oral appliances in the management of temporomandibular disorders … · oral appliances in the...

Vol. 107 No. 2 February 2009

ORAL MEDICINE Editor: Craig S. Miller

Oral appliances in the management of temporomandibular disordersGary D. Klasser, DMD,a and Charles S. Greene, DDS,b Chicago, IllinoisCOLLEGE OF DENTISTRY, UNIVERSITY OF ILLINOIS

Various types of oral appliances (OAs) have been used for over half a century to treat temporomandibulardisorders (TMDs), but there has been considerable debate about how OAs should be designed, how they should beused, and what they actually do therapeutically. However, there is enough information in the scientific literature atthis time to reach some evidence-based conclusions about these issues. The main focus of this review is on thematerials and designs of various OAs in terms of their proposed mechanisms of action and their claimed clinicalobjectives. Based on current scientific evidence, an analysis is presented regarding the role that OAs can or cannotplay in the management of TMDs. Finally, the concept that OAs may be an effective treatment modality for someTMDs owing to their potential for acting as an elaborate placebo rather than any specific therapeutic mechanism is
considered. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;107:212-223)
In the 21st century, it is safe to assume that dentists arefamiliar with 2 terms: oral appliances (OAs) and temporo-mandibular disorders (TMDs). However, some cliniciansmay be surprised to learn that each of these terms has beenredefined in light of research findings from the past 10-20years. Oral appliances, which used to be simple processedacrylic devices that covered all or most of the teeth in 1arch, are now available in a variety of materials anddesigns. The conceptual basis for designing and usingOAs as treatment devices also has changed considerably,ranging from simple jaw relaxation concepts to complexjaw repositioning rationales. Temporomandibular disor-ders, which used to be viewed as problems related to sometype of occlusal or skeletal disharmony, have undergone arather substantial paradigm shift. As the classic dental andskeletal etiologic theories have been challenged and refutedby studies conducted around the world, a biopsychosocialmedical model of orthopedics, pain phenomenology, andbehavioral factors has gradually replaced them.

The aim of this paper is to review the literature on

aAssistant Professor, Department of Oral Medicine and DiagnosticSciences.bClinical Professor, Department of Orthodontics.Received for publication May 18, 2008; returned for revision Oct 1,2008; accepted for publication Oct 8, 2008.1079-2104/$ - see front matter© 2009 Mosby, Inc. All rights reserved.
doi:10.1016/j.tripleo.2008.10.007
212

OAs, with a specific focus on their use in the treatmentof TMDs resulting in evidence-based conclusions re-garding these issues. In addition to describing the dif-ferences in materials used in the fabrication of OAs, thevarious designs of OAs are analyzed regarding theirproposed mechanisms of action and their claimed clin-ical objectives. Based on current scientific evidence, therole that OAs can or cannot play in the management ofTMDs is defined. Finally, the concept that OAs areeffective primarily owing to their potential for acting aselaborate placebos will be considered. To avoid confu-sion, the term “splints” (which often appears in thedental literature as a synonym for OAs) will not beused, because it has several other definitions in den-tistry that are unrelated to the management of TMDs.

TEMPOROMANDIBULAR DISORDERSThe first 50 years of interest in TMDs were charac-

terized by a narrow focus on mechanistic theories ofetiology.1,2 In addition, these complex problems wereoften described in simplistic terms with diagnostic la-bels such as temporomandibular joint (TMJ) syndrome,myofascial pain-dysfunction syndrome, or even justTMJ problems. Because these early etiologic conceptsrevolved mostly around theories of occlusal disharmo-nies and/or skeletal malalignments, dentists becamealmost exclusively responsible for their managementand OAs became a major treatment modality for TMD
patients. The application of OAs as a treatment was

OOOOEVolume 107, Number 2 Klasser and Greene 213

generally discussed in terms of producing occlusal dis-engagement, relaxing jaw musculature, restoring verti-cal dimension of occlusion (VDO), unloading thejoint(s), or TMJ repositioning. Even today, OAs aredescribed as deprogrammers or jaw repositioners thatcan establish ideal craniomandibular relationshipswhile also relieving pain and restoring function. Thesemechanistic concepts are seriously flawed for 3 rea-sons: their underlying assumptions that both myoge-nous and arthrogenous pain and dysfunction arise pri-marily from the “strain” of dealing with improperocclusal or craniomandibular relationships; their failureto recognize the multiple effects that OAs can produce,instead attributing all positive responses to their occlu-sion-changing or maxillomandibular repositioning ef-fects; and their presumption that, if the temporary oc-clusal changes produced by the OAs result insymptomatic improvement, they must be followed bypermanent alterations to the patient’s occlusion throughextensive and irreversible dental treatment(s).

Until the 1960s, no systematic well controlled or prop-erly designed clinical studies had been conducted to eval-uate the efficacy of treatments for patients with TMDs.Instead, there were a number of “scorecard” studies andanecdotal papers published that reported high levels ofsuccessful treatment for the majority of these patients,using a variety of mechanical (dental) approaches.3-7

Many of these treatment protocols included the use ofOAs, not only to relieve signs and symptoms, but also toestablish “ideal” or “correct” jaw relationships. For manypractitioners, these clinical successes endorsed their as-sumptions about how OAs function while also appearingto confirm their opinions about TMD etiology.

