Evaluation of the information provided in the instruction manuals of dental light-curing units.

OBJECTIVE: This study evaluated the completeness and accuracy of information in LCU instruction manuals from 40 manufacturers. MATERIALS AND METHODS: Instruction manuals from 40 LCUs (20 from leading manufacturers and 20 budget units) were reviewed. Twenty-eight parameters across five categories were assessed using a binary scale (0=incorrect/missing, 1=correct). The categories and their respective evaluation scores were: LCU characteristics (43%), instructions for use (7%), safety precautions (14%), maintenance recommendations (29%), and regulatory certification (7%). These scores were combined to produce a final score. RESULTS: Scores from leading manufacturers ranged between 46-86%, while the budget category ranged from 18-68%. All manuals provided information about the wavelength/spectrum of the LCU. Only Valo X and Valo Cordless reported power values and used the term "irradiance" instead of "intensity." Details such as LED type and active tip emission area were often missing. Instructions on how to use the LCU to photo-cure resins were frequently limited. Although most manuals addressed safety precautions, several lacked details on heat issues and general health precautions. All manuals included maintenance instructions, though information on replacement parts was often missing. Among the LCUs, 85% stated they were CE certified, 32% held both FDA and CE certification, and 63% claimed compliance with ISO and/or IEC standards. CONCLUSIONS: There were notable differences in the completeness and accuracy of the instruction manuals. Manuals from major manufacturers generally provided more comprehensive information than their budget counterparts. CLINICAL SIGNIFICANCE: Instruction manuals should contain accurate information to help clinicians deliver the highest standard of care. The lack of important information about the LCUs in the manuals is concerning.

Thermography and conversion of fast-cure composite photocured with quad-wave and laser curing lights compared to a conventional curing light.

OBJECTIVES: This study investigated effects of the different emittance-mode protocols from three light curing units (LCUs): (i) a Laser (Monet); (ii) a quad-wave (PinkWave); (iii) a conventional LED (Elipar S10) on the temperature rise (ΔT) and degree of conversion (DC) when photo-curing fast or conventional bulk-fill resin-based composites (RBC). The aim was to correlate ΔT and DC, and the radiant exposure delivered to RBC specimens. METHODS: A 3D-printed resin mold of 4 mm depth was filled with two bulk-fill RBCs: Tetric PowerFill® (fast photo-polymerised composite) (TPF) or Tetric EvoCeram® Bulk-Fill (EVO). Three LCUs were used: (i) Monet laser for 1 s and 3 s (MONET-1 s, MONET-3 s); (ii) PinkWave quad-wave used for 3 s in Boost mode (PW-3 s) and for 20 s in standard mode (PW-20 s); (iii) Elipar S10 for 5 s (S10-5 s) and for 20 s in standard mode (S10-20 s). 2-dimensional temperature maps were obtained before, during and for 60 s after the LCU had turned off using a thermal imaging camera. Thermal changes were analysed at five depths: (0, 1, 2, 3, and 4 mm from the top surface of the RBC). The maximum temperature rise (Tmax) and the mean temperature rise (ΔT) were determined. Cylindrical-shaped specimens were prepared from each material using a stainless-steel split mold (4 × 4 mm) and light-cured with the same protocols. The DC was measured for 120 s and at 1 h after LCU had turned off using Fourier Transform Infrared Spectroscopy (FTIR). Data were analysed using Three-way ANOVA, One-way ANOVA, independent t-tests, and Tukey post-hoc tests (p < 0.05). RESULTS: Radiant exposures delivered by the various irradiation protocols were between 4.5-30.3 J/cm2. Short exposure times from MONET-1 s and PW-3 s delivered the lowest radiant exposures (4.5 and 5.2 J/cm2, respectively) and produced the lowest ΔT and DC. The longer exposure times in the standard modes of PW-20 s, S10-20 s, and MONET-3 s produced the highest Tmax, ΔT, and DC for both composites. The ΔT range among composites at different depths varied significantly (31.7-49.9 °C). DC of TPF ranged between 30-65% and in EVO between 15.3-56%. TPF had higher Tmax, ΔT for all depths and DC compared to EVO, across the LCU protocols (p < 0.05), except for PW-20 s and MONET-3 s. The coronal part of the restorations (1-2 mm) had the highest ΔT. There was a positive correlation between ΔT and DC at 4-mm depth after 120 s SIGNIFICANCE: Longer, or standard, exposure times of the LCUs delivered greater radiant exposures and had higher DC and ΔT compared to shorter or high-irradiance protocols. The fast photo-polymerised RBC had comparatively superior thermal and conversion outcomes when it received a high irradiance for a short time (1-5 s) compared to the conventional Bulk-Fill RBC.

