In vivotemperature rise in anesthetized human pulp during exposure to a polywave LED light curing unit

Highlights

  • Accurate real-time, in vivo pulp temperature rise was measured in intact human first premolars.

  • Exposure to LED light at different exposure modes resulted in pulp temperature rise.

  • Positive relationship between radiant exposure and pulp temperature was noted.

Abstract

Objectives

This in vivo study evaluated pulp temperature (PT) rise in human premolars during exposure to a light curing unit (LCU) using selected exposure modes (EMs).

Methods

After local Ethics Committee approval, intact first upper premolars, requiring extraction for orthodontic reasons, from 8 volunteers, received infiltrative and intraligamental anesthesia. The teeth ( n = 15) were isolated using rubber dam and a minute pulp exposure was attained. A sterile probe from a wireless, NIST-traceable, temperature acquisition system was inserted directly into the coronal pulp chamber, and real time PT (°C) was continuously monitored while the buccal surface was exposed to polywave light from a LED LCU (Bluephase 20i, Ivoclar Vivadent) using selected EMs allowing a 7-min span between each exposure: 10-s either in low (10-s/L) or high (10-s/H); 5-s-turbo (5-s/T); and 60-s-high (60-s/H) intensities. Peak PT values and PT increases from baseline (Δ T ) after exposure were subjected to one-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). The 60-s/H mode generated the highest peak PT and Δ T ( p < 0.001), with some teeth exhibiting Δ T higher than 5.5 °C. A significant, positive relationship between applied radiant exposure and Δ T ( r 2 = 0.916; p < 0.001) was noted.

Significance

Exposing intact, in vivo anesthetized human upper premolars to a polywave LED LCU increases PT, and depending on EM and the tooth, PT increase can be higher than the critical Δ T , thought to be associated with pulpal necrosis.

Introduction

The great challenge for clinicians performing restorative procedures with resin composites is to reestablish tooth form and function in a short time and causing the least pulp trauma. Because heat is considered a primary cause of pulpal injury , the heat generated during some dental procedures may be causative factors: use of high and low speed handpieces, restorative materials with exothermic setting reactions , polishing techniques of such materials , as well as tooth exposure to light from either quartz–tungsten–halogen or light emitting diode (LED) light curing units (LCU) . Recently, the heat caused by light emitted by LED LCUs on prepared teeth has become an issue, because LED LCUs with radiant emittance values exceeding 2000 mW/cm 2 are now commercially available.

In an attempt to predict the thermal stimuli caused by light emitted by LCUs on teeth and to determine the relationship between radiant emittance and temperature rise into the pulp chamber, several in vitro studies measured the temperature rise during exposure to LCUs with thermocouples inserted into the pulp chamber of extracted teeth . Overall, the temperature increase observed during these exposures ranged from 1.5 to 23.2 °C. Such a wide range of temperature increase reported in literature is clearly related to different experimental approaches, LCUs, radiant emittance, and radiant exposure. For instance, some studies evaluated the increase in pulp chamber temperature in intact premolars and molars , while others tested anterior teeth: incisors, lateral, and canines . In addition, among the in vitro studies that evaluated posterior teeth, some investigators measured pulp temperature (PT) increase on teeth having occlusal or occlusal-proximal preparations prior to exposure to LCU light . Moreover, in an attempt to evaluate the influence of resin-based restorative materials, other studies also included restorative procedures using resin composites during PT change analysis . Based on these reports, there is a consensus that the use of some LED LCUs can result in a pulp chamber temperature rise to values higher than the threshold temperature increase of 5.5 °C, considered harmful for the pulp .

One of the most important aspects regarding the effects of LCU exposure on PT increase is to establish an accurate relationship between light exitance or radiant exposure and PT increase. In order to achieve that, an accurate beam profile analysis of the light emitted by the LCU is required so these parameters can be precisely determined. In this regard, most in vitro studies evaluating PT increase focused only on comparing a variety of LCU brands and models, and conventional, hand-held dental curing radiometers were used to provide a “guesstimate” radiant exposure , or even no light exitance was measured . In addition, even in studies that precisely measured LCU output , the differences in light beam profile from each LCU do not allow clear conclusions about a relationship between radiant exposure and PT increase. For this reason, although evidence in the literature clearly indicates that light emitted by LED LCUs can be harmful to the pulp, the relationship between radiant exposure and PT increase is still unclear.

