Examining the long-standing controversy about the role of occlusion in periodontal disease is a delightful look back at more than 100 years of periodontal theory and practice. The list of authors who have written on this topic in the past century reads like a "Who’s Who" of some of the brightest minds in dentistry, and the debate has endured through several defined eras in the history of the specialty of periodontics. From the days when periodontics was dominated by those initially trained as pathologists, through the period when the specialty was led by master clinicians headquartered at certain universities, through an era characterized by meticulously controlled human and animal studies conducted both in the United States and abroad, up to the current period of evidence-based therapy, the debate has persisted. It is a reminder that even in this modern era, dentistry still is very much an art as well as a science.
Treatment of occlusal trauma should be directed toward the specific instances in which occlusal trauma truly exists.
Like most long-standing controversies, the debate about occlusion and periodontal disease has narrowed considerably over the years. For example, no one now believes that excessive occlusal force initiates periodontitis, nor does any credible person believe that occlusal force is incapable of causing periodontal injury. As the edges of the debate have been nibbled away over time, the crux of the remaining argument is this: Can occlusal forces exacerbate the progression of periodontitis, and is eliminating occlusal discrepancies appropriate or necessary in the treatment of the disease?
The purpose of this article is to outline the clinical and histological response of the periodontium to excessive occlusal force, to review the clinical studies that have examined the relationship between occlusion and periodontitis, and to reiterate a rational approach to managing occlusion within the context of periodontal therapy.
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THE OCCLUSAL TRAUMA LESION
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The term "occlusal trauma" (or "trauma resulting from occlusion") refers to the pathological or adaptive changes to the periodontium caused by the excessive occlusal force known as "traumatogenic occlusion."1 Occlusal trauma, then, is an injury to the periodontium; traumatogenic occlusion is the etiologic factor causing the injury.
Similar in some respects to the tissue response to orthodontic forces, traumatogenic occlusion establishes distinct zones of tension and pressure within the periodontal ligament of the affected tooth. The location of these zones depends on the location and vector of the force, as well as on the position of the alveolar crest.2 The extent of the occlusal trauma lesion within the periodontal ligament space depends on the level of force. At low levels, the microscopic changes include increased vascularization, increased vascular permeability, vascular thrombosis, and disruption of fibroblasts and collagen fiber bundles. If the force is maintained, osteoclasts appear on the surface of the alveolus, leading to net bone resorption.2 At higher levels, occlusal forces may cause necrosis of periodontal ligament tissue, including lysis of cells, disruption of blood vessels and hyalinization of collagen fibers.3,4 Osteoclasts appear in marrow spaces adjacent to the alveolar bone, producing an undermining, rather than direct, resorption of bone.2,5 In addition, resorption of the root surface may be a feature of the occlusal trauma lesion.6–8
Not every mobile tooth suffers from occlusal trauma, but certainly every tooth with a sustained occlusal trauma lesion will become mobile.
The net effect of these microscopic changes is an adaptive response within the periodontium that allows it to compensate for the excessive force.2,9 The density of the alveolar bone decreases and the width of the periodontal ligament space increases at the expense of both the socket wall and the root surface. This leads to the two most distinctive clinical signs of occlusal trauma: increased tooth mobility and a radiographic widening of the periodontal ligament space, which may be either uniform or accentuated at the alveolar crest.4,5,10 An additional diagnostic sign of the occlusal trauma lesion is fremitus, or functional mobility, which refers to the palpable deflection of a tooth either on closure or during excursive movements.11
The effect of occlusal forces on periodontal attachment levels has been well-studied in animal models. When imposed upon a healthy periodontium, even if reduced in height, traumatogenic occlusion does not cause pocket formation or loss of clinical attachment.3,12 Though this finding is perhaps controversial, one of the two major research groups conducting animal studies of occlusal trauma observed that in certain circumstances, traumatogenic occlusion superimposed on pre-existing periodontitis lesions could lead to an increased loss of attachment.9,10 Assuming this to be true, it is important to note that this loss of attachment was found only in conjunction with an actual occlusal trauma lesion.
