Evidence-Based Dentistry

Stabilization Splint Therapy for the Treatment of Temporomandibular Myofascial Pain: A Systematic Review
Ziad Al-Ani, B.D.S., M.Sc., Ph.D.; Robin J. Gray, B.D.S., M.D.S., Ph.D., M.F.G.D.P.; Stephen J. Davies, B.D.S., M.D.Sc., D.G.D.P.; Philip Sloan, B.D.S., Ph.D., F.R.C. Path. F.D.S.; Anne-Marie Glenny, B.Sc., M.Med.Sci.
Abstract: The aim of this review is to establish the effectiveness of stabilization splint (SS) therapy in reducing symptoms in patients with myofascial pain. Searching of electronic databases, handsearching of relevant key journals, and screening of reference lists of included studies were undertaken. There was no language restriction, and unpublished research was sought. The selection criteria were randomized controlled trials comparing splint therapy to either no treatment or another active treatment. Data extraction and validity assessment were carried out independently and in duplicate. Studies were grouped according to treatment type. Twenty potentially relevant Randomized Controlled Trials (RCTs) were identified. Only twelve met the inclusion criteria. There is insufficient evidence either for or against the use of stabilization splint therapy over other active interventions for the treatment of temporomandibular myofascial pain. However, it appears that stabilization splint therapy may be beneficial for reducing pain severity at rest and on palpation and depression when compared to no treatment. The authors suggested the need for well conducted RCTs that pay attention to method of allocation, blind outcome assessment, sample size, and duration of follow-up. Various measures were adopted to assess the outcomes of treatment. Standardization of the methods used to measure outcomes of the treatment of myofascial pain should be established in future RCTs. Dr. Al-Ani is Clinical Lecturer in Restorative Dentistry, School of Dentistry; Dr. Gray is an Honorary Fellow in Dental Medicine and Surgery, School of Dentistry; Prof. Davies is a Lecturer in Dental Practice, School of Dentistry; Prof. Sloan is a Professor of Experimental Oral Pathology, School of Dentistry; and Ms. Glenny is a Lecturer in Evidence-Based Oral Health Care, Cochrane Oral Health Group, MANDEC, School of Dentistry—all at the University of Manchester, UK. Direct correspondence and requests for reprints to Dr. Ziad Al-Ani, TMD Unit, School of Dentistry, University of Manchester, Higher Cambridge Street, Manchester, UK M15 6FH; 44-0-161-275-6717 or 6788 phone; 44-0-161-275-6797 fax; ziad.al-ani@manchester.ac.uk. Key words: temporomandibular joint disorders, myofascial pain, systematic review, myofacial pain, stabilization splint, pain dysfunction syndrome Submitted for publication 8/3/05; accepted 8/22/05

yofascial pain is the most common temporomandibular disorder (TMD). There are many synonyms for this condition including facial arthromylagia, TMJ dysfunction syndrome, myofacial pain dysfunction syndrome, craniomandibular dysfunction, pain dysfunction syndrome (PDS), and myofacial pain dysfunction.1 The etiology of myofascial pain is multifactorial. Consequently, many different therapies, some conservative and reversible, others irreversible, have been advocated for patients with myofascial pain. A number of successful treatment outcomes have been reported, including occlusal splints, physiotherapy, muscle-relaxing appliances, and pharmacological interventions.

M

There are various types of occlusal splints (bite plates or intra-oral appliances of variable designs used in the management of TMD) described in the literature; they have different indications and functions. The stabilization splint (SS), one such type of occlusal splint, is also known as the Tanner appliance, the Fox appliance, the Michigan splint, or the centric relation appliance. The stabilization splint is a hard acrylic splint that provides a temporary and removable ideal occlusion (ideal contact between the teeth for the muscles and the temporomandibular joints).1,2 Providing an ideal occlusion by the use of splint therapy reduces abnormal muscle activity and produces “neuromuscular balance.”2 Normally, it is suggested that

