Shallow vestibular depth as a risk indicator for peri-implantitis: a retrospective analysis of 336 implants

Dental implants are one of the most commonly preferred treatment options today for the rehabilitation of missing teeth. Advances in surgical techniques and improvements in implant surface properties have resulted in high success rates. Thanks to these positive outcomes and long-term survival rates, dental implants have become one of the most widely accepted treatments among both patients and clinicians [1]. However, clinicians are paying increasing attention to epidemiological studies reporting peri-implant inflammatory diseases, particularly peri-implantitis [2].

The 2017 classification of peri-implant diseases, jointly published by the American Academy of Periodontology and the European Federation of Periodontology, defines peri-implant health, peri-implant mucositis, peri-implantitis, and peri-implant soft and hard tissue defects. According to this consensus, peri-implant health is characterized by the absence of peri-implant mucositis and peri-implantitis, and clinically, erythema, swelling, or suppuration are not expected. According to the current report by Tonetti et al. [3] although isolated bleeding at a single site that is not profuse is considered acceptable in a clinically healthy state, the absence of BOP is preferred. Peri-implant mucositis is defined by the presence of clinically evident inflammation, while peri-implantitis is characterized by inflammation of the peri-implant mucosa followed by progressive loss of supporting bone; typically presenting with increased PD (PD ≥ 6 mm) accompanied by bleeding and/or suppuration on probing and radiographic evidence of bone loss [4, 5].

Peri-implant diseases are a common global problem in implant patients and pose a significant challenge in modern implant dentistry; the main reasons for this are the need for early diagnosis/regular follow-up and the variable/unpredictable outcomes of peri-implantitis treatment [6]. In a recent systematic review and meta-analysis based on the 2017 World Workshop criteria, the weighted mean prevalence values calculated by meta-analysis were reported as 63.0% at the patient level and 59.2% at the implant level for peri-implant mucositis; and 25.0% at the patient level and 18.0% at the implant level for peri-implantitis [7].

The long-term success and sustainability of dental implants are closely related to the health and stability of peri-implant tissues. Matarasso et al. [8], reported approximately 96% survival in implants at 10-year follow-up, emphasizing the importance of MBL stability in maintaining long-term clinical success. Similarly, Iorio-Siciliano et al. [9], drew attention to the relationship between peri-implant soft tissue conditions and MBL stability in long-term follow-up.

According to the 2017 World Congress of Periodontology [10], the main risk factors for peri-implant diseases include a history of periodontitis, inadequate plaque control, and inadequate maintenance treatment. Various predisposing factors associated with peri-implantitis and facilitating biofilm accumulation have been identified; one of these is VD [11].

VD is defined as the distance between the coronal margin of the attached gingiva and the deepest point of the mucobuccal fold [12]. Adequate VD is generally considered necessary for maintaining proper oral hygiene [13]. It is thought that the combination of a narrow keratinized mucosal band and shallow VD facilitates food impaction during mastication and makes effective oral hygiene difficult [14]. Therefore, vestibuloplasty/mucogingival procedures aimed at increasing the VD may be considered to improve patient comfort and facilitate plaque control, particularly in selected cases where discomfort is reported during brushing and/or hygiene cannot be maintained [15].

The 2017 periodontal disease classification suggested that a shallower vestibular fornix may be associated with soft tissue inflammation, which can make plaque removal difficult and thus hinder effective oral hygiene [16]. Furthermore, sufficient VD in areas adjacent to dental implants has been reported as a parameter that may be related to long-term implant outcomes [17].

The number of studies in the literature that jointly address the relationship between VD peri-implant soft tissue parameters, MBL, and peri-implant disease status appears to be limited. The current literature focuses more on KM width and peri-implant phenotype, with VD mostly reported as a secondary or observational finding. This study aims to evaluate the possible relationship between VD and peri-implant soft tissue health, radiographic bone loss, and peri-implant diseases. It is thought that the findings will contribute to the evidence-based definition of this clinically important morphological parameter.

In our study, the prevalence of peri-implantitis was found to be 25.6% (n=86) and the rate of shallow VD was 26.5% (n=89), highlighting the clinical significance of the problem. These findings indicate that in clinical practice, peri-implantitis is encountered in approximately one in every four implants, and similarly, shallow VD is encountered in approximately one in every four implants. Furthermore, the prevalence of peri-implantitis in the shallow VD group was 38.2%, and in the multivariate GEE analysis (categorical threshold model: VD≤4 mm), shallow VD showed an independent association with peri-implantitis (OR=2.405; 95% CI: 1.233–4.690; p=0.010) supports the notion that VD may be a clinically important anatomical component in maintaining peri-implant health.

