Hani S. AlMoharib,Raed AlRowis,Abdulrahman AlMubarak,Hossam Waleed Almadhoon,Nahid Ashri
The relationship between matrix metalloproteinases-8 and peri-implantitis: A systematic review and meta-analysis
Peri-implantitis,Matrix Metalloproteinases-8,Biomarker,Implant,Meta-analysis
Background Peri-implantitis diagnosis typically involves evaluating inflammation, pocket depth, bleeding, and bone loss around dental implants. Although these methods are reliable and convenient, they mainly determine the history of the disease instead of the current activity or disease susceptibility. This meta-analysis evaluates whether the matrix metalloproteinase (MMP)-8 level in the peri-implant crevicular fluids (PICF) can be associated with peri-implantitis. Methods The research was conducted in February 2022, where three electronic databases were searched and complemented with a manual search. The search criteria included original cross-sectional and longitudinal studies that compared MMP-8 biomarkers in crevicular fluids around healthy implants with unhealthy implants (peri-implantitis). To assess the risk of bias, the Newcastle-Ottawa Quality Scale was used. The data was analyzed using the RevMan program, and the standardized mean difference (SMD) with a 95% confidence interval was applied to evaluate the MMP-8 levels, with a significance level of p less than 0.05. Results Out of 1978 studies, six were eligible. This meta-analysis included 276 patients divided into two groups; 121 patients (124 implants) in the peri-implantitis group and 155 patients (156 implants) in the health implants group. The quality of the included studies was evaluated as high to moderate. The meta-analysis showed a significant increase in MMP-8 levels in individuals with peri-implantitis compared to those with healthy implants (SMD = 1.43, 95% CI [0.19, 2.68], p = 0.02). Conclusion The current meta-analysis found that the levels of MMP-8 in PICF were significantly elevated in peri-implantitis cases compared to healthy controls, indicating a potential link between MMP-8 and peri-implantitis. However, the meta-analysis does not provide evidence for MMP-8 as a diagnostic test for peri-implantitis. Further research, specifically diagnostic accuracy studies, is needed to establish the value of MMP-8 as a diagnostic tool for peri-implantitis.
The relationship between matrix metalloproteinases-8 and peri-implantitis: A systematic review and meta-analysis

Peri-implantitis diagnosis typically involves evaluating inflammation, pocket depth, bleeding, and bone loss around dental implants. Although these methods are reliable and convenient, they mainly determine the history of the disease instead of the current activity or disease susceptibility. This meta-analysis evaluates whether the matrix metalloproteinase (MMP)-8 level in the peri-implant crevicular fluids (PICF) can be associated with peri-implantitis.

The research was conducted in February 2022, where three electronic databases were searched and complemented with a manual search. The search criteria included original cross-sectional and longitudinal studies that compared MMP-8 biomarkers in crevicular fluids around healthy implants with unhealthy implants (peri-implantitis). To assess the risk of bias, the Newcastle-Ottawa Quality Scale was used. The data was analyzed using the RevMan program, and the standardized mean difference (SMD) with a 95% confidence interval was applied to evaluate the MMP-8 levels, with a significance level of p less than 0.05.

Out of 1978 studies, six were eligible. This meta-analysis included 276 patients divided into two groups; 121 patients (124 implants) in the peri-implantitis group and 155 patients (156 implants) in the health implants group. The quality of the included studies was evaluated as high to moderate. The meta-analysis showed a significant increase in MMP-8 levels in individuals with peri-implantitis compared to those with healthy implants (SMD = 1.43, 95% CI [0.19, 2.68], p = 0.02).

The current meta-analysis found that the levels of MMP-8 in PICF were significantly elevated in peri-implantitis cases compared to healthy controls, indicating a potential link between MMP-8 and peri-implantitis. However, the meta-analysis does not provide evidence for MMP-8 as a diagnostic test for peri-implantitis. Further research, specifically diagnostic accuracy studies, is needed to establish the value of MMP-8 as a diagnostic tool for peri-implantitis.

