Effect of shade and thickness on the microhardness of resin-based composite specimens at different points considering curing light beam's inhomogeneity.

BACKGROUND: Recent studies have reported the inhomogeneity in the light emitted by dental light-curing units (LCUs). It is essential to understand how this uneven light distribution affects the physical properties of resin-based composites (RBCs) at various points across their surfaces. This study aimed to evaluate the effect of LCU beam's inhomogeneity on the microhardness of RBCs with different shades and thicknesses. METHODS: Four body (A1B, A2B, A3B, and A4B), one dentin (A3D), and one enamel shade (A3E) of RBC (Filtek Z350 XT) were examined. The specimens were fabricated in four thicknesses (1, 2, 3, and 4 mm) and subjected to a 40-second light-curing. Vickers microhardness testing was performed at the center point, and 3 mm left and right from the center at the bottom surface of each sample. The LCU beam profile was characterized using a beam profiler, while irradiance after specimen passage was measured using a spectrometer. One-way analysis of variance (ANOVA) and Tukey's post-hoc tests were used to analyze the effects of shades and thicknesses on irradiance and microhardness, respectively. One-way repeated-measures ANOVA was used to compare the microhardness across different points. Pearson's correlation analysis examined the relationship between irradiance and microhardness. RESULTS: The beam profile of LCU revealed inhomogeneous light distribution. Light irradiance was decreased with both the increase in thickness and darker shade of the specimens (p < 0.05). Microhardness was found to decline with an increase in sample thickness (p < 0.05), and was consistently higher at the center point compared to the periphery, particularly in thicker (3 and 4 mm) and darker shades (A3B, A4B, and A3D). A positive correlation was found between the irradiance and microhardness across all evaluated points (p < 0.05). CONCLUSIONS: Inhomogeneous light emission from LCU significantly influences the microhardness of RBC samples, depending on the thicknesses and shades. The findings underline the importance of considering LCU beam inhomogeneity in clinical settings to ensure optimal polymerization of RBC.

Influence of radiant exposure and material shade on the degree of conversion and microhardness of a resin-based composite.

This in vitro study evaluated the influence of radiant exposure and material shade on the degree of conversion (DC) and microhardness of a resin-based composite (RBC). Sixty-four RBC specimens in shades A1E (enamel) and A4D (dentin) were light cured at a calibrated exitance of 1000 mW/cm2 for 5, 10, 15, or 20 seconds, resulting in radiant exposure levels of 5, 10, 15, or 20 J/cm2. The DC was determined using Fourier-transform infrared spectroscopy (n = 3 per shade per exposure level). The Knoop hardness number (KHN) was measured on the top and bottom surfaces of each specimen (n = 5 per shade per exposure level). Data were analyzed using 2- and 3-way analyses of variance and post hoc Tukey tests (α = 0.05). The RBC shade did not affect the DC (P = 0.860), and the lowest DC values were achieved with an exposure level of 5 J/cm2 (P < 0.001). The shade did not affect the KHN on the top surface, but the radiant exposure level did, with the application of 5 J/cm2 resulting in significantly lower values (P < 0.05). For the bottom surface, shade A1E showed significantly higher KHN values than A4D (P < 0.001). An increase in the radiant exposure led to increased DC and KHN for both shades of RBC until reaching a saturation point of 10 J/cm2 for A1E and the top surface of A4D. The darker and more opaque shade was not adequately polymerized at a 2-mm depth, even when the highest radiant exposure level was applied.

Effect of light-curing time and direction on microhardness of a light-cured resin composite to cement CAD-CAM restorations.

PURPOSE: To evaluate the effect of light-curing exposure time and location on polymerization of a restorative bulk-fill resin composite to lute endocrowns. METHODS: A light-cured restorative bulk-fill resin composite (Filtek One Bulk Fill) was submitted to direct light-curing by a high-power LED light-curing unit for 20 seconds as the positive control group (n= 10). Five more groups (n= 10) were light-cured in a natural tooth mold from two sites (labial and lingual) through a nanohybrid resin composite CAD-CAM restoration (Lava Ultimate A2 LT), for different irradiation times: 90 seconds per site, 40 seconds per site, 30 seconds per site, 20 seconds per site and 10 seconds per site. Vickers microhardness measurements were made at two different depths and test/control ratios were calculated. Ratios of 0.8 were considered as an adequate level of curing. A quantile regression was run to identify the minimally sufficient time of light-curing, and a two-way ANOVA was used to compare the results to previous findings and evaluate the effect of curing location. RESULTS: Analysis showed that 40 seconds x 2 is the minimal irradiation time that presents a test/control ratio above 0.8. Quantile regressions showed that the required irradiation time to reach a test/control ratio of 0.8 at a confidence level of 95% is 41.5 seconds and 39.2 seconds at 200 µm and 500 µm depths in the luting agent, respectively. There was no statistically significant difference between microhardness of the two depths except for the irradiation time of 10 seconds. The two-site to three-site light curing comparison showed no statistically significant difference except for the 90-second time. CLINICAL SIGNIFICANCE: Systematic light-curing through the labial, lingual and occlusal surfaces of thick indirect restorations is not always required for sufficient polymerization and can even waste valuable clinical time especially in the case of multiple restorations luted with resin composites.

