la técnica de duplicación pilar un nuevo protocolo para restauraciones implantosoportadas...

The International Journal of Periodontics & Restorative Dentistry

2009 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART OF THIS ARTICLE MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

Fixed restorations on endosseousimplants are usually either screw- orcement-retained. For screw-retainedcrowns, the crowns are connected tothe implants with screws (either directlyor through a provisional abutment).For cement-retained crowns, abut-ments that have been contoured andshaped as prepared teeth for conven-tional fixed prosthodontics are con-nected to implants with abutmentscrews, and the crowns are cementedto the abutments. In the last few years,the cement-retained protocol hasgained popularity,1,2 particularly in par-tially edentulous patients.

The main reasons for this emerg-ing popularity include:

Easier correction of angulationproblems.3 The ideal anatomicalaxis for implant insertion, centeredbuccolingually in the alveolarprocess, may not correspond tothe ideal prosthetic axis, with thescrew access opening in the cen-tral fossa of clinical crowns. Thistends to present more frequentlyin the maxilla because of theresorption pattern seen there.Sometimes, the implant axis may

The Abutment Duplication Technique: A Novel Protocol for CementableImplant-Supported Restorations

Roberto Cocchetto, MD, DDS*Ingrid Resch, CDT**Marco Castagna, CDT**Giampaolo Vincenzi, MD, DDS***Renato Celletti, MD, DDS****

The purpose of this study was to present a new laboratory technique forcementable implant-supported restorations and to evaluate its efficacy in reduc-ing chair time for both patients and clinicians, while maintaining the precision ofan indirect procedure for crown fabrication. The technique consisted of the dupli-cation of the implant portion of a working cast prepared using double-pour orplastic base die systems for single or multiple crowns. For this purpose, a flaskpreviously intended for the production of ceramic inlays and onlays was used.Duplication was obtained using a high-precision addition silicon material and alow-shrinkage polyurethane resin. The duplicated implant abutment was used tofinalize the fixed partial denture restorations after the originals were delivered tothe patients. Fifty abutments were tested consecutively. The castings (19 singlecrowns, 31 fixed partial dentures) produced on the original abutments were seat-ed on the duplicate abutments and evaluated by two prosthodontists and twodental technicians using a visual inspection method (laboratory microscope at16 magnification). Forty-eight restorations were good (completely seated, nomarginal opening) and 2 were acceptable (incomplete seating but amendable),with a 98% success rate. The technique presented demonstrates efficacy and pre-dictability in reducing the number of clinical sessions for delivering precisely fit-ting cementable implant-supported restorations. (Int J Periodontics RestorativeDent 2010;30:415424.)

*Private Practice, Verona, Italy; Visiting Professor, University of Chieti, Chieti, Italy.**Dental Technician, Dentlab Resch, Verona, Italy.***Private Practice, Verona, Italy.****Professor of Periodontology, University of Chieti, Chieti, Italy; Private Practice, Rome, Italy.

Correspondence to: Dr Roberto Cocchetto, Via Albere n. 10, 37138 Verona, Italy; fax: 0039 045 577646; email: [email protected].

415

Volume 30, Number 4, 2010


be tilted intentionally in themesiodistal direction.4 In thesesituations, cemented restorationsmay be the treatment of choice.

Screw-retained implant crownsmay result in poor estheticsbecause of the location of thescrew access openings. Thisoccurs more frequently in themandible because the screwaccess openings tend to be morevisible. This situation was oncethought to be insignificant, butnow has greater importancebecause of the increased estheticexpectations of many patients.Moreover, screw access openingsweaken the integrity of theceramic layers of crown restora-tions when loaded during func-tion.5,6

When multiple implants aresplinted with fixed restorations,the use of cement-retained crownsallows for easier, more accurateadaptation. This has been impli-cated by decreasing stressbetween the fixed prosthesis andthe implant abutments throughthe use of controlled thicknessesof cement between the abut-ments and the crowns.79

Cement-retained protocols aremore familiar to restorative den-tists and laboratory techniciansbecause the procedures are simi-lar to those used in traditionalprosthodontics.2

Cement-retained protocols maybe implemented in several differentways.

