The coping-retained bridge: a modified approach to conventional bridge design – review and case report

Advantages of the coping bridge

Alignment problems

Malaligned abutment teeth can complicate the path of insertion of fixed bridgework.^4,6,7 Attempting to correct the malalignment of abutment teeth with excessive tooth preparation can compromise the vitality of the pulp and the resistance/retention form of the abutment^6,8 (Figure 1). Copings can be made to improve the path of insertion of divergent abutments, allowing the dentist the simpler task of preparing the abutment teeth down their long axis.^4,5,7,9

Disadvantages of the coping bridge

Aesthetic problems

Aesthetic problems are created by the need for the prepared abutments to accommodate both the coping and the superstructure, which can result in the creation of a bulbous metal-ceramic bridge. Further aesthetic compromises result from the coping having a margin milled onto it to which the superstructure fits. As these margins are placed supra-gingivally (Figure 2), both a coping margin and a superstructure margin can be visible.

Cost

Manufacture of a bridge with the additional costs of copings can be expensive. Traditionally, copings are manufactured using high grade gold alloy (Figure 3), although base metal alloys¹ titanium¹⁶ and zirconium^16,17 copings have also been described (Figures 4 and 5).

Technique

The dentist decides how many copings will be used to retain the superstructure following a thorough clinical and radiographic examination. As previously discussed, higher success rates are observed for appliances retained by a greater number of copings. The use of two canines and two first premolars has been associated with high survival rates.

The preparation features of teeth for copings have been described in the literature:^3,5,9,15

Following tooth preparation and impressions, the laboratory is instructed to fabricate the copings (Figures 6 and 7).

The materials that may be used to fabricate copings are:

The copings are manufactured to a minimum thickness of 0.3 mm^3,16 with a 2° angulation and a milled chamfer margin. These dimensions are consistent regardless of which material has been used.

The copings are tried-in, and attached to, the abutment teeth using a temporary cement (Temp Bond, Kerr). A master impression is recorded with the copings in place. The impression and copings are sent to the laboratory together with a jaw registration and appliance prescription.

The laboratory is instructed to manufacture the metal-ceramic bridge superstructure in the chosen shade and with the necessary porcelain characteristics (Figure 8).

Once received from the laboratory, the copings are permanently cemented. The use of zinc phosphate and glass ionomer cements have been reported^{2,3,4,15,18,19} for this purpose but self-adhesive resin cements (Rely-X Unicem, 3M ESPE) have recently shown promising results.¹⁵

The superstructure is tried in over the copings (Figure 9). The cement used to secure this is prepared according to the recommendations previously discussed.

The patient is given oral hygiene advice and appropriate maintenance visits are arranged.

Case report

Patient A is a 77-year-old lady who presented in general practice with functional and aesthetic problems. Her upper denture was in poor repair and she was unable to tolerate her lower denture (Figure 10). She reported that it was painful to chew food and that she was dissatisfied with her appearance. Her medical history revealed well controlled hypertension and previous surgery to remove a benign growth from the right carotid. She was a non-smoker.

The lip line at rest and during maximal reveal displayed only the maxillary denture teeth and not the acrylic flange area (Figure 11). The gingival margins of the lower teeth were not displayed.

Intra-oral examination revealed a poor complete upper denture which was severely worn. Roots were retained in UR7, UL7 and LL4. Teeth LR3/LL3 were present, but both were compromised by severe tooth surface loss. Caries was noted in LR3 and root surface caries in UL7.

A buccal sinus was noted adjacent to LR4. The periodontal assessment revealed no mobility and no probing depths >4 mm were noted. Attached gingiva and buccal sulcus depth was reduced. Mild alveolar bone loss had resulted secondary to loss of teeth (Figures 12 and 13). Plaque control was satisfactory.

A history of sensitivity was reported in unit LR3, though this tooth responded to sensibility testing. Radiographic assessment revealed moderate horizontal bone loss associated with LR3 and periapical radiolucency associated with LL4. Close proximity of the pulp chamber to the most coronal aspect of teeth LR3/LL3 was noted.