Unfortunately, the failure of a minority of patients torespond positively to such treatments was seen as a sign ofpsychologic disturbance (hypochondriasis, depression,malingering, secondary gain), rather than as a sign ofinappropriate or ineffective diagnosis and/or treatment.Even worse, failure to respond to occlusal therapy oftenwas used as the basis for attempting more aggressive andinvasive therapies, up to and including surgical procedures.8,9

When some early TMD studies in the 1960s and 1970swere conducted using placebo drugs or sham proceduresas controls, the investigators reported rather high levels ofpositive response to those placebo treatments.10-12 At first,these findings were dismissed as being some type oftrickery, and some investigators were even accused ofmisleading or duping patients by using placebos instead of“real” treatments. When Greene and Laskin13 and Good-man et al.10 reported using “placebo splints” as well as“placebo equilibrations” as forms of mock treatment forTMD patients, these outcomes were widely denounced;however, the fact that nonoccluding OAs helped over
40% of the patients, while mock equilibration helped
nearly two-thirds of them, made it difficult to ignore thosefindings. Subsequent researchers using both of these pla-cebo controls in their studies have reproduced similarresults.14 These findings obviously have required clini-cians to rethink the mechanisms of appliance efficacy, andto re-evaluate what the role of OAs might be in treatingTMD patients.

During that same time period, a number of other pla-cebo-controlled or comparative TMD treatment studieswere producing high rates of positive response, withoutperforming any irreversible dental or skeletal correctiveprocedures.15-20 In addition, longitudinal follow-up stud-ies showed that these short-term favorable responses toconservative treatments often persisted over periods ofmany years, even if the original treatment was only aplacebo.21-30 This accumulating evidence presented apowerful argument against the use of traditional mechan-ical TMD therapies, especially because the irreversiblenature of those treatments could significantly complicate anonresponding patient’s condition physically, psycholog-ically, and economically.31-33 An in-depth discussion re-garding this topic is beyond the scope of the present article,but for most TMD patients it has become clear that the linebetween reversible and irreversible treatments does not oftenneed to be crossed to produce good clinical outcomes.33

In recent years there has been an explosion in ourknowledge regarding the biochemical and neurophysio-logic basis for musculoskeletal pain,34-37 making some ofthe old notions about why joints or muscles hurt seemvery naive and simplistic (for example, terms such ascapsulitis, lactic acid buildup, or muscle spasms). Like-wise, the explanations for why pains persist in somepeople and not others has switched almost completelyfrom the field of psychology to the field of neuroscience,38

where extensive studies have shown that neuroplasticchanges in the nervous system are the most likely reasonfor developing chronic pain. In addition, it appears thatgenetic factors may determine in part who will developsuch chronic pain conditions.39-41 There is little doubt thatfuture therapies in the pain field will be targeted moreprecisely toward underlying pathophysiologic mecha-nisms of joint pain, muscle pain, and chronic pain, ratherthan at simple analgesia or other pain control strategies.

Do these fascinating scientific findings mean that oralappliances no longer have any place in a dentist’s arma-mentarium for managing TMD patients? The answer atthis point in time is clearly No, because OAs still can be avaluable adjunct in the management of certain subgroups ofTMD patients, as will be discussed subsequently.

ORAL APPLIANCESThe changes in our understanding of the pathophys-

iology of TMDs require that traditional ideas about
using OAs also must be reconsidered. Not only are

OOOOE214 Klasser and Greene February 2009

many of the old concepts mistaken or obsolete, but inaddition the semantics of describing OAs needs to bemodified. For example, calling an OA an occlusal ap-pliance may have seemed appropriate because it altersocclusion while wearing it; however, this is akin tocalling a back brace a dermatologic device because itrests on the skin of the torso while wearing it. AsOkeson42 has pointed out (Table I), there are at least 7hypotheses that have been offered to explain the effectsthat OAs can have on TMDs, but most of them simplyreflect the bias of certain clinical approaches. For ex-ample, if you presume that a patient has a verticaldimension problem, you might attribute the clinicalsuccess of OAs to the thickness of the plastic.

Oral appliance materials—fabrication issuesThere are basically 2 different materials, based upon

consistency, which are used in the fabrication of OAs.First, there are hard acrylic resin OAs that are eitherchemically cured or heat/pressure processed, resulting inhard and rigid tooth-borne and occlusal surfaces. Alterna-tively, there are soft or resilient OAs manufactured fromplastics or polymers, producing an appliance which has asomewhat flexible and pliable tooth-borne and occlusalsurface. There exists a third variation of material known asdual laminated, because it consists of hard acrylic resin onthe occlusal surface and a soft material on the inner aspect(tooth-borne surface). This produces an OA with the pos-itive qualities of a soft material (fitting well and providingcomfort for the supporting teeth), with the versatility of ahard acrylic resin adjustable occlusal surface. For ourpurposes, this style of OA will be discussed as belongingto the hard acrylic resin group.

