Long-term assessment of a modified tunneling technique for root coverage in lower anterior gingival recession: a retrospective study

Abstract

Purpose

Root coverage (RC) procedures require long-term evaluation. This study assessed the clinical validity and long-term stability of a modified tunneling technique for lower anterior gingival recession (GR) using a subepithelial connective tissue graft (SCTG) and a volume-stable collagen matrix.

Methods

Across 39 patients, 66 mandibular incisors with ≥1.0 mm of GR were examined before and after RC surgery. Clinical photographs documenting the results of RC were taken at baseline (T₀) and the most recent follow-up visit (T_l). Impressions were obtained either at baseline (T₀) or 3 weeks later (T₃). The recession depth, Miller classification, and rates of RC and complete root coverage (CRC) were assessed.

Results

This study analyzed 66 GR sites across 39 patients, with an average follow-up period of 41.3 months. Overall, the mean RC achieved was 86.2%±15.7%. Among single recessions, the RC was 85.2%±25.6% for Miller class I, 91.5%±10.4% for class II, and 79.2%±18.3% for class III. Regarding multiple recessions, the RC was 85.1%±16.2% for Miller class I, 87.0%±12.5% for class II, and 89.8%±16.0% for class III. By Miller classification, the RC was 85.1%±16.8% for class I, 88.7%±11.6% for class II, and 85.8%±17.3% for class III. Furthermore, the RC varied by follow-up duration: 72.5%±15.1% at 12 months, 90.1%±12.6% at 25–36 months, 89.0%±16.7% at 37–48 months, 91.10%±9.88% at 49–60 months, and 97.6±4.79% for longer than 61 months, with 77.8% of the last group achieving CRC. RC also differed based on the initial recession depth, at 88.0%±16.8% for 1–3 mm, 83.1%±14.1% for 3–6 mm, and 80.2%±5.04% for depths exceeding 6 mm.

Conclusions

A modified tunneling technique, utilizing SCTG and a volume-stable collagen matrix, appears to represent a reliable option for the long-term management of GR in the lower anterior region, even in cases involving multiple Miller class III GRs.

Graphical Abstract

INTRODUCTION

Gingival recession (GR) often leads to aesthetic concerns, hypersensitivity, plaque retention, or root caries [1]. Currently, the combination of a subepithelial connective tissue graft (SCTG) and a coronally advanced flap (CAF) is recognized as the gold standard for root coverage (RC) [2,3]. By augmenting the gingival tissue, this technique provides excellent aesthetic outcomes, including a high success rate, harmonious color matching with the surrounding tissue, and increased gingival dimensions [4]. However, growing appreciation for the benefits of minimally invasive surgery has led to the increased popularity of the tunneling technique [5].

Tunneling involves establishing a tunnel beneath the gingival tissue beyond the mucogingival line, without elevating the papillae [6]. A recent meta-analysis found that tunneling yields results comparable to those of CAF in terms of RC, complete root coverage (CRC), clinical attachment level, keratinized tissue width, probing depth, and recession coverage [7]. Key advantages of this technique include a reduced risk of papillary height loss in critical aesthetic areas, minimized scar formation, improved blood supply, and increased graft stability [5,8,9]. Despite these benefits, tunneling presents certain challenges and limitations. It is considered time-consuming, is technique-sensitive, and may not provide sufficient flap advancement, particularly in cases of isolated deep GR, high muscle pull, or shallow vestibule [10]. To overcome some of these limitations, modifications have been proposed. The modified tunneling technique employed in this study creates a complete soft tissue tunnel on the buccal side of the recipient site, ensuring optimal flap mobility and blood supply for the subsequent placement of the connective tissue graft [11].

Previously, the use of SCTGs or free gingival grafts required harvesting tissue from the palate for transplantation in RC procedures. However, recent advancements have increased convenience for both operators and patients by adopting minimally invasive methods to harvest the SCTG and by employing collagen matrices to maintain volume stability [11]. Moreover, a preclinical study of RC surgery using a tunneling technique found that collagen matrix provided comparable long-term postoperative volume stability to SCTG [12].