Effect of Tooth Brushing Cycles and Dentifrice Fluoride Concentration on a Glazed CAD/CAM Ceramic.

PURPOSE: To evaluate the effect of tooth brushing and dentifrice fluoride (F-) concentration on changes in color and translucency (ΔE00 and ΔT00, respectively), surface gloss (GS), surface roughness (Sa), and microstructure of a glazed CAD/CAM ceramic. MATERIALS AND METHODS: Ceramic blocks (e.max/CAD) were sectioned into rectangular plates (14 x 12 x 1 mm), and one surface of each sample was glazed. Samples were divided into three groups according to the F- concentration in the dentifrice (0, 1,100, and 5,000 µg/g) and were then subjected to 60,000 tooth brushing cycles. Luminosity and color were measured using a spectrophotometer at baseline and after every 20,000 cycles to obtain their ΔE00 and ΔT00 values. Another set of samples was prepared to measure the GS with a gloss meter and the Sa with a confocal laser microscope. The GS and Sa results were subjected to analysis of variance, Tukey test, and Dunnett test (α = .05). RESULTS: After 60,000 tooth brushing cycles, all of the variables were clinically acceptable, and there were no significant differences in the ΔE00, ΔT00, GS, or Sa among the fluoridated dentifrices. The GS values decreased significantly as the number of tooth brushing cycles increased. CONCLUSION: The ΔE00, ΔT00, GS, and Sa values were all clinically acceptable after the glazed e.max/CAD ceramic had been subjected to 60,000 tooth brushing cycles with dentifrices containing up to 5,000 µg/g of F-.

Skill Retention of Light-Curing Technique Using Only Verbal Instructions versus Using an Instructional Video: A 2-Year Follow-Up Study of Dental Students.

Purpose: To evaluate the retention of light-curing skills among dental students after two years of clinical experience and determine if there are any differences in the skills retention between students who received verbal instructions or those who had received an instructional video. The students' satisfaction with past learning, self-confidence, and general knowledge about light-curing were also evaluated. Methods: This study is a 2-year evaluation of previous work. Students had previously been divided into two groups: those who received only verbal instructions, and those who received only an instructional video about the correct light curing technique to use clinically. Each student had light-cured simulated restorations (anterior and posterior) for 10 sec using the Managing Accurate Resin Curing-Patient Simulator (MARC-PS) (BlueLight Analytics, Halifax, Nova Scotia, Canada) and a multiple-emission peak light-emitting-diode (Bluephase N, Ivoclar Vivadent, Schaan, Liechtenstein) curing light. Students then received instructions according to their assigned group and light-cured the simulated cavities again. Two years later, students from both groups light-cured the same simulated cavities. Then, they completed a modified version of the National League of Nursing (NLN) satisfaction and self-confidence questionnaire and answered light-curing knowledge questions. Statistical analysis: The mean radiant exposure values delivered before receiving specific instructions on light curing, immediately after, and two years after instruction for both teaching methods (Friedman test followed by Wilcoxon signed-rank post hoc test), and the difference between both teaching methods was assessed (two-sample Wilcoxon rank-sum test). The satisfaction and self-confidence scores were compared between teaching method groups (Wilcoxon rank-sum test) (p<0.05). Results: The mean and median irradiance values ranged between 194-1777 and 1223-1302 mW/cm2 before instructions, 320-1689 and 1254-1394 mW/cm2 immediately after instructions, and 95-1945 and 1260-1331 mW/cm2 two years later regardless of the simulated restoration or the teaching method. The mean and median radiant exposure values ranged between 2-23 and 12.5-13.6.4 J/cm2 before instructions, 3-28 and 12.8-14.3 mW/cm2 immediately after instructions, and 0.7-20 and 12.8-13.6 mW/cm2 two years later regardless of the simulated tooth being light cured and the teaching method. Students retained their light-curing skills after two years of clinical experience, with no significant differences between both groups. The instructional video group delivered significantly higher radiant exposure values (p=0.021) when light-curing the anterior tooth than the posterior. Students were satisfied with their past learning and confident in their light-curing skills (p=0.020). There were statistical differences in how well the two groups remembered what they had been taught about light-curing. Only 5.7% of students answered all knowledge questions correctly. Conclusion: Students retained their light-curing skills after two years of clinical experience, with no significant difference between verbal instructions or instructional video teaching methods. However, their knowledge about light curing remained very poor. Nevertheless, the students were satisfied with how they had been taught and had confidence in both teaching methods.