How does indirect air-cooling influence pulp chamber temperature in different volume teeth and absence/presence of resin-based composite during light curing?

BACKGROUND: Light-curing of materials during restorative dental procedures poses a risk for pulp tissue overheating. Therefore, the aim of this study was to investigate the effect of indirect air-cooling on pulp chamber temperatures during light-curing of varying volume teeth and absence/presence of resin-based composite (RBC) at different exposure time. METHODS: The volume of 11 human teeth was measured by micro computed tomograph. An experimental rig controlled the thermal environment of the teeth and a thermocouple inserted retrograde into the root canal measured temperature changes. Pulp chamber temperature was measured with and without air-cooling on teeth without and with RBC at 15 s, 30 s and 60 s intervals. Generalized estimating equations were used for statistical analysis. RESULTS: The temperature increase with air-cooling (versus no air-cooling) was lower in teeth despite absence/presence of RBC (ß = - 4.26, 95%CI - 5.33 and ß = - 4.47, 95%CI - 5.60, respectively). With air-cooling, the temperature increase in teeth with RBC was lower compared to teeth without RBC (ß = - 0.42, 95%CI -0.79; - 0.05). Higher teeth volume resulted in lower temperature increase with air-cooling than without air-cooling (ß = - 0.04, 95%CI -0.07; - 0.01 and ß = - 0.17, 95%CI -0.30; - 0.05, respectively). CONCLUSIONS: Air-cooling resulted in lower pulp chamber temperature increase. Using air-cooling, the temperature increase was lower in teeth with RBC compared to teeth without RBC. Lower volume teeth resulted in higher temperature increase, thus they seemed to benefit more from air-cooling compared to higher volume teeth. Air-cooling could be an effective tool in controlling pulp temperature increase during light-curing, especially when the tooth volume is small.

Influence of Primer Pre-curing and Co-curing on Shear Bond Strength of Orthodontic Brackets Using Three Light-cure Adhesive Systems: An In Vitro Study.

AIM: This study aimed to evaluate the shear bond strength (SBS) of orthodontic brackets with primer pre-curing and co-curing using three light cure adhesive systems. MATERIALS AND METHODS: In this in vitro study, 102 extracted premolar teeth mounted on self-cure acrylic resin blocks were separated into six groups based on primer pre-curing and co-curing with each group receiving stainless steel orthodontic premolar brackets bonded to the buccal surfaces. The following adhesives were used: Transbond XT (3M Unitek, CA, USA), Orthofix (Anabond Stedman, India), and Enlight (Ormco, India). In the groups with pre-curing, the primer was pre-cured for 20 seconds while in the groups with co-curing, the primer and adhesive were cured together. Shear bond strength tests and Adhesive Remnant Index (ARI) were assessed followed by an scanning electron microscope (SEM) view (×3000) of the enamel surface after debonding. Statistical analysis was done using a one-way analysis of variance (ANOVA) test. RESULTS: The descriptive statistics in the pre-cured groups showed a statistically significant difference. The highest mean SBS was observed for group I, i.e., Transbond XT with primer pre-curing (20.56 ± 3.22 MPa). The lowest mean SBS was for group IV, i.e., Orthofix with primer co-curing (7.57 + 0.49 MPa). The results of ANOVA revealed a significant difference among the groups. The ARI scoring and the SEM analysis also confirmed this finding. CONCLUSION: Shear bond strength of orthodontic brackets with primer pre-curing showed a better bond strength than brackets with co-curing. The ARI data suggested that the majority of bracket failure happened at the resin-bracket interface. Scanning electron microscope analysis also confirmed the ARI and SBS findings. CLINICAL SIGNIFICANCE: During the bonding of orthodontic brackets, the primer can be co-cured where the primer and adhesive resin are cured simultaneously or pre-cured where the primer is cured separately. Most orthodontic clinicians to save time co-cure primer. Both these methods affect the SBS of brackets.

Wavelength-dependent light transmittance in resin composites: practical implications for curing units with different emission spectra.

