Crowns and other extra-coronal restorations: Provisional ...

PRACTICE

BRITISH DENTAL JOURNAL VOLUME 192 NO. 11 JUNE 15 2002 619

Crowns and other extra-coronal restorations:Provisional restorations R. W. Wassell1 G. St. George2 R. P. Ingledew3 and J. G. Steele4

The important role of provisional restorations is often overlooked. This may be because they are left until the end of anappointment when time for construction is short or because they generally do not need to last for long. However, not onlycan good provisional restorations help produce better final restorations, they can also save a lot of time and expense atsubsequent appointments. In fact time spent in their construction will be more than repaid in time saved doing additionalprocedures, adjustments and remakes later on.

1*,4Senior Lecturer in Restorative Dentistry,Department of Restorative Dentistry, TheDental School, Newcastle upon Tyne NE24BW; 3Senior Dentist, Boots Dental Care,54-58 High Street, Maidenhead, BerkshireSL6 1PY; 2Higher Specialist Trainee,Eastman Dental Hospital, 256 Grays InnRoad, London WC1X 8LD*Correspondence to: Dr R. W. Wassell,Department of Restorative Dentistry, The Dental School, Newcastle upon Tyne NE2 4BWE-mail: [email protected]

Refereed Paper© British Dental Journal 2002; 192:619–630

● The functions of provisional (sometimes termed temporary) restorations● Diagnostic uses of provisional restorations● Provisional restorations for conventional preparations including: the concept of short,

medium, and long-term temporisation; materials; and direct and indirect provisionalrestorations

● Provisional restorations for adhesive preparations● Problem solving

I N B R I E F

This article discusses the need for provisionalrestorations, the types and materials available.Provisional restorations for adhesive restora-tions often pose a difficult problem and theseare considered separately. You may alsoencounter other difficulties with provisionalrestorations so we end the article on problemsolving.

Functions of provisional restorationsProvisional restorations are used in the inter-im between tooth preparation and fitting adefinitive restoration. The various functionsthey fulfil are described in Table 1. Withcrown preparations provisional restorationsare generally essential to cover freshly cutdentine and prevent tooth movement. Withadhesive preparations protection of exposeddentine is usually less of an issue and often aprovisional restoration is not needed, butthere are still occasions where it is importantto prevent unwanted tooth movement ormaintain aesthetics.

Provisional restorations can be invaluable fortesting out aesthetic and occlusal changes beforethey are incorporated in the definitive restora-tion. They can also help stabilise the periodontalcondition prior to definitive restoration. Thesediagnostic uses will be considered in more detailin the next section.

As well as the prophylactic and diagnosticuses, provisional restorations have other practi-cal applications. For example, callipers may beused to test the thickness of a provisionalrestoration to ensure sufficient tooth preparationto accommodate the proposed restorative mate-rial (Fig. 1). Occasionally, a provisional restora-tion may be used to provide a coronal build upfor isolation purposes during endodontic treat-

ment. A period of long-term provisional restora-tion may also be advisable to assess teeth ofdubious prognosis. Finally, a provisionalrestoration may find a use as a matrix for corebuild ups in grossly broken down teeth, simplyby removing the coronal surface to allow place-ment of restorative material.

DIAGNOSTIC USESProvisional restorations, especially those usedfor conventional preparations, are invaluable insituations where aesthetic, occlusal or periodon-tal changes to a patient’s dentition are planned.The principles behind such changes are dis-cussed later.

Aesthetic changesProposed changes to the shape of anterior teethare best tried out with provisional restorations toensure patient acceptance, and, approval fromfriends and family; clearly, it is easier to trim oradd acrylic than it is porcelain. Once happy, an

9

CROWNS AND EXTRA-CORONALRESTORATIONS:1. Changing patterns and

the need for quality2. Materials considerations3. Pre-operative

assessment4. Endodontic

considerations5. Jaw registration and

articulator selection6. Aesthetic control7. Cores for teeth with

vital pulps8. Preparations for full

veneer crowns9. Provisional restorations 10. Impression materials and

technique11. Try-in and cementation

of crowns 12. Porcelain veneers13. Resin bonded metal

restorations

Fig. 1 Provisional restorations have many functions otherthan just protection of the prepared tooth. Here anSvensen gauge is used to assess sufficient toothreduction to accommodate the proposed restoration

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620 BRITISH DENTAL JOURNAL VOLUME 192 NO. 11 JUNE 15 2002

alginate is recorded so that the technician cancopy the shape into the definitive restoration. Ifonly one or two teeth are involved it is perfectlypossible to contour provisional restorations atthe chair side. It is however important to balancethe time spent doing this against the advantagesof having a diagnostic wax up and matrix madein the laboratory (Fig. 2). Alternatively, indirectprovisional restorations can be prescribed whichwill be described later.

