Flap Versus Tunneling for Horizontal Ridge Augmentation With FDBA and i‐PRF: A Randomized Controlled Clinical Trial

ABSTRACT

Aim

This study evaluated the efficacy of conventional flap and tunneling techniques for horizontal alveolar ridge augmentation using freeze‐dried bone allograft (FDBA) particles combined with injectable platelet‐rich fibrin (i‐PRF).

Materials and Methods

Forty‐five patients were randomly allocated to one of three groups (n = 15 each): conventional flap (CF), tunneling with membrane (TM), or tunneling without membrane (TnM). Preoperative ridge width was measured via cone beam computed tomography (CBCT). All augmentation procedures incorporated FDBA and i‐PRF; an absorbable collagen membrane was applied in the CF and TM groups. Follow‐up assessments, including CBCT imaging and histomorphometric analysis, were conducted 6 months postoperatively. For normally distributed data, ANOVA with Tukey's post hoc test and paired samples t‐test were applied. Non‐normally distributed data were analyzed using Kruskal‐Wallis, Mann–Whitney U, and Wilcoxon signed‐rank tests.

Results

Statistical analysis was performed on 43 patients. All groups demonstrated an increase in ridge width after 6 months. At the 2 mm level, the mean width gain was 1.28 mm (95% CI: 0.17 to 2.40) in the TM group, 2.85 mm (95% CI: 1.80 to 3.89) in the TnM group, and 1.95 mm (95% CI: 1.07 to 2.83) in the CF group. However, statistical analysis revealed no significant intergroup variation (p > 0.05). Histomorphometric assessments similarly demonstrated comparable outcomes across all groups, with no statistically significant differences observed (p > 0.05).

Conclusion

Within the limitations of this study, the tunneling technique, regardless of membrane use, appears to be a clinically viable alternative to the conventional flap method for horizontal alveolar ridge augmentation. However, further studies with longer follow‐up periods are required to substantiate these findings.

Trial Registration: irct.behdasht.gov.ir identifier: IRCT 20101204005305N21

1. Introduction

Dental implant therapy serves as an effective modality for replacing missing teeth [1]. However, patients with deficient alveolar bone height and width often encounter limitations in achieving optimal implant placement. In such scenarios, ridge augmentation procedures are critical to reconstruct sufficient bone volume, thereby enabling proper implant positioning and supporting both functional and esthetic outcomes of implant‐supported prostheses ([2, 3]).

A variety of augmentation techniques are employed depending on the anatomical location, extent, and morphology of the bone defect [4, 5]. Among these, guided bone regeneration (GBR) is a widely accepted and routinely utilized approach for horizontal ridge reconstruction [6], when the residual alveolar ridge width is at least 3 mm [7, 8]. Clinical studies have demonstrated that implant success rates in GBR‐treated sites are comparable to those achieved in pristine, non‐augmented bone [9].

The conventional GBR technique involves the elevation of a full‐thickness mucoperiosteal flap to expose the surgical site [10]. While effective, this approach may increase the risk of soft tissue dehiscence along incision lines. As an alternative for alveolar ridge augmentation, the tunneling technique has gained attention, particularly for treating two‐walled defects in C‐shaped ridge morphologies [11]. Advantages of this minimally invasive method include improved wound healing, enhanced vascularization, and favorable esthetic outcomes [12]. Notably, preservation of the periosteum is beneficial, as it serves as a reservoir for stem and progenitor cells critical to tissue engineering and regeneration [13, 14, 15]. Despite these benefits, the tunneling approach presents technical challenges, including potential membrane instability and graft particle displacement [16, 17]. To address these limitations, the use of biomaterials without membrane coverage has been proposed as a viable strategy [18, 19].

Multiple grafting materials have been used for alveolar ridge augmentation. To avoid complications commonly associated with autogenous bone harvesting, alternative substitutes such as allografts have been successfully applied to small‐ and medium‐sized defects [20]. Allogeneic grafts offer several clinical advantages, including immediate availability, reduced donor site morbidity, and minimal immunogenicity [21]. However, their lack of intrinsic osteogenic properties often results in comparatively reduced regenerative outcomes compared to autologous grafts [22]. Advancements in biotechnology have introduced biologically active agents, such as platelet concentrates, to improve graft performance [23]. Platelet‐rich fibrin (PRF) has demonstrated efficacy in enhancing soft tissue healing, reducing postoperative discomfort, and accelerating epithelial regeneration [24, 25]. Successful outcomes have also been reported with PRF in managing periodontal intrabony defects and peri‐implant osseous deficiencies [26].

