Evaluation of AIS3+ car occupant injuries using deterministic and probabilistic methods in frontal crashes.

Computational modelling was used to assess the capability of a deterministic and a probabilistic method to predict the incidence of AIS3+ injuries in passenger car occupants by comparing the predictions of the methods to the actual injuries observed in real-world crashes. The likelihood of sustaining an injury was first calculated using a computer model for a selected set of injury criteria in different impact conditions based on real-world crashes; AIS3+ injuries were then predicted using each method separately. Regardless of the method, the number of serious injuries was over-predicted. It was also noted that the used injury criteria suggested the occurrence of specific injuries that were not observed in the real world. Although both methods are susceptible to be adapted to improve their predictions, the question of the suitability of using some of the most commonly accepted injury criteria used with crash test dummies for injury assessment with human body models deserves further research.

Influence of needle design and irrigation depth in the presence of vapor lock: A computational fluid dynamics analysis in human oval roots with apical ramification.

This paper aims to study the removal of a vapor lock located in the apical ramification of an oval distal root of a human mandibular molar, simulating different needles and irrigation depths with computational fluid dynamic. A geometric reconstruction of the micro-CT of the molar shaped up to a WaveOne Gold Medium instrument was used. A vapor lock located in the apical 2 mm was incorporated. Geometries with positive pressure needles (side-vented [SV], flat or front-vented [FV] and notched [N]) and the EndoVac microcannula (MiC) were created to run the simulations. Irrigation key parameters (flow pattern, irrigant velocity, apical pressure, wall shear stress) and vapor lock removal were compared among the different simulations. Each needle behaved differently that is, FV removed the vapor lock from one ramification and had the highest apical pressure and shear stress values; SV removed the vapor lock in the main root canal but not in the ramification and reached the lowest apical pressure from the positive pressure needles; N was not able to completely remove the vapor lock and showed low apical pressure and shear stress; MiC removed the vapor lock from one ramification, had negative apical pressure and the lowest maximum shear stress. The main conclusion is that none of the needles showed complete removal of vapor lock. MiC, N, and FV were able to partially remove the vapor lock from one out of the three ramifications. However, SV needle was the only simulation that showed high shear stress with low apical pressure.

CFD analysis on the effect of combining positive and negative pressure during the irrigation of artificial isthmuses.

Fluid dynamics generated by irrigation needles have not been deeply analyzed in root canal irregularities such as apical ramifications or isthmus where the cleaning capacity of irrigants might be compromised and hence the treatment outcome. The goal of this study was to compare the key irrigation parameters (flow pattern, irrigant velocity, apical pressure, and shear stress) between two irrigation needles and the additional effect of aspiration cannulas through computational fluid dynamics. A 3D-model consisting of two canals linked by an isthmus was modeled. The abovementioned needles irrigated the primary canal, whereas an aspiration cannula was located inside the secondary canal. Both the geometry definition and spatial discretization were carried out with ANSYS 16.2, through which six different simulations were performed: lateral exit (LE) needle, frontal exit (FE) needle, LE and cannula in crown (LEC), FE and cannula in crown (FEC), LE and cannula in middle third (LEM), FE and cannula in middle third (FEM). FE and FEM showed that the irrigation flow only passes through the isthmus in the most apical section (maximum irrigant velocity / shear stress = 8.44 m/s / 1628.44 Pa and 8.63 m/s / 1185.69 Pa, respectively). However, the remaining simulations showed the irrigation flow passing through the isthmus twice, through the most apical section first and through the upper part of the isthmus later (maximum irrigant velocity / shear stress = 8.48 m/s / 1298.24 Pa (LE), 8.61 m/s / 1261.36 Pa (LEM), 8.61 m/s / 1355.24 Pa (LEC), 8.59 m/s / 1256.87 Pa (FEC)). Furthermore, the highest velocity values were detected when aspiration cannulas were added.

Positive and negative pressure irrigation in oval root canals with apical ramifications: a computational fluid dynamics evaluation in micro-CT scanned real teeth.

AIM: To compare using computational fluid dynamics (CFD) the flow pattern, irrigant velocity, apical pressure and shear stress produced by negative (MiC) and positive pressure with different types of needles (side-vented (SV), front-vented (FV) and notched (N)) at two insertion depths in the apical ramification of oval root canals. METHODOLOGY: The micro-CT of a mandibular molar with an oval root canal with an apical ramification was used for computational analysis after preparation and geometric reconstruction. Geometries with the needles in two positions (1 and 3 mm from WL) were created to run the simulations. Key parameters of irrigation were displayed with CFD and compared. RESULTS: The penetration depth of the needle in the root canal strongly influenced shear stress and apical pressure. The three needles revealed that the highest shear stress, velocity and apical pressure were 1 mm from the WL and generated medium velocities. In N simulations, the fluid flow did not reach the apical ramification and the lowest shear stress values for positive pressure needles were found. The predominant axial component for FV revealed a different pattern of irrigation with high shear stress values and higher apical pressures than those exerted by other needles. SV simulations had generalized fluid flow in most of the main canal, the highest shear stress values and lower apical pressure than the threshold determined for risk of extrusion. MiC was associated with low velocity, shear stress and apical pressure. CONCLUSION: The SV needle demonstrated a combination of low positive pressure and high shear stress; while N had the lowest shear stress and FV the highest apical pressure. MiC generated fluid flow in part of the apical ramification with negative apical pressure values but low shear stress and velocity.