Repair of Porcelain/Metal Restoration with Resin Bonded Overcasting Morton Wood, D.D.S., M.Ed.,* Leonard J . Litkowski, D.D.S., M.S., Van P. Thompson, D.D.S., Ph.D.! and Timothy Church, B.A."
Porcelain occasionally fractures from ceramometal fured partial dentures following final cementation. Repair of these porcelain fractures can be a challenging task. When the problem occurs on anterior teeth, it is especially difficult because the repair must not only be durable, but esthetically pleasing as well. Although composite resins can be used for some repairs, it is often difficult to match the color and texture to the surrounding intact porcelain. In addition, the bonding between the resin and porcelain is susceptible to margin leakage, which may ultimately cause an esthetic failure. Techniques involving a cemented porcelain-fused-tometal overcasting have often been successful in restoring the fured partial denture to form and function. Although the esthetic result of a porcelain/metal overcasting can be quite successful, retention of the overcasting is sometimes poor. The compromised retention and resistance form is due to lack of interproximal walls on the underlying fractured unit. To improve the retention of the overcasting, the following technique of tin plating the overcasting and fractured unit prior to cementing with a composite resin cement is presented.
Case Report
S
mall porcelain fractures from porcelain-fused-tometal abutments or pontics can be repaired with several different composite resin products. The techniques used involve treating the exposed metal and/or porcelain with a silane coupler and adding a composite resin to match the porcelain color.' However,when large areas of porcelain fracture, chairside composite resin repairs often fail.2 This failure is most commonly due to the lack of a long-term strong stable bond between the porcelain and composite resin. As an alternative, various techniques for porcelain-fused-to-metal overcastings have been a d ~ o c a t e d .In ~ -an ~ attempt to improve retention of the overcasting, it can be cemented with a composite resin cement (i-e., Panavia, Kuraray Co., Osaka Japan/J. Morita Co, USA) that has increased bond strength when applied to tin-plated metal surfaces.6Since the inside of the casting and the outer surface of the fractured unit are both tin plated, the resulting metal-to-metal bond is quite strong.
A patient presented with a fixed partial denture inserted with a final cement for approximately 2 years when the majority of porcelain fractured off the pontics on both maxillary central incisors (Fig. 1). The fracture was most likely caused by either (1) inadequate framework design leading to unsupported porcelain or (2) contamination of the metal prior to porcelain application. Since the remainder of the restoration was sound with well fitting margins, favorable esthetics, adequate occlusion and anatomic contour, the treatment of choice was to repair rather than replace the prosthesis. Although the remaining metal substructure in the fractured pontic area was thin faciolingually and somewhat short incisogingivally,there was still a n adequate bulk of metal to prepare for an overcasting.
heparation/Impresswn The preparation phase consisted of using a coarse diamond bur to remove the remaining porcelain in the pontic areas. The metal substructure in the pontic areas was reduced on the facial and lingual sides to allow room for the inclusion of the porcelain-fused-tometal overcasting. All undercuts were removed, a path of draw was established, and distinct chamfer margins were placed on the lingual side (Fig. 2). Because of the tendency for the impression material to lock under the tissue side of the prepared pontics
*Assistant Professor. Department of General Dentistry: t Assistant Professor. kogram in Dental Materials. Department of General Dentistry: $Professor and Director of Dental Materials: Baltimore College of Dental surgery: K Senior Dental Student: Baltimore College of Dental Surgery, Dental School. University of Maryland at Baltimore. Baltimore. Maryland. Address reprlnt requests to Morton Wood. D.D.S.. M.Ed.. Department of General Dentistry, Baltimore College of Dental Surgery. Dental School. 666 West Baltimore St., Baltimore, MD 21201 0 1992 Decker Periodicals Inc.