Hard acrylic resin OAs can be custom fabricated atchairside and/or produced at a commercial laboratorywith the use of stone casts. The material for makingcertain types of soft OAs can be purchased from dentalsupply houses or found over the counter in many sport-ing goods stores and pharmacies, in a prefabricatedform. This type of OA (“boil and bite”) is molded and

Table I. Hypotheses for efficacy of oral appliances42

Dental reasons for efficacy Nondental reasons for efficacy

Alteration of the occlusalcondition

Cognitive awareness

Alteration of the condylarposition

Placebo effect

Increase in the verticaldimension of occlusion

Increased peripheral input to thecentral nervous systemdecreases motor activity

Regression to the mean (naturalfluctuation of symptoms)

adapted by the purchaser by boiling the product in

water and then placing the material intraorally with abiting force to establish the “correct” occlusion. An-other variation of the soft OA is a dental office–fabri-cated version, whereby the material is vacuum formedto fit stone casts, and the occlusion is later establishedat chairside. A third variety involves a similar process-ing technique which occurs at a commercial laboratory,with the occlusion established once again at chairside.

Hard acrylic resin OAs appear to have several ad-vantages over their soft counterparts. The fit of a hardacrylic resin OA, be it a hard or a hard-soft tooth-borneinterface, is generally more stable and more retentiveowing to the material(s) used and to the more accurate,consistent, and reliable method of fabrication. Adjust-ment to the occlusal surface of these OAs, using rotaryinstruments, can be accomplished more easily, quickly,and efficiently than with a soft material because of thehardness and resistance of the acrylic resin. Doing thistype of adjustment with a soft material often results ina less than adequate occlusal scheme. Furthermore,there is a possibility that wearing soft appliances maybe associated with occlusal changes.43,44

Owing to the hardness of the acrylic resin, a rigidtype of OA will provide greater longevity and durabil-ity than the soft version. The hard acrylic resin varietyis also less prone to discoloration as well as accumu-lation of food debris and resultant malodors, owing tothe porosity differences inherent in the composition ofthe different materials. Lastly, repairing a hard acrylicresin OA is easily achievable either at chairside or withreprocessing at a commercial laboratory, but this is notachievable with the soft type of OA. The advantages ofthe soft OA compared with the hard OA seem to bemainly economics and chairside adjustment time, be-cause the softer versions are usually less expensive forthe patient and less time consuming for the practitionerthan the more labor-intensive hard acrylic resin types.

Oral appliance materials—utilization issuesThe question of which material to use for the manage-

ment of TMDs as well as for sleep bruxism (SB) has beenand continues to be rather controversial. Soft OAs havebeen recommended by some investigators for the reduc-tion of both myogenous and arthrogenous TMD symp-toms.43,45-47 However, in an electromyography (EMG)study comparing hard and soft OAs involving 10 bruxismsubjects who wore hard appliances at first and then wereswitched to soft appliances after a washout period, it wasfound that 8 of the 10 subjects experienced a significantlyreduced nocturnal muscle activity with the use of hardOAs. In comparison, the soft OAs significantly reducedmuscle activity in only 1 participant and caused a statis-tically significant increase in EMG activity in 5 of the
participants.48 In another EMG study comparing the ef-


fects of hard and soft OAs on the activity of the temporalisand masseter muscles during controlled clenching, it wasfound that activity of the studied muscles was decreasedmore with use of a hard OA, and the soft OAs produceda slight increase in activity of both muscles, but particu-larly the masseter muscle.49 In another EMG study, it wasfound that activity of the masseter muscle was increasedafter the immediate insertion of a soft OA during maxi-mum clenching.50

Contrary to these outcomes, other studies involvingdirect comparisons between hard and soft OAs in TMDsubjects found no differences in either self-reportedsymptoms or in clinical findings between each OAgroup.45,47 Additionally, in a study by Wright et al.46

where 30 masticatory muscle pain subjects were ran-domly assigned to receive either a soft OA, palliativetreatment, or no treatment, it was found that thoseassigned to the soft OA group had a greater reduction inthe signs and symptoms of their muscle pain over theshort term.

It might seem from these studies that differences be-tween the use of soft and hard OAs in the management ofTMDs are not significant. However, the majority of sci-entific evidence48,51-53 has shown more consistent supportfor the use of hard acrylic resin OAs rather than soft onesfor the reduction of TMD symptoms. Additionally, owingto the material and adjustability advantages discussedearlier, it seems reasonable to recommend the use of ahard acrylic resin OA over a soft version for most patientswith appropriate TMD signs and symptoms. However,soft OAs may be useful as a short-term treatment measurein certain acute-onset TMD patients, as well as for thosepatients where cost is a concern.45,47 Because the mostcommon and well validated indication for appliancesmade with soft materials is as athletic mouthguards toprotect against and diminish injury to the oral struc-tures,54,55 they still have an important role in the dentalarmamentarium.

Oral appliance designs and related conceptsFlat plane stabilization appliance. The flat plane sta-

bilization appliance (also known as the Michigan splint,muscle relaxation appliance, or gnathologic splint) is gen-erally fabricated for the maxillary arch. Alternatively,some clinicians have argued that for reasons of enhancedesthetics and less effect on speech, this type of applianceshould be fabricated for the mandibular arch. The evi-dence from various studies suggests no differences inreduction of symptoms between either of these 2 de-signs.56 The appliance is fabricated so that the opposingdentition occludes uniformly, evenly, and simultaneouslywith the occluding surface of the appliance.

