The relationship between adequate keratinized mucosa and peri-implant disease: a systematic review and meta-analysis

Abstract

Background

Controversial conclusions have been drawn from recent researches that examined the impact of keratinized mucosa width on clinical parameters of peri-implant health status. The purpose of this meta-analysis is to assess the effect of keratinized mucosa width on these clinical parameters by combining data from different studies.

Methods

A systematic literature search was performed using PubMed, Web of Science, China National Knowledge Infrastructure (CNKI), and VIP Data from the beginning of the database until May 2024. Mean difference (MD) along with the 95% confidence interval (CI) were calculated for plaque index (PI), gingival index (GI), bleeding index (BI), probing depth (PD), clinical attachment level (CAL) and bone loss (BL). The Q test and I² statistic were used to determine heterogeneity. Publication bias was evaluated by Begg’s test and Egger’s test.

Results

A total of 30 articles were included for meta-analysis. Implants with adequate width of keratinized mucosa (≥ 2 mm) presented significantly reduced PI (MD: -0.30, 95% CI: -0.42 to -0.17), GI (MD: -0.26, 95% CI: -0.38 to -0.13), BI (MD: -0.20, 95% CI: -0.33 to -0.07), and BL (MD: -0.27, 95% CI: -0.42 to -0.12). Although significant heterogeneity was detected among the included studies, sensitivity analysis further demonstrated the robustness of the results.

Conclusions

The meta-analysis demonstrated that adequate width of keratinised mucosa (≥ 2 mm) around dental implants is associated with reduced plaque accumulation, tissue inflammation, and bone loss.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-025-05680-5.

Introduction

Dental implants are now accepted as a routine procedure for replacing missing teeth in the last few decades [1]. However, peri-implant inflammation, a pathological condition that begins in the soft tissues around dental implants, may lead to biological complications of the implant surrounding tissue, such as peri-implantitis and peri-implant mucositis [2]. Peri-implant mucositis affects the soft tissue only, if left untreated, it might eventually progress to peri-implantitis, which impacts both the soft and hard tissues [3]. These inflammatory complications are highly prevalent and adversely influence the long-term success of dental implant treatment [4]. Therefore, how to avoid the development of peri-implant inflammation has become a hot topic among academics. Several conditions, such as systemic disease, history of periodontitis, smoking, poor prosthesis contour and plaque control, have been recognized as potential risk factors for peri-implant inflammation [5]. One factor that is routinely investigated is the significance of keratinized mucosa on peri-implant health. To date, the adequate width of keratinized mucosa around dental implants for the maintenance of peri-implant health has been the subject of much debate.

The keratinized gingiva establishes a physical barrier between the oral environment and the periodontium’s connective tissues by being tightly connected to the teeth and underlying bone. A sufficient width of keratinized gingiva was thought to be critical for natural dentitions in order to preserve gingival health around natural teeth and slow the progression of periodontal disease [6]. The soft tissue around dental implants differs significantly from the soft tissue surrounding natural teeth in both anatomical and histologic ways. Collagen fibers in implants run parallel to the implant surface without direct anchorage [7]. This weak attachment, combined with reduced cellularity and vascularity in the peri-implant connective tissue, may make the peri-implant tissues more susceptible to breakdown than natural teeth during inflammatory disease processes [8]. However, still many investigations concluded that peri-implant tissue health could be maintained regardless of the presence or lack of keratinized mucosa [9, 10].

Good oral hygiene surrounding dental implants could be difficult to be achieved without the presence of keratinized mucosa [11]. Therefore, it seems reasonable that adequate width of keratinized mucosa is a crucial for keeping oral health and implant stability. In this regard, the most recent meta-analysis demonstrated that implants with sufficient width of keratinized mucosa had a reduced plaque index (PI), but probing depth (PD), soft-tissue recession, and marginal bone loss (BL) did not differ significantly between groups [12]. The strength of evidence from this meta-analysis was relatively low due to the insufficient statistical power, as only nine studies were included in their analysis, four of which were used for quantitative synthesis. Recently, several studies [9, 13–15] subsequent to that meta-analysis have emerged, not all confirmed the previous findings, and the controversy on this topic continues. Thus, whether insufficient keratinized mucosa is a risk factor for developing peri-implant inflammation remains unclear. With the most up-to-date evidence, we aimed to synthesize all available evidence to further comprehensively assess the influence of width of keratinized mucosa on peri-implant inflammation.

