In vivo findings associated with heat generation during thermomechanical compaction of gutta-percha. 1. Temperature levels at the external surface of the root

Heat conductive properties of set root canal sealers

OBJECTIVE

The aim of this study was to examine the thermal conductivity of five different root canal sealers in vitro.

MATERIALS AND METHODS

Sealapex, AH Plus, AH 26, Endomethasone and RoekoSeal root canal sealers were examined. These materials were prepared in accordance with the manufacturer's instructions and applied to standard molds. Three samples of each material were prepared. The samples were kept for 5 days under 37°C conditions. Measurements were taken using a heat conduction unit (P.A. Hilton Ltd. Stockbridge, Hants, UK). The thermal conductivity coefficient was calculated for each sample using the Fourier equation. Coefficients were analyzed statistically by the Kruskal-Wallis test.

RESULTS

Significant differences were found for thermal conductivity between some materials (p < 0.05). The conductivity coefficient of AH Plus was found to be higher than those of the other materials (p < 0.05). No statistically significant differences were found between AH 26 and RoekoSeal (p > 0.05) and the conductivity coefficients of these sealers were found to be lower than those of the other materials (p < 0.05). No statistically significant differences were found between Sealapex and Endomethasone (p > 0.05) and the conductivity coefficients of these sealers were found to be lower than that of AH Plus but higher than those of RoekoSeal and AH26 (p < 0.05).

CONCLUSIONS

The results showed that root canal sealers functioned as thermal insulators and had different heat-conductive properties that depended on their composition.

Evaluation of antifungal efficacy of erbium, chromium: yttrium-scandium-gallium-garnet laser against Candida albicans

OBJECTIVE

The purpose of this in vitro study was to investigate the ability of Er,Cr:YSGG laser irradiation at different energy settings to eliminate Candida albicans, either with or without 5.25% sodium hypochlorite (NaOCl) treatment.

METHODS

In total, 90 extracted human single-rooted teeth were shaped by using a crown-down technique with HERO Shaper rotary instruments and irrigated with 1 mL of 2.5% NaOCl between each instrument. The specimens were autoclaved and incubated with a suspension of C. albicans (ATCC 90028). Then the specimens were divided into six treatment groups (n = 15 per group): group 1, NaOCl + 1-W laser; group 2, 1-W laser; group 3, NaOCl + 0.75-W laser; group 4, 0.75-W laser, group 5, NaOCl; and group 6, no treatment. Aliquots of the experimental teeth were transferred onto Sabouraud's dextrose agar plates with paper points, and colony-forming units (CFUs) were counted as a measure of antifungal activity. One root from each group, which was not submitted to the sampling procedure, was fixed in glutaraldehyde, split into two halves, and evaluated with scanning electron microscopy (SEM). Statistical analysis was performed by using analysis of variance (ANOVA) and the Dunnett t test. Significance was set at alpha = 0.05.

RESULTS

All the treatment groups resulted in a significant reduction of C. albicans, but no sterilization, and all the groups were significantly different from each other (p < 0.0001). Group 1 (NaOCl and 1-W laser combination) exhibited the greatest reduction, whereas group 5 (NaOCl) resulted in a minimal reduction in CFUs of C. albicans. The SEM observations were in accordance with the microbiologic analysis.

CONCLUSIONS

The 5.25% NaOCl and 1-W laser treatment combination may be a valuable cleaning tool for root canals infected with C. albicans.

Effect of different water flows on root surface temperature during ultrasonic removal of posts

OBJECTIVE

This in vitro study evaluated rises in temperature on the outer root surface of human incisors during ultrasonic post removal with different water flows.

STUDY DESIGN

Thirty-six extracted teeth (12 maxillary central incisors, 12 maxillary lateral incisors, and 12 mandibular incisors) were used. After root canal preparation, the teeth were obturated, and prefabricated posts were cemented into the prepared spaces. Posts were ultrasonically instrumented dry and with irrigation at 20 mL/min and 40 mL/min. Temperature changes on the entire mesial outer surfaces of the roots were measured at 10-second intervals using an infrared thermal imaging camera.

