Fabrication of a Pontic Crown
Mike McBride, DDS; and Maurice W. Lewis, DDS
Metal ceramic restorations are a mainstay of conventional fixed prosthodontics. They have been used for more than 40 years.1-3 Despite the fact that the properties of the metals and porcelains have improved over the years, there remains the potential for failure of the restoration as a result of fracture of the fused porcelain. This may be from various reasons, including: the type of metal used, framework design,4 thickness of the metal, support for the porcelain, contamination of the metal oxide layer, incompatible thermal coefficients of expansion, trauma, and other factors. There are numerous studies concerning the causes of fixed partial denture (FPD) failure.5-11 One study showed that the failure of a FPD can be from many causes: the principle reason was caries (36%), followed by a worn occlusion (17%), and periapical involvement (15%). Porce-lain failure was 9%.5
There are often instances where porcelain has fractured from the pontic of a FPD. The preferred treatment of choice is fabrication of a new FPD; however, because of financial and possible health complications, this is not always an option. It must always be taken into consideration that some patients—because of age, immune system status, cardiovascular health, and many other possible health concerns—are not able to withstand long appointments and, therefore, the length of time of the appointment may contraindicate the fabrication of a new FPD. There are in-direct and direct methods of repair available. Indirect methods include preparation of the retainer, fabrication, and cementation of a new overlay crown.12 Probably the most common method is to repair the area with bonded composite.13-14 Although this technique may be adequate for a small area of fractured porcelain, it will generally not suffice in an area where the patient has occlusion. This article will present two case reports using an alternative method to restore a fractured pontic with a porcelain-fused-to-metal “pontic crown.”
A 69-year-old female patient presented to the clinic with no health-related conditions that would preclude normal dental treatment. She presented with an FPD with retainers on teeth Nos. 3, 4, 7, and 8. Pontics replaced teeth Nos. 5 and 6. The porcelain was fractured from the pontic replacing No. 6 (Figure 1). The patient was presented with the option of replacing the FPD with a new restoration. She stated that this would not be an option because of financial concerns. The option of a “pontic crown” was presented to her with possible concerns about longevity of the restoration. After considering the possibility of replacing the entire FPD, it was decided to modify the fractured pontic so that an overlay crown could be placed. The pontic area of the crown was prepared similar to what would be done for a crown preparation with particular attention to ensure the preparation had minimal taper. Re-tentive orientation grooves were placed where possible, and a lingual finish line was established. Fused porcelain also was left in place where possible (Figure 2 and Figure 3) so that this could later be etched to aid in the retention of the final restoration. The space gingival to the tissue side of the pontic was blocked out with wax and an impression was made. A provisional was fabricated from a prefabricated anterior and cemented (Figure 4).
A wax framework was made and cast in noble metal on the resulting die (Figure 5). The framework was extended to the gingival level to ensure proper porcelain support (Figure 6View Figure). The retentive features of the preparation were apparent on the intaglio surface of the casting (Figure 7). Porcelain was applied to the framework and fitted to the die (Figure 8). The case was then ready to deliver to the patient.
The restoration was tried in the mouth and the intaglio surface, and occlusion was adjusted as needed. Before the restoration was ready for cementation, the intaglio surface was air-abraded with 90-µm aluminum oxide from Danville Innovative Dental Products (San Ramon CA). This was followed by tin-plating with a MicroTin electroplater (Danville Innovative Dental Products) per manufacturer instructions. The prepared pontic metal was lightly air-abraded with 90-µm aluminum oxide from Danville Innovative Dental Products with the aid of high-vacuum suction. A small applicator brush was used to carefully treat the remaining porcelain on the prepared pontic with hydrofluoric acid gel. The space gingival to the tissue side of the pontic was blocked out with wax and the restoration was cemented with Panavia F2.0 and Primer II bonding agent (J. Morita, Tokyo, Japan) per manufacturer instructions (Figure 9 and Figure 10). The excess cement was removed, and the patient was provided with additional oral hygiene instructions.
The author has cemented several of these cases with other conventional definitive cements with reasonable success; these cases were those where sufficient pontic occlusal-gingival length was available for preparation. Cases which involved patients with heavy wear patterns were avoided. The author has found that the retention rate has been similar to a conventional crown with a short clinical crown. Although this is not the optimum treatment, it is a viable option when circumstances prevent remaking a FPD. If the occlusal-gingival height is sufficient, the retention of the prosthesis is very good. In these cases, proper occlusion with no eccentric contacts is necessary.