Methods

The current meta-analysis was carried out in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines [16].

PECO question

The focused clinical question of this meta-analysis was proposed by following PECO (Population, Exposure, Comparison, Outcome) principles [17]: Is sufficient keratinized mucosa width around dental implants protective against peri-implant disease?

Population: Patients with dental implants;

Exposure: Dental implants with inadequate width of keratinized mucosa (< 2 mm);

Comparison: Dental implants with adequate width of keratinized mucosa (≥ 2 mm);

Outcome: PI, gingival index (GI), bleeding index (BI), PD, clinical attachment level (CAL) and BL.

Search strategy

A systematic electronic search of PubMed, Web of Science, China National Knowledge Infrastructure (CNKI), and Chinese Science and Technology Periodical Citation Database (VIP) was performed from the beginning of the database until May 2024. Additionally, the reference lists of eligible studies and previously published review articles were further cross-checked in order to find more relevant studies. The keywords were as follows: (“attached gingiva” OR “keratinized gingiva” OR “keratinized mucosa” OR “attached mucosa” OR “soft tissue condition” OR “soft tissue volume” OR “gingiva volume” OR “soft tissue height” OR “gingiva height” OR “soft tissue width” OR “gingiva width”) AND (“peri-implantitis” OR “peri-implant pathology” OR “dental implant infections” OR “peri-implant bone loss” OR “peri-implant disease”). The literature search was undertaken by two authors (Z.Y.Z. and Z.Z) independently. When there was any disagreement, the senior author (Z.M.W.) was consulted to reach a consensus.

Selection criteria

We chose original research articles based on the following inclusion criteria: (1) human studies (could be defined as prospective or retrospective follow-up studies, or cross-sectional study); (2) studies on the impact of keratinized mucosa width on the development of peri-implantitis; (3) compared adequate width of keratinized mucosa (≥ 2 mm) vs. inadequate width of keratinized mucosa (< 2 mm) [18]; (4) studies on at least one periodontal index, including PI, GI, BI, PD, AL or BL; (5) the minimum follow-up time of the studies was six months; (6) articles published in the English or Chinese language.

The following exclusion criteria were applied: (1) animal study; (2) could not be published as a full report; (3) studies without available data; (4) studies without effective groups.

Data extraction

Data were collected and arranged in the following fields: first author, publication year, location, type of study, patient number, gender, age, implant number, follow-up time, clinical outcomes. Two independent authors (Z. Y.Z. and Z.Z) extracted relevant data from the included articles. Any discrepancy was resolved by discussion and consensus. If there was a lack of data information, we would try to contact the corresponding author in order to obtain required data.

Quality assessment

Two of the authors (Z.Y.Z. and Z.Z) independently assessed the quality of included studies by using the Newcastle-Ottawa Scale [19]. The Newcastle-Ottawa Scale uses a ‘star’ rating system to judge quality based on three aspects of the study: selection, comparability, and exposure. The quality assessment values ranged from 0 to 9 stars. Generally, studies with a score of 7 stars or more were considered to be of high quality.

Statistical analysis

The influence of keratinized mucosa on peri-implant clinical index was assessed using the difference values between adequate and inadequate keratinized mucosa width on peri-implant clinical index. And the total effect size was reported as mean difference (MD) with 95% confidence interval (CI). A p-value < 0.05 was considered to indicate statistically significant between groups. Statistical heterogeneity among studies was evaluated using the Q test and I² statistic. When p-value > 0.05 (Q test) and I² < 50%, it was considered to be non-existent heterogeneity. Then, the fixed-effects model was used to calculate the overall effect size. Otherwise, the random effects model was used. We conducted sensitivity analyses to assess the sources of heterogeneity and stability of the results. Publication bias was evaluated by Begg’s test and Egger’s test. A p-value < 0.05 was considered to indicate statistically significant publication bias. All analyses were conducted with Stata (version 12.0, Stata Corp, College Station, TX, USA).

