Cement-retained superstructure for a metal-resin fixed complete denture

Michael McCracken, DDS, PhD,a Bryhn Simmons, DDS,b and Wayne Simmons, DMDc

University of Alabama, Birmingham, School of Dentistry, Birmingham, Ala

This article describes a method of fabricating a metal-resin fixed complete denture using a cementedacrylic resin superstructure over a metal bar that is screw-retained. The primary advantage of this designover traditional designs is that there are no screw access openings in the acrylic resin or denture teeth.Advantages include improved esthetics, ease of fabrication and tooth arrangement, simplification ofprocedures, and the opportunity to easily replace worn teeth when necessary. (J Prosthet Dent2005;93:298-300.)

Metal-resin fixed complete dentures have provento be predictable and reliable.1-4 Some fabrication diffi-culties may exist, however, with traditional designs.Typically, these prostheses are made with acrylic resinprocessed directly to the bar, so that the entire structureis screwed to the implants (Fig. 1). This may requirescrew access openings that extend through the dentureteeth; therefore, the dentist or technician must modifythe teeth to provide access to the screws.5 These open-ings must then be filled after insertion of the prosthesis.While many methods to fill the openings have been de-scribed,6 closing screw access holes requires additionalprocedures. The screw openings are frequently an es-thetic compromise, and the location of the screw open-ings may make it more difficult to move teeth during thetrial insertion. If implants are placed at an unfavorableangle, screw access openings may exit through the buc-cal surface of a tooth. This article describes the use of anacrylic resin superstructure that is cemented overa screw-retained bar. The prosthesis is fabricated in 2pieces, eliminating the presence of screw access open-ings in the acrylic resin. The esthetic result is improved,and tooth arrangement is simplified.

TECHNIQUE

1. Fabricate a diagnostic waxing. Place implants and al-low them to osseointegrate. Next, begin the fabrica-tion of the prosthesis. Place transmucosal abutments(BioHorizons Implant Systems, Inc, Birmingham,Ala) on the implants to raise the prosthetic platformsto 1mm above the gingiva. Place appropriate impres-sion copings and make the definitive impression(Aquasil; Dentsply Caulk, Milford, Del). Fabricatethe definitive working cast and make an acrylic resinindex to verify the accuracy of the cast (Fig. 2).Make a centric relation record and fabricate adiagnostic waxing to determine tooth position andbar dimensions.

aAssociate Professor, Department of Prosthodontics and Biomaterials.bPrivate Practice, San Antonio, Tex.cPrivate Practice.

298 THE JOURNAL OF PROSTHETIC DENTISTRY

2. Place pattern abutments on the definitive cast.Construct the bar in the shape of an inverted ‘‘T’’(Fig. 3), using acrylic resin (GC Pattern Resin; GCAmerica, Alsip, Ill) for the bulk of the bar. Refinethe pattern with inlay casting wax (Blue InlayCasting Wax; KerrLab, Orange, Calif) to smoothand shape the pattern as needed. Make the inferiorsurface of the bar convex, to allow room for hygieneprocedures. Leave a 2-mm space between the inferiorsurface of the bar and the tissue for hygiene purposes.Make the vertical strut between the screw accessopenings 2 to 3 mm wide and 4 to 6 mm high.Cast the bar in a precious metal alloy (Argedent65SF; The Argen Corp, San Diego, Calif). Evaluatethe bar intraorally to confirm fit.

3. Make a record base on the bar (Triad Denture BaseMaterial;DentsplyTrubyte, York, Pa) and add aman-dibular wax occlusion rim (Fig. 4). Attach the barto the implants and insert the record base onto thebar (Fig. 5).

4. Fabricate a wax trial denture for the patient. Extendthe acrylic resin denture base to a maximum of 6mm beyond the distal extent of the bar.Alternatively, extend the bar to the full extent ofthe distal extension so that there is no unsupportedacrylic. After the patient accepts the trial dentureand maxillomandibular records are verified, processthe denture.

5. Adapt 1 layer of 0.001-inch tin foil (Buffalo Dental,Syosset, NY) over the bar before processing, to assistin removing the processed denture. Finish the wax tothe edge of the bar, to serve as an external finish line.Process the denture to the bar. After processing, re-move the denture from the bar and finish with coarsepumice, fine pumice (Whip Mix Corp, Louisville,Ky), and a buffing agent (Moldent Buffing Agent;Motloid Co, Chicago, Ill).

6. Place the bar on the implants and hand-tighten thescrews. Insert the denture. After the fit of the pros-thesis and occlusion are verified, remove the dentureand tighten the screws with a torque wrench(BioHorizons Implant Systems, Inc). Line the inta-glio surfaces of the acrylic resin superstructure with

VOLUME 93 NUMBER 3

THE JOURNAL OF PROSTHETIC DENTISTRYMCCRACKEN, SIMMONS, AND SIMMONS

provisional cement (TempBond; Kerr, Orange,Calif) (Fig. 6) and lute the bar into place. Use a stron-ger luting agent (IRM; Dentsply, York, Pa), if neces-

Fig. 1. Traditional metal-resin fixed partial denture designfrequently has screw access openings through acrylic resinportion of prosthesis or replacement teeth, compromisingesthetics.

