In vitro study of the pulp chamber temperature rise during light-activated bleaching

This study evaluated in vitro the pulp chamber temperature rise induced by the light-activated dental bleaching technique using different light sources. The root portions of 78 extracted sound human mandibular incisors were sectioned approximately 2 mm below the cementoenamel junction. The root cavities of the crowns were enlarged to facilitate the correct placing of the sensor into the pulp chamber. Half of specimens (n=39) was assigned to receive a 35% hydrogen peroxide gel on the buccal surface and the other halt (n=39) not to receive the bleaching agent. Three groups (n=13) were formed for each condition (bleach or no bleach) according to the use of 3 light sources recommended for dental bleaching: a light-emitting diode (LED)laser system, a LED unit and a conventional halogen light. The light sources were positioned perpendicular to the buccal surface at a distance of 5 mm and activated during 30 s. The differences between the initial and the highest temperature readings for each specimen were obtained, and, from the temperature changes, the means for each specimen and each group were calculated. The values of temperature rise were compared using Kruskal-Wallis test at 1% significance level. Temperature rise varied significantly depending on the light-curing unit, with statistically significant differences (p<0.01) among the groups. When the bleaching agent was not applied, the halogen light induced the highest temperature rise (2.38±0.66ºC). The LED unit produced the lowest temperature increase (0.29±0.13ºC); but there was no significant difference between LED unit and LED-laser system (0.35±0.15ºC) (p>0.01). When the bleaching agent was applied, there were significant differences among groups (p<0.01): halogen light induced the highest temperature rise (1.41±0.64ºC), and LED-laser system the lowest (0.33±0.12ºC); however, there was no difference between LED-laser system and LED unit (0.44±0.11ºC). LED and LED-laser system did not differ significantly from each other regardless the temperature rise occurred with or without bleaching agent application. It may be concluded that during light-activated tooth bleaching, with or without the bleaching agent, halogen light promoted higher pulp chamber temperature rise than LED unit and LED-laser system. The tested light-curing units provided increases in the pulp chamber temperature that were compatible with pulpal health.

Influence of pulse repetition rate on temperature rise and working time during composite filling removal with the Er : YAG laser

Objective: The purpose of this study was to assess the efficacy of Er:YAG laser energy for composite resin removal and the influence of pulse repetition rate on the thermal alterations occurring during laser ablation. Materials and Methods: Composite resin filling was placed in cavities (1.0 mm deep) prepared in bovine teeth and the specimens were randomly assigned to five groups according to the technique used for composite filling removal. In group I (controls), the restorations were removed using a high-speed diamond bur. In the other groups, the composite fillings were removed using an Er: YAG laser with different pulse repetition rates: group 2-2 Hz; group 3-4 Hz; group 4-6 Hz; and group 5-10 Hz. The time required for complete removal of the restorative material and the temperature changes were recorded. Results: Temperature rise during composite resin removal with the Er: YAG laser occurred in the substrate underneath the restoration and was directly proportional to the increase in pulse repetition rate. None of the groups had a temperature increase during composite filling removal of more than 5.6 degrees C, which is considered the critical point above which irreversible thermal damage to the pulp may result. Regarding the time for composite filling removal, all the laser-ablated groups (except for group 5 [10 Hz]) required more time than the control group for complete elimination of the material from the cavity walls. Conclusion: Under the tested conditions, Er: YAG laser irradiation was efficient for composite resin ablation and did not cause a temperature increase above the limit considered safe for the pulp. Among the tested pulse repetition rates, 6 Hz produced minimal temperature change compared to the control group (high-speed bur), and allowed composite filling removal within a time period that is acceptable for clinical conditions.

Recent changes in solar outputs and the global mean surface temperature. III. Analysis of contributions to global mean air surface temperature rise

A multivariate fit to the variation in global mean surface air temperature anomaly over the past half century is presented. The fit procedure allows for the effect of response time on the waveform, amplitude and lag of each radiative forcing input, and each is allowed to have its own time constant. It is shown that the contribution of solar variability to the temperature trend since 1987 is small and downward; the best estimate is -1.3% and the 2sigma confidence level sets the uncertainty range of -0.7 to -1.9%. The result is the same if one quantifies the solar variation using galactic cosmic ray fluxes (for which the analysis can be extended back to 1953) or the most accurate total solar irradiance data composite. The rise in the global mean air surface temperatures is predominantly associated with a linear increase that represents the combined effects of changes in anthropogenic well-mixed greenhouse gases and aerosols, although, in recent decades, there is also a considerable contribution by a relative lack of major volcanic eruptions. The best estimate is that the anthropogenic factors contribute 75% of the rise since 1987, with an uncertainty range (set by the 2sigma confidence level using an AR(1) noise model) of 49–160%; thus, the uncertainty is large, but we can state that at least half of the temperature trend comes from the linear term and that this term could explain the entire rise. The results are consistent with the intergovernmental panel on climate change (IPCC) estimates of the changes in radiative forcing (given for 1961–1995) and are here combined with those estimates to find the response times, equilibrium climate sensitivities and pertinent heat capacities (i.e. the depth into the oceans to which a given radiative forcing variation penetrates) of the quasi-periodic (decadal-scale) input forcing variations. As shown by previous studies, the decadal-scale variations do not penetrate as deeply into the oceans as the longer term drifts and have shorter response times. Hence, conclusions about the response to century-scale forcing changes (and hence the associated equilibrium climate sensitivity and the temperature rise commitment) cannot be made from studies of the response to shorter period forcing changes.