Occlusal changesA patient’s tolerance to changes in anteriorguidance or increased occlusal vertical dimen-sion is best tried out with provisional restora-tions. Again, a diagnostic wax up is advisable,and, with occlusal changes, the importance ofusing casts mounted on a suitable articulatorcannot be overstated (Fig. 3). Direct or indirectprovisional restorations are then constructedfrom these and cemented temporarily afteradjusting to provide even occlusal contact inthe intercuspal position and guidance or dis-clusion if required. The patient can then beexamined at a further appointment and theocclusal surfaces copied as long as the follow-ing criteria are met:

• Restorations are still cemented• Occlusal contacts have been maintained, with

no drifting of teeth• Teeth are not mobile, or existing mobility is

not increasing• There is no discomfort

Guidance surfaces can be copied betweenprovisional and definitive restorations by usinga custom guidance table as described in Part 5of the series.

Where it is decided to increase the patient’socclusal vertical dimension, provisional restora-tions provide a way of assessing tolerance to theincrease, as well as assessing aesthetics and theoverall occlusal scheme. However it is often wiseto make an initial assessment of such changeswith a more reversible method, such as a splint,before the teeth are prepared.

Periodontal changesIt may be necessary as part of a patient’s periodon-tal treatment to remove overhanging restorationsto allow access for cleaning and resolution ofinflammation. Long-term wear of properly fittingand contoured provisional restorations allows thehealth of the gingival margin to improve and itsposition to stabilise before impressions are record-ed for definitive restorations.

Following periodontal or apical surgery thetissues will also need time to stabilise before thefinal finish line is cut for definitive crowns.Where surgical crown lengthening is used toincrease clinical crown height, it is best to allow6 months before definitive restoration, especial-ly if the aesthetics are critical.1 If provisionalrestorations are provided soon after crownlengthening it is important to avoid taking thepreparations subgingivally as this may set up achronic gingivitis which is difficult to resolve.

Changes in tooth shape — avoiding problemsFor the majority of people, minor adjustments intooth shape are unlikely to cause any problems,but for others, eg singers and wind instrumentmusicians, the eventual restorations, if poorlyplanned, may interfere with the patient’s‘embouchure’. This term describes the fine mouthmovements and lip/tooth contact required forspeech production or sound generation in thecase of a musical instrument. Also the incorpo-

Table 1 The functions of provisional restorations

1) Comfort/tooth vitality To cover exposed dentine to prevent sensitivity, plaque build up,subsequent caries and pulp pathology.

2) Occlusion and positional stability To prevent unwanted tooth movement by the maintenance ofintercuspal and proximal contacts. It may be necessary toestablish a holding contact on the provisional restoration.Depending on the patient’s occlusal scheme, the provisionalrestoration may need to provide guidance in protrusive andlateral excursions, or disclude to prevent working or non workinginterferences. Interproximal contacts also need to be maintainedto prevent food packing.

3) Function Attention to 1) and 2) will ensure the patient continues tofunction adequately.

4) Gingival health and contour To facilitate oral hygiene and prevent gingival overgrowthprovisional restorations require accurate margins and cleansablecontours. They can be used in the interim where the level of thegingival margin has yet to stabilise (e.g. after crown lengtheningor removal of a crown with defective margins).

5) Aesthetics To provide an adequate interim appearance provisionalrestorations should either mimic the tooth just prepared, or thefinal intended restoration.

6) Diagnosis To assess the effect of aesthetic and occlusal changes. The abilityto re-shape can also be used to overcome phonetic problemsbefore construction of the definitive restoration.

7) Other practical uses To measure tooth reduction, to isolate during endodontics, toassess prognosis, to act as a matrix for core construction.

Fig. 2 A diagnostic wax-up is aninvaluable way of planning changes,which can be tried out with theprovisional restorations. The patientwould be more impressed by toothcoloured wax!

Fig. 3 Casts need to be mounted on a semi-adjustablearticulator to wax occlusal changes

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ration of wider cervical embrasure spaces, tofacilitate interproximal cleaning, may occasion-ally cause embarrassment because of air leak-age. Therefore it makes sense to copy the fea-tures of successful provisional restorations, toavoid patient dissatisfaction and expensiveremakes.

PROVISIONAL RESTORATIONS FORCONVENTIONAL PREPARATIONSThe variety of provisional restorations availablecan seem bewildering. To help you through themaze we need first to consider the materials andthen the techniques by which provisionals canbe made. Most provisionals are made directly atthe chair side, but for long term wear or diagnos-tic use there can be advantages in having themlaboratory-made.

It is worth emphasising that the length oftime between preparation of teeth and cemen-tation of final restorations can vary from afew days for straightforward cases (short-term), to several weeks (medium-term) oreven, in the case of complex reconstruction,several months (long-term). The longer provi-sional restorations are in the mouth, thegreater are the demands on the material fromwhich they are made.

MaterialsMaterials used in the surgery comprise pre-formed crowns (made of plastic or metal), selfcured or light cured resins or resin compositesand cements. Laboratory formed temporaries aregenerally made in self cured or heat curedacrylic, or cast metal.