RESULTS

Increases in root surface temperature were significantly lower when posts were instrumented with 40 mL/min water irrigation compared with dry vibration and 20 mL/min irrigation, which also significantly differed from each other. Statistical analysis among tooth groups showed differences in the mean temperature rise of maxillary central incisors and maxillary lateral incisors compared with mandibular incisors when posts were instrumented dry or with 20 mL/min irrigation. There were no significant differences in mean temperature rises between the studied groups when 40 mL/min irrigation was used.

CONCLUSIONS

Water cooling during ultrasonic post instrumentation significantly reduced temperature increases on the outer root surface; however, the intensity of the cooling was also important. Our results suggest that copious water irrigation during post removal is an effective method to protect the root's surrounding tissue.

Temperature rise during photo-activated disinfection of root canals

The aim of this study was to determine whether it is safe to use photo-activated disinfection (PAD) during root canal treatment without heating the periodontal tissues. Root canals of 30 freshly extracted single-rooted teeth were prepared using ProFiles up to size ISO 40 and then filled with photo-sensitiser: tolonium blue (1.2 mg/l). The 635 nm diode laser was used with the manufacturer's endo-tip. Samples were irradiated for 150 s (output power 100 mW, approximate energy density 106.16 J/cm(2)). Temperatures were recorded at working length on the external root surface. After 150 s of PAD irradiation, the average temperature rise was 0.16 +/- 0.08 degrees C. All values were lower than the 7 degrees C safety level for periodontal injury. It was concluded that, regarding the temperature increase, the use of PAD in root canals could be considered harmless for periodontal tissues.

Finite element analysis of the effects of thermal obturation in maxillary canine teeth

OBJECTIVE

The purpose of the present study was to determine the distribution and level of temperature, in a model of a maxillary canine, the surrounding periodontal tissues, and the bones, during a System B heat obturation technique simulation.

STUDY DESIGN

The temperature distribution was determined by using a three-dimensional finite element analysis. The tooth was assumed to have undergone an endodontic treatment before the application. Heat applications of 200 degrees C and 100 degrees C were considered.

RESULTS

By using the virtual model and the simulation technique, the maximum temperature in the periodontal ligament was found to be 43.5 degrees C.

CONCLUSIONS

Within the assumptions and the limitations of the study, it was determined that the simulation of System B technique created no potentially harmful levels of temperature throughout the maxillary canine model.

Evaluation of canal filling after using two warm vertical gutta-percha compaction techniques in vivo: a preliminary study

AIM

To evaluate the quality of root canal filling when comparing two warm gutta-percha filling techniques in vivo.

METHODOLOGY

Human teeth were randomly divided into two equal groups, with 30 canals each. The root canals were shaped by hand and ProFile 0.04 rotary instruments to size 20-40 at the end-point and then filled with gutta-percha cones and AH-Plus. In group A, a traditional warm vertical compaction technique was performed using the Touch'n Heat, and back-filling with the Obtura II. In group B, a modified warm vertical compaction technique was used: small amounts of gutta-percha were removed, and the remaining most apical 3 mm were compacted with a 1 mm movement; then thermomechanical back-filling was performed. The teeth were extracted, stored in dye, cleared, and the distance between the apex and apical limit of the filling, linear dye penetration, and voids were measured from the buccal, lingual, mesial and distal perspective. The homogeneity of variance and means was verified using Levene's test and t-test. ANOVA and Dunnett post hoc test were used to establish the significance and to analyse the effects through multiple comparisons.

RESULTS

Compared with the specimens of group A, the specimens of group B exhibited less mean linear dye penetration (P < 0.05), smaller void length (P < or = 0.05) and maximal width (P < or = 0.05) when examined in all four views, and a more precise filling when viewed from the buccal aspect (P < 0.05).

CONCLUSIONS

The modified warm vertical compaction technique with apical back-filling produced a more effective and precise three-dimensional filling.

Effects of intracanal carbon dioxide laser irradiation on cultured human fibroblasts

OBJECTIVE

The purpose of this study was to evaluate, under various conditions, the damage that might occur to viable cells after CO2 laser irradiation of the root canal.

STUDY DESIGN

A laser tip was placed within the root canal of extracted human teeth that were positioned above cultured fibroblasts (NB cells), and then irradiation was applied. The irradiation modes used were either pulse (40 pps) or super-pulse (151 pps). The laser energy was set at 32 J in both modes, and the tip of the laser beam was positioned to a point 2 mm from the fibroblasts.

