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Evaluation of in-vitro intrapulpal temperature rise when using the Bluephase 16i in different clinically relevant exposure scenarios

Dr. Fred Rueggeberg PURPOSE This project was instituted at the request of Ivoclar/Vivadent to investigate the effect on simulated intrapulpal temperature rise when the Bluephase 16i was used in scenarios simulating curing of a dentin bonding agent as well as when irradiating a restored tooth. The values obtained were compared to other Ivoclar light units used in similar “modes� and exposure durations.

MATERIALS AND METHODS Basic tooth model An extracted, human upper bicuspid was used. This tooth was obtained from an unknown individual, and the identity of that person will never be sought. Under these guidelines, our testing has been re-approved (10/18/04) as exempt by the Medical College of Georgia Human Assurance Committee.

The tooth had an intact, bifurcated root. A large, divergent Class V preparation was made on the facial surface, to within 1 mm of the facial wall of the pulp chamber. This distance was verified using X-rays. An access hole was made from the lingual surface into the pulp chamber. A K-type thermocouple was made and threaded through the access opening. The junction of the thermocouple was placed against the facial, pulpal wall, directly in line with the center of the axial wall of the Class V preparation. The lingual access opening and wires were sealed and stabilized using acid etching and a flowable composite. Approximately one-third of the root lengths were removed. The root canals were enlarged and small sections of 16-gage stainless steel tubing were attached to each root end using cyanoacrylate cement. A length of small diameter plastic tubing was attached to one of metal coupling tubes.


The prepared tooth was immersed into thermostatically controlled water up to the cementoenamel junction. The tubing from the tooth root was coiled to increase contact with the warmed water. The distal end of the tubing ran out of the water and was connected to 30 mL glass syringe, using leur lock connections. This syringe was filled with water, and the plunger end connected to a motorized drive so that the rate at which the piston moved down the syringe tube was accurately controlled at 0.0123 mL/min. This rate approximates the intrapulpal blood flow rate for a mass of pulp tissue found in a bicuspid of this size.

The thermocouple output was fed to an electronic cold junction compensator. The millivoltage output of this device was directed to a 16-bit A/D converter and read in real-time, on-screen at a minimal data acquisition rate of 10 data points per second. The millivoltage output with respect to time was then recorded.

Water temperature surrounding the partially immersed tooth was controlled to provide for a coronal intrapulpal temperature between 32째 and 35째 C. Previous studies found that this range is the normal in vivo intracoronal pulpal temperature, not 37째 C.

The light-curing tip was held at a fixed, repeatable position with respect to the cavity preparation (1 mm from the tooth surface). At the appropriate time into data recording, the light-curing unit was activated. Any increase in intrapulpal temperature was noted by an elevation in millivoltage output on the computer screen. Data were collected all throughout the exposure, until a point when it was evident the tooth was cooling toward baseline level. The millivoltage rise between baseline and the maximal value was then noted. This value was converted into temperature rise (째C) by referencing known conversion charts, relating millivoltage values for a K-type thermocouple and temperature value.

A diagrammatic presentation of the tooth set-up is seen in Figure 1, below:

Bluephase 16i intrapulpal temperature rise

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1 mm Light tip

0.75 - 1 mm thermocouple leads to cold junction compensator thermocouple junction

Tooth roots immersed in a thermostatically controlled water bath

Inlet for temperature-controlled water from infusion pump

water outlet

Figure 1 – Schematic diagram of experimental measurement of simulated intrapulpal temperature rise

Equipment calibration Temperature readings The thermocouple wire used was obtained from Omega Engineering (Stamford, CT), their item # TT-K-30-SLE (having special limits of error of ±1.1° C or 0.4%). To ensure proper voltage readings from the thermocouple, an electronic cold junction compensator was used between the thermocouple wire and the A/D converter (model MCJ-K, Omega Engineering). The millivoltage values were recorded using 16-bit precision. This device converts thermocouple voltages into 0° C referenced signals. The signals from this device (millivoltage values) was then converted to temperatures using the standard temperature-mv table. This table lists temperature values referenced to 0° C with respect to the milivoltage value that will be generated by that thermocouple. The table values are referenced from NIST monograph 125. As a further step to ensure temperature accuracy, the thermocouple was immersed in room temperature water along with a calibrated laboratory glass/mercury thermometer (Model #14-983-10C, Fisher Scientific, Norcross, GA; meeting accuracy standards of ANSI/SAMA Z236.2-1983).

