Temporomandibular disorder (TMD) is not just one disorder, but a group of conditions that painfully affect the temporomandibular joint (TMJ) and the muscles of mastication. The ADA estimates that 10 to 14 million Americans have TMJ disorders; 80% of these are women between 24 and 50 years of age.
Dental Compression Syndrome (DCS) is a contemporary name for the age-old condition of grinding and/or clenching of teeth. Capable of generating forces in excess of 500 pounds per square inch, DCS simultaneously applies pressure to the dentition, alveolar bone, and the TMJ.
WHAT IS THEIR RELATIONSHIP?
Although it is generally understood that TMD may have a variety of causes, such as a severe injury to the mandible, arthritis, teeth not fitting together correctly, and structural abnormalities, it is generally believed that the majority of TMJ disorders, now of epidemic proportions, is simply due to repetitive motion trauma from DCS. Since 1990 scores of published articles associate DCS with TMD. The implications are that since there is such a strong relationship between DCS and TMD, if a patient with TMD exhibits signs of DCS, the focus of treatment should be directed toward managing DCS in order to reduce stress on the TMJ. The purpose of this article is to review the etiology, signs, and management of DCS.
DENTAL COMPRESSION SYNDROME: UNDERSTANDING AN OLD PROBLEM
The flattened dentition of our ancestors tells us that DCS has been epidemic throughout the ages. What causes it? There is no doubt that life stress causes a majority of people to clench and grind their teeth, but other factors have to be considered when consulting with the patient.
ETIOLOGY OF DCS
Exercise/sports: rowing, water skiing, lifting weights, boxing, riding a motorcycle, or any sport where there is a bracing of the body.
Psychological: anxiety, fear, tension, pleasure, aggression, anger, dreaming, stress.
Medical: sleep apnea, oral pain, or pain in other parts of the body.
Drugs: caffeine, amphetamines, cocaine, ecstasy, fluoxetine, fluvoxamine, paroxetine, sertraline, haloperidol, and venlafaxine.
Bioengineering factors: DCS can be easily initiated by a violation of bioengineering principles in the stomatognathic system, such as prematurities, off-loading of teeth, horizontal distraction of the mandible upon closure, and misalignment of the TMJ components.
One reason DCS has been so successful over the centuries is that it works well within one’s subconscious.1,2 Since few patients affected with DCS are cognizant of it, it is imperative that the visual signs of compression be recognized so that the problem can be addressed. Besides the obvious signs of a flattened dentition and hypertrophied muscles of mastication, certain deformations appear in the oral environment whose causes or significance are barely recognized. They affect the dentition, bone, and restorative materials.
Deformations of the Dentition
Figure 1. Compression NCLs: tips of functional cusps.
Figure 2. Compression NCLs: gingival area.
Classified as noncarious lesions (NCLs),3-6 these defects typically are site specific in that they appear at the tips of functional cusps and the gingival area of teeth, where the susceptibility to stress is high (Figures 1 and 2). A finite element analysis of a tooth model confirms that stress is highest in these areas.7
Two distinct mechanisms are responsible for the loss of tooth structure during compression: tensile forces8 and positive ion egress.9-14 Engineers tell us that these high stresses may be responsible for the pain experienced by patients who have restorations in this area where tensile forces are powerful enough to pull apart the enamel prisms.8
Although NCLs can be caused by a variety of agents such as low pH and mechanical abrasion,3 compression NCLs distinguish themselves by a glassy sheen. Kornfeld published on the phenomenon in 1932 when he observed that these defects were hard, smooth, and almost glasslike in appearance.15 It is suggested that the glassy effect is due to the exit of positive ions from these focal points of high stress.9 The ions are produced by the compression of collagen in the dentition and alveolar bone (piezo-electric effect).
Figures 3 to 7. Various examples of compression NCLs.
It is to be noted that compression NCLs do not appear on every patient who clenches his or her teeth for a variety of reasons: variations in the intensity and frequency of DCS, but primarily genetics. They seem to be more prevalent and dramatic in patients with dense alveolar bone as compared to patients with periodontally compromised teeth.16 Compression NCLs have been the subject of controversy among dentists for decades. W.I. Ferrier once wrote (1931), “Their etiology seems to be shrouded in mystery.”17 But it is not such a mystery if we understand the science of biomechanics. Subject to distracting labels such as McCoy’s notches18,19 and abfractions,3 these defects require a more scientific identification, which is essential to understanding their significance.
