Effect of monomer type on the C C degree of conversion, water sorption and solubility, and color stability of model dental composites

Impact of erosive and abrasive wear on the surface characteristics of hybrid ceramic-polymer dental materials

PURPOSE

To evaluate the surface characteristics of hybrid ceramic-polymer materials before and after exposure to erosive and abrasive media.

METHODS

Samples were prepared from Vita Enamic (VE), Cerasmart (CS), VarseoSmile Crown plus (VSC), and VarseoSmile Temp (VST). Surface roughness (SR), scanning electron microscopy (SEM), and surface hardness (SH) analyses were performed before (T0) and after exposing the samples to gastric juice (GJ), toothbrushing (TB), or both (GJ TB) for a simulated period of one (T1) or two years (T2).

RESULTS

At T0, VSC and VST showed higher average (Ra) and maximum (Rz) roughness values, more homogeneous surfaces in SEM micrographs, and lower Vickers numbers (HV) than VE and CS. At T1 and T2, samples showed higher Ra values, greater surface damage on SEM micrographs, and reduced HV. The most pronounced changes were evident for GJ TB samples, followed in order by GJ (within VE and CS) and TB samples (within VSC and VST).

CONCLUSION

VE and CS showed initially lower SR and higher SH, lower resistance to GJ, and higher resistance to TB than VSC and VST, which would be essential when fabricating restorations for patients who are particularly susceptible to dental erosion and abrasion.

Effects of photopolymerization and autopolymerization of three different dual-polymerizing self-adhesive resin cements on cell viability

STATEMENT OF PROBLEM

While dual-polymerizing self-adhesive resin cements have been widely used because of their bonding capabilities and ease of use, there is a lack of comprehensive data on their biocompatibility, particularly concerning the cytotoxic effects of different polymerization methods on cell viability.

PURPOSE

The purpose of this in vitro study was to investigate the potential cytotoxic effects of 3 different dual-polymerizing self-adhesive resin cements polymerized by light polymerization or autopolymerization on L929 cells in vitro using by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide (MTT) test.

MATERIAL AND METHODS

Three different dual-polymerizing self-adhesive resin cements (Calibra Universal; Dentsply Sirona Inc, SpeedCEM Plus; Ivoclar AG, and TheraCem Ca; Bisco Inc) were light or autopolymerized in polytetrafluoroethylene (PTFE) molds containing Ø5-mm and 2-mm-thick cells in accordance to the manufacturer's instructions. The specimens were incubated in Dulbecco Modified Eagle Medium (DMEM-High; Capricorn Scientific GmbH) for 48 hours and the extracts were obtained. The 100% concentration of the extract was diluted and extracts at 66.7%, 44.4%, 29.6%, and 19.8% concentrations were obtained. Specimen extracts at 5 different concentrations were incubated with L929 (NCTC clone 929: CCL 1; American Type Culture Collection) mouse fibroblast cells in 96-well tissue culture plates at 37 °C and 5% CO2 for 24, 48, and 72 hours. At the end of the incubation period, the effects of the materials on cell viability were evaluated with the MTT test. The data were analyzed using a statistical software program (IBM SPSS Statistics, v25.0; IBM Corp) (α=.05), employing ANOVA and the Tukey's HSD test.

RESULTS

All tested cement specimens significantly reduced cell viability (P<.05). Cell viability decreased with increasing concentration and incubation time in all specimens tested. The light-polymerized SpeedCem Plus showed the least cytotoxicity regardless of concentration and incubation time, followed by TheraCem Ca. However, the autopolymerized Calibra Universal significantly reduced cell viability. Cell viability rate of all light polymerized cements was considerably higher than autopolymerized cements (P<.05).

CONCLUSIONS

All the tested self-adhesive resin cements caused a significant reduction in viability of L929 cells. The composition of the self-adhesive resin cement and the activation type of polymerization affected cytotoxicity.

Effect of acidic media on surface characteristics of highly filled flowable resin-based composites: An in vitro study

OBJECTIVE

To analyze and compare the impact of acidic media on the surface characteristics of highly filled flowable resin-based composites.

MATERIALS AND METHODS

Two hundred fifty-six specimens were divided into four groups: GUF (G-aenial Universal Flo), GUI (G-aenial Universal Injectable), TEF (Tetric EvoFlow), and FSF (Filtek Supreme Flowable Restorative). Surface characteristics were analyzed before (T0) and after specimens immersion in different media, such as gastric juice (GJ), fizzy drink (FD), citric juice (CJ), or artificial saliva (AS), for 9 h (T1) and 18 h (T2). The analyses included surface roughness (SR) measurements, where average roughness (Ra) was obtained, scanning electron microscopy (SEM) analysis, and surface hardness (SH) evaluation, with Vickers numbers (HV) reported. The differences in values among groups/subgroups within the same stage were assessed using two-way ANOVA and Tukey's post hoc test, whereas repeated measures ANOVA with Bonferroni post hoc test was performed to compare the changes in values through the stages. Data were presented as mean ± standard deviation (SD).

RESULTS

At T0, GUI and GUF revealed lower Ra values (p < 0.05), more evenness in SEM micrographs, and higher HV values (p < 0.05) than FSF and TEF. At T1 and T2, specimens of all groups/subgroups demonstrated an increase in Ra and a decrease in HV compared with T0 (p < 0.05), as well as the changes in surface morphology on SEM micrographs. The lowest Ra and highest HV values were observed in GUI group, in contrast to FSF group, and in specimens immersed in GJ.

CONCLUSIONS

GUI revealed lower SR and higher SH compared to GUF and FSF both before and after exposure to acidic media. The presence of acidic media, especially GJ, significantly increases SR and decreases SH of tested materials.

CLINICAL SIGNIFICANCE

Information on the changes in the surface characteristics of highly filled resin-based composites after exposure to acidic media may be essential for the longevity of restorations like composite veneers fabricated from these materials.

Influence of different polymeric materials of implant and attachment on stress distribution in implant-supported overdentures: a three-dimensional finite element study

PURPOSE

Investigating high performance thermoplastic polymers as substitutes to titanium alloy, in fabrication of implants and attachments to support mandibular overdenture, aiming to overcome stress shielding effect of titanium alloy implants. AIM OF STUDY: Assessment of stress distribution in polymeric prosthetic components and bone around polymeric implants, in case of implant-supported mandibular overdenture.

MATERIALS AND METHODS

3D finite element model was established for mandibular overdenture, supported bilaterally by two implants at canine region, and retained by two ball attachments. Linear static stress analysis was carried out by ANSYS 2020 R1. Three identical models were created with different materials for modeling of prosthetic components (implant body, gingival former, ball attachment and matrix). The Monolithic principle was applied as the same material was used in modelling all the prosthetic components in each model (Titanium alloy grade V, poly-ether-ether-ketone (PEEK) and poly-ether-ketone-ketone (PEKK)). Simultaneous Force application of 60 N was carried out bilaterally at the first molar occlusal surface area using 3 runs (vertical, lateral and oblique).

RESULTS

PEEK and PEKK prosthetic components exhibited the highest total deformation and critical Maximum von Mises stresses values in implant body and gingival former under lateral and oblique loads. The stress values approached the fatigue limit of both polymeric materials presenting low factor of safety (< 1.5). The Peri-implant cortical bone in case of PEEK and PEKK showed nearly double maximum principal stresses compared with the titanium model. Conversely, Maximum von Mises stresses in spongy bone were lower in polymeric models than those of titanium ones. Additionally maximum equivalent strain values in spongy peri-implant bone of polymeric models were also lower than those of titanium model.

CONCLUSION

Critical high stresses were induced in implant body and gingival former under oblique or lateral loadings, accordingly, fatigue failure of both PEEK and PEKK polymer prosthetic elements was estimated due to low factor of safety. Both PEEK and PEKK Polymer models offered no advantage over titanium one regarding stress shielding effect, due to low stress and strain values generated at spongy peri-implant bone in polymer models.

The in vitro assessment of resin coating materials containing calcium phosphate, bioactive glass, and polylysine for glass ionomer cement restorations

Objective

Glass ionomer cements (GICs) require protective surface coatings to enhance their clinical performance. This study developed novel protective resin coatings for GICs containing monocalcium phosphate monohydrate (MCPM), bioactive glass nanoparticles (BAGs), and poly-L-lysine (PLS) and evaluated their physical, mechanical, and biological properties when applied to GICs.

Materials and methods

Experimental resin coating materials were formulated with 5-10 wt% of MCPM, BAGs, and PLS. The degree of monomer conversion was measured usingAttenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) (n = 6). GICs coated with the experimental materials were evaluated for biaxial flexural strength and modulus after 24 h water immersion using a universal testing machine (n = 8). Vickers surface microhardness up to 4 weeks of water immersion was also determined (n = 5). Fluoride and elemental release in water were analyzed using a fluoride-specific electrode and inductively coupled plasma optical emission spectrometry (n = 3). Cell viability was assessed using an MTT assay with mouse fibrosarcoma (n = 3). A commercial resin coating (EQUIA Forte Coat, EQ) served as control. Data were analyzed using one-way ANOVA and Tukey HSD test.

Results

While EQ showed higher monomer conversion (87%) compared to experimental materials (72-74%) (p < 0.05), GICs coated with experimental materials demonstrated comparable strength to EQ-coated GICs. The experimental coatings exhibited similar F, Al, Na, and Si releases to EQ-coated GICs, with enhanced P release. All experimental coatings exhibited comparable cell viability (>70%) to the commercial material.