By combining these procedures, a method was developed to decrease donor-site discomfort by reducing the SCTG and to minimize recipient-site incisions through a modified tunneling technique. While its clinical effectiveness has been documented, long-term clinical data remain limited. The objective of this retrospective study was to evaluate the clinical efficacy of the modified tunneling technique using SCTG and volume-stable collagen matrix in treating GR in the lower anterior region over a 40-month follow-up period.

MATERIALS AND METHODS

Study design

This retrospective analysis included a continuous cohort of outpatients at the Department of Periodontology at Seoul National University Dental Hospital (SNUDH) between January 2018 and April 2024 who received RC for the treatment of lower anterior GR. The study was granted an exemption by the Institutional Review Board of SNUDH (IRB No. ERI24013) and was conducted in accordance with the Helsinki Declaration of 1975, as revised in 2013.

Study procedures

All patients underwent RC performed by a single periodontal specialist (S.K.), who holds an academic position and has over 20 years of clinical experience. The clinical cases selected for this study involved the use of the modified tunneling technique and were documented with both preoperative and postoperative photographs, with a follow-up period of at least 6 months. Clinical photographs, including preoperative and postoperative images, were captured at baseline (T₀) and at the most recent visit (T _l ) (Figure 1). Impressions of the maxilla and mandible were taken either at baseline (T₀) or 3 weeks later (T₃) using hydrocolloid material (Alginate GC Aroma Fine Plus; GC Co., Tokyo, Japan).

Figure 1. Study procedure. Clinical cases were documented with preoperative (T₀) and postoperative (T _l ) photographs.

T₀: baseline, T _l : latest visit.

Study population

The inclusion criteria stipulated that participants must be at least 18 years old and in good health, with no systemic diseases. They were also required to have no periodontal disease, as indicated by a probing pocket depth of 3.0 mm or less, and to exhibit a lower anterior GR of at least 1.0 mm with no endodontic lesions, caries, or restorative dental work in the defect area. Clinical photographs were taken before and after the surgical procedure, and dental impressions were obtained at least once during the study. Follow-up extended for a minimum of 6 months. The exclusion criteria included patients with medical conditions that could interfere with healing, those with periodontal disease, and those whose teeth did not exhibit a visible cementoenamel junction or mucogingival line on the clinical photographs.

Surgical procedure

The surgical process is depicted in Figure 2. Specifically, Figure 2A illustrates the lower anterior GR of tooth #41. Initially, the marginal gingival epithelium was excised using a blade or diamond bur, as indicated by the red line in Figure 2B. A vertical vestibular incision was then made in the interproximal region to separate the gingival flap, followed by subperiosteal tunneling with a CM9 surgical curette (Hu-Friedy, Chicago, IL, USA) (Figure 2C). After the papilla pedicle flap was closed with sutures, the SCTG was inserted into the tunnel and secured with 5-0 absorbable suture material (Vicryl Rapide; Ethicon, Cincinnati, OH, USA) (Figure 2D). Collagen matrix (Collagen Graft2; Genoss, Suwon, Korea) was then placed beneath the SCTG (Figure 2E), and the vestibular incision was also closed with 5-0 absorbable suture material (Figure 2F). To facilitate harvesting of the SCTG, a plastic surgical template was fabricated using a vacuum machine (Biostar; SCHEU, Iserlohn, Germany), as shown in Figure 3A. This template was used to accurately mark the palatal donor site with a blade (Figure 3B). Epithelial tissue at the donor site was removed using a rotating diamond bur (EX-21; Mani, Tochigi, Japan) (Figure 3C), and an SCTG of approximately 2.0 mm in depth was harvested (Figure 3D). The donor site was then sutured with 5-0 absorbable suture material (Figure 3E). Donor sites were protected using a surgical template produced with a vacuum former (Biostar; SCHEU).

