Viscosity and thermal kinetics of 10 preheated restorative resin composites and effect of ultrasound energy on film thickness

Clinical performance of preheating thermoviscous composite resin for non-carious cervical lesions restoration: A 24-month randomized clinical trial

OBJECTIVES

This 24-month, double-blind, split-mouth randomized clinical trial aimed to compare the retention rates of a preheated thermoviscous composite resin (PHT) compared to a non-heated composite resin (NHT) in non-carious cervical lesions (NCCLs).

METHODS

A total of 120 restorations were restored on NCCLs using a preheated (VisCalor bulk, Voco GmbH) and a non-heated (Admira Fusion, Voco GmbH) composite resins with 60 restorations per group. A universal adhesive in the selective enamel conditioning was applied. In the PHT group, composite was heated at 68 °C for using a bench heater. In the NHT group, no heating was employed. Both restorative materials were dispensed into caps and inserted into the NCCLs. The restorations were evaluated at baseline, 6, 12, 18, and after 24 months of clinical service using the FDI criteria. Statistical analysis was performed with Kaplan-Meier estimation analysis for retention/fracture rate and Chi-square test for the other FDI parameters (α=0.05).

RESULTS

After 24 months 108 restorations were assessed. Seven restorations were lost (two for PHT group and five for NHT group), and the retention rates (95 % confidence interval [CI]) were 96.7 % (81.5-99.9) for PHT group and 90.8 % (81.1-96.0) for NHT group, with no statistical differences between them (p > 0.05). The hazard ratio (95 % CI) was 0.52 (0.27 to 1.01), with no significant difference within groups. In terms of all other FDI parameters that were assessed, all restorations were deemed clinically acceptable.

CONCLUSIONS

Both composites showed high rates of retention rates after 24 months.

CLINICAL SIGNIFICANCE

The clinical performance of the new preheated thermoviscous was found to be as good as the non-heated composite after 24-month of clinical evaluation in non-carious cervical lesions.

REGISTRATION OF CLINICAL TRIALS

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Ceramic partial laminate veneers in anterior teeth: A literature review

STUDY SELECTION

Partial laminate veneers, defined as small ceramic restorations adhesively luted onto unprepared anterior teeth, are an interesting and conservative alternative to conventional ceramic and composite resin veneers in the anterior region. This literature review aimed to summarize the available laboratory and clinical data on ceramic partial laminate veneers. An electronic search of the MEDLINE/PubMed, EBSCO, and Web of Science databases was conducted. The keywords used were "partial veneer," "partial laminate veneer," "ceramic fragment," and "sectional veneer." The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. The risk of bias in the included studies was assessed using the QUIN tool.

RESULTS

Of the 266 identified articles, only 16 met the inclusion criteria (ten clinical reports, five laboratory studies, and one retrospective clinical study). To date, no randomized controlled clinical trials have been conducted. Most laboratory studies displayed a low risk of bias, with partial laminate veneers rendering adequate strength and color stability. Clinical reports have shown large variability in material selection, luting, and finishing/polishing protocols.

CONCLUSIONS

Low-quality evidence is available for ceramic partial laminate veneers. Available data from laboratory studies suggest good mechanical and optical performances comparable to those of conventional ceramic and composite resin veneers. Further clinical studies with longer follow-up periods are warranted.

Effect of preheating on the viscosity of composite resins

Aim

To determine the effects of time and temperature on the viscosity of preheated composite resins.

Materials and Methods

Eleven composite resins were heated to 60°C, and temperature analyses were performed at intervals of 1 min until they had cooled to 25°C. The permanent oscillatory shear test was performed at 25°C, 35°C, 50°C, and 60°C for three composite resins under a shear rate of 1s-1. One- and two-way analysis of variance were used for the analysis (α = 0.05).

Results

There was no significant interaction between the composite resin and time (P = 0.9304), and only the main effect time was significantly different (P < 0.0001). A difference was observed between T0 and T6 (P < 0.001), but not after T7. The increase in temperature resulted in a viscosity reduction (P < 0.05). At 25°C, Beautifil II presented higher viscosity. Palfique LX5 showed a significant viscosity reduction with increasing temperature compared with the others (P < 0.05). For Beautifil II and Z100, there was no difference at temperatures of 50°C and 60°C, while for Palfique LX5, no statistical difference was observed at 35°C, 50°C, and 60°C.

Conclusions

Ten minutes of preheating were sufficient to reach a temperature of 60°C, reducing viscosity by at least 84%. However, 5 min after removal, the composite resin cooled to room temperature.

Clinical Significance

Preheating composite resin has potential benefits. To determine how this approach will work in clinical practice, it is important to define the effects of time and temperature in the protocol of this technique and understand its limitations.

Effect of preheating and ultrasound application of resin-based luting agents on the failure load of a lithium disilicate glass-ceramic

PURPOSE

To assess the effect of preheating resin-based materials and ultrasound application on the failure load of a lithium disilicate glass-ceramic.

MATERIALS AND METHODS

Ninety ceramic specimens were produced (14×12×1.0 mm) and divided into 9 groups (n = 10) to be bonded to a dentin analog (Nema G10) with light-cured luting agent (LC), flowable resin composite (FL), and supra-nano filled resin composite (SN), as follows: LC/R - LC at room temperature; LC/P - preheated LC; LC/P/U - preheated LC and Ultrasound; FL/R - FL at room temperature; FL/P - preheated FL; FL/P/U - preheated FL and Ultrasound; SN/R - SN at room temperature; SN/P - preheated SN; SN/P/U - preheated SN and Ultrasound. The failure load test was performed in a universal testing machine with the aid of acoustic detection. The data was analyzed with two-way ANOVA (for failure load) and Weibull statistics (Weibull modulus - m and characteristic strength, based on 95% confidence intervals - CI).

