For treating patients with partially edentulous ridges, dental implants play an important role. While implant-supported restorations have been shown to be successful over the long run, biological complications, including peri-implantitis and technical complications, should be considered [1,2].

Peri-implant disease are pathological inflammatory changes that occur in the tissue surrounding an implant [3]. Peri-implantitis, a condition characterized by peri-implant mucosa inflammation and consequent loss of the supporting alveolar bone, poses a significant concern in periodontics. The condition typically occurs after peri-mucositis, which is a disease usually caused by plaque accumulation [4]. In addition, the configuration of inflammatory cells in peri-implantitis is different from periodontitis. Peri-implantitis mostly exhibits a more acute inflammatory pattern compared to the chronic inflammation pattern of periodontitis [5,6]. Numerous papers have presented varying incidence of peri-implantitis, collectively affirming their common occurrence [6]. As an inflammatory status affecting the surrounding tissues of dental implants, peri-implantitis has emerged as a significant concern for both patients and dental practitioners.

Implant-supported fixed prosthesis is a successful solution for patients with partially edentulous ridges. However, the choice between implant-supported bridge and splinted crowns remains controversial. Clelland et al. [7] have reported that splinted crowns are inclined to distribute the occlusal forces on implants, which leads to a lower incidence of prosthodontic complications and less strain on alveolar bone. Furthermore, proper oral hygiene maintenance, especially within interproximal spaces is critical to avoid peri-implantitis [7]. According to Ravidà et al. [8], implant-supported bridges had a lower prevalence of peri-implantitis and a higher survival rate compared to splinted crowns in a 3-unit edentulous area. Yi et al. [9] showed that pocket depth and plaque index were lower in implant-supported bridges compared to splinted crowns in 3-unit edentulous area, though both showed comparable success rates.

Although comparative studies between implant-supported bridges and splinted crowns have been conducted, information about the height of alveolar bone loss due to peri-implantitis is unavailable. As peri-implantitis has varying degrees, this is an important consideration. Therefore, this study was designed to investigate the prevalence and degree of peri-implantitis between implant-supported bridges and splinted crowns in 3-unit and 4-unit posterior edentulous areas and identify factors that could affect implant prognosis.

Study sample

The present study was designed to include 79 patients who underwent implant placement and prosthetic restoration between January 2011 and November 2020 in Kyungpook National University Dental Hospital. The number of subjects required for the Mann-Whitney U test is based on G*Power 3.1.9.7 program, for α=0.05, power (1-β)=0.95, a total of 70 subjects are required. The enrolled patients underwent treatment with 3-implant supported bridges or 4-implant supported splinted crowns in 4-unit posterior edentulous areas and 2-implant supported bridges or 3-implant supported splinted crowns in 3-unit posterior edentulous areas to restore the posterior free-end partial edentulous areas. In total, 86 patients were treated with 3-implant-supported splinted crowns, and 31 patients were selected to match the sex and age distribution of patients treated with 3-implant-supported bridges, 2-implant supported bridges, and 4-implant supported splinted crowns (Fig. 1, 2).

Fig. 1. The flow chart of the study sample selection.

Fig. 2. Illustration of the restoration types presented in the study: (A) 2-implant-supported 3-unit bridge (2-IB); (B) 3-implant-supported splinted crowns (3-IC); (C, D) 3-implant-supported 4-unit bridge (3-IB); (E) 4-implant-supported splinted crowns (4-IC).

This study was approved by the Institutional Review Board of Kyungpook National University Dental Hospital (KNUDH-2024-01-02-00).

Inclusion criteria

- Patients who received implant placements in posterior partially edentulous area.

- Patients who received prosthetic restoration after implant placement.

- The presence of opposing occlusion (implants or teeth).

Exclusion criteria

- Insufficient clinical records or radiographs.

- Not visiting the clinic for supportive periodontal treatment.

- Not visiting the clinic for >1 year after prosthetic restoration.

- Severe systemic diseases or conditions.

- Implants used in implant-assisted removable prostheses.

Data collection

Panoramic and periapical radiographs were obtained for evaluation before implant surgery, immediately after implant surgery and following prosthetic restoration. The radiographic examination was used to analyze the prevalence of peri-implantitis and assessment of radiographic bone levels. Radiographic examination of the alveolar bone level was conducted using the implant shoulder as the reference point. The measurement of radiographic marginal bone loss was respectively performed on the mesial and distal sides of the implants. The radiographs were evaluated by a single investigator and the length of the implant was used to correct for vertical distortion.

Factors associated with implants were recorded at each placement site, including the implant fixture’s length and diameter, implant abutment connection (external or internal), bone augmentation (or sinus augmentation), surgery stage, implant placement location, and distribution.

Definition and classification of peri-implantitis

In 2017 World Workshop, the guidelines to diagnose peri-implantitis were established. The guidelines suggest peri-implantitis is a condition characterized by plaque-associated disease with increased probing depth, the presence of bleeding on probing (BOP) and/or suppuration, or recession of the gingival margin, and radiographic alveolar bone loss seen on comparison with previous radiographs [4]. In this study, peri-implantitis was diagnosed using the classification system recently proposed by Froum and Rosen [10]:

Early stage: a pocket probing depth (PPD)≥4 mm with BOP and/or suppuration. Radiographic bone loss less than 25% of the implant length.

Moderate stage: a PPD≥6 mm with BOP and/or suppuration. Radiographic bone loss less within 25%–50% of the implant length.

Advanced stage: a PPD≥8 mm with BOP and/or suppuration. Radiographic bone loss more than 50% of the implant length.

