Review
Bruxism and prosthetic treatment: A critical review
Anders Johansson DDS, PhD
a,* , Ridwaan Omar BSc, BDS, LDSRCS, MSc, FRACDS, FDSRCSEd
b, Gunnar E. Carlsson DDS PhD
caDepartmentofClinicalDentistry–Prosthodontics,FacultyofMedicineandDentistry,UniversityofBergen,A˚ rstadveien17,5009Bergen,Norway
bDepartmentofRestorativeSciences,FacultyofDentistry,KuwaitUniversity,Kuwait
cDepartmentofProstheticDentistry,TheSahlgrenskaAcademy,UniversityofGothenburg,Go¨teborg,Sweden Received7February2011;accepted17February2011
Availableonline18May2011
Abstract
Purpose: Basedonthefindingsfromavailableresearchonbruxismandprosthetictreatmentpublishedinthedentalliterature,anattemptwas madetodrawconclusionsabouttheexistenceofapossiblerelationshipbetweenthetwo,anditsclinicalrelevance.
Studyselection: MEDLINE/PubMedsearcheswereconductedusingtheterms‘bruxism’and‘prosthetictreatment’,aswellascombinationsof theseandrelatedterms.Thefewstudiesjudgedtoberelevantwerecriticallyreviewed,inadditiontopapersfoundduringanadditionalmanual searchofreferencelistswithinselectedarticles.
Results: Bruxismisacommonparafunctionalhabit,occurringbothduringsleepandwakefulness.Usuallyitcausesfewseriouseffects,butcando soinsomepatients.Theetiologyismultifactorial.Thereisnoknowntreatmenttostopbruxism,includingprosthetictreatment.Theroleofbruxism intheprocessoftoothwearisunclear,butitisnotconsideredamajorcause.Asinformedbythepresentcriticalreview,therelationshipbetween bruxismandprosthetictreatmentisonethatrelatesmainlytotheeffectoftheformeronthelatter.
Conclusions: Bruxismmaybeincludedamongtheriskfactors,andisassociatedwithincreasedmechanicaland/ortechnicalcomplicationsin prosthodonticrehabilitation,althoughitseemsnottoaffectimplantsurvival.Whenprostheticinterventionisindicatedinapatientwithbruxism, effortsshouldbemadetoreducetheeffectsoflikelyheavyocclusalloadingonallthecomponentsthatcontributetoprostheticstructuralintegrity.
Failuretodosomayindicateearlierfailurethanisthenorm.
#2011JapanProsthodonticSociety.PublishedbyElsevierIreland.Allrightsreserved.
Keywords:Fixeddentalprostheses;Implant-supportedrestorations;Oralparafunction;Removabledentures;Toothwear;Prostheticdentistry
Contents
1. Introduction ... 128
2. Materialsandmethods... 128
3. Bruxism... 128
3.1. Effectsofbruxismonthemasticatorysystem ... 129
3.1.1. Toothwear ... 129
3.1.2. Treatmentofbruxism... 129
3.2. Effectsofbruxismonprostheticrestorationsonnaturalteeth ... 130
3.2.1. Biomechanicalfactors ... 131
3.3. Effectsofbruxismonimplantrestorations... 132
3.4. Effectsofbruxismonremovabledentures... 133
3.4.1. Completedentures... 133
3.4.2. Removablepartialdentures... 133
4. Discussion ... 133
5. Conclusions ... 135
References ... 135 www.elsevier.com/locate/jpor Available online at www.sciencedirect.com
JournalofProsthodonticResearch55(2011)127–136
*Correspondingauthor.Tel.:+4755586062;fax:+4755586489.
E-mailaddress:[email protected](A.Johansson).
1883-1958/$–seefrontmatter#2011JapanProsthodonticSociety.PublishedbyElsevierIreland.Allrightsreserved.
doi:10.1016/j.jpor.2011.02.004
1. Introduction
Bruxism, which can be considered an umbrella term for clenchingandgrindingof the teeth,is thecommonest of the many parafunctional activities of the masticatory system.
