Comparative evaluation of crestal bone level by flapless and flap techniques for implant placement: Systematic review and meta-analysis.

Aim: :To compare the crestal bone level of flapless technique of dental implant placement with the flap technique. Setting and Design: This Systematic review and Meta-analysis was conducted according to the Preferred Reporting Items For Systematic Review and Meta-Analyses (PRISMA) Guidelines and registered with PROSPERO. Materials and
Methods: Electronic search of Medline and Google scholar databases for articles from 2010 till March 2020 was performed. Studies comparing the crestal bone level with both the techniques were included. After the collection of data, the risk of bias was assessed for each study. Statistical Analysis Used: Meta-analysis was executed using RevMan 5 software version 5.3.
Results: 23 studies were included. Statistically significant difference in crestal bone level was found between flapless and flap surgery with mean difference of -0.14 (flapless placement versus flap surgery; 95% CI: -0.24 to -0.03; P = 0.01FNx01). The difference in crestal bone level between the 2 groups was not statistically significant with a mean difference of -0.05(Guided flapless placement versus flap surgery; 95% CI: -0.10 to 0.00; P=0.06). Meta-analysis of the freehand flapless surgery with flap surgery generated a mean difference of -0.20 which was found to be statistically significant (Freehand flapless placement versus flap surgery; 95% CI: -0.37 to -0.03; P=0.02FNx01). Conclusions: Flapless placement of implant can positively influence crestal bone loss in comparison with conventional flap technique.

INTRODUCTION

Dental implants facilitate mastication, phonation, and esthetics and are one of the most common treatment modalities used for the rehabilitation of missing teeth. To provide support for the dental prosthesis, implants form a direct connection with the surrounding bone known as “osseointegration.”[1] Enhancing patient comfort and predictability of treatment with precise presurgical treatment planning have been the goals of evolving implant dentistry.[2]

Branemark has advocated flap elevation technique for implant placement since the 1970s. The protocol by Branemark placed the incision line and sutures away from the implant location, reducing the risk of infection at the surgical site location.[34] The current advancements and incorporation of new technologies have led to an approach wherein the implants can be placed with minimal incision either freehand or with the assistance of surgical guide. Sustained efforts to incorporate this minimally invasive flapless technique have been made in the field of implantology. Although the scientific evidence to prove the accuracy is still not considered adequate, many researchers advocate this approach based on their assessment of the literature.[567] Chrcanovic et al. in 2014[5] in their systematic review stated that flapless approach significantly influenced the implant survival rate compared to conventional surgery. Lin et al.[6] and Lemos et al.[7] could not establish a significant difference in the survival rate or crestal bone loss between the two techniques. Although freehand implant placement is not considered as accurate as guided flapless surgery as reported by Nickenig et al. in 2010,[8] a review by Voulgarakis et al. in 2014[9] suggested that the surgical guides did not significantly influence the outcome.

No real conclusion has been reached to date which would clearly state the benefit of one approach over the other. This systematic review was thereby designed to compile the literature and compare the flapless and flap techniques in terms of crestal bone level.

MATERIALS AND METHODS

This systematic review was designed and performed in accordance with PRISMA guidelines laid down in 2015.[10] A specifically formulated protocol was registered with PROSPERO (CRD42020162689) before the start of the review.

Study question

“How is the crestal bone level by flapless technique compared to flap technique for dental implant placement?” which fulfills the PICOS framework [Table 1].

Table 1

PICOS framework

Domain	Description
P	Patients requiring dental implant surgery
I	Flapless technique
C	Flap technique
O	Crestal bone level around implant
S	Prospective clinical trials

Search strategy

Electronic search of MEDLINE and Google Scholar from 2010 to March 2020 was performed. Subject AND Adjective combinations were used:

Subject: Dental implant OR dental implant placement AND Adjective: flapless technique OR flapless placement OR open flap OR flap elevation OR flapless surgery OR Keywords – combinations of the following keywords: “crestal bone level;” “dental implant;” “surgery;” “flap;” and “flapless;” “Flapless versus Flap surgery;” and “crestal bone loss.” Furthermore, a manual search was conducted based on the references of selected studies.

Inclusion criteria

Studies on patients requiring rehabilitation with dental implant

Studies which had data regarding the crestal bone level of both the intervention and comparison groups

Prospective clinical studies

Full-text access of article

Primary language of article: English.