Conclusion

The novel GIC protective coatings containing MCPM, BAGs, and PLS demonstrated acceptable in vitro performance comparable to commercial materials while potentially offering enhanced remineralization through increased elemental release.

Residual TPO Content of Photopolymerized Additively Manufactured Dental Occlusal Splint Materials

Background/Objectives: Diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO) is widely used in the dental industry as a photoinitiator for resin-based materials, while its use may be further limited given its toxicological risks. The aim of this study was, therefore, to analyze the residual TPO content of 3D-printed resin-based dental splint materials. Methods: Six resin-based splint materials were analyzed: LuxaPrint Ortho Plus (DMG), FREEPRINT splint 2.0 (Detax), optiprint splint (Dentona), KeySplint Soft (KeyPrint), FREEPRINT ortho (Detax), V-Print splint comfort (Voco). Grid-shaped specimens were fabricated using the recommended workflow of each manufacturer (n = 18). TPO extraction was conducted using a maximum of eight extraction cycles of 72 h at a temperature of 37 °C until no more TPO eluates were detected by high-performance liquid chromatography (HPLC). The margin of safety (MoS) was calculated as the ratio between the Derived No-Effect Level (DNEL) and the estimated exposure based on the amount of TPO extracted. Results: The total amount of extracted TPO was the lowest for LuxaPrint Ortho Plus (Mean ± SD; 44.0 ± 17.1 ng/mL), followed by optiprint splint (80.6 ± 21.1 ng/mL), FREEPRINT splint 2.0 (127.4 ± 25.3 ng/mL), FREEPRINT ortho (2813.2 ± 348.0 ng/mL), V-Print splint comfort (33,424.6 ± 8357.9 ng/mL) and KeySplint Soft (42,083.5 ± 3175.2 ng/mL). For all tested materials, the calculated MoS was above the critical value of 1, demonstrating toxicological safety in the cured, clinically relevant state. Conclusions: Large differences in the residual TPO content were observed between the materials. Although the TPO content in the uncured state may exceed toxicological safety limits, appropriate curing of the investigated materials resulted in a significant reduction in TPO elution and, thus, in products with a very low toxicological risk for the patient.

Impact of silica nanoparticles incorporation on the properties of resin infiltration: an in vitro study

BACKGROUND

This study evaluated the effect of nano-silica (NS) incorporation with resin infiltrant on water sorption and solubility of resin infiltrant, mineral density of demineralized enamel, and resin tags penetration.

METHODS

NS (Sigma-Aldrich, St Louis, Missouri, USA) was added into the resin infiltrant (ICON, DMG, Hamburg, Germany) at two concentrations by weight. The tested groups were: ICON (control), ICON + 0.2, and ICON + 0.5 (n = 10 per group). Water sorption and solubility were assessed using mass variation after 60 days water storage. Mineral density and surface topography were assessed using micro-Computed Tomography scans. Resin tags penetration was measured using a scanning electron microscope. Data were analyzed using one-way Analysis of Variance and Tukey's post-hoc tests (P < .05).

RESULTS

ICON revealed the highest water sorption, solubility mean values (28.90, 7.61) followed by ICON + 0.2 (14.80, 4.82) and ICON + 0.5 (12.32, 0.81) respectively, and vice versa for resin tags penetration. Mineral density of demineralized enamel significantly increased after treatment with ICON + 0.2 and ICON + 0.5.

CONCLUSION

Incorporation of NS to resin infiltrant decreased its water sorption and solubility along with enhancing the mineral density of the demineralized enamel and the penetration of resin tags.

Resin infiltrant with antibacterial activity: effects of incorporation of DMAHDM monomer and NACP on physical and antimicrobial properties

OBJECTIVES

Considering the fact that resin infiltrants lack antibacterial activity, this study assessed the influence of the quaternary ammonium monomer dimethylaminohexadecyl methacrylate (DMAHDM) and amorphous calcium phosphate nanoparticles (NACP) on the physical and antibacterial properties of an experimental resin infiltrant (ERI).

METHODOLOGY

The following groups were established: ERI (75/25 wt.% TEGDMA/BISEMA), ERI + 2.5% DMAHDM (2.5DM), ERI + 5% DMAHDM (5DM), ERI + 2% NACP (NACP), ERI + 2.5% DMAHDM + 2% NACP (2.5DM_NACP), ERI + 5% DMAHDM + 2% NACP (5DM_NACP), and Icon® (IC), a commercial resin infiltrant. Degree of conversion (DC; n=4), sorption and solubility (SO/SOL; n=8), and contact angle (CA; n=10) tests were conducted. Biofilm biomass (BB; n=6) and bacterial metabolism (BM; n=8) were evaluated after Streptococcus mutans (UA159) cultivation for 48 h on material samples. Data were evaluated by one-way ANOVA and Tukey or Games-Howell post hoc tests (α=0.05).

RESULTS

IC exhibited the highest DC, with no difference from 2.5DM and 5DM. IC showed the lowest CA. IC had the lowest SO, followed by ERI, which had the lowest SOL, with no difference from IC. 5DM_NACP showed the lowest biofilm biomass, similar to 2.5DM and 5DM. Resin infiltrants containing DMAHDM showed reduced bacterial metabolism.

CONCLUSIONS

DMAHDM, with or without NACP, demonstrated significant antibacterial activity, while NACP impaired DC. Both DMAHDM and NACP increased the contact angle, sorption, and solubility of the resin infiltrant, which may affect the material's clinical performance.

Effect of ethylene oxide unit number in bis-EMA on the physical properties of additive-manufactured occlusal splint material

PURPOSE

To investigate the effects of the number of ethylene oxide units in bis-EMA on the physical properties of additively manufactured occlusal splints.

METHODS

Seven experimental materials containing bis-EMAs with three and 10 ethylene oxide units (BE3 and BE10, respectively) were prepared at different BE10 content rates (BE10-0%, -20%, -30%, -40%, -50%, -60%, and -80%). Half the specimens of each material were aged in boiling water. Flexural strength (FS), flexural modulus (FM), fracture toughness (FT), microwear depth (MD), degree of conversion (DC), water sorption (WSP), water solubility (WSL), color difference between non-aged and aged series (ΔE), and translucency (TP) were evaluated. All the evaluated properties other than FS and MD were analyzed by 1-way ANOVA and Tukey's post hoc analysis, while FS and MD were analyzed by Kruskal-Wallis's test and Bonferroni correction (α=0.05).

RESULTS

BE10-80% revealed the lowest FS (P < 0.01 for BE10-0%, -20%, and -30%) and FM (P < 0.01, for all), while revealing the highest DC, WSP, WSL (P < 0.01 for all) and TP (P < 0.01 for all other than BE10-60%). BE10-50% showed the highest FT (P < 0.01 for all). BE10-50%, -60%, and -80% revealed significantly lower ΔE than others (P < 0.01) and lower MD than BE10-0% (P < 0.05). Regardless of the BE10 content, FS, FM, and FT decreased with aging.

CONCLUSIONS

The number of ethylene oxide units affects the physical properties of additively manufactured occlusal splints. The higher number of ethylene oxide units in bis-EMA enhanced the microwear resistance, DC, WSP, WSL, color stability, and translucency, whereas it deteriorated the FS and FM.

Color-Stable Formulations for 3D-Photoprintable Dental Materials

Color stability is crucial for dental materials to ensure they perfectly match a patient's tooth color. This is particularly challenging in photoresist-based additive manufacturing. Although some studies have addressed this issue, the exact causes of discoloration and ways to minimize it remain unclear. In this study, the intrinsic causes of discoloration in materials intended for 3D printing are investigated by examining thin-film samples (1200 µm) of various compositions, which are stored under different conditions. The samples are evaluated by measuring the UV-Vis absorption spectra at regular intervals to monitor changes. The findings reveal that both the composition of the formulations and the storage conditions significantly influence the discoloration behavior. Furthermore, methods have been developed to reduce or completely prevent discoloration. The use of photoinitiators with sterically demanding benzoyl moieties, as well as the addition of stabilizers, effectively decreases the intensity of emerging discoloration. Furthermore, incorporating the oxidizing agent cumene hydroperoxide (CHP) results in materials that maintain color stability.

The color stability of artificial white spot lesions treated with resin infiltration after exposure to staining beverages

BACKGROUND

To evaluate the effect of staining beverages on the color-changing of resin-infiltrated artificial white spot lesions (WSLs).

METHODS

Thirty-five artificial WSLs were created by pH cycling on flat bovine teeth specimens. The WSLs were treated with resin infiltration and were divided into five groups based on staining beverages: artificial saliva, coffee, wine, green tea, and Coca-Cola. These specimens were subjected to a 28-day exposure to the respective beverages. Color stability was assessed using a spectrophotometer at different time points: baseline, after 7, 14, 21, and 28 days of exposure, and repolishing. The color difference (∆E) between each time point and the baseline was calculated. Statistical analysis was performed using two-way measures ANOVA with a significance level of p = 0.05.

RESULTS

All resin-infiltrated specimens exposed to staining beverages for 7 days exhibited more significant color changes than those exposed to artificial saliva. The color change patterns varied based on the type of beverage. The color alterations intensified with extended immersion in the wine and Coca-Cola groups, while there were no significant differences in the color of specimens after 28 days of immersion in the coffee and green tea groups. However, after cleaning with pumice powder, all specimens showed significantly reduced color changes compared to those observed after 28 days of immersion, except those immersed in coffee.