OBJECTIVES: To evaluate light transmittance as a function of wavelength for eight composite materials and compare the transmittance for blue light produced from two curing units with different emission spectra. MATERIALS AND METHODS: Light transmittance through 2- and 4-mm-thick composite specimens was recorded in real time during 30 s of curing using a broad-spectrum (peaks at 405 and 450 nm) and a narrow-spectrum (peak at 441 nm) LED-curing unit. The spectral resolution of 0.25 nm and temporal resolution of 0.05 s resulted in a large amount of light transmittance data, which was averaged over particular spectral ranges, for the whole measurement period. Statistical analysis was performed using Welch ANOVA with Games-Howell post hoc test, t test, and Pearson correlation analysis. The level of significance was 0.05 and n = 5 specimens per experimental group were prepared. RESULTS: Light transmittance varied as a function of wavelength and time, revealing significantly different patterns among the tested materials. Light transmittance for different parts of curing unit spectra increased in the following order of emission peaks (nm): 405 < 441 < 450. Of particular interest was the difference in transmittance between 441 and 450 nm, as these peaks are relevant for the photoactivation of camphorquinone-containing composites. A high variability in light transmittance among materials was identified, ranging from statistically similar values for both peaks up to a fourfold higher transmittance for the peak at 450 nm. CONCLUSION: Each material showed a unique pattern of wavelength-dependent light transmittance, leading to highly material-dependent differences in blue light transmittance between two curing units. CLINICAL RELEVANCE: Minor differences in blue light emission of contemporary narrow-peak curing units may have a significant effect on the amount of light which reaches the composite layer bottom.

Does the Translucency of Novel Monolithic CAD/CAM Materials Affect Resin Cement Polymerization with Different Curing Modes?

PURPOSE: The translucency of CAD/CAM blocks influences the polymerization efficiency of resin cement used underneath. The aim of this study is to evaluate the influence of the translucency parameters (TPs) of current monolithic CAD/CAM blocks on the microhardness of light-cured or dual-cured resin cement. MATERIALS AND METHODS: 100 specimens were prepared from five types of CAD/CAM blocks (Mark II, Suprinity, Enamic, e.max, Ultimate), and their TP values were measured by spectrophotometry; 100 resin cement specimens (Duolink) were cured underneath five ceramic specimen groups by indirect LED light for 40 seconds with dual-cure (with catalyst) and light-cure (without catalyst) polymerization modes. Control group resin cement specimens (n = 20) were cured with both polymerization modes by direct LED light without any ceramic disc, making 120 resin cement specimens in total. The specimens were then stored in a dry environment for 24 hours before measurement of the polymerization depth with a digital micrometer. Vickers hardness measurements were performed at different resin cement sections. The results were statistically analyzed with 1-, 2-, and 3-way ANOVA, Student's t-test and Tukey's HSD test (α = 0.05). RESULTS: The highest TP values occurred for Suprinity and Ultimate, whereas the lowest TP value occurred for Enamic (p < 0.01). The depth of cure and Vickers hardness values changed proportionally with TP value. In all specimens, dual polymerization provided higher depth of cure and Vickers hardness values than those obtained using light polymerization (p < 0.01). In all specimens except Enamic, the hardness value differences between the sections were statistically insignificant (p > 0.05). In Enamic, the hardness values for both polymerization types decreased significantly in the deeper sections (p < 0.01). CONCLUSIONS: Lower depth of cure was observed as the amount of transmitted light decreased in the investigated materials. In clinical practice, light-cured resin cements may result in inadequate polymerization for ceramic materials with lower TP values. Zirconia-reinforced lithium silicate and nanoceramic resins may be reliable restorative materials for a restoration with both optimal esthetics and sufficient mechanical strength resulting from proper polymerization.

Effect of mold diameter on the depth of cure of a resin-based composite material.

The purpose of this study was to examine the effect of mold diameter on depth of cure of a resin-based composite material for varying amounts of irradiation. A resin-based composite was light-cured for 10-80 s in stainless-steel molds of either 6 mm or 4 mm in diameter and then dark-stored for 24 h. Specimens were then scraped back and the length of the cured specimens was measured to provide depth of cure (DSB ). Radiant exposure to each of the mold diameters was determined by measuring the power. The DSB values using the 4-mm molds were lower than those of the 6-mm molds. The average difference between the two groups for each irradiation time was 0.45 ± 0.02 mm. A fixed depth of cure required about 39% more irradiation time for the 4-mm mold than for the 6-mm mold but 75% more radiant exposure. The difference in cure depth for a fixed radiant exposure was 0.79 mm. A better comparison of depth of cure is obtained by using identical radiant exposures for different mold diameters. It is believed that greater loss of light by absorption at the stainless-steel cylinder walls for the 4-mm-diameter cylinders accounts for the lower depth of cure when compared with the 6-mm molds.

