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Reliability, validity, and utility of various occlusal measurement methods and techniques
Reliability, validity, and utility of various occlusal measurement methods and techniques Kazuyoshi Baba, DDS, PhD,a Yoshihiro Tsukiyama, DDS, PhD,b and Glenn T. Clark, DDS, MSc Tokyo Medical and Dental University, Tokyo, Japan, Kyushu University, Fukuoka, Japan, and UCLA School of Dentistry, Los Angeles, Calif. Statement of problem. The controversy continues regarding the efficacy of several commercially available devices that are used as aids in the diagnosis of occlusal abnormalities.
Purpose. This article reviews the reliability, validity, and utility of instruments that claim to detect occlusal interferences and abnormal vertical dimension of occlusion. Material and methods. Data, opinions, and technical information from 37 published articles were reviewed. Evidence for method reliability, validity, and utility was assessed. Results. Although occlusal contact detection devices can document the occlusal contact patterns on teeth, the basic in vivo testing of their reproducibility and validity has not been performed. Moreover, while EMG and jaw tracking systems can indeed measure jaw muscle activation and jaw position, no cost-benefit analysis of these devices has yet been conducted. One manufacturer suggests that these instruments be used in conjunction with an electrical muscle stimulation device to find a new resting jaw position that is more open vertically. This new, more open position has been inappropriately labeled as evidence of vertical dimension of occlusion overclosure. Conclusion. None of the instruments reviewed can be said to be more than ancillary documentation devices and they have been inadequately tested for reliability and validity. Moreover, because scientifically acceptable disease definitions are not available for these 2 conditions, the issue of over-diagnosing becomes a substantial concern. (J Prosthet Dent 2000;83:83-9.)
CLINICAL IMPLICATIONS While the instruments reviewed in this article may have value as documentary devices, their practical use has not been established.
T
he purpose of this article was to discuss the reliability, validity, and practical utility (cost vs benefit) of various instruments that claim to assess occlusal characteristics. Although there are multiple recognized occlusal disorders (traumatic occlusal interferences, phantom bites, attrition, unstable intercuspal position, and severe morphologic malocclusions), this review addresses only 2 conditions: (1) instruments that claim to assess occlusal interferences and (2) overclosure of the vertical dimension of occlusion. These 2 conditions were selected not because they are the most important clinical problems, but because the instruments available in the commercial marketplace have largely focused on measurement of these 2 clinical parameters.
aAssistant
Professor, The First Department of Prosthodontics, Faculty of Dentistry, Tokyo Medical and Dental University. bAssistant Professor, Department of Prosthodontics II, Faculty of Dentistry, Kyushu University. cProfessor and Chair, Section of Orofacial Pain and Oral Medicine, UCLA School of Dentistry. JANUARY 2000
DEFINITION OF THE TWO OCCLUSAL DISORDERS Occlusal interferences Traditional concepts of traumatic occlusal interferences involve a single anterior or posterior tooth, which is in “supracontact” during maximum intercuspidation or on excursive jaw movement. These 2 situations are collectively called “occlusal interferences.”1 Detection of “occlusal interferences” and identification of other physical signs of occlusal trauma such as a wear facets, tooth pain, tooth mobility, or widened periodontal ligament spaces, are most commonly performed through a clinical and sometimes radiographic examination. This examination is typically performed by a dentist using: (1) a visual assessment of the gross form of the occlusion; (2) measurement of certain occlusal features with a millimeter ruler; (3) testing for occlusal contacts with Mylar (ET Dupont, Wilmington, Del.), articulating ribbon/ paper, or occlusal wax; (4) testing teeth for mobility and for fremitus; and (5) examining tooth contact patterns visually in various voluntary and manipulated jaw posiTHE JOURNAL OF PROSTHETIC DENTISTRY 83
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tions. The combination of all the subjective patientbased information (gathered during the history) plus the examination-based findings is presumed to allow the expert clinician to come to a high probability determination of the presence or absence of a specific occlusal disturbance or disorder. Unfortunately, the clinical occlusal examination itself, and each specific method within this examination, has undergone only limited assessment in terms of reliability and validity. Several investigators have attempted to look at the reproducibility of some of the clinical occlusal examination methods for accuracy. Gazit et al2 looked at the reproducibility of 2 occlusal marking techniques (photoocclusion technique and color-marking technique) and found that neither technique was highly reproducible. Durbin and Sadowsky3 described a silicone impression material method for examining occlusal contact patterns before and after orthodontic treatment. Although this method has good accuracy, it is impractical. However, it might serve as a gold standard against which other, easier-to-use clinical methods could be tested. Korioth4 reported on the number and location of occlusal contacts in intercuspal position using alginate impression material. Anderson et al5 reported on the reliability of dentists’ ability to evaluate occlusal contacts in the intercuspal position. They compared an articulating paper method against a Mylar paper method and found the latter to be more reliable. In a study of the thickness, strength, and plastic deformation of occlusal registration strips used to detect occlusal contact patterns, Halpern et al6 found that some recording methods (those with a stiff marking media) induced artifacts in the contact detection process. These investigations are a good beginning if a better understanding of the weaknesses and strengths of the entire clinical occlusal examination are ever to be achieved. The lack of research in this area is largely due to occlusal disorders themselves, which have never been formally defined using repeatable criteria. Nevertheless, the practicing clinician’s “gold standard” for diagnosing occlusal disorders is a combination of patient selfreport of problems and the occlusal examination.
Overclosed vertical dimension of occlusion The judgment that the mandible is overclosed is a difficult decision to make. This diagnosis is typically made in situations where there are multiple missing or severely worn teeth and the dimension between the alveolar ridges is inadequate to allow a prosthesis to be correctly made. The clinical examination criteria for detecting an abnormal vertical dimension involve 2 processes. In the dentate patient, dentists will fabricate diagnostic casts of the teeth and visually judge whether the space is inadequate to fabricate the needed restorations. In the edentulous patient, a trial denture or wax base rim is inserted and the patient is asked to put the 84
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jaw in a clinical rest position. Once this is achieved, the patient is asked to speak so that the adequacy of the “interocclusal rest space” can be assessed (typically 1 to 3 mm of space is considered adequate).
DOCUMENTATION VERSUS DIAGNOSIS If the claim is made that an instrument gives diagnostic data of value for disease detection and clinical decision making, the claim must be assessed. Such claims are typically evaluated through a diagnostic matrix analysis (testing the new device against a gold standard).7 A serious difficulty associated with conducting such a study is the lack of acceptable, proven, and widely accepted diagnostic criteria for the 2 conditions being reviewed in this article. If an instrument is not proposed as a “stand alone” diagnostic tool, but only a documentation tool, the criteria for acceptance is different. In the latter situation, the decision to use a documentary device is determined based on the accuracy and the cost-versus-benefit of the proposed method. Cost is a major concern, because it is possible to document every patient with a near infinite variety of relatively harmless documentary procedures (photographs, study models, video recordings, diet history, blood tests, strength, and sensory testing). Most would agree that collecting useless documentation is too costly. For this season, all documentation devices also need a cost-benefit analysis to be sure that they have enough value to warrant their routine use. If a new documentary instrument is proposed as a therapeutic monitoring tool, this new device must have a proven accuracy or else it is not only of low utility, it is also of no value.