CONCLUSIONS

Exposure of resin-infiltrated bovine tooth specimens to staining beverages resulted in a significant color alteration as the immersion time increased. However, the staining effect could be minimized by cleaning with pumice powder, except for the coffee group.

CLINICAL RELEVANCE

After resin infiltration treatment, patients should be advised to minimize the consumption of colored beverages to prevent staining that could impact esthetic appearance.

Mechanical and physical properties of splint materials for oral appliances produced by additive, subtractive and conventional manufacturing

OBJECTIVES

To investigate the flexural strength (FS), elastic modulus (E), Martens hardness (HM), water sorption (wsp), water solubility (wsl) and degree of conversion (DC) of 3D-printed, milled and injection molded splint materials.

METHODS

Specimens (N = 1140) were fabricated from five 3D-printed (GR-22 flex, GR-10 guide, ProArt Print Splint clear, V-Print Splint, V-Print Splint comfort), five milled (BioniCut, EldyPlus, ProArt CAD Splint clear, Temp Premium Flexible, Thermeo) and two injection molded (PalaXPress clear, Pro Base Cold) materials. FS, E, HM, wsp, wsl and DC were tested initially (24 h, 37 °C, H2O), after water storage (90 d, 37 °C, H2O) as well as after thermal cycling (5000 thermal cycles, 5/55 °C). Data were analyzed with Kolmogorov-Smirnov, Kruskal- Wallis, Mann-Whitney U test and Spearman's correlation (p < 0.05).

RESULTS

Initially, the mean flexural strength values ranged from 1.9 to 90.7 MPa for printed, 3.8 to 107 MPa for milled and 99.7 to 102 MPa for injection molded materials. The initial mean elastic modulus values were 0.0 to 2.4 GPa for printed, 0.1 to 2.7 GPa for milled and 2.8 GPa for injection molded materials. The initial mean Martens hardness values were 14.5 to 126 N/mm2 for printed, 50.2 to 171 N/mm2 for milled and 143 to 151 N/mm2 for injection molded materials. Initially, the mean water sorption values ranged from 23.1 to 41.2 μg/mm3 for printed, 4.5 to 23.5 μg/mm3 for milled and from 22.5 to 23.3 μg/ mm3 for injection molded materials. The initial mean water solubility values ranged from 2.2 to 7.1 μg/mm3 for printed, 0.0 to 0.5 μg/mm3 for milled and 0.1 to 0.3 μg/mm3 for injection molded materials. After water storage and thermal cycling most of the values decreased and some increased. The mean DC values ranged initially from 72.3 to 94.5 %, after water storage from 74.2 to 96.8 % and after thermal cycling from 75.6 to 95.4 % for the printed materials.

SIGNIFICANCE

The mechanical and physical properties of printed, milled and injection molded materials for occlusal devices vary and are influenced by aging processes. For clinical applications, materials need to be chosen according to the specific indications.

A comparative study on the mechanical and antibacterial properties of BPA-free dental resin composites

OBJECTIVE

The commonly used base monomer utilized in resinous commercial dental restorative products is bis-GMA which is derived from bisphenol-A (BPA) - a well-known compound which may disrupt endocrine functions. To address concerns about its leaching into the oral environment and to optimize the quality of dental composites, a BPA-free alternative base monomer, fluorinated urethane dimethacrylate (FUDMA), was designed by modifying a UDMA monomer system.

METHODS

Nine groups of composites were prepared by mixing the base monomers and TEGDMA in a ratio of 70/30 wt% to which were added silanized glass particles (mean diameter: 0.7 µm) in 3 different volume fractions (40, 45, and 50 vol%). Bis-GMA and UDMA base monomers were used as control groups in the same ratios. Various properties including degree of conversion (DC), flexural strength (FS) and flexural modulus (FM), water sorption (WS), solubility (SL), surface hardness and roughness, and initial adhesion property against S.mutans were investigated. One-way analysis of variance followed by Bonferroni test at α = 0.05 was used to analyze the results.

RESULTS

A significant difference in FS between FUDMA-based composite with 40 vol% filler (120.3 ± 10.4 MPa) and Bis-GMA-based composite with the same filler fraction (105.8 ± 10.0 MPa) was observed but there was no significant difference among other groups. The UDMA based group exhibited the highest WS (1.3 ± 0.3 %). Bis-GMA showed greater initial bacterial adhesion but was not statistically different from the other groups (p = 0.082).

SIGNIFICANCE

FUDMA-based resin composites exhibit comparable mechanical and bacterial adhesion properties compared with Bis-GMA and UDMA-based composites. The FUDMA composites show positive outcomes indicating they could be used as substitute composites to Bis-GMA-based composites.

Temperature rise in photopolymerized adhesively-bonded resin composite: A thermography study

OBJECTIVES

To assess visually and quantitatively the contributions of the adhesive layer photopolymerization and the subsequent resin composite increment to spatio-temporal maps of temperature at five different cavity locations, subjected to two irradiance curing protocols: standard and ultra-high.

METHODS

Caries-free molars were used to obtain 40, 2 mm thick dentin slices, randomly assigned to groups (n = 5). These slices were incorporated within 3D-printed model cavites, 4 mm deep, restored with Adhese® Universal bonding agent and 2 mm thick Tetric® Powerfill resin composite, and photocured sequentially, as follows: G1: control-empty cavity; G2: adhesive layer; G3 composite layer with no adhesive; and G4 composite layer with adhesive. The main four groups were subdivided based on two curing protocols, exposed either to standard 10 s (1.2 W/cm2) or Ultra high 3 s (3 W/cm2) irradiance modes using a Bluephase PowerCure LCU. Temperature maps were obtained, via a thermal imaging camera, and numerically analyzed at 5 locations. The data were analyzed using two-way ANOVA followed by multiple one-way ANOVA, independent t-tests and Tukey post-hoc tests (α = 0.05). Tmax, ΔT, Tint (integrated area under the curve) and time-to-reach-maximum-temperature were evaluated.

RESULTS

Two-way ANOVA showed that there was no significant interaction between light-curing time and location on the measured parameters (p > 0.05), except for the time-to-reach-maximum-temperature (p < 0.05). Curing the adhesive layer alone with the 10 s protocol resulted in a significantly increased pulpal roof temperature compared to 3 s cure (p < 0.05). Independent T-tests between G3 and G4, between 3 s and 10 s, confirmed that the adhesive agent caused no significant increases (p > 0.05) on the measured parameters. The ultra-high light-curing protocol significantly increased ΔT in composite compared to 10 s curing (p < 0.05).

SIGNIFICANCE

When the adhesive layer was photocured alone in a cavity, with a 2 mm thick dentin floor, the exothermal release of energy resulted in higher temperatures with a 10 s curing protocol, compared to a 3 s high irradiance. But when subsequently photocuring a 2 mm layer of composite, the resultant temperatures generated at pulpal roof location from the two curing protocols were similar and therefore there was no increased hazard to the dental pulp from the immediately prior adhesive photopolymerization, cured via the ultra-high irradiation protocol.

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.

Investigation of aging resistance for dental resin composites with and without glass flakes

OBJECTIVES

Outstanding physical-mechanical properties and aging resistance are key requirements for dental resin composite since it will be placed in the oral environment for a long time. In this work, a new dental resin composite mainly modified by glass flakes was fabricated, and the aging resistance was evaluated by comparing with commercial composites without glass flakes.

MATERIALS AND METHODS

The new dental resin composite was produced through hand blending of inorganic glass flakes/Si-Al-borosilicate glass (58wt%:7wt% of dental resin composite), POSS-MA (5wt% of resin matrix), Bis-GMA/TEGDMA(64.4wt%:27.6wt% of resin matrix), and CQ/EDMAB (0.9wt%:2.1wt% of resin matrix) together. The flexural strength, elasticity modulus, and hardness, as well as wear were tested for evaluating the aging resistance of different dental resin composite.

RESULTS

Among 6 kinds of commercial composites in this study, after 6-month water storage, the maximum percentage of performance degradation is that the flexural strength decreased 39.96%, elasticity modulus decreased 51.53% and hardness decreased 12.52%. In contrast, the new synthesized material decreased 14.53%, 20.88%, and 0.61%, respectively, and performed lesser wear depth compared to some other groups (P < 0.05).

CONCLUSIONS

It was observed that the new dental resin composite performed better performance stability and wear resistance when compared with commercial dimethacrylate-based or low shrinkage dental resin composite tested in this study.

CLINICAL RELEVANCE

This possibly paves a path for designing tailored dental composite for practical application. Since the aging resistance of dental resin composite modified by glass flakes is superior, it has the potential to be used for promoting the durability of dental resin composite.

