Characterization and effectiveness of a violet LED light for in-office whitening.

OBJECTIVES: This study characterized a violet LED light (V-LED; bright max whitening) tooth whitening device and evaluated its efficacy on stained enamel compared to hydrogen peroxide (HP). MATERIALS AND METHODS: Characterization of the V-LED beam profile was performed using a laser beam-profiler. The irradiance was measured throughout an exposure cycle at 0- and 8-mm distances using an integrating sphere and a spectral radiometer. Bovine enamel/dentin blocks stained with black tea (BT), cigarette smoke (CS), or without staining (CONT) were subjected to V-LED or 40% HP (n = 10/group). Color parameters (ΔL, Δa, Δb, and ΔE00) were measured using a digital spectrophotometer. Light transmission was estimated through 1-mm-thick bovine enamel slices (n = 5). ΔL, Δb, ΔE00, and irradiance were analyzed by two-way ANOVAs and Tukey's tests, Δa by Kruskal-Wallis and Mann-Whitney tests, and light transmission by t-test (α = 5%). RESULTS: Heterogeneous beam distribution was observed for the emitting V-LED chips. After 20 sequential exposures, irradiance levels were reduced 25-50%, regardless of the distance from V-LED. Localized irradiance values were statistically different between beam locations and different distances from the target. V-LED produced lower ΔE00, ΔL, Δa, and Δb values than HP for CONT and BT, with no differences for CS. Light transmittance decreased approximately 98% through 1-mm thick enamel. CONCLUSIONS: V-LED irradiance was heterogeneous and decreased throughout the exposure cycles and was also greatly reduced with increasing tip distance. V-LED produced a significantly lower whitening effect on BT and control teeth. CLINICAL RELEVANCE: This study contributes to the knowledge of V-LED and its clinical use.

Effects of extending duration of exposure to curing light and different measurement methods on depth-of-cure analyses of conventional and bulk-fill composites.

This study evaluated the effect of extending the duration of exposure to curing light on the depth of cure of two conventional (RBC1-conventional and RBC2-conventional) and two bulk-fill (RBC1-bulk and RBC2-bulk) resin composites. Polywave and single-peak photocuring units were used. Cylinder-shaped specimens were exposed to curing light either for the time period recommended by the manufacturer or twice the length of that time, and depth of cure was estimated using manual scraping (similar to the ISO-4049 standard) and solvent immersion techniques. Depth of cure was analyzed, using two-way ANOVA, for the factors measurement method and exposure time. For RBC1-conventional and RBC1-bulk, the solvent immersion technique estimated a greater depth of cure than did manual scraping; for RBC1-conventional, both techniques and both light-exposure time periods resulted in a depth of cure of >2 mm; and for RBC1-bulk, only the solvent method after photocuring for twice the manufacturer's recommended time resulted in a depth of cure of 5 mm. For RBC2-conventional and RBC2-bulk, neither technique nor exposure time resulted in estimated depths of cure that matched those indicated by the manufacturer. The results suggest that extending the duration of photopolymerization increases depth of cure. Also, calculation of depth of cure can vary according to the measurement technique used.

Effect of tooth brushing on gloss retention and surface roughness of five bulk-fill resin composites.

OBJECTIVES: To determine the effects of tooth brushing on five bulk-fill resin based composites (RBCs). METHOD: Ten samples of Filtek Supreme Enamel (control), Filtek One Bulk Fill, Tetric EvoCeram Bulk Fill, SonicFill 2, SDR flow+, and Admira Fusion X-tra were light cured for 20 seconds using the Valo Grand curing light. After 24 hours storage in air at 37°C, specimens were brushed in a random order using Colgate OpticWhite dentifrice and a soft toothbrush. Surface gloss was measured prior to brushing, after 5,000, 10,000 and 15,000 back and forth brushing cycles. Surface roughness was measured after 15,000 brushing cycles using atomic force microscopy (AFM) and selected scanning electron microscope (SEM) images were taken. The data was examined using ANOVA and pair-wise comparisons using Scheffe's post-hoc multiple comparison tests (α = 0.05). RESULTS: Surface gloss decreased and the surface roughness increased after brushing. Two-way ANOVA showed that both the RBC and the number of brushing cycles had a significant negative effect on the gloss. One-way ANOVA showed that the RBC had a significant effect on the roughness after 15,000 brushing cycles. For both gloss and roughness, brushing had the least effect on the nano-filled control and nano-filled bulk-fill RBC, and the greatest negative effect on Admira Fusion X-tra. The SEM images provided visual agreement. There was an excellent linear correlation (R2 = 0.98) between the logarithm of the gloss and roughness. CONCLUSION: After brushing, the bulk-fill RBCs were all rougher than the control nano-filled RBC. The nano-filled bulk-fill RBC was the least affected by brushing. CLINICAL SIGNIFICANCE: Bulk-fill RBCs lose their gloss faster and become rougher than the nanofilled conventional RBC, Filtek Supreme Ultra. The nanofilled bulk-fill RBC was the least affected by tooth brushing.

