Comparative Evaluation of Fracture Resistance of Premolar Teeth Restored with Monochromatic Composites and Nanocomposite in Class II Cavities – An in -vitro Study

Abstract

Background: The longevity and clinical success of posterior composite restorations depend largely on
their mechanical properties, particularly fracture resistance. With advancements in restorative dentistry,
newer monochromatic composites have been introduced to simplify shade matching while maintaining
acceptable strength and esthetics. However, limited evidence exists comparing their fracture resistance
with conventional nanocomposites in Class II restorations.
Aim: To evaluate and compare the fracture resistance of premolar teeth restored with two
monochromatic composites and one nanocomposite in standardized Class II cavities.
Materials and Methods: Forty extracted human premolar teeth were disinfected and mounted in
acrylic resin blocks 2 mm apical to the cementoenamel junction. Standardized Class II cavities were
prepared with an occlusal depth of 2 mm and proximal box depth of 1.5 mm. The specimens were
randomly divided into four groups (n = 10):
• Group I – Intact teeth (control)
• Group II – Restored with Omnichroma
• Group III – Restored with Vittra Unique APS
• Group IV – Restored with Filtek Z350
All cavity surfaces were etched using 37% phosphoric acid for 15 seconds, followed by application of
a universal bonding agent and light curing for 20 seconds. Restorations were completed using the
incremental layering technique. The specimens were subjected to thermocycling for 10,000 cycles
between 5°C and 55°C to simulate oral conditions. Fracture resistance was evaluated using a universal
testing machine with a 3 mm steel ball applied perpendicular to the restoration at a crosshead speed of
0.5 mm/min until fracture occurred. The obtained values were statistically analyzed using one-way
ANOVA and post hoc Tukey test with significance set at p < 0.05.
Results: Among the restored groups, Omnichroma demonstrated the highest fracture resistance values,
followed by Vittra Unique APS, whereas Filtek Z350 exhibited the lowest fracture resistance. Intact
teeth showed significantly greater resistance compared to all restored groups. Statistical analysis
revealed significant differences among the experimental groups (p < 0.05).
Conclusion: Monochromatic composites demonstrated superior fracture resistance compared to the
conventional nanocomposite tested in this study. Omnichroma showed the best performance, which
may be attributed to its advanced filler technology and higher filler loading. The findings suggest that
newer single-shade composites may provide enhanced mechanical durability and could be considered
reliable restorative materials for posterior Class II restorations.