OCCLUSAL CONTACT DETECTION INSTRUMENTS The reason that a clinician is interested in a patient’s occlusal contact pattern is so that he or she can ensure any new restoration being fabricated is in harmonious contact relative to the opposing teeth. Sometimes, however, the patient has tooth pain and one of the possible reasons for tooth pain is excessive occlusal loading. In this context, it is necessary to evaluate the tooth for the presence of a supracontact. This evaluation typically involves a clinical occlusal examination of the teeth for wear facets, mobility, fremitus, and the use of Mylar, occlusal ribbon, or occlusal wax. Several additional devices have been proposed to detect putative abnormal occlusal contact patterns. The claim that these instruments can provide the dentist information above and beyond what a clinical examination provides about the location, timing, direction, and magnitude of the occlusal contacts.
Occlusal sonography The first studies to detect tooth contact by the sounds generated during mouth closure began to VOLUME 83 NUMBER 1
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appear in the literature in the late 1960s.8 One commercial device was produced in Japan in the mid 1980s called “Dental Sound Checker” (Yoshida Dental Trade Distributing Co Ltd, Tokyo, Japan). The device, based on the principles put forth by Watt,8 was developed to evaluate occlusal contact sound patterns during closure in an attempt to detect occlusal disturbance. Kifune et al9 measured the duration of the occlusal sound in a single subject before and after occlusal adjustment and reported a clear decrease in the duration of the occlusal sound with adjustment. On the basis of this single subject, they suggested that this device has high efficacy for evaluation and tracking the improvement of occlusal conditions. However, the nature of occlusal sound varies depending on the way subjects close their teeth. A forceful slow closure would make large amplitude, long sound, and a soft rapid closure would make short, low amplitude sound. Therefore, recorded documents of occlusal sound are of limited value unless patients were well trained to close with constant force and speed. Good reproducibility studies have not been reported with this instrument. At best, these devices might help dentists to evaluate the occlusal fit of a newly fabricated single crown or loading on a new implant abutment. Research showing that this method is better than occlusal paper or a stethoscope held against the Mylar process is needed.
were applied to each sensor, and data were collected through 5 repetitive uses. Harvey et al12 found substantial variability in the results with unpredictable variations scattered among the uses, levels of force and articulator immediate side sift treatments. Hsu et al13 also reported on the sensitivity and reliability of the T-Scan system for occlusal analysis. They concluded that the sensors did not have the same sensitivity throughout their surface and the T-Scan always recorded fewer occlusal contacts than were actually present as checked by occlusal foils. Furthermore, Mizui et al14 measured the timing and force of occlusal contacts in both 60 normal subjects and 5 patients with an unspecified craniomandibular disorders (CMD) using the T-Scan system. They reported that in the normal subjects the timing and force of occlusal contacts were symmetrical and the center of effort was located in the first molar region. For patients with CMD, timing and force of occlusal contacts were asymmetric and the center of effort was not always located in the first molar region, as determined with the T-Scan system. Unfortunately, this report did not prove the clinical use of this system as a diagnostic method. Flaws of the study include, a small sample size, no blinding of the examiners, and no clear definition of who the patients with CMD were. In addition, these authors did not perform or report statistical analyses of their data.
Occlusal contact sensors
Pressure sensitive film
In 1987, Maness et al10 reported the development of the prototype of a new computerized occlusal analysis device (T-Scan system, Sentek Corp, Boston, Mass.). The T-Scan system was designed to analyze and display occlusal contact information gathered by the pressure sensitive film. With this system, it was possible to detect the distribution of tooth contacts and the relative timing of them. Moini and Neff11 conducted a study on the reproducibility of detecting occlusal contacts using silk marking paper versus T-Scan system and reported the pressure sensitive film method was not as accurate as the silk ribbon; however, there were several flaws of the study. Moini and Neff11 selected an artificial occlusal contact pattern, created by placing occlusal overlays on 3 teeth, as the outcome variable rather than study natural contact patterns. Their study did not answer the question, “Can the pressure sensitive film reliably identify natural multiple contacts on posterior teeth?” The results presented indicated that if only 3 teeth are in contact, then the pressure sensitive film device is reasonably accurate. Harvey et al12 conducted a preliminary test of the reproducibility of the same computerized occlusal analysis system by comparing 2 sets of occlusal data generated by an articulator that was set with 0 and 0.2 mm immediate side shifts. Randomly selected sensors were used in each of the 2 settings, 3 levels of load
A newer but essentially similar device has been introduced (Dental Prescale, Fuji Film, Tokyo, Japan). This device also records the location and force of contacts with the force sensitive film. Hattori et al16 evaluated the reliability of this device for occlusal force measurement, both on a subject and on casts. They reported the linear relationship between the applied and measured loads. They calculated occlusal force during maximum voluntary clenching of the subject was 8 to 60 N at premolars and 63 to 330 N at molars. Araki et al17 used this device in 5 patients with TMD and evaluated the distribution and area of the tooth contacts and the total occlusal force. They reported that they could detect a poor bilateral balance of the occlusal force in their patients. To date, no studies have demonstrated the reliability of this system. The primary limitation of the contact sensor and the pressure sensitive film device is that the recording medium is far too thick and results in heavier contacts on the posterior teeth than anterior teeth. Further, this sensor thickness disturbs the persons finding attempts to close into the intercuspal position. This is because a study on interocclusal thickness discrimination has shown that aluminum foil as thin as 20 µm can give bite-disturbing proprioceptive information to a subject.15 These devices might have documentary value of the occlusal contact patterns on the teeth; artifacts will like-
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Table I. A comparison of different occlusal detection systems
T-Scan system Dental Prescale Articulating paper
Thickness of sensor paper
Location
Force
Timing
60 µm 98 µm ~20 µm
+ + +
+ + –
+ – –
Available information
ly be a problem until a thinner recording paper is developed (Table I). The recording medium needs to be no more than 20 µm thick to avoid artifacts. Until such time that occlusal contact detection devices have been shown to be valid when recording multiple contacts on natural teeth and a cost-benefit analysis has been conducted, these instruments will have limited utility. Diagnostic matrix analysis research will also be needed to show if these devices have any diagnostic validity.
ABNORMAL VERTICAL DIMENSION DETECTION INSTRUMENTS The vertical dimension of occlusion usually becomes an issue when a dental clinician wants to consider changing it (typically by increasing it) to improve the quality of the restorative and prosthetic care they wish to deliver. As mentioned previously, evaluating a patient for evidence of an overclosed vertical dimension of occlusion involves a visual assessment of the alveolar ridge space and the length of the clinical crowns of the remaining teeth. Unfortunately, the reproducibility of this clinical judgment process has not been rigorously assessed. Recently, electronic instruments have been proposed to detect putative and abnormal vertical dimension of occlusion. The issues discussed later review what is known about the ability of these devices to measure this anatomic feature above and beyond what a clinical examination provides about intrajaw dimension.
