An evidence based letter on fluid mechanics on irrigant activation

Dear Editor, Irrigation is the primary debridement strategy that helps for an effective disinfection and cleansing of the root canal system.[1] However, it is critically challenging for the syringe needle to deliver the irrigant and enhance its activity in such a narrow and practically impossible root canal space. Hence, to enhance the three-dimensional cleansing, irrigant activation is deemed necessary before the obturation in every case. Irrigant activation induces a wide range of fluid mechanics, ultimately improving the wall shear stress, and leading to the removal of attached tissue debris and biofilm.[2] Considering the practical difficulties, it is impossible to simulate an exact clinical irrigation model to better assess the fluid mechanics. Laboratory-based studies can only provide an understanding of the fluid flow patterns that are encountered during the irrigant streaming in a completely shaped root canal system.[3] Various techniques, such as dye clearance methods, recovery trap devices, pressure assessment models, and computational fluid dynamics (CFD) analysis, were employed for understanding the irrigant mechanics in vitro.[3] The CFD analysis is claimed to be a reliable tool for real-time evaluation of the irrigant flow patterns, the mechanics, and the apical pressures.[4,5] The major limitation of the CFD analysis is that the flow rate needs to be standardized for assessments using this technique. The flow rate for CFD analysis should always be simulated as constant and continuous, which ideally differs in a clinical scenario. However, in the patient, it differs based on the various clinical limitations, which cannot be simulated with CFD in a single study design. Before understanding fluid mechanics, a practicing clinician needs to have an idea of various physical parameters such as velocity, turbulence, shear wall stress, intensity, and irrigant flow pattern, which play a major role in the overall dynamics and fluid flow pattern. Among the available evidence from the laboratory-based studies, many clinically important parameters such as taper, preparation sizes, curvatures, tooth type, canal complexity, choice of activation system used, level of tip placement, and even the region of assessment were also not standardized.[2] Clinically, the efficiency of irrigation systems varies when all the above-mentioned factors play a role. Although many parameters are evaluated to assess the irrigation efficacy, shear wall stress, irrigant flow pattern, irrigant exchange, and generated apical pressures are the prime factors that safeguard clinical irrigation. However, with the limited evidence available on the generated apical pressures and fluid dynamics, it’s impossible to justify the superiority of the single system. With low-level evidence from a systematic review published,[2] negative pressure irrigation systems performed well in terms of fluid mechanics and reduced apical pressures. Extrapolating the study results to clinical practice is highly impractical. Future research is warranted on assessing the irrigation dynamics of different activation systems with better simulation of the ideal clinical scenario. When the clinical relevance of the current topic needs to be addressed, the taper and preparation sizes should be optimal for the activation tip placement. It is questionable to maintain the balance with the flowing liquid and create apical pressures during root canal irrigation. Hence, the focus should be addressed on passive root canal debridement strategies to better improve the overall success of the treatment. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.