Comparison of the operative time and presence of voids of incremental and bulk-filling techniques on Class II composite restorations.

OBJECTIVES: To compare the operative time and presence of air voids on Class II restorations fabricated by dental practitioners with 1 to 5 years of experience using incremental and bulk-filling techniques. METHOD AND MATERIALS: Four techniques were evaluated: incremental, bulk-filling, bulk-filling with heated composite, and snowplow technique. Standardized mandibular first molars with a MOD (mesial, occlusal, and distal) cavity were used. Voluntary operators made two restorations using each technique and the time required for each restoration was recorded. The restorations were scanned by micro-computed tomography to calculate the volume of the restoration occupied by air voids. The "operative time" and "volume of air voids" were analyzed individually by two-way ANOVA and Tukey HSD post hoc (α = .05) for the factors operator and insertion technique. A correlation between "operative time" and "volume of air voids" was evaluated using Pearson coefficient (α = .05). RESULTS: The incremental technique required significantly longer time, yet no differences were observed between the bulk-filling techniques. There were no significant differences between techniques regarding the volume of air voids. A significant, but weak, and inverse linear correlation (P = .0059; r = -.29; r2 = 8.41%) was found between the operative time and volume of air voids. CONCLUSION: There were no significant differences in the volume of air voids among the evaluated techniques, although bulk-filling techniques required a shorter operative time. Hence, implementing bulk-filling techniques by dental schools and restorative dental practitioners with different levels of expertise may reduce chair time and produce a volume of air voids similar to the incremental technique.

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

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/cm2 emittance) and a homogenizer tip (HT, 946 mW/cm2 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.

Light Curing in Dentistry.

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

The dental curing light: A potential health risk.

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

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

OBJECTIVE: Exposure reciprocity suggests that, as long as the same radiant exposure is delivered, different combinations of irradiance and exposure time will achieve the same degree of resin polymerization. This study examined the validity of exposure reciprocity using real time degree of conversion results from one commercial flowable dental resin. Additionally a new fitting function to describe the polymerization kinetics is proposed. METHODS: A Plasma Arc Light Curing Unit (LCU) was used to deliver 0.75, 1.2, 1.5, 3.7 or 7.5 W/cm(2) to 2mm thick samples of Tetric EvoFlow (Ivoclar Vivadent). The irradiances and radiant exposures received by the resin were determined using an integrating sphere connected to a fiber-optic spectrometer. The degree of conversion (DC) was recorded at a rate of 8.5 measurements a second at the bottom of the resin using attenuated total reflectance Fourier Transform mid-infrared spectroscopy (FT-MIR). Five specimens were exposed at each irradiance level. The DC reached after 170s and after 5, 10 and 15 J/cm(2) had been delivered was compared using analysis of variance and Fisher's PLSD post hoc multiple comparison tests (alpha=0.05). RESULTS: The same DC values were not reached after the same radiant exposures of 5, 10 and 15 J/cm(2) had been delivered at an irradiance of 3.7 and 7.5 W/cm(2). Thus exposure reciprocity was not supported for Tetric EvoFlow (p<0.05). SIGNIFICANCE: For Tetric EvoFlow, there was no significant difference in the DC when 5, 10 and 15J/cm(2) were delivered at irradiance levels of 0.75, 1.2 and 1.5 W/cm(2). The optimum combination of irradiance and exposure time for this commercial dental resin may be close to 1.5 W/cm(2) for 12s.

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

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.

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

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.

Localised irradiance distribution found in dental light curing units.

