Dental implant placement with flapless and flapped technique: A systematic review

Affiliations: 1Department of oral and maxillofacial surgery, Azad university of Isfahan, Isfahan, Iran. 2 Department of Oral and Maxillofacial Surgery, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran. 3Department of Prosthodontics, Shahed University, Tehran, Iran. 4Department of Periodontics, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran. 5 Department of Orthodontics, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran.


INTRODUCTION.
Following tooth loss, which is associated with aesthetic and functional problems, dental implants can be placed. Although high success rate have been reported for dental implants 1 with little alveolar bone loss, 2,3 marginal bone loss is still a common complication that could happen for various reasons. 4,5 Following marginal bone loss, implants may fail and further treatment such as complicated reconstructive 6,7 or regenerative procedures 8,9 may be needed. Several tecnhiques have been employed to prevent alveolar bone loss and increase dental implant success rate. These attempts include implant surface modification (acid etch, sandblast and hydroxyapatite coating), 10 implant geometry alteration (conical and cylindrical fixtures) 11 and changes in implant threads (type, shape and depth of threads). 2,12 In addition, several modifications have been performed to reduce marginal bone loss following implant insertion. On the one hand, conventional implant placement technique involves full thickness flap prior to implant insertion. This approach allows the clinician to directly visualize the alveolar bone and assess bone morphology of the ridge. Also, using this technique, crestal ridge morphology alteration and augmentation could be performed. The current guidelines indicate this technique in case of lack of sufficient attached gingiva and a need of simultaneous recipient site augmentation. 13 However, this technique is relatively invasive and causes patient discomfort and marginal bone loss. When flap is reflected, catabolic activities shifts and osteoclastic activity and bone loss increase. 14 On the other hand, flapless implant insertion technique involves punching of the soft tissue without flap reflection. Reduced surgery time and less patient discomfort has been reported using this technique. 15 Although clinicians assume that using flapless technique results in less marginal bone loss due to the less invasive approach, the proposed disadvantage of this technique is reduced implant survival rate. 16 This approach is generally indicated for specific patients such as those who demand esthetic treatments, implants placed in esthetic areas, 17,18 fractured teeth, 18 endodontic failures, nonrestorable caries, and radicular caries. 19 In these cases, the periodontal tissue should be healthy prior to implant placement. Soft tissue dehiscence and fenestrations are considered as contraindication for flapless implant insertion. 19 Implant treatment outcomes by flapless approach have been reviewed previously. 20-22 A review of 13 studies revealed that flapless technique results in 97.2% survival rate of dental implants and a mean 1.45mm marginal bone loss during 1-4 years of follow up. 22 Another review also showed that using flapless technique the implant survival rate was 98.6% with 3.8% complication rate. 20 Flapless technique had 97.1% and 6.55% survival and complication rates respectively, for implants placed in the maxillary posterior region. 21 Comparison of implant treatment outcome and complications between flapped and flapless groups has been performed is some clinical studies, 23-35 and systematic reviews 5,36,37 In a clinical situation, clinicians should be able to predict the possible outcome of each treatment and systematic reviews are necessary for such evidence-based clinical decision making. 38 The main purpose of this study was to systematically review published randomized clinical trials (RCT) and prospective studies comparing implant survival rate, alveolar bone loss and post-operative pain between flapless and flapped implant insertion techniques and to update previous reviews.

Study design
This study was performed in compliance with the PRISMA statement. 39 In this current review, clinical studies evaluating the survival rate, alveolar bone loss and rate of complications between flapped and flapless techniques for implant insertion were included. Only RCTs and prospective studies were included. Use of flapless technique was necessary for inclusion. Also, the minimum number of patients for inclusion was 10 implants and only studies that used fixed partial dentures were included. Animal studies, case reports, case series, retrospective studies and review articles were excluded. Also, studies on patients with systemic diseases, fresh socket implant placement, studies with removable prosthesis and studies using short implants (less than 8mm length) were excluded.
Electronic search and study selection An electronic search was performed using PubMed and Cochrane Library up to June 16 th 2018 limited to English language and human studies. A combination of relevant keywords was used according to PICO (Table  1). Initial screening of titles and abstracts was carried out and full texts of the potentially eligible studies were obtained for further evaluation. Studies were included based on established inclusion/exclusion criteria by two reviewers separately. Disagreements were discussed with the third reviewer.

