Composite bond strength improvement with thermal vibration: an experimental non-randomised study

Background. Secondary caries formation is a relevant issue due to poor long-term quality of composite fillings, with inherent subsequent chipping and cracking of the material. We developed a method to improve physical, mechanical and chemical properties of available composites based on thermal vibration imposed on unpolymerised composite in the formed tooth cavity directly prior to polymerisation.Objectives. Effect assessment of thermal vibration exposure on bond strength in composite restorative polymer matrix in various composite brands.Methods. The study used synchronous thermal analysis, including differential scanning calorimetry and thermogravimetry, to estimate and register thermal effects of physical and chemical processes within a temperature programme, as well as determine gaseous release, air contact and decomposition-related sample mass variation, thermal stability, reaction kinetics, polymer and inorganic filler component chemical composition, humidity and softening degree. The study covered 90 specimens 30 mg each prepared of three different composites.Results. Synchronous thermal analysis revealed a statistically significant increase in polymer matrix bond strength in the composites Estelite Sigma Quick (Tokuyama Dental), Filtek Bulk Fill Posterior Restorative (3M Espe) and DentLight (VladMiVa) after thermal vibration exposure vs. classical polymerisation of same composites (p < 0.0001). The bond strength increased by 17.00, 22.51 and 11.31%, respectively.Conclusion. The developed exposure method for altering the composite filling physical and chemical properties has been shown advantageous in a laboratory setting. Thermal vibration-pretreated composite fillings had a higher polymer matrix bond strength vs. same composites polymerised under standard conditions.The pretreatment improves composite filling quality via directly affecting the material physical and mechanical properties of hardness and bending strength

Clinical Justification for Preliminary Thermal Exposure to Composite in the Treatment of Caries: Randomized Clinical Trial

Background. Polymer composites have good aesthetic characteristics and pronounced physicochemical properties, as compared to traditional restorative materials such as amalgam. However, the polymerization reaction of composite material containing bismethacrylate group commonly used in clinical practice is always accompanied by a different degree of volumetric shrinkage (2.7%~7.1%). The resulting stress can lead to adhesion failure and some other unfavorable clinical consequences, such as enamel destruction, microcracking of composite material and formation of microleakage between composite and tooth cavity wall, which can result in recurrent caries and postoperative sensitivity, thereby affecting the long-term effect of restoration. Therefore, studying the effect of preheating on composite restoration is important for its clinical application. Objective. To improve the effectiveness of treatment of patients with dental caries by improving the physicochemical properties of composite restorations.Methods. A randomized clinical trial enrolled 180 patients aged 18 to 45 years, diagnosed with dentin caries class I, according to Black (K02.1 in ICD). The study was conducted in the Dental Clinic of Kuban State Medical University, Russia. 180 composite restorations were performed in the treatment of dentin caries of molars. Patients were randomized into 2 groups): the control group — 90 patients and the main group — 90 patients. The control and main groups, in turn, were divided into three subgroups, depending on the composite used — Estelite Sigma Quick (Tokuyama Dental, Japan), Filtek Bulk Fill Posterior Restorative (3M Espe, USA) and DentLight (VladMiVa, Russia). Each subgroup consisted of 30 patients. In the control group, the classical method of filling with a composite material at “room temperature” was applied. In the main group, a composite heating conditioner “Ena Heat” (Micerium, Italy) was used to heat the composite to 55 °C before adapting the material in the formed cavity with subsequent photopolymerization. The quality of composite restorations within the clinical study was evaluated using the modified Ryge criterion immediately after treatment and after 6, 12, 18, 24 months. Statistical processing of the obtained data was carried out by means of one-factor analysis of variance using the GraphPadPrism 9 program (GraphPad Software, USA).Results. The duration of the clinical study comprised 24 months. The study revealed a statistically significant decrease in the quality of marginal fit of composite restorations (according to the Ryge score) by 20.1% (p = 0.0001) in the control group and by 5.7% (p = 0.0328) in the main group.  At the same time, no statistically significant changes in Ryge scores were reported in the subgroups of composite materials of the main group (pF = 0.9480, pE = 0.1837, pD = 0.2529). As a result of the study, an optimal time algorithm (7 seconds) for using a special furnace for preheating the composite before sealing with subsequent photopolymerization was obtained.Conclusion. The study revealed a statistically significant positive effect of the proposed algorithm for working with a heated composite on the quality of marginal fit in the long term after treatment in comparison with the classical method of working with a composite at “room temperature”