RESULTS

The analyses of failure load revealed no statistically significant difference among groups considering the type of luting agent (P = 0.075; F = 2,673), the application method (P = 0.772; F = 2,259), and the interaction between them (P = 0.297; F = 1,248). The characteristic strength did not show differences among groups (95% CI). The m, which indicates structural reliability, showed lower values for SN/P/U and SN/P, with a difference from other selected groups (95% CI).

CONCLUSION

Preheating of resin-based materials and ultrasound application did not affect the failure load of lithium disilicate glass-ceramic. Lower reliability was observed with supra-nano filled resin composite.

Does the use of preheated restorative resin composite as a luting agent influence the adaptation of fixed dental prostheses? A systematic review

STATEMENT OF PROBLEM

Although studies have explored the physical and mechanical properties of different composite resins with the preheating technique, evidence that the use of preheated restorative composite resin as a luting agent influences the adaptation of fixed dental prostheses is lacking.

PURPOSE

The purpose of this systematic review was to answer the question: Does the use of preheated restorative composite resin as a luting agent influence the adaptation of fixed dental prostheses?

MATERIAL AND METHODS

Seven databases and nonpeer-reviewed literature were searched, without language or year restrictions. Studies directly comparing the adaptation of fixed dental prostheses cemented with preheated restorative composite resin or resin cement were considered eligible for inclusion. Assessment of the risk of bias was based on a 9-item checklist.

RESULTS

Of 2109 retrieved articles, 4 in vitro studies met the inclusion criteria. Three of them concluded that preheated restorative composite resin produced a greater mismatch than resin cement, and the remaining study reported that composite resin improved the adaptation of fixed dental prostheses. All included studies had a medium risk of bias. The high level of heterogeneity among the studies precluded meta-analysis.

CONCLUSIONS

The use of preheated restorative composite resin as a luting agent seems to negatively influence the adaptation of fixed dental prostheses. It was not possible to evaluate whether variables such as the formulation of the resin material or its heating time and temperature influence the adaptation of fixed dental prostheses because of the high heterogeneity of the included studies.

Physicochemical and mechanical properties of preheated composite resins for luting ceramic laminates

This study analyzed and compared the physicochemical and mechanical properties of preheated resin composite with light-cured resin cement for luting indirect restorations. 210 specimens of resin cement/resin composite were prepared according to preheating treatment heated (Htd) or not (NHtd). Light-cured resin cement (Variolink Veneer, Ivoclar), and resin composite (Microhybrid-Z100, 3 M; Nanohybrid-Empress direct, Ivoclar; and Bulk fill-Filtek One, 3 M) were used (n = 10). Resin cement specimens were not preheated. The response variables were (n = 10): film thickness, microhardness, liquid sorption and solubility. Data were analyzed by 2-way ANOVA and Tukey HSD post-test (α = 0.05). Bulk fill NHtd resin had the highest film thickness values (p < 0.001). Microhybrid and nanohybrid Htd resins had the smallest thicknesses and did not differ from the cement (p > 0.05). The highest microhardness values were found for Bulk fill NHtd and Bulk fill Htd resins. The nanohybrid and microhybrid Htd resins showed the lowest microhardness values, with no difference in cement (p > 0.05). For liquid sorption, there was no significant difference between the groups (p = 0.1941). The microhybrid Htd resin showed higher solubility values than the other materials (p = 0.0023), but it did not differ statistically from resin cement (p > 0.05). Preheating composite resins reduced the film thickness. After heating, nanohybrid and Bulk fill resins retained stable microhardness, sorption, and solubility values.

A comprehensive review of resin luting agents: Bonding mechanisms and polymerisation reactions

The field of dentistry is constantly evolving and increasingly embracing minimally invasive approaches. One such approach, which is bonding to the tooth structure, particularly enamel, has been shown to offer the most predictable outcomes. However, there are instances where significant tooth loss may limit treatment options for a restorative dentist. In these scenarios, indirect restoration might be the preferred treatment option. This literature review provides a comprehensive examination of the currently available resin luting agents and their bonding requirements. It provides valuable insights for dental professionals seeking an in-depth understanding of the current state of the field and the future prospects of dental adhesion.

Comparative Evaluation of Microtensile Bond Strength in Three Different Dentin Luting Agents: An In vitro Study

Aim

Long-term clinical success on indirect restorations is largely determined by bonding efficiency of the luting agent, with adhesion to dentin being the main challenge. Therefore, aim of this study was to assess the microtensile bond strength when using flowable resin composite, preheated resin composite and dual self-adhesive resin cement as dentin luting agents.

Materials and Methods

Occlusal thirds of molar teeth were cut and randomly divided into 3 groups to be cemented: RelyX™U200, Filtek™ Z250 XT- preheated to 70° and Filtek Flow™ Z350XT. They were then thermocycled 5000 times between 5+/-2°C and 55+/-2°C. Subsequently, 10 microbars per group were prepared. The 30 samples were placed in saline solution for 24 hours at room temperature prior to microtensile test. This was performed with a digital universal testing machine at a crosshead speed of 0.5 mm/min. The bond strength values obtained were analyzed in Megapascals (MPa). Measures of central tendency such mean and measures of dispersion such standard deviation were used. In addition, the Kruskall Wallis non-parametric test with Bonferroni post hoc test was applied, considering a significance value of 5% (P < 0.05), with type I error.

Results

The dentin microtensile bond strengths of preheated resin composite, flowable resin composite and dual self-adhesive cement were 6.08 ± 0.66 Mpa, 5.25 ± 2.60Mpa and 2.82 ± 1.26Mpa, respectively. In addition, the preheated resin composite exhibited significantly higher microtensile bond strength compared to the dual self-adhesive cement (P < 0.001). While the flowable resin composite showed no significant difference with the dual self-adhesive cement (P = 0.054) and the preheated resin composite (P = 0.329).

Conclusions

The microtensile bond strength in dentin was significantly higher when using a preheated resin composite at 70°C as a luting agent compared to dual self-adhesive cement. However, the preheated resin composite showed similar microtensile bond strength compared to the flowable resin composite.