Jaw tracking devices The American Dental Association has approved 2 jaw tracking devices (jaw tracking system, model no. K6-I/CMS, Myotronics Noromed Inc, Seattle, Wash.; mandibular recording device, model no. BioEGN, BioResearch Inc, Milwaukee, Wis.) as “aids in the diagnosis of temporomandibular disorders.” Regarding the reproducibility of an electronic jaw tracking device, from the published literature it can be stated that these 2 devices have good reproducibility under rigorously controlled recording conditions. Moreover, the accuracy of these recordings is very good as long as the range of jaw motion being measured is under 40 mm of opening.18-22 Of course, additional in vivo test—retest research is needed and would be important to conduct 86
especially as newer models become available and under real world clinical environment conditions. In addition to measuring pathways of motion, jaw-tracking devices have been used for measurement of the distance between the positions of maximum intercuspidation and jaw rest position. This distance is called the interocclusal rest space and there is a claim by one manufacturer that when this space is found to be overly large, this is evidence of an abnormal vertical dimension of occlusion.23 As with other jaw movement patterns, no diagnostic matrix analysis research has yet been conducted evaluating jaw-tracking data for the specific purpose of diagnosing occlusal overclosure. The logical subjects for this research would be patients who have lost vertical dimension and asymptomatic, normal dentition patients. Because no clear diagnostic criteria exist, these 2 groups would have to be selected on the basis of designation by a panel of experts.
Jaw muscle stimulation devices One of the manufacturers of a jaw-tracking instrument recommends that it be used in conjunction with a muscle stimulator to assist the clinician with relaxing the jaw (Myomonitor, Myotronics-Noromed Inc, Seattle, Wash.).23 Of course, electronic muscle stimulation devices have been used in physical medicine to relax, massage, and increase blood flow in a muscle for many years. However, when muscle stimulators are used in the manner suggested previously, they are reputed to: (1) find the neuromuscular determined position for the jaw and (2) achieve a relaxed jaw position.24-27 Many scientists are skeptical that an instrument can set up a pattern of muscle contraction, which duplicates the brain function and achieves a “neuromuscular determined position” for the jaw. Moreover, the reproducibility of the jaw positions produced by stimulator has not undergone test-retest evaluation on a large group of patients. Nevertheless, supporters claim the jaw relationship achieved with this type of muscle stimulation is “delivered bilaterally via neural pathways to all masticatory muscles innervated by the mandibular division of the trigeminal nerve.” They also state the device is useful for discovering “a more accurate rest position of the mandible, than the assumed or accommodative pseudo-rest position.”27 In a study by Azarbal,28 a commercially available muscle stimulator (Myo-Monitor, Myotronics-Noromed Inc) was used to induce a jaw position that was recorded and compared with the patient’s centric occlusion and centric relation positions. They studied 20 healthy dental students who showed no symptoms of pain or dysfunction of the jaw system. The findings indicated that the stimulation-induced position was always anterior to both centric relation and centric occlusion, by an average of 3.8 and 1.8 mm, respectively. Azarbal28 also showed that in 18 of 20 subjects, the stimulation-induced position VOLUME 83 NUMBER 1
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also was to the right or to the left side of a protrusive midline. The final conclusion of this article was that reconstruction or adjustment of the occlusion into this position might be problematic. The stated rationale for how a muscle stimulator can achieve a position of the mandible that is an optimum neuromuscular relationship is as follows: “the Myomonitor instrument stimulates all of the jaw-closing muscles not only simultaneously but also in physiologic manner.”24 Advocates of these muscle stimulators imply that the device will elicit a reflex response that causes all of the jaw-closer muscles to contract simultaneously, and result in a reproducible physiologic jaw position that is independent of the patient’s voluntary activity.24-27 De Boever and McCall29 and Bessette and Quinlivan30 have shown that jaw-closing reflexes are not elicited, when stimulation is delivered by surface electrodes over the masseter muscles. Further, Dao et al31 recorded the masseteric electromyographic activity of single motor units with fine wire electrodes during muscle stimulation and analyzed the latency (the time between the onset of the stimulation and the beginning of the EMG response). Their data also strongly suggested that the stimulus does not cause reflex activation of the jaw closing muscles. They concluded that the reason the stimulation-induced position is anterior to centric occlusion was that the electrical pulse acted locally within the masseter muscle. This muscle is oriented to produce a forward trajectory of closure (especially when the temporalis is not substantially activated). In achieving a stimulator-induced “relaxed jaw position”, advocates of the muscle stimulator regard postural muscle activity with a level greater than 10 µV (as recorded from the skin surface of the muscle) as hyperactivity. They further postulate that this hyperactivity is induced by abnormal vertical dimension (specifically mandibular overclosure). The effect of this relaxation is that postural tone, which normally keeps the mandible partially elevated, is lost and the mandible jaw assumes a wider open position. The muscle stimulator advocates assume this wider open jaw position is the desired normal position for the mandible. The issue of jaw position means induced by a muscle stimulator was studied by Manns et al32 (Table II), who evaluated the position at which jaw closer muscles would achieve the lowest activity. They showed the superficial masseter was least active at 10 mm open, the anterior temporalis was least active at 12.5 mm, and the posterior temporalis was least active at 15.5 mm vertical separation. They concluded that it is not possible to establish a single standard vertical dimension at which all muscles are minimally active. This conclusion was made because, if the main closers are fully relaxed there is more space between the teeth than the traditionally assumed 1 to 3 mm of vertical separation that JANUARY 2000
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Table II. Vertical separation of the interincisal distance when muscle activity is lowest
Manns et al32 (8 normal subjects) Masseter Anterior temporal Posterior temporal Rugh and Drago34 (10 normal subjects) Masseter site (transfacial) 5 men 5 women
Point of minimal EMG activity
Clinical rest position
10 mm 12.5 mm 15.5 mm
No data No data No data
10.4 mm 6.8 mm
2.1 mm 2.1 mm
is described in the prosthodontic literature.33 Rugh and Drago34 also measured the transfacial jaw muscle activity using surface electrodes. Their study involved using biofeedback to find the degree of occlusal separation where the subjects were most relaxed (Table II). They used a low noise EMG preamplifier and integrator and studied 10 subjects with natural teeth and no symptoms of TMD. Each subject was given EMG biofeedback training to relax jaw and facial muscles. Subjects relaxed their jaw at different vertical dimensions ranging from 1 to 16 mm in 1-mm steps. A specific point of vertical separation where muscle activity was minimal was found for each subject. They discovered that this position was 5 to 13 mm open and varied greatly with postured changes of the head and neck. This most relaxed position of the mandible, found by Manns et al32 and Rugh and Drago,34 is clearly not the same as “clinical rest position” that prosthodontists use when assessing the freeway space. The prosthodontic 1 to 3 mm open rest position undoubtedly is one that is a learned postural position in which the jaw elevators have a certain level of muscle tone. Nevertheless the recommendations made by the muscle stimulator manufacturers is that, if the poststimulation space is more than 1 to 3 mm, this is an indication of abnormal vertical dimension. The manufacturer suggests that the muscle stimulator be combined with the jaw-tracking device to show how the jaw is clearly out of position and the vertical dimension of occlusion is incorrect and needs alteration. These claims appear to be unsupported by the evidence, since most of the normal subjects would be diagnosed as abnormal.