Staining potential differences between an infiltrative resin and an esthetic, flowable composite.

OBJECTIVE: To compare color change magnitude of an infiltrative resin and a flowable composite resin after immersion in commonly consumed beverages. MATERIALS AND METHODS: Disks (1 × 9 mm) of a flowable composite (Filtek Supreme Ultra Flowable) and a resin-infiltrative product (Icon) were made. Specimens were dark-stored in tap water (24 hours). Baseline color parameters (CIE L*a*b*) were obtained using a colorimeter (Easyshade V4, VITA). Specimens were immersed (dark stored, 37°C, 1 week) in commercial beverages: Kool-Aid, coffee, Coca-Cola, and tap water (control). ΔE00 between final and baseline conditions for each material/beverage combination was determined (N = 10/group). Initial analysis of variance indicated significant impact of major factors/interactions on ΔE00 . Subsequently, t-tests between ΔE00 values of restorative materials within each beverage was performed: alpha 0.05. RESULTS: Kool-Aid produced the greatest color change for flowable composite, with a ΔE00 significantly greater than the infiltrative product. No significant ΔE00 differences were noted between products immersed in coffee, however color parameters causing these differences were not similar. Water or Coca-Cola immersion showed lowest ΔE00 values for both materials, considered visually imperceptible: ΔE00 values <0.8. CONCLUSIONS: Color change potential of infiltrative resin or resin composite was highly dependent on beverage type, with no general trends observed in which material was affected more. CLINICAL SIGNIFICANCE: Staining potential of an infiltrative restorative resin differs from that of a filled, flowable composite material on a beverage-by-beverage basis. The potential for color change seems not related to the presence or absence of fillers in the restorative material.

Heat generation during removal of an abutment screw fragment from dental implants.

STATEMENT OF PROBLEM: Little information is available on the effect of drilling speed on surrounding bone during the removal of an abutment screw fragment. PURPOSE: The purpose of this in vitro study was to compare, in vitro, the peak temperature increase during the removal of fractured abutment screws from implants placed in a porcine mandible, using drilling speeds of 600 or 2000 rpm. MATERIAL AND METHODS: Twenty 4.3×13-mm dental implants were placed in 10 dissected porcine mandibles: 2 implants per mandible, 1 on each side. Localized defects were created in 20 surface-treated abutment screws, which were then tightened into each implant until a reproducible fracture occurred in each screw. The fractured screws were removed with a handpiece removal kit and irrigated with room-temperature water at either 600 or 2000 rpm. The temperature rise at the implant surface was measured at 3 levels with 3 type-K thermocouples. Repeated measure ANOVA was performed with the Tukey-Kramer post hoc test for mean pair-wise comparisons (α=.05 for all tests). RESULTS: Mean peak temperatures were significantly higher at 2000 rpm than at 600 rpm in the mid-body (P<.001) and crestal (P=.003) regions but not in the apical (P=.225) implant locations. No significant differences in mean peak temperatures were found among the 3 locations using 600 rpm (P=.179). In the 2000-rpm group, mean peak temperature in the mid-body area was consistently higher than that in the apical (P<.001) area, and more instances of temperature rise above 56°C and 60°C were observed. In 1 implant from this group, the estimated peak temperature exceeded the bone damage threshold value (50°C for 30 seconds). CONCLUSIONS: A drilling speed of 2000 rpm during the removal of abutment screw fragments caused overheating of the outer surface of the implant which may damage the surrounding bone; a speed of 600 rpm appears to be safe.

