Abstract
BACKGROUND: Resin-modified glass ionomer cements (RMGICs) are commonly used as base materials in restorative dentistry due to their fluoride release and chemical bonding properties. Incorporating bacterial cellulose nanocrystals (BCNCs) into RMGIC may improve its mechanical properties, especially fracture resistance (FR), which is critical in Class II restorations. This study aimed to evaluate the effect of BCNC-reinforced RMGIC on the fracture resistance and fracture patterns mesio-occluso-distal (MOD) cavities restored premolars using the sandwich technique. MATERIAL AND METHODS: Sixty sound human maxillary premolars were randomly divided into five groups (n = 12) based on the restoration protocol: Group I) intact teeth (positive control); Group II) MOD cavities left unrestored (negative control); Group III) MOD cavities restored with short-fiber reinforced composite (SFRC) only; Group IV) MOD cavities restored with conventional RMGIC + SFRC; Group V) MOD cavities restored with 1% BCNC-reinforced RMGIC + SFRC. The restorations in groups III to V were finally covered with 1 mm of nanohybride composite. All specimens underwent thermocycling. Fracture resistance was tested using a universal testing machine, and fracture patterns were classified as restorable or unrestorable based on the CEJ level. Data were analyzed using one-way ANOVA and Tukey's post-hoc test (P < 0.05). RESULTS: The negative control group (Group II) exhibited significantly lower fracture resistance compared to all other groups (P < 0.001). Group V (BCNC-modified RMGIC+SFRC) showed the highest fracture resistance, but no significant differences were found among Groups I (intact teeth), III (SFRC only), IV (RMGIC+SFRC), and V (P > 0.05). Group II had predominantly unrestorable fractures, while other groups showed a higher proportion of restorable fractures. CONCLUSIONS: The incorporation of BCNC into RMGIC as a base in Class II restorations improved fracture resistance and resulted in more favorable fracture patterns, suggesting its potential as a reinforcing agent in restorative dentistry.