Principles of occlusion in implant dentistry
Mahesh Verma, Aditi Nanda, Abhinav Sood
Department of Prosthodontics, Maulana Azad Institute of Dental Sciences, Delhi, India
|Date of Web Publication||31-Dec-2015|
Maulana Azad Institute of Dental Sciences, Bhadur Shah Zafar Road, New Delhi - 110 002
Source of Support: None, Conflict of Interest: None
Dental implants require different biomechanical considerations from natural teeth. Also, with one of the criteria for long-term implant success being “occlusion,” it becomes imperative for the clinician to be well versed with the different concepts when rehabilitating with an implant prosthesis. All endeavors must be made to reduce the overload and noxious forces on implants during mandibular movements. The occlusal rehabilitation schemes for implant-supported prostheses are derivatives of the occlusal scheme for natural dentition. The implant-protected occlusion (IPO) scheme has been designed to ensure the longevity of both prosthesis and implant. The article reviews the concepts of IPO and their applicability in different clinical scenarios.
Keywords: Biomechanical, guidelines, implant, occlusal scheme, occlusion
|How to cite this article:|
Verma M, Nanda A, Sood A. Principles of occlusion in implant dentistry. J Int Clin Dent Res Organ 2015;7, Suppl S1:27-33
|How to cite this URL:|
Verma M, Nanda A, Sood A. Principles of occlusion in implant dentistry. J Int Clin Dent Res Organ [serial online] 2015 [cited 2018 Mar 13];7, Suppl S1:27-33. Available from: http://www.jicdro.org/text.asp?2015/7/3/27/172924
Determining an occlusal scheme for the restoration of implants requires careful consideration. This stems from the fact that after osseointegration, mechanical stresses beyond the physical limits of hard tissues have been suggested as the primary cause of initial and long-term bone loss around implants.,,, Occlusal overload is often regarded as one of the main causes of peri-implant bone loss and implant prosthesis failure because it can cause crestal bone loss, thus increasing the anaerobic sulcus depth and peri-implant disease states., It can be rightly said that occlusion is a determining factor for implant success in the long run.,
The choice of occlusal scheme for implant-supported prosthesis is broad and often controversial. Almost all concepts are based on those developed with natural dentition and are transposed to implant support systems with a few modifications. The probable reason for this practise is the similarity (during mandibular movement) in the velocity, the pattern of movement and the operating muscles that are used by patients with implants and those with natural dentitions. Moreover, it has been established that the clinical success and longevity of implants can be achieved by biomechanically controlled occlusion. This implies that the occlusion provided must follow sound mechanical principles, direct forces predominantly along the long axis of the implant body, and minimize off-centered forces. The same should be aimed to impart and enhance biological stability.
However, there are a few innate differences between natural teeth and implants, which need to be considered when restoring implants. Natural teeth are associated with high occlusal awareness (proprioception) of about 20 µm. Occlusal proprioception is low in implants. For instance, between a tooth and an implant the proprioception is around 48 µm; between two implants it is around 64 µm; and between a tooth and an implant-supported overdenture it is around 108 µm.,,, The lack of proprioception and the absence of periodontal shock absorption are often associated with increased impact force with an implant-supported prosthesis than with a tooth-supported prosthesis.,,, Besides the proprioception, the presence of periodontal ligament as a shock absorber in a natural tooth brings about an apical intrusion by about 28 µm and lateral movement by around 50-108 µm. In the case of a similar load acting on an implant, no initial movement is seen and the delayed apical movement observed is around 10-50 µm. The same can be attributed to the viscoelastic properties of bone. Also, such a load acting on an implant is primarily concentrated on the crest of the implant.,
In case of occlusal trauma, mobility can develop in a tooth as well as in an implant. However, upon removal of the trauma, mobility can be reduced or controlled with a natural tooth, while no such response can be noted in an implant. In general the diameter of natural teeth is larger than the diameter of implants. Also, the cross-section of implants is rounded and the diameter is selected primarily according to bone available, not according to the load that it is anticipated to be subjected to. The cross-section of the root of a natural tooth, on the other hand, varies according to the force it has to withstand. For example, mandibular anterior teeth have wider diameters faciolingually, mainly to resist forces during protrusion. Likewise, the roots of canines are shaped to withstand lateral loads and those of molars to withstand axial loads.,,,
