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12.Morris HF, Asgar K, Brudvik JS, Winkler S, Roberts EP. Stress relaxation testing. Part IV: Clasp pattern dimensions and their influence on clasp behavior. J Prosthet Dent 1983;50:319-26.

13.Waldmeier MD, Grasso JE, Norberg GJ, Nowak MD. Bend testing of wrought wire removable partial denture alloys. J Prosthet Dent 1996;76:559-65.

14.Phoenix RD, Stewart KL, Cagna DR, DeFre-est CF. Stewart’s clinical removable partial prosthodontics.4th ed. Beijing: Quintes-sence; 2003. p. 58.

15.Sato Y, Abe Y, Yuasa Y, Akagawa Y. Effect of friction coefficient on Akers clasp retention. J Prosthet Dent 1997;78:22-7.

16.Ghani F, Mahood M. A laboratory examina-tion of the behaviour of cast cobalt-chromi-um clasps. J Oral Rehabil 1990;17:229-37.

17.Bates JF. Retention of partial dentures. Br Dent J 1980;149:171-4.

18.Sato Y, Tsuga K, Abe Y, Asahara S, Akagawa Y. Finite element analysis on preferable I-bar clasp shape. J Oral Rehabil 2001;28:413-7.

Corresponding author:Dr Hui ChengDepartment of ProsthodonticsSchool and Hospital of StomatologyFujian Medical University246 Yangqiao Middle StFuzhou, Fujian, 350001PR CHINAFax: 86 0591 83700838E-mail: ch.fj@163.com

AcknowledgementsThe authors thank Drs James Brudvik and John Wataha in the Department of Restorative Dentistry, University of Washington School of Dentistry, for their constructive comments. The authors also thank Ms Eugenie Fyfe from the University of Washington for her editing assistance.

Copyright © 2010 by the Editorial Council for The Journal of Prosthetic Dentistry.

Prosthesis fracture is a common complication associated with implant-retained overdentures. A new overdenture can be strengthened by incorporating a cast metal reinforcement during processing. The authors describe a technique for converting an existing conventional nonreinforced serviceable denture into an overdenture that includes a cast metal reinforcement and its attachments. (J Prosthet Dent 2010;104:397-400)

A technique for converting an existing denture into a cast metal-reinforced implant-retained overdenture

Ira H. Orenstein, DDS,a Bradley F. Weinstein, DMD,b Asher S. Gelman, DMD,c Serge Fiks,d and John W. McCartney, DDSe

James J. Peters Veterans Affairs Medical Center, Bronx, NY; Columbia University College of Dental Medicine, New York, NY; Mount Sinai School of Medicine, New York, NY; Department of Verterans Affairs Central Dental Laboratory, Washington, DC

aStaff, James J. Peters Veterans Affairs Medical Center; Assistant Clinical Professor, Columbia University College of Dental Medicine. bGeneral Practice Dental Resident, Mount Sinai School of Medicine/James J. Peters Veterans Affairs Medical Center. cGeneral Practice Dental Resident, Mount Sinai School of Medicine/James J. Peters Veterans Affairs Medical Center.dDental Laboratory Technician, Supervisor: Removable Prosthetics Division, Central Dental Laboratory.eAssociate Director, Central Dental Laboratory.

The implant-retained overdenture has been proposed as the standard of care for the restoration of the eden-tulous mandibular arch.1 The Mc-Gill Consensus statement of 20022 and the York consensus statement of 20093 discussed the advantages of the mandibular implant-retained overdenture when compared to the conventional complete denture pros-thesis. The benefits include improved stability, retention, function, and es-thetics, reduced ridge resorption, simplicity of fabrication, and the abil-ity to convert an existing denture into an overdenture.4

Acrylic resin denture base fracture is a complication associated with im-plant-retained overdentures.5,6 Frac-ture of the prosthesis is less likely to occur when there is sufficient space for the attachment system and den-ture teeth. Solutions for the patient with limited interarch space have been proposed, including performing alveoloplasty at the time of implant surgery and the use of a low-profile attachment system.7 To further re-

duce the risk of denture fracture, met-al reinforcement can be incorporated into the denture base.4,8-13 This rein-forcement is particularly helpful when the implant-retained overdenture opposes natural teeth or an implant-supported prosthesis.14