Peri-implantitis is a progressive stage of implant disease that affects the surrounding tissues by interrupting the peri-implant epithelial seal and developing peri-implant pocket and irreversible bone loss (Klokkevold and Newman, 2000, Lindhe and Meyle, 2008). Several factors have been attributed to peri-implantitis development, including bacterial infection, occlusal overloading, micro gaps, implant surgery trauma, and smoking (Lachmann et al., 2007, Lekholm et al., 1986, Meffert, 1992, Rosenberg et al., 1991, Tonetti and Schmid, 1994). Implant mobility can occur early when osseointegration does not occur, just before the development of peri-implantitis, since the latter usually occurs at an advanced stage of implant failure (Prashanti, Sajjan, & Reddy, 2011). However, the exact mechanism of destruction in peri-implantitis is still not completely known (Nomura et al., 2000). Peri-implantitis and implant failures have been reported to happen in 6%–10% of newly placed implants (H. Arakawa et al., 2012). Peri-implantitis diagnosis typically involves evaluating inflammation, pocket depth, bleeding, and bone loss around dental implants. (Armitage, 2003, Lang et al., 2000). Although these methods are reliable and convenient, they mainly determine the history of the disease rather than the present activity or disease susceptibility (Armitage, 1996, Armitage, 2004). In addition, all these measures are subjective, not specific, and can only give information about peri-implantitis at the moment of examination (Wolf & Lamster, 2011). Since research on gingival crevicular fluid (GCF) helps clarify periodontitis, analyses of the components of peri-implant crevicular fluid (PICF) may provide critical evidence about the inflammatory process and their mediators. Proteolytic enzymes such as inflammatory cytokines and matrix metalloproteinases (MMPs) and mediators such as prostaglandin E2 and interleukin-1β have been studied as potential diagnostic markers for peri-implantitis (Aboyoussef et al., 1998a, Aboyoussef et al., 1998b, Basegmez et al., 2012, Boutros et al., 1996, Kao et al., 1995, Panagakos et al., 1996, Paolantonio et al., 2000). MMP-8, also recognized as collagenase-2, is a product of neutrophils mainly but can be expressed by other cells, including odontoblasts, fibroblasts, keratinocytes, leukocytes, macrophages, and endothelial cells (Costa-Junior et al., 2013). This mediator has a high potential to initiate the inflammatory destruction of collagen, particularly type I and III, making it a crucial factor in the development of periodontal disease. (Gursoy et al., 2010). Therefore, MMP-8 has been implicated in having the same destructive feature in peri-implantitis (Gursoy et al., 2010, Kiili et al., 2002, Kinane, 2000; T. Sorsa et al., 2006; T. Sorsa, Tjaderhane, & Salo, 2004; T. Sorsa et al., 1988, Tervahartiala et al., 2000). Several studies have documented that MMP-8 can appear in the PICF, implying a role in the development and progress of peri-implantitis (Arakawa et al., 2012, Kivela-Rajamaki et al., 2003a, Kivela-Rajamaki et al., 2003b, Ma et al., 2000, Nomura et al., 2000, Teronen et al., 1997, Xu et al., 2008). This potential association between MMP-8 and peri-implantitis can aid in the early identification of the condition, which can lead to prompt treatment for the patient, and ultimately improve the longevity of the implant. Therefore, this review and meta-analysis aim to evaluate, in a systematic manner, the available data on the relationship between changes in MMP-8 levels in PICF and peri-implantitis.

This study followed the PRISMA-P and Cochrane handbook guidelines for systematic reviews and meta-analysis (Higgins et al., 2019, Page et al., 2021).

On 20 February 2022, PubMed via MEDLINE, Scopus, and Web of Science were searched using Boolean operators (OR, AND) to combine the following search keywords and accessible terms: “Matrix metalloproteinase-8,” “MMP-8,” “Collagenase-2,” “Dental Implants,” and “Peri-implantitis.” A search strategy was built and initially applied to PubMed and then amended to other databases (Supplementary file 1). Moreover, gray literature, Google Scholar, and reference lists of studies were searched for potential additional publications to complement the database search.

