Apical Pressure Measurement Of Er:YAG Laser-activated Irrigation In Single Root Canal Model

Objective:To measure apical pressure of Er:YAG laser activated endodontic therapy by high frequency sensor under different laser settings in single root canal models with different canal structure.Methods:(1)Er:YAG laser irrigation was performed at 5-50 mJ and 20-50 Hz with super short pulse model in single straight root canal model(Taper=0.06,apical diameter=0.5 mm).(2)Er:YAG laser irrigation was performed at 5-30 mJ and 15 Hz with super short pulse model in the single straight root canal models(Taper=0.02,0.04,0.06,0.08,apical diameter=0.5 mm)and the single curved root canal models(Curvature=30°,45°,60°,Taper=0.06,apical diameter=0.5 mm).Root canal model made of transparent Resin-A was filled with deionized water,with a 50 000 Hz pressure sensor inserted apically.The laser tip of Er:YAG laser was placed 3mm from the root canal orifice.The pressure acquisition system was triggered in still water for at least 1s to provide a baseline value of zero.Then,irrigated with Er:YAG laser for at least 5s.The spike positive pressure value of the last 30 pulses were recorded and averaged as peak apical pressure of Er:YAG laser activated irrigation.Results:(1)Under certain pulse energy that below 30mJ,the peak apical pressure of Er:YAG laser activated irrigation grew flatly as frequency increased in single straight root canal model;when pulse energy was not less than 30mJ,the peak apical pressure rose in step with frequency.Under certain frequency,the peak apical pressure variation followed segmented linear regression with the growth of pulse energy(R2>0.6,P<0.01),and could be divided into two stages:high energy and low energy stages.The slopes of regression equation of the high energy stage reached 10 times of the counterparts of the low energy stage(P<0.001).Once energy was set over the inflection point,accumulated apical pressure was frequently observed.Significantly elevated pressure was found as the power setting went up.(2)The greater the curvature of the root canal model was,the brisker the peak apical pressure grew in proportion to pulse energy(P>0.05).While the peak apical pressure was higher in root canal model with larger taper under the same pulse energy,the slopes of the pressure-energy linear regression had no significant difference in between(P<0.01).Conclusion:(1)The peak apical pressure increased mainly with the growth of pulse energy in single straight root canal model;when pulse energy was not less than 30mJ,it also increased in step with frequency.Accumulated apical pressure indicated a higher risk of apical damage under enhancive power.Thus,reasonable parameter setting is crucial to the safety of Er:YAG laser activated endodontic therapy.(2)The peak apical pressure increased in single root canal mode with greater curvature and taper under the same Er:YAG laser parameter.Decreasing the pulse energy of Er:YAG laser activated irrigation in clinical cases with large curvature and taper,could reduce the chance of apical damage.