Due to the scarcity of comparative studies evaluating the conventional flap (CF) and tunneling approaches, further clinical investigation is warranted. This randomized controlled trial was conducted to assess the radiographic and histological outcomes of horizontal alveolar ridge augmentation using freeze‐dried cortico‐cancellous bone allograft (FDBA) particles combined with injectable platelet‐rich fibrin (i‐PRF), implemented via CF and tunneling techniques.

2. Materials and Methods

This study was designed as a randomized controlled clinical trial with blinded outcome assessment, conducted in accordance with the Consolidated Standards of Reporting Trials (CONSORT) guideline.

The study conformed to the ethical standards set forth in the Declaration of Helsinki for research involving human participants. All clinical procedures were carried out at the Department of Periodontics, Kerman University of Medical Sciences (KMU), Kerman, Iran. Ethical approval was obtained from the KMU Institutional Review Board (IR.KMU.REC.1403.207), and the trial was registered with the Iranian Registry of Clinical Trials (IRCT 20101204005305N21). Participant recruitment commenced on September 2, 2024, following the acquisition of written informed consent from all individuals prior to their enrollment.

Participants were eligible for enrollment if they met the following conditions: (i) Male or female individuals aged ≥ 18 years; (ii) No medical contraindications to dental implant placement; (iii) Presence of horizontal alveolar ridge deficiency in the partially edentulous posterior maxilla or mandible, with at least two missing teeth; (iv) Alveolar ridge width between 2 and 4 mm; (v) Demonstrated good oral hygiene (O'Leary plaque index < 20%).

Subjects were excluded based on the following criteria: (i) Presence of systemic conditions such as uncontrolled diabetes mellitus, osteoporosis, or immunodeficiency disorders; (ii) Use of medications known to interfere with osseointegration, including corticosteroids and bisphosphonates; (iii) History of chemotherapy or radiotherapy; (iv) Pregnancy or lactation; (v) Heavy smoking habits, defined as consumption of > 10 cigarettes per day.

The sample size was calculated using G Power 3.1 software for a repeated measures analysis of variance (ANOVA), assuming three groups and four measurement levels per subject. A medium effect size of f = 0.4 (based on Cohen's conventions), a significance level of α = 0.05, and a statistical power of 80% were used as parameters. The analysis indicated that 12 participants per group were required to detect statistically significant intergroup differences. To account for an anticipated dropout rate of 20%, the final sample size was increased to 15 participants per group (Figure 1).

FIGURE 1.

CONSORT flow diagram showing enrolment, allocation, and follow‐up process.

Participants were randomly allocated to the treatment groups using block randomization to ensure balanced distribution of sites across groups. Allocation to the intervention groups was determined using sealed opaque envelopes, which were opened following administration of local anesthesia to maintain allocation concealment and minimize selection bias. One investigator (M.S.S), who did not participate in the treatment processes, supervised the overall study process. Both the patients and the outcome assessor (N.L., M.H., M.K.) were blinded to group assignments to minimize bias. Patients and outcome assessors were blinded to group allocation, whereas the operator could not be blinded due to the nature of the surgical procedures.

The authors categorized ridge morphology based on the buccal bone profile into the following types:

• C‐shape: Characterized by a concave contour of the buccal bone.

• Oblique: Defined by an angular relationship between the straight (non‐concave) buccal bone and the horizontal plane. Presents a broad‐based ridge with a triangular configuration in cross‐sectional view.

• Parallel: The buccal bone plate runs parallel to the lingual plate, and the buccolingual dimension at the ridge base is approximately equal to that at the crestal level.

2.1. Preoperative Protocol

All patients received prophylactic medication consisting of 1 g amoxicillin and 800 mg ibuprofen administered 1 h prior to surgery. To prepare i‐PRF, venous blood was drawn from the cephalic vein into sterile tubes and centrifuged immediately at room temperature using a protocol of 700 rpm for 3 min, corresponding to a relative centrifugation force (RCF) of 450 g (DUO, France). Additionally, patients rinsed with 0.2% chlorhexidine mouthwash for 1 min prior to anesthesia. Local anesthesia was achieved via infiltration of 2% lidocaine with 1:80000 epinephrine (Darou Pakhsh, Tehran, Iran).