The OR of 2.40 identified for shallow VD can be clinically interpreted as follows: the odds of peri-implantitis occurring in implants with shallow VD are approximately 2.4 times higher than in implants with adequate VD. This finding suggests that a shallow vestibule is not merely a condition that complicates oral hygiene practices; it may be independently associated with peri-implantitis even when other factors are controlled for in a multivariate model.

The presence of KM is generally considered advantageous for peri-implant tissues; although evidence is heterogeneous, increasing data suggest that a width of ≥2 mm of KM around implants may be associated with lower plaque indices, reduced inflammation, and minimal marginal bone loss [28‐32]. In this study, exploratory bivariate analyses showed that implants with shallow VD had a significantly higher proportion of KM width <2 mm (p<0.001), while adequate VD was associated with a higher prevalence of thick mucosa (p<0.001). Halperin-Sternfeld et al. [13], reported in their 6-year longitudinal follow-up studies that shallow VD regions had a gingival margin band approximately 1 mm narrower than regions with adequate VD. Similarly, Monje and Blasi [33], showed that 95.7% of implant regions with gingival margin width <2 mm had shallow VD. Current systematic reviews and clinical studies have shown that a KM width <2 mm, especially when combined with a thin gingival phenotype, may be associated with gingival recession, MBL, plaque accumulation, and an increased risk of peri-implantitis. Furthermore, a narrow KM has been associated with greater discomfort during brushing [34‐38]. Other studies have demonstrated that pro-inflammatory cytokine levels are significantly higher in peri-implant regions with a thin soft tissue phenotype [39, 40]. Reduced stability of peri-implant soft tissues in areas with both shallow VD and insufficient KM may promote plaque retention and bacterial colonization, thereby increasing the microbial load in peri-implant pockets; this is consistent with the findings of our study.

Although VD, CM width, and mucosal thickness are biologically related, our multivariate GEE analysis identified VD≤4 mm (categorical threshold model) as the only soft tissue parameter independently and significantly associated with peri-implantitis. This finding suggests that shallow VD may not merely be a reflection of other soft tissue characteristics and may be a clinically unique risk indicator. Although gingival margin width was not found to be an independent risk indicator in the model, shallow VD cases are often seen in conjunction with insufficient gingival margin width in clinical practice; therefore, a comprehensive soft tissue approach should be adopted in evaluation and treatment planning.

In our study, implants with shallow VD had higher mean mPI, mGI, BOP, and PD values compared to implants with adequate VD in exploratory bivariate analyses (p<0.001, p=0.014, p=0.022, and p=0.032, respectively). Halperin-Sternfeld et al. [13], reported that shallow VD was strongly associated with a narrow gingival margin, poor oral hygiene, and adverse peri-implant health outcomes at 6-year follow-up. Similarly, an increase in VD has been reported to be associated with lower mPI and mGI scores [41]. Furthermore, Di Leone et al. [42] also reported that VD was significantly associated with accumulation (mPI) at the implant level. It is known that shallow vestibules facilitate plaque accumulation, predisposing to gingival inflammation, gingival recession, and discomfort during oral hygiene. Previous reports have shown that shallow VD impedes plaque control and is closely related to inflammation, findings that are consistent with our study.

In our study, the amount of gingival recession in the shallow VD group was found to be statistically significantly greater than in the adequate VD group. A previous study focused on the relationship between inadequate VD and increased gingival recession in natural teeth [14]. Shallow vestibules have been reported to predispose to gingival recession [43]. Kadkhodazadeh et al. [44], emphasized that maximum soft tissue recession occurred in areas where thin biotype and shallow VD were present together. Insufficient VD may contribute to recession directly through muscle traction, while also indirectly increasing recession through the difficulty of oral hygiene procedures and soft tissue trauma. Indeed, Iorio-Siciliano et al. [45], reported that adequate height of keratinized tissues is critical for the long-term stability of peri-implant marginal tissues; they emphasized that adequate KM height preserves tissue health by facilitating biofilm control and reducing discomfort during brushing. These data support, from a biomechanical and hygienic perspective, why the shallow VD and accompanying narrow KM band detected in our study are associated with a higher rate of gingival recession and inflammation.

