Concepts of dental occlusion

Basic Science Review

Concepts of Dental Occlusion DAVID REITER, M.D., D.M.D.*

The otolaryngologist frequently encounters problems related to the form and function of the stomatognathic system. Much has been published over the past 50 years regarding the "ideal occlusion," but controversy continues to rage over the relevance of various occlusal parameters to the evaluation and management of problems involving occlusal dysfunction. A review of the literature on occlusion is offered, maintaining historical perspective while expanding each theory with relevant clinical correlates. A concept of occlusion is offered that may help in the evaluation and management of otolaryngologic problems involving the stomatognathic system.

The stomatognathic system is a convenient conceptualization for representing the structures concerned with mastication and deglutition, most of which also influence the articulation of speech. The system consists of the maxilla and mandible, the hyoid bone, the temporomandibular joint, the muscles of mastication and facial expression, multiple anchoring ligaments, the tongue, the teeth and supporting structures, the salivary glands, neurovascular and lymphatic channels, and overlying skin and mucous membrane. When functioning in harmony, the parts interrelate to produce smooth and controlled chewing, swallowing, and speaking while exercising self-protective measures in order to maintain their integrity. The system is frequently called upon for parafunctional activity as well, such as holding a pipe stem, carrying dressmaker's pins, or grinding the occlusal surfaces of the teeth together seemingly without purpose. The stomatognathic system is dynamic in nature. Constant adjustment in the variable ele-

ments and dimensions of the system compensates for such factors as transition from gum pads to deciduous to adult dentition, subsequent wear and loss of teeth, variation in bulk and character of occlusal loads, dental and periodontal disease, and the use of mechanical appliances for the replacement and restoration of the natural dentition. Diverse factors influence the functioning of the system, and an anatomically intact stomatognathic system may malfunction because of misuse. Occlusion has been defined as the contact between maxillary and mandibular teeth, in contrast to articulation, defined as antagonistic contacts between maxillary and mandibular teeth during gliding movements of the mandible? Ramfjord and Ash 2 add to the definition of occlusion the anatomic alignment of teeth and their relationship to the other elements of the stomatognathic system and point out that in many patients occlusal relationships have been mechanically "adjusted," with extensive reshaping of teeth and construction of prostheses, sole-

Accepted for publication December 12, 1979. *Assistant Professor of Otorhinolaryngology, University of Pennsylvania School of Medicine. Assistant Professor of Oral Medicine, University of Pennsylvania School of Dental Medicine. Attending Otolaryngologist, Hospital of the University of Pennsylvania, Children's Hospital of Philadelphia, The Graduate Hospital, The Pennsylvania Hospital, and Veteran's Administration Medical Center, Philadelphia, Pennsylvania. American Journal of Otolaryngology --Volume 1, Number 3, May 1980

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ly because the existing relationships failed to conform to an arbitrarily conceived standard for function or appearance. Different sets of occlusal parameters are considered optimal by different authors. However, no concept of occlusion has reached a level of acceptance even close to a consensus among oral health practitioners. Perhaps the most reasonable approach to the problems of occlusion is to gather controlled data relating to quantifiable parameters of function of the parts of the stoma° tognathic system and to correlate symptoms of occlusal dysharmony with demonstrable patterns of dysfunction within the system.

ANATOMY AND PHYSIOLOGY OF THE TEMPOROMANDIBULAR JOINT

The temporomandibular articulation is a bilateral joint between the temporal bone and the mandible. A biconcave fibrous articular disc separates the mandibular condyles from the articular eminences of the zygomatic processes of the temporal bones. Surrounded by a fibrous capsule and anchored to the temporal bone and mandible by several ligaments, the joint apparatus permits three modes of mandibular motion, relative to the temporal bones. This is discussed in detail further in this review. There are two compartments within the joint. The inferior compartment separates the articular disc from the articular surface of the condyle. The superior compartment separates the disc from the articular eminence of the temporal bone. Unlike most other joints in the human body, the articular surfaces of which are covered by hyaline cartilage, in the temporomandibular joint the articular surfaces are covered by fibrocartilaginous tissue. There is a locus of hyaline cartilage within the condylar head, however, that serves as a major mandibular growth center rather than a stress bearing surface. The articular disc is connected anteriorly with the capsule, and loose connective tissue bridges the posterior space between the disc and the capsule. The capsule has a fibrous outer layer, known as the temporomandibular ligament, connecting the zygomatic process of the temporal bone with the condylar neck. The thin synovial lining is well developed posteriorly but does not extend onto the articular surfaces. Although several investigators have tried to show consistent changes in the structural c o m -

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ponents of the joint with occlusal stress, no clear explanation of the relationship between occlusal dysharmony and temporomandibular joint symptoms has yet been offered.

THE DENTITION

Each tooth is a multilayered structure composed of hard and soft tissues. Enamel forms a protective covering over the portion of the tooth exposed to the oral environment in health, the so-called anatomic crown. A high content of crystalline mineral salts makes enamel the hardest calcified substance in the body. 3 It is quite brittle and is permeable to C '4 labeled urea, I TM, and food dyes. 46 Beneath the enamel is the dentin, a substance very similar in physical and chemical properties to bone. Dentin, which forms the bulk of the tooth, is highly elastic, a property that makes it an ideal supporting base for hard but brittle enamel. Dentin is vital tissue composed of odontoblasts and an intercellular matrix, which is calcified, though to a lesser extent than that of enamel. Afferent stimuli in response to thermal and mechanical stimulation originate in the dentinal layer, where sensitivity is greatest at or close to the dentinoenamel junction. Because of this, pain is an unreliable indicator of the proximity of stimulation or injury to the pulp. 7 The dental pulp is the soft tissue organ housed within the central chamber and canals of the teeth. It consists of loose connective tissue of mesodermal origin and contains myelinated (sensory afferent) and unmyelinated (sympathetic) nerve fibers mediating pain and vascular tone, respectively. The normal pulp is a highly vascular organ. Its primary function is the formation of dentin. The cell bodies of the odontoblasts line the periphery of the pulp chamber, and the cells project tubular processes radially into the dentin. The commonly accepted theory explaining the relationship between sensitivity and proximity to the dentinoenamel junction proposes that insults to the integrity of the dentinal tubules cause cytoplasmic leakage at the cut ends, resulting in osmotic stimulation of afferent free nerve endings. The surface of the tooth not covered by enamel is covered by cementum, another calcified substance that is not well suited to exposure within the oral environment. This portion of the tooth, from the cementoenamel junction to the root apices, is termed the anatomic root. Because