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patients wear the splint only at night. The splint needs to be adjusted (rebalancing of the splint to the new position of the jaw by grinding some of its surface points, since the lower jaw will adopt a new position as a result of wearing the splint) over several visits as the masticatory muscles relax until a consistent jaw relationship is reached. The patients then should be reviewed at regular intervals. After a period of successful splint therapy (normally between two to three months), patients can be weaned off the splint.2 The splint is constructed after taking impressions of the upper and lower dental arches, face bow registration, and recording of centric relation. A face bow is a calliper-like device used to record the spatial relationship of the upper teeth to some anatomic reference point or points and then enable transfer of this relationship to an articulator. It orients the dental cast in the same relationship to the opening axis of the articulator as the teeth relate to the jaw joints in the patient. A number of clinical studies have specifically evaluated the treatment of myofascial pain by SS therapy, and articles demonstrating clinical success have been published.3-5 When properly adjusted, the SS delivers a good method of providing centric relation occlusion (the position of the jaw relative to the skull when the muscles are at their most relaxed and least strained position), eliminating posterior interferences (any predominant contacts between the back teeth that interfere with or hinder harmonious jaw movement), providing anterior guidance on anterior teeth (the contact between the anterior teeth without any posterior contact during jaw movements), reducing neuromuscular activity, and obtaining stable occlusal relationships with uniform tooth contacts throughout the dental arch.1,2 The objective of this review was to determine the effectiveness of stabilization splint therapy in reducing symptoms in patients with myofascial pain, compared with any control group. The review was undertaken with the Cochrane Oral Health Group; a more detailed version of the review is available on the Cochrane Library (www.Cochrane.org).

Method
To be included in the review, the identified studies had to meet the following four criteria: 1. Study Design. Randomized or quasi-randomized controlled trials (RCTs), in which splint therapy is compared concurrently to no treatment, physiotherapy, relaxing appliances, pharmacological

interventions, other occlusal appliances, or any other active intervention. Data from conference abstracts were not included in the review. 2. Types of Participants. All patients with myofascial pain of all degrees of severity were included. A diagnosis of myofascial pain can be made if the patient exhibits more than one of the following signs and/or symptoms in any combination:5 • Pain on palpation of the temporomandibular joint. • Pain on palpation of associated mandibular muscles. • Limitation and/or deviation of mandibular movement. This was assessed by measuring the range of jaw movement, which is the only measurable parameter that can be objectively recorded in relation to temporomandibular disorder. • Joint sounds and headache. Headache alone or joint sounds alone are not diagnostic of myofascial pain. Joint sounds can be intermittent. Studies examining temporomandibular disorders other than those of primarily muscular origin were excluded. 3. Types of Interventions. Stabilization splint (Tanner appliance, the Fox appliance, the Michigan splint, or the centric relation appliance). Any control group (no treatment, physiotherapy, pharmacological intervention, other occlusal appliances, or any other active intervention). 4. Types of Outcome Measures. The outcome measures considered were improvement in pain of the temporomandibular joint, improvement in pain of associated mandibular muscles, improvement of the range of movement to a normal range of movement, and, when relevant, disappearance of joint sounds. Depression, dysfunction scores, treatment credibility, and quality of life were also examined. Response to treatment must be assessed subjectively and clinically. Subjective assessment requires patients to have recorded their present overall state at review as being cured, improved, static, or deteriorating. Since discrepancies between subjective and objective assessments have been reported,6 improvement in pain should also be confirmed clinically by palpating the muscles and the joints.

Search Strategy for Identification of Studies
For the identification of studies included or considered for this review, detailed search strategies

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were developed for each database searched (Cochrane Oral Health Group Trials Register; The Cochrane Central Register of Controlled Trials [CENTRAL], 2003, Issue 2; MEDLINE, 1966 to June 2001; EMBASE, 1966 to June 2001). This search was combined with the Cochrane Sensitive Search Strategy for RCTs.7 The search strategy developed for MEDLINE was revised appropriately for each database to take into account differences in controlled vocabulary and syntax rules. The search attempted to identify all relevant studies irrespective of language. The reference lists of all relevant trials obtained were checked, along with the reference lists of relevant review articles. In addition, reference lists from prosthetic dentistry textbooks on temporomandibular disorders and splint therapy were also checked. The following journals have been identified as being important to be handsearched for this review for the period 1960 to present: Journal of Prosthetic Dentistry, Acta Odontologica Scandinavica, Journal of the American Dental Association, and Journal of Oral Rehabilitation. The results of the searches were screened independently and in duplicate by two reviewers (MZA and RG). The full articles of all studies meeting, or potentially meeting, the defined inclusion criteria were obtained for further assessment.