Despite evidence that high-intensity LCUs can increase pulp chamber temperature, one must consider that in vitro conditions do not reproduce the complexities of an in vivo scenario. For example, most in vitro studies did not simulate the influence of the dental pulp. This tissue is highly vascularized and contains the main regulatory system for heat distribution in teeth, capable of dissipating the heat transferred by external thermal stimuli to the dentin/pulp complex . Even in vitro studies that simulate pulp flow were not capable of reproducing the dynamic changes in pulp fluid flow, when temperature changes in this tissue occur . Indeed, because any external thermal stimuli can change the fluid movement either inward or outward from the pulp depending on the stimuli, it is important to consider that the actual in vivo pulp regulatory system may be more effective in dissipating external heat than would be a simulated pulp flow condition. However, no information is available in the literature regarding the in vivo temperature increase within the human pulp when teeth are exposed to light from a high intensity LED LCU.

The purpose of this in vivo study was to evaluate PT increase of anesthetized, vital, unrestored, human upper premolars during exposure to a polywave, LED-based, dental light curing unit, applying varying values of radiant exposure. The tested alternative hypotheses were that (1) all exposure modes (EM) of the LCU will produce a significant PT increase over that of the baseline temperature values; (2) none of the applied EMs will produce a PT increase higher than the potentially harmful threshold temperature increase of 5.5 °C; and (3) there is a direct, positive relationship between applied radiant exposure and PT increase.

Materials and methods

In vivo measurement of pulp temperature increase

This study was approved by the Ethics Committee at the State University of Ponta Grossa (protocol # 255,945). Eight volunteers, ranging from 12 to 30 years, requiring extraction of upper right and left first premolars ( n = 15) for orthodontic reasons, were selected from the Orthodontic specialization program in Ponta Grossa, Brazil. All patients were recruited in February 2013, and were attended to between March and April 2013. Patient inclusion criteria included (1) treatment plans indicating premolar extractions for orthodontic reasons, (2) the presence of healthy, intact, non-carious, and non-restored, fully erupted treatment teeth, and (3) patients with well-controlled health conditions that allowed all procedures involved in the research to be performed with minimal risk. Exclusion criteria included (1) those patients who did not agree to volunteer for the study and (2) patients not meeting all of the inclusion criteria.