Opinionson the cause of bruxism are numerous andwidely varying.Currentreviewsindicatethattheetiologyisnotfully known but that it is probably multifactorial [1]. Although intermittent clenching and grinding are extremely common, they usually pose no serious consequences for the oral structures.Onthe otherhand,manifestbruxism canresultin problemsthatareasfrustratingforthepatientasforthetreating dentist.Sequelaeof bruxismthathavebeenproposedinclude tooth wear, signs and symptoms of temporomandibular disorders (TMD), headaches, toothache, mobile teeth, and variousproblemswithdentalrestorationsaswellaswithfixed andremovableprostheses [2,3].
As thetitleof thepapersuggests,thisreviewisconcerned with the relationships that may, directly or indirectly, exist between bruxism and prosthetic treatment. Although certain occlusalconditionsand/orincorrectly prostheticallymodified occlusionswerehistoricallybelievedtobepotentialcausesof bruxism, this has largely ceased to be the case. Also, the assumptionthat‘correction’ofsuchocclusalconditionscould reversebruxismhasalsobeendiscredited.Whatisimportantin thepresentcontext,however,isthepossibleeffectofbruxism onprostheticrestorations,arelationshipuponwhichthedental literaturewouldappearnottobeconclusive.
Itis,therefore,thepurposeofthispapertocriticallyreview thedentalliteratureregardingapossiblerelationshipbetween bruxismandprosthetic treatment.
2. Materialsandmethods
MEDLINE/PubMed searches were conducted for articles usingtheterms‘bruxism’and‘prosthetictreatment’.Sincethe literatureonsuchbroadsubjectswouldbeabundant,thereview focused on selected combinations of the two search terms, focusingon the relationship betweenbruxism and prosthetic treatment, including fixed and removable prostheses and implant-supported and implant-retained prostheses. Publica- tionsconsidered topresent thehighest levelofevidence, i.e.
clinical randomized controlled trials (RCT) and systematic reviewsofRCTs,werescarceornotavailable,and,therefore, studies of lower evidentiary strength were considered and criticallyevaluated.Asregardsreviewarticles,themostrecent oneonagiventopicwasselected.
The search of PubMed for ‘bruxism’ and ‘prosthetic treatment’,notsurprisingly,revealedextremelylargenumbers of titles and reviews of studies when the terms were used separately,butrelativelysmallnumbers whencombinedwith otherterms(Table1).ThetitleslistedbyPubMedrevealedthat themajority wereof no interestfor the present purpose,and were, therefore, excluded. Only one relevant RCT was retrieved, and was the same article listed for three of the combinations of terms that were searched [4]. Abstracts of potentially relevant articles were read and eventually full
paperswerereviewed.IntheCochranLibrary,noreviewonthe topicsofinterestwasfound.Amanualsearchofthereference lists andtextbooksreferredtointhe includedPubMedlisted articleswasalsoperformed.Thisadditionalsearchidentified20 relevant studies and reviews. A total of 66 relevant papers remained,andare discussedinthereviewthatfollows.
3. Bruxism
‘Bruxism’ originates from the Greek word brychein, meaningto‘gnashtheteeth’.Anearlyandcommondefinition of bruxismwas thus‘‘gnashing andgrindingof theteeth for non-functionalpurposes’’[5].Laterdefinitionshavebeenmore specific,for example, ‘‘involuntary, non-functional,rhythmic or spasmodic gnashing, grinding, and clenching of teeth, usuallyduringsleep’’[6].Thesamemedicaldictionary[6]adds thatcausesofbruxismmayberelatedtorepressedaggression, emotional tension, anger, fear, and frustration. In the dental literature,the etiology remainscontroversialuptonow, even though earlier opinions that occlusal disturbances or other morphologicalfactorsareimportantcausesmayhavebeenlong sinceabandonedduetolackofevidence[7].Instead,thefocus has been on psychosocial, pathophysiologic and genetic factors. Even though the literature is still not conclusive, it isagreedtodaythatbruxismhasamultifactorialetiology[1,8].