The issue of such differences between natural teeth and implants lead to the establishment of implant-protected occlusion (IPO), the credit for which goes to Dr. Carl Misch and Dr. MW Bidez. It is also called medially positioned lingulalized occlusion, and it stems from the change in relation of the edentulous maxillary ridge to the mandibular ridge due to resorption of edentulous ridges in a medial direction. As a result, a few unique concepts are associated with implant-supported prosthesis and these constitute the guidelines for IPO.,,
There are 14 considerations for following the IPO scheme that should be judiciously implemented before restoration. They are as follows:
Elimination of premature occlusal contacts
Premature contacts are defined as occlusal contacts that divert the mandible from a normal path of closure; interfere with normal smooth gliding mandibular movement; and/or deflect the position of the condyle, teeth, or prosthesis. It has been speculated that occlusal load from excessive lateral loads arising from premature contact may cause bone loss and implant failure. Prior to the evaluation of occlusion on implant reconstruction, the occlusion should be evaluated and all occlusal prematurities should be eliminated during maximum intercuspation and centric relation.,,,
While restoring an implant, a thin, articulating paper is used (<25 µm) for the initial implant occlusion adjustment in centric occlusion under light tapping forces. The implant prosthesis should barely make contact, and the surrounding teeth in the arch should exhibit greater initial contact. The implant crown should exhibit light axial contact. This is because a natural tooth exhibits greater vertical movement than an implant. Once equilibration under light occlusal force is completed, the occlusion is refined under heavy occlusal contact. A tooth may not return to its original position for several hours after the application of heavy occlusal force. As a consequence, light occlusal forces on the adjacent natural teeth are equilibrated first. The occlusal contact should remain axial over the implant body and may be of similar intensity on the implant crown and adjacent teeth when under greater bite force. This implies that all elements react similarly to heavy occlusal loads. The harmonization under light occlusal loads is followed by adjustment under heavy occlusal load. The heavy occlusal load positions the natural teeth closer to the depressed position of the implant, thereby permitting equal sharing of the load between the implant and the natural teeth. However, an important part of the philosophy behind IPO is the regular evaluation of occlusal contacts at regularly scheduled hygiene appointments so that minor variations occurring during long-term functioning help in preventing porcelain fracture and other stress-related complications.,,
Provision of adequate surface area to sustain load transmitted to the prosthesis
Increased load can be compensated for by increasing the implant width; reducing crown height; ridge augmentation if necessary; increasing the number of implants; or splinting the prosthesis.,
Controlling the occlusal table width
The width of the occlusal table is directly related to the width of the implant body., The wider the occlusal table, the greater the force developed to penetrate a bolus of food. However, a restoration mimicking the occlusal anatomy of natural teeth often results in offset load (increased stress), increased risk of porcelain fracture, and difficulties in home care (due to horizontal buccolingual offset/cantilever).,, As a result, in the nonaesthetic regions the width of the occlusal table must be reduced in comparison to a natural tooth.
Mutually protected articulation
This implies that during excursion the posterior teeth are protected by the anterior guidance, whereas during centric occlusion the anterior teeth have only light contact and are protected by the posterior teeth. It must be kept in mind that the anterior guidance of the implant prosthesis with anterior implants should be as shallow as practicable. The steeper the anterior guidance, the greater are the anticipated forces on anterior implants. In case of a single tooth implant replacing a canine, no occlusal contact is recommended on the implant crown during excursion to the opposite side. The rationale of mutually protected occlusion is that the forces are distributed to segments of the jaws with an overall decrease in force magnitudes. It must also be kept in mind that if anterior implants must disocclude the posterior teeth, two or more implants splinted together should help dissipate lateral forces whenever possible.