Shear bond strength of zirconia-based ceramics veneered with 2 different techniques.

STATEMENT OF PROBLEM: Delamination of veneering ceramic is reported as one of the most frequent problems associated with veneered zirconia restorations. PURPOSE: The purpose of this in vitro study was to compare the shear bond strength of sintered lithium disilicate to that of pressed fluorapatite glass-ceramic on a zirconia substrate. MATERIAL AND METHODS: Thirty zirconia blocks (20×15×2.5-mm thick) were cut, sintered, and divided into 2 groups. A pressed group, a zirconia liner, was applied and sintered, and the lost-wax technique was used to fabricate fluorapatite glass-ceramic blocks (3×3×3 mm), which were pressed onto the sintered zirconia blocks. A sintered group, lithium disilicate blocks, were cut (3×3×3 mm) and sintered to the sintered zirconia blocks by using a low-fusing glass-ceramic. The thickness of the low-fusing glass-ceramic was standardized to approximately 80 µm prior to sintering. The shear bond strength levels of the specimens were tested using a universal testing machine at a crosshead speed of 1 mm/min until failure. Representative separated specimen surfaces were examined for fracture characteristics, using scanning electron microscopy at ×50 magnification. Debonding data were compared using a 2-tailed, unpaired Student t test (α=.05). RESULTS: The sintered group demonstrated mean shear bond strength values (41.2 ±6.3 MPa), which were significantly higher (P<.001) than those of the pressed group (21.3 ±4.3 MPa). CONCLUSIONS: Sintering of computer-aided design and computer-aided manufacturing (CAD-CAM) lithium disilicate ceramic achieved higher shear bond strength values than pressing fluorapatite glass-ceramic to zirconia substructure material.

Mechanical Modeling of the Human Cricoid Cartilage Using Computer-Aided Design: Applications in Airway Balloon Dilation Research.

OBJECTIVES: Balloon dilation is generally considered first-line treatment for airway stenosis. Some dilation systems utilize a compliant balloon that can conform around rigid structures. Others use a noncompliant balloon that does not conform, allowing for dilation of more rigid stenoses. We hypothesized that subglottic dilation with a noncompliant balloon increases the likelihood of fracture of the cricoid when compared to a compliant balloon. METHODS: Three fresh human cricoid cartilages were placed in a universal testing system to determine the expansile force necessary for cricoid fracture. Using these data, a 3D printer was used to construct a synthetic cricoid model possessing near identical physical characteristics to the human cricoid. Simulated dilation was then performed on the model using a compliant and a noncompliant balloon. RESULTS: Human cricoid fracture occurred at 97.25 N (SD = 8.34), and the synthetic cricoid model fractured at 100.10 N (SD = 7.32). Both balloons fractured the model in every replicate experiment. Mean balloon internal pressure at fracture was 7.67 ATM (SD = 1.21) for the compliant balloon and 11.34 ATM (SD = 1.29) for the noncompliant balloon. CONCLUSIONS: These data show that fracture of the cricoid is a valid concern in balloon dilation procedures where the balloon spans the subglottis. Furthermore, the hypothesis was rejected in that the compliant balloon system was at least as likely to fracture the cricoid model as the noncompliant.

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.

In vitro mechanical analysis of complete-arch mandibular implant-supported fixed prostheses abutment screws after cyclic loading.