Pre-formed crownsAlso known as proprietary shells, these come ina series of sizes but usually need considerableadjustment marginally, proximally andocclusally. Plastic shells are made from polycar-bonate or acrylic, and, with good aesthetics, arecommonly used for anterior teeth including pre-molars. Metal shells may be made from alumini-um, stainless steel or nickel chromium and areonly used on posterior teeth. Both plastic andmetal shells can be relined with self cured resinto improve their fit.

Self or light cured resinsA variety of materials is available for eitherdirect or indirect techniques:

• Polymethyl methacrylate (self or heat cured) (eg Vita K&B Acrylics)

• Polyethyl methacrylate (eg Snap, Trim)• Bis acryl composite (eg Protemp, Quicktemp)• Urethane dimethacrylate (light cured) (eg

Provipont DC)• Restorative composite

Polymethyl methacrylate is strong, has ahigh wear resistance, is easy to add to, and hasgood aesthetics, which is maintained overlonger periods.2 However, it does have threemain disadvantages:

i) Polymerisation shrinkage which can affectfit

ii) Polymerisation exotherm which can damagepulp3

iii) Free monomer may cause pulp and gingivaldamage

It is, however, a good material for indirect pro-visional restorations. Self cured acrylic can bepolymerised under pressure in a hydroflask whicheffectively reduces porosity.4 Alternatively, heatcured acrylic can be used.

Polyethyl methacrylate (Fig. 4a) is suitablefor intra-oral use as it shrinks less and is lessexothermic than polymethyl methacrylate.However, strength, wear resistance, aestheticsand colour stability are not as good. Some pre-sentations come with a good colour range (egTrim II) while others have only light and darkshades (eg Trim).

Bis-acryl composites (Fig. 4b) produce lessheat and shrinkage during polymerisationthan other resins, resulting in a better margin-al fit.5 Despite being reasonably strong theyare brittle in thin section and difficult to addto. Aesthetically they are reasonable, but fewshades are available and they stain easily if theunpolymerised surface layer is not removedwhich may be accomplished with alcohol andpolishing. They are more colour stable thanpolyethyl methacrylate materials and aretherefore better suited for use as long-termprovisionals.6

Most recently, visible light cured resins havebeen introduced based on urethane dimethacry-late eg Provipont D.C. These relatively expensiveresins have good mechanical properties and,being light cured, the operator has some controlover the material’s working time. Generallymore shades are available than bis acryl com-posite and the colour is relatively stable, but isstill prone to staining. Marginal fit can be poor,

Fig. 4 Examples of resins used forprovisional restorations: (a) Polyethyl methacrylate (powder-liquid presentation); and (b) Bis-acryl composite (syringe mixed)

a

b

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but the material can be added to. Light curedmaterials, especially unfilled ones, have a higherexotherm than chemically cured materialsbecause of their greater speed of reaction.7 Thisexotherm may have implications for pulpalhealth.

Restorative composites, normally used forfilling teeth, can be used as a provisional materi-al for adhesive preparations, as described later.Other restorative composites are designed forlaboratory fabrication but may be useful forlong-term provisional restorations.

Cast metalAlloys used include nickel chromium, silver andscrap gold. Copings can be cast with externalretention beads for acrylic or composite. In lessaesthetically critical areas of the mouth, metalmay be used on its own. Cast metals are verydurable, but rarely used unless provisionalrestorations have to last a long time.

Provisional cementsProvisional restorations are usually cementedwith soft cement. Traditionally, a creamy mix ofzinc oxide eugenol was used, but nowadaysmost dentists prefer proprietary materials suchas Temp Bond (Fig. 5). This material comes witha modifier, which is used to soften the cement, asdescribed later in the article, to ease removal ofthe provisional restoration from more retentivepreparations. Temp Bond NE is a non-eugenolcement which may be used for patients witheugenol allergy or where there is concern overthe possible plasticising effect of residualeugenol on resin cements and dentine bondingagents. Certainly, surface hardness11 and shearbond strength of resin12 to resin can both beaffected by eugenol and it is worth noting thateugenol cements can significantly reduce thebond of resin cements to composite cores.16

However, resin bond strengths to enamel13 anddentine14 are not affected if the eugenol residueis removed with pumice and water before condi-tioning. Microleakage15 is also unaffected by theuse of eugenol.

Occasionally, hard cement is needed to retaina provisional on a short preparation. This is con-sidered later in the ‘problem solving’ section.

