on different dowel head designs- cores retention مشروع بحث لقسم العلاج التحفظي كلية طب الأسنان – جامعة عين شمس ,للإستكمال الجزئي لمتطلبات درجة الماجستير في التركيبات الثابتة

Summary 

This study was designed to investigate the effect of application of resin luting agent at post – core interface, different post head designs (square head post –flat head post) and different core materials (Amalgam – Composite – Resin modified glass ionomer) on the retention between post & core material

Sixty prefabricated posts were used in this investigation, posts were divided into two main groups according to head design (Group A with square head) and(Group B with flat head), each group was subdivided according to core material

-Amalgam subgroup (1), Composite resin subgroup (2) and resin modified glass ionomer subgroup (3), each subgroup was divided into two divisions (a,b) according to application of bonding agent

In division (a) (bonded), adhesive (A&B) were mixed (one drop from each bottle) and then by using Microbrush adhesive was applied to the post head then head was painted with the resin luting agent then followed by core material application in a specially designed post holder formed from three parts: Outer metallic case with diameter 3.5 cm & height 0.9 cm with central hole of diameter 0.2 cm to allow entrance of post without passage of the head , the second part is a plastic ring of a diameter 2.7cm encircling a two-piece Teflon mold , the third part is a two piece Teflon mold with diameter 2.2 cm & height 0.6cm with a central hole of diameter 0.7 cm , the two- piece teflon mold fits within the plastic ring , then both parts fit within the metallic case such that the central hole fits over the post head allowing condensation of core material with production of cores with standardized height & diameter with the core material completely covering the post head

In division (b) (unbonded) core material was applied directly into the Teflon mold after post placement then specimens were placed on testing machine using specially designed Specimen holder to maintain standard alignment of samples, the specimen holder formed from special custom made metallic case allows holding core in position & exposing tip of post to be grasped by a metallic jig

Specimens were placed in a fixture on a universal testing machine (Model LRX-plus; Lloyd Instruments Ltd., Fareham,UK) with a loadcell of 5kN and data were recorded using PC software (Nexygen-4.1; Lloyd Instruments) and loaded in tension until failure at a crosshead speed of 1 mm/min, the fixture allowed the dowel to extend through the hole in the base. The post was then grasped with a custom made grip attached to the upper member of the testing machine. This fixture ensured that the post was parallel to the load line and produced tensile loading. Failure loads were recorded in Newton of force.

Specimens were considered to have failed when the post separated from the core or post failure occured. The load-deflection curves were recorded with computer software (Nexygen; Lloyd Instruments Ltd).

The raw data were tabulated , means and standard deviations for each group were calculated., Multifactorial (Two way) analysis of variance ANOVA test was used to detect statistical significance. Pairwise t-test between gruops was done by Graph Pad Prism-4 for windows (P<0.05).

Mumdouh Mohamed Mostapha Ali