What we are actually seeing are multi-shaped examples of hard tissue fatigue (Figures 3 to 7). Fatigue applies to changes in the properties of a material due to repeated applications of stresses or strains20—in this case, compression failure from DCS. J.E. Gordon, a professor of materials at Reading University in England, describes fatigue as “one of the most insidious causes of loss of strength in a structure.”21
Figures 8 and 9. Gingival fatigue in tandem.
If an object such as a tennis ball rebounds to its original shape after repeated applications, then it is said to be elastic in nature. However, if an object exhibits residual defects or sets after repeated applications, then it is said to be of a plastic nature. Biological structures such as teeth and bone are termed viscoelastic. A similar phenomenon occurs in the spine. In orthopedics, these sites of destructive stress are termed compression or wedge fractures.22 Compression failure of an object occurs at its most vulnerable site. Teeth are most susceptible at the gingival area. If alveolar bone recedes, then the failure site will also be lowered. Figures 8 and 9 demonstrate defects appearing in tandem as the supporting bone atrophies, thus changing the fulcrum point. Also note in Figure 8 that the only occlusal contact is on the incline plane, forcing the bicuspid to be flexed toward the lingual when the patient clenches.
Deformations in Restorative Materials
Figure 10. Luder Lines in amalgam.
Figures 11. Luder Lines in acrylic. (Courtesy of Gregori M. Kurtzman, DDS.)
Fatigue easily manifests it-self in prostheses and restorative materials such as amalgam and acrylic. In engineering these wavy patterns are termed Lines of Luder5,9 or molecular slip bands. The explanation is that molecules in the alloy are rearranging themselves under the influence of compressive strain. One can demonstrate the effect by bending a metal coat hanger back and forth and examining the stress configuration that is produced. Figure 10 demonstrates Luder Lines in amalgam and Figure 11 in acrylic.
Deformations of the Bone (Exostosis)
Figures 12 and 13. Examples of exostosis.
Articles on torus palatinus and torus mandibularis have appeared since 1814 (Figures 12 and 13).23 Although there is no consensus on their etiology, many associate their occurrence with TMD and masticatory hyperfunction.24-26 The author has long suggested that the compression of collagen in the dentition and bone generates negative ions that result in exostosis9-11 (piezo-electric effect). A situation such as this may well explain the metallic taste that people experience from time to time.
A survey was taken of 100 patients (50 female, 50 male, age range 17 to 76) to determine how many exhibited signs and symptoms of DCS and TMD.11 The findings are summarized in the Table.
Management of Parafunction
The presence of deformations in the oral environment should stimulate a dialogue to determine if the patient is currently grinding and/or clenching his or her teeth, or whether this damage occurred during a prior stressful period in his or her life. Often a patient will deny any awareness of DCS, but upon returning will say something like, “You know, since you brought it to my attention, I catch myself all the time.” Management of DCS begins with awareness and proceeds with a 3-step treatment plan that consists of education, equilibration, and guard therapy.
Step 1: Education
The dental healthcare provider must educate the patient about DCS in the simplest terms. Patients need to understand that teeth should only touch upon swallowing, and should know the resting position of the mandible (lips together, teeth apart). The list of etiological agents should be reviewed. Patients should be asked to monitor their jaw position during waking hours and be sensitive to headaches and tension in muscles of mastication upon waking. If it is obvious that the patient is affected with DCS and is indifferent to the problem, then his or her dental records should indicate such and no further treatment should be initiated. However, if the patient is aware of and wants to eliminate or reduce the problem, the next step would be to analyze the occlusion in order to determine if the morphology of certain teeth needs to be modified.
Step 2: Equilibration
Figure 14. Vertical loading.
Figure 15. Neutralization.
Figure 16. Off-loading.