Historically,occlusal/articulationandskeletalfactorswere believedtoconstitutethegreatestriskforbruxism,butmodern studies have failed to demonstrate a consistently significant relationshipbetweensuchfactorsandbruxism.Factorswhich havebeenimplicatedashavinganincreasedriskfor bruxism includelowerage,femalegender,tobacco,alcoholandcaffeine usage,psychosocial factors(e.g.stress andanxiety), sleeping disorders (e.g. obstructive sleep apnea), genetics and certain medications or drugs. Some authors have emphasized that bruxism during sleep and during wakefulness should be regarded as two separate entities, probably with different etiologies, and with different presumed risk factors. The AmericanAcademyofSleepingDisordersproposedtheterms sleepandawakebruxism[9].Eventhoughmostoftheliterature does not differentiate between sleep and awake bruxism, studiesinsleep-laboratoriesarethoughttoproduceresearchof higher quality (sometimes called the ‘‘gold standard’’) than othertypesofstudies,manyofwhicharebasedonself-reports.
Itfollowsthatself-reportisnotanadequatemeasureofsleep
Table1
NumbersoftitleslistedinPubMed(November2010)forvariouscombinations oftheterms‘bruxism’and‘prosthetictreatment’.
Searchterm Citations Reviews RCTsa
Bruxism 2350 278 48
Prosthetictreatment 22,169 2502 463
Bruxismandprosthetictreatment 42 10 3(1)b
Bruxismanddentalimplants 69 13 1b
Bruxismandfixeddentalprosthesis 54 5 1b
Bruxismanddentures 132 10 0
a Randomizedcontrolledtrial;inparenthesesrelevantarticle.
b Denotesthesamepaper(Ref.[4]).
bruxismbecauseof diagnosticbias andconfounders[10–12].
Atthepracticallevel,however,theprocessofdiagnosingsleep bruxismbymeansofpolysomnography(PSG)iscomplicated, while detecting awake bruxism is easier as the patient can report it after becoming, or being made aware of the habit.
However, there are some promising recent developments in portable EMG measuring devices for diagnosing bruxism whichcorrelatewellwiththegoldstandard,viz.PSG[13,14].
Theprevalence ofbruxisminthe populationisdifficultto estimate because of the wide variations in methods and diagnosesapplied,typesofbruxismconsidered,anddifferences between samples examined in published studies. Indeed, epidemiologic studies have reported prevalences of bruxism rangingfrom6%to91%ofexaminedsamples[3].Itisevident thatclenching and grinding of teeth are extremely common, although the prevalence of manifest bruxism has been estimatedtobeabout 10%[1].
3.1. Effectsofbruxismonthe masticatorysystem
Sincebruxismisconsideredapossibleetiologicalfactorfor TMDandtoothwear,itsclinicalimportanceisobvious.Other effects of bruxism may include tooth movement and tooth mobility,as wellas changes inoralsoft tissues andjawbone [2,3].
3.1.1. Toothwear
Bruxism was for long considered a major cause of tooth wear.Inrecentyears,however,themultifactorialetiologyand theimportanceofotherfactorsrelatedtotoothwear,such as erosion,havebeenemphasized[15].Nevertheless,asystematic reviewconcludedthat‘‘attritionseemstobeco-existentwith self-reportedbruxism’’[16].Ratherthanconfirmingarelation- ship,this maybe indicative of acommon perception among bothpatientsanddentists.Forexample,apositiveself-response toaquestionaboutbruxismmaysimplyreflectapreconception on the part of the patient, or the dentist, about the de facto existenceofacausativerelationshipbetweentoothwear,and/or TMD-relatedsymptomsforthatmatter,andbruxism[10].This may,therefore,beanimportantexplanationforthesignificant correlationreportedbetweenself-reportedbruxism,toothwear and/orTMDinseveralstudies[17–23].Indeed,whennocturnal bruxismhas beendiagnosedmore robustly,withpolysomno- graphy, no consistent relationship has been found between bruxismandtoothwear,orbetweenbruxismandTMD.Infact, therehave been suggestionsthatan inverserelationshipmay apply [24,25]. A recent review concluded that a number of published observations strengthen the concept of the multi- factorialetiologyoftoothwear.Thereviewwentontostatethat it seemed fair to conclude that the overall significance of bruxismasacausativefactorfortoothwearisnotfullyknown, butitisevenfairertosaythatitisprobablyoverestimated[15].
