Initial fracture resistance and curing temperature rise of ten contemporary resin-based composites with increasing radiant exposure

Bulk-fill composite in challenging cavities: conversion rate, solubility, and water absorption analysis

In a deep, curved cavity, polymerization of a bulk fill composite can be challenging. The aim of this study was to investigate the solubility, water absorption, and conversion rate of bulk-fill composite samples prepared using molds with various slope angles. Bulk-fill composite resin (Filtek One Bulk Fill) was placed into cylindrical Teflon molds with a depth of 4 mm, angled at varying degrees (90°, 75°, 60°, 45°). Two different LED light-curing units (VALO Cordless, iLed Curing Light) were used to cure the samples. Polymerizations were performed at three different distances (0 mm, 2 mm, and 4 mm). Five samples per group were used, resulting in a total of 24 groups. The Fourier Transform Infrared Spectrometer was utilized to evaluate the conversion levels of the samples. Water sorption and solubility values were determined by storing the composites in distilled water at 37 °C for 21 days. The VALO light-curing unit applied closest to samples inserted in a 90° angulation mold had the highest mean degree of conversion (41.55%), while iLED light-curing unit group that applied from 4 mm to the samples inserted in a 45° angulation mold had the lowest mean conversion (8.97%). The angle of the cavity and the distance at which the light-curing unit is applied significantly affected bulk-fill composite resin conversion. In addition, the choice of light-curing unit impacted the conversion levels. However, with the tested conditions, the water sorption and solubility values of polymerized composite resin samples remain unaffected by these factors.

Thermal Sensing of Photo-Activated Dental Resin Composites Using Infrared Thermography

OBJECTIVE

The goal of this study was to compare the pulp temperature increase during light curing of different composite thicknesses in deep class I cavities using two thermal sensing tools.

METHODOLOGY

Round occlusal class I cavities with a remaining dentin thickness (RDT) of 1 mm from the cavity floor were performed on 15 extracted sound molars. Samples were divided into three groups (n = 5). In group A, cavities were restored using the Filtek Z350 XT conventional composite through the incremental filling technique, whereas group B cavities were restored using the Filtek Bulk-Fill flowable composite through the bulk-fill technique. Specimens of the Filtek Bulk-Fill flowable composite using the incremental filling technique were used to restore cavities in group C. An infrared thermal camera (IRT; Flir, Wilsonville, OR, USA) and K-type thermocouple (Perfect Prime TC0520, New York, NY, USA) were used to measure the heat generated during composite photo-polymerization.

RESULTS

There were no significant differences within the same group using either the thermocouple or IRT (p > 0.05). One-way ANOVA showed no significant differences between groups A and C (p > 0.05), whereas group B was significantly different from groups A and C with each sensing tool (p < 0.05).

CONCLUSION

IRT and thermocouple heat readings were comparable. Based on the current findings, the bulk-fill technique resulted in the lowest heat generation among the groups. Therefore, increasing the light-curing time and the number of composite increments was directly correlated with increases in intra-pulpal temperature.

Effect of Ceramic and Dentin Thicknesses and Type of Resin-Based Luting Agents on Intrapulpal Temperature Changes during Luting of Ceramic Inlays

The adhesive cementation of ceramic inlays may increase pulpal temperature (PT) and induce pulpal damage due to heat generated by the curing unit and the exothermic reaction of the luting agent (LA). The aim was to measure the PT rise during ceramic inlay cementation by testing different combinations of dentin and ceramic thicknesses and LAs. The PT changes were detected using a thermocouple sensor positioned in the pulp chamber of a mandibular molar. Gradual occlusal reduction obtained dentin thicknesses of 2.5, 2.0, 1.5, and 1.0 mm. Light-cured (LC) and dual-cured (DC) adhesive cements and preheated restorative resin-based composite (RBC) were applied to luting of 2.0, 2.5, 3.0, and 3.5 mm lithium disilicate ceramic blocks. Differential scanning calorimetry was used to compare the thermal conductivity of dentin and ceramic slices. Although ceramic reduced heat delivered by the curing unit, the exothermic reaction of the LAs significantly increased it in each investigated combination (5.4–7.9 °C). Temperature changes were predominantly influenced by dentin thickness followed by LA and ceramic thickness. Thermal conductivity of dentin was 24% lower than that of ceramic, and its thermal capacity was 86% higher. Regardless of the ceramic thickness, adhesive inlay cementation can significantly increase the PT, especially when the remaining dentin thickness is <2 mm.

Intrapulpal temperature changes during the cementation of ceramic veneers

Adhesive cementation of ceramic veneers may increase pulpal temperature (PT) due to the combined effect of heat generated by the curing unit and the exothermic reaction of the luting agent (LA). PT increase may induce pulpal damage. The aim was to determine the PT rise during the luting of ceramic veneers (CV) of different thicknesses with light- or dual-curing (LC, DC) adhesive cements as well as pre-heated restorative resin-based composites (PH-RBC). For this a thermocouple sensor was positioned in the pulp chamber of a prepared maxillary central incisor. LC, DC adhesive cements and PH-RBCs heated to 55 °C were used for the luting of CVs of 0.3, 0.5, 0.7, and 1.0 mm thicknesses. The exothermic reaction of LAs added significantly to the thermal effect of the curing unit. PT change ranged between 8.12 and 14.4 °C with the investigated combinations of LAs and ceramic thicknesses (p ≤ 0.01). The increase was inversely proportional to the increasing CV thicknesses. The highest rise (p ≤ 0.01) was seen with the polymerization of PH-RBCs. Temperature changes were predominantly influenced by the composition of the LA, which was followed by CV thickness.

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.

Hands-on training based on quantifying radiant exposure improves how dental students cure composites: Skill retention at 2-year follow-up

INTRODUCTION

The durability and longevity of composite restoration are much dependent on the accurate delivery of the energy required to polymerise the material. This study aimed to investigate the extent to which undergraduate dental students acquire and retain light-curing skills following hands-on training.