Temperature rise in cavities prepared by high and low torque handpieces and Er : YAG laser

Objective The aim of this study was to compare intrapulpal temperature increases produced by a high-speed high-torque (speed-increasing) handpiece, a high-speed low-torque handpiece (air-turbine) and an Er: YAG (Erbium: Yttrium-Aluminum-Garnet) laser. Subject and methods Thirty bovine incisors were reduced to a dentine thickness of 2.0 mm. Class V preparations were prepared to a depth of 1.5 mm, measured with a caliper or by a mark on the burs. A thermocouple was placed inside the pulp chamber to determine temperature increases (C). Analysis was performed on the following groups (n = 10) treated with: G1, low-torque handpiece; G2, high-torque handpiece; and G3, Er: YAG laser (2.94 mu m at 250 mJ/4 Hz), all with water cooling. The temperature increases were recorded with a computer linked to the thermocouples. Results The data were submitted to ANOVA and Tukey statistical test. The average temperature rises were: 1.92 +/- 0.80 degrees C for G1, 1.34 +/- 0.86 degrees C for G2, and 0.75 +/- 0.39 degrees C for G3. There were significant statistical differences among the groups (p = 0.095). All the groups tested did not have a change of temperature that exceeds the threshold of 5.5 degrees C. Conclusion Temperature response to the low and high torque handpieces seemed to be similar, however the Er: YAG laser generated a lower temperature rise.

Temperature rise during adhesive and composite polymerization with different light-curing sources

AIM: This study evaluated the temperature rise of the adhesive system Single Bond (SB) and the composite resins Filtek Z350 flow (Z) and Filtek Supreme (S), when polymerized by light-emitting diode (LED XL 3000) and quartz-tungsten halogen (QTH Biolux). METHODS: Class V cavities (3 yen2 mm) were prepared in 80 bovine incisors under standardized conditions. The patients were divided as follows: G1: Control; G2: SB; G3: SB + Z; G4: SB + S. The groups were subdivided into two groups for polymerization (A: QTH, B: LED). Light curing was performed for 40 s and measurement of temperature changes during polymerization was performed with a thermocouple positioned inside the pulp chamber. Data were statistically analyzed using ANOVA and Tukey tests. RESULTS: The factors material (P<0.00001) and curing unit (P<0.00001) had significant influence on temperature rise. The lowest temperature increase (0.15 degrees C) was recorded in G2 B and the highest was induced in G1 A (0.75 degrees C, P<0.05). In all groups, lower pulp chamber temperature measurements were obtained when using LED compared to QTH (P<0.05). CONCLUSION: QTH caused greater increases in tooth temperature than LED. However, both sources did not increase pulpal temperature above the critical value that may cause pulpal damage.

Influence of whitening gel on pulp chamber temperature rise by in-office bleaching technique

INTRODUÇÃO: O clareamento dental representa uma manobra conservadora na recuperação estética de dentes com alterações cromáticas. Contudo, os tratamentos clareadores são passíveis de causar efeitos adversos, quando não bem planejados e executados. OBJETIVO: Este estudo avaliou a influência do gel clareador no aumento da temperatura intra-câmara pulpar através da técnica de clareamento dental fotoativado realizado em consultório. MATERIAL E MÉTODO: Um incisivo central superior humano foi seccionado na porção radicular 3 mm abaixo da junção cemento-esmalte. O canal radicular foi alargado para permitir a introdução do sensor do termômetro na câmara pulpar, a qual foi preenchida com pasta térmica, favorecendo a transferência de calor das paredes dentárias para o sensor do termômetro digital com termopar tipo K (MT- 401A) durante o clareamento. Três agentes clareadores fotossensíveis (peróxido de hidrogênio a 35%) foram utilizados, sendo: Whiteness HP (FGM), Whiteness HP Maxx (FGM) e Lase Peroxide Sensy (DMC). Um aparelho fotopolimerizador de led (Flash Lite - Discus Dental) foi empregado para a ativação dos géis clareadores. Seis ciclos de clareamento foram realizados para cada grupo testado. Os resultados foram submetidos à ANOVA de um critério e ao teste t (LSD) (α<0,05). RESULTADO: A menor média de variação de temperatura (ºC) foi observada com o Lase Peroxide Sensy (0,20), enquanto que a maior com o Whiteness HP (1,50). CONCLUSÃO: Os géis clareadores Whiteness HP e Whiteness HP Maxx interferiram significativamente no aumento da temperatura intra-câmara pulpar durante o clareamento, sendo esta variação dependente do tipo de gel clareador empregado.

