Augmentation of keratinized tissue at tooth and implant sites by using autogenous grafts and collagen-based soft-tissue substitutes

Augmentation of keratinized tissue using autogenous soft-tissue grafts and collagen-based soft-tissue substitutes at teeth and dental implants: Histological findings in a pilot pre-clinical study

AIM

To histomorphometrically assess three treatment modalities for gaining keratinized tissue (KT) at teeth and at dental implants.

MATERIALS AND METHODS

In five dogs, the distal roots of the mandibular second, third and fourth premolars were extracted. Dental implants were placed at the distal root areas 2 months later. After another 2 months, KT augmentation was performed at both distal (implants) and at mesial root (teeth) areas in the presence (wKT groups) or absence (w/oKT groups) of a KT band at the mucosal/gingival level. Three treatment modalities were applied randomly: apically positioned flap only (APF), free gingival grafts (FGGs) and xenogeneic collagen matrices (XCMs). A combination of the above produced six groups. Two months later, tissue sections were harvested and analysed histomorphometrically.

RESULTS

The median KT height and length were greatest at implants with FGG in both wKT (3.7 and 5.1 mm, respectively) and w/oKT groups (3.7 and 4.6 mm), and at teeth with FGG in wKT groups (3.7 and 6.1 mm) and with APF in the w/oKT groups (3.9 and 4.4 mm). The XCM and APF produced more favourable results at teeth than at implants.

CONCLUSIONS

FGG was advantageous in gaining KT, especially at implants.

Keratinized tissue augmentation using collagen-based soft tissue substitute with/without epidermal growth factor on buccally positioned implants: a pilot preclinical study

OBJECTIVES

To investigate the effect of epithelial growth factor (EGF) with collagen matrix (CM) on the gain of KT for buccally positioned implants in dogs.

MATERIALS AND METHODS

In five dogs, four implants were placed buccally with the whole part of KT excision on the buccal side (two implants per each hemi-mandible). After one month, KT augmentation was performed: 1) free gingival grafts (FGG), 2) collagen matrix (CM) only, 3) CM soaked with 1 μg/g of EGF, and 4) CM soaked with 10 μg/g of EGF (n = 5 in each group). The experimental animals were sacrificed three months post-KT augmentation. Clinical, histologic, and histomorphometric analyses were performed.

RESULTS

The clinical KT zone was the highest in group FGG (5.16 ± 1.63 mm). Histologically, all groups presented buccal bony dehiscence. Regarding newly formed KT, no specific difference was found among the groups, but robust rete pegs formation in some specimens in group FGG. Histomorphometric KT height (4.66 ± 1.81 mm) and length (5.56 ± 2.25 mm) were the highest in group FGG, whereas similar increases were noted in the rest. The buccal soft tissue thickness at the coronal part of the implant did not exceed 2 mm in all groups.

CONCLUSION

All groups presented increased KT zone, but FGG treatment was more favored. The addition of EGF to CM appeared not to enhance KT formation.

CLINICAL RELEVANCE

FGG treatment was more favorable to re-establish the KT zone than other treatment modalities.

Tailoring the multiscale mechanics of tunable decellularized extracellular matrix (dECM) for wound healing through immunomodulation

With the discovery of the pivotal role of macrophages in tissue regeneration through shaping the tissue immune microenvironment, various immunomodulatory strategies have been proposed to modify traditional biomaterials. Decellularized extracellular matrix (dECM) has been extensively used in the clinical treatment of tissue injury due to its favorable biocompatibility and similarity to the native tissue environment. However, most reported decellularization protocols may cause damage to the native structure of dECM, which undermines its inherent advantages and potential clinical applications. Here, we introduce a mechanically tunable dECM prepared by optimizing the freeze-thaw cycles. We demonstrated that the alteration in micromechanical properties of dECM resulting from the cyclic freeze-thaw process contributes to distinct macrophage-mediated host immune responses to the materials, which are recently recognized to play a pivotal role in determining the outcome of tissue regeneration. Our sequencing data further revealed that the immunomodulatory effect of dECM was induced via the mechnotrasduction pathways in macrophages. Next, we tested the dECM in a rat skin injury model and found an enhanced micromechanical property of dECM achieved with three freeze-thaw cycles significantly promoted the M2 polarization of macrophages, leading to superior wound healing. These findings suggest that the immunomodulatory property of dECM can be efficiently manipulated by tailoring its inherent micromechanical properties during the decellularization process. Therefore, our mechanics-immunomodulation-based strategy provides new insights into the development of advanced biomaterials for wound healing.