2.2. Surgical Procedures

2.2.1. All Surgical Procedures Were Performed by One Experienced Periodontist

2.2.1.1. CF Group

A crestal incision was made at the edentulous site using a #15 scalpel blade, accompanied by two vertical releasing incisions placed mesially and distally, approximately one to two teeth away from the surgical site. A full‐thickness mucoperiosteal flap was elevated using a periosteal elevator, and alveolar ridge decortication was performed with a round surgical bur. A resorbable collagen membrane (TUTOPATCH, Germany) was secured using tacks, and FDBA (1000–2000 μm, Tissue Regeneration Corporation, Kish, Iran), rehydrated with sterile serum and i‐PRF, was placed beneath the membrane (Figure 2a). To enhance stability, the membrane was additionally secured using tacks positioned along the lingual/palatal aspect. Soft tissue closure was achieved using a combination of horizontal mattress, interrupted, and criss‐cross sutures (5–0 Supalon nylon suture, Supa Medical Devices, Tehran, Iran) (Figure 2b).

FIGURE 2.

Clinical steps of horizontal ridge augmentation. (a) Placement of FDBA combined with i‐PRF, (b) conventional flap closure, (c) tunneling technique with membrane placement, and (d) tunneling technique without membrane application.

2.2.1.2. Tunneling With Membrane (TM) Group

A vertical releasing incision was made at the mesial line angle of the tooth adjacent to the intended augmentation site. A subperiosteal tunnel was created by detaching the periosteum from the bone using a periosteal elevator. Ridge decortication was performed with a surgical bur. A resorbable collagen membrane (Accelullar Dermis Membrane, Iranian Tissue Products Co., Iran) was placed within the tunnel, followed by grafting with FDBA prepared similarly to the CF group. In the posterior mandible, graft placement was directed distally and coronally to minimize the risk of mental nerve injury. Primary closure was achieved using interrupted sutures (5–0 Supalon nylon suture, Supa Medical Devices, Tehran, Iran) (Figure 2c).

2.2.1.3. Tunneling Without Membrane (TnM) Group

This procedure mirrored the tunneling technique described above, with the exception that no membrane was placed and decortication was omitted (Figure 2d).

Following surgery, patients were instructed to rinse with 0.2% chlorhexidine mouthwash twice daily. Antibiotic regimen consisted of 500 mg amoxicillin administered three times daily for 7 days. For pain management, 400 mg ibuprofen was prescribed every 6 h as needed. Patients were advised to avoid brushing the surgical site and to consume soft foods for the first 2 weeks postoperatively. Sutures were removed 15 days after surgery.

2.3. Post‐Surgical Evaluations

2.3.1. Radiographic Assessment

Alveolar ridge width was evaluated using three‐dimensional cone beam computed tomography (CBCT). All CBCT images were acquired using a Planmeca unit (Classic, Helsinki, Finland) with a field of view of 8 × 8 cm, 90 kV, 13 mA, and a voxel size of 75 μm. All measurements were taken 6 mm distal to the posterior tooth adjacent to the edentulous site. Measurements were recorded at 0, 2, 4, and 6 mm apical to the alveolar crest, which was defined as the reference point. Horizontal and vertical changes in ridge dimensions were assessed using stable anatomical landmarks, including the inferior border of the mandible and the nasal floor, with adjacent teeth serving as reference points for alignment. Preoperative and postoperative CBCT scans were superimposed, and measurements were performed by two blinded clinicians (N.L. and M.H.).

2.3.2. Histologic and Histomorphometric Evaluation

In all groups, dental implants were inserted 6 months following the augmentation procedure (Figure 3). During implant placement, bone biopsies were obtained using a 2 mm trephine drill. Samples were harvested either from the buccal third of the alveolar ridge along its longitudinal axis or from the inter‐implant region.

FIGURE 3.

Clinical views of the augmented ridge at the time of implant placement in the (a) conventional flap, (b) tunneling technique with membrane, and (c) tunneling technique without membrane groups.

Biopsy specimens were fixed in 10% buffered formalin and decalcified using 13% nitric acid. Tissues were processed over 16 h and embedded in molten paraffin using L‐shaped aluminum molds. Longitudinal sections were obtained via microtome, deparaffinized, and stained with hematoxylin and eosin. Microscopic evaluation was conducted using a YX‐100 light microscope (Olympus Optical Co. Ltd., Tokyo, Japan) to assess new bone formation, residual graft material, foreign body reactions, and inflammatory responses (acute, chronic, or granulomatous).

