Comparison of clinical performance of flapless implant surgery and conventional flap elevation: a systematic review and meta-analysis

Krishankumar Lahoti^*, Sayali Dandekar, Jaykumar Gade, Megha J Agrawal, Minal N Soni and Karan V Jaiswal

^*Correspondence: Krishankumar Lahoti, Department of Prosthodontics, Swargiya Dadasaheb Kalmegh Smruti Dental College and Hospital, India, Email:

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Introduction

The Brane mark protocol for implant offers an extensive flap elevation approach and is considered as a conventional procedure which is practiced routinely [1]. This approach provides for good visibility of the available underlying bone and is quite frequently necessary for treating bone defects. Over the last few years emphasis is being placed on simplification of the implant placement procedure and for reducing the treatment time which has led the attention towards flapless implantation which entails implants being placed through the mucosa without reflection of the muco-periosteal flap. This can be carried out using blind or digitally planned static guide templates. Furthermore, dynamic navigation systems can be used for improved precision and accuracy [2].

Flapless implantation being less traumatic is known to have benefits like reduced bone resorption, decreased discomfort, shorter treatment duration [3,4]. It also helps to preserve the vascularity, soft‑tissue architecture. Flapless implantation allows the patient to resume normal oral hygiene measures immediately after the procedure [5]. Despite having several advantages, flapless procedure is still feared by many clinicians considering the risks associated with it. Though several reports and clinical trials have been reported but no definitive conclusion could be reached. Therefore, a meta-analysis of published trials was conducted to compare the clinical performance of flapless implant surgery with conventional flap elevation.

Materials and Methods

This review was according to the guidelines of the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) statement [6].

Study protocol

Before the start of the systematic review, a protocol was developed and registered (Prospero ID: CRD42020197218) aiming to answer the P.I.C.O. question

Population: Patients requiring placement of implant.

Interventions: Flapless implant placement.

Comparison: Conventional Flap Implant placement.

Outcomes: survival rate of implant placement.

Study design

A combination of in vivo studies involving either or both the arches, comparative prospective and randomized or Non-randomized and retrospective clinical trials were included. The presence of comparator and interventional group was a necessary criterion of inclusion.

Inclusion criteria

Prospective randomized or non-randomized studies

Retrospective studies

Exclusion criteria

Review articles on the topic

Case reports and case series

Preclinical studies in animal models

In vitro studies

Retrospective studies

Search strategy

Two electronic databases were used as sources in the search for studies satisfying the inclusion criteria: (a) The National Library of Medicine (MEDLINE via PubMed); (b) Google Scholar for studies published until June 2020.

Search terms combinations of the following key words: ‘‘dental implant’’; ‘‘surgery’’; ‘‘flap’’; and ‘‘flapless’’; “Flapless versus Flap surgery”; “survival rate” with the Boolean operator. Subsequently, a manual search was conducted based on the reference lists of studies included and relevant reviews.

Data extraction

Relevant information was extracted by reviewers for accuracy. Data collected comprised of authors; year of publication; study design; number, age range, and gender distribution of participants; number, type, system, and location of implants; tools for flapless surgery; freehand or guided flapless surgery; implant survival rate, marginal bone loss, follow-up.

Risk of bias in individual trials

Two reviewers independently assessed the risk of bias for each eligible study. The risk of bias of studies was estimated as “low”, “Moderate”, or “high” for each item including following aspects i.e. random sequence generation, allocation concealment, blinding of outcome assessment, incomplete outcome data, blinding of participants and personnel, selective reporting and other bias in the tool.

Statistical analysis

The statistical heterogeneity among studies was assessed using the Q test based on Chi square statistics as well as the I2 index in order to know the percentage of variation in the global estimate that was attributable to heterogeneity (I 2=25%: low; I 2=50%: moderate; and I 2=75%: high heterogeneity). The primary outcome of this meta-analysis was to evaluate the survival rate of implant placement with flapless and flap elevation surgical approach. In the case of dichotomous outcome (exposure events), the estimates of the effect were expressed in risk ratios and 95% CIs. Study estimates were pooled with both the fixed and random effect models. Subgroup analysis was performed considering the difference in the loading protocol and the follow up period of the studies included. Studies having follow up period more than or equal to 3 years were included in the meta-analysis of long term effect of the placement technique on implant survival. In the studies where implants were loaded immediately, analysis was performed to check the effect of immediate loading on the outcome.