MATERIALS AND METHODS

Hands-on training comprises faculty tutoring for critical aspects of the light-curing procedure, such as distance and angulation of the light-curing tip. Assessments of the students' ability to deliver a specified radiant exposure to class III and I simulated RBCs using a dental simulator (MARC-PS^® ) at three different time points after the training. Data were analysed using repeated measure ANOVA.

RESULTS

Immediately after the training, students' performance on curing was improved (p < .05). Overall, the radiant exposure increased after training, but the students lost some of the benefits with time. For curing in the anterior section (anterior sensor-class III), the mean radiant exposure values increased by approximately 20% after the training. After 2 years, the values were 15% greater than baseline values. For curing in the posterior section (posterior sensor-class I), the mean radiant exposure values increased by approximately 150% after the training. A significant decrease (p < .05) was observed; however, the radiant exposure values were still 82% greater than the baseline after 2 years.

CONCLUSION

A hands-on training dedicated to light-curing procedures facilitated acquisition and retention up to a 2-year follow-up of skill on how light cure composite inside the mouth. The training was more relevant for curing in posterior areas, where orientation can significantly impact light-curing. A hands-on training where the radiant exposure can be measure gave objective measurement metrics to guide the curing performance. This approach is an effective means of teaching practical skills to dental students.

The Ability of Dental Practitioners to Light-Cure Simulated Restorations

CLINICAL RELEVANCE

Using a patient simulator, dental professionals were tested to determine their ability to light-polymerize simulated restorations in their dental practice. After receiving specific instructions and training using the simulator, their ability to deliver sufficient light to polymerize restorations was significantly and substantially improved.

SUMMARY

Objectives: To determine the ability of dental professionals to deliver a radiant exposure of at least six J/cm2 in 10 seconds to simulated restorations.Methods and Materials: The study initially examined 113 light-emitting-diode (LED) light polymerization units (LPUs) used in dental offices to determine if they could deliver at least 6 J/cm2 radiant exposure (RE) in 10s. This assessment was completed by using a laboratory-grade light measuring device (checkMARC, BlueLight Analytics, Halifax, NS, Canada). The participating dental professionals whose LPUs could deliver 6 J/cm2 then used their own LPU to light-cure simulated anterior and posterior restorations in the MARC Patient Simulator (BlueLight Analytics). They then received specific instructions and were retested using the same LPUs. Data were statistically analyzed with a series of one-way analysis of variance (ANOVA), two-way ANOVA, paired-samples t-tests, Fisher post hoc multiple comparison tests, and McNemar tests with a preset alpha of 0.05 (SPSS Inc).Results: Ten (8.8%) LPUs could not deliver the required RE to the checkMARC in 10s and were eliminated from the study. For the anterior restoration, most dental practitioners (87.3%) could deliver at least 6 J/cm2 before instructions. After receiving additional light-curing instructions, only two (1.9%) participants were unable to deliver 6 J/cm2 to the anterior location. At the posterior location, only 55.3% (57) participants could deliver at least 6 J/cm2 before the instructions. After receiving these instructions, an additional 32 participants delivered at least 6 J/cm2. Overall, after receiving instructions on how to use the LPU correctly, the participants improved the amount of RE they delivered to anterior and posterior restorations by 22.5% and 30%, respectively.Conclusion: This study revealed that at the baseline, 44.7% of participating dental professionals failed to deliver 6 J/cm2 in 10s to the posterior simulated restoration when using their own LPU.

Utilizing Light Cure Units: A Concise Narrative Review

The use of photo-curable resin composite restorations is an essential treatment modality in modern dental practice. The success and longevity of these restorations depend on achieving predictable and effective polymerization. Understanding the dynamics of the polymerization and the effect of light cure units (LCUs) on this process is paramount. The goal of this concise narrative review is to provide a simplified presentation of basic principles of composite chemistry, polymerization reactions, and photo-curing with relevant terminologies. Clinical guidelines for choosing and maintaining LCUs, as well as safety precautions and factors under the control of the clinician are listed. Finally, clinical recommendations of LCUs’ usage and monitoring are included to aid practitioners in achieving predictable polymerization during the placement of direct resin composite restorations.

Degree of conversion and in vitro temperature rise of pulp chamber during polymerization of flowable and sculptable conventional, bulk-fill and short-fibre reinforced resin composites

OBJECTIVE

Determine the degree of conversion (DC) and in vitro pulpal temperature (PT) rise of low-viscosity (LV) and high-viscosity (HV) conventional resin-based composites (RBC), bulk-fill and short-fibre reinforced composites (SFRC).

METHODS

The occlusal surface of a mandibular molar was removed to obtain dentine thickness of 2 mm above the roof of the pulp chamber. LV and HV conventional (2 mm), bulk-fill RBCs (2-4 mm) and SFRCs (2-4 mm) were applied in a mold (6 mm inner diameter) placed on the occlusal surface. PT changes during the photo-polymerization were recorded with a thermocouple positioned in the pulp chamber. The DC at the top and bottom of the samples was measured with micro-Raman spectroscopy. ANOVA and Tukey's post-hoc test, multivariate analysis and partial eta-squared statistics were used to analyze the data (p < 0.05).

RESULTS

The PT changes ranged between 5.5-11.2 °C. All LV and 4 mm RBCs exhibited higher temperature changes. Higher DC were measured at the top (63-76%) of the samples as compared to the bottom (52-72.6%) in the 2 mm HV conventional and bulk-fill RBCs and in each 4 mm LV and HV materials. The SFRCs showed higher temperature changes and DC% as compared to the other investigated RBCs. The temperature and DC were influenced by the composition of the material followed by the thickness.

SIGNIFICANCE

Exothermic temperature rise and DC are mainly material dependent. Higher DC values are associated with a significant increase in PT. LV RBCs, 4 mm bulk-fills and SFRCs exhibited higher PTs. Bulk-fills and SFRCs applied in 4 mm showed lower DCs at the bottom.