110
Repair with Resin Bonded Overcasting
overcasting was developed with acrylic (Duralay, Reliance Dental Manufacturing Company, Worth, 11) and cast in a nonprecious alloy (Figs. 3A and 3B). The porcelain was then added in a conventional manner to the metal substructure. Clinical Phase
The porcelain was characterized and glazed to match the porcelain on the surrounding abutment teeth. The remaining lingual collar of the overcasting was polished and the internal surfaces were freshly air abraded with aluminum oxide. The overcasting was then placed in an ultrasonic bath to remove any debris and finally dried before tin plating. All metal surfaces (on the fractured unit and the inside of the overcasting) that would be in frictional contact were tin plated. The inner surface of the overcasting was tin plated first using a battery operated plater (Microtin, Danville Engineering, Inc. Danville, CAI. In order to make a circuit, the overcasting (cathode) is contacted by a metal wire or alligator clips which connect to the negative (-) end of the plating pencil. A cotton or felt swab is placed on the end of the metal anode terminal. The swab is then saturated in the clear tin plating solution. The surface is then electroplated by completing the circuit and brushing the area with the metal-soaked tip for 4-6 seconds (Fig. 4). Care must be exercised so that the surface is not "over plated." The ideal amount of tin deposited to the surface should be between 0.2-0.5 microns. When the depth exceeds 0.5 microns, the bond to the luting resin wiU start to decrease. Proper plating is estimated by time, change in the metal surface to a whitish or silver color, and a distinct residue left on the swab (Fig. 5). Before cementing the overcasting, the surfaces of the pontic areas that are in contact with the inside of the overcasting are also tin plated. A rubber dam must be utilized to prevent moisture contamination and protect the underlining tissues from potential contact with the tin plating solution. If possible, the bonded surfaces of the prepared pontics should be air abraded intraorally. If this system is not available, the metal could then be cleansed of contaminants by coating it with a 37% phosphoric acid gel for 60 seconds followed by a thorough rinsing and drying. The electroplating of the pontics is performed in the same fashion as the overcasting, making sure to use a fresh and well-soaked swab on the tip of the anode (Figs. 6A and 6B). The overcasting is cemented using a thin mix of Panavia, which was spread over the tin plated area of the pontics (Fig. 7)as well as the tin plated surfaces of the overcasting. Panavia is an extremely oxygen inhibited composite resin and has a long working time provided that it is applied in a thin layer. To ensure a favorable esthetic result and prevent the appearance of an opaque "cement line," use only the tooth-colored resin. Following seating of the restoration, excess resin is removed using a stiff-pointed brush (Fig. 8).Once the excess is removed the Oxyguard gel is placed around all the margins. This gel prevents oxygen from contacting
Figure 1. The porcelain veneers fractured as a unit from the facial surfaces of the pontics. This type of fracture is too large to be repaired with a chairside porcelain repair material.
and become distorted upon removal from the mouth, these areas were carefully blocked out using a soft beading wax. The wax was placed gingival to the lingual finish lines and the tissue. The block out aids in producing an accurate impression and a detailed model. If necessary, an acrylic provisional restoration can be placed and cemented with a temporary cement during the time of laboratory fabrication. It should be noted that the purpose of the provisional restoration is primarily for esthetics and should be contoured to have minimal occlusal contacts so that it will not be dislodged.
Laboratory Phase A stable stone model is essential, therefore removable dies should not be used. The metal "sleeve" of the
METAL FRAMEWORK OF OVERCASTING
PORCELAIN FUSED TO METAL
Figure 2. This cross-section of the overcasting reveals the nature of the preparation and finish lines as well as the lack of interproximal walls for retention/resistance form.
111
JOURNAL OF ESTHETIC DENTISTRY VOLUME 4, NUMBER 4 July/August 1992
Figures. Whentinplatingiseffectivetherewillbeabrownish residue that forms on the cotton swab. When plating a new area, be sure to use a clean cotton swab.
Figure 3A. The facial view of the metal framework of the overcasting.
Figure 3B. The lingual view of the metal framework demon-
Figure 6tL The alligator clips make contact with the prepared pontic while the moistened swab is brushed back and forth.
strates the fit of the overcasting to the finish line of the preparation. This design will allow porcelain to overlap from facial to ling~~al, improve the esthetics, and increase the surface area for fusing porcelain.
the cement and ensures a rapid setting reaction of the resin. In most cases the original pontic sections have modified ridge lap designs in which porcelain extends from the facial to the lingual side, making light tissue contact. When all the porcelain, including the tissue side, is removed to make an overcasting, the resulting contour creates a gingival concavity that is difficult to clean and is prone to development of plaque around the pontics and abutment teeth. The impact of this design on periodontal health is well do~umented.~ It is therefore important that the patient is aware of this limitation and that appropriate homecare instructions and techniques are given. These should include the proper use of dental floss and floss threaders with supplemental periodontal aids to access the lingual and proximal areas (e.g., hoxibrush,John 0.Butler Co., Chicago, IL). The original restoration has been salvaged with a functional and esthetically pleasing repair that is well cemented (Figs. 9A and 9B).
