Although osteoma does not cause pain, it can cause symptomatic changes in occlusion and mouth opening. Osteomas of the mandible, especially in the condylar region, can provoke limited mouth opening, malocclusion accompanied by mandibular midline deviation, and facial asymmetry [1,2]. Surgical removal of osteoma is not always mandatory, but the scope and extent of surgery may be determined depending on the patient’s pertinent symptoms and signs. Large osteomas of the condyle region are uncommon. Although osteomas exhibit painless slow growth, they can cause functional or aesthetic problems due to downward displacement of the affected side of the mandible. Surgical intervention may be preferred in such cases to restore occlusal function and facial symmetry. However, surgical intervention must be accompanied by immediate joint rehabilitation. Temporomandibular joint (TMJ) replacement with an alloplastic prosthesis can yield satisfactory results for those with relevant aesthetic and functional symptoms [3]. Temporomandibular joint replacement with computer-assisted surgical simulation (CASS) and computer-aided design/computer-aided manufacturing (CAD/CAM) technology is an accurate and effective treatment strategy [4]. Appropriate surgical plans can be accurately transferred to the operation room through pre-fabricated surgical guides.

A 52-year-old female was referred to the Department of Oral and Maxillofacial Surgery at Seoul National University Dental Hospital for a radiographically observed mass of the left TMJ. The patient’s chief complaints were aggravation of facial asymmetry with previous discomfort in the left TMJ. The patient reported that her lower dental midline used to match the upper midline but had noticed that the lower midline had shifted over the years. Upon clinical examination, facial asymmetry due to a rightward mandibular midline shift was noted. Anterior edge-bite and 3 mm lower midline deviation to the right side were noted. Premature contact of right molars and less occlusal contact of left molars was also observed. The patient exhibited a mouth opening of 34 mm without pain. Cone-beam computed tomography (CBCT) for three-dimensional (3D) facial revealed an irregular radiopaque bony mass at the left TMJ, encasing the condyle head. Mass was centered at the posterior root of the zygomatic arch, with mediolateral and anteroposterior expansion to partially include the squamous part of the temporal bone. The size of the lesion was approximately 26.30 mm×28.95 mm×12.25 mm. Erosive and sclerotic changes in the left condyle head were observed as well (Fig. 1). Based on the above subjective and objective evidence, it could be deduced that tumorous expansion had caused a downward and anterior displacement of the left condyle process. Jaw rotation to the right side provoked advancement of the lower anterior teeth, leading to anterior edge bite and premature contact of the right molars.

Figure 1. Preoperative: Clinical photo (A, B) shows lower midline deviation of 3 mm to right side. (C) Axial view of cone-beam computed tomography (CBCT) for three-dimensional (3D) facial shows expansion of tumor encasing left condyle head. (D) Lateral view of CBCT for 3D facial shows mediolateral and anteroposterior expansion of the tumor. Postoperative: Clinical photo (E, F) at 2-year follow-up shows stable occlusal harmony without compromise of aesthetics. (G) Coronal view of CBCT for 3D facial shows osteotomized condyle and resected tumor. (H) Lateral view of CBCT for 3D facial shows total joint replacement with alloplastic prosthesis and Biomet fossa. We received the patient’s consent form about publishing all photographic materials.

Simple grinding of the lesion without reconstruction was not recommended for this patient because massive removal would result in a vertical reduction of the left side, causing yet another occlusal disharmony with possible mandible shifts to the left side. Therefore, considering long-term surgical and occlusal stability, customized total joint replacement (TJR) of the left mandible was planned for the patient. Preoperative 3D facial CBCT DICOM file was used for Virtual surgical planning (VSP) with FACEGIDE^® system (Megagen implant, Daegu, Korea). VSP and CASS were utilized to design the most appropriate condyle part. Exact positions of CAD/CAM-printed customized condyle and Biomet fossa (Biomet Microfixation Inc., Jacksonville, FL, USA) were pre-determined with CASS. Then, surgical guides were designed and printed with CAD/CAM technology to transfer the surgical plan accurately. The occlusal wafer was fabricated to restore a normal occlusal relationship (Fig. 2). Pre-auricular and submandibular incision was made on the left side to expose the lateral surface of the mandible ramus, condyle head, and the zygomatic arch. The temporomandibular lesion was removed with low-speed burs and piezoelectric devices. Surgical guides were applied for osteotomy of the left condylar neck and confirmation of prosthesis and screw positions (Fig. 3). Histopathological examination of the specimen sent during surgery confirmed osteoma. The patient recovered uneventfully. A postoperative CT scan confirmed stable results. Clinically, the patient showed improvements in facial symmetry and stable occlusal harmony. The patient exhibited temporary symptoms of frey syndrome. At a 2-year follow-up, the patient still showed morphological and occlusal stability (Fig. 1). No complications or recurrence of the lesion were observed.