In addition, digital images of stained sections were captured using a Nikon i50 camera (Japan). Quantitative analysis of mineralized and non‐mineralized tissue, as well as residual graft particles, was performed using ImageJ software (National Institutes of Health, USA; http://imagej.nih.gov/ij/). Results were expressed as percentages of newly formed bone, residual graft material, and non‐mineralized tissue relative to the total biopsy area.

Newly formed bone was distinguished from pristine bone based on the following histological criteria:

• Lack of organized lamellar structure

• Increased cellularity and neovascularization

• Abundant osteocytes

• Enhanced hematoxylin staining intensity relative to eosin.

Histomorphometric analysis was conducted at 40× and 100× magnifications, with all samples standardized for length, width, and pixel resolution. Evaluations were performed by an experienced oral pathologist (M.K.) blinded to group allocation.

2.4. Statistical Analysis

Statistical analyses were performed using per‐protocol analysis with SPSS software (version 27.0; SPSS Inc., IL, USA). Data normality was assessed using the Shapiro–Wilk test. For normally distributed data, ANOVA with Tukey's post hoc test and paired samples t‐test were applied. Non‐normally distributed data were analyzed using Kruskal‐Wallis, Mann–Whitney U, and Wilcoxon signed‐rank tests.

The Friedman test was used to evaluate changes in horizontal ridge dimensions across different measurement levels. Fisher's exact test was employed to compare categorical variables, such as ridge morphology, across groups. Spearman's rank correlation was used to assess relationships between ridge width gain and two baseline parameters: the ridge base width and the ratio of ridge base width to crest width. The Mann–Whitney U test was used to examine associations between ridge form and ridge width increase. A p‐value < 0.05 was considered statistically significant.

3. Results

Two participants from the TM group were excluded from the final analysis due to non‐attendance at follow‐up sessions. One patient was lost to follow‐up due to relocation, and another was unresponsive to repeated telephone contact attempts. Consequently, the study included 43 patients (11 males and 32 females) in the final evaluation. Inter‐examiner reliability for horizontal bone width measurements obtained from CBCT scans using the Intraclass Correlation Coefficient (ICC) demonstrated a high level of agreement (r = 0.89).

In the CF group, three patients experienced minor wound dehiscence, all of which resolved spontaneously with chlorhexidine application. One patient in the same group developed a localized infection at the distal aspect of the wound, which was successfully treated through drainage and administration of amoxicillin and metronidazole. No wound dehiscence was observed in either tunneling group, and no cases of paresthesia were reported across any study groups. One patient in the CF group and another in the TM group required additional GBR at the time of implant placement. Overall, no major complications were observed, and all events were managed successfully. Baseline characteristics of these individuals are summarized in Table 1. No statistically significant differences were observed between the treatment groups, with the exception of horizontal ridge width at 6 mm level, which was significantly greater in the TnM group compared with the CF group (p = 0.02).

TABLE 1.

Characteristics of the included participants.

Variable	Group			p
	Tunneling with membrane	Tunneling without membrane	Conventional flap
	N (%)	N (%)	N (%)
Sex
Male	5 (38.5)	5 (33.3)	1 (6.7)	0.12 a
Female	8 (61.5)	10 (66.7)	14 (93.3)
Jaw
Mandible	13 (100.0)	14 (93.3)	13 (86.7)	0.76 a
Maxilla	0 (0.0)	1 (6.7)	2 (13.3)
Ridge form
Oblique	7 (53.8)	11 (73.3)	12 (80.0)	0.35 a
C shape	6 (46.2)	4 (26.7)	3 (20.0)
Age (year)	Mean (SD)	Mean (SD)	Mean (SD)
	49.31 (10.51)	47.73 (10.05)	50.33 (9.77)	0.78 b
Ridge base (mm)	7.81 (1.90)	8.68 (1.63)	8.14 (2.41)	0.51 b
Base/crest ratio	3.34 (1.23)	4.92 (2.60)	3.66 (2.17)	0.12 b
Dimension (distance from crest)	Mean (SD) Mean rank	Mean (SD) Mean rank	Mean (SD) Mean rank
Horizontal (0 mm)	2.53 (0.66) 24.12	2.15 (0.91) 19.40	2.49 (0.62) 22.77	0.59 c
Horizontal (2 mm)	4.18 (0.89)	4.14 (0.86)	3.83 (0.74)	0.47 b
Horizontal (4 mm)	5.77 (1.38) 22.88	5.91 (1.35) 25.60	5.25 (1.09) 17.63	0.21 c
Horizontal (6 mm)	7.05 (1.77) 22.12	7.48 (1.87) 27.20	6.28 (1.70) 16.70	1&2 = 0.28 d 1&3 = 0.25 2&3 = 0.02

Abbreviation: N, number.