Results

Literature search

After the search strategy, a total of 4187 records were identified, and the selection process is summarized in Figure 1.

Figure 1. PRISMA flow diagram for study selection process.

One thousand eight hundred eighty-seven records were excluded for duplicated titles and abstracts, with 2300 records retained. After screening the titles and abstracts, 2238 records were further excluded based on the prespecified inclusion and exclusion criteria. Consequently, 62 records were suitable for full-text screening. After full-text screening, 39 articles that did not meet the requirement were further excluded, of which 8 did not have control group, 10 were reviews or meta-analysis, 5 articles did not have adequate data for meta-analysis/ or had other outcome measures, 14 studies had a follow up of less than 1 year and 2 studies were in vitro/animal studies. Eventually, a total of 23 publications were included in the meta-analysis.

The Cohen’s Kappa value for measuring the agreement strength between the reviewers during study selection were 0.91 in the initial screening of articles and 0.96 in full text assessment indicating “almost perfect” interagreement.

Description of the Studies

These included studies consisted of 23 clinical studies out of which 10 were randomized controlled trails and 2 were retrospective. The descriptive details of these studies are listed in Table 1.

Table 1: PICOS framework.

A total of 1372 patients with 2320 implants were included in the meta-analysis. The age of the patients ranged from 18 to 85 years. Follow up time ranged from minimum of 1 year to 9 years. Of the 23 included studies, 7 of the included studies have a long follow-up of 3 years or more. [7-22] In 10 of the included studies, flapless surgery was performed by guided approach [23-25] while remaining 13 were performed by the free hand approach. Six studies used soft tissue punch in the flapless technique while other 16 studies were performed by direct drill preparation through the soft tissue and in 1 study a crystal relief incision was used for implant placement. In 5 studies, implant placement was performed only in the mandibular jaw [26-35].

Information about loading time was also stated. In 5 studies, implants were loaded with immediate/early loading protocol after the placement for both the flapless and flap surgery groups [36]. Sixteen studies applied a conventional delayed loading protocol [37] whereas 2 studies [38] involved both immediate/early loading and delayed loading Figure 2 to Figure 4.

Figure 2. Forest plot of meta-analysis results comparing survival rates of flapless and flap surgery group.

Figure 3. Forest plot of meta-analysis results comparing long term survival rates of flapless and flap surgery group.

Figure 4. Forest plot of meta-analysis results comparing survival rates of immediately loaded flapless implants and flap surgery group.

Among the 23 studies, 1306 implants were placed through a flapless procedure with failure of 37 implants (2.8%) and 1209 implants were placed through a flapped procedure with failure of 20 implants (1.6%). Implant survival ranged from 87.2-100% for Flapless implant placement and 92–100% for flap elevation surgery.

No implant failure was found in 9 studies. All the articles included data regarding the implant survival rate and surgical technique used. None of the studies directly correlated the survival rates with the surgical technique used [39].

Quality Assessment

Quality assessment was done pertaining to the following aspects: random sequence generation, allocation concealment, blinding of outcome assessments, and incomplete outcome data. If all criteria were met, the study was considered to be at low risk of bias. The study was classified as having a high risk of bias if two or more criteria were not met. The assessment of each trial is summarized in Tables 2 and 3.

Table 2: Details of studies included in meta-analysis.

Table 3: Results of quality assessment.

Among the 23 studies, 4 were judged to be at moderate risk of bias, [40-43] 9 were at low risk of bias.[44-45] and rest 10 were considered of high risk of bias Table 4.

Table 4: Summary of excluded articles.

Meta-analysis

For comparison of marginal bone loss between the two surgical approaches, 23 studies were included with 2320 implants placed in 1372 patients.