Estimation of the tolerance threshold for the irradiance of modern LED curing units when simulating clinically relevant polymerization conditions

The study aims to characterize various LED light curing units (LED-LCU) in order to determine the tolerance threshold for varying the polymerization conditions. Two violet-blue and two blue LED-LCUs were analyzed by using a laboratory-grade spectrophotometer system. Fifty-five curing conditions were simulated in each LED-LCU by varying the position (centered and with an offset of 3-mm to the left, right, lower and upper direction) and the exposure distance (0 mm to 10 mm in 1-mm steps). Irradiance decreased with increasing exposure distance, while the effect of the LCU position was significant and LCU-specific. Only one LED-LCU enables the irradiance threshold of 1,000 mW/cm² to be achieved in all positions up to an exposure distance of 4 mm. LCUs with a more homogeneous light beam profile more easily tolerate deviations from the ideal curing conditions. The study enables dentists to identify the limits of modern LED-LCUs and to estimate potential deviations from ideal curing conditions for clinically relevant situations.

Correlation of the mechanical and biological response in light-cured RBCs to receiving a range of radiant exposures: Effect of violet light

OBJECTIVE

This study correlates the mechanical and biological response of commercially available resin-based composites (RBCs) to clinically relevant light-curing conditions.

METHODS

Two RBCs (Venus and Venus Pearl; Kulzer) that use different monomer and photo-initiator systems, but have a similar filler volume and shade, were exposed to either just blue light, or violet and blue light from two different LCUs (Translux Wave and Translux 2Wave; Kulzer). Distance and exposure times were adjusted so that both LCUs delivered 5 similar levels of radiant exposures (RE) between 1.5 J/cm²-25 J/cm² in the blue wavelength range. Thus, the violet light was additional light. The top and bottom of 2-mm thick specimens were subjected to a depth-sensing indentation test (Martens hardness/HM, Vickers hardness/HV, indentation modulus/Y_HU, mechanical work/W_total, plastic deformation work/W_plas, creep/Cr). The viability of human gingival fibroblasts was assessed after three days of exposure to RBC eluates. One and multiple-way analysis of variance (ANOVA), the Tukey honestly significant difference (HSD) post-hoc tests (α = 0.05), t-test and a Spearman correlation analysis were used.

RESULTS

As the RE increased, the mechanical properties increased at a greater rate at the top compared to the bottom of the RBCs. Values measured at the bottom of 2-mm increments approached the values measured at the top only when RE > 25 J/cm² of blue light was delivered. Toxicity decreased with RE and elution cycles and was lower for Venus Pearl. Within one RE level, addition of violet light resulted in significantly improved properties (in 131 out of 150 comparisons, p < 0.05). This effect was stronger for Venus Pearl. There was a good correlation between mechanical and biological parameters. This correlation decreased as the number of eluates increased.

CLINICAL SIGNIFICANCE

The mechanical and biological response to variation in RE is interrelated. The addition of violet light has a positive effect, particularly at low RE.

Spatial Distribution of the Micro-Mechanical Properties in High-Translucent CAD/CAM Resin-Composite Blocks

Industrially cured, high-translucent computer-aided design/computer-aided manufacturing (CAD/CAM) resin-based composites (RBC) are the most recently launched dental restoratives. Clinical treatments and laboratory tests are based on a homogeneous distribution of properties within CAD/CAM blocks to obtain constant and reproducible results. The study therefore aims to determine the spatial distribution of various micro-mechanical parameters (Vickers hardness, Martens hardness, indentation modulus, creep, elastic and total indentation work) in five representative CAD/CAM RBCs. The properties of the tooth structure were evaluated under similar conditions. Filler size and shape were analyzed by scanning electron microscopy. A multivariate analysis (general linear model) identified a very strong influence of the material on all measured properties (p < 0.001; partial eta squared η_P² > 0.943), whereby the most sensitive parameters when identifying differences within regions were the indentation modulus and the elastic indentation work. CAD/CAM RBC blocks show gradually varying properties that can increase or decrease from central to peripheral areas regardless of the chemical composition of the materials or the inorganic filler fraction. The degree of variation in the measured properties is material-specific and less than 8.7%. Clinical applications and in vitro study designs should consider slight inhomogeneity in CAD/CAM RBC blocks, while the location of the regions with best mechanical performance depends on the material.

Irradiance of Different Curing Modes of Common Light Cure Devices: An In Vitro Study

Aim:

The aim of this study was to test the irradiance values of different curing modes of commonly available light cure devices (LCDs).

Materials and Methods:

An in vitro investigation was carried out to compare the irradiance output of 10 brands of LCDs available in Saudi Arabia measured using a digital radiometer. Values were recorded for three time points when applicable (0, 10, and 20s). This technique was repeated five times for each LCD. Normal, high-intensity, and soft-start modes were evaluated for all brands with the features available. Irradiance values between brands were analyzed using one-way analysis of variance followed by Bonferroni method. Changes in irradiance between different time points were analyzed using one sample t test for normal and high-intensity modes and using paired t test for soft-start mode. All comparisons were carried out at 0.05 significance level.

Results:

The highest values were reported for Ortholux Luminous, Elipar DeepCure-S, Elipar DeepCure, and KaVo mini-LED with values above 1000 mW/cm². All LCDs showed values above 600 mW/cm². Three LCDs had high-intensity mode and only one device had soft-start mode. Changes over the different time points were not statistically significant exept for soft-start mode.

Conclusion:

All tested LCDs had irradiance values sufficient for adequate polymerization of resin composite. Only four of these are capable of curing bulk-fill composites.

Fracture mechanics of circular discs with a V-notch subjected to wedging

OBJECTIVE

A method proposed for determining the fracture toughness (FT) of dental materials involves a 'roller' wedging open a V-notch in a cylindrical specimen. There are a number of problems with the design of this test and its mechanical analysis, and thus with the validity of the results obtained, were it to be used. Firstly, friction is ignored in calculating the horizontal wedging force. Secondly, the test specimen does not make use of a pre-crack at the notch tip. The aim of this study was to evaluate the effects of these factors on the FT calculated.

