|Year : 2012 | Volume
| Issue : 1 | Page : 13-18
Canine protected occlusion
Neeta Pasricha, Venus Sidana, Satpreet Bhasin, Monika Makkar
Department of Prosthodontics, National Dental College & Hospital, Dera Bassi, India
|Date of Web Publication||27-Sep-2012|
Department of Prosthodontics, National Dental College, Dera Bassi, Punjab
Source of Support: None, Conflict of Interest: None
Over the years several concepts of occlusion have been developed and have gained varying degrees of popularity. No single type of functional occlusion has been found to predominate in nature. To suggest that one occlusal scheme is superior to other is not scientifically defensible. However, current emphasis in fixed and restorative dentistry has been on the concept of canine-protected occlusion as canines act as the first line of control to keep mandible functioning more vertically. Canine-protected occlusion reduces the chances of temporomandibular dysfunction, since it decreases lateral tooth contact and the possibility of interfering contacts. This article reviews canine-protected occlusion, its biomechanics, similarities and differences with group function, and components of anterior guidance.
Keywords: Occlusion, canine protected occlusion, group function
|How to cite this article:|
Pasricha N, Sidana V, Bhasin S, Makkar M. Canine protected occlusion. Indian J Oral Sci 2012;3:13-8
| Introduction|| |
Dentists at one time or other have been exposed to the gnathological concept of occlusion. The study of occlusion involves not only the static relationship of teeth but also their functional interrelationships and all components of the masticatory system. Every restoration, whether a simple amalgam filling or complex crown and bridgework, that involves the occlusal surface will affect the occlusion.  Therefore restorations should be planned so that they do not cause effects that exceed the adaptive tolerance. Based primarily on laterotrusive movements from centric occlusion several functional occlusal types are recognized or advocated -- balanced occlusion, group function, canine-protected occlusion, mixed canine-protected occlusion and group function, flat plane, and multivareied occlusion. The evidence in favor of one occlusal scheme over other is scarce. Pragmatically, however, it is worth considering that canine-protected occlusion is far less likely to be associated with occlusal interference on the nonworking side due to the steep inclined palatal surface of canine.
The basic premise of canine-protected function is that on laterotrusive movements of mandible only the canine contacts and therefore protects remaining dentition from adverse occlusal torsional forces to and from centric relation and centric occlusion  or as defined in GPT-8 the canine-protected occlusion is a form of mutually protected occlusion in which vertical and horizontal overlap of canines disengages posterior teeth in excursive movement of mandible. This concept of occlusion is also known as canine guidance, canine disclusion or canine rise from the gnathology school of occlusion. The theory of canine-protected occlusion is attributed to Nagao, Shaw, and D'Amico and is based on the fact that canines are the most appropriate teeth to guide mandibular excursion. There are a number of reasons. 
The canines have a good crown root ratio capable of tolerating high occlusal forces.
Canines provide high proprioception.
The shape of the palatal surface of canine is concave and is suitable for guiding lateral movements.
Posterior teeth are better suited to accept vertical versus lateral forces. Lateral forces placed on posterior teeth can result in a fracture or excessive wear. Lateral forces should be directed toward the anterior teeth especially canines due to the root length and position of these teeth being at a distance from the temporomandibular joint. Canine-protected occlusion reduces the chances of temporomandibular dysfunction, since it reduces the lateral tooth contact and possibility of interfering contacts. Consequently the chance of muscular dysfunction is reduced.
| Review of Literature|| |
Over a century ago Bonwill and Gysi recommended balanced occlusion for denture construction. In 1930, McLean contended that this concept could also be applied to the natural dentitions. However Macmillan took a different view at the same time and suggested unilateral balanced occlusion for both natural and prosthetically restored dentition. Destructive forces associated with nonworking side contacts were first observed by Schuyler who concluded that they were traumatic to the natural dentition. Further work by other investigators resulted in balanced occlusion being replaced with unilateral balanced occlusion also known as group function. Canine-protected occlusion has its origin in the work of D'Amico, Stuart, Stallard, and Lucia.  The requisite for canine-protected occlusion is that only canines contact on the working side during eccentric lateral mandibular movement, whereas on the nonworking side, there are no balancing contacts. After this work these two working side schemes took precedence.
Various epidemiological studies have been attempted to discover which type of occlusal scheme is found in untreated natural dentition. Beyron's  work was the earliest and showed quite conclusively that Australian aborigines had predominance of group function. Weinberg  in 1964 found that 81% of sample had group function and 5% had canine-protected occlusion. Scaife and Holt  examined 1200 individuals from North America less than 25 years of age and found that majority had unilateral or bilateral canine-protected occlusion. They also correlated that canine-protected occlusion was associated with Angle class II occlusion and then with class I and least with class III. Panek et al, in a study on 834 subjects found that the frequency of canine-protected occlusion decreased with age. It was concluded from the study that canine-protected occlusion seems to be most suitable pattern for orthodontic and prosthetic rehabilitation planned in younger patients.