In order to determine the need for an equilibration, the patient’s present occlusion must be compared to a standard of excellence, ie, ideal occlusion. Based upon nature’s original design, the most ideal occlusion is where the occlusal contact is confined to the tip of the functional cusp. There are 2 noteworthy observations. One is the minimal contact confined to the tip of the functional cusp, and the other is the generous space between the incline planes of the cusps, termed the intra-incline space.11 From these observations it is interesting to note that teeth do not require large areas of contact in order to maintain their position, work efficiently, and be comfortable. But what was nature’s intention in providing such clearance between the incline planes? From an engineering point of view, there are several advantages:
Vertical loading (Figure 14). The intraincline space (between the incline planes) ensures vertical loading. Misch and Bidez describe vertical compression forces as normal and explain that they act perpendicular to and maintain the integrity of the alveolar bone.27
Neutralization (Figure 15). This is the desired buccal-lingual position of the tooth by reciprocal action of the muscles of the tongue and cheek. When the incline planes do not touch, the tooth is free to assume a neutral position.28
|Figures 17 and 18. Indicator wax demonstrating incline plane contacts resulting in off-loading.|
Figures 19 and 20. Anterior guard.
Prevention of off-loading (Figures 16 to 18). When the incline planes of the cusps are in contact, bending or off-loading of the tooth is likely during mastication and compression, resulting in destructive shearing forces that act parallel to the alveolar bone.27
Condylar seating. The intra-incline space plays a very important role in condylar seating. Angle once stated (1899), “So it will be seen that the occlusion of the teeth is maintained first by the occlusal inclined planes of the cusps.”29 This is a valid statement, but is it what we want? Our objective is for centric relation (CR) to equal centric occlusion (CO). What if, due to clenching and grinding, the mandible has worked its way forward so that CO is anterior to CR and that position is locked in by the incline planes? If the incline planes of the cusps do not touch, then there would be no occlusal resistance when the contracting swallowing muscles retract the mandible up and back upon closure. If there is no resistance, then there should be no impediment to achieving CR.
Methods of Equilibration Indirect Method:
• Reposition condyles.
• Mount models on 3-dimensional articulator.
• Adjust occlusion on models.
• Repeat with natural dentition.
• Utilizes patient’s own stomatognathic system as a biological articulator.
• Occlusal indicator wax demonstrates contacts in closure.
• Areas of displaced wax are analyzed.
• Contacts on incline planes are eliminated.
Advantages: more accurate; less time; inexpensive; easy to facilitate.
An equilibration is a reduction of the working cusp inclines. For easy patient understanding it is suggested that the procedure be described as “a sharpening of functional cusps.” Terms like equilibration and coronoplasty are too formal and require further definition. The patient needs to be informed that the teeth are never shortened, and the benefits (increased comfort and diminished DCS) will far outweigh the conservative loss of enamel. The entire procedure should take no longer than 15 to 20 minutes. The patient should be seen in a week or two for final analysis and polishing. Informed consent must take place. We have been cautioned against imposing occlusal changes based upon the clinician’s concept of the ideal.30 However, it is correct to reshape worn, deformed teeth in order to regain their original configuration with intra-incline space. A review of 15 articles on occlusal equilibrations published in professional journals reveals generalized agreement on the following points:31-45
• Prophylactic adjustments in the absence of pathology are not acceptable.
• Occlusal adjustment is a misunderstood and an underutilized procedure.
• CR should equal CO.
• There should be no interferences in lateral excursions.
• The height of the buccal cusps should never be shortened except to eliminate interference in lateral excursions.
• Traumatic occlusal relationships should be eliminated before restorative procedures.
• Cusps should touch loosely in the opposing fossae.
• Inclined planes should not touch to ensure axial loading.
• Occlusal indicator wax is the most effective way to demonstrate how teeth touch.
• There should be no flat-plane occlusion in humans.
• Cuspid guided occlusion is preferred.
A recent publication confirms the relationship between equilibration and gingival fatigue. This 17-year study evaluated the relationship between gingival fatigue due to DCS and its relief by sharpening the functional cusps.46 Over a 17-year span, 246 teeth were verified as having hypersensitivity from gingival fatigue, which was resolved by equilibration in 2 visits. The study confirmed that the equilibration specifically involved reduction of the working cusp inclines, and that it significantly reduced cervical dental hypersensitivity.
Step 3: Occlusal Guards
Proper management of the patient who is affected with DCS entails addressing the problem on 3 separate levels. The sharpening procedure satisfies the engineering requirement, and educating the patient can certainly help in stress management during waking hours. But only a guard can ensure protection while sleeping.47-50 But what kind—hard, soft, full-arch, anterior?
Unfortunately, there are conflicting studies.51,52 Which is best? Again, we have to evaluate our objectives from an engineering point of view.