^a Fisher's exact test.

^b ANOVA.

^c Kruskal‐Wallis test.

^d Mann–Whitney U test.

Table 2 presents post‐operative measurements of ridge width and height at different levels. No statistically significant intergroup differences were detected. All treatment groups demonstrated a statistically significant increase in ridge width post‐operatively at 2, 4, and 6 mm levels, whereas changes at the crestal level were not statistically significant (Table 3). No significant differences in ridge width gain were also found among the groups (Figure 4).

TABLE 2.

Post‐operative horizontal and vertical ridge dimensions.

Dimension (mm) (distance from crest)	Group			p value
	Tunneling with membrane	Tunneling without membrane	Conventional flap
	Mean (SD) Mean rank	Mean (SD) Mean rank	Mean (SD) Mean rank
Horizontal (0 mm)	2.72 (2.16)	2.95 (1.84)	2.74 (1.70)	0.94 a
Horizontal (2 mm)	5.46 (1.97)	6.99 (2.15) 26.47	5.78 (1.69) 19.03	0.10 a
Horizontal (4 mm)	7.77 (1.76)	8.57 (2.21)	7.73 (1.49)	0.39 a
Horizontal (6 mm)	9.02 (1.60)	9.77 (1.71)	8.46 (1.40)	1&2 = 0.43 b 1&3 = 0.62 2&3 = 0.07
Vertical	−0.59 (0.84)	0.01 (0.83)	−0.41 (0.63)	0.13 a

^a ANOVA.

^b Tukey's post hoc test.

TABLE 3.

Increase in horizontal dimension six‐month postoperatively.

Distance from the crest	Tunneling with membrane			Tunneling without membrane			Conventional flap
	M diff (SD) mm a	Z b	p value b	M diff (SD) mm a	Z b	p value b	M diff (SD) mm a	Z b	p value b
0 mm	0.19 (2.17)	−0.25	0.81	0.79 (2.01)	−1.59	0.11	0.24 (1.75)	−0.54	0.59
2 mm	1.28 (1.84)	−1.92	0.05	2.85 (1.89)	−3.35	0.001	1.95 (1.59)	−3.12	0.002
4 mm	2.00 (1.8)	−2.76	0.006	2.67 (1.7)	−3.24	0.001	2.48 (1.45)	−3.41	0.001
6 mm	1.97 (1.83)	−2.94	0.003	2.29 (1.28)	−3.35	0.001	2.18 (1.46)	−3.3	0.001

^a Mean difference.

^b Wilcoxon signed‐ranks test.

FIGURE 4.

Mean increase in horizontal dimensions in different treatment groups. CF, conventional Flap; TM, tunneling with membrane; TnM, tunneling without membrane The wrong filefore figure 4 was in advertently uploaded during the submission process. we apologize fore oversight. please replace currect figure 4 with the correct figure 4 file attched.

In TnM groups, ridge width increase at 2 mm level was positively correlated with the base‐to‐crest width ratio (p = 0.02). A similar correlation was also noted at 4 mm level in the TnM group (p = 0.02). Within the TM group, ridge morphology influenced outcomes: at 6 mm level, C‐shaped ridges exhibited significantly greater width gain compared to oblique ridges (p = 0.02). A similar trend was observed at the crestal level in the TnM group, though it did not reach statistical significance (p = 0.09). Although tunneling is commonly indicated for C‐shaped ridges in previous studies, different ridge morphologies were considered in this study. Three ridge types defined based on buccal bone plate, only the patients with C‐shaped and oblique forms were observed and included in the analysis. The ridge base width did not significantly affect width gain at any measured level or within any group (Table 4).

TABLE 4.

Increase in horizontal ridge width relative to baseline anatomic characteristics.

