Punctiform contacts clearly define the progression of force or how the incorrect position of a contact can put transverse load on a tooth. Before a description of how forces act on a tooth is given, here follows a brief explanation of the physical principles governing forces and how they are combined: Forces can be represented as vectorial values; ie, they can be illustrated as arrows. The length of the arrow is a measure of the size of the force, and the direction of the arrow is the direction of the force. The forces on a rigid body (in this case, the tooth) can only be displaced along their line of action, ie, on a line that is an extension of the (force) vector; parallel displacement is not possible.
Punctiform contacts are the best form of occlusion. This explanatory model is primarily intended to show why the occlusal contacts must be created as punctiform during systematic reconstruction of masticatory surfaces. The main advantages of punctiform occlusal contacts include the following:
One conceptual model would be to represent opposing cusps as spheres laid out in the pattern of occlusion. The spheres would lie in the deepest areas of the masticatory surfaces, the contact areas. Given a pronounced occlusal relief, a sphere rests in a stable position and thereby displays three-point (tripod) contact. If the tooth had no cusps, the sphere would roll to and fro.Thus, centric stops in their contact areas do not contact the antagonists at a single point, but each tooth has at least two contact areas on which centric stops of the opposing teeth lie.
An essential distinction is made between two fundamentally different contact situations in relation to the teeth. First, there are the approximal contacts of the teeth within the dentition, which happen in the contact points.The second type lies occlusally between the maxillary and mandibular dentitions when occluding.
Why the dentition is made up of individual teeth needs to be explored. A permanently fused ridge of bone, for example, would be a feasible alternative. However, the individual teeth are anchored in the bone with ligaments, and the teeth are able to tip. Why the teeth are arranged in a curved arch also needs to be explained; an angular dental arch could indeed be conceivable.
The malpositions in the frontal plane are the various forms of reverse articulation or transverse malocclusions, when the dental arches are deformed in the transverse direction and cross over in occlusion. These occur both as localized occlusal variations and as symmetric anomalies. Reverse articulations are usually symptoms that accompany other forms of dysgnathia and rarely occur in isolation. The term reverse articulation is generally used to denote a malocclusion in the area of the posterior teeth, when the mandibular posterior teeth have migrated in a vestibular direction and do not lie in their normal cusp-fossa relationships. This reverse articulation of the occlusion of the posterior teeth may be bilateral or merely unilateral (Figs 5-39 and 5-40).
The symmetric arrangement of the teeth in relation to the middle of the skull or face can be seen in the frontal view of the dental arches. All the teeth in the maxillary and mandibular dentitions have a characteristic inclination (Figs 5-36 and 5-37). The maxillary teeth are inclined in a vestibular direction, while the mandibular teeth and their masticatory surfaces are inclined lingually (except the mandibular incisors). The alveolar ridges also have this inclination. The inclination of the teeth and alveolar ridges is a definite requirement because it means the masticatory forces are mainly transmitted axially to the periodontium: When food is being ground by the posterior teeth, the mandible glides from outward (out of a lateral position) into the terminal occlusal position. Therefore, food tends to be crushed by the mandible gliding from buccal to lingual, the direction of forces corresponding to the inclination of the alveolar ridges.
Occlusal anomalies in the sagittal direction can be described as malocclusions according to Angle's classification. Starting with neutro-occlusion (Class I), a distinction is made between unilateral or bilateral disto-occlusion (Class II) and unilateral or bilateral mesio-occlusion (Class III).
In the sagittal plane, the rows of teeth can be described in their state of intercuspation. Different views of the teeth become visible, depending on which sagittal plane is chosen: The medial plane shows the rows of teeth from the lingual; if the sagittal plane lies outside the dental arches, the rows of teeth are seen from the vestibular view. The intercuspation of the teeth can be seen in each view and follows a regular pattern.
The development of the dentition may be disrupted, leading to variations from the normal positioning of teeth (Figs 5-16 to 5-18). A distinction is drawn between rotation, tipping, and displacement of teeth (Fig 5-19). An incorrect tooth position may be caused by displacement of a tooth germ, an incorrect tooth germ, or external influences during normal eruption, such as thumb sucking, lip biting, tongue thrusting, or persistence of primary teeth.