EVALUATION OF TEMPRETUR RISETHE EXTERNAL ROOT SURFACE DURING THE APPLICATION

EVALUATION OF TEMPRETUR RISETHE EXTERNAL ROOT SURFACE DURING THE APPLICATION

1. Evaluation of temperature rise on the external root surface during the application of laser in root canals: An in vitro study JOURNAL CLUB PRESENTATION BY DR. ABDUL KADIR MDS 3RD YEAR DEPARTMENT OF CONSERVATIVE DENTISTRY AND ENDODONTICS

2. INTRODUCTION In endodontics, different laser systems are used as new alternative disinfection. Owing to the various parameters such as laser wavelength, power levels, and pulse repetition rate, laser energy can concentrate and cause thermal damages that are mainly governed by photoabsorptive properties of tissue being irradiated.

3. Among the various laser systems available in current times, (   ERBIUM-DOPED YTTRIUM ALUMINUM GARNET) Er:YAG laser and ( NEODYMIUM-DOPED YTTRIUM ALUMINUM GARNET) Nd:YAG laser have been used as a viable means of photothermal disinfection of root canal. The wavelength of Er:YAG laser (2940 nm) is well absorbed by water and hydroxyapatite crystals, which leads to better ablation of dental hard tissues, and as far as Nd:YAG laser (1064 nm) is concerned, it is poorly absorbed by water, and moreover, the Nd:YAG when enters the biological tissue, instead of getting absorbed, it gets scattered. This results in microexplosions leading to formation of microparticles of organic and inorganic tissue.

4. Better disinfection and hard tissue ablation can be achieved with increased energy levels as it has been demonstrated in various studies. Laser system is found to be effective in removing the smear layer along with NaOCl and EDTA irrigation without significant additional loss of mineral content. However, with the increasing energy levels, the chances of damaging adjacent periodontal tissue also increase.

5. In an attempt to keep the benefits of laser irradiation in endodontics while minimizing the potential damages to the adjacent periodontium, the purpose of this in vitro study was to evaluate the temperature changes on the root's middle and apical thirds during Nd:YAG and Er:YAG laser irradiation at various power levels. Null hypothesis-temperature rise on the external root surface by application of laser with different power levels during root canal irrigation does not have any damaging effect on periodontium.

6. AIM OF THE STUDY To compare and evaluate the effect of temperature rise on the external root surface during the application of laser in root canals.

7. METHODOLOGY 60 single rooted mand. premolars samples collected Divided into 2 groups ( 30 each ) Stored in 0.1% thymol at 4 C and checked radiographically Access opening done and access is gained with 15 k file Root canals were shaped

8. Final irrigation was done with 10ml of distilled water and dried with paper points All the teeth were embedded in self-cure acrylic resin block with the help of mold, to form a test apparatus and fix the roots. Two holes (1 mm in diameter) were drilled in the test apparatus, one at 2 mm from the apex (apical third) and another at 5 mm from the apex (middle third). These holes were drilled to provide access to the thermocouple wire to the external root surface.

9. LASER IRRADIATION Two types of laser systems were applied to the root canals Nd:YAG laser (Group I) system and Er:YAG laser (Group II) system. The ten root canals for each experimental group were irradiated at 1, 1.5, and 2 Watt power of Nd:YAG and Er:YAG lasers, respectively. Before laser irradiation, each canal was filled with 1 ml of distilled water. During laser irradiation, endodontic fiber optic cable of 200 mm was used in repetitive pulse mode. Each canal was continuously irradiated from apical foramen to the canal orifice in a circular motion for 20 s. Laser irradiation was performed in cycles of 5 s with 5 s recovery time. Each root canal was irradiated four times (total 20 s).

10. The study was performed in a temperature-controlled room, and the baseline temperature of all samples was standardized at 25°C. Digital thermometer with K-type thermocouple wire with temperature range of − 58°F–1832°F was used to measure the temperature. Temperature alterations were calculated by subtracting the highest value recorded during intracanal irradiation and the initial value of 25°C.

11. STATISTICAL ANALYSIS Un paired Student's t-test and two-way ANOVA were applied to detect significant effects of groups and power levels. P < 0.05 was considered statistically significant.

12. RESULTS On comparing the temperature rise (°C) between the groups for apical third region, it was found that at power level of 1 Watt, the difference in mean temperature rise between the two groups was not found to be significant (P = 0.250). At power level of 1.5 and 2 Watt, the difference in mean temperature rise between the two groups was found to be statistically significant, i.e., P = 0.005 and P = 0.036, respectively. On comparing the temperature rise (°C) between the groups for middle third region, it was found that at power level of 1 and 1.5 Watt, the difference in mean temperature rise between the two groups was not significant, i.e., P = 0.087 and P = 0.152, respectively, whereas at power level of 2 Watt, the difference in mean temperature between the two groups was statistically significant (P = 0.007).

13. DISCUSSION In the field of endodontics, lasers are serving as an important tool, and over a short period, it has gained significant interest of researchers. Temperature rising over the root surface beyond a particular threshold can be detrimental for surrounding periodontium. A temperature rise of 47°C for 1 min is considered to be tolerable threshold for bone. That means approximately 10°C increase in temperature for 1 min can be well tolerated. However, temperature rise of 11°C for 5 min or 13°C for 1 min is the critical threshold for periodontium.

14. In the present study, the temperature rise at the apical area was 4.47°C, 6.30°C, and 9.11°C at three different power levels (1, 1.5, and 2 Watt, respectively) with the use of Nd:YAG laser and 4.02°C, 7.75°C, and 10.05°C with the use of Er:YAG laser at respective power levels. Similarly, the temperature rise at the middle third was 2.02°C, 4.49°C, and 6.69°C at three different power levels (1, 1.5, and 2 Watt, respectively) with the use of Nd:YAG laser and 2.52°C, 5.04°C, and 7.91°C with the use of Er:YAG laser at respective power levels. However, the temperature rise for all the test groups remained below the critical threshold of 11°C for 5 min and 13°C for 1 min.

15. Maximum temperature rise was observed with 2 Watt power level at the apical third, which almost approached the critical threshold. This can be explained as the apical third of root has least dentin thickness, and dentin acts as thermal insulator and helps in better transmission of heat. Hence, while irradiating the apical third, proper care should be taken to avoid an irreversible thermal damage to the periodontium.

16. CONCLUSION Both Nd:YAG laser and Er:YAG laser at various power levels lead to rise in temperature on external root surface, but the temperature changes in both the tested groups remained below the critical threshold. Hence, lasers can be a better treatment option when used within safe yet effective power levels.

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