Development of a novel resin-based dental material with dual biocidal modes and sustained release of Ag+ ions based on photocurable core-shell AgBr/cationic polymer nanocomposites.

Research on the incorporation of cutting-edge nano-antibacterial agent for designing dental materials with potent and long-lasting antibacterial property is demanding and provoking work. In this study, a novel resin-based dental material containing photocurable core-shell AgBr/cationic polymer nanocomposite (AgBr/BHPVP) was designed and developed. The shell of polymerizable cationic polymer not only provided non-releasing antibacterial capability for dental resins, but also had the potential to polymerize with other methacrylate monomers and prevented nanoparticles from aggregating in the resin matrix. As a result, incorporation of AgBr/BHPVP nanocomposites did not adversely affect the flexural strength and modulus but greatly increased the Vicker's hardness of resin disks. By continuing to release Ag+ ions without the impact of anaerobic environment, resins containing AgBr/BHPVP nanoparticles are particularly suitable to combat anaerobic cariogenic bacteria. By reason of the combined bactericidal effect of the contact-killing cationic polymers and the releasing-killing Ag+ ions, AgBr/BHPVP-containing resin disks had potent bactericidal activity against S. mutans. The long-lasting antibacterial activity was also achieved through the sustained release of Ag+ ions due to the core-shell structure of the nanocomposites. The results of macrophage cytotoxicity showed that the cell viability of dental resins loading less than 1.0 wt% AgBr/BHPVP was close to that of neat resins. The AgBr/BHPVP-containing dental resin with dual bactericidal capability and long term antimicrobial effect is a promising material aimed at preventing second caries and prolonging the longevity of resin composite restorations.

Color stability of ceramic laminate veneers cemented with light-polymerizing and dual-polymerizing luting agent: A split-mouth randomized clinical trial.

STATEMENT OF PROBLEM: The color stability of luting agents influences the esthetics of ceramic laminate veneers. Clinical studies that have evaluated the color changes of veneers cemented to enamel with light- and dual-polymerizing resin cement are lacking. PURPOSE: The purpose of this split-mouth randomized clinical trial was to evaluate the color change and marginal discoloration of dual- and light-polymerizing cement used for cementation of ceramic laminate veneers. MATERIAL AND METHODS: In 10 participants, 0.3-mm-thick ceramic laminate veneers were cemented on the buccal surface of the second premolars without tooth preparation. A randomized application of light-polymerized cement was used on one side and a dual-polymerized cement on the contralateral side. The operator and participants were blinded to the activation mode. Color was evaluated by a blinded evaluator with a spectrophotometer at 24 hours and at 2, 6, 12, and 24 months after cementation. The CIELab (ΔE*ab) and CIEDE2000 (ΔE*00) formulas were used to quantify color alteration, and Δa*, Δb*, and ΔL* were calculated between the first and subsequent measurements. US Public Health Service guidelines were used to evaluate the marginal discoloration. RESULTS: Wilcoxon tests did not show a statistical difference in ΔE*ab and ΔE*00 between the groups (P>.05). At 24 months, the median ΔE*ab was 2.31 (interquartile ranges [IQR]: 3.34) for the light-polymerizing mode and 1.57 (IQR: 0.41) for the dual-polymerizing mode, while the median ΔE*00 was 1.65 for the light-polymerizing mode (IQR: 2.34) and 1.18 for the dual-polymerizing mode (IQR: 0.25). The thresholds for clinically acceptable color changes ΔE*ab>3.46 and ΔE*00>2.25 were found for both curing modes. Marginal discoloration was observed from the 2-year assessment. CONCLUSIONS: The color stability of ceramic laminate veneers was similar for both of the polymerizing modes for all evaluated periods. Marginal discoloration increased over a 2-year period for both the light- and the dual-polymerizing modes.

Effectiveness of high-power LEDs to polymerize resin cements through ceramics: An in vitro study.

