Effect of indirect restorative material and thickness on light transmission at different wavelengths

Application of near-infrared-to-blue upconversion luminescence for the polymerization of resin cements through zirconia discs

OBJECTIVES

To investigate a near-infrared-to-blue luminescence upconversion curing method for polymerizing resin cements under zirconia discs.

METHODS

Lava zirconia discs of different thicknesses (0.5-2.0 mm) were manufactured. First, the transmittances of the NIR and two blue lights (BLs) (LED and halogen lights) through these discs were measured. Second, NaYF4:Yb3+/Tm3+ upconversion phosphor (UP) powder was milled into 0.5-μm particle sizes. A light-curable resin cement VariolinkII base was chosen as the control (UP0), and an experimental cement (UP5) was prepared by adding 5 % UPs. These two cements were examined using multiphoton excitation microscopy for particle distribution. UP5 and UP0 were polymerized with or without zirconia shielding then subjected to a microhardness test. A multifold analysis was performed to examine the effects of zirconia thickness, curing protocols (pure BL or combined BL and NIR curing), and cement type.

RESULTS

The transmittance of NIR was superior to that of BL through zirconia discs of all thicknesses. UP particles were homogeneously distributed in UP5 and emitted blue luminescence under 980-nm NIR excitation. UP5 showed higher microhardness values than UP0 under any curing protocol or zirconia shielding condition. The combination of 20-s BL and 40-s NIR curing yielded the highest microhardness in uncovered UP5. However, combining 40-s BL and 20-s NIR curing surpassed the other groups when the zirconia discs were thicker than 0.5 mm.

SIGNIFICANCE

NIR exhibits higher transmission through zirconia than BL. UP particles work as strengthen fillers and photosensitizers in cements. NIR upconversion curing could be a new strategy for polymerizing resin cements under thick zirconia restorations.

Comparison of Blue and Infrared Light Transmission Through Dental Tissues and Restorative Materials

OBJECTIVES

The depth of cure using blue-light photocuring units (BL) is limited by tooth structure and qualities of the restorative material through which the activating wavelength must pass. Recent developments incorporate an infrared (IR) activated upconversion (UC) fluorescence of a lining agent filled with nanocrystals of NaYF4 and doped with YB+3 and Tm+3 that emit both blue and violet light locally at the interface of the liner and restorative resin. The purpose of this study was to evaluate the BL and 975 nm infrared (IR) light power transmission through dental tissues and restorative materials.

METHODS AND MATERIALS

Power transmissions of the IR laser (975 nm) and a monowave blue-only light-curing unit (Bluephase 16i) through dental tissues (enamel, dentin, and enamel/dentin junction, or DEJ), eight (8) various dental resin composites, and eight (8) dental ceramics, each at four thicknesses (1, 2, 3 and 4 mm) were evaluated (n=5) using a thermopile sensor (PM10, Coherent Inc) connected to a laser power meter (Fieldmate, Coherent Inc). Power transmission values of each light source and restorative material were subjected to analysis of variance and Tukey test at a pre-set alpha of 0.05.

RESULTS

A linear correlation (r=0.9884) between the supplied current and emitted IR power of the laser diode was found, showing no statistical power reduction with increased distances (collimated beam). For tooth tissues, the highest power transmissions for both light sources were observed using 1.0 mm enamel while the lowest values were found for 2.0 mm dentin and an association of 2.0 mm DEJ and 1.0 mm dentin. The only group where IR demonstrated significantly higher transmission when compared to BL was 1.0 mm enamel. For all resin composites and dental ceramics, increased thickness resulted in a reduction of IR power transmission (except for EverX Posterior fiber-reinforced composite and e.max HT ceramic). IR resulted in higher transmission through all resin composites, except for Tetric EvoCeram White. The highest BL transmission was observed for SDR Flow, at all thicknesses. Higher IR/BL ratios were observed for EverX Posterior, Herculite Ultra, and Lava Ultimate, while the lowest ratio was observed for Tetric EvoCeram White. Reduced translucency shades within the same material resulted in lower power ratio values, especially for BL transmission. Higher IR/BL ratios were observed for e.Max LT, VitaVM7 Base Dentin, and e.max CAD HT, while the lowest values were found for VitaVM7 Enamel and Paradigm C.