STATEMENT OF PROBLEM: Clinicians question when to evaluate for worn or loose implant-supported retainer screws to prevent possible clinical complications. PURPOSE: The purpose of this study was to compare differences among initial and postdynamically loaded detorque values and identify physical structural changes of prosthetic retaining screws in a simulated implant-supported mandibular complete fixed prosthesis. MATERIAL AND METHODS: Nine groups and nonloaded controls comprising a 5-implant-supported, milled titanium framework were fabricated and assembled (screw torque 35 Ncm). Dynamic loading (20 to 220 N) was applied to simulate 2 years of oral function. After testing, screw detorque values were measured (ΔT, initial-detorque value). A scanning electron microscopic analysis of screw threads was used to assess physical changes. Data were analyzed by 2-way ANOVA to determine the influence of loading and implant position on ΔT (α=.05). RESULTS: ΔT values of loaded and nonloaded groups were compared separately at each implant position and showed a significant difference only for the implant in the central position (P=.002). All positions were compared in terms of ΔT values separately for loaded and nonloaded conditions. A significantly higher ΔT was found in 1 cantilever area of the loaded group, whereas a significantly lower ΔT value was found in the central position in the nonloaded group. No statistically significant differences were found in physical changes between loading and nonloading or among implant positions. CONCLUSIONS: When delivering a multiimplant supported prosthesis, the application of dynamic loading and the sequence in which implant screws are tightened could influence the subsequent detorque value of a screw; they have no effect on the physical appearance of screws after extended function.

Accuracy and precision of as-received implant torque wrenches.

STATEMENT OF PROBLEM: Previous implant torque evaluation did not determine if the target value fell within a confidence interval for the population mean of the test groups, disallowing determination of whether a specific type of wrench met a standardized goal value. PURPOSE: The purpose of this study was to measure both the accuracy and precision of 2 different configurations (spring style and peak break) of as-received implant torque wrenches and compare the measured values to manufacturer-stated values. MATERIAL AND METHODS: Ten wrenches from 4 manufacturers, representing a variety of torque-limiting mechanisms and specificity of use (with either a specific brand or universally with any brand of implant product). Drivers were placed into the wrench, and tightening torque was applied to reach predetermined values using a NIST-calibrated digital torque wrench. Five replications of measurement were made for each wrench and averaged to provide a single value from that instrument. The target torque value for each wrench brand was compared to the 95% confidence interval for the true population mean of measured values to see if it fell within the measured range. RESULTS: Only 1 wrench brand (Nobel Biocare) demonstrated the target torque value falling within the 95% confidence interval for the true population mean. For others, the targeted torque value fell above the 95% confidence interval (Straumann and Imtec) or below (Salvin Torq). CONCLUSIONS: Neither type of torque-limiting mechanism nor designation of a wrench to be used as a dedicated brand-only product or to be used as a universal product on many brands affected the ability of a wrench to deliver torque values where the true population mean included the target torque level.

Effect of build orientation in gloss, roughness and color of 3D-printed resins for provisional indirect restorations.

OBJECTIVES: The purpose of this study was to evaluate the effect of build orientation of 3D-printed provisional resins (3DRs) on gloss (Gs), surface roughness (Sa), maximum profile valley depth (Rv), and color difference (∆E00). METHODS: PMMA CAD/CAM blocks (Vita Temp/Vita) were sectioned and served as a Control. Four 3DRs (Cosmos-SLA/Yller, Cosmos-DLP/Yller, PriZma-Bioprov/Makertech, Nanolab/Wilcos) were obtained as discs (15-mm diameter, 2.5-mm thickness) in three orientations (0°, 45°, and 90°) using different 3D printers (Form 2/Formlabs, P30/Straumann, Hunter/Flashforge, W3D/Wilcos, respectively). Samples were then cleaned with isopropyl alcohol prior to post-curing in specific post-curing units. Half of the samples' surface was covered with an adhesive tape and submitted to 10,000 toothbrushing (TB) cycles. The Gs and Sa at the brushed and not brushed surfaces were evaluated with a glossmeter (Novo-curve) and a laser confocal microscope (OLS5000) (n = 10), which also obtained the Rv and 3D representative images of the interface between not brushed and brushed surfaces. Electron microscopy images of the surface of some samples was also performed (n = 3). On another set of samples (n = 5), the coordinates of luminosity and color were obtained with a spectrophotometer (Easyshade V) at baseline and after 16.7 h and 200 h of UVB aging, to calculate the ∆E00 using CIEDE:2000 formula. Additionally, 3DRs photoinitiators were identified using a minispectrometer (USB2000 +) (n = 5). Data of Gs and Sa were submitted to three-way-, Rv to two-way-, and ∆E00 to mixed-ANOVA tests, followed by Tukey's test (α = 0.05). For all variables, results from experimental groups were compared to control using Dunnett's test (α = 0.05). Student's t-test was used to compare the control at different TB cycles (Gs, Sa) or aging periods (∆E00) (α = 0.05). RESULTS: Build orientation of 3DRs did not influence any of the variables studied. The 10,000 TB cycles resulted in a decrease in Gs and increase in Sa for all resins tested. The control showed higher Gs after 10,000 TB cycles than Cosmos-SLA and Nanolab resins. Compared to all 3DRs, Control presented lower ∆E00 after 200 h of UVB aging. All 3DRs presented higher ∆E00 than the clinically acceptable after 200 h of UVB aging. Lucirin® TPO was identified in all 3DRs, although PriZma might also present other photoinitiators and Nanolab might present Irgacure 369. SIGNIFICANCE: Alterations in build orientation are very useful and frequently performed in the day-today of 3D-printing, thus its effect in the optical properties and in the topography of 3D-printed restorations is very relevant. For the evaluated 3D-printed provisional resins, build orientation did not influence any of the variables studied (Gs, Sa, Rv, and ∆E00), even after toothbrushing cycles and UVB aging.

