With the evolution of dental implantology, the design of the mucogingival flap has changed to render it more to be preservative and less traumatic.1 Changes in the flap design have been introduced through modifications of the surgical technique of implant placement (Fig. 1). Advanced technology has made implant placement more precise, less time consuming, and more conservative in terms of tissue distraction and patient morbidity.1,3 Over time, flapless (FL) dental surgery has become more common in the practice of dental implants. Many studies have investigated the aspects of the FL technique, from its convenience to the patient to crestal bone resorption and inflammation.4,5 However, full-thickness (FT) surgery is the necessary approach in many cases and conditions. A wide raised flap is required in many implant cases, and the choice of a hard or soft graft depends on clinician preference.6 In this study, we attempted to compare the 2 main flap designs used in implant dentistry. This comparison addressed the pros and cons of both flap techniques (Table 1). In addition, this study used simple classifications regarding flap preservation in the scope of tissue distraction (Table 2) and the limitations of these flap techniques (Table 3). Most of the previous studies have addressed the morbidity, crestal bone resorption, and convenience of the FL and FT methods (Table 4). This review attempts to address and differentiate outcomes from preclinical and clinical studies. In addition, it evaluates the possible histological and biological differences between the 2 procedures.
Materials and Methods
A MEDLINE search (PubMed) was conducted, and works published in the English language from 1970 until 2015 were included in the review (Fig. 2). The following search terms were used in different combinations: “flapless,” “full-thickness flap,” “crestal bone resorption,” “gingival blood circulation,” and “biological width.” Titles and abstracts were screened, and a full-text analysis was performed for relevant publications. A manual search was conducted for the following journals from 1978 until 2015: Clinical Implant Dentistry and Related Research; Clinical Oral Implants Research; International Journal of Oral & Maxillofacial Implants; Journal of Clinical Periodontology; Journal of Dental Research; Journal of Pediatric Surgery; International Journal of Periodontics and Restorative Dentistry; Journal of Periodontology; Journal of Cell Science; Journal of Oral Pathology; Cytokine; Australian Dental Journal; Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontics; Journal of Endodontics; British Journal of Oral and Maxillofacial Surgery; Bone; Journal of Oral and Maxillofacial Surgery; Endodontic Topics; and Journal of Prosthetic Dentistry.
Studies including the following designs, which directly compare the effects of FL to flap approach, were included.
- Randomized controlled clinical trials, controlled trials, and prospective and retrospective clinical studies
- In vitro studies
- Preclinical studies
- Flap design and principles
- Case reports or case series studies
- Studies in a language other than English or without an English-language abstract
The combinations of search terms resulted in a list of 112 titles (PubMed until 2015, manual searching in specified journals, and searching company websites). Following the screening of titles and abstracts by applying the defined inclusion and exclusion criteria, 50 potentially relevant publications were identified in which a full-text analysis was performed.
Fourteen reported articles and 1 book were not directly related to flap design but were reviewed to better understand the process of gingival tissue healing and gingival blood circulation. Five reported articles discussed the principles of oral surgery and flap design.
Crestal bone resorption
Studies1,13–21 showed that crestal bone resorption is less in FL technique but still it is not significant in comparison with FT.
Immediate loading is more applicable when the FL is used as it causes less morbidity to the patient and reduces the time of the surgery.22–25
The technique of FL provides dental papillae preservation and less gingival margin recession that improves the gingival tissue contour that is needed when the implant is placed in the esthetic zone.26–32
Guided implant placement
There is no significant difference between FL and FT in implant position and angulation when guided implant placement is used.3,28,33
There are no significant differences in the implant survival rate between FL and FT.16,21,33–35
Histological and Laboratory Studies
Crestal bone resorption
FL implant surgery improved the bone height around the implant in comparison with the FT technique.36,37
Longitudinal dimension of the biological width was higher for the FT than the FL technique.38–40
Flap tissue circulation during the healing period
We observed an obvious conflict in the results of the different studies regarding the vascular density in FL and FT techniques.26,41,42
Increase in the numbers of inflammatory cells in the FT compared with the FL technique during the postoperative 12 weeks was noticed. There was increased fibroblast migration in the FT compared with the FL technique, whereas the expression of reepithelialization-associated genes was reduced in the FT technique. There was significant increase in the vascular endothelial growth factor (VEGF) expression, periimplant crevicular fluid (PICF) volume, aspartate aminotransferase, and alkaline phosphatase activities in the PICF in the FT compared with the FL technique.21,26,36,41,43–48
Crestal bone resorption
FT flap can cause blood supply reduction to the adjacent bone, which may enhance bone resorption. Many literature reviews have been conducted to evaluate crestal bone resorption and complications with the FL and FT techniques.1,13–16 All these literatures have concluded that crestal bone resorption is not significant between 2 procedures over the long term.1,13–16 But a study conducted by Vlahović et al17 on pigs compared crestal bone resorption on radiographs. This study reported that after 4 weeks, the difference in crestal bone resorption between the FL and FT techniques was negligible but was significant after 3 months (FL technique with less bone resorption). Another clinical study18 claimed that FL is advantageous for preserving the crestal bone and mucosal health and that crestal bone resorption is reduced when the gingival tissue is thick (≥3 mm).