CONCLUSION

IR power transmission through enamel was higher when compared to blue light, while no difference was observed for dentin. The power transmission of IR was higher than BL for resin composites, except for a high value and low chroma shade. Fiber-reinforced resin composite demonstrated the highest IR/BL power transmission ratio. A greater IR/BL ratio was observed for lower translucency ceramics when compared to high translucency.

Effect of the violet light from polywave light-polymerizing units on two resin cements that use different photoinitiators

STATEMENT OF PROBLEM

Some light-emitting diode polymerization lights have been promoted as multiple peak or polywave lights that use multiple light-emitting diodes to produce both violet and blue light. However, whether the addition of violet light is required to light-activate resin cements that use bis(4-methoxybenzoyl)diethylgermane (Ivocerin) as the photoinitiator is unclear.

PURPOSE

This in vitro study evaluated the effect of violet, blue, or a combination of violet and blue light through ceramic on the degree of conversion of 2 resin cements that use either camphorquinone or Ivocerin as the photoinitiator.

MATERIAL AND METHODS

A Bluephase Style polywave light-emitting diode polymerizing unit delivering 6.4 J/cm2 of violet and blue light was used. This comprised 1.4 J/cm2 of violet (385 to 420 nm) and 5.0 J/cm2 of blue light (420 to 515 nm). The light-emitting diode emitters in a second modified Bluephase Style were connected directly to a power supply so that either just violet (1.4 J/cm2) or just blue (5.0 J/cm2) light was emitted. RelyX Veneer and Variolink Esthetic LC resin cements were either directly light-activated or through 0.5 or 1.5 mm of lithium disilicate ceramic (IPS e.max CAD). The degree of conversion was monitored by using Fourier-transform infrared spectroscopy. Data were subject to a 3-way analysis of variance followed by the Tukey honest significant difference multiple comparison tests (α=.05).

RESULTS

All factors had a significant effect (P<.001). Increasing the ceramic thickness decreased the degree of conversion only for RelyX Veneer cement (P<.001). The effect of the thickness of ceramic was most noticeable when just violet light was delivered to RelyX Veneer. A significant reduction (P<.001) was found in the degree of conversion of RelyX Veneer when just violet light was delivered. Variolink Esthetic LC had significantly higher degree of conversion values than RelyX Veneer, irrespective of the light type used (P<.001).

CONCLUSIONS

A multiple-peak light is not required to photopolymerize a resin cement that uses either camphorquinone or Ivocerin as its photoinitiator. Adding the violet light produced no significant increase in the degree of conversion of the Variolink Esthetic LC cement.

Light transmittance through resin-matrix composite onlays adhered to resin-matrix cements or flowable composites

OBJECTIVE

The aim of this study was to evaluate the influence of the thickness of resin-matrix composite blocks manufactured by CAD-CAM on the light transmittance towards different resin-matrix cements or flowable composites.

METHODS

Sixty specimens of resin-matrix composite CAD-CAM blocks reinforced with 89 wt% inorganic fillers were cross-sectioned with 2 or 3 mm thicknesses. The specimens were conditioned with adhesive system and divided in groups according to the luting material, namely: two dual-cured resin-matrix cements, two traditional flowable resin-matrix composites, and one thermal-induced flowable resin-matrix composite. Specimens were light-cured at 900 mW/cm2 for 40s. Light transmittance assays were preformed using a spectrophotometer with an integrated monochromator before and after light-curing. Microstructural analysis was performed by optical and scanning electron microscopy (SEM). Nanoindentation tests were performed to evaluate mechanical properties for indirect evaluation of degree of monomers conversion.

RESULTS

Optical and SEM images revealed low thickness values for the cementation interfaces for the traditional flowable resin-matrix composite. The cement thickness increased with the size and content of inorganic fillers. The highest light transmittance was recorded for the onlay blocks cemented with the traditional flowable resin-matrix composites while a group cemented with the dual-cured resin-matrix cement revealed the lowest light transmittance. The elastic modulus and hardness increased for specimens with high content of inorganic fillers as well as it increased in function of the light transmittance.

