|Year : 2012 | Volume
| Issue : 3 | Page : 124-128
Group function occlusion
Venus Sidana, Neeta Pasricha, Monika Makkar, Satpreet Bhasin
Department of Prosthodontics, National Dental College, Dera Bassi, Punjab, India
|Date of Web Publication||29-Apr-2013|
Department of Prosthodontics, National Dental College, Dera Bassi, Punjab
Source of Support: None, Conflict of Interest: None
The study of occlusion involves not only the static relationship of teeth but also their functional interrelationship and all components of the masticatory system. Anterior guidance is essential to a harmonious functional relationship in natural dentition and is critical to functional occlusion. Anterior guidance can be categorized as canine guided and group function. Both techniques are divergent in philosophy and technique. The purpose of this article is to review group function occlusion. The group function occlusion on working side distributes the occlusal load and prevents teeth on non working side from being subjected to the destructive, obliquely directed forces.
Keywords: Group function, occlusion, unilateral balanced occlusion
|How to cite this article:|
Sidana V, Pasricha N, Makkar M, Bhasin S. Group function occlusion. Indian J Oral Sci 2012;3:124-8
| Introduction|| |
Occlusion has been, and is still to some extent, a controversial issue in conventional removable and fixed prosthodontics. There is increasing interest in biological and behavioral aspects of occlusion in contrast to earlier emphasis on technical and biomechanical principles. The collective arrangement of the teeth in function is quite important and has been subjected to great deal of analysis and discussion over years. As the mandible moves laterally, the lower posterior teeth leave their centric contact with upper teeth and travel sideways down a path dictated by the condyles at the back and by the lateral anterior guidance in front. In the diversified literature on occlusion and its role for functional pattern of masticatory system two concepts stands out (1) canine guidance as described by D'Amico is said to favor the vertical chewing pattern and to prevent wear of teeth, as in lateral occlusion where the canines guide the mandibular movement directly or indirectly through periodontal receptors (2) group function as described by Beyron implies contact and stress on several teeth in lateral occlusion and indicates abrasion as positive and inevitable adjustment.The reason for bringing any teeth into lateral function is to distribute stress and wear over more teeth. Group function occlusion, which is also commonly known as unilateral balanced occlusion, is a widely accepted and used method of tooth arrangement in restorative dental procedures today.  Glossary of Prosthodontic Terms defines Group function as multiple contact relations between maxillary and mandibular teeth in lateral movements on the working side whereby simultaneous contact of several teeth acts as a group to distribute occlusal forces. The group function of the teeth on working side distributes the occlusal load. The obvious advantage is maintenance of the occlusion. The group function philosophy appears to be one of the physiologic wear. Several authors have suggested that occlusal wear is a natural, beneficial and inevitable in a well-developed dentition.
There has been great deal of emphasis on canine guidance or disclusion since it was first postulated by D'Amico. According to some authorities the canines should receive all the eccentric tooth contact in lateral movements of the mandible however canine guidance is not the only factor of importance in medial guidance of mandible. Young children in most formative years of their lives (ages 6-12 years) have no canine guidance. It seems that if canines were the only teeth of importance in medial guidance of jaws, nature would have placed these teeth early in mouth. If teeth are the primary guiding factor for occluding. It is obvious at the age of 6 it is cusps of molars that guide the mandible laterally followed by premolars. 
The clinician should understand the possible combination of both occlusal schemes as each has its advantages, disadvantages, indications and contraindications. In the mouth the unworn cuspids will act as a first line for vertical control. If the cuspids eventually wear down the patient will go into working-side group function which has been built into posterior crowns. The working side group function acts as second line of control to prevent nonworking contact.  Restoration must be planned and designed to fit harmoniously with the complexities of the neuromuscular control system, temporomandibular joint and supporting structures without introducing occlusal interferences. A stable posterior occlusion with smooth uninterrupted protrusive and lateral movement of mandible is necessary. 
