Influence of light exposure techniques on in vitro pulp temperature rise during bulk fill composite Class I restorations.

This in vitro study assessed peak temperature and temperature increase (ΔT) within the pulp chamber during different extended photoactivation techniques (EPT-applying similar radiant exposure values) to resin-based composites (RBCs) placed in a Class I cavity preparation in an extracted human lower third molar. A T-type thermocouple was placed in the pulp chamber and connected to a temperature analysis device (Thermes, Physitemp). The tooth was attached to an assembly simulating the in vivo environment (controlled baseline pulp chamber temperature and fluid flow). The real-time pulp chamber temperature was evaluated throughout the photoactivation (Bluephase N, Ivoclar Vivadent) of two bulk-fill RBCs: Tetric N Ceram Bulk Fill (TBF; shade: IVA; Ivoclar Vivadent); Surefill SDR flow + (SDR, shade: Universal; Dentsply Sirona), which were exposed to different curing techniques: 40 s-occlusal surface; 20 s-occlusal + 10 s-buccal + 10 s-lingual surfaces; 10 s-buccal + 10 s + lingual + 20 s-occlusal surfaces. Each EPT delivered 42.4 J/cm2. Vickers hardness (VHN) was measured on the removed, sectioned RBC restorations at the top and bottom middle areas after curing. ΔT and VHN data were analyzed using 2-way ANOVA followed by Bonferroni post-hoc test (α = 0.05). Peak temperature data were analyzed using one-way ANOVA and Dunnett's post-hoc test (α = 0.05). SDR showed higher ΔT values than TBF (p = 0.008) in some EPTs. Neither technique resulted in ΔT values greater than 5.5 °C. Both composites had acceptable bottom/top hardness ratios (greater than 80%), regardless of the photoactivation technique. The evaluated EPTs may be considered safe as a low-temperature increase was noticed within the pulp chamber.

Effect of extended light activation and increment thickness on physical properties of conventional and bulk-filled resin-based composites.

OBJECTIVES: To evaluate the biaxial flexural strength (BFS), flexural modulus (BFM), and Knoop microhardness (KHN) of incremental and bulk-filled resin-based composites (RBCs) using extended curing exposure times. MATERIALS AND METHODS: Disc specimens (n = 8; 6-mm diameter) were fabricated using three stacked molds (0.5-mm thick for the top and bottom molds, and a 1-mm-thick center mold for the conventional and 3-mm thick for the bulk-fill RBCs). Conventional (Tetric EvoCeram/TCE and Filtek Z250/FIZ) and bulk-fill RBCs (Tetric EvoCeram Bulk Fill/TBF and Filtek One Bulk Fill Restorative/FOB) were evaluated. The stacked RBC-filled molds were light-cured for (1) the manufacturer-recommended exposure (MRE) duration; (2) 50%, and (3) 100% extension of the MRE. The BFS, BFM, and KHN of the top and bottom discs were measured. BFS and BFM were analyzed by three-way ANOVA (material*curing time*depth) and Tukey's post hoc (α = 0.05). KHN was analyzed by two-way ANOVA (curing time*depth) and Tukey's post hoc (α = 0.05). RESULTS: Extending the exposure duration did not change the BFS and BFM on the top of the RBCs, but the BFS and KHN increased at the bottom of bulk-fill RBCs. For the conventional RBCs, TCE showed the highest increase on BFS at the bottom, going from 53.6 MPa at T1 to 69.9 at T3. Among the bulk-fill RBCs, FOB presented the highest increase on the bottom BFS (T1: 101.0 ± 19.9 MPa, T3: 147.6 ± 12.9 MPa). For all RBCs and exposure times, BFS and KHN were lower at the bottom. Only FIZ and FOB reached a bottom-to-top hardness ratio of 80%, at T3 and T2. CONCLUSION: A significant increase on the BFS and KHN on the bottom of bulk-fill RBCs can be observed when the time of exposure to the curing light is double the MRE. However, extended exposure does not eliminate differences on the BFS and KHN between the shallow and deep regions of RBCs. TCE and TBF failed to reach an acceptable B/T hardness ratio at all evaluated exposure times. CLINICAL RELEVANCE: Mechanical properties of RBCs can be affected by insufficient polymerization, specially at deeper regions of the increment. Therefore, clinicians should consider applying twice the MRE to curing-light to polymerize the maximal increment thickness of bulk-fill RBCs.