CONCLUSIONS

The light transmittance of flowable resin-matrix composites was higher than that for resin-matrix cement after cementation to resin-matrix composites blocks. The type, size, and content of inorganic fillers of the luting material affected the thickness of the cement layer and light transmittance through the materials.

CLINICAL RELEVANCE

On chair-side light curing, the transmission of visible light can be interfered by the chemical composition and viscosity of the luting materials. The increase in size and content of inorganic fillers of resin-matrix composites and luting materials can decrease the light transmittance leading to inefficient polymerization.

Effect of surface treatments on optical, topographical and mechanical properties of CAD/CAM reinforced lithium silicate glass ceramics

OBJECTIVES

To investigate the effect of different surface treatments on optical, topographical and mechanical properties of CAD/CAM lithium silicate-based glass ceramics (LSC's) and their combined effect on the output of a light curing unit (LCU).

METHODS

Four CAD/CAM LSC's were investigated: Lithium Disilicate (Emax CAD; EC), Zirconia-reinforced silicates (Vita Suprinity; VS and Celtra Duo;CD) and Lithium Aluminum Disilicate (CEREC Tessera; CT). Ceramic specimens (n = 240) were divided into six subgroups according to their surface treatment: (a) Control, (b) Hydrofluoric acid (HF) 5%, (c) HF 5% + Neutralizing agent (N), (d) HF 9%, (e) HF 9% +N and (f) Self-etching ceramic primer (SEP). Irradiance, power and radiant exposure of a LCU were measured with MARC-LC following ceramic specimen interposition. Direct light transmission (T%) and absorbance (Abs%) of the specimens were measured with UV-Vis spectrophotometry. Roughness (Sa, Sq) and wettability (θ°) were measured with optical profilometry and sessile drop profile analysis, respectively. Biaxial flexural strength (σ) of the ceramic specimens was measured by the ball-on-three-balls method and ceramic specimens were examined microscopically. Statistical analyses was performed by two-way ANOVA followed by post hoc multiple comparisons (α = 0.05).

RESULTS

Acid neutralization decreased T% and increased Abs% in all LSC's and highest T% was exhibited with VS. Neutralized EC, VS and CD displayed higher Sa in HF9, while neutralized CT displayed higher Sa in HF5. Self-etch primer significantly reduced θ° (p < 0.001). σ was observed in the followed ascending order: HF9 +N < HF9 < HF5 +N < HF5 < SEP < Control for all LSC's.

SIGNIFICANCE

Optical, topographical and mechanical properties of the CAD/CAM ceramic blocks were strongly dependent on the type of surface treatment. Results of neutralization post-etching indicate promising potential for future investigations.

Effect of inorganic fillers on the light transmission through traditional or flowable resin-matrix composites for restorative dentistry

OBJECTIVES

The aim of this in vitro study was to evaluate the light transmission through five different resin-matrix composites regarding the inorganic filler content.

METHODS

Resin-matrix composite disc-shaped specimens were prepared on glass molds. Three traditional resin-matrix composites contained inorganic fillers at 74, 80, and 89 wt. % while two flowable composites revealed 60 and 62.5 wt. % inorganic fillers. Light transmission through the resin-matrix composites was assessed using a spectrophotometer with an integrated monochromator before and after light curing for 10, 20, or 40s. Elastic modulus and nanohardness were evaluated through nanoindentation's tests, while Vicker's hardness was measured by micro-hardness assessment. Chemical analyses were performed by FTIR and EDS, while microstructural analysis was conducted by optical microscopy and scanning electron microscopy. Data were evaluated using two-way ANOVA and Tukey's test (p < 0.05).

RESULTS

After polymerization, optical transmittance increased for all specimens above 650-nm wavelength irradiation since higher light exposure time leads to increased light transmittance. At 20- or 40-s irradiation, similar light transmittance was recorded for resin composites with 60, 62, 74, or 78-80 wt. % inorganic fillers. The lowest light transmittance was recorded for a resin-matrix composite reinforced with 89 wt. % inorganic fillers. Thus, the size of inorganic fillers ranged from nano- up to micro-scale dimensions and the high content of micro-scale inorganic particles can change the light pathway and decrease the light transmittance through the materials. At 850-nm wavelength, the average ratio between polymerized and non-polymerized specimens increased by 1.6 times for the resin composite with 89 wt. % fillers, while the composites with 60 wt. % fillers revealed an increased ratio by 3.5 times higher than that recorded at 600-nm wavelength. High mean values of elastic modulus, nano-hardness, and micro-hardness were recorded for the resin-matrix composites with the highest inorganic content.

