Objectives: It is important to detect and treat the early periodontal destruction, however, the initial hight of the cementoenamel junction and alveolar bone in the conventional intraoral radiograph is not well studied.  The purpose of this study is to investigate the relationship between the anatomical and the radiographical location of cementoemnamel junction.  Methods: Four sets of upper/lower incisors, premolars, and molars were prepared. Radiograph was taken for each tooth by paralleling/bisection technique using imaging plate.   Additional radiographs were taken with small metal pieces placed on the mesial, distal, buccal and lower cementoenamel junctions as reference images.  Each image was entered into a personal computer as the 256 grayscale image.  Five examiners marked the cementoenamel junctions on the computer screen, and accuracy was monitored.  Results: Results indicated that paralleling technique marked more precise cementoenamel junctions than the bisection technique.  In the bisection technique, the buccal and lingual cementoenamel junctions were marked coronally and apically, respectively.

Vertical distance apical to the reference points in interproximal cementoenamel junctions was measured.

                                    Upper                                                Lower           (mm)

                      Incisors  Premolars  Molars               Incisors  Premolars  Molars 

Paralleling   -0.47±0.58  -0.65±0.84  0.05±0.42  -0.24±0.87  0.13±0.57  -0.06±0.68

Bisection      -0.39±0.79  -0.78±0.60  0.14±0.54  -0.33±0.92  0.37±0.68  0.01±0.76

Statistical analysis was performed among each upper/lower teeth group using ANOVA. Molars' interproximal cementoenamel junctions were marked more precisely than the incisors and premolars in both techniques(p<0.05).  This was considered as a result of the flat cementoenamel junction line in interproximal area of the molars. Conclusions: The relationship between the anatomical and the radiographical location of cementoemnamel junction was studied. Paralleling technique was proved to be more accurate than bisection technique, and molars' interproximal cementoenamel junction could be recognized easily because of the flat buccolingual cementoenamel junction line.