Comparison of light transmittance and color changes between polyurethane and copolyester retainer materials after staining and destaining.

BACKGROUND: Retainers are the only effective approach to prevent orthodontic relapse. The aim of this study was to compare the changes in color and light-transmittance of rough and smooth thermoformed polyurethane and copolymer retainer samples after staining in different solutions and destaining with different approaches. METHODS: Four hundred copolyester (Essix® ACE) and 400 polyurethane (Zendura®) samples with different surface textures, smooth and rough, were stained in 4 different solutions (n = 100 per solution) over 28 days. Each of the four groups of 100 stained samples of each material was subdivided into 5 groups of 20 samples and subjected to different destaining solutions. Light transmittance and color changes were evaluated using a spectrometer and a spectrophotometer. Mean differences were compared using a two-way analysis of variance (ANOVA) and posthoc multiple comparison tests at P = 0.05. RESULTS: No significant differences in light transmittance were found between both untreated materials. Both materials were stained in a similar fashion and showed no significant differences between two materials after staining. Coffee and tea stained both materials more significantly than wine, but there was a significant difference of changes of color and light transmittance between rough and smooth surfaces during the destaining in coffee- and tea-stained samples of copolyester material. All destaining solutions were effective at removing all stains on the samples. The surface roughness of the material plays a significant role in the ability of the materials to be destained, demonstrating a more significant greater effect on cleaning rough samples for improvements in light-transmittance and greater changes in color. CONCLUSIONS: This study concluded that the surface of materials plays a significant role in the material destaining and staining. In addition, the different polymers used for retainer fabrication exhibited different responses during the destaining process depending on types of stains.

Direct materials for restoring caries lesions: Systematic review and meta-analysis-a report of the American Dental Association Council on Scientific Affairs.

BACKGROUND: The goal of restoring caries lesions is to protect the pulp, prevent progression of the disease process, and restore the form and function of the tooth. The purpose of this systematic review was to determine the effect of different direct restorative materials for treating cavitated caries lesions on anterior and posterior primary and permanent teeth. TYPE OF STUDIES REVIEWED: The authors included parallel and split-mouth randomized controlled trials comparing the effectiveness of direct restorative materials commercially available in the United States placed in vital, nonendodontically treated primary and permanent teeth. Pairs of reviewers independently conducted study selection, data extraction, and assessments of risk of bias and certainty of the evidence using the Grading of Recommendations Assessment, Development and Evaluation approach. The authors conducted pair-wise meta-analyses to summarize the evidence and calculated measures of association and their 95% CIs. RESULTS: Thirty-eight randomized controlled trials were eligible for analysis, which included data on Class I and Class II restorations on primary teeth and Class I, Class II, Class III, Class V, and root surface restorations on permanent teeth. Included studies assessed the effect of amalgam, resin composite, compomer, conventional glass ionomer cement, resin-modified glass isomer cement, and preformed metal crowns. Moderate to very low certainty evidence suggested varying levels of effectiveness across restorative materials. CONCLUSIONS AND PRACTICAL IMPLICATIONS: Owing to a relatively low event rate across various outcomes indicating restoration failure, there was limited evidence to support important differences between direct restorative materials used in practice.

The Effects of Staining and Cleaning on the Color and Light Transmittance Changes of a Copolyester Retainer Material with Different Surface Textures.

This study evaluated the efficacy of different cleaning methods with respect to changes in the color and light transmittance of both rough and smooth thermoformed, copolyester retainer specimens, after staining in different solutions. Four hundred copolyester sheets (Essix ACE) specimens were fabricated over molds with different surface textures, smooth and rough. The specimens were stained in four different solutions (n = 100 per solution) over 28 days; then, each of the four groups of 100 stained specimens was sub-divided into five groups of 20 specimens and subjected to a different destaining solution. The specimens were sub-divided with half subjected to an additional ultrasonic cleaning procedure. Light transmittance and color changes were analyzed using a spectrometer/integrating sphere assembly and a spectrophotometer. Mean difference comparisons were performed using appropriate statistical tests at p = 0.05. All five destaining solutions proved to be effective at removing coffee and tea stains. The surface roughness of the retainer material plays a significant role in the ability of cleaning solutions to remove stains, demonstrating a greater effect on cleaning rough specimens with respect to improvements in light transmittance and greater changes in color. Additionally, an ultrasonic cleaning unit generally enhanced the ability of all five solutions to clean the tea-stained specimens. However, the enhancements were only significant for light transmittance.