Effects of shades of a multilayered zirconia on light transmission, monomer conversion, and bond strength of resin cement.

OBJECTIVE: To evaluate the influence of shades of a multilayered zirconia on light transmission, resin cement degree of conversion, and shear bond strength of resin cement. MATERIALS AND METHODS: The light transmission through opaque (OPQ) and translucent (TNS) regions of Katana UTML zirconia (Kuraray Noritake Dental) were evaluated for using a spectroradiometer (n = 5). Degree of conversion of dual-cure resin cement (Panavia V5, Kuraray Noritake Dental) was measured after light-activation through OPQ or TNS regions and direct exposure. Composition of the zirconia was analyzed with energy dispersive x-ray spectroscopy (EDS). Shear bond strength (SBS) was evaluated on the OPQ and TNS regions after 24 h and 1 year from specimen preparation (n = 15). RESULTS: The OPQ region produced higher irradiance loss (95.1%) than TNS one (92.9%), and lower degree of conversion (52.4%) than TNS (71.2%) at 24 h post-light activation. EDS analysis did not show differences on the microstructure of the OPQ and TNS regions. There were no significant differences on the SBS between zirconia regions. For both zirconia regions, a significant reduction on the SBS occurred after aging, being 31.7% for OPQ and 38% for TNS. CONCLUSION: Both OPQ and TNS regions affected the light transmission through the multilayered zirconia. The OPQ region yielded the highest light attenuation and the lowest degree of conversion of resin cement. Different regions of the zirconia did not influence the SBS. Clinical significance Although opaque and translucent regions of the multilayered zirconia reduced the light transmission from LED curing unit and the degree of conversion of resin cement, the regions did not affect the resin cement adhesion.

Flexural strength and microhardness of bulk-fill restorative materials.

BACKGROUND: Bulk-fill materials can facilitate the restorative procedure mainly for deep and wide posterior cavities. The purpose of this study was to evaluate flexural strength (biaxial flexural strength [BFS]) and microhardness (Knoop microhardness [KHN]) at different depths of bulk-fill materials. METHODS: Five bulk-fill materials were tested: two light-curable composite resins, one dual-cure composite, one bioactive restorative, and a high-viscosity glass ionomer. A conventional composite was used as control. BFS and KHN were tested at different depths. Data was analyzed by two- and one-way ANOVAs, respectively and Tukey's post-hoc (α=0.05). RESULTS: The high-viscosity glass ionomer material presented the lowest BFS at all depths. KHN for the two light-curable and the dual-cure bulk-fill resin composites was reduced following an increase in restoration depth, while the conventional composite, the bioactive material, and the high-viscosity glass ionomer were not affected. CONCLUSION: There are differences in the properties of the tested materials at 4 mm depth, showing that the studied properties of some materials vary according to the cavity depth, although the results are material dependent. CLINICAL SIGNIFICANCE: Mechanical properties of light-cured, bulk-fill materials may be affected by inadequate polymerization. Clinicians should consider complementary strategies to achieve adequate polymerization at high-increment depths.

Effect of Composite Polymerization Stress and Placement Technique on Dentin Micropermeability of Class I Restorations.

PURPOSE: To investigate the effect of polymerization stress and insertion technique on dentin micropermeability of composites placed under pulpal pressure. MATERIALS AND METHODS: One high-viscosity conventional (HC; Filtek Supreme Ultra; 3M Oral), one low-viscosity conventional (LC; Filtek Supreme Ultra Flowable; 3M Oral), one high-viscosity bulk fill (HBF; Filtek Bulk Fill Restorative; 3M Oral), and one low-viscosity bulk fill (LBF; Filtek Bulk Fill Flowable; 3M Oral) composite were evaluated. Polymerization stress was measured with materials bonded to acrylic rods in a universal testing machine (n = 5). Class I preparations were made in extracted molars, in which tooth roots were removed and the pulpal chambers cleaned. Preparations were coupled to a hydraulic device to simulate pulpal pressure during composite placement (n = 5). Conventional composites were placed in two horizontal increments, while bulk fill materials were placed in one, single increment. Fluid flow rate (µl/min) and dentin micropermeability (%) were monitored. The restoration interface was observed under confocal laser scanning microscopy. RESULTS: LC and LBF presented statistically significant higher polymerization stress than HC and HBF. Fluid flow rate and dentin micropermeability did not differ among the groups. However, different patterns of fluid infiltration and interface integrity were observed. HC and HBF presented well-sealed surrounding margins with small gaps along the pulpal wall, while HBF demonstrated more cracks in the adhesive layer. LC and LBF restorations had larger gaps along all bonded interfaces. CONCLUSION: No difference in polymerization stress was found when conventional and bulk fill composites with similar viscosities were compared. Neither polymerization stress or placement technique demonstrated a significant effect on dentin micropermeability. The incremental placement technique using a conventional, high-viscosity composite exhibited qualitatively better marginal integrity.

