Evaluation of Proximal Contact Integrity and Associated Factors in Posterior Resin Composite Restorations: A Cross-sectional Study in Nairobi, Kenya

Background The global shift from dental amalgam to direct posterior resin composite restorations (RCRs), driven by aesthetic demands and the Minamata Convention, has increased the need to evaluate their clinical performance. Establishing proper proximal contact tightness (PCT) in Class II restorations is a critical, technique-sensitive parameter required to prevent food impaction, periodontal disease, and restoration failure. In Nairobi, Kenya, there is a lack of local data regarding technical failures like deficiencies in proximal contact integrity. This study aimed to evaluate the proximal contact tightness of Class II posterior RCRs placed over a five-year period in selected dental institutions in Nairobi. Methods A cross-sectional study was conducted at three sites: a private facility (UoNDP), a teaching hospital (UoNDS), and a public hospital (KNHDD). A total of 159 Class II RCRs placed between 2014 and 2019 were selected for clinical examination. PCT was assessed using a tactile method with dental floss and categorized as tight, too tight, loose, or open, utilizing a modified United States Public Health Survey (USPHS) tool. Data were analyzed using STATA version 19, employing Chi-square tests and multivariate analysis to identify associated factors. Results Of the 139 assessable restorations (20 were excluded due to missing adjacent teeth), 56.8% (n = 79) had tight contacts, while 43.2% (n = 60) exhibited unacceptable proximal tightness (22.3% loose and 20.9% open). Disparities between facilities were significant; 75% of restorations at KNHDD had unacceptable contacts, compared to 26.7% at UoNDP and 30% at UoNDS. Multivariate analysis revealed that placement at KNHDD was strongly associated with both open (aRRR = 4.71, p = 0.008) and loose contacts (aRRR = 33.88, p < 0.001). Additionally, secondary caries showed a significant association with loose contacts (aRRR = 6.08, p = 0.02). Conclusions The study found a high prevalence (43.2%) of inadequate proximal contacts in Class II posterior RCRs in Nairobi, Kenya. This underscores a critical quality gap in restorative procedures, particularly in public hospital settings. There is an urgent need for enhanced educational initiatives and professional development to improve clinical techniques and ensure the long-term success of composite restorations in the region.