Effect of build orientation in accuracy, flexural modulus, flexural strength, and microhardness of 3D-Printed resins for provisional restorations.

PURPOSE: This study evaluated the effects of 3D-printing build orientation on accuracy, flexural modulus (FM), flexural strength (FS), and microhardness of selected, commercial 3D-printed provisional resins (3DRs). MATERIAL AND METHODS: PMMA CAD/CAM provisional material (Vita Temp/Vita) served as Control. Four 3DRs (Cosmos-SLA/Yller, Cosmos-DLP/Yller, PriZma-Bioprov/Makertech, Nanolab/Wilcos) were used in three printing orientations (0°, 45°, and 90°). Printed samples were cleaned with isopropyl alcohol prior to post-curing in specific post-curing units. For each group, 20 bar-shaped samples (25 × 2x2 mm) and ten disc-shaped samples (15-mm diameter, 2.5-mm thick) were obtained. The dimensions of bar samples were measured and the mean percent errors were compared to the reference (digital) values to obtain "accuracy" (n = 20). Samples were then aged in distilled water at 37 °C and half were submitted to a three-point bend test in a universal testing machine after 24 h and the other half after 1 year (n = 10). Disc samples were polished prior to microhardness evaluation (n = 10). Microstructure and elemental composition of filler particles in the 3DRs were analyzed using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) (n = 3). Accuracy and microhardness were submitted to two way-, and FM and FS to three way-ANOVA, followed by Tukey's tests. Results of experimental groups were compared to a milled PMMA Control using Dunnett's tests, and Student's t-tests compared FM and FS to Control at different aging periods (α = 0.05). RESULTS: Except for Cosmos-DLP, the 90° orientation demonstrated the best overall accuracy in all dimensions evaluated. The overall accuracy of Cosmos-SLA was not significantly different from Control and higher than other 3DRs. The FM of all 3DRs was lower than Control, regardless of orientation and aging period. After 1 year of aging, FS of 45°-Cosmos-SLA and all orientations of PriZma were not different from Control, while 90°-Cosmos-SLA was higher. Build orientation had no influence on microhardness of the 3DRs: Nanolab was the only resin harder than Control. Very few nanometric spherical filler particles were found in Cosmos-SLA, Cosmos-DLP, and PriZma, while Nanolab presented higher number of particles having irregular shapes and sizes. CONCLUSIONS: In general, although build orientation did not influence microhardness results, the 90° -orientation resulted in the best overall accuracy for most 3DRs. After 1-year water storage, Cosmos-SLA printed vertically showed the highest FS, while the PMMA Control obtained the highest FM for both aging periods.

Irradiance differences in the violet (405 nm) and blue (460 nm) spectral ranges among dental light-curing units.