Results

Search and screening

The initial search yielded a total of 2028 articles, including 1068 from PubMed, 824 from Web of Science, 62 from CNKI, 67 from VIP Data and seven from manual searching. Then, 1451 articles were chosen after duplicates were eliminated, and 51 potentially pertinent publications were selected following the article title and abstract were scrutinized, of which three articles were not found full text (inter-reviewer agreement, κ = 0.85). After reading the full text of the 48 remaining articles, we also disregarded 18 studies because they failed to meet one or more inclusion criteria (inter-reviewer agreement, κ = 0.727). Finally, the meta-analysis included 30 publications (Fig. 1). The excluded studies and reasons for exclusion were listed in Supplementary Table 1.

Fig. 1.

Flow chart from identification of eligible studies to final inclusion

Characteristics of included studies

A summary of the 30 included studies is given in Table 1. These studies were published between 1994 and 2024. All except one [20] of the studies were single-center clinical trials. Fifteen of them are prospective cohort studies [9, 13, 20–32], 13 cross sectional studies [15, 33–44], and two retrospective studies [14, 45]. The included studies involved a total of 1773 subjects, ranging in number from 15 to 130. According to eight studies [20, 22, 33, 34, 36, 37, 43, 44], 2.9–28% of the participants were smokers at the time of the study. There were 5241 implants in all. Three studies reported having only mandibular implants [20, 21, 25], 18 studies reported having both maxillary and mandibular implants [9, 13–15, 22–24, 27, 29–31, 34, 39, 40], and the remaining studies did not report the location of implant placement. Keratinized mucosa width was assessed at the mid-buccal aspect in 15 studies [13–15, 22, 24–28, 30, 36–38, 40, 43], and two studies provided mean values for the assessed mesial, mid-buccal, and disto-buccal aspects [35, 42]. The measurements of keratinized mucosa width were collected at the mid-buccal and mid-lingual aspects in three studies [20, 21, 41], and were either addressed as average values or reported separately for the two aspects. The follow up time varied from 6 months to 25 years.

Table 1.