Exclusion criteria

Duplicate studies, In vitro studies, case reports, opinions, letters, and reviews.

Data collection

After the studies were scanned for information, relevant data were tabulated which comprised authors of the study, study year, technique of placement, crestal bone changes, and other outcome measures. Any disagreements were resolved by discussion. The data were compiled to perform meta-analysis.

Risk of bias for individual studies

Bias assessment for randomized studies was done based on the fulfillment of criteria of sequence generation, blinding, allocation concealment, and addressed outcome measures. For nonrandomized studies, the Newcastle–Ottawa scale was used.

Statistical analysis

Crestal bone level was the primary outcome measure, which was treated as a continuous data variable. Aggregate analysis using a fixed-effects model and a random-effects model was carried out. Heterogeneity was tested. Forest plot was generated showing standardized mean difference as the effect measure. Funnel plot was drawn to check for publication bias. The analysis was performed by using Review Manager (RevMan) [Computer program]. Version 5.3. Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration, 2014.

RESULTS

Study selection

Four thousand four hundred and forty-three records were obtained by the selection process [Figure 1]. After removing duplicate records, 2343 were held back. Fifty-seven records were reached after 2286 were scanned according to eligibility criteria. Thirty-four articles were removed after full-text reading for reasons mentioned in Table 2. In the end, only 23 articles were retained for meta-analysis.

Figure 1

PRISMA flow diagram for study selection process

Table 2

List of excluded studies

Reason for exclusion	References
No control group	Nikzad and Azari[11]Jeong et al.[12]Lee et al.[13]Tee[14]Kareem et al.[15]Oliver et al.[16]Komiyama et al.[17]Altinci et al.[18]Jesch et al.[19]
Review articles	Lin et al.[6]Chrcanovic et al.[5]Vohra et al.[20]Romero-Ruiz et al.[21]Llamas-Monteagudo et al.[22]Zhuang et al.[23]Yadav et al.[24]Cai et al.[25]
Data inadequate for crestal bone loss	Arisan et al.[26]Berdougo et al.[27]Bashutski et al.[28]Voulgarakis et al.[9]Meizi et al.[29]Yadav et al. (2018)[30]Gupta et al.[31]
Retrospective studies	Nickenig et al.[8]Rousseau et al.[32]De Bruyn et al.[33]Nguyen et al.[34]Yue et al.[35]
Immediate implant placement	Stoupel et al.[36]Mazzocco et al. (2017)[37]
Other outcome comparison studies	Danza and Carinci[38]Lindeboom and van Wijk[2]Kaur et al.[39]

Description of included studies

This review consisted of 23 studies listed in Table 3. Total data from 948 patients rehabilitated with 1407 implants were included. Of the 23 studies, 3 studies had a follow-up time of up to 3 months.[435658] Six had a long follow-up of 3 years or more.[4246474851] In 8 studies, flapless surgery was done with the help of computed tomography (CT)-guided or surgical stent,[56464748545961] while the remaining 15 were performed by the freehand approach. Some studies used a submerged protocol,[41445356] whereas others used a nonsubmerged protocol,[404345495152575860] and two studies involved both the protocols.[4655] Loading time of the implants was also mentioned in the studies. In five studies, implants were loaded immediately or early for both the groups.[4350596061] Fourteen studies applied a delayed loading protocol,[4041424445474849515253545557] whereas two studies[4654] involved both protocols of loading, and in two studies, the implants were not loaded.[5658]