The

millivoltage-converted-to-temperature value of the thermocouple reading was verified with that of the visual reading of the laboratory mercury thermometer.

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Fluid flow The volume of the tooth’s pulp chamber was determined using previously performed experimentation (unpublished: Langer CIH. The effect of dental curing light on the intrapulal temperature rise during preparation and restoration of premolars. Master’s of Science in Oral Biology Thesis, The Medical College of Georgia, Augusta, GA

July, 2002). From this volume,

the mass of pulpal tissue was calculated, and the intrapulpal blood flow through the tooth was determined using methods published in the literature (Kim S. Microcirculation of the dental pulp in health and disease. Journal of Endodontics 11:465-471, 1985). The fluid flow rate needed was calculated to be 0.0125 mL/min. A value near this fluid flow rate (0.0123) was obtained using an infusion pump (model 600-900 multi-speed infusion/withdrawal pump, Harvard Apparatus Company, Dover, MA) having gear-selectable extrusion rates from a glass syringe reservoir. Previously, the output of this device over a time period of 4 hours was measured and compared very well with the selected rate desired (approximately 3 mL).

Part 1: Intrapulpal temperature rise when simulating light-curing of a dentin bonding agent In order to provide maximal, clinically relevant temperature rise information, the light unit was shown on the bare preparation to simulate exposure of a thin layer of dentin bonding agent. This bonding agent was NOT present, only exposure of the bare preparation to the light source was made. The minimal curing exotherm from such a thin layer is considered minimal with respect to that resulting from exposure to the light source itself.

The tooth was securely fixed in position, partially immersed in the temperature-controlled water, with simulated intrapulpal circulation flowing.

Conditions were stabilized such that baseline

temperature values were those noted above. The distal end of a light-curing tip was placed in contact with the tooth surface and then the digital recording of the temperature values begun. The light unit was activated for the prescribed duration value (below) and data recording continued until it is noted that temperature trends indicated a return of values toward baseline level. All light units were activated for 10 seconds in their “low power” mode.

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lights/conditions tested (3 types) 1. Astralis 10 (sn 500202) 2. Bluephase (sn1535699) 3. Bluephase 16i prototype (sn prototype 03)

Replications Five (5) replications were made for each test condition

Part 2: Intrapulpal temperature rise when simulating light exposure to a restored tooth The empty preparation was coated with a thin silicone lubricant film to aid in composite removal following exposure.

An increment of uncured composite (lot #030221, exp date 02/2006,

EsthetX shade A2) was placed and contoured to match the facial outline of the tooth. Generally, this material was 2 mm thick. The restoration was then light-exposed using the Astralis 10 light in high power mode for 30 seconds. The tooth with cured composite was placed into the water bath, the intrapulpal circulation started, and the temperature monitored as above to ensure that the baseline values are similar to those previously stated. The light tip was securely held 1 mm from the uncured composite surface. Once the intrapulpal temperature stabilized to baseline value, the light unit was activated for the required time interval. During this time, the millivoltage output of the thermocouple was monitored as above. Once the exposure was over, and the trend for intrapulpal temperature showed a declining trend, monitoring was stopped. The tooth was then allowed to cool to baseline levels once again. All units were used in their “high power� modes for 20 seconds.

lights/conditions tested (3 types) 1. Astralis 10 (sn 500202) 2. Bluephase (sn1535699) 3. Bluephase 16i prototype (sn prototype 03)

Exposure durations tested 1. 10 seconds 2. 20 seconds

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Replications Five (5) replications were made for each test condition

RESULTS Part 1: Empty preparations Values for empty preparations (when simulating exposure of a dentin bonding agent) are displayed in tabular and graphical format. Statistical analysis was made using a 1-way ANOVA and the Tukey-Kramer post hoc test for pair-wise comparisons.

All statistical testing was

performed at a pre-set alpha of 0.05.

Table 1 Average peak intrapulpal temperature during 10-s simulated exposure of bonding agent PEAK TEMP LIGHT UNIT

(째 C)

stdev

Astralis 10

3.30

0.07

2.71

0.19

2.45

0.16

Conventional BluePhase BluePhase 16i prototype

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PEAK TEMPERATURE DURING BONDING SCENARIO BluePhase 16i prototype

2.45

Conventional BluePhase

2.71

Astralis 10

0.00

3.30

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

TEMPERATURE (deg C)

Figure 1 Peak intrapulpal temperature rise when simulating exposure for dentin bonding agent N = 5 specimens per experimental group Horizontal bar = +1 stdev

Statistical testing revealed a significant difference among all temperature values with the Astralis 10 > conventional Bluephase > Bluephase 16i.