			Distance from crest
			0 mm	2 mm	4 mm	6 mm
Tunneling with membrane	Ridge base	Spearman's rho	0.27	0.30	0.02	−0.44
		p‐value a	0.38	0.32	0.95	0.14
	Base/crest ratio	Spearman's rho	0.30	0.44	−0.13	−0.48
		p‐value a	0.33	0.13	0.68	0.10
	Ridge form	Mean (SD) Oblique ridge	0.87 (2.24)	1.38 (2.05)	1.61 (1.84)	1.02 (1.29)
		Mean (SD) C shape ridge	−0.60 (1.96)	1.38 (2.05)	2.46 (1.80)	3.07 (1.81)
		p‐value b	0.25	0.67	0.48	0.02
Tunneling without membrane	Ridge base	Spearman's rho	0.19	0.18	0.12	0.03
		p‐value a	0.51	0.52	0.68	0.91
	Base/crest ratio	Spearman's rho	0.35	0.60	0.61	0.21
		p‐value a	0.20	0.02	0.02	0.44
	Ridge form	Mean (SD) Oblique ridge	1.31 (1.92)	3.34 (1.78)	2.91 (1.72)	2.38 (1.41)
		Mean (SD) C‐shape ridge	−0.64 (1.72)	1.48 (1.70)	1.99 (1.67)	2.05 (0.94)
		p‐value b	0.09	0.13	0.36	0.60
Conventional flap	Ridge base	Spearman's rho	−0.30	−0.34	−0.32	−0.22
		p‐value a	0.27	0.21	0.25	0.44
	Base/crest ratio	Spearman's rho	−0.08	−0.24	−0.40	−0.38
		p‐value a	0.79	0.40	0.14	0.16
	Ridge form	Mean (SD) Oblique ridge	0.13 (1.79)	1.99 (1.65)	2.38 (1.46)	1.91 (1.23)
		Mean (SD) C‐shape ridge	0.70 (1.88)	1.78 (1.63)	2.90 (1.67)	3.27 (2.13)
		p‐value b	0.67	0.77	0.94	0.19

^a Spearman's Correlation Coefficient.

^b Mann–Whitney U test.

Histopathological analysis revealed no signs of acute, chronic, or granulomatous inflammation. Histomorphometric assessment showed no significant differences among the groups in terms of residual graft material or non‐mineralized tissue (Figures 5 and 6). Histomorphometric analysis in the present study also revealed comparable levels of new bone formation across all groups, with mean values of approximately 50%–51% and no statistically significant intergroup differences (p > 0.05)(Table 5).

FIGURE 5.

Representative histological sections of the study groups (100× magnification). (a) conventional flap, (b) tunneling technique with membrane, and (c) tunneling technique without membrane. The white star indicates newly formed bone, and the white arrow indicates connective.

FIGURE 6.

Histomorphometric analysis showing percentages of newly formed bone (a), residual graft material (b), and non‐mineralized tissue (c) across the study groups.

TABLE 5.

Histomorphometric findings six‐month postoperatively.

Histomorphometry	Group			p
	Tunneling with membrane	Tunneling without membrane	Conventional flap
	%Mean (SD)% Mean rank	%Mean (SD)% Mean rank	Mean (SD)% Mean rank
New bone formation	51.13 (9.01)	50.00 (9.64)	50.93 (3.98)	0.95 a
Residual graft material	12.62 (3.96) 12.56	13.35 (5.71) 13.36	14.87 (5.86) 16.86	0.53 b
Non‐mineralized tissue	34.60 (6.04) 12.78	36.66 (5.71) 15.82	35.35 (6.76) 12.71	0.61 b

^a ANOVA.

^b Kruskal‐Wallis test.

4. Discussion

Vertical and horizontal alveolar ridge augmentation are frequently required in implant dentistry to achieve adequate bone volume, given that ridge resorption may impede optimal implant placement. Various grafting approaches and materials have been employed to reconstruct deficient bone structures (H. S. [27]). This study aimed to assess radiographic and histological outcomes following horizontal ridge augmentation using cortico‐cancellous FDBA combined with i‐PRF, applied via flap and tunneling techniques.

All treatment modalities resulted in increased ridge width after 6 months, with the most substantial gains at 4 mm and 6 mm levels. The TM group exhibited the smallest increase at 2 mm, and the CF group showed comparatively lower gains at 4 mm and 6 mm levels than the tunneling approaches. Nevertheless, intergroup differences at all measured levels did not reach statistical significance.

At the 2‐mm level, mean increases were 1.28 mm (95% CI: 0.17–2.40) in the TM group, 2.85 mm.

(95% CI: 1.80–3.89) in the TnM group, and 1.95 mm(95% CI: 1.07–2.83) in the CF group (Table 3). By comparison, Ahmed et al. reported a net ridge width gain of 2.24 mm at the 3‐mm level after 4 months using the tunneling technique with mineralized plasmatic matrix (MPM) and without a membrane [28]. Although Ahmed's study involved a shorter follow‐up period, the current investigation demonstrated slightly greater gains, particularly in the tunneling groups. These findings suggest that tunneling, whether performed with or without a membrane, can achieve ridge width gain comparable to techniques employing space‐maintaining approaches.