A Blinded Comparative Study of Four Commercially Available LEDs and a Laser Light Curing Device.

OBJECTIVE: This study determined the effectiveness of five light-curing units (LCUs; four light-emitting diode [LED] and one laser) used on different settings to photo-activate four conventional resin-based composites (RBCs). MATERIALS AND METHODS: A total of 108 RBC specimens were photo-activated in a white Delrin mold representing a mesial-occlusal-distal (MOD) class II restoration in a molar tooth. The proximal boxes were 5 mm deep, and the mesial-distal length was 12 mm. Immediately after photo-curing, the RBC specimens were immersed in a solvent to remove the uncured materials, after which they were photographed and deidentified. A Research Electronic Data Capture survey was created using these images and sent to respondents who blindly assessed the ability of the various LCUs to photo-cure the MOD restorations. RESULTS: There were significant differences in how the five curing lights had cured RBCs. One-way analysis of variance (ANOVA), pairwise t-test, Welch's one-way ANOVA, and Kruskal-Wallis rank test in the blinded survey data showed significant differences between the LED curing lights used for two 10-second cures and the laser curing light used for 1 second, and LED lights at lower settings. CONCLUSION: There was a significant difference in how the curing lights could photo-cure the RBCs used in this study. The laser curing light used for 1 second produced the worst results in all four RBCs. CLINICAL SIGNIFICANCE: When used for 1 second, the laser curing device does not photo-cure conventional RBC materials as well as the LED curing lights used for 10 seconds.

Effect of thickness on the degree of conversion of two bulk-fill and one conventional posterior resin-based composites at high irradiance and high temporal resolution.

OBJECTIVES: This study: 1) measures the effect of sample thickness and high irradiance on the depth-dependent time delay before photopolymerization reaction onset; 2) determines if exposure reciprocity exists; 3) measures the conversion rate at four irradiance levels; 4) determines the time, t0, at which the maximum DC rate is reached for two bulk-fill and one conventional posterior resin-based composites (RBCs). METHODS: Tetric PowerFill IVA shade (Ivoclar Vivadent) and Aura bulk-fill ultra universal restorative (SDI), and one conventional posterior resin-based composite (RBC), Heliomolar A3 (Ivoclar Vivadent), that were either 0.2 mm, 2 mm, or 4 mm thick were photocured using a modified Bluephase G4 (Ivoclar Vivadent) light-curing unit (LCU) that delivered a single emission band (wavelength centered at 449 nm). The same radiant exposure of 24 J/cm2 was delivered at irradiances ranging from 0.5 to 3 W/cm2 by adjusting the exposure time. PowerFill was also photocured for 3 s or 6 s using a Bluephase PowerCure LCU (Ivoclar Vivadent) on the 3 s mode setting. The degree of conversion (DC) was measured in real-time at a high temporal resolution at 30 °C using Attenuated Total Reflection (ATR) FTIR spectroscopy with a sampling rate of 13 DC data points per second. The DC data were analyzed using a phenomenological autocatalytic model. The RBC viscosity was measured at 21 °C and 30 °C. Light transmission through the RBC samples at 22 °C was monitored with time to calculate the extinction coefficients of the RBCs. RESULTS: The time delay before photopolymerization started increased as the RBC thickness increased and the irradiance decreased. An autocatalytic model described the DC data. The time t0 was less than 77 ms for the 0.2 mm thick samples of PowerFill irradiated using the highest irradiance of 3 W/cm2. Among the three RBCs for each sample thickness and irradiance level, the PowerFill had the smallest time t0. There was a time delay of 0.59 s and 1.25 s before the DC started to increase at the bottom of 4 mm thick samples for the PowerFill and Aura, respectively, when an irradiance of 1 W/cm2 was delivered. The time delay increased to 3.65 s for the Aura when an irradiance of 0.5 W/cm2 was delivered. The extinction coefficients near 449 nm were 0.78 mm-1, 0.76 mm-1, and 1.55 mm-1 during the first 2 s after the start of photocuring of PowerFill, Aura, and Heliomolar, respectively. Only PowerFill followed exposure reciprocity. At T = 30 °C, the viscosity was 3400, 17000, and 5200 Paˑs for PowerFill, Aura, and Heliomolar, respectively. SIGNIFICANCE: The time delay between when photopolymerization starts at the top and bottom of 2- or 4-mm thick RBC restorations may affect the structural integrity of the bond between the tooth and the bottom of the restoration. Only PowerFill followed exposure reciprocity between irradiance levels of 0.5 to 3 W/cm2. Exposure reciprocity did not occur for Aura or Heliomolar, neither of which are optimized for short light exposure or high irradiance conditions.