RESULTS

When the pulse mode irradiation was applied, there was significant difference (P < .05) in the percentage of viable cells between teeth with closed apical foramen (1-mm wall between root canal and root apex) and the #15 group (No. 15 K-file used), #30 group (No. 30 K-file), or #50 group (No. 50 K-file). The difference between the #30 group and the #50 group (P < .05) was also significant. The larger the diameter of the apical foramen became, the lower was the percentage of viable cells.

CONCLUSION

If a CO2 laser irradiates a root canal system enlarged to within 1 mm of the root canal length, little damage to the periapical tissues would be expected to occur.

Root Surface Temperature Rises In Vitro During Root Canal Obturation Using Hybrid and Microseal Techniques

The aim of this in vitro study was to measure the temperature rise on the outer surface of roots during filling with hybrid technique and Microseal. Twenty extracted human maxillary and mandibular premolars with a single canal were randomly divided into two groups of 10 teeth each. In the first group, the teeth were filled with hybrid technique (thermomechanical compaction with Engine Plugger used following lateral condensation of the apical part of the canal), the second group was filled using Microseal. After root canal obturation the filling material was removed and the obturation procedure was repeated. A total of 20 obturations in each group were performed. Temperature changes were measured using a thermal imaging camera. The temperature of certain regions of the mesial surface was analyzed and the highest temperature values were recorded. Statistical analysis was performed using the Mann-Whitney U test. The mean increase of temperature during the hybrid technique with Engine Plugger was 23.8 degrees C, while during Microseal it was significantly lower (p = 0.000001) at 5.5 degrees C. The temperature rise generated by Microseal was below the critical level and should not damage supporting structures, however, the hybrid technique generated a relatively high temperature rise that may cause periodontal tissue damage.

Temperature Variation at Soft Periodontal and Rat Bone Tissues during a Medium-Power Diode Laser Exposure

OBJECTIVE

The aim of this study was to evaluate temperature variation induced by a diode laser in periodontal repair.

BACKGROUND DATA

A diode laser operating with medium power can constitute an alternative device for bacterial reduction at periodontal pockets. This procedure will probably avoid any kind of undesirable thermal damage to the irradiated tissues.

METHODS

The temperature variation induced by a 810-nm diode laser was investigated in an in vitro study, varying the soft tissue thickness, and in an in vivo study for soft periodontal and bone tissues. The laser powers used were 600 mW, 800 mW, 1.0 W, and 1.2 W, and the light was delivered by a 300-microm fiber.

RESULTS

The laser parameters and irradiation time used did not induce a temperature variation high enough to cause thermal irreversible damage to the periodontal tissues investigated.

CONCLUSIONS

This study contributes to the establishment of thermally safe working parameters of a diode medium power laser.

External temperature during KTP-Nd:YAG laser irradiation in root canals: an in vitro study

To avoid the damage of periodontal tissues during laser irradiation of the root canal, the conditions of lasering must be carefully controlled. The aim of this study was to determine the safety parameters of the irradiation conditions during the use of a KTP-Nd:YAG laser in root canals. Root canals of 60 freshly extracted teeth were prepared (step-back technique) and filled with a photosensitiser (Acid Red 52). Different irradiation conditions [output power (P), pulse width (PW), pulse repetition rate (PRR, Hz)] were used. The laser beam was delivered by means of the KTP-Nd:YAG fibre tip with a beam spot-size diameter of 200 microm. The temperature increases were measured on the external apical third of the root surface using a thermocouple. The results showed that the temperature rise was always below 7 degrees C at the following laser settings: (1) single irradiation, P < or = 4 W, PW < or = 2.55 ms and PRR < or = 20 Hz; (2) repetitive irradiation series, five pulses of 1 s each, four resting times of 1 s each, P < or = 2.25 W, PW < or = 2.55 ms and PRR < or = 20 Hz. The use of resting times was necessary so as to avoid thermal cumulative effects. In these in vitro irradiation conditions, the use of the KTP-Nd:YAG laser in endodontics may be considered harmless for periodontal tissues.

Ultrasonic condensation of gutta-percha: the effect of power setting and activation time on temperature rise at the root surface - an in vitro study

AIM

To determine the effect of power setting and duration of activation on the temperature rise at the root surface during root canal obturation by ultrasonic condensation of gutta-percha.