Becker et al19 placed 79 implants in 57 patients using the FL technique. Baseline radiographs (mean 0.7 mm, SD 0.5 mm) and follow-up radiographs were taken after 10 months (mean 0.8 mm, SD 0.5 mm). The changes in crestal bone levels were insignificant. The authors explained the insignificant bone loss by several factors that included minimal countersinking and the use of a FL procedure. The study by Becker et al lacked a direct comparison between the FL and FT techniques.
A study was performed by Ozan et al20 in which 12 patients were selected randomly. Intraoral radiographs of the implants were acquired immediately after implant placement and every 6 months thereafter. The marginal bone resorptions after 9 months were 0.5 ± 0.3 mm for the FL and 0.6 ± 0.3 mm for the FT techniques and were not significantly different (P = 0.38).
Jeong et al21 observed no significant difference between FT and FL in terms of the effects on bone healing around the implant as evaluated by radiograph between stage 1 and stage 2 surgeries.
Postoperative changes in the crestal bone level from the time of implant placement to the time of implant uncovering were assessed with conventional dental radiographs. The average bone losses were 0.26 ± 0.46 mm in the FT group and 0.20 ± 0.36 mm in the FL group, and this difference was not significant. This study reported that bone loss appeared to be greater in men than in women and greater in the mandible than the maxilla, but these differences were also nonsignificant.
The FL technique is more convenient for the immediate loading of multiple implant placements in the edentulous ridges because no flap is raised and no suturing is needed, which is not facing the difficulty of removing the prosthesis after issue reflection.22 FL can optimize the advantages of immediate loading because it causes less swelling and discomfort and because the patient can use the prosthesis immediately.23 Even when the implant is placed with FL, the principles of immediate loading should still be achieved and the FL procedure is preferred because of surgical convenience and reduced trauma to the soft tissue.22,24 In other words, FL does not provide advantages in terms of decreasing the healing period or enhancing early osseointegration for immediately placed implants. The use of the FL procedure with CAD/CAM for immediate implant loading can achieve a good implant survival rate, even after several years. Smoking may eventually compromise the efficacy of this treatment concept25
In terms of esthetics, more preservative procedures are typically recommended. One of the issues of implant placement in esthetic zones is the prevention of detachment of the interdental papillae because frequent detachment may cause loss of the periodontium and blood supply in the adjacent teeth. A study conducted by Lei et al26 with beagle dogs revealed that buccal gingival recession was less pronounced in the FL group than in the flap group after 4 and 8 weeks. Another study conducted by Oh et al27 in patients with single missing teeth in esthetic areas used the FL technique. This study concluded that FL surgery provides esthetic soft tissue results in terms of the marginal gingival level and papillary fullness. However, this study did not compare FT and FL or evaluate the gingival biotype or the implant site conditions before implant placement.
The FT flaps can still maintain the interdental papillae when a papillae-preserving flap is designed (Table 5). This type of FT is performed with 2 vertical buccal incisions that are joined into one crestal incision. FL procedures have advantages and drawbacks; despite preserving the tissue and blood supply, FL can cause dramatic esthetic disasters.28 The blind implant placement associated with the FL procedure might result in the placement of the implant in thin buccal bone or buccal bone dehiscence.28 Buccal bone dehiscence can cause gingival recession and implant or abutment exposure that leads to esthetic implant failure.29,30 In contrast, the FT is the flap of choice for compromised areas in the esthetic zone.31,32
Guided implant placement
Despite the use of computer-guided surgery to place the implant, there are still some complications that arise from the blind procedure of FL.28 Another study found that FL computer-guided implant placement can be performed without any risk of damage to the anatomical structure.33 This study examined only the FL procedure in terms of evaluating the rehabilitation of the edentulous arch following guided implant placement (Table 5). Edentulous patients have the advantage of being eligible for transmucosal computer-assisted placement and immediate loading of the mandibular implants, which is predictable approach to mandibular edentulism that provides immediate treatment while being minimally invasive.3 Pozzi et al22 conducted a study comparing computer-guided implant placement with FL to FT without templates and with raised flaps. The study attempted to compare the 2 procedures in terms of prosthesis, implant failures, complications, and periimplant bone level changes. This study concluded that there were no significant differences between the 2 procedures.