D'Amico  stated that canine protection favors the vertical chewing pattern and prevents the wear of teeth. Jemt, Lundquist, and Hedegard  found that lateral displacement and total displacement of mandible was greater with group function than with canine-protected occlusion.
Lee  pointed out that from the biological point of view, based on proprioceptive cuspid guidance, group function is not ideal. Group function results in too flat and broad occlusal surfaces to function efficiently.
Williamson and Lundquist  in 1983 studied that posterior disclusion reduced the activity of temporal and masseter muscles. Ash and Ramjford  believed that a steep canine rise on Michigan splint can reduce the EMG activity of masseter and temporalis. Murray  described a technique for the provision of canine riser restoration, which deliberately altered the cuspal inclines in canine teeth to provide canine guided occlusion. According to him these restorations may help to control excessive loading, limit the tooth wear, and assist in management of TMJ disorders. Jiang, Su, and Cheng  evaluated the clinical treatment effect on bruxism using group functional splint and canine protect occlusal splint. The successful rate of treatment of bruxism was 83.33% in canine-protected occlusion and 79.1% with functional splint. According to Henke and Friedrich  the canine-protected occlusion decreased lateral stresses on posterior teeth and is preferred over group function for restoring and altering the anterior guidance. Goldstein  found the relationship of canine-protected occlusion to periodontal index. The teeth of mouth having canine-protected occlusion had significantly lower mean periodontal indices.
Biomechanics in canine-protected occlusion
In canine-protected occlusion maximum intercuspation coincides with optimal condylar position of mandible. Here functional loading is directed axially by limiting the contact of supporting cusps of posterior teeth to their opposing fossa at or near their intercuspal position. The anterior teeth either contact lightly or are very slightly out of contact (by approximately 25 μm), relieving them of laterally directed forces. During lateral excursion all the teeth lose contact except for the upper and lower canine on the working side. Mastication mainly occurs with pounding motion and chewing strokes are mainly sagittal from frontal aspect. Functional efficiency is increased by well-formed marginal ridges, triangular ridges, grooves and fossa so that occluding cusps can readily penetrate fibrous food. In other words the canines are situated and inclined in such a way that, while they allow full contact of all teeth in centric occlusion, they force the jaw to open as the upper and lower canine slide over each other. This disengages all the cusp of teeth as person begins to grind side to side, this phenomenon is called as cuspid rise in deference to fact that most articulators are hinged in such a way that upper teeth move instead of lower. This artificial way of mounting the models make upper canine rise instead of lower drop, which is what happens in real mouth. According to this concept of occlusion, anterior teeth bear the load when posterior teeth are disoccluded in any excursive movement of mandible. The reason for redirecting the occlusal forces are that anterior teeth are located far away from TMJ and thereby have better leverage to offset the closing muscles of mastication.  Keen proprioception and strategic location protect anterior teeth from overstress when occlusion is to function properly.
A better understanding of the role of the central nervous system and learning process as well as muscle physiology and proprioception shows that occlusion is more than mechanics. It has been postulated that there is a biofeedback mechanism which comes into action when canines contact during lateral excursion. D'Amico stated that the canines protect the periodontium and supporting structures from lateral excursion. Upon functional contact by canines, the periodontal proprioceptive impulses are transmitted to the mesencephalic root of trigeminal nerve, which alter the motor impulses to the musculature.  The resultant involuntary reaction relaxes the muscles and reduces the stresses to the periodontal ligament. Kawamura  demonstrated that those teeth most sensitive to pressure were incisors, canines, premolars, followed by molar. Kruger and Michel  discovered that canines had higher concentration of neurons than any other teeth.
In order for the stomatognathic system to function, teeth must work independently of each other. The canines, due to their size, structure, root length, strategic location from fulcrum, stress-breaking capabilities were the most likely candidates for this function; they prevent the lateral enmeshment of working side posterior teeth. It has been observed that when this canine protection is taken away, muscles stay active leading to clenching, grinding of teeth, abfraction, and gum recession. Canine guidance is considered the most physiologic of all occlusal relationships because it protects the teeth from wear and tends to prevent bruxing in most persons who are likely to brux occasionally. In the absence of chronic bruxing habit these relationships persist throughout life.
Similarities and differences between group function and canine-protected occlusion
McAdam  summarized some similarities and differences between canine-protected occlusion and group function.
Both must provide multiple posterior contact with intercuspal position (centric occlusion) located either coincident with centric relation or within 1 mm of protrusion in a straight sagittal direction.
There must be the absence of posterior contact during mediotrusion.
There should be no posterior contact during anterior incision whenever anatomic arrangement permits.