Implant body orientation and influence of load direction
Whether the occlusal load is applied to an angled implant body or an angled load is applied to an implant body perpendicular to occlusal plane, the biomechanical risk increases. This is attributed to the anisotropic nature of the bone, resulting in separation of the load to compressive, shear, and tensile stresses. Anisotropy refers to the character of bone whereby the mechanical properties depend on the direction in which the bone is loaded. The greater the angle of the load, the greater is the shear component of the load. It must be borne in mind that cortical bone is the strongest and most able to withstand compressive forces. Its ability to withstand tensile and shear forces is 30% and 65% less, respectively, than its ability to withstand compressive forces.,,
Additionally, a force at a 30-degree angle decreases the bone strength limit by 10% under compression and by 25% under tension. The increase in the shear component of stresses is by almost three times, which predisposes the bone to increased crestal bone loss and impairs successful bone growth. During loading, the primary component of occlusal forces should be directed along the long axis of the implant body. The three conditions where one can anticipate angled loads are: Angled abutments, angled implant bodies, and premature occlusal contact. Angled abutments are used to improve the path of insertion of the prosthesis or to improve the final aesthetic results. The implant body should be placed perpendicular to the occlusal plane and along the primary occlusal contact. Premature occlusal contacts result in the localized lateral loading of opposing contacting crowns. Because the surface area of a premature contact is small, the magnitude of stress in bone increases. Also, the contact is most often on an inclined plane; therefore, it increases the horizontal component of load and increases the tensile crestal stress. In general, whenever lateral/angled loads cannot be eliminated, a reduction in force magnitude or additional surface area of the implant surface is indicated to reduce the risk of bone loss or of implant component fracture. Such measures include increasing the diameter of angled implants, selecting implant design with greater surface area, adding an additional implant next to the most angled implant, and splinting of implants.,,
Crown cusp angle
It is important to control this, as the angle of force to the implant body may be influenced by cusp inclination, which in turn will increase crestal bone stress. The occlusal contact over an implant crown should, therefore, ideally be on a flat surface perpendicular to the implant body. This positioning is accomplished by increasing the width of the central groove to 2-3 mm in posterior implant crowns, which are positioned over the center of the implant abutment. It may be necessary to recontour the opposing cusp to occlude in the central fossa over the implant body. If the implant crown mimics the natural cusp angle, the premature contact will occur on a cuspal incline and the resulting direction of load may be 30 degrees to the implant body.,,
Cantilevers and IPO
Cantilevers are class-1 levers, which increase the amount of stress on implants. Twice the load applied at the cantilever will act on the abutment farthest from the cantilever, and the load on the abutment closest to cantilever is the sum of the other two components. Cantilevers also add to noxious stresses (force on a cantilever is compressive, while force on a distal abutment is tensile).,, The force and the length of the cantilever are directly proportional to the force on the implant. For a system with 4-6 implants, the following cantilever lengths are recommended: Maxillary anteriors-10 mm; maxillary posteriors-15 mm; mandibular posteriors-20 mm. In general the goal should be to reduce the length and hence the force on the cantilever. In addition, a gradient type of occlusal contact force along the length of cantilever may be beneficial.,,,
Crown height and IPO
An increased crown height acts as a vertical cantilever, magnifying the stress at the implant-bone interface. It also leads to angled load with a greater lateral component of force. It is important to note that crown height is determined at the time of diagnosis and that all methods of either reducing the load or reducing the crown-implant ratio should be applied before restoration.
Occlusal contact position
The ideal occlusal contact is over the implant body. This contact leads to the axial loading of implants. A posterior implant is hence placed under the central fossa of the implant crown. A buccal cusp contact is an offset or cantilever load. A marginal ridge contact is also a cantilever load, as the marginal ridge may also be several millimeters away from the implant body. In fact, the marginal ridge contact may be more damaging than the buccal offset, as the mesio-distal dimension of the crown often exceeds the buccolingual dimension. Moreover, the moment of force on the marginal ridge may contribute to forces that increase abutment screw loosening. Thus, the ideal primary occlusal contact should reside within the diameter of the implant within the central fossa. The secondary occlusal contact should remain within 1 mm of the periphery of the implants to decrease the moment loads. The marginal ridge contact is not an offset load when located between implants splinted to one another, and is acceptable only under such circumstances. Moreover, adjacent crowns should preferably be splinted in order to decrease occlusal stresses to crestal bone and to reduce screw loosening.