Effect of Curing Light Barriers and Light Types on Radiant Exposure and Composite Conversion.

PURPOSE: Previous research investigated the effects of curing tip barriers on light output and composite properties, but no study has measured the effect of a wide variety of barriers and curing light types on delivered radiant exposure and the resulting composite cure 2 mm below the radiated surface. MATERIALS AND METHODS: Six barrier materials and six curing light types were tested. Spectroradiometry was used to measure irradiance with and without barriers for each light type, and radiant exposure values were determined for a commercial camphorquinone-based dental composite material. Composite monomer conversion was measured at 10 minutes following exposure for each light type/barrier condition (N = 5) using infrared spectroscopy. Results were subjected to one-way analyses of variance for radiant exposure and conversion among barrier types within a given curing light: preset alpha 0.05. RESULTS: All barriers significantly reduced radiant exposure compared with the uncovered tip, but the use of the two polywave LEDs covered with a latex-based barrier demonstrated significantly lower conversion values. CONCLUSIONS: Although light-curing barriers reduce radiant exposure to a restorative material over a recommended exposure, this reduction is not sufficient to cause significant reduction in composite cure, except when using a latex-based barrier and a polywave LED curing light. CLINICAL SIGNIFICANCE: Clinicians need to be aware of the possible interaction between curing light barriers and curing light type in order to optimally photocure restorative materials.

Resistance of glaze application on indirect restorative CAD/CAM materials against abrasive toothbrushing wear.

PURPOSE: The aim of this study was to evaluate the effect of toothbrushing on the surface roughness (Sa), roughness profile (Rv), gloss units (GU) and surface morphology of three glazed ceramics. MATERIALS AND METHODS: Specimens (n=7) from different CAD/CAM materials 1- Lithium disilicate-based glass ceramic (IPS e.max CAD); 2- Zirconia-reinforced lithium silicate glass ceramic (Celtra Duo) and 3- 6 mol% yttria partially-stabilized zirconia (InCoris) were evaluated. IPS e.max CAD and InCoris specimens were sintered and all the groups were pre-polished and glazed according to the manufacturer's recommendations: IPS Ivocolor Glaze Paste (Ivoclar Vivadent) or Universal Overglaze High Flu (Dentsply/Sirona). Sa, Rv, GU and morphology were analyzed before and after brushing at 30.000, 120.000 and 180.000 cycles. The data of Sa and GU were analyzed by ANOVA two-way and post-hoc Tukey's test (α=0.05). Rv was analyzed by Kruskal-Wallis and Student-Newman-Keuls. The surface morphology was analyzed qualitatively. RESULTS: The Sa decreased significantly after 180.000 toothbrushing cycles for all materials tested. CE showed higher Rv than EM and IN, and IN showed the highest GU after 180.000 toothbrushing cycles, which promoted a polishing effect for all materials. CONCLUSION: Long-term toothbrushing was not able to jeopardize the glazed-surface of all tested materials compared to unbrushed.

Influence of filler addition, storage medium and evaluation time on biaxial flexure strength and modulus of adhesive systems.

OBJECTIVE: This study evaluated the effects of filler addition, storage medium and time on biaxial flexural strength and flexural modulus of six adhesive systems. MATERIALS AND METHODS: The adhesives were either unfilled resins: Single Bond, Prime&Bond 2.1 and One-Step; or filled resins: Single Bond Plus, Prime&Bond NT and One-Step Plus. Resin discs of each product (0.5 mm thick × 6.0 mm diameter) were prepared using silicon molds (n = 10). The discs were stored dry, in water, mineral oil or ethanol for 1 week or 3 months before biaxial flexural testing. Data were statistically analyzed by 3-way ANOVA and Tukey's post-hoc test (α = 0.05). The specimens were tested in a universal testing machine at 1.27 mm/min until failure occurred. RESULTS: In general, the storage in ethanol led to significantly lower flexural strength and flexural modulus values than the other storage conditions for all adhesives in both storage periods. Filler addition increased flexural strength and flexural modulus for Prime&Bond NT, when it was stored dry or in water for 1 week. For Single Bond Plus, the filler addition resulted in higher flexural modulus, when it was stored for 1 week in oil and in ethanol. No significant differences in flexural modulus were observed between One-Step and One-Step Plus in any storage medium. CONCLUSIONS: Results suggested that filler addition does not necessarily have to increase the flexural strength and flexural modulus. Ethanol and oil storages tended to yield opposite effects.

