BackgroundHydroxyapatite (HA) is the main mineral component of the tooth structure, which exhibits considerable biological behavior and its incorporation might improve microhardness of dental materials. Microhardness of restorative materials, like glass-ionomer, is critical for the clinical longevity of restorations. The aim of this study was to evaluate the microhardness of two glass-ionomers types by incorporating different percentages of microhydroxyapatite.Material and MethodsIn this study, 80 disc-shaped experimental specimens (6 mm in diameter, 2 mm in height) were prepared in 8 groups, including resin-modified glass-ionomer (RMGI, GC, Gold Label, Japan), zirconia-reinforced glass-ionomer (Zirconomer, Shofu, Kyoto, Japan), and their mixture with 0, 5, 15 and 25 wt% of microhydroxyapatite (Sigma-Aldrich, Germany). All the specimens were stored in deionized water at 37ºC for 24 hours. Then Vickers microhardness test was carried out on the both sides of specimens and data were analyzed using two-way ANOVA and paired t-test (P<0.05).ResultsMicrohardness of Zirconomer and RMGI increased significantly due to adding 5 and 15 wt% of micrhydrox-yapatite (P<0.001). The highest Vickers hardness number (VHN) was recorded in the RMGI group with 5 wt% of microhydroxyapatite. In addition, in all the study groups RMGI exhibited higher microhardness values than Zirconomer (P<0.001). However, microhardness values decreased significantly after adding 25 wt% of microhydroxyapatite to Zirconomer (P<0.001). Similarly, VHN decreased in RMGI groups containing 25 wt% of HA compared to control groups (without HA) (P<0.001).ConclusionsIncorporation of 5 and 15 wt% of microhydroxyapatite to RMGI and Zirconomer improved microhardness, while adding 25 wt% of HA decreased hardness with both experimental materials compared to the control groups (without HA). Key words:Microhardness, Resin-modified glass-ionomer, Zirconia-reinforced glass ionomer, Microhydroxyapatite.

Background:Odontogenic cysts are relatively common lesions which can cause different complications. As demographic information is lacking in Iran and specially in Isfahan, the aim of this study was to determine the prevalence of odontogenic cysts according to age, gender and affected area among patients referring to the Oral Pathology Department of the Dental School of Isfahan University of Medical Sciences (Iran) over a 23-year period.Materials and Methods:A total of 7412 diagnosed lesions recorded in the Oral Pathology Department archives of Isfahan Dental School between 1988 and 2010 were reevaluated, then odontogenic cysts were separated through reviewing microscopic slides according to the 2005 World Health Organization classification and variables such as age, gender, the infected jaw, and its specific region were obtained by SPSS Version 16.0 from the recorded database.Results:21.62% of the lesions were odontogenic cysts, of which 48.72% were inflammatory and 51.28% were developmental cysts. These cysts were more common in the mandible. The mean age of patients was 29.53 ± 16.1. Male to female ratio was 1.31:1. The four most frequent odontogenic cysts were radicular cysts (35.12%), dentigerous cysts (25.77%), odontogenic keratocysts (22.58%) and residual cysts (12.98%).Conclusion:Odontogenic cysts are fairly frequent jaw lesions (21.62%), of which radicular cyst was the most common cyst. The four most common lesions constituted a sum of 96.45% of the total. In general, the prevalence rates in our study are similar to the studies from other geographic parts of the world but with a lower incidence of inflammatory cysts, higher prevalence of dentigerous cysts and residual cysts and also mandibular predominance for residual cysts.

BackgroundHome bleaching agents may exert some negative effects on surface hardness of restorative materials such as glass-ionomer cements (GICs). Since some studies have shown that some components such as hydroxyapatite (HA), as a bioactive glass, can improve the mechanical properties of dental materials, the effect of bleaching agents on surface hardness of GICs containing hydroxyapatite is questionable. This study was designed to evaluate the effect of home bleaching agents on the surface hardness of two different commercially available GICs containing hydroxyapatite.Material and Methods80 disk-shaped specimens were made from two different GICs, including resin modified glass-ionomer and Zirconomer. Each material was divided into four groups (n=10): 1. control, 2. 20 %wt. hydroxyapatite-containing, 3. bleached and 4. bleached 20 %wt. hydroxyapatite-containing. Group 1 and 2 specimens were stored in distilled water for 2 weeks while group 3 and 4 specimens were treated with 15% carbamide peroxide in that period. Surface hardness was tested with Vickers surface hardness tester. Data were analyzed with 3-way ANOVA and mean comparison done by post hoc Tukey tests (p<0.05).ResultsIn general RMGI had a significantly highest Vickers surface hardness value among all groups. 15% carbamide peroxide reduced surface hardness compared to control groups (RMGI and Zr) significantly. In the HA-containing GICs groups, bleaching agent did not significantly changed the surface hardness value.ConclusionsIn this study we concluded that applied treatments (bleaching and adding HA) in implicit percentages reduced surface hardness of GICs. Also we suggest more studies in clinical conditions be done to verify these results. Key words:Home bleaching, Resin Modified Glass-ionomer cement, surface hardness, Zirconia-reinforced glass ionomer, hydroxyapatite.