PROBLEM: Previous studies identified nonuniformity in the irradiance at the tip end of a variety of dental light-curing units (LCUs) and correlated those differences with potential clinical implications, but the spectral dependence of the irradiance uniformity has not yet been addressed. PURPOSE: This study examined the irradiance uniformity across emitting tips of LCUs at two emission wavelengths, 405 and 460 nm. Two broadband emission light units (quartz-tungsten-halogen [QTH] and plasma arc [PAC]), and four commercial light-emitting diode (LED)-type LCUs were examined. MATERIALS AND METHODS: The spectral radiant power from six LCUs was measured using a laboratory grade spectroradiometer (Ocean Optics, Dunedin, FL, USA). The spatial and spectral characteristics of irradiance across the emitting tips of these light units were recorded through 10-nm wide bandpass filters (centered at 405 nm [violet] or 460 nm [blue]) using a laser beam analyzer (Ophir-Spiricon, Logan, UT, USA). Irradiance distributions were reported using two-dimensional contour and three-dimensional isometric color-coded images. Irradiance uniformity at the tip end was determined using the Top Hat Factor (THF) for each filtered wavelength. RESULTS: Irradiance distributions from the QTH and PAC units were uniformly distributed across the tip end of the light guide, and THF values, measured through the 405 and 460-nm filters, were not significantly different. However, the three polywave LED units delivered non-uniform irradiance distributions with THF values differing significantly between the 405 and 460-nm emission wavelengths for each unit. Areas of nonuniformity were attributed to the locations of the various types of LED chips within the LCUs. CONCLUSION: All three polywave LED units delivered a nonuniform irradiance distribution across their emitting tip ends at the two important emission wavelengths of 405 nm and 460 nm, whereas the broadband light sources (QTH and PAC) showed no evidence of spectral inhomogeneity at these wavelengths.

In vivo temperature measurement: tooth preparation and restoration with preheated resin composite.

STATEMENT OF THE PROBLEM: Composite preheating has shown to improve material physical properties in vitro, but no data exist on the use of this technique in vivo during placement. PURPOSE: The study aims to measure in vivo prepared tooth surface temperature during a restorative procedure using resin composite either at room temperature (23.6°C) or preheated to 54.7°C in a commercial compule heating device set to heat at 60°C. METHODS: Class I preparations (N=3) were made on a patient requiring multiple posterior restorations. A probe containing two thermocouples was used to record temperature values at the tooth pulpal floor and 2mm higher (top of the tooth preparation/restoration) after tooth preparation (prep), acid etching (etch), placement and curing of a bonding agent (BA), and during placement of composite used at room temperature (RT) or preheated in a commercial device (Calset(TM) , AdDent Inc., Danbury, CT, USA) set to 60°C. Data were compared with two-way analysis of variance, Tukey-Kramer post hoc test (α=0.05). RESULTS: No significant difference in pulpal floor temperature existed between prep (27.8°±1.3°C) and etch (26.3°±1.3°C), which were significantly lower than BA (30.5°±1.3°C) (p=0.0001). Immediate placement of preheated composite resulted in significantly higher pulpal floor (36.2°±1.9°C) (p=0.0025) and top composite temperatures (38.4°±2.2°C) (p=0.0034) than RT values (30.4°±2.2°C and 29.6°±0.9°C, respectively). CONCLUSIONS: In vivo use and placement of preheated resin composite resulted in temperature increase of 6° to 8°C than room temperature material. These values, however, were much lower than expected. CLINICAL SIGNIFICANCE: Although having many potential benefits, composite preheating may not be as clinically effective in delivering resin of predetermined temperature at the time of cure as laboratory experiments would suggest. Despite only moderate composite temperature increase over use of room temperature material, preheating still provides advantages in terms of ease of handling and placement.

Irradiance uniformity and distribution from dental light curing units.