Figure 4. The alligator clips make metal contact while the moistened cotton swab is placed inside the casting and moved back and forth for several seconds.
112
Repair with Resin Bonded Overcasting
Figure 6B. This view contrasts the difference between the original pontic and one that has been plated. The grey frosted surface of the right incisor indicates the proper appearance of a tin plated surface.
Figure QA. The facialview of the cemented overcastingreveals a very esthetic result.
Figure 7. The tooth colored Panavia is thinly painted over the
Figure QB. The occlusal of the cemented overcasting demon-
tin plated surfaces of the pontics and a disposable brush.
strates that the h a l result is not bulky and that arch form is well maintained.
REFERENCES 1. Stangel ID, Nathanson D, Hsu CS. Shear strength of the composite bond to etched porcelain. J Dent Res 1987: 66(9):1460-1465. 2. Finger IM. Salvaging the restoration. Dent Clin North Am 1897; 31:487-503. 3. Cohen B. Weiner S. Restoration of fixed partial dentures with fractured porcelain veneers using an overcasting. J Prosthet Dent 1989:64:390-392. 4. GelbmanJ.Biber CL. Salvagingthe broken porcelain fused to metal partial prosthesis. Clin Rev Dent 1986;8:22-23. 5. Dent RJ.Rep& ofporcelain-fused-to-metalrestorations. J Prosthet Dent 1979:41(6):661-664. 6. Yamashita A Kondo Y,Fujita M. Adhesive strength of adhesive resin Panavia EX to dental alloys. J Jpn Prostho Soc 1984 28:1023-1033. 7. Silness J. Periodontal conditions in patients treated with dental bridges. J Periodont Res 1970:560-68.
Figure 8. While holding the overcastingin place, excess resin is removed with a stiff tapered brush
113
Porcelain occasionally fractures from ceramometal fured partial dentures following final cementation. Repair of these porcelain fractures can be a challenging task. When the problem occurs on anterior teeth, it is especially difficult because the repair must not only be durable, but esthetically pleasing as well. Although composite resins can be used for some repairs, it is often difficult to match the color and texture to the surrounding intact porcelain. In addition, the bonding between the resin and porcelain is susceptible to margin leakage, which may ultimately cause an esthetic failure. Techniques involving a cemented porcelain-fused-tometal overcasting have often been successful in restoring the fured partial denture to form and function. Although the esthetic result of a porcelain/metal overcasting can be quite successful, retention of the overcasting is sometimes poor. The compromised retention and resistance form is due to lack of interproximal walls on the underlying fractured unit. To improve the retention of the overcasting, the following technique of tin plating the overcasting and fractured unit prior to cementing with a composite resin cement is presented.
Case Report
S
mall porcelain fractures from porcelain-fused-tometal abutments or pontics can be repaired with several different composite resin products. The techniques used involve treating the exposed metal and/or porcelain with a silane coupler and adding a composite resin to match the porcelain color.' However,when large areas of porcelain fracture, chairside composite resin repairs often fail.2 This failure is most commonly due to the lack of a long-term strong stable bond between the porcelain and composite resin. As an alternative, various techniques for porcelain-fused-to-metal overcastings have been a d ~ o c a t e d .In ~ -an ~ attempt to improve retention of the overcasting, it can be cemented with a composite resin cement (i-e., Panavia, Kuraray Co., Osaka Japan/J. Morita Co, USA) that has increased bond strength when applied to tin-plated metal surfaces.6Since the inside of the casting and the outer surface of the fractured unit are both tin plated, the resulting metal-to-metal bond is quite strong.
