Publications by authors named "Richard B Price"

63 Publications

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

J Mech Behav Biomed Mater 2021 Dec 7;124:104884. Epub 2021 Oct 7.

Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada. Electronic address:

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/cm and 209 mW/cm, 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/cm and 209 mW/cm 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/cm and 209 mW/cm irradiance levels, respectively, are within two standard deviations of the corresponding transition times.

Significance: At an irradiance level much greater than 1000 mW/cm, 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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jmbbm.2021.104884DOI Listing
December 2021

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

J Esthet Restor Dent 2021 Aug 23. Epub 2021 Aug 23.

Department of Dental Clinical Sciences, Faculty of Dentistry, Dalhousie University, Halifax, Canada.

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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/jerd.12815DOI Listing
August 2021

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

J Can Dent Assoc 2021 04;87:l6

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.
View Article and Find Full Text PDF

Download full-text PDF

Source
April 2021

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

Compend Contin Educ Dent 2021 Feb;42(2):93-94

Professor, Department of Dental Clinical Sciences, School of Biomedical Engineering Medicine, Dalhousie University, Halifax, Nova Scotia, Canada.

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.
View Article and Find Full Text PDF

Download full-text PDF

Source
February 2021

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

Dent Mater 2021 02 2;37(2):e47-e58. Epub 2020 Nov 2.

Department of Restorative Dentistry, Piracicaba Dental School, University of Campinas, Avenida Limeira 901, 13414-903 Piracicaba, SP, Brazil. Electronic address:

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/cm emittance) and a homogenizer tip (HT, 946 mW/cm 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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.dental.2020.10.003DOI Listing
February 2021

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.

J Mech Behav Biomed Mater 2020 11 25;111:103987. Epub 2020 Jul 25.

Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada. Electronic address:

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/cm, 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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jmbbm.2020.103987DOI Listing
November 2020

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

Int Dent J 2020 Dec 21;70(6):407-417. Epub 2020 Jul 21.

Faculty of Dentistry, Dalhousie University, Halifax, NS, Canada.

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/cm ), and the irradiance received at the surface (also in mW/cm ) are used to describe the output from LCU. The concept of using an irradiance beam profile to map the radiant exposure (J/cm ) 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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/idj.12582DOI Listing
December 2020

Authors' response.

J Am Dent Assoc 2019 12;150(12):991

Professor, Department of Applied Oral Sciences, Dalhousie University, Halifax, Nova Scotia, Canada.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.adaj.2019.10.012DOI Listing
December 2019

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

J Am Dent Assoc 2019 12;150(12):1051-1058

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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.adaj.2019.08.012DOI Listing
December 2019

Disinfection of dental loupes: A pilot study.

J Am Dent Assoc 2019 08 20;150(8):689-694. Epub 2019 Jun 20.

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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.adaj.2019.03.008DOI Listing
August 2019

Effect of Resin Cement Mixing and Insertion Method into the Root Canal on Cement Porosity and Fiberglass Post Bond Strength.

J Adhes Dent 2019 ;21(1):37-46

Purpose: To evaluate the method of resin cement mixing and insertion into the root canal on resin cement porosity and fiberglass-post push-out bond strength (PBS).

Materials And Methods: One hundred twenty human single-rooted teeth were sectioned to a length of 15 mm, en-do-dontically filled, and received a fiberglass post cemented with 3 self-adhesive resin cements (RelyX U200, seT, Panavia SA) using 4 mixing methods/insertion techniques (handmix/endodontic file, handmix/Centrix syringe, automix/conventional tip, automix/endo tip). The samples were scanned using micro-CT. Two slices from the cervical, middle, and apical thirds were submitted to push-out bond strength (PBS) testing, and failure modes were classified. The PBS, volume of resin cement, and porosity data were analyzed using ANOVA and Tukey's test.

