Border Movements

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Mandibular movements are limited by the temporomandibular joints and ligaments, the neuromuscular system, and the teeth. Posselt was the first to describe the extremes of mandibular movement, which he called border movements (Fig. 4-13). His classic work is well worth reviewing as one attempts to understand how the determinants control the extent to which movement can occur.

Posselt used a three-dimensional representation of the extreme movements the mandible is capable of (Fig. 4-13, B). All possible mandibular movements occur within its boundaries. At the top of both illustrations, a horizontal tracing represents the protrusive movement of the incisal edge of the mandibular incisors.

Starting at the intercuspal positions in the protrusive pathway, the lower incisors are initially guided

Mandibular Movement Diagram

Fig. 4-9. Right lateral mandibular movement in the hori- Fig. 4-11. Lateral movement in the frontal plane.

zontal plane.

Protrusive Jaw Movement

Fig. 4-10. Protrusive mandibular movement in the hori- Fig. 4-12. Protrusive movement in the frontal plane.

zontal plane.

Fig. 4-10. Protrusive mandibular movement in the hori- Fig. 4-12. Protrusive movement in the frontal plane.

zontal plane.

Posselt Diagramm

Fig. 4-13. A, Mandibular border movement in the sagittal plane. B, Posselt's three-dimensional representation of the total envelope of mandibular movement. 1, Mandibular incisors track along the lingual concavity of the maxillary anterior teeth. 2, Edge-to-edge position. 3, Incisors move superiorly until posterior tooth contact recurs. 4, Protrusive path. 5, Most protrusive mandibular position.

Fig. 4-13. A, Mandibular border movement in the sagittal plane. B, Posselt's three-dimensional representation of the total envelope of mandibular movement. 1, Mandibular incisors track along the lingual concavity of the maxillary anterior teeth. 2, Edge-to-edge position. 3, Incisors move superiorly until posterior tooth contact recurs. 4, Protrusive path. 5, Most protrusive mandibular position.

Teeth Protrusive PathwayCondylar Guidance Angle
Fig. 4-14. Posterior determinants of occlusion. A, Angle of the articular eminence (condylar guidance angle). 1, Flat; 2, average; 3, steep. B, Anatomy of the medial walls of the mandibular fossae. 1, Greater than average; 2, average; 3, minimal sideshift.

by the lingual concavity of the maxillary anterior teeth. This leads to gradual loss of posterior tooth contact as the incisors reach the edge-to-edge position. This is represented in Posselt's diagram by the initial downward slope. As the mandible moves farther protrusively, the incisors slide over a horizontal trajectory representing the edge-to-edge position (the flat portion in the diagram), after which the lower incisors move upward until new posterior tooth contact occurs. Further protrusive movement of the mandible typically takes place without significant tooth contact.

The border farthest to the right of Posselt's solid (see Fig. 4-13, B) represents the most protruded opening and closing stroke. The maximal open position of the mandible is represented by the lowest point in the diagram. The left border of the diagram represents the most retruded closing stroke. This movement occurs in two phases: The lower portion consists of a combined rotation and translation, until the condylar processes return to the fossae. The second portion of the most retruded closing stroke is represented by the top portion of the border that is farthest to the left in Posselt's diagram. It is strictly rotational.

Incisal Guidance And Vertical Overlap

Fig. 4-15. Anterior determinants of occlusion. Different incisor relationships with differing horizontal and vertical overlaps (HO and VO) produce different anterior guidance angles (AGA). A, Class 1. B, Class 11, Division 2 (increased VC; steep AGA). C, Class 11, Division 1 (increased HO; flat AGA).

Fig. 4-15. Anterior determinants of occlusion. Different incisor relationships with differing horizontal and vertical overlaps (HO and VO) produce different anterior guidance angles (AGA). A, Class 1. B, Class 11, Division 2 (increased VC; steep AGA). C, Class 11, Division 1 (increased HO; flat AGA).

Posterior and Anterior Determinants (Table 4-3). The characteristics of mandibular movement are established posteriorly by the morphology of the temporomandibular joints and anteriorly by the relationship of the anterior teeth.

The posterior determinants (Fig. 4-14)-shape of the articular eminences, anatomy of the medial walls of the mandibular fossae, configuration of the mandibular condylar processes-cannot be controlled, nor is it possible to influence the neuromus-cular responses of the patient, unless it is done by indirect means (e.g., through changes in the configuration of the contacting teeth or by the provision of an occlusal appliance). If a patient has steeply sloped eminences, there will be a large downward component of condylar movement during lateral and protrusive excursions. Similarly, the anatomy of the medial wall of each fossa normally will allow the condyle to move slightly medially as it travels forward (mandibular sideshift, or transtrusion). The sideshift will become greater as the extent of medial movement increases. However, the anatomy of the joint dictates the actual path and timing of condylar movement. Movement of the laterotrusive or working condylar process is influenced predominantly by the anatomy of the lateral wall of the mandibular fossa. The amount of the sideshift is, of course, a function of the mediotrusive or nonworking condyle; on the working side, however, it is the anatomy of the lateral aspect of the fossa that guides the working condyle straight out or upward and downward. The amount of sideshift does not appear to increase as the result of a loss of occlusion .6

The anterior determinants (Fig. 4-15) are the vertical and horizontal overlaps and the maxillary lingual concavities of the anterior teeth. These can be altered by restorative and orthodontic treatment. A greater vertical overlap causes the direction of mandibular opening to be more vertical during the early phase of protrusive movement and creates a more vertical pathway at the end of the chewing stroke. Increased horizontal overlap allows a more horizontal jaw movement.

Although the posterior and anterior determinants combine to affect mandibular movement, no correlation has been established7; that is, patients with steep anterior guidance angles do not necessarily have a steep posterior disclusion, and vice versa.

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  • GILLY
    WHAT IS THE NORMAL HUMAN TEETH VERTICAL OVERLAP?
    8 years ago
  • Karis
    What is mandibular side shift diagram?
    8 years ago
  • gastone marino
    What is border movement diagram?
    8 years ago
  • sari sillanp
    What are border movements?
    8 years ago
  • norman
    Which teeth are touching in protrusive movement?
    7 years ago
  • lillian
    How to get plane border of teeth?
    3 years ago
  • peter
    What are posterior determinants of occlusion?
    2 years ago

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