A patient presented with a fixed partial denture inserted with a final cement for approximately 2 years when the majority of porcelain fractured off the pontics on both maxillary central incisors (Fig. 1). The fracture was most likely caused by either (1) inadequate framework design leading to unsupported porcelain or (2) contamination of the metal prior to porcelain application. Since the remainder of the restoration was sound with well fitting margins, favorable esthetics, adequate occlusion and anatomic contour, the treatment of choice was to repair rather than replace the prosthesis. Although the remaining metal substructure in the fractured pontic area was thin faciolingually and somewhat short incisogingivally,there was still a n adequate bulk of metal to prepare for an overcasting.
heparation/Impresswn The preparation phase consisted of using a coarse diamond bur to remove the remaining porcelain in the pontic areas. The metal substructure in the pontic areas was reduced on the facial and lingual sides to allow room for the inclusion of the porcelain-fused-tometal overcasting. All undercuts were removed, a path of draw was established, and distinct chamfer margins were placed on the lingual side (Fig. 2). Because of the tendency for the impression material to lock under the tissue side of the prepared pontics
*Assistant Professor. Department of General Dentistry: t Assistant Professor. kogram in Dental Materials. Department of General Dentistry: $Professor and Director of Dental Materials: Baltimore College of Dental surgery: K Senior Dental Student: Baltimore College of Dental Surgery, Dental School. University of Maryland at Baltimore. Baltimore. Maryland. Address reprlnt requests to Morton Wood. D.D.S.. M.Ed.. Department of General Dentistry, Baltimore College of Dental Surgery. Dental School. 666 West Baltimore St., Baltimore, MD 21201 0 1992 Decker Periodicals Inc.
110
Repair with Resin Bonded Overcasting
overcasting was developed with acrylic (Duralay, Reliance Dental Manufacturing Company, Worth, 11) and cast in a nonprecious alloy (Figs. 3A and 3B). The porcelain was then added in a conventional manner to the metal substructure. Clinical Phase
The porcelain was characterized and glazed to match the porcelain on the surrounding abutment teeth. The remaining lingual collar of the overcasting was polished and the internal surfaces were freshly air abraded with aluminum oxide. The overcasting was then placed in an ultrasonic bath to remove any debris and finally dried before tin plating. All metal surfaces (on the fractured unit and the inside of the overcasting) that would be in frictional contact were tin plated. The inner surface of the overcasting was tin plated first using a battery operated plater (Microtin, Danville Engineering, Inc. Danville, CAI. In order to make a circuit, the overcasting (cathode) is contacted by a metal wire or alligator clips which connect to the negative (-) end of the plating pencil. A cotton or felt swab is placed on the end of the metal anode terminal. The swab is then saturated in the clear tin plating solution. The surface is then electroplated by completing the circuit and brushing the area with the metal-soaked tip for 4-6 seconds (Fig. 4). Care must be exercised so that the surface is not "over plated." The ideal amount of tin deposited to the surface should be between 0.2-0.5 microns. When the depth exceeds 0.5 microns, the bond to the luting resin wiU start to decrease. Proper plating is estimated by time, change in the metal surface to a whitish or silver color, and a distinct residue left on the swab (Fig. 5). Before cementing the overcasting, the surfaces of the pontic areas that are in contact with the inside of the overcasting are also tin plated. A rubber dam must be utilized to prevent moisture contamination and protect the underlining tissues from potential contact with the tin plating solution. If possible, the bonded surfaces of the prepared pontics should be air abraded intraorally. If this system is not available, the metal could then be cleansed of contaminants by coating it with a 37% phosphoric acid gel for 60 seconds followed by a thorough rinsing and drying. The electroplating of the pontics is performed in the same fashion as the overcasting, making sure to use a fresh and well-soaked swab on the tip of the anode (Figs. 6A and 6B). The overcasting is cemented using a thin mix of Panavia, which was spread over the tin plated area of the pontics (Fig. 7)as well as the tin plated surfaces of the overcasting. Panavia is an extremely oxygen inhibited composite resin and has a long working time provided that it is applied in a thin layer. To ensure a favorable esthetic result and prevent the appearance of an opaque "cement line," use only the tooth-colored resin. Following seating of the restoration, excess resin is removed using a stiff-pointed brush (Fig. 8).Once the excess is removed the Oxyguard gel is placed around all the margins. This gel prevents oxygen from contacting
Figure 1. The porcelain veneers fractured as a unit from the facial surfaces of the pontics. This type of fracture is too large to be repaired with a chairside porcelain repair material.
and become distorted upon removal from the mouth, these areas were carefully blocked out using a soft beading wax. The wax was placed gingival to the lingual finish lines and the tissue. The block out aids in producing an accurate impression and a detailed model. If necessary, an acrylic provisional restoration can be placed and cemented with a temporary cement during the time of laboratory fabrication. It should be noted that the purpose of the provisional restoration is primarily for esthetics and should be contoured to have minimal occlusal contacts so that it will not be dislodged.
