Functional analysis to: a. determine functional factors associated with the malocclusion; b. detect deleterious habits; and c. detect temporomandibular joint dysfunction (TMD), which may require additional diagnostic procedures. Tonus in the inferior lateral pterygoids positions the condyles anteriorly against the posterior slopes of the articular eminences. Noteworthily, the first molar values were approximately 90° relative to the FOP. Cephalograms were obtained with the subjects seated in the upright position and the Frankfort horizontal (FH) plane parallel to the floor. However, this position is not the sound orthopedically stable joint position dedicated by the elevator muscles. [14,15] For mechanically beneficial occlusion, the maxillary first molar should be perpendicular to the FOP. Therefore every mobile joint has a musculoskeletally stable position. Dynamic occlusion that occurs on the canines (on the working side) during lateral excursions of the mandible. Significant differences in the axial angulations were noted between the maxillary and mandibular dentitions as previously shown by model analysis.[5]. In the postural position, without any influence from the occlusal condition, the condyles are stabilized by muscle tonus of the elevators and the inferior lateral pterygoids. Functional Neuroanatomy and Physiology of the Masticatory System, 3. The maxillary lateral teeth are angulated more mesially than the mandibular ones relative to the FOP. The mandible, a bone attached to the skull by ligaments, is suspended in a muscular sling. Occlusion is determined by the shape of the head, jaw length and width and the position of the teeth. As discussed, the masticatory system is an extremely complex and interrelated system of muscles, bones, ligaments, teeth, and nerves. In the malocclusion with mandibular lateral displacement (MLD), it is difficult to establish the functional occlusion by orthodontic means. The purpose of the disc is to separate, protect, and stabilize the condyle in the mandibular fossa during functional movements. DORLAND’S MEDICAL DICTIONARY defines the verb occlude as “to close tight, as to bring the mandibular teeth into contact with the teeth in the maxilla.”1 In dentistry, occlusion refers to the relationship of the maxillary and mandibular teeth when they are in functional contact during activity of the mandible. This does not suggest that all patients must have these features to be healthy. In this position, force can be applied to the posterior aspect of the disc, inferior retrodiscal lamina, and retrodiscal tissues. When spaces between dentition are closed through orthodontics or natural forces following tooth loss, the resultant mesial drift of the maxillary dentition can create inappropriate esthetics. A healthy joint appears to permit very little posterior condylar movement from the MS position.22 Unfortunately the health of the joint may be difficult to assess clinically. In the late 1970s the concept of dynamic individual occlusion emerged. On the other hand, the mean axial angulations of the mandibular canine, first premolar, second premolar, and first molar were 77.3°, 85.2°, 85.4°, and 84.4°, respectively. One factor may be the prominent mesial axial angulation of the maxillary lateral teeth relative to the FOP. and were treated according to the six keys for normal occlusion and functional occlusal parameters (centric relation, vertical dimension, lateral and anterior guidances, occlusal contacts and direction of forces applied on the teeth). Five cephalometric variables are shown in Table 1. b. determine the functional status of the patient’s occlusion. This tendency was more prominent in the first premolar than in the second premolar, because the first premolar is not prevented from tipping mesially before the eruption of the canine. 3,4 The smile presentation can appear improper due to inconsistent tooth morphology. Each subject was instructed to swallow, lightly contact the molars to bring the mandible into the natural intercuspal position, and breathe naturally during radiography. An easy-to-understand approach advances your skills with the latest evidence-based clinical research, and reinforces knowledge with chapter … [6] Each subject gave written informed consent for participating in the study. Learn vocabulary, terms, and more with flashcards, games, and other study tools. In most joints this movement is very small (1 mm or less). As the condyles are positioned downward and forward, the disc complexes follow; thus forces to the bone are dissipated effectively. Crowding is a malocclusion with irregularly positioned teeth caused by arch length discrepancy (ALD). Over the years several concepts of occlusion have been developed and have gained varying degrees of popularity. for certain extended or border joint movements. The articular disc cannot not be displaced from the condylar head if the discal ligaments are intact and functional. The popularity of the concept of CR grew and was soon carried over into the field of fixed prosthodontics. Balanced occlusion was developed primarily for complete dentures, the rationale being that this type of bilateral contact would aid in stabilizing the denture bases