Many practitioners advocate the incorporation of ca-
nine-protected articulation to disocclude the posterior
teeth during eccentric movements. Some studies sug-gest that the use of this design in asymptomatic indi-viduals is more effective in reducing muscle activ-ity.57,58 However, several other studies have shown nodifferences in muscle activity in healthy subjects59 or inTMD symptom reduction60,61 by adding the canine-protected articulation feature to an appliance.

Ideally, when a stabilization type of appliance isplaced intraorally, there is minimal change to the max-illomandibular relationship other than that produced bythe thickness of the material. This is the most com-monly used type of intraoral appliance, and when prop-erly fabricated it has the least potential for adverseeffects to the oral structures. The intent of this appli-ance as outlined by the American Academy of Orofa-cial Pain guidelines62 is to “provide joint stabilization,protect the teeth, redistribute the [occlusal] forces, relaxthe elevator muscles, and decrease bruxism.” Addition-ally, it is stated that “wearing the appliance increasesthe patient’s awareness of jaw habits and helps alter therest position of the mandible to a more relaxed, openposition.”

Traditional anterior bite plane. The use of anteriorplatform appliances seems to have originated within theorthodontic profession many years ago. Various clini-cians’ names (e.g., Hawley, Sved, Shore) have beenassociated with these OAs, and in many cases theappliances were modified to either move or retain max-illary anterior teeth. In general, they are designed as apalatal-coverage horseshoe shape with an occlusal plat-form covering 6 or 8 maxillary anterior teeth. Advo-cates for using such appliances to treat TMDs haveargued that they prevent clenching, because posteriorteeth are not engaged in closing or in parafunctionalactivities. However, some critics have argued that theseappliances can lead to overeruption of posterior teeth(which is extremely unlikely if worn only at night) andothers have worried that the TMJs will be overloadedwithout posterior support.

Minianterior appliances. The concept of making anoral appliance that engaged only a small number ofmaxillary anterior teeth (usually 2-4 incisors) was firstintroduced in the mid 1900s as the Lucia jig. Within thepast several years, there have been several variationsthat have appeared on the market. They include theNociceptive Trigeminal Inhibition Tension Suppres-sion System (NTI), the Best Bite, and the AnteriorMidline Point Stop (AMPS) devices. All of these arehard acrylic resin appliances that are either developeddirectly at chairside or commercially produced in pre-fabricated designs. The commercial versions requirecustom fitting at chairside by relining the interior aspectwith acrylic resin or hard elastic impression materials to
fit on the maxillary incisors, after which the occluding


surface is adjusted to allow 2-4 mandibular incisors tocontact a platform. According to the advocates of theseOAs, their purpose is to disengage the posterior teeth,thereby eliminating the influences of the posterior oc-clusion on the masticatory system. This design isthought to be effective in treating TMDs, SB, andheadaches. However, because of the recent popularityof these appliances, a more thorough discussion of theliterature is required so that the profession can considerusing them based on scientific evidence rather than onexperience-based claims and business interests.

The initial study63 which allowed the U.S. Food andDrug Administration (FDA) to categorize the NTI as amedical device and approve its marketing in the diag-nosis and treatment of headaches was based on thereported results that the NTI was slightly more effectivethan a “full coverage appliance” for the reduction ofheadache pain. Interestingly, the control appliance wasonly a bleaching tray, for which no studies evaluatingeffectiveness in treating either TMDs or headache painhave ever been reported. Clearly, the study would havebeen vastly improved by comparing the NTI against aconventional flat plane stabilization appliance. Addi-tionally, the approval of a medical device as opposed toa drug requires a much less stringent approval process,because new devices which are similar to previouslyapproved devices can apply for the same FDA ap-proval. Because the majority of the oral appliancesbeing marketed for headache are categorized as “jawrepositioning” devices, and carry the FDA approval assuch, it is easy to understand how the NTI and similarappliances were approved.

In a double-blind randomized parallel trial compar-ing the NTI to a flat plane stabilization appliance inTMD subjects with headache, no differences betweenappliances were reported over a 3-month period regard-ing muscle tenderness upon palpation, self-reportedTMD-related pain and headache, or improvement onjaw opening.64 In a study comparing the AMPS deviceto a flat plane stabilization appliance, there was nosignificant difference between the appliances in theirefficiency in relieving myogenous pain.65 In anotherwell designed randomly controlled study, the NTI wasfound to be less effective than a flat plane stabilizationappliance in the treatment of TMDs.66

The possibility of adverse occlusal effects occurringwith this type of minianterior appliance with continu-ous and long-term use is significant. Because the designof the appliance only covers the maxillary anteriorteeth, there is the potential for overeruption of theunopposed posterior teeth resulting in an anterior openbite. Development of an anterior open bite also couldresult from the intrusion of the maxillary anterior teeth
which retain the appliance, or from a combination of
both factors. It also is possible that the 1-point designfor occlusal contact with the mandibular anterior teethmay create unfavorable mobility of these teeth, or in-stead the maxillary teeth supporting the appliance maybe displaced by the occlusal forces. Furthermore, owingto the small size of these devices, there is a possibilityof a serious life-threatening event in which the appli-ance may be swallowed or aspirated; reports of suchcatastrophic events have been recorded.64