Figure 2. Schematic illustration of the modified tunnel technique. (A) Lower anterior gingival recession. (B) De-epithelization of the marginal gingiva surrounding the gingival recession. (C) Vertical vestibular incision in the interdental area and subperiosteal tunneling with a CM9 surgical curette. (D) Suturing of the papilla pedicle flap at the recession site and fixation of the SCTG. (E) Application of collagen matrix beneath the SCTG. (G) Suturing of the vestibular incision.

SCTG: subepithelial connective tissue graft.

Figure 3. Schematic illustration of the subepithelial connective tissue graft. (A) A surgical stent was used to establish the palatal donor site. (B) The palatal donor site was marked with a blade guided by the stent. (C) De-epithelialization was performed using a rotating diamond bur. (D) The SCTG was harvested to a depth of approximately 2.0 mm. (E) The incision was closed with simple interrupted sutures, and a prefabricated hemostatic device was applied.

SCTG: subepithelial connective tissue graft.

Study assessments

For this study, we employed the methods outlined in our previous research [11]. We recorded patient characteristics, including age, sex, tooth type, and Miller classification of defects, for each surgical procedure. Impressions of the maxilla and mandible were taken either at baseline (T₀) or at 3 weeks (T₃) using a hydrocolloid material (Alginate GC Aroma Fine Plus; GC Co.). These impressions were utilized to determine the actual length of the teeth, which was then compared to the length measured on the clinical photographs. Digital calipers (CAS Co., Yangju, Korea) were employed to measure the length of tooth #31 (or #21) from the incisal edge on each cast model. To ensure the comparability of preoperative and postoperative photographs, we used PowerPoint (Microsoft, Redmond, WA, USA) to analyze the exposed root length on each clinical photograph. The recession depth (RD) was defined as the distance from the cementoenamel junction to the marginal gingiva. This measurement was obtained from clinical photographs taken at T₀ and T _l using the proportional ratio between the RD and the incisal edge. On a graphic tablet, we drew 2 reference lines: (1) a mesiodistal horizontal line at the incisal edge of the crown and (2) a mid-facial vertical line from the most coronal part of the crown to the mucogingival line (Figure 4). These lines served as references to assess the comparability of magnification. The RD and the percentage of RC were evaluated using the formulas shown below [13].

Figure 4. Measurement of the amount of root coverage on clinical photographs. (A) Before the operation. Gingival recession is visible in the lower anterior teeth. A horizontal black line was drawn on the incisal edge, and another line was drawn perpendicular to it. The length from the CEJ (dotted line) to the area contacting the apical point of the gingival recession was termed the gingival recession depth. (B) After the operation. The gingival recession had been resolved.

CEJ: cementoenamel junction.