Jaw muscle electromyography (EMG) devices Another instrument used to document an abnormal occlusal vertical dimension is a multichannel surface EMG recording apparatus. The American Dental Association has approved 2 EMG recording devices (Electromyograph model no. K6-1/EMG, MyotronicsNoromed Inc; and electromyograph model no. 87
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BioEMG, BioResearch Inc) as “aids in the diagnosis of temporomandibular disorders”.35 This approval was granted largely because surface EMG is a well-known and reasonably reproducible measurement method used in muscle relaxation training (biofeedback). Second, jaw muscle assessment (through palpation) is a standard aspect of a temporomandibular function examination and because an EMG of the jaw muscles can assess muscle spasm, it is also considered to be an aid in the diagnostic process. In the specific case in which a patient’s vertical dimension of occlusion is being assessed, the EMG device is typically used in conjunction with the previously described jaw-tracking devices and the muscle stimulator to identify a more relaxed position after muscle stimulation therapy. That EMG can accurately document the amount of postural muscle tone in the masseter and temporalis muscles is not an issue of great contention. The relevant question is, “what does the data mean?” Are the EMG and jaw-tracking data simply documentation of transient effects produced by the muscle stimulator or are the data representative of true abnormality? The latter point of view is one that has questionable supporting scientific data in the literature. Cooper and Rubuzzi36 demonstrated the problems with the method. In their study, the diagnostic value of a jaw-tracking EMG system in combination with an electrical jaw muscle stimulation method to determine the putative correct jaw position and vertical relationship was evaluated on a group of asymptomatic subjects. From the resulting data, the authors concluded that the jaw-tracking-EMG-muscle stimulator method identified abnormalities in 21 of the 26 asymptomatic subjects. These subjects were not yet aware of the disease, according to their abnormality criteria. A major study design flaw includes no TMD subjects tested as a comparison group. Such a group might have helped to define an appropriate cutoff point for the diagnostic categories used in the study. Moreover, no repeated measures were made on the same subject to assess reliability of the method and no calibration data were provided. The examiner was never blind to subject status, a situation that lends itself to great systematic bias. No inferential statistics were used to assess the differences in EMG level data, and descriptive statistics did not include standard deviations. Because no evidence exists that vertical dimension is more than a restorative inconvenience, the use of the previously described jaw-tracking-EMG-muscle stimulation system must be questioned. The statements by Widmer et al37 that there were no papers in the literature, which calculated the sensitivity and specificity of these instruments, is still true today. This conclusion was upheld in the 3 subsequent reviews by Mohl et al.38-40 Until well-controlled clinical trials, with appropriately defined control groups, demonstrate that these or 88
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similar devices have high sensitivity and specificity, they should not be used, except as documentation devices. It is incumbent on all clinicians who use them to be cautious and to recognize their limitations. Finally, to date, no cost-benefit analysis research has been conducted on the value of a standard clinical examination used alone and in combination with jaw-tracking and EMG devices to diagnose patients’ jaw function problems or occlusal vertical dimension abnormalities. This lack of data leaves the question of utility of these instruments in doubt.
SUMMARY There is a need for additional research on all diagnostic procedures used in dentistry. This research should be directed at identifying the test-retest precision of all methods and instruments. A cost-benefit analysis assessment of all ancillary documentary procedures and devices is needed, especially for those instruments or methods that have a substantial cost associated with their use. When advocates of an instrument put forth a claim that a specific device has diagnostic potential, a rigorous scientific protocol must be followed that tests these claims. The only current diagnostic criteria (gold standard) for occlusal disorders is a global clinical examination–thorough history performed by an expert examiner. For the time being, none of the instruments reviewed in this report (occlusal contact recording methods, surface EMG monitoring of the jaw closers, jaw-tracking devices) can be said to be more than ancillary documentation devices. They have no proven reliability or diagnostic validity and their use is not proven by the research. REFERENCES 1. Academy of Prosthodontics. The Glossary of Prosthodontic Terms. J Prosthet Dent 1999;81:48-106. 2. Gazit E, Fitzig S, Lieberman MA. Reproducibility of occlusal marking techniques. J Prosthet Dent 1986;55:505-9. 3. Durbin DS, Sadowsky C. Changes in tooth contacts following orthodontic treatment. Am J Orthod Dentofacial Orthop 1986;90:375-82. 4. Korioth TW. Number and location of occlusal contacts in intercuspal position. J Prosthet Dent 1990;64:206-10. 5. Anderson GC, Schulte JK, Aeppli DM. Reliability of the evaluation of occlusal contacts in the intercuspal position. J Prosthet Dent 1993; 70:320-3. 6. Halperin GC, Halperin AR, Norling BK. Thickness, strength, and plastic deformation of occlusal registration strips. J Prosthet Dent 1982;48:5758. 7. Clark GT, Tsukiyama Y, Baba K, Simmons M. The validity and utility of disease detection methods and of occlusal therapy for temporomandibular disorders. Oral Surg Oral Med Oral Pathol 1997;83:101-6. 8. Watt DM. Recording the sounds of tooth contact: a diagnostic technique for evaluation of occlusal disturbances. Int Dent J 1969;19:221-38. 9. Kifune R, Honma S, Hara K. The development of a new occlusal sound checker. J Jpn Assoc of Periodontology 1985;27:482-91. 10. Maness WL, Benjamin M, Podoloff R, Bobick A, Golden RF. Computerized occlusal analysis: a new technology. Quintessence Int 1987;18:28792. 11. Reza Moini M, Neff PA. Reproducibility of occlusal contacts utilizing a computerized instrument. Quintessence Int 1991;22:357-60. 12. Harvey WL, Osborne JW, Hatch RA. A preliminary test of the replicabili-
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30. Bessette RW, Quinlivan JT. Electromyographic evaluation for the MyoMonitor. J Prosthet Dent 1973;30:19-24. 31. Dao TTT, Feine JS, Lund JP. Can electrical stimulation be used to establish a physiologic occlusal position?. J Prosthet Dent 1988;60:509-14. 32. Manns A, Miralles R, Guerrero F. The changes in electrical activity of the postural muscles of the mandible upon varying the vertical dimension. J Prosthet Dent 1981;45:438-45. 33. Zarb GA, Bolender CL, Carlsson GE. Boucher’s Prosthodontic Treatment for edentulous patients. 11th ed. St Louis: CV Mosby: 1997. p. 212-3. 34. Rugh JD, Drago CJ. Vertical dimension: a study of clinical rest position and jaw muscle activity. J Prosthet Dent 1981;45:670-5. 35. ADA council on scientific affairs. Report on acceptance of TMD devices. J Am Dent Assoc 1996;127:1615-6. 36. Cooper BC, Rabuzzi DD. Myofacial pain dysfunction syndrome: a clinical study of asymptomatic subjects. Laryngoscope 1984;94:68-75. 37. Widmer CG, Lund JP, Feine JS. Evaluation of diagnostic tests for TMD. J Calif Dent Assoc 1990;18:53-60. 38. Mohl ND, McCall WD Jr, Lund JP, Plesh O. Devices for the diagnosis and treatment of temporomandibular disorders. Part I: introduction, scientific evidence, and jaw tracking. J Prosthet Dent 1990;63:198-201. 39. Mohl ND, Lund JP, Widmer CG, McCall WD Jr. Devices for the diagnosis and treatment of temporomandibular disorders. Part II: electromyography and sonography. J Prosthet Dent 1990;63:332-6. 40. Mohl ND, Ohrbach RK, Crow HC, Gross AJ. Devices for the diagnosis and treatment of temporomandibular disorders. Part III: thermography, ultrasound, electrical stimulation, and electromyographic biofeedback. J Prosthet Dent 1990;63:472-7. Reprint requests to: DR GLENN T. CLARK SECTION OF OROFACIAL PAIN AND ORAL MEDICINE UCLA SCHOOL OF DENTISTRY BOX 951668, RM 43-009 CHS 10833 LE CONTE AVE LOS ANGELES, CA 90095-1668 FAX: (310) 206-5539 E-MAIL: [email protected] Copyright © 2000 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2000/$12.00 + 0. 10/1/103749
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Purpose. This article reviews the reliability, validity, and utility of instruments that claim to detect occlusal interferences and abnormal vertical dimension of occlusion. Material and methods. Data, opinions, and technical information from 37 published articles were reviewed. Evidence for method reliability, validity, and utility was assessed. Results. Although occlusal contact detection devices can document the occlusal contact patterns on teeth, the basic in vivo testing of their reproducibility and validity has not been performed. Moreover, while EMG and jaw tracking systems can indeed measure jaw muscle activation and jaw position, no cost-benefit analysis of these devices has yet been conducted. One manufacturer suggests that these instruments be used in conjunction with an electrical muscle stimulation device to find a new resting jaw position that is more open vertically. This new, more open position has been inappropriately labeled as evidence of vertical dimension of occlusion overclosure. Conclusion. None of the instruments reviewed can be said to be more than ancillary documentation devices and they have been inadequately tested for reliability and validity. Moreover, because scientifically acceptable disease definitions are not available for these 2 conditions, the issue of over-diagnosing becomes a substantial concern. (J Prosthet Dent 2000;83:83-9.)