STATEMENT OF PROBLEM: The cementation of ceramic veneers using light-polymerized resin cement is largely dependent on the proper light activation of the cement. Light activation using high irradiance could shorten the time required to lute multiple restorations. PURPOSE: The purpose of this in vitro study was to evaluate the light transmission of dental light-polymerizing units through ceramic cylinders and its effect on the polymerization kinetics of a resin cement. MATERIAL AND METHODS: Ceramic ingots (IPS Empress Esthetic, shade ET1) were sectioned to produce cylinders 0.5, 1.0, and 2.0 mm thick. Two light-emitting diode units were evaluated: SmartLite Focus and Valo Cordless, the latter used in either Standard or Xtra Power (XP) modes. Light transmission (average of irradiance, total energy, and light-emission profile) through the cylinders was measured (n=3). The polymerization kinetics of a resin cement light polymerized through the ceramic was monitored for 5 minutes (n=3). The degree of conversion was measured again after 72 hours. Data were individually analyzed with 2-way ANOVA and the Tukey HSD test (α=.05). RESULTS: Valo at XP presented the highest values of irradiance and SmartLite the lowest, irrespective of the ceramic thickness. Regarding the total energy, XP showed the lowest values. The total energy and irradiance lessened with the increase in ceramic thickness. In general, except for Valo at XP, the ceramic thickness did not affect the degree of conversion. Valo at XP and interposing 2.0 mm ceramic resulted in the lowest values of Rpmax. CONCLUSIONS: The reduction of total energy and irradiance by ceramic interposition had only a slight effect on polymerization kinetics.

[Curing mode of universal adhesives affects the bond strength of resin cements to dentin].

OBJECTIVE: To determine the effects of curing mode of one-step and two-step universal adhesives on the micro-tensile bond strength (µTBS) of different dual-cure resin cements to dentin. METHODS: One-step universal adhesive Single Bond Universal (SBU), and two-step universal adhesive OptiBond Versa (VSA) were chosen as the subjects, one-step self-etching adhesive OptiBond All in One (AIO) and two-step self-etching adhesive Clearfil SE Bond (SEB) were control groups, and two dual-cure resin cements RelyX Ultimate (RLX) and Nexus 3 Universal (NX3) were used in this study. In this study, 80 extracted human molars were selected and the dentin surface was exposed using diamond saw. The teeth were divided into 16 groups according to the adhesives (AIO, SBU, SEB, VSA), cure modes of adhesives (light cure, non-light cure) and resin cements (RLX, NX3). The adhesives were applied on the dentin surface following the instruction and whether light cured or not, then the resin cements were applied on the adhesives with 1 mm thickness and light cured (650 mW/cm(2) for 20 s. A resin was built up (5 mm) on the cements and light cured layer by layer. After water storage for 24 h, the specimens were cut into resin-cement-dentin strips with a cross sectional area of 1 mm×1 mm and the µTBS was measured. RESULTS: Regarding one-step universal adhesive (SBU) light cured, the µTBS with RLX [(35.45±7.04) MPa] or NX3 [(26.84±10.39) MPa] were higher than SBU non-light cured with RLX [(17.93±8.93) MPa)] or NX3 [(10.07±5.89) MPa, P<0.001]. Compared with AIO, light-cured SBU combined with RLX presented higher µTBS than AIO group [(35.45±7.04) MPa vs. (24.86±8.42) MPa, P<0.05]. When SBU was not lighted, the µTBS was lower than AIO [(17.93±8.93) MPa vs. (22.28±7.57) MPa, P<0.05]. For two-step universal adhesive (VSA) and control adhesive (SEB), curing mode did not affect the µTBS when used with either RLX or NX3 (25.98-32.24 MPa, P>0.05). CONCLUSION: Curing mode of one-step universal adhesive may affect the µTBS between dual-cure resin cements and dentin, while for two-step universal adhesive, the curing mode and the type of resin cements did not influence the µTBS.

Diffusion of light through quartz fiber-reinforced epoxy resin double taper posts.

PURPOSE: The aim of this study was to evaluate the progression of the light through a series of translucent posts available on the market (D.T. Light-post, R.T.D.). MATERIALS & METHODS: nine D.T. Light-posts (DTLPs) were analyzed, 3 for each available measure. Each post was trans-illuminated both in vertical trans-ilumination (VTI) and oblique trans-illumination (OTI), via a light curing unit (LCU) (V.I.P., Bisco), in complete darkness conditions, and the resulting image of the post, was digitally acquired with a 1:1 ratio. The images were then analyzed using digital image analysis software (Image Pro plus 4.1, Media Cybernetics) previously performing the light intensity calibration, of the LCU, by means a radiometer (Curing Radiometer model 100, Demetron Corp.). The evaluation of the progression of the light through the posts was conducted for each post along its longitudinal axis. RESULTS: no significant differences concerning VTI vs OTI for DTLP n.1 (p = 0.341) and DTLP n. 3 (p = 0.115), while for DTLP n.2 a significant difference was observed (p = 0.041); Conclusion: The results demonstrate that the greater the section of the post, the greater its ability to transmit light at a distance; also the vertical Trans-illumination of the post is to be preferred to the oblique one.

Microtensile Bond Strength of Resin-bonded Hightranslucency Zirconia Using Different Surface Treatments.