The purpose of this article is to review group function occlusion. The data was collected from journals indexed in medline using pubmed search.
| Review of Literature|| |
The literature credits Schulyer with enlightening clinicians as to destructive forces associated with balanced contacts. He observed that even though these contacts were essential for stability of complete dentures, they were traumatic to natural dentition causing TMJ dysfunction, periodontal involvement or excessive wear. As a result of research conducted by Schulyer and other investigators balanced occlusion was replaced with functional relationship unilateral balanced occlusion or group function occlusion.  Schulyer,  and other advocates of group function viewed occlusal wear as a compensatory adaptive change that distributed stress to create a normal functional relationship. Moses.  deduced it was nature's plan for the cusps to wear in a particular and beneficial manner which is related to the vigorous function that primitive man was believed to have exhibited. Beyron.  conducted a serial investigation of the progressive occlusal changes in the natural dentition. He demonstrated that group function was conducive to occlusal wear, and was capable of allowing an even distribution of stress. Scaife and Holt,  demonstrated that the percentage of patients with wear facets increased in direct proportion to degree of group function, thus actually providing evidence to reinforce the theory of group function.
Fereidoun Parnia and Elnaz Moslehi,  studied pattern of occlusal contacts in eccentric mandibular position in dental students. They found that most of the working contact pattern was group function (60%). Ingervell.  recorded tooth contact pattern in laterotrusion, protrusion and retrusion of mandible in young men with varying type of occlusion. He found that on laterotrusion most subjects had group function on the functional side. Rinchuse, Kandasamy and Sciote.  stated that single type of occlusion has not been predominant in nature. according to them canine protected occlusion is one of several possible optimal functional occlusion. According to them group function occlusion and balanced occlusion (with no interference) appears to be acceptable functional occlusal scheme depending on patient characteristics. O' Ieary, Shanley and Drake,  found that teeth in group function occlusion had less mobility than teeth in cuspid protection occlusion.
Panek,  et al., concluded from their study on dynamic occlusion in natural dentition that bilateral canine protected occlusion seems to be most typical occlusion for younger patients while group function occlusion was more common for older patients. According to them canine protected occlusion seems to be the most suitable pattern for orthodontic and prosthetic rehabilitation planned in younger adults while group function occlusion may be good pattern for prosthetic rehabilitation in older patients. Jemt T and Lundiquist S,  stated that chewing pattern may be influenced by the type of occlusion. They found angle of departure was steeper than angle of approach and these angles were slightly greater with group function. Mandibular velocity was higher for group function than canine guidance. Duration of chewing was stable for both of them. Valenzula,  et al., conducted a study to determine the effect of canine protection and group function occlusion on suprahyoid and infrahyoid EMG activity. They found that EMG activity was significantly not different for both the schemes. Su, Jiang and Cheng,  evaluated the clinical treatment effect of bruxism by using group function and canine protected occlusion splint. They found that both splints have similar curative effect for bruxism.
Canine protected occlusion versus group function occlusion
The job of discluding the non functioning side is always the responsibility of the working side. How the working side discludes the non functioning side is an important decision that must be made for each patient. We must decide which teeth are capable of carrying how much load and assign the load accordingly.
Group function of working side is indicated whenever the arch relationship does not allow the anterior guidance to do its job of discluding the nonfunctioning side. The anterior guidance cannot do its job in conditions like Class 1 occlusion with extreme over jet, Class 3 occlusion with all lower anterior teeth outside of upper, some end to end bites and anterior open bite.
While assigning group function the rule which applies is that the contacting inclines must be perfectly harmonized to border movements of the condyles and the anterior guidance. Partial group function allows some of posterior teeth to share load in lateral excursion, whereas others contact only in centric relation.
For group function to be effective in reducing the lateral stress, the cusp inclines must harmonize with the lateral border movements of mandible. Posterior cusp inclines that are not contoured to match mandibular movements are disoccluded or they interfere if incline is too steep than the lateral movement. If rule of stress distribution is understood, it is practical to distribute stress over some or all the posterior teeth. 