Results: The porosity was lowest in the cervical third and highest in the apical third, irrespective of the resin cement. The porosity was lower in the the automix/endo tip group compared to the handmix/endodontic file group. The use of Centrix or endo tip reduced the porosity and increased the PBS in the apical third compared with the use of endodontic files. The root canal depth reduced the PBS for U200 and seT when handmix/endodontic files were used. U200 and seT using the automix method increased the PBS, thus eliminating the effect of root region, irrespective of the insertion technique. In general, U200 showed higher PBS and Panavia lower PBS. Adhesive failure between root dentin and resin cement was predominant.

Conclusions: Automixing the cement and using an endo tip produces fewer voids and increased the bond strengths.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3290/j.jad.a41871DOI Listing
October 2019

Post-curing in dental resin-based composites.

Dent Mater 2018 09 23;34(9):1367-1377. Epub 2018 Jun 23.

Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada. Electronic address:

Objective: To determine the post-curing in six commercial contemporary resin-based composites (RBCs) using axial shrinkage, the degree of conversion, and Vickers hardness.

Methods: Five Bulk Fill and one conventional RBCs from three companies were selected with a wide range of filler volume content. The axial shrinkage of samples that were 1.00mm thick by 9-10mm diameter was measured using a modified bonded disk method over a time between 15h and 19h at temperatures of 26°C and 34°C (mouth temperature). The degree of conversion (DC) was collected continuously for 10min using mid-infrared spectroscopy in the attenuated total reflectance geometry. Vickers hardness was measured at 1h post-irradiation using a load of 300gf. For all three tests, the samples were irradiated at five exposure times, 20, 5, 3, 1.5 and 1s with a light curing unit radiant exitance of 1.1W/cm. Three samples (n=3) were used for each experimental condition.

Results: After light exposure, the axial shrinkage and degree of conversion exhibited a functional time dependence that was proportional to the logarithm of time. This suggests an out-of-equilibrium polymer composite glass that is transitioning to thermal equilibrium. At a sufficiently long time and among the RBCs investigated, the shrinkage related physical aging rate was found to vary between 1.34 and 2.00μm/log(t). The rate was a function of the filler content. Furthermore, 15h after light exposure, the post-curing shrinkage was estimated to be an additional 22.5% relative to the shrinkage at 100s for one RBC at T=34°C. The hardness in the photo-cured RBC was varied by using different light exposure times. The first two experimental techniques show that the higher the initial DC 10min after light exposure, the smaller is the post-curing shrinkage related and DC related physical aging rates. A direct correlation was observed between the shrinkage related and the DC related physical aging rates.

Significance: Post-curing shrinkage should be evaluated for longer than 1h. The post-curing shrinkage 15h after light exposure in dental RBCs can be appreciable. The long-term development of built-in stress within the tooth wall structure may shorten the restoration's lifespan.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.dental.2018.06.021DOI Listing
September 2018

Visible Light Curing Devices - Irradiance and Use in 302 German Dental Offices.

J Adhes Dent 2018 ;20(1):41-55

Purpose: To determine the irradiance delivered by visible-light curing (VLC) units and obtain information about the exposure times and the maintenance protocols used by dentists.

Materials And Methods: The irradiance (mW/cm2) delivered by 526 VLCs from 302 dental offices from the Rhine-Main area, Germany, was measured using an integrating sphere (IS) and a MARC patient simulator (M-PS); additional information was gathered using a survey.

Results: Irradiance was measured from 117 standard quartz-tungsten-halogen (QTH), 5 high-power QTH, 2 LED 1st-generation, 333 LED 2nd-generation, 61 LED 3rd-generation, and 8 plasma-arc curing (PAC) units. Depending on the measurement method, 8% (IS) or 11% (M-PS) of the VLCs delivered < 400 mW/cm2. Depending on the VLC, the shortest exposure times required to deliver a radiant exposure of 16 J/cm2 ranged from 7 to 294 s. The number of exposure cycles used by dentists when light curing a restoration ranged from 1 to 14. The shortest total exposure time used by dentists on a restoration was 5 s, the maximum was 200 s, and the median was 20 s. Of the 526 VLCs, 41% had intact, undamaged light tips. Only half of the dental offices checked the irradiance from their VLCs regularly, 97% disinfected the VLC, and 86% used eye protection.

