Comparative dental anatomy

shapes

Bunodont Form

Tooth form characterized by tooth-bearing conical cusps; primates are relatively isognathous and have limited lateral jaw movement according to the lecture. //

Lophodont

A tooth form in which cusps are in line. //

Isognathous

Equally jawed or jaws of the same width; pigs are given as an example. //

Anisognathous

Unequal jaws; the lecture gives domestic animals and humans as examples and states that the lower dental arch is narrower than the upper dental arch. //

Selenodont Molars

Molars with crescent-shaped cusps. //

Four Phylogenetic Classes of Tooth Forms

Haplodont, Triconodont, Tritubercular molars, and Quadritubercular molars. //

Haplodont

Reptilian stage characterized by single-cone teeth. //

Triconodont

Tooth form with three cusps arranged in a line. //

Tritubercular Molars

Tooth form with three cusps arranged in a triangle. //

Quadritubercular Molars

Tooth form with four cusps arranged in a quadrangle. //

Reptilian Stage / Haplodont

Simplest form of tooth, represented by a single cone; usually includes many teeth in both jaws, limits jaw movement, and has no tooth occlusion; teeth are used mainly for prehension/combat and procurement of food. //

Early Mammalian Stage / Triconodont

Posterior teeth develop three cusps; the largest/original cusp is centered with smaller anterior and posterior cusps; examples include dogs and carnivorous species. //

Triangular Stage / Tritubercular Molars

Teeth have a three-cornered triangular shape; projections occlude with antagonists in the opposing jaw. //

Quadritubercular Stage

Teeth have four projections that establish occlusion with tritubercular upper molars; seen in teeth of apes. //

10. GEOMETRIC SHAPES OF THE TEETH

Geometries of Crown Outlines

Tooth crown aspects, except incisal or occlusal aspects, can be schematically outlined using three geometric figures: triangle, trapezoid, and rhomboid. //

Triangle Form

Has a wide base of the crown for strength and tapered labial and lingual outlines leading to a thin ridge to facilitate penetration of food. //

Trapezoid Form

Provides interproximal spaces that accommodate interproximal tissue; spacing between roots allows sufficient bone investment. //

Occlusion and Trapezoid Form

Each tooth in either dental arch generally occludes with two adjacent teeth in the opposing arch except the mandibular central incisor and maxillary third molar. //

Same-Arch Tooth Contact

Contact between teeth in the same dental arch helps protect interproximal gingival tissue from trauma during mastication. //

Rhomboid Form

The rhomboidal outline inclines crowns lingually to the root bases, bringing cusps into proper occlusion with opposing cusps. //

Rhomboid and Forces of Mastication

The axes of crowns and roots are kept parallel so the line of force during mastication is parallel to the long axes of teeth. //

Rhomboid and Cheek Protection

Lingual inclination allows upper molars to overlap lower molars and helps protect the inner surface of the cheek from being bitten during mastication. //

Facial and Lingual Outline of All Teeth

May be represented by trapezoids of various dimensions; the shortest uneven side is toward the tooth cervix and the longest uneven side toward the occlusal/incisal aspect. //

Proximal Crown Outline of Anterior Teeth

Triangular; the base is toward the cervix and the apex is toward the incisal ridge. //

Proximal View of Incisors and Canines

They appear triangular. //

Proximal Crown Outline of Maxillary Posterior Teeth

Trapezoidal; the largest uneven side is toward the cervix and the shortest uneven side is toward the occlusal surface. //

Proximal Crown Outline of Mandibular Posterior Teeth

Rhomboidal. //

Rhomboid Location

According to the lecture, the rhomboid outline can be seen in mandibular posterior teeth. //

Triangle Distribution

The six anterior teeth of the maxillary and mandibular arches have triangular outlines from the mesial and distal aspects. //

Trapezoid Distribution: Anterior

All anterior teeth have trapezoidal outlines from the labial and lingual aspects. //

Trapezoid Distribution: Posterior

All posterior teeth have trapezoidal outlines from the buccal and lingual aspects. //

Trapezoid Distribution: Maxillary Posterior Proximal

All maxillary posterior teeth have trapezoidal outlines from the mesial and distal aspects, with the shortest uneven side toward the occlusal surface. //

Rhomboid Distribution

All mandibular posterior teeth have rhomboidal outlines from the mesial and distal aspects. //