ABSTRACT
The purpose of this in vitro study was to investigate the sealing performance [microleakage] of different glass ionomer formulations and to measure their wear rate. For microleakage assessment, a total of 120 class V cavities were prepared in upper and lower premolars and were used in this investigation. The cavities were divided into two main groups according to the location of the cervical margin. In group I: The cervical margin of the cavity was located 0.5 mm above the cement-enamel junction. In group II: The cervical margin was located 0.5 mm below the cemtno-enamel junction. Each group was further subdivided into three subgroups A, B, and C [20 each] according to the restorative material used. A resin modified glass ionomer [Vitremer], a polyacid modified resin composite [F2000], and a giomer restorative filling material [beautifil] were used. Each of the previous subgroups was again subdivided into two groups [10 each]. In groups A+, B+, and C+, the restored specimens were subjected to mechanical load cycling and thermal fluctuation before microleakage assessment. In groups A-, B-, and C-, microleakage assessment was carried out 24 hours after immersing the restored teeth in distilled water at room temperature. For wear determination a total of 15 cylindrical specimens were prepared, a two-body abrasion machine was used and the wear data were deducted to calculate the wear rate in gm/sec
Results: There was no statistically significant difference between the microleakage scores above and below the cement-enamel junction for all materials. Furthermore, there was no statistically significant difference between the microleakage scores of the three materials tested. In group I [above CEJ]; Vitremer [A] and giomer [C] showed a statistically higher percentage of [+] specimens with leakage than [-] specimens. There was no statistically significant difference between [+] and [-] specimens in material [B]. However, in group II [below CEJ]: All materials showed a statistically significantly higher percentage of [+] specimens with leakage than [-] specimens. The mean wear rate showed a statistically significant difference between the three materials [P<0.001]. Scheffe's test showed that material [A] showed the highest mean wear rate. There was no statistically significant difference between materials [B] and [C]; both showed the lowest mean wear rate
Conclusion: Microleakage is a multifactorial phenomenon; it is not only affected by the bonded tissues but also by the interfacial mechanism of attachment as well as the mechanical load cycling and thermal fluctuation. The compositional differences between the resin/glass ionomer formulations in terms of resin matrix, filler size, filler loading and mode of filler bonding influenced their wear resistance
Clinical relevance: Microleakage is greatly affected by the bonding mechanism, the mechanical load cycling and thermal fluctuation. Compomer and Giomer are safely used in class V cavities
ABSTRACT
This study was conducted to evaluate the stability of three different ceramic systems after their immersion in solutions with different pH values regarding the surface texture and ionic release. A total of 45 ceramic disc specimens were prepared. They were divided into 3 groups, 15 each according to the type of the tested ceramic material. These groups were further subdivided into 3 subgroups, 5 each depending on the proposed test media. Evaluation of the surface texture was carried out quantitatively by analyzing the surface roughness of the ceramic specimens before and after immersion in different test solutions using the Image analysis software. For qualitative analysis, scanning electron microscope was done to study the effect of immersion in different conditioning media with different pH values on the surface morphology of the three tested ceramic materials. The determination of elements leached from the ceramic materials [aluminum, silicon, lithium, sodium and potassium] was done with inductively coupled plasma optical emission spectroscopy
Results: The surface roughness; the control group of IPS Empress 2 exhibited the least surface roughness value which was significant among the other control groups. A significant increase in the mean Ra values was found over the experimental period for all tested ceramics immersed in different solutions. Concerning each ceramic, Duceram showed no significant change in its surface roughness in the three storage media. Meanwhile Duceram LFC's surface roughness was significantly different in the three immersion media, where citric acid caused the highest surface damage and lactic acid caused the least one. regarding IPS empress 2, conditioning in either acetic or citric acid caused comparable surface damage which was significantly higher than that caused by lactic acid. Interceramic comparisons revealed that acetic acid storage caused comparable surface damage to both Duceram LFC and IPS Empress 2. Their values were significantly higher than half of Duceram. On the other hand, citric acid immersion caused a significant increase in surface roughness of Duceram LFC followed by IPS Emress 2 and then Duceram. Finally lactic acid conditioning medium was destructive in a similar way to the surfaces of both Duceram and IPS Empress 2. Their Ra values were significantly higher than that of Duceram LFC
The ion release; all materials used released different ions which varied in amounts according to the storage media in which they were immersed. Generally, citric acid solution was the most corrosive one for the three ceramic materials regarding the aluminum, silicon and lithium ion release while lactic acid solution was the least corrosive medium. On the other hand lactic acid solution was the most corrosive medium for the three materials regarding sodium ion release and citric acid solution released the least amount of sodium. Concerning potassium ion release, interceramic comparisons revealed that in acetic acid solution, Duceram LFC recorded the highest value followed by IPS Empress 2 and finally Duceram. Meanwhile, in citric acid solution, IPS empress 2 occupied the first position, Duceram the second and Duceram LFC the last. In lactic acid solution, the comparable values of potassium ion release from Duceram LFC and IPS Empress 2 were significantly lower than that of Duceram
Conclusion: Surface roughness and chemical durability of the tested ceramic materials are dramatically affected by the pH values of the storage media and the composition of each ceramic system as well as their processing technique. The type and the amount of ion release from each ceramic varied according to the solution medium. Surface roughness and microstructure are influenced by the type and the amount of ion release from each ceramic system
Clinical relevance: Good oral hygiene is mandatory to avoid any possible damages to the surface as well as the microstructure of cceramic materials as they might be affected by variations in pH values
ABSTRACT
The purpose of this in vitro study was two-fold. First the effectiveness of ozone, as a bleaching agent, in comparison with other commercJaJJy available bleaching products was evaluated by measuring the change in color index of teeth. Second the presence of any surface damages, which may occur in enamel surface following bleaching, was investigated by measuring the surface roughness of enamel as this may have an implication on the functional properties of the surface. One bleaching gel with two different concentrations [Opalescence 10% and 20%], and an Ozone gas [O3] were used in this study. The Ozone was incorporated into: 10% carbamide peroxide gel, neutral KY gel and distilled water. Twenty five intact maxillary first premolars were used. The teeth were randomly divided into five groups. Group J was treated with ozonated 10% carbamide peroxide, group fl was exposed to ozonated water, group III was treated with ozonated KY gel, group IV and V were subjected to 10% and 20% carbamide peroxide respectively. For each specimen, a photomicrograph was undertaken before and after treatment by a digital camera attached to a zoom stereo microscope. The tricolor index (RGB system) for brightness index measurement and the surface roughness (Ra) 'were automatically calculated using image analysis software. The value of the blue color parameter was specifically registered.