Anterior repositioning appliance. The anterior repo-sitioning appliance (also known as an orthopedic repo-sitioning appliance) purposefully alters the maxillo-mandibular relationship so that the mandible assumes amore anterior position. This is accomplished with theaddition of an acrylic guiding ramp to the anteriorone-third of the maxillary appliance which, upon clos-ing, forces the mandible into a more forward position.Originally, this type of appliance was supposed to beused to treat patients with internal derangements (usu-ally anterior disk displacements with reduction). It wasthought that by altering the mandibular position in thismanner, anteriorly displaced disks could be “recap-tured,” after which the new condyle-disk relationshipcould be “stabilized” through comprehensive dental orsurgical occlusal procedures.67 Currently it is recom-mended that repositioning appliances should be usedprimarily as a temporary therapeutic measure to allowfor symptomatic control of painful internal derange-ments, but not to “permanently” recapture the TMJdisk. The potential dangers with long term use of thisappliance are permanent and irreversible occlusal andeven skeletal changes. Therefore, this type of applianceshould be used with discretion, and only for shortperiods of time.

Neuromuscular appliances. Advocates of so-calledneuromuscular dentistry (NMD) have claimed that theuse of jaw muscle stimulators and jaw-tracking ma-chines enables them to produce an oral appliance at theideal vertical and horizontal position of the mandiblerelative to the cranium.68 Space does not permit a fulldiscussion of these complex issues, which have beenreviewed elsewhere.69-72 At the very least, one wouldhave to accept the entire NMD concept to believe thenotion that such appliances are the most ideal ones.After using these appliances to treat a TMD patient,proponents of this methodology usually recommenddental reconstruction at the new jaw relationship.

Posterior bite plane appliances. Posterior bite planeappliances (also known as mandibular orthopedic repo-sitioning appliances) are customarily made to be wornon the mandibular arch. The design is bilateral hardacrylic resin platforms located over the mandibularposterior teeth (usually molars and premolars) and con-
nected with a lingual metal bar. This design creates a


disocclusion of the anterior teeth. The purpose of thisappliance is to produce changes to the vertical dimen-sion and alter the horizontal maxillomandibular rela-tionship. It also has been claimed that this type ofappliance has the ability to increase overall physicalstrength and enhance athletic performance73-75; how-ever, the scientific evidence does not support thisclaim.76-78

According to its supporters,79 this type of appliancewas supposed to produce an “ideal” maxillomandibularrelationship, to be followed by occlusal procedures topermanently maintain that relationship. No evidencewas offered to support this concept. The major concernregarding this appliance design is that occlusion onlyoccurs on posterior teeth, thereby allowing for overe-ruption of the unopposed anterior teeth and/or intrusionof the opposing posterior teeth, resulting in an iatro-genically created posterior open bite.

Pivot appliances. The pivoting appliance is con-structed with hard acrylic resin that covers either themaxillary or mandibular arch and incorporates a singleposterior occlusal contact in each quadrant. This con-tact is placed as far posteriorly as possible. The purposeof this design is to reduce intra-articular pressure bycondylar distraction as the mandible “fulcrums” aroundthe pivot, resulting in an “unloading” of the articularsurfaces of the joint. This appliance was recommendedfor patients with internal derangements and/or osteoar-thritis. However, studies80,81 have indicated that occlu-sal pivots have no distractive effect on the TMJ andinstead can actually lead to joint compression. A dif-ferent version of this appliance involves the use of aunilateral pivot inserted in the posterior region. It isthought that closing the mandible on this pivot will loadthe contralateral joint and slightly distract the ipsilateraljoint.80 However, owing to biomechanical principles, itis not possible for a class III lever such as the mandibleto rotate around a secondary fulcrum; all claims to thecontrary are simply not plausible (see the next section).Because of the design and force vectors created by thisappliance, a potential adverse effect with its use may beocclusal changes manifesting as a posterior open bitewhere the pivot was placed.

Hydrostatic appliance. This unique appliance wasdesigned by Lerman82 over 30 years ago. In its originalform, it consisted of bilateral water-filled plastic cham-bers attached to an acrylic palatal appliance, and thepatient’s posterior teeth would occlude with thesechambers. Later this was modified to become a devicethat could be retained under the upper lip, while thefluid chambers could be positioned between maxillaryand mandibular posterior teeth. The concept was thatthe mandible would automatically “find” its ideal po-
sition because the appliance was not directing where
the jaw should be. No independent research has beenoffered to substantiate this claim.

What oral appliances can and cannot doAs if it were not confusing enough to have so many

different OA designs, the rationales offered for usingthem in the treatment of TMDs are wildly divergent.Part of this problem stems from different concepts andideologies about what needs to achieved to “success-fully” treat a TMD patient. However, another importantconfounding issue arises from mistaken beliefs aboutwhat OAs can or cannot actually do. In this section, wediscuss that topic in terms of the available scientificevidence (Table II).