A single tooth at a time from a volunteer was treated by receiving infiltrative and intraligamental anesthesia, using approximately 1.8 ml of 2% Mepivacaine Hidrocloryde (36 mg) with 1:100,000 Epinephrine (18 μg) (Mepiadre, Nova DFL Industria e Comercio, Rio de Janeiro, RJ, Brazil), after which the tooth was isolated using rubber dam. A small, occlusal preparation was made in the center of the tooth using a round diamond bur (#1015, KG Sorensen, Cotia, SP, Brazil) in a high speed handpiece, providing air-water spray, until the preparation pulpal floor was near the buccal pulp horn. Then, a small, pencil-shaped diamond bur (#2134, KG Sorensen) was used to produce a minute pulp exposure, with no pulp bleeding. Care was taken to ensure that the same water flow and air pressure were used for each tooth, as well as the same time spent for each preparation. A wireless, NIST-traceable, temperature acquisition system (Temperature Data Acquisition – Thermes WFI, Physitemp Instruments Inc., Clifton, NJ, USA) was used to measure PT. Two 1-cm long tip, calibrated temperature probes (Model MT-D, Type T, time constant: 0.025 s, Physitemp Instruments Inc.), were connected to that system and both were immersed in a room temperature, 0.9% sterile saline solution, while tooth preparation was performed. After pulp exposure, one probe was removed from the water and immediately inserted into the pulp chamber through the occlusal access opening and was positioned to remain stable, while PT was measured. A small groove was created on the buccal cusp, close to the cusp tip, to allow the probe to rest on the cusp tip incline and ensure that the 1-cm long probe tip penetrated approximately 4 mm into the pulp chamber: in a similar position for all teeth. The other probe was kept in the saline solution at room temperature (approximately 22.0 °C), as a reference. The room temperature was stable, and controlled by air conditioning set to approximately 22 °C. The preparation was then filled with provisional restorative material (Cavitec, CaiTHEC Ltda, SC, Brazil), to minimize heat loss from the tooth through the occlusal preparation walls and pulp access. After probe stability was confirmed, real-time temperature data were continuously acquired every 0.2 s, until a stable PT was reached: between 15 min and 20 min . The LCU tip was placed against the buccal tooth surface with the lower edge of the light guide sheath just above the facial free gingiva, and in a similar position with respect to the curing unit body, and the tooth was sequentially exposed to the radiant output from a polywave LED LCU (bluephase ® 20i, Ivoclar Vivadent, Schaan, Liechtenstein) using the following EMs: 10-s in low intensity (10-s/L); 10-s in high intensity (10-s/H); 5-s in Turbo intensity (5-s/T); and 60-s in high intensity (60-s/H). A 7-min time span between each exposure was allowed for the PT to return to baseline levels. The sequence of EMs was randomly determined and the operator was not aware of which mode was being used. The time into the data acquisition when each light mode was applied was recorded, so that a time-based overlay of light activation and temperature could be made. At the end of the temperature data acquisition, the probe was carefully removed from the tooth, which was then atraumatically extracted as treatment planned. The probe was then reinserted into the pulp chamber of the extracted tooth and X-ray images were obtained from the proximal side, with the probe in position as it was intraorally, to confirm that the probe was properly inserted into the pulp chamber during temperature measurement.

Time constant analysis of the temperature acquisition system

To determine the response time (time constant) of the temperature acquisition instrument, three probes were connected to the system: one probe was immersed in water at RT (≈25.5 °C) in a beaker, and another was immersed in water at 60 °C in a heated circulating water bath with electronic temperature control (SL-155/22, Solab, Piracicaba, SP, Brazil). An additional probe was placed in the RT water, and was intermittently moved from that fluid to the higher-temperature one. Real-time temperature data were continuously acquired every 0.2 s from the three probes for 10 min. During this time, one probe was removed from the RT water, and immediately immersed in water at 60 °C, where the probe was left for 10 min. Afterwards, the probe was removed from the hot water and returned to RT water again, for 10 min. This procedure was repeated 8 times ( n = 8). For each probe movement, a temperature vs time plot was developed, and the average time corresponding to 63.2% of the total temperature increase (time constant – τ ) was determined for all probe movements, and was compared using a student’s t -test (Statistics 19, SPSS Inc., IBM Company, Armonk, NY, USA). No statistical difference (pre-set alpha 0.05) was found for τ between direction of temperature change ( p = 0.1760), so the overall average of the 16 measurements and its standard deviation were determined.

Radiant emittance measurement and radiant exposure calculation of the LCU

The spectral power of the different EMs was recorded five times each, using a laboratory grade spectroradiometer (USB 2000, Ocean Optics, Dunedin, FL, USA) and a 6-in integrating sphere (Labsphere, North Sutton, NH, USA), previously calibrated using a NIST-traceable light source. The LCU tip end was positioned at the entrance of the integrating sphere, so all light emitted from the unit was captured. Wavelength-based, spectral power emission during each EM was recorded using software (SpectraSuite v2.0.146, Ocean Optics) between 350 nm and 550 nm, which also provided a total emitted power value for that wavelength range. The optical emitting area of the distal end of the light guide was calculated, and this value was divided into the integrated spectral power value to derive the total radiant emittance from the curing light for each EM (mW/cm 2 ). This value was then multiplied by the light exposure duration to derive the value of radiant exposure applied to each tooth surface for each light output mode (J/cm 2 ).

