Pathogenesis

Our understanding of the host-driven inflammatory response of each patient to a pathogenic bacterial biofilm is growing exponentially.³⁷ Each individual’s susceptibility appears to be so specific that the patient is actually his or her only reference with regard to the interpretation of possible contributing factors to the progressive loss of supporting bone. In addition, we can see that destructive events may be episodic, and they are clearly site specific. Our diagnostic responsibility includes the careful measurement of periodontal structures in the entire circumference of each tooth, accurate documentation, and timely reassessment. Periodontal deterioration that occurs rapidly or that is excessive for a person’s age should prompt the clinician to investigate any variable that may amplify that patient’s periodontitis. If a local factor such as an occlusal relationship can influence the course of the disease, then its analysis must be as precise as any other aspect of the periodontal examination.

Evidence-Based Decision Making

In a perfect world, all of our diagnostic and therapeutic decisions would reflect evidence from multiple prospective clinical trials that have been subject to systematic review. Prospective human investigations of occlusal trauma are considered unethical, so periodontics has conscientiously struggled to reach discipline-wide consensus regarding the interaction of a patient’s occlusion with his or her periodontal status.¹⁴ To be clinically applicable, the investigation’s methodology must parallel the clinical diagnosis and treatment of an individual patient with periodontitis.¹⁶ Historically, data management and statistical credibility and methodology within retrospective studies limited the ability of dedicated researchers to interpret the role of occlusion in an individual’s periodontitis experience.^17,36,39 The grouping of data points, especially in large study populations, departs from the site specificity that periodontal diagnosis requires. If occlusal trauma is affecting a tooth, the effect on the periodontium is site specific for only that tooth. Treatment for a patient with periodontitis would never be based on an average of diagnostic references but rather on their unique susceptibility, anatomy, occlusion, and history.

In 2001, Nunn and Harrell³² reported the retrospective findings of a group of patients with periodontitis in which the analysis was based on the measurement of the loss of attachment of each individual tooth and the presence or absence of occlusal interferences. This study and a similar investigation⁴ confirmed that trauma from occlusion amplified the loss of attachment. Harrell and Nunn¹⁵ also reported that eliminating occlusal interferences had a positive influence on the outcome of treatment when trauma from occlusion was found to be a contributing local factor. The positive influence of occlusal adjustment on the outcome of both surgical and nonsurgical periodontal therapies had also been reported by Burgett.⁶ Evidence now appears to support the possibility that trauma from occlusion has the capability to amplify damage to an inflamed periodontium.

Interest in the occlusion within the discipline of periodontics appears to be increasing, especially with the rapid growth of the replacement of missing teeth with implants. Despite some conflicting evidence in the literature, common ground for consensus exists. There is general agreement that occlusal force has an effect on the periodontium (see Chapter 15) and that susceptibility to periodontitis is unique to each patient. Occlusal forces present themselves across a broad spectrum. No or minimal occlusal contact on a tooth results in disuse atrophy of the periodontium, which may result in the instability of that tooth. Harmonious occlusal force on a tooth stimulates the physiologic arrangement of its periodontal attachment fibers and its osseous architecture and encourages its stability. Forces that exceed the tolerance of the periodontium result in resorption of the bone and disruption of the attachment.^19,29,31 In the healthy person, the periodontium around teeth that are subject to excessive occlusal force experiences adaptation and repair or remodeling with no loss of attachment, which often occurs with orthodontics. For the patient who is losing bone as a result of periodontitis, coupling the ongoing inflammatory disease with excessive occlusal force may result in the amplification of destruction and damage to the periodontium of affected teeth.³² If this conclusion is valid, then the clinician has the responsibility to correlate the precise analysis of the periodontal status of each tooth with its occlusal responsibilities and its possible occlusal excesses.