An in vitro assessment of biaxial flexural strength, degree of monomer conversion, color stability, and ion release in provisional restorations containing Sr-bioactive glass nanoparticles

This study examined the mechanical and chemical properties of an experimental provisional restoration containing Sr-bioactive glass nanoparticles (Sr-BGNPs) compared to commercial provisional materials. The experimental material (TempS10) contained dimethacrylate monomers with added 10 wt% Sr-BGNPs. The degree of monomer conversion (DC) of self-curing (n = 5), biaxial flexural strength (BFS)/modulus (BFM) (n = 5), and color changes (ΔE*00) of materials in red wine (n = 5) were determined. Additionally, ion release (Ca, P, and Sr) in water at 2 weeks was examined (n = 3). The commercial materials tested included polymethyl methacrylate-based provisional material (Unifast) and bis-acrylic materials (Protemp4 and Cooltemp). TempS10 exhibited a comparable degree of monomer conversion (49%) to that of Protemp4 (60%) and Cooltemp (54%) (p > 0.05). The DC of Unifast (81%) was significantly higher than that of other materials (p < 0.05). TempS10 showed a BFS (126 MPa) similar to Cooltemp (102 MPa) and Unifast (123 MPa), but lower than Protemp4 (194 MPa). The immersion time for 2 weeks exhibited no detrimental effect on the strength and modulus of all materials. The highest ΔE*00 at 24 h and 2 weeks was observed with TempS10, followed by Cooltemp, Unifast, and Protemp4. Only TempS10 showed a detectable amount of Ca (0.69 ppm), P (0.12 ppm), and Sr (3.01 ppm). The experimental provisional resin restoration containing Sr-BGNPs demonstrated polymerization and strength comparable to those of bis-acryl provisional restorations but with the added benefit of ion-releasing properties. However, the experimental material demonstrated unsatisfactory color stability.

The effect of in-office bleaching agents on the Vickers hardness and surface topography of polished and unpolished CAD/CAM composite materials

In-office bleaching, using hydrogen peroxide, is effective to remove dental enamel stains. However, bleaching agents can deteriorate surface properties of CAD-CAM materials. This in vitro study aimed to investigate the effect of in-office bleaching agents on Vickers hardness and surface topography of polished and unpolished dental CAD-CAM composite materials (Grandio blocs, Lava Ultimate, BRILLIANT Crios, Cerasmart), and a polymer-infiltrated ceramic network block (Vita Enamic). The specimens were randomly divided into two groups: unpolished or polished. The micro-hardness and surface topography of each group were measured before bleaching, after a 60 min bleaching period, and 24-h and one-month post-bleaching. In-office bleaching significantly influenced the Vickers hardness of both the polished and unpolished CAD/CAM composite blocks, with Vita Enamic exhibiting the least hardness stability among all groups. Furthermore, in-office bleaching significantly influenced the surface roughness of unpolished CAD/CAM composite blocks. There was a significant difference in hardness reduction between the polished and unpolished specimens for most of the investigated materials at different time points. The bleaching did not influence the surface roughness of the investigated polished group, except for Vita Enamic and Lava Ultimate. However, it did influence the surface roughness of the investigated materials in the unpolished group.

Color stability and degree of conversion of gingiva-colored resin-based composites

OBJECTIVES

To evaluate gingiva-colored resin-based composites' (GCRBC) color stability and degree of conversion (DC%).

METHODS

Eight discs (8 × 1 mm) of 20 shades of GCRBC were prepared. Color coordinates were measured against a gray background with a calibrated spectroradiometer, CIE D65 illuminant and the CIE 45°/0° geometry at baseline and after 30 days of storage in distilled water, coffee, and red wine. Color differences ( ∆ E 00 ) between final and baseline conditions were calculated. An ATR-FTIR spectrometer with a diamond tip was used to calculate DC%. The results were analyzed statistically using ANOVA and Tukey post-hoc test. The level of significance was p < 0.05.

RESULTS

DC% and color stability correlated with each other and with the GCRBC brand. DC% ranged between 43% and 96%, highest values correspond to flowable composites. All composites have experienced color changes after immersion in water, wine and coffee. However, the magnitude of the color change has varied widely depending on the immersion medium and the GCRBC. Color changes generated by the wine were, globally, greater than those induced by coffee (p < 0.001) and above the acceptability thresholds.

CONCLUSIONS

The DC% of GCRBCs is sufficient to achieve adequate biocompatibility and physicomechanical properties, but the high susceptibility to staining could compromise aesthetic long-term results.

CLINICAL SIGNIFICANCE

The degree of conversion and the color stability of gingiva-colored resin-based composites correlated with each other. All composites have experienced color changes after immersion in water, wine and coffee. Color changes generated by wine were, globally, greater than those induced by coffee and above the acceptability thresholds that could compromise aesthetic long-term results.

Mechanical Properties and Liquid Absorption of Calcium Phosphate Composite Cements

Calcium phosphate cements present increased biocompatibility due to their chemical composition being similar to that of the hydroxyapatite in the hard tissues of the living body. It has certain limitations due to its poor mechanical properties, such as low tensile strength and increased brittleness. Thus, the optimal way to improve properties is through the design of novel composite cements. The purpose was fulfilled using a 25% hydroxyethyl methacrylate (HEMA) mixed with 3% urethane dimethacrzlate (UDMA) base matrix with various ratios of polyethylene glycol (PEG 400) and polycaprolactone (PCL). Mineral filler is based on tricalcium phosphate (TCP) with different chitosan ratio used as bio-response enhancer additive. Four mixtures were prepared: S0-unfilled polymer matrix; S1 with 50% TCP filler; S2 with 50% chitosan + TCP filler; and S3 with 17.5% chitosan + TCP mixed with 17.5% nano hydroxyapatite (HA). The mechanical properties testing revealed that the best compressive strength was obtained by S2, followed by S3, and the worst value was obtained for the unfilled matrix. The same tendency was observed for tensile and flexural strength. These results show that the novel filler system increases the mechanical resistance of the TCP composite cements. Liquid exposure investigation reveals a relative constant solubility of the used filler systems during 21 days of exposure: the most soluble fillers being S3 and S2 revealing that the additivated TCP is more soluble than without additives ones. Thus, the filler embedding mode into the polymer matrix plays a key role in the liquid absorption. It was observed that additive filler enhances the hydrophobicity of UDMA monomer, with the matrix resulting in the lowest liquid absorption values, while the non-additivated samples are more absorbent due to the prevalence of hydrolytic aliphatic groups within PEG 400. The higher liquid absorption was obtained on the first day of immersion, and it progressively decreased with exposure time due to the relative swelling of the surface microstructural features. The obtained results are confirmed by the microstructural changes monitored by SEM microscopy. S3 and S2 present a very uniform and compact filler distribution, while S1 presents local clustering of the TCP powder at the contact with the polymer matrix. The liquid exposure revealed significant pore formation in S0 and S1 samples, while S3 and S2 proved to be more resistant against superficial erosion, proving the best resistance against liquid penetration.

Clinical Applications and Mechanical Properties of CAD-CAM Materials in Restorative and Prosthetic Dentistry: A Systematic Review

Clinical outcomes of dental restorations depend primarily on the choice of materials used, and nowadays, dental CAD-CAM (Computer-Aided Design Computer-Aided Manufacturing) materials have strongly changed daily clinical practice. The aim of this systematic review is to analyze CAD-CAM dental materials according to their mechanical properties and in relation to their clinical applications. A literature review was performed on PubMed, Scopus, Web of Knowledge, and the Cochrane Library. Articles addressing at least one of the following topics regarding dental materials for CAD-CAM systems: manufacturers, mechanical features, materials' composition, optical properties, clinical indications, and/or outcomes were included in the review. A flowchart was performed as described in the PRISMA guidelines. Among the 564 articles found, 63 were analyzed and evaluated. Within the limitations of this systematic review, it can be concluded that CAD-CAM materials present a wide range of clinical applications due to their improved mechanical properties. Specifically, in addition to materials that have been in use for a long time (such as feldspathic ceramics), resin block composites can also be used for permanent restorations.

Radiopacity and physical properties evaluation of infiltrants with Barium and Ytterbium addition

Radiopaque properties in the infiltrant should be interesting for clinicians to feel more confident to indicate this treatment. Thus, the aim of this study was to evaluate the effect of the incorporation of barium and ytterbium particles on the physical properties of resin infiltrants. Groups were divided according to the addition of ytterbium oxide (Y) alone (30 or 40%) or Y with barium (YB) (15/15% or 20/20% respectively) in the Icon commercial infiltrant and in the experimental infiltrant base. Digital radiography (n=5), Microradiography (n=5), Microtomography (n=3), degree of conversion (n=5), water sorption (n=16), solubility (n=16), contact angle (n=16), flexural strength (n=16), elastic modulus (n=16) and Energy dispersive X-ray Spectroscopy (n=10) were performed. Analyses were performed using the R program, with a significance level of 5%, and microradiography and Microtomography analyses were evaluated qualitatively. In groups with 30 or 40% of ytterbium, radiopacity was higher or equal to enamel. Microradiography and Microtomography appear to have more radiopacity in groups with 40% (Y). Among the groups with no particle addition, those of the experimental infiltrant presented a higher degree of conversion than those of Icon®. In most groups, there was solubility below the ISO-recommended levels. The addition of particles resulted in higher viscosity. Groups with Icon had higher flexural strength and elastic modulus than groups with experimental infiltrant. The addition of 40% (Y) improved polymerization, had low solubility, and had greater radiopacity than enamel, however negatively affected the viscosity increasing then. Experimental groups with the base showed a higher water sorption than Icon groups.

Color stability of bulk-fill compared to conventional resin-based composites: A scoping review

OBJECTIVES

To conduct a scoping review on color stability of bulk-fill compared to conventional resin-based composites exposed to colored beverages.

MATERIALS AND METHODS

In vitro studies, investigating bulk-fill resin-based composites color stability submitted to artificial staining by colored beverages were included. Studies investigating color change induced by smoke and whitening treatments as well as papers not written in English language were excluded. A systematic search, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) was performed on four databases (Embase, Medline, Scopus, Web of Science) for articles published until October 01st 2022. The study selection was then performed by two authors who screened the abstracts independently and followed the JBI approach.