There should be anterior group functional guidance during the protrusive movement accompanied by a posterior disclusion where the anatomic arrangement permits.
The manner in which teeth function in laterotrusion.
In canine guidance the horizontal forces are minimized by limiting the contact of the supporting cusps to their opposing fossae at or near their intercuspal position. All other lateral contacts are prevented by steeper inclines of the canines; this results in chewing stroke being more sagittal in frontal view.
In group function the first contact is not between supporting cusp and opposing fossa but instead at a lateral location followed by slide to centric occlusion, this will result in some horizontal forces but these can be minimized by
- Striking simultaneously as many as working contacts as possible
- Reducing the angle of incline
- Reducing the friction by removing irregularities and roughness
- Slightly round off the facio-occlusal line angle.
| Components of Anterior Guidance|| |
The anterior dentition is of paramount importance when reconstructing the stomatognathic system. The primary and permanent anterior teeth erupt into contact first, and establish the anterior stop for the mandible. This allows the posterior teeth to erupt into position at the proper vertical dimension and centric relation. The canines are often considered the primary protectors of the gnathological system because they direct a vertical (rather than a horizontal) masticatory pattern. Without this protection, damaging horizontal forces can severely wear the posterior occlusion
Harmonizing the lingual contours of the maxillary anterior teeth with the facial contours of the mandibular incisors and the neuromuscular system is the single most important factor in the health and stability of the occlusal system.
According to Wynne  in a proper canine-guided occlusion, there are two centric stops on each of the central incisors and one stop on each lateral incisor and canine. During straight protrusive occlusion, two paths are evident on each central incisor on the lingual marginal ridge region. Occasionally there may be anterior protrusive marks on the canines. The paths on the central incisors extend until the incisal edges of the two maxillary central incisors and four incisal edges of mandibular incisors are engaged. At this point, these teeth should be able to slide smoothly [Figure 1]. After this point, the canines glide smoothly over the polished and rounded lingual aspect of each tooth until the support is transferred to the incisal edges of the maxillary incisors. This transition should be a smooth, gliding path.
|Figure 1: Incisal view of the maxillary and mandibular teeth showing proper occlusal pattern of function in a canine-guided occlusion|
Click here to view
In the centric relation position, the relationship between the maxillary incisors and mandibular incisors becomes clear [Figure 2]. The facio-incisal leading edge of the mandibular incisors engages the lingual aspect of the maxillary incisors and canines. To maintain this relationship in a reconstruction, it is necessary to hollow out approximately 0.5 mm of space on the gingival aspect of the centric holding marks. This provides the freedom to close the mandible either into centric relation or slightly anterior without varying the vertical dimension of the anterior teeth.
The end-to-end position is indeed a rest position. Here, the pitch of the maxillary and mandibular teeth is complementary, allowing the maxillary central incisors and four mandibular incisors to function in the same plane [Figure 3].
To create a smooth path in straight protrusive and when moving into the crossover position, the lingual incisal line angle of the mandibular incisors should be polished or rounded in order to create a smooth transition from the incisal edge onto the lingual aspect of the teeth [Figure 4]. In addition, there should be no rough edges on the lingual incisal aspect of either mandibular canine; these areas should also be rounded. These considerations will help create a smooth, friction-free transition in all functional directions.
Establishing ideal distribution of stress on the anterior teeth in lateral excursion (anterior guidance) can be accomplished by either group function [Figure 5] or canine guidance [Figure 6]. If group function exists, there is no need to create canine guidance. In this case, changing to canine guidance would increase the force on the canines, which may destabilize the system. If canine guidance exists and there is no tooth mobility or alveolar bone loss, then rebuilding canine guidance is appropriate.
The next consideration in development of the occlusion is lateral movement into what is called the crossover position, which is defined as the portion of the occlusal path after the canines have contributed their support and the incisors then assume the support [Figure 7],[Figure 8],[Figure 9],[Figure 10] and [Figure 11]. The functional path is a smooth, lateral movement until the tips of the canines are in contact.
| Conclusion|| |
Both canine-protected and group function articulation are commonly found in nature. The question of canine guidance or group function depends upon individual case, preexisting relationship, crown root ratio, degree of mobility and fremitus of concerned teeth. In patients with anterior open bite, extreme Angle class II division 1 or class III malocclusion and crossbite, mandible cannot be guided by anterior teeth and canine guidance cannot be achieved. In order for canine-protected occlusion to function, the anterior teeth must be healthy. The patient's existing occlusal scheme should not be altered unless such alterations are required to correct a nonphysiological dentition. If the restoration must reestablish lateral guidance canine-protected occlusion is preferred when remaining canines are present and not periodontally compromised. Canine guidance reduces horizontal forces on posterior teeth and promotes a more vertical chewing cycle. 
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11]