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various factors influence the actual location of the free gingival margin on the crown or root of each tooth, the term "clinical crown" may be used to described the portion of the tooth exposed to the oral environment.

THE A T T A C H M E N T

APPARATUS

Each tooth is anchored within its alveolar socket by the periodontal ligament, a highly complex system of connective tissue fibers, nerves, blood vessels, and formative elements for cementum and alveolar cortical bone, the boundary elements. The collagenous fibers are arranged into groups such that occlusal forces are redirected within the fiber system to act on cementum and alveolar bone. The vasculature of the ligament acts as a hydraulic reservoir, helping to dissipate forces causing lateral or intrusive displacement of the tooth. Resorption and deposition of cementum and alveolar bone occur in response to the forces delivered to them by the periodontal ligament through the fiber system, which is firmly anchored within these two surfaces.

THE D Y N A M I C S MOTION

OF M A N D I B U L A R

The mandible is suspended in space by musculotendinous slings and is freely movable within the limits imposed by the interconnecting muscles and ligaments that attach it to the skull and other skeletal elements. There are three primary ligamentous attachments, the temporomandibular, sphenomandibular, and stylomandibular ligaments. 8 The temporomandibular ligament links the deep aspect of the condylar neck to the inferolateral aspect of the zygomatic arch between the capsular ligament and the articular eminence. The sphenomandibular ligament connects the inner aspect of the ramus of the mandible, at the lingula, to a small spine on the inferior surface of the greater wing of the sphenoid bone. The stylomandibular ligament attaches to the styloid process of the temporal bone and the posteroinferior border of the ramus and angle of the mandible. There is evidence for the presence of afferent innervation within the joint capsule and ligaments, which may initiate reflex changes in the activity of the muscles of mastication, suggesting that the ligaments perform more than a

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mechanical role in the control of mandibular motion. 9 Celenza 1° proposes that the limiting factors in mandibular retrusion are neuromuscular rather than ligamentous, as was proposed by Posselt. 11There is much support in the literature for the concept of active definition of the envelope of mandibular motion. 1217 Because neuromuscular control of skeletal relationships has no fixed reference point in space, there can therefore be no exactly duplicable or objectively definable positioning of the jaws. Celenza TM correctly points out the clinical utility of considering occlusal relationships in terms of their acceptability rather than their reproducibility. There have been many attempts to define optimal positioning of the mandibular condyles within the glenoid fossae. Each of these definitions is followed by an anthology of joint disorders based upon the individual conception of normal joints relationships. It should be clear from the prior review of temporomandibular joint anatomy that articulation occurs between the anterosuperior surface of the condyle and the articular eminence of the zygomatic process of the temporal bone. However, there is controversy regarding the relationships between the condyles and temporal bones, such that authors debate whether temporomandibular articulation is constant or intermittent during mastication.19. 20 Regardless of the functional subtleties of condylar positioning, there is general agreement about the nature of condylar motion. Three distinct motional modes are demonstrable. A hinging motion occurs in the condylar head with reference to the articular disc. The lateral pterygoid muscles are primary opening muscles, with assistance from the digastric, platysma, geniohyoid, and mylohyoid. This hinge rotation permits about 25 millimeters of interincisal opening. 2~A gliding motion occurs between the articular disc and the articular eminence, permitting protrusion of the mandible relative to the maxilla. The lateral pterygoid muscles are most important in this movement. There is also some translational movement of the mandible relative to the maxilla. 2~ Much has been written about the adaptability of the temporomandibular articulation in response to occlusal changes. Hiniker and Ramfjord22, 33 showed that anterior and posterior displacement of the mandible, accomplished by occlusal adjustment, produced insignificant adaptive changes in the structures or relationships of the temporomandibular joint, but that

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severe destructive changes in the dentition and supporting structures were observed. Adaptive repositioning of the teeth occurred until the joint relationships returned to their premanipulation states. These data and similar studies support the concept of altering the occlusion to facilitate temporomandibular joint function, suggesting that the joint will continue to exert a deleterious effect on the occlusion until the shapes or positions of the teeth are altered to eliminate "occlusal disorders." It is appropriate at this point to introduce the concepts of "centric occlusion" and "centric relation." These terms are in common use in the dental literature and are at the center of major controversy among occlusal therapists. Centric relation is defined by Posselt 24 as the posterior superior terminal hinge position of the mandible, i.e., the position in which the condylar heads are posteriormost and superiormost in the glenoid fossae. This is thought by Ramfjord and Ash 25 to be a ligament-limited position and is therefore considered "stable and reproducible" by them. There is controversy over this point, however, for Moffett26 stresses the concept that ligaments and joint capsules are biologically adjustable structures that function normally as sensory end organs rather than as mechanically restricting cables. An alternative concept of centric relation is offered by Celenza 27 as " . . . the most anterior superior physiological position of the condyles against the slope of the eminentia permitted by the limiting structures of the temporomandibular joints at a given degree of vertical dimension. It is a position that is not commonly coincident with maximum intercuspation. It is an acceptable reference point for treatment." Centric occlusion is defined by most authors as the position of maximal interdigitation of the teeth, and does not coincide with centric relation (however that is defined) in the "average, healthy human dentition. ''28 The emphasis in occlusal therapy over the past century has been to reshape the dentition in order to superimpose centric occlusion on centric relation. Major controversies regarding this philosophy include the following questions: Should centric relation be the goal of occlusal adjustment? Which skeletal relationships are represented by "centric relation"? Is "centric relation" a reproducible position? Will a reshaped and repositioned dentition maintain the new interrelationships for a long enough period of time to be clinically useful in the treatment of musculoskeletal or periodontal symptoms within the stomatognathic system?

