Distance and protective barrier effects on the composite resin degree of conversion

Double bond conversion of preheated composite resin beneath lithium disilicate standardized occlusal veneers

The purpose of the study was the investigation of the polymerization of a preheated composite resin beneath lithium disilicate. First, lithium disilicate discs in two shades (HT A2 and HT A4) and three different thicknesses (2, 4, and 6 mm) were bonded on dentine with preheated composite resin that was photo-polymerized for 20 s. The composite resin microhardness, the double bond conversion (DC) and their correlation were estimated. Second, standardized occlusal veneers of two shades and two different thicknesses (4 and 6 mm) were bonded with preheated composite resin and photopolymerized for 60 or 270 s. A microhardness line profiling was performed on the cross-section of each specimen and the correspondence DC was calculated. Shade and thickness of lithium disilicate were found to have a significant impact on micro-hardness and DC of the composite resin. Beneath standardized occlusal veneers DC can reach clinically acceptable level if photopolymerization duration is extended properly.

An Evaluation of the Efficacy of LED Light Curing Units in Primary and Secondary Dental Settings in the United Kingdom

OBJECTIVE

This study aimed to evaluate the irradiance and the quality of LED light curing units (LCUs) in primary and secondary clinics in the UK and to assess the effect of damage, contamination, use of protective sleeves, and distance of light tips to target on the irradiance and performance of LCUs.

METHODS

The irradiance levels (mW/cm2) of 26 LED LCUs from general dental practices and 207 LED LCUs from two dental hospitals were measured using a digital radiometer (Blue Phase II, Ivoclar, Vivadent, Amherst, NY). Ten LED light guide tips (Satelec Mini, Acteon, Merignac, France) were selected to evaluate the effect of chipping, contamination (tip debris), and use of protective sleeves and tips to sensor distance on irradiance (mW/cm2) using a MARC Resin Calibrator (Blue Light Analytics, Halifax, Canada). Homogeneity of the light output was evaluated using a laser beam profiler (SP620; Ophir-Spiricon, North Longan, UT, USA). Statistical analysis was conducted using a one-way analysis of variance (ANOVA) with post hoc Tukey test (α=0.05) and linear regression with stepwise correlation tests.

RESULTS

Thirty-three percent of the LCUs delivered irradiance output less than 500 mW/cm2. The condition of the light curing tips was poor, with 16% contaminated with resin debris, 26% damaged, and 10% both contaminated and damaged. The irradiance output was significantly reduced in contaminated (62%) and chipped (50%) light curing tips and when using protective sleeves (24%) (p<0.05). Irradiance was also reduced when increasing the distance with 25% and 34% reduction at 7 mm and 10 mm, respectively (p<0.05).

CONCLUSION

There remains a lack of awareness of the need for regular monitoring and maintenance of dental LCUs. Damaged and contaminated light curing tips, use of protective sleeves, and increasing the distance from the restoration significantly reduced the irradiance output and the performance of the LCUs.

Effect of infection control barriers on the light output from a multi-peak light curing unit

OBJECTIVES

Curing lights cannot be sterilized and should be covered with an infection control barrier. This study evaluated the effect of barriers when applied correctly and incorrectly on the radiant power (mW), irradiance (mW/cm2), emission spectrum (mW/nm), and beam profile from a multi-peak light-curing unit (LCU).

METHODS

Five plastic barriers (VALO Grand, Ultradent; TIDIShield, TIDI Products; Disposa-Shield, Dentsply Sirona; Cure Sleeve, Kerr; Stretch and Seal, Betty Crocker) and one latex-based barrier (Curelastic, Steri-Shield) were tested. The radiant power (mW) and emission spectrum (mW/nm) from one multi-peak LCU (VALO Grand, Ultradent) was measured using an integrating sphere. LCU tip internal diameter (mm) was measured, then the tip area and irradiance (mW/cm2) were calculated. The beam profiles were measured using a laser beam profiler.

RESULTS

When applied correctly, the plastic barriers reduced the radiant power output by 5-8%, and the latex-based barrier by 16%. When the plastic seam or barrier opaque face was positioned over the LCU tip, the power output was reduced by 8-11%. When the plastic barriers were wrinkled, the power output was significantly reduced by 14-26%. The wrinkled latex-based barrier reduced by 28%, and further reduced the violet light. The beam profiles illustrated the importance of correctly barrier use without wrinkles over the tip.

CONCLUSIONS

Plastic barriers applied correctly reduced the light output (mW) by 5-8%. The barriers applied incorrectly significantly reduced the light output by 14-26%. The latex-based barrier wrinkled also reduced the amount of violet light.

CLINICAL RELEVANCE

Infection control curing light barriers should be used to prevent cross-infection between patients. However, they must be applied correctly to reduce their negative effects on the light output.

Influence of biosafety materials of the laser output power

Biosafety materials used in the correct handling of low power laser equipment may interfere on the power delivered at the target tissue and, possibly, on the effects on biological tissues. The aim of this study was to evaluate the interference of the use of polyvinyl chloride (PVC) and polyethylene (PEAD) protection materials on the output power of low power lasers. Two low power diode laser devices with different wavelengths (red and infrared) were used. For each wavelength, two protection materials and two evaluation times (before and after protection) were considered. The output power (mW) was measured with the tip positioned in close contact with the power meter receiver. Parametric statistical test, two-way ANOVA for repeated measures (protection material and time), was performed considering the level of significance of 5%. In respect to "time", all groups had the output power reduced after placing the protective material (p < 0.05). Comparing the protection materials, the PEAD showed a greater reduction in output power than the PVC for both red and infrared wavelengths. It was concluded that, among the biosafety materials tested, PVC is the most suitable for the protection of the tip of the low power lasers.