Previous reports described vari-ous methods for incorporating a metal framework into a newly fabri-cated implant-retained overdenture using conventional denture fabrica-tion procedures.14-16 The conversion of an existing mandibular prosthe-sis into an implant-supported over-denture (without incorporation of a cast framework) has also been de-scribed.17-21

To date, the authors have identi-fied no published report that combines these techniques into a convenient and predictable method for converting an existing denture into a metal-reinforced implant-retained overdenture. The au-thors present a technique for converting a serviceable complete denture into a cast metal-reinforced implant-retained overdenture with attachments; this

method requires only one additional office visit.

During the surgical phase of im-plant treatment, the intaglio surface of the patient’s denture is usually re-lieved and relined several times with tissue conditioner. This procedure may cause gradual deterioration of the denture base acrylic resin and weak-ening of the denture prosthesis. The technique presented replaces a sig-nificant portion of the denture with newly processed acrylic resin.

Incorporating a framework into an existing denture necessitates that the prosthesis be surrendered by the pa-tient. In the technique described, it is necessary for the dentist to duplicate the existing denture prior to its con-version to provide the patient with an interim prosthesis. This additional procedure can, however, serve other functions. The duplicated denture can also be used as a scanning template during 3-dimensional imaging (bari-um sulfate can be incorporated into the acrylic resin at the time of du-plicate denture fabrication, thereby

Noteworthy Abstracts of the Current Literature

Bone changes around early loaded chemically modified sandblasted and acid-etched surfaced implants with and without a machined collar: A radiographic and resonance frequency analysis in the canine mandible

Valderrama P, Jones AA, Wilson TG Jr, Higginbottom H, Schoolfield JD, Jung RE, Marcel Noujeim M, Cochran DL.Int J Oral Maxillofac Implants 2010;25:548-57.

Purpose. The purpose of this study was to evaluate the radiographic bone level and stability changes around early loaded chemically modified sandblasted and acid-etched implants with and without a machined collar.

Materials and Methods. Seventy-two chemically modified sandblasted and acid-etched implants 4.1 mm in diameter and 8 mm in length were placed in six dogs. Thirty-six implants had no machined collar (NMC) and 36 had a 2.8-mm machined collar (MC). Resonance frequency measurements were obtained at placement and weekly for 3 weeks. All implants were loaded 21 days after surgery. Standardized periapical radiographs were obtained at baseline, at 3 weeks, and at 3, 6, 9, and 12 months. The radiographs were randomized and digitized, and linear measurements of the distance from the first bone-to-implant contact to the shoulder of the implant were performed at the mesial and distal aspects of each implant. For statistical analysis, mixed-model repeated-measures analysis of variance was used.

Results. All implants achieved hard and soft tissue integration clinically and radiographically and were clinically im-mobile. From placement to week 3, the mean implant stability increased for MC implants by more than 5 ISQs and for NMC implants by more than 7 ISQs. Radiographically, there were significant differences between treatment groups beginning at 3 months. After 12 months of loading, the MC implants presented a mean bone loss of 1.00 mm and the NMC implants presented a mean bone gain of 0.11 mm.

Conclusions. Chemically modified sandblasted and acid-etched implants without a machined collar presented bone gain, and implants with a machined collar showed bone loss after a 1 year following early (21-day) loading. The ten-dency toward a coronal apposition of bone observed under these conditions may be attributed to the osteoconduc-tive properties of the chemically modified surfaces of these implants and to the absence of the machined collar.

Reprinted with permission of Quintessence Publishing.

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making the prosthesis orientation vis-ible on the radiographic images) and can be modified for use as a surgical template. The duplicated denture can also be used in the future if the de-finitive prosthesis needs to be surren-dered by the patient for maintenance or repair.

A framework placed into an over-denture that has thin areas of acrylic resin may compromise esthetic goals if it becomes visible in function. Opaque media formulated to address this potential problem are available that can be applied onto the metal surfaces prior to processing the pros-thesis.

