The construction of dental condition models is one of the useful methods for analysis of epidemiological surveys. The purpose of this investigation was to make a simple model with clear turning points for the longitudinal tooth-loss patterns of Japanese adults by means of multi-plane regression analysis. Since 1957, the Japanese Ministry of Health and Welfare has carried out national surveys of dental conditions every six years. The data of present tooth numbers by age (24-79 years) and sex from these surveys were used for this study. When there are turning points between two variables, intersecting straight lines regression is a valid means. However, a new method was developed so that the data of this study had three variables. The new three-dimensional model by multi-plane regression analysis seemed to fit tooth-loss patterns of Japanese adults within three phases. Younger subjects are represented in the first phase followed by the third phase of elders, where tooth loss was rather slow. However, in the second phase, middle-aged subjects, people lost their teeth rapidly. Thus, prolongation of the first phase could be an important factor to improve overall dental health. Copyright (C) 2002 John Wiley Sons, Ltd.