PARAMETERS OF OCCLUSION

There are some objective parameters of occlusion. The most well known and most widely used is the classification of Angle, relating maxillary to mandibular first molars. The Angle class I dentition is one in which the mesiobuccal cusp of the mandibular first molar occludes with the interproximal area between the maxillary second premolar and first molar. The Angle class II dentition is one in which the mesiobuccal cusp of the mandibular first molar occludes with the central fossa of the maxillary first molar, and the Angle class III dentition is one in which the mesiobuccal cusp of the mandibular first molar occludes with the interproximal area between the maxillary premolars. These occlusal classifications are based solely on tooth to tooth relationships, regardless of whether the primary disproportion is a result of skeletal relationships or malpositioning of teeth within a normal skeleton. These are unilateral classifications, and the two sides of a dentition may differ in their Angle classification. Relationships between the maxillary and mandibular incisors are definable and quantifiable, according to standard nomenclatural categories. Overbite is the amount of vertical overlap of the maxillary and mandibular incisors at the maximal intercuspal position (centric occlusion). Overjet is the horizontal distance between incisal edges in the maximal intercuspal position. Both are conventionally measured and expressed in millimeters. Incisal guidance refers to the slope of the lingual surface of the maxillary incisors, which acts as a guide to mandibular disarticulation during protrusive movements of the mandible. Many clinicians and researchers have attempted to quantify the angular relationships between skeletal reference planes, such as the Frankfort horizontal, and paths of condylar motion. Such paths have been defined according to anatomic restrictions on mandibular movement, so-called "condylar guidance." This factor appears to be constant in an individual patient, on the basis of skeletal anatomic relationships, and is not thought to be subject to therapeutic alteration. Because of this, numerous theories relating condylar guidance to incisal guidance have been offered. No consistent relationship between condylar guidance and incisal guidance has been shown, despite the prevalence of concepts of occlusion suggesting such a relationship/9 Developing a functional concept of occlusion necessitates understanding the dynamics of CONCEPTS OF DENTAL OCCLUSION

tooth to tooth relationships during mastication and swallowing. An interference may be defined as any contact between maxillary and mandibular teeth that interferes with smooth jaw movements while contact is maintained between the dental arches. Lateral excursions of the mandible define the working side as the side toward which the mandible is moved, and the nonworking or balancing side as the contralateral one. There is great debate in the literature over the aspects of the maxillary cusps that should guide the mandibular teeth during lateral movements of the mandible. Most schools teach that the lingual aspects of the buccal cusps of the maxillary teeth on the working side should serve as guides for the buccal aspects of the buccal cusps of the working mandibular teeth. However, there is something of a consensus suggesting that working guidance may satisfactorily be provided by the maxillary canines in many physiologic occlusions (the concept of canine or cuspid guidance). Regardless of the source of working guidance, there is almost universal agreement about the lack of desirability of nonworking interferences in the natural dentition. (Full dentures are often constructed in accord with guidelines permitting balancing contacts, in an effort to stabilize the mandibular denture.) The slope of guiding cuspal inclines varies from patient to patient, some exhibiting steeply sloping cusps and deep fossae and others having a virtually flat occlusal surface on the posterior teeth. To some degree, incisal guidance and cuspal inclines would seem to be related. However, the average healthy dentition is characterized by a primarily anterior guidance, with little detrimental effect demonstrable. No concept of occlusion with which I am familiar advocates reduction of incisal guidance by grinding the lingual aspects of the incisors to bring posterior teeth into contact during protrusive movements of the mandible. However, an extremely deep overbite with little or no overjet may result in anterior occlusal trauma and may on occasion require correction through measures to increase (restore) lost vertical dimension posteriorly2° The anatomy of the periodontium may be considered in terms of its contribution to the dynamics of occlusion. When viewed in buccolingual cross section, the tooth and supporting structures can be seen to form a smooth inclined plane, with the gingival margin approximating the tooth just below its height of contour. This smooth transition permits the flow of foodstuff gingivally, without causing impingement upon DAVID REITER

the free gingival margin. Lubricated by saliva, the particles are then recirculated by the cheeks and tongue until a satisfactory bolus is produced for deglutition. The dynamics of food flow, combined with the anatomic relationships described, account for the self-cleansing capacity of healthy teeth and supporting structures2 ~

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THE DYNAMICS OF MANDIBULAR POSITIONING When in an upright position, the human organism maintains its mandible in a stable position without occlusal contact. This position is the end point of balance between gravitational forces acting in a downward (opening) direction and antigravity pull of the muscles of mastication that close the mandible, primarily the temporalis and medial pterygoid muscles2 ~ The maxillary and mandibular teeth are separated by approximately 2 to 4 mm., this interocclusal dimension being known as "freeway space." The position of physiologic rest is known as the postural position. 33 The postural position is therefore dependent upon all the factors that influence the muscles of mastication. Some of these are the size and position of the tongue and lips, the age and state of health of the patient, neuromuscular tone, fatigue, and the presence of such problems as bruxism and mouth breathing2 4, 35 A loss of freeway space, either because of restorations that are too "high" or because of supraeruption of posterior teeth, adversely affects occlusal function. Likewise a loss of vertical dimension, as seen with loss of posterior teeth or extensive occlusal wear, increases freeway space and affects the occlusion adversely. Adverse effects on the occlusion include loss of efficiency of mastication, pain and spasm in the muscles of mastication, preventable wear on the dentition, loosening and migration of teeth, destruction of the periodontium, aggravation of pre-existing inflammatory lesions of the gingiva and periodontium, and failure of mechanical prostheses.