Direct provisional restorations — techniquesMost provisional restorations will be madedirectly in the mouth. As mentioned earlier it isworth taking time in their construction. As a ruleof thumb, the time taken to temporise a toothshould be similar to the time taken to prepare it.This approach ensures sufficient time is devotedto good fit and contour. The techniques availableare listed overleaf:

Fig. 5 Temp Bond and Temp Bond NE: The modifier (central tube) can be mixed with Temp BondBase and Catalyst to ease crown removal with retentive preparations. Regular Temp Bond containseugenol, which can soften composite cores. Temp Bond NE (shown to right of photograph) does notcontain eugenol and will avoid this problem

Fig. 6 (a) A familiar polycarbonateshell crown relined with Trim; and(b) The provisional is carefullytrimmed to help maintain gingivalhealth

a

b

Fig 7 (a) Aluminium shell crowns are convenient, butsuitable only for short term use on posterior teeth; and(b) Crimping of the crown margins will improveretention and fit

a

b

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• Shells (proprietary or custom)• Matrices (either formed directly in the mouth

or indirectly on a cast)• Direct syringing

To avoid confusion with terminology, a shellis incorporated into the provisional restorationwhereas a matrix is merely used to form it.

Proprietary shellsShells can be divided into proprietary and cus-tom made. Proprietary shells made of plastic(Fig. 6) or metal (Fig. 7) are used commonly inpractice when only one or perhaps two prepara-tions are involved.

Proprietary plastic shells: A crown with thecorrect mesio-distal width is chosen and placedon the tooth preparation. The cervical marginsare trimmed to give reasonable seating and adap-tation. The preparation is then coated with petro-leum jelly and the crown, containing a suitableresin eg Trim, is reseated. While the resin is stillincompletely set, the proximal excess is removedusing a sharp bladed instrument such as a halfHollenback amalgam carver. The crown is thenremoved and replaced several times to preventresin setting in undercuts. Finally, the crown isadjusted and polished using steel or tungstencarbide burs and Soflex discs. Diamond burs arebest avoided, as they tend to melt the shell andresin because of the heat generated.

Proprietary metal shells: Aluminium crownsare really only suitable for short-term use asthey are soft resulting in wear and deformation.Furthermore, they can produce galvanic reac-tions in association with amalgam restorations.Their fit is usually poor unless considerable timeis spent trimming and crimping the margins fol-lowed by relining with a resin. Stainless steel ornickel chromium crowns may occasionally beused on molar teeth opposed by flat cusps whereheavy occlusal loading would quickly wear orbreak a resin crown.

Custom shellsSome operators favour custom shells for multi-ple tooth preparations. The shell is made inadvance of tooth preparation so the desiredexternal contours are pre-formed, but reliningand careful marginal trimming are necessaryprior to fitting. Custom shells are of two types,either beaded acrylic or ‘Mill Crowns’. Both offerthe advantage of being able to use the superiorproperties of polymethyl methacrylate, whilstavoiding pulpal damage by constructing theshell out of the mouth.

The beaded acrylic shell is formed within animpression taken of the teeth prior to preparationor of a diagnostic wax up. A thin shell of poly-methyl methacrylate is constructed in the impres-sion by alternately placing small amounts ofmethyl methacrylate monomer followed by poly-mer, taking care not to make the shell too thick,otherwise it will need time-consuming adjust-ment later. Once set, it is trimmed and then relinedin the mouth as with polycarbonate crowns.

Mill Crowns are formed by first cutting mini-mal crown preparations on a stone cast. A pre-preparation matrix is then filled with poly-methyl methacrylate and placed over thepreparations. The trimmed and adjusted provi-sional crowns are again relined in the mouth.

MatricesMany operators prefer matrices (Fig. 8) to shellcrowns for making single or multiple provision-al crowns. This is because matrices closely dupli-cate the external form of satisfactory existingteeth, or, if changes are required, a diagnosticwax up. If the matrix is carefully seated minimaladjustments are generally needed other thantrimming flash at the crown margin.

There are three main types of matrix:

• Impression (alginate or elastomer)• Vacuum formed thermoplastic• Proprietary celluloid

The simplest way of making a matrix is torecord an impression of the tooth to be preparedeither in alginate or silicone putty. Impressionmatrices are quick, easy and inexpensive, andcan be formed while the local anaesthetic isallowed to take effect. When impression matri-ces are used some judicious internal trimmingmay be helpful to improve seating and bulk outcritical areas of the provisional restoration.These aspects are covered later when we dealwith problem solving. Alginate matrices arebest at absorbing the resin exotherm3 —although the temporary should have beenremoved before this stage of set. Elastomericimpression matrices have the advantage ofbeing reusable, allowing them to be disinfectedand stored in case they are required again.Polyvinylsiloxane putty impressions are fre-quently used because of their ease of handlingand long-term stability.

Fig. 8 (a) A commonly used matrix isan alginate impression of theunprepared tooth; and (b) The flashmust be removed and the linkedprovisionals trimmed prior tocementation

a

b

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If a tooth is broken down or its shape needsto be changed, it will first need to be built up.Soft red wax can be used for this purpose, butanyone who has tried this will know that itdoes not stick well. Adhesion can be improveddramatically by first painting the tooth with acoat of varnish (eg copal ether or glassionomer varnish) and allowing it to dry. Theopposing teeth are smeared with petroleumjelly to allow their form to be stamped into thewax should it be necessary to build up theocclusal surface. Rather than try and achieveperfection with an intra-oral wax-up it is bet-ter to aim for a slight over-contour, which canbe corrected by trimming the provisionalrestoration. It is best to avoid putty for makingthe matrix as it can distort or displace the waxwhen the impression is seated.