Characteristics of eligible studies included in this meta-analysis

First author	Year	Location	Type of study	No. of patient	Gender (%Female)	Age	Systemic condition	No. of implant	Implant position	Follow-up time	Outcomes
Mericske-Stern	1994	Switzerland	Prospective cohort study	33	51.5%	69.0 ± 7.0	NA	66	Mandible	5 years	PI, BI, PD, AL
Chung	2006	America	Prospective cohort study	69	59.4%	61.3 ± 13.6	Diabetes: 6 Non-diabetes: 63	339	Maxilla: 198 Mandible: 141	> 3 years	PI, GI, BI, PD, BL
Bouri	2008	America	Cross sectional study	76	NA	> 18	NA	200	NA	1 year	PI, GI, PD, BL
Adibrad	2009	Iran	Cross sectional study	27	56.0%	63.1 ± 6.9	Without conditions known to affect bone metabolism	66	Maxilla: 24 Mandible: 42	2 years	PI, GI, BI, PD, AL, BL
Kim	2009	Korea	Prospective cohort study	100	48.0%	52.2 ± 10.8	NA	276	Maxilla: 132 Mandible: 144	13 months	PI, GI, PD, BL
Schrott	2009	America	Prospective cohort study	73	52.1%	58.0 ± 9.6	Without conditions known to affect bone metabolism	386	Mandible	5 years	PI, BI
Crespi	2010	Italy	Prospective cohort study	29	37.9%	25–67	Without systemic diseases	164	Maxilla: 132 Mandible: 32	4 years	PI, GI, BI, PD
Esper	2012	Brazil	Cross sectional study	109	NA	16–50	Without systemic diseases	202	NA	1 year	PI, GI, PD
Boynueğri	2013	Turkey	Prospective cohort study	15	53.3%	54.0 ± 10.0	Without systemic diseases	36	Mandible	1 year	PI, GI
Amponpan	2014	Thailand	Cross sectional study	51	70.6%	33–71	Without conditions known to affect bone metabolism	82	NA	42 months	PI, GI, BI, PD, AL
Zhang	2014	China	Prospective cohort study	25	44.0%	45.5 ± 9.9	Without conditions known to affect bone metabolism	40	NA	1 year	PI, GI, PD, BL
Askin	2015	Turkey	Prospective cohort study	18	55.6%	47.5 ± 11.3	Without systemic diseases	60	Maxilla: 32 Mandible: 28	6 months	PI, GI, PD, BL
Romanos	2015	Germany	Retrospective cohort study	118	46.6%	62.6 ± 13.7	NA	320	NA	> 2.6 years	PI, BI
Esfahanizadeh	2016	Iran	Cross sectional study	36	47.2%	30–76	Without conditions known to affect bone metabolism	110	NA	3 years	PI, GI, BI, PD
Souza	2016	Brazil	Cross sectional study	80	68.8%	52.0 ± 11.7	Without uncontrolled diabetes	269	Maxilla: 129 Mandible: 140	1 year	PI, PD, AL
Ueno	2016	Japan	Cross sectional study	60	61.7%	60.7 ± 12.9	Diabetes: 1 Non-diabetes: 59	90	Maxilla: 30 Mandible: 60	> 1 year	PI, GI, PD
Yang	2017	China	Prospective cohort study	120	37.5%	51.6 ± 4.4	Without conditions known to affect bone metabolism	156	NA	6 months	PI, BI, PD, BL
Crespi	2018	Italy	Prospective cohort study	42	59.5%	28–71	Without systemic diseases	123	Maxilla Mandible	8 years	PI, GI, BI, PD
Perussolo	2018	Brazil	Prospective cohort study	71	66.7%	55.7 ± 10.7	Without conditions known to affect bone metabolism	202	Maxilla: 106 Mandible: 96	4 years	PI, PD, AL
Qian	2018	China	Prospective cohort study	58	36.2%	51.4 ± 8.3	Without conditions known to affect bone metabolism	158	Maxilla: 78 Mandible: 80	4 years	PI, BI, PD
Fatih	2019	Iraq	Cross sectional study	39	61.5%	20–65	Without systemic diseases	157	Maxilla: 101 Mandible: 56	1–9 years	PI, BL
Grischke	2019	Germany	Cross sectional study	52	55.8%	67.6 ± 10.3	Without conditions known to affect bone metabolism	231	NA	3–25 years	GI
Monje	2019	Spain	Cross sectional study	37	37.6%	49.9 ± 12.9	Without conditions known to affect bone metabolism	66	Maxilla Mandible	≥ 3 years	PI, BI, PD, BL
Sukuroglu	2019	Turkey	Prospective cohort study	29	10.3%	36–65	Without systemic diseases	71	Maxilla Mandible	6 months	PI, GI, PD
Ravidà	2020	America	Cross sectional study	40	55.0%	64.5 ± 9.0	10% presented with hyperglicaemia	68	Maxilla: 39 Mandible: 39	> 1 year	PD, BL
Kabir	2021	Germany	Cross sectional study	130	54.6%	70 ± 10.32	Without compromised immune system and hyperglycemia	130	Anterior: 38 Posterior: 92	1–31 years	PI, GI, BI, PD
Babayiğit	2023	Turkey	Prospective cohort study	31	58.1%	21–69	Without uncontrolled systemic diseases	87	Maxilla: 40 Mandible: 47	2 years	PI, GI, PD, BL
Gurbuz	2023	Turkey	Prospective cohort study	34	53.2%	53.55 ± 1.72	Without conditions known to affect bone metabolism	34	Maxilla Mandible	2 years	PI, BI, PD, BL
Carvalhaes	2024	Brazil	Retrospective cohort study	84	67.9%	61.9 ± 10.1	Without conditions known to affect bone metabolism	242	Maxilla: 80 Mandible: 162	5–15 years	PI, BI, PD, BL
Eroglu	2024	Turkey	Cross sectional study	87	65.5%	48.1 ± 7.7	Without conditions known to affect bone metabolism	87	Maxilla: 33 Mandible: 54	> 1 year	PI, GI, PD, BL