CONCLUSIONS

A high content of inorganic fillers at 89 wt.% decreased the light transmission through resin-matrix composites. However, certain types of fillers do not interfere on the light transmission, maintaining an optimal polymerization and the physical properties of the resin-matrix composites.

CLINICAL SIGNIFICANCE

The type and content of inorganic fillers in the chemical composition of resin-matrix composites do affect their polymerization mode. As a consequence, the clinical performance of resin-matrix composites can be compromised, leading to variable physical properties and degradation.

Effect of thickness of CAD/CAM materials on light transmission and resin cement polymerization using a blue light-emitting diode light-curing unit

OBJECTIVE

Evaluate the effect of thickness of high-translucency (HT) CAD/CAM materials on irradiance and beam profile from a blue light-emitting diode light-curing unit (LCU) and on the degree of conversion (DC) and maximum polymerization rate (Rp_max ) of a light-cured resin cement (LCC).

MATERIAL AND METHODS

The direct output from the LCU, the light transmission and irradiance ratio (IR) through one conventional composite and nine HT CAD/CAM materials (0.5, 1.0, 1.5, or 2.0-mm thick; n = 5) were measured with a integrating sphere coupled to a spectrometer. The light beam was assessed with a beam profiler camera. The DC at 600 s and the Rp_max of one LCC was determined using a Fourier transform infrared spectrometer (n = 5). Data were analyzed by ANOVA followed by Tukey's tests, and Dunnett's test was also used for irradiance data (α = 0.05).

RESULTS

A significant decrease in irradiance through all materials occurred as thickness increased. Thin CAD/CAM materials improved light homogeneity, which decreased with the increase in thickness. The DC of the LCC directly exposed to light was the same as when exposed to 45%, 25%, 15%, or 5% IRs. Rp_max decreased with the decrease in IR.

CONCLUSIONS

Although the HT CAD/CAM materials reduced the irradiance from the LCU, minor effects were observed in the LCC's DC.

CLINICAL SIGNIFICANCE

Despite the light attenuation of blue light through different CAD/CAM materials that were up to 2-mm thick, the degree of conversion of one brand of light-cured resin cement was clinically acceptable when the LCU was used for 30 s.

A new technique for incorporation of TiO2 nanotubes on a pre-sintered Y-TZP and its effect on bond strength as compared to conventional air-borne particle abrasion and silicatization TiO2 nanotubes application on pre-sintered Y-TZP

OBJECTIVE

This study evaluated the microshear bond strength of a resin cement to Y-TZP after different methods of TiO₂ nanotubes (nTiO₂) incorporation on pre-sintered Y-TZP surfaces.

METHODS

nTiO₂ were synthesized and incorporated on Y-TZP slices as follows (n = 15): 1) nTiO₂ mixed with isopropyl alcohol/manual application (MAl); 2) nTiO₂ mixed with acetone/manual application (MAc); 3) nTiO₂ mixed with isopropyl alcohol/high-pressure vacuum application (HPVAl); 4) nTiO₂ mixed with acetone/high-pressure vacuum application (HPVAc). As controls, surfaces were sandblasted with Al₂O₃ (OX) or Rocatec silicatization (ROC). All ceramics were sintered after nTiO₂ incorporation. Surface treatments of OX and ROC were made after sintering. Surfaces were characterized by confocal laser microscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Resin composite cylinders (1.40 mm diameter and 1 mm height) were cemented with a resin cement, stored in water at 37 °C for 24 h and thermocycled for 10 000 cycles before microshear bond strength evaluation. Data were analyzed with one-way ANOVA and Games-Howell (α = 0.05), and fracture analysis was performed using a stereomicroscope.