The technique described gives the clinician and patient flexible treat-ment choices. The patient can have a conventional denture fabricated and can retain the option of having it con-verted into a cast metal-reinforced overdenture in the future.

TECHNIQUE

Clinical procedures

1. Duplicate the definitive prosthe-sis (DP) (Denture Duplicator; Lang Dental Mfg Co, Wheeling, Ill) follow-ing the manufacturer’s instructions, using autopolymerizing acrylic resin (Jet Acrylic; Lang Dental Mfg Co) to fabricate an interim prosthesis (IP).

2. Insert the abutments (Loca-

tor; Zest Anchors, Escondido, Calif ) onto the implants at the torque value recommended by the manufacturer. Position the Locator denture caps with black low-density polyethylene patrices (retentive elements) onto the abutments to function as transfer copings (Fig. 1).

3. Relieve the entire intaglio sur-face of the DP with a bur suitable for trimming acrylic resin (H251E Tung-sten Carbide Cutter; Brasseler USA, Savannah, Ga), and confirm that each abutment/processing cap complex does not contact the denture.

4. Transfer the processing caps us-ing a closed-mouth reline impression technique (Permadyne Garant 2:1; 3M ESPE, St. Paul, Minn).22 Upon re-moval of the prosthesis, confirm that the processing caps are fully seated in the impression material (Fig. 2).

5. Reline the IP with a resilient lin-ing material (Coe-Comfort Edentu-lous Tissue Conditioner; GC America, Inc, Alsip, Ill). Instruct the patient to wear the IP while the DP is being al-tered. Send the DP to the dental labo-ratory.

Laboratory procedures

6. Insert the aluminum matrix an-alogs into the processing caps in the impression. Box and pour a definitive cast (Modern Materials Denstone Golden Type III; Heraeus Kulzer, Inc,

Armonk, NY) (Figs. 3 and 4).7. Fabricate a plaster (Modern

Materials Lab Plaster Regular Type II; Heraeus Kulzer, Inc) index (Fig. 5). Remove the pink acrylic resin base from the DP, leaving the denture teeth connected to each other.

8. Fabricate a refractory cast using investment material (V.R. Investment System; Dentsply Austenal, York, Pa) suitable for casting a cobalt-chromi-um framework.

9. Develop a wax pattern (Wire Wax Half Round Blue 12GA; Henry Schein, Inc, Melville, NY) for the fabri-cation of a cast metal reinforcement, with the denture teeth positioned in the plaster matrix that is seated on the refractory cast (Fig. 6).

10. Cast the framework and repo-sition it on the definitive cast (Fig. 7). Develop a wax pattern to recreate the denture base (Fig. 8).

11. Flask and heat polymerize the acrylic resin (Lucitone 199 Denture Base Resin, Light; Dentsply Intl), and then finish the denture using dental laboratory pumice (Laboratory Pum-ice Med/Fine; Henry Schein, Inc) and polishing compound (Ti-Gleam Pol-ishing Compound: Ticonium Division of CMP Industries, Albany, NY) (Fig. 9).

12. Return the prosthesis to the clinician so that the black low-density polyethylene patrices can be replaced with nylon replacement patrices (de-

1 Processing caps used to capture orientation of abut-ments require less denture relief than taller impression copings offered by manufacturer.

2 Processing caps transferred in rebase impression.

4 Definitive cast with keyways placed in land area to ori-ent plaster index.

7 Completed cast metal reinforcement.

5 Land area of master cast is lubricated and plaster index is fabricated.

8 Plaster index is used to wax denture base pattern to its original contours.

3 Aluminum analogs inserted into processing caps in preparation for fabrication of definitive cast.

6 Plaster index and denture teeth placed on refractory cast permit technician to precisely develop wax pattern for cast metal overdenture reinforcement.

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Orenstein et alOrenstein et al

making the prosthesis orientation vis-ible on the radiographic images) and can be modified for use as a surgical template. The duplicated denture can also be used in the future if the de-finitive prosthesis needs to be surren-dered by the patient for maintenance or repair.

