Case report no. 94 The replacement of old metal ceramic crowns with metal-free zirconia crowns (94)

Our female patient, 46, reported to our clinic with the following requests and complaints:

  • Her old metal ceramic crowns had lost some of their aesthetic appeal.

  • She felt an aesthetic makeover was all-important for her to feel at ease to smile again.

  • She wanted to have beautiful and uniform teeth.

  • She was considering having metal free crowns installed.

  • First off she only wanted to focus on front crowns, but would, in due course, have her rear bridges replaced as well.

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After

At the first encounter a panoramic radiograph and photographs were taken of the initial condition of the teeth.

A panoramic radiograph recording the initial condition

The radiograph and the thorough examination of the mouth revealed that the teeth were in good condition but the aesthetics of the crowns has compromised. The upper right central incisor had to be reinforced with a metal post and core abutment so it could safely accommodate a crown. The zirconia framework can fully cover the metal post and core and discoloured teeth, which an E. Max full ceramic crown is incapable of. The options were discussed with the patient and we jointly decided in favour of zirconia crowns to replace the old crowns mounted on the upper incisors. Aesthetics can be best restored with metal-free restorations, but seeing as the teeth had been root canal treated and reinforced with post and core abutments, zirconia crowns enjoyed precedence over full ceramic crowns in our decision.

The finished tooth preparations. The discolorations caused by the root canal treatment are readily visible and could show through a full ceramic crown. Zirconia crowns, on the other hand, would ensure complete coverage even in the case of discoloured and post and core enforced teeth.

The translucency of zirconia crowns is confusingly similar to natural teeth, which cannot be said for conventional metal ceramic crowns

Since our patient was also after whiter teeth, we also offered her teeth whitening. She opted for home teeth whitening so impressions were taken for the preparation of home whitening splints, and professional tartar removal and polishing were performed for her to be able to begin home whitening. When whitening is complete, the colour of the zirconia front crowns can be matched to that of the newly whitened teeth.

Once home whitening was complete, the removal of the old crowns and preparation of the teeth were due. Following the filing and preparation of the teeth, a so-called precision impression was taken which was sent to the dental laboratory alongside all requests, questions and photographs taken prior to the treatment. Until the completion of the permanent crowns provisional acrylate crowns (prepared with the Scutan method) are mounted on the tooth preparations in order to protect them and provide the patient with reasonable aesthetics for this interim period. The provisional crowns are prepared at the chairside immediately after the treatment, so that the patient does not have to leave with filed-down tooth stumps. These provisional acrylate crowns can be removed and placed back on during the trial fittings as many times as required.

The selection of tooth colour following teeth whitening. The old crowns have already been replaced with provisional crowns

Trial fittings are indispensable to the treatment, allowing for the timely discovery and remedy of any issues that may arise.

The trial fitting of the framework is the first of the trial fittings, allowing to verify the accuracy of the impressions taken earlier, and the trueness of zirconia framework of the replacement tooth. All replacement teeth must seamlessly fit the so-called master cast. With this trial fitting the length of the framework and the teeth, too, can be verified, as can the central position of the central incisors and the appropriate rearward curve of the arch. This is crucial to aesthetics, since if, for instance the framework is too long, the tooth may appear to too long with the ceramic sintered on. If everything is found in order at the trial fitting of the framework, the trial fitting of the crowns may ensue. The white coloured framework of the zirconia crowns is milled by a computer controlled CAD/CAM machine.

The white interior (white framework) of the zirconia crown

At the trial fitting of the crowns, the crowns will have received their ceramic coating (with the ceramic sintered on with a matte finish). At this trial fitting, occlusion, the shape and colour of the crowns, the central line and smile line can be verified with even better accuracy (aesthetic trial fitting).

Following the trial fitting of the crowns the last session is that of handover during which the crowns are permanently cemented in place. At handover the patient is shown the ins and outs of cleaning and the tools with which they can keep their new teeth clean at all times.

Upper front zirconia crowns on the master cast prior to being cemented in place. With zirconia frameworks the black or grey margin remains invisible even in the event of gum recession

Cast metal post and core on the master cast to bolster the upper right central incisor

Cast metal post and core to bolster the upper right central incisor

Follow-up panoramic radiograph of the natural tooth retained zirconia crowns

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