Itfollowsthattherearesignificantlimitationswithself-reports toprovideareliablediagnosisofsleepbruxism.Therefore,in muchofthediscussionthatfollows,theuseofthetermbruxism impliesanacceptanceofthislimitation,andthatwhatitrefers to might equally be just heavy loading through high biting/
chewingforcesoperatingasadirectfactor,ratherthanitbeing categoricallyduetoparafunctionalactivity.
Irrespectiveof the etiology, restoration of wornteeth that will frequentlyinvolveprosthetic treatmentwill beneededin somepatients.Becausesuchtreatmentistypicallycomplexand oftenextensive,thereisatendencytodefertreatmentuntilthe tooth wear is well advanced. This complicates treatment further, and with greater mechanical vulnerability to the restoration provided. There is a scarcity of studies on the outcomeofprostheticrestorationofworndentitions,leadingto widely differing opinions among prosthodontists indifferent countriesabouthowthesecomplextreatmentsituationsshould bemanaged [15,26].
3.1.2. Treatment ofbruxism
Currently, no specific treatment exists thatcan stop sleep bruxism even though many methods, including prosthetic treatment,havebeentriedovertheyears.Ontheotherhand,it hasbeensuggestedthatvarioustreatments,basedonbehavior modification such as habit awareness, habit reversal therapy, relaxation techniques, and biofeedback massed therapy, may eliminate awake bruxism. Although these methods are not harmfultothepatients,thereisnostrongevidencethatanyof them is effective in the treatment of bruxism [27,28].
Nevertheless, even without strong scientific evidence, the simple measure of increasing the patient’s awareness of the habitshouldbetried:itmayhelpthepatienttostartcontrolling it and thereby possibly decreasing the frequency and/or intensityofdaytime toothcontactandmuscle tension.
The absence of a definitive treatment to permanently eliminatebruxism hasled tothe developmentof strategiesto reduceitsdeleteriouseffects.Themostcommonmethodused topreventthedestructiveeffectsofbruxismisthroughdifferent typesof interocclusalappliances (e.g.occlusal splints,night- guards,etc.).Recentreviewshaveconcludedthatinterocclusal appliances are useful adjuncts in the management of sleep bruxismbutdonotofferadefinitiveor‘‘curative’’treatmentof bruxism,or thesignsandsymptomsof TMD[29].Similarly, their efficacy in reducing nocturnal muscle activity and craniofacialpainisunclear[30].
Occlusal splintsarecommonly usedtopreventtoothwear caused by bruxism and/or heavy loading. A survey among general dental practitioners in Sweden showed that they consideredthefirstindicationforhardinterocclusalappliances was for protecting the dentition from wear, followed by for managingTMDproblems[31].Anearlierlong-termstudyof patientswithextensivetoothwearprovidedwithstabilization splints showed thatusage patterns by patients varied widely [32].Onlyafew patientscontinuedtouse thesplints forthe whole follow-up period and the mean period of usage was approximately2years.Inmostpatients,toothwearprogression rateover6–10yearswasslowandtheamountwassmall.The role of the splints in the minimal continuing tooth wear observedwasnotconclusive:ingeneral,thesplintswereused for less than a third of the follow-up period and, besides bruxism, several other possible causes of tooth wear were evident [32]. Nevertheless, in spite of the paucity of strong
evidence,arecentbookonbruxismstates thatthereis‘‘total consensusthatbruxismsplintsplayapositiveroleinprotecting dentalhardtissues’’[28].
Giventheforegoingbackgroundabouttherealdifficultiesof treatingbruxismdefinitivelyorpredictably,orforthatmatter, beingabletoadequatelyprotecttheteethfromitseffects,the association between bruxism and prosthetic treatment, as suggestedinthetitleofthispaper,willofnecessityrefertothe effectsof bruxismonprostheticreconstructions(Fig.1).