Table 3

Description of studies

Name	Published time	Study	Patients	Follow-up time	Age range (years)	Failed implants	Survival rate	Loading time
Anumala et al.[40]	2019	P	30 patients30 implants	6 months	25-50	NM	NM	Conventional
Kumar et al.[41]	2018	RCT	20 patients20 implants	1 year	25-60	1/10 (T)0/10 (C)	NM	Conventional
Naeini et al.[42]	2018	P	49 patients53 implants	6-9 years	28-85	0/26 (T)0/27 (C)	100% (T)100% (C)	Conventional
Singla et al.[43]	2018	RP	20 patients20 implants	3 months	30-50	NM	NM	Immediate
Shamsan et al.[44]	2018	RCT	12 patients16 implants	6 months	20-60	0/10 (T)1/10 (C)	NM	Conventional
Wang et al.[45]	2017	RCT	40 patients40 implants	2 years	19-45 (39±13.2)	0/20 (T)0/20 (C)	100% (T)100% (C)	Conventional
Bömicke et al.[46]	2017	RCT	38 patients38 implants	3 years	53 (21-70)	6/19 (T)5/19 (C)	95% (T)100% (C)	Immediate (T)Conventional (C)
Froum and Khouly[47]	2017	RCT	60 patients60 implants	8.6 years	NM	0/30 (T)0/30 (C)	100% (T)100% (C)	Conventional
Pisoni et al.[48]	2016	RCT	40 patients69 implants	3 years	61.69±14.23	5/39 (T)2/30 (C)	87.2% (T)93.3% (C)	Conventional
Maier[49]	2016	P	80 patients195 implants	1 year	18-78	0/95 (T)0/100 (C)	100% (T)100% (C)	Conventional
Maló et al.[50]	2016	P	40 patients72 implants	3 years	19-79	1/32 (T)0/40 (C)	96.8% (T)100%(C)	Immediate nonfunctional
Prati et al.[51]	2016	P	60 patients132 implants	3 years	25-72	2/64 (T)1/65 (C)	96.9% (T)98.5% (C)	Conventional
Samad et al.[52]	2016	P	60 patients60 implants	6 months	19-75	1/30 (T)1/30 (C)	96.6% (T)96.6% (C)	Conventional
Kanwar et al.[53]	2016	P	10 patients20 implants	6 months	20-60	0/10 (T)0/10 (C)	100% (T)100% (C)	Conventional
Pozzi et al.[54]	2014	RCT	51 patients51 implants	1 year	28-84	0/25 (T)1/26 (C)	100% (T)96.2% (C)	Immediate and Conventional
Sunitha and Sapthagiri[55]	2013	P	40 patients40 implants	2 years	25-62	0/20 (T)0/20 (C)	100% (T)100% (C)	Conventional
Katsoulis et al.[56]	2012	P	40 patients195 implants	3 months	20-79 (61±9)	0/85 (T)0/110 (C)	100% (T)100% (C)	Not loaded
Tsoukaki et al.[57]	2013	RCT	20 patients30 implants	12 weeks	47.47±9.72 (T)46.40±9.52 (C)	0/15 (T)0/15 (C)	100% (T)100% (C)	Conventional
Al-Juboori et al.[58]	2013	P	9 patients22 implants	12 weeks	27-62 (50)	0/11 (T)0/11 (C)	100% (T)100% (C)	Implants not loaded
Froum et al.[59]	2011	P	52 patients52 implants	12 months	NM	0/27 (T)0/25 (C)	100% (T)100% (C)	Early Loading
Cannizzaro et al.[60]	2011	RCT	40 patients143 implants	1 year	22-65	2/76 (T)2/67 (C)	97.3% (T)97% (C)	Immediate
Marcelis et al.[54]	2012	P	20 patients20 implants	1 year	48.7±16.4	0/16 (T)1/18 (C)	100% (T)94.4% (C)	Conventional
Van de Velde et al.[61]	2010	RCT	13 patients70 implants	18 months	39-75 (55.7)	1/36 (T)0/34 (C)	97.2% (T)100% (C)	Immediate

P: Prospective study, RCT: Randomized controlled trial, RP: Radiographic prospective, T: Test group (Flapless surgery), C: Control group (flap surgery), MBL: Marginal bone loss, NM: Not mentioned, CT: Computed tomography, PPD: Probing pocket depth, PI: Plaque index, GI: Gingival Index

Among the 23 studies, 694 implants were placed by flapless technique and 713 implants were placed by flap technique. Implant survival ranged from 87.2% to 100% for flapless implant placement and 93.3% to 100% for flap technique. 100% survival was found in 10 studies.[42454749535556575859] Significant results indicating less crestal bone loss with flapless technique were reported by studies.[424449515758]

Risk of bias assessment of the studies

The Newcastle–Ottawa scale, as shown in Table 4a, showed that all the studies had low bias considering the number of stars. For randomized studies, if studies did not fulfill two or more of the four criteria, the risk of bias was considered high. Among the ten randomized studies, five were low risk,[4145576061] two were judged to be at moderate risk,[4647] and the remaining three were at high risk of bias [Table 4b].[414448]

Table 4a

Quality assessment of nonrandomized controlled trials by the Newcastle-Ottawa scale