Effect of Contamination, Damage and Barriers on the Light Output of Light-Curing Units

Background:

Light-curing is a crucial step during the application of composite resin restorations. The clinical success of composite depends on the Light-Curing Units (LCU) to deliver adequate light energy to polymerize the resin. However, light-curing usually does not receive the proper awareness it deserves.

Objective:

This study aims to evaluate the effect of contamination and debris of the LCU’s tip on its light output. Determine the effect of damage to the LCU’s tip such as chipping, dents and scratches. Additionally, it evaluates the effect of plastic barrier sleeves.

Methods:

Sixty LED LCUs were tested using MARC™ Resin Calibrator (BlueLight Analytic Inc., Halifax, Canada) to measure their irradiance and energy before and after cleaning their tips. They were also tested with and without a clear plastic barrier. Additionally, four damaged LCUs received new tips and were tested again. Kruskal-Wallis H and One-Way ANOVA tests were used for statistical analysis.

Results:

Cleaning the LCUs’ tips showed significant improvement, an average increase of 8.2%. However, some units increased by up to 47% in irradiance and energy values. Replacing the damaged tip with a new one significantly improved the output of the LCUs, increasing light energy by up to 73%. The barrier used in this study caused 7% reduction in the energy delivered by the LCUs. The statistical analysis showed that cleaning the LCUs and replacing their damaged tips resulted in a significant increase in energy (p<0.05).

Conclusion:

Unclean or damaged LCUs’ tips can drastically reduce the light output of the LCUs, reducing the quality of the composite restorations. Clinicians are strongly recommended to regularly monitor, clean and maintain their curing lights.

Does translucency influence cure efficiency and color stability of resin-based composites?

OBJECTIVE

To determine if material's translucency influences the cure efficiency and color stability of resin-based composites (RBCs).

METHODS

Four commercially-available RBCs indicated for aesthetic restorations were selected in different translucent/opaque shades: IPS Empress Direct (IED) A3 Dentin, A3 Enamel, Trans 20, and Trans 30; Filtek Z350 XT (FZX) A3D, A3B, A3E, and CT; Estelite ∑ Quick (EQ) OA3, A3, and CE; and Opallis (OP) DA3, EA3, and T-Neutral. Color was obtained in the L'C'h' system at three distinct periods: 24h after photoactivation (baseline), after 30d of water storage (WS), and after 30d of coffee storage (CS). The translucency parameter (TP) of each RBC was calculated at baseline. The degree of CC conversion (DC) was obtained by Fourier-transform infrared spectroscopy at 0.05mm (top) and 2mm (bottom) surfaces; the cure efficiency considered the bottom/top ratio. The CIEDE2000 color difference (ΔE₀₀) was calculated considering the WS-baseline and CS-baseline values. Data were submitted to two-way ANOVA and Tukey's post-hoc test (α=0.05). Pearson's tests were used to analyze the correlations between TP and DC, and between TP and ΔE₀₀.

RESULTS

For all RBCs, cure efficiency was not affected by materials' translucency. A positive, significant correlation was observed between TP and DC at the bottom surface for FZX only. For all RBCs, the higher the TP, the higher the ΔE₀₀. The ΔE₀₀ was higher after CS than after WS, except for EQ A3. Positive correlation between TP and ΔE₀₀ were observed for all materials.

CONCLUSION

The translucency did not influence the cure efficiency but affected the color stability for all RBCs.

CLINICAL SIGNIFICANCE

High-translucent RBCs presented lower color stability and should be used carefully.

Light Curing in Dentistry

The ability to light cure resins 'on demand' in the mouth has revolutionized dentistry. However, there is a widespread lack of understanding of what is required for successful light curing in the mouth. Most instructions simply tell the user to 'light cure for xx seconds' without describing any of the nuances of how to successfully light cure a resin. This article provides a brief description of light curing. At the end, some recommendations are made to help when purchasing a curing light and how to improve the use of the curing light.

Light curing in dentistry and clinical implications: a literature review

Contemporary dentistry literally cannot be performed without use of resin-based restorative materials. With the success of bonding resin materials to tooth structures, an even wider scope of clinical applications has arisen for these lines of products. Understanding of the basic events occurring in any dental polymerization mechanism, regardless of the mode of activating the process, will allow clinicians to both better appreciate the tremendous improvements that have been made over the years, and will also provide valuable information on differences among strategies manufacturers use to optimize product performance, as well as factors under the control of the clinician, whereby they can influence the long-term outcome of their restorative procedures.

Evaluation of effect of different disposable infection control barriers on light intensity of light-curing unit and microhardness of composite - An in vitro study

Aims:

This study evaluated effect of infection control barriers on light intensity (LI) of light-curing unit (LCU) and microhardness of composite.

Materials and Methods:

Four different disposable barriers (n = 30) were tested against the control. LI for each barrier was measured with Lux meter. One hundred and fifty Teflon molds were equally divided into five groups of thirty each. Composite was filled in bulk in these molds and cured without and with barrier. Microhardness was evaluated on top and bottom surface of composite specimen with microhardness testing machine and hardness ratio (HR) was derived.

Statistical Analysis Used:

One-way analysis of variance, Tukey's honestly significant difference test, and paired t-test using SPSS version 18 software.

Results:

All barriers had significantly reduced the baseline LI of LCU (P < 0.0001), but only Cure Elastic Steri-Shield and latex cut glove pieces (LCGP) significantly reduced the microhardness of the composite (P < 0.05). However, HR determined inadequate curing only with LCGP.

Conclusions:

Although entire tested barrier significantly reduced the LI; none, except LCGP markedly affected the degree of cure of the composite.