Narrow Results

Within the dental sphere it is advantageous to be able to bond the restoration to dentine in order to avoid clinical problems such as marginal leakage with subsequent caries. Dentine bonding agents are normally employed to create an effective interface between the restoration and hard tissue with the formation of chemical links. The measurement of the bond strength between dental restorations or implants and surrounding hard tissue is generally achieved through the use of an experimental push-out test. However, these bond strengths have been found to be quite variable between laboratories even when similar chemical bonding agents have been used. This variability may be due to a number of factors including experimental differences such as, material moduli effects, specimen loading and changes in the thickness and properties of the interdiffusional zone (IDZ) that forms following polymerization of the bonding agent.

In this work, these variables have been explored using the finite element method initially through a 2-D description of the geometrical set up and subsequently a 3-D discretization. The results indicate that the loading and specimen support during testing have a significant effect on the measured push-out values. Furthermore the effects of a gradually changing modulus in the uppermost rings of the IDZ can have a significant influence on the support bearing property of the bonding agent. These changes in modulus of the IDZ may be the result of fluoride leaching to bring about increases in properties and modulus. A mixed moduli IDZ where the uppermost layer is approximately double the value of the remaining material can lead to increases in push-out values of 10% or more.

This study evaluated the effects of filling technique and light irradiation distance on the push-out bond strength of dual-cured (DC) and light-cured (LC) core materials to the root canal dentin. DC and LC core materials were filled with a bovine root canal post space of 8mm deep, and polymerized under two different filling procedures, i.e., an 8mm bulk filling (I) and two times of 4mm incremental filling (II), multiplying two different light irradiation distances (0 or 5mm) from top of the root canal. After 24h water storage, specimens were horizontally sectioned to obtain $1\pm 0.1$mm thick core/dentin slices, and five slices were obtained for each root. After the slicing process, push-out tests were performed. Among all groups, the highest bond strength was observed in DCI5 (13.7 $\pm$ 4.3MPa), whereas the lowest was observed in LCI0 ($10.3\pm 3.7$MPa). Consequently, the recommended curing procedure between DC and LC core materials differed. Combination of LC core material with incremental filling technique and of DC core material with bulk filling technique indicated higher bond strength. Higher bond strength was measured at a 5mm light irradiation distance for both LC and DC core materials.

Shear connector is a part of steel-concrete composite beam, and it is the key to ensure the whole performance of composite beam. This paper presents the effects of flange and web thickness, height and width of angle shear connectors by using experimental and FE Analysis. 6 push-out tests were carried out to verify the correctness of FE models. In this experiment, the failure mode was the concrete crushing splitting with the angle steels yielded at the junction of web and flange. Specimens had a plastic behavior before failure. As the angle shear connectors concentrate the applied load on the root of flange, the thickness and width of flange and web are the main factors that influence the ultimate strength of angle shear connectors. The height of flange and web could hardly affect the ultimate strength.