There is no doubt that the above technique isinvaluable, however, when dealing with multi-ple crowns it is a much better strategy to firstcarry out a diagnostic wax up on mounted casts(Fig. 3). The intended aesthetics and occlusioncan be formed much more efficiently andpatients appreciate being able to see a ‘blueprint’ of the definitive restorations on the articu-lator. Moreover, the wax up can be used to forma suitable indirect matrix.

Indirect matrices can be made from impres-sion material (Fig. 9a) or you can ask yourlaboratory for a vacuum formed matrix madeof clear plastic (Fig. 9b). If you decide to makean indirect matrix from impression materialremember to first soak the cast for five min-utes. In this way you will avoid the embarrass-ment of sticking impression to cast. Immer-sion in warm water (not hot) has theadvantage of speeding up the impressionmaterial’s setting time.

Vacuum formed matrices are made of clearvinyl sheet produced on a stone duplicate of the

waxed up cast. This is necessary to avoid melt-ing the wax when the hot thermoplastic materialis drawn down. Not everyone is enthusiasticabout using a vacuum formed matrix becausethey are flexible and can distort when seated,especially if there are few or no adjacent teeth toaid location. Where it is necessary to rely on thesoft tissues for matrix location we prefer to usean impression matrix.

Whilst vacuum formed matrices are not with-out problems, being made of clear plastic theyare indispensable for moulding light curedresins. A proprietary celluloid matrix can beused if only a single provisional crown is to beformed using light cured resin.

Whatever matrix is chosen care must betaken in its use. After tooth preparation, a thinsmear of petroleum jelly is placed over thereduced tooth and adjacent teeth. The matrix isblown dry and the mixed resin is syringed intothe deepest part of the appropriate tooth recess,taking care not to trap air, especially at theincisal angles. After reseating, the matrix is leftuntil the resin reaches a rubbery stage. It is thenremoved and interproximal excess removed inthe same way as for the proprietary shell. Settingcan be monitored to some extent by testing theconsistency of a small portion of materialsyringed onto the front of the seated impression.Following removal, the crowns are trimmed,polished and cemented.

Direct syringingWhen no shell temporary can be found to fitand, for whatever reason, no matrix is availableit can be useful to syringe material directlyaround a preparation. For this purpose the poly-ethyl methacrylate materials are best as they canbe mixed to sufficient viscosity not to slump butare still capable of being syringed. This propertywhereby a material undergoes an apparentdecrease in viscosity at high rates of shear, aswhen passed through a syringe nozzle, is called‘shear thinning’. It is also seen with the polyethermaterial, Impregum.

When syringing, start at the finish line andspiral the material up the axial walls. Overbuildthe contours slightly as it is easier to trim awayexcess than to have to add later.

Indirect provisionalsMany dentists will not have used indirect provi-sional restorations and may find it hard to justifylaboratory costs. However, indirect provisionalsoffer certain advantages with complex casesneeding long-term temporisation. Firstly, materi-als which are stronger and more durable can beused eg heat cured acrylic or self cured acryliccured in a hydroflask. Secondly, if aesthetic orocclusal changes are to be made these can bedeveloped on an articulator. Indirect provisionalscan certainly save clinical time, especially withmultiple restorations and most particularly wherethere is to be an increase in vertical dimension,especially where the patient is a bruxist (Fig. 10).

Whether or not major changes are indicat-

Fig. 9 Where aesthetic or occlusalchanges are proposed, provisionalcrowns can be formed in the mouthwith laboratory-made matrices: (a) A putty or alginate matrix can beformed directly on the wax-up(remember to soak cast first); and(b) A vacuum formed matrix canalso be made, but on a stoneduplicate of the wax-up to preventthe wax from melting (matrix shownprior to trimming)

a

b

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ed, it is best to decide on the type of provi-sional restoration during treatment planning.If indirect restorations are chosen, sufficienttime can be scheduled either to make themwhilst the patient waits or an additionalappointment can be made to fit those made inthe laboratory.

Some operators favour making indirect pro-visional restorations from self cured acrylic atthe same appointment the teeth are prepared. Ifthe surgery has an on site technician (or suit-ably trained nurse) this can be a very efficientway of working as it allows the dentist to dosomething else while the provisional restora-tions are being made. An alginate impression isrecorded of the prepared teeth and this is castup in quick setting plaster. The plaster model isthen coated with cold-mould seal and a suit-able shade of self cured acrylic mixed up. Theacrylic is then flowed into a matrix made fromthe diagnostic wax up (eg silicon putty or vacu-um formed) which is then seated onto the castand its position stabilised with elastic bands,taking care not to distort it. Polymerisationtakes place within a hydro flask followingwhich the matrix is removed; the relatively softplaster dug out and the acrylic flash trimmedback to the margin. Additions may need to bemade to the margins of the crowns where poly-merisation shrinkage has produced a gap. Thiscan be done in the mouth or on a cast. If donein the mouth, then the tooth needs lubricatingwith petroleum jelly and the crowns removedbefore excessive heat is generated.

