The effect of drinking yogurt on the microhardness of posterior composites resin

Abstract

Background :This study was conducted to evaluate the effect of yogurt on the
surface microhardness of two types of composite resins; (Filtek™ P90 Low Shrink
Posterior Restorative, 3M ESPE,USA), and (Filtek™ Z350 Posterior Restorative, 3M
ESPE,USA).
Forty samples of composite were prepared by using cylindrical mold (2mm in
hight and 8mm in diameter )..All specimens were stored in plastic container that
contain distilled water and incubated 37cº for 24 hours before they were tested. twenty
samples of each type of composite were divided into two groups (10) for each ,
baseline measurements for surface microhardness test was taken for all composite
samples using the micromet microhardness tester (Vichers hardness tester) with a
l00g load was applied for 15 seconds in which three indentations were made for each
sample and converted into Vickers Hardness Number (VHN ) .After baseline
measurement 10 samples of each type of composite were alternately immersed
manually by holding the specimen by a pair of tweezers from its sides, , in drinking
yogurt (Activia ,KSA) and artificial saliva for 10 cycles 5 seconds each at room
temperature (25cº). This was repeated three times a day (8am,4pm,12am) at 8hours
intervals for one week. the other 10 samples for each type of composite were
immersed in artificial saliva only. The total soaking time in both drinking yogurt and
saliva was 100 seconds. After the soaking sequence was completed the specimen was
rinsed with distilled water and subjected to surface microhardness test (Vichers
hardness tester).
Descriptive statistics(mean values and standard deviations with the minimum and
maximum values and Statistical analysis of data by using student t - test for all groups
was carried out between the means of each type of composites ,the results showed a
significant reduction in VHN values (at P<0.05)of Filtek™ Z350 Posterior
Restorative composites after immersion in artificial saliva, while the (Filtek™ Z350
Posterior Restorative, 3M ESPE) composite showed a highly significant reduction in
VHN values (at P<0.01)after immersion in drinking yogurt. Filtek™ P90 Low Shrink
Posterior Restorative composites showed a non significant reduction in VHN values
(at P>0.05) after immersion in artificial saliva and after immersion in drinking yogurt.
Filtek™ P90 Low Shrink Posterior Restorative composites have highest VHN
value than Filtek™ Z350 Posterior Restorative composites, and surface microhardness
results showed that drinking yogurt highly significantly effect on the Filtek™ Z350
Posterior Restorative composites while it has non significant effect on the Filtek™
P90 Low Shrink Posterior Restorative composite