3.2. Effectsofbruxismonprosthetic restorationson naturalteeth
Fixed dental prostheses (FDP) are successful prosthetic restorations in partially dentate patients. Systematic reviews havedemonstratedsurvivalratesofconventionalFDPsof94%
after5yearsand89%after10years[33,34].Themostcommon technical failures reported included loss of retention and fractureofmaterial.Itisoftensuggestedthattheoccurrenceof such failures is greatest in patients with bruxing habits. For example,when prosthetic restoration isbeing provided for a worn dentition (usually with teeth having short clinical crowns), it will be difficult to achieve adequate mechanical retention and resistance forms for conventionally cemented
restorations. Furthermore, the potentially greater load on restorations if there is bruxism, heavy chewing forces, or unfavourable loading directions between teeth, means that greatcautionisneededinthedesignoftherestorationiftherisk ofmechanicalfailureistobereduced.Wefoundnocontrolled study in thisregard, although several reportshave noted the possible association between bruxism and survival of FDPs [35,36].
Likewise, theliterature onthematerials recommendedfor useinFDPfabricationinpatientswithseverebruxismissparse, and the choice needs often to be made on the basis of commonsenseratherthanonscientificdata[37,38].Thechoice of material to be used could be criticalif, for example, it is opposed by naturalteeth [39,40]. Some anecdotal reportsof wear on natural teeth and prosthetic restorations opposing variousmaterialshaveappeared,andafewexamplesofsuch occurrencesareshowninFigs.2and3.Theprocessofwearthat affects restorative materials is almostalways studied experi- mentallyinlaboratorytrials.Results arethenextrapolated to theextremelyvariableintraoralconditions,whereasonlylong- termclinicalinvestigationscandemonstratethe trueoutcome [41]. With an opposing occlusion of tooth enamel, most cliniciansandresearchersagree thatametal occlusalsurface, andpreferablyoneofhighnoblecontent,ispreferredinorderto minimizewear of the naturaldentition. Unpolishedceramics could beespecially hazardoustoopposingnaturalteeth.It is also necessary to consider other factors which influence the
Fig.1. A60-year-oldmanwithalonghistoryoffracturesofdifferenttypesof fixeddentalprostheses,includingmetal–ceramicandgold–acrylicconstruc- tions,mostlikelyduetoexcessiveloadingandbruxism.Anewlycemented metal–ceramicprosthesis(A)andsufferingseveralporcelainfracturesafter1 year(B).
Fig. 2. A49-year-old woman with 3-year-old metal–ceramic fixeddental prostheses(FDPs)inbothmaxillaryandmandibularjaws(AandB).Extensive porcelainfracturesdevelopedrapidly,especiallyinthemandibleprobablydue toinadequatemetalsupport,comparedtothepalatalmetalsupportprovidedin themaxillaryFPD(B).TheseFDPswereremadebecauseofsimilarfailures withaprevioussetofFDPs.
wearresistanceofnaturalteeth,viz.erosiveinfluences,salivary secretory and lubricatory factors, among others. In cases of heavy occlusal load such as, for example, in bruxers, the situation becomes very complexas we need toconsider not onlytheriskforwearoftherestorativematerialitselfandthe opposingdentition,butalsotheneedforsufficientstrengthin allthecomponentsofthesuperstructuretobeabletowithstand the appliedload.Besides therisk of mechanical failures and lossofretentionunderconditionsofexcessiveload,biological failuresareevenmorelikely,e.g.caries,marginaldegradation, andendodonticproblems [38].The sequenceof theseevents may be difficult to determine, and it may be that loss of retention occurs first andis then followed by caries and the otherbiologicalproblems[42].Allthingsconsidered,metalor metal–ceramicrestorationsseemtobethesafestchoiceincases of high load conditions [37], although under extreme conditions, there is no material that will last for too long (Figs.4–6).Becauseoftheriskofchippingofceramicveneers in metal–ceramic restorations, many clinicians prefer gold–
acrylic FDPs for heavy bruxers. The few clinical studies publishedonwearofmaterialsinbruxersindicateonlysmall differences inwearresistance ofgoldandceramicmaterials, whereas resin-based materials showed 3–4 times more substanceloss thangoldor ceramics[37,40].During thelast few years, new ceramics, for example zirconia, have demonstrated improved mechanical properties in laboratory studies and may be promising in the treatment of bruxism-
related tooth wear [43,44]. However, a systematic review of zirconiaFDPshasshownthattherearecomplicationswhenthe material meetsclinical reality.Improvementof theveneering systems is especially required as chipping was the most frequentmechanicalcomplication[45].