RESULTS

EDS confirmed the presence of TiO₂ on treated Y-TZP. The confocal analysis showed higher roughness for HPVAc and OX. There were significant differences between surface treatments (p < 0.001). HPVAl (22.96 ± 10.3), OX (34.16 ± 7.9) and ROC (27.71 ± 9.4) showed higher microshear bond strengths and were statistically similar (p > 0.05). MAC showed intermediary values, and HPVAc and MAl presented decreased bond strength, with a high percentage of premature debonding.

CONCLUSION

High-pressure vacuum application of nTiO₂ mixed with isopropyl alcohol was able to produce bond strength values compared to conventional air abrasion and Rocatec silicatization.

SIGNIFICANCE

The infiltration of TiO₂ nanostructures on the pre-sintered Y-TZP is an interesting approach that can improve bond strength without the need of sandblasting methods.

Composite Resin Preheating Techniques for Cementation of Indirect Restorations

Purpose

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

Results

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

Conclusions

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

Characterization and effectiveness of a violet LED light for in-office whitening

OBJECTIVES

This study characterized a violet LED light (V-LED; bright max whitening) tooth whitening device and evaluated its efficacy on stained enamel compared to hydrogen peroxide (HP).

MATERIALS AND METHODS

Characterization of the V-LED beam profile was performed using a laser beam-profiler. The irradiance was measured throughout an exposure cycle at 0- and 8-mm distances using an integrating sphere and a spectral radiometer. Bovine enamel/dentin blocks stained with black tea (BT), cigarette smoke (CS), or without staining (CONT) were subjected to V-LED or 40% HP (n = 10/group). Color parameters (ΔL, Δa, Δb, and ΔE₀₀) were measured using a digital spectrophotometer. Light transmission was estimated through 1-mm-thick bovine enamel slices (n = 5). ΔL, Δb, ΔE₀₀, and irradiance were analyzed by two-way ANOVAs and Tukey's tests, Δa by Kruskal-Wallis and Mann-Whitney tests, and light transmission by t-test (α = 5%).

RESULTS

Heterogeneous beam distribution was observed for the emitting V-LED chips. After 20 sequential exposures, irradiance levels were reduced 25-50%, regardless of the distance from V-LED. Localized irradiance values were statistically different between beam locations and different distances from the target. V-LED produced lower ΔE_00, ΔL, Δa, and Δb values than HP for CONT and BT, with no differences for CS. Light transmittance decreased approximately 98% through 1-mm thick enamel.

CONCLUSIONS

V-LED irradiance was heterogeneous and decreased throughout the exposure cycles and was also greatly reduced with increasing tip distance. V-LED produced a significantly lower whitening effect on BT and control teeth.

CLINICAL RELEVANCE

This study contributes to the knowledge of V-LED and its clinical use.

Effects of shades of a multilayered zirconia on light transmission, monomer conversion, and bond strength of resin cement

OBJECTIVE

To evaluate the influence of shades of a multilayered zirconia on light transmission, resin cement degree of conversion, and shear bond strength of resin cement.

MATERIALS AND METHODS

The light transmission through opaque (OPQ) and translucent (TNS) regions of Katana UTML zirconia (Kuraray Noritake Dental) were evaluated for using a spectroradiometer (n = 5). Degree of conversion of dual-cure resin cement (Panavia V5, Kuraray Noritake Dental) was measured after light-activation through OPQ or TNS regions and direct exposure. Composition of the zirconia was analyzed with energy dispersive x-ray spectroscopy (EDS). Shear bond strength (SBS) was evaluated on the OPQ and TNS regions after 24 h and 1 year from specimen preparation (n = 15).

RESULTS

The OPQ region produced higher irradiance loss (95.1%) than TNS one (92.9%), and lower degree of conversion (52.4%) than TNS (71.2%) at 24 h post-light activation. EDS analysis did not show differences on the microstructure of the OPQ and TNS regions. There were no significant differences on the SBS between zirconia regions. For both zirconia regions, a significant reduction on the SBS occurred after aging, being 31.7% for OPQ and 38% for TNS.

CONCLUSION

Both OPQ and TNS regions affected the light transmission through the multilayered zirconia. The OPQ region yielded the highest light attenuation and the lowest degree of conversion of resin cement. Different regions of the zirconia did not influence the SBS. Clinical significance Although opaque and translucent regions of the multilayered zirconia reduced the light transmission from LED curing unit and the degree of conversion of resin cement, the regions did not affect the resin cement adhesion.