Assuring the Safety of Dental Materials: The Usefulness and Application of Standards.

The formal history of standards and dentistry in the United States goes back to World War I and was prompted by the government's need to buy large quantities of dental materials to treat "an army of teeth in disrepair." This article covers the use of scientific research to establish specifications and standards used to evaluate dental materials and products, and how a practitioner can use these standards to assure the safety and performance of the materials that they use in their everyday practice.

Validating cleanability of dental rotary diamond instruments soiled with 2 clinically relevant dental test soil components.

BACKGROUND: The aim of this study was to produce a dental test soil, with 2 clinically relevant soil components, to be quantified for cleaning process validation. Another goal was to soil diamond instruments with the 2 soil components and validate the efficacy of cleaning instructions, developed and detailed in this study, using both qualitative and quantitative techniques. METHODS: To simulate worst-case clinical use conditions, the authors used each soiled instrument to prepare a 9-millimeter-deep access cavity on a noncarious extracted molar. Afterward, the authors applied a mixture of pooled human saliva and blood test soil to each instrument and air-dried it for 30 minutes. The authors cleaned each instrument using documented multistep cleaning instructions, which were then validated via both qualitative and quantitative assessment of protein and enamel-dentin residues using spectrophotometric analysis and microscopy images. RESULTS: After thorough cleaning, neither protein nor enamel-dentin residues were found at quantifiable levels (spectrophotometric analysis) on the soiled and cleaned diamond instruments, which was qualitatively verified (microscopy images). CONCLUSIONS: The results of this study show the successful development of a dental test soil with 2 clinically relevant soil components. Furthermore, using these soil components as test markers, the authors found that when the established cleaning instructions are properly followed, a soiled diamond instrument can be cleaned in a quantifiable manner. PRACTICAL IMPLICATIONS: Thorough cleaning is a critical step in reprocessing multiuse dental instruments. In accordance with US Food and Drug Administration guidance, the described process for quantification of soil components, using 2 clinically relevant soil markers, on cleaned diamond instruments can be helpful to dental instrument manufacturers in the development and validation of cleaning instructions for their reusable instruments.

Fracture toughness of zirconia with a nanometer size notch fabricated using focused ion beam milling.

OBJECTIVES: Zirconia with 3 mol% yttria (3Y-TZP) has been used for dental crowns and bridges due to its excellent mechanical behavior. Performing fracture toughness testing on this nanograin material, however, can be a challenge. For reliable results, fracture toughness testing requires an extremely sharp notch in the test specimen that closely approximates a very sharp crack. This study was to investigate an alternative method to produce nanometer-sized notches, which are less than the average grain size of 3Y-TZP, during the preparation of single-edge V-notched beam specimens and report the resulting fracture toughness value. METHODS: We present a method using focused ion beam (FIB) milling to fabricate nanometer-sized notches in 3Y-TZP. The notch tip is <100 nm wide, which is smaller than the grain size, and is consistent throughout the thickness of the specimen. RESULTS: The FIB-notched specimens show a much reduced average fracture toughness of 5.64 ± 1.14 MPa√m compared to 8.90 ± 0.23 MPa√m for the specimens without FIB-notches. The FIB-milling did not appear to create any monoclinic phase prior to fracture toughness testing. Fractures originated at the FIB-notches, and the notch size can be readily identified post-mortem using a microscope. A considerable amount of tetragonal-to-monoclinic phase transformation was observed throughout the fracture surfaces. SIGNIFICANCE: FIB milling provides an alternative method to fabricate nanometer-sized notches that are smaller than the grain size of tetragonal zirconia polycrystal. The fracture toughness determined using FIB-notches was ~5.64 MPa√m, smaller than the specimens with V-notches fabricated using saw blades.

Polymerization pattern characterization within a resin-based composite cured using different curing units at two distances.