AL, attachment loss; BI, bleeding index; BL, bone loss; GI, gingival index; PD, probing depth; PI, plaque index

Risk of bias assessment

Based on the Newcastle-Ottawa Scale, an average score of 6.43 was achieved after the assessment of study quality. Sixteen studies had an overall high risk of bias (4 to 6 stars) and 14 studies (7 to 9 stars) were judged to have a low risk of bias (inter-reviewer agreement, κ = 0.732). Summarized results of the assessment of risk of bias are presented in Supplementary Table 2.

Meta-analysis of clinical indices

Compared with implants with inadequate width of keratinized mucosa, PI (MD: -0.30, 95% CI: -0.42 to -0.17), GI (MD: -0.26, 95% CI: -0.38 to -0.13) and BI (MD: -0.20, 95% CI: -0.33 to -0.07) values of implants with adequate width of keratinized mucosa were significantly reduced (P < 0.05) (Figs. 2 and 3). There was significant heterogeneity across studies for PI (I² = 95.5%, P < 0.01), GI (I² = 91.5%, P < 0.01) and BI (I² = 97.0%, P < 0.01).

Fig. 2.

Forest plot of clinical index related to plaque accumulation

Fig. 3.

Forest plot of clinical indices related to gingival inflammation

Sensitivity analysis of clinical indices

Heterogeneity appeared significant for PI, GI and BI, so we conducted further sensitivity analysis investigating the influence of a single study on the combined effect size by omitting one study in each turn. The findings of the sensitivity analysis showed that PI, GI and BI results were stable, deleting any of the studies did not have a significant impact on the experimental results (Fig. 4A, B and C).

Fig. 4.

Sensitivity analysis of clinical indices. A, plaque index. B, gingival index. C, bleeding index

Meta-analysis of clinical parameters

The overall effect sizes of comparison between implants with “adequate” and “inadequate” width of keratinized mucosa on PD and CAL were − 0.03 (95% CI: -0.16 to 0.10) and − 0.09 (95% CI: -0.22 to 0.04) respectively (Fig. 5). BL value of implants with adequate width of keratinized mucosa was significantly reduced (MD: -0.27, 95% CI: -0.42 to -0.12) (Fig. 6). Heterogeneity analysis showed that PD (I² = 83.1%, P < 0.01) and BL (I² = 80.8%, P < 0.01) had significant heterogeneity.

Fig. 5.

Forest plot of clinical parameters related to gingival tissue destruction

Fig. 6.

Forest plot of clinical parameter related to alveolar bone destruction

Sensitivity analysis of clinical parameters

To explore the robustness of the results of PD and BL, we performed sensitivity analyses by omitting one study at a time and calculating the combined effect size for the remaining studies. We found that the PD and BL results were stable and credible, none of the individual studies appeared to have appreciable impacts on the overall combined effect sizes (Fig. 7).

Fig. 7.

Sensitivity analysis of clinical parameters. A. probing depth. B. bone loss

Publication bias analysis

Funnel plots revealed that PI, GI and CAL scatter were basically symmetric, while BI, PD and BL scatter were slightly asymmetric (Fig. 8). Egger’s test suggested that BL had obvious publication bias. Trim-and-fill analysis indicated there was no difference between the adjusted value of BL and the original value. For PD and BI, four potentially missing studies were detected. Additionally, there was no significant difference between BI adjusted values and the original values. Nevertheless, the PD adjusted value differs significantly from the original value (Table 2).

Fig. 8.

Funnel plots for the meta-analysis

Table 2.