Statistical analyses

The chi-square test was used to determine the association between prosthetic characteristics, implant position, and the prevalence of peri-implantitis. The Mann-Whitney U test was used to compare the mean difference between implant platform and bone levels in splinted crowns and implant-supported bridges.

The level of statistical significance was set at 5% (α=0.05). Statistical analysis was done using IBM SPSS Statistics (version 29.0; IBM Corp., Armonk, NY, USA) for Windows.

A total of 229 implant sites from 79 patients were included in the study. A total of 2 implants failed, which results in a survival rate of 99%. The follow up period ranged from 2 to 12 years.

Data on patient demographics, including sex (male: 48%; female: 52%), age (mean: 60.99 years), and patient-related factors, are presented in Table 1. Variables such as sex, smoking, diabetes, and osteoporosis did not significantly impact the risk association (p>0.05, Fisher’s exact test and chi-square test) (Table 1).

Details on the type of restoration, bone augmentation (or sinus augmentation) performed; stage of the surgery; and diameter, length, distribution and location of the implant placements are presented in Table 2. Among the 79 restorations recorded, 17 were 2-implant-supported 3-unit bridges (34 implants), 22 were 3-implant-supported 4-unit bridges (66 implants), 31 were 3-implant-supported splinted crowns (93 implants), and 9 were 4-implant-supported splinted crowns (36 implants). Bone augmentation and implantation sites had a statistically significant relationship with the prevalence of peri-implantitis, with mandibular implants showing a low risk of association (p<0.05, Fisher’s exact test). Implants with a diameter >5 mm were classified as wide, whereas those <5 mm were classified as regular. Overall, 96% of the implants were of the regular type, and the diameter did not have statistically significant association with the incidence of peri-implantitis. Furthermore, other factors did not show a statistically significant association on the risk of peri-implantitis (Table 2).

Peri-implantitis occurred around 14% of the implants (13% on bridges and 15% on splinted crowns). According to the chi-square analysis, the restoration type was not statistically significant (Table 3).

Peri-implantitis was classified using the Froum and Rosen classification, as shown in Table 4. The middle implants (P2 in 3-unit edentulous areas, P2–P3 in 4-unit edentulous areas) had the highest rate of peri-implantitis compared with other implant positions.

Additionally, the differences in mean distance between implant platform and marginal bone levels in implants with implant-supported bridges or splinted crowns were not statistically significant (Fig. 3).

Fig. 3. Box plot diagram illustrating radiographic evidence of the distance between implant platform level and bone level (in mm) for implant-supported bridge and implant-supported splinted crown.

In this study, the severity and the prevalence of peri-implantitis was analyzed regarding the restoration type, specifically comparing implant-supported bridges and splinted crowns in the posterior edentulous area. The restoration type did not have statistically significant impact in the prevalence or severity of peri-implantitis. These results are in accordance with the findings of Yi et al. [9], who reported no significant difference in the prevalence of peri-implantitis according to restoration type in the posterior 3-unit edentulous region. However, another study indicated that both non-splinted and splinted crowns demonstrated a greater prevalence of peri-implantitis than that of implant-supported bridges in 3-unit edentulous area [8].

Middle implants (P2 in 3-unit edentulous areas, P2–P3 in 4-unit edentulous areas) demonstrated the higher percentage of peri-implantitis than other implant positions. This finding is consistent with the results of a peri-implantitis analysis, which showed that middle implants had the highest risk [9].

Bone augmentation demonstrated significant association with the prevalence of peri-implantitis. The dimension of alveolar ridge plays an important role for primary implant stability and long-term success of implants [10]. A recent meta-analysis and systematic review showed that lateral ridge augmentation has been shown to provide peri-implant health with reduced mucosal inflammation and a lower risk of alveolar bone loss [11]. Additionally, Jung et al. [12] reported the stability of marginal bone level of the implant after guided bone regeneration in a long-term observation.

The implant site also has significant association with the peri-implantitis. Moraschini et al. [13] presented that maxilla (38.3%) showed a greater risk of peri-implantitis compared to the mandible (28.9%), including data from both anterior and posterior areas. However, in the posterior maxilla, the prevalence of peri-implantitis was 18% (range: 5.2%–46.4%) which is slightly lower than the posterior mandible which was 19% (range: 7.2%–48.6%) [13]. Few studies have investigated the relationship between the prevalence of peri-implantitis and implant location. In majority of these studies, a higher incidence of peri-implantitis in the posterior mandible was reported [14,15]. However, Serino and Turri [16] demonstrated that implants in the maxilla are mostly associated with peri-implantitis, primarily in the anterior maxilla. Because of the maxilla’s large medullary part, there are more cellular and vascular components, which leads to lower bone density [16]. The researchers proposed that bone quality may have impact on peri-implantitis and consequently results in progressive bone loss, which may be exacerbated by occlusal force. According to Bidez and Misch [17], using three implants can reduce bending moments by half compared to using two implants. For D2 bone quality, pontics can be placed between 2-implant-supported bridges; however, for D3 bone quality, one implant per missing tooth is necessary [18]. Therefore, clinicians should consider each patient’s bone quality when deciding between implant-supported bridges and splinted crowns.

In the current study, no statistically significant difference was observed in the prevalence of peri-implantitis between 1- and 2-stage surgical procedures. Gheisari et al. [19] presented there was no significant difference in alveolar bone loss between 1- and 2-stage procedure. Although various surgical methods have been discussed, no studies have identified the surgical procedure stage is associated with the prevalence of peri-implantitis [20].

None.

The authors declare that they have no competing interests.