Direct method

A prefabricated abutment is con-nected to an implant and preparedintraorally with rotary instruments.Anatomically preshaped abutments,straight or angled, are available toclinicians in most implant systems.Unfortunately, intraoral preparation ofimplant abutments is more difficult toaccomplish when compared to crownpreparations of natural teeth. Metal orzirconia abutments, because of theirdifferent physical properties, tend tospread small pieces of debris fromthe abutments into the surroundingsoft tissues. The definitive restorationsare made from intraoral impressionsfabricated using conventional fixedpros thodontic impression materials.Intraoral impression procedures forimplant abutments tend to be moredifficult than impressions of naturalteeth, especially those with subgingi-val margins. Retraction cord place-ment into the peri-implant sulcus maydamage the epithelial attachment,which forms onto the sulcular surfaceof abutments. However, if a retractioncord is not used, there is the possibil-ity for fragments of the impressionmaterial to remain undetected in thesulcus and produce inaccurate impres-sions. Retained subgingival impres-sion material may induce pocketformation and fistulae.

Working casts are then developedin die stone or epoxy resin. The diesare sectioned and trimmed in a con-ventional fashion for fabrication of thecrown restorations. The quality of amarginal adaptation when the crownrestoration is made on an abutmentduplicated in stone or epoxy resin from

a traditional impression procedure issignificantly inferior when comparedto that prepared via indirect proce-dures.10 Therefore, there is increasedrisk of open margins, bacterial prolif-eration, and gingival inflammation.

Indirect method

Implant abutments are fabricated ina laboratory on a cast obtained froman implant-level impression. The mas-ter cast contains an implant analogthat replicates the orientation of theimplant intraorally, as well as the peri-implant soft tissue contours. Prefab -ricated titanium or zirconia abutmentsare placed onto the analog in themaster cast and prepared, much asone would prepare a natural toothfor a crown restoration. As an alter-native, abutments can be producedvia waxing and casting customizedabutments or can be custom-milledfrom a computer-generated dataset.The indirect method allows for anideal and precise abutment design.

Provisional crowns may also befabricated in a dental laboratory andsent with the abutments to clinicians ifa provisional loading phase is planned.One protocol also requires that thesuperstructure is waxed and cast onthe abutments, tried in the mouth, andthen sent back to the laboratory forceramic baking. Provisional loading istherefore eliminated and sometimesthis may negatively affect the clinicaloutcome. Moreover, the abutmentsare connected and disconnected tothe implants several times, with possi-ble detrimental effects on soft tissuestability through repeated disruptions

416



of the epithelial attachments aroundthe implants.11 Another possible con-sequence of this protocol comes fromthe fact that if an abutment is reposi-tioned on an implant at different times,a phenomenon defined as slidingmisfit can occur. This can lead to a dif-ference in the rotational position ofthe abutment on the implants, result-ing in possible problems with the seat-ing of the superstructure.12

As an alternative, superstructuresmay be cast on the original abutments,which are then placed into functionwith provisional crowns. At a later time,the superstructures are repositionedon the abutments and a transferimpression is made. This impression isused to fabricate the secondary cast forthe definitive prostheses. This hasbeen the technique preferred by theauthors because it combines precisemarginal adaptation of the crownsonto the abutments along with theadvantages of temporary loading. Themajor disadvantage of this techniqueis that it requires a clinical appoint-ment for the transfer impression todevelop the secondary cast. Moreover,during temporary loading, one ormore implants may fail and the super-structure, previously cast, must be dis-carded. This represents a financial lossto the practitioner and potentially, tothe patient.

Direct/indirect method

In some cases, provisional abutments(usually composed of durable, strongplastic materials) are connected to theimplants, prepared intraorally, andloaded with provisional restorations.

For the definitive restorations, an indi-rect protocol is followed, starting withan implant-level impression. Cliniciansand dental laboratory technicians mayencounter some or all of the problemsdescribed previously. This technique isoften part of an immediate loadingprocedure. However, it may not beused on a routine basis because of theincreased costs associated with usingtwo different abutments.

Double-milled abutmentmethod

Recently, a computer-aided design/computer-assisted manufacturing pro-tocol was proposed2 in which twoabutments are milled from the samedataset. One abutment is placed intra-orally for the provisional phase and thesecond abutment is positioned in theoriginal master cast for the construc-tion of the definitive restoration. Withthis technique, the authors have foundthat the differences in the two abut-ments are minimal. However, the majorproblem associated with this methodis the significantly increased costs.