Canine disclusion may provide a cuspid protected occlusion in parafunctional lateral movements that may be beneficial if posterior teeth have significant bone loss, considerable occlusal wear or number of cracks and if patient clenches or grinds the teeth. Canine disclusion is preferred to group function the conditions as follows [Flowchart 1[Additional file 1]]:
Whether any tooth should share the lateral stress should be decided by its resistance to lateral stresses. 
- If both canines on one side have little or no bone loss the first condition for the use of canine guidance is met. The radiographs should show normal sized canine roots that have little evidence of bone loss. If canine occlude in lateral movements toward the side in which these teeth are present canine rise is logical approach. If sound maxillary and mandibular canines do not occlude in lateral movement, canine disclusion cannot be achieved. If posterior teeth have little or no bone loss, group function is the objective. If posterior teeth have moderate to severe bone loss and canines are essentially sound, canines may be restored to create canine disclusion or orthodontic positioning of canines can be used to permit it.
- If one or both canines on one side have moderate to severe bone loss and guided tissue regeneration is not feasible, canine disclusion should be discarded as an objective. If adjacent teeth have moderate to severe bone loss as do canines, splinting to distribute the loading more evenly is necessary. If mobility is minimal selective grinding to smooth out group function will suffice. 
The occlusal concepts (balanced, group function, canine protected occlusion) have been successfully adopted for implant supported prosthesis. Occlusal consideration while restoring various clinical situation with implant supported prosthesis are as shown in [Table 1].
Occlusal relationship of the teeth in group function
There is general agreement that balancing side contact is not desirable in lateral movements.
A Balancing side interference is a contact on balancing side that causes disclusion of the working side or that interferes with smooth gliding movements.
A working side interference is a contact on the working side that causes working side disclusion or displacement of mobile tooth on the working side.
When the mandibular teeth make their initial contact with the maxillary teeth in right or left lateral occlusal relation they bear a right or left lateral relation to centric occlusion. The canines, premolars and molars of one side of the mandible make their occlusal contact facial to their facial cusp ridges at some portion of their occlusal thirds. Those points on the mandibular teeth make contact with maxillary teeth at points just lingual to their facial cusp ridges. The central and lateral incisors of the working side are not usually in contact at the same time if they are the labio-incisal portion of the mandibular teeth of that side are in contact with linguo-incisal portions of maxillary teeth. 
If we intend to provide group function on working side we should be aware all teeth do not stay in excursive contact for same length of stroke. As the mandible starts its move to the working side, all of the posterior teeth may contact in harmony with the anterior guidance and condyle, as mandible moves further to the side, the first teeth to disengage from contact are the most posterior molar. The disengagement is progressive, starting with back molar, which has shortest contact strokes, forward to canines, which has the longest contact stroke.
The molar contact is maintained for only a fraction of inclined surface, whereas the canine contact is often maintained all the way to the incisal tip. The reason for giving canine such a long contact ride and progressively shorter contact as we go distally is based on factors of geometry and stress. As the working condyle rotates the path travelled around the centre of rotation lengthens as the distance from the condyle increases.
While the canine is travelling the full length of its incline from centric to its incisal edge, the second molar is traveling about half that far. When the canine reaches its incisal edge, the molar still has some incline left on which it could ride out. However, if the molar continued its contact after the canine was disengaged; the stress would no longer be shared by the protective anterior guidance. It would instead be loaded entirely on to the outer incline of the molar and would create lateral torque in the extremely stressful position near the condylar fulcrum.