CLINICAL CORRELATES SYMPTOMS OF OCCLUSAL TRAUMA. m o n e s t symptom of occlusal trauma

The com-

is mobility of teeth2 6 Severe occlusal trauma of even short duration may produce percussion sensitivity as 249

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well, with pain on mastication. Pulpal hyperemia may cause thermal sensitivity also. Myofascial pain around the temporomandibular joint, within the temporalis, masseter, and pterygoid muscles, frequently accompanies occlusal trauma. SIGNS OF OCCLUSAL TRAUMA. A physiologic occlusion permits the distribution of occlusal forces to various structural elements in the stomatognathic system, according to their capacities for dissipating these forces. There should be no signs of occlusal trauma where a physiologic occlusion is subjected to normal forces. Each element in the system is subject to wear and traumatic breakdown. Enamel is reduced in bulk by abrasion, resulting in clearly defined facets in areas of heavy contact where shearing forces are being applied. Dentin is much less resistant to abrasion than enamel and shows wear soon after being exposed to occlusal stress. Cementum, like dentin, is not exposed to the oral environment in health, and is rapidly worn away when the protection of the periodontium is lost. The pulp of a tooth suffering from occlusal trauma responds with hyperemia. Long term effects of occlusal trauma on the pulp include calcification and loss of vitality. The periodontal ligament transmits stresses of occlusal trauma to cementum and alveolar bone, both of which respond with resorption under compression, and deposition under tension. Migration of teeth may result from unidirectional stress, and thickening of the ligament and mobility of the tooth result from cyclic or multidirectional stress. It is well accepted that traumatic occlusion alone cannot produce inflammatory lesions of the periodontium. However, equally well accepted is the idea that occlusal trauma can aggravate and hasten the destruction associated with pre-existing periodontal inflammatory disease. Mild gingival inflammation, for example, that resulting from suboptimal oral hygiene but limited to the gingiva, may progress rapidly to periodontitis, with inflammation and destruction of the attachment apparatus, if occlusal trauma is superimposed. RADIOGRAPHIC EVIDENCE OF OCCLUSAL TRAU-

There is a radiographically demonstrable sequel to each kind of destruction or alteration just described. Widening of the periodontal ligament is evident radiographically as an increase in the width of the radiolucent line separating alveolar cortical bone from the cemental surface of the tooth root. The lamina dura itself is also MA.

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responsive to occlusal stress in a radiographically demonstrable way. Thickening of this cortical bone suggests increased occlusal stress, and discontinuity is characteristic of occlusal trauma27 Widening of the periodontal ligament space, accompanied by resorption of the lamina dura, is highly suggestive of occlusal trauma. 3~ Resorption of the apical part of tooth roots is often seen with heavy occlusal stresses, as, for example, during extensive and rapid orthodontic movement and in teeth serving as abutments for multiunit prostheses. Hypercementosis also occurs under these circumstances and may cause root apices to assume a globular appearance radiographically. The use of arch bars and wires for intermaxillary fixation may exert forces on teeth that are both excessive and poorly directed (i.e., laterally rather than apically). One should be aware of the radiographic signs described in order to prevent damage to the dentition and supporting structures from the use of such appliances. CONCEPTS OF OCCLUSION IN HISTORICAL PERSPECTIVE

McCollum39 described gnathology in 1937 as " . . . the science that treats of the masticating mechanism, that is, the morphology, anatomy, histology, physiology, pathology, and the therapeutics of the oral organ, especially the jaws and teeth, and the vital relations of this organ to the rest of the body." Periodontology was in its infancy in the 1920's, at which time a relationship between traumatic occlusion and periodontal disease was being noticed. It was thought at that time that occlusal trauma caused inflammatory gingival lesions, such as clefts and pockets. 4° A series of experiments and observations by early periodontists failed to demonstrate a relationship between gingival disease and changes in the periodontal ligament. 4' This failure seemed to refute the then-prevalent idea that gingival disease was caused by occlusal trauma.42, 43 The demonstration of inflammatory lesions and degenerative changes as two separate entities marked the beginning of a long controversy, for there have remained periodontists who believe that occlusal trauma causes inflammatory lesions of the periodontium. Regardless of the mechanism, occlusal trauma was consistently thought to be a significant factor in the development of clinical signs and symptoms of periodontal disease, if the occlusion in question failed to meet some arbitrary standards. CONCEPTS OF DENTAL OCCLUSION

From the beginning, occlusal trauma was separated into two basic categories. Primary occlusal trauma is defined and accepted as a pathologic change in the dentition or its supporting structures resulting from the application of supraphysiologic forces to a physiologic system. Secondary occlusal trauma is the result of normal forces acting on a system weakened by pre-existing disease. The literature is primarily concerned with primary occlusal trauma, since this is, by far, the more commonly encountered situation in clinical practice. A discussion of secondary occlusal trauma is more appropriately reserved for the periodontal-prosthodontics literature and is not included in this review. Concern over occlusal trauma led to attempts to adjust the dentition, to redistribute forces acting on the system. In 1923 Schuyler44anecdotally reported his initial efforts to reshape the teeth to eliminate the factors he thought were contributing to lesions of the periodontium. He employed a process he termed "spot grinding" to meet the following goals of occlusal therapy: maximal distribution of stress in centric maxillomandibular relation, retention of physiologic freeway space, coordinated contacts of guiding inclines, reduction of guiding incline slopes to minimize nonaxial forces on the teeth and periodontium, retention of sharp "cutting cusps," increased food exits, and decreased contacting surface area. This approach firmly established the principle of removing tooth structure to lessen masticatory forces. Implicit in these concepts is the assumption that the teeth contact with significant force over a significant enough period of time to affect the periodontium during mastication, an assumption that has been called into question. 45 The process of occlusal adjustment by removing the tooth surface is called selective grinding and is practiced widely today. Goals and objectives, as well as guidelines for achieving them, vary greatly among different groups. Indications for selective grinding also vary from location to location and from one historical period to another. Different observations relating differing patient populations possibly account for the wide variation in concepts of occlusion and clinical methods for implementing them. In 1935 Costen 46-4s published in the medical literature three articles describing and elaborating upon a syndrome of ear and sinus symptoms that he believed were caused by malocclusion. Along with other authors, he advocated correction of the occlusion as the therapeutic method of choice, citing pressure of the improperly DAVID REITER