Toothbrushing effects on the surface roughness and cement volume loss of bonded enamel-ceramic interface

This study evaluated the effect of toothbrushing on enamel-cementing material-ceramic bonded interfaces, using different cementing materials.

MATERIALS AND METHODS

Thirty enamel and thirty ceramic blocks were bonded with cementing materials to produce the samples that were bonded with three types of cementing materials: 1- RelyX Ultimate resin cement (REXU), 2- RelyX Unicem 2 self-adhesive resin cement (REU2) and 3- heated Z100 restorative composite (60°C). Bonded interfaces of the samples were toothbrushed and the surfaces of the 3 cementing materials were evaluated for roughness (RG, in µm), roughness profile (RP, in µm), and volume loss (VL, in µm3) (baseline and after 20,000 and 60,000 toothbrushing cycles). Data were evaluated by Generalized Linear Analysis (two factors: "material" and "toothbrushing cycle") and Bonferroni test (α=0.05).

RESULTS

REXU and Z100 exhibited lower RG than that presented by REU2, except after 60,000 toothbrushing cycles when only Z100 differed from REU2. The increase in toothbrushing cycles increased the RG and RP for all materials. REU2 also showed higher RP than those showed by REXU and Z100 when it was analyzed regarding the enamel. The VL of Z100 was the lowest with 20,000 toothbrushing cycles, regarding the enamel and ceramic. For 60,000 cycles, REXU showed the lowest VL regarding the ceramic, and REU2 had the highest VL regarding the enamel and ceramic.

CONCLUSION

In general, REXU and Z100 showed the best results regarding the evaluations performed and the REU2 exhibited the highest RG, RP, and VL.

Luting laminate veneers: Do resin-composites produce less polymerization stress than resin cements?

OBJECTIVES

Regular composites could produce less polymerization stress than resin cements when luting laminate veneers but there is no proper evidence to support this theory. The current study aimed to determine the degree of conversion, volumetric shrinkage, polymerization stress and the resultant elastic moduli of materials currently used for adhesive cementation and to determine possible correlations.

METHODS

The study considered (i) regular resin composites (Admira Fusion, Gradia, Grandioso, Palfique, Sirius Z, Viscalor and Z100) at room and pre-warmed (PW) at 69ºC, (ii) flowable composites (Sigma Flow and Grandioso Flow); (iii) solely light-activated cements (AllCem Veneer, Variolink Esthetic and RelyX Veneer); and (iv) one dual-activated resin cement (SpeedCEM). Degree of conversion (DC, n = 3) was accessed with FTIR 1 h after irradiation. Bonded-disk and Bioman II instruments were used to access polymerization shrinkage strain and shrinkage stress, respectively, for 60 min at 23 ± 1◦C (n = 3). The elastic modulus was determined by 3-point bending flexural test (n = 6). The results were submitted to analyse s of variance, Tukey's, and correlation tests.

RESULTS

For regular composites, the pre-warming did not affect DC, shrinkage and modulus but significantly increased the stress magnitude. Correlation tests indicated a significant relationship only between stress and polymerization shrinkage (r = 0.811343).

SIGNIFICANCE

Regular composites can produce less polymerization stress than resin cements when luting laminate veneers. Polymerization stress was dependent on the shrinkage magnitude, but not on the degree of conversion nor the elastic modulus.

Effect of a Diode Laser (445 nm) on Polymerization Efficiency of a Preheated Resin Composite Used for Luting of Indirect Composite Restorations

PURPOSE

The aim of this study was to evaluate the polymerization efficiency of a preheated resin composite used as a luting agent for indirect restorations light-cured by a blue diode laser (445 nm).

METHODS

Bronze molds were used to prepare cylindrical specimens of a laboratory composite (Ceramage) with dimensions 2, 3, and 4 mm in height and 8 mm in diameter. The molds had additional height of 120 μm for the placement of the preheated resin composite. A nanohybrid resin composite (Enamel Plus HRi) was preheated at 55°C to use as a luting agent. Photopolymerization was followed for 20 seconds using three light sources: a diode laser emitting at 445 nm (SiroLaser Blue) and two light-emitting diode (LED) units (Bluephase Style and Valo). Degree of conversion (DC) of the preheated resin composite was evaluated using Fourier transform infrared spectroscopy.

RESULTS

The results indicated that the main effects of the analysis were significant for both material thickness (p<0.001) and polymerization method (p<0.001). The preheated resin composite was not polymerized under 4-mm-thick specimens, independent of the light-curing unit. For 2-mm material thickness, there was no difference among the three light-curing units (p=0.383), while 3-mm Bluephase Style presented very low DC.

CONCLUSIONS

Diode laser (445 nm) achieved better polymerization efficiency at the same fluence compared to the LED unit at 3-mm depth, implying a better mechanical behavior and potential improved adhesion of the luting material to dentin.

Various ways of pre-heating a bulk-fill thermoviscous composite in restoration in non-carious cervical lesions: 12-month randomized clinical trial

OBJECTIVE

The objective of the study is to evaluate through a randomized clinical trial the best method to preheat a composite resin, if using a Caps dispenser device associated with Caps Warmer (CD) or with a VisCalor Caps dispenser/warmer (VD) for restorations in non-carious cervical lesions (NCCLs).

MATERIAL AND METHODS

One hundred and twenty restorations were distributed to two groups (n = 60) according to the pre-heating way of thermoviscous bulk-fill composite resin. For the CD group, pre-heating was carried at 68 °C using a heating bench for 3 min. For the VD group, pre-heating was performed at 68 °C using a heating gun for 30 s. After that, pre-heated bulk-fill composites were directly inserted in the NCCLs. The total working time was recorded. The restorations were evaluated after 6 and 12 months of clinical performance according to the FDI criteria. Statistical analysis was performed using the Student's t test for unpaired samples for working time, and the Chi-square test for restoration clinical performance (α = 0.05).

