Abstact: A variety of problems involving the masticatory system can be partially attributed to parafunctional habits such as bruxism. These include occlusal trauma, abfractions, tooth migration, as well as temporomandibular dysfunction. Since bruxism is considered a contributing factor to the above-mentioned dental problems, it is essential to consider parafunctional habits in the diagnosis and treatment planning before doing any occlusal reconstruction. However, the problem lies in the lack or absence of a simple device or gauge useful to be able to diagnose and evaluate the occlusal schemes in the patient's grinding pattern. In this study, we have developed a very simple device (BruxChecker) for evaluating the grinding patterns in sleep bruxism. Using the BruxChecker, it was possible to visualize real or actual interferences during sleep bruxism. Therefore, examination of the grinding pattern using this device is necessary and crucial for making the proper treatment plan for each patient.
Bruxism is generally defined as a diurnal or nocturnal parafunctional activity involving: clenching, grinding, bracing and gnashing of the teeth. During bruxism, excessive forces can be generated for extended periods of time that exceed the approximately 20-minute tooth contact. Some literature even reported a case of bruxism involving more than two hours of tooth contact.2 Sleep bruxism can generate tremendous biomechanical occlusal forces, which at times can be significantly greater than bruxing with conscious effort by an individual during the waking hours). (3-5) As a result, significant load can be distributed to the dentition, the alveolar and periodontal supporting structures, and the temporomandibular (TM) joints. Simultaneously, hyperactivity of masticatory muscles occurs, thus compromising the health of these muscles.
Several types of degenerative occlusal conditions such as occlusal trauma, abfractions, dental compression syndromes, tooth migration, as well as temporomandibular dysfunction have long been described in dentistry. Stresses from active bruxism appear to cause a physical or physiochemical loss of cervical tooth structure and may result in dentin hypersensitivity in these regions due to the progressive exposure of dentinal tubules. (6) A high correlation between patients with active bruxism and the development of abfractive lesions was also reported. (7) It is suggested that repetitive overloading of the temporomandibular joint via dentition causes parafunctional activities such as bruxism and clenching can be considered as significant contributors to repetitive overloading of the temporomandibular joint structures. (8-10) Bruxism, which is a common source of microtrauma, usually results in the elongation of the capsular and diskal ligaments coupled with thinning of the articular disk as well as muscle incoordination.
Almost all of the above-mentioned problems regarding the dental, oral, and masticatory system are closely related to bruxism. Thus, every dentist must have sufficient knowledge of the fundamental aspects of occlusion as affected by the strong biomechanical load created by bruxism and treat these conditions on a routine basis in their practice. However, the problem lies in the absence of a simple device or gauge usable for diagnosing and evaluating the occlusal schemes in the patient's grinding pattern. The purpose of this study is to introduce a very simple method for evaluating grinding patterns and examining the individual occlusal schemes during sleep bruxism.
Materials and Methods
Fabrication of the BruxChecker
The BruxChecker is a thin plate, 0.1 mm thick, clear transparent sheet, composed of polyvinyl chloride (ScheuDental, Germany). The BruxChecker was fabricated in a vacuum press in which the 0.1 mm thick transparent sheet was heated at 230[degrees] C for 15 seconds and sucked over a maxillary plaster cast using Biostar (Scheu-Dental, Germany). The device was then trimmed along the gingival margins, and the occlusal surface was painted with a red dye (Acid Red 51, Morimoto Chemical Co. Ltd, Tokyo, Japan) dissolved in shellac-ethanol solution (Shellac Co. Ltd, Tokyo, Japan) in order to visualize the grinding facets. Acid red 51, also known as Red No. 3 or erythrosine B, is a dye used in artificial food coloring. Figure 1 shows the BruxChecker on the upper dentition of the patient.
Thirty-six (36) volunteers (16 males and 20 females, aged 23 to 24, mean age: 24 years 8 months) and fifty patients (9 males and 41 females, aged 15 to 58, mean age: 26 years 2 months) from the orthodontic department of the Kanagawa Dental College, who complained of temporomandibular joint (TMJ) symptoms such as joint noise and limitation of mouth opening, accompanied by pain, were selected and instructed to use the BruxChecker for the evaluation of their grinding patterns during sleep bruxism. Thirty-six (36) volunteers with no TMJ symptoms presenting with a full set of dentition from central incisor to second molar with no severe malocclusion or major prosthodontic treatment were also evaluated as a comparison group. All subjects were instructed to wear the BruxChecker at night during sleep for two consecutive nights.