Results: There was no statistically significant difference between the control and the experimental specimens for the groups I, II and IV [p > 0.05]. However, by looking at the results of the blue color paramcL-r; there was a statistically significant difference between the control and the experimental speomens of group IV. This difference was not observed for group I and JI respectively. Regarding groups III and V a significant difference in color index and blue color parameter was observed between the control and the experimental specimens [p< 0.05] indicating a good brightness effect. By comparing the changes in color indices of the five groups, there was a statistically significant difference [p< 0.05] among them. Groups III and V showed a significantly higher color index than the other groups. The most effective bleaching regimen was obtained when the teeth were treated with 20% carbamide peroxide and ozonated KY gel respectively. In general, there was an increase in the 1 average surface roughness [Ra] with all different treatments. By comparing the surface roughness of the five groups, there was a statistically significant difference between the five groups and they were ranked as follow [from the lowest to the highest]: Group II, Group I, Group IV, Group III and Group V. Pearson correlation coefficient showed no correlation between the color iadex -and Ra for group I, while the correlation between color indices and Ra for the rest of the groups were not statistically significant. In general, no relation between surface roughness and color index could be established.
Conclusions: The use of Ozone is an effective and viable method for bleaching teeth. Bleaching has an adverse effect on the surface roughness of enamel. Although the correlation between the color index and the surface roughness was not significant, yet there was a trend showing that the brighter the bleached teeth the higher the surface roughness. The change in the blue color parameter is an appropriate descriptor of brightness. Clinical Relevance The use of Ozone as a bleaching agent should provide a fast, effective and harmless method to whiten teeth. It should be easily supplied and integrated in dental offices. The potential adverse effects of bleaching must be known to the dentist in order to be able to overcome these effects. Clinically, brightness index from computer analysis of digitized photographic images may be useful for monitoring the effectiveness of bleaching.
ABSTRACT
Anstract: The purpose of this study was twofold, first to evaluate the effect of 50% hydrogen peroxide bleaching agents on surface morphology, ultra-structure of resin-dentin interface and the shear bond strength of resin composite to dentin. Second, to evaluate the effect of application of two different forms of antioxidants on the bleached dentin surface on the fore mentioned properties. One adhesive system [Dentastic Uno]. Epic TMPT microfilled composite. 50% bleaching gel and two antioxidants namely sodium ascorbate and vitamin C were used in this study. 56 intact maxillary first premolars were used. The teeth were equally divided into four groups, fourteen specimens each. Group I was directly bonded with composite resin without bleaching, group II was subjected to bleaching prior to composite bonding, whereas group III and IV were treated with sodium ascorbate and vitamin C antioxidants respectively after bleaching then bonded with resin composite. The teeth were examined by SEM to investigate dentin surface topography and resin- dentin interface. All samples were also subjected to shear bond strength testing using a universal testing machine
Results: The unbleached specimens showed adequate removal of the smear layer with effective opening of the dentinal tubules. The hybrid layer revealed a uniform distribution with resin tags positively extending in the demineralized dentin. On contrary, the bleached specimens showed the presence of smear layer and no opened dentinal tubules were evident. This resulted in forming thin, irregular and crumbly hybrid layer, with less resin tags extensions in dentinal tubules. SEM of cut dentin surface treated with sodium ascorbate after hydrogen peroxide bleaching, showed adequate removal of smear layer with a well distinct hybrid layer similar to that of control group. While the SEM of cut dentin surface treated with vitamin C after bleaching, showed a well established smear layer with no evidence of etching. The hybrid layer was very thin with few and short resin tags. The mean and standard deviation values of shear bond strength in MPa indicated that the least mean shear bond strength value was shown by the bleached dentin group[4.56 MPa] while the highest mean shear bond strength value [14.45 MPa] was shown by the unbleached group. There was insignificant difference between the sodium ascorbate treated group and the unbleached control group
Conclusions: Hydrogen peroxide bleaching dramatically affects the dentin surface morphology, the hybridization quality as well as the shear bond strength of resin bonded composite to dentin. Application of sodium ascorbate as a biological antioxidant reverses the oxidation effect of hydrogen peroxide bleaching on dentin surface topography and restores the compromised shear bond strength. Different chemical formulations of antioxidants produced various interfacial structures of bleached dentin and finally the shear bond strength of composite to dentin is intimately related to the quality of hybrid layer and the resin tag infiltration