positioned condyles on nerves and the eustachian tube as the causative element in the syndrome. He published several articles in the dental literature proposing occlusal adjustment as the cure for various symptoms. 4951 Sicher52 was able to refute these assertions by demonstrating the anatomic impossibility of such severe condylar malpositioning. Widespread poor results from tampering arbitrarily with the vertical dimension led to the abandonment of the principles of Costen by most occlusal therapists. ~3 As the decade of the 1940's progressed, a new concept became popular. Interest was centered on the phenomenon of parafunction, i.e., tooth to tooth contact other than for mastication and deglutition. The prototype of parafunction is bruxism, the habit of clamping and grinding the maxillary and mandibular teeth together. This was seen as a primary factor in the development of trauma related lesions of the dentition and periodontium by many investigators. Selective grinding was proposed, again, as a method for controlling occlusal trauma associated with bruxism. ~4 Investigation of the role of the vertical dimension in occlusal trauma was also popular in the 1940's. Thompson and Brodie 55 concluded that the presence or absence of teeth has little significant effect on the postural position of the mandible, that the syndrome described by Costen was due to overclosure of the mandible during function (loss of vertical dimension), and that impingement on freeway space by occlusal alteration results in accomodation of the teeth or alveolar processes to reopen freeway space to its physiologic dimension. Several important principles were discovered or described in the 1950's. Posselt 56was actively engaged in clinical investigation that would lead to a major book about the physiology of occlusion, based in part on observations of a group of healthy dental students. He concluded that patterns of mandibular movement during mastication varied from subject to subject, that the habitual path of closure of the mandible is usually anterior to the dorsal limit of mandibular movement, and that the absolute borders of mandibular movement were replicable in any given patient. He also made the observation that in over 90 per cent of the subjects studied there was a discrepancy between centric occlusion and centric relation in the absence of symptoms and signs of occlusal traumaY Another significant contribution to the study of occlusion came from the work of Jankelson

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and his group. 58Beginning with the premise that tooth to tooth contact may not be a significant factor in mastication, they demonstrated that such contact occurs infrequently in function. In addition, they showed that any tooth to tooth contact that may occur when the bolus of food is pierced by opposing cusps is of a very brief duration because of reflex reversal of the action of the muscles of mastication. Jankelson promoted a concept of occlusion that favored selective grinding to superimpose centric occlusion on centric relation, because he believed that this was the most physiologic state. The last major contribution from research in the 1950's was the demonstration of the independence of the gingival blood supply from that of the attachment apparatus and alveolar support. This finding strengthened the premise that occlusal trauma alone would not cause inflammatory lesions of the periodontium. 5961 Research in the 1960's centered around the nature of tooth to tooth contact. So many conflicting opinions were offered regarding the optimal area of interarch contact, the optimal position in which it should occur, and the best method for improving contact that it is difficult to present a cogent argument for or against any of them. In view of major advances in earlier decades, it may be said that little further progress was made in unifying the concepts of authorities in the field regarding either the nature of occlusion or occlusal therapy. The present decade has seen the distillation of various historical concepts and observations into a few schools of thought. The bulk of this material has been gathered into a single work, the Proceedings of the Occlusion Focus held in Las Vegas in 1976. 62 Several noted authorities gathered for the purpose of reducing misunderstanding about their individual concepts of occlusion, and in doing so attempted to reach some agreement about the areas of condylar positioning in centric occlusion, the character of centric occlusion, and the character of eccentric movement of the mandible. Following the presentation of nine position papers, the participants were given a six part questionnaire dealing with concepts of occlusion. There was a great deal of uniformity of opinion among these experts on several points regarded as controversial in the earlier literature. No participant believed that the condyles should be in their most posterior postition in centric occlusion. The participants were evenly split when asked whether centric relation was

primarily a position of convenience for the prosthodontist or an acceptable position for treatment. There was good agreement that centric relation should be a treatment goal only when there is evidence of occlusal disease and that the temporomandibular joints must be healthy in order to accomplish this. Most interesting to the student of occlusion is the unanimity of opinion that a discrepancy between centric occlusion and centric relation is not a precursor to occlusal trauma, and that arbitrarily adjusting the occlusion as a preventive measure is wrong. Interestingly enough, however, most of the participants did agree that such a discrepancy can " . . . contribute to a parafunctional habit." This would appear to reflect hesitancy to abandon the old concepts, for more than 90 per cent of healthy occlusions have such a discrepancy, as cited earlier in Posselt's work. Therefore, statistical analysis of the relationship between parafunction and a discrepancy between centric occlusion and centric relation w o u l d appear to be difficult to do.