Oral appliances and TMJ loading. It has beenclaimed that OAs can unload the normal pressure ex-isting inside the human TMJ. As discussed above, onetype of appliance was designed with “pivots” placed inthe molar area to create a fulcrum that would distractthe condyle from its fossa upon jaw closing. Unfortu-nately, this concept ignores a fundamental biomechani-cal fact that has been demonstrated repeatedly by Hy-lander83,84 and other anatomists, namely, that the

Table II. Descriptions of appropriate uses and limita-tions for oral appliances (OAs)

What OAs can do What OAs cannot do

Decrease/alter loading on TMJ byreducing force intensity,frequency, and/or duration of oralparafunctional activities

Unload the TMJ bydistracting condyle orby pivoting on molarcontacts

Briefly reduce muscle activity byintroducing “foreign body” ofocclusal platform

Retrain muscles to be lessactive after splint isremoved

Reduce headache intensity orfrequency if it is triggered by SB-induced myalgia or arthralgia

Relieve headacheconditions that areprimarily neurovascularor vascular in origin

Improve internal derangementsymptoms of locking/catchingupon awakening related to strongnocturnal muscle activity(clenching/grinding)

Recapture displaced disks,enhance retrodiskaltissue healing, preventprogression from ADD-R to ADD-NR

Disrupt neuromuscular engrams thatdetermine TMJ-fossa relationships(“de-programming”)

Produce an “ideal”neuromuscular/occlusalrelationship

Protect occlusal surfaces of teethand dental restorations from SBforces

Permanently reduce oreliminate SB activities

Establish “correct”vertical dimension ofocclusion

TMJ, temporomandibular joint; SB, sleep bruxism; ADD-R, anteriordisk displacement with reduction; ADD-NR, anterior disk displace-ment without reduction.

human mandible is a class III lever, and as such it


cannot fulcrum around any point that is anterior to themasticatory muscles. Therefore, neither a pivot appli-ance nor any other type of OA can possibly “unload”the human TMJ. However, it can be argued that loadinginside the TMJ could be reduced or redirected by thepresence of an OA. This may occur due to a reduction inthe amount and intensity of muscle activity, or it may bedue to the condylar loading area being shifted elsewhere.

Oral appliances and muscle activity. There is bothempirical and experimental evidence that OAs can pro-duce a decrease in nocturnal muscle activity in manypatients. Clark et al.51 have explained this as a reflexiveresponse to the presence of a “foreign object” between theteeth, leading to an avoidance behavior. This effect alsohas been observed and measured in sleep laboratory stud-ies.85 However, it also has been shown that nocturnalmuscle activity returns to baseline levels in nearly allpatients shortly after discontinuing OA usage, and in somepatients that may occur even while still using the OA.Therefore, if long-term pain relief and/or protection ofteeth are needed, those patients must wear OAs indefi-nitely. Clinicians also need to be aware that, in a smallpercentage of cases, paradoxic results may occur whenpatients are given OAs, with previously painless sleepbruxers developing symptoms of TMD; this is thought tobe due to a reflexive increase in muscle activity rather thanthe expected decrease, and it requires a change of treat-ment strategy for those patients.

Oral appliances and headache. Several studies havefound associations between TMDs and headache.86-88 Inpatients referred for treatment of TMDs, headache hasbeen reported in more than 70%.89,90 This complicates thedifferential diagnosis of head and facial pain, but fortu-nately there is an extensive classification of headachedisorders with detailed diagnostic criteria that has beendeveloped by the International Headache Society.91 Thisclassification includes both primary and secondary head-aches, with the spectrum of etiologies ranging from neu-rovascular and vascular causes to central nervous systemlesions. In the section describing diagnostic criteria fortension-type headache (TTH), the IHS material states thatincreased pericranial tenderness elicited by manual palpa-tion is the most significant abnormal finding in patientswith this form of headache. In addition, a common findingin patients with TMDs and TTH is masticatory musclepain upon palpation.92 However, no clear causal relation-ship has been found between these 2 conditions, so thisfinding may simply reflect a comorbid situation. Anothertheory is that the jaw muscle pain generated by SB mayserve as a trigger to both TTH and migraine headaches insusceptible patients, but it should be remembered that themajority of SB patients do not experience any craniofacial
pain problems.93,94
Randomized controlled treatment studies have founda decrease in intensity and frequency of TTH whenpatients with TMDs of myogenous and/or arthrogenousorigin are successfully treated with OAs.89,95 A com-mon finding in each study was a reduction in thenumber of masticatory muscles tender to palpation.Therefore, if pain in the masticatory or pericranialmuscles is reported by a patient upon awakening, thosepains may be related to muscle activity associated withSB. Although the mechanism for OAs providing head-ache reduction is unknown, one possible theory (asdiscussed above) is that this kind of positive outcomemay be due to a reduction in nocturnal jaw muscleactivity. Therefore, OAs should be viewed as an ad-junctive treatment for TMD management in those pa-tients who also present with headache, rather than as aspecific treatment for primary headache conditions.