A framework placed into an over-denture that has thin areas of acrylic resin may compromise esthetic goals if it becomes visible in function. Opaque media formulated to address this potential problem are available that can be applied onto the metal surfaces prior to processing the pros-thesis.

The technique described gives the clinician and patient flexible treat-ment choices. The patient can have a conventional denture fabricated and can retain the option of having it con-verted into a cast metal-reinforced overdenture in the future.

TECHNIQUE

Clinical procedures

1. Duplicate the definitive prosthe-sis (DP) (Denture Duplicator; Lang Dental Mfg Co, Wheeling, Ill) follow-ing the manufacturer’s instructions, using autopolymerizing acrylic resin (Jet Acrylic; Lang Dental Mfg Co) to fabricate an interim prosthesis (IP).

2. Insert the abutments (Loca-

tor; Zest Anchors, Escondido, Calif ) onto the implants at the torque value recommended by the manufacturer. Position the Locator denture caps with black low-density polyethylene patrices (retentive elements) onto the abutments to function as transfer copings (Fig. 1).

3. Relieve the entire intaglio sur-face of the DP with a bur suitable for trimming acrylic resin (H251E Tung-sten Carbide Cutter; Brasseler USA, Savannah, Ga), and confirm that each abutment/processing cap complex does not contact the denture.

4. Transfer the processing caps us-ing a closed-mouth reline impression technique (Permadyne Garant 2:1; 3M ESPE, St. Paul, Minn).22 Upon re-moval of the prosthesis, confirm that the processing caps are fully seated in the impression material (Fig. 2).

5. Reline the IP with a resilient lin-ing material (Coe-Comfort Edentu-lous Tissue Conditioner; GC America, Inc, Alsip, Ill). Instruct the patient to wear the IP while the DP is being al-tered. Send the DP to the dental labo-ratory.

Laboratory procedures

6. Insert the aluminum matrix an-alogs into the processing caps in the impression. Box and pour a definitive cast (Modern Materials Denstone Golden Type III; Heraeus Kulzer, Inc,

Armonk, NY) (Figs. 3 and 4).7. Fabricate a plaster (Modern

Materials Lab Plaster Regular Type II; Heraeus Kulzer, Inc) index (Fig. 5). Remove the pink acrylic resin base from the DP, leaving the denture teeth connected to each other.

8. Fabricate a refractory cast using investment material (V.R. Investment System; Dentsply Austenal, York, Pa) suitable for casting a cobalt-chromi-um framework.

9. Develop a wax pattern (Wire Wax Half Round Blue 12GA; Henry Schein, Inc, Melville, NY) for the fabri-cation of a cast metal reinforcement, with the denture teeth positioned in the plaster matrix that is seated on the refractory cast (Fig. 6).

10. Cast the framework and repo-sition it on the definitive cast (Fig. 7). Develop a wax pattern to recreate the denture base (Fig. 8).

11. Flask and heat polymerize the acrylic resin (Lucitone 199 Denture Base Resin, Light; Dentsply Intl), and then finish the denture using dental laboratory pumice (Laboratory Pum-ice Med/Fine; Henry Schein, Inc) and polishing compound (Ti-Gleam Pol-ishing Compound: Ticonium Division of CMP Industries, Albany, NY) (Fig. 9).

12. Return the prosthesis to the clinician so that the black low-density polyethylene patrices can be replaced with nylon replacement patrices (de-

1 Processing caps used to capture orientation of abut-ments require less denture relief than taller impression copings offered by manufacturer.

2 Processing caps transferred in rebase impression.

4 Definitive cast with keyways placed in land area to ori-ent plaster index.

7 Completed cast metal reinforcement.

5 Land area of master cast is lubricated and plaster index is fabricated.

8 Plaster index is used to wax denture base pattern to its original contours.

3 Aluminum analogs inserted into processing caps in preparation for fabrication of definitive cast.

6 Plaster index and denture teeth placed on refractory cast permit technician to precisely develop wax pattern for cast metal overdenture reinforcement.