OBJECTIVE: To measure the localised irradiance and wavelength distributions from dental light curing units (LCUs) and establish a method to characterise their output. METHODS: Using a laboratory grade integrating sphere spectrometer system (Labsphere and Ocean Optics) the power, irradiance, and spectral emission were measured at the light tips of four LCUs: one plasma-arc (PAC) unit, one single peak blue light-emitting diode (blue-LED) unit, and two polywave LED (poly-LED) units. A beam profiler camera (Ophir Spiricon) was used to record the localised irradiance across the face of the light tips. The irradiance-calibrated beam profile images were then divided into 45 squares, each 1mm(2). Each square contained the irradiance information received from approximately 3200 pixels. The mean irradiance value within each square was calculated, and the distribution of irradiance values among these 45 squares across the tip-ends was examined. Additionally, the spectral emission was recorded at various regions across each light tip using the integrating sphere with a 4-mm diameter entrance aperture. RESULTS: The localised irradiance distribution was inhomogeneous in all four lights. The irradiance distribution was most uniformly distributed across the PAC tip. Both the irradiance and spectral emission from the poly-LED units were very unevenly distributed. CONCLUSIONS: Reporting a single irradiance value or a single spectral range to describe the output from a curing light is both imprecise and inappropriate. Instead, an image of both the irradiance distribution and the distribution of the spectral emission across the light tip should be provided. CLINICAL SIGNIFICANCE: The localised beam irradiance profile at the tip of dental LCUs is not uniform. Poly-LED units may deliver spectrally inhomogeneous irradiance profiles. Depending on the photoinitiator used in the RBC and the orientation of the LCU over the tooth, this non-uniformity may cause inadequate and inhomogeneous resin polymerisation, leading to poor physical properties, and premature failure of the restoration.

Evaluation of ocular hazards from 4 types of curing lights.

OBJECTIVE: To assess the risk of ocular damage from 4 types of light curing units (LCUs) and to estimate the maximum permissible ocular exposure times from each LCU during an 8-hour workday. METHODS: Extracted human maxillary teeth were mounted in a dentoform. Four types of LCUs (plasma arc, low-power and high-power light-emitting diode, and quartz-tungsten-halogen) were used to cure a simulated restoration in the maxillary central incisor from the facial and palatal aspects. To simulate ocular exposure, the spectral irradiance (W/[cm2 · nm]) from the LCUs was measured 5 times at each of 3 distances (30 cm, 50 cm and 100 cm) from the tooth, using a cosine-corrected probe attached, via a fibre optic cable, to a calibrated spectroradiometer. The weighted blue-light and effective ultraviolet (UV) irradiances that would be received by the eye from each LCU were calculated. RESULTS: The maximum permissible daily exposure limits for UV light exceeded 8 hours at all distances and orientations. The maximum permissible cumulative daily exposure time to blue light was as low as 6 seconds when curing from the palatal aspect with the plasma arc LCU and as high as 1.5 hours when the low-power light-emitting diode LCU was used from the facial aspect. CONCLUSIONS: The 4 LCUs tested did not pose a risk of UV-mediated ocular damage. The higher-powered lamps showed potential to cause blue-light-mediated ocular damage at shorter distances, with damage potentially occurring after cumulative viewing of only 6 seconds at the 30-cm distance during an 8-hour workday.

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.

Knoop hardness of five composites cured with single-peak and polywave LED curing lights.

OBJECTIVE: To compare the ability of four light-emitting diode (LED) curing lights to polymerize five composite resins in 10 seconds at 4 and 8 mm. METHOD AND MATERIALS: Two second-generation, single-peak LED curing lights (Bluephase 16i, Ivoclar Vivadent, and LEDemetron II, Kerr) and two third-generation polywave LED curing lights (UltraLume 5, Ultradent, and Bluephase G2, Ivoclar Vivadent) were compared. Three examples of each brand of curing light were used, and their light outputs were measured with a spectro-radiometer. Five composite resins (Filtek Supreme A2B, 3M ESPE; Vit-l-escence A2, Ultradent; Aelite LS Posterior A2, Bisco; and Tetric EvoCeram A2 and Tetric EvoCeram Bleach M, both Ivoclar Vivadent) were polymerized for 10 seconds at 4 and 8 mm from the end of the light guide. The Knoop microhardness (KHN50gf) was measured at 49 locations across the top and bottom surfaces of the specimens to determine the ability of each light to cure each brand of composite in 10 seconds. RESULTS: At 4 and 8 mm, the Bluephase G2 light delivered the broadest spectral range of wavelengths, greatest irradiance, and energy density. The Bluephase G2 always produced harder, better-cured resins compared to the other three lights. Overall, the ability of the lights to cure these five composites was ranked from highest to lowest: Bluephase G2, UltraLume 5, Bluephase 16i, and LEDemetron II (ANOVA with REGWQ multiple comparison test, P < .01). CONCLUSION: This study suggests that polywave LED curing lights should be used in preference to single-peak LED curing lights.

