مجله تحقیق در علوم دندانپزشکی
سال بیست و دوم شماره 2 (پیاپی 84، تابستان 1404)

In multi-unit fixed prostheses, the connector areas are places where stress and failure accumulate due to thinness and need strengthening. The purpose of this research is to investigate the effect of changing the surface area of connectors of zirconia three-unit fixed prostheses on their bending strength.

 In this experimental  - laboratory study thirty, first molar and first premolar teeth of the lower jaw were prepared as base teeth for the FPD prosthesis on the plastic model of the jaw. Zirconia FPD samples were made for them in two groups with silhouette and elliptical connector shapes, each group having three subgroups with connector areas of 8 mm2, 10 mm2, and 12 mm2, with CAD/CAM system. Finally, 5 samples were considered in these 6 groups. Then, the samples were cemented, and their bending strength was measured with the universal testing machine and a three-point bending test.Two-way analysis of variance and LSD post hoc test were used in SPSS version 22 software for statistical analysis.

Considering the significance level of P value (P< 0.05), there is no significant difference in bending strength between silhouette and elliptical shapes (P value = 0.339). The bending strength in the area of 12 mm square is significantly higher than the area of 8 and 10 mm square (P value = 0.001).

In fixed three-unit zirconia prostheses, changing the area has significant effect on the bending strength, but the shape has no effect.

Improper dimensional changes in impression materials, including of additional silicone impression materials can cause the failure of prosthetic treatments. The aim of this study was to investigate the effect of different temperatures on the dimensional stability of polyvinyl siloxane impression material.

In this in vitro study, 99 Harmony medium (Elsodent-France) additional silicone impression were prepared according to the manufacturer's instructions. The impressions were kept in the environment with temperatures of 4, 25 and 40 C°. Then with time intervals: one hour, one day and one week after molding, plastering was done. The diameter, width and height of plaster casts were measured by S.D.M digital caliper. Dimensional changes were analyzed by Two Way ANOVA and POST HOC test

Changes in the diameter dimension; at the temperature of 25 °C at all times compared to each other and at 40 °C during 1 week compared to 1 hour and 1 day, there were significant differences. Changes in the width dimension; at 4°C, 1 hour compared to 1 day, at 25°C, 1 week compared to 1 hour and 1 day, and at 40°C, 1 hour compared to 1 week had a significant difference. Changes in the height dimension; at 25 °C and 40 °C, there were significant differences between 1 week compared to 1 hour and 1 day (p < 0.05). Changes at 25 °C in 1 hour, 4 °C in 1 day and 4 °C in 1 week were within the clinical standard range (1.5%).

In the scope of the present study, it seems that the dimensional stability of the investigated additional silicone is influenced by the temperature of the storage environment and the impression time, and the best time and temperature is 1 hour and 25 °C.

 The placement of mini-implants in the posterior maxilla requires accurate assessment of interradicular distances to ensure stability and avoid complications. The purpose of this study was to evaluate the interradicular distance in the posterior maxilla of Persian adults with class I, II and III sagittal skeletal patterns using cone beam computed tomography (CBCT), aiming to identify the optimal site for mini-implant insertion in this region.

This cross-sectional study was conducted on CBCT images of 90 individuals aged 18-50 years to measure the interradicular spaces at 2, 4, 6 and 8 mm from the cementoenamel junction (CEJ) from the distal of the canine to the mesial of second molar in maxilla. The participants were divided equally among three sagittal skeletal classes. Data were analyzed by ANOVA and Tukey’s post hoc test (alpha = 0.05).

The results demonstrated that the interradicular spaces gradually increase from the CEJ toward the apex. The widest interradicular distances were observed between the first and second premolars, particularly at 6 and 8 mm from the CEJ in all skeletal classes. There was a significant difference in interradicular distances based on skeletal patterns. Gender differences were minimal but statistically significant in specific regions. Age differences were not significant within the limits of this study.

Based on the findings of this study, while individual differences should be taken into consideration, the region between the first and second premolars at 8 mm from the CEJ seems to be the most favorable site for mini-implant insertion in the posterior maxilla in all sagittal skeletal patterns.

The purpose of this study was to evaluate the educational status of the Oral and Maxillofacial Surgery Department at the Islamic Azad University, Tehran, using the CIPP evaluation model during the academic year 2023-2024.

This descriptive-analytical study was conducted on general dentistry students in the 7th, 8th, 10th, and 11th semesters. The CIPP evaluation model was utilized, assessing the context and product domains through questionnaires based on this model. The first part of the questionnaires included questions about the personal characteristics of the students. In the subsequent parts, the context and product domains of the educational program in the Oral and Maxillofacial Surgery Department were evaluated.

In the context domain, the mean scores were as follows: 7th semester, 2.336 ± 0.51; 8th semester, 2.077 ± 0.52; 10th semester, 2.224 ± 0.53; 11th semester, 2.715 ± 0.49. In the product domain, the mean scores were: 7th semester, 1.46 ± 0.25; 8th semester, 1.97 ± 0.49; 10th semester, 2.24 ± 0.40; 11th semester, 2.16 ± 0.3.