CLINICAL IMPLICATIONS While the instruments reviewed in this article may have value as documentary devices, their practical use has not been established.
T
he purpose of this article was to discuss the reliability, validity, and practical utility (cost vs benefit) of various instruments that claim to assess occlusal characteristics. Although there are multiple recognized occlusal disorders (traumatic occlusal interferences, phantom bites, attrition, unstable intercuspal position, and severe morphologic malocclusions), this review addresses only 2 conditions: (1) instruments that claim to assess occlusal interferences and (2) overclosure of the vertical dimension of occlusion. These 2 conditions were selected not because they are the most important clinical problems, but because the instruments available in the commercial marketplace have largely focused on measurement of these 2 clinical parameters.
aAssistant
Professor, The First Department of Prosthodontics, Faculty of Dentistry, Tokyo Medical and Dental University. bAssistant Professor, Department of Prosthodontics II, Faculty of Dentistry, Kyushu University. cProfessor and Chair, Section of Orofacial Pain and Oral Medicine, UCLA School of Dentistry. JANUARY 2000
DEFINITION OF THE TWO OCCLUSAL DISORDERS Occlusal interferences Traditional concepts of traumatic occlusal interferences involve a single anterior or posterior tooth, which is in “supracontact” during maximum intercuspidation or on excursive jaw movement. These 2 situations are collectively called “occlusal interferences.”1 Detection of “occlusal interferences” and identification of other physical signs of occlusal trauma such as a wear facets, tooth pain, tooth mobility, or widened periodontal ligament spaces, are most commonly performed through a clinical and sometimes radiographic examination. This examination is typically performed by a dentist using: (1) a visual assessment of the gross form of the occlusion; (2) measurement of certain occlusal features with a millimeter ruler; (3) testing for occlusal contacts with Mylar (ET Dupont, Wilmington, Del.), articulating ribbon/ paper, or occlusal wax; (4) testing teeth for mobility and for fremitus; and (5) examining tooth contact patterns visually in various voluntary and manipulated jaw posiTHE JOURNAL OF PROSTHETIC DENTISTRY 83
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tions. The combination of all the subjective patientbased information (gathered during the history) plus the examination-based findings is presumed to allow the expert clinician to come to a high probability determination of the presence or absence of a specific occlusal disturbance or disorder. Unfortunately, the clinical occlusal examination itself, and each specific method within this examination, has undergone only limited assessment in terms of reliability and validity. Several investigators have attempted to look at the reproducibility of some of the clinical occlusal examination methods for accuracy. Gazit et al2 looked at the reproducibility of 2 occlusal marking techniques (photoocclusion technique and color-marking technique) and found that neither technique was highly reproducible. Durbin and Sadowsky3 described a silicone impression material method for examining occlusal contact patterns before and after orthodontic treatment. Although this method has good accuracy, it is impractical. However, it might serve as a gold standard against which other, easier-to-use clinical methods could be tested. Korioth4 reported on the number and location of occlusal contacts in intercuspal position using alginate impression material. Anderson et al5 reported on the reliability of dentists’ ability to evaluate occlusal contacts in the intercuspal position. They compared an articulating paper method against a Mylar paper method and found the latter to be more reliable. In a study of the thickness, strength, and plastic deformation of occlusal registration strips used to detect occlusal contact patterns, Halpern et al6 found that some recording methods (those with a stiff marking media) induced artifacts in the contact detection process. These investigations are a good beginning if a better understanding of the weaknesses and strengths of the entire clinical occlusal examination are ever to be achieved. The lack of research in this area is largely due to occlusal disorders themselves, which have never been formally defined using repeatable criteria. Nevertheless, the practicing clinician’s “gold standard” for diagnosing occlusal disorders is a combination of patient selfreport of problems and the occlusal examination.
Overclosed vertical dimension of occlusion The judgment that the mandible is overclosed is a difficult decision to make. This diagnosis is typically made in situations where there are multiple missing or severely worn teeth and the dimension between the alveolar ridges is inadequate to allow a prosthesis to be correctly made. The clinical examination criteria for detecting an abnormal vertical dimension involve 2 processes. In the dentate patient, dentists will fabricate diagnostic casts of the teeth and visually judge whether the space is inadequate to fabricate the needed restorations. In the edentulous patient, a trial denture or wax base rim is inserted and the patient is asked to put the 84
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jaw in a clinical rest position. Once this is achieved, the patient is asked to speak so that the adequacy of the “interocclusal rest space” can be assessed (typically 1 to 3 mm of space is considered adequate).
DOCUMENTATION VERSUS DIAGNOSIS If the claim is made that an instrument gives diagnostic data of value for disease detection and clinical decision making, the claim must be assessed. Such claims are typically evaluated through a diagnostic matrix analysis (testing the new device against a gold standard).7 A serious difficulty associated with conducting such a study is the lack of acceptable, proven, and widely accepted diagnostic criteria for the 2 conditions being reviewed in this article. If an instrument is not proposed as a “stand alone” diagnostic tool, but only a documentation tool, the criteria for acceptance is different. In the latter situation, the decision to use a documentary device is determined based on the accuracy and the cost-versus-benefit of the proposed method. Cost is a major concern, because it is possible to document every patient with a near infinite variety of relatively harmless documentary procedures (photographs, study models, video recordings, diet history, blood tests, strength, and sensory testing). Most would agree that collecting useless documentation is too costly. For this season, all documentation devices also need a cost-benefit analysis to be sure that they have enough value to warrant their routine use. If a new documentary instrument is proposed as a therapeutic monitoring tool, this new device must have a proven accuracy or else it is not only of low utility, it is also of no value.