OBJECTIVES: To investigate the relationship of the irradiance-beam-profile areas from six different light-curing units (LCUs) with the degree of conversion (DC), microhardness (KH), and cross-link density (CLD) throughout a resin-based composite (RBC) cured at two clinically relevant distances, and to explore the correlations among them. MATERIALS AND METHODS: A mapping approach was used to measure DC using micro-Raman spectroscopy, KH using a Knoop indentor on a hardness tester, and %KH reduction after ethanol exposure, as an indicator for CLD within a nano-hybrid RBC increment (n = 3) at various depths. These sample composites were cured from two distances while maintaining the radiant exposure, using six different light-curing units: one quartz-tungsten-halogen; two single and three multiple-emission-peak light-emitting-diode units. Irradiance beam profiles were generated for each LCU at both distances, and localized irradiance values were calculated. Points across each depth were analyzed using repeated measures ANOVA. Correlations across multiple specimen locations and associations between beam uniformity corresponding with polymerization measurements were calculated using linear mixed models and Pearson correlation coefficients. RESULTS: Significant non-uniform polymerization patterns occurred within the specimens at various locations and depths. At 2-mm curing distance, the localized DC = 52.7-76.8%, KH = 39.0-66.7 kg/mm2, and %KH reduction = 26.7-57.9%. At 8-mm curing distance, the localized DC = 50.4-78.6%, KH = 40.3-73.7 kg/mm2, and %KH reduction = 28.2-56.8%. The localized irradiance values were weakly correlated with the corresponding DC, KH, and %KH reduction, with only a few significant correlations (p < 0.05). CONCLUSIONS: Although significant differences were observed at each depth within the specimens, the localized irradiance values for all LCUs did not reflect the polymerization pattern and did not seem to have a major influence on polymerization patterns within the RBC, regardless of the curing distance. CLINICAL RELEVANCE: Commonly used LCUs do not produce uniform polymerization regardless of the curing distance, which may contribute to the risk of RBC fracture.

Long-term effects of various cleaning methods on polypropylene/ethylene copolymer retainer material.

OBJECTIVES: To evaluate long-term light transmittance, surface roughness, and flexural modulus of polypropylene/ethylene copolymer retainer material after exposure to different cleaning methods. MATERIALS AND METHODS: Standardized polypropylene/ethylene copolymer retainer specimens (n = 70, 50.8 mm × 12.7 mm × 1.0 mm) were subjected to seven chemical cleaning solutions: Invisalign cleaning crystals, Retainer Brite, Polident, Listerine mouthwash, 2.5% acetic acid, 0.6% NaClO, and 3% H2O2 for 6 months. The specimens were exposed to the different solutions twice a week for 15 minutes or according to manufacturer's instructions, then stored in artificial saliva at 37°C. Another group of specimens (n = 10) were brushed with a standardized toothbrushing machine for 2 minutes twice a week. At baseline and 6 months, light transmittance, surface roughness, and flexural modulus of the specimens were quantified using spectrophotometry, profilometry and three-point bend testing, respectively. Qualitative analysis was performed using a scanning electron microscope (SEM). Statistical analyses were performed at a significance level of .05. RESULTS: The results showed that light transmittance decreased significantly from baseline for all cleaning methods at 6 months. For an individual method, no significant differences were observed between specimens at baseline and 6 months in surface roughness and flexural modulus. No discernible differences in surface features were observed on SEM images. CONCLUSIONS: The results indicate that different cleaning methods affect the long-term light transmittance of the studied polypropylene/ethylene copolymer retainer material. However, for an individual cleaning method, no significant differences were shown for surface roughness or flexural modulus values at 6-months compared to baseline.

Long-term effects of different cleaning methods on copolyester retainer properties.