Oral appliances and internal derangements. The useof OAs to treat internal derangements of the TMJ hasled to many problematic outcomes, mainly due to mis-conceptions about why TMJ disks become displaced aswell as what should be done about it. Beginning in the1970s, disk displacements (even in painless clickingpatients) were thought to be forerunners of degenera-tive disease and painful dysfunctions. Therefore, someclinicians advocated early intervention to avoid suchdevelopments, and the primary treatment tool was aso-called anterior repositioning appliance (ARA). Theconcept was to “recapture” the displaced disk and togradually “walk it back” to a normal position, but whenthis proved to be nearly impossible, some cliniciansadvocated major occlusion-changing procedures to“stabilize the recaptured disk” in its new anteriorposition.96

As evidence continued to mount showing the futility(not to mention the non-necessity) of this extremelyinvasive approach,97 some modified concepts of ARAutilization became popular. For example, some peopleargued that wearing an ARA98 could help patientsavoid progression from clicking to “locking” (nonre-ducing disk displacement), and others argued that anARA should be worn for 6-12 months to permit retro-diskal tissues to heal.98

Obviously, what was missing from those clinicalarguments was the evidence needed to support any ofthe treatment approaches. Over time, several studies ofconservatively treated (and even untreated) patientsshowed that a series of fairly predictable adaptationswere likely to occur in the majority of internal derange-ment patients.99 Therefore, what patients actuallyneeded from clinicians was symptomatic relief frompainful episodes, as well as proper counseling aboutwhat was happening inside their joints.100 As a result,
the role that either conventional or repositioning OAs


could play became much more limited, and today thereare only 3 likely indications for their use in internalderangement cases. First, for patients with acute TMJpain, OAs may reduce muscle activity and redirectloading inside the TMJ; second, for sleep bruxers whoawaken with TMJ pain due to nocturnal muscle activ-ity, an OA worn at night could be helpful to reduce painand dysfunction; and third, for patients whose TMJsbecome “locked” at night, but who are able to success-fully click open during the day, an OA can reduce thefrequency of these episodes or prevent their occurrencein some cases.

Oral appliances and “deprogramming” concepts.One popular idea about OAs is that they can “depro-gram” the TMJ musculature, and thereby produce“ideal” jaw relationships. This is a good example of anidea that contains a kernel of truth, but which hasserious theoretic and practical flaws when applied toactual patients. It is true that every patient’s brain is“programmed” by their occlusion to guide the variousmovements of the mandible; the scientific term for thisprogram is “engram,” which means that neuromuscularactivity is determined in large part by the morphologyof the moving structures. This type of brain program isvery stable as long as morphology remains unchanged,but it is capable of changing as peripheral structuresundergo changes.

Therefore, if you interfere with the engram producedby occlusal contact (e.g., by wearing an OA), the man-dible will close in a different manner. The problem liesin making an assumption that the new version is betterthan the original one, an assumption that exists at thecore of all centric occlusion-centric relation or otherjaw-repositioning occlusion concepts in dentistry. Bydescribing the new position as ideal, the teeth are castin the role of “interfering” with proper closure of themandible and the need arises to do something aboutthat. An in-depth discussion regarding deprogrammingconcepts is beyond the scope of the present article, butit should be recognized that they have played a hugerole in all of the occlusal/skeletal theories of TMDetiology. Although readers are encouraged to pursuethis debate101-103 about which occlusal concepts andprocedures are best for treating their regular dentalpatients, they should not interpret success of OAs intreating certain TMD patients in terms of deprogram-ming concepts.

Oral appliances and establishing “correct” verticaldimension. There were reports in the early TMD litera-ture that OAs can reduce “abnormal muscle activity” andassociated pain by restoring the patient’s original VDOthat was reduced by tooth wear or loss of posterior sup-port.3,104 That belief is based on the premise that a loss in
VDO is an etiologic factor for TMD, as originally pro-
posed by Costen in 1934.105 However, so-called normalVDO has been found to be a highly variable measurementin the general population, and regardless of the measure-ment or apparent loss of occlusal tooth structure, mostindividuals do not report signs and symptoms of TMD.106

Therefore, the success of an OA in reducing pain shouldnot be interpreted as a confirmation of lost VDO simplybecause the occlusion has been temporarily elevated. Ob-viously, the danger of interpreting outcomes this way isthat clinicians might conclude that permanent changes inVDO will be required to establish long-term health, andthis always requires some type of major invasive dentalintervention.

Nonoccluding appliances and placebo effectsNonoccluding OAs, as the name implies, do not have

an occlusal platform that contacts the opposing denti-tion, so they cannot directly alter either condylar posi-tioning or vertical dimension. In the first study to in-vestigate the clinical efficacy of nonoccluding OAs,Greene and Laskin13 studied 71 patients with myoge-nous TMDs (masticatory muscle pain, limitation, devi-ation, and/or tenderness) who were treated by differentOA designs. They found that 40% of the patientsshowed remission or noticeable improvement in theirsymptoms with the use of a nonoccluding OA. In thefirst random-assignment placebo-controlled study ofOAs for treating myogenous TMD,107 one group re-ceived a traditional OA and the other group a nonoc-cluding OA; the results showed improvement in bothgroups without any statistically significant before orafter treatment differences between the groups. Dao etal.108 evaluated the therapeutic efficacy of OAs using aparallel, randomized, controlled, and blind design byassigning masticatory myalgia subjects to 1 of 3groups: 1) passive control: full occlusal OA worn only30 min at each appointment; 2) active control: nonoc-cluding OA worn 24 h/day; and 3) treatment: fullocclusal OA worn 24 h/day. They found that all painratings decreased significantly with time, and quality oflife improved for all 3 groups. However, there were nosignificant differences between groups in any of theassessment variables. They concluded that the reduc-tion in intensity and unpleasantness of muscle pain andimprovement in quality of life was nonspecific and notdirectly related to the type of treatment. Additionalstudies in myalgia and arthralgia subjects reported nosignificant differences in overall reduction of subjectiveand objective measures of pain and dysfunction (exceptfor TMJ clicking) after treatment with either nonoc-cluding or occluding OAs, both resulting in positiveoutcomes.109,110 In studies evaluating EMG massetermuscle activity in SB patients, it was found that oc-
cluding and nonoccluding OAs were equally effective


in reducing nocturnal muscle activity in certain indi-viduals for a period of time.85,111,112