Effect of the BruxChecker Wearing on the EMG Activities
In order to examine the effect on the masticatory muscles of wearing the BruxChecker, the activity of the masseter and temporalis muscles were recorded using electromyography (EMG) with surface electrodes. The subject was instructed to grind initially without the BruxChecker for a few seconds and then repeat the same procedure with the BruxChecker on. Then the corresponding EMG recording was made. This procedure was necessary prior to the study in order to determine whether the BruxChecker induces masticatory muscle activity.
Evaluation of Tooth Contacts on the Articulators
All maxillary dental casts were mounted in a SAM 2 articulator (SAM prazisionstechnik, Munich, Germany) as referenced to the axis orbital plane (AOP) by means of an anatomical face bow transfer (SAM prazisionstechnik, Munich, Germany). The lower casts were mounted in the unstrained border position of the TMJ (reference position, RP) achieved using chin point guidance. Tooth contacts of the maxillary and mandibular casts were evaluated by manually moving the casts, using the subject's actual sagittal condylar inclination (SCI) value during excursive movements of the condylar hinge axis, to imitate the parafunctional movement. Classification of the tooth grinding contacts on the laterotrusive side of the upper and lower dentition during excursive movement were separated into four groups: 1. incisor-canine, 2. incisorcanine-premolar, 3. incisor-canine-premolar-molar, and 4. no contact. The mediotrusive side tooth contacts were also classified into three groups: 1. mediotrusion-contact, 2. mediotrusion-grinding, and 3. no mediotrusion contact. In the evaluation of mediotrusive tooth contacts, tooth contact and tooth grinding were differentiated. Tooth contact was defined as a cusp contact during mediotrusive movement of the condyle, while tooth grinding was defined as a wider and expanded facet around the cusp and oblique surface of the cusp rather than cusp contact seen on the articulator.
In order to evaluate the significance of the difference in frequency of grinding pattern between no-TMJ symptom and TMJ symptom groups, we applied the Chi-square test. Statistical significance was evaluated at the p=0.05 level.
Applicability of the BruxChecker Device to Evaluate Bruxism Activity
There was no significant difference between the activity of the masseter and temporalis muscles with and without the BruxChecker in the mouth during grinding as seen in the EMG results (Figure 2). After wearing the BruxChecker for two consecutive nights, the grinding pattern of the subjects was transferred to the surface of the BruxChecker as marked by the painted areas, which were ground off by tooth grinding. The grinding site, as well as the grinding pattern, could then be evaluated and observed easily by putting the BruxChecker onto the original cast (Figure 3). The BruxChecker presented different grinding patterns in sleep bruxism that could be classified into four groups: canine-dominance grinding (CG), canine-dominance grinding with mediotrusion grinding (CG+MG), canine-premolar-molar grinding (group grinding, GG) without mediotrusion grinding, and canine-premolar-molar grinding (group grinding) with mediotrusion grinding (GG+MG). Figure 4 shows different grinding patterns of the BruxChecker.
[FIGURE 2 OMITTED]
Evaluation of Grinding Movement during Sleep Bruxism
The observation of the grinding pattern during sleep bruxism seen in the BruxChecker indicated that a wide oval-shaped retrusive grinding was the predominant pattern shown in Figure 5. Two different patterns were also observed when the relationship between the grinding area and intercuspal position (ICP) were compared. The first pattern involved the ICP being located within the grinding field, which indicated the latero-retrusive movement of the mandible. The second pattern involved the ICP and was located outside the grinding field, which indicated that the mandible jumped into the grinding area from ICP prior to the bruxism activity (Figure 6).
[FIGURE 5 OMITTED]
Most of the cases showed that the ICP was located in an anterior position relative to the grinding field, indicating that the bruxism activity of the mandible is basically latero-retrusive in orientation from ICP. There were no subjects who showed protrusive grinding from ICP.
Comparison of Tooth Grinding Patterns between the Articulator Mounted Study Casts and as Seen in the BruxChecker
The tooth grinding contacts were classified as laterotrusive side and mediotrusive side tooth contacts of the upper and lower dentition during excursive movement (Table 1). In the no-TMJ symptom group, an incisor-canine-premolar grinding on the BruxChecker was predominant (38.9%), while an incisor-canine grinding was predominant (44.4%) on the laterotrusive side of the articulator. Furthermore, high frequency of mediotrusive grinding on the BruxChecker was 63.9%, although on the articulator, the mediotrusive contact was predominant (58.3%).
The TMJ-symptom group showed that incisor-canine-premolar-molar grinding was 52.0% on the articulator and 94.0% on the BruxChecker, which was significantly different, suggesting more group function type of laterotrusive grinding in the symptomatic group. In addition to these, more than 80.0% of the symptomatic patients had mediotrusive grinding on the BruxChecker, while only 10.0% of mediotrusive grinding was observed on the articulator.