$$\mathrm{R}\mathrm{e}\mathrm{c}\mathrm{e}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{ }\mathrm{D}\mathrm{e}\mathrm{p}\mathrm{t}\mathrm{h}\mathrm{ }=\mathrm{ }\frac{\mathrm{L}\mathrm{e}\mathrm{n}\mathrm{g}\mathrm{t}\mathrm{h}\mathrm{ }\mathrm{o}\mathrm{f}\mathrm{ }\mathrm{t}\mathrm{h}\mathrm{e}\mathrm{ }\mathrm{I}\mathrm{n}\mathrm{c}\mathrm{i}\mathrm{s}\mathrm{a}\mathrm{l}\mathrm{ }\mathrm{E}\mathrm{d}\mathrm{g}\mathrm{e}\mathrm{ }\mathrm{o}\mathrm{f}\mathrm{ }\mathrm{R}\mathrm{e}\mathrm{f}\mathrm{e}\mathrm{r}\mathrm{e}\mathrm{n}\mathrm{c}\mathrm{e}\mathrm{ }\mathrm{T}\mathrm{e}\mathrm{e}\mathrm{t}\mathrm{h}\mathrm{ }\mathrm{i}\mathrm{n}\mathrm{ }\mathrm{I}\mathrm{m}\mathrm{p}\mathrm{r}\mathrm{e}\mathrm{s}\mathrm{s}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}}{\mathrm{L}\mathrm{e}\mathrm{n}\mathrm{g}\mathrm{t}\mathrm{h}\mathrm{ }\mathrm{o}\mathrm{f}\mathrm{ }\mathrm{t}\mathrm{h}\mathrm{e}\mathrm{ }\mathrm{I}\mathrm{n}\mathrm{c}\mathrm{i}\mathrm{s}\mathrm{a}\mathrm{l}\mathrm{ }\mathrm{E}\mathrm{d}\mathrm{g}\mathrm{e}\mathrm{ }\mathrm{o}\mathrm{f}\mathrm{ }\mathrm{R}\mathrm{e}\mathrm{f}\mathrm{e}\mathrm{r}\mathrm{e}\mathrm{n}\mathrm{c}\mathrm{e}\mathrm{ }\mathrm{T}\mathrm{e}\mathrm{e}\mathrm{t}\mathrm{h}\mathrm{ }\mathrm{o}\mathrm{n}\mathrm{ }\mathrm{t}\mathrm{h}\mathrm{e}\mathrm{ }\mathrm{C}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{i}\mathrm{c}\mathrm{a}\mathrm{l}\mathrm{ }\mathrm{P}\mathrm{h}\mathrm{o}\mathrm{t}\mathrm{o}} \times \mathrm{R}\mathrm{e}\mathrm{c}\mathrm{e}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{ }\mathrm{D}\mathrm{e}\mathrm{p}\mathrm{t}\mathrm{h}\mathrm{ }\mathrm{o}\mathrm{n}\mathrm{ }\mathrm{t}\mathrm{h}\mathrm{e}\mathrm{ }\mathrm{C}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{i}\mathrm{c}\mathrm{a}\mathrm{l}\mathrm{ }\mathrm{P}\mathrm{h}\mathrm{o}\mathrm{t}\mathrm{o}$$

$$Root Coverage =\mathrm{ }\frac{(\mathrm{P}\mathrm{r}\mathrm{e}\mathrm{o}\mathrm{p}\mathrm{e}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{v}\mathrm{e}\mathrm{ }\mathrm{R}\mathrm{e}\mathrm{c}\mathrm{e}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{ }\mathrm{D}\mathrm{e}\mathrm{p}\mathrm{t}\mathrm{h} - \mathrm{P}\mathrm{o}\mathrm{s}\mathrm{t}\mathrm{o}\mathrm{p}\mathrm{e}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{v}\mathrm{e}\mathrm{ }\mathrm{R}\mathrm{e}\mathrm{c}\mathrm{e}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{ }\mathrm{D}\mathrm{e}\mathrm{p}\mathrm{t}\mathrm{h})}{\left(\mathrm{P}\mathrm{r}\mathrm{e}\mathrm{o}\mathrm{p}\mathrm{e}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{v}\mathrm{e}\mathrm{ }\mathrm{R}\mathrm{e}\mathrm{c}\mathrm{e}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{ }\mathrm{D}\mathrm{e}\mathrm{p}\mathrm{t}\mathrm{h}\right)} \times 100 \left(\%\right)$$

Statistical analysis

All parameters were reported as mean ± standard deviation or percentage. Statistical analyses were conducted using IBM SPSS Statistics 21 (IBM Corp., Armonk, NY, USA). RC and CRC were calculated as percentages.

RESULTS

Demographic data of the study population

The analysis included a total of 66 RC sites across 39 patients (Supplementary Table 1). Table 1 presents the distribution of the study population and the details of the target teeth. The average age of the patients was 30.2 years, with women comprising 36 of the 39 patients. The RC types were nearly evenly distributed, with 18 cases of single RC and 21 of multiple RC. Regarding the Miller classification, the cases included 14 of class I, 9 of class II, and 16 of class III. The duration of patient follow-up ranged from 6 to 80 months, with a mean follow-up duration of 41.3 months (Table 1). At T₀, the average RD was 2.60±1.54 mm. The overall mean RC rate achieved was 86.2%±15.7%.