Implant crown contour
Due to ridge resorption, the direction of the remaining ridge shifts lingually and the implant body is most often not under the buccal cusp tip position of natural teeth. In fact, it may be either under or near the central fossa or more lingual under the lingual cusp of a natural tooth, depending on the resulting position of the remaining ridge due to resorption. Hence, making the buccal contour the same as the original, natural tooth will lead to buccal offset load to the implant. All attempts should be made to provide a narrow occlusal table with reduced buccal contour, facilitating daily home care, improving axial loading, and reducing the risk of porcelain fracture. Crown contour in Division A bone has been described in the respective figures [Figure 1], [Figure 2], [Figure 3]. In Division B-Division D bone, the implant position is often lingual to the position of the natural tooth. Care has to be taken in case of mandibular posterior implants regarding the limitation imposed by the submandibular fossa. In case of excessive medial positioning of the implant, it may be necessary to use angulated abutment and a straight lingual profile. Maxillary posterior implants in division B-D bones may often require restoration in crossbite [Figure 4]. In case of Division C and D bone, all attempts must be made to perform a bone augmentation procedure and create a condition as close as possible to Division B bone.,,
|Figure 1: maxillary natural tooth vs mandibular implant-supported prosthesis in division a bone,|
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|Figure 2: maxillary implant-supported prosthesis vs mandibular natural tooth in division a bone,|
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|Figure 3: maxillary implant-supported prosthesis vs mandibular implant-supported prosthesis in division a bone,|
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|Figure 4: maxillary implant-supported prosthesis vs mandibular natural tooth in division b-d bone, might require cross-arch relation of teeth,|
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Design of the prosthesis should favor the weakest arch
Usually the maxilla is the weaker of the two arches, predominantly due to less dense bone. From a biomechanical perspective, an implant-restored premaxilla is often the weakest section compared with the other regions of the mouth. Compromised anatomical conditions include narrow ridges and the need for narrow implants, the use of facial cantilevers, oblique centric contacts, lateral forces in excursion, reduced bone density, the absence of a thick cortical plate at the crest, and accelerated bone loss in the incisor region often resulting in instability when placing central and lateral incisor implants without substantial augmentation procedures. In the anterior premaxilla, 15% higher maximum bone strain for a straight abutment has been predicted compared to an angled abutment. It has been suggested that, when restoring implants in the anterior maxilla, the use of an angled abutment, compared to a straight abutment, may decrease the strain on the bone. In fact, it has been recommended to increase the number and the diameter of implants and provide splinting when force factors are great.
The selection of occlusal materials depends on the opposing dentition, the remaining dentition, and the quadrant to be restored. The selection is usually made from among porcelain, zirconia, metal, and resin-based materials.,
Many studies have reported that parafunctional activities and improper occlusal designs are correlated with implant bone loss and failures. Further, it has been proposed that the numbers and distribution of occlusal contacts had major influences on the distribution of force. Naert et al., reported that overloading from parafunctional habits such as clenching or bruxism seemed to be the most probable cause of implant failure and marginal bone loss. According to them, shorter cantilevers, proper location of the fixtures along the arch, a maximum fixture length, and night-guard protection should be prerequisites to avoid parafunctional habits or the overloading of implants in these patients.
Timing of loading
Implant loading can be either delayed (submerged), progressive bone loading or immediate bone loading. Bone density is the key determinant in deciding the amount of time between implant placement and prosthesis restoration.,, Progressive bone loading is specifically indicated for less dense bones. Progressive bone loading allows a “development time” for load-bearing bone and allows bone adaptability to loading via the gradual increase in loading. The concept is based on incorporating time intervals (3-6 months), diet (avoiding chewing with a soft diet, then progressing to harder food), occlusion (gradually intensifying the occlusal contacts during prosthesis fabrication), prosthesis design, and occlusal materials (from resin to metal to porcelain) for poor bone quality conditions.