Contrary to the above studies, Ekberg et al.113 eval-uated the efficacy of a traditional OA (treatment group)compared with a nonoccluding OA (control group) inarthrogenous TMD subjects using a randomized dou-ble-blind controlled protocol. They found improvementof overall subjective symptoms in both groups, butsignificantly more often in the treatment group than inthe control group (P � .006). Additionally, the fre-quency of daily or constant pain showed a significantreduction in the treatment group compared with thecontrol group (P � .02). However, they concluded thatboth the stabilization appliance and the control appli-ance had some amount of positive effect on TMJ pain.Similar findings by these investigators and others114-117

have been reported regarding the treatment of signs andsymptoms of myogenous pain. The results from bothshort-term and long-term trials led those authors toconclude that traditional OAs are more efficacious thannonoccluding OAs.

Implications of current placebo theory for theclinical use of OAs

Caution must be advised regarding interpretion of thenumerous studies that have looked at the issue of oc-cluding versus nonoccluding OAs. Those studies havevarious methodologic limitations; for example, differ-ent inclusion and exclusion criteria were used in thevarious studies, with some poorly defining the targetedstudy population. Furthermore, there may have beenseveral confounding variables influencing the treatmentoutcomes, some of which were not recorded or ac-counted for in presenting the results of the studies. Inspite of these potential shortcomings, it appears that thegeneral trend reported from these studies is that non-occluding OAs, at the minimum, have a considerableamount of positive effect on TMD signs and symptomsin a significant percentage of subjects. Because thesenonoccluding OAs are not altering the occlusion ormaxillomandibular relationships of patients, theirmechanism of action must be at least partially due totheir ability to function as a behavioral interventionrather than as a mechanical device.

Recent research into the mechanisms of placebo ef-fects has broadened our understanding of how placeboswork. Brain imaging studies using functional magneticresonance imaging and positron-emission tomographicscanning have made it possible to better understand thevery specific biologic activity occurring in the brains ofboth pain patients and volunteer subjects. When sub-jects are exposed to painful stimuli, their responses toboth placebo treatments and “real” treatments are in-
fluenced by their pre-existing pain condition as well as
by the context of each treatment. A recent paper byGoddard et al. (G. Goddard, DDS, personal communi-cation, February 15, 2008) summarizes these develop-ments in the placebo field and presents implications forthe management of TMD patients. Dao and Lavigne,118

in a review paper regarding the use of OAs, commentedthat despite their lack of true efficacy, splints should beused as a treatment modality for some subgroups ofTMD patients because they are “effective” treatments(that is, they produce positive subjective responses),and they are harmless when properly used. Obviously,this implies that as long as clinicians stay in the domainof conservative and reversible care, there will be avariety of other effective treatments available in addi-tion to OAs that are likely to be helpful in treating theirTMD patients. Combined with cognitive-behavioral ed-ucation of patients and an awareness of important psy-chosocial factors (especially in chronic TMD patients),this approach should lead to “effective” treatment pro-tocols and the avoidance of aggressive ones.

CONCLUSIONSOver the past 10-20 years, the conceptual basis for

using oral appliances in treating temporomandibulardisorders and SB has been dramatically redefined. Thishas happened largely as a consequence of extensiveresearch conducted around the world during that pe-riod, which has led to new understandings of theseconditions. Currently, OAs are still regarded as usefuladjuncts for treating certain kinds of TMD patients, butthe emphasis is entirely on their conservative applica-tion. Evidence derived from clinical studies suggeststhat OAs are more effective for treating myogenousTMD problems than they are for intracapsular condi-tions, but they can be helpful for both in properlyselected patients. Rather than trying to establish newhorizontal or vertical jaw relationships, OAs todayshould be viewed as “oromandibular crutches,”118

which are analogous to back braces or ankle supportorthotics because they provide symptomatic reliefwhile patients are recovering.

Thinking about OAs this way will enable cliniciansto use OAs as they treat TMD patients conservativelyand reversibly, as long as they avoid full-time wear orspecific designs that lead to permanent occlusal chang-es; the worst-case outcome should be nothing morethan a failure to relieve symptoms. As for treating sleepbruxism, there is no question that OAs can provideprotection against excessive attrition of patients’ teeth.They do not stop people from performing parafunc-tional activities at night, but they may diminish theduration, frequency, or intensity of those activities forsome patients and for variable amounts of time. The
only negative possibility is development or continua-


tion of morning muscular pain in a small number ofpatients, which requires a change of strategy; for themajority of SB patients, however, these devices can bevery helpful.

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Reprint requests:

Dr. Gary D. Klasser, DMDAssistant ProfessorDepartment of Oral Medicine and Diagnostic SciencesCollege of DentistryUniversity of Illinois at Chicago801 South Paulina Street, Room 569C (M/C 838)Chicago, IL 60612-7213
[email protected]
mailto:[email protected]

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