Abstract
In order to clarify the forms and conditions of the accessory canals on the pulpal chamber floor of human primary molars, serial sectional specimens of 76 human primary molars obtained from child skulls were examined histologically. Photographic images of the anatomical forms of the pulpal chamber floors were processed by computer to determine the size of the accessory canals. The travel patterns and forms of the accessory canals were analyzed three-dimensionally. Comparative studies between mature (root formed) and immature (root unformed) human primary molars were also carried out in order to understand the aged changes in the anatomical structure of the pulpal chamber floor and age related conditions of the accessory canals. The following results were obtained:
1. Dentin in the pulpal chamber floor of mature primary molars was found to be composed by two layers, but this two-layered structure was not found in immature primary molars. The thickness of the pulpal chamber floor was significantly greater in mature primary molars than in immature primary molars (p< 0.01).
2. Accessory canals were observed in all 76 primary molars (275 canals in total, with an average of 3.6 per tooth). There was, however, no significant difference in the number of occurrences of accessory canals between mature and immature primary molars.
3. The travel patterns of the accessory canals were classified into four different types. The number of accessory canals of the transporting type was significantly higher in immature primary molars than in mature primary molars (p< 0.01).
4. There were no significant differences in the lengths and inner diameters of the accessory canals between mature and immature primary molars. The lengths and inner diameters of the accessory canals of the transporting type were much larger than those of the non-transporting type. The wider accessory canals were generally found to run longer than the narrow ones.
5. Two different forms of accessory canals, tubular type and coral-shaped, were found. The number of tubular type accessory canals was significantly greater than the number of coral-shaped canals.