Quantitative analysis of publication bias

Outcome	Studies trimmed/total studies	Trim-and-fill analysis		Begg’s test (P-value)	Egger’s test (P-value)
		Mean difference	95% Confidence interval
Plaque index	0/28	-0.30	-0.42, -0.17	0.42	0.65
Gingival index	0/18	-0.26	-0.38, -0.13	0.60	0.81
Bleeding index	4/19	-0.31	-0.43, -0.19	0.49	0.12
Probing depth	4/29	-0.14	-0.28, -0.004	0.56	0.53
Attachment loss	0/5	-0.09	-0.22, 0.04	1.00	0.62
Bone loss	0/14	-0.27	-0.42, -0.12	0.06	0.01

Subgroup analysis

The results of subgroup analyses according to study design, general condition, implant position, length of follow-up, and Newcastle-Ottawa Scale are presented in Supplementary Table 3. Both prospective cohort and cross-sectional studies showed that implants with adequate keratinized mucosa displayed considerably lower PI, GI, BI, and BL than implants with inadequate keratinized mucosa. Keratinized mucosa width had a significant relationship with PI, GI and BI in most subgroups but not in the subgroup of retrospective cohort studies for PI and GI, or subgroup with follow-up time > 3 years for GI and BI. For PD and BL, a substantial association was observed with keratinized mucosa width in subgroup with Newcastle-Ottawa Scale ≥ 7.

Discussion

The literature on the significance of keratinized mucosa for peri-implant health is inconsistent. The influence of keratinized mucosa width on peri-implant inflammation was assessed in the present meta-analysis. We included a total of 30 original studies, and six clinical indicators, including PI, GI, BI, PD, CAL and BL were used to determine the status of peri-implant inflammation. The present meta-analysis showed that adequate keratinized mucosa implants, compared with inadequate keratinized mucosa implants, significantly reduced PI by -0.30 (95% CI: -0.42 to -0.17), GI by -0.26 (95% CI: -0.38 to -0.13), BI by -0.20 (95% CI: -0.33 to -0.07) and BL by -0.27 (95% CI: -0.42 to -0.12). Nevertheless, comparisons of other clinical indicators (PD and CAL) did not reach statistically significant differences.

The accumulation of dental plaque is widely recognized as a primary pathogenic factor contributing to peri-implant inflammation [46]. Previous meta-analyses have discovered a statistically significant association between a minimum of 2 mm of keratinized mucosa and reduced plaque accumulation [12, 47, 48]. This conclusion is consistent with the results obtained from our meta-analysis. We found that implants with adequate keratinized mucosa (≥ 2 mm) had significantly lower plaque accumulation than those with inadequate keratinized mucosa. The reliability of this finding has been reinforced by analyzing the outcomes of prospective and cross-sectional studies separately. A lack of keratinized mucosa may simplify plaque accumulation, owing to the increased mobility of the lining mucosa, which facilitates plaque accumulation in the pockets [44]. Consistent results on plaque accumulation across multiple meta-analyses imply that having a sufficient width of keratinized mucosa is advantageous for improving oral hygiene around dental implants. When placing dental implants, the presence of sufficient amounts of keratinized tissue should be considered.

The GI, which has been used to clinically define the degree of gingival inflammation, can also be utilized to evaluate the peri-implant health [49]. Unfortunately, this important outcome of inflammation (GI) at peri-implant sites was not taken into consideration by the most recent meta-analysis [47]. According to previous studies, soft tissue grafting procedures for keratinized tissue gain could result in a significantly greater improvement of GI values [49]. This suggested that GI is an important indicator for evaluating the clinical effects of keratinized tissue. In our meta-analysis, eighteen studies reported the GI values and eight of these studies reported lower values of GI in implants with adequate keratinized mucosa (≥ 2 mm) [22, 24, 25, 27, 32–34, 37]. The findings of the combined investigation support the results of the eight previously mentioned studies. Based on the present meta-analysis, we speculate that inadequate keratinized mucosa is likely to be a contributing factor to peri-implant inflammation. However, as the GI was initially introduced to asses inflammation around teeth and not implants, these conclusions should be considered with some caution.