The potential 'blue light hazard' from LED headlamps.

Many dental personnel use light-emitting diode (LED) headlamps for hours every day. The potential retinal 'blue light hazard' from these white light headlamps is unknown. METHODS: The spectral radiant powers received from direct and indirect viewing of an electronic tablet, an LED curing light, a halogen headlamp, and 6 brands of LED headlamps were measured using integrating spheres attached to fiberoptic spectroradiometers. The spectral radiant powers were measured both directly and indirectly at a 35 cm distance, and the maximum daily exposure times (tMAX) were calculated from the blue weighted irradiance values. RESULTS: The headlamps emitted very different radiant powers, emission spectra, and color temperatures (K). The total powers emitted at zero distance ranged from 47 mW from the halogen headlamp to 378 mW from the most powerful LED headlamp. The color temperatures from the headlamps ranged from 3098 K to 7253 K. The tMAX exposure times in an 8 h day when the headlamps were viewed directly at a distance of 35 cm were: 810 s from the halogen headlamp, 53 to 220 s from the LED headlamps, and 62 s from the LED curing light. Light from the LED headlamps that was reflected back from a white reference tile 35 cm away did not exceed the maximum permissible exposure time for healthy adults. Using a blue dental dam increased the amount of reflected blue light, but tMAX was still greater than 24 h. CONCLUSIONS: White light LED headlamps emit very different spectra, and they all increase the retinal 'blue light hazard' compared to a halogen source. When the headlamps were viewed directly at a distance of 35 cm, the 'blue light hazard' from some headlamps was greater than from the LED curing light (tMAX = 62 s). Depending on the headlamp brand, tMAX could be reached after only 53s. The light from the LED headlamps that was reflected back from a white surface that was 35 cm away did not exceed the maximum permissible ocular exposure limits for healthy adults. CLINICAL RELEVANCE: Reflected white light from dental headlamps does not pose a blue light hazard for healthy adults. Direct viewing may be hazardous, but the hazard can be prevented by using the appropriate blue-light blocking glasses.

Power output from 12 brands of contemporary LED light-curing units measured using 2 brands of radiometers.

