Journal of Dental Medicine
Year:2012 | Volume:24 | Issue:4 (69)|Papers Count:9

Background and Aims: Disc displacement is the most common temporomandibular joint disorder and magnetic resonance imaging (MRI) is the gold standard in its diagnosis. This disorder can lead to changes in signal intensity of magnetic resonance (MR). The purpose of this study was evaluation of correlation between relative signal intensity of MR images of retrodiscal tissue, superior and inferior head of lateral ptrygoid muscle with type of anterior disk displacement and condylar head flattening in patients with temporomandibular disorder (TMD).Materials and Methods: In this retrospective study, 31 MR images of patients who had anterior disc displacement were evaluated. After relative signal intensity measurement for retrodiscal tissue, superior and inferior head of lateral ptrygoid muscle, the correlation between relative signal intensity and type of anterior disc displacement was evaluated with repeated measure ANOVA test. In each of these 3 areas, t-test was used to compare the groups with and without condylar head flattening.Results: The correlation between relative signal intensity of MR images and type of anterior disc displacement in retrodiscal tissue, superior and inferior head of lateral ptrygoid muscle was not significant. There was also no statistically significant correlation between relative signal intensity of MR images and flattening of condylar head in retrodiscal tissue, superior and inferior head of lateral ptrygoid muscle (P>0.05).Conclusion: According to findings of this study, relative signal intensity of MR images in retrodiscal tissue, superior and inferior head of ptrygoid muscle is not a good predictor for type of anterior disc displacement and flattening of condylar head. It seems that this cannot be used as a diagnostic marker for TMD progression.

Background and Aims: Reliable bonding between tooth substrate and zirconia-based ceramic restorations is always of great importance. The laser might be useful for treatment of ceramic surfaces. The aim of the present study was to investigate the effect of laser irradiation on the shear bond strength of zirconia ceramic surface to dentin.Materials and Methods: In this experimental in vitro study, 40 Cercon zirconia ceramic blocks were fabricated. The surface treatment was performed using sandblasting with 50-micrometer Al2O3, CO2 laser, or Nd:YAG laser in each test groups. After that, the specimens were cemented to human dentin with resin cement. The shear bond strength of ceramics to dentin was determined and failure mode of each specimen was analyzed by stereo-microscope and SEM investigations. The data were statistically analyzed by one-way analysis of variance and Tukey multiple comparisons. The surface morphology of one specimen from each group was investigated under SEM.Results: The mean shear bond strength of zirconia ceramic to dentin was 7.79±3.03, 9.85±4.69, 14.92±4.48 MPa for CO2 irradiated, Nd:YAG irradiated, and sandblasted specimens, respectively. Significant differences were noted between CO2 (P=0.001) and Nd:YAG laser (P=0.017) irradiated specimens with sandblasted specimens. No significant differences were observed between two laser methods (P=0.47). The mode of bond failure was predominantly adhesive in test groups (CO2 irradiated specimens: 75%, Nd:YAG irradiated: 66.7%, and sandblasting:41.7%).Conclusion: Under the limitations of the present study, surface treatment of zirconia ceramics using CO2 and Nd:YAG lasers was not able to produce adequate bond strength with dentin surfaces in comparison to sandblasting technique. Therefore, the use of lasers with the mentioned parameters may not be recommended for the surface treatment of Cercon ceramics.

Background and Aims: The aim of this study was to evaluate the quality of an experimental hydrofluoric acid (HF) for preparation of porcelain and to compare it with two commercial hydrofluoric acids in Iranian trademark.Materials and Methods: A- Evaluation of etch pattern of experimental HF using scanning electron microscope (SEM): 6 feldespathic discs were divided into 3 groups. Each group was etched with related HF (experimental, Ultradent and Kimia) for 1 minute. SEM images were recorded at 3 magnifications. B- Bond strength test: 18 feldespathic discs were considered for each acidic group. Then the porcelain surfaces were etched and bonded to composite with unfilled resin. Consequently, the microshear test was done. C- Microleakage test: 54 discs were divided into 3 groups (n=18). Then the porcelain surfaces were etched and bonded to composite with unfilled resin and finally observed under stereomicroscope. The data were analyzed with one-way ANOVA and Smirnov tests.Results: SEM analysis showed no difference between groups in terms of etch pattern. Microshear bond strength values for experimental, Kimia, and Ultradent HF were 28.53 (±4.92), 28.21 (±6.61), and 26.14 (±7.61) MPa, respectively. There was no significant difference between the bond strength of test groups (P<0.05). Furthermore, no significant difference was found between the microleakage of test groups (P>0.05).Conclusion: Quality of experimental HF in terms of etch pattern, microshear bond strength and microleakage of composite/porcelain interface was similar to that of two commercial hydrofluoric acids.

Background and Aims: Composite restorative materials and dental adhesives are usually cured with light sources. The light direction may influence the bond strength of dental adhesives. The aim of this study was to evaluate the effect of light direction on the microtensile bond strength of fifth and sixth generation dental adhesives.Materials and Methods: Prime & Bond NT and Clearfil SE bond were used with different light directions. Sixty human incisor teeth were divided into 4 groups (n=15). In groups A and C, Clearfil SE bond with light curing direction from buccal was used for bonding a composite resin to dentin. In groups B and D, Prime & Bond NT with light curing direction from composite was used. After thermocycling the specimens were subjected to tensile force until debonding occurred and values for microtensile bond strength were recorded. The data were analyzed using two-way ANOVA and Tukey post hoc test.Results: The findings showed that the bond strength of Clearfil SE bond was significantly higher than that of Prime & Bond NT (P<0.001). There was no significant difference between light curing directions (P=0.132).Conclusion: Light curing direction did not have significant effect on the bond strength. Sixth generation adhesives was more successful than fifth generation in terms of bond strength to dentin.

