DENTAL TECHNIQUE

Assistant ProDentistry, Kyu

668

Completely digital approach to fabricating a crown under anexisting partial removable dental prosthesis by using an

intraoral digital scanner in a single appointment

Ju-Hyoung Lee, DDS

ABSTRACTRetrofitting a crown to an existing partial removable dental prosthesis (PRDP) is difficult, laborintensive, and time consuming. This article presents an alternative technique for fabricating a crownunder an existing PRDP by using an intraoral digital scanner and computer-assisted design andcomputer-aided manufacturing (CAD/CAM) technology. This technique involves less human errorand provides a well-fitting restoration. (J Prosthet Dent 2016;115:668-671)

Fabricating a crown to restorean abutment for an existingpartial removable dental pro-sthesis (PRDP) is compli-cated.1 Numerous reportspertaining to the fabrication ofa new crown to fit an existing

Figure 1. Evaluation of adequate clearance between abutment andmetal framework.

PRDP have been published over the past 4 decades.1-26

A technique has been introduced to fabricate a crownwith a laboratory scanner and computer-assisted designand computer-aided manufacturing (CAD/CAM) tech-nology, in which the critical portions such as theretentive area, guiding plane, and rest seat are preciselyreproduced with a resin coping.1 However, making aconventional impression is still necessary.1 Anothertechnique used an intraoral scanner to restore a frac-tured tooth with a crown by scanning an existingdiagnostic cast and a definitive cast.10 However, thelong-term storage of a diagnostic cast is not alwayspossible.

The accuracy of the digital impression compares withthat of the conventional impression.27-29 The appropriateadaptation and retentive force of retrofitted crowns withCAD/CAM technology has recently been reported.30 Thisarticle introduces a technique for fabricating a retrofittedcrown under an existing PRDP with an intraoral scannerand CAD/CAM technology in a single visit. The fabri-cation of an interim crown, the conventional laboratoryprocedure, and the long-term storage of a cast aretherefore eliminated.

fessor, Department of Dentistry, Catholic University of Daegu School of Mengpook National University, Daegu, South Korea.

TECHNIQUE

1. Place the existing PRDP to evaluate proper clear-ance between the maxillary left second molar andthe PRDP framework (Fig. 1).

dicine, and Graduate Student, Department of Prosthodontics, School of

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Figure 2. Crown pattern under existing partial removable dentalprosthesis.

Figure 3. Software view of crown pattern and partial removable dentalprosthesis.

Figure 4. Software view of complete crown pattern.

Figure 5. Software view of partially captured abutment.

Figure 6. Software view of completely captured abutment withoutapplication of partial removable dental prosthesis.

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2. Extrude polyvinyl siloxane occlusal registrationmaterial (Regisil; Dentsply Caulk) over the toothwith a smaller diameter tip.1,2 Ensure that thismaterial is applied to the critical portions and wipeexcess material from the outer surface of the PRDPframework with wet cotton before it polymerizes(Fig. 2).1,2 Have the patient close to maximal inter-cuspal position until this material polymerizes.2

3. After removing the PRDP and the pattern, assessthe critical portions of the pattern. Draw a line onthe buccal and occlusal surfaces of the pattern.Reseat the PRDP and the pattern.

4. Register a digital laboratory order and touch an iconof the tooth on the screen of an intraoral scanner(TRIOS Color Pod; 3Shape Inc). Check “Crown” forthe prosthesis type and “Pre-preparation” for a scanof the pattern.

5. Make a digital impression of the maxillary teeth,pattern, and PRDP (Fig. 3). Retrieve the pattern andthe PRDP. Grasp the noncritical area of the patternwith cotton pliers for an extraoral digital impression.Rescan the pattern starting from the bucco-occlusal

e

area to facilitate data acquisition (Fig. 4). During thescan, the previously captured metal framework im-age on the pattern is deleted, and the imprint imageof the framework is captured simultaneously.

6. Evaluate the removed region around the tooth.Because the adjacent tooth, the first molar, is ab-sent, reinsert the PRDP so that the scanner systemcan easily identify the oral situation during theabutment scan. If the adjacent tooth exists in

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Figure 7. A, Software view of superimposed image of abutment andcrown pattern (blue color). B, Software view of definitive crown (graycolor). Note that critical portions are preserved.

Figure 8. Retrofitted milled crown under existing partial removabledental prosthesis.

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another clinical situation, reinserting the PRDP isnot necessary. Scan the tooth as much as possible(Fig. 5). After removing the PRDP, scan theuncaptured area (Fig. 6). Scan the antagonist andobtain the maxillomandibular relationship. Send thescan data to a laboratory. Keep the pattern to pro-vide the technician with the visual information ofthe pattern for the crown design.1,2

7. Design the crown with CAD software (3Shape’sDental Systems; 3Shape Inc) (Fig. 7). The criticalportions of the crown should be designed bythe registered corresponding portions of thepattern.1,2,31 Establish the occlusal surface and theaxial contour.

8. Send the design information to a 5-axis simulta-neous milling machine (Arum 5X-200; DoowonIDCo) and mill a cobalt-chromium alloy block (M3;Medipion).

9. Inspect the milled crown intraorally to verify theocclusal contacts, marginal adaptation, and fit to thePRDP framework.1. Lute the crown with cement(RelyX Ultimate Adhesive Resin Cement; 3M ESPE)(Fig. 8).

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DISCUSSION

Fabrication of the milled crown beneath the existingPRDP was described. If a resin material is used for thecrown pattern, the pattern may lock into the undercutaround the adjacent teeth. However, as described byLivaditis,2 use of polyvinyl siloxane occlusal registrationmaterial eliminated this situation and provided a precisefit against the metal framework. The second advantage ofthis technique is that the crown can be milled in 30 mi-nutes, and the crown fabricated in a day. However, theclinician must perform the scan procedure carefully, andthe technician must have a complete understanding ofthe PRDP design and crown pattern.2

SUMMARY

Using intraoral digital scanner and CAD/CAM technol-ogy, the crown was fabricated against the existing PRDPefficiently and with less human error.

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Corresponding author:Dr Ju-Hyoung LeeCatholic University of Daegu School of Medicine3056-6 Daemyung-4-DongNamgu, DaeguSOUTH KOREAEmail: jus2u@cu.ac.kr

Copyright © 2016 by the Editorial Council for The Journal of Prosthetic Dentistry.

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