite in most cases

  • Overjet near normal

Class III (3)

Buccal groove of the mandibular fire perm molar is mesial to the mesibuccal cusp of the maxillary first permanent molar by at least the width of a premolar 

• Canine 

  • Distal surface of mandibular canine is mesial to the mesial surface of the axillary canine by at least the width of 1 premolar

Considerations for classifications:

• It is possible to have a mixed conditions 

• Difficult to tell the classification if the 1st molar is missing or crown is present, use canine instead

Displacements

If a tooth is out of alignment it can be either be pushed:

• Lingually = linguoversion 

• Buccally = buccoversion 

• Mesially = mesioversion

• Distally = distoversion 

• Infraversion 

• Torsiversion 

• Labioversion 

• Supraeruption/supra-erupted/supraversion 

• Intrusion/intruded 

• Transversion/ transportation

 linguoversion

• When a tooth has assumed a position lingual to normal

• ex.) a tooth inside the arch formed towards the tongue 

buccoversion 

• When a tooth has assumed a position buccal to normal

• ex.) #2 buccoversion 

mesioversion

When a tooth has assumed a position mesial to normal

distoversion

When a tooth has assumed a position distal to normal

Infraversion

• When a tooth has assumed a position that is depressed below the line of the occlusion 

• Ex.) A tooth that has not erupted to the occlusal plane, a primary tooth submerged or ankylosed (attached to bone)

Torsiversion

• A tooth that has assumed a position that is turned or rotated 

• Can be partial or full

Labioversion

• A tooth that has assumed a position more labial to normal 

• Ex.) an incisor or canine outside of arch towards lips

Supraeruption/ supra-erupted/ supraversion

• Tooth that as alonged above the line of the occlusion 

Intrusion/intruded 

• Went back into bone 

• Ask the patient (otherwise cant tell)

Transversion/ transportation

Teeth are in wrong sequential order (wrong region)