Figure 2. Virtual surgical planning of (A) condyle prosthesis design and size, location of Biomet fossa, and screw hole positions, and (B) surgical guide designs for osteotomy of left condyle and joint replacement.

Figure 3. Intraoperative clinical photos of (A) Biomet fossa fixation through pre-auricular incision and, (B) customized condyle prosthesis fixation through submandibular incision.

Because of their sessile nature, osteomas remain undetected unless relevant symptoms occur [5]. Pertaining to the mandible, osteomas may be detected during radiographic and clinical examination of chief complaints such as mouth opening limitation or associated facial asymmetry. Surgical intervention may be preferred when function and aesthetics are compromised. Following complete resection of osteoma, periodic follow-ups with radiographic exams are recommended for possible recurrence [6]. In the surgical treatment of condylar osteoma, condyle resection may be inevitable. However, simple resection cannot maintain normal occlusal relationship and masticatory function; rehabilitation of TMJ is mandatory. Immediate one-stage TJR with condyle prosthesis followed by resection of the lesion should be considered for the stability of function and aesthetics [7]. Prosthetic replacement of TMJ is a permanent and irreversible procedure. Therefore, each patient must be meticulously evaluated before moving on to the surgery.

There are two options when considering alloplastic total TMJ reconstruction: custom and stock prosthesis. First is individually custom-made TMJ prosthesis such as TMJ Concepts (Ventura, CA, USA). Completely individualized condyle and fossa components are designed and used. Anatomical abnormalities and aesthetic variations can be reflected in the design of the prosthesis. The individualized design of alloplastic condyle is biomechanically and functionally outstanding [8]. However, there are real limitations in that this system is not imported into the Republic of Korea. Therefore, this custom prosthesis was not an option for our patient. The second TMJ reconstruction option is stock prosthesis such as Biomet/Lorenz Microfixation TMJ replacement system (Biomet Microfixation Inc.). Mandibular and fossa components are available in several sizes, and the surgeon may select the appropriate size for a patient. Although the stock system is cost-effective and more flexible, stock prostheses may not always suit some patients. Because stock prosthesis does not consider anatomical variations of individual patients, the stock system may not be the best option for patients with distorted anatomy in the TMJ area [9]. In addition, a stock system may not be the most appropriate option for the restoration of the symmetry of the mandible. In our case, aesthetic reconstruction and restoration of the symmetry of the mandible were fundamental. Therefore, reconstruction with stock condyle was inappropriate.

For our patient, a combination of stock fossa part and custom-made condyle prosthesis was used in order to overcome the disadvantages of stock condyle prosthesis. As in our case, individualized design and precise transfer of surgical plan can yield optimal results of TJR. CAD/CAM-assisted TJR using VSP with CASS is a helpful tool in multidimensionally designing a patient-specific condyle prosthesis and planning individualized surgery [4]. However, because the fossa part is not customized, it may not always perfectly fit according to an individual’s anatomy. In such cases, we considered two options: 1) insertion of an implant at the gap between the patient’s bone and the fossa part, or 2) minor grinding of the patient’s bone to better fit the fossa part. In cases where the gap was small, minor grinding, according to computer simulation, was performed before placement of the fossa part; when the gap was large, insertion of CAD/CAM-assisted customized implant was performed for a more stable fit of the fossa part.

CASS allows preoperative evaluation of the lateral surface of the ramus that may require smoothening for an ideal fit of condyle prosthesis. Bulged lesions that require removal can also be calculated three-dimensionally, and osteotomy lines can be pre-determined and reflected on CAD/CAM-printed surgical guides. Screw positions can also be designed to help avoid nerve injury [10]. Our case of large condylar osteoma shows TJR with individualized condyle prosthesis with reliable results. Although long-term follow-up was missing, facial asymmetry and occlusal harmony, which were the patient’s original chief complaints, were resolved and remained stable after two years. In addition, radiographic images also confirmed stable joint prostheses. In conclusion, CAD/CAM-assisted TJR with customized condyle prosthesis can be an effective and predictable treatment option for large condylar osteomas.

The authors have nothing to disclose.