Occlusal Schema Visualized by Grinding Pattern
The occlusal schemes were classified into four categories based on the grinding patterns observed in the BruxChecker, (Figure 7).
[FIGURE 7 OMITTED]
Canine-Dominated Grinding (CG): The canine tooth on the laterotrusive side provided the predominant guidance during bruxism with signs of slight grinding in the first and second premolar areas and none in the molars.
Canine-Dominated Grinding with Mediotrusive Grinding (CG+MG): The canine tooth on the laterotrusive side was guided predominantly during bruxism as described previously with grinding facets on the lingual cusps of the mediotrusive side, mainly first and second molars.
Group Grinding (GG): The canine tooth up to the molars on the laterotrusive side are ground off as a group with no signs of grinding in the molars on the mediotrusive side during sleep bruxism.
Group Grinding with Mediotrusive Grinding (GG+MG): Laterotrusive group guidance up to the molars with signs of grinding facets in the lingual cusps of the 1st and 2nd molars on the mediotrusive side.
The BruxChecker, a thin vacuum pressed-sheet, is fabricated using a simple and quick method. It's application in the patient's mouth causes no apprehension on the patient's part because the device is not invasive. Patients are simply instructed to wear the device immediately before going to bed and to remove it upon waking up in the morning for two consecutive days.
One of the advantages of the Bruxchecker is that it is very thin (0.1 mm thickness), providing almost no interferences to occlusion or mandibular movement, and does not induce unnecessary masticatory muscle activity. Several investigators (11,12) have used the same type of vacuum pressed-sheets such as the bruxcore (which is composed of laminated plastic sheets of different colors with the surface covered with microdots. However, it is still difficult to prove whether the thickness of the bruxcore (0.6 mm) has an effect on the bruxism activity (i.e., creating interferences or increasing muscle activity), thus making the quantification of bruxism activity questionable and inaccurate.
In clinical practice, it is important for the clinician to examine the position and distance of inclined plane of the cusps where abrasion facets appear. Quite often, the discrepancy between the interferences on the articulator-mounted casts and wear facets on the tooth surfaces can be seen. In other words, although the mounted stone cast does not show any posterior interference, the wear facets can be seen in the posterior dentition. This only means that there is a discrepancy between the clinical observation of articulation and tooth contacts and in the actual grinding pattern during actual sleep bruxism. The aim of this study was to document the individual's real grinding pattern during actual sleep bruxism using the BruxChecker.
Clinically, the grinding contact of the upper and lower teeth in powerful bruxism is quite important. Stability after any occlusal reconstruction depends upon the effect of certain craniomandibular functions such as parafunctional activity (i.e., bruxism). With the use of the BruxChecker, it was possible to visualize actual interferences that happen during sleep bruxism. Everytime the patient attempts to grind, particularly during sleep, the greatest threat to the masticatory system is when the anterior teeth provide a lack of posterior disclusion to reduce excessive muscle activities and an extremely steep overlap resulting in a too steep disclusion angle. In a bruxing movement, the excessively steep angle allows more friction and generates more muscle activity with subsequent wear of the involved surfaces. (13) Therefore, in the reconstruction of occlusion, we must provide dynamic occlusion without posterior interferences. This should follow the natural rules of dentition, which show sequentially-arranged inclination of occlusal guidance from posterior to anterior.
Although dentistry has made numerous exhaustive attempts to understand occlusion, it has unsuccessfully treated occlusion without first taking into consideration the parafunctional activity of the masticatory organ. During bruxism, condylar movement patterns and occlusal guiding planes must be harmonized. While grinding movements during sleep bruxism are still not completely understood, the use of the BruxChecker may offer important information prior to the reconstruction of occlusion.
As shown in this study, the TMJ symptom group had more posterior tooth contact and mediotrusive contact during sleep bruxism (Table 1), suggesting that the posterior interferences potentially cause deflective effects on TMJ function. The most valued benefit of the BruxChecker for clinicians is that actual tooth contacts during sleep bruxism are not only visualized using a simple and inexpensive method, but is also instructive to the patient. Treatment planning, based on the grinding pattern of the BruxChecker, may be possible to reduce the need for reconstruction treatment. It is also very important to apply the BruxChecker after reconstruction treatment to verify treatment results.
Occlusion concepts such as canine guidance, group function, balanced occlusion, etc. have long been advocated in dentistry. These concepts were observations based on intraoral or articulator mounted casts. The results of this investigation offer new occlusion schemes based on grinding movement. Since bruxism has long been recognized as a causative factor for abrasion, abfraction, tooth supporting tissues distraction, temporomandibular dysfunction, head, neck and shoulder pain syndrome and destruction of the prosthodontic appliances, it is extremely important to reconstruct occlusion based on strong grinding movement.