Because of the multiple variablesinvolved in the aforementioned pro-cedures, the purpose of this paper is topresent and evaluate a new protocolfor cement-retained implant prosthe-ses. This protocol was developed toproduce repeatable technical resultsand reduce the total chair time andthe costs associated with the proto-cols just described.

417



Method and materials

The proposed abutment duplicationtechnique relies on duplication of partof a sectioned working cast, namelythe abutments assembled to theimplant analogs. The duplicated sec-tion can be used on the original cast tocomplete the definitive restorationsafter the original abutments have beenplaced in the patients mouth. This maybe accomplished using cast systemsthat can be sectioned to compensatefor the linear expansion of dental stone(double-pour or plastic base die sys-tems). The casts produced with thesesystems have been demonstrated tobe more accurate than solid casts.1315

Two systems were used in devel-oping this technique: the Zeiser system(Zeiser Dentalgerte) and the Giroformsystem (AmannGirrbach).

Both systems include duplicatingflasks (a single, adjustable flask for theGiroform system and four differentsizes for the Zeiser system). Thesedevices were originally developed to

duplicate stone dies in refractory mate-rial for teeth prepared to receiveceramic inlays or onlays. Similarly, theycan be used to duplicate the implantsection of working casts.

After the cast was prepared con-sistent with the system used, it wassectioned and separated into twoparts: the implant-supported portionand the remaining portion of the den-tal arch (Figs 1 and 2). The cast wasmounted on an articulator and theimplant abutments were developedaccording to optimal mechanical andanatomical requirements (ie, height,taper, emergence profile, and type offinishing line) (Fig 3). The superstruc-ture for a cement-retained prosthesiswas waxed and cast onto the definitivefinished and polished abutments fol-lowing the indirect method previouslydescribed (Fig 4). The screw accessopenings in the abutments were oblit-erated with cotton pellets and a softcomposite material prior to waxing ofthe superstructures.

418


Fig 1 Two posterior mandibular implants were used to replacethe right second premolar and first molar.

Fig 2 The master cast with the implant analogs in place. The dieswere sectioned within the cast.


The nonimplant portion of theworking cast was removed and theduplicating flask was connected to the cast plate around the implant-supported section (Fig 5). An accurateaddition-curing silicon impressionmaterial (Adisil Blue, Siladent DrBhme and Schps) was vacuum-mixed for 40 seconds at a precisebase/catalyst ratio of 9:1 by weight,and poured into the flask. Care wastaken to avoid forming any bubblesand to completely cover the abutment

(Fig 6). The material was left to set for30 minutes and the flask was disas-sembled. A polyurethane resin (PXExtrarock, PX Dental) was chosen asthe duplicating material because of itsexcellent physical properties; in par-ticular, its linear retraction (0.29% for a50-mm-thick sample). The material wasmixed according to the manufacturersinstructions (component A and com-ponent B were mixed at a precise 9:1ratio by weight) and poured into theperfectly dried impression mold in

419


Fig 3 The premachined abutments were prepared and finishedon the implant lab analogs in the original master cast.

Fig 4 The superstructure was waxed and cast on the preparedabutments seen in Fig 3.

Fig 5 The duplicating flask was mounted on the cast base, includ-ing the section to be duplicated.

Fig 6 The addition reaction silicon was poured into the flask.


small increments until the mold wasfilled completely (Fig 7). Care wastaken to avoid trapping any air bub-bles. The cast plate was reconnectedto the duplicating flask after new castpins were placed into positions cor-responding to the section to beduplicated. The resin hardened inapproximately 1 hour. At this point,the cast was reassembled and the

result was a hybrid cast, in whichthe implant-supported section wasa precise replica of the original abut-ment/analog set (Fig 8). This pro-vided sufficient accuracy to the cast;the superstructure could be waxedand cast as it would on the originalabutments.