Numerous studies have explored i‐PRF as a regenerative biomaterial due to its capacity to enhance cellular migration, proliferation, differentiation, and collagen synthesis. Additionally, i‐PRF exhibits notable antibacterial and anti‐inflammatory properties [29]. Furthermore, the use of “sticky bone”, a composite of bone graft material and autologous fibrin, has demonstrated significant clinical and radiographic benefits in multiple oral surgical interventions, particularly in alveolar ridge augmentation [30]. The subperiosteal tunneling technique offers a minimally invasive alternative that maintains periosteal integrity, thereby reducing postoperative pain, swelling, and complications. However, it carries a risk of graft particle dispersion, which may negatively impact the predictability of bone regeneration outcomes [31]. In this study, FDBA was combined with i‐PRF to enhance graft stability within the tunneling site, as particulate grafts alone often lack cohesion and may migrate apically, thereby compromising regenerative outcomes. The incorporation of i‐PRF supplied a fibrin matrix that improved graft integrity and handling, ultimately contributing to more favorable clinical results. The outcomes of the present study are in agreement with previous investigations assessing the role of platelet‐derived bioactive materials in ridge augmentation. Zahedi et al. reported a mean horizontal ridge width gain of 3.17 mm at the 2‐mm level when FDBA was combined with i‐PRF [32]. Likewise, Eskan et al. documented an average gain of approximately 2.9 mm at the crestal level using platelet‐rich plasma (PRP) in conjunction with a resorbable membrane during GBR [33]. Collectively, these findings reinforce the biological consistency of platelet‐derived growth factors in stimulating bone formation and enhancing the regenerative potential of grafting materials.

The outcomes observed in the tunneling group of the present study are consistent with previous research comparing tunnel and flap techniques using a combination of FDBA, particulate bovine graft, and a titanium‐reinforced non‐resorbable membrane. That study reported comparable clinical results between both surgical approaches. The investigators concluded that the tunneling technique was associated with reduced wound dehiscence and membrane exposure, a shorter course of postoperative antibiotics, and fewer follow‐up appointments [34]. According to a recent systematic review, the tunneling approach may offer several advantages for bone augmentation procedures irrespective of the grafting material used. The variability in reported outcomes across studies is likely due to differences in study design, patient demographics, defect morphology, surgical protocols, and follow‐up durations [35]. Consequently, additional high‐quality randomized controlled trials are required to establish clear clinical guidelines.

An additional finding from the present study was that, aside from the 2 mm level, the TnM group demonstrated greater ridge width gains at the 4 and 6 mm levels compared with other treatment groups. To the authors' knowledge, no prior research has directly compared the efficacy of tunneling techniques (with and without membrane) to the flap approach for horizontal ridge augmentation using FDBA combined with i‐PRF. A pilot clinical study demonstrated that vertical ridge augmentation using a tunnel pouch technique and deproteinized bovine bone mixed with autologous blood, without membrane coverage, resulted in stable outcomes maintained over a four‐year period [36]. Animal studies also suggest that while collagen membranes may accelerate early bone remodeling, they do not significantly enhance the amount of new bone formation [37]. Given the technical challenges of membrane placement in tunneling procedures due to limited access, both current and prior evidence indicate that membrane use may not provide substantial clinical advantages in this context.

Although collagen membranes are considered highly biocompatible, their placement in GBR procedures inevitably elicits an immune response, which may result in inflammation and compromise bone healing (Gou, Wang, Xie, & Song, 2024). Beyond these biological limitations, collagen membranes also present practical drawbacks: their application prolongs surgical time, increases cost, and demands greater operator skill, particularly when stabilization with tacks or pins is necessary. Because of these disadvantages of collagen membranes and benefits of preserved periosteum such as progenitor cells, we didn't use a membrane in the TnM group. On the other hand, when biologically active matrices such as sticky bone are employed, the necessity of an additional collagen membrane becomes debatable. The intrinsic fibrin matrix provided by i‐PRF offers natural stability, angiogenic support, and protection of the grafted site, potentially obviating the need for an external barrier. This approach may reduce the risk of membrane exposure and infection while preserving favorable regenerative outcomes [38].