This review answers the following question: for healthy patients with a dental implant, can the increase in MMP-8 levels in the PICF be associated with peri-implantitis? The study adopts the following items: population, exposure, comparison, outcome, and setting. • P: Healthy participants who received a minimum of one loaded dental implant. • E: Peri-implantitis. • C: Healthy implants. • O: Mean difference in MMP levels between the two groups. • S: Cross-sectional and prospective longitudinal studies. For this review, the exclusion criteria include: the existence of systemic/chronic diseases or disorders; unreported levels of MMP-8 in the crevicular fluids; sample collection during an early stage of osseointegration (less than six months); uncertain/unreported criteria of peri-implant disease; articles written in languages other than the English language; and studies of other types, such as animal studies and reviews.

Three independent authors (HA, RA, and AA) manually reviewed titles and abstracts of the studies that resulted from the database search after exporting them to EndNote software, removing the duplicates, and transforming them into Microsoft Excel. The data was extracted from studies that met the inclusion criteria. A detailed report was obtained regarding all articles that appeared to meet the inclusion criteria and articles where insufficient information from the title/abstract stage to judge. This report classified the potential studies into three categories: included, excluded, or indefinite articles. In case of uncertainty on including any article, a senior author (NA) was consulted. The same authors then deeply reviewed the full texts of each potentially included article, and finally, a list of the final included articles was made. Any further indecision in the full-text screening step was resolved by consulting a senior reviewer whenever needed. Cohen’s k coefficient was calculated to identify the inter-reviewer reliability.

Two authors (HA and RA) used a standardized Excel sheet to perform the data extraction phase. The following information was extracted: study ID; patients and implants/teeth numbers per group; characteristics of participants; exposure characteristics, including implant function time, assessed biomarkers, type of assay/kit, characterization of peri-implant/periodontal tissues, clinical parameters, and biomarker outcomes.

The cross-sectional subscale of the Newcastle-Ottawa scale allocated the included studies according to the quality of their methodology. According to the scale, the quality of studies can be given the highest score of 10 stars and categorized the studies based on their score into low quality (0–3 stars), moderate quality (4–6 stars), or high quality (≥7 stars). Two assessors (HA and AA) completed the quality assessment of included studies independently, and a third author (NA) was referred to in cases of indecision. The possibility of publication bias could not be assessed in this meta-analysis owing to the limited number of included studies (less than ten studies).

Review manager software (RevMan) was used to conduct the current meta-analysis and heterogeneity tests. Program settings were adjusted to compare the levels of MMP-8 between the groups using a standardized mean difference (SMD) and confidence interval (CI) of 95%. Two tests (Chi2 and I2) were used as indicators for the level of heterogeneity between the included studies. When the heterogeneity between studies at Chi2 of less than 0.1 and p-value I2 greater than 50%, analysis settings were adjusted in the program to be on the random-effect model. Outcome findings with a p-value of less than 0.05 were considered statistically significant.

The database search identified 1975 potentially eligible articles in addition to 3 resulting studies in the manual search (1978 studies in total), of which 530 articles were deleted using the duplicate deletion feature in EndNote, and other 1265 articles were excluded after titles/abstracts were reviewed. Subsequently, the remaining 14 potentially eligible articles remained for deep full-text screening. Finally, five eligible articles (Figueiredo et al., 2020, Gao et al., 2018, Hentenaar et al., 2021, Song et al., 2019, Wang et al., 2016) were included (PRISMA flowchart; Fig. 1). Cohen’s k coefficient for inter-reviewer agreement in the title/abstract screening and full-text screening was 0.83 and 0.86, respectively, which indicates a reliable agreement among the assessors.

Table 1 displays the summary and baseline information of the included studies in this meta-analysis. Five articles (Figueiredo et al., 2020, Gao et al., 2018, Hentenaar et al., 2021, Song et al., 2019, Wang et al., 2016) were included in this meta-analysis, and all of them are cross-sectional studies, which were conducted in the Netherlands (Hentenaar et al., 2021), Brazil (Figueiredo et al., 2020), the USA (Gao et al., 2018), and China (Song et al., 2019). Worthy to note that as one study (Gao et al., 2018) assessed MMP-8 levels in two different populations, “Han” and “Uygur”, we considered it as two separate studies in the meta-analysis in order to detect if there were any potential influences of these different ethnicities. Overall, 316 patients were investigated in the included studies; only 276 patients were of our meta-analysis scope. This review included 121 patients (124 implants) in the peri-implantitis group and 155 patients (156 implants) in the control group, with their mean ages ranging from 38.2 to 65.3 years. In the included studies, implant function time was not less than six months to assess the MMP-8 level and other biomarker levels, such as IL-1β, IL-6, GSH-Px, MDA, TNF-α, TIMP. Different biomarker assessment assay/kits were used to evaluate the MMP-8 level, including Multiplex immunoassay, Enzyme-linked immunosorbent assay, ProcartaPlex TM Multiplex Immunoassay, PCR; Relative quantification tool, and Custom human Quantibody arrays.