PURPOSE: To evaluate the effect of a novel surface treatment intended to improve bond strength to high-translucency zirconia. MATERIALS AND METHODS: Fully sintered high-translucency zirconia disks (Incoris TZI) were divided into four groups according to the surface treatment received: modified fusion sputtering technique, selective infiltration etching, low pressure particle abrasion using 30-µm alumina particles, while 50-µm particle abrasion served as control. Surface roughness was evaluated quantitatively using a contact profilometer. The disks were bonded to pre-aged composite resin disks using a light-polymerized adhesive resin (RelyX ultimate). The bilayered disks were sectioned into microbars and zirconia-resin bond strength was evaluated using the microtensile bond strength test (MTBS). The test was repeated after 3 months of water storage (37°C). Scanning electron microscopic examination of the zirconia resin interface was performed at different magnifications. A repeated measures ANOVA and Bonferroni post-hoc test were used to analyze the data (n = 20, α = 0.05). RESULTS: One-way ANOVA revealed significant differences in average surface roughness (Ra) between the tested groups (p < 0.001). The highest Ra value was recorded for fusion sputtering (12.23 ± 0.11 µm), followed by 50-µm particle abrasion (6.400 ± 0.887), then low pressure 30-µm particle abrasion (2.4 ± 0.15 µm), while the lowest surface roughness was recorded for the selective infiltration group (0.368 ± 0.04 µm). Modified fusion sputtering and selective infiltration etching produced significantly higher MTBS values at each of the tested intervals (p < 0.001) compared to particle abrasion using different particle sizes. Water storage resulted in reduction in the bond strength of 30-µm abraded specimens, which was attributed to structural defects observed at the zirconia/ resin interface. Scanning electron microscopic examination revealed a nanoporous surface characteristic of selective etching surface treatment, and modified fusion sputtering resulted in the creation of surface-fused microbeads. CONCLUSION: Within the limitations of this study, selective infiltration etching and modified fusion sputtering techniques established a strong, stable, durable bond to high-translucency zirconia.

Influence of Surface Conditioning Protocols on Reparability of CAD/CAM Zirconia-reinforced Lithium Silicate Ceramic.

PURPOSE: To test the effect of surface conditioning protocols on the reparability of CAD/CAM zirconia-reinforced lithium silicate ceramic compared to lithium-disilicate glass ceramic. MATERIALS AND METHODS: Zirconia-reinforced lithium silicate ceramic (Vita Suprinity) and lithium disilicate glass-ceramic blocks (IPS e.max CAD) were categorized into four groups based on the surface conditioning protocol used. Group C: no treatment (control); group HF: 5% hydrofluoric acid etching for 60 s, silane (Monobond-S) application for 60 s, air drying; group HF-H: 5% HF acid etching for 60 s, application of silane for 60 s, air drying, application of Heliobond, light curing for 20 s; group CO: sandblasting with CoJet sand followed by silanization. Composite resin (Tetric EvoCeram) was built up into 4 x 6 x 3 mm blocks using teflon molds. All specimens were subjected to thermocycling (5000x, 5°C to 55°C). The microtensile bond strength test was employed at a crosshead speed of 1 mm/min. SEM was employed for evaluation of all the debonded microbars, the failure type was categorized as either adhesive (failure at adhesive layer), cohesive (failure at ceramic or composite resin), or mixed (failure between adhesive layer and substrate). Two-way ANOVA and the Tukey's HSD post-hoc test were applied to test for significant differences in bond strength values in relation to different materials and surface pretreatment (p < 0.05). RESULTS: The highest microtensile repair bond strength for Vita Suprinity was reported in group CO (33.1 ± 2.4 MPa) and the lowest in group HF (27.4 ± 4.4 MPa). Regarding IPS e.max CAD, group CO showed the highest (30.5 ± 4.9 MPa) and HF the lowest microtensile bond strength (22.4 ± 5.7 MPa). Groups HF, HF-H, and CO showed statistically significant differences in terms of all ceramic types used (p < 0.05). The control group showed exclusively adhesive failures, while in HF, HF-H, and CO groups, mixed failures were predominant. CONCLUSIONS: Repair bond strength to zirconia-reinforced lithium silicate ceramics and lithium-disilicate glass ceramic could be improved when ceramic surfaces are sandblasted with CoJet sand followed by silanization.

Self-adhesive Luting of Partial Ceramic Crowns: Selective Enamel Etching Leads to Higher Survival after 6.5 Years In Vivo.