BACKGROUND: Given the increasing use of photo-activated resins in dentistry, dentists and researchers need a user-friendly dental radiometer to measure the power output from dental light-curing units (LCUs). OBJECTIVE: Our goal was to measure the accuracy of two brands of dental radiometers in reporting the power (mW) from twelve brands of contemporary LCUs compared to a 'gold standard' (GS) reference value obtained from an integrating sphere attached to a fiberoptic spectroradiometer. METHODS: The power output was measured from two units of 12 brands of LCUs, five times on the ''GS" system, five times on two Bluephase Meter II dental radiometers, and five times on two Mini Gig hand-held spectroradiometers. The emission spectrum was also recorded using the 'GS' integrating sphere. The power values reported by each meter were subjected to t-tests to compare the two examples of each LCU, and 3-way ANOVA followed by Bonferroni's post-hoc tests. Regression analyses were also performed to determine the relationship between the data from the hand-held radiometers and the 'GS' integrating sphere. RESULTS: There was a large difference in the power values (mW) and the emission spectra from the 12 brands of LCUs on their standard-settings (p<0.001). Except for one LCU (Dental Spark @ 15.1%), the differences between the two LCUs of the same brand were less than 5.3% when measured using the 'GS' integrating sphere. Regression analyses showed a highly significant agreement between the power values reported from the two brands of radiometers and the 'GS' integrating sphere (R2 > 98%). CONCLUSION: We concluded that the power values reported from both brands of dental radiometers we tested were accurate, provided that the light source did not emit wavelengths of light that were beyond the radiometer's detection limit.

Comparison of the operative time and presence of voids of incremental and bulk-filling techniques on Class II composite restorations.

OBJECTIVES: To compare the operative time and presence of air voids on Class II restorations fabricated by dental practitioners with 1 to 5 years of experience using incremental and bulk-filling techniques. METHOD AND MATERIALS: Four techniques were evaluated: incremental, bulk-filling, bulk-filling with heated composite, and snowplow technique. Standardized mandibular first molars with a MOD (mesial, occlusal, and distal) cavity were used. Voluntary operators made two restorations using each technique and the time required for each restoration was recorded. The restorations were scanned by micro-computed tomography to calculate the volume of the restoration occupied by air voids. The "operative time" and "volume of air voids" were analyzed individually by two-way ANOVA and Tukey HSD post hoc (α = .05) for the factors operator and insertion technique. A correlation between "operative time" and "volume of air voids" was evaluated using Pearson coefficient (α = .05). RESULTS: The incremental technique required significantly longer time, yet no differences were observed between the bulk-filling techniques. There were no significant differences between techniques regarding the volume of air voids. A significant, but weak, and inverse linear correlation (P = .0059; r = -.29; r2 = 8.41%) was found between the operative time and volume of air voids. CONCLUSION: There were no significant differences in the volume of air voids among the evaluated techniques, although bulk-filling techniques required a shorter operative time. Hence, implementing bulk-filling techniques by dental schools and restorative dental practitioners with different levels of expertise may reduce chair time and produce a volume of air voids similar to the incremental technique.

Photo-polymerization kinetics of a dental resin at a high temporal resolution.

OBJECTIVES: This study: 1) aims to measure with high temporal resolution the intrinsic rate of the degree of conversion (DC) of a dental resin-based composite (RBC) photo-cured at two irradiances; 2) aims to determine the transition time at which the DC rate is maximum; 3) used two different irradiances to measure the shift in transition time; 4) aims to compare transition times measured using DC and shrinkage strain. METHODS: Samples (n = 20) 1 mm thick by 10 mm diameter of Filtek One bulk-fill restorative A2 shade (3M Oral Care) were photocured for 20 s with a single emission peak (wavelength centered at 455 nm) light-emitting-diode-based light-curing unit at irradiance levels of 890 mW/cm2 and 209 mW/cm2, and initial sample temperature of T = 23 °C. The DC was measured in real-time using Attenuated Total Reflection (ATR) FTIR spectroscopy with a sampling rate of 13 DC data points per second. The data were analyzed within a phenomenological autocatalytic model. In addition, the axial shrinkage strain was measured using 3 samples of the RBC with the same outer dimensions and under similar experimental conditions using the bonded disk method and an interferometric technique. RESULTS: For the 890 mW/cm2 and 209 mW/cm2 irradiance levels, the DC with time was found to agree with the model enabling the determination of transition times of 0.66 ± 0.05 s and 2.3 ± 0.2 s, and the DC at these times of 5.5 ± 0.2% and 6.4 ± 0.2%. The maximum linear strain rate at 0.76 ± 0.01 s and 1.98 ± 0.02 s for the 890 mW/cm2 and 209 mW/cm2 irradiance levels, respectively, are within two standard deviations of the corresponding transition times. SIGNIFICANCE: At an irradiance level much greater than 1000 mW/cm2, the photo-polymerization kinetics of a dental RBC may be too fast to be measured accurately using ATR-FTIR spectroscopy. A viable alternative to monitor the kinetics is through the measurements of the axial shrinkage strain employing the bonded disk method and an interferometric technique.