Spontaneous regeneration of keratinized tissue at implants and teeth

AIM

To investigate the spontaneous regeneration of the implanto-mucosal and dento-gingival unit after complete removal of keratinized tissue (KT).

MATERIALS AND METHODS

One hemi-mandible per dog (n = 4) was allocated to receive three dental implants (test sites, premolar region), whereas three premolars on the contralateral side were controls. After osseointegration, the entire KT (buccal + lingual) was surgically excised on all test and control sites, leaving the bone exposed. Clinical measurements were performed before excision (T0 ) and after 12 weeks (T1 ). Following healing, the animals were euthanized, and the specimens were histologically processed. Descriptive statistical analyses were performed.

RESULTS

Clinical measurements revealed that at T1 , on all teeth, a band of KT was spontaneously regenerated (mean width: 2.60 ± 0.66 mm), whereas on implants, KT was detected only occasionally at mesial or distal but not at buccal sites (mean total: 0.35 ± 0.53 mm; p < .0001). Histologically, spontaneous regeneration of the dento-gingival unit was evident, displaying masticatory mucosa. At the implant sites, on the other hand, the implanto-mucosal unit was characterized by a non-keratinized epithelium and elastic fibres, indicating the characteristics encountered in alveolar mucosa.

CONCLUSION

After excision of KT at implant sites, the spontaneous regeneration of the soft tissue is characterized by a non-keratinized epithelium typical for alveolar mucosa, while at tooth sites the spontaneous regeneration was characterized by soft tissue resembling gingiva.

Regeneration of keratinized tissue around teeth and implants following coronal repositioning of alveolar mucosa with and without a connective tissue graft: An experimental study in dogs: Fifty years after Karring's landmark study: Fifty years after Karring's 71 landmark study

AIM

To compare clinical and histological keratinized tissue formation around teeth and implants following coronal repositioning of alveolar mucosa with or without a connective tissue graft (CTG).

MATERIALS AND METHODS

In nine beagle dogs, the third and fourth premolars (P3 and P4) were extracted from one side of the maxilla. Three months after the tooth extraction, a full-thickness buccal flap was raised and two implants were placed in those healed areas. On the contra-lateral side, a buccal flap was also raised at the P3 and P4 areas. Before suturing, the dogs were randomly assigned to three study groups (control, non-keratinized tissue [NKT], and non-keratinized tissue CTG [NKT-CTG]). In the control group, the buccal flaps were re-positioned around the teeth (P3 and P4) on one side, and implants on the other side, presenting an adequate band of keratinized tissue (KT). For the NKT and NKT-CTG groups, this buccal KT was then excised. In the NKT group, the buccal flap without KT (alveolar mucosa) was re-positioned around the teeth and implants. In the NKT-CTG group, a CTG taken from the excised KT was sutured to the buccal alveolar mucosa and then both were re-positioned around the teeth and implants. The clinical height of the KT was measured at baseline and at 1, 2, and 3 months of healing. The animals were sacrificed at 3 months, at which point the KT height was measured histologically.