The mean radiographic bone loss was also found to be significantly higher in the shallow VD group. Consistent with our study, Halperin-Sternfeld et al. [13], reported greater radiographic bone loss in shallow VD areas. Some studies have suggested that soft tissue grafting around the implant may reduce MBL, biofilm accumulation, and peri-implant inflammation [39, 46]. Therefore, in areas with shallow VD and soft tissue insufficiency, procedures such as vestibuloplasty or soft tissue grafting may be considered in selected cases to help prevent peri-implant bone loss.

This study demonstrated that peri-implant health was significantly higher in areas with adequate VD, while peri-implantitis was more common in areas with shallow VD. It has been suggested that a shallow vestibule may increase the risk of peri-implantitis by limiting toothbrush access to the mucosal margin of implant-supported restorations [47]. A recent cross-sectional study also reported an association between shallow VD (≤4 mm), absence of attached mucosa, and peri-implantitis [48]. Kadkhodazadeh et al. [44], demonstrated a significant association between plaque accumulation, shallow VD, and peri-implantitis in their retrospective study involving 139 implants. In our multivariate GEE analysis, VD≤4 mm was found to be independently associated with peri-implantitis even when age, smoking, KM width, and mucosal thickness were controlled for. Considering all these findings together, it can be said that shallow VD may be a clinical peri-implant phenotype component associated with peri-implantitis.

One of the most striking findings of our study is the linear relationship between VD and the odds of peri-implantitis. VD was found to be statistically significant not only as a categorical threshold value (4 mm and below) but also when analyzed in a multivariate GEE (continuous model: VD, mm) (p = 0.034). According to our multivariate analysis results, a 1 mm increase in VD was associated with an approximately 11.7% decrease in the odds of peri-implantitis (OR = 0.883). This finding supports that the effect of VD is not limited to a fixed “breakpoint” but is associated with a protective mechanism directly related to the amount of depth.

There are significant anatomical differences in VD between the maxillary anterior and mandibular posterior regions; our findings indicate that VD is generally wider in the maxillary anterior, whereas in the mandibular posterior it is frequently ≤4 mm due to anatomical/muscular connections. However, despite the inclusion of the implant site in the GEE model, the persistence of an independent association between shallow VD and peri-implantitis suggests that this relationship may not be explained solely by regional anatomy and that shallow VD may be a clinically significant risk indicator. Therefore, careful evaluation of soft tissue conditions in implant planning, particularly in regions such as the posterior mandible, and consideration of approaches to increase VD in selected cases may be appropriate.

Insufficient VD, when combined with insufficient KM width, can further compromise oral hygiene by increasing food impaction during mastication. Consequently, correction of shallow vestibules may be considered to facilitate effective oral hygiene and ensure long-term peri-implant health [49]. While the current literature mostly focuses on KM width and the general peri-implant phenotype, this study considers VD as a specific component of the peri-implant soft tissue phenotype and demonstrates that it is a risk indicator that shows an independent relationship with peri-implantitis even when other soft tissue parameters are controlled.

This study has some limitations. The retrospective and cross-sectional design prevents establishing a causal relationship between VD and peri-implantitis. Since peri-implant soft tissue health and implant success are influenced by numerous local and systemic factors, it is difficult to completely isolate the independent contribution of VD. Although calibrated with ImageJ, the use of panoramic radiographs in MBL assessment may limit measurement accuracy compared to periapical or 3D imaging. The small sample size in the shallow VD and KM=0 mm groups necessitated categorization (e.g., KM <2 mm), which may affect generalizability. Although intra-observer reliability (ICC/Kappa) was not formally analyzed, all measurements were performed by a single experienced expert to minimize variability. Finally, excluding restorations that obstruct PD measurement may lead to selection bias and limited generalizability. However, considering that observations in patients with multiple implants are not independent, the use of the GEE approach can be considered an important aspect that increases the power of statistical modeling.

The findings of this study suggest that shallow VD may be associated with peri-implant health indicators and the presence of peri-implantitis. Implants in areas with shallow VD showed significantly more plaque accumulation, gingival inflammation, bleeding, and radiographic bone loss compared to areas with adequate VD. Furthermore, shallow VD may be associated with mucosal trauma and gingival recession, along with difficulties in maintaining adequate oral hygiene. Overall, the combination of shallow VD and inadequate KM appears to be associated with a phenotype in which peri-implantitis is more frequently observed. However, larger-scale, prospective, and longitudinal studies are needed to confirm the causality and clinical implications of these observed associations.