Examination of the grinding pattern during bruxism is necessary and should be incorporated in the diagnosis of occlusion in order to make the proper treatment plan for each patient. It is imperative to provide the patient physiologic tooth contacts during sleep bruxism to avoid or lessen the occurrence of degenerative occlusal conditions. In this study, the BruxChecker is shown to be a useful tool in examining the grinding pattern during sleep bruxism.
This work was performed in Kanagawa Dental College, Research Institute of Occlusion Medicine and supported by grant-in-aid for Open Research from the Japanese Ministry of Education, Culture, Sports, Science and Technology.
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Manuscript received December 13, 2004; revised manuscript received June 27, 2006; accepted June 30, 2006
Dr. Toshimi Kawagoe is a postgraduate student in Kanagawa Dental College. She received her D.D.S. from Kanagawa Dental College in 2003. Her major interest is the epidemiological research for interrelation of dysfunction of the temporomandibular joint with bruxism activity.
Dr. Kenichi Sasaguri is an assistant professor in the Department of Craniofacial Growth and Development Dentistry, Kanagawa Dental College. He received his D.D.S. from Kanagawa Dental College in 1985 and his D.D.Sc in 1989 from the same school. His major research interests include function and dysfunction of the craniomandibular system and the molecular mechanisms in stress and masticatory organ functions.
Dr. Cynthia Protacio-Quismundo was a professorial lecturer at the University of the Philippines from 1992-1998 and is currently a private practitioner in Manila. She received her D.D.S. at the Centro Escolar University in 1987 and her certificate in orthodontics at the Kanagawa Dental College in 1991. She is also the founder of the MEAW Study Club of the Philippines.
Dr. Sadao Sato is a professor and head of the Department of Craniofacial Growth and Development Dentistry, Kanagawa Dental College. He received his D.D.S. from Kanagawa Dental College in 1971 and his D.D.Sc in 1978 from the same school. Since 1992, he is a member of the EH Angle Society of Orthodontists. His major research interests include function and dysfunction of the masticatory organ, emotional role of bruxism activity, and craniofacial growth and malocclusions.
Address for reprint requests: Dr. Sadao Sato Department of Craniofacial Growth and Development Dentistry Kanagawa Dental College 82 Inaoka-Cho, Yokosuka, Kanagawa, Japan E-mail: firstname.lastname@example.org
Kanji Onodera, D.D.S.; Toshimi Kawagoe, D.D.S.; Kenichi Sasaguri, D.D.S.; Cynthia Protacio-Quismundo, D.D.S.; Sadao Sato, D.D.S.
Dr. Kanji Onodera received his D.D.S. from Tokyo Dental College in 1995 and had a clinical practice in the Department of Conservative Dentistry at the same school from 1996-1999. He received a certificate in orthodontics in 2001 from Kanagawa Dental College. His major research interest is the interrelation of craniomandibular dysfunction with bruxism.
Table 1 Patterns of Tooth Contact Evaluated on the Articulator or BruxChecker in No-TMJ Symptom and TMJ Symptomatic Subjects No-TMJ symptomatic subjects (n=36) Articulator BruxChecker Laterotrusion side Incisor-canine 16 (44.4) 11 (30.6) Incisor-canine-premolar 9 (25.0) 14 (38.9) Incisor-canine-premolar-molar 10 (27.8) 11 (30.6) No-laterotrusion contact 1 (0.03) 0 Mediotrusion side Mediotrusion contact 21 (58.3) 13 (36.1) ([dagger]) Mediotrusion grinding 2 (0.06) 23 (63.9) ([double dagger]) No-mediotrusion contact 13 (36.1) 0 TMJ symptomatic subjects (n=36) Articulator BruxChecker Laterotrusion side Incisor-canine 8 (16.0) * 2 (4.0) Incisor-canine-premolar 15 (30.0) 2 (4.0) Incisor-canine-premolar-molar 26 (52.0) * 43 (94.0) No-laterotrusion contact 1 (2.0) 0 Mediotrusion side Mediotrusion contact 28 (56.0) 8 (16.0) * ([dagger]) Mediotrusion grinding 5 (10.0) 42 (84.0) * ([double dagger]) No-mediotrusion contact 17 (34.0) 0 * Significantly different from No-TMJ symptom group at p<0.05 ([dagger]) Contact: defined as a cusp contact during mediotrusive movement of the condyle ([double dagger]) Grinding: defined as a wider and expanded facet around the cusp and oblique surface of the cusp than the cusp contact (): Percent