Direct measurement of time-dependent anesthetized in vivohuman pulp temperature

Highlights

  • Actual in vivo human coronal pulp temperature values were obtained.

  • The cooling effects of cavity preparation on in vivo pulp temperature were assessed.

  • In vivo human coronal pulp temperature values are lower than the human body core.

  • In vivo pulp temperature values had less variation than in vitro studies.

  • Use of a water-cooled high-speed handpiece reduces in vivo pulp temperature.

Abstract

Objectives

Human intrapupal tooth temperature is considered to be similar to that of the body (≈37 °C), although the actual temperature has never been measured. This study evaluated the in vivo , human, basal, coronal intrapulpal temperature of anesthetized upper first premolars.

Methods

After approval of the local Ethics Committee was obtained (protocol no. 255,945), upper right and left first premolars requiring extraction for orthodontic reasons from 8 volunteers, ranging from 12 to 30 years old, received infiltrative and intraligamental anesthesia. The teeth ( n = 15) were isolated using rubber dam and a small, occlusal preparation was made using high-speed handpiece, under constant air–water spray, until a minute pulp exposure was attained. The sterile probe from a wireless, NIST-traceable, temperature acquisition system (Thermes WFI) was inserted directly into the coronal pulp. Once the probe was properly positioned and stable, real-time temperature data were continuously acquired for approximately 25 min. Data (°C) were subjected to 2-tailed, paired t -test ( α = 0.05), and the 95% confidence intervals for the initial and 25-min mean temperatures were also determined.

Results

The initial pulp temperature value (31.8 ± 1.5 °C) was significantly lower than after 25-min (35.3 ± 0.7 °C) ( p < 0.05). The 95% confidence interval for the initial temperature ranged from 31.0 to 32.6 °C and from 35.0 to 35.7 °C after 25 min. A slow, gradual temperature increase was observed after probe insertion until the pulp temperature reached a plateau, usually after 15 min.

Significance

Consistent coronal, human, in vivo temperature values were observed and were slightly, but significantly below that of body core temperature.

Introduction

Pulp health integrity is crucial to any restorative treatment, and is a clinical challenge, because teeth are subjected to trauma by heat generated during restorative procedures, such as from use of high and low speed handpieces , restorative materials with exothermic setting , restoration finishing and polishing , as well as from application of high power light emitting diode (LED) curing units and laser sources to polymerize resin-based materials . For these reasons, the consequences of heat, or other external stimuli, on pulp chamber temperature have been investigated .

Initial in vivo effects of heat on pulp temperature (PT) and its biological consequences were performed by Zach and Cohen in 1965 . In that study, a 5.5 °C PT increase in rhesus monkeys, from application of a hot metal source to the facial enamel surface, induced necrosis in 15% of evaluated pulps. Because of the high expense of animal testing, in vitro techniques using extracted teeth were developed to evaluate pulp chamber temperature change under simulated clinical conditions, while applying various external heat sources . In these reports, the pulp chamber temperature, prior to application of temperature-raising effects, was pre-set at 37 °C (human body temperature) , or at room temperature , or was not mentioned in the study . Others simulated the influence of pulpal blood flow in vitro , to evaluate how this parameter might dissipate internal tooth heat generated by exposure to dental light curing units . Conversely, these studies set the initial, baseline pulp chamber fluid temperature between 33 °C and 34 °C , or between 34 °C and 35 °C . Using a finite element model, along with in vitro simulation of restorative procedures, a simulated temperature excursion at the pulp–dentin junction during photocuring of a dental restoration was calculated . In that study, the authors observed that some exposure protocols may cause potentially dangerous PT increase, mainly when using high intensity lights, or when curing a thin resin layer. Although such studies provide important information regarding the effects of external heat sources on the temperature increase in ex vivo human tooth pulps, it is evident that accurate data on the thermal effects of such heat sources will depend on the actual in vivo temperature of human pulp tissue. However, no literature concerning in vivo baseline temperature of the human pulp can be found.