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CLINICAL STUDIES
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Tooth mobility has been described as the "hallmark" of occlusal trauma.5 Whether progressive as the injury occurs or simply increased after compensation has taken place, tooth mobility is a universally recognized component of occlusal trauma.2–6,9,12 Not every mobile tooth suffers from occlusal trauma, but certainly every tooth with a sustained occlusal trauma lesion will become mobile. Most clinical studies that have examined the relationship between occlusion and periodontitis, however, have focused on teeth with occlusal discrepancies rather than teeth with traumatic lesions.
Yuodelis and Mann13 reported on the relationship between periodontal parameters and molar nonworking contacts using the records, radiographs and study models of 54 patients with periodontal disease. Fifty-three percent of molar teeth had nonworking contacts, and the authors determined that probing depths and bone loss were greater for those teeth. Conversely, Shefter and McFall14 looked at occlusal disharmonies in a group of 66 young patients with mild-to-moderate periodontitis. Seventy-eight percent had a deviation from centric relation to centric occlusion, and 56 percent had nonworking contacts in lateral movements. The authors found no relationship between the occlusal disharmonies and periodontal findings.
A more recent study by Nunn and Harrel15 investigated the association between occlusal discrepancies and periodontitis in a private practice setting. These researchers compared 41 patients who received all recommended treatment, including adjustment of occlusal discrepancies, with 48 patients who received partial treatment or no treatment. They found that 56 (62.92 percent) of the 89 total patients and 307 (13.35 percent) of 2,147 teeth had occlusal discrepancies; these discrepancies were listed as a vertical slide greater than or equal to 1 millimeter from a premature contact and balancing contacts in lateral movement. The authors reported that teeth with occlusal discrepancies had significantly deeper initial probing depths, more mobility and poorer prognoses than teeth without discrepancies.
Other clinical studies aimed specifically at evaluation of teeth with occlusal trauma lesions have failed to make this connection. Pihlstrom and colleagues,16 in a study of various clinical parameters of the maxillary first molars of 300 patients, found that while 60.4 percent of teeth had wear facets, 66.4 percent had centric relation contacts and 7.5 percent had nonworking contacts, only 4.2 percent had a widened periodontal ligament space and functional mobility associated with occlusal trauma. They concluded that teeth with occlusal contacts in centric relation and in working, nonworking or protrusive positions had no more severe periodontitis than did teeth without these contacts.
Jin and Cao17 examined 32 patients with moderate-to-advanced periodontitis to determine the reliability of several selected signs of occlusal trauma. Since the total number of teeth examined is not included in the article, it is difficult to determine the percentage of teeth with occlusal discrepancies versus the number with more objective signs of occlusal trauma. That said, the authors reported no significant differences in pocket depths, attachment levels or alveolar bone height between teeth with and without various abnormal occlusal contacts.
The determining factor of whether an occlusal contact produces occlusal trauma is the presence of periodontal injury, not the physical manifestations of the teeth, temporomandibular joints or muscles of mastication.
The evidence linking occlusal adjustment to improvements in periodontal parameters is extremely limited. Burgett and colleagues18 randomly assigned 50 patients with periodontitis into two groups based on occlusal adjustment. As part of the initial therapy, 22 patients received occlusal adjustment, with the goal of achieving even and stable contacts in centric occlusion, freedom in centric occlusion, smooth gliding contacts and elimination of balancing interferences. The remaining 28 subjects did not receive occlusal adjustment. All patients then received definitive surgical or nonsurgical periodontal therapy. Two years after treatment, the occlusal adjustment group had a slightly greater (0.4-mm) gain in attachment level than did the no-adjustment group. The authors noted that there was no difference in posttreatment probing depth reduction or mobility levels between the two groups.