Effects of argon plasma and aging on the mechanical properties and phase transformation of 3Y-TZP zirconia.

To evaluate the flexural strength (FS) and flexural modulus (FM) of a commercial 3Y-TZ0P ceramic after artificial aging and either without or with two application times of non-thermal plasma treatments (NTP). In addition, changes in crystalline phase transformation and surface nano-topography after NTP application, during different aging periods, were evaluated. Ninety 3Y-TZP bars (45x4x3 mm) were made for FS and FM testing, and assigned to nine groups (n=10): no NTP/no aging (Control); no NTP/4h aging; no NTP/30h aging; 10s NTP/no aging; 10s NTP/4h aging; 10s NTP/30h aging; 60s NTP/no aging; 60s NTP/4h aging and 60s NTP/30h aging. Artificial accelerated aging was simulated using an autoclave (134º C at 2 bar) for up to 30h. FS and FM were assessed using a universal testing machine and data analyzed using a ANOVA and Tukey test (α=0.05). The volume change in zirconia monoclinic phase (MPV) was evaluated using X-ray diffraction and surface nano-topography was assessed using atomic force microscopy (baseline until 30h-aging). NTP application did not influence the FS and FM of zirconia. Compared to the Control (no NTP/no aging), the FS of zirconia samples treated for 30 hours in autoclave ("no NTP/30h aging" group) increased. Artificial aging for 30 hours significantly increased the FM of zirconia, regardless of NTP application. MPV tended to increase following the increase in aging time, which might result in the surface irregularities observed at 30h-aging. NTP did not alter the zirconia properties tested, but 30h-aging can change the zirconia FS, FM and MPV.

Synthesis, characterization, and incorporation of upconverting nanoparticles into a dental adhesive.

The purpose of this study was to describe the synthesis, characterization, and functionalization of b-NaYF4:30%Yb/0.5%Tm upconverting nanocrystals for use as nanofillers in a dental adhesive and microscopically evaluate the interface between the particles and a commercial adhesive. The upconverting nanoparticles were synthesized and purified by thermal decomposition, and their chemical composition determined by energy dispersive X-Ray spectroscopy. The crystalline structure was characterized using X-Ray diffraction and morphology and size were observed with scanning and transmission electron microscopy. Upconverting emission was evaluated by spectrophotometry irradiating the particles with a 975 nm diode laser. Particles were functionalized with polyacrylic acid and the success was confirmed by measurement of Zeta Potential and transmission electron microscopy. The results of X-ray diffraction found a pure hexagonal phase crystalline pattern. Scanning electron microscopy showed uniform dispersion of hexagonal-shaped particles of approximately 150 nm. Upconversion emission was observed in 344 nm, 361 nm, 450 nm, 474nm, 646 nm, 803 nm. Functionalization success was confirmed by formation of a stable aqueous colloid with a Zeta potential of -29.5mV and the absence of voids in the particle-adhesive interface on the transmission electron microscopy images. The reported synthesis and functionalization process produced upconverting nanoparticles emitting photons within the blue spectral region (450 nm and 474 nm).

Micromorphology of resin-dentin interfaces using one-bottle etch&rinse and self-etching adhesive systems on laser-treated dentin surfaces: a confocal laser scanning microscope analysis.

