A preliminary investigation into the impact of soft tissue augmentation-based periodontal phenotype modification therapy for patients exhibiting class III decompensation

Abstract

Background: Patients with skeletal angle Class III malocclusion usually have inadequate hard and soft tissue volume at the mandibular anterior teeth. The labial proclination at the teeth may lead to gingival recession. The purpose of this study was to explore whether periodontal phenotype modification therapy with soft tissue augmentation (PhMT-s) can prevent gingival recession in these patients.

Methods: Four patients with skeletal Class III malocclusion and a thin periodontal phenotype underwent surgical-orthodontic treatment. Prior to tooth movement, they underwent a minimally invasive vestibular incision with subperiosteal tunnel access combined with autogenous connective tissue grafts for periodontal phenotype modification with soft tissue augmentation (PhMT-s). The labial gingival thickness of the anterior mandibular teeth was measured at three distinct levels: at the cementoenamel junction (GT0), 3 mm apical to the CEJ (GT3), and 6 mm apical to the CEJ (GT6). These measurements were taken at baseline, three months following PhMT-s, and after tooth decompensation. Additionally, a biopsy sample was obtained from the PhMT-s site of one patient. All sections were subsequently stained using hematoxylin and eosin, Masson trichrome, Sirius Red, and immunohistochemistry.

Results: The thickness of the labial gingiva was increased about 0.42 to 2.00 mm after PhMT-s. At the end of pre-orthognathic surgical orthodontic treatment, the thickness of the labial gingiva was increased about - 0.14 to 1.32 mm compared to the baseline and no gingival recession occurred after the pre-orthognathic surgical orthodontic treatment. The histologic results demonstrated that the grafts obtained from the PhMT-s site exhibited increased deposition of collagen fibers. Moreover, the proportion of type III collagen increased and the grafts displayed significantly reduced positive expression of CD31 and OCN.

Conclusions: PhMT-s increased the thickness of the soft tissue, stabilizing the gingival margin for teeth exhibiting a thin periodontal phenotype and undergoing labial movement. This is attributed to the increased deposition of collagen fibers.

Keywords: Gingival recession; Periodontal phenotype modification; Skeletal angle class III malocclusion; Soft tissue augmentation; Soft tissue grafting.

Fig. 1

The measurement of the labial gingival thickness on the cross-sectional CBCT images with Mimics software. A The pattern diagram of the measurement of the labial gingival thickness. Point A, B, C presented the CEJ, 3 mm apical to the CEJ and 6 mm apical to the CEJ. Line a presented the long axis of the measured tooth. Then, we drew three lines perpendicular to line a through point A, B, C and got Line AD, BE, CF. Finally, measure the thickness of the labial gingiva on the Line AD, BE, CF. B The gingival thickness was measured at the level of the CEJ and at distances of 3 mm and 6 mm apical to the CEJ

Fig. 2

Cephalometric radiographs, CBCT and clinical photographs of case 1. A The comparison of the cephalometric radiographs of the baseline and the end of pre orthognathic surgical orthodontic treatment. B The superimposition images of the #31#32#41#42 CBCT data at baseline and at the end of pre orthognathic surgical orthodontic treatment. C The appearance of the anterior mandibular teeth with thin periodontal phenotype at baseline. D Subperiosteal tunnel was extended from the vestibular to the gingival margin, which accommodated a 2 mm thick and at least 5 mm apico-coronal-dimensioned autogenous connective tissue graft. E The photographs at three months after the PhMT-s surgery. F The photographs at the end of orthognathic surgery

Fig. 3

Cephalometric radiographs, CBCT and clinical photographs of case 2. A The comparison of the cephalometric radiographs of the baseline and the end of pre orthognathic surgical orthodontic treatment. B The superimposition images of the #31#32#41#42 CBCT data at baseline and at the end of pre orthognathic surgical orthodontic treatment. C The appearance of the anterior mandibular teeth with thin periodontal phenotype at baseline. D Subperiosteal tunnel was extended from the vestibular to the gingival margin, which accommodated a 2 mm thick and at least 5 mm apico-coronal-dimensioned autogenous connective tissue graft. E The photographs at three months after the PhMT-s surgery. F The photographs at the end of orthognathic surgery

Fig. 4

Cephalometric radiographs, CBCT and clinical photographs of case 3. A The comparison of the cephalometric radiographs of the baseline and the end of pre orthognathic surgical orthodontic treatment. B The superimposition images of the #31#32#41#42 CBCT data at baseline and at the end of pre orthognathic surgical orthodontic treatment. C The appearance of the anterior mandibular teeth with thin periodontal phenotype at baseline. D Subperiosteal tunnel was extended from the vestibular to the gingival margin, which accommodated a 2 mm thick and at least 5 mm apico-coronal-dimensioned autogenous connective tissue graft. E The photographs at three months after the PhMT-s surgery F The photographs at the end of orthognathic surgery

Fig. 5

Cephalometric radiographs, CBCT and clinical photographs of case 4. A The comparison of the cephalometric radiographs of the baseline and the end of pre orthognathic surgical orthodontic treatment. B The superimposition images of the #31#32#41#42 CBCT data at baseline and at the end of pre orthognathic surgical orthodontic treatment. C The appearance of the anterior mandibular teeth with thin periodontal phenotype at baseline. D The photographs at the end of orthognathic surgical treatment. E A second surgical procedure aimed at restoring the gingival contour to its desired shape were conducted. Biopsies were obtained from beneath the soft tissue flap and from the exact surface of the alveolar bone. F The photographs at three months after the surgery aimed at restoring the gingival contour

Fig. 6

The results of hematoxylin and eosin H&E, Masson’s trichrome MT and Sirius Red staining. A The gingival connective tissue at the soft tissue augmentation site that develops following the transplantation of the palatal graft exhibits a higher density compared to the palatal subepithelial connective tissue. On the contrary, the palatal subepithelial connective tissue is richer in blood vessels than the gingival connective tissue that arises from the palatal graft transplantation. Notably, neither of these tissues demonstrates the presence of inflammatory cells. B Upon examination of sections stained with Masson’s trichrome the soft tissue formed following the transplantation of the palatal graft exhibited an increase in collagen fiber deposition and a corresponding decrease in angiogenesis. Furthermore, a distinct difference was apparent between the tissues sampled from beneath the soft tissue flap and those obtained from the surface of the alveolar bone. Tissue harvested from the alveolar bone surface exhibited a higher density of collagen fibers, greater homogeneity in fiber arrangement, and reduced vascularity. C Morphological differences between type I and type III collagen were analyzed through Sirius Red staining. We noted alterations in the collagen content, specifically in the subepithelial connective tissue graft from the palate and the soft tissue formed following the transplantation of the palatal graft. In the subepithelial connective tissue graft from the palate, type I and type III collagen were intertwined, with type I collagen being the dominant component surrounded by a minor amount of green-tinged type III collagen. Conversely, in tissues collected from beneath the soft tissue flap, type III collagen was predominant, encircled by a minor quantity of type I collagen exhibiting an orange hue. Notably, the proportion of type I and type III collagen in tissues harvested from the surface of the alveolar bone was approximately equal

Fig. 7

The immunochemistry of CD31 and OCN. The expression levels of CD31and OCN were significantly elevated in the subepithelial connective tissue graft from the palate compared to the soft tissue formed following the transplantation of the palatal graft