Part 2: Exposure of a restored tooth Values for exposing the restored tooth to the various lights are displayed in tabular and graphical format below. Statistical analysis was made using a 1-way ANOVA and the TukeyKramer post hoc test for pair-wise comparisons. All statistical testing was performed at a preset alpha of 0.05.

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Table 2 Average peak intrapulpal temperature during 20-s exposure of restored tooth LIGHT UNIT

PEAK TEMP

stdev

Astralis 10

2.38

0.13

Conventional BluePhase

1.60

0.12

BluePhase 16i prototype

2.68

0.12

PEAK TEMPERATURE RESTORED TOOTH 10s exposure BluePhase 16i prototype

2.68

Conventional BluePhase

1.60

2.38

Astralis 10

0

1

1

2

2

3

3

TEMPERATURE (deg C)

Figure 2 Peak intrapulpal temperature rise when exposing the restored tooth for 10 seconds N = 5 specimens per experimental group Horizontal bar = +1 stdev

Statistical analysis indicated that peak temperature rise values were significantly different among all test groups with Bluephase 16i > Astralis 10 > BluePhase Conventional.

Table 3 Bluephase 16i intrapulpal temperature rise

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Average peak intrapulpal temperature during 20-s exposure of restored tooth PEAK LIGHT UNIT

TEMP

stdev

Astralis 10

3.98

0.21

3.43

0.13

5.34

0.24

Conventional BluePhase BluePhase 16i prototype

PEAK TEMPERATURE RESTORED TOOTH 20s exposure BluePhase 16i prototype

5.34

Conventional BluePhase

3.43

3.98

Astralis 10

0

1

2

3

4

5

6

TEMPERATURE (deg C)

Figure 3 Peak intrapulpal temperature rise when exposing the restored tooth for 20 seconds N = 5 specimens per experimental group Horizontal bar = +1 stdev

The results of the statistical testing revealed that the temperature value from all three lights were significantly different from one another with Bluephase 16i > Astralis 10 > conventional Bluephase.

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Presentation of all data in an overlaid graphical format is presented below in Figure 4

PEAK TEMPERATURE RISE 5.34 C

FILLED PREP (20s)

3.43 A 3.98 B

2.68 C

FILLED PREP (10s)

BLUEPHASE 16i BLUEPHASE ASTRALIS 10

1.60 A 2.38 B

2.45 A

EMPTY PREP (10s)

2.71 B 3.30 C

0

1

2

3

4

5

6

TEMPERATURE (deg C) Figure 4 Peak intrapulpal temperature rise when exposing the restored tooth for all exposures and restorative scenarios N = 5 specimens per experimental group Horizontal bar = +1 stdev

Within each of the three exposure scenarios, all temperature values among light types were significantly different as denoted by the lettered grouping.

PROJECT SUMMARY Bluephase 16i intrapulpal temperature rise 10

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Peak intrapulpal temperatures in an extracted, human bicuspid were obtained using conditions very closely simulating the clinical condition: maintenance of pulp change temperature near 35째 C at baseline and provision of a simulated intrapulpal blood flow. Temperature rise values were noted when using 10-s exposures in low power mode from all three light curing units. The tooth was then restored, and peak intrapulpal temperature rise values were noted when each light was exposed for 20 seconds in high power mode from a distance of 1 mm from the restored facial restoration.

The results indicated that, when using the lights for curing a dentin bonding agent, the Bluephase 16i actually developed the lowest intrapulpal temperature rise of all lights. However, when exposing the restored tooth for 10 or 20s, the Bluephase 16i resulted in the highest peak intrapulpal temperature rise of all lights tested in that group.

It should be noted that, at the recommended exposure duration of 10s, the BluePhase 16i peak intrapulpal temperature was less than half (2.68째 C) that of the generally accepted value of 5.5째 C where a significant in crease in pulpal necrosis was found in Rhesus monkeys (Zach L, Cohen G. Pulp response to externally applied heat. Oral Surgery, Oral Medicine, and Oral Pathology 19:515-530, 1965).

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