RESULTS

Working time was shorter for VD with a statistically significant difference compared to CD (p = 0.01). Few restorations were lost or fractured after 12 months of clinical evaluation (p > 0.05). The retention rates were 96.7% (CI 95 %: 88.6-99.1%) for CD and 98.3% (CI 95 %: 91.1-99.7%) for VD. The other FDI parameters were considered clinically acceptable.

CONCLUSIONS

The different pre-heating ways did not influence the clinical performance of thermoviscous bulk-fill composite restorations in NCCLs after 12 months.

CLINICAL RELEVANCE

Regardless of the bulk-fill thermoviscous composite resin pre-heating ways, the restorations are clinically acceptable after 12 months.

Removing Fractured Endodontic Files with a Tube Technique-The Strength of the Glued Joint: Tube-Endodontic File Setup

One recommended technique for removing broken root canal instruments is to glue the fragment into a cannula adapted to it (i.e., the tube technique). The aim of the study was to determine the influence of the adhesive kind and length of the joint on the breaking force. During the investigation, 120 files (60 H-files and 60 K-files) and 120 injection needles were used. Fragments of broken files were glued into the cannula using one of three materials: cyanoacrylate adhesive, composite prosthetic cement, or glass ionomer cement. The lengths of the glued joints were 2 and 4 mm. After the polymerization of adhesives, a tensile test was carried out to find a breaking force. The results were statistically analyzed (p < 0.05). For 4 mm lengths of glued joints, the breaking force was higher than for 2 mm for both file types (K and H). In the case of K-type files, the breaking force was higher for cyanoacrylate and composite adhesives than glass ionomer cement. For H-type files, no significant difference in joint strength was found between binders at 4 mm, while at 2 mm, a much better connection was obtained for cyanoacrylate glue than prosthetic cements.

Adhesion to lithium disilicate glass-ceramics after aging: Resin viscosity and ceramic surface treatment effects

OBJECTIVE

To evaluate the influence of intaglio ceramic surface treatments, resin cement viscosities, and storage regimens on the microshear bond strength of lithium disilicate ceramic. In addition, to investigate the dynamic viscosity of the resin-based luting agents.

MATERIALS AND METHODS

Ceramic slices were randomly allocated into eight groups (n = 19) considering three factors: ceramic surface treatment (hydrofluoric acid followed by silane, HF; or self-etching ceramic primer, E&P), resin cement viscosity (high, HIGH; or low, LOW) and storage regimen (baseline or aging). Surface treatments were performed, resin cement cylinders were built and microshear bond strength tests (μSBS, wire-loop method, speed: 1.0 mm/min) were run according to the storage factor. Failure mode, topographic and dynamic viscosity (37 °C; shear rate of 1.0-100 s^-1) of resin cement components (base, high and low catalyst) were also performed.

RESULTS

Resin cement viscosity and the association among ceramic surface treatment, resin cement viscosity, and storage regimen were statistically significant factors (p < 0.05). Worse behavior was identified for the E&P_HIGH group compared to the E&P_LOW and HF_LOW in the baseline condition. After aging, the HF_HIGH group (16.78 MPa) presented the worst result among the aged groups (21.44-25.25 MPa). Most of the failures were adhesive. Surface micrographs revealed a distinct pattern after etching, more aggressive by HF and milder by E&P. High viscosity catalyst is 5.3 and 8.5-fold more viscous than the base and low viscosity catalyst, respectively (high > base > low).

CONCLUSION

Differences in filler content can impact the resin viscosity of the material (more fillers increase the viscosity), which in turn can influence the bond strength of a lithium disilicate ceramic, depending on the surface treatment and storage regimen.

Effect of preheating on mechanical properties of a resin-based composite containing elastomeric urethane monomer

This study investigated the effect of preheating an elastomeric urethane monomer (Exothane-24) experimental resin composite on its physicochemical properties. Two resin matrices were formulated: (a) 50 wt% Bisphenol-glycidyl methacrylate (Bis-GMA) and 50 wt% triethylene glycol dimethacrylate (TEGDMA); and (b) 20 wt% Exothane-24, 40 wt% Bis-GMA and 40 wt% TEGDMA. A photoinitiator system (0.25 wt% camphorquinone and 0.50 wt% ethyl-4-dimethylamino benzoate) and 65 wt% of the inorganic filler (20 wt% 0.05 μm silica and 80 wt% 0.7 μm BaBSiO₂ glass) were added to both matrices. These formulations were then assigned to four groups: Exothane-24 (E); Exothane-24 plus preheating (EH); no Exothane-24 (NE); and no Exothane-24 plus preheating (NEH). NEH and EH were preheated at 69 °C. The dependent variables were as follows: film thickness (FT); polymerization shrinkage stress (PSS); gap width (GW); maximum rate of polymerization (Rp_max); and degree of conversion (DC). Data were statistically analyzed by two-way ANOVA and Tukey's test (α = 0.05). Preheating reduced FT for both composites. PSS and GW were significantly lower for EH, when compared with E. The DC for EH and NEH and the Rp_max for EH increased significantly. Preheating improved most of the physicochemical properties (FT, PSS, GW, and DC) of the experimental resin composite containing Exothane-24.

Effect of thickness and CAD-CAM material on fatigue resistance of endodontically treated molars restored with occlusal veneers

PURPOSE

To evaluate the influence of the thickness and type of computer-aided design and computer-aided manufacturing (CAD-CAM) material on the fatigue resistance and failure mode of endodontically treated teeth (ETT) restored with occlusal veneers (OV).

MATERIALS AND METHODS

Seventy-five (N = 75) ETT were restored with Herculite XRV in the endodontic access. Five experimental groups (n = 15) were tested. Four groups had two different thicknesses (0.6-0.7 mm or 1.4-1.6 mm) and two different CAD-CAM materials: zirconia-reinforced lithium-silicate (LS/Celtra Duo) and composite resin (RC/Cerasmart). The fifth group (control) did not have occlusal veneers. All the specimens were subjected to accelerated fatigue (5 Hz frequency) with an occlusal load increasing up to 1800 N and 131,000 cycles. The number of cycles was recorded when the machine stopped or at the completion of the test. Fatigue resistance was analyzed using the Kaplan-Meier survival test (95% significance level, log-rank post hoc pairwise comparisons). The samples were categorized according to failure mode. The CAD-CAM materials were examined through scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS).