The Oral and Maxillofacial Surgery Department at the Islamic Azad University, Tehran, was evaluated as satisfactory in the context domain by all students from the 7th to 11th semesters in 2023. In the product domain, the department was deemed satisfactory by students in the 8th, 10th, and 11th semesters, while students in the 7th semester rated it as unsatisfactory.

 Dental students are exposed to various levels of stress that may affect their mental and physical health, academic performance, and quality of life. This study aimed to examine the level of psychological stress and perceived stressors among clinical students at the Zahedan School of Dentistry.

The study population consisted of clinical dental students. Participants were assessed using the validated Depression, Anxiety, and Stress Scale (DASS-21) and the Dental Environmental Stress Questionnaire (DES). A p-value of less than 0.05 was considered statistically significant.

The score for dental environmental stress among students was 101.19 ± 17.51 (out of 152) (66.57%), indicating moderate stress. The main sources of stress for students were related to clinical education, patient treatment, and university efficiency, while the least stressful factor was related to internal beliefs. A significant positive correlation was found between dental environmental stress and depression, anxiety, and stress among both male and female students, across different academic years, and among students living with family and in dormitories.

The highest level of dental environmental stress is experienced by third-year students, who exhibit higher anxiety levels compared to other students. Fourth-year students show higher levels of depression than their peers. Sixth-year students report the lowest levels of stress, anxiety, and dental environmental stress, while fifth-year students experience the least depression.

 oral Lichen Planus  with unknown etiology, chronic nature and the possibility of malignancy can increase the stress level of patients. Mental disorders such as stress, anxiety and depression affect the severity of oral lichen disease. The aim of this study was to examine the mental health of patients with oral lichen planus and its association with disease severity.

This cross-sectional study was conducted in 2021-2022 on patients with oral lichen planus referred to the Department of Oral and Maxillofacial Diseases, Faculty of Dentistry, Mashhad University of medical Sciences, Iran. Patients’ mental health  were assessed using the GHQ-28 questionnaire and Data were analyzed using the SPSS software through descriptive statistics and statistical tests.

In examining the mental health of the patients, the results show that 67% of the patients had a negative GHQ and their mental health was not impaired. In 33% of patients, 24% mild, 7% moderate and 2% severe mental health disorders were found, which was not significant according to the age and gender of the patients. The mental health of the patients had no significant relationship with the severity of the lesions (p = 0.285). Also, 42 patients with lichen planus, despite having symptoms such as pain and burning, did not have any disorder in their mental health, and the symptoms of the disease had no significant relationship with their mental health. )p =0.713)

In the current study, 33% of patients with lichen planus had mental health disorders, but age, gender, pain and burning mouth, clinical appearance, and severity of lesions did not affect the mental health of patients.

The aim of this study is to evaluate concept of periodontists and general dentists about scope of periodontics.

In this cross-sectional- descriptive analytical study, at first a questionnaire in obligatory ranking method was designed, then 199 general dentists and 33 periodontists were selected with stratified sampling in Isfahan city and a questionnaire was given to each of them to evaluate their concept. Then the questionnaires were collected and the data were analyzed using SPSS 20 software, t-test and Pearson correlation test.

The most important statements in general dentists and periodontists were "promote oral and dental hygiene using information to prevent gingival and periodontal tissue diseases", "retain oral health by removing calculus and plaque", "treat infections and advanced gingival and periodontal disease surgically" respectively and the least important statement was "application of laser" and the most and least important statements in both were similar.

Concepts of general dentists and periodontists were similar to each other and both groups consider instruction and prevention more important than treatment, and treatment more important than regeneration procedures and they also consider activities which is doing for retaining natural dentition functionally and in healthy condition, more important than replacement of natural teeth with implants and both groups believe in remaining periodontics on its main aim which is to retain normal periodontium with natural dentition.

The design and manufacture of dental restorations with the help of milling machines has developed at a high speed since their introduction and offers more precision and options. The paradigm shift from traditional techniques to CAD/CAM technology has created a revolutionary change in the methods for fabrication of restorations. Modern milling machines dedicated to dental care are kinematic structures that work in 4 or 5 axis and represent one of the key parts of CAD/CAM. 4-axis and 5-axis machines are guided by the feed angle control and the direction of the milling cutter, which depends on the contact surface between the cutting tool and the block being turned, enabling a higher quality of surface integrity. The purpose of this review article is to investigate the types and applications of milling machines in dentistry.

This review study was conducted using the electronic version of articles available in the search engines PubMed and Google Scholar from 2000 to the end of 2024 using the keywords milling machine, CAD/CAM, 5-axis milling machine, 4-axis milling machine. All articles were in English and finally 32 articles were selected and reviewed.

Milling machines are available both for dental offices and general dental laboratories and for industrial dental laboratories. These machines increase the precision and quality of dental restorations. Restorations prepared by milling machines provide better results than conventional methods in terms of mechanical strength in chewing and aesthetics.