الفهرس 
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Abstract
The aim of this study was to chemically analyze two mineral inserts of the silicate group (quartz and opal) and to investigate their influence as inserts and fillers on polymerization shrinkage strain, microleakage in MOD cavities of an experimental resin composite as well as assessment of shear bond strength of these inserts to experimental resin composite with examination of insert/composite/tooth interfaces under Polarized Light and Scanning Electron Microscope.
The following chemical analysis tests were investigated: X-ray diffraction analysis (XRD), X-ray flouresence (XRF), Differential thermal Analysis (DTA), Thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) analysis.
Experimental composites were made using two different types of fillers (quartz and opal), separately. The two fillers used were sieved up to size ≤ 10 µ and silane treated. The monomers were composed of 70% Bis-GMA and 30% TEGDMA by weight for all groups. Camphorquinone and DMAEMA were used as photo initiator system. Two types of inserts (quartz and opal) were used and etched with phosphoric acid. Silanization of inserts was done in an attempt to yield a stronger bond to the dental resin composite. Experimental composites were divided into six groups according to their filler and insert type and were compared to a commercial packable composite (Filtek P60).
Shear bond strength of inserts to dental resin composites was measured using the Universal Testing Machine. A chisel bladed shearing device was fixed to the upper compartment of the testing machine and aligned at the resin/ composite interface. The load was applied at a cross head of 0.5 mm/min until debonding had occurred. Shear bond strength was calculated by dividing the maximum load by the cross sectional area of the bonded interface.
The post–gel shrinkage strain (PGSS) of these composites was measured via using strain gages whose leads are connected to the strain monitoring device.
The study also included testing microleakage in class II MOD composite restorations using the dye penetration method. Teeth were examined under a stereomicroscope.
The restored teeth were examined using Polarized Light Microscope to demonstrate the petrographical characteristics of the different interface layers. The teeth were sectioned mesiodistally with diamond saw and then ground with diamond disk to the required thickness 30 µ suitable for petrographic studies.
Insert/composite/tooth interfaces were examined using Scanning Electron Microscope. A representative sample for each group was cut mesio-distally exposing the insert/composite/tooth interfaces. Specimens were then sputter coated and subjected to an electron probe micro-analyzer for examination of the interface.
Results of the XRD analysis, which was only applied to crystalline mineral (quartz), showed the main d-spacing lines that are representative to quartz mineral.
For the XRF analysis, the Fe2O5% was higher in opal compared to quartz which is the principal factor that determines the grayish color and of the darker shade of the opal sample when compared to quartz.
DTA revealed the enothermic behavior of the quartz and opal and showed that neither of them reacts or forms any components upon heating to 8000C and consequently they are thermally stable inside patient mouth.
TGA analysis was performed to detect any organic impurities and moisture in the fillers. TGA analysis showed no weight loss at high temperatures, thus no organic content, which indicated the previous heat treatment of the fillers at 800oC for 4 hours.
As for the BET analysis, it was performed to verify the surface area of both types of fillers for calculation of the quantity of silane needed to obtain a chemically bonded silane monolayer on the fillers, surface. The average surface area for quartz and opal fillers was 203.5 and 241.9 m2/g repectively.
Results of shear bond strength test using the Universal Testing Machine showed that the opal insert showed an increase in mean shear bond strength when compared to quartz insert. Opal insert bonded to composite (Opal filler) showed the highest shear bond strength compared to all groups while there was no difference between opal insert bonded to both composite (quartz fillers) and Filtek P60. The lowest shear bond strength values were observed in quartz insert bonded to Filtek P60, composite (quartz fillers) and composite (opal fillers), with no difference from each other.
On investigating the Post gel shrinkage strain (PGSS), composite (quartz filler) without inserts showed the highest PGSS among the tested composites groups. On the other hand, the polymerization shrinkage strain was reduced in the control Filtek P60 with no difference from composite (opal fillers). On the contrary, there was a decrease in PGSS values of composite (opal fillers) bonded to opal insert in comparison to all tested groups. There was a decrease in PGSS of tested composites used with opal insert in comparison to those used with quartz inserts or the mere composite resrorations. The use of quartz insert with composite (quartz fillers) showed higher mean PGSS values than those used with Filtek P60 and composite (opal fillers). While using opal insert with composite (quartz fillers) showed higher PGSS than with both composite (opal fillers) and Filtek P60.
Results of microleakage test using the dye penetration method showed an increase in microleakage scores in Filtek P60 without insert among the tested composites. On the contrary, the composite (opal fillers) bonded to opal insert showed the lowest microleakage score among the tested groups. There was a decrease in microleakage scores in composites bonded to either opal or quartz inserts compared to the mere composite restorations. There was no difference in microleakage between the mere composite restorations. Also, there was no difference between all composite restorations used with quartz insert. However, There was an increase in microleakage score of opal insert bonded to Filtek P60 composite compared to opal insert bonded to both composite (quartz fillers) and composite (opal fillers).
Petrography of the tested specimens showed a solid interfacial hybrid layer was observed in the specimens used with either quartz or opal insert at composites\ insert interface. Opal insert bonded to composite (opal fillers) showed a strong hybrid layer at composite\insert interface with complete impregnations of the opal insert into composites. Also there was an optical continuity that existed along opal insert /composite interface reflecting a solid gap free contact. The investigation of (opal fillers) specimens used with opal insert revealed a thin as well as uniform hybrid layer at composite\dentin interface.
Scanning Electron Microscopic examination of insert/ composite/tooth interfaces showed that both quartz and opal inserts showed an intact insert/ composite interface with no gap formation. Specimens without inserts showed an interfacial gap between the composite and the tooth. Placement of quartz insert in experimental composite specimens (opal fillers) showed thick bonding zone with non-uniform thickness. While a very homogenous hybrid zone was noticed in (opal fillers) specimens bonded to opal insert indicating a strong adhesive junction at composite \ tooth interface.
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