CLINICAL EVALUATION OF OCCLUSAL FUNCTION An understanding of the various concepts of occlusion is of no value to the otorhinolaryngologist without some way of translating this knowledge into clinically useful information. The area in which such knowledge is most useful is in the evaluation of the "temporomandibular joint syndrome." The problems of pain in and around the temporomandibular joint are correctly called the "myofascial pain dysfunction syndrome" and are frequently encountered by practitioners in any field encompassing the head and neck. Pain and spasm in the muscles of mastication may result in deviation of the mandible on opening, limited mandibular movement, and subjective tinnitus, dizziness, and headache. Such patients most often have parafunctional habits, either bruxism per se or such activity as carrying a pipe stem or dressmaker's pins in the teeth. A temporal relationship to dental restoration is highly suggestive of an occlusal etiology, for even a minor change in the vertical dimension on one side may cause sufficient imbalance to precipitate painful spasm on the side with less stable occlusal contact. Increased severity in symptoms is usually seen on awakening in the morning, when nocturnal bruxism is the primary etiologic factor. CONCEPTS OF DENTAL OCCLUSION

Signs of bruxism include prominent wear facets on opposing occlusal surfaces, mobility of teeth, and percussion sensitivity. Radiographic evidence includes loss of continuity of cortical alveolar bone and widening of the periodontal ligament space. When there is pre-existing inflammatory periodontal disease, rapid progression of periodontal destruction may be seen in periodic examinations. An evaluation encompassing the foregoing information is essential in order to make clinical sense of problems of the stomatognathic system. The minimal evaluation necessary includes a thorough clinical examination, specifically noting interincisal opening, any mandibular deviation during opening, tooth mobility or sensitivity, patterns of wear, crepitance in the temporomandibular joint itself, and tenderness in each of the muscles of mastication, and a thorough otolaryngic examination. Radiographs should be taken of the temporomandibular joints in closed and open positions. A full series of periapical dental radiographs should be obtained as well. Although a panoramic radiograph of the mandible is useful in evaluating the periodontal architecture, specific information regarding the periodontal ligament and alveolar bone characteristics can be obtained more accurately with periapical views. The panoramic view is therefore not a satisfactory substitute. It is, however, a useful aid in the periodic examination, in order to follow progressive loss of alveolar bone and the development of periapical lesions. THE ROLE OF OCCLUSAL THERAPY IN HEAD AND NECK SYMPTOMATOLOGY

It is easy to demonstrate deviations from the "ideal occlusion" in most patients. As a point of reference, Strang's description of the normal occlusion is offered: " . . . that structural composite consisting fundamentally of the teeth and jaws and characterized by a normal relationship of the so-called occlusal incline planes of teeth that are individually and collectively located in architectural harmony with their basal bones and with cranial anatomy, exhibit correct proximal contacting and axial positioning and have associated with them a normal growth, development, location, and correlation of all environmental tissues and parts." This kind of descriptive doubletalk is of little clinical value, as it represents an arbitrary ideal rather than a statistical or functional norm. GoldDAVID

REITER

man and Cohen 63 point out that to consider the ideal occlusion (to which Strang applied the term "normal"), a reasonable treatment goal would be to advocate occlusal adjustment for over 90 per cent of the population. It is therefore inappropriate to attribute all manner of head and neck symptoms to malocclusion simply because some deviation from ideal occlusion is demonstrable. An occlusal etiology for pain and spasm in the muscles of mastication may be suspected when an identifiable change in the occlusion has been followed by development of the symptom(s). Myofascia] pain may also develop when progressive loss of posterior teeth is uncorrected, resulting in posterior bite collapse with instability and a decrease in the vertical dimension. Pain in the muscles of mastication may also follow restorative dentistry, as has been discussed. Pain originating in the periodontal ligament of a tooth subjected to greater than normal forces, as seen in patients with parafunctional habits, may be confusing to the clinician. Radiation patterns throughout the distribution of the trigeminal nerve may obscure the source, with only the history giving a clue to the etiology. Inflammation within the periodontal ligament may cause apparent otalgia, atypical facial pain, or diffuse headache. Radiographic findings in combination with clinical symptoms and signs, as previously described, help make the diagnosis in many cases. Occlusal adjustment limited to the offending tooth or restoration may be entirely appropriate for well defined problems such as an overcontoured restoration. However, one should consider occlusal adjustment as a procedure that is likely to accomplish little for the majority of patients with atypical facial pain. Attention to the occlusion, which is not likely to be the primary etiologic agent in most patients with myofacial pain, carries with it the danger of induced dental a w a r e n e s s - - t h e phenomenon in which the patient becomes acutely aware of the dentition and its functional and architectural characteristics. The minor occlusal irregularities that are present in over 90 per cent of the population become focal points for the patient with induced dental awareness. Once the occlusion has been "identified" as an etiologic factor in the patient's discomfort, it is extremely difficult to succeed with any other form of therapy. The primary factor that makes common occlusal abnormalities take on etiologic significance in head and neck pain is stress. Tension and anxiety frequently result in or aggravate tenden-

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cies toward parafunction, turning a physiologic occlusion (i.e., an occlusion in which no disease is demonstrable and that functions satisfactorily despite minor problems) into a pathologic one. Occlusal adjustment often takes the attention of both the therapist and the patient away from this fact and makes it difficult to return to this from a therapeutic standpoint. When occlusal awareness or previous occlusal therapy makes stress relief a poorly accepted therapeutic modality, an appliance may be fabricated that disarticulates the teeth completely, helping to reorient the patient. This consists of a removable acrylic block adapted to the palate and held in place by wire clasps around the maxillary teeth. Such an appliance is called a Hawley bite plane and may provide nocturnal relief from bruxism while"deprogramming" the patient regarding occlusal function. This may facilitate focusing on stress relief and alleviate occlusal trauma. Occlusal adjustment is doomed to failure when stress is the primary etiologic agent. The general experience with stress relief is that it is a clinically useful category of therapeutic effort for myofascial pain when no demonstrable organic disease exists as an etiologic agent. Prophylactic occlusal adjustment is most often contraindicated.64 Other contraindications to occlusal adjustment include the presence of few remaining teeth, significant mobility in the remaining teeth, marked mandibular displacement, heavy enamel wear, and pronounced crossbite (reversal of normal buccolingual relationships, with the buccal surfaces of the mandibular teeth lateral to those of the opposing maxillary teeth). THE PHYSIOLOGIC OCCLUSION Goldman and Cohen 65 describe the physiologic occlusion as one that " . . . s e e m s to be in a harmonious state of function with its environment in that a state of balance seems to exist between injury and repair." This is an excellent functional concept for the otolaryngologist. The definition of a pathologic occlusion, then, would be one in which there are signs of breakdown, lesions of the dentition or supporting structures as evidenced by historical, physical, and radiographic findings. When such lesions are present and are related to identifiable occlusal abnormalities that were not present prior to the onset of symptoms, occlusal adjustment or other local therapy may be appropriate. However, investigation into other local and systemic causes of the

