Occlusion week 6

Week 6

Occlusion

The contact relationship between the maxillary and mandibular teeth when the jaws are in a fully closed position, as well as the relationship between the teeth in the same arch.

Occlusion develops when 

the primary teeth erupt, during which oral motor behavior develops and masticatory skills are acquired.

Occlusion of the erupting permanent teeth is dependent on the 

occlusion of the primary teeth as they are being shed.

Several interrelated factors are involved in the development of the occlusion, such as

The associated musculature

Neuromuscular pattern

TMJ joint functioning

Normal Occlusion is when

closure of 32 teeth results in the optimum of 138 occlusal contacts.  This seldom occurs.  However, the position of the dentition in centric occlusion serves as the standard for describing a normal occlusion.

Centric Occlusion (CO) 

It refers to the position of the dentition when the jaws are closed.  This position allows the maximum interdigitation of the teeth.

When the teeth are in the position of centric occlusion, each tooth of one arch is in 

occlusion with two others in the opposing arch, except for the mandibular central incisors and maxillary third molars.  

When the teeth normally occlude in centric occlusion

the maxillary dental arch overhangs the mandibular arch facially.

Overjet

is a normal amount of horizontal overlap between the two arches. 

Overbite

is a normal amount of vertical overlap between the two arches.

The teeth within each dental arch create

contact areas as they contact their same-arch neighbors on their proximal surfaces (except for the last tooth in the arch).  These contacts serve to protect the interdental gingiva, and to stabilize each tooth in the dental arch.. 

Each arch of the permanent dentition is divided into three segments:

anterior segment

Middle segment

Posterior segment

anterior segment

includes the anterior teeth

middle segment

includes the premolars

posterior segment

includes the molars

Canines and first molars cooperate in more than one segment and they function as

anchor supports for both arches

Phase one of arch development

eruption of the permanent first molars. 

Phase two of arch development

eruption of the permanent anterior teeth

Phase three of arch development

eruption of the premolars.

Phase four of arch development

eruption of the canines and the second molars.

Phase five of arch development

eruption of the third molars.

Leeway space

s the difference in size mesiodistally between the primary molars and the permanent premolars.

Primate spaces

are the largest spaces (diastemas) often found mesial to the maxillary canines and distal to the mandibular canines.

Curve of Spee

the maxillary arch is convex occlusally, and the mandibular arch is concave

Curve of Wilson

 a concave curve which results when a frontal section is taken through each set of both maxillary and mandibular molars.

When the teeth are in centric occlusion they have

maximum interdigitation.

The three areas of centric contacts or centric stops between the two arches are:

the height of cusp contour

the marginal ridges

the central fossae

Supporting cusps: are the cusps that function during centric occlusion, which include: 

the lingual cusps of the maxillary posterior teeth

the buccal cusps of the mandibular posterior teeth 

the incisal edges of the mandibular anterior teeth

Centric Relation (CR)

It refers to the position of the mandible relative to the maxillae.  It is the position when the mandible is in the most retruded position, and is determined by the maximum contraction of the muscles of the jaw.

Evaluation of lateral occlusion is made by

moving the mandible either to the right or left until the canines on that side are in a cusp-to-cusp relationship.

working side

The side to which the mandible has been moved 

non-working side or balancing side.

The side of the arch opposite to the working side

canine rise

In normal occlusion, the canine should be the only tooth in function during lateral occlusion

protrusive occlusion

the eight most anterior teeth of both arches are normally in contact.

interocclusal clearance

When the mandible is in rest position, an average space of 2-3 mm is noted between the masticatory surfaces of the maxillary and mandibular teeth.  

Malocclusion

the lack of an overall ideal form in the dentition while in centric occlusion.

Dental Classification

It is based on the relationship of the teeth.  Usually the permanent first molars and canines are used in dental classification.

Angle’s classification system

Class I Malocclusion

Class II Malocclusion: division I,   division II

  Class III Malocclusion

Skeletal Consideration

Many malocclusions are based on the relationship of the maxilla to the mandible.  

The classification of skeletal malocclusions involves three basic spatial planes:

Horizontal malocclusions

Vertical malocclusions

Transverse malocclusions

Horizontal malocclusions 

either Class II or Class III malocclusions (similar to Angle’s classification).

Vertical malocclusions 

include open bites and severe overbites

Transverse malocclusions

include crossbites

Primary Occlusion

A mesial step

A flush terminal plane

A distal step

A mesial step

in which the primary mandibular second molar is mesial to the maxillary second molar

A flush terminal plane

in which the primary maxillary and mandibular second molars are in an end-to-end relationship.

A distal step

in which the primary mandibular second molar is distal to the maxillary second molar

Parafunctional Habits

Clenching

Bruxism

Thumb/finger sucking