BI and bleeding on probing (BOP) have frequently been utilized as indicators of the existence of an inflammatory lesion in the peri-implant mucosa [2, 50]. In contrast to implants with inadequate keratinized mucosa, implants with adequate keratinized mucosa exhibited a substantial decrease in BOP, but not in BI value, according to the most recent meta-analysis [47]. Considering only seven original studies were included for the BI quantitative synthesis, the inconsistent results in previous meta-analysis might be attributed to the unreliable results caused by the limited number of original studies investigating BI. In the present meta-analysis, 15 of the 30 studies reported the BI, with seven of these studies showing significantly higher BI at implant sites with inadequate compared to adequate width of keratinized mucosa [20, 24, 28, 29, 37, 42, 45]. Pooled analyses revealed that implants with inadequate keratinized mucosa had a considerably higher BI. In light of the aforementioned findings, we speculate that implants with inadequate keratinized mucosa are more prone to gingival inflammation and bleeding. This might result in subsequent bone loss, then leading to failure of the implant.

The long-term outcome and stability of the dental implant mainly depend on the peri-implant bone level [40]. In clinical investigations, long-term peri-implant inflammation has been found to stimulate the loss of supporting bone around implants [51]. A recent meta-analysis stated that the lack of keratinized mucosa was significantly associated with higher prevalence of peri-implantitis defined by marginal BL ≥ 2 mm [52]. Another meta-analysis summarized individual studies but failed to detect a significant association of keratinized mucosa width with bone levels around dental implants [48]. In our meta-analysis, bone levels differed significantly between implants with “adequate” and “inadequate” width of keratinized mucosa, favoring implants with adequate keratinized mucosa (≥ 2 mm). This result supports the findings of previous meta-analyses, which revealed a considerable increase in BL at implants with inadequate keratinized mucosa (< 2 mm) in comparison to the control sites [47]. Our findings provide additional evidence that adequate keratinized mucosa might be beneficial to prevent BL around dental implants.

We must emphasize that while the width of the keratinized gingival plays a significant role, other risk factors such as oral hygiene, implant design, periodontal diseases, smoking habits, and the patient’s overall systemic health can also profoundly impact the development and progression of peri-implant diseases. Therefore, when assessing peri-implant diseases, it is crucial to consider all these factors in conjunction with the width of the keratinized mucosa. To ascertain the potential impact of systemic diseases on our analysis, we conducted subgroup analyses on patients with and without systemic diseases. The results indicate that systemic diseases did not significantly affect the outcomes of this study. However, given that the majority of studies do not report smoking and non-smoking status, it poses a challenge for us to conduct a separate analysis for smokers and non-smokers.

Some limitations should be considered in our meta-analysis. First, we limited our investigation to articles published in English or Chinese. We did not consider studies in other languages. Second, the analysis included studies with a variety of confounding factors (e.g., implant position, implant system, population selection, number of patients, calculated outcome measures, and follow-up time), which contributed to the significant degree of heterogeneity among the studies. Third, variations in the location and methodology of keratinized mucosa measurement employed in various investigations may impact the precision of the analysis findings. Finally, there is publication bias in some studies. The author perhaps more likely to publish if favorable results are acquired.

Conclusion

Within these limitations, it was concluded that inadequate keratinized mucosa around dental implants was associated with increased plaque accumulation, soft-tissue inflammation and marginal bone loss. Hence, clinicians might think about soft-tissue grafting to augment keratinized mucosa in cases where it is inadequate in order to support peri-implant health. However, given the limitations of the meta- analyses, further prospective clinical studies are required, with homogenous case definitions and similar analysis, in order to confirm what is stated in the current meta-analysis.

Electronic supplementary material

Below is the link to the electronic supplementary material.

Author contributions

W-ZM, Z-ZY, and ZZ designed the study. ZZ, and Z-ZY acquired the study data. W-PC and Z-YZ analyzed and interpreted the data. Z-ZY and W-PC wrote the first draft of the manuscript. All authors revised the manuscript and approved it for publication.

Funding

This work was funded by the Natural Science Foundation of Tianjin (No.23JCYBJC01130), the Key Discipline Construction Project of Tianjin Stomatological Hospital (No.2022P01), Tianjin High-level Talents Development Program for the Health Fields (No. TJSQNYXXR-D2-114) and Tianjin Health Research Project (No. TJWJ2023MS034).

Data availability

The data for the current study are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.