RESULTS

Of 717 screened abstracts, 59 were selected for full-text analysis. Finally, 19 studies were included in this review. They investigated 19 different bulk-fill composites and different artificial-staining-by-liquids-protocols including coffee, red wine, tea, coke, and others. Seven papers reported higher color change in the investigated bulk fill materials than in conventional resin-based composites, while nine studies reported the opposite. SonicFill showed the highest color stability for most of the papers.

CONCLUSIONS

The available evidence suggests that bulk-fill materials show variability in color stability. This behavior can be attributed to the heterogeneity of composition and staining procedures in the selected studies.

CLINICAL SIGNIFICANCE

Clinicians should keep in mind that bulk-fill materials may change color when exposed to colorant drinks or food.

Experimental Investigation of Dental Composites Degradation After Early Water Exposure

While dental composite long-term aging has already been studied in the past, no data exist about the early aging while it might be detrimental regarding the composites' longevity. This study aims to better understand the effects of early water exposure on dental composites. Dental resin composites with different fillers ratio were subjected to water exposure during 24 h, 1 week, or 1 month. After photopolymerization, the samples were stored at different conditions, whether in wet or dry condition (W, D, respectively) and in wet conditions after a first 24 h storage in dry conditions (DW). Three-point bending tests were performed to measure the flexural modulus. The samples were then subjected to a sorption/desorption protocol. While the matrix alone did not undergo any mechanical degradation with exposure time, the composites matrices presented a decrease in elastic modulus. This decrease was the highest for the matrix with nonsilanized fillers. Interestingly, the DW condition was detrimental for all the samples. Regarding the sample with nonsilanized fillers in DW for 1 month presented an elastic modulus lower than the matrix alone. These results were assigned to the sorption capacity of the polymer matrix, suggesting that the diffusion mechanisms and the nature of water molecules are determinant in the composite degradation. This study showed that dental composite early degradation mechanisms after water exposure are involved in the polymer matrix postpolymerization process as soon as after 24 h. Such mechanisms are detrimental in terms of the dental composite efficiency and have to be understood.

Effect of monomer composition and filler fraction on surface microhardness and depth of cure of experimental resin composites

This study evaluated microhardness profiles and calculated depths of cure at 80% of the surface microhardness of experimental dental resin composites having different base monomer compositions and different filler fractions. Composites were prepared using four different base monomers (bisphenol A-glycidyl methacrylate [Bis-GMA], urethane dimethacrylate [UDMA], ethoxylated bisphenol-A dimethacrylate [Bis-EMA], and Fit-852) with triethylene glycol dimethacrylate (TEGDMA) used as a co-monomer at three filler:resin matrix weight percent fractions (50:50, 60:40, and 70:30). Uncured material was placed in 3D printed molds and light cured for 40 s from the top surface only. Knoop microhardness was measured at the top of the specimen, and at every 0.5 mm up to 4 mm in depth. Microhardness at the surface increased in all experimental composites as the filler fraction increased. When comparing base monomers, microhardness was the highest in UDMA-based composites, while Bis-GMA-based composites showed the lowest values. When comparing depth of cure as a function of base monomer type, both Bis-GMA and Bis-EMA showed significantly lower values than UDMA or Fit-852. Composites having 50 wt% filler showed a significantly higher depth of cure than those with 60 and 70 wt% filler. Base monomer and filler fraction significantly influence microhardness and depth of cure in these experimental composites.

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.

Comparative Evaluation of Colour Stability and Surface Roughness of Nanohybrid Composite Resins in Mouth Rinse and Colouring Beverages

Objectives An ideal restorative material should be capable of supplanting the biological, functional, and aesthetic qualities of a healthy tooth structure. There has always been a search for optimal and aesthetically pleasing restorative materials. This study aims to evaluate the surface roughness and colour stability of three nanohybrid composite resins post-exposure to mouth rinse and colouring beverages. Methods One hundred and twenty specimens of dimension 10 mm x 8 mm x 1 mm were randomly allocated into three equal-sized groups and fabricated using three different nanohybrid composites (Group A: Filtek Z250 XT, Group B: Tetric N-Ceram, and Group C: Solare Sculpt). Sixty samples, comprising 20 from each group, were examined for colour stability and 60 for surface roughness after exposure to chlorhexidine and coffee. Baseline and post-exposure readings of the surface roughness and colour absorbance of the specimens were obtained by atomic force microscopy and spectrophotometer, respectively. A one-way analysis of variance (ANOVA) test followed by a post hoc Tukey's test and an independent t-test were used for data analysis, considering a p-value<0.05 as significant. Results Irrespective of the composite, the surface roughness and colour change were substantially higher in the samples exposed to coffee (p-value<0.01). Filtek Z 250XT showed significantly minor changes in colour and surface roughness, followed by Solare Sculpt and Tetric N-Ceram (p-value<0.05). Conclusion Coffee caused more surface roughness and colour changes compared to chlorhexidine. Filtek 250 XT showed minor changes in colour and surface roughness on exposure to both solutions.

Color Stability of Resin Cements after Water Aging

The color stability of resin cements plays a key role in the achievement of esthetically-pleasant restorations. Resin luting materials can be mainly divided into two main classes: adhesive (relying on previous application of adhesive systems) or self-adhesive (also known as one-step cements). The different chemical compositions determine their physio-mechanical characteristics which, in turns, influence their color stability. To evaluate the color variations of different dual-cured resin cements after water aging, 80 disc-shaped specimens (15 mm in diameter and 1.2 mm thick) were obtained from the following resin cements (n = 10): (1) Maxcem Elite Universal, MCU (Kerr); (2) RelyX Universal, RXU (3M); (3) Calibra Ceram, CAL (Dentsply); (4) Multilink, MUL (Ivoclar-Vivadent); (5) Panavia V5, PAN (Kuraray); (6) Calibra Universal, CUN (Dentsply); (7) SpeedCEM Plus, SCP (Ivoclar); and (8) Panavia SA, PSA (Kuraray). After light-polymerization, the specimens were measured with a spectrophotometer and CIELab* values were recorded. The specimens were then placed in a digitally controlled thermostatic water bath at 60° for 30 days and afterwards the color measurements were repeated. Color differences were calculated for each specimen before and after water-aging procedures with ΔEab formula and the data were statistically analyzed (p < 0.05). The type of cement statistically influenced the ΔEab (p < 0.05), with MCU showing the lowest color variations (4.3 ± 0.7) whereas RXU and PSA the highest (16.9 ± 1.6 and 16.8 ± 1.2, respectively). No differences were observed between CAL, CUN and SCP (p = 0.05). Color stability is related to the chemical composition of the resinous luting materials, thus material dependent.

Effect of modeling liquids on resin composite roughness and color parameters after staining and toothbrushing

This study evaluated surface roughness, color stability, whitening index, and opacity of different types of modeling liquids for resin composite coating after exposure to staining and toothbrushing. Disc-shaped resin composite (Vittra APS, FGM) specimens were fabricated and divided into four groups (n = 10 each): control group, Composite Wetting resin (Ultradent Products), Adper Scotchbond Multipurpose adhesive (3M ESPE), and Adper Universal adhesive (3M ESPE). Surface roughness (Ra) was measured using a rugosimeter, while color stability (∆E00), whitening index (WI), and opacity (%) were measured using a spectrophotometer. Assessments were made at four time points: after polishing (baseline, T1), after immersion in red wine for 24 h (T2), and after 5,000 (T3) and 10,000 (T4) cycles of toothbrushing. Scanning electron microscopy images were captured to analyze the scratches created. The data were statistically analyzed by two-way repeated-measures analysis of variance and Tukey's honestly significant difference tests (α = .05). Modeling with the Wetting resin resulted in higher surface roughness (p < 0.05) and low color stability, which were attributable to porosities. Higher color change values were observed in the control group after staining. Both adhesives showed the lowest mean ΔE00 values (p < 0.005). WI decreased after staining, except with the use of the Universal adhesive (p < 0.005). The lowest opacity values were observed at baseline for all groups (p < 0.005). The Universal and Scotchbond adhesives had lower surface roughness, better color stability, higher WI, and the lowest opacity values after staining with red wine and toothbrushing.

Effects of the Incorporation of Bioactive Particles on Physical Properties, Bioactivity and Penetration of Resin Enamel Infiltrant

Purpose

The resinous infiltrant lacks remineralizing activity. This research aimed to develop and evaluate bioactivity, physico-mechanical properties and penetration of resin infiltrants containing Biosilicate or nanohydroxyapatite.

Methods

Experimental resin infiltrant (ERI; 75/25 wt.% TEGDMA/BisEMA) was divided among the groups Pure Experimental (PE); ERI + Biosilicate 5 or 10% (Bio5; Bio10), ERI + 10% nanohydroxyapatite (Hap10), and Icon (DMG, Germany). Bioactivity was analyzed by SEM, EDS and FT-IR/ATR after soaking in SBF. Degree of conversion (DC), sorption and solubility (SO; SOL), flexural strength, modulus of elasticity (FS; E-modulus), contact angle (CA) and penetration were characterized. Extent of penetration was analyzed by treating white spot lesions (WSL) in human dental enamel samples with the infiltrants and subsequently analyzing specimens by confocal laser scanning microscopy. Data from each test were submitted to ANOVA and Tukey's tests (p < 0.01).

