The aim of the present study was to investigate the relationship between developmental changes in sagittal occlusion and the presence of caries on the occlusal surface of the lower first permanent molars. Dental casts were taken from 60 children at 2-monthly dental examinations after the emergence of the lower first molars through to when they reached 22 years of age. Data on the state of the occlusal surfaces of 120 lower first permanent molars were collected from these examinations and each occlusal surface classified into one of the following two categories: (1) sound, or (2) caries (filled). Sagittal occlusion of the first permanent molars was classified as Angle Class I, II, or III at each developmental stage. The data were analyzed to assess the relationship between changes in the occlusal characteristics and the presence of caries (fillings) in the lower first permanent molars. Of a total of 120 lower first permanent molars, 36 (30.0%) were filled by the end of the study period. Occlusal caries attacks occurred most commonly between 24 and 72 months after emergence of first permanent molars. New occlusal caries continued to occur thereafter, however, even though the teeth had already erupted for as long as 14 and 16 years. A Class II occlusal relationships in the lower permanent molars throughout the study period showed a significantly stronger correlation with caries than when it changed from Class II to Class I. With a Class II occlusal relationship, the percentage of teeth with fillings showed a continual increase, even though those teeth had already been erupted for between 10 and 16 years by the end of the study. These results suggest that occlusal sealing is still indicated for 3 or more years after eruption when the lower first permanent molars occlude in a Class II relationship as their risk for caries remains relatively high.