BACKGROUND AND OBJECTIVES: This study evaluated the hybrid layer (HL) morphology created by three adhesive systems (AS) on dentin surfaces treated with Er:YAG laser using two irradiation parameters. STUDY DESIGN: Occlusal flat dentin surfaces of 36 human third molars were assigned into nine groups (n = 4) according to the following ASs: one bottle etch&rinse Single Bond Plus (3M ESPE), two-step Clearfil Protect Bond (Kuraray), and all-in-one S(3) Bond (Kuraray) self-etching, which were labeled with rhodamine B or fluorescein isothiocyanate-dextran and were applied to dentin surfaces that were irradiated with Er:YAG laser at either 120 (38.7 J/cm(2)) or 200 mJ/pulse (64.5 J/cm(2)), or were applied to untreated dentin surfaces (control group). The ASs were light-activated following MI and the bonded surfaces were restored with resin composite Z250 (3M ESPE). After 24 hours of storage in vegetable oil, the restored teeth were vertically, serially sectioned into 1-mm thick slabs, which had the adhesive interfaces analyzed with confocal laser microscope (CLSM-LSM 510 Meta). CLSM images were recorded in the fluorescent mode from three different regions along each bonded interface. RESULTS: Non-uniform HL was created on laser-irradiated dentin surfaces regardless of laser irradiation protocol for all AS, while regular and uniform HL was observed in the control groups. "Stretch mark"-like red lines were found within the HL as a result of resin infiltration into dentin microfissures, which were predominantly observed in 200 mJ/pulse groups regardless of AS. Poor resin infiltration into peritubular dentin was observed in most regions of adhesive interfaces created by all ASs on laser-irradiated dentin, resulting in thin resin tags with neither funnel-shaped morphology nor lateral resin projections. CONCLUSION: Laser irradiation of dentin surfaces at 120 or 200 mJ/pulse resulted in morphological changes in HL and resin tags for all ASs evaluated in the study.

The effect of curing mode on extent of polymerization and microhardness of dual-cured, self-adhesive resin cements.

PURPOSE: To compare the effect of curing mode (self- or light-cure) on the extent of polymerization (%EP1 as measured using differential scanning calorimetry, (DSC) and microhardness of two dual-cured, self-adhesive resin cements, using a conventional, dual-cured resin cement as control. METHODS: Small amounts of the commercial self-adhesive cements Maxcem and RelyX Unicem or Panavia F2.0 dual-cure resin based cement used as control were polymerized within the DSC chamber at 35 degrees C under a nitrogen atmosphere. 10 specimens were light-cured immediately (20 seconds, 600 mW/cm2) and left undisturbed for 2 hours and 10 additional specimens were left to self-cure in the dark for 2 hours. Following DSC treatment, microhardness of the specimens was measured (Vickers). For each test parameter, data were analyzed with a two-way ANOVA and the Tukey post hoc test. RESULTS: %EP and microhardness of all cements were higher when the light-cure mode of dual-activation was used (P<0.05) instead of only self-curing. No significant difference in %EP was found between either self-adhesive cement or the control using either the light- or self-curing modes. In the light-activated mode, the conventional, dual-cure control cement demonstrated lower microhardness than the self-adhesive cements (P<0.05).

In vivo temperature rise and acute inflammatory response in anesthetized human pulp tissue of premolars having Class V preparations after exposure to Polywave® LED light curing units.

OBJECTIVE: To evaluate the influence of light emitted from two Polywave®, LED light-curing units (LCU) on in vivo pulp temperature (PT) rise and signs of acute inflammatory response in pulps of human premolar having deep Class V preparations. METHODS: Sixty intact, first premolars from 15 volunteers requiring extraction received infiltrative anesthesia. A sterile thermocouple probe was inserted within the pulp tissue through a minute occlusal pulp exposure in only 45 teeth (n = 9) to continuously monitor PT (°C). A deep buccal Class V preparation was created, and the surface was exposed to light from a commercial Polywave LCU (Bluephase 20i (20i), Ivoclar Vivadent) or from an experimental LCU (Exp) using the exposure modes (EM): 1s/Exp and 2s/Exp, 10s/20i, 20s/20i, and 60s/20i. Peak PT and PT rise values above baseline (ΔT) data were evaluated using a one-way ANOVA followed by Tukey's post-hoc test (α = 5%). Teeth used for histological and immunohistochemical analyses (n = 3) were extracted approximately 2 h after exposure to the LCU. RESULTS: No significant difference in peak PT and ΔT values was noted between 2s/Exp and 20s/20i groups, which both exhibited higher values than 1s/Exp and 10s/20i groups (p < 0.001). Dilated and congested blood vessels were seen after exposure to 1s/Exp, 2s/Exp, or 60s/20i EMs. The expression of IL-1ß and TNF-α tended to be more intense when higher irradiance was delivered. SIGNIFICANCE: Although higher irradiance delivered over a short exposure caused lower PT rise than 5.5 °C, such EMs should be used with caution, as they have more potential to harm the pulp tissue.