As statistically significant heterogeneity was (Chi2=4.02, df=13, p=0.99; I2=0%) not observed across the studies, a fixed effect model was carried out. In this study, failure rate of dental implants was affected by different insertion technique with a RR of 1.55 (flapless placement vs flap surgery; 95% CI: 0.94 to 2.57; P=0.09) indicating that failures in flapless procedure are 1.55 times likely to happen when compared with flapped procedure but the effect was not found to be statistically significant. Thus the relative risk reduction is -55% which indicates that flapless surgery has 55% more risk of implant failure. Since RR could be affected by risk of bias all the low bias studies were also pooled separately and RR of 1.35 resulted (295% CI: 0.55-3.35, P=0.51) which was not significant. Regarding the implant survival rate over the follow up period of three years or more, 7 studies were included in the meta-analysis. As low heterogeneity was found between the studies (Chi2=7.26, df=6, p=0.30; I2=0%), fixed effect model was carried out and forest plot was generated. The test of overall effect showed that the difference in implant survival rate between the 2 groups was statistically significant with a RR of 2.39(95% CI: 1.07 to 5.34; P= 0.03) indicating that in the studies with follow up of 3 or more years, flapless surgery has more failures compared to that seen with flap surgery. Meta-analysis of the immediate loading flapless surgery with flap surgery generated a fixed effect model based on the low heterogeneity (Chi2=2.13, df=13, p=0.91; I2=0%) with RR of 1.12 which was not statistically significant (95% CI: 0.49 to 2.53; P=0.79) indicating that immediately loaded implants placed with flapless technique have failure rates comparable to the flap surgery.

Publication bias

The funnel plot did not show asymmetry when the studies reporting the survival rate were analyzed indicating absence of publication bias. (Figures 5 to Figure 7).

Figure 5. Funnel plot for studies reporting outcome of survival rate.

Figure 6. Funnel plot for studies reporting long term survival outcome.

Figure 7. Funnel plot for studies reporting outcome of immediately loaded flapless implants.

Discussion

The current systematic review and meta-analysis compares the survival rates of the implants placed with flapless and flap surgery with extended evidence of the long term clinical performance and the effect of immediate loading of the placement technique.

Earlier reviews [46] provided controversial evidence regarding the flapless implant placement approach compared with flap elevation. Some studies [47] showed similar survival rates of the implants placed with the flapless as well as flap elevation approach while Chranovic et al and Zhuang et al found significant difference between the survival rates between the two approaches indicating that flapless implantation increased the risk of implant failure.

The implant prognostic criteria were previously described by Albrektsson and Zarb. Implants were considered successful if the following criteria were met: Absence of mobility, absence of paresthesia or pain, absence of peri-implant pathology or radiographic radiolucency’s, and marginal bone loss < 1mm during the first year and < 0.2mm/year in the following years. For the analysis of the implant survival minimum follow up period of 1 year was considered excluding the studies with follow up less than one year or unloaded implants. As the authors sought to eliminate the studies that followed participants for limited time, this systematic review can be considered to have robust data [48-50].

Evidence from total of 23 studies indicated that there was no significant difference between the implant survival rates of the two techniques which is in accordance with the previous review by Cai et al and Lin et al. In the present meta-analysis, it was identified that the that the risk of implant failure was 1.55 times higher in flapless implantation approach than the conventional flap elevation which is slightly less than the findings of Altinci et al [51] and Voulgarakis et al [52]. The findings showed that there is increased risk of failure in flapless placement of implants which could be attributed to this technique being a “blind” approach. Possible reasons of high implant failure in the flapless surgery may be interference in Osseo integration [53] and less accessibility due to poor vision. In recent studies computer guided flapless implantation are widely used to control the direction and depth of the implant. So the blind flapless approach can now be compared with the Conventional flap elevation technique if it is aided by the pre-operative three-dimensional planning. To maximize the treatment outcome it is important to correlate the restoratively driven implant position with the alveolar bone which can be achieved with the CT imaging and fabrication of surgical guides. As both the approaches have comparable effects with regard to the survival rates flapless surgery could be considered safe in patients having sufficient amount of alveolar bone and keratinized tissue. Three controlled studies, comparing guided flapless surgery with conventional open flap surgery and reporting on patient-centered outcomes [53-59] demonstrated a statistically significant reduction in immediate postoperative pain, use of analgesics, swelling, edema, hematoma, hemorrhage, and trismus when flapless guided surgery was performed. Chang et al in 2018 [60], evaluated the accuracy of implant placement with a computer-aided fabricated surgical template concluding that both the median of the linear deviation and angular deviation with surgical templates was in the clinically acceptable range.