Occlusal guidelines for different clinical situations
In case of a full-arch fixed prosthesis, if the opposing arch is a complete denture, balanced occlusion is recommended. Group function or mutually protected occlusion with shallow anterior guidance is recommended when opposing natural dentition or a full-arch fixed prosthesis. There should be no working side and balancing contact on the cantilever.,,,,, The infraocclusion of the cantilever segment should be by 100 µm , and freedom in centric should be 1-1.5 mm. In case of overdentures, bilateral balanced occlusion with lingualized occlusion should be used. In case of severely resorbed ridges, monoplane occlusion should be used.,
If the posterior arch is rehabilitated with a fixed prosthesis, contacts should be centered over the implant body, and narrow occlusal tables, flat cusps with minimized cantilever should be employed. Where necessary, the posterior occlusion must be placed in crossbite. Anterior guidance should be with the natural dentition, and group function occlusion should be employed with compromised canines.,
Guidelines for choice of reconstruction and occlusal concept when rehabilitating the edentulous mandible with oral implants have been suggested by Quirynen M et al. In case of the fully edentulous maxilla, whether the mandibular rehabilitation is done on an overdenture supported on two implants or on a mucosal-implant-supported overdenture (four implants with a bar attachment), a balanced occlusal scheme (bilateral/lingualized/monoplane) is recommended. In conditions where a Kennedy class I partially edentulous condition is present in the maxillary arch and mandibular mucosa-implant supported (four implants with a bar attachment) or an implant-supported prosthesis is planned for the mandibular arch, balanced occlusion is recommended. In case of a maxillary arch presenting with Kennedy class II condition, if a mucosal-implant-supported prosthesis is planned for the mandibular arch, balanced occlusion is recommended. If an implant-supported prosthesis is advised for the mandibular arch, group function or mutually protected occlusion is advised. In case of Kennedy's class I in maxillary arch that has been restored with fixed denture prosthesis (FDP) or with implants, and a mandibular implant-supported prosthesis is advised, it is recommended to follow group function or mutually protected occlusion. In cases where the maxillary arch presents with Kennedy's class III and IV and implant-supported prosthesis is advised for the mandible, group function or mutually protected occlusion is recommended. Lastly, in case of the fully dentate maxilla and implant-supported prosthesis, group function or mutually protected occlusion is recommended.
A poor selection of occlusal scheme can lead to biological and mechanical complications.,, The various consequences that can be encountered are implant failure, early crestal bone loss, screw loosening, uncemented restorations, component failure, porcelain fracture, prosthesis fracture, and peri-implant disease.,. An IPO scheme addresses several conditions to minimize overload on bone/implant interfaces and implant prostheses, thus restricting implant loads within physiological limits. The guidelines need to be implemented in specific conditions to decrease stresses and develop an occlusal scheme to allow the restoration to function in harmony with the rest of the stomatognathic system and to maximize the longevity of the implants and prosthesis.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
by Gordon J. Christensen, DDS, MSD, PhD
Q I have been practicing for several years, and I've observed many changes in occlusion in my patients that have occurred without any intervention on my part. What factors cause these changes, and what can I do to reduce or control the changes?
A Your question is a very important one, and many years of practice are necessary to see these changes in occlusion occur. I will discuss the various factors that change occlusion over a patient's lifetime, some of which you can influence (Fig. 1), and others that are beyond your control (Fig. 2).
|Fig. 1 -- This patient has had a tooth removed from a complete arch of teeth, causing collapse of occlusion. If she had had the missing tooth replaced when it was removed instead of later in life, she would have had a much less complicated restorative challenge.|
If you or I were to discuss occlusion with almost any other dentist, we would receive a different view on the importance of occlusion, the presence and potential causes of deviant occlusal conditions, the diagnosis of them, and how to treat each of them.[Native Advertisement]
|Fig. 2 -- The occlusion of this patient is obviously not normal. She has had many permanent teeth not form and the retention of numerous primary teeth. However, there is nothing a dentist can do to prevent the malocclusion. Only a combination of orthodontic, surgical, and restorative procedures can overcome the esthetic and functional challenges.|
In my opinion, human dental occlusion is one of the most confused and controversial areas of the profession. There are numerous, highly opinionated groups who feel they're right and others are wrong. The respective occlusal groups agree on only a few basic concepts. This situation has caused many dentists to omit most occlusal diagnosis or treatment from their practices.
As a prosthodontist with many years of experience observing thousands of patients who have occlusal problems, I am convinced that occlusion is a constantly changing, dynamic state that is almost never the same from day to day.
What are the apparent causes of changes in occlusion? If we can agree on the reasons for changes, it may be possible to prevent or treat some of the occlusal maladies that dentists see on a daily basis.
In contemplating this subject, I consulted with a well-known and respected dentist who has been long associated with occlusion, Dr. John O. Grippo, concerning his views on the causes of change in occlusion. I combined Dr. Grippo's thoughts with my own observations and information in the literature, and I have summarized in my reply here the reasons for occlusal changes and what we can do to prevent them.
The following conditions are usually identified as being related to tooth movement. Other than the first few conditions, it is impossible to prioritize them on the basis of severity or magnitude of tooth movement. The list is in approximate order of most to least commonly occurring, based on my opinion and observations.