To evaluate the efficacy of this pro-cedure, a clinical method was chosen

according to similar studies.16 For thisreport, 50 consecutive clinical restora-tions (single units or short-span fixedpartial dentures [FPDs]) have beenincluded (Table 1). The total number ofimplants restored was 112; 18 implantshad an external-hexagon prostheticconnection (Osseotite, Biomet 3i) and94 had an internal connection (Certain,Biomet 3i).

420


Fig 7 Polyurethane resin was poured into the silicone mold. Fig 8 The duplicated polyurethane abutments were placed onthe original master cast.

Table 1 Types of restorations

Maxilla Mandible Total

Single-unit 12 7 19Two-unit (splinted) 7 6 13Three-unit (splinted) 7 4 11Three-unit FPDs (one pontic) 3 4 7Total 29 21 50


Every patient was assigned con-secutively to one of the two duplicationsystems used in the study. In everypatient, the abutments were producedand duplicated, then the superstruc-tures were waxed on the original abut-ments and cast in noble alloy forporcelain-fused-to-metal restorations.Each finished casting was seated ontothe original abutments and then trans-

duplicated cast was not usable to fin-ish the restoration), accep t able(some difficulties in seating but amend-able), or good (no problem in seat-ing and good marginal adaptation). Inall patients, the provisional crownswere then cemented to the abutments(Figs 10 to 12), followed by the defini-tive crowns made on the duplicatecasts (Figs 13a and 13b).

ferred onto the duplicated abutments,which had been previously reposi-tioned on the cast (Figs 9). The castingswere examined with a laboratorymicroscope at 16 magnification bytwo qualified dental technicians andtwo prosthodontists. For each sample,ease of seating and marginal adapta-tion on the duplicated abutments wereevaluated and scored as poor (the

421


Fig 9 The castings placed on the duplicated abutments. This castwas used for the definitive metal-ceramic restorations.

Fig 10 Provisional crowns were transferred to the duplicate abut-ments on the master cast.

Fig 11 Titanium abutments were placed intraorally on theimplants. The buccal margins were designed to be slightly subgin-gival for optimal esthetics.

Fig 12 The provisional crowns were cemented onto the definitiveabutments intraorally. Note the bleaching of the marginal gingivaaround the second premolar because of the initial shaping effect ofthe crowns emergence profiles.


Results

No sample was scored as poor; onlytwo were scored as acceptable andthe rest were scored as good. In allpatients, the duplicated sectionsallowed for easy and predictable com-pletion of the definitive restorations.The two restorations that were scoredacceptable were both FPDs (onethree-unit and one two-unit), and bothhad been duplicated using the Zeisersystem. When the casts were trans-ferred to the duplicated dies, they didnot seat completely and had to be cutand soldered. Both cases were com-pleted on a secondary master castdeveloped from a transfer impression.

Discussion

Cement-retained implant-supportedrestorations are widely used and maybe fabricated with either direct or indi-rect protocols. The ideal clinical andlaboratory protocol should be precise,repeatable, cost effective, and biolog-ically and clinically acceptable. It shouldalso minimize the number of clinicalsessions and use simple intraoral pro-cedures that respect the delicate peri-implant attachment apparatus. Atechnique in which the definitive abut-ment is positioned and never discon-nected is considered to be ideal, butproblems are associated with fabrica-tion of the definitive restoration on areplica of the original abutment in alaboratory. This may be accomplished

by making an intraoral impression ofthe abutment, but as demonstratedby Ganz, this may not lead to consis-tently accurate results in terms of mar-ginal adaptation.10

The results obtained in the presentstudy (2 acceptable restorations, 48good restorations; cumulative suc-cess rate, 98%) were satisfactory. Bothrestorations that required modificationwere external-hexagon implantsrestored with UCLA-type abutments. Inthese restorations, the maximum pre-load was obtained by delivering atorque force of 35 Ncm to the abut-ment screws. In these situations, one ormore abutments can undergo rota-tional displacement, which, even ifminimal, prevents the full seating of themultiple-unit splinted superstructure.

422


Figs 13a and 13b (left) The definitive restorations were cemented intraorally. (right) The verification radiograph indicates precise marginaladaptation between the crowns, abutments, and implants.