Clearly, an extra appointment will be neces-sary if indirect provisional restorations aremade in an outside laboratory. In the interimdirect provisional restorations will also beneeded. This approach can be very effective,however, where an increase in vertical dimen-sion is prescribed. A number of strategic teethcan be prepared and interim provisionalrestorations made directly to conform to theexisting occlusion (eg from polyethylmethacrylate or Bis acryl composite). Onreturn, the indirect provisional restorationscan be used to establish the increased verticaldimension on multiple teeth. Often these casesrequire minimal or no occlusal preparation asocclusal clearance is provided by the increasein vertical dimension. When this happens theinterim provisional restoration will resemble atube with no occlusal surface, which is usuallyacceptable for short periods.

PROVISIONAL RESTORATION OF ADHESIVEPREPARATIONSProvisional restorations for conventional toothpreparations (eg full veneer crowns, 3/4 crowns,and onlays) obtain retention in a similar way tothe final restorations ie via cement on prepara-tions with long, minimally tapered axial walls.The lack of conventional retention provided bymost adhesive preparations results in temporarycements being ineffective. A number of strate-gies can be used to deal with this problem, some

of which are more appropriate for certain situa-tions than others:

• No temporary coverage may be necessary egwith veneer preparations involving minimaldentine exposure and not removing intercus-pal or proximal contacts. Where space hasbeen created with a Dahl appliance, the appli-ance can be used in the interim to retain theteeth in position

• A simple coat of zinc phosphate cement toprotect exposed dentine eg in tooth prepara-tions which are not aesthetically critical andwhere the occlusion is either not involved orthe restoration can be returned rapidly fromthe laboratory and fitted before significanttooth movement occurs

• Composite resin bonded to a spot etched onthe preparation eg veneer preparations whichare aesthetically critical or occlusally criticalor have sensitive, fresh cut dentine. The provi-sional restoration is fabricated using eitherdirectly placed composite which is time con-suming, or composite and a clear vacuumformed matrix made from a preoperative cast.For longer lasting provisionals, acrylicveneers may be made in the laboratory. Limit-ing the area of bonding facilitates compositeremoval, but the bonded area must be groundback to tooth substance when the definitiverestoration is fitted. If the composite is cutwithout water spray it is easier to distinguishbetween the powdery surface of the groundcomposite and the glassy appearance of theunderlying tooth

• Composite resin bonded to the opposing toothto maintain occlusal contact and preventover-eruption (eg shims or veneers wheresome additional occlusal reduction isrequired). After the definitive restoration isplaced, the opposing composite is removed

Fig. 10 Metal and acrylicprovisionals used in the occlusalreconstruction of a bruxist: (a) A relined NiCr shell at tooth LL7 (37) where the previous acrylicprovisional crown had fracturedrepeatedly; and (b) The upper archhas acrylic heat cured onto beadedmetal copings in an attempt toimprove fracture resistance —however a good bond between metaland acrylic is needed for success

a

b

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• Conventional provisional restorationscemented with either a non-eugenol tempo-rary cement or a hard cement such as zinc car-boxylate. This approach may be used foradhesive restorations having some mechani-cal retention eg an inlay or resin bondedcrown. The choice of cement will depend onhow retentive the preparation is.

It is sensible to expect provisionals for adhe-sive preparations to be effective only in the shortterm. Certainly, their diagnostic usefulness intesting changes in aesthetics and occlusion ismuch more limited than with provisionalrestorations for conventional preparations.

PROBLEM SOLVINGA number of problems are encountered whenmaking provisional restorations. Some of theseare discussed below:

Insufficient bulk of materialThe axial walls of resin provisionals are oftenthin which makes them prone to damage duringremoval from the mouth. This is particularly thecase when minimal amounts of tooth areremoved eg preparations for gold crowns. To

prevent damage, the provisional should be madetemporarily wider by relieving the appropriatepart of the impression with a large excavator(Fig. 11). The excess resin can be contoured afterit has completely set.

Gross occlusal errors, air blows and voidsAn impression matrix not being reseated fullyoften causes gross occlusal errors and may occurfor two reasons:

• Fins of interproximal impression materialbeing displaced and sandwiched between theimpression and the occlusal surface — trimaway any suspect areas from the inside of theimpression with a scalpel or scissors beforereseating

• Hydrostatic pressure built up within the unsetresin during reseating of the impressionmatrix — consider cutting escape vents cutfrom the crown margin to the periphery of theimpression with a large excavator.

Avoid voids by syringing material directlyonto preparations. Of course, material is alsoloaded into the impression, ensuring the tip isalways in the resin, to prevent the incorporationof air.

