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[Observation of bone morphology in furcation defects of mandibular molars using cone beam computed tomography].

OBJECTIVE
To observe mesial-distal bone morphology in classes II and III furcation involvements (FI) of mandibular molars using cone beam computed tomography (CBCT), to develop a classification system of mesial-distal bone morphology of furcation defects and to observe the intrabony defects on CBCT images.


METHODS
Based on the existing CBCT data, the mandibular molars with horizontal bone defects in furcation area were observed. One hundred and seventeen sites of 81 mandibular molars with class II or class III FIclassified on CBCT images were included. The classification system of mesial-distal bone morphology of furcation defects was developed. According to the location of the line drawn from mesial to distal alveolar bone crest (AC-line) of the tooth and bone level under furcation fornix, the bone morphology was classified into three types, including concave type, flat type and protruding type. The concave type was divided into two subtypes according to the location of AC-line and furcation fornix (Fx), which were subtype 1(AC-line coronal or equal to Fx)and subtype 2 (AC-line apical to Fx).The frequency of each type was calculated and analyzed. The intrabony defects was observed on sagittal CBCT images.


RESULTS
In the 117 sites with FI, the flat type appeared with the highest rate (64.10%) and the protruding type appeared with the lowest rate (6.84%). The rates of subtype 1 and subtype 2 of concave type were 13.68% and 15.38%, respectively. The rate of subtype1 which was supposed to be beneficial for bone regeneration was 8.96% in class II FI and 20.00% in class III FI. Thirtyone intrabony defects were found among the 117 FI, 29 of which appeared in proximal aspect of the tooth and the left 2 appeared in furcation area. The highest frequency of the intrabony defects was found in subtype 1 of concave type.


CONCLUSION
The classification of mesial-distal bone morphology on CBCT images may be helpful for clinicians to make accurate treatment plan before surgery and could be used in future studies to understand the influence of bone morphology on regenerative therapy for furcation defects.