METHODS

An analytical solution for the mode-I stress intensity factor (K_I) of the compact tension specimen, which bears some similarities, is taken to be applicable. The mechanics of the specimen has been reanalysed, with a finite-element study of the resultant stresses, and compared with the compact-tension test.

RESULTS

The assumed analytical solution can provide accurate estimates for K_I for the V notched specimen. However, the apparent agreement is due to the fortuitous combination of an overestimated horizontal wedging force and an underestimated stress singularity at the crack tip. In any case, ignoring friction will lead to an overestimate of FT.

SIGNIFICANCE

It is concluded that the test as presented is invalid.

Accuracy of Irradiance and Power of Light-Curing Units Measured With Handheld or Laboratory Grade Radiometers

Abstract This study measured and compared exitance irradiance and power of 4 commercial dental light-curing units (LCU) (Elipar S10, Elipar DeepCure-S, Corded VALO and Bluephase Style) using different types of radiometers. The devices used to analyze the LCU were classified as either handheld analog (Henry Schein, Spring, Demetron 100A, Demetron 100B and Demetron 200), handheld digital (Bluephase 1, Bluephase II, Coltolux, CureRite and Hilux), or laboratory instruments (Thermopile and Integrating Sphere). The laboratory instruments and the Bluephase II radiometer were also used to measure the LCU’s power (mW). The LCU’s were activated for 20 s (n=5). Data were analyzed using Kruskal-Wallis and Student-Newman-Keuls multiple comparison test (a=0.05). Among the LCU, the laboratory instruments presented different irradiance values, except for Corded VALO. The Coltolux and Hilux radiometers measured greater irradiance values compared to the laboratory instruments for the four LCUs tested. Within a given LCU, handheld analog units measured lower irradiance values, compared to handheld digital and laboratory instruments, except using the Spring radiometer for the Elipar S10 LCU. None of the handheld radiometers were able to measure similar irradiance values compared to laboratory instruments, except for Elipar S10 when comparing Bluephase 1 and Thermopile. Regarding power measurement, Bluephase II always presented the lowest values compared to the laboratory instruments. These findings suggest that the handheld radiometers utilized by practitioners (analog or digital) exhibit a wide range of irradiance values and may show lower outcomes compared to laboratory based instruments.

Effect of Simulated Pulpal Microcirculation on Temperature When Light Curing Bulk Fill Composites

Objectives:

To evaluate the effect of light curing bulk fill resin composite restorations on the increase in the temperature of the pulp chamber both with and without a simulated pulpal fluid flow.

Methods and Materials:

Forty extracted human molars received a flat occlusal cavity, leaving approximately 2 mm of dentin over the pulp. The teeth were restored using a self-etch adhesive system (Clearfil SE Bond, Kuraray) and two different bulk fill resin composites: a flowable (SDR, Dentsply) and a regular paste (AURA, SDI) bulk fill. The adhesive was light cured for 20 seconds, SDR was light cured for 20 seconds, and AURA was light cured for 40 seconds using the Bluephase G2 (Ivoclar Vivadent) or the VALO Cordless (Ultradent) in the standard output power mode. The degree of conversion (DC) at the top and bottom of the bulk fill resin composite was assessed using Fourier-Transform Infra Red spectroscopy. The temperature in the pulp chamber when light curing the adhesive system and resin composite was measured using a J-type thermocouple both with and without the presence of a simulated microcirculation of 1.0-1.4 mL/min. Data were analyzed using Student t-tests and two-way and three-way analyses of variance (α=0.05 significance level).

Results:

The irradiance delivered by the light-curing units (LCUs) was greatest close to the top sensor of the MARC resin calibrator (BlueLight Analytics) and lowest after passing through the 4.0 mm of resin composite plus 2.0 mm of dentin. In general, the Bluephase G2 delivered a higher irradiance than did the VALO Cordless. The resin composite, LCU, and region all influenced the degree of cure. The simulated pulpal microcirculation significantly reduced the temperature increase. The greatest temperature rise occurred when the adhesive system was light cured. The Bluephase G2 produced a rise of 6°C, and the VALO Cordless produced a lower temperature change (4°C) when light curing the adhesive system for 20 seconds without pulpal microcirculation. Light curing SDR produced the greatest exothermic reaction.

Conclusions:

Using simulated pulpal microcirculation resulted in lower temperature increases. The flowable composite (SDR) allowed more light transmission and had a higher degree of conversion than did the regular paste (AURA). The greatest temperature rise occurred when light curing the adhesive system alone.

Comparison of microleakage between bulk-fill flowable and nanofilled resin-based composites

Aim

The objective was to compare the marginal leakage (silver nitrate uptake) of nanohybrid resin-based composite (RBC) and two bulk-fill flowable RBCs with specific clinical protocols.

Methods

Four experimental groups of RBC were investigated including conventional composite Filtek™ Supreme in 2 mm increment (FS2), Filtek™ Supreme in 4 mm increment (FS4), Filtek™ Supreme Flowable (BFF), and SureFil^® SDR^® flow (SDR). Class II box preparation (4 × 4 × 3 mm) in extracted intact human molars was carried out and restored using the experimental groups, all according to the manufacturers’ recommendations except FS4. Samples were aged by thermocycling (2,000 cycles). Microleakage was calculated by measuring dye penetration in sectioned teeth using a stereomicroscope. Level of significance was set at P < 0.05.

Results

BFF and FS2 exhibited the least dye penetration and microleakage measurement with no significant difference between the two groups, followed by SDR. FS4 showed the highest microleakage with significant difference in comparison with BFF and FS2. Gingival microleakage was found to be significantly higher than occlusal microleakage.

Conclusion

The microleakage of the bulk-fill composites BFF and SDR are comparable with conventional composite FS2; however, it is more predictable to use FS2.

Original and Repair Bulk Fracture Resistance of Particle Filler and Short Fiber-Reinforced Composites

OBJECTIVE

This study aimed to evaluate the original (OR) and repair (RR) fracture resistance of a semi-interpenetrating polymer network (semi-IPN)-based short fiber-reinforced composite compared to dimethacrylate-based composite materials by means of the V-notch test.