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problem should be undertaken before implicating common occlusal findings. Perhaps the most significant contributor to head and neck pain not clearly of other cause is stress. Behavior modification, progressive relaxation, biofeedback, and other stress relief techniques are valid clinical tools for both the diagnosis and management of myofascial pain and associated problems. Occlusal adjustment in the absence of demonstrable disease temporally related to the onset of the symptom is usually wrong. Stress alone may make the difference between a physiologic occlusion and a pathologic occlusion. SUMMARY There is a large body of literature relating to occlusion, covering most of the twentieth century. Despite intensive investigation by numerous authors, no clear definition of occlusal disease or therapeutic occlusal goals exists. Occlusal therapy has been advocated for a wide variety of head and neck symptoms but is frequently employed empirically and without definable justification. Over 90 per cent of the population have demonstrable deviations from the so-called ideal occlusion, yet symptoms are infrequently seen as a chief complaint. Guidelines have been provided for initial occlusal evaluation, and referral to an oral health practitioner is suggested when a reasonable suspicion of an occlusal etiology exists. The otolaryngologist is cautioned to avoid routinely identifying the occlusion as an etiologic agent of head and neck symptoms.

References 1. Bauer, A., and Gutowski, A.: Gnathology - - Introduction to Theory and Practice. Chicago, Quintessence Books, 1976, pp. 53-54. 2. Ramfjord, S. P., and Ash, M. M.: Occlusion. Ed. 2. Philadelphia, W. B. Saunders Company, 1971, p. 67. 3. Sicher, H.: Orban's Oral Histology and Embryology. Ed. 6. St. Louis, The C. V. Mosby Company, 1966, p. 39. 4. Wainwright, W. W., and Lemoine, F. A.: Rapid diffuse penetration of intact enamel and dentin by carbon '4labelled urea. J. Am. Dent. Assoc., 41:135-145, 1950. 5. Bartelstone, H. J., Mandel, I. D., Oshry, E., and Seidlin, S. M.: Use of radioactive iodine as a tracer in the study of the physiology of the teeth. Science, 106:132, 1947. 6. Jansen, M. T., and Visser, J. B.: Permeable structures in normal enamel. J. Dent. Res., 29:622-632, 1950. 7. Sicher, H.: Op. cir., p. 123. 8. Brill, N., Lammie, G. A., Osborne, J., and Perry, H. T.: Mandibular positions and mandibular movements. Br. Dent. J., 106:391-400, 1959. 9. Kawamura, Y.: Neurophysiologic background of occlusion. J. Am. Soc. Periodont., 5:175-183, 1967. 10. Celenza, F. V., and Nasedkin, J. N.: O c c l u s i o n - - T h e

CONCEPTS OF DENTAL OCCLUSION

State of the Art. Chicago, Quintessence Books, 1978, pp. 31-34. 11. Posselt, U.: Studies in the mobility of the human mandible. Acta Odontol. Scand., 10(Suppl. 10), 1952. 12. Boucher, L., and Jacoby, J.: Posterior border movements of the human mandible. J. Prosthet. Dent., 11:836--841, 1961. 13. McMillen, L. B.: Border movements of the human mandible. J. Prosthet. Dent., 27:524-532, 1972. 14. Celenza, F. V.: An investigation of the consistency and placement of the centric position in dentulous subjects. M. S. D. thesis, New York University College of Dentistry, April 1972. 15. Galagna, L. J., Silverman, S. I., and Garfinkel, G.: Influence of neuromuscular conditioning on centric relation registrations. J. Prosthet. Dent., 30:598-604, 1973. 16. Shafagh, I., Yoder, J., and Thayer, K.: Diurnal variance of centric relation position. J. Prosthet. Dent., 34:574582, 1975. 17. Grasso, J., and Sharry, J.: The duplicability of arrowpoint tracings in dentulous subjects. J. Prosthet. Dent., 20:106-115, 1968. 18. Celenza, F. V., and Nasedkin, J. N.: Op cit., p. 33. 19. Sicher, H.: Functional anatomy of the temporomandibular joint. In Sarnat, B. (Editor): The Temporomandibular Joint. Springfield, Illinois, Charles C Thomas, 1951, pp. 3-40. 20. Ramfjord, S. P., and Ash, M. M.: Op. cit., p. 18. 21. Ibid., p. 19. 22. Hiniker, J. J., and Ramfjord, S. P.: Anterior displacement of the mandible in adult Rhesus monkeys. J. Prosthet. Dent., 16:503-512, 1966. 23. Hiniker, J. J., and RamOord, S. P.: Distal displacement of the mandible in adult Rhesus monkeys. J. Prosthet. Dent., 16:491-502, 1966. 24. Posselt, U.: Studies in the mobility of the human mandible. Acta Odontol. Scand., lO(Suppl. 10), 1952. 25. Ramfjord, S. P., and Ash, M. M.: Op. cit., p. 95. 26. Moffett, B.: A biologic consideration of centric relation based on skeletal and connective tissue responses. In Celenza, F. A., and Nasedkin, J. N.: O c c l u s i o n - The State of the Art. Chicago, Quintessence Books, 1978, pp. 13-18. 27. Celenza, F. V., and Nasedkin, J. N.: Op. cit., p. 34. 28. Ramfjord, S. P., and Ash, S. M.: Op. cit., p. 95. 29. Ibid., p. 71. 30. Beyron, H. L.: Characteristics of functionally optimal occlusion and principles of occlusal rehabilitation. J. Am. Dent. Assoc., 48:648-656, 1954. 31. Goldman, H. M., and Cohen, D. W.: Periodontal Therapy. Ed. 4. St. Louis, The C. V. Mosby Company, 1968, p. 56. 32. Carlsoo, S.: Nervous coordination and mechanical function of the mandibular elevators. Acta Odontol. Scand., 10(Suppl. 11), 1952. 33. Posselt, U.: Physiology of Occlusion and Rehabilitation. Ed. 2. Oxford, Blackwell Scientific Publications, Ltd., 1968, p. 32. 34. Atwood, D. A.: A cephalometric study of the clinical rest position of the mandible. Part I. The variability of the clinical rest position following the removal of occlusal contacts. J. Prosthet. Dent., 6:504-519, 1956. 35. Fish, S. F.: The respiratory associations of the rest position of the mandible. Br. Dent. J., 116:149-159, 1964. 36. Ram~ord, S. P., and Ash, M. M.: Op. cit, p. 257. 37. Massler, M.: Changes in the lamina dura during tooth movement. Am. J. Orthod., 40:364-372, 1954. 38. McCall, J. O.: The radiogram as an aid in the diagnosis and prognosis of periodontal lesions. J. Am. Dent. Assoc., 14:2073-2082, 1927. 39. McCollum, B. B.: Is it necessary to replace missing teeth? J. Am. Dent. Assoc., 24:442--448, 1937.