Factors affecting the energy delivered to simulated class I and class v preparations.

PURPOSE: To determine the effect of operator, curing light and preparation location, as well as any correlations among these variables, on the amount of light energy delivered to simulated cavity preparations. MATERIALS AND METHODS: Each of 10 dentists and 10 fourth-year dental students light-cured a Class I preparation in tooth 26 and a Class V preparation in tooth 37 in a dental mannequin head. The operators exposed each preparation for 10 seconds with each of 3 LED-based curing lights (Bluephase G2 on high power, Demi and VALO on standard power). Each operator also used the VALO unit in the plasma mode for 2 sequential 3-second curing cycles. For each combination of operator, curing light and preparation, the irradiance (mW/cm(2)) received at the base of the preparation was measured with a laboratory-grade spectroradiometer, and software was used to calculate the energy density delivered in real time. The statistical analysis included 3-way analysis of variance (ANOVA) and the Fisher protected least significant difference (PLSD) test for post hoc pairwise comparisons. RESULTS: There was a large qualitative and quantitative variation in the irradiance delivered to the preparations by each operator. Three-way ANOVA showed no statistically significant differences between dentists and dental students in terms of the amount of energy delivered (p = 0.90). However, there were statistically significant differences in energy delivered by the various curing lights (p < 0.001) and between the 2 preparation locations (p < 0.001). According to the Fisher PLSD test for post hoc pairwise comparison of means, the VALO unit used in the plasma mode for two 3-second curing cycles delivered the most energy (16.4 +/- 3.1 J/cm(2)) to the Class I preparation, and the same light used for 10 seconds in the standard mode delivered the least amount of energy (9.9 +/- 2.4 J/cm(2)) (p < 0.001). For the Class V preparation, the VALO unit used in the plasma mode for two 3-second curing cycles delivered the most energy (12.5 +/- 4.0 J/cm(2)), and the Demi unit, used for 10 seconds, delivered the least energy (7.4 +/- 2.5 J/cm(2)). CONCLUSIONS: The energy delivered by a curing light to a preparation in a simulated clinical environment was affected by the operator's light-delivery technique, the choice of curing light and the location of the preparation.

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.

Quantifying light energy delivered to a Class I restoration.

PURPOSE: To measure the amount of light energy that dental students actually deliver to a Class I preparation in a dental mannequin. MATERIALS AND METHODS: Approval for the study was obtained from the Dalhousie University Health Sciences Research Ethics Board. Each of 20 third-year dental students light-cured a Class I preparation in tooth 27 in a mannequin head. A photodetector located at the bottom of the cavity preparation measured how much light would be received by a restoration. Each student cured the simulated restoration for 20 seconds using a quartz-tungsten-halogen curing light (Optilux 401). The irradiance received (mW/cm2) was recorded in real time, and the energy per unit area (J/cm2) delivered to the detector by each student was calculated. The students were then given detailed instructions on how to effectively use the curing light, and the experiment was repeated. RESULTS: When the curing light was fixed directly over the tooth, the greatest amount of light energy delivered to the detector in 20 seconds was 13.9 +/- 0.4 J/cm2. Before instruction, the students delivered between 2.0 and 12.0 J/cm2 (mean +/- standard deviation [SD]: 7.9 +/- 2.7 J/cm2). After receiving detailed instructions, the same students delivered between 7.7 and 13.4 J/cm2 (mean +/- SD: 10.0 +/- 1.4 J/cm2). A paired student"s t test showed that instruction resulted in a significant improvement (p < 0.001). CONCLUSIONS: Although instruction yielded improvements, the mean energy delivered was much less (7.9 J/cm2 before instruction and 10.0 J/cm2 after instruction) than the expected 13.9 J/cm2. To maximize the energy delivered, the operator should wear eye protection, should watch what he or she is doing and should hold the light both close to and perpendicular to the restoration.