METHODS AND MATERIALS

Circular specimens (5×2 mm) with a centrally machined 90° V-shaped notch were prepared. Four bulk fill (Filtek Bulk Fill, Venus Bulk Fill, TetricEvo Ceram Bulk Fill, SDR), three microfilled hybrid (GC-Anterior, GC-Posterior, Z250), one nanofilled (SupremeXTE), and two short fiber-reinforced (Alert, everX Posterior) composites were selected. EverX Posterior was the semi-IPN material. Specimens (n=12/group) were either dry or water stored for 7 and 30 days, respectively, at 37°C and then loaded in two-point load until fracture. One-half of each tested specimen was used for the repair procedure. Repairing surfaces were diamond-bur ground, etched, and treated with silane containing universal adhesive (Scotchbond Universal) before repair.

RESULTS

Three-way analysis of variance revealed a significant statistical difference between the groups ( p<0.05). The fracture resistance of dry-stored groups was greater than that of water-stored groups. The highest OR was observed for dry-stored Alert (23.4 N/mm), which significantly deteriorated in water (17.4 N/mm) ( p<0.05). The highest RR was observed for everX Posterior (20.0 N/mm), which did not deteriorate in water significantly (19.0 N/mm) ( p>0.05). The everX Posterior preserved the specimens' integrity at the final fracture load (ductile fracture), whereas all other materials fractured into two halves at the interface (adhesive failure).

CONCLUSIONS

The only material that provided enhanced repair strength that was close to the original cohesive strength of the material was everX Posterior. The endurance of repaired restorations can be improved by using semi-IPN-based filling material.

Guidelines for the selection, use, and maintenance of LED light-curing units - Part 1

Light curing is a critical step in the restorative process when using light-activated resin-based composites, but it is frequently not given the attention it deserves. The selection of a reliable light curing unit (LCU) that meets the practitioner's needs is an important equipment purchase. Using an inappropriate LCU may seriously compromise the quality of care without the practitioner realising their mistake until years later. The importance of the subject is reflected by the rapidly increasing use of light-cured composites and the decline in the use of amalgam. Many changes have occurred in the equipment and materials available for making light-cured restorations in the last twenty years. This article is part of a two-part series that will describe those changes and recommend guidelines for the selection, use, and maintenance of light emitting diode light-curing units (LED LCUs). This paper (Part 1) discusses terminology, clinical studies, the development of LCUs in dentistry, the aims of light-curing, and the need to deliver an adequate amount of energy. The interaction between light source and material is briefly described to demonstrate the complex nature of the resin photopolymerisation process.

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.

Partial Ceramic Crowns Prepared by Dental Students: Clinical Performance Up to Five Years

Partial ceramic crowns (PCCs) are an accepted treatment option for the restoration of posterior teeth with deficient tooth substance. Data on the survival of PCCs fabricated by dental students are scarce. The aim of this retrospective clinical study was to investigate the clinical performance and longevity of PCCs placed by dental students in the last year of their training program at the University of Basel, Switzerland. Eighty-eight patients who had received at least one PCC (n=108) in the program were considered for clinical assessment; their records were analyzed to detect previous complications or failures; and they were contacted by telephone. Criteria regarding aesthetic, functional, and biological aspects were rated with a scoring system from 1=clinically excellent to 5=clinically poor. The response rate was 66.3% (55 of 83 included patients), and 72.2% (n=78) of the PCCs were included in the analysis. Five PCCs had been lost within ten to 78 months after treatment. Six PCCs were recorded as failures (score 5), and ten received clinically unsatisfactory gradings (score 4). The risk of a clinically poor outcome was 14% after five years (86% survival), while the overall success rate was 63.5%. These results suggest that the clinical procedure of PCCs was successfully implemented by these students with satisfactory clinical survival.

Effect of High-Irradiance Light-Curing on Micromechanical Properties of Resin Cements

This study investigated the influence of light-curing at high irradiances on micromechanical properties of resin cements. Three dual-curing resin cements and a light-curing flowable resin composite were light-cured with an LED curing unit in Standard mode (SM), High Power mode (HPM), or Xtra Power mode (XPM). Maximum irradiances were determined using a MARC PS radiometer, and exposure duration was varied to obtain two or three levels of radiant exposure (SM: 13.2 and 27.2 J/cm²; HPM: 15.0 and 30.4 J/cm²; XPM: 9.5, 19.3, and 29.7 J/cm²) (n = 17). Vickers hardness (H_V) and indentation modulus (E_IT) were measured at 15 min and 1 week. Data were analyzed with nonparametric ANOVA, Wilcoxon-Mann-Whitney tests, and Spearman correlation analyses (α = 0.05). Irradiation protocol, resin-based material, and storage time and all interactions influenced H_V and E_IT significantly (p ≤ 0.0001). Statistically significant correlations between radiant exposure and H_V or E_IT were found, indicating that high-irradiance light-curing has no detrimental effect on the polymerization of resin-based materials (p ≤ 0.0021). However, one resin cement was sensitive to the combination of irradiance and exposure duration, with high-irradiance light-curing resulting in a 20% drop in micromechanical properties. The results highlight the importance of manufacturers issuing specific recommendations for the light-curing procedure of each resin cement.

Light-curing units used in dentistry: factors associated with heat development-potential risk for patients

Objectives

To investigate how heat development in the pulp chamber and coronal surface of natural teeth with and without cusps subjected to irradiance using light-emitting diode (LED)–light-curing units (LCUs) is associated with (i) irradiance, (ii) time, (iii) distance, and (iv) radiant exposure.

Materials and methods

Three different LED-LCUs were used. Their irradiance was measured with a calibrated spectrometer (BlueLight Analytics Inc., Halifax, Canada). An experimental rig was constructed to control the thermal environment of the teeth. The LED-LCU tip position was accurately controlled by a gantry system. Tooth surface temperature was measured by thermography (ThermaCAM S65 HS, FLIR Systems, Wilsonville, USA) and pulp chamber temperature with a thermocouple. LED-LCU tip distance and irradiation times tested were 0, 2, and 4 mm and 10, 20, and 30 s, respectively. Ethical permission was not required for the use of extracted teeth.

