Abstract
The purpose of this study was to clarify the change, with age, of three dimensional morphology in the orifice portion of the root canal of maxillary deciduous second molars using Micro-CT. The materials were teeth extracted from twenty Indian child dry skulls which were classified into four groups based on tooth eruption, namely, the Deciduous Dentition Stage, The Early Mixed Dentition Stage 1, The Early Mixed Dentition Stage 2 and The Middle Mixed Dentition Stage, respectively. The status of teeth eruption of each stage was as follows. Deciduous Dentition stage: in the teeth from the deciduous central incisor to the second deciduous molar reached the occlusion line. Early Mixed Dentition Stage 1: in addition to the Deciduous Dentition Stage, the first molar reached the occlusion line. Early Mixed Dentition Stage 2: in addition to the Early Mixed Dentition Stage 1, the central incisor reached the occlusion line. Middle Mixed Dentition Stage: in addition to the Early Mixed Dentition Stage 2, the lateral incisor reached the occlusion line. The skulls were the collections of the Department of Anatomy, Tokyo Dental College.
Each tooth was examined by Micro-CT to obtain raw data of its internal structures. There dimensional computer image was reconstructed from the raw data. Using each reconstructed 3-D image, diameters of the root canal orifices and volume ratio of the pulp cavity in the region of interest were measured, in addition to optical observation of the morphology.
The results were as follows;
1) The mesiobuccal root canal was crushed mesiodistally with age. The structure'at the middle area in the buccolingual direction was specially prominent. After the Early Mixed Dentition Stage 1, complicated divergence of the root canal was observed. The structures of the distobuccal root canal and lingual root canal were remarkable at the diverging side of the distobuccal and lingual roots.
2) From the Deciduous Dentition Stage to the Early Mixed Dentition Stage 1, all of the orifices decreased remarkably in diameter (mesiobuccal orifice; from 1.42 mm to 0.95 mm, distobuccal orifice; from 1.25 mm to 0.88 mm, lingual orifice; 2.47 mm to 1.89 mm). Similar tendencies were them observed in the mesiobuccal orifice from the Early Mixed Dentition Stage 2 to the Middle Mixed Dentition Stage and in distobuccal and lingual root canals from the Early Mixed Dentition stage 1 to the Early Mixed Dentition stage 2.
3) The volume of the orifice portion of root canal decreased remarkably from the Deciduous Dentition Stage to the Early Mixed Dentition Stage 2 (from 15.94% to 8.96%). However, only a few changes were observed from the Early Mixed Dentition Stage 2 to the Middle Mixed Dentition Stage.