Knoop microhardness mapping used to compare the efficacy of LED, QTH and PAC curing lights.

This study used a hardness mapping technique to compare the ability of seven curing lights to polymerize five composites. Six curing lights (Sapphire [plasma-arc: PAC], Bluephase16i [light emitting diode: LED], LEDemetron II [LED], SmartLite IQ [LED], Allegro [LED] and UltraLume-5 [Polywave LED]) were compared to an Optilux 501 (halogen: QTH) light. Five resin composites (Vit-1-escence, Tetric Evoceram, Filtek Z250, 4 Seasons and Solitaire 2) were polymerized at 4 mm and 8 mm from the end of the light guide. Four composites were light cured for the following times using these lights: Sapphire (5 seconds), Bluephase16i (5 seconds), LEDemetron II (5 seconds), SmartLite IQ (10 seconds), UltraLume-5 (10 seconds), Allegro (10 seconds) and Optilux 501 (20 seconds). Solitaire 2 required double these irradiation times. On each specimen, the Knoop microhardness (KHN) was measured at 49 locations across a 3 x 3 mm grid to determine the ability of each light to cure each brand of composite. The PAC light delivered the broadest spectrum of wavelengths, the greatest irradiance and hardness values that were 4.7 to 18.1 KHN(50gf) harder than the other lights. The ability of the lights to cure these five composites was ranked from highest to lowest: Sapphire, Optilux 501, Allegro, UltraLume-5, SmartLite IQ, LEDemetron II and Bluephase16i (ANOVA with REGWQ multiple comparison adjustment, p < 0.01).

Effect of configuration factor on shear bond strengths of self-etch adhesive systems to ground enamel and dentin.

Self-etch bonding systems are easy to use and popular in dental practice. The current study examined the in vitro shear bond strengths to dentin and ground enamel of four self-etch bonding systems and a two-step etch-and-rinse bonding system. Two hundred extracted non-carious human molars were used. Approximately 0.5 mm of enamel was removed from the buccal surface of 100 teeth and the bond strengths of this enamel surface were determined. The buccal surface of the remaining 100 teeth was ground away to create a standardized smear layer on dentin. Five adhesive systems were used: Adper Single Bond Plus (ASB): two-step etch-and-rinse); Adper Scotchbond SE (AS), Clearfil SE Bond (CSE-both two-step self-etch); XENO V (X) and Adper Easy Bond (AE): both one-step self-etch). Filtek Z250 composite was bonded to the tooth using each adhesive system in a low configuration (C) factor (0.2) and a high C-factor (4.4) mold (10 teeth in each group). The specimens were thermal cycled 2,000x, then subjected to a shear bond strength test. The data were compared with analysis of variance using the Fisher's PLSD multiple comparison tests. A three-factor ANOVA showed that, overall, the shear bond strength was significantly higher in the low C-factor group 4.33 MPa (p < 0.0001). There was also a significant difference in the shear bond strengths among the bonding systems (p < 0.0001). The higher C-factor molds had the same adverse effect on all bonding systems and on both enamel and dentin, but the bonding systems acted differently on enamel and dentin (three-factor ANOVA p < 0.0001). The two-step etch-and-rinse system (ASB) consistently delivered the highest bond strengths (34.6-41.5 MPa). Fisher's PLSD comparisons showed that, in the high C-factor mold, there was no significant difference between the shear bond strengths of SB, EB and CSE to dentin, and SB, X and SE to enamel (p > 0.05). The one-step self-etch AE system delivered the lowest shear bond strengths (23.9 MPa) to enamel (p < 0.05). The two-step self-etch system AS delivered the lowest shear bond strengths (23.9 MPa) to dentin (p < 0.05).

Effect of delivering light in specific narrow bandwidths from 394 to 515nm on the micro-hardness of resin composites.