Results

Maximum surface and pulp chamber temperatures were recorded in tooth without cusps (58.1 °C  ± 0.9 °C and 43.1 °C ± 0.9 °C, respectively). Radiant exposure explained the largest amount of variance in temperature, being more affected by time than irradiance.

Conclusions

At all combinations of variables tested, repeated measurements produced consistent results indicating the reliability of the method used. Increased exposure time seems to be the factor most likely to cause tissue damage.

Clinical relevance

Risk of superficial tissue damage at irradiances >1200 mW/cm² is evident. There is a risk of pulp damage when only thin dentin is left at higher irradiances (>1200 mW/cm²). Clinicians should be aware of LED-LCU settings and possible high temperature generated.

The dental curing light: A potential health risk

Powerful blue-light emitting dental curing lights are used in dental offices to photocure resins in the mouth. In addition, many dental personnel use magnification loupes. This study measured the effect of magnification loupes on the "blue light hazard" when the light from a dental curing light was reflected off a human tooth. Loupes with 3.5x magnification (Design for Vision, Carl Zeiss, and Quality Aspirator) and 2.5x magnification (Design for Vision and Quality Aspirator) were placed at the entrance of an integrating sphere connected to a spectrometer (USB 4000, Ocean Optics). A model with human teeth was placed 40 cm away and in line with this sphere. The light guide tip of a broad-spectrum Sapphire Plus (Den-Mat) curing light was positioned at a 45° angle from the facial surface of the central incisor. The spectral radiant power reflected from the teeth was recorded five times with the loupes over the entrance into the sphere. The maximum permissible cumulative exposure times in an 8-hr day were calculated using guidelines set by the ACGIH. It was concluded that at a 40 cm distance, the maximum permissible cumulative daily exposure time to light reflected from the tooth was approximately 11 min without loupes. The weighted blue irradiance values were significantly different for each brand of loupe (Fisher's PLSD p < 0.05) and were up to eight times greater at the pupil than when loupes were not used. However, since the linear dimensions of the resulting images would be 2.5 to 3.5x larger on the retina, the image area was increased by the square of the magnification and the effective blue light hazard was reduced compared to without the loupes. Thus, although using magnification loupes increased the irradiance received at the pupil, the maximum cumulative daily exposure time to reflected light was increased up to 28 min. Further studies are required to determine the ocular hazards of a focused stare when using magnification loupes and the effects of other curing lights used in the dental office.

Emission Characteristics and Effect of Battery Drain in “Budget” Curing Lights

Recently, “budget” dental light-emitting diode (LED)–based light-curing units (LCUs) have become available over the Internet. These LCUs claim equal features and performance compared to LCUs from major manufacturers, but at a lower cost. This study examined radiant power, spectral emission, beam irradiance profiles, effective emission ratios, and the ability of LCUs to provide sustained output values during the lifetime of a single, fully charged battery. Three examples of each budget LCU were purchased over the Internet (KY-L029A and KY-L036A, Foshan Keyuan Medical Equipment Co, and the Woodpecker LED.B, Guilin Woodpecker Medical Instrument Co). Major dental manufacturers provided three models: Elipar S10 and Paradigm (3M ESPE) and the Bluephase G2 (Ivoclar Vivadent). Radiant power emissions were measured using a laboratory-grade thermopile system, and the spectral emission was captured using a spectroradiometer system. Irradiance profiles at the tip end were measured using a modified laser beam profiler, and the proportion of optical tip area that delivered in excess of 400 mW/cm2 (termed the effective emission ratio) was displayed using calibrated beam profile images. Emitted power was monitored over sequential exposures from each LCU starting at a fully charged battery state. The results indicated that there was less than a 100-mW/cm2 difference between manufacturer-stated average tip end irradiance and the measured output. All the budget lights had smaller optical tip areas, and two demonstrated lower effective emission ratios than did the units from the major manufacturers. The budget lights showed discontinuous values of irradiance over their tip ends. One unit delivered extremely high output levels near the center of the light tip. Two of the budget lights were unable to maintain sustained and stable light output as the battery charge decreased with use, whereas those lights from the major manufacturers all provided a sustained light output for at least 100 exposures as well as visual and audible indications that the units required recharging.

Effect of mold type, diameter, and uncured composite removal method on depth of cure

OBJECTIVE

This study compared the effects of mold material and diameter on the thickness of cured composite remnants and depth of cure (DOC) of resin-based composites (RBC).

MATERIAL AND METHODS

One Polywave® curing light was used to photo-cure two shades of the same "bulk-fill" RBC in 4, 6, or 10-mm internal diameter metal or white Delrin® molds. For 60 specimens, the uncured RBC was manually scraped away as described in the ISO 4049 depth of cure test. The remaining 60 specimens were immersed in tetrahydrofuran for 48 hours in the dark. Maximum lengths of remaining hard RBC and their DOC values were compared using analysis of variance (ANOVA) and Tukey-Kramer post hoc multiple comparison tests (α = 0.05).

RESULTS

Specimen thickness and DOC were always greater using the white Delrin® molds compared to metal molds (p < 0.001). Increase in mold diameter significantly increased specimen thickness and DOC when made in the metal molds and in the 6-mm diameter Delrin® molds (p < 0.01). Increasing the diameter of the Delrin® molds to 10-mm did not increase specimen thickness or DOC. Sectioning and staining of specimens revealed an internal, peripheral transition zone of porous RBC in the solvent-dissolved specimens only.

CONCLUSION

Mold material and internal diameter significantly influenced cured composite remnant thickness as well as depth of cure. The existence of an outer region of RBC that is hard, yet susceptible to solvent dissolution, requires further investigation.

