SWJTTON EDITOR

Anterior guidance: Group function/canine guidance. A literature review

Linda J. Thornton, D.D.S.* U.S. Army Dental Activity, Fort Sam Houston, Texas

Anterior guidance, which can be categorized as group function or canine guidance, is essential for esthetics, phonetics, and mastication. This article reviews the historical development and philosophies of both occlusal schemes. There is no scientific evidence that supports one occlusal scheme over the other. Where anterior guidance must be reestablished or where it changes, there currently appear to be more authorities who favor canine guidance over group function. (J PROSTHETDENT~QQ~;~~:~~Q-~~.)

A nterior guidance is essential to a harmonious functional relationship in the natural dentition and is crit- ical to a functional occlusion. Schuyler’* 2 emphasized the importance of anterior guidance over condylar guidance. He observed that anterior guidance was controlled by an unyielding consistent tooth-to-tooth contact, whereas condylar guidance varied due to the flexibility of the joint.

Anterior guidance can be categorized into two occlusal schemes. These are group function and canine guidance. Canine guidance is also known as canine-protected occlu- sion, mutually protected occlusion, canine disclusion, ca- nine-lift, and canine rise. This article reviews the history and current relevance of the theoretical background for anterior guidance.

HISTORY

Although these occlusal guidance systems are clearly di- vergent in both philosophy and technique, they both appear to have evolved from the common roots of bilateral balanced occlusion. Group function appears to have been the direct descendent of the balanced occlusion theory.3 This theory was conceived from Von Spee’s observations of the condylar path, which stated that “the course of move- ments which serve to grind food is determined not only by the mechanical configuration of the temporomandibular joint but is also very substantially affected by the occlusal anatomy of the teeth. Accordingly both are fitted to each other in a harmonious manner.“4 Advocates of balanced occlusion refer to this observation as the doctrine from which the theory germinated.3 The balanced occlusion

Presented before the National Capital Area Section of the Amer- ican College of Prosthodontists, Washington, D.C.

*Lieutenant Colonel, U.S. Army, DC; Fixed Prosthodontic Ser- vice.

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theory was based on Von Spee’s observations and on early research pioneered by such investigators as Christensen,5 Gysi,6 Monson,’ and Hal1.8 In the 1950’s Stuart,g-12 Stallard,g* l1 and McCollumlo originally advocated the use of balanced occlusion as the key to obtaining a harmonious relationship between condylar guidance and the occlusal surfaces of the teeth during all functional excursions. These clinicians later abandoned balanced occlusion in the natu- ral dentition due to clinical failures.13-l5 Grangerr6* l7 defended the use of this theory in the natural dentition as well as in complete dentures. He observed that a true bal- anced occlusion maintained the entire dentition in a state of functional equilibrium.

GROUP FUNCTION

The literature credits Schuyler18-20 with enlightening clinicians as to the destructive forces associated with bal- anced contacts. He observed that even though these con- tacts were essential for stability of complete dentures, they were traumatic to the natural dentition, causing temporo- mandibular joint (TMJ) dysfunction, periodontal involve- ment, or excessive wear. As a result of research conducted by Schuyler and other investigators,21-2” balanced occlu- sion was replaced with unilateral balanced occlusion or group function.

The group function philosophy appears to be one of physiologic wear. Schuylerz4 and other advocates of group function25-27 viewed occlusal wear as a compensatory adap- tive change that distributed stress to create a normal func- tional relationship. Several authors28”’ have suggested that occlusal wear was natural and beneficial. Moser332 de- duced “it was nature’s plan for the cusps to wear in a par- ticular and beneficial manner which is related to the vigor- ous function that primitive man was believed to have ex- hibited. This wear was an inevitable accompaniment of well-developed and well-sustained dentitions.“32 Beyron33 conducted a serial investigation of the progressive occlusal

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changes in the natural dentition. He demonstrated that group function was conducive to occlusal wear, and was ca- pable of allowing an even distribution of stress. As the nat- ural dentition matured, normal occlusal wear progressed, which maintained the teeth in a balanced state. It is indeed ironic that the findings of canine guidance advocates, for example, Scaife and Holt, 34 demonstrating that the per- centage of patients with wear facets increased in direct proportion to the degree of group function, actually pro- vided evidence to reinforce the theory of group function.