Terminology

The following is a list of key descriptive terms that are used in this chapter, along with their common synonyms:

Occlusal Function and Dysfunction

Excellent sources for a comprehensive understanding of dental anatomy and function include texts by Wheeler,³ McNeill,²⁷ and Dawson.^9,10 The determination of whether trauma from occlusion is occurring is made on the basis of the conclusion that the composite of all occlusal forces on a specific tooth exceeds the tolerance or adaptability of its periodontium. The identification of masticatory system disharmonies begins with an appreciation of physiologic norms; this allows the clinician to recognize dysfunctional relationships, which may influence the accuracy of the diagnosis.^10,31,33

Centric relation is a term that is used to describe the position of both condyles when they are fully seated in the fossae of their respective temporomandibular joints (TMJs). Rotation of the mandible around an axis through both condyles is called the centric relation closure arc (see Chapter 20). This is strictly a skeletal relationship until tooth contact occurs. Maximum intercuspation occurs when opposing teeth make contact, with optimal interdigitation, at the most stable endpoint of mandibular closure. Stability is enhanced by the simultaneous bilateral contact of multiple posterior teeth with occlusal forces in the long axis of most posterior teeth. If the initial tooth contact in the centric relation arc of closure occurs simultaneously with maximum intercuspation, then the teeth do not displace the condyles. Conversely, if the teeth are firm and any contact occurs before maximum intercuspation, then incline relationships of opposing occlusal surfaces will guide the mandible into intercuspal position, thereby requiring one or both condyles to become dislocated from their fossa.^10,32 If the teeth are mobile and contact first in the centric relation closure arc, then they may move away from opposing teeth rather than cause condylar displacement.

Cusp–fossa or cusp–marginal ridge relationships of the posterior teeth provide resistance to vertical loading and functional stability for the patient’s dentition. When occlusal forces load teeth in their long axis, the periodontium is the most resistant and supportive.9,10 The anterior teeth can be stable with little occlusal loading in centric occlusion if they are favorably influenced by the oral musculature. If the anterior teeth are in contact in maximum intercuspation, they are coupled. Movement of the mandible from centric occlusion is called an excursion. Movement forward is called a protrusive excursion, and movement to either side is called a lateral excursion. If the mandible can move posteriorly, it is called retrusion. There is evidence that the contact of posterior teeth in excursions can overload those teeth, which results in negative dental, periodontal, muscular, and TMJ consequences.^{1,7,10,33,44,45,46} The ideal relationship may be a light coupling of the anterior teeth in centric occlusion with immediate separation (also called disclusion) of all posterior teeth in all excursions.⁴⁵ During a lateral excursion, posterior teeth that make contact on the same side as the direction of mandibular movement are described as having a working contact. Posterior teeth that make contact on the side opposite the direction of the lateral excursion are described as having a nonworking contact. Although nonworking contacts are classically associated with more potential negative consequences,⁴⁶ the analysis of working contacts and the function of anterior teeth are critically important. Contacts that are disruptive to mandibular movement or stressful to individual teeth are called occlusal interferences or discrepancies. Our ability to analyze the occlusion to identify contacts that may amplify a patient’s periodontitis, thereby affecting certain teeth, is strategic to the making of the correct diagnosis.

Inflammation disrupts the integrity of the attachment apparatus, which results in less resistance to force from opposing teeth. When bone loss has occurred, less root surface area is supported,2,18 and there are fewer sensory fibers in the periodontal ligament, which limits the protective muscle modulation of the occlusal forces.³⁸ The clinician must differentiate among inflammation-caused intolerance to occlusal forces, normal forces on teeth with reduced periodontal support, excessive occlusal forces, and well-tolerated forces on teeth affected by periodontitis.

Parafunction

Bruxism may cause occlusal forces on teeth that are susceptible to periodontitis to be increased in intensity or frequency, thereby magnifying the potential amplification of damage.8,22,23,42 Daytime occlusal parafunction is commonly limited to clenching of the teeth during incidents that require a person’s focused effort or mental concentration. Nighttime bruxing of the teeth can take the form of grinding the teeth during various excursions or clenching of the teeth. Sleep bruxism is probably an extension of the rhythmic masticatory muscle activity that is also observed in nonbruxers. Why nuclei in the brain stem allow for bruxing to occur in some individuals while others are spared is unclear.^8,22,23 Bruxing is associated with the greater frequency and persistence of TMJ dysfunction, orofacial pain, and possibly periodontal attachment loss.⁴² The sensory input of teeth that are subject to bruxism is probably dampened, which may interfere with both diagnosis and treatment.³⁵ There seems to be limited influence on bruxing tendencies from occlusal interferences.²⁴ Selective serotonin reuptake inhibitors such as Prozac have been reported to encourage bruxism.¹³

Evidence is emerging that sleep-disordered breathing may influence or be associated />