CLINICAL RELEVANCE

The depth of cure results obtained from a 4-mm diameter metal mold may not represent the true potential for evaluating composite depth of cure. A universally acceptable mold material and diameter size need to be established if this type of testing is to be useful for evaluating the relative performance of a given type of LCU and RBC.

Effect of a broad-spectrum LED curing light on the Knoop microhardness of four posterior resin based composites at 2, 4 and 6-mm depths

OBJECTIVE

To measure the Knoop microhardness at the bottom of four posterior resin-based composites (RBCs): Tetric EvoCeram Bulk Fill (Ivoclar Vivadent), SureFil SDR flow (DENTSPLY), SonicFill (Kerr), and x-tra fil (Voco).

METHODS

The RBCs were expressed into metal rings that were 2, 4, or 6-mm thick with a 4-mm internal diameter at 30°C. The uncured specimens were covered by a Mylar strip and a Bluephase 20i (Ivoclar Vivadent) polywave(®) LED light-curing unit was used in high power setting for 20s. The specimens were then removed and placed immediately on a Knoop microhardness-testing device and the microhardness was measured at 9 points across top and bottom surfaces of each specimen. Five specimens were made for each condition.

RESULTS

As expected, for each RBC there was no significant difference in the microhardness values at the top of the 2, 4 and 6-mm thick specimens. SureFil SDR Flow was the softest resin, but was the only resin that had no significant difference between the KHN values at the bottom of the 2 and 4-mm (Mixed Model ANOVA p<0.05). Although the KHN of SureFil SDR Flow was only marginally significantly different between the 2 and 6-mm thickness, the bottom at 6-mm was only 59% of the hardness measured at the top.

CLINICAL SIGNIFICANCE

This study highlights that clinicians need to consider how the depth of cure was evaluated when determining the depth of cure. SureFil SDR Flow was the softest material and, in accordance with manufacturer's instructions, this RBC should be overlaid with a conventional resin.

Real-Time Analysis of Temperature Changes in Composite Increments and Pulp Chamber during Photopolymerization

Objective. The aim of this study was to evaluate the temperature change at various sites within the composite and on the pulpal side of dentin during polymerization of two composite increments. Materials and Methods. Class I cavities prepared in third molars were restored in two composite increments (n = 5). Temperatures were measured for 110 s using eight thermocouples: bottom center of cavity (BC), top center of 1st increment (MC), top center of 2nd increment (TC), bottom corner of cavity (BE), top corner of 1st increment (ME), top corner of 2nd increment (TE), pulpal side of dentin (PD), and center of curing light guide tip (CL). Results. Maximum temperature values (°C) measured during polymerization of 1st increment were MC (59.8); BC (52.8); ME (51.3); CL (50.7); BE (48.4); and PD (39.8). Maximum temperature values during polymerization of 2nd increment were TC 58.5; TE (52.6); MC (51.7); CL (50.0); ME (48.0); BC (46.7); BE (44.5); and PD (38.8). Conclusion. Temperature at the floor of the cavity was significantly higher during polymerization of 1st increment compared to 2nd increment. Temperature rise was higher at the center than at the corner and at the top surface than at the bottom surface of each increment.

Light-Curing Units

For improved interstudy reproducibility, reduced risk of premature failures, and ultimately better patient care, researchers and dentists need to know how to accurately characterize the electromagnetic radiation (light) they are delivering to the resins they are using. The output from a light-curing unit (LCU) is commonly characterized by its irradiance. If this value is measured at the light tip, it describes the radiant exitance from the surface of the light tip, and not the irradiance received by the specimen. The value quoted also reflects only an averaged value over the total measurement area and does not represent the irradiance that the resin specimen is receiving locally or at a different moment in time. Recent evidence has reported that the spectral emission and radiant exitance beam profiles from LCUs can be highly inhomogeneous. This can cause nonuniform temperature changes and uneven photopolymerization within the resin restoration. The spectral radiant power can be very different between different brands of LCUs, and the use of irradiance values derived from dental radiometers to describe the output from an LCU for research purposes is discouraged. Manufacturers should provide more information about the light output from the LCU and the absorption spectrum of their resin-based composite (RBC). Ideally, future assessments and research publications should include the following information about the curing light: 1) radiant power output throughout the exposure cycle and the spectral radiant power as a function of wavelength, 2) analysis of the light beam profile and spectral emission across the light beam, and 3) measurement and reporting of the light the RBC specimen received as well as the output measured at the light tip.

Examining exposure reciprocity in a resin based composite using high irradiance levels and real-time degree of conversion values

OBJECTIVE

Exposure reciprocity suggests that, as long as the same radiant exposure is delivered, different combinations of irradiance and exposure time will achieve the same degree of resin polymerization. This study examined the validity of exposure reciprocity using real time degree of conversion results from one commercial flowable dental resin. Additionally a new fitting function to describe the polymerization kinetics is proposed.

METHODS

A Plasma Arc Light Curing Unit (LCU) was used to deliver 0.75, 1.2, 1.5, 3.7 or 7.5 W/cm(2) to 2mm thick samples of Tetric EvoFlow (Ivoclar Vivadent). The irradiances and radiant exposures received by the resin were determined using an integrating sphere connected to a fiber-optic spectrometer. The degree of conversion (DC) was recorded at a rate of 8.5 measurements a second at the bottom of the resin using attenuated total reflectance Fourier Transform mid-infrared spectroscopy (FT-MIR). Five specimens were exposed at each irradiance level. The DC reached after 170s and after 5, 10 and 15 J/cm(2) had been delivered was compared using analysis of variance and Fisher's PLSD post hoc multiple comparison tests (alpha=0.05).

RESULTS

The same DC values were not reached after the same radiant exposures of 5, 10 and 15 J/cm(2) had been delivered at an irradiance of 3.7 and 7.5 W/cm(2). Thus exposure reciprocity was not supported for Tetric EvoFlow (p<0.05).

SIGNIFICANCE

For Tetric EvoFlow, there was no significant difference in the DC when 5, 10 and 15J/cm(2) were delivered at irradiance levels of 0.75, 1.2 and 1.5 W/cm(2). The optimum combination of irradiance and exposure time for this commercial dental resin may be close to 1.5 W/cm(2) for 12s.