Tooth extraction without subsequent restorative dentistry
This is probably the most common cause of tooth movement and is well known to all dentists. The result of removal of teeth without any placement of restorations to avoid surrounding or opposing tooth movement often results in significant tooth movement in all directions. Such movement is usually nearly impossible to return to a normal state.
Prevention: When possible, place restorations preventing tooth movement, such as a fixed or removable partial denture.
Movement of teeth related to differences in wear characteristics of restorative materials
Resin-based composites were introduced as restorations for Class II locations in about 1968 with a material named Adaptic from J&J. At that time, many dentists initiated use of resin in Class II situations, only to see occlusion collapse and teeth drift mesially as a result of resin wear. Nonworking interferences were created as the occlusal aspects of the resin wore or "plucked" away. As proximal resin wore, the affected teeth moved into abnormal mesial-distal relationships with teeth on opposing arches. Fortunately, current restorative materials have better wear characteristics, and this malady has been somewhat overcome. However, restorative material wear is often dissimilar to tooth wear.
On the opposite side of these statements, some restorative materials, such as numerous ceramics used in crowns and fixed prostheses, rapidly wear opposing teeth. All dentists have observed extreme opposing tooth wear caused by abrasive restorations.
Prevention: Use restorative materials with wear characteristics that are similar to enamel.
Dental carious lesions develop on the occlusal and proximal surfaces
These conditions, rampant in some geographic locations, allow teeth to drift both occlusally and proximally with resultant collapse of occlusion.
Prevention: When possible, restore affected teeth into normal occlusal relationships as soon as possible.
Wear of teeth caused by parafunction
Many patients in any typical general practice have bruxism or clenching habits. These patients have occlusal collapse, their teeth move mesially, and incisal guidance and canine rise increase (clenching) or decrease (bruxism). The result of these changes makes rehabilitation of occlusion in middle age very difficult because of extreme tooth wear.
Prevention: Observe the presence of parafunction habits early in life and conduct treatment, such as occlusal splints, to reduce the effect of the conditions.
As the periodontium decreases in support as a result of ongoing periodontal disease, the teeth become mobile. They move in every direction, often allowing occlusal collapse and creating a "long centric" from centric relation to maximum intercuspation.
Prevention: Early diagnosis and treatment of periodontal disease, orthodontic treatment if necessary, and retainers to maintain teeth in optimum locations.
Unfortunately, dentists have bad days just like people in other professions. Restorations are often left too high or too low or without adequate contact relationships. These conditions stimulate tooth movement. Dentists can inadvertently cause negative conditions related to occlusion.
Prevention: Negative clinical situations caused by a dentist that could contribute to occlusal problems are often observed. Patients should be tactfully advised of the challenges of this type of treatment provided by a previous practitioner, and with the patient's acceptance, remedial treatment should be accomplished.
Obviously, orthodontic treatment purposely causes tooth movement. However, when teeth are moved to the desirable functional and esthetic locations, they are unstable for a significant period of time. Most orthodontists provide stabilizing removable splints or rigid splinting to allow the mobile teeth to become stable. Even with these precautions, many completed orthodontic patients have drifting teeth, open contact areas, and ensuing occlusal problems.
Prevention: Immediately after orthodontic appliances are removed and teeth are still mobile but in their desired locations, I suggest a minor occlusal equilibration to stabilize the patient's occlusion that was previously held in the proper position by orthodontic appliances. In my opinion, the lack of occlusal stabilization after removing orthodontic appliances is one of the significant reasons for teeth moving into undesirable locations.
Tooth or restoration proximal surface wear
When teeth are extracted, it is common to see wear on the proximal surfaces of the extracted teeth. The phenomenon causing this wear, often called "mesial drift," is significant. Enamel-to-enamel contact areas that occur over time can wear on both the mesial and distal surfaces as a result of the "anterior component of force," a well-known subject in occlusion. However, abrasive or nonabrasive adjacent materials wear at different rates, allowing abnormal movement of teeth in a mesial direction.