Transmission of violet and blue light and current light units through glass-reinforced ceramics with different thicknesses

Purpose To evaluate the effect of glass-reinforced ceramics (leucite and lithium disilicate) with different thicknesses (1, 2, and 3 mm) on the wavelength and irradiance spectrum of blue and violet lights. In addition, the effect of the ceramics on four current light-curing units (LCUs) was evaluated: a halogen lamp, a single peak LED, and two multi-peak LEDs.Methods Ceramic discs of different thicknesses (1, 2, and 3 mm) were obtained from computer-aided design and computer-aided manufacturing (CAD-CAM) blocks. The irradiance, radiant exposure, and emission spectrum of the four LCUs were analyzed using a spectrometer-based instrument. To evaluate the violet and blue lights, a specific device that provides a narrow emission spectrum was used.Results The ceramics reduced the irradiance of all the tested LCUs. However, the wavelength of the transmitted light was only altered slightly. The effect of leucite and lithium disilicate varied according to the type of LCU and thickness of the ceramic disc evaluated .Conclusions From the results, it could be concluded that the thickness of the leucite and lithium disilicate ceramic significantly reduced the irradiance of the light emitted by the LCUs, with minimal changes on the wavelength spectrum of the lights. The effects of the ceramic on irradiance and transmitted wavelengths of the blue and violet lights was slightly different.

Relationship Between the Cost of 12 Light-curing Units and Their Radiant Power, Emission Spectrum, Radiant Exitance, and Beam Profile

OBJECTIVES

To correlate the radiant power (mW), radiant exitance (or tip irradiance in mW/cm2), emission spectrum (mW/cm2/nm), and beam irradiance profile of 12 light-curing units (LCUs) available in the Brazilian market with their market cost.

METHODS AND MATERIALS

Six LCUs that cost more than US$900 (Bluephase G4,VALO Grand, VALO Cordless, Radii Xpert, Elipar DeepCure-S, and Radii plus) and six low-cost LCUs costing less than US$500 (Radii Cal, Optilight Max, High Power LED 3M, Emitter D, Emitter C, and LED B) were examined. Radiant power (mW) and emission spectrum (mW/nm) were measured using an integrating sphere connected to a fiber-optic spectroradiometer. The internal tip diameter (mm) of each LCU was measured using a digital caliper and was used to calculate the average radiant exitance (mW/cm2). Irradiance profiles at the light tip were measured using a commercial laser beam profiler. The cost of each LCU in Brazil was correlated with internal tip diameter, radiant power, and tip irradiance.

RESULTS

None of the low-cost LCUs were broad spectrum multiple peak LCUs. There was no correlation between the cost of the LCUs and their averaged tip irradiance; however, there was a high positive correlation between the cost of the LCUs and the radiant power and tip diameter. The VALO Grand, Elipar DeepCure-S, VALO Cordless, and Bluephase G4 all emitted a higher radiant power. They also had a significantly greater tip diameter than other LCUs. For the LCUs with a nonuniform output, some areas of the light tip delivered less than 400 mW/cm2, while other areas delivered more than 2500 mW/cm2.

CONCLUSIONS

In general, LCUs that had a higher cost (US$971-US$1800) delivered more power (mW) and had a greater tip diameter (mm), which covered more of a tooth. In general, the low-cost LCUs (US$224-US$470) emitted a lower radiant power and had a smaller tip diameter.