Statistical analyses

Peak PT (°C) and the PT increase during exposure to the LCU over that of the pre-exposure baseline value (Δ T ) were subjected to a one-way, repeated measures ANOVA, followed by the Bonferroni’s post hoc test. Linear regression analysis was performed to examine the relationship between applied radiant exposure level and Δ T . The total spectral power and radiant exposure delivered by the evaluated EMs were compared using a one-way ANOVA followed by Tukey’s post hoc test at a pre-set alpha of 0.05. Post hoc power analysis was performed for the statistical analyses of peak PT values, Δ T , emitted spectral power, and radiant exposure. All statistical analyses were performed using commercial statistical software (Statistics 19, SPSS Inc., IBM Company).

Materials and methods

In vivo measurement of pulp temperature increase

This study was approved by the Ethics Committee at the State University of Ponta Grossa (protocol # 255,945). Eight volunteers, ranging from 12 to 30 years, requiring extraction of upper right and left first premolars ( n = 15) for orthodontic reasons, were selected from the Orthodontic specialization program in Ponta Grossa, Brazil. All patients were recruited in February 2013, and were attended to between March and April 2013. Patient inclusion criteria included (1) treatment plans indicating premolar extractions for orthodontic reasons, (2) the presence of healthy, intact, non-carious, and non-restored, fully erupted treatment teeth, and (3) patients with well-controlled health conditions that allowed all procedures involved in the research to be performed with minimal risk. Exclusion criteria included (1) those patients who did not agree to volunteer for the study and (2) patients not meeting all of the inclusion criteria.

A single tooth at a time from a volunteer was treated by receiving infiltrative and intraligamental anesthesia, using approximately 1.8 ml of 2% Mepivacaine Hidrocloryde (36 mg) with 1:100,000 Epinephrine (18 μg) (Mepiadre, Nova DFL Industria e Comercio, Rio de Janeiro, RJ, Brazil), after which the tooth was isolated using rubber dam. A small, occlusal preparation was made in the center of the tooth using a round diamond bur (#1015, KG Sorensen, Cotia, SP, Brazil) in a high speed handpiece, providing air-water spray, until the preparation pulpal floor was near the buccal pulp horn. Then, a small, pencil-shaped diamond bur (#2134, KG Sorensen) was used to produce a minute pulp exposure, with no pulp bleeding. Care was taken to ensure that the same water flow and air pressure were used for each tooth, as well as the same time spent for each preparation. A wireless, NIST-traceable, temperature acquisition system (Temperature Data Acquisition – Thermes WFI, Physitemp Instruments Inc., Clifton, NJ, USA) was used to measure PT. Two 1-cm long tip, calibrated temperature probes (Model MT-D, Type T, time constant: 0.025 s, Physitemp Instruments Inc.), were connected to that system and both were immersed in a room temperature, 0.9% sterile saline solution, while tooth preparation was performed. After pulp exposure, one probe was removed from the water and immediately inserted into the pulp chamber through the occlusal access opening and was positioned to remain stable, while PT was measured. A small groove was created on the buccal cusp, close to the cusp tip, to allow the probe to rest on the cusp tip incline and ensure that the 1-cm long probe tip penetrated approximately 4 mm into the pulp chamber: in a similar position for all teeth. The other probe was kept in the saline solution at room temperature (approximately 22.0 °C), as a reference. The room temperature was stable, and controlled by air conditioning set to approximately 22 °C. The preparation was then filled with provisional restorative material (Cavitec, CaiTHEC Ltda, SC, Brazil), to minimize heat loss from the tooth through the occlusal preparation walls and pulp access. After probe stability was confirmed, real-time temperature data were continuously acquired every 0.2 s, until a stable PT was reached: between 15 min and 20 min . The LCU tip was placed against the buccal tooth surface with the lower edge of the light guide sheath just above the facial free gingiva, and in a similar position with respect to the curing unit body, and the tooth was sequentially exposed to the radiant output from a polywave LED LCU (bluephase ® 20i, Ivoclar Vivadent, Schaan, Liechtenstein) using the following EMs: 10-s in low intensity (10-s/L); 10-s in high intensity (10-s/H); 5-s in Turbo intensity (5-s/T); and 60-s in high intensity (60-s/H). A 7-min time span between each exposure was allowed for the PT to return to baseline levels. The sequence of EMs was randomly determined and the operator was not aware of which mode was being used. The time into the data acquisition when each light mode was applied was recorded, so that a time-based overlay of light activation and temperature could be made. At the end of the temperature data acquisition, the probe was carefully removed from the tooth, which was then atraumatically extracted as treatment planned. The probe was then reinserted into the pulp chamber of the extracted tooth and X-ray images were obtained from the proximal side, with the probe in position as it was intraorally, to confirm that the probe was properly inserted into the pulp chamber during temperature measurement.