OCCLUSAL CONTACT DETECTION INSTRUMENTS The reason that a clinician is interested in a patient’s occlusal contact pattern is so that he or she can ensure any new restoration being fabricated is in harmonious contact relative to the opposing teeth. Sometimes, however, the patient has tooth pain and one of the possible reasons for tooth pain is excessive occlusal loading. In this context, it is necessary to evaluate the tooth for the presence of a supracontact. This evaluation typically involves a clinical occlusal examination of the teeth for wear facets, mobility, fremitus, and the use of Mylar, occlusal ribbon, or occlusal wax. Several additional devices have been proposed to detect putative abnormal occlusal contact patterns. The claim that these instruments can provide the dentist information above and beyond what a clinical examination provides about the location, timing, direction, and magnitude of the occlusal contacts.
Occlusal sonography The first studies to detect tooth contact by the sounds generated during mouth closure began to VOLUME 83 NUMBER 1
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appear in the literature in the late 1960s.8 One commercial device was produced in Japan in the mid 1980s called “Dental Sound Checker” (Yoshida Dental Trade Distributing Co Ltd, Tokyo, Japan). The device, based on the principles put forth by Watt,8 was developed to evaluate occlusal contact sound patterns during closure in an attempt to detect occlusal disturbance. Kifune et al9 measured the duration of the occlusal sound in a single subject before and after occlusal adjustment and reported a clear decrease in the duration of the occlusal sound with adjustment. On the basis of this single subject, they suggested that this device has high efficacy for evaluation and tracking the improvement of occlusal conditions. However, the nature of occlusal sound varies depending on the way subjects close their teeth. A forceful slow closure would make large amplitude, long sound, and a soft rapid closure would make short, low amplitude sound. Therefore, recorded documents of occlusal sound are of limited value unless patients were well trained to close with constant force and speed. Good reproducibility studies have not been reported with this instrument. At best, these devices might help dentists to evaluate the occlusal fit of a newly fabricated single crown or loading on a new implant abutment. Research showing that this method is better than occlusal paper or a stethoscope held against the Mylar process is needed.
were applied to each sensor, and data were collected through 5 repetitive uses. Harvey et al12 found substantial variability in the results with unpredictable variations scattered among the uses, levels of force and articulator immediate side sift treatments. Hsu et al13 also reported on the sensitivity and reliability of the T-Scan system for occlusal analysis. They concluded that the sensors did not have the same sensitivity throughout their surface and the T-Scan always recorded fewer occlusal contacts than were actually present as checked by occlusal foils. Furthermore, Mizui et al14 measured the timing and force of occlusal contacts in both 60 normal subjects and 5 patients with an unspecified craniomandibular disorders (CMD) using the T-Scan system. They reported that in the normal subjects the timing and force of occlusal contacts were symmetrical and the center of effort was located in the first molar region. For patients with CMD, timing and force of occlusal contacts were asymmetric and the center of effort was not always located in the first molar region, as determined with the T-Scan system. Unfortunately, this report did not prove the clinical use of this system as a diagnostic method. Flaws of the study include, a small sample size, no blinding of the examiners, and no clear definition of who the patients with CMD were. In addition, these authors did not perform or report statistical analyses of their data.
Occlusal contact sensors
Pressure sensitive film
In 1987, Maness et al10 reported the development of the prototype of a new computerized occlusal analysis device (T-Scan system, Sentek Corp, Boston, Mass.). The T-Scan system was designed to analyze and display occlusal contact information gathered by the pressure sensitive film. With this system, it was possible to detect the distribution of tooth contacts and the relative timing of them. Moini and Neff11 conducted a study on the reproducibility of detecting occlusal contacts using silk marking paper versus T-Scan system and reported the pressure sensitive film method was not as accurate as the silk ribbon; however, there were several flaws of the study. Moini and Neff11 selected an artificial occlusal contact pattern, created by placing occlusal overlays on 3 teeth, as the outcome variable rather than study natural contact patterns. Their study did not answer the question, “Can the pressure sensitive film reliably identify natural multiple contacts on posterior teeth?” The results presented indicated that if only 3 teeth are in contact, then the pressure sensitive film device is reasonably accurate. Harvey et al12 conducted a preliminary test of the reproducibility of the same computerized occlusal analysis system by comparing 2 sets of occlusal data generated by an articulator that was set with 0 and 0.2 mm immediate side shifts. Randomly selected sensors were used in each of the 2 settings, 3 levels of load
A newer but essentially similar device has been introduced (Dental Prescale, Fuji Film, Tokyo, Japan). This device also records the location and force of contacts with the force sensitive film. Hattori et al16 evaluated the reliability of this device for occlusal force measurement, both on a subject and on casts. They reported the linear relationship between the applied and measured loads. They calculated occlusal force during maximum voluntary clenching of the subject was 8 to 60 N at premolars and 63 to 330 N at molars. Araki et al17 used this device in 5 patients with TMD and evaluated the distribution and area of the tooth contacts and the total occlusal force. They reported that they could detect a poor bilateral balance of the occlusal force in their patients. To date, no studies have demonstrated the reliability of this system. The primary limitation of the contact sensor and the pressure sensitive film device is that the recording medium is far too thick and results in heavier contacts on the posterior teeth than anterior teeth. Further, this sensor thickness disturbs the persons finding attempts to close into the intercuspal position. This is because a study on interocclusal thickness discrimination has shown that aluminum foil as thin as 20 µm can give bite-disturbing proprioceptive information to a subject.15 These devices might have documentary value of the occlusal contact patterns on the teeth; artifacts will like-
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Table I. A comparison of different occlusal detection systems
T-Scan system Dental Prescale Articulating paper
Thickness of sensor paper
Location
Force
Timing
60 µm 98 µm ~20 µm
+ + +
+ + –
+ – –
Available information
ly be a problem until a thinner recording paper is developed (Table I). The recording medium needs to be no more than 20 µm thick to avoid artifacts. Until such time that occlusal contact detection devices have been shown to be valid when recording multiple contacts on natural teeth and a cost-benefit analysis has been conducted, these instruments will have limited utility. Diagnostic matrix analysis research will also be needed to show if these devices have any diagnostic validity.
ABNORMAL VERTICAL DIMENSION DETECTION INSTRUMENTS The vertical dimension of occlusion usually becomes an issue when a dental clinician wants to consider changing it (typically by increasing it) to improve the quality of the restorative and prosthetic care they wish to deliver. As mentioned previously, evaluating a patient for evidence of an overclosed vertical dimension of occlusion involves a visual assessment of the alveolar ridge space and the length of the clinical crowns of the remaining teeth. Unfortunately, the reproducibility of this clinical judgment process has not been rigorously assessed. Recently, electronic instruments have been proposed to detect putative and abnormal vertical dimension of occlusion. The issues discussed later review what is known about the ability of these devices to measure this anatomic feature above and beyond what a clinical examination provides about intrajaw dimension.
Jaw tracking devices The American Dental Association has approved 2 jaw tracking devices (jaw tracking system, model no. K6-I/CMS, Myotronics Noromed Inc, Seattle, Wash.; mandibular recording device, model no. BioEGN, BioResearch Inc, Milwaukee, Wis.) as “aids in the diagnosis of temporomandibular disorders.” Regarding the reproducibility of an electronic jaw tracking device, from the published literature it can be stated that these 2 devices have good reproducibility under rigorously controlled recording conditions. Moreover, the accuracy of these recordings is very good as long as the range of jaw motion being measured is under 40 mm of opening.18-22 Of course, additional in vivo test—retest research is needed and would be important to conduct 86
especially as newer models become available and under real world clinical environment conditions. In addition to measuring pathways of motion, jaw-tracking devices have been used for measurement of the distance between the positions of maximum intercuspidation and jaw rest position. This distance is called the interocclusal rest space and there is a claim by one manufacturer that when this space is found to be overly large, this is evidence of an abnormal vertical dimension of occlusion.23 As with other jaw movement patterns, no diagnostic matrix analysis research has yet been conducted evaluating jaw-tracking data for the specific purpose of diagnosing occlusal overclosure. The logical subjects for this research would be patients who have lost vertical dimension and asymptomatic, normal dentition patients. Because no clear diagnostic criteria exist, these 2 groups would have to be selected on the basis of designation by a panel of experts.