Table 1. Demographic information.

Variables			Values
Patient-based assessments (n=39)
	Age (yr)		30.2±7.04
	Sex
		Male	3 (7.7)
		Female	36 (92.3)
	Recession type (single/multiple)
		Single	18 (46.2)
		Multiple	21 (53.8)
	Miller classification
		Class I	14 (35.9)
		Class II	9 (23.1)
		Class III	16 (41.0)
	Follow-up period (mo)		41.3±19.1
Tooth-based assessments (n=66)
	Recession depth (mm)		2.60±1.54
	Root coverage rate (%)		86.2±15.7

Age, follow-up period, root coverage rate, and recession depth are recorded as the mean ± standard deviation. Data shown are number (%) not otherwise specified.

RC results for the recipient site

Table 2 presents the percentage of RC based on the type of recession (single vs. multiple). In cases of single recession (n=18), RC was achieved at rates of 85.2%±25.6%, 91.5%±10.4%, and 79.2%±18.3% for Miller classes I, II, and III, respectively. In cases of multiple recessions (n=48), the RC rates were 85.1%±16.2% for class I, 87.0%±12.5% for class II, and 89.8%±16.0% for class III. CRC was achieved in 39.1% of Miller class I cases, 40.0% of class II cases, and 60.0% of class III cases. Table 3 presents the RD, RC, and CRC according to the Miller classification. The RC for GR defects classified as Miller class I (n=26) was 85.1%±16.8%; for class II defects (n=16), it was 88.7%±11.6%, and for class III (n=24), it was 85.8%±17.3%.

Table 2. Results of root coverage accomplished with the modified tunneling technique according to recession type.

Miller classification	Single recession (n=18)			Multiple recession (n=48)
	I (n=3)	II (n=6)	III (n=9)	I (n=23)	II (n=10)	III (n=15)
Follow-up period (mo)	50.7±29.0	38.3±18.6	47.8±13.1	32.0±18.3	33.4±20.4	48.5±16.0
Recession depth at T0 (mm)	1.97±0.942	4.04±1.79	3.42±1.99	1.71±0.752	3.35±1.58	2.5±1.37
Root coverage at T l (mm)	1.52±0.204	3.56±1.22	2.74±1.61	1.45±0.638	2.88±1.36	2.30±1.30
Root coverage rate at T l (%)	85.2±25.6	91.5±10.4	79.2±18.3	85.1±16.2	87.0±12.5	89.8±16.0
Complete root coverage at T l	2 (66.7)	3 (50.0)	2 (22.2)	9 (39.1)	4 (40.0)	9 (60.0)

Data are provided as mean ± standard deviation or number (%).

T₀: baseline, T _l : latest visit.

Table 3. Results of root coverage accomplished with the modified tunneling technique according to the Miller classification (I to III).

Miller classification	I (n=26)	II (n=16)	III (n=24)
Recession depth at T0 (mm)	1.74±0.759	3.61±1.64	2.85±1.65
Root coverage at T l (mm)	1.46±0.302	3.14±1.31	2.46±1.40
Root coverage rate at T l (%)	85.1±16.8	88.7±11.6	85.8±17.3
Complete root coverage at T l	11 (42.3)	7 (43.8)	11 (45.8)

Data are provided as mean ± standard deviation or number (%).

T₀: baseline, T _l : latest visit.