400 Volume 104 Issue 6

The Journal of Prosthetic Dentistry Roe and PatelOrenstein et al

9 Completed definitive prosthesis. Black low-density polyethylene patrices will be exchanged for nylon replace-ment patrices.

finitive retentive elements) (Locator; Zest Anchors). The clinician should then perform insertion procedures to verify the fit and occlusion of the new prosthesis.23

SUMMARY

A complete denture is generally fabricated without metal reinforce-ment. Fracture of the acrylic resin denture base is a complication asso-ciated with the overdenture prosthe-sis. Using the technique described, an existing denture can be converted into a cast metal-reinforced implant-retained overdenture prosthesis, with only one additional office visit re-quired.

REFERENCES

1. Burns DR. The mandibular complete overden-ture. Dent Clin North Am 2004;48:603-23.

2. Thomason JM, Feine J, Exley C, Moynihan P, Müller F, Naert I, et al. Mandibular two implant-supported overdentures as the first choice standard of care for edentulous patients--the York Consensus Statement. Br Dent J 2009;207:185-6.

3. Feine JS, Carlsson GE, Awad MA, Chehade A, Duncan WJ, Gizani S, et al. The McGill consensus statement on overdentures. Montreal, Quebec, Canada. May 24-25, 2002. Int J Prosthodont 2002;15:413-4.

4. Doundoulakis JH, Eckert SE, Lindquist CC, Jeffcoat MK. The implant-supported overdenture as an alternative to the com-plete mandibular denture. J Am Dent Assoc 2003;134:1455-8.

5. Shor A, Goto Y, Shor K. Mandibular two-implant-retained overdenture: prosthetic design and fabrication protocol. Compend Contin Educ Dent 2007;28:80-8.

6. Hemmings KW, Schmitt A, Zarb GA. Com-plications and maintenance requirements for fixed prostheses and overdentures in the edentulous mandible: a 5-year report. Int J Oral Maxillofac Implants 1994;9:191-6.

7. Pasciuta M, Grossman Y, Finger IM. A prosthetic solution to restoring the eden-tulous mandible with limited interarch space using an implant-tissue-supported overdenture: a clinical report. J Prosthet Dent 2005;93:116-20.

8. Vallittu PK. A review of methods used to reinforce polymethyl methacrylate resin. J Prosthodont 1995;4:183-7.

9. Jagger DC, Harrison A, Jandt KD. The reinforcement of dentures. J Oral Rehabil 1999;26:185-94.

10.Ohkubo C, Kurtz KS, Suzuki Y, Hanatani S, Abe M, Hosoi T. Comparative study of maxillary complete dentures constructed of metal base and metal structure framework. J Oral Rehabil 2001;28:149-56.

11.Shimizu H, Ikeda T, Wakabayashi N, Ohya-ma T. Effect of metal strengthener length on stress distribution in acrylic denture bases: a finite element study. J Oral Rehabil 2004;31:879-83.

12.Shor A, Shor K, Goto Y. Implant-retained overdenture design for the malpositioned mandibular implants. Compend Contin Educ Dent 2006;27:411-9.

13.Gonda T, Ikebe K, Dong J, Nokubi T. Effect of reinforcement on overdenture strain. J Dent Res 2007;86:667-71.

14.Zitzmann NU, Marinello CP. A review of clinical and technical considerations for fixed and removable implant prostheses in the edentulous mandible. Int J Prosthodont 2002;15:65-72.

15.Rodrigues AH. Metal reinforcement for implant-supported mandibular overden-tures. J Prosthet Dent 2000;83:511-3.

16.Nerli SR, Patil R. A simple method to ob-tain uniform thickness of acrylic resin around a grid strengthener embedded in a denture base. J Prosthet Dent 2004;92:95-6.

17.Daher T. A simple, predictable intraoral technique for retentive mechanism attach-ment of implant overdenture attachments. J Prosthodont 2003;12:202-5.

18.Sadig WM. Special technique for attach-ment incorporation with an implant over-denture. J Prosthet Dent 2003;89:93-6.

19.Toothaker R, Soultanis I, Ojha A, Ashcraft-Olmscheid DL, Chang MW. Retrofitting an existing implant overdenture to a new and redesigned intraoral framework: a clinical report. J Prosthodont 2004;13:47-51.