Jaw muscle stimulation devices One of the manufacturers of a jaw-tracking instrument recommends that it be used in conjunction with a muscle stimulator to assist the clinician with relaxing the jaw (Myomonitor, Myotronics-Noromed Inc, Seattle, Wash.).23 Of course, electronic muscle stimulation devices have been used in physical medicine to relax, massage, and increase blood flow in a muscle for many years. However, when muscle stimulators are used in the manner suggested previously, they are reputed to: (1) find the neuromuscular determined position for the jaw and (2) achieve a relaxed jaw position.24-27 Many scientists are skeptical that an instrument can set up a pattern of muscle contraction, which duplicates the brain function and achieves a “neuromuscular determined position” for the jaw. Moreover, the reproducibility of the jaw positions produced by stimulator has not undergone test-retest evaluation on a large group of patients. Nevertheless, supporters claim the jaw relationship achieved with this type of muscle stimulation is “delivered bilaterally via neural pathways to all masticatory muscles innervated by the mandibular division of the trigeminal nerve.” They also state the device is useful for discovering “a more accurate rest position of the mandible, than the assumed or accommodative pseudo-rest position.”27 In a study by Azarbal,28 a commercially available muscle stimulator (Myo-Monitor, Myotronics-Noromed Inc) was used to induce a jaw position that was recorded and compared with the patient’s centric occlusion and centric relation positions. They studied 20 healthy dental students who showed no symptoms of pain or dysfunction of the jaw system. The findings indicated that the stimulation-induced position was always anterior to both centric relation and centric occlusion, by an average of 3.8 and 1.8 mm, respectively. Azarbal28 also showed that in 18 of 20 subjects, the stimulation-induced position VOLUME 83 NUMBER 1
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also was to the right or to the left side of a protrusive midline. The final conclusion of this article was that reconstruction or adjustment of the occlusion into this position might be problematic. The stated rationale for how a muscle stimulator can achieve a position of the mandible that is an optimum neuromuscular relationship is as follows: “the Myomonitor instrument stimulates all of the jaw-closing muscles not only simultaneously but also in physiologic manner.”24 Advocates of these muscle stimulators imply that the device will elicit a reflex response that causes all of the jaw-closer muscles to contract simultaneously, and result in a reproducible physiologic jaw position that is independent of the patient’s voluntary activity.24-27 De Boever and McCall29 and Bessette and Quinlivan30 have shown that jaw-closing reflexes are not elicited, when stimulation is delivered by surface electrodes over the masseter muscles. Further, Dao et al31 recorded the masseteric electromyographic activity of single motor units with fine wire electrodes during muscle stimulation and analyzed the latency (the time between the onset of the stimulation and the beginning of the EMG response). Their data also strongly suggested that the stimulus does not cause reflex activation of the jaw closing muscles. They concluded that the reason the stimulation-induced position is anterior to centric occlusion was that the electrical pulse acted locally within the masseter muscle. This muscle is oriented to produce a forward trajectory of closure (especially when the temporalis is not substantially activated). In achieving a stimulator-induced “relaxed jaw position”, advocates of the muscle stimulator regard postural muscle activity with a level greater than 10 µV (as recorded from the skin surface of the muscle) as hyperactivity. They further postulate that this hyperactivity is induced by abnormal vertical dimension (specifically mandibular overclosure). The effect of this relaxation is that postural tone, which normally keeps the mandible partially elevated, is lost and the mandible jaw assumes a wider open position. The muscle stimulator advocates assume this wider open jaw position is the desired normal position for the mandible. The issue of jaw position means induced by a muscle stimulator was studied by Manns et al32 (Table II), who evaluated the position at which jaw closer muscles would achieve the lowest activity. They showed the superficial masseter was least active at 10 mm open, the anterior temporalis was least active at 12.5 mm, and the posterior temporalis was least active at 15.5 mm vertical separation. They concluded that it is not possible to establish a single standard vertical dimension at which all muscles are minimally active. This conclusion was made because, if the main closers are fully relaxed there is more space between the teeth than the traditionally assumed 1 to 3 mm of vertical separation that JANUARY 2000
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Table II. Vertical separation of the interincisal distance when muscle activity is lowest
Manns et al32 (8 normal subjects) Masseter Anterior temporal Posterior temporal Rugh and Drago34 (10 normal subjects) Masseter site (transfacial) 5 men 5 women
Point of minimal EMG activity
Clinical rest position
10 mm 12.5 mm 15.5 mm
No data No data No data
10.4 mm 6.8 mm
2.1 mm 2.1 mm
is described in the prosthodontic literature.33 Rugh and Drago34 also measured the transfacial jaw muscle activity using surface electrodes. Their study involved using biofeedback to find the degree of occlusal separation where the subjects were most relaxed (Table II). They used a low noise EMG preamplifier and integrator and studied 10 subjects with natural teeth and no symptoms of TMD. Each subject was given EMG biofeedback training to relax jaw and facial muscles. Subjects relaxed their jaw at different vertical dimensions ranging from 1 to 16 mm in 1-mm steps. A specific point of vertical separation where muscle activity was minimal was found for each subject. They discovered that this position was 5 to 13 mm open and varied greatly with postured changes of the head and neck. This most relaxed position of the mandible, found by Manns et al32 and Rugh and Drago,34 is clearly not the same as “clinical rest position” that prosthodontists use when assessing the freeway space. The prosthodontic 1 to 3 mm open rest position undoubtedly is one that is a learned postural position in which the jaw elevators have a certain level of muscle tone. Nevertheless the recommendations made by the muscle stimulator manufacturers is that, if the poststimulation space is more than 1 to 3 mm, this is an indication of abnormal vertical dimension. The manufacturer suggests that the muscle stimulator be combined with the jaw-tracking device to show how the jaw is clearly out of position and the vertical dimension of occlusion is incorrect and needs alteration. These claims appear to be unsupported by the evidence, since most of the normal subjects would be diagnosed as abnormal.