during mandibular movement. In addition, the axial angulations were significantly correlated to each other. Progressive mesial tipping of the maxillary lateral teeth was noted. Introduction. [12,13] Therefore, maxillary anterior crowding with high canines and slight mandibular incisor crowding may involve completely different mechanisms; however, the cause of this malocclusion has not been fully elucidated. Why would this orthopedic principle be any different for the TMJ? A sagittal view of the TMJ. Occlusion according to The Glossary of Prosthodontic Terms Ninth Edition is defined as 'the static relationship between the incising or masticating surfaces of the maxillary or mandibular teeth or tooth analogues'.. An accumulation of these features will represent the optimal functional occlusion. E-mail: milm@hiroshima-u.ac.jp, Department of Orthodontics and Craniofacial Developmental Biology, Hiroshima University Graduate School of Biomedical Sciences, Hiroshima. The directional force of the primary elevator muscles (temporalis, masseter, and medial pterygoid) is to seat the condyles in the fossae in a superoanterior position. The t-test was used to compare the mesiodistal angulation between maxilla and mandible. The more posterior the force placed on the mandible, the more elongation of the ligament will occur and the more posterior the condylar position will be. Balanced occlusion and articulation refers to occlusion with simultaneous bilateral contacts of the occlusal surface of the teeth in all mandibular positions. As in any other joint, positional stability is determined by the muscles that pull across the joint and prevent dislocation of the articular surfaces. Crowding is classified on the basis of etiology: one category is the inherent discrepancy between tooth size and jaw size, mainly of genetic origin. Jacobson[7] concluded that a representative FOP would be a more appropriate plane for craniofacial analysis. What is the optimal functional occlusion? Increased muscle activity is likely. Dynamic occlusion was determined in regulated lateral (0.5 mm and 3 mm lateral to the intercuspal position) and protrusive movements of the mandible by intraoral examination with the aid of shimstock. It can thus be seen that CR and the musculoskeletally stable (MS) position are the same. This lateral functional shift may be caused only by a premature contact (etiology No. Crowding is a malocclusion with irregularly positioned teeth caused by arch length discrepancy (ALD). As discussed in Chapter 7, there are great variations among healthy populations. The dentist must determine which occlusal configuration is most likely to eliminate this pathology. Forward movement of the mandible brings the condyles down the articular eminences. It was during this time that the term gnathology was first used. The major differences between this position and the MS position lie in muscle function and mandibular stability. The increased mesial axial angulation of the maxillary lateral teeth may have the possibility to cause space deficiency for the alignment. Once again viewing Figure 5-3, the posterior aspect of the mandibular fossa is seen as quite thin and apparently not meant to bear stress. If this ligament is tight, there may be very little difference between the most superior retruded position, the most superior position (Dawson’s position), and the superoanterior (MS) position. the relationship of teeth in the same jaw as well as the relationship of teeth in opposing jaws. If you slide you teeth to your right, and only your right canines contact during this lateral excursion, then you have canine guidance. This definition of CR is becoming widely accepted.21. In an attempt to determine which conditions seem least likely to cause any pathologic effects, this chapter examines certain anatomic and physiologic features of the masticatory system. The elephant in the room of temporomandibular joint disorders, occlusion, and functional disease is force—repetitive force that exceeds the patient’s capacity to adapt. When the elevator muscles (the masseter, medial pterygoid, and temporalis) function, their contraction raises the mandible such that contact is made and force is applied to the skull in three areas: the two temporomandibular joints (TMJs) and the teeth (Figure 5-1). By definition, malocclusion is an abnormality in the position of the teeth. (The same idea applies to the left of course.) Therefore, for the patient to open and close in the intercuspal position (which is of course necessary to function), the inferior lateral pterygoid muscles must maintain a contracted state to keep the condyles from up to the most superoanterior positions. The natural head posture was determined by visual feedback in a mirror. This is reckoned to be a good thing, as canines are excellent at coping with lateral forces. C. ... During a right lateral movement of the mandible, the left side of the mandible is termed the ___-_____ _____. Dawson16 suggested that there is not, which implies that if the condyles move either anteriorly or posteriorly from the most superior position, they will also move inferiorly. Individualized extrusion and crown lingual torque of the upper first premolars were