Conclusion: Approximately 10% of the VLCs delivered < 400 mW/cm2 and 14% of the dental offices used no form of eye protection. To achieve sufficient light curing of RBC restorations, more awareness about the VLCs used in the dental office is required.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3290/j.jad.a39881DOI Listing
January 2019

Light Curing in Dentistry.

Dent Clin North Am 2017 10;61(4):751-778

Department of Dental Clinical Sciences, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada. Electronic address:

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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.cden.2017.06.008DOI Listing
October 2017

The Feasibility and Functional Performance of Ternary Borate-Filled Hydrophilic Bone Cements: Targeting Therapeutic Release Thresholds for Strontium.

J Funct Biomater 2017 Jul 14;8(3). Epub 2017 Jul 14.

School of Biomedical Engineering, Dalhousie University, Halifax, NS B3H 1X7, Canada.

We examine the feasibility and functionality of hydrophilic modifications to a borate glass reinforced resin composite; with the objective of meeting and maintaining therapeutic thresholds for Sr release over time, as a potential method of incorporating antiosteoporotic therapy into a vertebroplasty material. Fifteen composites were formulated with the hydrophilic agent hydroxyl ethyl methacrylate (HEMA, 15, 22.5, 30, 37.5 or 45 wt% of resin phase) and filled with a borate glass (55, 60 or 65 wt% of total cement) with known Sr release characteristics. Cements were examined with respect to degree of cure, water sorption, Sr release, and biaxial flexural strength over 60 days of incubation in phosphate buffered saline. While water sorption and glass degradation increased with increasing HEMA content, Sr release peaked with the 30% HEMA compositions, scanning electron microscope (SEM) imaging confirmed the surface precipitation of a Sr phosphate compound. Biaxial flexural strengths ranged between 16 and 44 MPa, decreasing with increased HEMA content. Degree of cure increased with HEMA content (42 to 81%), while no significant effect was seen on setting times (209 to 263 s). High HEMA content may provide a method of increasing monomer conversion without effect on setting reaction, providing sustained mechanical strength over 60 days.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/jfb8030028DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5618279PMC
July 2017

Shrinkage stress kinetics of Bulk Fill resin-based composites at tooth temperature and long time.

Dent Mater 2016 11 21;32(11):1322-1331. Epub 2016 Aug 21.

Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada. Electronic address:

Objective: To determine the shrinkage stress kinetics at up to 12h after light exposure and at tooth temperature during placement of selected Bulk Fill resin-based composites (RBCs).

Methods: Five representative Bulk Fill RBCs from four companies were chosen with a wide range of viscosity and filler volume content. The shrinkage stress kinetics at T=33°C was measured continuously over a period of 12h using a modified tensometer with the ability to measure the cantilever beam deflection to better than 40nm accuracy at a sampling rate of up to 200 samples/s, and thermally stable resulting in a measurement accuracy better than 0.05MPa at 12h. The tensometer compliance was 0.105μm/N. A custom made heater was used to control the RBC sample temperature at T=33°C with a temperature gradient across the sample of less than 1°C. The samples were irradiated for 20s with irradiance of 1.1W/cm and total energy density of 22J/cm. Three samples (n=3) were used for each RBCs.

Results: The shrinkage stress at 12h for the five Bulk Fill RBCs ranged from 2.21 to 3.05MPa, maximum stress rate ((dS/dt)) varied from 0.18 to 0.41MPa/s, time at which the maximum stress rate occurred (t) were between 1.42 to 3.24s and effective gel time (t) varied from 50 to 770ms. Correlations were observed between (dS/dt) and t (r=-0.946), t and filler volume fraction (r=-0.999), and between the shrinkage stress at 12h and t (r=0.994). However, no correlation was observed between the stress at 12h and filler volume fraction.

