This study was conducted to evaluate microshear bond strength of self adhering flowable composite to enamel and dentin, without surface treatment and after different surface treatment protocols compared to flowable composite.
Thirty two carious free extracted molars were selected in the current study. The teeth were wet ground to expose fresh flat enamel or dentin surfaces where each surface will carry five specimens. Teeth were randomly divided into two main groups according to restorative tested material; either flowable composite (Filtek™ Z350 XT Flowable) or self-adhering composite (Fusio™Liquid Dentin). Each group was divided into four subgroups according to surface pretreatment; either without any surface treatment, with acid etching only, with self etching adhesive system and with etch and rinse bonding system. Each subgroup was divided into two classes according to type of substrate; either enamel or dentin. Sixteen subgroups were created (n=10) with a total number of 160 specimens.
A plastic tube (tygon tube), 0.7 mm in diameter and 1mm in length was held securely and immobilized using cotton pliers on the indicated substrate with or without surface treatment, then was restored for microshear bond strength testing according to manufacturer instructions. Microshear bond strength test was conducted immediately after 24 hours using universal testing machine at crosshead speed of 0.5 mm/min till specimens fail, bond strength was calculated and failure modes were analyzed.
The results showed that Filtek™ Z350 XT Flowable with surface treatment using etch and rinse bonding system has the highest statistically significant bond strength to enamel, while least statistically significant bond strength was for Fusio™Liquid Dentin with surface treatment using self etch system and without any surface pretreatment. In dentin, the highest statistically significant bond strength was for Fusio™Liquid Dentin with surface treatment using self etch system, while the least bond strength was for Fusio™Liquid Dentin with etching only and Fusio™Liquid Dentin without surface treatment, in addition applying Filtek™ Z350 XT Flowable without surface treatment following manufacturer instructions showed premature failure for both enamel and dentin.
In the present study, the failure mode was either cohesive within composite, adhesive or mixed failure type. The results of comparison between failure modes revealed that there was no statistically significant difference between them, so it could not be stated that the bond strength values correlate with the failure types.
Under the limitations of this study the following conclusions were derived:
1- When applied according to manufacturers’ instructions self adhering flowable composite produced comparable results to conventional flowable composite combined with either etch-and-rinse and self-etch adhesive system for dentin substrate.
2- Enhancing bonding performance of self adhering flowable composite to enamel could be achieved with preceding it with etching or etch-and-rinse adhesive, while for dentin bonding performance can be enhanced by preceding it with self-etch adhesive.
3- Still etch and rinse adhesive system is the gold standard technique when bonding to enamel.

Clinical recommendations:
Self adhering flowable composite simplified the procedure of applying flowable composite material with comparable results to standard techniques and requires further clinical investigations to recommend its usage in clinical situations.

The control of stresses and liquid pressure surges in pipes is an important problem in the design of hydraulic pipe networks. The method of characteristics has been used to solve the transient stresses and pressures in liquid-filled piping systems. The friction force is included in the equations of motion for the fluid and the pipe wall. The maximum pressure and maximum stress at any point along the length of the pipe are evaluated for the entire simulation time. A nonlinear search technique has been developed using the simplex method. The optimal valve closure is sought, that will minimize the maximum pressure and/or stresses. A continuous optimal valve closure policy is specified using spline functions. Numerical examples are presented showing the reduction of the dynamic pressure and the dynamic stress from linear valve closure to optimal valve closure for a simple pipeline and a complex pipeline. Also, a method for choosing the shortest time of closure which will keep the stresses below specified allowable stresses is presented.