Development of physico-chemical and surface mechanical properties of a fast photo-polymerised resin-based composite

Abstract

The advancement of fast photo-polymerised resin-based composites (RBCs) offers promising potential for improving efficiency in restorative dentistry by reducing curing times while maintaining desirable mechanical properties. However, concerns regarding their thermal response, degree of conversion (DC), and long-term stability under different curing conditions and exposure to the oral environment necessitate further investigation. This thesis explores the conversion, thermography, physical-mechanical, and chemical characteristics of RBCs designed for rapid polymerisation, addressing their behaviour under various light-curing protocols and post-curing environmental conditions. The first experimental study examined the impact of laser, quad-wave, and conventional LED curing protocols on mean temperature rise (ΔT) and DC of both fast and conventional bulk-fill RBCs at 4-mm depth. Results showed that high-intensity short-exposure curing generated lower radiant energy but still achieved efficient polymerisation, particularly in fast-cure RBCs. Standard exposure times resulted in higher DC and ΔT, with a positive correlation observed between temperature rise and conversion efficiency. The findings underscore the role of optimised irradiation in enhancing polymerisation effectiveness while controlling heat generation. Building on this, the second study assessed the influence of polymerisation protocols on water sorption, solubility, and hygroscopic expansion over 120 d in distilled water. Fast-cure RBCs demonstrated lower water uptake and solubility compared to conventional bulk-fill composites, with minimal variation between 3 s and 20 s curing. In contrast, conventional RBCs exhibited increased water sorption and solubility under rapid polymerisation, suggesting a material-dependent response. These results highlight the stability of fast-cure RBCs in aqueous environments, reinforcing their suitability for clinical application. The final study focused on the effects of solvent storage on surface hardness and bulk viscoelastic properties. After 30 d in 75% ethanol/water and distilled water, all materials exhibited reduced hardness, particularly at the bottom surface, with ethanol exposure exacerbating these effects. Despite this, the fast-cure RBC maintained comparable viscoelastic performance to conventionally cured materials. The data suggest that filler composition significantly influences mechanical integrity, contributing to resistance against deformation under prolonged solvent exposure. This research provides valuable insights into the optimisation of light-curing protocols for enhancing the performance of RBCs designed for rapid polymerisation. By demonstrating their efficient polymerisation, reduced water sensitivity, and mechanical resilience, this work supports their clinical application, particularly in high-demand restorative procedures. The findings contribute to the refinement of material formulations and curing strategies, aiding in the development of durable and efficient RBCs for modern dental practice.

Date of Award	27 May 2025
Original language	English
Awarding Institution	The University of Manchester
Supervisor	David Watts (Main Supervisor) & Nick Silikas (Co Supervisor)