Based on the quality assessment tool for cross-sectional studies, the quality of the included studies was determined to be high. Some of the included studies have a high risk related to blinding the outcome assessment. Moreover, most included studies have not described the response ratio or the features of the responders and the non-responders. The results of the quality assessment for the studies included in the analysis are shown in Table 2.

Five studies (Figueiredo et al., 2020, Gao et al., 2018, Hentenaar et al., 2021, Song et al., 2019, Wang et al., 2016) reported MMP-8 levels in individuals with healthy implants and peri-implantitis. The meta-analysis showed a statistically significant increase in MMP-8 levels in peri-implantitis patients compared to those with healthy implants (SMD = 1.43, 95% CI [0.19, 2.68], p = 0.02) (Fig. 2). The results were heterogeneous (p less than 0.00001, I2 = 95%), with the study by Song et al. (Song et al., 2019) identified as the main source of heterogeneity. Removing this study reduced the heterogeneity but did not completely resolve it [(0.32, 95% CI; −0.33 to 0.97, p = 0.33); p = 0.0002, I2 = 82%]. However, this heterogeneity is justified due to using different biomarker assessment assays/kits in the included studies.

Abnormal MMP-8 expression has been linked to disease development throughout the body and has been related to neuro-inflammation, gene polymorphism, cancer development, and others (Arechavaleta-Velasco et al., 2014, Lee et al., 2014). Several studies used MMP-8 to diagnose and monitor periodontitis progression and treatment (Emingil et al., 2014, Farhad et al., 2013, Nizam et al., 2014). Consequently, MMP-8 association with peri-implantitis seems a logical sequence of investigation. To the authors' knowledge, this is the first meta-analysis that evaluated all literature related to the diagnosis of peri-implantitis using the MMP-8 biomarker. Meta-analysis results revealed a significant increase in MMP-8 levels in peri-implantitis compared to healthy implant cases. However, this result was consistent with previous reports that associated increased MMP-8 levels with early implant failures (Basegmez et al., 2012, Thierbach et al., 2016). A recent systematic review highlighted moderate evidence in the literature to support using biomarkers such as MMP-8 to explore peri-implant diseases. Qualitatively, this review (Ghassib, Chen, Zhu, & Wang, 2019) indicated MMP-8 levels elevation in peri-implant diseases. Other studies supported that MMP-8 has the potential to be used to evaluate the progression of periodontal and peri-implant diseases (Hikaru Arakawa et al., 2012; Timo Sorsa et al., 2016). Contrary to previously mentioned results, Aboyoussef et al. (Aboyoussef et al., 1998a, Aboyoussef et al., 1998b) found that MMP biomarkers, including MMP-8, were unreliable indicators of implant health. Although implant structural and histological features differ from natural teeth, peri-implantitis pathology appears similar to periodontitis. Since research on GCF aided in understanding periodontitis, analyses of the components of PICF may offer critical information about the inflammatory process and its mediators. Proteolytic enzymes such as MMPs and inflammatory cytokines and mediators such as prostaglandin E2 and interleukin-1β have been studied as diagnostic markers for peri-implantitis (Aboyoussef et al., 1998a, Aboyoussef et al., 1998b, Basegmez et al., 2012, Boutros et al., 1996, Kao et al., 1995, Panagakos et al., 1996, Paolantonio et al., 2000). MMPs are a group of zinc-dependent metallopeptidases that have similar structures but differ genetically (Ryan and Golub, 2000, Ryan et al., 1996). During tissue repair or destruction, MMPs can collectively cleave and metabolize all extracellular matrix substrates (Ryan and Golub, 2000, Ryan et al., 1996). Generally, MMPs are released as a result of stimuli by major inflammatory cells and residing connective tissue cells during the process of pathologic tissue destruction or remodelling, including implant osseointegration (Arakawa et al., 2012, Costa-Junior et al., 2013). MMPs enzymes comprise five basic subgroups: stromelysin, collagenases, gelatinases, matrilysins, and membrane-type MMPs (H. Arakawa et al., 2012). The collagenase subgroup of MMPs