The purpose of this in vivo study was to develop a method to measure the baseline PT of locally anesthetized, human upper premolars. The research hypotheses were that (1) consistent and reproducible intrapulpal temperature values can be obtained using a well-controlled measurement system, and that (2) the in vivo temperature of locally anesthetized human pulp tissue is similar to that of the human body (the baseline temperature from which subsequent temperature rise values could be measured).

Materials and methods

Study design

The study design was approved by the Ethics Committee at State University of Ponta Grossa (protocol no. 255,945). Eight volunteers, ranging from 12 to 30 years, requiring extraction of upper right and left first premolars for orthodontic reasons were selected from the Orthodontic specialization program in Ponta Grossa, Brazil, were recruited in February, 2013, and 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, (2) patients not meeting all of the inclusion criteria.

Intrapulpal temperature measurement

After written consents were obtained, each study volunteer received local, 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), and the teeth ( n = 15) were isolated using rubber dam, one at a time. As there is no previous human study to base sample size on, the present study was used as its own pilot. A small, occlusal preparation was made, using a round diamond bur (no. 1015, KG Sorensen, Cotia, SP, Brazil) in a high-speed handpiece, under air–water spray, until the preparation floor was near the buccal pulp horn ( Fig. 1 a ). Then, a small, pencil-shaped diamond bur (no. 2134, KG Sorensen) was used to produce a minute pulp exposure, with no pulp bleeding ( Fig. 1 b). Care was taken to ensure that the same water flow and air pressure were used for each tooth, as well as the same time for each preparation. A wireless, NIST-traceable, temperature acquisition system (Temperature Data Acquisition—Thermes WFI, Physitemp, Clifton, NJ, USA) was used to measure PT. Two probes were connected to that system and both were immersed in a 0.9% sterile saline solution at room temperature (RT), while the tooth was prepared. After pulp exposure, one probe was removed from water storage, inserted into the pulp chamber, and positioned to remain stable while PT was recorded in real-time ( Fig. 1 c). A small groove was created on the buccal cusp, close to the cusp tip ( Fig. 1 d), to allow the probe to rest on the cusp tip and ensure that the 1-cm long probe tip penetrated approximately 4 mm into the pulp chamber: in a similar position for all teeth ( Fig. 1 e). The other probe remained in the RT saline solution (approximately 22.0 °C), as a reference. Room temperature was stable and controlled by air conditioning: 22 °C. The occlusal preparation was then filled with a provisional restorative material (Cavitec, CaiTHEC Ltd, Rio do Sul, SC, Brazil) to minimize heat loss from the internal cut tooth surfaces ( Fig. 1 d). After probe stability was confirmed, real-time temperature data were continuously acquired every 0.2 s, for approximately 25 min, during which a stable PT was reached. This procedure was followed to avoid any possible effect of tooth cooling as a result of the occlusal surface endodontic access opening, resulting from water and air spray of the handpiece, which could be a potential confounding variable. At the end of data acquisition, the probe was carefully removed, and a small amount of additional interim restorative material was placed to cover the hole left from probe removal. The same process was then performed on the contralateral tooth, using a freshly autoclaved probe. When temperature measurements for both teeth were completed, each tooth was atraumatically extracted, as treatment planned. Following extraction, each probe was reinserted into the pulp chamber of its corresponding extracted tooth, and proximal surface X-rays were taken with the probe in position ( Fig. 1 e), to confirm probe placement during temperature acquisition. No form of bias was introduced in the study, because each patient was treated in the same manner. Results were strictly observational, with no imposed external variable applied.

Fig. 1
(a) Deep occlusal preparation made to produce a minor pulp exposure. (b) Pulp exposure after use of a pencil-shaped diamond bur. (c) Probe insertion into the pulp chamber. (d) Cavity sealing with provisional restorative material. (e) X-ray analysis after tooth extraction to confirm if the probe was properly positioned into the pulp chamber.