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

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

Comparison of in vivo and in vitro models to evaluate pulp temperature rise during exposure to a Polywave® LED light curing unit.

OBJECTIVES: To measure and compare in vivo and in vitro pulp temperature (PT) increase (ΔTEMP) over baseline, physiologic temperature using the same intact upper premolars exposed to the same Polywave® LED curing light. METHODOLOGY: After local Ethics Committee approval (#255,945), local anesthesia, rubber dam isolation, small occlusal preparations/minute pulp exposure (n=15) were performed in teeth requiring extraction for orthodontic reasons. A sterile probe of a temperature measurement system (Temperature Data Acquisition, Physitemp) was placed within the pulp chamber and the buccal surface was sequentially exposed to a LED LCU (Bluephase 20i, Ivoclar Vivadent) using the following exposure modes: 10-s low or high, 5-s Turbo, and 60-s high. Afterwards, the teeth were extracted and K-type thermocouples were placed within the pulp chamber through the original access. The teeth were attached to an assembly simulating the in vivo environment, being similarly exposed while real-time temperature (°C) was recorded. ΔTEMP values and time for temperature to reach maximum (ΔTIME) were subjected to two-way ANOVA and Bonferroni's post-hoc tests (pre-set alpha 0.05). RESULTS: Higher ΔTEMP was observed in vitro than in vivo. No significant difference in ΔTIME was observed between test conditions. A significant, positive relationship was observed between radiant exposure and ΔTEMP for both conditions (in vivo: r2=0.917; p<0.001; in vitro: r2=0.919; p<0.001). CONCLUSION: Although the in vitro model overestimated in vivo PT increase, in vitro PT rise was close to in vivo values for clinically relevant exposure modes.

In Vivo Measurement of Root Canal Wall Temperature at Different Stages Prior to Fiber Post Cementation.

OBJECTIVE: This study measured the in vivo temperature of prepared root canal walls during various stages of treatment prior to endodontic postcementation. MATERIALS AND METHODS: One tooth each from five patients requiring endodontic treatment received conventional gutta-percha obturation. The coronal 4 mm of gutta-percha was removed by drilling and the canal wall temperature was measured. A sterile, saline rinse was applied, and another temperature value was recorded. Paper points were placed, and the wall temperature was recorded. A standardized period of 1.5 minute passed, simulating time needed to mix and place the resin cement and post (no resin was placed), after which the final wall temperature was obtained. The tooth was temporized and scheduled for prosthetic reconstruction. A one-way repeated measure analysis of variance (with Tukey's post hoc test) was performed among mean temperature values for each treatment stage (preset α 0.05). RESULTS: Significant temperature differences were found among the treatment stages. Canal space drilling yielded the highest temperature (35.5 ± 0.8°C), while the lowest was obtained after saline rinsing (34.0 ± 0.9°C). The temperature of prepared root canal wall prior to postplacement (34.9 ± 1.2°C) and following paper point drying (34.8 ± 1.1°C) presented intermediate results, with no statistical difference between them. CONCLUSIONS: This study suggested that root canal wall temperature varied during various stages of preparation prior to endodontic post.

Effect of indirect restorative material and thickness on light transmission at different wavelengths.

PURPOSE: The aim of this study was to evaluate the influence of indirect restorative material type and thickness on the transmission of different wavelengths from a broad-banded dental curing light. METHODS: Four dental indirect restorative materials for computer-aided design and computer-aided manufacturing (CAD/CAM) were evaluated: [RC] resin/ceramic hybrid material (Lava Ultimate), [FC] feldspathic ceramic (VitaBlocs), and two zirconia-based ceramics ([ZK] Katana; and [ZL] Lava). Total loss of irradiance (TL) was measured for blue (WB, 425-490nm) and violet (WV, 350-425nm) wavelengths. Specimens of 15×15mm with varying thicknesses (0.5, 1.0, 1.5, and 2.0mm) were fabricated (n=5). A plasma-arc dental light-curing unit was used (Arc Light-II). To assess TL as a function of wavelength, a software (Spectra Suite v5.1) connected to a spectroradiometer (USB2000) and an integrating sphere (CTSM-LSM-60-SF) was used. Data was subjected to statistical analysis (two-way ANOVA and post-hoc Tukey test, α=0.05). RESULTS: A 0.5mm interposition resulted in TL from 50.5 to 67.2%, depending on material. Increased thickness resulted in higher TL for all materials. FC showed less TL compared to ZK. In general, WV showed higher TL than did WB, and WV/WB proportion decreased with increasing thickness. CONCLUSIONS: Indirect materials significantly reduced TL, and this effect is greater with increasing thickness. WV showed lower penetration compared to WB.