A 67-year-old man reported to the clinic with the chief complaint of a piece of his bridge breaking off. Although this patient had some significant medical issues in his health history, none were contrain-dicative of general dental treatment. Clinical examination revealed a 4-unit porcelain-fused-to-metal (PFM) FPD with retainers on teeth Nos. 7, 8, and 10. The mesioincisal angle of No. 8 was chipped but this was not an issue of concern for this patient. The pontic replacing No. 9 had the porcelain facing fractured from the restoration (Figure 11). The patient had attempted to address the problem by replacing the facing using a common cyanoacrylate cement he had purchased from a hardware store. The repair had remained in place for several months but subsequently fractured again. A subsequent attempt to re-cement the broken piece failed and the patient sought professional help.
Because of the patient’s limited finances, he was reluctant to consider replacement of the entire FPD and was accepting of attempting to repair the FPD with a pontic crown. The cyanoacrylate residue was cleaned from the facing and the bridge, the pontic was tacked back into place using DYCAL® (DENTSPLY Caulk, Milford, DE) as a temporary cement and an alginate impression was made of the area to expedite fabrication of a provisional crown. The pontic area was prepared, leaving ridges created by the diamond burs to facilitate retention and creating specific facial and lingual finish lines (Figure 12). The gingival area was blocked out using red rope wax and a polyvinyl siloxane impression was made. An alginate impression of the mandibular dentition was made to make the opposing model. Interocclusal records, including a facebow registration, were done. An acrylic provisional crown was constructed using the alginate template and cemented with Durelon® cement (3M ESPE, St. Paul, MN).
The case was mounted on a Hanau semi-adjustable articulator (Waterpik® Technologies, Fort Collins, CO) with the incisal guide table generated in acrylic. A wax coping was made on the trimmed die and cast in noble metal. Porcelain was applied to the coping and fitted to the mounted case. The finished crown was then taken to the clinic for try-in and delivery.
The provisional pontic crown was re-moved and all cement residue was cleaned away. Very little adjustment of the completed pontic crown was necessary, as the marginal fit was accurate and the occlusion was very satisfactory after minor re-finement. The pontic crown was cemented using GC Fuji PLUS glass ionomer cement (GC America, Inc, Alsip, IL)(Figure 13). Excess cement was removed and the accessible interface margins were re-polished using the Dialite® intraoral polishing kit (Brasseler USA, Savannah, GA). The patient was very pleased with the result. He was most recently seen for a prophylaxis recall, and the restoration is functioning well after 5 years (Figure 14).
Porcelain fracture on the pontic of a PFM FPD does not necessarily imply the removal and replacement of the damaged FPD. The use of a pontic crown can, in many cases, be a time and expense saver for both the patient and the dentist. This technique may also be the treatment of choice for those patients who, because of physical limitations as well as financial limitations, may be unable to undergo replacement of the FPD. The use of this technique can possibly be the tool that is required to satisfy a patient who could very easily develop resentment toward the treating dentist who insists upon replacement of the broken FPD without sufficient regard for the patient’s well-being. This technique is not difficult and may very well bring about the most effective and positive form of advertisement for the doctor, that is, the word of mouth advertising of a truly satisfied patient.
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|Figure 1 Preoperative view of the pontic with fractured porcelain.||Figure 2 Facial view of the pontic preparation.|
|Figure 3 Occlusal view of the pontic preparation.||Figure 4 Provisional restoration from a prefabricated anterior.|
|Figure 5 Occlusal view of the working die.||Figure 6 Facial view of the metal casting.|
|Figure 7 Intaglio view of the casting.||Figure 8 The crown on the die.|
|Figure 9 Occlusal view of the final cemented PFM crown.||Figure 10 Facial view of the final restoration.|
|Figure 11 The damaged pontic.||Figure 12 Pontic preparation. Note the ridges created by the diamond burs.|
|Figure 13 The pontic crown cemented with GC Fuji PLUS glass ionomer cement.||Figure 14 Five-year follow-up.|
|About the Authors|
|Mike McBride, DDS |
Director, Division of Prosthodontics
Department of Restorative Dentistry
University of Tennessee College of Dentistry
|Maurice W. Lewis, DDS |
Director, University Dental Practice
Department of Restorative Dentistry
University of Tennessee College of Dentistry