Effect of repeated heating and cooling cycles on the degree of conversion and microhardness of four resin composites.

OBJECTIVE: This study evaluated the effect of repeatedly heating and cooling four resin-based composites (RBCs) for up to six cycles. MATERIALS AND METHODS: Four commercial RBCs were heated to 68°C and cooled to room temperature for up to six cycles before photocuring at 30°C. Specimens spent a total of 0, 30, 60, 90, 120, 150 min, or 7 days at 68°C. The degree of conversion (DC) was measured at the bottom of the specimens immediately after photocuring. The Vickers microhardness was measured at the top and bottom of the RBC surfaces 24 h after photocuring. The data were analyzed using one-way analysis of variance, Dunnett's or Bonferroni post-hoc tests, and Spearman correlation analysis (α = 0.05). RESULTS: For two brands of RBC, the DC decreased at various time points; however, these decreases were small, and there was no correlation (negative or positive) between the number of heating cycles and the DC for any of the RBCs. Repeated heated and cooling resulted in small changes in the hardness (compared to the control) in both directions (Dunnett; p < 0.05). Two of the RBCs showed a significant, positive correlation between the number of heating cycles and their hardness at the bottom surface. CONCLUSION: Repeated heating, cooling, and then reheating the RBCs for up to 1 week had little overall effect on their DC and microhardness values. The 2 mm thick specimens of all four RBCs achieved a bottom: top hardness ratio exceeding 0.8 after a 20 s exposure to light from a commercial LED curing light CLINICAL SIGNIFICANCE: Six repeated dry heating and cooling cycles of up to 1 week in duration had little effect on the DC and the microhardness of four commercial resin-based composites.

Gloss Retention on Enamel and Resin Composite Surfaces After Brushing Teeth with Commercial and Modified Dentifrices.

OBJECTIVES: We examined the surface gloss and roughness of a dental composite and human enamel after brushing with a new bioactive glass (BCF201) additive designed to treat dentine hypersensitivity. METHODS: We prepared 2 cohorts of samples: a resin-based composite (RBC) and human enamel. Each cohort received 20 000 brushing cycles with Colgate Optic White Enamel (Colgate Optic), Sensodyne Whitening Repair and Protect (Sensodyne), Colgate Enamel Health Sensitivity Relief (Colgate-EN) with and without BCF201 added or Germiphene Gel 7 HT (Gel 7) with and without BCF201 added. The average gloss and roughness of the enamel and RBC surfaces were measured before brushing and after 20 000 back-and-forth brushing cycles. A linear regression function was applied to the gloss results, and the data were analyzed using ANOVA and a Tukey post-hoc test (α = 0.05). RESULTS: After 20 000 brushing cycles, the control (Gel 7) had no significant effect on the gloss or roughness of the RBC. However, the choice of dentifrice had a significant effect on both gloss and roughness (p < 0.001). With respect to RBC, after brushing, surface roughness was ranked from smoothest to roughest: Gel 7 = Gel 7 plus BCF201 > Colgate-EN plus BCF201 = Colgate Optic = Colgate-EN > Sensodyne. With respect to enamel, the smoothest to the roughest surfaces after brushing were: Gel 7 plus BCF201 = Sensodyne = Colgate-EN plus BCF201 > Gel 7 = Colgate Optic = Colgate-EN. CONCLUSION: The bioactive glass additive had no adverse effect on the surface roughness or gloss of human enamel or RBC. SIGNIFICANCE: The addition of BCF201 appears to have a polishing effect on RBC and enamel and reduced the abrasive effects of Colgate-EN on RBC and enamel.

2021 Trends in Restorative Dentistry: Composites, Curing Lights, and Matrix Bands.

Composite materials remain a mainstay as a restorative option in dentistry. This article reviews some of the most recent updates and projected future trends in dental composites, along with curing lights and matrix systems.