Results

SEM, EDS and FT-IR showed the formation of precipitates and increase in the rates of Ca and P in the groups with bioactive particles, after storage in SBF. Hap10 showed higher DC and CA values than all the other groups. Groups Bio5 and Bio10 showed CA values similar to those of Icon, higher SO and SOL values, and reduction in other properties. All infiltrants were capable of penetrating into the WSLs.

Conclusion

The incorporation of Biosilicate (5 or 10%) or nanohydroxyapatite (10%) into ERI induced mineral deposition on the surface and did not compromise infiltration and penetration into WSLs, however, compromising their physico-mechanical properties.

Evaluation of the color stability of 3D printed resin according to the oxygen inhibition effect and temperature difference in the post-polymerization process

The aim of this study was to determine the color stability of 3D printed resin according to the post-curing conditions (polymerization conditions and temperature). Specimens were post-polymerized under different conditions of oxygen inhibition, such as on glycerin immersion (GLY), medium-low vacuum environment (VA), and oxygen contact (CON, the control group), and temperature (35 °C, 60 °C, and 80 °C). The degree of conversion (DC), water sorption (Wsp) and solubility (Wsl), surface roughness (Ra) were measured. Additionally, surface free energy (SFE), pH values of colorants were measured. Grape juice (grape), coffee, and curry were used as the colorants, and distilled water (DW) was used as a control. And the color value was measured before and after immersion using a spectrophotometer. Then, Calculated the color change. For statistical methods, The Shapiro-Wilk test performed to check for normality revealed that the data presented a normal distribution (p>0.05). ΔE values were analyzed using three-way ANOVA. DC, Wsp, Wsl, SFE, and Ra were analyzed using two-way ANOVA. To confirm the linear correlation, Pearson's correlation coefficient was determined. The threshold for significance (p) was set at 0.05 (95% confidence interval) for all tests. DC was the highest at 80 °C in the GLY group (95.08 ± 4.88%). And Wsl decreased with increasing temperature, and was lowest at 80 °C in the GLY group (0.46 ± 0.30 um/mm3). After the colorants were immersed for 30 days, as the temperature increased, ΔE decreased in the GLY group but not in the VA and CON groups, and was the lowest at 80 °C in the GLY group: (DW, 0.95 ± 0.45 [mean± SD]; grape, 6.45± 0.69; coffee, 4.50± 0.56; curry, 9.37± 1.40). There was also a significant inverse relation between DC and ΔE. A significant inverse relation was found between Wsl and DC, and a significant positive correlation was found between Wsl and ΔE. Wsp, SFE, and Ra did not affect color stability. In the post-polymerization process, increasing the temperature and GLY were effective in reducing ΔE, which was lowest at 80 °C in the GLY group. It was also observed that a complex mechanism between the DC, Wsl of 3D printed resin affects ΔE of the resin.

WATER SORPTION, SOLUBILITY AND COLOR STABILITY OF DIFFERENT BULK-FILL RESTORATIVE MATERIALS

Objectives: The aim of this study was to evaluate the color stability, water sorption and solubility of recent bulk-fill restorative materials. Materials and Methods: Seventy disc shaped specimens (height:1mm, diameter:15mm) were prepared with a micro-hybrid composite resin (Z250; Filtek Z250, 3M ESPE), two resin-based bulk-fill (Filtek One Bulk Fill, 3M ESPE and EBF; Estelite Bulk-Fill Flow, Tokuyama Dental), glass ionomer-based restorative (Equia FF; Equia Forte Fil, GC Dental), self-cure and light-cure alkasite (CN; Cention N, Ivoclar Vivadent) and indirect composite resin (Gradia P; Gradia Plus, GC Dental) (n=10). Baseline color measurements were performed and mass of the samples (m1) were noted. Color measurements were repeated after 24 h and 28 days immersion of the specimens in water. After the 28-days immersion, mass was noted as m2. Specimens were kept in desiccators and final mass (m3) were recorded. The color change (ΔE00) water absorption (WSP) and water solubility (WSL) of the specimens were calculated. Results: After 28-days immersion, Gradia P showed significantly lower water sorption than EBF and Equia FF groups (p0.05). The lowest solubility was observed in Z250and Gradia P. The lowest (ΔE00) was observed in self-cured CN group (p

Effect of alpha-humulene incorporation on the properties of experimental light-cured periodontal dressings

The objective of this study was to formulate an experimental light-cured periodontal dressing containing alpha-humulene and to compare its physical, antimicrobial, and cytotoxicity properties with commercial gold standards (Barricaid® and Periobond®). Two periodontal dressing formulations were developed (a and b). The formulations were divided into 5 groups according to the alpha-humulene concentration as follows: Ea - control group, Ea1 - 1%, Ea5 - 5%, Ea10 - 10%, and Ea20 - 20%; Eb - control group, Eb1 - 1%, Eb5 - 5%, Eb10 - 10%, and Eb20 - 20%. Materials characterization was performed using the degree of conversion, cohesive strength, sorption, and solubility assays. Antimicrobial assay was performed using the modified direct contact test against E. faecalis and S. aureus. Cytotoxicity was assessed by the cell viability experiment using L929 fibroblasts. In general, the cohesive strength values of materials decreased as the alpha-humulene concentration increased. All the experimental dressings showed antimicrobial activity against both bacteria tested. Cell viability results for the Ea, Ea1, Eb, and Eb1 groups showed moderate cytotoxic effect. The formulations containing alpha-humulene showed similar behavior to the commercial references. Thus, formulations containing alpha-humulene have potential to be used as periodontal dressing.

ANTİ-HALİTOSİS GARGARALARININ REZİN BAZLI RESTORATİF DENTAL MATERYALLERİN YÜZEY ÖZELLİKLERİ ÜZERİNE ETKİSİ

Amaç: Bu in-vitro çalışmanın amacı anti-halitosis etkili beş farklı ağız gargarasının iki farklı restoratif materyalin renk stabilitesi ve yüzey pürüzlülüğü üzerine olan etkisinin araştırılmasıdır. Gereç ve Yöntemler: Çalışmada nano-hibrit (Filtek Z550, 3M ESPE) ve giomer (Beautifill II, Shofu Dental) yapıda olan iki çeşit reçine bazlı restoratif materyal kullanılmıştır. Her iki materyalden test edilmek üzere toplam 120 adet kompozit disk üretici talimatları doğrultusunda 10x2mm ebatlarında silindir kalıplar kullanılarak hazırlanmıştır. Rastgele seçilen örnekler, 5 farklı ağız gargarası (Listerine Fresh Burst, Listerine Total Care, Colgate Plax, Oderol, Halitosil) ve 1 kontrol grubunda (distile su) bekletilmek üzere toplam 6 farklı gruba ayrılmıştır. Başlangıç renk koordinatları CIELAB renk sistemine göre spektrofotometre (Easyshade Compact) ile yüzey pürüzlülük değerleri (Ra) ise kontakt profilometre (Surtronic 25) ile ölçülmüştür. Tüm örnekler 37°C'de ağız gargaralarında 12boyunca bekletilmiş ardından renk ve pürüzlülük ölçüm prosedürleri aynı şekilde gerçekleştirilmiştir. Elde edilen veriler SPSS 24.0 programı ile Kruskal-Wallis H ve Bonferroni Post Hoc testleri kullanılarak 0.05 anlamlılık düzeyinde analiz edilmiştir. Bulgular: Bu çalışmanın sonuçları, yüzey pürüzlülük değerlerinde istatistiksel olarak anlamlı bir artış olmadığını göstermiştir. Ağız gargaralarında bekletilen Beautifil II materyallerinin tamamında CIELAB değerlerinde önemli bir değişiklik olmuştur (P

Effects of Sr/F-Bioactive Glass Nanoparticles and Calcium Phosphate on Monomer Conversion, Biaxial Flexural Strength, Surface Microhardness, Mass/Volume Changes, and Color Stability of Dual-Cured Dental Composites for Core Build-Up Materials

This study prepared composites for core build-up containing Sr/F bioactive glass nanoparticles (Sr/F-BGNPs) and monocalcium phosphate monohydrate (MCPM) to prevent dental caries. The effect of the additives on the physical/mechanical properties of the materials was examined. Dual-cured resin composites were prepared using dimethacrylate monomers with added Sr/F-BGNPs (5 or 10 wt%) and MCPM (3 or 6 wt%). The additives reduced the light-activated monomer conversion by ~10%, but their effect on the conversion upon self-curing was negligible. The conversions of light-curing or self-curing polymerization of the experimental materials were greater than that of the commercial material. The additives reduced biaxial flexural strength (191 to 155 MPa), modulus (4.4 to 3.3), and surface microhardness (53 to 45 VHN). These values were comparable to that of the commercial material or within the acceptable range of the standard. The changes in the experimental composites' mass and volume (~1%) were similar to that of the commercial comparison. The color change of the commercial material (1.0) was lower than that of the experimental composites (1.5-5.8). The addition of Sr/F-BGNPs and MCPM negatively affected the physical/mechanical properties of the composites, but the results were satisfactory except for color stability.

