The lack of vertical bone in the posterior maxilla frequently precludes proper implant placement in this region. Increasing the absolute vertical bone height can be achieved by internal augmentation of the maxillary sinus floor . Sinus floor elevation was first described by B oyne & J ames . The space created between the maxillary alveolar process, the elevated Schneiderian membrane, and the rotated lateral sinus wall is filled with graft material.

A variety of grafting materials for sinus augmentation have been reported in the literature, but the most frequently used material that has shown the most predictable results is autologous bone material . Autogenous bone graft can be harvested from the iliac crest, tibia, calvarium, mandibular symphysis region, mandibular angle or maxillary tuberosity, and it is considered the gold standard as a graft material in sinus grafting procedures .

As an autogenous bone graft, the mandibular symphysis has been used for sinus augmentation, reconstruction of the orbital floor, as an interpositional graft in the treatment of nonunion or malunion of maxillary and mandibular fractures, in conjunction with Le Fort I maxillary advancement, in the reconstruction of alveolar clefts, and most popularly, in the reconstruction of alveolar defects and ridge augmentation . Compared with other intraoral sites, the symphyseal region can provide higher quantities of bone . The volume of bone available at the donor site can play an important role in achieving adequate grafting and good results.

The procedures for measuring the volume of the maxillary sinus and symphysis bone graft have changed with advances in medical techniques, such as water displacement , cadaveric skull measurements , plain radiograph, computed tomography (CT) , and magnetic resonance imaging. For a precise estimation of the volume change, three-dimensional (3D) CT has recently become a highly used technique .

The objective of this study was to evaluate the maximum amount of harvestable bone graft in the mandibular symphysis and the augmentation volume needed for different sinus lift levels (from 10 to 18 mm), in addition to calculating which sinus lift level can be acquired using the individual’s symphysis bone graft volume with 3D CT and software.

Material and methods

Data from 15 head and neck CT scans acquired from 15 adult patients (10 males, five females) taken for various reasons was used in this study. Patients who had maxillary sinus or mandibular symphysis pathology that could prevent size and volume calculations were excluded from the study. CT was performed with a 16-detector-row CT scanner (Aquillon; Toshiba Medical Systems, Tokyo, Japan) during one breath hold (16–24 s). Scans were obtained with 16 × 0.5-mm collimation, 0.5-mm slice thickness, 120 kV and 300 (mAs). The CT data, in DICOM format, was import into Mimics software from Materialize (Leuven, Belgium). In order to reconstruct 3D images based on Hounsfield units (HU), the appropriate voxels were grouped accordingly. To this end, a mask was created containing voxels with the predefined Hounsfield units. Since the authors were interested in constructing the mandible and maxillary sinus, two masks were created with segmentation and region growing, and a 3D model of the mandible and right maxillary sinus were constructed. The maxillary sinus masks ranged from −485 to −1024 HU. The mandible was defined through the masks with an HU value between 226 and 3071. After maxillary sinus mask construction, the coronal slice in which the bottom level of the sinus was shown was determined. All sinus lift levels from 10 to 18 mm were measured on this coronal slice ( Fig. 1 ). 3D models of sinus lift were obtained for each level and the volume of these models was calculated using Mimics software ( Fig. 2 ). These measurements and calculations were made for all patients. Symphyseal bone graft boundaries were determined on the mandibular mask, from 5 mm below the lower incisal teeth root apex, 5 mm anterior to the position of the mental foramen, and cephalad to the inferior border of the mandible on the axial and sagittal CT slices ( Fig. 3 ). The cortical bone and cancellous bone were identified based on the HU on the mask, and the lingual cortex was removed from the mask. A 3D image of the symphyseal corticocancellous bone graft was constructed and combined with the 3D mandibular image ( Fig. 4 ). The volume was measured on the 3D symphyseal bone graft using Mimics software.

CT slices show sinus lift augmentation levels 12, 15 and 18 mm, respectively.

3D images of sinus augmented for 12, 15 and 18 mm levels, respectively.

Symphyseal bone graft boundaries on the axial and sagittal CT slices.

A 3D image of the symphyseal corticocancellous bone graft and mandible.