RESULTS

The control group presented normal healing with a band of KT surrounding the teeth and implants. In the NKT and NKT-CTG groups, a new KT band approximately 2 mm in height (measured clinically and histologically) spontaneously formed around all teeth, regardless of whether a CTG had been placed. In the NKT implant group, no new KT was observed (clinically or histologically). Around the implants in the NKT-CTG group, a small amount of KT was formed in just two of the six implants.

CONCLUSIONS

After surgical excision of KT, spontaneous KT is formed around teeth but not around implants, regardless of the placement of a CTG.

Minimal invasiveness in soft tissue augmentation at dental implants: A systematic review and meta-analysis of patient-reported outcome measures

The aim of this study was to compare patient-reported outcome measures (PROMs) of soft tissue substitutes versus autogenous grafts for soft tissue augmentation procedures at implant sites. Comprehensive and systematic literature searches were performed until December 2021. A focused question was formulated based on the Population, Intervention, Comparison and Outcome criteria (PICO): In patients with dental implants undergoing soft tissue augmentation (P), do soft tissue substitutes (I) compared to autogenous soft tissue graft (SCTG [subepithelial connective tissue graft]) (C) limit the post-operative morbidity and other patient reported-outcomes measures (O). Randomized controlled clinical trials, prospective-, retrospective- and case-series studies were included. Meta-analyses were performed whenever possible and the results were expressed as weighted mean differences (WMD). A total of 29 clinical studies were included. For mucosal thickness gain, soft tissue substitutes significantly reduced the pain perception compared to SCTG (n = 4; WMD = 14.91 Visual Analog Scale [VAS] units; 95% confidence interval [CI] 6.42-23.40; P < .0006) based on a 0-100 VAS scale. Based on a 0-10 VAS scale, a borderline significance of pain reduction was found when soft tissue substitutes were applied (n = 4; WMD = 1.62 VAS units; 95% CI 0.01-3.23; P = .05). For keratinized tissue gain, soft tissue substitutes significantly reduced the pain perception after keratinized tissue augmentation compared to SCTG based on a 0-100 VAS scale (n = 2; WMD = 21.43 VAS units; 95% CI 12.58-30.28; P < .0001). Based on the 0-10 VAS scale, soft tissue substitutes significantly reduced the pain as compared to SCTG (n = 4; WMD = 1.65 VAS units; 95% CI 0.66-2.64; P = .001). Regarding pain medication, soft tissue substitutes required less painkillers (n = 6; WMD = 1.56 tablets; 95% CI 1.22-1.91; P < .00001) after soft tissue augmentation. The surgery time was significantly reduced when soft tissue substitutes were used (n = 5; WMD = 10.9 minutes; 95% CI 4.60-17.19; P < .00001). There were no significant differences in satisfaction, aesthetics, and quality of life (OHIP-14) between soft tissue substitutes and autogenous grafts following soft tissue augmentation at implants sites. Soft tissue substitutes, compared to autogenous grafts, significantly improve PROMs following soft tissue augmentation at implant sites. Soft tissue substitutes can reduce pain perception, amounts of painkillers and surgery time while achieving similar levels of patient´s satisfaction as autogenous grafts without impairing the clinical outcomes. The current evidence indicates that they constitute a valid and reliable alternative to minimize the invasiveness in soft tissue augmentation procedures at implant sites.

Dimensional Changes in Free Epithelialized Gingival/Mucosal Grafts at Tooth and Implant Sites: A Prospective Cohort Study

BACKGROUND

A study was made of the dimensional changes in free epithelialized gingival/mucosal grafts (FEGs) used to augment keratinized tissue (KT) at tooth and implant sites, and of the confounders influencing the dynamic changes over 6 months of follow-up.

MATERIAL AND METHODS

A prospective cohort interventional study was made of implant and tooth sites needing keratinized tissue augmentation by means of an apically positioned flap and FEG. Six intraoperative variables were recorded at baseline (T0). In addition, graft width (GW), graft length (GL) and graft dimension (GD) were assessed at three weeks (T1), three months (T2) and 6 months of follow-up (T3). Univariate and multivariate analyses were performed to explore associations between the demographic and intraoperative variables and the outcomes over the study period.