Surface Characteristics and Color Stability of Dental PEEK Related to Water Saturation and Thermal Cycling

(1) Background: The study was undertaken to evaluate the surface characteristics, microhardness, and color stability of PEEK materials related to water saturation and in vitro aging. (2) Methods: Custom specimens of unmodified and modified PEEK CAD/CAM materials were investigated: BioHPP, a ceramic reinforced PEEK, and Finoframe PEEK and Juvora medical PEEK, 100% PEEK materials. Forty-eight plates were sectioned in rectangular slices. The specimens were immersed in distilled water at 37 °C for a period of 28 days, and then subjected to aging by thermal cycling (10,000 cycles). Surface roughness was measured with a contact profilometer; nanosurface topographic characterization was made by Atomic Force Microscopy; Vickers hardness measurements were performed with a micro-hardness tester; color changes were calculated. All registrations were made before immersion in water and then subsequently once a week for 4 weeks, and after thermocycling. (3) Results: The studied reinforced and unfilled PEEK materials reached water saturation after the first week of immersion, without significant differences between them. The most affected from this point of view was the reinforced PEEK material. Thermocycling induces a significant increase inmicroroughness, without significant differences between the studied materials. In relation to the nanosurface topography and roughness, the reinforced PEEK material was the least modified by aging. The color changes after 4 weeks of water immersion and one year of simulated in vitro aging ranged from extremely slight to slight, for all materials. (4) Conclusions: Water absorption was associated with a decrease in microhardness. Surface characteristics are affected by water immersion and thermocycling. Perceivable or marked color changes of the materials were not detected during the study.

Evaluation of surface characterization and mechanical features of resin-matrix ceramics before and after different surface treatments

STATEMENT OF PROBLEM

Surface treatments (STs) required for micromechanical interlocking can lead to alterations in the surface characterization and mechanical features of the resin-matrix ceramics (RMCs), which may jeopardize the long-term outcome of an indirect restoration. However, evidence on this issue is lacking.

PURPOSE

The purpose of this in vitro study was to assess the influence of different STs on the surface roughness (SR), water contact angle (WCA), and flexural strength (FS) of RMCs.

MATERIAL AND METHODS

Two hundred rectangular plates (12×14×1 mm) were prepared from 5 different RMC ingots, including a polymer-infiltrated ceramic network (Vita Enamic [VE]), 2 resin nanoceramics (Lava Ultimate [LU], Grandio Blocks [GB]), a flexible nanoparticle-filled resin (GC Cerasmart [GC]), and a reinforced composite resin (Brilliant Crios [BC]). Plates of each RMC group were further divided into 4 subgroups according to the ST applied: Control, no treatment (C); airborne-particle abrasion with aluminum oxide particles (APA); 2W- and 3W-Er,Cr:YSGG laser irradiations (LI^2W, LI^3W) (n=10 per ST). The SR (Ra) of each plate was recorded with a contact profilometer. WCAs (θ) of distilled water on the plates were determined by using the sessile-drop method. The FS (MPa) of each plate was measured with a universal testing machine. Data acquired for SR, WCA, and FS were statistically analyzed (α=.05). Weibull statistics were also conducted to determine the reliability of each material.

RESULTS

The 2-way ANOVA showed that SR, WCA, and FS values were significantly influenced not only by all tested variables but also by their interaction terms (P<.001). All STs significantly increased the SR values (P<.05). Maximum and minimum SR values were recorded in GC-LI^3W (7.06 ±0.16) and GC-C (0.07 ±0.02) groups. After STs, WCA values significantly diminished (P<.05). Maximum and minimum WCA values were recorded in LU-C (61.74 ±2.45) and VE-APA (40.38 ±1.56) groups. All STs significantly reduced the FS values (P<.05). The upper and lower FS bounds were 140.7 ±17.07 and 60.66 ±6.31, respectively, set by VG-C and GC-APA. Weibull distribution indicated that the untreated groups presented the highest m values. Among the treated groups, BC-LI^3W demonstrated superior reliability (m=14.04).

CONCLUSIONS

APA for LU, LI^2W for VG and BC, and LI^3W for GC and VE can be preferred. Although APA increased the SR and provided more wettable surfaces, it caused considerable loss of FS. Therefore, LI can be recommended as a safer ST for RMCs.

Physical-chemical characterization and bond strength to zirconia of dental adhesives with different monomer mixtures and photoinitiator systems light-activated with poly and monowave devices

Introduction: Bonding to crystalline zirconia is currently a challenge. Properly cured adhesives are crucial to optimize this bond, and that in turn is influenced by the initial mobility of the system, as well as by the reactivity of the initiators. Aim: This study aimed to characterize adhesives containing monomer mixtures of different viscosities and double and triple photoinitiator systems; and to evaluate the bonding to Y-TZP zirconia, when adhesives were light-activated with monowave or polywave light-curing units (LCU). Materials and methods: Adhesives were formulated at a 1:1 weight proportion of Bis-GMA/TEGDMA or Bis-GMA/Bis-EMA. To these mixtures 0.5 wt% of CQ, 0.5–1.0 wt% of DABE, 0.5–1.0 wt% of DPIHP, or 0.5–1.0 wt% of TAS-Sb were added and used as photoinitiator systems. A total of ten adhesives were prepared. Resin composite cylinders were cemented on zirconia slices and 6000 thermal cycles were performed. Degree of conversion (DC), sorption (SO) and solubility (SL) after 7 days of water storage, and microshear bond strength (µSBS) were evaluated. Data were analyzed with three-way ANOVA and Tukey’s HSD (α = 0.05). Results: Bis-GMA/Bis-EMA combined with either CQ/DABE or CQ/DABE/TAS-Sb presented the highest DC, and no significant differences were observed for LCUs (p = .298). CQ/DABE < CQ/DABE/TAS-Sb ≈ CQ/DABE/DPIHP and the polywave LCU showed smaller overall SO (p < .05). Bis-GMA/TEGDMA with CQ/DABE cured with the polywave LCU presented the lowest SO. SL varied as follows: CQ/DABE/TAS-Sb < CQ/DABE/DPIHP < CQ/DABE (p < .001). For µSBS, only the factor photoinitiator system was significant (p = .045). All mean values were above 30 MPa, with higher values being observed for BIS-GMA/TEGDMA and CQ/DABE. Conclusion: It can be concluded that the adhesive containing CQ/DABE/TAS-Sb as coinitiator of Bis-GMA/Bis-EMA mixtures produced a material with higher DC and lower SL, while bond strength values were similar to the ones obtained by CQ/DABE.

Monomer Release from Dental Resins: The Current Status on Study Setup, Detection and Quantification for In Vitro Testing

Improvements in mechanical properties and a shift of focus towards esthetic dentistry led to the application of dental resins in various areas of dentistry. However, dental resins are not inert in the oral environment and may release monomers and other substances such as Bisphenol-A (BPA) due to incomplete polymerization and intraoral degradation. Current research shows that various monomers present cytotoxic, genotoxic, proinflammatory, and even mutagenic effects. Of these eluting substances, the elution of BPA in the oral environment is of particular interest due to its role as an endocrine disruptor. For this reason, the release of residual monomers and especially BPA from dental resins has been a cause for public concern. The assessment of patient exposure and potential health risks of dental monomers require a reliable experimental and analytical setup. However, the heterogeneous study design applied in current research hinders biocompatibility testing by impeding comparative analysis of different studies and transfer to the clinical situation. Therefore, this review aims to provide information on each step of a robust experimental and analytical in vitro setup that allows the collection of clinically relevant data and future meta-analytical evaluations.

Evaluation of the Surface Roughness of Bulk-Fill Composite Resins after Submission to Acidic and Abrasive Aggressions

This in vitro study aimed to assess the erosive effect of hydrochloric acid in association with toothbrushing procedure on the surface condition of three bulk-fill composite resins used for direct restoration. A total of 480 samples (160 from each composite resin): X-tra Fil (VOCO, Germany)—group A, Filtek Bulk-fill Posterior (3M-ESPE, St. Paul, MN, USA)—group B, G-aenial Posterior (GC Japan)—group C were prepared, submitted to chemical attack for 60 min with hydrochloric acid 30% and, subsequently, submitted to the abrasive effect of toothbrushing using 10,000 cycles with medium and hard bristles, at three different times (immediately and after 30 min after acid attack or without any chemical attack). The surface roughness of the samples was measured using a noncontact profilometer (Dektak XT, Bruker, Billerica, MA, USA). The values were analyzed using ANOVA and post hoc Bonferroni tests, with a p < 0.05. Chemical attack for 60 min associated with one year of toothbrushing with toothbrushes having medium or hard bristles increase the surface roughness of tested bulk-fill composite resins. No differences were recorded between toothbrushing with medium or firm bristles immediately or 30 min after acidic challenge for each of the three bulk-fill composite resins. Exposure to hydrochloric acid determines no effect on surface roughness of bulk-fill composite resins.

Remineralization of caries-affected dentin and color stability of teeth restored after treatment with silver diamine fluoride and bioactive glass-ceramic

OBJECTIVES

The aim of this study was to evaluate the microhardness of caries-affected dentin and color stability of teeth restored after treatments with silver diamine fluoride (SDF) associated to potassium iodide (KI) and Biosilicate.