In the other cases, the implantsused had internal implant-abutmentconnections where the maximum pre-load was obtained with only a 20-Ncmtorquing force to the abutment screw.This effectively eliminated the risk ofthe previously mentioned sliding mis-fit. Moreover, the majority of cases(83 implants) were treated withpreparable premachined titaniumabutments (GingiHue Posts, Biomet3i). Generally, these premachined tita-nium abutments have a more precisefit with implants compared to castableUCLA-type abutments, which canundergo unpredictable dimensionalmodifications resulting from the manyvariables of the casting process.

The high predictability demon-strated by the presented technique canbe ascribed to the accuracy of theimpression technique and the proper-ties of the resin material. The siliconeimpression material used in this studyhas reproduction accuracy, according tothe manufacturer, within 0.001 mm.Moreover, the duplication systems usedin this study have been in use for sev-eral years. The flasks have been used fordifferent indications than thosedescribed here, but have been widelyaccepted in prosthodontic practice.

The use of epoxy resin dies inprosthodontics is well documentedin the literature, but very little hasbeen published on polyurethaneresins. Darrien and Sturtz,17 usingscanning electron microscopy andtwo-dimensional profilometry, demon-strated that both epoxy andpolyurethane resins can reproducedetails of 1 to 2 m, while artificialstone could not reproduce detailssmaller than 20 m. In another study,18

tested by the authors are widely usedin many dental laboratories, especiallyin Europe, and therefore the proposedtechnique may be of some interest toa number of clinicians.

The need for a duplicate cast foran easier and more precise indirecttechnique has produced interestingresults, such as computer-milled abut-ment technology.2 This confirms pre-existing interest in this aspect ofrestorative implant treatment. Thetechnique proposed in this paper doesnot require sophisticated technologiesand can be applied to any type ofabutment production technique at asignificantly lower cost. Moreover, thehigh accuracy of the duplication tech-nique may allow the use of duplicatedabutments as primary dies for waxingand casting superstructures with greatpredictability. A study is currentlyongoing to verify this hypothesis.

Conclusions

With the simple, repeatable, and costeffective laboratory proceduredescribed in this paper, the prostheticprotocol for cement-retained implantrestorations has been modified toobtain several advantages for clini-cians, dental laboratory technicians,and patients.

The definitive abutments are pro-duced through an indirect, pre-cise, laboratory procedure.

It is possible to connect abut-ments to implants with the optimalpreload at the time of provision-alization. In this one abut-mentone time concept, the

the authors stated that incorporatingsilica fillers in the resin reduced dimen-sional variations and improved accu-racy. Kenyon et al19 compared sevendie materials and found that poly -urethane resin had a combination oflinear expansion and shrinkage.According to the manufacturer, thematerial used in the present studytends to shrink minimally. Therefore, itis not surprising that the castingsseated easily onto the duplicatedabutments, with no visible marginalopenings. If the dies were undersizedsignificantly, this would be easilydetected under the 16 magnifica-tion microscope used in this study.Therefore the casts with the duplicatedsections were safely used for the defin-itive crown restorations, while the orig-inal abutments were already in clinicaluse. There was no need for furtherimpressions to develop a secondarycast. Based on the 4 years of experi-ence that the authors have with thistechnique for single crowns and smallFPDs, it was often possible to avoidclinical try-in appointments with por -celain in bisque bake. The authorsfound that this appointment was elim-inated and treatment could movedirectly to the insertion of the definitiverestorations, with only small adjust-ments of the interproximal contactareas needed.

The additional costs of the proce-dures were limited to purchasing ofthe duplicating flasks. These flaskswere developed for indefinite labora-tory use. Another limitation with thisprotocol may be that the techniquecan be applied only to sectioned castsystems, which include duplicatingflasks. However, the two systems

423



definitive abutments do not haveto be removed from the implantsat any future date in the restorativeprocess. This allows a stableepithelial attachment to formdirectly onto the abutments. Thiseliminates disturbance of the del-icate epithelial attachment withunnecessary multiple disconnec-tions and reconnections and withinvasive procedures such as pack-ing retraction cord and intrasulcu-lar impressions to develop mastercasts. This also reduces the chairtime associated with restorativeprocedures.

This protocol allows patients tohave rapid restoration of theiresthetics and function at the clin-ical session following the initialimpression, with provisionalcrowns cemented onto definitiveabutments. In case of provisionalcrown fracture, the crowns can berepaired easily or remade on theduplicated casts.

