Comparison of two soft tissue substitutes for the treatment of gingival recession defects: an animal histological study

Abstract Objectives: This study aimed to compare two different soft tissue replacement grafts in their ability to treat gingival recession defects and successfully integrate with the surrounding tissues. Methodology: Nine beagle dogs were included and followed up to 10 weeks. Sites for intervention were allocated to one of the grafting materials investigated. Treatment consisted of coronally advanced flap combined with one of the two soft tissue substitutes on a previous surgically created defect. Materials employed were porcine-derived acellular dermal matrix (ADM) [Novomatrix™ (Test)] and collagen-based matrix (CBM) [Mucograft® (Control)]. Animals were sacrificed at 2, 6, and 10 weeks postoperatively and compared using descriptive histology and histomorphometric outcomes. Results: Macroscopic findings were similar between test and control groups at all intervals. After 10 weeks, both groups demonstrated successful incorporation of the grafting materials without signs of rejection and with comparable tissue integration. The histomorphometric data were similar between groups at 2 weeks; however, the test group provided greater root coverage and increase in tissue thickness than the control at 6- and 10-weeks post surgically. Conclusions: Both porcine-derived ADM and CBM revealed similar histological outcomes with successful integration and absence of adverse events. Test group provided superior outcomes regarding root coverage and increase in tissue thickness.


Introduction
Soft tissue augmentation procedures have been extensively employed for the correction of mucogingival deformities, especially soft tissue recession defects.
This condition affects a large portion of the population regardless of the oral hygiene standards; 1 the estimation is that 23.8 million people (22.5%) in the United States over 29 years old present at least one tooth surface with ≥3mm gingival recession (GR). 2 The extent, prevalence, and severity of these mucogingival deformities increase with age 2 and continue 3 to progress with the apical displacement of the gingival marginal, if left untreated. GR is also associated with a series of undesirable consequences including esthetic disharmony, hypersensitivity, and root caries.
Consequently, the prevention and treatment of GR defects remain as the focus in the periodontal plastic surgery investigations. As such, multiple approaches have been employed and investigated for the correction of GR including, but not limited to; guided tissue regeneration (GTR), 4 coronally advanced flap (CAF), 5 tunneling techniques, 6 and lateral pedicle flap (LPF). 7 These techniques have been used alone or combined with different auto-, allo-, and xenografts. 8 To date, the use of autogenous connective tissue graft (CTG) has no equivalent regarding its properties, predictability, and long-term outcomes 8 (8). Although CTG is considered the gold standard, the use of alternative grafting materials presents several advantages, namely reduced morbidity, reduced surgical time, and unlimited availability.
Hence, investigators continue to seek non-autogenous soft tissue grafting substitutes and other alternative methods. Among these are: acellular dermal matrix (ADM), 9 porcine collagen matrix, 10,11 enamel matrix derivatives, 12 and GTR. 4 ADM represents one of the most widely used substitutes for autogenous connective tissue. Since its introduction in the 1990s, numerous studies have investigated the use of ADM in periodontal plastic surgery procedures. 9,13,14 Increase in root coverage and in tissue thickness, and augmentation of the keratinized tissue have been reported after treatment with ADM. 9,14,15 In addition, it has been demonstrated that neither the orientation nor the processing technique for ADM play a role in the final outcomes. 14,16 Consequently, the use of ADM is considered nowadays a predictable alternative for the treatment of GR defects.

Methodology Study design
This investigation was conducted on 9 beagle dogs (Canis familiaris), with an age range from 16 -36 months. Four sites per animal (maxillary and mandibular canines) were included and allocated to one of the grafting materials. As such, a total of 36 sites were surgically treated, 18 as control and 18 as test.
Three animals were sacrificed at each interval (at 2, 6, and 10 weeks postoperatively) providing a total of 12 (6 test and 6 control) sites for evaluation. Approval Before surgery, all teeth included were carefully debrided by manual instrumentation (Figure 1a). Later,   Photographs of the sites were taken every two weeks using appropriate labels and scale. After 2, 6, and 10 weeks after surgery, euthanasia was carried out by an intravenous injection of a sodium pentobarbital-based euthanasia solution. The portion of the jaw containing the defects was removed from the head. The jawbone was trimmed as needed to remove excess bone, while carefully preserving the integrity of soft tissues at and near the sites. After trimming, the defect sites were placed in 10% neutral buffered formalin (10% NBF).

Tissue Preparation for Histological Analysis
After fixation, the defect sites were processed using    Figure 4B, 5B, 6B).

B) Acellular Dermal Matrix (ADM):
Two weeks after implantation, histologic assessment showed ADM was integrated into the surrounding soft tissues, showing slight degradation ( Figure 4C).
Healthy soft tissues were present at the implantation bed; tissue response was favorable, and the implanted material was non-irritant as indicated by the absence of multinucleated giant cells and lymphocytes.
However, only slight infiltration of neutrophils was observed ( Figure 4D).
Six weeks after implantation, ADM was integrated into the surrounding tissues, being moderately degraded ( Figure 5C). No signs of any local inflammation were present ( Figure 5D).
Ten weeks after implantation, ADM was integrated into the surrounding tissues, being moderately degraded ( Figure 6C). Further observations were similar to that reported at six weeks; local inflammatory infiltrate was absent ( Figure 6D).

Histomorphometric Outcomes
Histomorphometric analysis was performed to evaluate the root coverage and gingival thickness of the samples studied. All data are shown in Table 1 and  (Table 2). These changes between both groups were statistically significant only for vascularization (p<0.05).

Discussion
This study investigated two different porcine-  GR defects. While the employment of porcine-derived grafting materials is not new in the periodontal field, 21 this is the first study, to the best of our knowledge, to histologically evaluate this porcine-derived ADM for the treatment of GR defects. Another grafting substitute, CBM, was selected as a control group for two main reasons: the common origin, and the extensively documented use of CBM in the literature in many   significantly different for the total mean of buccolingual tissue thickness and the distance from the gingival margin to the notch. As for the 6 weeks time point, and to account for the lack of measurements for these parameters, two means were reported for those values: one mean in which all values were included (including the 0.0 values) and one mean in which only positive values were included (Table 1)