Abstract
This study was to investgate the intial stage and the progress of carious invasion of the upper and lower primary molars. The materials were 341 primary teeth in total 98 upper first molars,103 upper second molars,63 lower first molars,73 lower second molars which had been extracted from children between the age of 6 to 14. The occlusal surfaces of each tooth were devided into 405 parts to observe the carious invas ion in each pit and fissure. The initial stage of the caries which was found to be a white spot or a colored spot.
The results w e r e as followes; 1) The initial stages of the caries on the occlusal surface were found on the distal pit of the upper primary molars and the lower first primary molars, and on the mes ial pit and the pit of the lingual groove of the lower second primary molars.2) There was a tendency for caries to spread faster on the bucco-lingual groove than on the mesiodistal groove.3) The direction of the carious progress was as follows.