PURPOSE: To investigate the influence of selective enamel etching on long-term clinical performance of partial ceramic crowns (PCCs) luted with a self-adhesive luting material (RXU: RelyX Unicem). MATERIALS AND METHODS: At baseline, 34 patients received the intended treatment: two PCCs (Vita Mark II; Cerec 3D) for the restoration of extended lesions with multiple-cusp coverage were placed in a split-mouth design with a self-adhesive luting material, one without (RXU) and one with selective enamel etching (RXU+E). Patients were evaluated clinically (modified USPHS criteria) at baseline and up to 6.5 years (70 to 88 months). The chi-square test was used for statistical analyses (α=0.05). Clinical survival of all restorations (n=68) after 6.5 years was evaluated by Kaplan-Meier analysis. RESULTS: After 6.5 years, 18 patients (9 male, 9 female; median age 41, range 25 to 59 years) with 36 RXU and RXU+E restorations were available for clinical assessment (patient recall rate: 53%), with 13 RXU and 14 RXU+E PCCs placed in molars and 5 RXU and 4 RXU+E PCCs in premolars. Clinically, no statistically significant differences between the luting procedures were detected. Both RXU and RXU+E revealed significant changes over time with respect to marginal adaptation (significant deterioration) and marginal discoloration (significant increase). RXU revealed no cases of postoperative hypersensitivity and RXU+E only did so at baseline (n=5). Kaplan-Meier analysis showed a cumulative survival for RXU of 60% and for RXU+E of 82%, indicating a significantly higher survival rate for RXU+E. CONCLUSION: Clinically, RXU and RXU+E perform similarly. In PCC restorations with multiple-cusp coverage, lack of retention due to adhesive preparation, and little dentin available for adhesion caused by extensive core buildups or cavity linings, selective enamel etching is recommended.

Different Strategies to Bond Bis-GMA-based Resin Cement to Zirconia.

PURPOSE: To evaluate the effect of different bonding strategies on short- and long-term bis-GMA-based resin cement bond strengths to zirconia. MATERIALS AND METHODS: One hundred twenty samples of fully-sintered zirconia (Prettau Zirconia) were sandblasted and randomly distributed into 5 groups (n = 24): UA: Scotchbond Universal Adhesive; SZP: Signum Zirconia Bond I + II; ZPP: Z-Prime Plus; EXP: MZ experimental primer; CO: no primer application (control). After performing these surface treatments, translucent tubes (0.8 mm diameter and 1.0 mm height) were placed on the zirconia specimens, and bis-GMA-based cement (Duo-Link) was injected into them and light cured. Specimens were tested for microshear bond strength either 24 h or 6 months (m) after water storage (37°C) and surfaces were characterized by SEM and EDX. Two-way ANOVA and Tukey's post-hoc test (p < 0.05) were used to evaluate bond strength results. RESULTS: The mean bond strengths (MPa ± SD) were: UA=14.6 ± 4.7a (24 h); 16.0 ± 4.8a (6 m); SZP = 14.0 ± 5.4ab (24 h); 11.9 ± 2.6ab (6 m); ZPP=8.0 ± 1.8b (24 h); 8.6 ± 3.3b (6 m); EXP = 1.2 ± 0.5c (24 h); 0.6 ± 0.7c (6 m); CO=1.0 ± 1.2c (24 h); 1.3 ± 1.2c (6 m). Bonding strategy significantly influenced bond strength (p = 0.0001), but storage time did not (p = 0.841). Groups UA and SZP showed a homogeneous layer covering the zirconia surface. In these groups, EDX demonstrated the presence of phosphorus. Group ZPP resulted in a nonhomogeneous layer, exposing the zirconia substrate underneath. EXP application resulted in an undetectable layer. CONCLUSION: Water storage did not affect resin cement bond strengths to zirconia irrespective of the surface treatment. Bis-GMA-based resin cement bond strengths to zirconia are affected by specific bonding strategies.

Accelerated Fatigue Resistance of Thick CAD/CAM Composite Resin Overlays Bonded with Light- and Dual-polymerizing Luting Resins.

PURPOSE: To evaluate the accelerated fatigue resistance of thick CAD/CAM composite resin overlays luted with three different bonding methods. MATERIALS AND METHODS: Forty-five sound human second mandibular molars were organized and distributed into three experimental groups. All teeth were restored with a 5-mm-thick CAD/CAM composite resin overlay. Group A: immediate dentin sealing (IDS) with Optibond FL and luted with light-polymerizing composite (Herculite XRV). Group B: IDS with Optibond FL and luted with dual-polymerizing composite (Nexus 3). Group C: direct luting with Optibond FL and dual-polymerizing composite (Nexus 3). Masticatory forces at a frequency of 5 Hz were simulated using closed-loop servo-hydraulics and forces starting with a load of 200 N for 5000 cycles, followed by steps of 400, 600, 800, 1000, 1200 and 1400 N for a maximum of 30,000 cycles. Each step was applied through a flat steel cylinder at a 45-degree angle under submerged conditions. RESULTS: The fatigue test generated one failure in group A, three failures in group B, and no failures in group C. The survival table analysis for the fatigue test did not demonstrate any significant difference between the groups (p = 0.154). The specimens that survived the fatigue test were set up for the load-to-failure test with a limit of 4600 N. The survival table analysis for the load-to-failure test demonstrates an average failure load of 3495.20 N with survival of four specimens in group A, an average failure load of 4103.60 N with survival of six specimens in group B, and an average failure load of 4075.33 N with survival of nine specimens in group C. Pairwise comparisons revealed no significant differences (p < 0.016 after Bonferroni correction). CONCLUSION: Within the limitations of this in vitro study, it can be concluded that although the dual-polymerizing luting material seems to provide better results under extreme conditions, light-polymerizing luting composites in combination with IDS are not contraindicated with thick restorations.