Significance: The shrinkage stress for four of the five Bulk Fill RBCs were not significantly different (p<0.05) at 6h and beyond after photo-curing and that fully developed stress induced by photo-cured RBCs may only be reached at times longer than 12h.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.dental.2016.07.015DOI Listing
November 2016

Erratum to: Effect of mold type, diameter, and uncured composite removal method on depth of cure.

Clin Oral Investig 2016 Nov;20(8):2321

Department of Dental Clinical Sciences, Faculty of Dentistry, Dalhousie University, Halifax, NS, Canada.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s00784-016-1733-3DOI Listing
November 2016

The dental curing light: A potential health risk.

J Occup Environ Hyg 2016 08;13(8):639-46

e Department of Operative Dentistry , University of Maryland , Baltimore , Maryland.

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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1080/15459624.2016.1165822DOI Listing
August 2016

Effect of curing light emission spectrum on the nanohardness and elastic modulus of two bulk-fill resin composites.

Dent Mater 2016 Apr 10;32(4):535-50. Epub 2016 Feb 10.

Dept of Dental Clinical Sciences, Faculty of Dentistry, Dalhousie University, Halifax, Nova Scotia, Canada. Electronic address:

Objective: To determine the nanohardness and elastic moduli of two bulk-fill resin based composites (RBCs) at increasing depths from the surface and increasing distances laterally from the center after light curing.

Methods: Two bulk-fill dental RBCs: Tetric EvoCeram Bulk Fill (TECBF) and Filtek Bulk Fill Flowable (FBFF) were light cured in a metal mold with a 6mm diameter and a 10mm long semi-circular notch. The RBCs were photo-polymerized for 10s using a light emitting diode (LED) Bluephase Style curing light, with the original light probe that lacked the homogenizer. This light has two blue light and one violet light LED emitters. By changing the probe orientation over the mold, the light output from only two LEDs reached the RBC. Measurements were made using: (i) the light from one violet and one blue LED, and (ii) the light from the two blue LEDs. Five specimens of each RBC were made using each LED orientation (total 20 specimens). Specimens were then stored in the dark at 37°C for 24h. Fifty indents were made using an Agilent G200 nanoindentor down to 4mm from the surface and 2.5mm right and left of the centerline. The results were analyzed (alpha=0.05) using multiple paired-sample t-tests, ANOVA, Bonferroni post-hoc tests, and Pearson correlations.

Results: The elastic modulus and nanohardness varied according to the depth and the distance from the centerline. For TECBF, no significant difference was found between the spatial variations in the elastic modulus or hardness values when violet-blue or blue-blue LEDs were used. For FBFF, the elastic modulus and nanohardness on the side exposed to the violet emitter were significantly less than the side exposed to the blue emitter. A strong correlation between nanohardness and elastic modulus was found in all groups (r(2)=0.9512-0.9712).

Significance: Resin polymerization was not uniform throughout the RBC. The nanohardness and elastic modulus across two RBC materials were found to decline differently according to the orientation of the violet and blue light LED emitters within the curing light.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.dental.2015.12.017DOI Listing
April 2016

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

Clin Oral Investig 2016 Sep 3;20(7):1699-707. Epub 2015 Dec 3.

Dalhousie University, Halifax, NS, Canada.

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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s00784-015-1672-4DOI Listing
September 2016

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.

J Dent 2016 Feb 22;45:14-8. Epub 2015 Nov 22.

Dental Clinical Sciences, Dalhousie University, P.O. Box 15000, Halifax, NS B3H4R2, Canada. Electronic address:

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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jdent.2015.11.004DOI Listing
February 2016

Effect of curing light and restoration location on energy delivered.

Compend Contin Educ Dent 2015 Mar;36(3):208-10, 212, 214

Director of the Gavel Center for Restorative Research, Associate Clinical Professor, Tufts University School of Dental Medicine, Boston, Massachusetts.