Prevention: Nothing can be done about natural movement of the occlusion in an anterior or mesial direction when enamel is contacting enamel on the proximal surfaces. However, dentists should seek and use products for restorations on proximal surfaces that wear at a similar rate with enamel. Occlusion should be monitored and changes recorded on a routine basis to ensure that the mesial movement of teeth is in a stable position and not causing occlusal discrepancies. Diagnostic casts, especially postorthodontic treatment casts, also provide valuable information about changes in occlusion.
Many people eat highly abrasive foods that wear teeth aggressively. Consumed routinely, such foods cause occlusal changes.
Prevention: Advise patients to avoid abrasive foods or reduce their consumption of them.
Biocorrosion/abfraction or the effects of stress combined with endogenous and exogenous acids
The combined mechanisms of biocorrosion/stress (manifested as abfraction) were introduced by Grippo, Simring, and Schreiner in their landmark paper, "Abfraction, abrasion, biocorrosion, and the enigma of noncarious cervical lesions: a 20-year perspective." This concept has led to many debates internationally; however, it is not my purpose to continue the debate. The significant point is that there is obvious tooth structure missing in the Class V areas, primarily on the facial surfaces of the teeth, and to a much lesser degree on lingual surfaces, usually attributed to increased salivary flow to these areas. However, changes in occlusion are apparent in the formation of Class VI lesions, which manifest as invaginations or dimples on the occlusal and incisal surfaces. It appears that a combination of chemical and biochemical activity, termed biocorrosion, and concentrated stress initiate such tooth destruction frequently observed by dentists.
Prevention: Reduce or eliminate acid presence in the mouth from regurgitation of many causes. Reduce obvious occlusal discrepancies.
These occur frequently and cause major changes in occlusion due to tooth avulsion, teeth pushed into supporting bone, broken facial or jaw bones, temporomandibular joint damage, and broken teeth. In my experience, a person who has had a significant accident requires several years for the occlusion to stabilize, during which time the person needs frequent evaluation and potential treatment to help the occlusion to be stable.
Prevention: There is nothing preventive that can be done after an accident. However, promotion and delivery of athletic mouthguards for those involved with body contact sports, and overall preventive education about driving and other hazardous activities, is advisable.
Skeletal growth differences – variations in skeletal growth or pathological skeletal growth
The result of large people reproducing with small people can be children with abnormal skeletal growth patterns. Such children often have peculiar occlusal patterns and subsequent abnormal occlusion and tooth movement. Additionally, many pathological skeletal developmental challenges, including cleft palate, are often difficult to treat.
Prevention: There appears to be little that can be done for prevention of these conditions. However, dentists should be observant and follow such deviant occlusal conditions as they develop. Appropriately timed orthodontic or surgical treatment can be accomplished to correct them.
Dental occlusion is a constantly changing condition. Many factors cause tooth movement, some slowly and others rapidly. Dentists should monitor, record, and evaluate occlusion routinely, instituting preventive procedures to reduce or eliminate occlusal changes, or to treat those that are treatable. That is our goal, but in my opinion the profession has a long way to go to reach that goal. Occlusion is still a relatively neglected part of dentistry and has been the traditional battleground of dentistry for decades. Almost every aspect of dental practice is concerned with occlusal function and occlusal therapy, but there has been obvious lack of practitioner concern regarding concepts, principles, and methods for evaluating and treating dysfunctional relations of the masticatory system. It is time to become more involved with this vitally important area of dentistry.
References available upon request
Gordon Christensen, DDS, MSD, PhD, is a practicing prosthodontist in Provo, Utah. He is the founder and director of Practical Clinical Courses, an international continuing-education organization initiated in 1981 for dental professionals. Dr. Christensen is a cofounder (with his wife, Dr. Rella Christensen) and CEO of CLINICIANS REPORT (formerly Clinical Research Associates).
In this monthly feature, Dr. Gordon Christensen addresses the most frequently asked questions from Dental Economics® readers. If you would like to submit a question to Dr. Christensen, please send an email to firstname.lastname@example.org.
Additional information on this subject
PCC has the following hour-long DVDs available on occlusion. They can be ordered individually or in a package.
"Occlusal Splints – Predictable, Frequent Use" (Item #V3104)
"Simple TMD Therapy for Your Practice" (Item #V3106)
"Uncomplicated Occlusal Equilibration" (Item #V3105)
"Bruxism and Clenching – Prevention and Treatment" (Item #V3162)
For more information, view our website at www.pccdental.com or call PCC at (800) 223-6569.
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