In the epidemiological studies of this thesis, the aims were to elucidate the prevalence of incisal and occlusal wear in a normal Swedish population, and to present factors related to incisal and occlusal wear in that population. In the clinical studies, the aims were to develop methods for and to perform in vivo studies of wear of prosthodontic materials and to present quantitative and qualitative data of occlusal contact wear in these materials. The epidemiological part of this study consisted of 585 randomly selected dentate individuals from the Community of Jönköping, Sweden, who in 1983 reached the age of 20, 30, 40, 50, 60, 70 or 80 years. The results showed that the severity and prevalence of incisal and occlusal wear increased with age. Men presented more teeth with occlusal wear than women. An individual tooth wear index (IA), with the potential to rank individuals with respect to incisal and occlusal wear, has also been introduced. Factors which were found to correlate significantly to increased incisal and occlusal wear were: number of teeth, age, sex, occurrence of bruxism, use of snuff and the saliva buffer capacity. From the in vivo studies, data of occlusal contact wear of gold, porcelain and some resin based materials in four different persons, with earlier histories of occlusal wear of teeth and/or restorations, were presented. The in vivo models combined two methods: removable segments or double crowns, and a replica technique. The combination of a polyvinylsiloxane impression material (President) and an epoxy resin (Metapox) was chosen for the replica model technique. All materials tested showed increased wear rate when the opposing material was porcelain. Gold and porcelain showed equal wear resistance when opposing porcelain. The resin-based materials showed at least a three to four times higher wear rate. No difference in wear resistance could be observed between gold type III and type IV. Gold showed a combined abrasive and fatigue type of wear and porcelain mainly a fatigue type of wear. The resin-based materials showed a fatigue type of wear, sometimes in combination with a tribochemical reaction.