The survival rates of implants that are placed with FL and FT have been evaluated and reported in clinical retrospective and prospective studies and review articles. Many variables can affect implant failure and survival rate results, for example, whether the implant is placed in the maxilla or mandible and patient habits.34 Additional factors that may influence the outcomes of a clinical study are the standardization of the implant placement and having a single operator place the implants. The contributions of multiple centers to a single study have been reported to significantly influence the results.35 Most studies reported that there are no significant differences between FL and FT in short- or long-term follow-up.16,21 Most clinical studies lack proper study design, randomization and blinded methods, which deter them from being considered scientifically documented reports. Additionally, there are no direct comparisons of the FL and FT techniques in a single sample.33
Histological and Laboratory Studies
Crestal bone resorption
Jeong et al36 reported that FL surgery can achieve results that are superior to those of surgeries with reflected FT flaps. FL implant surgery improved the bone height around the implant after surgery.
One study had a design that involved implant placements in 6 mongrel dogs; 2 implants were placed in each side of the mandible by either FT or FL procedures. After a healing period of 8 weeks, microcomputerized tomographies of the implantation sites were performed. The height of the periimplant bone was measured.
The mean periimplant bone heights were greater at the FL sites (10.1 mm) than the FT sites (9.0 mm). The author concluded that when soft tissue flaps are reflected, the blood supply from the soft tissue to the bone (ie, the supraperiosteal blood supply) is also removed, which leaves only poorly vascularized cortical bone and ultimately promotes bone resorption during the initial healing phase. These findings contradicted those of a study that compared FL and FT in 5 young adult hound Labrador mongrel dogs.37 The implants were placed using a split-mouth design; 4 implants were placed into each mandibular jaw quadrant using FL or FT in a 1-stage surgical approach. The average bone levels were nonsignificantly different between the FL (1.6 ± 0.3 mm) and FT (1.1 ± 0.6 mm) sites.
The study conducted by Blanco et al39 compared the FL and FT techniques in terms of the biological width 3 months after nonsubmerged implant placement in dogs. The results showed that the mean value of the longitudinal dimension of the biological width at the buccal aspect was higher for the FT approach than the FL approach, and this difference was significant in the anteriorly placed implant. Longer follow-up is needed as significant changes occur in the biological width dimension after 12 months of implant loading.38,39
Flap tissue circulation during the healing period
A study by Muller et al41 reported significantly greater blood vessel densities or neoangiogenesis with the FL technique compared with the FT technique. A study by Lei et al26 revealed that VEGF expression increased significantly in the 2-week FT group compared with the 2-week FL group, although microvascular density and VEGF expression were significantly lower in the 8-week FL group than in the 8-week FL group. We can thus observe an obvious conflict between the results of the studies of Muller and Lei regarding vascular density.
A study by Muller et al41 revealed greater numbers of inflammatory cells (macrophages, neutrophils, and lymphocytes) following the FT technique compared with the FL technique in the 1st, 2nd, 4th, and 12th postoperative weeks, with decreasing numbers from the 1st to 2nd and 4th to 12th weeks. This finding indicates that the inflammatory process resolves slower with the FT approach than with the FL approach. Increased numbers of macrophages in FTs indicate that more tissue destruction occurs with this technique43–47 (Table 6). Muller's study assumed that increased fibroblast migration in the FT technique compared with the FL technique leads to the development of thick fibrous mucosa around the FT implant, which may provide more protection and elicit less gingival recession compared with the FL technique. Increased reepithelialization was observed with the FL technique in this study, whereas the expression of reepithelialization-associated genes was reduced by using the FT technique (Table 6).
A study conducted by Lei et al26 on beagle dogs revealed that VEGF expression, PICF volume, and aspartate aminotransferase and alkaline phosphatase activities in the PICF were significantly increased in the 2-week FT group compared with the 2-week FL group.
This review revealed that the results of the studies that have been conducted on animals have produced different findings than those that have been conducted on humans. The best example of this difference is the study by Jeong et al21 that was conducted on animals and indicated the superiority of FL in terms of crestal bone preservation; 1 year later, the same author published a clinical human study and reported that there was no significant difference between the FL and FT techniques.36 These differences may be due to tissue remodeling differences between animals and human beings because tissue remodeling is 2.5-fold greater in animals than in humans.48–50 We recommend that the type of specimen under study (whether human or animal) be considered during comparisons between FL and FT.
The comparison of both flap techniques regarding immediate loading, biological width, inflammation, guided implant placement, and esthetics shows better results when the FL technique is used. The survival rate is not significantly different between the 2 techniques, but more well-designed research is necessary. Regarding crestal bone resorption, the most histological and laboratory studies that have been conducted in animals have indicated the superiority of the FL over the FT technique. Moreover, even the oral examination that was conducted in animals revealed the superiority of the FL technique. However, the human clinical study discussed here indicated that there are no clinically significant differences in crestal bone loss between the FT and FL techniques. Thus, the study specimen type (human or animal) played a role in our comparative study.
The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.
This study is self-funded.
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