الفهرس 
Historical prospective and success rate of dental implantOnly 14 pages are availabe for public view
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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.