3.2.1. Biomechanicalfactors
Asidefromthepossibleeffectsof bruxismonthe occlusal and materials-related aspects of FDPs just discussed, certain designandstructuralconsiderationsforplannedrestorationsin apatientwithbruxismand/orheavyloadingcanbementioned.
Inthisscenario,restorationswillbevulnerabletofailureasa resultofstressconcentrationfromdifferentialwearandpoorly planned or faulty occlusal contacts. Thus, for conventional fixed prosthodontics, single crowns should be constructed wheneverpossibleandFDPsshouldbeofminimalextension.
An effective way to increase the retention of conventionally retained crownsonshort,wornabutmentsistoincludeinthe preparation, boxes and grooves, or parallel pins [37,46,47].
Splinting shouldbe avoidedwheneverpossible, especiallyin
Fig.3. (AandB)A58-year-oldmanwithsevereloweranteriortoothwear causedbyacombinationofdifferentfactors,includingincreasedloadproduced by bruxism and/orheavy loaddue to loss ofposterior support, opposing unglazed porcelain,and most likely dental erosionas anothercontributing factor(CourtesyoftheDepartmentofProsthodontics,SchoolofOralHealth Science,FacultyofHealthSciences,UniversityoftheWitwatersrand,Johan- nesburg,SouthAfrica).
Fig.4. (A–C)A55-year-oldmanwithmaxillarymetal–ceramiccrownsanda deepbite.Heavyloadduetobruxismandanabsenceofposteriorsupport, opposingporcelaincrowns,incombinationwithdentalerosionhavemostlikely contributedtotheexcessivewearseenonthemandibularincisors.
cases of confirmed bruxism. Similarly, splinted secondary abutmentsascompensationforashort,poorlyretentiveprimary abutment is contraindicated: the chances of cementation failure, rather than being reduced, will probably be as great asattheshortabutment.Inthisway,physiologictoothmobility will be unrestrained; additionally, torqueing forces are minimized and, incaseof cementation failure,the condition wouldbemoreeasilydetected,andbemoreeasilycorrectable [15].Afurtherargumentthatfavoursrestorationsthatarenot rigidlyconnectedisthattherichsensoryinformationprovided by the periodontal mechanoreceptors of unsplinted teeth is preserved.Thiswasrecentlysuggestedbasedontheresultsof clinicalneurophysiologicexperimentsinsubjectswithnatural teeth compared to patients with extensive tooth-borne or implant-supportedFDPs[48].
Among clinicians as well as in textbooks, it is often proposedthatpatientswithseveretoothwearandrehabilitated withextensiveFDPs,shouldreceiveaprotectiveocclusalsplint for use at night [49]. Even if this seems to be a prudent recommendation(andgivingthedentistaclearconscience,but perhapsalsoafalsesenseofsecurity),nocontrolledstudiesof theefficacyofsuchaprotectivedeviceinprosthetictreatment by means of FDPs on natural teeth have been published.
Regardingimplant-supportedrestorations,onestudyreporteda higher frequency of ceramic/porcelain fractures in bruxism patientsnotwearing aprotectiveocclusaldevice[50].
In a study of 11 patients, conducted 3 years after rehabilitation with large FDPs because of extensive tooth wear,itwasfoundthatthemandibularmovementpatternhad changedaftertheprosthetictreatment.Twopatientsdisplayed obviouswearoftherestorativematerialandoneFDPhadtobe remade because of fracture of abutment teeth. Interestingly, despitethe changedmovementpatternatthegrouplevel,the heavyocclusalload wasstill present,at leastinsomeof the patients,aftertheprostheticrehabilitation [51].
