This study was carried out to clarify the morphology of the root canal orifices using 86 human mandibular primary molars from several Chinese children within an age range of 3-8 years. After a dental X-ray was taken, and following removal of the roof of pulp chamber and pulpectomy, a silicone impression of the pulp orifice was obtained directly from the primary molars. By this means, an epoxy-resin replica was made and sliced at two points: 0.5 and 1 mm from the pulpal floor, respectively. Several variables were considered for the morphometric study of the pulp orifice such as width (mesio-distal distance), length (bucco-lingual distance), area, frequency and size of the concavity at the selected levels. The distance between the pulpal floor and the furcation area (thickness of the floor of pulp chamber ) and the mesio-distal width of each orifice, were measured using the X-ray films. The samples were divided into three groups according to age in order to findout any influence according to age. T-test and analysis of variance (ANOVA) was used for data analysis whenever appropriate.
The following conclusions were obtained:
1. The width (mesio-distal distance) of the pulp orifices in first primary molars showed a greater value at the mesial root than at the distal root, while in the second molars it was just the opposite. The values obtained by measuring the X-ray films were slightly greater than those obtained from the resin models. The length (bucco-lingual distance) in the first primary molar showed a smaller value at the mesial root than at the distal root while in the second primary molar the two values were similar. The area in both first and second primary molars, was smaller at the mesial root than at the distal one. The orifice seemed to taper to the apex as observed when comparing the obtained values at 0.5and 1 mm. The concavity of the root canal did not appear on the outer surface of the mesial root canal of the first primary molars and was more evident on the inner surface of the orifices of the each root canal. The size of the concavity was bigger on the inner surface of the orifices except in the mesial root canal of the first primary molars. There was no-aging influences except at the area in the mesial root of the second primary molars.
2. With regard to the influence of age, the thickness of the floor of the pulp chamber increased in both first and second molars. The size of the root canal orifices did not however change significantly. This could be explained by the coronal shift of the pulp orifices due to dentinal apposition in conjunction with age.
3. The obtained data in this study are of great importance when selecting the size of the instrument during endodontic therapy specially while pulpotomy is undertaken.