Determination of Optimal Separation Times for Dual‐Pulse SWEEPS Laser‐Assisted Irrigation in Different Endodontic Access Cavities

BACKGROUND AND OBJECTIVES: The purpose of this ex vivo study is to investigate whether it is possible to pre‐determine and set the optimal separation times for the SWEEPS Er:YAG laser pulses pair during laser‐assisted irrigation of endodontic root canals based on known lateral dimensions of the endodontic access cavities of different types of teeth. STUDY DESIGN/MATERIALS AND METHODS: As the optimal SWEEPS laser pulse pair separation for enhanced shockwave generation depends on the life‐cycle of a single‐pulse bubble, measurements of the oscillation time T (B) of the Er:YAG laser‐generated bubble were made in 23 different endodontic access cavities of different types of teeth progressively widened in three different steps, into larger cavities, for a total of 69 cavities of different shapes and sizes. Different fiber‐tip geometries (flat and radial), laser pulse energies (10 mJ and 20 mJ) and depth of fiber‐tip insertion (2 mm and 4 mm) were also investigated. The obtained data were then analyzed using the reported relationship between the bubble oscillation time and the diameter of a cylindrically shaped cavity. RESULTS: A good fit to the relation analogue for ideal cylindrical cavities was found by taking the characteristic diameter of the access cavity to be represented by the cavity diameter either in the mesiodistal (D (min)) or buccolingual (D (max)) direction, or alternatively by the average of the two diameters (D (ave)). The best fit was obtained for D (min) (R (2) = 0.73) followed in order by D (ave) (R (2) = 0.71) and D (max) (R (2) = 0.63). CONCLUSION: In spite of the endodontic cavities being non‐cylindrical and of varied shape and size, the bubble oscillation time T (B) and the corresponding optimal SWEEPS separation time can be well predicted using a single characteristic dimension of the access cavity. This finding enables a simple and practical method for determining optimal conditions for shock wave generation and enhanced photodynamic streaming in differently shaped and sized root canals, leading to improved treatment efficacy and safety of root canal irrigation. Lasers Surg. Med. 2020. © 2020 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals LLC