Locking in of provisional restorationsProvisional restorations are often locked in byextruded material engaging the undercutsformed by the proximal surfaces of adjacentteeth. The technique of cutting out a triangularwedge of material from the gingival embrasurespace with a half Hollenback instrument hasalready been mentioned. This must be done whilethe material is still soft and before any attempt ismade to remove the provisional restoration fromthe preparation. Once removed, any thin flashshould be trimmed with a pair of scissors, and thecrown reseated a number of times to ensure itdoes not lock into place when set.

Provisional inlays can be a particular prob-lem because of the difficulty in removing excessresin proximally on posterior teeth. A time sav-ing technique is possible using two light curedresins,8 a soft one for the cavity floor and base ofthe box (eg Fermit), and a harder one for theocclusal surface (eg Provipont DC). A vacuumformed, transparent matrix is also needed. Thesofter resin is condensed into the cavity using aconventional matrix band to limit proximalextrusion. The cavity is filled to the level of theproximal contacts after which the resin surfaceis pock marked with a condensing instrument toprovide mechanical retention for the harderresin. Following light curing the matrix band isremoved. The coronal portion of the restorationis formed from the harder resin by means of thevacuum formed matrix. After light curing, thematrix is removed along with the provisionalrestoration, which can be further cured from thefitting surface. The amount of flash produced bythis method is minimal, and the manufacturingof the inlay up to the point of trimming can becompleted in less than 4 minutes.8

Marginal discrepanciesAlthough polymerisation shrinkage can causemarginal discrepancies, it is our opinion thatmost problems are caused simply by distor-tion of the margin when the provisionalcrown is first removed from its preparation.Such distortion results from excess materialengaging proximal undercuts and can easilybe prevented by following the advice in theprevious section.

Should a marginal discrepancy occur witha provisional resin crown, the simplest solu-tion is to reline it. A useful tip is to flare outthe inside of the crown margin with a bur. Thisapproach provides a greater bulk of relinematerial and more area for it to bond. To facil-itate seating it is best not to fill the wholecrown with resin, but to confine the relinematerial to the inner aspect of the crown mar-gin, thus reducing hydrostatic pressure.

Multiple crownsWhen several adjacent preparations require provi-sional restorations, reseating an impression con-taining resin invariably results in all the restora-tions being joined together as material passesthrough the thin and often torn interproximal

Fig. 11 Where the resultingprovisional restoration would be toothin, the inside of the alginatematrix can be trimmed to give agreater bulk of resin

PRACTICE


area. Splinting teeth together in this way has theadvantage of preventing drift due to poor inter-proximal and occlusal contacts. However, it isextremely important to ensure the gingivalembrasures are opened sufficiently to give goodaccess to tooth brushing (Fig. 12a-c). This is bestaccomplished with a flame shaped bur (Fig. 12d).

Ideally, provisional crowns should be sepa-rate, but separation can result in unwanted gapsbetween them. One way9 of overcoming this isto place small pieces of celluloid strip, roughly1cm long, between the teeth to be prepared. Thestrips should have holes punched in their buccaland lingual portions with a rubber dam punchto aid retention in the over-impression. A smallamount of alginate is smeared over the celluloidstrip’s retentive holes before seating the tray.When the impression is removed, the strips stayembedded in the alginate and separate the resincrowns while they are made.

Premature decementationPremature loss of provisional restorations isfrustrating for both patient and dentist. Thisproblem can be largely avoided by ensuring har-mony with the occlusion. A few seconds spentmarking up and adjusting occlusal contacts willsave time in the long run.

Occasionally, it is necessary to use a strongercement, such as zinc polycarboxylate, especiallywhere retention is limited.

Partial denture abutmentsA provisional crown used as a partial dentureabutment is made best from an acrylic resin(eg Trim) as additions are easy to make. Thefollowing technique is recommended: The pro-visional crown should initially be kept clearfrom where rest seats and guide planes are tocontact. Fresh resin is then placed in theseareas before reseating the partial denture with

its components lubricated with petroleum jelly.After the resin has set, the denture is removedand the crown is finished.

Eugenol containing temporary cements andadhesionAs discussed previously, eugenol-containingcements should be avoided where it is intendedto cement the definitive restoration to an under-lying composite core.

Removing temporary crownsAlthough it is desirable for provisional crownsto remain cemented during function, theyshould still be easily removed when impres-sions are taken, adjustments are needed, ordefinitive restorations need cementing. Whenpreparations are of optimal height and taper,the use of even comparatively weak tempo-rary cements may make removal difficult,especially when the provisional restorationneeds to remain undamaged for recementa-tion or when definitive crowns are cementedon a temporary basis.