performed to obtain guidance between the mandibular canines during lateral jaw movements. Some clinicians17,18 suggest that none of these definitions of CR indicates the most physiologic position and that the condyles should be ideally positioned downward and forward on the articular eminences. The use of a stable orthopedic position is essential to treatment. In this concept the condyles are described as being in their optimal position when they are translated to some degree down the posterior slopes of the articular eminences (Figure 5-6). The study design adhered to the tenets of the amended Declaration of Helsinki and approved by the Local Ethics Committee. [9] Hanai[10] reported that the arrangement of the teeth germs from the canine to the second molar straightens labiolingually and the second premolar germ descends to the level of the first premolar germ, although the canine germ is still in the highest position in the upper half of the maxillary process during the mixed dentition. 3. the relation of the teeth of both jaws when in functional contact during activity of the mandible. The study included six Japanese men (24.8 [1.3] years) and 24 Japanese women (20.7 [2.7] years) selected from student volunteers with normal occlusion in the period between 2011 and 2013. When the mandible is elevated, force is applied to the cranium in three areas: (1 and 2) the TMJs and (3) the teeth. This question has stimulated much discussion and debate. occlusion [ŏ-kloo´zhun] 1. obstruction. In a previous study,[5] the crowns of the maxillary lateral teeth had erupted mesially in relation to the functional occlusal plane (FOP) in patients with Angle’s Class I malocclusion and high canines and had been uprighted by nonextraction orthodontic treatment. This description is not complete, however, until the position of the articular discs is considered. By way of summary, then, the most orthopedically stable joint position as dictated by the muscles occurs when the condyles are located in their most superoanterior position in the articular fossae, fully seated and resting against the posterior slopes of the articular eminences. Since the retrodiscal tissues are highly vascularized and well supplied with sensory nerve fibers,23 they are not anatomically structured to accept force. Further, the first molar is located perpendicular to the FOP in most patients. It may be explained in part by a fact that the angle of mesial angulation of erupting maxillary premolar relative to reference plane[8] on panoramic X-ray films showed the same results in the growing patients with mixed dentitions used as the subjects in the previous report. Scan D is a 2-D frame showing the first closure contacts. This movement is certainly possible and represents the functional movement of protrusion. FUNCTIONAL OCCLUSION:“Refers to tooth contacts that occur in the segment of the arch towards which the mandible moves”. This directional force will tend to drive the condyles to the superoanterior position as already described (MS). Anatomy and Function of the Lateral Pterygoid. Therefore some degree of condylar movement posterior to the intercuspal position is normal during function. To position the condyles downward and forward on the posterior slopes of the articular eminences, the inferior lateral pterygoid muscles must contract. Group Function Occlusion: During lateral movement, the buccal cusps of the posterior teeth on the working side are in contact. In addition, the maxillary and mandibular dentitions show different patterns of crowding,[4] even if tooth-size/jaw-size discrepancy is the cause of crowding in both the arches. The MS position is now described in the Glossary of Prosthodontic Terms as CR.21 Although earlier definitions9–11 of CR emphasized the most retruded position of the condyles, most clinicians have come to appreciate that seating the condyle in the superoanterior position is far more orthopedically acceptable. To examine the correlations among the axial angulations, Pearson’s correlation was employed. [11] In general, the maxillary lateral teeth are angulated more mesially than the mandibular ones. This last causes the discs to be rotated on the condyles as far forward as the discal spaces (determined by interarticular pressure) and the thickness of the posterior border of the discs will allow. It was accepted so completely that patients with any other occlusal configuration were considered to have a malocclusion and were often treated merely because their occlusion did not conform to the criteria thought to be ideal. These cephalometric parameters and their correlation with each other have contributed to the development of functional cephalometric analysis for diagnosis, treatment planning, and assessment of treatment results. Five cephalometric indicators of vertical growth (FH-FOP angle, SN-MP angle, FMA, gonial angle, and Y-axis) were also measured [Figure 2]. The term centric relation has been used in dentistry for many years. First premolars tended to express this more than the second premolars but the tipping values were roughly 90º relative to the FOP on the first molars. Etiology of Functional Disturbances in the Masticatory System, 14. In order to examine the