Safety and Long-term Scleral Biomechanical Stability of Rhesus Eyes after Scleral Cross-linking by Blue Light

Purpose: To assess the safety and long-term scleral biomechanical stability of rhesus eyes after blue light scleral CXL by investigating the biomechanical and microstructural changes.Methods: Seven rhesus monkeys (14 eyes) were observed in this study. All right eyes received blue light scleral CXL at the superior temporal equatorial sclera, and the left eyes served as controls. Biological ocular parameters were followed up to 1 year after scleral CXL. Stress-strain measurements of three rhesus sclera were measured, three rhesus retinas were examined histologically by H&E and TUNEL staining. And the microstructure of both the sclera and retina were observed by transmission electron microscopy at 1 year.Results: As for the retinal thickness, choroidal thickness, flow density of retinal superficial vascular networks and flash electroretinography (f-ERG) results, no significant differences were observed between the paired eyes at 1 year (P >.05). At the same time, the scleral collagen fibril distribution was much tighter, and the scleral biomechanical properties were significantly increased in the experimental eyes. However, apoptotic cells and retinal ultrastructural changes could still be found in the retina of the experimental eyes.Conclusion: This study demonstrates that blue light scleral CXL could effectively increase the scleral stiffness of the rhesus eye for at least 1 year, but ultrastructural change was still observed in the retina of scleral CXL eye. Therefore, the long-term intraocular safety of the blue light scleral CXL technique for preventing myopia progression should be investigated further.

Effect of exposure time and moving the curing light on the degree of conversion and Knoop microhardness of light-cured resin cements

OBJECTIVE

To evaluate the effect of exposure time and moving the light-curing unit (LCU) on the degree of conversion (DC) and Knoop microhardness (KH) of two resin cements that were light-cured through ceramic.

METHODS

Two resin cements: AllCem Veneer APS (FGM) and Variolink Esthetic LC (Ivoclar Vivadent) were placed into a 0.3 mm thick matrix in 6 locations representing the canine to canine. The resins were covered with 0.5 mm thick lithium disilicate glass-ceramic (IPS e.max CAD, Ivoclar Vivadent). A motorized device moved the LCUs over the ceramic when the LCU was on. Two single-peak LCUs: Elipar DeepCure-L (3M Oral Care) and Emitter C (Schuster), and one multi-peak: Bluephase G2 (Ivoclar Vivadent) were used with 3 different exposure protocols: a localized exposure centered over each tooth for 10 or 40 s; moving the tip across the 6 teeth for a total exposure time of 10 or 40 s; and moving the tip across the 6 teeth resins for a total exposure time of 60 or 240 s. After 24 h, the DC and KH were measured on the top surfaces and the data was analyzed using three-way ANOVA and Tukey's tests (α = 0.05).

RESULTS

Interposition of 0.5 mm of ceramic reduced the irradiance received by the resin by approximately 50%. The 40 s localized exposure over each tooth always produced significantly higher DC and KH values. Moving the LCUs with a total exposure time of 10 s resulted in the lowest DC and KH. There was no beneficial effect on the DC or KH when the multi-peak (violet-blue) LCU (Elipar DeepCure-L or Bluephase G2), but the lower light output from a small tip LCU reduced the DC and KH values (Emitter C).

SIGNIFICANCE

Moving the LCUs when photo-curing light-cured resin cements is not recommended. This study showed that a single-peak LCU could activate a resin cement that uses Ivocerin™ as well as the multi-peak LCU.

Effects of extending duration of exposure to curing light and different measurement methods on depth-of-cure analyses of conventional and bulk-fill composites

This study evaluated the effect of extending the duration of exposure to curing light on the depth of cure of two conventional (RBC1-conventional and RBC2-conventional) and two bulk-fill (RBC1-bulk and RBC2-bulk) resin composites. Polywave and single-peak photocuring units were used. Cylinder-shaped specimens were exposed to curing light either for the time period recommended by the manufacturer or twice the length of that time, and depth of cure was estimated using manual scraping (similar to the ISO-4049 standard) and solvent immersion techniques. Depth of cure was analyzed, using two-way ANOVA, for the factors measurement method and exposure time. For RBC1-conventional and RBC1-bulk, the solvent immersion technique estimated a greater depth of cure than did manual scraping; for RBC1-conventional, both techniques and both light-exposure time periods resulted in a depth of cure of >2 mm; and for RBC1-bulk, only the solvent method after photocuring for twice the manufacturer's recommended time resulted in a depth of cure of 5 mm. For RBC2-conventional and RBC2-bulk, neither technique nor exposure time resulted in estimated depths of cure that matched those indicated by the manufacturer. The results suggest that extending the duration of photopolymerization increases depth of cure. Also, calculation of depth of cure can vary according to the measurement technique used.