As shown in Table 4, the RC varied over time. At 12 months (n=10), the RC was 72.5%±15.1%. This value increased to 90.1%±12.6% for the 25–36-month period (n=11). During the 37–48-month period (n=14), the RC was slightly lower, at 89.0%±16.7%. For the 49–60-month period (n=12), RC reached 91.10%±9.88%. For patients with a follow-up period longer than 61 months (n=9), RC was 97.6%±4.79%, with 77.8% achieving CRC. Overall, we noted an increasing trend in coverage over the 5 years examined. Table 5 presents the RC and CRC based on the RD. Among the 66 target teeth, the RD was categorized as 1–3 mm in 45 teeth, 3–6 mm in 17, and >6 mm in 4. The RC for teeth with an RD of 1–3 mm was 88.0%±16.8%, for depths of 3–6 mm it was 83.1%±14.1%, and for depths greater than 6 mm it was 80.2%±5.04%.

Table 4. Results of root coverage accomplished with the modified tunneling technique according to follow-up period.

Follow-up period	Up to 12 mo (n=10)	13–24 mo (n=10)	25–36 mo (n=11)	37–48 mo (n=14)	49–60 mo (n=12)	>61 mo (n=9)
Recession depth at T0 (mm)	2.95±2.07	1.83±1.07	2.72±1.72	3.15±1.21	2.90±1.68	1.65±0.802
Root coverage at T l (mm)	2.21±1.61	1.37±0.772	2.34±1.31	2.90±1.27	2.57±1.35	1.59±0.738
Root coverage rate at T l (%)	72.5±15.1	75.6±17.9	90.1±12.6	89.0±16.7	91.1±9.88	97.6±4.79
Complete root coverage at T l	-	2 (20.0)	6 (54.5)	8 (57.1)	6 (50.0)	7 (77.8)

All data are provided as mean ± standard deviation or number (%).

T₀: baseline, T _l : latest visit.

Table 5. Results of root coverage accomplished with the modified tunneling technique according to recession depth.

Recession depth	<3 mm (n=45)	3–6 mm (n=17)	≥6 mm (n=4)
Recession depth at T0 (mm)	1.77±0.775	3.87±0.720	6.51±0.366
Root coverage at T l (mm)	1.59±0.749	3.23±0.926	5.21±0.345
Root coverage rate at T l (%)	88.0±16.8	83.1±14.1	80.2±5.04
Complete root coverage at T l	24 (53.3)	5 (29.4)	-

Data are provided as mean ± standard deviation or number (%).

T₀: baseline, T _l : latest visit.

DISCUSSION

Building on our previous research, the present study aimed to assess the long-term clinical effectiveness of a modified tunneling technique with SCTG for RC in lower anterior GR [11]. Compared to the previous data, the number of patients increased from 27 to 39, and the average follow-up period was extended from 14.5 to 41.3 months. Over a follow-up period exceeding 5 years, an RC of approximately 98% was observed. Notably, Miller class III defects involving multiple recessions displayed RC values of up to 90%. These findings suggest that the modified tunneling technique may represent a promising treatment option for RC in lower anterior GR. In our earlier study, which involved 17 patients (27 teeth) and the same technique, a mean RC of 89.1%±11.7% was reported after an average follow-up duration of 14.5 months [11]. In the present study, the mean RC was 86.2%±15.7% with a mean follow-up period of 41.3 months. Compared to a previous systematic review, this result was slightly higher than the mean RC of the tunneling technique for localized GR (82.75%±19.7%) and slightly lower than that for multiple GRs (87.87%±16.45%) [14]. This difference likely stems from the inclusion of both localized and multiple GRs in the present study.

In a previous study evaluating the long-term results of RC with SCTG and the modified tunneling technique, the RC decreased over time [15]. However, the trend of RC increasing to 97% at 60 months is a noteworthy outcome, which can be attributed to the occurrence of creeping attachment over time. Prior research has demonstrated that creeping attachment does not diminish after 1 year and can persist for 10 to 27 years [16]. In the present investigation, the RC was 83.1% for sites with 3–6 mm RD, compared to 80.2% for sites with >6 mm RD; that is, sites with greater RD demonstrated substantially less RC. This finding may relate to the limitations of the tunneling technique. These challenges become more pronounced in challenging clinical situations involving isolated deep recession defects, where surgical access is restricted by minimal incisions and inadequate coronal advancement of the flap compared to CAF [5]. Reportedly, the tunneling technique may limit the mobility of the overlying flap, reducing CRC in single GR defects [17]. A connective tissue graft with a double pedicle graft for mandibular incisors has been shown to yield better clinical outcomes than the CAF technique [18]. Furthermore, a report indicated that the mean RC values of CAF combined with SCTG, the tunneling technique combined with CTG, and lateral sliding flap combined with SCTG were 77.2%, 82.3%, and 85.3%, respectively, in teeth with Miller class II or III recession [10].

