Volumetric analysis of chin and mandibular retromolar region as donor sites for cortico-cancellous bone blocks

AimTo test whether the mandibular retromolar region renders different results from the chin region with respect to the amount of bone available for the harvesting of block grafts. Material and methodsSixty cone beam computed tomography (CBCT) scans of mandibles of adult patients without pathologic findings in the chin and retromolar region were included. According to the number of mandibular teeth, 20 CBCT data sets were allocated to each of the following groups: group M1: dentition 36-46; group M2: dentition 37-47; and group M3: dentition 38-48. For the potential donor sites in the chin and the retromolar regions, the volume (V-Chin, V-Retro), the length (L-Chin, L-Retro), the height (H-Chin, H-Retro) and the width (H-Chin, H-Retro) were assessed using a computer software. Moreover, the chin was examined for the presence and the localization of the mandibular incisive canal. To compare the donor sites in the chin and in the retromolar regions, the quotients V-Retro/V-Chin, L-Retro/L-Chin, H-Retro/H-Chin and W-Retro/W-Chin were calculated and tested using the Wilcoxon signed-rank test or the sign test. ResultsThe mean bone volume V-Chin measured 3.51.3cm(3) (SD), whereas the overall V-Retro amounted to 1.8 +/- 1.1cm(3) (SD). V-Retro amounted to 2.6 +/- 1.4cm(3) (SD) in the group M1, 1.8 +/- 0.5cm(3) in the group M2 and 1.0 +/- 0.4cm(3) in the group M3. For the group M1, V-Retro/V-Chin measured 82 +/- 39% (P=0.036). V-Retro/V-Chin reached 57 +/- 20% in the group M2 and 32 +/- 12% in the group M3 (P<0.001). The mandibular incisive canal was detected in 97% of the CBCT scans. The distance between the mandibular incisive canal and the apices of the central incisors measured 10.5 +/- 3.5mm. ConclusionThe amount of bone available for the harvesting of cortico-cancellous blocks in the chin region was superior in comparison with the mandibular retromolar region. In the absence of the second and the third molars, the amount of bone harvestable in the retromolar region reached approximately 80% of the bone volume available in the chin region. In the majority of the cases, the mandibular incisive canal was detected within the donor site in the chin region.