Evaluation of proximal contact tightness 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 tightness. This study aimed to evaluate the proximal contact tightness of Class II posterior RCRs placed over a five-year period and their associated factors 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 recorded using a modified United States Public Health Survey (USPHS) tool modified to include class II PCT categorized as either tight, loose, or open. Data were analyzed using STATA v.19, employing Chi-square tests and multivariate analysis to identify associated factors. RESULTS: Of the 139 assessable restorations, 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 associated with both open (aRRR = 6.17, p = 0.038) and loose contacts (aRRR = 38.73, p = 0.005). Secondary caries showed an association with loose contacts (aRRR = 6.78, p = 0.001). The age of the restoration was found to confound the relationship between both facility and secondary caries, and PCT. CONCLUSIONS: The prevalence of inadequate proximal contacts in class II posterior RCRs across three Nairobi dental facilities was high (43.2%), with open and loose contacts associated with the facility and loose contacts associated with secondary caries, highlighting the need for standardized protocols, better training, improved access to materials, and future studies to investigate the impact of procedural and operator factors in resource-limited settings.