PROBLEM: The irradiance from dental light-curing units (LCUs) is commonly reported as a single number, but this number does not properly describe the light output. PURPOSE: This study examined the irradiance uniformity and distribution from a variety of LCUs as well as the effect of different light guides. MATERIALS AND METHODS: Five LCUs representing quartz-tungsten-halogen, plasma arc, and light emitting diode units were evaluated. One LCU was evaluated using two different light guides (Standard or Turbo style). The total power emitted from each LCU was measured and the irradiance calculated using conventional methods (I(CM)). In addition, a beam profiler was used to determine the optically active emitting area, the mean irradiance (I(BP)), the irradiance distribution, and the Top Hat Factor (THF). Five replications were performed for each test and compared using analysis of variance with Fisher's PLSD tests at a pre-set alpha of 0.05. RESULTS: The spatial distribution of the irradiance from LCUs was neither universally symmetrical nor was it uniformly distributed across the tip end. Significant differences in both the emitted power and THF were found among the LCUs. The THF values ranged from a high of 0.74 +/- 0.01 to a low of 0.32 +/- 0.01. Changing from a standard to a turbo light guide increased the irradiance, but significantly reduced beam homogeneity, reduced the total emitted power, and reduced the optical tip area by 60%. CONCLUSIONS: Using different light guides on the same LCU significantly affected the power output, irradiance values, and beam homogeneity. For all LCUs, irradiance values calculated using conventional methods (I(CM)) did not represent the irradiance distribution across the tip end of the LCU. CLINICAL SIGNIFICANCE Irradiance values calculated using conventional methods assume power uniformity within the beam and do not validly characterize the distribution of the irradiance delivered from dental light curing units.

The effect of chlorine-based disinfectant on wettability of a vinyl polysiloxane impression material.

STATEMENT OF PROBLEM: Extended contact of impression materials with chemical disinfectant could remove surfactant, significantly altering the contact angle and wettability characteristics of an impression material. PURPOSE: The purpose of this study was to determine the effect of contact time of chemical disinfectant solution on the dynamic contact angle of a commercial vinyl polysiloxsane impression material. MATERIAL AND METHODS: Discs (3.5 × 25 mm) of heavy-body and wash consistencies of material (n=5) were fabricated and either left untreated, or subjected to spray treatment with a commercial disinfectant for various lengths of time (1, 20, or 60 minutes, or 24 hours). Treated specimens were washed and dried, after which dynamic contact angle measurements of a water droplet were determined at various points in time after deposition: 0, 2, 5, 10, 15, and 20 seconds. The same wash product was used without added surfactant (control). For a given type of impression material, contact angles were subjected to 1-way ANOVA within each droplet deposition time for all periods of disinfectant contact (α=.05). The Tukey-Kramer post hoc test was applied for pairwise means comparisons. RESULTS: For each impression material type, significant increases in contact angles were found as the duration of disinfectant contact increased, at each measured droplet deposition time point. For both materials containing surfactant, extended contact with chemical disinfectant resulted in increased contact angles that were not significantly different from those of the nonsurfactant-containing control product. CONCLUSIONS: Increasing the contact time between a surfactant-containing impression material and a disinfecting solution can significantly alter the resulting contact angle of the impression material and render it similar to a material depleted of surfactant. Following manufacturer-recommended chemical disinfection times reduces surfactant loss and only minimally affects surface wettability.

The effect of acid etchant type and dentin location on tubular density and dimension.

STATEMENT OF PROBLEM: Coronal and radicular dentin may react differently to the type of acid treatment used when bonding to these substrates. PURPOSE: The purpose of this study was to characterize and compare dentin morphology, tubular density, and cross-sectional area in deep coronal (around an exposed pulp horn) and root canal dentin at the cervical third in the intact state and after acid etching with phosphoric acid or self-etching dentin primer. MATERIAL AND METHODS: Extracted, human, caries-free premolars were fixed. Smear layer-free sections (control) were obtained and divided into 3 groups: left intact, etched with phosphoric acid, or etched with a self-etching primer from a dentin bonding system. Specimens were examined using scanning electron microscopy. Tubular density and cross-sectional area were determined from the images using software. Values were submitted to multifactorial ANOVA (alpha=.05). RESULTS: Tubular density was not significantly affected by acid type or by dentin location. Acid type significantly (P<.001) affected tubular cross-sectional area: phosphoric acid > self-etching resin > intact dentin, irrespective of dentin location. All acid-treated specimens showed demineralization, and irregular surface morphology was not affected by either acid treatment. CONCLUSIONS: Tubular density was not significantly different between deep coronal and root canal dentin nor affected by acid treatment type. Tubular cross-sectional area did not differ between deep coronal or root canal dentin, regardless of acid treatment. Both acid types significantly increased tubular cross-sectional area at both dentin locations, phosphoric acid to a greater degree than the self-etching primer. Root canal dentin did not display peritubular dentin.