In a clinical trial nine years later, Harrel and Nunn19 reported on the response to treatment of 89 untreated, partially treated and fully treated patients with periodontitis. Patients in each group were divided further on the basis of the presence or absence of occlusal discrepancies (premature contact with vertical slide 1 mm or greater or balancing contact in lateral movement) and whether occlusal adjustment was performed as part of treatment. Each patient received a follow-up examination at least 12 months after undergoing treatment or, for those electing not to receive treatment, the initial examination. Reporting their results only on the basis of the occlusal status, the authors observed a difference in probing depth changes after treatment, with a mean increased probing depth of 0.066 mm per year at sites with untreated occlusal problems, compared with a decreased probing depth of 0.048 mm per year at sites with no occlusal problems and 0.122 mm per year at sites with treated occlusal problems.
Though both Burgett and colleagues18 and Harrel and Nunn19 suggested a slight positive effect of occlusal therapy on the clinical outcome, the use of these studies as an endorsement for routine occlusal adjustment during the initial treatment of periodontitis is questionable.
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DISCUSSION
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There are several possible physiologic responses to excessive occlusal contact between teeth, and it is possible that two or more of these may occur simultaneously. The path of mandibular closure may be altered to avoid the excessive contact, the occlusal or incisal surfaces may wear leaving facets or even enamel fractures, pulpal symptoms may occur or the force may cause injury to the periodontium known as occlusal trauma.20 When discussing the relationship between occlusion and periodontal disease, however, it is important to remember that the determining factor of whether an occlusal contact produces occlusal trauma is the presence of periodontal injury, not the physical manifestations of the teeth, temporomandibular joints or muscles of mastication.4 If the periodontium is reduced enough, even a normal occlusal contact may produce occlusal trauma. Similarly, it is possible that even the worst deflective contact or balancing interference does not cause a traumatic lesion. Since the term "occlusal trauma" refers to the tissue injury rather than the occlusion, an increased occlusal force is not traumatic if no injury is present.4
The fact that not every occlusal discrepancy causes occlusal trauma is important when one considers that occlusal discrepancies are quite common in the general population.21,22 In fact, both the Yuodelis and Mann13 and Shefter and McFall14 studies described earlier reported that more than one-half of the patients had occlusal discrepancies and one-half of all molar teeth had balancing contacts. Certainly not all of those contacts required occlusal adjustment to maintain periodontal health. Sixty-eight percent of all teeth with occlusal discrepancies in the Nunn and Harrel15 patient group were nonmobile and, therefore, likely did not manifest an occlusal trauma lesion. It is difficult to understand the purpose of occlusal adjustment for these teeth.
Occlusion has been proposed as a risk factor for periodontitis.23 We believe it is possible that in certain cases, traumatogenic occlusion can exacerbate periodontal destruction, and, therefore, occlusal adjustment occasionally is indicated as part of periodontal therapy. However, we also believe that since not every tooth with an occlusal discrepancy is suffering from occlusal trauma—and, in fact, most are not—not every occlusal discrepancy in a patient with periodontitis needs adjustment. This philosophy is best summed up by Ramfjord and Ash,24 who stated that "the need for adjustment should be based on a definite diagnosis of a traumatic lesion rather than the location of some occlusal interferences which may be of no significance."
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CONCLUSION
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A treatment philosophy not calling for the early adjustment of occlusal discrepancies does not necessarily ignore the potential role of occlusion in periodontitis. We believe, as has been stated by others,5,22 that the initial treatment of the periodontitis lesion should focus on control of inflammation by means of patient oral hygiene and non-surgical therapy. In situations in which an obvious occlusal discrepancy is directly related to a clinically and/or radiographically evident traumatic lesion, it may be appropriate to adjust the occlusion at this stage. Conversely, occlusal discrepancies that are not accompanied by signs or symptoms of occlusal trauma generally do not require adjustment. After initial therapy, the dentist should re-evaluate the patient to assess the results. At this time, if indicated by persistent hypermobility or patient discomfort, further occlusal therapy may be indicated. In our view, this is the approach best supported by the available evidence, and it is the best way to ensure that treatment of occlusal trauma is directed toward the specific instances in which occlusal trauma truly exists.
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THE OCCLUSAL TRAUMA LESION
CLINICAL STUDIES