Background and Aims: The seal provided by a root canal filling may be compromised by post space preparation. The aim of this study was to compare coronal microleakage around cast posts and prefabricated pins.Materials and Methods: Thirty-eight extracted single-rooted, maxillary human teeth were prepared with step back method and filled with gutta-percha and sealer. After removing 8 mm of coronal gutta-percha with peesoreamer drills #2 in twenty canals, the teeth were divided into three groups: cast post & core, prefabricated pin, and gutta-percha (without any post or pin). After thermocycling, the samples were immersed in India ink for seven days. Finally, the specimens were cleared and the coronal microleakage of dye was then measured by the stereomicroscope. The data were analyzed by One-way ANOVA and Tukey HSD tests.Results: According to the results, the mean dye penetration in cast posts, pins, and group without post or pin was 3.3 (0.39), 5.2 (0.47), and 7.2 (0.15) mm, respectively. There was no statistically significant difference between the groups (P>0.05).Conclusion: Considering the importance of adequate filling of crown for prevention of microleakage, the method for coronal filling must be selected with caution. According to the results of this study, no significant difference between microleakage of cast posts and prefabricated pins was observed.

Background and Aims: A large number of investigations have revealed that physical and chemical alterations and weight loss could occur in composite materials exposed to acidic phosphate fluoride (APF) gel. The purpose of this study was to assess the microleakage of a fissure sealant and a flow composite exposed to acidulated phosphate fluoride (APF) gel.Materials and Methods: In this in vitro study, 60 intact human extracted premolar teeth were used. After preparing the occlusal groove, the teeth were divided into two groups (n=30). Teeth were filled with either Helioseal fissure sealant (Vivadent, Germany) or Tetric flow composite (Vivadent, Germany). After that, each group was divided into two subgroups (n=15): 1.23% APF gel (Sultan, U.S.A) was applied in the case subgroups, while control subgroups were preserved in normal saline solution. All of teeth were covered with 2 layers of nail varnish except for the filling zone and 1mm around the border of filling. After submerging in 0.5% fushin solution, specimens were sectioned buccolingually. Then dye penetration through the filling and fissure sealant was assessed by means of a stereo-microscope. The depth of dye penetration was scored. The data were analyzed using One-way ANOVA and Levene test.Results: The mean values of dye penetration were 1.26±1.09, 1.4±1.05, 1.2±1.37, and 1.4±1.35 for fissure sealant+gel, composite+gel, composite+normal saline, and normal saline groups, respectively. No significant difference was found in inter-groups (P=0.96).Conclusion: Considering the result of the present research, APF gel had no significant effect on the microleakage of Tetric flow composite filling and Helioseal fissure sealant and thus, it can be applied for routine usage.

Background and Aims: Evaluation of the training is a principle for successful education. This study evaluated the effect of the theoretical course of community oral health on knowledge, attitude and self-reported practice of preventive dentistry in dental students at Tehran University of Medical Sciences and assessed the students’ satisfaction from the course.Materials and Methods: The intervention group comprised the forth-year students of Tehran University of Medical Sciences, Dental School and the controls were the fourth year students of Shahid Beheshti Medical University. The questionnaire included questions on backgrounds, knowledge, attitude and practice of students towards preventive dentistry, and students’ satisfaction from the course. The intervention was 17 weekly sessions (hours) of the community oral health course. The sum of scores for questions on backgrounds, knowledge, attitude and practice were calculated and changes were analyzed by General Linear Model.Results: The mean baseline knowledge score in the intervention group was 16.9 (SD=4.0) and for the control group 16.3 (SD=3.5). Corresponding figures were 23.7 (SD=3.4) and 17 (SD=3.3) after intervention. General linear model showed the intervention to be successful in increasing the students’ knowledge scores on preventive dentistry (P<0.0001). Most students (92%) were satisfied with learning several new items during the course.Conclusion: The students’ knowledge was successfully increased by passing the theoretical course of community oral health delivered by teacher-centered method of lecture. Student-centered methods may help in changing the students’ attitude and practice of preventive dentistry.

Background and Aims: Teaching of clinical skills is one of the most important aspects in training medical students. The aim of this study was to compare the effectiveness of videotaped and live demonstrations for applying fissure sealant on permanent molar teeth at Zahedan University of Medical Sciences (2010-2011).Materials and Methods: Thirty 8th-semester dental students were randomly assigned in two groups (n = 15). In group 1, fissure sealant placement was taught using live demonstration; while, in group 2, education was performed by videotaped demonstration. Then, each student applied fissure sealant on the patient’s permanent molar tooth. The procedure of fissure sealant placement was assessed and scored by a pedodontist. The students were subsequently asked to rate how helpful the videotape or live demonstration had been. The data were analyzed using T-test and Chi-square test.Results: The mean students’ scores for videotaped and live demonstration were 16.5 and 16.53, respectively. There was no significant difference between the teaching methods according to students’ scores (P>0.05). 33% of students rated videotaped demonstration as “good” for its helpfulness and 66% as “very good”. However, live demonstration was rated as “good” and “very good” by 66% and 33% of students, respectively. There was no significant difference between two groups (P>0.05).Conclusion: Both teaching methods were equally effective. Therefore, videotaped demonstration can be used in combination with live demonstration or as an alternative for it.