Effect of 457 nm diode-pumped solid state laser on the polymerization composite resins: microhardness, cross-link density, and polymerization shrinkage

OBJECTIVE

The purpose of the present study was to test the usefulness of 457 nm diode-pumped solid state (DPSS) laser as a light source to cure composite resins.

MATERIALS AND METHODS

Five different composite resins were light cured using three different light-curing units (LCUs): a DPSS 457 nm laser (LAS), a light-emitting diode (LED), and quartz-tungsten-halogen (QTH) units. The light intensity of LAS was 560 mW/cm(2), whereas LED and QTH LCUs was ∼900 mW/cm(2). The degree of polymerization was tested by evaluating microhardness, cross-link density, and polymerization shrinkage.

RESULTS

Before water immersion, the microhardness of laser-treated specimens ranged from 40.8 to 84.7 HV and from 31.7 to 79.0 HV on the top and bottom surfaces, respectively, and these values were 3.3-23.2% and 2.9-31.1% lower than the highest microhardness obtained using LED or QTH LCUs. Also, laser-treated specimens had lower top and bottom microhardnesses than the other LCUs treated specimens by 2.4-19.4% and 1.4-27.8%, respectively. After ethanol immersion for 24 h, the microhardness of laser-treated specimens ranged from 20.3 to 63.2 HV on top and bottom surfaces, but from 24.9 to 71.5 HV when specimens were cured using the other LCUs. Polymerization shrinkage was 9.8-14.7 μm for laser-treated specimens, and these were significantly similar or lower (10.2-16.0 μm) than those obtained using the other LCUs.

CONCLUSIONS

The results may suggest that the 457 nm DPSS laser can be used as a light source for light-curing dental resin composites.

Localised irradiance distribution found in dental light curing units

OBJECTIVE

To measure the localised irradiance and wavelength distributions from dental light curing units (LCUs) and establish a method to characterise their output.

METHODS

Using a laboratory grade integrating sphere spectrometer system (Labsphere and Ocean Optics) the power, irradiance, and spectral emission were measured at the light tips of four LCUs: one plasma-arc (PAC) unit, one single peak blue light-emitting diode (blue-LED) unit, and two polywave LED (poly-LED) units. A beam profiler camera (Ophir Spiricon) was used to record the localised irradiance across the face of the light tips. The irradiance-calibrated beam profile images were then divided into 45 squares, each 1mm(2). Each square contained the irradiance information received from approximately 3200 pixels. The mean irradiance value within each square was calculated, and the distribution of irradiance values among these 45 squares across the tip-ends was examined. Additionally, the spectral emission was recorded at various regions across each light tip using the integrating sphere with a 4-mm diameter entrance aperture.

RESULTS

The localised irradiance distribution was inhomogeneous in all four lights. The irradiance distribution was most uniformly distributed across the PAC tip. Both the irradiance and spectral emission from the poly-LED units were very unevenly distributed.

CONCLUSIONS

Reporting a single irradiance value or a single spectral range to describe the output from a curing light is both imprecise and inappropriate. Instead, an image of both the irradiance distribution and the distribution of the spectral emission across the light tip should be provided.

CLINICAL SIGNIFICANCE

The localised beam irradiance profile at the tip of dental LCUs is not uniform. Poly-LED units may deliver spectrally inhomogeneous irradiance profiles. Depending on the photoinitiator used in the RBC and the orientation of the LCU over the tooth, this non-uniformity may cause inadequate and inhomogeneous resin polymerisation, leading to poor physical properties, and premature failure of the restoration.

Contemporary issues in light curing

This review article will help clinicians understand the important role of the light curing unit (LCU) in their offices. The importance of irradiance uniformity, spectral emission, monitoring the LCU, infection control methods, recommended light exposure times, and learning the correct light curing technique are reviewed. Additionally, the consequences of delivering too little or too much light energy, the concern over leachates from undercured resins, and the ocular hazards are discussed. Practical recommendations are provided to help clinicians improve their use of the LCU so that their patients can receive safe and potentially longer lasting resin restorations.

Influence of various irradiation processes on the mechanical properties and polymerisation kinetics of bulk-fill resin based composites

OBJECTIVES

To assess the effect of irradiation time and distance of the light tip on the micro-mechanical properties and polymerisation kinetics of two bulk-fill resin-based composites at simulated clinically relevant filling depth.

METHODS

Micro-mechanical properties (Vickers hardness (HV), depth of cure (DOC) and indentation modulus (E)) and polymerisation kinetics (real-time increase of degree of cure (DC)) of two bulk-fill resin-based composites (Tetric EvoCeram(®) Bulk Fill, Ivoclar Vivadent and x-tra base, Voco) were assessed at varying depth (0.1-6mm in 100μm steps for E and HV and 0.1, 2, 4 and 6mm for DC), irradiation time (10, 20 or 40s, Elipar Freelight2) and distances from the light tip (0 and 7mm). Curing unit's irradiance was monitored in 1mm steps at distances up to 10mm away from the light tip on a laboratory-grade spectrometer.

RESULTS

Multivariate analysis (α=0.05), Student's t-test and Pearson correlation analysis were considered. The influence of material on the measured mechanical properties was significant (η(2)=0.080 for E and 0.256 for HV), while the parameters irradiation time, distance from the light tip and depth emphasise a stronger influence on Tetric EvoCeram(®) Bulk Fill. The polymerisation kinetics could be described by an exponential sum function, distinguishing between the gel and the glass phase. The above mentioned parameters strongly influenced the start of polymerisation (gel phase), and were of less importance for the glass phase.

CONCLUSIONS

Both materials enable at least 4mm thick increments to be cured in one step under clinically relevant curing conditions.

CLINICAL SIGNIFICANCE

The susceptibility to variation in irradiance was material dependent, thus properties measured under clinically simulated curing conditions might vary to a different extent from those measured under ideal curing conditions.