Fundamental aspects of dental resin-composite stability

Abstract

Dental resin-composite is a material made of inorganic filler phase and organic matrix phase with a coupling agent that bonds the filler to the matrix. These materials became popular in dentistry for their improved aesthetic and clinical performance. The indications of these materials had expanded to involve restoration of anterior and posterior teeth including the more extensive restorations. The introduction of Bulk fill materials made their clinical applications less time consuming especially with their claimed improved clinical performance such as less shrinking ability, less water sorption and more stability in the oral environment.In this research we aimed to study the general stability of a wide group of resin-composite materials with regard of their polymerisation shrinkage, the effect of solvents storage on their mass and volume, their sorption and solubility and the effect of the solvents storage on the diametral strength and surface hardness of these materials. Bonded disk method was used to assess the polymerisation shrinkage strain and its rate was then obtained using a numerical differentiation method. For the polymerisation stress, Bio-man instrument was used. Modulus of elasticity was then calculated from the measured stress and strain at 60 min. The results demonstrated different shrinkage behaviour that is strongly related to the different monomer systems of the materials. The nature of the monomer system determines the amount of the bulk contraction that occurs during polymerization and the resultant stress. Higher values of shrinkage strain and stress were demonstrated by the investigated flowable materials. The bulk fill materials showed comparable result when compared to traditional resin-composites. The effect of three different solvents was investigated in which the materials were stored for a total storage time of 180d. Generally the materials were most greatly affected by MEK storage compared to the other two solvents. However, the glass-fibre-reinforced material (EVX) was mostly affected by water immersion. The pattern of change/recovery behaviour of the materials, during solvent challenge, was similar to the pattern of viscoelastic creep/recovery behaviour of resin-composite materials.The surface micro-hardness of the material and the diametral strength were studied after a period of solvents storage. The storage time and the type of solvent have a significant influence on these properties. In general, MEK showed more drastic reduction in the material micro-hardness with an exception of G-aenial universal flo (GA-F) which showed similar results in water/ethanol and MEK. The bulk-fill materials showed no superior results compared with the other materials. The significant decrease in the surface micro-hardness of the investigated materials makes their long-term stability open to question. For the bulk-fill materials that are designed to be used as a base, their penetration by the solvents may be shielded.

Date of Award	31 Dec 2015
Original language	English
Awarding Institution	The University of Manchester
Supervisor	David Watts (Supervisor) & Nick Silikas (Supervisor)