20.Pasciuta M, Grossmann Y, Finger IM. A prosthetic solution to restoring the edentulous mandible with limited interarch space using an implant-tissue-supported overdenture: a clinical report. J Prosthet Dent 2005;93:116-20.

21.Saha S, Ray-Chaudhuri A. Mandibular implant-retained complete overdenture using retentive abutments: a case report. Dent Update 2009;36:154-8.

22.Christensen GJ. Relining, rebasing partial and complete dentures. J Am Dent Assoc 1995;126:503-6.

23.Zarb GA, Bolender CL, Eckert SE, Jacob RF, Fenton AH, Merickse-Stern R. Prosth-odontic treatment for edentulous patients: complete dentures and implant-supported prostheses. 12th ed. St. Louis: Elsevier; 2003. p. 401-19.

Corresponding author:Dr Ira H. OrensteinDental Service (160)James J. Peters VA Medical Center130 West Kingsbridge RdBronx, NY 10468Fax: 718-741-4618E-mail: ira.orenstein@va.gov

Copyright © 2010 by the Editorial Council for The Journal of Prosthetic Dentistry.

Fabrication of a modified repositioning key for relining provisional restorations

Phillip Roe, DDS, MS,a Rishi D. Patel, BDS, MSb

Loma Linda University School of Dentistry, Loma Linda, Calif

aAssistant Professor, Department of Restorative Dentistry.bAssistant Professor, Department of Restorative Dentistry.(J Prosthet Dent 2010;104:401-402)

1 A, Facial view of definitive cast with completed provisional restoration. B, Clear splint sheet is placed over auto-polymerizing acrylic resin so that incisal edges are visible.

The fabrication of a provisional restoration is an important step in achieving an optimal definitive pros-thetic result.1,2 It requires care and attention, as the contours of the pro-visional restoration are fundamental in the development and maintenance of the gingival architecture, while also providing important information for the fabrication and placement of the definitive restoration.1,2 To create a provisional restoration which is ideal in contour, durable, and has long-term color stability, an indirect laboratory-fabricated provisional restoration is typically required.1,3 An indirect pro-visional restoration also serves to minimize the time involved with the chairside reline procedure.3 Unfortu-nately, in certain situations, the inta-glio surface of provisional restorations may be poorly adapted to the clini-cally prepared tooth or implant abut-ment, rendering the relining procedure unreliable, as the orientation of the

provisional restoration can vary in 3 dimensions. In such situations, a re-positioning key can be advantageous.

Simeone and Pilloni2 first described the use of a repositioning key in 2004. The purpose of this device was to aid in the clinical relining phase. This rigid plaster key allowed the clinician to ac-curately position the provisional resto-ration, eliminating any variability in its 3-dimensional orientation.2 However, when a repositioning key is used for a reline procedure, it is important to ensure that the provisional restora-tion is in the proper position.

This article describes a technique for fabricating a repositioning key with a transparent incisal/occlusal display. This acrylic resin repositioning key en-ables the clinician to correctly orient the provisional restoration while allow-ing direct visual access to the incisal/occlusal surface to ensure complete seating. This procedure is intended to simplify the clinical fit of the pro-

visional restoration by confirming its complete seating, thereby minimizing adjustments following relining.

PROCEDURE

1. Prepare the tooth on the diag-nostic cast with a diamond rotary cutting instrument (no. 6856.016; Brasseler USA, Savannah, Ga). Fabri-cate a laboratory provisional restora-tion using conventional techniques1 (Fig. 1, A).

2. Apply a generous amount of petroleum jelly (Vaseline; Unilever, Englewood Cliffs, NJ) onto the provi-sional restorations and the adjacent teeth as a separating medium.

3. Mix autopolymerizing acrylic resin (Pattern Resin; GC America, Inc, Alsip, Ill) in a mixing cup until it reaches a dough stage.

4. Apply petroleum jelly to prevent the acrylic resin from sticking to the gloves. Manipulate the autopolymer-

A B