Study	Selection				Comparability		Outcome			Total (9/9)
	Representativeness of the exposed Cohort	Selection of the nonexposed Cohort	Ascertainment of exposure	Demonstration that the outcome of interest was not present at the start of study	Comparability of Cohorts on the basis of the design or analysis		Assessment of outcome	Was follow-up long enough for outcomes to occur	Adequacy of follow-up of Cohorts
					Main factor	Additional factor
Anumala et al.[40]	*	*	*	*	*	0	*	0	*	7/9
Naeini et al.[42]	*	*	*	*	*	0	*	*	*	8/9
Singla et al.[43]	*	*	*	*	*	0	*	0	*	7/9
Maier[49]	*	*	*	*	*	0	*	*	*	8/9
Maló et al.[50]	*	*	*	*	*	0	*	*	*	8/9
Prati et al.[51]	*	*	*	*	*	0	*	*	*	8/9
Samad et al.[52]	*	*	*	*	*	0	*	0	*	7/9
Kanwar et al.[53]	*	*	*	*	*	0	*	0	*	7/9
Sunitha and Sapthagiri[55]	*	*	*	*	*	0	*	*	*	8/9
Katsoulis et al.[56]	*	*	*	*	*	0	*	0	*	7/9
Al-Juboori et al.[58]	*	*	*	*	*	0	*	0	*	7/9
Froum et al.[59]	*	*	*	*	*	0	*	*	*	8/9
Marcelis et al.[54]	*	*	*	*	*	0	*	*	*	8/9

At least 1-year follow-up was considered adequate for the outcome. *-Present, 0-Absent

Table 4b

Quality assessment of randomized controlled trials

Name	Published time	Sequence generation	Allocation concealment	Incomplete outcome data addressed	Blinding	Estimated potential risk of bias
Kumar et al.[41]	2018	Yes	Unclear	Yes	Unclear	High
Shamsan et al.[24]	2018	No	Inadequate	No	No	High
Wang et al.[44]	2017	Yes	Adequate	Yes	Yes	Low
Pisoni et al.[48]	2017	Yes	Unclear	Yes	No	High
Froum and Khouly[47]	2017	Yes	Unclear	Unclear	Yes	Moderate
Bömicke et al.[46]	2017	Yes	Adequate	Yes	No	Moderate
Pozzi et al.[54]	2014	Yes	Adequate	Yes	Yes	Low
Tsoukaki et al.[57]	2012	Yes	Adequate	Yes	Yes	Low
Cannizzaro et al.[60]	2011	Yes	Adequate	Yes	Yes	Low
Van de Velde et al.[61]	2010	Yes	Adequate	Yes	Yes	Low

Meta-analysis of the studies

Twenty-three studies were included with 1407 implants placed in 948 patients. On account of the heterogeneity (Tau2 = 0.04, Chi-square = 126.96, df = 21, P < 0.00001; I2 = 83%), a random-effects model was used. Meta-analysis revealed statistically significant difference in crestal bone level with MD of −0.14 (flapless placement vs. flap surgery; 95% confidence interval [CI]: −0.24–−0.03; P = 0.01FNx01), indicating the positive effect of flapless technique on the outcome measure in comparison with flap technique, as shown in Figure 2.

Figure 2

Forest plot of meta-analysis results comparing crestal bone level of flapless and flap surgery groups

For subgroup analysis, meta-analysis of eight studies was performed. Low heterogeneity (Chi-square = 7.77, df = 7, P = 0.35; I2 = 10%) led to the fixed-effects model. The results indicated that the difference in crestal bone level between these guided flapless and flap technique groups was not statistically significant with a mean difference of −0.05 (guided flapless placement vs. flap surgery; 95% CI: −0.10–0.00; P = 0.06) [Figure 3]. Subgroup analysis of the freehand flapless surgery with flap surgery generated a random-effects model due to the high heterogeneity (Tau2 = 0.07, Chi-square = 110.60, df = 13, P < 0.00001; I2 = 88%) with MD of −0.20, which was found to be statistically significant (freehand flapless placement vs. flap surgery; 95% CI: −0.37–−0.03; P = 0.02FNx01) [Figure 4].

Figure 3

Forest plot of meta-analysis results comparing crestal bone level of guided flapless and flap surgeries

Figure 4

Forest plot of meta-analysis results comparing crestal bone level of freehand flapless and flap surgery groups

Publication bias

Funnel plot indicated the absence of publication bias, as shown in Figures 5-7.

