Research On The Wear Effects Of Some Dental Meaterisls In Vitro

Wear is a common phenomenon in dentistry that occurs when two surfaces undergo slipping or sliding movements as a load is applied. Intra-oral wear of dental restoratives is highly complex due to the variable movement involved. It is not a single process, but the overall result of at least five underlying processes, which seldom act in isolation. These may include erosive, corrosive, abrasive, impact and other minor types of wear. As the teeth, together with any restorations, move in contact with one another wear is inevitable. Its progress will depend upon the structure of the surfaces, the contact stress, the activity of any lubricating layer, the temperature and duration of contact. Essential differences in the wear of prosthetic materials, and the hard tissue of teeth may result in the dysfunction of the stomatognathic system. In some patients wear may cause aesthetic functional or restorative problems. An important feature of materials used in the restoration of occlusal surfaces of fixed and removable partial dentures is resistance to wear and the lack of a negative influence on the opposite teeth.Ideally, an restoration should wear at approximately the same rate as the enamel it replaces(reported by Lambrechts 1986 to be 20-40 i?m per year). Therefore it can be seen that the tooth wear and restoration wear need to be studied in relation to one another. Research into the wear of dental materials has increased dramatically since the introduction of composite (Bowen 1963). By contrast, only limited research has been carried out on the effect materials may have on the wear of opposing dental enamel. Wear testing poses numerous problems. In vivo investigations are time-consuming, expensive and unfortunately inaccurate in many instances due to the number of variables involved.A delay between material development and final acceptance is also inevitable. In vitro experiments have attempted to overcome the problems by accelerating the wear rate in a simulated oral environment. Several indirect techniques have been investigated. The pin and plate method is essentially a two-body abrasion test that compares pairs of materials against one another. The pin is loaded against another material, which is usually a rotating disk, Wear assessment can then be made by measuring the weight loss of the specimen, the pin height, and the dimensions of the wear scar. Enamel abraders used in two-body wear tests suffer the disadvantage that standardization is difficultor impossible to obtain. To overcome the inconsistencies due to differences in morphology, composition, and microstructure, this study used a good enamel substitute--- the steatite abrader--- in a two-body wear test. The wear rates and coefficients of friction of the two abraders against various composites and an amalgam were well correlated although the wear rates were slightly higher with steatite. In addition, the substitute enamel abrader produce wear in a similar way to enamel. Manufacturers generally quote indentation hardness values when predicting the clinical wear potential of newly introduced dental materials. The first objective of this study was to determine whether in vitro two-body wear correlated well with hardness. Several typical dental materials were tested .the conclusion is that the correlation between these wear rates and the measured hardness values is poor. Wear appears to be more related to roughness and fracture resistance than strict hardness values. Dental por...