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40. Stillman, P., and McCall, O.: A Textbook of Clinical Periodontia. New York, The Macmillan Company, 1927. 41. Orban, B., and Weinmann, J.: Signs of traumatic occlusion in average human jaws. J. Dent. Res., 13:216, 1933 (abstract). 42. Stillman, P.: The pathology of occlusion. J. Am. Dent. Assoc., 138:1081-1085, 1926. 43. Orban, B.: Tissue changes in traumatic occlusion. J. Am. Dent. Assoc., 15:2090-2106, 1928. 44. Schuyler, C.: Fundamental principles in the correction of occlusal dysharmony, natural and artificial. J. Am. Dent. Assoc., 22:1193-1202, 1935. 45. Manly, R. S., and Braley, L. C.: Masficatory performance and efficiency. J. Dent. Res., 29:448---462, 1950. 46. Costen, J. B.: A group of symptoms frequently involved in general diagnosis, typical of sinus and ear disease and of mandibular joint pathology. J. Mo. Med. Assoc., 32:184, 1935. 47. Costen, J. B.: Neuralgias and ear symptoms involved in general diagnosis due to mandibular joint pathology. J. Kans. Med. Soc., 36:315, 1935. 48. Costen, J. B.: Neuralgias and ear symptoms. J. Am. Med. Assoc., 107:252-255, 1936. 49. Costen, J. B.: Syndrome of ear and sinus symptoms dependent upon disturbed function of the temporomandibular joint. Ann. Otol. Rhinol. Laryngol., 43:115, 1934. 50. Costen, J. B.: Some features of the mandibular articulation as it pertains to medical diagnosis, especially in otolaryngology. J, Am. Dent. Assoc., 24:1507-1511, 1937. 51. Costen, J. B.: Correlation of x-ray findings in the temporomandibular joint with clinical signs, especially trismus.J. Am. Dent. Assoc., 26:405-407, 1939. 52. Sicher, H.: Temporomandibular articulation in mandibular overclosure. J. Am. Dent. Assoc., 36:121-129, 1948. 53. Weisgold, A. S.: A review of the various concepts of o c c l u s i o n - a historical perspective. Alpha Omegan, 66:9-15, 1973. 54. Leof, M.: Clamping and grinding habits: their relation to periodontal disease. J. Am. Dent. Assoc., 31:184-194, 1944. 55. Thompson, J. R., and Brodie, A. G.: Factors in the position of the mandible. J. Am. Dent. Assoc., 29:925942, 1942. 56. Posselt, U., and Posselt, A.: Some correlations between the occlusal pattern, function and pathology of the masticatory system. Paradontologie, 13:3-9, 1959. 57. Posselt, U.: Movement areas of the mandible. J. Prosthet. Dent., 7:375-365, 1957. 58. Jankelson, B., Hoffman, G., and Hendron, J. A.: The physiology of the stomatognathic system. J. Am. Dent. Assoc., 46:375-386, 1953. 59. Keeler, G. J., and Cohen, D. W.: India ink perfusion of the vascular plexus of oral tissues. Oral Surg., 8:539-542, 1955. 60. Anderson, D. J., and Picton, D. C. A: Tooth contact during chewing. J. Dent. Res., 36:21-26, 1957. 61. Ramfjord, S. P.: Bruxism, a clinical and electromyographic study. J. Am. Dent. Assoc., 62:21-24, 1961. 62. Celenza, F. V., and Nasedkin, J. N,: Op. cit. 63. Goldman, H. M., and Cohen, D. W.: Op. cit., p. 580. 64. Posselt, U.: Physiology of Occlusion and Rehabilitation. Ed. 2. Oxford, Blackwell Scientific Publications Ltd., 1968, p. 227. 65. Goldman, H. M., and Cohen, D, W.: Op. cit., p. 584.

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