The present study demonstrates that the modified tunneling technique is an effective treatment modality for gingival augmentation in cases of Miller class III recession. In these cases, only partial RC can be expected due to interproximal tissue loss or tooth displacement [19]. Thus, one may reasonably assume that Miller class III sites would benefit most from the described protocol, with an anticipated RC of up to 90%. For treatment of multiple Miller class III GRs, surgery using the tunneling technique in conjunction with SCTG resulted in 82% RC and 38% CRC at 12 months of follow-up [20], while using the tunneling technique and SCTG advanced to the coronal side resulted in 78% RC and 50% CRC at 12 months [21]. This suggests that the modified technique used in this study establishes a tunnel through a vertical incision on the buccal side of the recipient site and extends the periosteal dissection beyond the mucogingival junction. This provides the necessary mobility for coronal advancement of the graft while minimizing surgical trauma and papillary rupture [10]. Some studies have reported that in the aesthetic zone, this technique can minimize the risk of gingival margin height loss, maximize blood supply to the gingival margin and adjacent tissues, and stabilize the graft for optimal wound healing [8,22].

Recently, collagen matrix has been introduced as a potential alternative to SCTG to minimize patient discomfort. Notably, however, SCTG remains the gold standard for RC. While studies have indicated that collagen matrix may be less effective than SCTG in covering denuded roots [23,24,25,26], it can reduce the size of the graft needed and improve gingival thickness through biotype modification, yielding better long-term results [4,27,28]. Histomorphometric analysis has shown that a porcine collagen matrix can promote superior tissue regeneration and new periodontal attachments in surgically created recession in vivo [29,30]. Additionally, a previous study showed a positive correlation between flap thickness and mean RC following RC procedures [31]. Increasing the thickness of the covering tissue is also thought to contribute to long-term stability [32]. Therefore, collagen matrix offers the advantage of increasing tissue thickness in cases of limited graft thickness [33].

Pizzo et al. assessed the initial healing outcomes at palatal donor sites from which an SCTG was harvested. Among patients who received a free gingival graft, 50% achieved complete epithelialization at 3 weeks, and 100% reached this milestone by the 4-week mark [34]. In a separate study examining de-epithelialized gingival grafts, which are designed to facilitate integration with the graft, the de-epithelialized gingival graft recipients exhibited a greater increase in buccal soft tissue thickness compared to those who simply received connective tissue [35].

The present study has several limitations. First, the retrospective design of the research may have introduced bias. Second, the inclusion of both single and multiple GR results could have added variability to the findings. Third, the methodological approach employed does not consider the precise RD. Additionally, the use of millimeter calibration restricted our ability to detect small changes in gingival length and volume. Furthermore, the use of conventional impressions to measure post-treatment changes is highly dependent on the skill level of the operator. In future studies, intraoral scanning should be used to precisely measure the width of keratinized gingiva, papilla height, and other relevant parameters [36]. We also recommend that randomized controlled clinical trials be conducted to compare the outcomes of the modified tunneling technique with CAF, including assessments of patient discomfort. Despite these limitations, this long-term retrospective study suggests that the modified tunneling technique employing SCTGs is a promising method for RC in cases of lower anterior GR.

SUPPLEMENTARY MATERIAL

Supplementary Table 1

Study population and results of root coverage using the modified tunneling technique at T₀ and T _l