RESULTS

No differences were found between the thicknesses, regardless of the type of the CAD-CAM material. The thick LS OV outperformed the RC and control groups. The thin RC OV and control groups showed a higher percentage of repairable and possibly repairable failures than the other groups. LS was more homogeneous under SEM, and the EDS analysis detected Si and Zr, but not Li.

CONCLUSIONS

A larger thickness did not improve the resistance of the CAD-CAM materials. Thick LS showed a higher cumulative survival rate to fatigue than the RC and control groups. The direct composite alone (control) survived similarly to the experimental groups, except for the thick LS.

Effect of pre-heating methods and devices on the mechanical properties, post-gel shrinkage, and shrinkage stress of bulk-fill materials

This study evaluated the effect of using two different pre-heating methods on the three resin-based composite (RBCs). Three paste viscosity bulk-fill RBCs (VisCalor Bulk [VC]; VOCO; x-tra fil Caps [XF], VOCO; Filtek One Bulk Fill [FO], 3 M) were pre-heated using either a VisCalor Dispenser (VOCO) to 65 °C, or the Caps Warmer (VOCO) to 37 °C, 54 °C, or 68 °C. The temperature inside the capsules and cavity was monitored before and after insertion into the matrix. Within 30 s of inserting the RBC, they were light-activated using a VALO (Ultradent) curing light for 20 s. The post-gel shrinkage (Shr - %), Flexural Strength (FS - MPa), Elastic Modulus (E - MPa), degree of conversion (DC - %), Knoop Hardness (KH - N/mm²), diametral tensile strength (DTS - MPa), and compressive strength (CS - MPa) of the RBCs were measured (10 specimens per group). The shrinkage stress was calculated using three-dimensional finite element analysis. Data were analyzed using one-way, two-way ANOVA and Tukey's test (α = 0.05). The temperature fell rapidly after the RBC was inserted into the cavity. Pre-heating the RBCs did not affect the mechanical properties. FO had the lowest E, DC, and KH values, VC had intermediate values, and XF achieved the highest values. The DTS and CS values were not affected by the various pre-heating methods, the temperature, or RBC. Pre-heating methods at 37 °C produced higher shrinkage for all RBCs. VC pre-heated to 65 °C produced the lowest stress when measured at 10 min after light activation.

Effect of preheating on the physicochemical properties and bond strength of composite resins utilized as dental cements: An in vitro study

STATEMENT OF PROBLEM

Little is known regarding the use of preheated composite resins to bond indirect restorations and its impact on mechanical properties when compared with resin cements.

PURPOSE

The purpose of this in vitro study was to compare the chemical and physical properties and bond strength to enamel and ceramics of preheated composite resins and resin cements.

MATERIAL AND METHODS

Two composite resins, the microhybrid Filtek Z250XT and the nanoparticulate Z350XT were tested, and 2 commercially available resin cements, the dual-polymerized Rely-X ARC and the light-polymerized Rely-X Veneer were used as controls. A device (HotSet) was used to preheat the composite resins to 69 °C before light-polymerization. The following properties were tested: flexural strength, modulus of elasticity, fracture toughness, microshear bond strength to enamel and ceramics, degree of conversion, flow, sorption and solubility, and color stability. Statistical analysis was done with ANOVA and Holm-Sidak for multiple comparisons (α=.05).

RESULTS

Preheating had no significant effect on the degree of conversion, flexural strength, fracture toughness, solubility, or microshear bond strength to the enamel of the tested composite resins (P>.05). However, preheating increased the sorption and reduced the microshear bond strength to the ceramic (P<.05). The flowability of the composite resins increased with heating but showed lower values when compared with both resin cements (P<.05). Color stability was more affected in the preheated composite resins than in the resin cements.

CONCLUSIONS

The preheating process resulted in little to no benefit in the evaluated properties for the composite resins. Resin cements appear to be the best option for cementing indirect restorations.

Effect of Pre-Heating on the Monomer Elution and Porosity of Conventional and Bulk-Fill Resin-Based Dental Composites

The pre-heating of dental resin-based composites (RBCs) improves adaptability to cavity walls, reducing microleakages. However, the rapid cooling of the pre-heated RBC may change the polymerization kinetics, and thus the final network configuration of the RBC. It is well known that unreacted monomers remaining in the set RBC can leach into the oral cavity. However, it is still not clear how the pre-heating and cooling of RBCs alter monomer elution (ME). Thus, the purpose was to determine the ME from room-temperature and pre-heated RBCs, in addition to determining the closed porosity (CP) volume. Bulk-filled RBCs and layered conventional RBC samples were prepared. The pre-polymerization temperature was set at 24 °C and 55/65 °C. The ME from RBC samples was assessed with high-performance liquid chromatography using standard monomers. CP was measured with micro-computed tomography. ME decreased significantly from bulk fills and increased from layered samples as a result of pre-heating. Pre-heating was unfavorable in terms of CP in most RBCs. Based on the effect size analysis, ME and CP were greatly influenced by both material composition, pre-polymerization temperature, and their interaction. While the pre-heating of high-viscosity bulk-fill RBCs is advantageous from a clinical aspect regarding biocompatibility, it increases CP, which is undesirable from a mechanical point of view.

Operator versus material influence on film thickness using adhesive resin cement or pre‐heated resin composite

OBJECTIVE

There is a growing interest in using pre-heated composites instead of dual-cured cements when luting indirect restorations. This study evaluated the film thickness obtained from two pre-heated composites and two resin cements, by two different operators. The influence of the materials and the level of expertise of the operator were analyzed.

