Abstract
This study aimed to investigate the influence of ultrasonic heat before photo-polymerization on the structural and physical properties of dental composites. Commercially available bulk-fill, nano-hybrid, micro-hybrid, and flowable composites were used. The samples were divided into three groups i.e., (i) without ultrasonic activation, (ii) ultrasonic activation at 15 Hz for 30 s, and (iii) ultrasonic activation at 15 Hz for 60 s. The degree of conversion percentage (DC%) and structural changes were evaluated with Fourier transform infrared spectroscopy. The presence of voids in restored tooth cavities were investigated with micro-computed tomography. The statistical analysis was performed using a one-way analysis of variance (ANOVA) post hoc Tukey’s test. The DC% was significantly increased with ultrasonic application in all groups except for flowable composites, whereby flowable composite showed a significant increase with 30 s ultrasonic activation only. The highest DC% was observed in 60 s ultrasonically activated nano-hybrid and micro-hybrid composites. The voids were reduced linearly with ultrasonic application in flowable and bulk-fill composites; however, non-linear behavior was observed with micro-hybrid and nano-hybrid composites, whereby the difference was significant within the groups. The frequency and time of the ultrasonic application is an important factor to consider and can be used to preheat composites before clinical application.
Highlights
Many patients are looking for dental restorations other than amalgam restorations mainly because of esthetic reasons [1]
The SDR showed a maximum rise in temperature compared to other composites, where after 30 s and 60 s of ultrasonic application, the recorded temperature was 46 ± 0.62 ◦ C and 60.82 ± 0.69 ◦ C, respectively
Within the limitations of this study, it is concluded that the effect of ultrasonic scaler was observed in the degree of conversion, and change in the void volume of composites was observed
Summary
Many patients are looking for dental restorations other than amalgam restorations mainly because of esthetic reasons [1]. In October 2013, a new international binding treaty instrument called the Minamata Convention on Mercury opened for signature [2]. There is a strong perception that eventually mercury-based amalgam restorations will phase out from clinical practices. Resin-based composites are most preferred among patients and clinicians [3]. Almost five hundred million resin-based restorations are used per year [4]. Modern resin composite has evolved and enables clinicians to provide restorations that are both esthetic and biologically conservative [5]. The major limitations associated with resin-based composites are polymerization shrinkage, microleakage, and the presence of unreactant monomers [6,7]
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