Influence of beam homogenization on bond strength of adhesives to dentin.

OBJECTIVE: This study evaluated the effect of beam homogeneity on the microtensile bond strength (µTBS) of two adhesive resins to dentin. METHODS: One polywave light-emitting-diode (LED) LCU (Bluephase Style, Ivoclar Vivadent AG) was used with two different light guides: a regular tip (RT, 1010 mW/cm2 emittance) and a homogenizer tip (HT, 946 mW/cm2 emittance). The emission spectra and beam profiles were measured from both light guides. Extracted third molars were prepared for µTBS evaluation using two adhesive systems: Excite F (EXF) and Adhese Universal (ADU). Bond strength was calculated for each specimen (n = 10) at locations that correlated with the output of the two LED chips emitting blue (455 nm) and the one chip that emitted violet light (409 nm) after 24-hs and after one-year water-storage. The µTBS was analyzed using a four-way analysis of variance (factors: adhesive system, light guide, LED wavelength, and storage time) and post-hoc Tukey test (α = 0.05). RESULTS: EXF always delivered a higher µTBS than ADU (p < 0.0001), with the µTBS of ADU being about 20% lower than EXF. The light guide (p = 0.0259) and storage time (p = 0.0009) significantly influenced the µTBS. The LED wavelengths had no influence on the µTBS (p > 0.05). SIGNIFICANCE: Homogeneity of the emitted light beam was associated with higher 24-h µTBS to dentin, regardless of the adhesive tested. Also, differences in the composition of adhesives can affect their compatibility with restorative composites and their ability to maintain bonding over one year.

A standardized method to determine the effect of polymerization shrinkage on the cusp deflection and shrinkage induced built-in stress of class II tooth models.

OBJECTIVES: Using standardized aluminum tooth models, this study: 1) measured the deflection along the cusp wall of models with a Class II cavity restored using either bulk filling or horizontal incremental filling techniques, and 2) calculated the cusp deflection and built-in stress within the restored tooth models for both filling techniques using a finite element (FE) model. METHODS: Standardized tooth models with Class II cavities 4 mm deep, 4 mm high and 6 mm wide were machined out of aluminum. The models were restored using Filtek Posterior Restorative A2 shade resin-based composite (RBC). Both bulk filling and horizontal incremental filling techniques were used to restore the tooth models. After photocuring for 20 s from a single peak wavelength light-curing unit (LCU) with a radiant exitance of 1.25 W/cm2, the deflection of the cusp wall surface was measured using a profilometer. A FE model was used to predict the cuspal deflection and built-in stress of the restored tooth models. RESULTS: The elastic modulus within the FE model was parameterized using cusp deflection data obtained on a bulk filled tooth model. An agreement was found between the measured and predicted cusp deflection only when considering partial stress relaxation within the first incremental layer for the two-layer incremental filling technique. The calculated built-in stress was significantly reduced within the RBC and along the cavity walls when the cavity was filled incrementally in a horizontal direction compared to when it was bulk filled, resulting in a significantly smaller cusp deflection. SIGNIFICANCE: The FE model was first calibrated and then validated using measured cusp deflection data. Partial stress relaxation may play a significant role in the horizontal incremental filling technique. The model can be used to predict where the built-in stress within the tooth model occurs. This study explains why for a given RBC, a horizontal incremental filling and curing technique results in lower built-in stress within the restored tooth and lower cusp deflection compared to the bulk curing technique.

The light-curing unit: An essential piece of dental equipment.