The long term clinical performance was assessed by the meta-analysis of the studies having followed up time of 3 or more years. Seven studies were included with follow up ranging from 3 to 9 years. The result of the meta-analysis showed that implants placed with flapless approach are 1.51 times more likely to fail than with conventional approach which was found to be statistically significant. The technique used for flapless surgery could have influenced the outcome as earlier studies used free hand flapless approach without the 3D pretreatment planning and CT guided templates.

Flapless implantation surgeries are also known to have better patient acceptance because of the less discomfort and pain [61-65]. Campelo and Mazzocco, et al. [66] have concluded that patients that received flapless implants did not require any pain management. Cannizzaro, et al. concluded that flapless implant placement is associated with significantly less pain, post-surgical swelling and was more preferred by the patients. Boardman et al suggested that flapless procedure yielded higher pink esthetic scores [67-69]. Furthermore, flapless procedure can be beneficial to the health of the peri-implant soft tissue. Studies by Tsoukaki, You, Al-Juboori have found that flapless approach produced better values concerning probing depth, gingival index, BOP. Healthy peri-implant tissue will lead to better resistance to inflammation and bacterial invasion [70,73].

The original Branemark protocol required a two-stage surgery with a submerged healing period of at least 3 months in the mandible and 6 months in the maxilla, allowing the implant to Osseo integrate without exposure to external trauma. Under defined circumstances early or immediate loading are now deemed viable alternatives as it is assumed that immediate loading of implants may have positive biomechanical stimuli on the bone during healing enhancing biological fixation of implants. The ultimate goal is to reduce the number of surgical interventions and to shorten the treatment time, all without compromising the success of the implants. Immediate loading can be either functional occlusal loading or non-functional loading where the implant prosthesis is kept out of direct occlusal contact. Different from the results of the meta-analysis by Zhuang, et al. 2018, the current analysis did not establish a significant difference in the survival rates of the immediately loaded implants with the 2 techniques. The results showed that implants placed with flapless approach that are loaded immediately are 1.22 times more likely to encounter implant failure compared to flap elevation. As significant difference was not obtained both the procedures could be considered equally reliable when the implants are loaded immediately which is in agreement with several previous reports that have recommended flapless procedures to be used in immediately loaded implants [74,76].

However, it is not always possible to avoid reflection of flap for implant placement. Flapless approach cannot be performed when the bone is inadequate or in the presence of bone defects and bone grafting is required. Also, when there is a need for periodontal plastic surgeries or very less volume of soft tissue is available conventional flap elevation technique would provide for superior results. Few studies have also changed the technique while performing the implant placement as flapless placement could not be possible.

This systematic review provides enough evidence about flapless surgery being a possible alternative as it has comparable outcomes with the conventional procedure. The results of the studies should be interpreted with caution as few studies with high and moderate risk of bias were included as excluding these studies would exclude the data of significant value. Furthermore, success of implant therapy cannot be only defined according to the survival rates. Another shortcoming of the study is the inclusion of 2 retrospective studies and the nature of retrospective studies is inherently associated with flaws which are either manifested as gaps in information or incomplete data. The authors strongly believe that, for a more definitive conclusion double blinded high strength randomized controlled trials with greater sample are required. The use of CT guided templates with flapless approach and the use and efficacy of dynamic implant placement are still needed to be explored.

Conclusion

The overview of the selected studies indicated that both the approaches for implant placement have comparable survival rates irrespective of the technique used for placement loading protocol. Hence, flapless technique should be given consideration in patients whenever appropriate conditions pertaining to the alveolar bone and soft tissue are available.

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