OBJECTIVES: This study investigated the wavelength-dependent photosensitivity of eleven resin composites (Admira A2, Heliomolar A2, Herculite XRV A2, Pyramid Dentin A2, Solitaire 2 A2, Z250 A2, AElite LS A2, Vit-l-escence A2, Tetric Ceram Bleach XL, Tetric Ceram A2, Pyramid Enamel Neutral). METHODS: Resin composites 1.6mm thick were exposed to narrow bandwidths of light at the following peak wavelengths: 394, 400, 405, 410, 415, 420, 430, 436, 442, 450, 455, 458, 467, 470, 480, 486, 493, 500, 505, and 515+/-5nm. A spectroradiometer was used to ensure that the same irradiance (mW/cm(2)) and total energy density (J/cm(2)) was delivered through each filter. For each resin composite, three specimens were exposed through each filter. The Knoop micro-hardness at the top and bottom of the composites was then measured. The wavelength-dependent photosensitivity of each resin composite was analyzed by plotting the mean hardness achieved at each wavelength. RESULTS: The composites responded variably when they received light through the narrow bandpass filters. Six resin composites had a single peak of wavelength-dependent photosensitivity at approximately 470nm. Four resin composites had two peaks of wavelength-dependent photosensitivity at approximately 470 and approximately 405nm. One resin composite had a single peak of wavelength-dependent photosensitivity at approximately 405nm and was only sensitive to light below 436nm. SIGNIFICANCE: Using light delivered through narrow bandpass filters is a convenient method to determine the wavelength-dependent photosensitivity of resins and can be used to predict the performance of dental curing lights.

Third-generation vs a second-generation LED curing light: effect on Knoop microhardness.

Third-generation light-emitting diode (LED) curing lights use several different types of LEDs within the light to deliver a broader spectral output compared with the narrower spectral output of second-generation curing lights. This study determined the benefits of this broader spectral output. A third-generation LED curing light was modified so that the 4 peripheral LEDs, which provide the lower wavelengths, could be turned on or off, allowing the light to be used as a third- or a second-generation LED curing light. Twelve composites of A2 and lighter shades were packed into molds 2 mm deep with an internal diameter of 12 mm, and then irradiated for 20 seconds. A laboratory-grade spectroradiometer was used to ensure that all the specimens received the same irradiance and total energy (16.82 J/cm2) from the curing light in both the second- and third-generation modes. The results showed the benefits of using a broader spectrum third-generation LED curing light. This light produced composites that were as hard as when the narrower spectrum second-generation LED curing light was used (P < or = .01). In 7 of the 12 resin composites, the top surface was harder when the third-generation LED curing light was used (P < or = .01).

Effect of reduced exposure times on the microhardness of 10 resin composites cured by high-power LED and QTH curing lights.

PURPOSE: To compare the effect of reduced exposure times on the microhardness of resin composites cured with a "second-generation" light-emitting diode (LED) curing light and a quartz-tungsten-halogen (QTH) curing light. METHODS: Ten composites were cured with a LED curing light for 50% of the manufacturers" recommended exposure time or a QTH light at the high power setting for 50% of the recommended time or on the medium power setting for 100% of the recommended time. The composites were packed into Class I preparations in extracted human molar teeth and cured at distances of 2 or 9 mm from the light guide. The moulds were separated, and the Knoop microhardness of the composites was measured down to 3.5 mm from the surface. RESULTS: The LED light delivered the greatest irradiance at 0 and 2 mm, whereas the QTH light on the standard (high power) setting delivered the highest irradiance at 9 mm. According to distribution-free multiple comparisons of the hardness values, at 2 mm from the light guide the LED light (50% exposure time) was ranked better than or equivalent to the QTH light on the high power setting (50% exposure time) or on the medium power setting (100% exposure time). At 9 mm, the LED light was ranked better than or equivalent to the QTH light (both settings) to a depth of 1.5 mm, beyond which composites irradiated by the LED light were softer (p < 0.01). At both distances, the QTH light operated on the high power setting for 50% of the recommended exposure time produced composites that were as hard as when they were exposed on the medium power setting for 100% of the recommended exposure time. CONCLUSIONS: The ability to reduce exposure times with high-power LED or QTH lights may improve clinical time management.