GAP Australasian-Dentist-Mar Apr 2019

Category 64 AustrAlAsiAn Dentist sectional Matrix system) at rhondium that addresses all the problems associated with large direct restorations and takes no longer to place, while removing all of the direct restoration problems associated with contact points and occlusal anatomy. When deciding on how to treat a badly damaged tooth, the dentist is often faced with the conundrum of what to do with a single remaining cusp, which may or may not be weakened, and struggle with the decision to overlay a cusp or not. if a crown had already been suggested, then all the cusps were going to be reduced anyway, so continuing to an onlay design instead is not problematic from this perspective. there is a simple guide as towhether a cusp should be overlaid or not. Ask the patient to chew on a piece of bite paper, to generate all the functional contacts on the tooth. if there are strong contacts on the occlusal planes of the cusp, the underlying dentin will be placed in tension, something that causes cracks to establish and propagate. looking to potential future failures, these cusps generally need protecting. if the occlusal load is on the buccal or palatal side of the cusps, the underlying dentin is in compression and these cusps tend to be functionally stable. if there is a cusp that should not be removed, and a custom adhesive CAD/ CAM or lab generated is not an option for the patient, then the remaining option is a conventional direct composite. However, there are a significant number of teeth that truly benefit from the placement of an OVC 3 , helping maintain the biomechanical integrity of the tooth by minimizing the reduction of the cervical half of the tooth. Minimally invasive philosophies and techniques have to balance the desire to retain as much tooth structure as possible, with the need to design a restoration that has the best chance of longer-term success. the OVC 3 helps address the challenges of large direct restorations, while maintaining simplicity and predictability. Failures in large direct restorations can be immediate. Open contacts, poor occlusal contour and anatomy, debonding induced post insertion sensitivity being the primary issues. Once a fully bonded onlay solution is placed, be it lithium disilicate, zirconia or hybrid restorations, all function very effectively at the clinical level. Once bonded, the hybrid composite OVC 3 performs at the same level as all the onlay techniques, with the huge advantage of being able to be placed in a single visit, no lab fees and no problems with temporization. A Brief Summary of OVC 3 the technical simplicity of placing the OVC 3 has beenmadepossibledue to several technical and material developments. essentially, it is a strong, preformed, lab generated, heat-cured, highly processed zirconia hybrid composite occlusal onlay, with a layer of the same uncured hybrid composite on the intaglio surface. the onlays come in five sizes per tooth, with a simple measuring gauge to choose the correct size. A plastic onlay replica helps guide the occlusal reduction required. Advanced wedging and separator systems combine with a revolutionary custom matrix system, that matches the onlay shapes, simplifying the placement and establishment of correct contacts and contours. the system is very flexible, allowing for deep margin elevation techniques and if aesthetic demands are high, light-cured resin fissure staining can be placed. Basic OVC 3 Technique (Direct) Once the mesio-distal size has been determined, the tooth is prepared, and the occlusal reduction is guided by the plastic replica. if needed, any bio-base build-up or deep margin elevation can be performed at this stage and the prep remodified to ensure correct occlusal clearance. A contoured wedge system has been developed that assists in areas with deep interproximal margins. the McDonald Matrix Band is placed and wedged with either wooden wedges or stretch-Wedges that have a separation force that exceeds that of the Vring system. Following bonding of the tooth, the OVC 3 is placed, aligning the marginal ridges with the adjacent teeth. excess unset composite is then removed and the restoration light cured. Following removal of the matrix band, any excess composite on the buccal and lingual is contoured and polished. the time taken ranges from ½ to 1 hour, depending on the complexity or need for any bio-base build- up or core fibre reinforcing that may be indicated. Brief Case Study (courtesy Dr Venkat Canakapalli) A patient presented with acute pulpitis associated with a deep distal cavity and undermined cusps with developing fractures. Following endo, a fibre reinforced core was placed and a biobase built up to replace the lost dentin volume. the goal with a biobase is to reduce the potential space between the OVC 3 onlay to about 1mm. this reduces the risk of composite shrinkage leading to a dentin debond. the matrix placement is aided by the use of the stretch Wedges, which also proved a separation force double that of the Vring system. the matrix is thin, allowing it to be burnished out, combining with the strong separation of the stretch Wedges (or wooden wedges) to create predictable contacts. Fig 2. The left cusp is in compression, the underlying dentin is in compression and unlikely to develop a crack at the base. The load on the right cusp is placing the underlying dentin into tension and increases the probability of a crack developing over time Fig 3 Fig 5 Fig 4: the OVC 3 is then placed, excess material removed, cured, then final contouring and polishing. u References available – email: gapmagazines@optusnet.com.au lInICal