OBJECTIVE: To evaluate light transmittance, surface roughness, and flexural modulus of copolyester retainer material after long-term exposure to different cleaning methods. MATERIALS AND METHODS: Standardized copolyester retainer specimens (ACE) were subjected to seven chemical cleaning solutions for 6 months: Invisalign cleaning crystals, Retainer Brite, Polident, Listerine mouthwash, 2.5% acetic acid, 0.6% NaClO, and 3% H2O2. Seventy specimens (n = 10 per method, 50.8 mm × 12.7 mm × 1.0 mm) were exposed to the different solutions twice a week for 2 minutes or according to manufacturer's instructions and stored in artificial saliva at 37°C. Another group of specimens (n = 10) was brushed with a standardized toothbrushing machine for 2 minutes twice a week. At baseline and 6 months, light transmittance, surface roughness and flexural modulus of the specimens were quantified using spectrophotometry, profilometry, and three-point bend testing, respectively. Qualitative assessment was performed using scanning electron microscopy (SEM). Statistical analyses were accomplished at a significance level of .05. RESULTS: The results indicated that light transmittance through the specimens decreased significantly from baseline for all cleaning methods at 6 months. Flexural modulus of the specimens decreased significantly for all cleaning methods except Invisalign crystals and Retainer Brite ( P > .05). The Listerine group demonstrated the worst light transmittance change while H2O2 demonstrated the greatest change in flexural modulus of the specimens compared with other cleaning methods; however, no qualitative difference was observed using SEM analysis. CONCLUSIONS: The results suggest that different cleaning methods affect long-term physical properties of the ACE retainer material. At the present time, none of these cleaning methods is ideal for copolyester retainer material.

Long-term effects of seven cleaning methods on light transmittance, surface roughness, and flexural modulus of polyurethane retainer material.

OBJECTIVES: To evaluate the long-term effects of seven different cleaning methods on light transmittance, surface roughness, and flexural modulus of a polyurethane retainer material. MATERIALS AND METHODS: Polyurethane retainer specimens (Vivera®, Align Technology Inc) (70 specimens, n = 10 per method, 50.8 mm × 12.7 mm × 1.0 mm) were exposed to seven cleaning methods twice a week for 6 months. Before treatment and after 6 months, light transmittance, surface roughness, and flexural modulus of the specimens were quantified. Qualitative assessment of randomly selected specimens from each solution was performed at baseline and after 6 months using a scanning electron microscope. Statistical analyses were performed at the .05 significance level. RESULTS: Of the three test variables, light transmittance through the specimens was the only one that changed significantly from baseline to 6 months for all cleaning solutions, with all of them causing a decrease. However, except for 0.6% sodium hypochlorite showing a change in surface roughness values and 2.5% vinegar and toothbrushing showing an increase in flexural modulus, none of the other four cleaning methods resulted in significant changes in surface roughness or flexural modulus values for the polyurethane specimens between baseline and after 6 months. CONCLUSIONS: Of the seven cleaning methods, Invisalign® cleaning crystals, Polident®, and Listerine® showed the least amount of change in light transmittance values for the polyurethane specimens over 6 months, and they had no effect on surface roughness and flexural modulus values.

Degree of conversion and cross-link density within a resin-matrix composite.

The aims of this study were to profile light radiated from two light-curing units (LCUs) and evaluate profile relationship to polymerization patterns within a resin-matrix composite (RMC). Beam profiles of one multiple emission peak light-emitting-diode and one quartz-tungsten-halogen curing-unit were measured using a beam profiler/spectrometer system. A camera-based profiler and an integrating sphere/spectrometer assembly were used to evaluate each LCU beam. Polymerization patterns within a nano-hybrid RMC were investigated using a mapping approach by assessing the degree of conversion utilizing micro-Raman spectroscopy and indirectly estimating cross-link-density by repeated microhardness testing before and after exposure to ethanol (%KH reduction, n = 3). The irradiance received on the top and bottom specimen surfaces from both LCUs was measured using a MARC-RC system. The investigated beam profile area from both LCUs was non-uniform and yielded localized discrepancies in DC (55.7-74.9%) and %KH reduction (26.7-54.1%). The LCU irradiance received at the bottom of the specimens was ∼10% of the top value. This study demonstrated that LCU beam profiles were non-uniform in the area explored. Localized differences in DC and %KH reduction existed throughout the RMC specimens but did not follow a specific pattern. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1496-1504, 2018.

Comparison of the transformation temperatures of heat-activated Nickel-Titanium orthodontic archwires by two different techniques.