Data Assessment and Synthesis
All potentially relevant articles and reports were assessed independently by two reviewers (MZA and RG) using a previously prepared data extraction form. The two reviewers knew the names of the authors, institutions, journal of publication, and results when applying both the inclusion criteria and during data extraction. After assessment of the studies, the results were compared and discussed until consensus was achieved. Disagreements were handled by discussion and by consulting a third reviewer (PS). Additional information was sought from the authors when necessary. To reduce pre-formed opinions of experts in the area that can bias the assessment of the relevance of articles, one reviewer was not an expert in the area. Each study included was quality assessed independently by two reviewers (MZA and RG). In the case of discrepancies, the authors were contacted for details of randomization where necessary. Three main quality criteria were assessed: 1) randomization and allocation concealment; 2) blind

outcome assessment—participants and investigators cannot be blinded to splint therapy; however, it is feasible to blind the outcome assessor and all included studies were assessed for blinding of the outcome assessment; and 3) completeness of the follow-up. Uncertainty about methodology employed during the quality assessment phase was resolved by contacting the authors when necessary. The significance of discrepancies in the estimates of treatment effects from the different trials was assessed by inspection of a graphical display and by means of Cochrane’s test for heterogeneity. The Cochrane Oral Health Group’s statistical guidelines were followed and relative risk (RR) values calculated along with 95 percent confidence intervals (CI) for binary data. Weighted mean difference (WMD) was used for continuous data. Meta-analysis was to be undertaken using a random effects model in the absence of clinical and statistical heterogeneity. Data were analyzed using Review Manager program and the main results of the studies presented separately for pain (TMJ, muscles and jaw movements), movement of the jaw (deviation in mouthopening, range of mouth opening, lateral movements), TMJ clicking, depression level, Helkimo dysfunction score (an index for anamnestic and clinical dysfunction and occlusal state), treatment credibility, and quality of life. If data allowed, a sensitivity analysis had to be conducted to see how the quality of the studies affects the findings.

Results
Twenty RCTs were identified as being potentially relevant. All were published in English. Eight trials were excluded due to use of splint therapy other than stabilization splint or due to the participants’ not meeting the criteria for myofascial pain.8-15 Twelve RCTs fulfilled the inclusion criteria. Details are presented in Table 1. Apart from one study with vague descriptions of the splint used,16 all other studies provided some information about splint construction and adjustment to centric relation. Comparison groups included acupuncture,16,17 bite-plates,18 biofeedback, 19,20 visual feedback, 21 non-occluding splints,22-24 relaxation/hypnorelaxation,25,26 jaw exercises,27 and minimal/no treatment.17,20,22,25 The study participants consisted of patients who had been referred for treatment for myofascial pain to a special clinic. In two studies,22,24 patients

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were recruited through announcements published in a local journal. The number of participants ranged from twenty18,21 to eighty patients.20 The number of patients per study group was twenty or less in four studies. Five studies gave detailed criteria for inclusion and/or exclusion of patients in the study.17,20,22-24 Information about previous TMD treatment was reported in only one study.17 The number of follow-up visits was standardized in both the study and control treatments in all studies included. However, the period of treatment/ follow-up varied from four to twelve weeks across included studies. The type of outcomes measures varied between the studies (Table 1). Pain was measured using a Visual Analogue Scale (VAS)17,22,25 and the Pain Severity Scale (PSS), Muscle Palpation Index (PPI),20 and a pain diary.24 Two studies reported number of patients reporting pain on movement of mandible or pain on retrusion of the mandible.16,22 Other outcomes measured included electromyographic analyses,18 quality of life,22 clinical dysfunction scores,17,19,27 depression,20 range of jaw movement, sound, locking, and deviation in opening of mouth.16,21,25 The methodological quality of included studies is as follows: randomization and concealment procedures—one of the included studies reported on the method used to generate the randomization sequence or allocation concealment; blind outcome assessment—blind outcome assessment was clearly stated in only two trials;22,25 and drop-outs—drop-outs were reported in six studies,7 none of which undertook a full intention to treat analysis.2,18,20,22-24

patients showing an improvement in intensity of pain at rest.22 Johansson et al. compared SS with acupuncture and a no intervention control group.17 Both of the treatment groups showed a statistically significant improvement in pain post-treatment compared to the non-intervention group (p