RESULTS

Based upon an a priori power sample size calculation, a total of 56 consecutive patients were recruited, of which 52 were available for assessment. A total of 73 graft units were included in 122 sites. At T3, the mean change in GD in FEG was 40.21%. In particular, the mean changes in GL and GW were 12.13% and 33.06%, respectively. Statistically significant changes in GD were recorded from T0 to T1 (p<0.0005) and from T1 to T2 (p<0.0005), but not from T2 to T3 (p = 0.13). The change in GD at T3 was 33.26% at tooth and 43.11% at implant site level (p = 0.01). Age and GW assessed at T0 proved to be related to the changes in GD and GW in the univariate and multivariate analyses. The univariate analysis showed the avascular area (AA) to be related to the changes in GD and GW at the implant sites, while graft thickness (GT) was associated to changes in GD and GW at the tooth sites in the univariate and multivariate analyses.

CONCLUSIONS

Free epithelialized grafts are exposed to dimensional changes that result in a reduction of approximately 40% of the original graft dimension - the changes being approximately 10% greater at the implant sites than at the tooth sites (NCT04410614). This article is protected by copyright. All rights reserved.

Osteoconductive Properties of a Volume-Stable Collagen Matrix in Rat Calvaria Defects: A Pilot Study

Volume-stable collagen matrices (VSCM) are conductive for the connective tissue upon soft tissue augmentation. Considering that collagen has osteoconductive properties, we have investigated the possibility that the VSCM also consolidates with the newly formed bone. To this end, we covered nine rat calvaria circular defects with a VSCM. After four weeks, histology, histomorphometry, quantitative backscattered electron imaging, and microcomputed tomography were performed. We report that the overall pattern of mineralization inside the VSCM was heterogeneous. Histology revealed, apart from the characteristic woven bone formation, areas of round-shaped hypertrophic chondrocyte-like cells surrounded by a mineralized extracellular matrix. Quantitative backscattered electron imaging confirmed the heterogenous mineralization occurring within the VSCM. Histomorphometry found new bone to be 0.7 mm² (0.01 min; 2.4 max), similar to the chondrogenic mineralized extracellular matrix with 0.7 mm² (0.0 min; 4.2 max). Microcomputed tomography showed the overall mineralized tissue in the defect to be 1.6 mm³ (min 0.0; max 13.3). These findings suggest that in a rat cranial defect, VSCM has a limited and heterogeneous capacity to support intramembranous bone formation but may allow the formation of bone via the endochondral route.

Keratinized tissue gain after free gingival graft augmentation procedures around teeth and dental implants: A prospective observational study

AIM

The primary goal was to compare the amount of keratinized tissue width (KTW) gain after free gingival graft (FGG) procedures around implants and teeth after 6 and 12 months of healing.

MATERIALS AND METHODS

Patients with mucogingival defects (<2 mm of KT) around teeth and implants underwent a gingival augmentation procedure by means of a FGG. Clinical measurements were performed with an individual stent to determine keratinized tissue width (KTW), length (KTL), graft shrinkage (GS) and gingival margin position (GMP) at 2 weeks, 6 weeks, 3 months, 6 months and 12 months after surgery.

RESULTS

Twenty-nine patients (35 sites) participated in this prospective study. After surgery, KTW decreased and GS increased significantly in both treatment groups during the whole follow-up period, but the biggest changes were observed at 6 weeks. When comparing both treatment groups, implant sites showed significantly more reduction in KTW and more GS. Thus, at 12 months, KTW and GS reduced 2.03 ± 2.1 mm and 36.74 ± 38.2% in the teeth group and 2.91 ± 12.03 mm and 61.8 ± 36.25% around implants, respectively.

CONCLUSIONS

A significantly greater reduction in KTW and more GS might be expected at implant sites.