Several investigators35*38 questioned the efficacy of ca- nine guidance. Schuyler,35 who was in the vanguard of the group function advocates, commented: “Why place all of the stress upon the cuspid? At all times when the promi- nence of cuspid teeth preclude contact of all the other teeth in eccentric positions, functional efficiency, comfort and the most desirable or favorable distribution of functional force to the periodontium is negated.“35 Lucia,36 an advo- cate of canine guidance, queried: “What happens to the proprioceptive protection if the cuspids are missing, badly broken down, or periodontally involved?“36 In order for canine-protected occlusion to function, the anterior teeth must be healthy; otherwise a balanced type of occlusion was necessary. Weinberg37 questioned whether the “strategic location” of the canines away from the fulcrum was effec- tive in reducing the compression to the TMJ. He illustrated in canine guidance that the TMJ was capable of superior displacement and compression due to unsupported poste- rior muscle force. Alexander38 suggestedthere was no clin- ical, biologic, or histologic evidence supporting a “protec- tive mechanism” associated with canine teeth. Tooth mo- bility would occur when the functional forces exceeded the physiologic limits of the periodontium of any tooth. Whether physiologic tooth movement was greater during group function or canine guidance is still debatable. O’Le- ary et a1.,3g observing the mean mobility of teeth, discov- ered that the canines approached a more physiologic func- tion with group function vis-a-vis canine guidance. The reason for this phenomenon was discovered by DiPietro,40 who categorized canine guidance as being associated with a low-degree Frankfort mandibular angle (FMA) and an increased biting force, while group function was associated with a high-degree FMA and a decreased biting force.

The philosophy advocated by Schuyler was incorporated with those of Pankey and Mann to form a concept of treat- ment known as the Pankey-Mann-Schuyler philosophy for complete occlusal rehabilitation29 41 Since its conception, the objective of this philosophy has been to achieve the principles of occlusion developed by Schuyler, which in- clude maximum contact of the teeth in centric relation; si- multaneous contact of the anterior and posterior teeth on the working side during lateral excursions; anterior disclu- sion of posterior teeth in protrusion; and no contacts on the balancing side teeth during lateral excursions. These goals were sequentially accomplished by first emphasizing ex- amination, diagnosis, and treatment planning; establishing

an anterior guidance that has the best possible esthetics, function, and comfort; selecting and restoring a lower pos- terior occlusion that was in harmony with anterior guid- ance and condylar guidance; and using the functionally generated path technique to restore the upper posterior occlusion in harmony with anterior guidance and condylar guidance. This philosophy of occlusal rehabilitation can be used to fulfill the goals of a theoretically ideal occlusion, which consists of no TMJ dysfunction, no periodontal in- volvement, and little or no occlusal wear.

CANINE GUIDANCE

Canine guidance is disclusion by the canines of all other teeth in lateral excursions.42 D’Amico,3 and Scaife and Holt34 suggested that the concept of canine guidance had its genesis in Nagao’s43 refutation of Von Spee’s observa- tions of the condylar path, in which he stated “the curve of Spee is not closely related either to the manner of move- ment of the lower jaw, or to the efficiency of mastication.“43 Von Spee may have planted the seeds of canine guidance when he made reference to the overbite of the upper canines, although he considered this observation insigni- ficant.4 Fick,44 a German anatomist, questioned Von Spee’s findings. However, he was unable to sufficiently disprove them. Nagao43 undertook his comparative study on the curve of Von Spee in order to substantiate Fick’s objec- tions. The significance of Nagao’s research was either overlooked or ignored because the preponderance of clini- cians were advocates of balanced occlusion. In fact, bal- anced occlusion was considered essential to any organized dentition.‘j It was against such a background that Nagao’s study was introduced. Therefore to suggest that balanced occlusion could be considered destructive to the natural dentition was a charge that had to be issued with extreme caution. A significant contribution swaying clinical opinion away from balanced occlusion was made by Shaw.45 This anthropologist interpreted balanced occlusion appearing in the natural dentition as malocclusion.

Ironically, the clinical application of canine guidance was initiated by Stuart and Stallardg and by McCollum and Stuart,lO who were originally staunch advocates of bal- anced occlusion. While researching the balanced occlusion theory, these clinicians concluded that the theory was flawed and they were courageous enough to admit “the majority of their cases did not stand the rigid test of time and were failures.“17 They attributed this failure to the trauma caused by multitudinous, simultaneous contacts that resulted in occlusal wear, periodontal involvement, or TMJ dysfunction. Influenced by Shaw and by clinical ex- periences, Stuart and Stallardg concluded that occlusal wear was not a functional aim, which was their original hy- pothesis, but was one of nature’s unavoidable mistakes. Stuart and StalIard clinically examined Shaw’s theories by making full coverage restorations on maxillary canines in patients showing evidence of occlusal wear to facilitate posterior disclusion during eccentric movements. They

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ANTERIOR GUIDANCE: A REVIEW

suggested that this procedure was not only acceptable to the patient but provided a canine lift that would halt the rate of wear.ll Stuart12 concluded that natural dentition, where teeth interdigitate in centric relation but have no cross-tooth or tooth-mouth balance, had the slowest rate of wear. It was his contention that the use of this technique was a preventive measure to future periodontal disease. Its primary purpose was to save the teeth and in turn the periodontium.12 Other investigators, such as Scott and Baum46 and Shooshan, viewed the lost canine function as primarily a mechanical problem and suggested during ex- cursive movements a distance of at least 0.5 mm between the posterior opposing teeth. These investigators postu- lated that there was no apparent harm if the restoration created a greater separation.