Statistical analysis

Normal distribution of continuous variables was tested by the Shapiro–Wilk test. PT at the time of initial probe insertion and after 25-min in place (expressed in degree Celsius—°C) were subjected to 2-tailed, paired t-tests (pre-set alpha = 0.05). The 95% confidence intervals of population means obtained at these two evaluation periods were also calculated. All statistical analyses were performed using personal statistical software (Statistics 19, SPSS Inc, IBM Company, Armonk, NY, USA).

Temperature acquisition system response time

To determine the response time (time constant) of the temperature acquisition instrument, three probes were connected to the system: one probe was immersed in distilled water at RT (≈25.5 °C), and other was immersed in distilled water at 60 °C. 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. No statistical difference (pre-set α = 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, was determined.

Materials and methods

Study design

The study design was approved by the Ethics Committee at State University of Ponta Grossa (protocol no. 255,945). Eight volunteers, ranging from 12 to 30 years, requiring extraction of upper right and left first premolars for orthodontic reasons were selected from the Orthodontic specialization program in Ponta Grossa, Brazil, were recruited in February, 2013, and 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, (2) patients not meeting all of the inclusion criteria.

Intrapulpal temperature measurement

After written consents were obtained, each study volunteer received local, 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), and the teeth ( n = 15) were isolated using rubber dam, one at a time. As there is no previous human study to base sample size on, the present study was used as its own pilot. A small, occlusal preparation was made, using a round diamond bur (no. 1015, KG Sorensen, Cotia, SP, Brazil) in a high-speed handpiece, under air–water spray, until the preparation floor was near the buccal pulp horn ( Fig. 1 a ). Then, a small, pencil-shaped diamond bur (no. 2134, KG Sorensen) was used to produce a minute pulp exposure, with no pulp bleeding ( Fig. 1 b). Care was taken to ensure that the same water flow and air pressure were used for each tooth, as well as the same time for each preparation. A wireless, NIST-traceable, temperature acquisition system (Temperature Data Acquisition—Thermes WFI, Physitemp, Clifton, NJ, USA) was used to measure PT. Two probes were connected to that system and both were immersed in a 0.9% sterile saline solution at room temperature (RT), while the tooth was prepared. After pulp exposure, one probe was removed from water storage, inserted into the pulp chamber, and positioned to remain stable while PT was recorded in real-time ( Fig. 1 c). A small groove was created on the buccal cusp, close to the cusp tip ( Fig. 1 d), to allow the probe to rest on the cusp tip and ensure that the 1-cm long probe tip penetrated approximately 4 mm into the pulp chamber: in a similar position for all teeth ( Fig. 1 e). The other probe remained in the RT saline solution (approximately 22.0 °C), as a reference. Room temperature was stable and controlled by air conditioning: 22 °C. The occlusal preparation was then filled with a provisional restorative material (Cavitec, CaiTHEC Ltd, Rio do Sul, SC, Brazil) to minimize heat loss from the internal cut tooth surfaces ( Fig. 1 d). After probe stability was confirmed, real-time temperature data were continuously acquired every 0.2 s, for approximately 25 min, during which a stable PT was reached. This procedure was followed to avoid any possible effect of tooth cooling as a result of the occlusal surface endodontic access opening, resulting from water and air spray of the handpiece, which could be a potential confounding variable. At the end of data acquisition, the probe was carefully removed, and a small amount of additional interim restorative material was placed to cover the hole left from probe removal. The same process was then performed on the contralateral tooth, using a freshly autoclaved probe. When temperature measurements for both teeth were completed, each tooth was atraumatically extracted, as treatment planned. Following extraction, each probe was reinserted into the pulp chamber of its corresponding extracted tooth, and proximal surface X-rays were taken with the probe in position ( Fig. 1 e), to confirm probe placement during temperature acquisition. No form of bias was introduced in the study, because each patient was treated in the same manner. Results were strictly observational, with no imposed external variable applied.

Nov 23, 2017 | Posted by in Dental Materials | Comments Off on Direct measurement of time-dependent anesthetized in vivohuman pulp temperature
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