School of Dentistry, Tongji University Oral physiology Occlusion ZHANG LEI School of Dentistry, Tongji University

Occlusion Concept 1. the act or process of closure or of being closed or shut off 2. the static relationship between the incising or masticating surfaces of the maxillary or mandibular teeth or tooth analogues

INTERCUSPAL OCCLUSION: the complete intercuspation of the opposing teeth, independent of condylar position. “Centric occlusion”

Intercuspal occlusion: mesial-distal aspects each tooth of one arch in occlusal contact with portions of two others in the opposing arch with the exception of the mandibular central incisors and the maxillary third molars.

When a tooth is lost, the adjoining teeth in the same arch may migrate in an effort to fill the void. And tooth movement changes occlusal relations with antagonists in opposing dental arches. The common result is hypereruption of the tooth opposing the space left by the lost tooth.

Occlusal key “First molars, the key to normal occlusion”: Angle 1. They are the biggest teeth and their anchorage is strongest. 2. Their local position in the occlusal arch supports the main masticatory duty and operation . 3. They influence the vertical distance of upper and lower jaws, the occlusal height and aesthetic proportions. 4. As the permanent molars are the first erupting teeth of permanent dentition, they have “mighty” control on the teeth erupting later behind and in front of them, as they are forced to position to the already erupted and in occlusion functioning 1st molars.

Intercuspal occlusion: labial-lingual aspects Over jet and over bite OVERJET: the projection of teeth beyond their antagonists in the horizontal plane. OVERBITE: the distance teeth lap over their antagonists as measured vertically.

Over jet and over bite Normal overbite and overjet: 2-4 mm Deep overbite Deep overjet

Open bite Edge to edge bite Cross bite

Over jet and over bite The overlapping of the maxillary teeth over the mandibular teeth has a protective feature: during opening and closing movements of the jaws, the cheeks, lips, and tongue are less likely to be caught. likely to be caught.

Intercuspal occlusion: occlusal aspects Concept of “138 points occlusal contacts” : Hellman

Curvatures of occlusal planes CURVE OF SPEE: beginning with the cusp tip of the mandibular canine and following the buccal cusp tips of the premolar and molar teeth, continuing through the anterior border of the mandibular ramus, ending with the anterior most portion of the mandibular condyle.

Curvatures of occlusal planes CURVE OF WILSON: in the mandibular arch, that curve (viewed in the frontal plane) which is concave above and contacts the buccal and lingual cusp tips of the mandibular molars; in the maxillary arch, that curve (viewed in the frontal plane) which is convex below and contacts the buccal and lingual cusp tips of the maxillary molars.

References for normal intercuspal occlusion Consistency of the maxillary and mandibular central lines Each tooth has two antagnists except for maxillary third molars and mandibular first incisors. Normal canine relationship Neutral first molar relationship Normal oberbite and overjet

Malocclusion Angle's classification: Malocclusions can be divided mainly into three types, based on the relative position of the maxillary 1st molar. The mesiobuccal cusp of the upper first molar should rest on the mesiobuccal groove of the mandibular first molar.

Malocclusion Class I: Neutrocclusion Here the molar relationship of the occlusion is normal or as described for the maxillary first molar, but the other teeth have problems like spacing, crowding, over or under eruption, etc.

Malocclusion Class II: Distocclusion In this situation, the upper molars are placed not in the mesiobuccal groove but anteriorly to it. Usually the mesiobuccal cusp rests in between the first mandibular molars and second premolars.

Malocclusion Class III: Mesiocclusion is when the lower front teeth are more prominent than the upper front teeth. In this case the patient very often has a large mandible or a short maxillary bone.

Facial landmarks Glabella Lateral canthus Tragus of ear Auricula Nasal ala Labial commissure

Surface landmarks on the face Frankfort horizontal plane: a plane established by the lowest point on the margin of the right or left bony orbit and the highest point on the margin of the right or left bony auditory meatus. Camper’s line: a line running from the inferior border of the ala of the nose to some defined point on the tragus of the ear, usually considered to be the tip of the tragus. Ala-tragus line

Surface landmarks on the face Balkwill angle: the angle formed between the plane of two lines drawn from the articulating surfaces of the condyles to the incisor point and the occlusal plane, 26°in average. Bonwill triangle: a 4 inch equilateral triangle bounded by lines connecting the contact points of the mandibular central incisor’s incisal edge to each condyle and from one condyle to the other. Curve of Monson: a proposed ideal curve of occlusion in which each cusp and incisal edge touches or conforms to a segment of the surface of a sphere 8 inches in diameter with its center in the region of the glabella.

Surface landmarks on the face Proportions

Surface landmarks on the face Labial-tooth relationship Upper central incisors can be seen in rest position: Young：3.37 mm Elderly：1.26 mm （Vig & Brundo)

Smile line Gingiva exposed no more than 2-3 mm Anterior teeth exposed <75% Gingiva exposed no more than 2-3 mm 75-100% 100% and part of gingiva

Negative space

Consistency of the face and dentition central line