Abstract
While the typical anatomical form for human maxillary first premolars shows two distinct roots (the buccal and the palatal) with a single canal in each root, there is a small percentage that have one broad root with two canals and a common foramen. Occasionally, three canals in maxillary premolars having two buccal roots and a single palatal root may occur. In this study, artificial maxillary first premolars with the presence of radiolucency related to bifurcated canals at mid-root level and a single apical foramen for pre-clinical endodontics were newly designed in cooperation with Nissin Co., Japan. The teeth were made from DGEBA (Diglycidyl ether of bisphenol A), a glass filler with presence of radiolucency and other materials. The purpose of the study was to investigate the anatomical morphology of the teeth and the root canals. An interstitial tubercle (marginal tubercle) was situated on the mesio-marginal ridge of the tooth crown. A mild bayonet, the so-called "S" shaped curve of the root, was seen at the buccal and lingual aspects of the teeth. The root form in the proximal aspects showed tapering at the root tips. The lengths of the pulp chambers were longer in these teeth. Roentogenograms in the mesiodistal direction revealed the following: 1. a large pulp chamber with broad buccolingual dimension 2. presence of two pulpal horns 3. a single root with two parallel bifurcated canals at mid-root level, and a single apical foramen 4. severe buccal curve of the lingual canal Cross sections at three levels of the root revealed in micro CT findings. Cervical level: the pulp chamber was very wide in the buccolingnal direction. Mid-root level: the canals were slightly ovoid. Apical third level: although the canals were long ovoid, the apical canal tended to continue. In measurements (in mm) of the teeth (average only), the length of teeth was 22.84mm, length of crown 9.42mm, length of root 13.42mm, mesio-distal diameter of crown 8.11mm, and bucco-lingual diameter of crown 10.06mm. The average reading was slightly longer than the average length reported by Fujita et al., but it was nearly the same as Japanese human teeth. In cross sections, the buccal and lingual canals in the mid-root third showed a wide oval shape with fin-like projections buccolingually. The buccal canal diameter was buccolingually 2.05>mesiodistally 0.95mm under the bifurcated area, 1.51>0.74mm at the apical third, and so 0.63>0.36mm at the apical single canal level. The lingual canal diameter was buccolingually 1.70>mesiodistally 0.97mm under the bifurcated area, and so 1.48>0.87mm at the apical third level. The canal walls tended to become thinner in width at the mesial areas with proximal grooves. The diameter ranged from 0.84 to 1.30mm. This tooth model produced the proper radiodensity similar to natural teeth. The results indicated the feasibility of the model as a teaching model for pre-clinical endodontic practice.
