Contribution of three-dimensional images in the planning of
Cementoblastomas represent less than 1% of all odontogenic tumors. More than 75% occur in the mandible, most often in the molar or premolar region. Cementoblastomas are most common in children and young adults, with 50% occurring before age 20 and 75% occurring before age 30. These tumors are usually associated with an erupted permanent tooth. On two-dimensional (2D) radiographs and CT images, they appear as periapical, sclerotic, sharply delineated lesions with a low-attenuation halo. A helpful feature in the differential diagnosis with other sclerotic lesions is that cementoblastomas fuse to the root of the adjacent tooth. Management of cementoblastomas typically involves complete removal of the tumor and the associated tooth to reduce the likelihood of recurrence.

A 19-year-old male presented with a swollen left mandible and a palpable mass at the level of element 37. He had mild pain for a few weeks. The symptoms had been attributed to a dental problem by a local dentist, and root canal treatment had been performed, without any effect on the pain or swelling. At the initial consultation, a mass was clearly palpable. A panoramic image showed a sclerotic, sharply delineated lesion with a low-attenuation halo, fused with the root of the adjacent molar. A panoramic radiograph obtained 3 years earlier, for post- orthodontic treatment evaluation, did not show any tumor sign. CBCT showed a heterogeneous mandibular mass associated with element 37 causing compression and inferio-lingual displacement of the inferior alveolar and mental nerve. The mandibular cortex was thinned at the vestibular side and absent at the lingual side. Despite the relatively rapid growth, the diagnosis of benign cementoblastoma was proposed based on the classic appearance as a periapical, sclerotic, sharply delineated lesion with a low-attenuation halo, directly fused to the root of the tooth. 3D renderings showing the affected anatomic area were obtained. Considering lesion size and location, a possible pathological fracture of the mandible pre or post-operatively was considered.

In order to prepare for such risks or complications, 3D planning and printing were made available. The virtual 3D planning was performed in PROPLAN software (Materialise, Leuven, Belgium). The pre-operative CT patient Digital Imaging and Communications in Medicine (DICOM) images were imported into the software where the threshold was applied to segment the mandible and the lesion. Both objects were further manually refined and 3D models were created. The inferior alveolar mandibular nerves were traced and 3D models were created. All 3D models were revised by the surgeon prior to export. These models have then been exported as Standard Template Library (STL) files for 3D printing. The STL files were imported into the software of the professional Objet Connex 350 printer (Stratasys, Eden Prairie, MN) which is a polyjet printer with a layer thickness of 30 µm. The mandible was printed in transparent hard material while the lesion and nerves were in hard white material. The 3D printed model allowed for possible fast and accurate (pre)bending of an osteosynthesis plate. Furthermore, considering the tumor size as well as the size of the expected post-surgical bone defect, the possibility of needing a bone graft was also taken into account.

A standard surgical approach was used. The tumor could be completely dissected, and the mental nerve could be separated from the tumor without injuring the nerve. Element 37 was removed. The cementoblastoma was split into pieces using a surgical drill, and the pieces were carefully removed, taking care to avoid mandibular fracture or nerve injury. The inferior alveolar nerve could be identified at the bottom of the resection cavity and appeared intact. The mandibular wisdom tooth was not removed in order to minimize the risk of pre-and postoperative fracture. While the mandibular cortex was deficient at the lingual side (as shown pre-operatively by the CBCT images and 3D model), the lower part of the mandibular bone could be kept intact during the procedure and fracture did not occur. The resection cavity was filled with 8 L-PRF membranes. Tight intermaxillary fixation was applied for 6 weeks. No bone grafts were placed in order to facilitate interpretation of the post-operative evolution, taking into account the possibility of tumor recurrence. The postoperative course was uneventful. Follow-up imaging obtained 4 years and 6 months after surgery showed normal healing with progressive new bone formation and closure of the bone defect.