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Bdj_2011Resin Bonded Bridges Techniques for Success

Bonded Bridges Techniques
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  Resin bonded bridges:techniques or success K. A. Durey, 1 P. J. Nixon, 2 S. Robinson 3 and M. F. W.-Y. Chan 4  VERIFIABLE CPD PAPER By using a RBB it is possible to provide axed replacement or missing teeth whichis essentially reversible and does not com-promise the abutment tooth. This is espe-cially important or young patients whomay be more likely to experience endo-dontic complications as a result o exten-sive tooth preparation.Despite this recognised advantage, therole o RBBs as denitive restorationsremains somewhat controversial due to alack o long term prospective data regard-ing success. The majority o inormationis based on the results o longitudinalstudies, many o which have been poorly controlled, used a variety o cements andpreparation techniques making it dicultto isolate actors aecting outcome. 4 Recent systematic reviews have esti-mated the ve-year survival rates or bridgework as 87.7% or resin bondedprostheses 4 and just over 90% or con- ventional bridges depending on design. 5   Although these rates are lower than the94.5% success 6 reported or implantretained single crowns over the same ve year ollow up, resin bonded bridgework has the advantages o being less invasive,requiring a shorter total treatment timeand less nancial commitment.In contrast to these avourable esti-mations o RBB success, Hussey  et al  . 7  reported high ailure rates when they usedthe number o recement ees claimed togauge the success o RBBs in NHS gen-eral practice. Additionally, a recent study o RBB designs employed by dentists in INTRODUCTION Resin bonded or resin retained bridges(RBBs/RRBs) are minimally invasive xedprostheses which rely on composite resincements or retention. These restorationswere rst described in the 1970s and sincethis time they have evolved signicantly.The rst type o RBB was the RochetteBridge, which relied on the retentiongenerated by resin cement tags througha characteristic perorated metal retainer. 1  However, longevity o this type o restora-tion was limited and in an eort to addressthis, methods o altering the surace o the metal retainer to enhance microme-chanical retention were developed. 2 Theterm ‘Maryland Bridge’ resulted rom thedevelopment o a type o electrochemi-cal etching at the University o Maryland.More recently bridge retention has beenenhanced by the development o resincements which bond chemically to boththe tooth surace and the metal alloy.From a clinician’s perspective, the mainadvantage o RBBs is that, in compari-son to conventional bridge preparations,they are conservative o tooth structure. 3   Resin bonded bridges are a minimally invasive option or replacing missing teeth. Although they were rst described over30 years ago, evidence regarding their longevity remains limited and these restorations have developed an undeservedreputation or ailure. This article provides a brie review o the literature regarding bridge success and continues to high-light aspects o case selection, bridge design and clinical procedure which may improve outcome. both general practice and hospital settingsreported that a high proportion o prac-titioners used unavourable techniques. 8  It seems reasonable to assume that withimproved education and careul planning,outcome could be improved.The aim o this article is to re-evaluatethe role o RBBs in xed prosthodonticsand provide a guide or practitioners withregard to case selection, bridge design andclinical techniques in order that successuloutcomes may be achieved. FACTORS AFFECTING SUCCESSCase selection i) Patient factors  Restoration o missing teeth aims toimprove oral unction, aesthetics andrestore occlusal stability. However, inter- vention should be considered careully asin some cases it may be detrimental to theremaining dentition. 9-11  General actors such as the health, age o the patient, their expectations, local actorsrelated to dental health and the missingtooth itsel need to be taken into account.For example in older patients with reducedmanual dexterity it may be appropriate toaccept a shortened dental arch rather thanreplacing a lost posterior unit. I a toothmust be replaced, a RBB may be preerableto a removable partial denture (RPD) espe-cially where there is a history o signi-cant periodontal disease or dental caries. 