How to Compensate For Discolored Preps

Matt Roberts, CDT · Technical · Jan 2014

  • Restorative Challenge

  • Figure 1:
    Provisional restorations and models of the preparations remain essential for digitally designing restorations. In this case, the preparation model and opposing model were scanned into the 3Shape Digital Design program. The incisal edge matrix that would validate the orientation of the provisional scan to the working model scan was created from the incisal edge position of the provisional restorations on an articulator prior to scanning.

  • Figure 2:
    The provisional restorations were scanned to enable the ceramist to compare the position and shape of the final design to those of the provisional.

  • Figure 3:
    The ceramist created a preliminary digital design.

  • Figure 4:
    The incisal edge position was verified with the matrix created from the provisional restorations.

  • Figure 5:
    The case was oriented on a digital articulator to adjust functional pathways and occlusal stops.

  • Figure 6:
    Blue marks indicated contact areas with the opposing models during excursive movements. Contact intensity was indicated by the color intensity of the mark.

  • Figure 7:
    The heavy canine function and lighter lateral interference were clearly visible in the occlusal view and required adjustment. To evaluate restorative material thickness, the cross sectional tool was used. The underlying preparation color and restorative thickness were key to proper ingot selection for optimal esthetic results. The facial thickness of tooth #8 was shown to be .49mm.

  • Figure 8:
    Then, the “slice to plane” tool created the ideal contacts. The vertically oriented groove in the incisal matrix helped to orient the vertical midline for the case.

  • Figure 9:
    The slice tool used in Figure 8 resulted in a vertically oriented flat contact that required minimal adjustment after milling.

  • Figure 10:
    The ceramist performed a virtual try in of the digital design prior to milling the restorations and made the necessary changes.

  • Figure 11:
    Due to the dark underlying preps, the canines were fabricated from Zenostar zirconia from Ivoclar Vivadent. The software enabled the ceramist to cut back the facial surface by .3mm—his standard cutback for pre-colored Zenostar material—prior to milling.

  • Figure 12:
    The Zenostar zirconia restorations were milled using the Zenotec mini from Ivoclar Vivadent, while the IPS e.max restorations were milled in Zenotec Wax for the pressing technique. An appropriate pre-colored disc of the Zenostar material was selected for milling, after which additional color gradients and incisal effects were created using a water color staining technique on the milled zirconia prior to sintering. The post-sintering result was a nice color gradient and incisal effect directly in the zirconia.

  • Figure 13:
    To establish a bonding surface to the zirconia and enhance the material’s color gradient, a layer of IPS Zirliner was applied. This color gradient allowed the use of very thin layers of enamel ceramic, yet it achieved nice, esthetic results in a restoration that was much stronger than it would be with the thicker layering ceramic usually associated with zirconia-based restorations.

  • Figure 14:
    All functional surfaces were left without layering to maximize strength and durability. The facial aspects of the canines were layered with .3mm of IPS e.max Ceram.

  • Figure 15:
    The IPS e.max restorations were pressed and stained on stumpf dies to match the color of the Zenostar restorations. For the canines to be restored with Zenostar, it was necessary for the dark die color to closely match the preparation color. The new, more translucent zirconia materials do allow some effects from underlying color, so it was critical to evaluate this in the laboratory.

  • Figure 16:
    Facial incisal cutback for layering was completed on teeth #7 through #10, after which enamel layering with IPS e.max Ceram was performed on the anterior restorations. The posterior restorations were left monolithic lithium disilicate for maximum durability.

  • Figure 17:
    A correction firing was performed to optimize shape and form.

  • Figure 18:
    The exposed zirconia surfaces were not glazed, but rather diamond polished to create a surface that would be kinder to opposing natural dentition. Studies indicate that highly polished zirconia wears opposing enamel less than enamel against enamel and that glazed zirconia wears more. Unpolished, rough zirconia wears most of all.* It’s important to note that zirconia restorations must be repolished if any adjustment occurs chairside.
    *Luangruangrong P, Cook NB, Sabrah AH, Hara AT, Bottino MC. Influence of Full-Contour Zirconia Surface Roughness on Wear of Glass-Ceramics. J Prosthodont. 2013 Jul 22. [Epub ahead of print].
    Kim MJ, Oh SH, Kim JH, Ju SW, Seo DG, Jun SH, Ahn JS, Ryu JJ. Wear evaluation of the human enamel opposing different Y-TZP dental ceramics and other porcelains. J Dent. 2012 Nov;40(11):979-88. Epub 2012 Aug 11.

  • Figure 19:
    The restorations demonstrated continuity of color and form between the IPS e.max pressed restorations and the Zenostar zirconia canines.

  • Figure 20:
    Micro-layering of the facial incisal aspect can produce nice, soft incisal effects while maintaining the strength of the 400MPa pressed material on the lingual incisal edge.

  • Figure 21:
    When verified on the model prior to delivery, the combination of restorations demonstrated esthetic harmony.