Data extraction
Relevant data including study methodology, number of patients, number of implants and mean length and diameter, mean age, and surgical procedure data including flapped or flapless technique, brand and type of implants, a h e a d o f p r i n t ] implant insertion site, and loading protocol as well as implant therapy outcome including follow up duration, success, failure and survival rates, marginal bone loss and post-operative pain were extracted from each study. Outcome of the longest follow up was extracted.

Data analysis
Included studies were evaluated in a qualitative manner and no statistical and meta-analyses were performed. Assessed outcomes were implant survival and success rate, alveolar bone loss, pain, and other complications.

Search process
Study design is illustrated in figure 1. Initial search resulted in 1872 studies which was reduced to 249 studies in the PubMed database and 38 in Cochrane Library after limiting the results to human and English language studies.

Age
The age of the patients ranged in between 18 and 86 years. Age range was not reported in two studies. 23, 43 Gender Only six studies 23,25,33,47,54,55 did not mention the gender distribution in their study. In the other 24 studies a total of 627 females and a total of 597 male patients were included. The study of Jané-Salas et al., 56 showed that the patients in the flapless group had less complications, pain and mouth opening reduction compared to the patients in the flap group.

DISCUSSION.
When lost teeth will be substituted by dental implants, several factors concerning dental implant properties and surgical and prosthetic methods should be considered in order to increase success rate of the treatment as well as patient satisfaction. The clinician should use proper materials and methods in each case. One of the important factors that thought to affect implant treatment outcome is flap design at the time of implant insertion. 20, 21 In clinical situations, the surgeon should choose between flapped and flapless approaches prior to the implant insertion procedure. Each of these approaches has been reported to have its own advantages and disadvantages. While flapped technique permits visual evaluation of the insertion site, 60 flapless approach is associated with less surgical time 24,33 and less patient discomfort. 26,31,61 However, in recent dentistry, such clinical decision making should be evidence-based. Systematic reviews can provide reliable evidence through the gathering of information from previous single clinical trials. 62 The aim of the current study was to systematically review the articles comparing implant treatment outcome between flapped and flapless implant insertion techniques. The results were categorized based on implant survival rate, amount of marginal bone loss and post-operative complications. The results indicate no difference in implant survival rate while the flapless technique seems to be associated with comparable or less marginal bone loss and less pain and discomfort. Previously, some studies have reviewed and compared these techniques and reported comparable outcome. 5, 36, 37 Lin et al., 36  different designs and showed that the mean survival rate of implants in flapped and flapless techniques was 98.6% and 97%, respectively. No statistically difference was found when the difference was analysed considering study design. Also comparison of the mean marginal bone loss showed a difference of 0.03mm, a result that was also was not statistically different between the two surgical techniques. A systematic review by Chen et al. 63 showed similar survival rate and clinical outcome between implants inserted immediately and those inserted using a delayed approach in healed sites. In a review of Vohra et al. 5 only studies that inserted dental implants in healed alveolar ridge were included. Ten studies were included that showed that in half of those studies there was no difference in marginal bone loss between the two techniques while the other half reported less marginal bone loss in the flapless groups.
In comparison to mentioned reviews, 5,36 a metaanalysis by Chrcanovic et al., 37 showed a significantly higher implant survival rate in the flapped group compared to the flapless group. The analysis included 23 studies and the reported odds ratio of implant failure in flapless technique compared to flapped technique was 1.75 (p=0.04). This means that implant placement using flapless technique increased the risk of implant failure by 75%. The reason for this controversy might be due to the fact that in their review, all studies comparing implant treatment outcome between flapped and flapless technique were included regardless of sample size, study design and follow up period. They also compared postoperative complication of flapped and