METHODOLOGY

A human maxillary canine was used in an in vitro split tooth model to allow repeated obturation of the root canal system using an ultrasonic device to thermocompact gutta-percha. Combinations of power settings (1, 3 and 5) and durations of activation (4, 10 and 15 s) were used to test their effect on temperature rise at the root surface using eight K-type thermocouples at the mid-root and apical levels. At the end of each obturation, the tooth was disassembled to remove the gutta-percha in preparation for the next obturation (n = 10 for each combination). Multiple linear regression models were used to investigate the effects of power setting, duration of activation and thermocouple location on the maximum temperature rise recorded.

RESULTS

Only one combination of power setting (5) and duration of activation (15 s) resulted in temperature rise in excess of 10 degrees C. The maximum temperature rise at the mid-root level was significantly (P < 0.001) greater than that recorded apically. It is also significantly affected by the combination of power setting and duration of activation.

CONCLUSIONS

Temperature rises at the root surface during ultrasonic condensation of gutta-percha in excess of 10 degrees C were evident in only one combination of power (5) and time (15 s) settings at the mid-root level.

Thermal Effect and Morphological Changes Induced by Er:YAG Laser with Two Kinds of Fiber Tips to Enlarge the Root Canals

OBJECTIVE

The aim of this study was to assess the application of Er:YAG laser root canal preparation using two fiber tip systems.

BACKGROUND DATA

Previous studies have not shown the thermal effect of Er:YAG laser using cone-shaped fiber tip.

MATERIALS AND METHODS

The ability of Er:YAG laser to enlarge root canals at a pulse energy set at 30 or 20 mJ and constant pulse rate of 10 pps (pulses per second) was tested. A cone-shaped (84 degrees top angle) or a flat fiber tip of Er:YAG laser was used for comparison. Four groups of 15 artificial root canals with fixed dimension were prepared from bovine teeth. Irradiation was accompanied by sterilized distilled water spray (2 mL/min). The temperature changes on the root surface were recorded with an infrared apparatus, and the thermal images were captured with a thermocamera. The morphological changes of irradiated root canals were examined by a scanning electron microscope (SEM).

RESULTS

The mean temperature rises were 9.4 degrees C and 7.1 degrees C with the cone-shaped fiber tip at a pulse energy of 30 and 20 mJ, respectively, and were 11.0 degrees C and 6.5 degrees C with flat fiber tip at a pulse energy of 30 and 20 mJ, respectively. Marked difference in temperature change between the cone-shaped and flat fiber tips was noted at pulse energy of 30 mJ, but not at 20 mJ. The thermal distribution using the cone-shaped fiber tip (in contrast to the flat tip) had an elliptical shape around the fiber tip and was limited to the apical end of the root canals. SEM observation found that irradiation with cone-shaped fiber tip (in comparison to the flat tip) produced a cleaner surface.

CONCLUSION

Our results suggest that the cone-shaped fiber tip of Er:YAG laser produced fewer thermal effects and morphological changes as compared to the other type of fiber tip.

In vitro evaluation of the thermal alterations on the root surface during preparation with different Ni-Ti rotary instruments

The present study evaluated, in vitro, the temperature alterations on the external root surface during instrumentation with four different rotary systems. A total of 20 extracted human maxillary lateral incisors were instrumented using either the ProFile, MicroMega, Quantec or K³ systems and the thermal alterations on the root surface were recorded by means of three thermocouples attached to the coronal, middle and apical portions of the root. Mean temperature increases no higher than 0.4ºC ± 1.0ºC (ProFile system) were recorded, which indicates that these instruments are safe for the surrounding periodontal tissues.

Removal of gutta-percha from root canals using an Nd:YAG laser

AIM

To examine the use of an Nd:YAG laser in removing gutta-percha fillings from root canals when used in conjunction with eucalyptol, dimethylformamide (DMF) or no solvent.

