CS2-13 Occlusal Terminology, Mandibular Movements PDF

DTC200 2. Class Theoretical Committee CS2 Fixed Prosthodontics Subcommittee Occlusal Terminology, Mandibular Movements and Determinants Muhammad. Saleh, DDS, PhD Near East University faculty Dentistry- Department of Prosthodontic dentistry The Learning Goals Student will be able to mention the co...

DTC200 2. Class Theoretical Committee CS2 Fixed Prosthodontics Subcommittee Occlusal Terminology, Mandibular Movements and Determinants Muhammad. Saleh, DDS, PhD Near East University faculty Dentistry- Department of Prosthodontic dentistry The Learning Goals Student will be able to mention the components of TMJ. Student will be able to explain mandibular movements in three plane for analysis. Student will be able to mentioned the terminal landmarks on Posselt’s chart Introduction • Most restorative procedures affect the shape of the occlusal surfaces. • Proper dental care ensures that functional occlusal contact relationships are restored in harmony with both dynamic and static conditions. • Maxillary and mandibular teeth should contact uniformly on closing to allow optimal function, minimize trauma to the supporting structures, and allow for uniform load distribution throughout the dentition. • The malocclusion may be associated with undesirable changes to the teeth, the musculature, the temporomandibular joints (TMJs), or the periodontium. This chapter reviews the anatomic structures important to the study of occlusion and includes a discussion of mandibular (lower jaw) movement. The concept of ideal versus pathologic occlusion is introduced, as is the history of occlusal theory. Temporomandibular Joints (TMJs) The major components of the TMJs: • cranial base, • mandible, • muscles of mastication with their innervation and vascular supply. An articular disk separates the mandibular fossa and the articular tubercle of the temporal bone from the condylar process of the mandible. • The articular disk consists of avascular dense connective tissue. • it is attached (posteriorly) to loose highly vascularized and innervated connective tissue: the retrodiscal pad. • Medially and laterally, the articular disk is attached firmly to the poles of the condylar process. • Anteriorly, it fuses with the capsule and with the superior lateral pterygoid muscle. • Superior and inferior to the articular disk are two spaces: the superior and inferior synovial cavities. Ligaments The body of the mandible is attached to the base of the skull by muscles and three paired ligaments: • temporomandibular ligaments • Sphenomandibular ligaments • stylomandibular ligaments Ligaments cannot be stretched significantly, and thus joint movement is limited. Musculature Several muscles are responsible for mandibular movements. muscles of mastication suprahyoid muscles. The muscles of mastication: • Temporal muscle • Masseter muscle • Medial pterygoid muscle • Lateral pterygoid muscle The suprahyoid muscles: • Geniohyoid muscle • Mylohyoid muscle • digastric muscle Dentition The maxillary and mandibular teeth contact simultaneously when the condylar processes are fully seated in the mandibular fossae, and the teeth do not interfere with harmonious movement of the mandible during function. Ideally, in the fully bilateral seated position of the condyle–articular disk assemblies, the maxillary and mandibular teeth exhibit maximum intercuspation. These functional cusps can then act as stops for vertical closure without excessively loading any one tooth, while left and right TMJs concurrently are in an unstrained position. Dentition If the mesiobuccal cusp of the maxillary first molar is aligned with the buccal groove of the mandibular first molar, the orthodontic relationship is considered Angle class I . In such a relationship, the anterior teeth overlap both horizontally and vertically: • Horizontal overlap 2mm overjet • Vertical overlap 2mm overbite CENTRIC RELATION Centric relation is defined as the maxillomandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective articular disks with the complex in the anterosuperior position against the shapes of the articular eminences. This position is independent of tooth contact. MANDIBULAR MOVEMENT As any other movement in space, complex three dimensional mandibular movement can be divided into two basic components: • Translation, in which all points within a body have identical motion, • Rotation, in which the body is turning about an axis. Every possible three-dimensional movement can be described in terms of these two components Reference Planes It is easier to understand mandibular movement when the components are described as projections in three perpendicular planes: • Sagittal, • Horizontal, • Frontal. Reference Planes (Sagittal Plane ) In the sagittal plane, the mandible is capable of a purely rotational movement, as well as translation. Rotation occurs around the terminal hinge axis, an imaginary horizontal line through the rotational centers of the left and right condylar processes. The rotational movement is limited to about 12 mm of incisor separation before the temporomandibular ligaments and structures anterior to the mastoid process force the mandible to translate. Reference Planes (Horizontal Plane ) In the horizontal plane, the mandible is capable of rotation around several vertical axes. lateral movement consists of rotation around an axis situated in the working (laterotrusive) condylar process with relatively little concurrent translation. A slight lateral translation of the condyle on the working side in the horizontal plane—known as laterotrusion, Bennett movement, or mandibular side shift. This may be in a slightly forward direction (lateroprotrusion) or slightly backward direction (lateroretrusion). The orbiting (nonworking) condyle travels forward and medially as limited by the medial aspect of the mandibular fossa and the temporomandibular ligament. In addition, the mandible can make a straight protrusive (anterior) movement. Reference Planes (Frontal Plane ) In a lateral movement in the frontal plane, the nonworking (mediotrusive) condyle moves down and medially, whereas the working (laterotrusive) condyle rotates around the sagittal axis perpendicular to this plane. Again, as determined by the anatomy of the medial wall of the mandibular fossa on the mediotrusive side, transtrusion may be observed; as determined by the anatomy of the mandibular fossa on the laterotrusive side, this movement may be lateral and upward (laterosurtrusion) or lateral and downward (laterodetrusion). A straight horizontal tracing represents the protrusive movement of the incisal edge of the mandibular incisors. Starting from the maximum intercuspation position, in the protrusive pathway, the lower incisors are initially guided by the lingual concavity of the maxillary anterior teeth. As a result, posterior tooth contact is gradually lost as the incisors reach the edge-to-edge position. Posselt’s diagram The anterior determinant of mandibular movement: • The anterior determinants (articulation of the teeth), • The posterior determinants (temporomandibular controls and their associated structures) The posterior determinants: • shape of the articular eminences, • Anatomy of the medial walls of the mandibular fossae, • Configuration of the mandibular condylar processes The posterior determinants cannot be altered by the dentist. The anterior determinants are the vertical and horizontal overlaps of the anterior teeth and the form of the lingual concavities of the maxillary anterior teeth. These can sometimes be altered by restorative and orthodontic treatment. More vertical overlap causes increased downward mandibular incisor movement during the early phase of protrusive movement and a more vertical pathway at the end of the chewing stroke. Horizontal overlap allows a more horizontal mandibular movement. End of Lecture References [1] Contemporary Fixed Prosthodontics, chapter 4, pages (92-100)