Time constant analysis of the temperature acquisition system

To determine the response time (time constant) of the temperature acquisition instrument, three probes were connected to the system: one probe was immersed in water at RT (≈25.5 °C) in a beaker, and another was immersed in water at 60 °C in a heated circulating water bath with electronic temperature control (SL-155/22, Solab, Piracicaba, SP, Brazil). An additional probe was placed in the RT water, and was intermittently moved from that fluid to the higher-temperature one. Real-time temperature data were continuously acquired every 0.2 s from the three probes for 10 min. During this time, one probe was removed from the RT water, and immediately immersed in water at 60 °C, where the probe was left for 10 min. Afterwards, the probe was removed from the hot water and returned to RT water again, for 10 min. This procedure was repeated 8 times ( n = 8). For each probe movement, a temperature vs time plot was developed, and the average time corresponding to 63.2% of the total temperature increase (time constant – τ ) was determined for all probe movements, and was compared using a student’s t -test (Statistics 19, SPSS Inc., IBM Company, Armonk, NY, USA). No statistical difference (pre-set alpha 0.05) was found for τ between direction of temperature change ( p = 0.1760), so the overall average of the 16 measurements and its standard deviation were determined.

Radiant emittance measurement and radiant exposure calculation of the LCU

The spectral power of the different EMs was recorded five times each, using a laboratory grade spectroradiometer (USB 2000, Ocean Optics, Dunedin, FL, USA) and a 6-in integrating sphere (Labsphere, North Sutton, NH, USA), previously calibrated using a NIST-traceable light source. The LCU tip end was positioned at the entrance of the integrating sphere, so all light emitted from the unit was captured. Wavelength-based, spectral power emission during each EM was recorded using software (SpectraSuite v2.0.146, Ocean Optics) between 350 nm and 550 nm, which also provided a total emitted power value for that wavelength range. The optical emitting area of the distal end of the light guide was calculated, and this value was divided into the integrated spectral power value to derive the total radiant emittance from the curing light for each EM (mW/cm 2 ). This value was then multiplied by the light exposure duration to derive the value of radiant exposure applied to each tooth surface for each light output mode (J/cm 2 ).

Statistical analyses

Peak PT (°C) and the PT increase during exposure to the LCU over that of the pre-exposure baseline value (Δ T ) were subjected to a one-way, repeated measures ANOVA, followed by the Bonferroni’s post hoc test. Linear regression analysis was performed to examine the relationship between applied radiant exposure level and Δ T . The total spectral power and radiant exposure delivered by the evaluated EMs were compared using a one-way ANOVA followed by Tukey’s post hoc test at a pre-set alpha of 0.05. Post hoc power analysis was performed for the statistical analyses of peak PT values, Δ T , emitted spectral power, and radiant exposure. All statistical analyses were performed using commercial statistical software (Statistics 19, SPSS Inc., IBM Company).

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Nov 23, 2017 | Posted by in Dental Materials | Comments Off on In vivotemperature rise in anesthetized human pulp during exposure to a polywave LED light curing unit
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