MATERIALS AND METHODS

Forty specimens of human dentin and composite discs were prepared and divided into four groups depending on the luting process. Each group was randomly equally divided to be handled by two operators with different levels of experience. Two of the initial four groups were luted using dual-cured cements and the two remaining groups using light-cured pre-heated composites. Specimen discs were cut after luting, and film thickness was measured using a Digital microscope. Data were analyzed using a 2-way ANOVA with the Holm-Sidak pairwise multiple comparison procedure (p < 0.05).

RESULTS

Mean film thickness ranged from 156.16 ± 4.7 to 33.82 ± 0.7 μm. Significant differences (p < 0.001) were noticed between expert and novice results with pre-heated composites.

CONCLUSION

Within the limits of this study, using pre-heated composites as a luting cement requires a better level of expertise to achieve a clinically acceptable film thickness.

CLINICAL SIGNIFICANCE

Using pre-heated composites as luting agent for indirect restorations requires an experimented skill level to achieve a clinically recommended film thickness.

Update on Dental Luting Materials

A dental luting material aids in the retention and stability of indirect restorations on the prepared tooth structure. In dentistry, clinicians are using a wide range of luting materials for the cementation of indirect restorations. Zinc oxide eugenol and non-eugenol cements, zinc phosphate cement, zinc polycarboxylate cement, glass ionomer cement and resin cements are common dental cements used in dentistry. Each luting material or cement possesses unique properties and clinical implications. An ideal luting cement should be biocompatible, insoluble, resistant to thermal and chemical assaults, antibacterial, aesthetic, simple and easy to use. It should have high strength properties under tension, shear and compression to resist stress at the restoration-tooth interface, as well as adequate working and setting times. So far, no luting material possesses all of these properties of an ideal cement. Scientists have been modifying the conventional luting cements to improve the material's clinical performance and developing novel materials for clinical use. To achieve the best clinical outcome, clinicians should update their knowledge and gain a good understanding of the luting materials so that they can make a wise clinical decision on the material selection and obtain an insight into the development of luting cements. Therefore, the objective of this study is to provide a discussion on the physical, chemical, adhesive and aesthetic properties of common luting materials. The clinical indications of these luting materials are suggested based on their properties. In addition, overviews of the modification of the conventional luting materials and the newly developed luting materials are provided.

Amyloid-Mediated Remineralization in Pit and Fissure for Caries Preventive Therapy

The pits and fissures of teeth have high caries susceptibility, and sealing these areas is considered as an effective method to prevent caries. However, long-term caries prophylaxis cannot be maintained because of the negative effects derived from the technical sensitivity and disadvantages of sealing materials. Herein, a new strategy is proposed to occlude fossae by amyloid-mediated biomimetic remineralization. In contrast to conventional inward blocking from the outside of fossae, amyloid-mediated biomimetic mineralization delivers an amyloid-like protein nanofilm into the deepest zone of the fossae and induces the formation of remineralized enamel inside. Such assembly from lysozyme conjugated with poly (ethylene glycol) enriches the interface with strongly bonded ionsand directs in situ nucleation to achieve enamel epitaxial growth. Not only is the structure of the enamel-like crystalline hydroxyapatite layer but also its mechanical stability is similar to that of natural enamel. Furthermore, the layer shows good biocompatibility and antibacterial properties. On the basis of the findings, it is demonstrated that amyloid-like protein aggregation may provide an enamel remineralization strategy to modify the current clinically available methods of pit and fissure sealing and shows great promise in preventing caries.

Effect of Thickness and Bonding Technique on Fatigue and Fracture Resistance of Feldspathic Ultra-Thin Laminate Veneers

OBJECTIVES

 To evaluate the fatigue and fracture resistance of ultra-thin laminate veneers (UTLV) with two different thicknesses and two different bonding protocols.

MATERIALS AND METHODS

 A total of 64 flat enamel surfaces were assigned to either 0.2 or 0.4 mm UTLV. The UTLV were further subdivided and assigned to one of two bonding techniques: adhesive resin cement(RC( or preheated restorative resin composite (HC) (n = 16). Eight samples were fatigued with 750,000 mechanical cycles and 8,000 thermal cycles between 5 and 55°C in a chewing simulator, and the failure mode was evaluated using a stereomicroscope and SEM. The other eight samples from each group were loaded to failure in a universal testing machine to test the fracture resistance. Fisher's exact Probability test was used to analyze the fatigue test results, and two-way analysis of variance and Bonferroni's test were used to analyze the fracture resistance test results.

RESULTS

 The difference in fatigue resistance between failure proportions in different groups was statistically different (p < 0.05). The 0.4-mm-thick UTLV had similar results regardless of the bonding technique, while 0.2-mm-thick UTLV only showed comparable results when cemented with preheated HC. No statistically significant difference was found in fracture resistance between the tested groups (p > 0.05).

CONCLUSION

 The Bonding technique and the thickness of the UTLV had impacted fatigue resistance but had no significant effect on the fracture resistance. bonding of UTLV with preheated composite increases their fatigue resistance. Different testing approaches delivered different results.

Luting indirect restorations with resin cements versus composite resins: Effects of preheating and ultrasound energy on film thickness

OBJECTIVE

This study aims to evaluate and compare the film thickness obtained with a resin cement and two composite resins, preheated and/or ultrasonically vibrated, as luting agents.

MATERIALS AND METHODS

One hundred and twenty-six (126) pairs of resin discs were randomly assigned to six experimental groups (n = 21) according to luting agent (Variolink Esthetic LC, IPS Empress Direct or Estelite Omega) and cementation technique (preheating at 68°C and/or ultrasonic vibration). Specimens were luted by applying a controlled force. Following sectioning and film thickness measurement through field emission gun scanning electron microscopy, statistical analysis was carried out considering a 5% significance level.