Influenced by earlier investigators,sy 45, 48 D’Amico,4s in his treatise on canine-protected occlusion, proselytized this theory to its popularity. He analyzed occlusal wear in light of its significance to man’s relatives, thus raising consider- able skepticism as to whether the balanced occlusal rela- tionship of man’s teeth or of the teeth of any other mem- ber of the primate family ever existed. D’Amico4g studied the function of the canines from the anthropoid apes to modern man. He theorized that the overlapping of the ca- nines was originally displayed in the great apes due to their nonabrasive diet. As man’s diet and environment changed, so did the form and function of the canines. Occlusal wear caused a progressive reduction of vertical relation, edge- to-edge occlusion, and a wide range of lateral and protru- sive movements. With the advent of a soft diet there was a gradual change back to the overlapping relationship of the canines. D’Amico deduced from this “the canines have been casualties of function rather than casualties of evolution.“4s Another tenet of D’Amico’s theoryso was that the canines acted as “nature’s stressbreakers” to protect the periodontium and supporting structures from lateral stress during eccentric movements. Upon functional con- tact by the canines, the periodontal proprioceptive im- pulses are transmitted to the mesencephalic root of the fifth cranial nerve, which altered the motor impulses to the musculature. The resultant involuntary reaction relaxed the muscles and thus decreased the adverse effects of the lateral force to the periodontium. D’Amico concluded, if all natural teeth had this “involuntary physiologic factor,” balanced occlusion could be applied without fear of peri- odontal or restorative failure. The literature is replete with investigators who substantiated D’Amico’s findings. Stuar@i observed the canines had a higher minimal lateral pressure threshold. Corbin and Harrison52 reported the canines were the most sensitive intraoral structures to blunt stimulation. Another study by Kruger and Miche153 revealed that canines had a higher concentration of neu- rons than any other teeth. More recent research by Kawamura54 demonstrated that those teeth most sensitive to pressure were the incisors, canines, and premolars, fol- lowed by the molars, which were the least sensitive.

Siebert55 upheld the view that the movement of the canines during canine guidance was well within its physiologic lim- its and that canine-protected occlusion was “the only one which could prevent disclusion or even traumatogenic occlusion. “55 Goldstein56 used periodontal disease index scores to substantiate these findings and showed that the canines and molars in canine guidance had a lower mean periodontal index than their counterparts in group func- tion. D’Amico50 further expounded that if the canines were not allowed to have a horizontal overlap of approximately 1 mm to establish a slight freedom of movement during centric occlusion, the effectiveness of the proprioceptive impulses would be destroyed. If this occurred, it would cause “havoc to the periodontium and the TMJ articulation.“50 Di’Amico’s findings were not substantiated by Scaife and Holt,s4 who discovered that out of 1200 pa- tients, 91.5% exhibited canine contact in centric occlusion.

The research conducted by Shaw,45 by Stuart and Stallard,g and by D’Amico4s was incorporated into the present gnathologic concept. 57 Proponents of this concept believed that each tooth had a specialized function. The incisors were used for biting, the posterior teeth were used for grinding and crushing, and the canines were used for grasping and tearing. In order for the stomatognathic sys- tem to function, teeth must work independently of each other. The canines, due to their crown-root ratio, strategic location away from the fulcrum, and stress-breaking capa- bilities, were the most likely candidates for this function. Hence the term “canine disclusion” was formulated.

SUMMARY

The historical development and philosophies of both anterior occlusal schemes have been discussed. To suggest that one occlusal scheme is superior to the other is not sci- entifically defensible. When the anterior guidance system must be reestablished or changed, current wisdom appears to number more proponents of canine guidance than of group function techniques.

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Reprint requests to: DR. LINDA J. THORNTON 2422 LEDGE HOLLOW SAN ANTONIO, TX 78232

Contributing authors Furmon M. Gardner, D.D.S., Colonel, U.S. Army, DC, 102nd Med DET (DS), USA Dentac-Vincenza, APO New York. Vincent A. Petrucci, D.D.S., Colonel, U.S. Army, DC, Fort Jackson, S.C.

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