Influence of Class V preparation on in vivo temperature rise in anesthetized human pulp during exposure to a Polywave® LED light curing unit.

OBJECTIVE: This in vivo study evaluated pulp temperature (PT) rise in human premolars having deep Class V preparations during exposure to a light curing unit (LCU) using selected exposure modes (EMs). METHODS: After local Ethics Committee approval, intact first premolars (n=8) requiring extraction for orthodontic reasons, from 8 volunteers, received infiltrative and intraligamental anesthesia and were isolated using rubber dam. A minute pulp exposure was attained and sterile probe from a wireless, NIST-traceable, temperature acquisition system was inserted into the coronal pulp chamber to continuously monitor PT (°C). A deep buccal Class V preparation was prepared using a high speed diamond bur under air-water spray cooling. The surface was exposed to a Polywave® LED LCU (Bluephase 20i, Ivoclar Vivadent) using selected EMs, allowing 7-min span between each exposure: 10-s in low (10-s/L), 10-s (10-s/H), 30-s (30-s/H), or 60-s (60-s/H) in high mode; and 5-s-Turbo (5-s/T). Peak PT values and PT increases over physiologic baseline levels (ΔT) were subjected to 1-way, repeated measures ANOVAs, and Bonferroni's post-hoc tests (α=0.05). Linear regression analysis was performed to establish the relationship between applied radiant exposure and ΔT. RESULTS: All EMs produced higher peak PT than the baseline temperature (p<0.001). Only 60-s/H mode generated an average ΔT of 5.5°C (p<0.001). A significant, positive relationship was noted between applied radiant exposure and ΔT (r2=0.8962; p<0.001). SIGNIFICANCE: In vivo exposure of deep Class V preparation to Polywave® LED LCU increases PT to values considered safe for the pulp, for most EMs. Only the longest evaluated EM caused higher PT increase than the critical ΔT, thought to be associated with pulpal necrosis.

Effect of Ceramic Interposition and Post-activation Times on Knoop Hardness of Different Shades of Resin Cement.

The aim of this study was to evaluate Knoop hardness of different shades of a resin cement light-cured directly or through ceramic discs, measured 15 min or 24 h after light exposure, and at different depths. Specimens of a commercial resin cement (Variolink Veneer) in seven shades, were fabricated in an elastomeric mold, covered with a mylar strip, a 0.7 mm thick ceramic disc (IPS e.max Press) was placed and the cement was light-activated for 20 s using a blue LED (Radii-Cal). The cured resin cement specimens were transversely wet-flattened to their middle portion and microhardness (Knoop) values were recorded at 15 min after light exposure and after deionized water storage at 37 ºC for 24 h. Five indentations were made in the cross-sectional area at 100 and 700 µm depths from the top surface. Ten specimens were made for each test conditions. Data were submitted to ANOVA split-plot design (shade, post-cure time, mode of activation and depth), followed by Tukey post hoc test (α=0.05). Significant differences for shade (p<0.0001), mode of activation (p<0.001), post-cure time (p<0.0001) and depth (p<0.0001) were detected. No significant interactions (p>0.05) were found, except for shade x post-cure time (p<0.0045) and mode of activation x post-cure time (p<0.0003). Resin cement shade has a significant effect on Knoop hardness. Indirect activation through a ceramic material reduced significantly Knoop hardness. Hardness Knoop significantly increased after 24 h in all cements shades compared to values obtained after 15 min. Resin cement depth significantly reduced Knoop hardness.

Light curing in dentistry and clinical implications: a literature review.

Contemporary dentistry literally cannot be performed without use of resin-based restorative materials. With the success of bonding resin materials to tooth structures, an even wider scope of clinical applications has arisen for these lines of products. Understanding of the basic events occurring in any dental polymerization mechanism, regardless of the mode of activating the process, will allow clinicians to both better appreciate the tremendous improvements that have been made over the years, and will also provide valuable information on differences among strategies manufacturers use to optimize product performance, as well as factors under the control of the clinician, whereby they can influence the long-term outcome of their restorative procedures.