RESULTS

Statistically significant lower film thickness was observed in Variolink Esthetic LC group when compared to all composite resin groups (p < 0.001), except IPS Empress Direct preheated and ultrasonically vibrated group (p = 0.073). IPS Empress Direct with ultrasonic vibration yielded statistically lower film thickness values than Estelite Omega groups, regardless of luting technique (p < 0.05). Ultrasonically vibrated Estelite Omega groups showed statistically lower film thickness values than solely preheated groups (p < 0.05).

CONCLUSIONS

Both Variolink Esthetic LC and IPS Empress Direct preheated and ultrasonically vibrated provided the lowest film thickness. The addition of ultrasonic vibration during cementation proved to be effective in reducing film thickness of both tested composite resins.

CLINICAL SIGNIFICANCE

The cementation technique will have variable results depending on the luting material. Adhesive cementation protocols with composite resins should mainly consider ultrasonic vibration, but also preheating, as strategies for reducing film thickness. The tested resin cement, alongside with IPS Empress Direct composite resin preheated and ultrasonically vibrated, provided the lowest film thickness among the tested materials and techniques.

Ultrasound-assisted preparation of chitosan/nano-silica aerogel/tea polyphenol biodegradable films: Physical and functional properties

In this study, chitosan(CS), nano-silicon aerogels(nSA) and tea polyphenols(TP) were used as film-forming materials and processed with ultrasonication to form films using the tape-casting method. The effects of ultrasonication time, temperature and frequency on the properties of CS/nSA/TP film were explored via material property testing. The results of response surface showed that the maximum tensile strength of the film was 4.036 MPa at ultrasonication time(57.97 min), temperature(37.26 °C) and frequency(30 kHz). The maximum elongation at break of the film was 279.42 % at ultrasonication time(60.88 min), temperature(39.93 °C) and frequency(30 kHz). Due to cavitation and super-mixing effects, ultrasonication may make the surface of the film smoother and easier to degrade. After ultrasonication, TPs were protected by the 3D network structure composed of CS and nSA. Ultrasonication improved the antioxidant and antibacterial properties of the film. These results show that ultrasonication is an effective method to improve the properties of films.

A Comparison of Microtensile Bond Strength, Film Thickness, and Microhardness of Photo-Polymerized Luting Composites

The aim of this study was to evaluate the effect of CAD/CAM composite thickness on micro-tensile bond strength (µTBS), microhardness (HV), and film thickness (FT) of different luting composites. Composite blocks (6.8 mm × 6.8 mm) were divided into 12 groups according to: CAD/CAM thickness and luting composite. For each group, 21 rods (1 mm × 1 mm) were tested in tension at crosshead speed of 1 mm/min. Fracture modes were categorized as adhesive, mixed, and cohesive. Microhardness (n = 5/group) was assessed using microhardness tester. Film thickness (12-rods/group) was evaluated using a stereomicroscope (×40). Data were analyzed using the two-way ANOVA/Tukey’s HSD test (p = 0.05). Parameters “thickness”, “cement”, and “thickness x cement” showed significant difference on µTBS and HV (p < 0.05). At 2 mm, heated x-tra fil composite showed the highest µTBS (45.0 ± 8.5 MPa), while at 4 mm thickness, Grandio Flow revealed the lowest µTBS (33.3 ± 6.3 MPa). Adhesive, mixed, and cohesive failures were reported. The HV of all composites decreased when photo-polymerized through 4 mm thickness (p < 0.05). Regardless of CAD/CAM thickness, photo-polymerized composites can be successfully used for luting CAD/CAM composite.

Composite Resin Preheating Techniques for Cementation of Indirect Restorations

Purpose

Resin-based materials have been preheated by using different techniques and commercial devices. However, a consensus on the clinical protocol for cementing with preheated composite resins is lacking. The aim of this scoping review was to identify the different methods used for heating composite resins as used for cementing indirect adhesive restorations and to determine the benefits and limitations. Study Selection. A search was performed on PubMed/MEDLINE, Embase, Cochrane, Web of Science, Scopus, LIVIVO, and the nonpeer-reviewed literature database. Studies on preheating composite resins for cementing indirect restorations were included, with no restrictions on the type of study, year of publication, or language. The following data were extracted: preheating technique, the device used for preheating, preset temperature, and warming time.

Results

In total, 304 studies were identified. After removing duplicates, 270 articles were selected, and 14 articles were included in the final evaluation. Half of the included studies reported similar preheating techniques using the Calset device for composite resins. The temperatures of 54°C and 68°C were most frequently reported, with a mean warming time of 5 minutes.

Conclusions

Preheating composite resins for the cementation of indirect restorations reduces viscosity, but the material must be used promptly after removal from the device. Practical Implications. Different methodologies for preheating composite resins have been reported and used in clinical dental practice. To achieve good results and guide the clinician on use, the techniques for heating composite resins for cementation need to be standardized. Keeping the material warm until the restorative procedure, the thickness of the indirect restoration, and the composition of the composite resins can directly affect the outcome of the procedure.

A systematic review and meta-analysis on using preheated resin composites as luting agents for indirect restorations

OBJECTIVES

This systematic review investigated the hypothesis that preheated resin composites (RCs) used as luting agents improve the mechanical properties, physicochemical performance, and color of indirect ceramic restorations.

MATERIALS AND METHODS

Literature search was performed in three databases (Medline/PubMed, Scopus, and Web of Science) and in the grey literature (OpenGrey, ProQuest, and Catalog of Theses & Dissertations from CAPES). Eligibility criteria included only studies comparing at least one preheated RC used as a luting agent with resin cements.

RESULTS

Data regarding the mechanical properties, physicochemical characteristics, and color were analyzed qualitatively, and the microtensile bond strength and film thickness were also evaluated by meta-analysis. The search strategy identified 3894 papers, and 28 were full-text screened. Seven studies were included in the review, and 5 were included in the meta-analysis. No significant difference was found for microtensile bond strength (P = 0.14). Preheated RCs showed significantly higher film thickness than resin cements (P = 0.001).

CONCLUSION

Overall, the use of preheated RCs as luting agents offers similar to poorer performance than using resin cements for bonding indirect restorations.