METHODOLOGY

Root-canal fillings (sealer and gutta-percha) were removed with laser irradiation of 20 Hz/1.5 W from 30 roots randomly divided in three groups. In group 1, the solvent was eucalyptol; in group 2, the solvent was DMF; and in group 3, no solvent was used. Laser irradiation was performed until the temperature measured on the root surface increased by 4 degrees C over room temperature. The treatment was deemed complete when the apical foramen was reached with the optical fibre and a reamer. The samples were split longitudinally, and the area of remaining gutta-percha on the root-canal walls was determined with the aid of a computer program. The total number of laser pulses to achieve length and the highest temperature recorded was determined for each tooth. The results were statistically analysed using Student's t-test (P < 0.05) for independent samples.

RESULTS

The average temperature increase in group 1 was 9.17 +/- 0.56 degrees C; in group 2, 9.56 +/- 0.28 degrees C; and in group 3, 8.29 +/- 0.41 degrees C. The shortest time to achieve length was in group 3 (6.4 +/- 0.49 min), then in group 1 (6.7 +/- 0.85 min) and group 2 (7.05 +/- 0.79 min). The area of remaining gutta-percha was the largest in group 2 (6.13 +/- 5.76%), whilst the smallest was for group 3 (4.69 +/- 4.03%), but the difference was not statistically significant. The number of pulses was not statistically significant between the groups.

CONCLUSIONS

Use of an Nd:YAG laser alone is capable of softening gutta-percha. The addition of solvents did not improve the retreatment, either in terms of the time required for the procedure or in terms of the area of remaining gutta-percha on root-canal walls.

Radicular temperatures associated with thermoplasticized gutta-percha

Thermoplasticized gutta-percha has been used to obturate root canals. The continuous wave of condensation technique uses the System B Heat Source with the choice of different-sized pluggers. The purpose of this study was to measure the temperatures within the root canal and on the root surface at different radicular levels while using the System B Heat Source. Fine, Fine-Medium, and Medium pluggers were evaluated at temperature settings of 200 degrees C, 250 degrees C, and 300 degrees C. The Obtura II gutta-percha delivery system following the manufacturer's instructions and ultrasonically thermoplasticized gutta-percha were used for comparative purposes. The highest mean temperature change on the internal root surface was 74.19 degrees C with the system B at the 6 mm level (6 mm coronal to working length) when the Fine-Medium plugger was set at 300 degrees C. The lowest mean temperature change on the internal root surface was 2.09 degrees C at the 0 mm level (at working length) when the F plugger was set at 200 degrees C. With the Obtura II, the lowest mean internal temperature change was 5.22 degrees C at the 0 mm level, whereas the highest mean internal temperature change was 26.63 degrees C at the 6 mm level. With ultrasonic lateral compaction the lowest mean internal temperature change was 5.01 degrees C at the 0 mm level, whereas the highest mean internal temperature change was 28.95 degrees C at the 6 mm level. At no time did the System B, the Obtura II, or ultrasonic delivery of warm gutta-percha exceed an increase of 10 degrees C at any thermocouple level on the external root surface.

Comparison of lateral condensation and thermomechanically compacted warm alpha-phase gutta-percha with a single cone for obturating curved root canals

OBJECTIVE

To evaluate and compare the sealability and radiographic quality of root fillings in extracted teeth by using lateral condensation of gutta-percha or alpha-phase gutta-percha in conjunction with a single gutta-percha cone.

STUDY DESIGN

A total of 108 single-rooted teeth were divided into 2 groups of 54 teeth based on canal shape. Canals were prepared to a minimum 0.055 taper and enlarged to a size 35 at the working distance. Irrigation was done with 17% EDTA and 2.5% sodium hypochlorite (NaOCl) to remove smear layer. One group was obturated by using cold lateral condensation of gutta-percha; the other group was obturated with thermomechanically compacted alpha-phase gutta-percha and a single cone of gutta-percha. Apical extrusion of sealer or gutta-percha was recorded. Sealability of each technique was assessed by dye penetration. The radiographic quality of obturation was also determined.

RESULTS

Root canals filled with alpha-phase gutta-percha and a single cone had significantly more extrusion of sealer than canals filled by lateral condensation. Lateral condensation achieved significantly better scores for radiographic quality. There was no significant difference between the 2 filling techniques in terms of apical or coronal leakage.

CONCLUSIONS

Thermomechanically condensed alpha-phase gutta-percha used in conjunction with a single gutta-percha cone had poorer radiographic quality than laterally condensed gutta-percha.