This study determined how long it would take skilled operators to deliver 16 J/cm2 to an anterior or a posterior restoration using different light-curing units (LCUs). Three skilled operators used the following LCUs at two locations in the MARC-patient simulator: Optilux 501 standard mode for 20 s; Sapphire Supreme for 5 s; Elipar™ S10 for 5 s and 20 s; Demi™ Plus standard mode for 5 s; SmartLite® Max boost mode for 5 s and continuous mode for 20 s; Radii Plus for 30 s; Valo (main version) in standard mode for 20 s and Xtra Power mode for 3 s; and Valo Cordless in standard mode for 20 s and Xtra Power mode for 3 s. The three MARCtrained operators made 30 readings with each light over 7 days. The energy (J/cm2) delivered to the anterior Class III and posterior Class I simulated restorations in MARC was recorded using a laboratory-grade spectroradiometer, and the time each light would take to deliver 16 J/cm2 calculated. ANOVA and Fisher's PLSD tests compared differences in the time to deliver 16 J/cm2 of energy, α = 0.05. Three-way ANOVA showed there was no significant difference between the operators, but there was a difference between the lights and locations. The Valo main and Valo Cordless in the Xtra Power mode delivered 16 J/cm2 in the shortest time at both locations. The Radii Plus took the longest to deliver 16 J/cm2, taking twice as long in the posterior location.
View Article and Find Full Text PDF

Download full-text PDF

Source
March 2015

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

Dent Mater 2015 May 21;31(5):583-93. Epub 2015 Mar 21.

Dalhousie University, Department of Dental Clinical Sciences, Faculty of Dentistry, Halifax, Canada. Electronic address:

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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.dental.2015.02.010DOI Listing
May 2015

Effect of the irradiance distribution from light curing units on the local micro-hardness of the surface of dental resins.

Dent Mater 2015 Feb 5;31(2):93-104. Epub 2014 Dec 5.

Bonn-Rhein-Sieg, University of Applied Sciences, Department of Natural Sciences, Rheinbach, Germany. Electronic address:

Objective: An inhomogeneous irradiance distribution from a light-curing unit (LCU) can locally cause inhomogeneous curing with locally inadequately cured and/or over-cured areas causing e.g. monomer elution or internal shrinkage stresses, and thus reduce the lifetime of dental resin based composite (RBC) restorations. The aim of the study is to determine both the irradiance distribution of two light curing units (LCUs) and its influence on the local mechanical properties of a RBC.

Methods: Specimens of Arabesk TOP OA2 were irradiated for 5, 20, and 80s using a Bluephase® 20i LCU in the Low mode (666mW/cm(2)), in the Turbo mode (2222mW/cm(2)) and a Celalux® 2 (1264mW/cm(2)). The degree of conversion (DC) was determined with an ATR-FTIR. The Knoop micro-hardness (average of five specimens) was measured on the specimen surface after 24h of dark and dry storage at room temperature.

Results: The irradiance distribution affected the hardness distribution across the surface of the specimens. The hardness distribution corresponded well to the inhomogeneous irradiance distributions of the LCU. The highest reaction rates occurred after approximately 2s light exposure. A DC of 40% was reached after 3.6 or 5.7s, depending on the LCU. The inhomogeneous hardness distribution was still evident after 80s of light exposure.

Significance: The irradiance distribution from a LCU is reflected in the hardness distribution across the surface. Irradiance level of the LCU and light exposure time do not affect the pattern of the hardness distribution--only the hardness level. In areas of low irradiation this may result in inadequate resin polymerization, poor physical properties, and hence premature failure of the restorations as they are usually much smaller than the investigated specimens. It has to be stressed that inhomogeneous does not necessarily mean poor if in all areas of the restoration enough light intensity is introduced to achieve a high degree of cure.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.dental.2014.11.003DOI Listing
February 2015

Correlation between the beam profile from a curing light and the microhardness of four resins.

