OBJECTIVETo evaluate the difference of mesiodistal root angulation between panoramic radiograph and panoramic images reconstructed from cone beam computed tomography (CBCT) by different methods.

METHODSCBCT and panoramic radiograph of twenty patients were collected. The InvivoDental 5.0 was separately applied for maxillary or mandibular panoramic image reconstruction. The reconstruction method was combined by two head positions, the Frankfort plane horizontal position (P1) and the occlusal plane horizontal position (P2), and three central planes of focal trough (root apical plane, tooth center plane and crown marginal plane referring to the central incisor). Variation of tooth morphology in reconstructed panoramic images and panoramic radiograph was firstly observed. And then measurement for maxillary or mandibular anterior tooth intersection angle (contiguous angles among 321 123 were named as UA1-UA5; and those among 321 123 were named as LA1-LA5 ) was taken. The difference of intersection angles between reconstructed panoramic images and panoramic radiograph (ΔUA and ΔLA) were calculated. Wilcoxon Rank Sum Test was finally applied to compare the intersection angles' differences between P1 and P2 with the same central plane of focal trough.

RESULTSPanoramic images reconstructed from CBCT by tooth center plane with P1 for maxilla and P2 for mandible appeared to fulfill the clinically diagnostic demand through the observation. Among the 15 couples of comparison of intersection angles' differences between P1 and P2 by choosing the same central plane of focal trough for maxilla, 7 couples of ΔUA revealed a statistically smaller value in P1 while 1 couple of ΔUA showed an adverse result.In mandible with the same comparison method, 10 couples of comparison did not show statistical difference between P1 and P2, while 4 couples of ΔLA revealed a statistically smaller value in P2 and 1 couple ΔLA showed an opposite result.

CONCLUSIONSBy choosing the tooth center plane, the panoramic images reconstructed from CBCT with the Frankfort plane horizontal position in maxilla and the occlusal plane horizontal position in mandible were equally effective. The reconstructed panoramic images can be used as the panoramic radiograph in the assessment of the mesiodistal root angulation.