If our goal is to diminish the force on the TMJ and reduce muscle tension, then the best design is a small, thin, hard acrylic appliance that covers the lingual surfaces of the maxillary anterior teeth. It is often referred to as a deprogrammer or mandibular repositioner. A common question regarding this design is, “Do the posterior teeth supererupt?” No, it is not like the Hawley retainer that is worn a majority of the time. Posterior teeth do not supererupt overnight—consider the mouth breather.
Regarding hard or soft appliances, a recent study suggests that soft and hard splints are equal in reducing masticatory muscle pain.53 Although this may be true, there is an additional factor that the study did not include. In my private practice I had considerable experience with soft guards and found that yes, they were effective in reducing TMJD, but often patients were encouraged to compress against them simply because they were resilient. Generally, studies agree that there is an overall reduction of oral-facial pain (78%) when DCS is treated with any type of guard,54 but the smaller anterior deprogrammer seems to work best (Figures 19 and 20).
If the intensity of DCS is such that the above 3-step treatment therapy is not effective, then biofeedback, hypnotism, physical therapy, and drug therapy must be considered.
DCS AND PERIODONTAL DISEASE
DCS can create periodontal disease through a disturbance of the physiology. Fire-stone and Miller (1947) demonstrated how DCS, generated by psychosomatic factors, can facilitate changes in salivary composition and blood calcium levels, and produce extreme alveoloclasica.55,56 A recent study confirms the relationship between psychosomatic factors and periodontal disease, but curiously does not consider that DCS is the vehicle that is initiated by the stress and delivers the untoward forces to the periodontium.57
DCS AND THE ORAL IMPLANT PATIENT
In the reconstruction of the edentulous patient with endosteal implants, one has to consider that the loss of the patient’s natural dentition may have been due to DCS.58 During the consultation phase, patients should be questioned as to their awareness of DCS. If the patient is semi-edentulous, the patient’s remaining dentition will reveal valuable information. The remaining occlusion should be evaluated to determine if a reduction of the working cusp inclines might be beneficial. As with natural teeth, implants require axial loading. If there is an engineering discrepancy between vertical loading of the implant and a natural antagonist, then the occlusion of the opposing tooth must be modified to ensure vertical loading of the implant.
PROBLEM-SOLVING FOR TMD
If a patient presents with oral-facial pain and/or discomfort in the TMJ, then the dentist should consider that DCS might be the source of the problem. Traditionally, clenching and grinding have been the most agreed upon cause of TMD.59-64 If this is confirmed either by the patient or by information gained by examining the dentition, then the 3-step management therapy should be initiated to reduce the stress on the TMJ.
If a patient’s condyles have migrated down and forward, then there are 3 traditional methods of management. One is to reposition the condyles manually and then equilibrate the dentition. Another is to have the patient wear a splint (mandibular repositioner/deprogrammer) for a period of time and then equilibrate. A third is to use neuromuscular instrumentation. For general practitioners there is a fourth method that is simple and effective and produces immediate, positive results. If occlusal indicator wax is used to diagnose the occlusal contacts, then it is common to see that, due to DCS, the mandible has worked its way forward and cannot return during swallowing/closure because the incline planes of the cusps are engaged. If this is the case, then recreation of the intra-incline space will allow the condyles to assume their natural position.
The focus of what we have been taught is on the position of the mandible/condyles upon closure (CR=CO), rather than the occlusion of the dentition. We have to consider that the teeth themselves may be preventing CR from assuming its proper position. Another consideration: CR can only equal CO when the head is vertical with the body. Many natural COs occur when the head deviates from the vertical, as when one leans forward or is reclining. We have to be comfortable with all of our COs.
Fifty years ago, McCollum and Stuart described a subtle pathology of function in the human masticatory system that was difficult to understand.65 That subtle pathology is the damage that results from compression of teeth. It is subtle because often the patient is unaware. It is pathologic because it applies untoward stress to the dentition, alveolar bone, and the TMJ. It is difficult to understand for many reasons: multiple etiology, few patient complaints, poor understanding of the deformations caused by DCS, the role of equilibration during treatment is unclear, and the dissimilar ways it takes its toll.
For proper management of DCS, the general dentist should monitor for signs of compression and wear, educate the patient about the problem, and provide treatment. While every patient with a flattened dentition should not have their teeth dramatically altered or reconstructed, the dental profession should form a consensus that the natural, sharp morphology of teeth is superior to a flattened dentition, and should be preserved throughout one’s lifetime.
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