includes mainly MMP-1, MMP-8, and MMP-13 (Hernandez et al., 2007, Hernandez et al., 2006, Kiili et al., 2002; T. Sorsa et al., 2011; T. Sorsa et al., 2006; T. Sorsa et al., 1988, Tervahartiala et al., 2000). Reports have documented increased levels of these collagenases in cases of gingivitis, chronic periodontitis, and peri-implantitis (Arakawa et al., 2012, Basegmez et al., 2012). MMP-8 is the most potent proteinase to induct the process of collagen type I and III destructions, which renders MMP-8 a vital biomarker in the pathogenesis of periodontal diseases. Thus, MMP-8 has been implicated in having the same destructive feature in peri-implantitis (Gursoy et al., 2010, Kiili et al., 2002, Kinane, 2000; T. Sorsa et al., 2006; T. Sorsa et al., 2004; T. Sorsa et al., 1988, Tervahartiala et al., 2000). In addition, several studies have documented that MMP-8 can be detected in PICF, implying a role in the incidence and progress of peri-implantitis (Arakawa et al., 2012, Kivela-Rajamaki et al., 2003a, Kivela-Rajamaki et al., 2003b, Ma et al., 2000, Nomura et al., 2000, Teronen et al., 1997, Xu et al., 2008). This potential relation can play a role in the early detection of peri-implantitis. Thus, it can help provide early treatment for the patient and longer implant survival. In the literature, many articles investigated different aspects of MMP-8 biomarker in PICF and GCF as an indicator for peri-implantitis/implant diseases. For instance, Kivela-Rajamaki et al. (Kivela-Rajamaki et al., 2003a, Kivela-Rajamaki et al., 2003b) in their two consecutive studies about the characteristics of MMP-8 in PICF. They collected 72 healthy control and diseased implant fluid samples and used western immunoblotting to detect MMP-8. MMP-8 levels were found to be significantly elevated in the PICF of diseased implants compared to healthy implants. Both studies concluded that MMP-8 could be a useful chair-side diagnostic biomarker when observing peri-implantitis progress and treatment through PICF. Nomura et al. (Nomura et al., 2000) supported the studies above when they found that the levels of MMP-8 were significantly higher in the PICF and GCF of diseased implants than in the GCF of healthy implants, whereas there was no significant difference in MMP-8 levels between the diseased PICF and GCF. In addition, Xu et al. (Xu et al., 2008) compared MMP-8 levels in GCF and PICF of 19 patients with either gingivitis, chronic periodontitis, or peri-implantitis. Although the number of sites is relatively low, they concluded that in similar cases of deep chronic periodontitis sites, PICF confined higher MMP-8 levels and activity than GCF. Genetically, Costa-Junior et al. (Costa-Junior et al., 2013) supported these findings by examining the connection between the C-799 T polymorphism in the MMP-8 gene and early implant failure in 180 healthy and diseased implants. They found that the polymorphism in the MMP-8 gene, specifically in the promoter region, was associated with early implant failure, suggesting that it could be a genetic biomarker for the risk of implant loss. Basegmez et al. (C. Basegmez et al., 2012) collected PICF samples from 72 implants in 3-, 6-, 12-, and 18-months intervals by a masked examiner and reported that MMP-8 levels increased from the 3rd to the 18th-month samples. This increase was also correlated with plaque and gingival indices score increase. The study concluded that MMP-8 could be an early predictor for peri-implantitis. Salvi et al. (Salvi et al., 2012) examined and compared implants to natural teeth for a 6-week follow-up. Their result showed that MMP-8 was higher around the implants than gingiva around the tooth. MMP-8 decreased after oral hygiene restarting, concluding MMP-8 reversibility. MMP-8 reached the peak around implants on day 21, the last day for plaque accumulation and refraining from oral hygiene. This study concluded that the early increase in the level of MMP-8 could be used to predict peri-implantitis. Arakawa et al. (H. Arakawa et al., 2012) performed a prospective study on 64 randomly selected patients and followed up for at least one year. PICF were collected, and clinical parameters were assigned to classify the severity of peri-implantitis based on annually adjusted vertical bone loss. PICF were collected