The treatment options discussed with the patient were:

The patient considered her current situation unsatisfactory and wished to proceed with treatment. Implants were declined due to cost. Owing to the previous difficulties with a lower denture, the presence of caries in, and history of sensitivity with, LR3 the patient elected to have treatment with a complete denture opposing a coping-retained bridge.

Initial therapy was directed at removal of UL7 and LL4. Oral hygiene and periodontal scaling was carried out.

The clinical heights of LR3/LL3 were augmented with crown lengthening surgery (Figure 14). A lower surgical stent was made to plan the procedure.²⁰

An eight unit canine-to-canine bridge with first premolar cantilever pontics was proposed. This design was based on work carried out by Nyman et al,²¹ which documented the success of long span bridgework supported by a few isolated abutments.

A review appointment was made 20 weeks following crown lengthening surgery. It has been demonstrated that stability of the gingival crest after surgery occurs at this time.²²

Primary maxillary denture impressions were recorded in impression compound using modified metal stock trays. Units LR3/LL3 were prepared for copings (Figure 15) using the guidelines outlined above. A double retraction cord technique^3,4,7 was used and impressions were taken in modified stock trays (Figure 16) using polyether (Impregum, 3M ESPE). Master maxillary denture impressions were recorded in zinc oxide eugenol paste (SS White materials, Prima Dental Group) using a special tray.

Copings were manufactured in gold alloy and tried-in. Fit was satisfactory and temporary cement (Tempbond, Kerr) was used to fix the copings to teeth LR3/LL3.

The lower anterior ridge was anaesthetized and a periodontal probe used to measure the distance from the gingival crest to the alveolar ridge. A gingival rotary curettage technique was used to score the ridge^7,23 to allow space for fabrication of ovate bridge pontics (Figure 17). Ovate pontics have been shown to reduce bending of the appliance in response to functional loads and create a favourable emergence profile.⁷. A master impression was recorded in polyether (Impregum) and jaw registration and facebow transfer were recorded. The shade and porcelain characteristics were prescribed to the technician.

A visit was arranged for trial assessment of the complete denture which was approved by both the operator and the patient. Caries removal from LR3 was carried out and confirmed using caries indicator dye (Snoop, Pulpdent). The copings were re-tried on the abutment teeth and cemented permanently (Figure 18) using zinc phosphate cement (Heraeus Kulzer Ltd). A resin-based lute may also be used for this purpose and conveys the advantage of having a thinner viscosity, which may reduce problems of incomplete coping seating.

The bridge framework was tried-in and fit was satisfactory. The casting was returned to the laboratory for porcelain application.

The finished superstructure was received from the laboratory after the application of porcelain. The fit was again verified to ensure no distortion had occurred after porcelain application. The patient was shown and approved the appliance. The superstructure was cemented to the copings using the technique described by Wise⁴ (Figures 19 and 20). The complete maxillary denture was fitted and bilaterally balanced occlusal contacts were observed (Figure 21).

Discussion

The use of a coping-retained bridge allows the restoring dentist to provide the patient with a fixed solution for the replacement of missing teeth while overcoming the problems of poor abutment tooth alignment and abutment teeth of uncertain prognosis. The technique can allow the dentist to plan for future modifications without the need for costly appliance remakes. Patients for whom dental implants or removable dentures are unsuitable may benefit from this technique.

When planning this procedure, dentists and their patients should be aware of the higher cost of manufacture compared with conventional bridgework due to the need to fabricate copings.

The aesthetic compromise created by the presence of visible coping and bridge margins means that careful evaluation of the lip line and the patient's aesthetic expectations are required. The use of zirconium copings may improve aesthetics in some cases but it should be noted that the appliance may be considered over-contoured compared with a conventional bridge.

The main advantage of these appliances is their retrievability. Removal of the superstructure is afforded by using a weak cement to attach it to the copings. While this allows great flexibility for future treatment planning, both patient and dentist need to be aware that this may contribute to the superstructure becoming uncemented at an inconvenient time.

Coping selection is important for future treatment planning and the use of multiple abutments allows more flexibility in this regard. The use of two canine and two premolar abutments has been recommended as a favourable design.

When prescribed in appropriate cases the coping bridge may provide a long lasting and modifiable solution for the fixed replacement of missing teeth.