flapless techniques and showed no significant difference. Similar to the other reviews, 5,36 comparison of mean marginal bone loss between flapped and flapless techniques in the study of Chrcanovic et al. 37 showed no significant difference. A systematic review by Moraschini et al. 22 was performed on implant treatment outcome using flapless technique only. They included 13 studies from PubMed and Cochrane databases and revealed that flapless technique would result in 97.2% survival rate and a mean 1.45mm marginal bone loss during 1-4 years of follow up. In the meta-analysis studies which placed more than five implants in each patient were included. It is mentioned that surgical and prosthetic complications may happen using this technique and more studies are required to more precisely assess flapless technique. Another two reviews on outcome of dental implant treatment in flapless technique show 98.6% 20 and 97.1% 21 of survival rate and a rate of post-operative complication of 3.8% 20 and 6.55% 21 using this technique.
Regarding the level of evidence,21 out of 32 reviewed studies were randomized clinical trials (RCTs). 26 33 Some factors could influence implant treatment outcome which were not considered in this review. Gingival biotype could influence implant treatment outcome as the facial bone loss in thick biotypes is less than 1 mm while it is 1-1.5mm in thin biotypes. 64 Also, oral hygiene has an important role in the success of dental implant treatment 65 which was not considered in the included studies. A definitive factor which could influence survival rate of dental implants is smoking. Marginal bone loss has been demonstrated to be increased in smokers compared to non-smokers. 66 It has been stated that survival rate of implant for non-smokers and smokers using flapless technique is 98.9% and 81.2%, respectively and the extent of marginal bone loss was 1.2 and 2.6mm, respectively. 67 However, none of the reviewed studies reported implant treatment outcome in flapped and flapless groups based on patients smoking habits. Finally, the experience of the surgeon also could influence treatment outcome 68 as some surgeons may be more skilful in flapped technique while others may prefer flapless technique.
The results of this review could be interpreted into clinical situations considering the inclusion criteria of the The limitations of this systematic review should also be considered. Most studies were RCT (n=21). Also, the method of the studies including study design, duration and periods of follow ups, protocols for loading dental implants, insertion of dental implants in healed, fresh socket or augmented sites, smoking, and implant site, differed. In addition, the included studies assess marginal bone loss by comparing periapical radiographs. However, this technique might not be able to properly show amount of facial bone loss. Finally, this review only included studies in the English language and is prone to publication bias.
Further well designed randomized controlled trials should be performed with longer follow ups and larger sample sizes to further investigate this issue. It is suggested to consider patient hygiene, smoking, soft tissue biotype, previous procedures on the recipient site, protocols for loading dental implants, and implant site. Future studies should be performed to investigate the effect of the aforementioned factors on implant treatment outcomes and compare implant success rate, marginal bone loss and rate of complications between flapped and flapless groups considering these factors. Also, it is suggested to perform RCTs measuring amount of facial bone loss using cone bean computed tomography (CBCT) considering ethical issues.

CONCLUSION.
Considering the limitations of this systematic review, the results could be summarized as follows: There was no significant difference in success and survival rate of implants between two techniques except for one study that reported higher success rate in flapless group. Therefore, implant survival rate using flapped and flapless technique is comparable.
Twelve studies reported higher marginal bone loss in flapped groups compared to flapless technique. Six of these studies were RTCs. However, the difference was not significant in eight studies, five of them RCTs. So, marginal bone loss using flapless technique is similar or less than using flapped technique.
Less post-operative pain in flapless group compared to flapped group was reported in nine RCTs while flapless group reported more pain in another RCT. Less edema in flapless group was reported in a RCT. Therefore, it seems that flapless technique would probably have less postoperative pain and edema.
Shorter surgical time using flapless technique was reported in two studies and one RCT.
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