[ effect of thiourea on shear bond strengths of composite to bleached enamel]

Reduced composite-tooth bond strength after bleaching inhibits immediate tooth restoration. To determine the effect of thiourea as a free radical scavenger on shear bond strength of composite to bleached enamel. Enamel surfaces of 96 sound human premolars were randomly assigned to six experimental groups [n=12] which were bleached with%15 CP, and two control groups 1, 2 [n=12] bonded without bleaching. The specimens in groups 3 and 4 [n=24] were bonded 24 hours after bleaching. Groups 5 and 6 [n=24] were bleached with a mixture of%15 CP and thiourea followed by bonding. Groups 7 and 8 [n=24] were bleached, immersed in water and left for 1 week. In odd groups, single bond and in even groups Excite were used. Composite Cylinders were bonded and the shear bond strengths were determined 24 hours later. Data were subjected to one-way ANOVA and Tukey HSD at a significant levels of p<0.05. There was no statistically significant difference between diverse groups. Mean bond strength was lowest in groups 3 and 4 and highest mainly in group 8 and with a little decrease in group 5. Bleaching with 15% carbamid peroxide caused insignificant reduction in composite-enamel bond strengths in bonding either after 24 hours or one week following the application of 2 types of bonding agents. Application of thiourea in combination with bleaching agents may be useful for immediate composite restorations

[Evaluation of curing light intensity in private dental offices [2005]]

Success rate in composite restorations is associated with the degree of polymerization and light intensity. The aim of this study was to evaluate the light intensity of curing units in private offices in Qazvin 2003. In this analytical study the light intensity of 62 light curing units were investigated before and after cleaning their light emitting tips using a radiometer. The results were classified in 3 groups as follows: A: sufficient intensity > 300 mw/cm2, B: borderline intensity [200-299 mw/cm2], and C: insufficient intensity < 200 mw/cm2. Data were analyzed using chi-square and Pearson correlation tests. Mean intensity of curing units was 350.96mw/cm2 which increased significantly to 371.6mw/cm2 [p=0.01]. Before cleaning, 67.8% of curing tips were in group A, 14.5% in B and 17.7% in C. After cleaning, 72.6% were in sufficient intensity group, 11.3% in borderline intensity, and 14.1% in insufficient intensity. Removing curing tips' contamination caused a significant increase in light intensity [p=0.01]. Periodic assessment of light intensity and quality control of light curing units are mandatory

Evaluating the effect of ferrule preparation and its length on fracture resistance of maxillary central incisors with cast post-core and PFM crowns

Endodontically treated teeth are weaker than vital teeth and more prone to fracture. One of the special considerations in their restoration is the application of ferrule preparation. Evaluating the effect of ferrule and its length on fracture resistance of maxillary central incisors with cast post-core and PFM [porcelain fused to metal] crowns. This was an experimental study in which 30 extracted intact maxillary central incisors with similar dimensions were selected and randomly classified into three groups. Initially, the roots of teeth were treated after crown reduction and later, while considering the simulation of orthodontically crown lengthening, the teeth were fixed in acrylic blocks followed by making cast post and cores and luted with zinc phosphate cement. In first group [control group], ferrule wasn't prepared but in second and the third groups one millimeter and two millimeters ferrule were prepared, respectively. Later, PFM crowns were made for all specimens and luted with Zinc Phosphate cement. Finally, the specimens were loaded under compressive static loading by Zwick testing machine, using a crosshead speed of 2.5 millimeter per minute with an angle of 135 degrees to the long axis from palatal aspect to fracture. The primary failure loads were recorded as fracture resistance in Newton. Data were subjected to Kruskal-Wallis at a significant level of 5. The average and standard deviation of fracture resistance in first group [without ferrule] was 581.37 +/- 141.12 N, in second group [with one millimeter ferrule] 606.37 +/- 114.38 N, and in third group [with two Millimeters ferrule] 569.44 +/- 61.69. No significant difference between three groups was found, statistically [p>0.05]. Preparing one millimeter ferrule and increasing its length to two millimeters- while orthodontically crown lengthening is required- makes no significant effect on fracture resistance of maxillary central incisors with cast post-core and PFM crowns

[Evaluating antibacterial effects of three disinfectants on dental operatory surfaces]

Dental operatory surfaces are in continuous contact with microbial agents however, conventional techniques are unable to effectively disinfect these surfaces, thus efforts in achieving a new approach to successfully eliminate microorganisms from these surfaces are of prime importance. To evaluate the effectiveness of three different disinfectants on different surfaces of dental operatory. This was an experimental study in which 167 samples from different operatory surfaces were investigated. The samples included dental chairs [n=54], cabinets [n=54], and the control buttons [n=54] which were experimentally contaminated with Staphylococcus aureus and Pseudomonas aeruginosa [81 each]. Three surfaces were left intact as negative control groups and 2 samples contaminated but not disinfected were regarded as positive control groups. All contaminated surfaces were brought into contact with disinfectant solutions for time intervals of 1, 3, and 5 minutes followed by sampling and cultured on blood agar. Colony counts [CFU/ml] were performed following 24-hour incubation time. The data were further analyzed using SPSS. In all specimens including those disinfected with Micro 10 and Deconex and negative control groups, no bacterial growth were seen whereas in positive control groups and all surfaces contaminated with staphylococcus and disinfected with Sanosil for 1 and 3 minutes, colony formation were detected. Among the specimens contaminated with Pseudomonas and staphylococcus and disinfected with Sanosil for 5 minutes, no detectable bacterial growth were observed. Deconex and Micro10 at 1 min and Sanosil at 5 min intervals were capable of inhibiting the growth of two kinds of oral microorganisms. The choice and the proper use of disinfectants are of prime importance and should be steadily under strict monitoring as disinfection of operatory is among the simplest ways in preventing transmission of diseases through dental practice

[Assessment of students' research proposals and reports in Qazvin UMS]

Through a checklist 68 proposal and 28 reports of students' researchers submitted to student research committee of QUMS [from 2004 to 2006] were assessed. Most of the researches [48.5%] were medical students. Most of the teachers [72.1%] were from Faculty of Medicine; of these 17.6% were pharmacologist and 11.8% anatomist. Most of the researches [35.5%] were experimental studies. Only 13.2% of their results were published in journals or seminars. The most weakness of the proposals were in "sampling" and "objectives and hypothesis". The weakness of the reports was evident in "abstract". It seems that teachers must advise their students in writing proposals and reports more than before

[ relation between maxillary constriction and hearing loss]

Maxillary constriction and high palatal vault can change the location of soft palate and may cause Eustachian tube dysfunction and even stenosis. The purpose of this study was to evaluate the relationship between maxillary constriction and conductive hearing loss. This case-control study included one hundred twenty patients whom were divided into two equal groups. The patients' ages ranged from 7 to 40 years. Hearing level was measured in all patients with a digital audiometer. The control group consisted of sixty participants with normal hearing level [under 15 db], wherease patients who had the hearing level of more than 15 db were the cases with conductive hearing loss. Then maxillary constriction was examined in both groups according to skeletal posterior cross bite and high palatal vault. These two groups were compared applying of chi-square test. This study showed that maxillary constriction was seen in 7 patients [11.7%] in control group and 19 patients [31.7%] in case group [P < 0/05]. People suffering from hearing loss were faced with maxillary constriction 3.5 times more than others. There is a significant relationship between maxillary constriction and conductive hearing loss. Thus, it is recommended that to prevent from hearing loss, maxillary constriction should be treated appropriately