9   As they are minimally invasive, RBBs canalso provide a temporary option or young 1* Specialist Registrar in Restorative Dentistry, 2,4 Con-sultant in Restorative Dentistry, Leeds Dental Institute,Clarendon Way, Leeds, LS2 9PU; 3 Senior Lecturer inClinical Dentistry, University o Queensland, Universityo Queensland, Turbot Street, Brisbane, Australia*Correspondence to: Dr Kathryn DureyEmail: Refereed PaperAccepted 16 June 2011DOI: 10.1038/sj.bdj.2011.619 © British Dental Journal 2011; 211: 113-118 ã   Gain a contemporary understandingo the role o resin bonded bridges inreplacing missing teeth. ã   Learn how to improve survival andaesthetics o resin bonded bridges. ã   A ‘quick reerence’ summary o thingsto consider clinically and technically, toimprove outcome. IN BRIEF P  R  A  C  T  I     C  E   BRITISH DENTAL JOURNAL  VOLUME 211 NO. 3 AUG 13 2011 113  PRACTICE patients who have suered the early losso an anterior tooth. This situation wouldotherwise condemn the patient to yearso denture wear until growth has ceasedand an implant or denitive bridge canbe considered.RBBs have the advantages o takingminimal clinical time 12 and rarely requiringanaesthetic, thereore they may be appro-priate or patients who are apprehensive o dental treatment or unable to commit tomore involved treatment involving mul-tiple appointments. However, the patientshould still be dentally motivated andcaries and periodontal disease should beunder control beore embarking on xedprosthodontics. In addition, managingexpectations with regard to aesthetic out-come and longevity should be consideredan important part o treatment planning. 13  I expectations are unrealistic, patient sat-isaction with the nal result is likely tobe low. ii) Abutment tooth selection  When selecting abutment teeth, investi-gations should be carried out to ensureendodontic and periodontal health.Periodontal support should be assessedconsidering bone levels and root congu-ration. Although a history o periodontaldisease and reduced bone support doesnot exclude bridgework (Fig. 1), the useo abutments with active periodontal dis-ease should be avoided as increased unc-tional loading may increase the rate o periodontal destruction. 14 Coronally, there should be sucientenamel available or bonding. The denti-tions o hypodontia patients are requently associated with a degree o microdontiareducing the amount o tooth structureavailable. Surace area may also be com-promised i teeth are restored or wherethere has been signicant tooth wear. Additionally, the alignment or angulationo teeth may aect the degree to which aretainer can be extended. Crowding may reduce access and rotations may mean thatull wraparound is dicult to achieve. Anunconventional approach may be neces-sary, or example in Figure 1, where abuccal retaining wing has been used on alingually tilted molar in an eort to avoidthe undercut lingual area that proved di-cult to access.I periodontal support and coronal con-dition are avourable, any teeth, includingretained deciduous teeth, 15 can act as abut-ments over an appropriate span. Deciduousmolars can make particularly good abut-ments as they are multirooted and have alarge coronal surace area which allowsull extension o the retainer wing. Theroots o retained deciduous teeth are likely to have undergone some resorption andhave reduced length however, they may also be ankylosed and so are well placedto act as abutments. iii) Occlusal features   When planning or RBBs, a detailed assess-ment o both static and dynamic occlusalrelationships is crucial to optimise success. A wax up on articulated casts gives a valu-able view rom the palatal aspect aidingthe assessment o the amount o interoc-clusal space available or the retainer wings and pontics. 13 It is important thatthe pontic is not involved in guidance dur-ing mandibular excursive movements. 16 I this is unachievable, guidance should beshared with other natural teeth.I there is insucient space or an aes-thetic pontic, adjustment o opposing teethcould be considered. Alternatively space Fig. 1 a) Older patient with a history o successully treated periodontal disease anddissatisaction with partial denture. b) Remaining teeth lingually tilted with increasedmobility. c) Provision o multiple (5) cantilever RBBs mimicking root exposure and staining o natural teeth. d) Note novel bucco-occlusal retaining wing used on lingually tilted molar toothFig. 