Figure 5

Funnel plot for studies reporting outcome of crestal bone levels of freehand flapless and flap surgeries

Figure 7

Funnel plot for studies reporting outcome of crestal bone levels of freehand flapless and flap surgeries

Funnel plot for studies reporting outcome of crestal bone levels of guided flapless and flap surgeries

DISCUSSION

Implant placement with flap reflection is a traditional well-accepted approach, while flapless placement has been an experimental evolving technique which still requires a backup of substantial evidence. It is much of a controversy with versatile opinions, and no specific conclusion has still been reached. Thus, this review was aimed to compare the available literature to reach a more specific conclusion with evidentiary support from meta-analysis.

Narrowing the inclusion criteria to only randomized trials could have enhanced the homogeneity, but it was noticed that it could exclude several studies with significant data.

The latest meta-analysis concerning the outcome was published in 2020 by Cai et al.[25] They included only six studies with high heterogeneity (I2 = 78%) in the meta-analysis and failed to state a statistical difference in long-term crestal bone loss. Results of the analysis performed by Cai et al.[25] should be interpreted with caution because of the limited number of studies included. Furthermore, they included only the long-term studies which excluded all the literature published after 2017.

In this meta-analysis, 23 studies were included. The result showed that the flapless placement significantly reduced the crestal bone loss with the mean difference of −0.14. This reduced bone loss could be explained by intact periosteum and blood supply which is a known advantage of flapless technique.[62] In flap technique, the branches of supraperiosteal vessels get compromised, affecting the blood supply.[63] Kim et al. in 2009[64] in their study on dogs stated that flapless implant placement presented a much richer vascularization. Al Juboori et al.[58] and Kim et al.[64] attributed lesser bone with flapless technique to the excellent defense to bacterial invasion because of the intact bloody supply. Jeong et al. in 2007[65] showed that sites with flapless technique had a greater bone–implant contact and less bone loss. Similar findings of reduced bone loss with flapless technique were noted by You et al.,[66] Mazzocco et al.,[37] Kumar et al.,[41] Shamsan et al.,[44] Maier,[49] and Sunitha and Sapthagiri.[55] The flapless technique ensures a favorable healing environment for the soft-tissue architecture as well as hard-tissue volume with reduced time for stable remodeling.[67]

Studies[5061] with the view that flapless surgery leads to more crestal bone loss than conventional flap failed to prove a significant difference. One of the reasons for more bone loss associated with flapless technique could be because of the contamination of the surgical site with the epithelial and connective tissue cells from the oral mucosa.[68]

Interestingly, several studies[454851535659] and reviews[520] showed comparable outcome with both the surgical techniques. The flapless surgery can thus be considered as an acceptable treatment option based on the evidence obtained from the literature. The use of CT scans, advanced planning software, surgical guides, and dynamic navigation systems can help to improve the predictability and precision.

Subgroup analysis comparing the guided flapless approach with the conventional surgery did not yield a significant result. This could be attributed to the limited data available and the variability of the guided approach used. Furthermore, there remain concerns with the deviations in the inclination and positioning of implants by flapless surgery from the ideally planned position, which could affect the outcome.[5]

Comparison of the freehand flapless placement with conventional surgery showed a significant difference, indicating that flapless surgery can affect the crestal bone loss even without the use of a guided approach.

Based on the results of this study, the choice of surgical technique significantly affects crestal bone level which is in agreement with a previous systematic review by Zhuang et al. in 2018.[23] However, the studies included have high heterogeneity, and the authors in cases of doubt have opted for direct visualization of the surgical field. Presurgical planning is a must to reduce the possible complications. The fear of such complications should not stop the clinicians to acknowledge the benefits that the flapless technique can provide. With the upcoming digital trends in implantology, flapless surgeries have the capacity to evolve with a greater safety margin.

The results of this review should be interpreted with caution because of its limitations. Confounding factors may have affected the outcomes. Further, less emphasis was given on local or systemic condition of patients. Furthermore, heterogeneity of the included studies was high. Double-blinded randomized controlled trials with broader pool of patients to determine the effect of flapless implant surgery on patient outcome variables are required to reach definitive conclusions.

CONCLUSIONS

Flapless technique of dental implant placement has significantly less crestal bone loss compared to the flap technique. Therefore, flapless implant surgery can be considered as a promising alternative to conventional flap

The use of a guided or freehand approach of flapless surgery both showed less crestal bone loss compared to flap surgery; however, significant results could not be obtained.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.