OBJECTIVES: The purpose of this study was to investigate the suitability of the Bend and Free Recovery (BFR) method as a standard test method to determine the transformation temperatures of heat-activated Ni-Ti orthodontic archwires. This was done by determining the transformation temperatures of two brands of heat-activated Ni-Ti orthodontic archwires using the both the BFR method and the standard method of Differential Scanning Calorimetry (DSC). The values obtained from the two methods were compared with each other and to the manufacturer-listed values. METHODS: Forty heat-activated Ni-Ti archwires from both Rocky Mountain Orthodontics (RMO) and Opal Orthodontics (Opal) were tested using BFR and DSC. Round (0.016 inches) and rectangular (0.019×0.025 inches) archwires from each manufacturer were tested. The austenite start temperatures (As) and austenite finish temperatures (Af) were recorded. RESULTS: For four of the eight test groups, the BFR method resulted in lower standard deviations than the DSC method, and, overall, the average standard deviation for BFR testing was slightly lower than for DSC testing. Statistically significant differences were seen between the transformation temperatures obtained from the BFR and DSC test methods. However, the Af temperatures obtained from the two methods were remarkably similar with the mean differences ranging from 0.0 to 2.1°C: Af Opal round (BFR 26.7°C, DSC 27.6°C) and rectangular (BFR 27.6°C, DSC 28.6°C); Af RMO round (BFR 25.5°C, DSC 25.5°C) and rectangular (BFR 28.0°C, DSC 25.9°C). Significant differences were observed between the manufacturer-listed transformation temperatures and those obtained with BFR and DSC testing for both manufacturers. SIGNIFICANCE: The results of this study suggest that the Bend and Free Recovery method is suitable as a standard method to evaluate the transformation temperatures of heat-activated Ni-Ti orthodontic archwires.

Contemporary esthetic nickel-titanium wires: do they deliver the same forces?

OBJECTIVE: To test for differences in loading and unloading forces delivered by six coated nickel-titanium wires and their noncoated equivalents. MATERIALS AND METHODS: From six commercial companies, 0.016-inch diameter round and 0.016 × 0.022-inch rectangular cross-section nickel-titanium wires were procured "as is": Rocky Mountain Orthodontics (Denver, Colo), TP Orthodontics (La Porte, Ind), American Orthodontics (AO; Sheboygan, Wis), G&H (Franklin, Ind), Opal Orthodontics (South Jordan, Utah), and Forestadent USA (St Louis, Mo) (round only). The wires were evaluated using a three-point bending test based on the method in ISO Standard 15841. RESULTS: No statistically significant differences (P > .05) in force values were found between coated and noncoated wires, listed by deflection in three-point bending, for these specific groups: 1 mm, TP round; 2 mm, TP round and G&H rectangular; 3 mm, G&H round and G&H rectangular; 2.5 mm,TP round and G&H rectangular; 1.5 mm, TP round, G&H round, G&H rectangular, and AO rectangular; and 0.5 mm, AO rectangular and G&H round. CONCLUSION: Some manufacturers market esthetic wires delivering forces similar to the equivalent noncoated wires, when tested according to a standard three-point bend method.

Comparison of an absolute and surrogate measure of relative translucency in dental ceramics.

PURPOSE: The objective was to compare absolute translucency with a frequently used surrogate measure of relative translucency (contrast ratio) from 14 all-ceramic materials having a wide range of translucencies. MATERIALS AND METHODS: Standardized disks were fabricated from fourteen ceramics, varying both thickness (0. 3mm, 0.5 mm, 1.0 mm, and 1.5 mm) and chroma (high and low). Absolute translucency (percent transmission) was measured using a spectroradiometer with an integrating sphere. Relative translucency was measured using a spectrophotometer as contrast ratio (contrast ratio; ratio of L* values recorded on black and white backgrounds). Non-linear regression was used to compare measurements of absolute versus relative values for each of the spectrophotometers. RESULTS: Contrast ratio was not able to characterize translucency across the range of materials studied and became less sensitive with increasing opacity. A non-linear correlation was found between percent transmission and contrast ratio down to 50% transmission (r(2)=0.97) and contrast ratio was insensitive to transmission differences below 50% transmission. CONCLUSION: Contrast ratio is not a direct measure of translucency and cannot be used below 50% transmission.