CLINICAL RELEVANCE

Despite the claim that preheated RC could be used as a luting agent, further studies should investigate the effect of clinically unacceptable film thickness.

Survival of Prosthodontic Restorations Luted with Resin-Based versus Composite-Based Cements: Retrospective Cohort Study

The purpose of this study was to evaluate clinical performance, survival, and complications of indirect composite inlays, onlays, and overlays on posterior teeth. Digital records of 282 patients treated between 2014 and 2018 were accessed and analyzed retrospectively. The included patients received 469 composite restorations luted with seven different resin-based types of cement, i.e., Filtek Ultimate Flow, Enamel Plus, Relyx Ultimate, Harvard Premium Flow, Relyx Unicem, Filtek Bulk Fill Flowable, and Filtek Ultimate. The restorations had been clinically and radiographically evaluated annually. The mechanical and clinical complications, e.g., debonding, fracture, and secondary caries, were evaluated and recorded. The examined restorations exhibited a high survival rate (84.9%), and failure was found in only 71 cases. Fracture was the most common cause (n = 36), followed by prosthetic work release (n = 19) and secondary caries (n = 16). There was a statistically significant difference between failure and cement material (Sig. < 0.001); the composite-based cements (87.2%) had a high survival rate compared to the resin-based cement (72.7%). Similarly, the cements with high viscosity (90.2%) had significantly higher survival rates than the low-viscosity cements (78.9%). Moreover, onlays showed higher longevity compared to overlays (Sig. = 0.007), and patients aged under 55 years showed less complications (Sig. = 0.036). Indirect composite restoration was a successful solution to tooth structure loss. The material of the cementation is an important part of the success. Higher survival rate was found in our study when the fixation materials with high viscosity were used, thus suggesting using these materials with indirect restorations. Composite-based cements had significantly higher survival rate than resin-based cements.

Pre-Heating Effect on Monomer Elution and Degree of Conversion of Contemporary and Thermoviscous Bulk-Fill Resin-Based Dental Composites

Detection of unreacted monomers from pre-heated resin-based dental composites (RBC) is not a well-investigated topic so far. The objectives were to determine the temperature changes during the application and polymerization, the degree of conversion (DC) and unreacted monomer elution of room temperature (RT), and pre-heated thermoviscous [VisCalor Bulk(VCB)] and high-viscosity full-body contemporary [Filtek One Bulk(FOB)] bulk-fill RBCs. The RBCs' temperatures during the sample preparation were recorded with a K-type thermocouple. The DC at the top and bottom was measured with micro-Raman spectroscopy and the amounts of eluted BisGMA, UDMA, DDMA, and TEGDMA were assessed with High-Performance Liquid Chromatography. The temperatures of the pre-heated RBCs decreased rapidly during the manipulation phase. The temperature rise during photopolymerization reflects the bottom DCs. The differences in DC% between the top and the bottom were significant. RT VCB had a lower DC% compared to FOB. Pre-heating did not influence the DC, except on the bottom surface of FOB where a significant decrease was measured. Pre-heating significantly decreased the elution of BisGMA, UDMA, DDMA in the case of FOB, meanwhile, it had no effect on monomer release from VCB, except TEGDMA, which elution was decreased. In comparison, RBC composition had a stronger influence on DC and monomer elution, than pre-cure temperature.

Rheological and Mechanical Properties of Resin-Based Materials Applied in Dental Restorations

Resin-based materials have been prevalent for dental restorations over the past few decades and have been widely used for a variety of direct and indirect procedures. Typically, resin-based dental materials are required to be flowable or moldable before setting and can provide adequate mechanical strength after setting. The setting method may include, but is not limited to, light-curing, self-curing or heating. In this review, based on different indications of resin-based dental materials (e.g., dental filling composite, dental bonding agent, resin luting cement), their rheological and mechanical properties were reviewed. Viscous and flexible properties were focused on for materials before setting, while elastic properties and mechanical strength were focused on for materials after setting. At the same time, the factors that may affect their rheological and mechanical properties were discussed. It is anticipated that the insightful information and prospections of this study will be useful to the future development and fabrication of resin-based dental restorative materials.

Effect of Die Spacer Thickness on the Microshear Bond Strength of CAD/CAM Lithium Disilicate Veneers

Aim

The aim of this study was to compare the microshear bond strength of ceramic veneers with digital die spacer settings at 20, 40, and 100 µm.

Materials and Methods

Eighteen milled lithium disilicate microdiscs (IPS e.max CAD, Ivoclar Vivadent) were divided into three groups (n = 6) according to their digital die spacer settings: group A = 20 µm, group B = 40 µm, and group C = 100 µm. Six randomly selected sound maxillary premolars received three microdiscs each. Each microdisc was 1 mm in diameter and 1 mm in height. The buccal surfaces of the premolars were prepared with a 0.5 mm depth in enamel. After cementation, the specimens were thermocycled for 2,500 cycles between 5 and 55°C. Microshear bond strength testing was performed using a universal testing machine until bonding failure. Failure modes were evaluated using a stereomicroscope. Statistical analyses included one-way ANOVA, Tukey's post hoc test, and chi-square test with a 5% alpha error and 80% study power.

Results

The mean microshear bond strength values were calculated in MPa for group A = 31.91 ± 12.41, group B = 29.58 ± 5.03, and group C = 13.85 ± 4.12. One-way ANOVA (p ≤ 0.05) showed a statistically significant difference in microshear bond strength among the three groups. Tukey's post hoc test showed significant differences between groups A and C (p=0.004) and between groups B and C (p=0.011). The failure modes were presented as cohesive, adhesive, and mixed failures. Chi-square test indicated that the failure mode distribution was not significantly different among the three groups (p=0.970).

Conclusion

Higher digital die spacer settings decrease the microshear bond strength of CAD/CAM lithium disilicate veneers.

Effect of Ultrasonic Vibration on Structural and Physical Properties of Resin-Based Dental Composites

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.