Laser-induced thermal events in empty and pulp-filled dental pulp chambers

BACKGROUND AND OBJECTIVE

The purpose of this investigation was to evaluate: 1. thermal events during laser irradiation @2.1 microns of the pulp; 2. whether these effects are adequately modeled using an empty pulp chamber/root canal.

STUDY DESIGN/MATERIALS AND METHODS

In extracted human teeth, pulpal access was prepared and thermocouples placed 2, 3 mm apical to the center of the irradiation spot. Pulp-filled or empty pulp chambers were irradiated using a Ho:YAG laser: Spot Size: 1 mm; Power: 1, 2, 3.5, 4.5 W; PRR: 5, 12 Hz;

DURATION

10 sec. Thermal measurements were repeated 3x.

RESULTS

Thermal trends did not differ significantly and correlated positively with power (P < 0.01), PRR (P < 0.01), irradiation duration (P < 0.05). No significant difference was determined between temperatures in empty and pulp-filled chambers at all parameters at 5 Hz and at 1-2 W at 12 Hz (P < 0.05, 2-tailed Student's t-test). At 12 Hz and > 3.5 W, pulp chamber temperatures exceeded those in pulpal tissue (P < 0.05).

CONCLUSION

Pulp tissues must be present to ensure clinical relevance of thermal measurements.

Comparison of two vertical condensation obturation techniques: Touch 'n Heat modified and System B

AIM

The aims of this study were firstly to compare the area of canal occupied by gutta-percha, sealer or voids using the System B heating device with that obtained by a modified vertical condensation technique using the Touch 'n Heat: and secondly to compare the temperature changes at the root canal wall and external root surface during obturation with the above techniques.

METHODOLOGY

Forty-five resin blocks, each with a standardized, simulated, prepared main root canal and five lateral canals, were assigned to three equal experimental groups. The canals were obturated using either the System B technique at two different temperature settings, or vertical condensation with a Touch 'n Heat instrument as the heat source. A heat transfer model was used to simultaneously record internal and external root surface temperature elevations during obturation by the three techniques. Data were analysed using unpaired Student's t-test and Mann-Whitney U-test.

RESULTS

Both obturation techniques produced root fillings consisting of over 90% gutta-percha at most levels, although the percentages of sealer and voids 2-3 mm from the working length following System B obturation were higher than those found following modified vertical condensation. Modified vertical condensation resulted in more gutta-percha in lateral canals. Obturation was accomplished more quickly using the System B, and temperature elevations produced during obturation with the System B were significantly less (P < 0.001) than with vertical condensation. An elevation of external root surface temperature by more than 10 degrees C occurred during vertical condensation.

CONCLUSIONS

The results suggest that the System B may produce an acceptable obturation and that the use of a Touch 'n Heat source during vertical condensation may result in damage to the periodontium.

Laser-induced thermal events in empty and pulp-filled dental pulp chambers

BACKGROUND AND OBJECTIVE

The purpose of this investigation was to evaluate: 1. thermal events during laser irradiation @2.1 microns of the pulp; 2. whether these effects are adequately modeled using an empty pulp chamber/root canal.

STUDY DESIGN/MATERIALS AND METHODS

In extracted human teeth, pulpal access was prepared and thermocouples placed 2, 3 mm apical to the center of the irradiation spot. Pulp-filled or empty pulp chambers were irradiated using a Ho:YAG laser: Spot Size: 1 mm; Power: 1, 2, 3.5, 4.5 W; PRR: 5, 12 Hz;

DURATION

10 sec. Thermal measurements were repeated 3x.

RESULTS

Thermal trends did not differ significantly and correlated positively with power (P < 0.01), PRR (P < 0.01), irradiation duration (P < 0.05). No significant difference was determined between temperatures in empty and pulp-filled chambers at all parameters at 5 Hz and at 1-2 W at 12 Hz (P < 0.05, 2-tailed Student's t-test). At 12 Hz and > 3.5 W, pulp chamber temperatures exceeded those in pulpal tissue (P < 0.05).

CONCLUSION

Pulp tissues must be present to ensure clinical relevance of thermal measurements.

