الفهرس | Only 14 pages are availabe for public view |
Abstract Until the 1980s the missing single tooth was most often replaced with a fixed or removable partial denture. Insertion of these conventional prostheses usually requires preparation of one or more abutment teeth. Today, when the abutment teeth exhibit no caries or previous restorations, such irreversible preparation may be considered unacceptable. Placement of single tooth implants in such situations is both functional and esthetic. Implantsupported single tooth replacements are not problem free. The anatomic configuration of the osseous structures may dictate placement of implants, and the position and angulation of the teeth adjacent to the edentulous space must also be considered. Angulated abutments may be used to overcome non-ideal implant location due to a lack of bone. Using angulated abutments with different types of restorative materials to construct the overlaying crowns are significant factors in determining the amount and distribution of the stresses loaded onto the superstructure and implant under functional forces. Therefore the aim of current study was to evaluate the fracture resistance and marginal adaptation of IPS E-max press and Lava Ultimate crowns over different abutment angulations straight, 15o and 25o abutment. Beside that the strain on implant will be assed. Thirty identical DENTIS implant analogs were chosen to replicate anterior upper region substitutes, and were vertically embedded in supportive resin. These were mounted by thirty DENTIS abutments, 10 straight, 10 15o angled and 10 25o angled. After closing the access hole, a digital impression was performed was taken via CEREC AC Connect with Omnicam scanning unit and the designing process was performed on CEREC 4 computer software for fabrication of 15 crown of Lavatm Ultimate. An adult central was chosen from CEREC database and milling procedure was commenced via the The InLab MC XL milling unit. The Lava Ultimate block was chosen for restoration of groups equally. The restorations were then finished and polished according to manufacturer’s instructions. Silicon molds were fabricated over the crowns for three abutment angulations formed from Lava Ultimate blocks and used to guide wax pattern formation of the pressed crowns so that it had the same thickness and external dimensions as Nano-ceramic composite crown. 15 crowns were fabricated from ceramic ingots of IPS E-max by anatomic contour waxing (without cutback) for the lost wax and pressed method by 1 master technician. One layer of die spacer was then the abutments were lubricated followed by dipping n hot wax. A wax pattern for the full contoured crown was fabricated using wax addition technique on the abutments with guiding of each have of silicon mold. The wax patterns were sprued at the Inscisal edge and then investment and placed in the center of the hot press furnace and the recommended pressing program for IPS E-max Press LT was used. The crowns were deinvested then finished and polished according manufaturer’s instructions. Marginal gap was measured with digital microscope at 40x magnification before cementation then the crowns were cemented with Provitemp temporary cement. Two 1mm strain gauges were bonded on collar of implant analogue at labial and lingual surface using strain gauge cement. All samples were mounted in a 45o angulation custom made Jig and the load was performed with custom made steel bar with flat surface contacting 3/4 of the incisal edge width of the crown applied at across head speed of 0.5 mm/sec until reach to load of 150 N so strain measurement was recorded then load continue until fracture of crown or sudden reduction in force indicated by the testing device and maximum force up to this point was recorded as force of fracture. The values were recorded in Newtons (N), then the results were tabulated and statistically analysed The crowns were inspected visually to determine mode of failures. Analyses were performed with a digital microscope with a gradual increase in magnification. The most representative failed samples of each group were further observed using a scanning electron microscope (SEM). The result of marginal adaptation showed that Lava Ultimate crowns had significantly lower marginal gap than the IPS E-max press crowns with all abutment angulations and there was no statistically difference between marginal adaptations of Lava Ultimate crowns with different abutment angulations. While with IPS E-max press crowns on the 25o angled abutment had statistically significant higher marginal gap than straight and 15o angled abutment. The result of strain showed that angled abutment had statistically significant lower stain transmitted to implant on buccal and lingual side. While Lava Ultimate crowns had statistically lower strain transmitted to implant in buccal side only. The result of fracture resistance showed that Lava Ultimate crowns had statistically significant higher fracture strength than IPS E-max press crowns with angled abutment. Factographic analysis showed that crack initiated from contact of load at incisal edge and propagate into inner surface with Lava Ultimate crowns with angled abutment, while with straight abutment and with E-max crowns crack initiated from cervical margin and propagate incisally. |