Previous studies have identified alveolar ridge morphology and base width as critical determinants in two‐stage horizontal ridge augmentation protocols [39, 40, 41]. The present study further examined the relationship between base‐to‐crest width ratio and the extent of ridge width gain. In the TnM group, increases in ridge width at the 2 mm and 4 mm levels were positively correlated with higher base/crest ratios. However, base width alone did not significantly influence ridge width gain at any measured level or in any group. These findings suggest that preoperative evaluation of ridge configuration may aid in selecting the most appropriate augmentation technique. To the authors' knowledge, no comparative studies have yet addressed these anatomical variables across augmentation methods, underscoring the need for future research to clarify their clinical relevance.

In this study, ridge morphology was classified into three configurations: C‐shaped, oblique, and parallel. However, only cases with C‐shaped and oblique ridge forms met the inclusion criteria, and no parallel ridges were identified. The results indicated no statistically significant differences in bone gain between the C‐shaped and oblique forms across all treatment groups. Because no parallel cases were available, direct comparison with this configuration was not possible. Future investigations with larger sample sizes and inclusion of all ridge types are warranted to more comprehensively assess the influence of ridge morphology on the outcomes of bone augmentation procedures.

In a randomized clinical trial, Zahedi et al. reported a significant increase in newly formed bone, rising from 45% in the FDBA‐alone group to 51% in the FDBA + i‐PRF group, thereby confirming the positive influence of platelet‐derived growth factors on bone regeneration and maturation [32]. Similarly, Eskan et al. observed a higher proportion of vital bone (51%) in sites treated with PRP and allograft compared with 36% in the control group; however, this difference did not reach statistical significance [33]. Taken together, these findings suggest that the incorporation of platelet concentrates such as i‐PRF into allograft materials can enhance the quality and maturity of regenerated bone, even when overall bone volume remains comparable among different augmentation techniques.

One limitation of this study is the exclusive use of allograft particles, which may restrict the generalizability of the results to other grafting materials. The use of different collagen membranes between groups can be a confounding factor and is considered a limitation of this study. Additionally, the relatively small number of augmentation sites in the maxillary arch necessitates cautious interpretation. A further consideration is the comparatively low prevalence of C‐shaped ridge configurations in both the TnM and CF groups, which may have contributed to the observed differences in morphology‐related results when compared to the TM group. Further well‐designed studies are warranted to clarify the role of membrane application and cortical perforation in guided bone regeneration. Surgical time, analgesic use, and patient‐reported outcomes (PROMs) were not evaluated in the present study. Given the comparable radiographic and histological outcomes observed across groups, further studies with larger sample sizes and a longer follow‐up period are recommended to confirm these findings.

5. Conclusion

Within the limitations of this study, comparable radiographic and histological outcomes were observed among the conventional flap technique and tunneling approaches, regardless of membrane application. These findings suggest that the tunneling technique without membrane application may be a feasible option for horizontal ridge augmentation in appropriately selected clinical situations. However, the present results should be interpreted with caution, and no definitive conclusions regarding its superiority or equivalence can be drawn. Further well‐designed studies with larger sample sizes, longer follow‐up periods, and rigorous control of potential confounding factors are needed to confirm these findings and to evaluate the long‐term stability of the augmented ridge as well as the survival rates of implants placed in these sites.

Author Contributions

All authors made substantial contributions to the conception and design of the study. N.L. performed the randomization process and allocation concealment and did not participate in the treatment procedures. (N.L., M.H.) conducted the radiographic measurements and served as a blinded outcome assessor. M.K.K. carried out histomorphometric evaluations as an experienced oral pathologist and was blinded to group allocation. M.M., as the corresponding author and supervisor, oversaw the study design, supervised the methodological workflow, and provided guidance throughout data interpretation and manuscript preparation. All authors contributed to data interpretation, drafting of the manuscript, and critical revision for important intellectual content. All authors read and approved the final version of the manuscript and agree to be accountable for all aspects of the work, ensuring that any questions related to accuracy or integrity are appropriately investigated and resolved.

Funding

The study was supported by Kerman University of Medical Sciences, Kerman, Iran.

Ethics Statement

This study was approved by the Ethics Committee of Kerman University of Medical Sciences, Kerman, Iran (IR.KMU.REC.1403.207) and registered in the Iranian Registry of Clinical Trials (IRCT 20101204005305N21).

Consent

Written informed consent was obtained from all patients prior to their enrollment.

Patient recruitment started on September 2, 2024.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.