3.3. Effectsofbruxismonimplantrestorations
In contrast with the paucity of studies on bruxism and prosthetictreatmentonnaturalteeth,anumberofpublications
werefoundrelatingtobruxismandimplantrestorations.Early papers on survival of fixed prostheses on osseointegrated implantsoftenreferredtobruxismandheavyocclusalloading asthecauseofimplantfailures[52].But,inaprospective15- year follow-up study of mandibular implant-supported fixed prostheses, smoking andpoor oral hygiene hada significant influenceonboneloss,whileocclusalloadingfactorssuchas bruxism,maximalbiteforceandlengthofcantileverswereof minorimportance[53].Further,astudyusingocclusalwearasa proxyforbruxism,gavenoindicationthatimplantsinpatients withocclusalwearhaveanincreasedrateofbonelossorhigher Periotestvalue[54].
Systematic reviews have concluded that a causative relationshipbetweenocclusalforcesandlossofosseointegra- tion hasnever beendemonstrated [55,56]. Although bruxism was included among risk factors, and was associated with increasedmechanicaland/ortechnicalcomplications,ithadno impactonimplantsurvival[57].However,severalstudieshave indicatedthatpatientswithbruxismhaveahigherincidenceof complications on the superstructures of both of fixed and removableimplant-supportedrestorations[35,58–60] (Figs.7 and8).Onceagainthe unreliabilityof self-reported bruxism has tobe stressed: the complications reported in the various studies maywell have been causedby other load-increasing factors, poorly planned occlusion or inadequate mechanical design of the reconstructions. Equally, without a definitive diagnosisof bruxism havingbeen established, it is acknowl- edged that some of the outcomes illustrated in some of the
Fig.5. (AandB)Severewearontheanteriormandibularteethrestoredwitha varietyofdentalmaterials.Theopposingmaxillaryteetharerestoredwith metal–ceramiccrowns.
Fig.6. (AandB)Wearofmetalcrownsveneeredwithacrylicopposingnatural teeth.Unfavourableocclusalloadingwithoutmolarsupportprobablyexplains theextensivewear.
clinicalcasesthatappearinthispapermaybeduetosuchload- increasingormaterials-relatedfactors,ratherthantobruxism perse.
The only RCT found that related to bruxism and prosthetictherapy was a 1-year follow-up study ofimplant survivalafter1-and2-stagesinusinlaybonegrafts.Bruxism and postoperative infections were the only parameters that could be related to implant failure [4]. However, the diagnosisofbruxismwasbasedonself-report,thenumberof patientswassmall,andtheobservationperiodwasshort,allof which indicate that the results should be interpreted with caution.
3.4. Effectsofbruxismonremovabledentures
Systematicstudiesontheeffectsof bruxismonremovable denturesdonotseemtobeavailableintheliterature.
3.4.1. Completedentures
Textbooksoncompletedenturefabricationoftenmention that clinical experience indicatesthat bruxism is afrequent causeofcomplaintofsorenessofthedenture-bearingmucosa.
Therelationshipbetweenoralparafunctionsandresidualridge resorptionhasnotbeeninvestigated,butitistempting,evenif anecdotally, to include parafunctions as a possible factor related to the magnitude of ridge reduction [61] (Figs. 9 and10).
3.4.2. Removablepartialdentures
Thequestionofrestoringlostposteriorsupportbymeans of mandibular distal extension removable partial dentures (RPDs) in moderately shortened dental arches remains controversial [62]. However, systematic reviews have con- cludedthatshorteneddentalarches comprisinganteriorand premolar teeth generally fulfill the requirements of a functional dentition without the need for prosthodontic extension,especiallyinolderpatients[63,64].Inthisregard, thefindingsofastudyofocclusalactivity,includingbruxism, insubjects withmoderately shorteneddentalarcheswith or without mandibular distal extension removable partial
dentures and subjects withcomplete dentitions arelisted in Table 2 [65].
In a similar way as described for complete denture wearers, heavy bruxism may have detrimental effects on the residual dentition and the denture-bearing tissues in patientswithRPDs,althoughthishasnotbeensystematically studied.
A paper described the management of four patients with severesleepbruxism,andwhowereusingconventionalRPDs.
Eachpatientwasprovidedwithasplint-likeRPD,calledanight denture,andfollowed-upfor2–6yearsusingthenightdenture.
The authors concludedthatthe night denture appearedto be effective in managing problems related to sleep bruxism in patientswithRPDs[66].