INTRODUCTION: This article describes the features that should be considered when describing, purchasing and using a light-curing unit (LCU). METHODS: The International System of Units (S.I.) terms of radiant power or radiant flux (mW), spectral radiant power (mW/nm), radiant exitance or tip irradiance (mW/cm2 ), and the irradiance received at the surface (also in mW/cm2 ) are used to describe the output from LCU. The concept of using an irradiance beam profile to map the radiant exposure (J/cm2 ) from the LCU is introduced. RESULTS: Even small changes in the active tip diameter of the LCU will have a large effect on the radiant exitance. The emission spectra and the effects of distance on the irradiance delivered are not the same from all LCUs. The beam profile images show that using a single averaged irradiance value to describe the LCU can be very misleading. Some LCUs have 'hot spots' of high radiant exitance that far exceed the current ISO 10650 standard. Such inhomogeneity may cure the resin unevenly and may also be dangerous to soft tissues. Recommendations are made that will help the dentist when purchasing and then safely using the LCU. CONCLUSIONS: Dental manufacturers should report the radiant power from their LCU, the spectral radiant power, information about the compatibility of the emission spectrum from the LCU with the photoinitiators used, the active optical tip diameter, the radiant exitance, the effect of distance from the tip on the irradiance delivered, and the irradiance beam profile from the LCU.

Shedding light on a potential hazard: Dental light-curing units.

BACKGROUND: Dental light-curing units (LCUs) are powerful sources of blue light that can cause soft-tissue burns and ocular damage. Although most ophthalmic research on the hazards of blue light pertains to low levels from personal electronic devices, computer monitors, and light-emitting diode light sources, the amount of blue light emitted from dental LCUs is much greater and may pose a "blue light hazard." METHODS: The authors explain the potential risks of using dental LCUs, identify the agencies that provide guidelines designed to protect all workers from excessive exposure to blue light, discuss the selection of appropriate eye protection, and provide clinical tips to ensure eye safety when using LCUs. RESULTS: While current literature and regulatory standards regarding the safety of blue light is primarily based on animal studies, sufficient evidence exists to suggest that appropriate precautions should be taken when using dental curing lights. The authors found it difficult to find on the U.S. Food and Drug Administration database which curing lights had been cleared for use in the United States or Europe and could find no database that listed which brands of eyewear designed to protect against the blue light has been cleared for use. The authors conclude that more research is needed on the cumulative exposure to blue light in humans. Manufacturers of curing lights, government and regulatory agencies, employers, and dental personnel should collaborate to determine ocular risks from blue light exist in the dental setting, and recommend appropriate eye protection. Guidance on selection and proper use of eye protection should be readily accessible. CONCLUSIONS AND PRACTICAL IMPLICATIONS: The Centers for Disease Control and Prevention Guidelines for Infection Control in the Dental Health-Care Setting-2003 and the Occupational Safety and Health Administration Bloodborne Pathogen Standard do not include safety recommendations or regulations that are directly related to blue light exposure. However, there are additional Occupational Safety and Health Administration regulations that require employers to protect their employees from potentially injurious light radiation. Unfortunately, it is not readily evident that these regulations apply to the excessive exposure to blue light. Consequently employers and dental personnel may be unaware that these Occupational Safety and Health Administration regulations exist.

Disinfection of dental loupes: A pilot study.

BACKGROUND: Magnification loupes are not disposable and must be cleaned and disinfected between each patient. In this pilot study, the authors determined the efficacy of infection-control procedures used by dental students between patients. METHODS: Visibly clean loupes owned and used by 25 dental students were swabbed for bacteria using a standard microbiology method at baseline and then cleaned with surface disinfectant before they were returned. The students then used and disinfected their loupes for 5 days as they treated patients, after which time the loupes were retrieved and swabbed again. After the samples had been cultured, the numbers of aerobic and anaerobic colony-forming units (CFUs) were enumerated. The authors report the contamination levels at baseline, after cleaning, and after being used for 5 days. RESULTS: At baseline, the number of CFUs ranged from 0 through more than 100. When used according to the manufacturers' instructions, the disinfectant reduced the count to no more than 2 CFUs. After the loupes were used for 5 days, 20% of loupes were highly contaminated (> 100 CFUs), 20% were moderately contaminated (20-100 CFUs), and 60% had less than 20 CFUs. Students who performed a restoration on day 5 were 12 times more likely (P < .01) to have loupes contaminated with aerobic bacteria than those who had not performed a restoration on day 5. CONCLUSIONS: The recommended prophylaxis and disinfection protocol worked well when used correctly, but it was likely that the protocol often was not followed properly or consistently. PRACTICAL IMPLICATIONS: Visibly clean loupes may be a source of cross-contamination.