SMBC is rare, with reported incidence rates ranging from 0.1 to 0.48% in the literature [7, 8]. However, its consistent detection has been increased recently due to the increased utilization of dental services and the widespread use of panoramic radiography. In most SMBC cases, patients are asymptomatic, and the lesions are typically identified in panoramic radiographs by chance. In this study, lesions were discovered in panoramic radiographs taken for other reasons in all cases except for one instance where surgery was performed. Notably, all patients in the study had any discomfort or symptoms. Previous literature indicates that the incidence rate of SMBC is reported to be 4.0 to 5.0 times higher in males compared to females, based on gender differences [1, 9, 10]. In the study conducted by Philipson et al. [11], SMBC was found to have a higher incidence in males at a ratio of 6:1, while Morita et al. [12] reported that SMBC predominantly occurs in males at a ratio of 7:3. This gender difference corresponds to the results of our study, demonstrating a male predominance with a prevalence of 81.25%, compared to 18.75% in females, in line with a higher incidence of SMBC in males. SMBC is rarely observed in individuals between the ages of 10 s and 30 s, and it is predominantly detected in individuals aged 40 s and above, particularly in those in their middle-aged and older years [3, 11]. In this study, the average age at which SMBC was detected was 54.3 years, consistent with the previous research that SMBC is predominantly found in middle-aged and older populations. Notably, cases of SMBC in individuals under 30 s were rare, accounting for only 3 cases (9.38%), and no instances were observed in 10 s. This pattern, where SMBC is rarely identified during childhood and is predominantly detected in middle-aged and older individuals, provides support for the hypothesis that SMBC develops as a consequence of a progressive process rather than being congenital in nature.

Previous studies have reported that the size of the bone defect in SMBC is typically in the range of 1–3 cm in diameter on panoramic images. It has been noted that when the horizontal length exceeds 3 cm, the continuity of the mandibular border may be interfered with, allowing palpation of the lesion from the overlying skin [13, 14]. In this study, the size of SMBC was measured, with an average horizontal length of 16.6 mm, an average vertical length of 10.6 mm, and a maximum diameter of 32.4 mm. These measurements are in accordance with previous research findings. However, there were cases in which the continuity of the mandibular border was maintained even when the horizontal length exceeded 30 mm (Fig. 5). Conversely, instances were also observed where the continuity of the mandibular border was disrupted even when the horizontal length was less than 30 mm (Fig. 6).

The continuity of the mandibular border was maintained even when the horizontal length exceeded 30 mm

The continuity of the mandibular border was disrupted even when the horizontal length was less than 30 mm

Prior studies have attempted to categorize buccal cortical bone patterns of SMBC using CBCT. Ariji et al. [15] categorized SMBC based on the depth of mandibular bone infiltration measured with computed tomography. However, this classification method did not account for cases where the buccal cortical bone on the affected side was perforated, and it varies depending on the interpretation by the dentist reading the images. Additionally, there are limitations in this approach for periodic follow-up of SMBC, as it cannot provide objective numerical measurements of changes in lesion size. Hence, to objectively assess changes in SMBC during follow-up, a new classification method utilizing measurements of the remaining buccal cortical bone thickness on CBCT is needed. However, there have been no documented classifications based on the actual cortical bone thickness in the literature. The average buccal cortical bone thickness on the affected side of the mandible has been reported as 1.33 ± 0.38 mm [16]. Based on this, SMBC cases can be categorized based on an average buccal cortical bone thickness of 1.3 mm in the affected mandible (Fig. 7).

The new classification based on the thickness of buccal cortical bone with a reference thickness of 1.3 mm. In type I, the thickness of buccal cortical bone exceeds 1.3 mm. In type II, the thickness of buccal cortical bone is above 0 mm but not exceeding 1.3 mm. In type III, the thickness of buccal cortical bone is 0 mm

Numerous prior studies classify the location of SMBC into two primary variants: the posterior variant, found in the posterior region of the mandible, distal of the lower premolars, and the anterior variant, located in the anterior region of the mandible, mesial of the lower premolars. The majority of SMBC cases fall within the posterior variant category, with the anterior variant being a rare occurrence [17]. In all cases of this study, SMBC appeared as the posterior variant, located in the posterior region of the mandible, including the distal area of the lower premolars and the mandibular angle. The rarity of the anterior variant originating in the anterior region of the mandible poses challenges in terms of differential diagnosis, particularly when the radiographic features of SMBC, observed unilocular, overlap with other anatomical structures like the root of the anterior tooth on X-ray images. This overlap can lead to misdiagnosis as odontogenic benign tumors or periapical cysts that commonly occur in the anterior mandible [18, 19]. Regarding the relationship between the mandibular canal and the location of SMBC, this study observed where SMBC includes the mandibular canal in 3 cases (9.38%). This finding is consistent with previous research, which reported a similar result that the majority of SMBC cases are situated below the mandibular canal, with approximately 14.6% of cases showing a pattern that includes the mandibular canal [13].

In typical cases, distinguishing SMBC from other lesions can be achieved by recognizing its clinical characteristics and features on panoramic radiographs and CBCT scans, as described earlier. However, when it remains difficult to differentiate the lesion even with the information provided, consideration should be given to alternative diagnostic methods. One such method is sialography. SMBC with ductal involvement can be visualized in sialography, revealing the ductal structure of the lesion on the imaging [20]. Several studies have reported the observation of portions of salivary gland ducts inside or around SMBC using sialography [20, 21]. This diagnostic approach enables the differentiation of SMBC from other lesions. Another diagnostic method for differential diagnosis is magnetic resonance imaging (MRI). MRI offers excellent soft tissue resolution and contrast, allowing for the observation of internal structures, and vascular patterns, and aiding in the differentiation of SMBC from true cysts containing only fluid. However, it should be noted that MRI can be costly and may impose a financial burden on patients. Additionally, field distortion artifacts can occur due to intraoral dental prostheses, which is a limitation of this imaging modality [22].

Since SMBC is typically asymptomatic and lacks complications, surgical intervention is not necessary. Instead, it requires periodic radiographic follow-up. Lesions suspected to be SMBC should undergo regular radiographic follow-up at intervals of 12 months to monitor any changes in the size and morphology of the lesion [23]. If changes in the lesion are observed during follow-up, it is recommended to consider surgical intervention and tissue biopsy for the purpose of differential diagnosis from other lesions. In one case in this study, surgical intervention and tissue biopsy were performed due to changes in the size of the lesion, aiming to differentiate it from salivary gland tumors. The biopsy revealed lymphocytic sialadenitis. Another indication for surgical intervention is when the defect leads to the weakening of the mandibular bone structure itself. In such cases, to prevent the risk of fractures, it is necessary to remove the soft tissue within the defect and reinforce the mandibular bone structure using materials like titanium plates.