2 Hypodontia case demonstrating two cantilever RBBs to replace UL 3 and ULE. Note the extent o coverage o metal retainers,characterisation o porcelain work and ovate style pontic to achieve good aesthetics acdb 114 BRITISH DENTAL JOURNAL  VOLUME 211 NO. 3 AUG 13 2011  PRACTICE be maintained separately to restorativetreatment, either with removable ortho-dontic retainers or orthodontic bondedwire retainers. I a xed-xed design isrequired, contact in excursive movementsand intercuspation should be on theretainer only. 19 i) Retainer wing coverage  The surace area covered by an RBB retainer has been shown to aect retention. It isaccepted that 180° wraparound retainersconstitute the ideal design, but this mustbe balanced with the demand or aesthet-ics. Retainers on posterior teeth may beextended to include coverage o the palataland lingual cusps and a proportion o theocclusal surace (Fig. 2) to increase the sur-ace area and improve retention. I neces-sary, the surace area or bonding can bemaximised by crown lengthening, either with conventional periodontal faps or withelectrosurgery (Fig. 3). Electrosurgery is par-ticularly relevant or young patients whohave short clinical crown heights, a substan-tial proportion o whom present ollowingorthodontics wearing retainers which can beassociated with gingival hyperplasia. I teethare restored, llings should be replaced withresh composite restorations, which willbond more avourably to the resin cementenhancing retention o the bridge. 26 ii) Technical features   Any fexing o the metal bridge retainer exerts stress on the cement lute thateventually leads to atigue ailure. 27 Basemetal alloys are highly rigid and thereorecan be used in thin section without risk o fexing, making them ideally suited or use in RBB retainers. In vitro research hasshown that base metal retainers o lessthan 0.7 mm thickness have less resistanceto dislodgement 28 and thereore 0.7 mmas a minimum dimension should be stipu-lated in the technical prescription. Wherethere is insucient interocclusal space toaccommodate a retainer o this thickness,teeth can be reduced to create space or thebridge can be cemented high as previously described. 17,18 Clinicians should veriy adequate thickness o the metal retainer beore cementation to ensure sucientrigidity, or example using an Iwanssoncrown gauge (UnoDent Ltd, Witham,Essex, UK). A locating tag or seating lug should beextended over the incisal edge o anterior teeth (Fig. 4) to help to locate the retainer may be gained with localised anterior composite build ups to adjust guidancepatterns or by cementing the restorationat an increased OVD on the retainer. 17   With both o these options the occlusionwould then be allowed to re-establish over a period o months through passive erup-tion. 18 Cementing restorations high doesnot appear to increase the risk o abut-ment teeth proclining or the restorationdebonding, 19 however, the authors suggestthat this technique should be used to makeonly modest and controlled changes tothe occlusion.Paraunctional orces increase the likeli-hood o restoration ailure, especially wherethe occlusion has not been accounted or. Any habits should be identied during theassessment phase and the patient shouldbe counselled to avoid habits like nail andpen biting. Where bruxism is suspected theprescription o a night guard or occlusalsplint should be considered. 2   Bridge design It has been widely reported that RBBsare more successul as cantilevers thanas xed-xed restorations. 20-23 Despitethis evidence a high number o dentistscontinue to use xed-xed designs anddouble abutments. 8 Resin bonded bridges with multiple abut-ments are more likely to debond due to thedierential movement o abutment teeth,especially where occlusal contact involvesthe natural tooth surace. In these casesocclusal orce leads to the tooth and theretainer being driven apart causing ailureo the cement lute. 19 Where two abutmentteeth have been used it is unlikely thatboth retainers will debond simultaneously. When only one retainer ails, the bridgeis likely to remain in situ promoting thedevelopment o caries beneath the ailedretainer. 20,21,24  There are, however, some situations inwhich a xed-xed design may be themost appropriate. These include largepontic spans and where abutment teethare small and sucient surace area or retention can only be gained by using oneabutment at either end o the span. It hasalso been suggested that xed-xed RBBscan provide a orm o orthodontic reten-tion, particularly where teeth have beende-rotated. 25 However, it is the view o theauthors that orthodontic retention should Fig. 3 Upper central incisor ollowinglengthening o clinical crown height usingelectrosurgeryFig. 