Jaw muscle electromyography (EMG) devices Another instrument used to document an abnormal occlusal vertical dimension is a multichannel surface EMG recording apparatus. The American Dental Association has approved 2 EMG recording devices (Electromyograph model no. K6-1/EMG, MyotronicsNoromed Inc; and electromyograph model no. 87
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BioEMG, BioResearch Inc) as “aids in the diagnosis of temporomandibular disorders”.35 This approval was granted largely because surface EMG is a well-known and reasonably reproducible measurement method used in muscle relaxation training (biofeedback). Second, jaw muscle assessment (through palpation) is a standard aspect of a temporomandibular function examination and because an EMG of the jaw muscles can assess muscle spasm, it is also considered to be an aid in the diagnostic process. In the specific case in which a patient’s vertical dimension of occlusion is being assessed, the EMG device is typically used in conjunction with the previously described jaw-tracking devices and the muscle stimulator to identify a more relaxed position after muscle stimulation therapy. That EMG can accurately document the amount of postural muscle tone in the masseter and temporalis muscles is not an issue of great contention. The relevant question is, “what does the data mean?” Are the EMG and jaw-tracking data simply documentation of transient effects produced by the muscle stimulator or are the data representative of true abnormality? The latter point of view is one that has questionable supporting scientific data in the literature. Cooper and Rubuzzi36 demonstrated the problems with the method. In their study, the diagnostic value of a jaw-tracking EMG system in combination with an electrical jaw muscle stimulation method to determine the putative correct jaw position and vertical relationship was evaluated on a group of asymptomatic subjects. From the resulting data, the authors concluded that the jaw-tracking-EMG-muscle stimulator method identified abnormalities in 21 of the 26 asymptomatic subjects. These subjects were not yet aware of the disease, according to their abnormality criteria. A major study design flaw includes no TMD subjects tested as a comparison group. Such a group might have helped to define an appropriate cutoff point for the diagnostic categories used in the study. Moreover, no repeated measures were made on the same subject to assess reliability of the method and no calibration data were provided. The examiner was never blind to subject status, a situation that lends itself to great systematic bias. No inferential statistics were used to assess the differences in EMG level data, and descriptive statistics did not include standard deviations. Because no evidence exists that vertical dimension is more than a restorative inconvenience, the use of the previously described jaw-tracking-EMG-muscle stimulation system must be questioned. The statements by Widmer et al37 that there were no papers in the literature, which calculated the sensitivity and specificity of these instruments, is still true today. This conclusion was upheld in the 3 subsequent reviews by Mohl et al.38-40 Until well-controlled clinical trials, with appropriately defined control groups, demonstrate that these or 88
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similar devices have high sensitivity and specificity, they should not be used, except as documentation devices. It is incumbent on all clinicians who use them to be cautious and to recognize their limitations. Finally, to date, no cost-benefit analysis research has been conducted on the value of a standard clinical examination used alone and in combination with jaw-tracking and EMG devices to diagnose patients’ jaw function problems or occlusal vertical dimension abnormalities. This lack of data leaves the question of utility of these instruments in doubt.
SUMMARY There is a need for additional research on all diagnostic procedures used in dentistry. This research should be directed at identifying the test-retest precision of all methods and instruments. A cost-benefit analysis assessment of all ancillary documentary procedures and devices is needed, especially for those instruments or methods that have a substantial cost associated with their use. When advocates of an instrument put forth a claim that a specific device has diagnostic potential, a rigorous scientific protocol must be followed that tests these claims. The only current diagnostic criteria (gold standard) for occlusal disorders is a global clinical examination–thorough history performed by an expert examiner. For the time being, none of the instruments reviewed in this report (occlusal contact recording methods, surface EMG monitoring of the jaw closers, jaw-tracking devices) can be said to be more than ancillary documentation devices. They have no proven reliability or diagnostic validity and their use is not proven by the research. REFERENCES 1. Academy of Prosthodontics. The Glossary of Prosthodontic Terms. J Prosthet Dent 1999;81:48-106. 2. Gazit E, Fitzig S, Lieberman MA. Reproducibility of occlusal marking techniques. J Prosthet Dent 1986;55:505-9. 3. Durbin DS, Sadowsky C. Changes in tooth contacts following orthodontic treatment. Am J Orthod Dentofacial Orthop 1986;90:375-82. 4. Korioth TW. Number and location of occlusal contacts in intercuspal position. J Prosthet Dent 1990;64:206-10. 5. Anderson GC, Schulte JK, Aeppli DM. Reliability of the evaluation of occlusal contacts in the intercuspal position. J Prosthet Dent 1993; 70:320-3. 6. Halperin GC, Halperin AR, Norling BK. Thickness, strength, and plastic deformation of occlusal registration strips. J Prosthet Dent 1982;48:5758. 7. Clark GT, Tsukiyama Y, Baba K, Simmons M. The validity and utility of disease detection methods and of occlusal therapy for temporomandibular disorders. Oral Surg Oral Med Oral Pathol 1997;83:101-6. 8. Watt DM. Recording the sounds of tooth contact: a diagnostic technique for evaluation of occlusal disturbances. Int Dent J 1969;19:221-38. 9. Kifune R, Honma S, Hara K. The development of a new occlusal sound checker. J Jpn Assoc of Periodontology 1985;27:482-91. 10. Maness WL, Benjamin M, Podoloff R, Bobick A, Golden RF. Computerized occlusal analysis: a new technology. Quintessence Int 1987;18:28792. 11. Reza Moini M, Neff PA. Reproducibility of occlusal contacts utilizing a computerized instrument. Quintessence Int 1991;22:357-60. 12. Harvey WL, Osborne JW, Hatch RA. A preliminary test of the replicabili-
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30. Bessette RW, Quinlivan JT. Electromyographic evaluation for the MyoMonitor. J Prosthet Dent 1973;30:19-24. 31. Dao TTT, Feine JS, Lund JP. Can electrical stimulation be used to establish a physiologic occlusal position?. J Prosthet Dent 1988;60:509-14. 32. Manns A, Miralles R, Guerrero F. The changes in electrical activity of the postural muscles of the mandible upon varying the vertical dimension. J Prosthet Dent 1981;45:438-45. 33. Zarb GA, Bolender CL, Carlsson GE. Boucher’s Prosthodontic Treatment for edentulous patients. 11th ed. St Louis: CV Mosby: 1997. p. 212-3. 34. Rugh JD, Drago CJ. Vertical dimension: a study of clinical rest position and jaw muscle activity. J Prosthet Dent 1981;45:670-5. 35. ADA council on scientific affairs. Report on acceptance of TMD devices. J Am Dent Assoc 1996;127:1615-6. 36. Cooper BC, Rabuzzi DD. Myofacial pain dysfunction syndrome: a clinical study of asymptomatic subjects. Laryngoscope 1984;94:68-75. 37. Widmer CG, Lund JP, Feine JS. Evaluation of diagnostic tests for TMD. J Calif Dent Assoc 1990;18:53-60. 38. Mohl ND, McCall WD Jr, Lund JP, Plesh O. Devices for the diagnosis and treatment of temporomandibular disorders. Part I: introduction, scientific evidence, and jaw tracking. J Prosthet Dent 1990;63:198-201. 39. Mohl ND, Lund JP, Widmer CG, McCall WD Jr. Devices for the diagnosis and treatment of temporomandibular disorders. Part II: electromyography and sonography. J Prosthet Dent 1990;63:332-6. 40. Mohl ND, Ohrbach RK, Crow HC, Gross AJ. Devices for the diagnosis and treatment of temporomandibular disorders. Part III: thermography, ultrasound, electrical stimulation, and electromyographic biofeedback. J Prosthet Dent 1990;63:472-7. Reprint requests to: DR GLENN T. CLARK SECTION OF OROFACIAL PAIN AND ORAL MEDICINE UCLA SCHOOL OF DENTISTRY BOX 951668, RM 43-009 CHS 10833 LE CONTE AVE LOS ANGELES, CA 90095-1668 FAX: (310) 206-5539 E-MAIL: [email protected] Copyright © 2000 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2000/$12.00 + 0. 10/1/103749
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