An experimental fibre-reinforced dental resin composite

PhD ThesisFibre-reinforced dental resin composites (FRCs) have shown increased fracture resistance and tensile strength compared with particulate filled composites (PFC). However, clinically successful restorative materials require adequate bond strength and wear resistance along with high strength. An experimental FRC (ST) was developed and tested as a dentine replacement. It has randomly distributed E-glass fibres above their critical length of 0.5-1.6 mm. This work aimed to evaluate the possibility of using ST as a single restorative material by assessing its three-body wear resistance and surface contact fatigue. The polymerisation shrinkage, water sorption, and bond strength of ST were also assessed. Two commercially available materials; an FRC (Build It FR) and PFC (Z250) were used as comparators. ST showed significantly lower wear resistance and higher contact fatigue. No significant difference was found regarding polymerisation shrinkage but ST had significantly higher water sorption, lower shear bond strength (SBS) to human dentine. SBS of the interfacial layers within and between the dental resin composites was evaluated after 24 hours and 1 year of water storage in the absence of an oxygen inhibition layer. Build It/Z250 showed a significantly higher SBS at both time intervals. The presence of an oxygen inhibited layer increased the interfacial strength in all groups except ST/Z250. ST formulations were varied in resin/diluent (Bis-GMA/TEGDMA) ratios, filler loading and fibre lengths for development. Wear testing found changing the Bis-GMA/TEGDMA ratio from 60/40 to 70/30 decreased the wear resistance regardless of filler loading and fibre length. In summary, wear resistance of ST and its variants was insufficient to recommend its use as a single restorative material without a surface veneer of PFC. As a dentine replacement, ST was only comparable with Z250 and Build It in polymerisation shrinkage and SBS between composites in the absence of an oxygen inhibition layer

Utilizing Light Cure Units: A Concise Narrative Review

The use of photo-curable resin composite restorations is an essential treatment modality in modern dental practice. The success and longevity of these restorations depend on achieving predictable and effective polymerization. Understanding the dynamics of the polymerization and the effect of light cure units (LCUs) on this process is paramount. The goal of this concise narrative review is to provide a simplified presentation of basic principles of composite chemistry, polymerization reactions, and photo-curing with relevant terminologies. Clinical guidelines for choosing and maintaining LCUs, as well as safety precautions and factors under the control of the clinician are listed. Finally, clinical recommendations of LCUs’ usage and monitoring are included to aid practitioners in achieving predictable polymerization during the placement of direct resin composite restorations

Effect of Light Curing Distance on Microhardness Profiles of Bulk-Fill Resin Composites

Bulk-fill (BF) dental resin composites are made to be polymerized in increments of up to 5 mm rather than the 2 mm increment recommended for conventional composites. This project aimed to determine microhardness (MH) profiles of BF resin composites at different depths and varying light cure (LC) distances from the light source in an attempt to mimic varying clinical situations. Forty-eight cylindrical specimens (4 mm diameter and 6 mm height) were prepared from 3 BF composites: Tetric N-Ceram Bulk-Fill (TBF), Filtek One Bulk-Fill (FBF), and Sonic-Fill 2 (SF2). Four different distances (0, 2, 4, and 6 mm) from the LC unit were investigated. Vickers MH was measured at the top and bottom of the samples and at every 1 mm, by creating 3 indentations at each depth. The bottom-top microhardness ratio (MHR) and percentage reduction in MHR were also measured. Data was analyzed using mixed-model repeated-measure ANOVA at 0.05 significance level. The main variables effects “material, LC distance, and depth” were significant (p < 0.001). Increasing LC distance and the depth of the tested BF significantly affected Vickers MH and MHR. None of the tested BF materials had sufficient MHR at the depths of 4–6 mm. SF2 showed the least MHR reduction

The effect of thermal aging on flexural strength of CAD/CAM hybrid and polymeric materials

The field of dentistry is consistently innovating with the introduction of novel hybrid and polymer materials for computer-aided design and manufacturing (CAD/CAM). It is noteworthy that the temperature within the oral cavity has a significant impact on the strength of new biomaterials utilized for CAD/CAM fabrication of fixed partial dentures (FPDs). Studies have demonstrated that alterations in intraoral temperature may significantly affect the longevity and durability of dental restorative materials. This study aimed to evaluate the flexural strength, flexural modulus, and effect of thermal aging on CAD/CAM restorative materials. Five CAD/CAM materials were investigated: nano-ceramic-hybrid (GR), polymer-infiltrated-ceramic-network (VE), polyether-ether-ketone (PK), fiberglass-reinforced epoxy-resin (CT), and Feldspar Ceramic (VB). A total of 100 bar-shaped specimens were prepared (N = 20). Each group was subdivided into thermocycling (TC) and no-thermocycling (NTC) subgroups (n = 10). All the specimens underwent a 3-point bending test. The mean flexural strengths and moduli were statistically analyzed using paired t-test, analysis of variance (ANOVA), and Bonferroni pair-wise comparison (p < 0.05). Significant differences were observed in the flexural strength (FS) and modulus (E) between the materials (p < 0.001). GR had the highest FS among tested hybrid materials. NTC CT had the highest FS (924.88 ± 120.1 MPa), followed by GR (385.13 ± 90.73 MPa), then PK (309.56 ± 46.84 MPa). The FS of brittle ceramic VB was the lowest (p < 0.001), but similar to that of PICN VE. Only resin-containing VE and CT significantly decreased in E after thermocycling (p < 0.01, p = 0.013), showing the softening effect of thermocycling on their resin matrix. It can be concluded that new hybrid materials (GR) had higher flexural strength than feldspar ceramic and other resin/polymeric CAD/CAM materials. Polymeric PEEK and GR hybrid materials were resistant to significant deleterious effects of TC. Therefore, they would be appropriate for situations with a higher stress load