MATERIAL AND METHODS

Different samples from bovine teeth were obtained. For color readings, 80 cavities (6 mm × 6 mm × 2 mm) were prepared, and for microhardness, teeth were flattened into dentine to obtain 40 samples. All samples were submitted to cariogenic challenge and separated in 4 groups, according to the treatment used: 12% SDF + KI; 38% SDF; Biosilicate and control (no treatment). Cavities were restored with resin-modified glass-ionomer cement (RMGIC, Vitremer, 3 M ESPE) or composite resin (CR, Z350, 3 M ESPE). After restoration, the samples were submitted to thermo-mechanical cycling (TMC) for 1,200,000 cycles. Color readings (EasyShade, Vita) were performed after restorations, after TMC, and 30 days after TMC. Knoop microhardness was evaluated on the planned samples before and after cariogenic challenge, after treatments, and after 30 days. Scanning electron microscopy (SEM) evaluated the dentine surface after treatments. Data were analyzed (ANOVA, Bonferroni, p < .05).

RESULTS

The results showed a higher color alteration for RMGIC than CR. The time of analysis was significant (p < .05) for the 12% SDF + KI and control group. There was no difference (p < .05) in microhardness between groups. However, there was evidence of dentin remineralization after treatments.

CONCLUSIONS

It was concluded that the samples treated with Biosilicate resulted in a color alteration similar to control. The treatments presented dentin remineralizing potential for microhardness, below the demineralization level, caused by the cariogenic challenge.

CLINICAL RELEVANCE

Considering the remineralizing potential presented by Biosilicate, this agent is a promising alternative that overcomes the SDF adverse effects such as tooth staining.

The use of an elastomeric methacrylate monomer (Exothane 24) to reduce the polymerization shrinkage stress and improve the two-body wear resistance of bulk fill composites

OBJECTIVES

Characterize the chemical structure of an elastomeric monomer (Exothane 24) and evaluate the degree of conversion (DC), polymerization shrinkage stress (PSS), rate of polymerization (Rp), flexural strength (F_Strenght), flexural modulus (F_Modulus), Vickers hardness (V_Hardness) and two-body wear resistance of dental bulk fill composites (BFCs) containing Exothane 24.

METHODS

The Exothane 24 was characterized using mass spectroscopy, elemental analysis, ¹³C- and ¹H NMR. BFCs were formulated containing Exothane 24 (E10, E25, and E50). Similar BFCs containing regular UDMA (U10, U25, and U50), commercial conventional, and BFCs were used as control groups. ATR-FTIR spectroscopy was used to measure DC and the Rp of the composites. The PSS was measured using the universal testing machine method. Specimen bars were used to assess the F_Strenght, F_Modulus, and V_Hardness. RBCs were submitted to a two-body wear test using a chewing simulator machine; the rate and volumetric wear loss were evaluated using an optical scanner. Data were analyzed statistically with α = 0.05 and β = 0.2.

RESULTS

Exothane 24 is a urethane isophorone tetramethyl methacrylate monomer with polymerization stress-relieving properties. No differences were found in the DC up to 4 mm in depth for E25. All BFCs had similar F_Strenght, except for E50. E25 had the lowest volumetric wear loss and wear rate. E25 had approximately 30% lower PSS and slower Rp than commercial BFCs with similar wear resistance to conventional commercial composites.

SIGNIFICANCE

The Exothane 24 reduced the PSS and increased the wear resistance of BFCs; however, the formulation is important to optimize the properties of the BFCs.

Effects of Monomer Composition of Urethane Methacrylate Based Resins on the C=C Degree of Conversion, Residual Monomer Content and Mechanical Properties

(1) Background: This study investigated the influence of Bis-GMA, TEGDMA, UDMA, and two different polyethylene glycol (PEG)-containing, UDMO-based co-monomers on the Young’s modulus and flexural strength, degree of methacrylate C=C double bond conversion and residual monomer elution of experimental dental resins. (2) Methods: Urethane methacrylate-based monomer was synthesised via a radical chain growth polymerization mechanism using PEG in order to improve the mechanical properties. Dental resins were formulated using Bis-GMA, UDMA, or UDMO as base monomers combined with TEGDMA as a dilution monomer and DMAEM + CQ as the photo-initiator system. Degree of conversion (DC), mechanical properties, and residual monomer content of light-activated methacrylate resin formulations were evaluated and statistically analysed by ANOVA and a Tukey’s test. (3) Results: PEG-containing UDMO resins had lower Young’s modulus and elastic strength than UDMA-derived resin for all irradiation times. The highest DC (67,418%) was observed for the PEG-containing UDMO-based resin formulation when light cured for 40 s. For all samples, DC increased with the photo-polymerization time. The amount of residual monomer decreased after increasing the light-curing period from 20 to 40 s, resin with UDMO content 0.01 mol of PEG having the smallest amount of free eluted monomer. (4) Conclusions: A strong structure–property relationship exists in photo-cured dimethacrylate-based dental resins. The time and quantity of the photochemical initiation system can influence the physical–mechanical properties of the resins but also the monomers in their composition.

Novel Polymerization of Dental Composites Using Near-Infrared-Induced Internal Upconversion Blue Luminescence

Blue light (BL) curing on dental resin composites results in gradient polymerization. By incorporating upconversion phosphors (UP) in resin composites, near-infrared (NIR) irradiation may activate internal blue emission and a polymerization reaction. This study was aimed to evaluate the competency of the NIR-to-BL upconversion luminance in polymerizing dental composites and to assess the appropriate UP content and curing protocol. NaYF₄ (Yb³⁺/Tm³⁺ co-doped) powder exhibiting 476-nm blue emission under 980-nm NIR was adapted and ball-milled for 4–8 h to obtain different particles. The bare particles were assessed for their emission intensities, and also added into a base composite Z100 (3M EPSE) to evaluate their ability in enhancing polymerization under NIR irradiation. Experimental composites were prepared by dispensing the selected powder and Z100 at different ratios (0, 5, 10 wt% UP). These composites were irradiated under different protocols (BL, NIR, or their combinations), and the microhardness at the irradiated surface and different depths were determined. The results showed that unground UP (d50 = 1.9 μm) exhibited the highest luminescence, while the incorporation of 0.4-μm particles obtained the highest microhardness. The combined 20-s BL and 20–120-s NIR significantly increased the microhardness on the surface and internal depths compared to BL correspondents. The 5% UP effectively enhanced the microhardness under 80-s NIR irradiation but was surpassed by 10% UP with longer NIR irradiation. The combined BL-NIR curing could be an effective approach to polymerize dental composites, while the intensity of upconversion luminescence was related to specific UP particle size and content. Incorporation of 5–10% UP facilitates NIR upconversion polymerization on dental composites.

Long-term hydrolytic stability of CAD/CAM composite blocks

This study aimed to assess water sorption and solubility of CAD/CAM composite blocks compared to CAD/CAM ceramic after 8 months storage in water and artificial saliva. Eight CAD/CAM blocks were investigated: Five resin-composite blocks (RCBs), one polymer-infiltrated ceramic network (PICN) block, one ceramic-filled polyetheretherketone (PEEK) block, and one feldspathic ceramic block. One hundred and twelve specimens were prepared comprising 14 specimens of each of the eight materials. From each group of specimens, seven randomly selected specimens were immersed in 10 mL of water, while the other seven specimens were immersed in artificial saliva. All specimens were stored at 37°C and weighed at various time intervals. The data were analysed via repeat measures ANOVA, one-way ANOVA and Tukey's post hoc test (α = 0.05 for all tests). Sorption values (mean [SD]) in water were within the range -1.21 (0.4) to 39.3 (2.1) μg/mm³ and in artificial saliva between -0.7 (0.2) and 41.6 (1.3) μg/mm³ . Solubility values in water were between -0.43 (0.08) and 0.34 (0.18) μg/mm³ and in artificial saliva between -0.53 (0.07) μg/mm³ and 0.33 (0.2) μg/mm³ . CAD/CAM composite blocks were hydrolytically stable under long-term storage (according to ISO 4949:2009), although not as stable as ceramic. Water sorption of CAD/CAM composite blocks was dependent on the resin-matrix and was influenced by the filler weight %.

Effect of Light-Sources and Thicknesses of Composite Onlays on Micro-Hardness of Luting Composites

The aim of this study was to compare three different light-curing-units (LCUs) and determine their effectiveness in the adhesive cementation of indirect composite restorations when a light-curing resin cement is used. Two resin composites were selected: Enamel Plus HRI (Micerium) and AURA (SDI). Three thicknesses (3 mm, 4 mm and 5 mm) were produced and applied as overlays and underlays for each resin composite. A standardized composite layer was placed between underlay and overlay surfaces. Light curing of the resin-based luting composites was attained through the overlay filters using LCUs for different exposure times. All specimens were allocated to experimental groups according to the overlay thickness, curing unit and curing time. Vickers Hardness (VH) notches were carried out on each specimen. Data were statistically evaluated. The curing unit, curing time and overlay thickness were significant factors capable of influencing VH values. The results showed significantly decreased VH values with increasing specimen thickness (p < 0.05). Significant differences in VH values were found amongst the LCUs for the various exposure times (p < 0.05). According to the results, a time of cure shorter than 80 s (with a conventional quartz–tungsten–halogen LCU) or shorter than 40 s (with a high-power light-emitting diode (LED) LCU) is not recommended. The only subgroup achieving clinically acceptable VH values after a short 20 s curing time included the 3 mm-thick overlays made out of the AURA composite, when the high-power LED LCU unit was used (VH 51.0). Composite thickness has an intense effect on polymerization. In clinical practice, light-cured resin cements may result in insufficient polymerization for high thickness and inadequate times. High-intensity curing lights can attain the sufficient polymerization of resin cements through overlays in a significantly shorter time than conventional halogen light.