Because of these reasons the lingual incline of the upper buccal cusps should be contoured to prevent posterior contact from occurring after the lower canine reach the incisal edge of the upper canine. 
| Summary|| |
It is usually possible to achieve the interference free occlusal relationship with either canine guidance or group function. It has been found that muscle activity is reduced with canine guidance. Further canines are considered to be stronger than the other teeth so it becomes customary to speak of cuspid protection occlusion however this situation is not customary observed except in younger patient. The arbitrary selection of canine protected occlusion for all patients ignores the value and importance of every person's unique stomatognathic and neuromuscular functional status. Perhaps patients with different craniofacial structures or chewing patterns might adapt better to one type of occlusion. Group function is most often encountered in elderly. With this type of occlusion it is possible to achieve harmonious balance of all involved structures including muscles, temporomandibular joint, teeth and their occlusal anatomy. Furthermore a patient with parafunctional bruxing habit might welcome the lateral excursive freedom of group function. Consideration of a patient's chewing pattern, craniofacial morphology, static occlusion type, current oral health status, parafunctional habits might provide the important and relevant information about the suitable functional occlusion type for each patient.
| References|| |
|1.||Parnia F, Moslehi E, Sadar K, Motiagheny N. Pattern of occlusal contacts in eccentric mandibular position in dental students. J Dent Res Dent Clin Dent Prospect 2008;2:85-9. |
|2.||Claude Rufenachi R. Fundamentals of esthetics. Chapter physiology of occlusion. Illinois: Quintessence publishing Co, 1990. p. 155. |
|3.||Robert lee. Anterior guidance. Advances in occlusion. Boston: John Wright P.S.G; 1982. p 64-5. |
|4.||McCullock AJ. Making occlusion work: 2. Practical considerations. Dent Update 2003;30:218-9. |
|5.||Thornton LJ. Anterior guidance: Group function/canine guidance. A literature review. J Prosthet Dent 1990;64:479-82. |
|6.||Schyuler CH. The function and importance of incisal guidance in oral rehabilitation. J Prosthet Dent 2001;86:219-32. |
|7.||Moses CH. The significance of stress in the practice of preventive and restorative dentistry. J Dent Med 1952;7:101-3. |
|8.||Beyron HL. Occlusal changes in adult dentition. J Am Dent Assoc 1954;48:674-86. |
|9.||Scaife RR Jr, Holt JE. Natural occurrence of cuspid guidance. J Prosthet Dent 1969;22:225-9. |
|10.||Ingervell B. Tooth contacts of functional and non functional side in children and young adults. Arch Oral Biol 1972;17:191-200. |
|11.||Rinchuse DJ, Kandasamy S, Sciote J. A contemporary and evidence-based view of canine protected occlusion. Am J Orthod Dentofacial Orthop 2007;132:90-102. |
|12.||O Leary TJ, Shanley DB, Drake RB. Tooth mobility in cuspid protected and group function occlusions. J Prosthet Dent 1972;27:21-5. |
|13.||Panek H, Matthews-Brzozowska T, Nowakowska D, Panek B, Bielicki G, Makacewicz S, et al. Dynamic Occlusion in natural permanent dentition. Quintessence Int 2008;39:337-42. |
|14.||Jemt T, Lundquist S, Hedegard B. Group function or canine protection. J Prosthet Dent 1982;48:719-24. |
|15.||Valenzula S, Baeza M, Miralles R, Cavada G, Zúñiga C, Santander H. Laterotrusive occlusal schemes and their effect on supra-hyoid and infrahyoid electromyographic activity. Angle Orthod 2006;76:585-90. |
|16.||Su SW, Jiang YH, Cheng Z. Evaluation of the treatment effect of bruxism using two occlusal splint. Shanghai Kou Qiang Yi Xue 2010;19:253-4. |
|17.||Dawson PE. Functional occlusion from TMJ to smile design. United States: Mosby publication; 2007. P 222-8. |
|18.||Hall WB. Critcal decision in periodontology. 4th ed. London: B C Decker Inc; 2003. p. 1289. |
|19.||Shantanu J, Mohit K, Mukund K. Occlusion and Occlusal consideration in Implantology. IJDA 2010;2:125-30. |
|20.||Wheeler RC. Dental Anatomy, Physiology, Occlusion. 7 th ed. Philadelphia: W.B Saunders publication; 1974. p 450 |