le0210

Temperature rise on external root surface (Part I)

research _ laser endodontic therapy I Successful endodontic therapy mainly depends ontheeliminationofmicro-organismfromtheroot canalsystemwhichistraditionallyaccomplishedby themeansofbiomechanicalinstrumentationofthe root canal. Studies have shown however, that the completeremovalofmicroorgansimsfromtheroot canal system is virtually impossible (Bystrom and Sundquist 19815 , Sjogren et al 199026 ) and a smear layer covering the instrumented walls of the root canalisformed(McCombandSmith197520 ,Mood- nik et al 197621 , Mader et al 198418 ). Peters et al (2001)23 clearly demonstrated that morethan35%ofthecanalssurfacearearemained unchanged following instrumentation of the root canal using four Ni-Ti preparation techniques. The presence of bacteria in the dentinal tubules of infected teeth at approximately half the distance between the root canal walls and the cemento- dentinal junction was also reported (Ando and Hoshino 19902 , Armitage et al 19833 ). These finding justifytherationaleandtheneedfordevelopingef- fectivemeansofremovingthesmearlayerfromroot canal walls following biomechanical instrumenta- tion.Thiswouldallowdisinfectantsandlaserirradi- ation to reach and destroy micro-organisms har- bored in the dentinal tubules. Gutknecht et al (2004)10 in his research using a 980 nm diode laser showed that the 980 nm diode laser can eliminate bacteria that have immigrated deepintothedentin,thusbeingabletoincreasethe success rate in endodontic therapy. Benedicenti et al. (2008)4 did an in vitro study to investigate the bactericidal effects on root canals using an 810 nm diode laser and found that when used as an adjunct to conventional therapy, it results in increasing treatmentefficiencyandsignificantlybetterdecon- tamination of the root canal. However it also con- comitantly results in a rise in the external root sur- face temperature which can be hazardous to the surrounding periodontal tissues and the bone if temperature rises above 10 °C (Ericson et al 19838 ). The threshold temperature level of 7 °C is com- monly considered as the highest temperature limit biologically accepted to avoid periodontal damage (Saunders 199025 , Nammour et al 200422 ). Studieshavebeendonewith810nmand980nm diode laser which show rise in temperature on ex- ternalrootsurfaceofteethfollowingdiodelaseras- sistedrootcanaltherapy(Gutknechtetal200511 ,Al- fredoetal20081 ).Gutknechtetal200511 foundthat there was temperature rise of not more than 7 °C when irradiated upto 1.5 W and thus can be considered safe for use in laser assisted endodontic therapy. Heysselaeretal200712 usinga980nmlaserused 3 W, 2 W and 1 W in continuous mode and found average rise in temperature at 20.7 ± 0.3 °C, 9.3 ± 0.4 °C and 5.8 ± 0.8 °C for 3 W, 2 W and 1 W of laser irradiation on external root surface. Results showed that the use of diode laser in root canal treatments may be harmful for periodontal tissues if the irradiation conditions are not strictly re- spected. Manos and Gutknecht 200719 did a study using 980 nm diode laser with the same power settings of 2.5 W at continuous mode and chopped mode and foundthatthetemperaturerisingneverexceedsthe threshold point of thermal bone necrosis of 47 °C and thus can be considered safe for periodon- taltissuesduringlaserassistedrootcanaltreatment. laser2_2010 1W,Continuous 30 4.17 1.262 0.230 7 2 1W,Gated 30 1.80 0.664 0.121 3 1 2W,Continuous 30 6.47 1.756 0.321 11 3 2W,Gated 30 2.43 0.774 0.141 4 1 Total 120 3.72 2.166 0.198 11 1 Laser Treatment N Mean Standard Deviation Standard Error Maximum Minimum Fig. 2_Tooth being held between the fingers and thermocouple while in contact with the tooth surface to measure temperature changes with the laser in activated mode. Table 1_Descriptive statistics for four treatments on apical third. Fig. 2