Aesthetic Rehabilitation of the Maxillary Central Incisors
Predictable Laboratory Sequence
In fabricating a single tooth or single teeth in the esthetic zone, the ceramist faces numerous technical challenges. Achieving a proper shade match is paramount, whether the restorations mask varying substrates or the adjacent natural dentition, and natural light reflection and refraction are treatment imperatives. Careful treatment planning and disciplined laboratory protocols are essential to achieving an esthetic treatment outcome. This presentation documents a predictable laboratory fabrication sequence used to restore two central incisors to a natural esthetic result.
When fabricating a single tooth or single teeth in the anterior maxilla, the ceramist must address numerous technical challenges. In addition to fit and a functional result, a proper shade match is paramount in this highly visible region, whether the restorations mask substrates of varying color or the adjacent natural dentition, and natural light dynamics (eg, absorption, reflection, refraction) are treatment imperatives. Careful treatment planning and communication among the clinician and ceramist and should be combined with disciplined laboratory protocols in order to achieve an esthetic treatment outcome. As shown in the following presentation, contemporary ceramic materials--with a range of effect powders and porcelain shades--enable the laboratory technician to develop restorations that are virtually indistinguishable from the natural dentition.
Examination and Treatment Planning
A 35-year-old male patient presented for definitive restoration of his maxillary central incisors, which had undergone trauma approximately one year earlier. At that time, the fractured incisors had been provisionally restored with composite resin and their vitality was monitored. Prior to presenting for definitive restoration one year post-trauma, the patient whitened his dentition in order to enhance the esthetic outcome (Figure 1).
Full-coverage crowns were necessary for teeth #8 and #9 due to the extent of the tooth structure lost to the previous trauma, and tooth preparation was conducted accordingly. Interproximal contacts were broken and light, 360-degree shoulder margins were prepared on both teeth. Minimal tooth structure was removed on the facial enamel, and the incisal edges were rounded. The lingual aspects were then wrapped to complete the preparation. Impressions were made, the teeth were provisionalized, and all related data and photography were conveyed to the dental laboratory to enable restoration fabrication.
Once the impressions were poured, models were created, and all dies separated and trimmed, restoration fabrication was initiated. All models were mounted on a semi-adjustable articulator to a facebow and bite registration received from the clinician. Prior to the fabrication of the restorations, an incisal matrix was created from the provisional model (Figure 2). This guide would be referenced throughout the procedure, enabling the ceramist to control internal effects and to avoid any overbuilding during the ceramic buildup. A wash/foundation firing was conducted using a non-diluted body-shaded porcelain, which was applied in thin layers to water-soaked dies, which were lightly tapped to ensure smooth, even coverage of margin areas. The porcelain was then dabbed with a facial tissue to remove any moisture and was placed into the porcelain furnace for firing (Figure 3). The dies were fired to 925°C.
When firing was complete, the dies were soaked in water and replaced into the duplication tray. Referring to the incisal edge matrix, the first buildup was performed using a 1:1 mix of body- and neutral-shaded porcelains. The former was diluted because it was judged to be too dense for this application (Figure 4). The porcelain was applied to the gingival half of the wet dies, then feathered out to receive an application of an equal mix of a body and neutral porcelains. This mix was built up onto the incisal edges to form the internal lobes. The porcelain was continually blotted for ideal moisture control. No condensing was performed. A porcelain knife was used to cut through the contact area to separate the two teeth, and the dies were fired again to a maturation temperature of 915°C. Once the dies had cooled, they were replaced in the duplication tray on the articulator, then closed into the incisal matrix to verify that the lobes had not been overbuilt and were in the correct position.
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The dies were remoistened in water to accept the next porcelain application. The body/neutral and body/neutral mixes were applied as they were previously to compensate for porcelain shrinkage. Enamel-shaded porcelain was placed to the outsides of the mesial and distal lobes, and a slight yellow-orange enamel was applied to the insides of the mesial and distal lobes, mimicking what was observed in the natural dentition (Figure 5). The porcelain was fired again to 915°C (Figure 6). The fired buildup was placed onto the articulator and against the incisal matrix to ensure that the lobes and internal effects were still correct. The lobes were filled in alternating effects powders, completing the initial shape of the teeth. Small white flecks of stain were applied directly onto the wet porcelain to simulate faint hypocalcification areas, and the porcelain was fired once more at 915° C.
The cooled dies were placed into the tray and the matrix was re-examined. A micro diamond disc was used to remove a small amount of excess porcelain from the mesial and distal surfaces. Following an evaluation of color and effects, the final contour was created by alternating enamel porcelain and effect powders over the entire surface of the teeth. The lingual aspects were completed in the same fashion, keeping within the form of the matrix (with the exception of compensation for porcelain shrinkage). A small amount of neutral-shaded enamel porcelain was beaded across the incisal edges with a brush to create halos on the finished porcelain. The teeth were separated with a porcelain blade, a small amount of porcelain was added to the contact areas, and the porcelain was fired once more.
The cooled restorations were tried in individually against the adjacent teeth. Using marking tape, areas of heavy contacts were identified and subsequently relieved. The contacts were then checked with Mylar tape. With one adjacent piece of the model in place, the contact between teeth #8 and #9 was adjusted carefully so as to not shift the midline (Figure 7). The adjacent teeth were then removed and placed into the tray to permit re-examination of all contacts. Finally, all components were tried in together on the model.
The complete model was placed on the articulator and any necessary adjustments were made for centric relation. Protrusive and canine movements were also verified, and minor adjustments were made to the incisal edges to shorten the length to that of the provisional restorations. Final contouring was achieved by using the diamond bur and the microdisc (Figure 8). Final morphology was refined using a flame-shaped diamond. Perikymata were created with a light sweep of the bur horizontally across the surface.
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Once the restorations had been refined and were ready to glaze, the porcelain was steamed to remove any debris. A glaze paste was thinned with glaze and applied to each restoration with a small stain brush. The restorations were fired to 830°C and allowed to cool. A diamond-impregnated wheel was then used to lightly refine the graininess remaining in the glaze. A Robinson Bristel brush, along with a medium porcelain polishing paste was used to bring the porcelain to a medium luster (Figure 9).
The restorations were steam cleaned then divested using glass beads at 80 psi. Any remaining porcelain around the margins was removed with the impregnated rubber wheel prior to fitting to the master dies. They were then seated to master dies and the margins were verified under magnification. The master dies were returned to the duplication tray, and both restorations were carefully placed. Minor adjustments were made to the contacts as needed, and the restorations were fit to the solid model. The margins, contacts, and occlusion were checked once more, then final polishing commenced for both crowns.
Prior to case delivery, the internal aspects of the restorations were lightly sandblasted with 50 µm aluminum oxide and etched using a ceramic hydrofluoric porcelain etch for one minute. They were then rinsed with water, placed in a neutralizing solution for 30 seconds, allowed to soak in a cup of alcohol in an ultrasonic cleaner for 5 minutes, and finally, air dried. The entire case was then packed for delivery and cementation (Figures 10 and 11).
In order to produce natural, highly esthetic restorations, the dental technician must master the art of shade matching and the nuances of a porcelain buildup. The maxillary incisors represent the focal point of a person’s smile. It is, therefore, important for the dental technician to consider the effect each ceramic layer will have on the appearance of the final restorations placed in these areas.
*Dental technician, CMR Dental Laboratory, Idaho Falls, ID.