Silk mat has been widely studied as a membrane for guided tissue regeneration (GTR) [13, 15]. Silk mat shows a similar level of bone regeneration compared to collagen membrane in the animal model [16]. In this clinical study, silk mats showed similar levels of bone regeneration compared to dPTFE membranes (Fig. 3). Both silk mat and dPTFE membrane showed better bone regeneration compared to the non-graft/membrane group (Fig. 3). To the best of our knowledge, this is the first clinical comparative study of silk mats.
The bony defect in the distal surface of the mandibular second molar can be induced by impacted third molar [2]. The size of the defect is dependent on the local environment adjacent to the impacted teeth, such as the degree of impaction, oral hygiene, and systemic disease [2, 4]. If the bony defect after the third molar removal is not reached at the critical-sized defect (CSD), it will be healed without applying graft. To the best of our knowledge, there has been no volumetric analysis for CSD in human third molar surgery. Pocket depth in the distal surface of the second molar has been used as an indicator for CSD determination. In this study, patients with a minimum 3-mm bony defect were included [17]. In our study, the BG for the nonregenerative/nongraft procedure group was 1.4 mm and 2.5 mm at 3 and 6 months, respectively (Fig. 3). The application of PTFE has been shown to improve tissue regeneration compared to the nonregenerative/nongraft procedure group [18, 19]. Additional bone grafts with GTR do not show a synergistic effect after extraction [19].
Silk mat has many benefits compared to other types of membrane. The tensile strength in wet conditions is higher in silk mats than in collagen membranes and dPTFE membranes [16]. Considering the presence of saliva in the oral cavity, the high tensile strength of silk mat in wet conditions is beneficial for clinicians to manage. The production procedure for silk mats is simple [15]. Accordingly, the price for silk mat is also expected to be cheap compared to other types of membrane. The price of material has been an obstacle for the application of membrane in third molar surgery. In addition, silk sericin has bone regeneration ability [20]. Silk mat contains abundant silk sericin as its natural form [14].
In this study, panoramic radiogram was used to measure bone height at the distal surface of the mandibular second molar. Panoramic radiograms have different magnification ratios according to the anatomic site [21]. The shape of jaw bones may also influence image sharpness. Compared to cone-beam computerized tomograms (CBCT), error due to image distortion is higher in panoramic radiograms [21]. However, measurement in panoramic radiographs is highly correlated with that in CBCT and can be used in the posterior alveolus of the mandible [22]. However, CT has three-dimensional and multiple slices of images. Averaging bony defects along the distal surface of the second molar will be time-consuming. As panoramic radiogram is a two-dimensional image, it may have a benefit for measuring the average distance of the overlapped structure. The linear measurements show similar accuracy between CBCT and digital panoramic view [23].
The limitation of this study was that the samples in the control group (nonregenerative/nongraft procedure) were collected separately from 3 months and 6 months because most patients did not have postoperative follow-up radiograms. Accordingly, the controls at 3 months and at 6 months were different. In future studies, the samples for control should also be collected prospectively and in a controlled manner.