To make removal easier, the cement shouldbe applied in a ring around the inner aspect ofthe margin. Alternatively, the manufacturer’s

Fig. 12 Provisional restorations andgingival embrasures: (a) No gingivalembrasure space provided betweenthe maxillary incisors; (b) Bleedingfrom the resulting gingivalinflammation prevented impressionsbeing recorded; and (c) Patientsmaintain gingival health best wherethere are open gingival embrasures(as shown in this provisional bridge)to allow toothbrush penetrationinterproximally; and (d) Gingivalembrasures under linked provisionalsneed to be opened out with a flameshaped bur

a b

c d

Fig. 13 A handy tip to facilitateremoval of set cement (either hardor soft); loop floss under eachconnector of linked crowns andapply petroleum jelly to externalsurfaces

1. Wise M D. Stability of gingival crestafter surgery and before anteriorcrown lengthening. Br Dent J 1985;53: 20-23.

2. Crispin B J, Caputo A A. Color stabilityof temporary restorative materials. JProsthet Dent 1979; 42: 27-33.

3. Moulding M B, Teplitsky P E.Intrapulpal temperature during directfabrication of provisionalrestorations. Int J Prosthodont 1990;3: 299-304.

4. Donovan T E, Hurst R G, Campagni WV. Physical properties of acrylic resinpolymerized by four differenttechniques. J Prosthet Dent 1985; 54:522-524.

5. Tjan A H, Castelnuovo J, Shiotsu G.Marginal fidelity of crowns fabricatedfrom six proprietary provisionalmaterials. J Prosthet Dent 1997; 77:482-485.

6. Lang R, Rosentritt M, Leibrock A, BehrM, Handel G. Colour stability ofprovisional crown and bridgerestoration materials. Br Dent J 1998;185: 468-471.

7. Gulati A J. Physical properties ofprovisional restorative materials[MSc]. University of Newcastle UponTyne, 1996.

8. Nicholson J W, Chan D C. Two-step

PRACTICE


provisional technique for onlaypreparations. J Esthetic Dent 1992; 4:202-207.

9. Liebenberg W H. Improvinginterproximal access in directprovisional acrylic resin restorations.Quintessence Int 1994; 25: 697-703.

10. Shillingburg H T, Hobo S, Whitsett L D.Provisional Restorations.Fundamentals of FixedProsthodontics. 4 ed pp.225-256.Chicago: Quintessence international,1998.

11. Civjan S, Huget E F, De Simon L B.Compatibility of resin compositeswith varnishes, liners and bases. JDent Res (Special issue) 1973; 52: 65(Abstract no.27).

12. Dilts W E, Miller R C, Miranda F J,Duncanson M G J. Effect of zinc oxide-eugenol on shear bond strength ofselected core/cement combinations. J Prosthet Dent 1986; 55: 206-208.

13. Schwartz R S, Davis R D, Mayhew RW. The effect of a ZOE temporarycement on the bond strength of aresin luting agent. Am J Dent 1990; 3:28-31.

14. Schwartz R, Davis R, Hilton T J. Effectof temporary cements on the bondstrength of a resin cement. Am J Dent1992; 5: 147-150.

15. Woody T L, Davis R D. The effect ofeugenol-containing and eugenol-free temporary cements onmicroleakage in resin bondedrestorations. Operative Dent 1992;17: 175-180.

16. Millstein P L, Nathanson D. Effects oftemporary cementation onpermanent cement retention tocomposite resin cores. J Prosthet Dent 1992; 67: 856-859.

modifier should be added to the cement (Fig.5). Equal lengths of base and catalyst with athird of a length of modifier will soften thecement appreciably. Therefore, the proportionof modifier needs to be gauged for each case.Either finger pressure or instruments such astowel clips can then remove the restorations,without risking damage to the preparationmargin.

Removal of excess cementTemporary cement removal is facilitated bypre-applying petroleum jelly to the outside ofthe restorations and placing floss under eachconnector of linked crowns before seating(look at Fig. 13). Once set, the excess cement iseasily removed with the strategically posi-tioned floss.

CONCLUSIONQuality restorative dentistry needs qualityprovisional restorations for predictableresults. Dentists therefore need to be familiarwith the range of materials and techniques forshort term, medium-term and long-term tem-porisation. Forethought and planning are alsoneeded to ensure the most appropriate provi-sional is used, especially when multiple teethare to be prepared or where occlusal or aes-thetic changes are envisaged. Such changesare best tried out with provisionals so thatmodifications can easily be made intra-orallyand when satisfactory copied into the defini-tive restorations. In this respect an initialdiagnostic wax-up is invaluable to facilitatethe construction of laboratory formed provi-sionals or matrices.

List of products mentioned in the text:

Fermit Ivoclar-Vivadent UK Ltd, Leicester, UK

Protemp II (hand-mix) ESPE, Seefeld, Germany

Protemp Garant (syringe mix) ESPE, Seefeld, Germany

Provipont DC Ivoclar-Vivadent UK Ltd, Leicester, UK

Quicktemp Davis, Schottlander & Davis Ltd, Letchworth, UK

Snap Parkell, Farmingdale, USA

Soflex Discs 3M Dental Products, St Paul, USA

Temp Bond Kerr UK Ltd, Peterborough, UK

Temp Bond NE Kerr UK Ltd, Peterborough, UK

Trim II Harry J. Bosworth Co, Illinois, USA

Vita Autopolymerizing Panadent, London, UKK+B Acrylics

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