Temperature rise during Er:YAG cavity preparation of primary enamel

This study aimed to assess in vitro thermal alterations taking place during the Er:YAG laser cavity preparation of primary tooth enamel at different energies and pulse repetition rates. Forty healthy human primary molars were bisected in a mesio-distal direction, thus providing 80 fragments. Two small orifices were made on the dentin surface to which type K thermocouples were attached. The fragments were individually fixed with wax in a cylindrical PlexiglassA (R) abutment and randomly assigned to eight groups, according to the laser parameters (n = 10): G1 -aEuro parts per thousand 250 mJ/ 3 Hz, G2 -aEuro parts per thousand 250 mJ/ 4 Hz, G3 -aEuro parts per thousand 250 mJ/ 6 Hz, G4 -aEuro parts per thousand 250 mJ/10 Hz, G5 -aEuro parts per thousand 250 mJ/ 15 Hz, G6 -aEuro parts per thousand 300 mJ/ 3 Hz, G7 -aEuro parts per thousand 300 mJ/ 4 Hz and G8 -aEuro parts per thousand 300 mJ/ 6 Hz. An area of 4 mm(2) was delimited. Cavities were done (2 mm long x 2 mm wide x 1 mm thick) using non-contact (12 mm) and focused mode. Temperature values were registered from the start of laser irradiation until the end of cavity preparation. Data were analyzed by one-way ANOVA and Tukey test (p a parts per thousand currency signaEuro parts per thousand 0.05). Groups G1, G2, G6, and G7 were statistically similar and furnished the lowest mean values of temperature rise. The set 250 mJ/10 and 15 Hz yielded the highest temperature values. The sets 250 and 300 mJ and 6 Hz provided temperatures with mean values below the acceptable critical value, suggesting that these parameters ablate the primary tooth enamel. Moreover, the temperature elevation was directly related to the increase in the employed pulse repetition rates. In addition, there was no direct correlation between temperature rise and energy density. Therefore, it is important to use a lower pulse frequency, such as 300 mJ and 6 Hz, during cavity preparation in pediatric patients.

Temperature rise-times in pneumatic tires. Interim report.

Transportation Systems Center, Cambridge, Mass.

Transient temperature rise in a mouse due to low-frequency regional hyperthermia

A refined nonlinear heat transfer model of a mouse has been developed to simulate the transient temperature rise in a neoplastic tumour and neighbouring tissue during regional hyperthermia using a 150 kHz inductive coil. In this study, we incorporate various bio-energetic enhancements to the heat transfer equation and numerical validations based on experimental findings for the mouse, in terms of nonlinear metabolic heat production, homeothermy, blood perfusion parameters, thermoregulation, psychological and physiological effects. The discretized bio-heat transfer equation has been validated with the commercial software FEMLAB on a canonical multi-sphere object before applying the scheme to the inhomogeneous mouse voxel phantom. The time-dependent numerical results of regional hyperthermia of mouse thigh have been compared with the available experimental temperature results with only a few small disparities. During the first 20 min of local unfocused heating, the temperature in the tumour and the surrounding tissue increased by around 7.5 degrees C. The objective of this preliminary study was to develop a validated electrothermal numerical scheme for inductive hyperthermia of a small mammal with the intention of expanding the model into a complete numerical solution involving ferromagnetic nanoparticles for targeted heating of tumours at low frequencies. In addition, the numerical scheme herein could assist in optimizing and tailoring of focused electromagnetic fields for hyperthermia.

Effects of intrapulpal temperature change induced by visible light units on the metabolism of odontoblast-like cells

Purpose: To investigate the effects of intrapulpal temperature changes induced by a quartz tungsten halogen (QTH) and a light emitting diode (LED) curing units on the metabolism of odontoblast-like cells. Methods: Thirty-six 0.5 mm-thick dentin discs obtained from sound human teeth were randomly assigned into three groups: QTH, LED and no light (control). After placement of the dentin discs in pulp chamber devices, a thermistor was attached to the pulpal surface of each disc and the light sources were applied on the occlusal surface. After registering the temperature change, odontoblast-like cells MDPC-23 were seeded on the pulpal side of the discs and the curing lights were again applied. Cell metabolism was evaluated by the MTT assay and cell morphology was assessed by SEM. Results: In groups QTH and LED the intrapulpal temperature increased by 6.4 degrees C and 3.4 degrees C, respectively. The difference between both groups was statistically significant (Mann-Whitney; P< 0.05). QTH and LED reduced the cell metabolism by 36.4% and 33.4%, respectively. Regarding the cell metabolism, no statistically significant difference was observed between both groups (Mann-Whitney; P> 0.05). However, when compared to the control, only QTH significantly reduced the cell metabolism (Mann-Whitney; P< 0.05). It was concluded that the irradiance of 0.5 mm-thick human dentin discs with a QTH in comparison to a LED curing unit promoted a higher temperature rise, which propagates through the dentin negatively affecting the metabolism of the underlying cultured pulp cells. (Am J Dent 2009;22:151-156).