4. Discussion
Researchfocusingontherelationshipbetweenbruxismand prosthetictherapyisscarce.OnlyoneRCTwasfound[4],but even this was of only limited value for the present review.
Relativelyfewrelevantarticleswiththesearchtermsusedwere listedinPubMed,andadditionalvaluabletextswerefoundby means of manual searching of the reference lists of articles foundandinrecenttextbooks.
There is noevidence thatprosthetic therapy, or anyother availabletreatment,caneliminatebruxism.Equally,thereisno evidencethatbruxismcanbecausedbyprosthetictherapy.The
Fig.7. A57-year-oldman(A)withimplantfractureintheregionof25(B)duetooverloading.
Table2
Conclusionsofastudyofocclusalactivity,includingbruxism,insubjectswith moderatelyshorteneddentalarcheswithorwithoutmandibulardistalextension removablepartialdenturesandsubjectswithcompletedentitions[65].
Similarfrequenciesforreportedawarenessofbruxism
Similarocclusalwearofloweranteriorteeth;incontrast,premolarshad significantlymoreocclusaltoothwear
SimilarfrequenciesofsignsandsymptomsrelatedtoTMD
Noclinicallyrelevantdifferencesofanteriorrelationshipsintermsofvertical andhorizontaloverlap
PosteriorocclusalsupportbymandibulardistalextensionRPDsintermsof occlusalcontactsinintercuspalpositionwaslimited;themoreposterior thedentureteeth,thelessocclusalcontacts
reviewwas,therefore,directedtowardstheeffectsofbruxism onvariouskinds ofprosthodonticrestorations.Butevenhere, the evidence was concentrated in certain areas, for example implant-supported prostheses, and the effects of excessive loadingonopposingnaturalteeth,restorativematerialsandthe structuralintegrityofprostheses.Theneedforresearchinthis areaisclearlygreat.
Fig.8. A72-year-oldmanwithmaxillaryandmandibularimplantsupported fixeddentalacrylicprostheses(FDPs)atdelivery(A).Patientisprobablya bruxer and after only 2years a definite wear pattern emerged, which is indicativeofheavyloadandfunction(B).FouryearslatertheFDPfractured (C)(CourtesyofDr.AlfEliasson,PostgraduateCenterforDentalEducation, O¨ rebro,Sweden).
Fig.9. Wearofacrylicteethofamaxillarycompletedenture(AandC)and opposingmetalcrowns(B)ina65-year-oldman.Theprosthetictreatmenthad beenprovided3yearsearlierbecauseofahistoryofextensivewearofsimilar previousreconstructions.
5. Conclusions
Bruxismisacommonparafunctionalhabit,occurringboth during sleepand wakefulness,andsleep bruxism andawake bruxismshouldbedifferentiated.
Bruxismusually has no serious effects, but may,in some patients,havepathological consequences.
Theetiologyofbruxismisnotwellknown,butitisagreed thatit ismultifactorial.
Thereisnospecifictreatmentavailableatthistimetostop bruxism,sothatthefocushasbeentoreducetheadverseeffects ofthe habit.
Theuseofinterocclusalappliancesisthemostcommonand accepted way to prevent wear of teeth and prosthodontic restorationsinspiteoflackofstrongevidenceforitsefficacy.
The role of bruxismin themultifactorial processof tooth wearisnotclear,butitisingeneralnotthemajorcause,ashas beenafrequentlystatedearlierview.
Toothwearisanaturalandgenerallyslowprocess,andworn teethseldomneedprostheticrehabilitation.In extensivetooth wear, the decision to treat or not should be based on the patient’sperceivedneed,theseverityofthewearandriskofits progressionwithrespecttothepatient’sage.
Whenprostheticinterventionisindicatedinapatientwith bruxism,effortsshouldbemadetoreducetheeffectsofheavy occlusal loading on all the components that contribute to prostheticstructuralintegrity.
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Fig.10. Wearofporcelainteethofcompletedenturesina55-year-oldwoman.
Thereasonwhyshehaddentureswithporcelainteethfabricated5yearsago wasbecauseshehadpreviouslyrapidlyworndowntheacrylicteethonher dentures.