Technicians finalize prostheses onoriginal casts with duplicatedreproductions of the definitiveabutments. This is done withoutadditional impres sions. The lab-oratory portion of the treat mentcan be planned at times mostconvenient for the patients, clini-cians, and laboratory technicians.After completing the treatment,the casts and provisional crownsare stored at the office and can beused again if the need arises (ie,ceramic fracture or repair).

Acknowledgments

The authors would like to thank Dr Carl Dragofor his help and contributions in editing themanuscript.

References

1. Hebel KS, Gajjar RC. Cement-retained ver-sus screw-retained implant restorations:Achieving optimal occlusion and estheticsin implant dentistry. J Prosthet Dent1997;77:2835.

2. Michalakis KX, Hirayama H, Garefis PD.Cement-retained versus screw-retainedimplant restorations: A critical review. Int JOral Maxillofac Implants 2003;18:719728.

3. Lewis S, Avera S, Engleman M, Beumer J3rd. The restoration of improperly inclinedosseointegrated implants. Int J OralMaxillofac Implants 1989;4:147152.

4. Aparicio C, Perales P, Rangert B. Tiltedimplants as an alternative to maxillary sinusgrafting: A clinical, radiologic, and Perioteststudy. Clin Implant Dent Relat Res 2001;3:3949.

5. Karl M, Graef F, Taylor TD, Heckmann SM.In vitro effect of load cycling on metal-ceramic cement- and screw-retainedimplant restorations. J Prosthet Dent 2007;97:137140.

6. Torrado E, Ercoli C, Al Mardini M, GraserGN, Tallents RH, Cordaro L. A comparisonof the porcelain fracture resistance ofscrew-retained and cement-retainedimplant-supported metal-ceramic crowns.J Prosthet Dent 2004;91:532537.

7. Misch CE. Screw-retained versus cement-retained implant-supported prostheses.Pract Periodontics Aesthet Dent 1995;7:1518.

8. Taylor TD, Agar JR, Vogiatzi T. Implantprosthodontics: Current perspective andfuture directions. Int J Oral MaxillofacImplants 2000;15:6675.

9. Randi AP, Hsu AT, Verga A, Kim JJ.Dimensional accuracy and retentivestrength of a retrievable cement-retainedimplant-supported prosthesis. Int J OralMaxillofac Implants 2001;16:547556.

10. Ganz SD, Desai N, Weiner S. Marginalintegrity of direct and indirect castings forimplant abutments. Int J Oral MaxillofacImplants 2006;21:593599.

11. Abrahamsson I, Berglundh T, Lindhe J. Themucosal barrier following abutmentdis/reconnection. An experimental study indogs. J Clin Periodontol 1997;24:568572.

12. Lang LA, Wang RF, May KB. The influenceof abutment screw tightening on screwjoint configuration. J Prosthet Dent 2002;87:7479.

13. Vigolo P, Millstein PL. Evaluation of mastercast techniques for multiple abutmentimplant prostheses. Int J Oral MaxillofacImplants 1993;8:439446.

14. Aramouni P, Millstein D. A comparison ofthe accuracy of two removable die systemswith intact working casts. Int J Prosthodont1993;6:533539.

15. Wee AG, Cheng AC, Eskridge RN.Accuracy of 3 conceptually different diesystems used for implant casts. J ProsthetDent 2002;87:2329.

16. Nomura GT, Reisbick MH, Preston JD. Aninvestigation of epoxy resin dies. J ProsthetDent 1980;44:4550.

17. Darrien G, Sturtz G. Comparison of trans-verse strength and dimensional variationsbetween die stone, die epoxy resin, and diepolyurethane resin. J Prosthet Dent 1995;74:569574.

18. Darrien G, Le Menn G. Evaluation of detailreproduction for three die materials byusing scanning electron microscopy andtwo-dimensional profilometry. J ProsthetDent 1995;74:17.

19. Kenyon BJ, Hagge MS, Leknius C, DanielsWC, Weed ST. Dimensional accuracy of 7die materials. J Prosthodont 2005;14:2531.

424



la técnica de duplicación pilar un nuevo protocolo para restauraciones implantosoportadas...

Documents