Pairing orthodontic adhesive resins and light-curing units for optimal degree of conversion.

OBJECTIVES: The purpose of this study was to identify the combination of orthodontic adhesive resins and light-emitting diode (LED) light-curing units (LCUs) that result in the highest degree of resin conversion (DC). The hypothesis tested was that pairing orthodontic resins with LCUs from the same manufacturer produces higher DC versus unpaired resins and LCUs. METHODS: Pre-polymerization spectra of adhesive resins (Transbond XT [3M Unitek], BracePaste [American Orthodontics] or Opal Bond MV [Opal by Ultradent]) were obtained at oral temperature (37°C) using an attenuated total reflectance (ATR) diamond crystal (Golden Gate, Specac) in a Fourier-transform infrared (FTIR) spectrometer (Nicolet IS50). Resin specimens were polymerized using various LCUs (Ortholux Luminous [3M Unitek], Blue Ray 3 [American Orthodontics], or VALO Ortho Cordless [Ultradent Products, Inc.]) before obtaining post-polymerization infrared (IR); spectra. Twelve LCU-resin combinations were tested (n = 20/combination), half with a bracket present (Mini Diamond Twin, Ormco) and half without. DC values (%) were calculated using the two-frequency method and tangent-baseline technique. Data for each resin were statistically analyzed using General Linear Models and Student-Newman-Keuls post hoc tests (α = 0.05). RESULTS: Statistically significant differences were found within each resin for the groups without brackets present (P < 0.0001), the groups with brackets present (P < 0.0001), and the groups with brackets when compared with the manufacturer-paired group without a bracket (P < 0.0001). CONCLUSIONS: Adhesive resins and LCUs from the same manufacturer did not consistently result in statistically higher mean DC values than unpaired combinations. Metal brackets do not uniformly reduce the degree of conversion of adhesive resins when assessed using IR spectrometry.

Effect of sodium sulfinate salts on the polymerization characteristics of dual-cured resin cement systems exposed to attenuated light-activation.

OBJECTIVES: To evaluate the effectiveness of sodium sulfinate salt co-initiators on the degree of conversion (DC) of dual-cured cementing systems [combination of bonding agent (BA) and resin cement (RC)] when the activating light is attenuated or not available. METHODS: Two 5th generation products [Prime&Bond NT Dual-Cure/Calibra (Dentsply), and Excite DSC/Variolink II (Ivoclar/Vivadent)] were applied, either with or without co-initiators (sodium sulfinate salts) added to the bonding agents, to the surface of a horizontal attenuated-total-reflectance unit, and were polymerized using one of four conditions: self-cure (SC), or direct light exposure (DLE/XL3000/3M) through a glass slide or through pre-cured resin discs (shades A2 or A4/2mm-thick) (Z250/3M-ESPE). Real-time infrared spectra were obtained after placing components (uncured) and during 10 min (cured) (16 scans at 2 cm(-1), FTS-40/Digilab/Bio-Rad) to obtain polymerization kinetics. DC and maximum rate of polymerization (Rpmax) were calculated using standard techniques of observing changes in aliphatic-to-aromatic peak ratios pre- and post-curing. Data (n=5) were analyzed by two-way ANOVA and Tukey's test (p=0.05). RESULTS: The addition of co-initiators increased the DC in most of the groups. No significant difference in DC was observed between Prime Bond NT Dual-Cure/Calibra and its version without co-initiator using the DLE curing mode. All DLE groups exhibited the highest DC after 10 min. No significant difference in DC was observed between A2 and A4 pre-cured overlay groups. The SC groups exhibited lower DC than the light-activated groups regardless of the presence of co-initiator. Use of co-initiators increased the Rpmax only in the SC groups. The A2 and A4 groups exhibited lower Rpmax than DLE groups, regardless of the presence of co-initiator. CONCLUSION: The detrimental effects of light attenuation on the DC were not avoided by inclusion of sodium sulfinate salts, despite their ability to eliminate the chemical incompatibility between acidic monomers and self-curing components.