Effect of power settings on temperature change at the root surface when using a Holmium YAG laser in enlarging the root canal

The aim of this study was to determine the maximum amount of power, in watts, that a Holmium YAG laser could deliver via a 245-micron fiberoptic to the canal surface and still not raise the temperature (delta T) of the cementum by > 5 degrees C. Sixty single-rooted teeth were divided into three groups according to power selection (0.50, 0.75, and 1.00 W). The three main outcome variables were: change in apical temperature, change in coronal temperature, and maximum size of an endodontic file that could fit into the canal after lasing. The group means for apical delta T were: 1.00 W = 2.2 degrees C, 0.75 W = 2.68 degrees C, and 0.50 W = 1.58 degrees C. The group means for coronal delta T were: 1.00 W = 1.15 degrees C, 0.75 W = 0.99 degree C, and 0.50 W = 0.56 degree C. The group means for file size were: 1.00 W = 41.25, 0.75 W = 38.75, and 0.50 W = 40.75. The canal size was increased from a size 25 file up to approximately a size 40 file with all power groups. There were no significant differences between the groups for change in apical temperature (p = 0.32), coronal temperature (p = 0.17), or maximum file size (p = 0.86) when adjustments were made for tooth dimensions. In all groups studied, the delta T was < 5 degrees C. This represents a safe and predictable laser procedure.

Effect of ND:YAG laser irradiation and root planing on the root surface: structural and thermal effects

Effects of ND:YAG laser irradiation on untreated and root planed tooth roots were investigated to determine whether a cleaning effect and/or removal of smear layer could be achieved without concomitant microstructural or thermal damage. Sixty (60) healthy extracted teeth were either untreated, irradiated only, root planed only, or irradiated and root planed. Intra-pulpal and surface temperatures were monitored during irradiation, then SEM was performed. Smear layer elimination was achieved without inducing hard tissue microstructural damage at 5W, using pulse durations and intervals of 0.1 s, a fluence of 0.77 J/cm2, and a total energy density of approximately 700 J/cm2. However, these results were not consistent in all samples. At these parameters, intra-pulpal temperature increases of 9 to 22 degrees C and surface temperature increases of 18 to 36 degrees C were recorded. Thus, despite their effectiveness for smear layer removal, these parameters may not be appropriate for clinical use as an adjunct to conventional periodontal therapy.

Comparison of concentric condensation technique with laterally condensed gutta-percha

Sixty mandibular premolars with large, straight canals and 60 nonjoining narrow, curved canals from mesial mandibular molar roots were obturated with gutta-percha via 1 of 3 methods: lateral condensation with sealer, or concentric condensation without sealer. The sealer used was a zinc oxide-eugenol without radiopacifiers. The premolar teeth were radiographed next to a step wedge, both before and after obturation. All teeth were exposed to India ink as a test for linear dye leakage, then cleared, and the leakage recorded. The pre- and postobturation radiographs were scanned at 2 and 6 mm from the apex using a Joyce-Loebel microdensitometer to establish the radiographic density of the obturation material, and a density ratio for the obturation was calculated using the cross-sectional diameter of the obturating material. The incidence of gutta-percha extrusion and Micro-Flow Compactor breakage was recorded. Two-way analysis of variance for linear dye leakage revealed no significant differences between the lateral and concentric condensation groups when sealer was used (p > 0.05). The concentric condensation without sealer groups exhibited significantly greater leakage (p < 0.00001) than the other groups, showing the importance of using sealers. One-way analysis of variance found no significant differences in radiographic density ratios between groups at 2 mm (p > 0.05) or 6 mm from the apex (p > 0.05). The incidence of extrusion was not significant, but a high rate of #30 condensor breakage was found.

Root canal preparation using the second harmonic KTP:YAG laser: a thermographic and scanning electron microscopic study

Thermal and microstructural events resulting from KTP laser use during root canal preparation were investigated in 30 extracted single-rooted human teeth. In the first section of this study, thermal events occurring on the root surfaces of 18 teeth during and after exposure of the root canal were measured using thermography. A variety of parameters were used to determine settings that would be effective without causing thermal damage to the periodontal ligament. In the second section of the study, root canals of 12 teeth exposed to KTP laser irradiation at parameters derived from section 1 were evaluated using Scanning electron microscopy. KTP laser application at a power setting of 3 W, an exposure time of 2 s, and a frequency of 5 Hz, applied five times, removed smear layer and debris from the root canal surface at temperatures below the thermal injury threshold for periodontal tissue.