The effect of excitation laser power in Raman spectroscopic measurements of the degree of conversion of resin composites

Comparison of degree of conversion performance of bulk-fill resin composites: A systematic review and network meta-analysis of in vitro studies

OBJECTIVES

To systematically compile data on the degree of conversion (DC) for bulk-fill composites using a network meta-analysis.

METHODS

A systematic search for in vitro studies of DC of bulk-fill composites was performed in PubMed, Web of Science, Scopus, and Open Grey. Risk of bias within studies and due to missing evidence was assessed using the Joanna Briggs Institute scoring system and ROB-MEN tool, respectively. The primary outcome was the DC of bulk-fill composites. Surface Under the Cumulative Ranking curve (SUCRA) was used to rank relative performance. Inconsistencies in the model were investigated to ensure its validity and the level of confidence in the network meta-analysis (CINeMA) was assessed.

RESULTS

A total of 28 studies were included in the quantitative analysis. The average DC values (%) for 0-h/top, 0-h/bottom, 24-h/top, and 24-h/bottom were 59.09, 57.14, 66.73, and 63.87, respectively. According to their SUCRA ranking, the best-performing composites were: SonicFill, Venus Bulk Fill, and SDR (0-h/top), Reveal HD, i-Flow Bulk Fill, and Venus Bulk- Fill (0-h/bottom), Venus Bulk Fill, SDR, and QuiXfil (24-h/top), and Venus Bulk Fill, Aura Bulk Fill, and i-Flow Bulk Fill (24-h/bottom). Incoherence between direct and indirect evidence was identified as the most significant factor affecting confidence.

CONCLUSIONS

DC values of bulk-fill composites were within the range commonly reported for previous generations of "conventional" composites, with flowable composites tending to perform better than sculptable composites. High variability in DC data was observed, which may be attributed to incompletely understood methodological differences.

CLINICAL SIGNIFICANCE

DC is a fundamental parameter that influences multiple mechanical and biological properties of resin composites and is particularly relevant for the group of bulk-fill composites that are designed for use in thick layers.

Influence of Ionizing Radiation on Fluoride-Releasing Dental Restorative Materials

This study aimed to investigate the effects of radiotherapy on the mechanical, chemical, and surface properties of two recently introduced restorative dental materials (a glass hybrid and an alkasite), while two conventional restorative materials served as references. Material specimens of the experimental groups (irradiated) were compared to the specimens of the control groups that underwent the same preparation procedure but without irradiation. The experimental groups of restorative material specimens were irradiated with a total of 70 Gy over 35 days (2 Gy/day × 35 days), while the control groups received no treatment. The following properties were evaluated: surface microhardness (Vickers), surface roughness, color change, flexural strength, flexural modulus, material reliability, and infrared spectra. For the experimental groups, measurements were performed 24 h after specimen preparation, i.e., before radiotherapy and after the completion of the irradiation protocol. For the control groups, measurements were performed after the corresponding periods of no treatment. A statistically significant increase in microhardness (p = 0.001-0.004) and surface roughness (p = 0.013) was observed as a result of material aging/maturation in both the control and experimental groups. However, the only statistically significant difference between the control and experimental groups was observed in the discoloration of the conventional reference material (p < 0.001). In conclusion, no statistically significant negative effects of a therapeutic dose of radiotherapy on any of the tested properties of the alkasite and glass hybrid materials were observed, whereas only a minor negative effect of radiotherapy in terms of discoloration was found for a conventional resin composite that was used as a reference material.

Degree of conversion of experimental resin composites containing bioactive glass 45S5: the effect of post-cure heating

Resin composites containing reinforcing inert glass fillers combined with bioactive glass (BG) can aid in the prevention of secondary caries, which is a major cause of failure of contemporary composite restorations. A series of previous studies on experimental resin composites filled with BG 45S5 has demonstrated that methacrylate resin polymerization can be impaired by the addition of unsilanized BG, leading to lower degrees of conversion (DC). In order to distinguish whether the polymerization inhibition is caused by a direct (temperature-independent) effect of BG or an indirect (temperature-dependent) effect of restricted mobility of reactive species, this study used Raman spectroscopy to evaluate the DC values of experimental composites post-cured at 37 °C and 150 °C. The potential of BG to adversely affect DC was highly dependent on the resin system. The highest DC reduction was observed in the resin system based on ethoxylated bisphenol A dimethacrylate (Bis-EMA), followed by bisphenol A glycidyl methacrylate (Bis-GMA). In contrast, the DC for urethane dimethacrylate (UDMA) was not compromised by BG. Increasing the mobility of reactive species by heating at 150 °C showed limited potential for increasing the DC in the Bis-EMA and Bis-GMA resin systems, indicating a direct inhibitory effect of BG on polymerization.

Synthesis of antibacterial dimethacrylate derived from niacin and its application in preparing antibacterial dental resin system

In this research, a bio-based monomer 1,3-bis(methacryloyloxy)propyl-carbonyl- hexylpyridinium bromide (QANMA) that derived from niacin was synthesized and incorporated into Bisphenol A glycidyl methacrylate (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) (50 wt/50 wt) with a series of mass fraction as antibacterial agent. The double bond conversion (DC), volumetric shrinkage (VS), mechanical properties, water sorption (WS) and solubility (SL) were investigated among groups with different QANMA concentrations. Antibacterial activity against S. mutans were conducted by bacteria colony counting and bacteria LIVE/DEAD staining. The results showed that QANMA had no influence on DC of dental resin (p > 0.05), but would lead to lower volumetric shrinkage (p < 0.05). Only dental resin with 10 wt% and 20 wt% of QANMA showed obviously antibacterial activity. Mechanical properties, WS and SL of dental resin could be impaired by incorporation QANMA, flexural strength and modulus were decreased with the increasing of QANMA concentration (p < 0.05), while WS and SL were increased with the increasing of QANMA concentration (p < 0.05). Dental resin with 10 wt% of QANMA seemed to be the optimal resin system in this research, for it showed significant antibacterial activity and its flexural strength was still met the requirement of ISO standard. This work suggested that bio-based monomer QANMA could be used as antibacterial agent in dental materials, but further optimization experiment and biocompatibility evaluation should be taken in future.