twice from patients with peri-implantitis and matched to randomly selected healthy controls to compare the levels of MMP-8 of both groups. The result showed a higher level of MMP-8 in peri-implantitis subjects compared to randomly selected healthy controls. Also, they concluded that MMP-8 is found in peri-implantitis cases only, leading to the same conclusion of previous studies (Arakawa et al., 2012, Basegmez et al., 2012). Ma et al. (Ma et al., 2000) investigated the correlation of MMP-8 to vertical bone loss and found that MMP-8 levels were significantly higher in the cases of bone loss (greater than3 mm) than in the patients with less bone loss. This result indicates the levels of MMP-8 increased according to the severity of the bone loss. Hence, its initial increase seems normal and indicative of disease initiation, which correlates with the other review studies. With all diagnostic technologies present for the practitioner in the literature, a question arises of what level of MMP-8 is considered healthy, peri-implant mucositis, or peri-implantitis. Aboyoussef et al. (Aboyoussef et al., 1998a, Aboyoussef et al., 1998b) could not differentiate between the levels of MMP-8 in peri-implant mucositis and healthy mucosa. They suggested more critical analysis is needed. Salvi et al. (Salvi et al., 2012) examined the level of MMP-8 after restraining oral hygiene for 21 days and found a rise in MMP-8 level to 3000 pg/site. MMP-8 level returned to normal after oral hygiene reconstruction. This suggests an increase in MMP-8 level with mucositis compared to healthy mucosa. Kivela-Rajamaki et al. (Kivela-Rajamaki et al., 2003a, Kivela-Rajamaki et al., 2003b) measured the mean value of the MMP-8 level. They found that the mean values of peri-mucositis and peri-implantitis are 6.74 and 7.69, respectively, which is not statistically significant. Therefore, according to this study, MMP-8 cannot be used to distinguish between peri-implantitis and peri-implant mucositis. In periodontitis cases, Sorsa et al. (T. Sorsa et al., 2010) established that healthy levels of MMP-8 were less than 14 ng, whereas levels of diseased sites were higher than 14 ng. Prescher et al. (Prescher et al., 2007) demonstrated healthy values to be less than 7.4 ng and diseased values to range from 6 to 65 ng. However, specific values differentiating peri-implant and healthy conditions have not yet been documented, unlike periodontal diseases. This systematic review and meta-analysis has certain limitations that must be considered when assessing the results. One major concern is the small sample size of the meta-analysis and the limited number of studies included (five studies). This may affect the generalizability of the meta-analysis findings. Additionally, the high level of reported heterogeneity among the studies suggests that methodological variations may not be fully accounted for in the analysis. Therefore, future studies should be conducted with a larger sample size and a more rigorous study design to confirm the relationship between MMP-8 and peri-implantitis. Additionally, research should focus on evaluating the diagnostic value of MMP-8 in order to increase the understanding of the underlying mechanisms and biological pathways that may be associated with peri-implantitis.

The current meta-analysis found that the levels of MMP-8 in PICF were significantly elevated in peri-implantitis cases compared to healthy controls, indicating a potential link between MMP-8 and peri-implantitis. However, the meta-analysis does not provide evidence for MMP-8 as a diagnostic test for peri-implantitis, as it does not assess diagnostic accuracy. Further research, specifically diagnostic accuracy studies, is needed to establish the value of MMP-8 as a diagnostic tool for peri-implantitis.

No funding was received from any public, commercial, or non-profit organizations for this study.

Due to the nature of study being a review of existing literature, no institutional eithical board review was conducted.

Hani S. AlMoharib: Conceptualization, Investigation, Methodology. Raed AlRowis: Methodology. Abdulrahman AlMubarak: Data curation. Hossam Waleed Almadhoon: . Nahid Ashri: Supervision, Conceptualization, Investigation, Methodology.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.