The influence of two different curing regimens on light energy transmission through bulk-fill resin composites and Vickers hardness.

PURPOSE: To compare the total light energy transmission (J/cm2) through bulk-fill composite materials (BFMs) and Vickers hardness (VH) using a single-peak light curing unit (LCU) using two curing regimens. METHODS: Samples (n= 5) of viscous BFMs, Tetric EvoCeram Bulk Fill (TBF), X-tra fil (XF), and flowable BFMs, SureFil SDR (SDR), and X-tra base (XB) were prepared in 4 mm deep rings. The control was Tetric EvoCeram (TEC), a conventional composite. Using MARC-RC, the irradiance delivered to the top surface of the samples was adjusted to either 800 mW/cm2 for 20 seconds (16 J/cm2) or 1,600 mW/cm2 for 10 seconds (16 J/cm2). Samples were stored post-irradiation at 22 ± 2°C for 24 hours. Top and bottom-surface VH were measured and Bottom/Top (B/T) VH ratios were calculated. Data were analyzed using one-way ANOVA (α= 0.05). RESULTS: Total energy transmission for all materials ranged from 1.0 J/cm2 (6.1%) to 2.7 J/cm2 (16.9%). There was a statistically significant difference for total energy transmission to the bottom surface, more being transmitted at 800 mW/cm2 x 20 (P< 0.001). XB and TEC were significantly different, with higher B/T VH ratio when cured at 800 mW/cm2 x 20 seconds (P< 0.001). There was no statistically significant difference for TBF, XF and SDR (P> 0.05) with either curing regimen. CLINICAL SIGNIFICANCE: The degree of cure was material-dependent and increasing curing time may be more important than LCU tip irradiation values. Manufacturer's recommended total energy regimen may not always be adequate for effective curing. Some bulk-fill materials, containing additional photo-sensitivity to lower wave lengths, may be adequately cured using a single-peak LCU.

Heat generated during light-curing of restorative composites: Effect of curing light, exotherm, and experiment substrate.

PURPOSE: To investigate temperature rise, separating heat caused by irradiation and exotherm for three composites polymerized with three curing lights. The effect of substrate on temperature measurements was also determined. METHODS: Composite samples (n= 5) (Filtek Supreme Ultra, Filtek LS, and EsthetX HD) were placed on a thermocouple tip inside three substrates (aluminum, Delrin, and tooth). The composites were photoactivated using three curing lights (Elipar 2500 QTH, SmartLite Max LED, DemiUltra LED) at 1 mm distance. Irradiance was 798, 980, and 1,135 mW/cm2, respectively. Exotherm was determined by subtracting post-cure from the polymerization temperature curves. ANOVA and Student-Newman-Keuls post-hoc tests were used to analyze differences among peak temperatures and exotherms (significance level 0.05). RESULTS: SmartLite LED curing light resulted in higher peak temperatures and exotherms compared to the DemiUltra LED and QTH for all tested composites (16.9-20.4°C vs 12.3-14.7°C vs 8.9-9.7°C). Thus, the LEDs produced higher temperature rises than the QTH, and the LED with lower irradiance caused higher temperature rise than the LED with higher irradiance. The silorane-based Filtek LS generated significantly higher exotherm than the methacrylate-based EsthetX HD and Filtek Supreme Ultra (6.2-7.6°C vs 3.6-4.5°C vs 2.7-3.6°C). Substrate affected temperatures significantly. Temperature profiles found in Delrin substrate were comparable to tooth substrate, while aluminum substrate reduced temperatures 10-20 degrees. CLINICAL SIGNIFICANCE: Curing of restorative composites raises the temperature under a restoration due to irradiation and exothermic reaction; how much the temperature increases depends on curing light design, type of composite, and surrounding substrate. The silorane-based Filtek LS generated significantly higher exotherm than the methacrylate-based EsthetX HD and Filtek Supreme Ultra.