Dental Asia November/December 2022

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USER REPORT All-ceramic restoration on discoloured teeth Dr Christopher Ho outlines strategies to overcome the challenges of restoring a severely discoloured tooth with high-aesthetic requirements. With the increasing use of all ceramic restorations, clinicians may encounter difficulty matching shades on discoloured teeth. This discolouration may be due to many factors, including metallic post and core, previous restoration, or other extrinsic or intrinsic factors. There is often a need to mask discolouration. However, allceramic restorations have inherent translucency within the material. It may be advantageous in most situations but may allow shine through of underlying dark stumps, negatively impacting the final shade match. Several strategies can be adopted to influence the final colour of the restoration including: • Choice of resin cement. Most dental companies manufacture shaded and opaque resin cement, which may assist in blocking discolouration. However, it should be noted that with the cement film thickness being 80-120 microns, it may not assist sufficiently in blocking the dark tooth. In my experience, it improves the situation by 10-15%. • Selecting an opaque ceramic material. The majority of materials for indirect restorations are available in different opacities and translucencies. Advising the ceramist that the tooth is dark and taking photographs of the stump shade may result in the selection of an opaquer ceramic material (e.g., Zirconia first generation materials, lithium disilicate – medium opacity ingot). The opaque ceramic will block the underlying dark tooth from showing through. • Thickness of material and preparation depth. All-ceramic restorations allow more conservative preparation, but with a dark tooth substrate, there may be the need to prepare deeper to allow greater material thickness which will be better at masking the dark tooth. Duraes et al. (2022) reported that the best thickness and opacity combination for masking discoloured dental substrates is to use 1.2mm thickness and LT (low translucency)/MO (medium opacity) lithium disilicate restorations. 38 DENTAL ASIA NOVEMBER / DECEMBER 2022
USER REPORT Fig. 1: Patient wants to replace the crown on tooth 11 due to poor marginal fit and discolouration of underlying stump Fig. 2: Removal of old crown reveals dark tooth substrate Fig. 3: Sub-opaquing the discoloured stump with opaque resin tints e.g., Kerr Kolor Plus A1 opaque, GC masking liner, Cosmedent Pink opaquer Fig. 4: Final all-ceramic crown • Porcelain fused to metal (PFM) crown. A conventional PFM restoration with a metallic coping is blocked out with an opaquer allowing the ceramist to start the layering on a white canvas. It should not be forgotten as a possible option. Clinicians, however, must remember that the depth of preparation would need to be at least 1.5mm with a shouldertype margin to achieve adequate thickness for the metal coping and the overlying feldspathic porcelain. • Sub-opaquing the stump. The final technique is to sub-opaque the stump with an opaque resin tint. Several manufacturers provide opaque resin tints that are thin and possess titanium dioxide, which effectively scatters light providing white opacity to block out discolouration. This opaquer is like a flowable resin applied by adhesive bonding and placed precisely with a thin layer that extends along the axial wall extending sub-gingivally when tissue biotype is thin (Figs. 1-4). Matching discoloured teeth is always a challenge; both the clinician and laboratory team need to work synergistically to achieve an ideal outcome. Communication is paramount to success with clinicians providing detailed instruction about the stump colour as well as allowing sufficient thickness and understanding the selection of materials to effectively block any dark stump colour. Possessing other strategies such as the sub-opaquing method may reduce the difficulty in the shade matching by having an idealcoloured substrate and should be part of your armamentarium in tackling these tough cases. DA ABOUT THE AUTHOR Dr Christopher Ho is a specialist prosthodontist who completed postgraduate studies in Masters of Clinical Dentistry in Prosthodontics from the University of London, and a Doctorate in Clinical Dentistry in Prosthodontics from the University of Sydney. He is a fellow of the Pierre Fauchard Academy, American College of Dentists, and a special field member of the Royal Australasian College of Dental Surgeons in Prosthodontics. He is the head of the School of Postgraduate Dentistry, Australasian College of Dental Practitioners, and a visiting lecturer for the postgraduate oral implant diploma and prosthodontic programmes at the University of Sydney, and Kings College London, UK. DENTAL ASIA NOVEMBER/ DECEMBER 2022 39
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Dental Asia November/December 2022

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