Laboratory Phase A stable stone model is essential, therefore removable dies should not be used. The metal "sleeve" of the
METAL FRAMEWORK OF OVERCASTING
PORCELAIN FUSED TO METAL
Figure 2. This cross-section of the overcasting reveals the nature of the preparation and finish lines as well as the lack of interproximal walls for retention/resistance form.
111
JOURNAL OF ESTHETIC DENTISTRY VOLUME 4, NUMBER 4 July/August 1992
Figures. Whentinplatingiseffectivetherewillbeabrownish residue that forms on the cotton swab. When plating a new area, be sure to use a clean cotton swab.
Figure 3A. The facial view of the metal framework of the overcasting.
Figure 3B. The lingual view of the metal framework demon-
Figure 6tL The alligator clips make contact with the prepared pontic while the moistened swab is brushed back and forth.
strates the fit of the overcasting to the finish line of the preparation. This design will allow porcelain to overlap from facial to ling~~al, improve the esthetics, and increase the surface area for fusing porcelain.
the cement and ensures a rapid setting reaction of the resin. In most cases the original pontic sections have modified ridge lap designs in which porcelain extends from the facial to the lingual side, making light tissue contact. When all the porcelain, including the tissue side, is removed to make an overcasting, the resulting contour creates a gingival concavity that is difficult to clean and is prone to development of plaque around the pontics and abutment teeth. The impact of this design on periodontal health is well do~umented.~ It is therefore important that the patient is aware of this limitation and that appropriate homecare instructions and techniques are given. These should include the proper use of dental floss and floss threaders with supplemental periodontal aids to access the lingual and proximal areas (e.g., hoxibrush,John 0.Butler Co., Chicago, IL). The original restoration has been salvaged with a functional and esthetically pleasing repair that is well cemented (Figs. 9A and 9B).
Figure 4. The alligator clips make metal contact while the moistened cotton swab is placed inside the casting and moved back and forth for several seconds.
112
Repair with Resin Bonded Overcasting
Figure 6B. This view contrasts the difference between the original pontic and one that has been plated. The grey frosted surface of the right incisor indicates the proper appearance of a tin plated surface.
Figure QA. The facialview of the cemented overcastingreveals a very esthetic result.
Figure 7. The tooth colored Panavia is thinly painted over the
Figure QB. The occlusal of the cemented overcasting demon-
tin plated surfaces of the pontics and a disposable brush.
strates that the h a l result is not bulky and that arch form is well maintained.
REFERENCES 1. Stangel ID, Nathanson D, Hsu CS. Shear strength of the composite bond to etched porcelain. J Dent Res 1987: 66(9):1460-1465. 2. Finger IM. Salvaging the restoration. Dent Clin North Am 1897; 31:487-503. 3. Cohen B. Weiner S. Restoration of fixed partial dentures with fractured porcelain veneers using an overcasting. J Prosthet Dent 1989:64:390-392. 4. GelbmanJ.Biber CL. Salvagingthe broken porcelain fused to metal partial prosthesis. Clin Rev Dent 1986;8:22-23. 5. Dent RJ.Rep& ofporcelain-fused-to-metalrestorations. J Prosthet Dent 1979:41(6):661-664. 6. Yamashita A Kondo Y,Fujita M. Adhesive strength of adhesive resin Panavia EX to dental alloys. J Jpn Prostho Soc 1984 28:1023-1033. 7. Silness J. Periodontal conditions in patients treated with dental bridges. J Periodont Res 1970:560-68.
Figure 8. While holding the overcastingin place, excess resin is removed with a stiff tapered brush
113