Dent Mater 2014 Dec;30(12):1345-57

Dental Clinical Sciences, Dalhousie University, Halifax, NS, Canada.

Objective: To demonstrate the effect of localized irradiance and spectral distribution inhomogeneities of one LED-based dental light-curing unit (LCU) on the corresponding microhardness values at the top, and bottom surfaces of four dental resin-based composites (RBCs), which contained either camphorquinone (CQ) alone or a combination of CQ and monoacylphosphine oxide (TPO) as photoinitiators.

Methods: Localized irradiance beam profiles from a polywave LED-based LCU were recorded five times using a laser beam analyzer, without and with either a 400 nm or 460 nm narrow bandpass filter placed in front of the camera lens. Five specimens of each of the four RBCs (two containing CQ/TPO and two containing CQ-only) were exposed for 5-, 10-, or 30-s with the light guide directly on the top surface of the RBC. After 24 h, Knoop microhardness values were measured at 45 locations across the top and bottom surfaces of each specimen. Microhardness readings for each RBC surface and exposure time were correlated with localized patterns of the LCU beam profile, measured using the 400 nm and 460 nm bandpass filters. Spearman rank correlation was used to avoid relying on an assumption of a bivariate normal distribution for the KHN and irradiance.

Results: The local irradiance and spectral emission values were not uniformly distributed across the light tip. There was a strong significant positive correlation with the irradiance beam profile values from the LCU taken through bandpass filters and the microhardness maps of the RBC surfaces exposed for 5 and 10 s. The strength of this correlation decreased with increasing exposure time for the RBCs containing CQ only, and increased for the RBCs containing both CQ and TPO.

Conclusions: Localized beam and spectral distributions across the tip end of the light guide strongly correlated with corresponding areas of microhardness in both the top and bottom surfaces among four RBCs with different photoinitiator contents. Significance: A light-curing unit with a highly inhomogeneous light output can adversely affect localized microhardness of resin-based composites and this may be a contributing factor for premature failure of a restoration.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.dental.2014.10.001DOI Listing
December 2014

Light curing explored in Halifax.

Oper Dent 2014 Nov-Dec;39(6):561-3

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.2341/1559-2863-39.6.561DOI Listing
September 2016

Understanding light curing, Part I. Delivering predictable and successful restorations.

Dent Today 2014 May;33(5):114, 116, 118 passim; quiz 121

View Article and Find Full Text PDF

Download full-text PDF

Source
May 2014

Riboflavin-sensitized photo-crosslinking of collagen using a dental curing light.

Biomed Mater Eng 2014 ;24(4):1659-71

School of Biomedical Engineering, Dalhousie University, Halifax, NS, Canada.

Background: Photo-crosslinking of biomolecules such as collagen and fibrinogen is an emerging area of research interest. The use of a small dental curing light with a non-toxic photosensitizer represents a novel, practical approach to periodontal wound treatment.

Objective: This study evaluated the effects of riboflavin-sensitized photo-oxidation using a dental curing light on two collagenous biomaterials, as a preliminary step towards developing a medical technology for wound closure/healing.

Methods: A collagenous biomaterial (DBP) and type I collagen gels were treated by this photo-oxidative technique and characterized by hydrothermal isometric tension (HIT) analysis, amino acid analysis, SDS-PAGE, and rheology.

Results: HIT analysis suggested that dental curing light exposure for 300 s with riboflavin produced heavily crosslinked DBP. Dental curing light exposure for 300 s with riboflavin also showed a reduction in lysine concentration of DBP. SDS-PAGE showed that dental curing light exposure for 30 or 300 s with riboflavin resulted in crosslinked collagen gels. Dental curing light exposure for 30 s with riboflavin yielded a collagen gel with the strongest rheological characteristics.

Conclusions: This novel approach to wound treatment has potential for wide adoption and clinical use, particularly because dental curing lights, riboflavin, and collagen biomaterials are all used clinically, but not yet combined together as one technology for broad application.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3233/BME-140979DOI Listing
February 2015
-->