characteristics of the cranio-fac … In pursuing the most stable position for the TMJs, the muscles that pull across the joints must be considered. This study has some limitations due to the sample size being relatively small, and while this method is established to compare data easily, cephalometric analysis provides only two-dimensional data, therefore, is not as reliable as a three-dimensional (3D) diagnostic tool. In establishing the criteria for the optimal orthopedically stable joint position, the anatomic structures of the TMJ must be closely examined. It became useful to the prosthodontist because it was a reproducible mandibular position that could facilitate the construction of complete dentures.11 At that time it was considered the most reliable, repeatable reference point obtainable in an edentulous patient for accurately recording the relationship between mandible and maxilla and ultimately for controlling the occlusal contact pattern. For the remainder of this text, CR is taken to mean the most superoanterior position of the condyles in the articular fossae with the discs properly interposed. The wear facets on the incisal edges of the mandibular lateral incisors are caused by occlusion with the A. maxillary central incisors only. Muscles stabilize joints. A single examiner (HU) performed all the relevant measurements. Earlier definitions described centric relation (CR) as the most retruded position of the condyles.9–11 Since this position is determined mainly by the ligaments of the TMJ, it was described as a ligamentous position. Thus these areas must be examined closely to determine the optimal orthopedic relationship that will prevent, minimize, or eliminate any breakdown or trauma. If changes occur in the structures of the joint, however, such as elongation of the TM ligament or joint pathology, the anteroposterior range of movement can be increased. a. LATERAL FUNCTIONAL OCCLUSION:“Tooth contacts that occur on canines and posterior teeth on the side towards which the mandible moves”. This position therefore represents a “muscle stabilized” position, not a “musculoskeletally stable” position. This author does not believe that it is reasonable to separate the dynamics of force application to human tissue and the disease and dysfunction experienced by that same tissue. Such a border relationship would not be considered optimal for any other joint. Studies of the mandibular chewing cycle demonstrate that in healthy subjects the rotating (working) condyle moves posterior to the intercuspal position during the closing portion of the cycle (Chapter 2). For example, with different degrees of excursion, the lateral occlusion scheme might differ. Although it has had a variety of definitions, it is generally considered to designate the position of the mandible when the condyles are in an orthopedically stable position. Most patients who have a unilateral posterior crossbite shift their mandibles toward the side of the crossbite when closing into centric occlusion. Earlier definitions described centric relation (CR) as the most retruded position of the condyles. This may be accurate in the young healthy joint, but all joints are not the same. All the values showed statistical significance among maxillary teeth. 3. The study of gnathology has come to be known as the exact science of mandibular movement and resultant occlusal contacts. © Copyright 2020 – APOS Trends in Orthodontics – All rights reserved. The position of the discs in the resting joints is influenced by the interarticular pressures, the morphology of the discs themselves, and the tonus in the superior lateral pterygoid muscles. Nevertheless, for years in dentistry, the use of this border ligamentous position as an optimal functional position for the condyles was discussed. However, if the TM ligament is loose or elongated, an anteroposterior range of movement can occur while the condyle remains in its most superior position (Figure 5-4). Alignment and Occlusion of the Dentition, 7. The controversy arises as to whether there is an anteroposterior range in the most superior position of the condyle. Therefore when force is applied to this area, there is a great potential for eliciting pain and/or causing breakdown.24–28. After examination of numerous patients with a variety of occlusal conditions and no apparent occlusion-related pathology, the merit of this concept became evident. Further, any functional occlusion is subjected to changes with time, yet without manifestation of physiological abnormalities2. ECCENTRIC OCCLUSION:“An occlusion other than centric occlusion”. Dynamic occlusion was determined in regulated lateral (0.5 mm and 3 mm lateral to the intercuspal position) and protrusive movements of the mandible by intraoral examination with the aid of shimstock. SD – Standard deviation; FH – Frankfort horizontal; FOP – Functional occlusal plane. “THE CLINICIAN MANAGING THE MASTICATORY STRUCTURES NEEDS TO UNDERSTAND BASIC ORTHOPEDIC PRINCIPLES.”. The condyles are not down the posterior sloop of the eminences. The major emphasis should be on guiding or directing the condyles to their most superoanterior positions in the fossae. 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