Fig. 3. Bar is cast in inverted ‘‘T’’ design.

Fig. 5. Bar in place at time of recording centric relation.

MARCH 2005

sary, to provide more retention. Remove excesscement (Fig. 7).

Fig. 2. Acrylic resin index transferred intraorally to verifyaccuracy of definitive cast.

Fig. 4. Wax rim adapted to bar to make centric relationrecord. Acrylic resin record base used to support wax andprovide repeatable seating of record base on bar.

Fig. 6. Provisional cement placed in acrylic resin superstruc-ture.

299

THE JOURNAL OF PROSTHETIC DENTISTRY MCCRACKEN, SIMMONS, AND SIMMONS

DISCUSSION

The technique described offers several advantagesover traditional approaches. The primary advantage isthat there are no screw access openings in the dentureteeth. Themaking of centric relation records and adjust-ments to the wax trial denture are simplified by havinga superstructure that is easy to remove from the mouth.If denture teeth need to be repaired or the implant barneeds to be removed, the superstructure can be sepa-rated from the bar. The prosthesis may be disassembledby cutting a small groove in the acrylic resin on bothsides of the arch in the region of the first premolar andinserting a small screwdriver into the groove to pry offthe superstructure. Access is then gained to abutmentscrews, and the bar can be removed. The superstructureis recemented, and the small slots can be repaired withautopolymerizing acrylic resin. If more retention ofthe superstructure is desired, zinc phosphate cementor another similar material can be used. Alternatively,set screws can be tapped into the bar and used to securethe superstructure from the facial aspect of the denture.

A limitation for using this technique is minimalinterarch distance. The minimum space requirementfor this prosthesis is 12 mm (2 to 3 mm of space belowthe bar for cleanability, 2 mm for the convex base of thebar, 4 mm of height for the vertical strut for retention,and 3 mm of acrylic resin for the superstructure).Disadvantages of this technique include superstructureloosening, superstructure fracture, and debonding of

Fig. 7. Definitive restoration.

300

denture teeth. It is recommended that acrylic resin beat least 3 mm in thickness in an occlusal-gingival direc-tion and at least 2 mm in the buccal-lingual directionto prevent fracture of the superstructure.

SUMMARY

The proposed technique uses an acrylic resin super-structure that is cemented onto an implant-supportedbar to create a metal-resin fixed complete denture.This cement-retained superstructure offers several ad-vantages over traditional acrylic resin designs, includingease of fabrication, insertion, and improved esthetics.

The authors thank Mr Curtis Mitchell for his assistance with

laboratory and processing techniques.

REFERENCES

1. Jeffcoat MK, McGlumphy EA, Reddy MS, Geurs NC, Proskin HM. A

comparison of hydroxyapatite (HA) -coated threaded, HA-coated cylindric,

and titanium threaded endosseous dental implants. Int J Oral Maxillofac

Implants 2003;18:406-10.

2. Romeo E, Lops D, Margutti E, Ghisolfi M, Chiapasco M, Vogel G. Long-

term survival and success of oral implants in the treatment of full and par-

tial arches: a 7-year prospective study with the ITI dental implant system.

Int J Oral Maxillofac Implants 2004;19:247-59.

3. Timmerman R, Stoker GT, Wismeijer D, Oosterveld P, Vermeeren JI, van

Waas MA. An eight-year follow-up to a randomized clinical trial of partic-

ipant satisfaction with three types of mandibular implant-retained overden-

tures. J Dent Res 2004;83:630-3.

4. Testori T, Meltzer A, Del Fabbro M, Zuffetti F, Troiano M, Francetti L, et al.

Immediate occlusal loading of Osseotite implants in the lower edentulous

jaw. A multicenter prospective study. Clin Oral Implants Res 2004;15:

278-84.

5. Fredrickson EJ, Stevens PJ, Gress ML. Implant prosthodontics: clinical and

laboratory procedures. 2nd ed. St. Louis: Mosby; 2000. p. 122.

6. Howell JC Jr, Caldwell WD. Custom-made cover screws to fit fixed detach-

able implant prosthesis access openings. J Prosthet Dent 1997;78:209-11.

Reprint requests to:

DR MICHAEL MCCRACKEN

SDB 606

1919 SEVENTH AVE SOUTH

BIRMINGHAM, AL 35294

FAX: (205) 975-6108.

E-MAIL: mikemc@uab.edu

0022-3913/$30.00

Copyright � 2005 by The Editorial Council of The Journal of Prosthetic

Dentistry.

doi:10.1016/j.prosdent.2004.12.014

VOLUME 93 NUMBER 3