Dental Tribune Indian Edition

19Dental Tribune Indian Edition - July 2013 Cosmetic Figure 15: Pre-op image of old PFM. The patient was unhappy with the opacity and metal display at margin. Category 3 or 4 material is required for this case. Figure 16: Post-op image of a LAVA co- ping with the new LAVA Digital Veneering System (3M ESPE). Figure 17: Post-op image of teeth 18 and 20 in a case with subgingival margins and poor bonding. Metal ceramics with a co- ping (CAPTEK). bution is present, and it is impossible to obtain and maintain bond and seal (e.g., most posterior full-crown situa- tions with subgingival margins; Figs. 15 & 16). Category 4: Metal ceramics Guidelines For almost half a century, metal ce- ramics have been the standard for aesthetic full-crown restorations. Generally, they have the same indi- cations as Category 3 zirconia-based restorations. With metal ceramics, manufacturers have eliminated the complications throughout the years; these materials do not have the same thermal firing sensitivity as zirconia does. However, anterior teeth metal ceramics need to be approximately 0.3 mm thicker to have the same aes- thetics as properly designed zirconia/ porcelain crowns. When porcelain- fused to metal restorations are indi- cated, the CAPTEK (Precious Che- micals USA) system has been the material of choice at the UCLA Cen- ter for Esthe tic Dentistry owing to its superior aesthetic properties. Aesthetic factors 1. Space requirements for workabili- ty: 1.5–1.7 mm is required for ma- ximum aesthetics. 2. Substrate condition: The substrate is not as critical, since the metal core supports the veneering material. 3. Flexure risk assessment: The risk is high or below. For high-risk si- tuations, core design and structural support for porcelain become more critical. 4. Tensile and shear stress risk asses- sment: The risk is high or below. For high-risk situations, core de- sign and structural support for por- celain become more critical. 5. Bond/seal maintenance risk asses- sment: If the risk of obtaining or losing the bond or seal is high, then metal ceramics are an ideal choice for a full-crown restoration. Summary Metal ceramics are indicated in all full-crown situations, esp. when all risk factors are high (Fig. 17). Conclusion This article has presented a syste- matic process of clinical evaluation and rationale for material selection. The most important point is that the most-conservative restoration should be done if the clinical criteria are met; for example, a full-coverage crown or deep-cut glass-ceramic restoration should not be performed when a more conservative porcelain restoration is indicated. Editorial note: A complete list of references is available from the publisher.DT Prof. Edward A. McLaren, DDS, MDC, is the founder and director of UCLA postgraduate aesthetics, and Director of the UCLA Center for Es- thetic Dentistry in Los Angeles, Cali- fornia. Yair Y. Whiteman, DMD, is a full- time faculty member at the UCLA Center for Esthetic Dentistry. Contact Info PHILADELPHIA, Pa., USA: New research from the U.S. has sugge- sted that two proteins involved in taste detection play a crucial role in sperm development too. The scientists found that blocking the proteins led to malformed and fewer sperm in mice. They be- lieve that the findings may hold important implications for infertile men. The researchers found a connection between the taste system and male reproduction while breeding mice for another taste-related study. They re- cognized that mice missing TAS1R3, a component of the sweet and umami taste receptor, and GNAT3, a protein needed to convert the taste receptor signal into a nerve cell response, were unable to produce offspring. In addition, their experiments esta- blished that adding clofibrate, a drug prescribed for treating lipid disorders, such as high blood cholesterol and triglycerides, led to a blockage of the TAS1R3 receptor, leaving the mice without any functional TAS1R3 and GNAT3 protein. The mice then be- came sterile owing to malformed and fewer sperm. However, the condition could be reversed by removing clofi- brate from the mice’s diet. The researchers hypothesized that even low levels of the drug can lower sperm count and negatively affect male fertility, an increasing problem worldwide. They suggested that a bet- ter understanding of the mechanism of these extraoral proteins could help infertile men or aid the development of a nonhormonal contraceptive for men. The study, titled “Genetic Loss or Pharmacological Blockade of Testes- Expressed Taste Genes Cause Male Sterility,” was published online on July 1 in the Proceedings of the Na- tional Academy of Sciences of the United States of America. It was con- ducted at the Monell Chemical Senses Centre. DT Blocked taste genes may cause male sterility Some taste receptors have been found in testes and sperm as well. However, their function was unknown. Now, researchers have sugge- sted that they affect sperm development and maturation. (Photo: FCG/Shutterstock) Laser microscopy considered useful in detecting allergies to dental metals KYOTO & TOKYO, Japan: Despi- te the increasing use of non-metal materials in dental treatment, con- tact allergies to different metals remain a problem for almost one in five dental patients worldwide, according to the latest figures from health organisations. Clinicians from universities in Tokyo and Kyo- to in Japan have recommended re- flectance confocal laser microscopy (RCLM) for evaluating allergic contact dermatitis owing to dental materials such as alloys. The imaging method has already been used in dermatology since the 1980s for detecting early signs of dif- ferent kinds of cancers, among other skin conditions. Instead of capturing a full image, RCLM illuminates only small points of the area under obser- vation, which is scanned using a laser beam and reconstructed on a compu- ter, providing the opportunity to cap- ture images at selected depths of an object, such as human skin. Owing to this ability to determine and analyse different levels in the skin minimally invasively up to a depth of 300 μm in vivo, the method can help to detect changes in the skin faster and more accurately than commonly used methods such as biopsy, the clinicians reported in a guest article in a book recently published by open-access publisher InTech. These include patch testing, which has to be conducted over several days and is considered inaccurate because it is subject to the experience and knowledge of the exa- mining person. In a comparison test conducted by several members of the research team in 2010, RCLM demonstrated advantages over patch testing for vi- sualising features of allergic contact dermatitis due to nickel and cobalt, two substances that have been found to cause the highest incidence of al- lergies in dental patients in addition to chrome, palladium, gold, and silver. “While it might become a real-time diagnostic or adjunctive tool to iden- tify a suspicious lesion or to delinea- te tumour margins”, RCLM still has limitations, such as the inability to detect deep objects in the dermis of normal skin, the researchers stated in the report. In addition, a thick stratum corneum and vesicle formation can restrict visualisation. In order to di- stinguish between different cells and determine pathological characteri- stics better, higher and better contrast is needed for these devices, they re- commended. DT (DTI/Photo Dragon Images/Shutterstock)