4 Extension o retainer wing into existing palatal access cavity to improve resistanceand retention orm. Also note incisal seating lug BRITISH DENTAL JOURNAL  VOLUME 211 NO. 3 AUG 13 2011 115  PRACTICE correctly and resist cervical displacemento the retainer during cementation. It canbe removed with a bur ater cementationand the metal polished as needed. iii) Aesthetics  The aesthetics o a RBB are determined by the retainer wing, the porcelain work andhow the sot tissues are managed. Metalconnectors may shine-through translucentincisors causing them to appear grey andin act Djemal et al. 19 reported that themetal o the retainer was the most com-mon reason or patient dissatisaction withtheir RBB.Greying can be reduced to a degreeby the use o opaque cement and careulretainer design, avoiding extending themetal to within 2 mm o the incisal edge,where the enamel becomes relatively moretranslucent. In cases where the retainer cannot be disguised by opaque cements, itmay be necessary to reconsider the choiceo abutment tooth or place composite labi-ally as a veneer.The shade o the porcelain should beconveyed to the technician by means o a shade map, which can include detailso characterisation eatures i appropriate(Fig. 2). The shade should be taken in natu-ral light at the beginning o the appoint-ment when the teeth are hydrated. A goodquality digital photograph with the chosenshade tab in situ can be a valuable aid or the technician. iv) Pontic design Several alternatives or pontic design havebeen described based on the pontic-ridgerelationship. The most commonly usedo these is the modied ridge lap pontic,which allows reasonable aesthetics andacilitates hygiene. In aesthetically criti-cal areas, the authors’ preerred alterna-tive to this is the ovate pontic, which hasa convex prole to the sot tissue ttingsurace helping to create a good emergenceprole (Fig. 2). When designing the pontic,it is important to relate the gingival levelto that o the adjacent natural teeth. Clinical techniques i) Need for tooth preparation The need or tooth preparation or RBBs isa subject o debate. Previous research usedmore extensive preparations to enhanceretention, 29 however, most authorities nowadvocate minimal preparation, withinenamel, 30 or no preparation at all. 17,19   Vertical grooves are the particular ea-ture which has been identied as reducingstresses on the cement bond 31 and increas-ing resistance to debonding orces. 29,32  However, preparation involves irrevers-ible damage to abutment teeth or whatis reported to be only a limited benet, 19  and even when minimal preparation isintended, dentine exposure is likely duringpreparation. 24 Bond strength to dentine islower than that that can be achieved toenamel which may aect bridge retention. Additionally dentine exposure increasesthe chance o sensitivity between appoint-ments and the risk o caries i the area isnot sealed adequately at cementation. A situation in which more extensivepreparation can be justied is when teethare restored. Preparation may be devel-oped into restorations to produce longi-tudinal grooves, occlusal rests and boxeson posterior teeth, and into access cavity restoration on anterior teeth. This helps topromote axial loading and creates resist-ance orm (Fig. 4). ii) Cementation Developments in resin cements havehelped to increase restoration longevity.Early composite resin materials exhibiteddegradation and reduced bond strengthwith time. In contrast, Panavia (Karrary Co. Ltd, Osaka, Japan) demonstrates pro-longed high bond strengths. This is dueto ormation o a chemical bond betweenthe phosphate group o the cement mon-omer and the oxide layer o the metalretainer. Sandblasting to create micro-mechanical interlocking should be car-ried out beore cementation to urther enhance retention.RBB cementation requires an uncontam-inated, etched and primed enamel or den-tine surace to generate maximum bondstrengths. In vitro research has shownthat achieving uniorm and ideal etchingo enamel suraces is variable, especially on lingual suraces o lower posterior teeth where moisture control is dicult. 33   Audenino et al  . 34 ound that the use o rub-ber dam during cementation reduced therisk o the restoration debonding; however,in contrast, Marinello et al. 35 reported theisolation method used had no signicanteect on bridge outcome. It is the experi-ence o the authors that, i patients arecompliant, adequate moisture control canbe achieved in the upper anterior regionusing the cotton wool rolls and saliva ejec-tors. Elsewhere in the mouth rubber damis advisable and a split dam techniquecan be utilised to acilitate seating o the restoration. Fig. 5 a) Young patient presenting with developmentally missing lateral incisors. Note thecentral incisors are barrel shaped and the canines diminutive. b) Ridge preparation at thepontic site, note the central incisors and canines have been built up using composite resinto improve dimensions. c) Resin bonded bridges in situ replacing the lateral incisors. d) Theemergence profle created ollowing ridge preparation and use o an ovate pontic gives apleasing aesthetic result acbd 116 BRITISH DENTAL JOURNAL  VOLUME 211 NO. 3 AUG 13 2011
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