Journal of Dental Medicine

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Statement of Problem: Computer Sciences, in radiology, like other fields, is of high importance. It should also be noted that the accuracy of the technique and work conditions affects the radiographs information considerably. There for, in order to get more accurate diagnostic information, it seems necessary to investigate different digitized radiographic techniques and to compare them with the conventional technique.
Purpose: The aim of this study was to compare the accuracy of conventional and digitized radiographic images by three digitization techniques in proximal caries detection.
Material and Methods: In this research study, sixty extracted human canines, premolars and molars were mounted in blocks and imaged on E-Kodak film, similar to bitewing radiographs. Ten bitewing radiographs were then scanned at 600 d.p.i with flat bed scanner and a digital camera, then digitized at 300 d.p.i with another digital camera. The digitized images were displayed randomly on a high-resolution monitor. Six
observers assessed the caries status of 120 proximal surfaces by conventional and digitized images. The observer's scores were compared with the results of the macroscopic examination. Reliability of each technique was calculated. Data were analyzed using chi-square and ANOVA tests.
Results: No significant differences were detected between different techniques in intact proximal surfaces and enamel caries diagnosis. However, digital techniques were more sensitive in dentin caries detection (P<0.05).
Conclusions: When conventional film images are digitized, medium resolution (300 d.p.i) seems to be sufficient. At this resolution the file size is decreased and there is no significant loss of the information necessary for caries diagnosis.

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Background and Aim: Preserving canal curvature during different phases of canal preparation is an important point. In Endodontic therapy all efforts are made to prepare canal in a way that final canal follows the primary canal curvature. The purpose of this study was to evaluate the efficacy of root canal preparation performed by students at Endodontic Department of Dental School, Tehran University of Medical Sciences.

Materials and Methods: In this retrospective study, classic method of step- back technique was investigated for preserving canal curvature in mesial roots of first mandibular molars and mesiobuccal roots of first maxillary molars between years 2000 and 2004. A randomly selected sample of 400 dental patient records was investigated by 4 observers (Endodontic department professors), searching for procedural errors. A clear explanation sheet of curvature preservation and procedural errors such as ledge formation, apical foramen transportation, zipping and stripping and a questionnaire were prepared for observers. The observers went through reliability test and kappa value for agreement between every two observers. The results were above 0.8. Data were analyzed by EPI6 statistical computer program, using Chi-Square and Fisher exact test with P<0.05 as the limit of significance.

Results: This study consisted of 152 first maxillary molars and 248 first mandibular molars. The prevalence of curvature preservation in mesial root of first mandibular molars and mesiobuccal root of first maxillary molars were 38.5% and 47.6% respectively. Procedural errors detected consisted of 33% ledge formation, 26.1% apical foramen transportation, 1.8% zipping and 4.1% stripping for mesial root of the first mandibular molars. The results for the first maxillary molars were 27%, 19%, 3.2% and 3.2% respectively.

Conclusion: The study results revealed the efficacy of endodontic education and the proficiency of junior and senior students in preparing curved posterior root canals. The results obtained in this retrospective study are comparable to prospective studies.

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Background and Aim: Many methods and techniques of canal preparation work well in large and relatively straight canals. However, in severely curved canals, the complexity increases markedly, and techniques rendering good results in usual cases may be unsuccessful. The aim of this study was to compare the effect of five root canal preparation techniques on original canal anatomy in simulated severely curved canals.

Materials and Methods: In this experimental in vitro study, 100 simulated canal blocks with similar hardness were made from polyester. The degree of curvature was 45º with a radius of 2.55 mm and a straight part of 8mm. The blocks were prepared with five different techniques (20 canals in each group) as follows: 1-Stepback 2- Passive step back 3- Balanced force using flex-R files 4- Balanced force using Ni-Ti hand instruments 5- Hybrid using a rotary Ni-Ti system (XtremRace). Digital photographs were taken from pre- and post instrumentation colored canals. Then images were superimposed and analyzed by an image editing software. The amount of removed material from the inner and outer canal walls was measured at five levels: 1-The canal orifice (O) 2-The halfway between the orifice and the beginning of the curve (HO) 3-The beginning of the curve (BC) 4-The apex of the curve (AC) and 5-The endpoint of preparation (EP). Additionally, the time of instrumentation, instrument failure and changes in working length were recorded. Data were analyzed by ANOVA and Kruskall-Wallis tests with p<0.05 as the limit of significance.

Results: Mean transportation was towards the outer aspect of the curve at the EP in all canals but there were no significant differences between the studied groups. At the BC point, all of the canals were transported towards the inner aspect of the curve and there were significant differences for both transportation values & direction among different groups. The highest amount of transportation was in step back and the lowest, in hybrid group. The highest transportation value was in step back and the lowest in balanced force group. Fractured and deformed instruments were observed in Flex-R files. The shortest canal preparation time was seen in XtremRace and the slowest, in Passive step back groups (P<0.001).

Conclusion: Based on the results of this study, changes in canal curvature were less with techniques using nickel titanium instruments and the fastest technique with least transportation was XtremRace.

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Background and Aims: The aim of this study was to evaluate the effect of zirconia and base metal cores on the color of restorations. Furthermore, the effect of different backings on the color of cercon zirconia was evaluated.
Materials and Methods: The specimens were Cercon zirconia and metal ceramic discs with "high Au" and "base metal" alloys. Cercon zirconia discs were veneered with veneering shade of A2 and two thickness of porcelain (0.7 mm, 1.2 mm). There were 3 discs in each group. Metal ceramic discs were made of "nickel-chromium" alloy (Verobond) and "high Au" alloy (World 89) and two shades (A2, A3.5) and two thicknesses of veneering porcelain. 3 types of backing (high Au, nickel-chromium and A3 shade composite) were made for Cercon zirconia discs. Spectrophotometric evaluation of zirconia discs (on 3 backings) and metal ceramic discs was done. One-way ANOVA and Tukey tests were used for data analysis.
Results: There were no significant differences between the amounts of L*, a*, b* for Cercon zirconia on different backings (P>0.05). In comparison between different core groups, a* was significantly higher in metal ceramic groups compared with that of zirconia groups (P<0.05).
Conclusion: Cercon zirconia can completely mask the underlying backing.

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Background and Aims: Regarding the diversity of reported low- back pain among dentists in different countries and lack of control group in most of the previous studies, the purpose of this study was to compare low- back pain and related risk factors between male general dentists and pharmacists to determine the relation between dentistry and development of low back pain.

Materials and Methods: In this cross-sectional study, 261 male dentists were compared with 193 male pharmacists as a control group with Standardized Nordic Questionnaire (low back section). Subjects were at least one year in clinical practice after becoming qualified and did not suffer from connective tissue diseases and history of a traumatic event causing fracture in spinal column. The data were analyzed by Chi- square, T-test and logistic regression analyses.

Results: The prevalence of low back pain in the past 12 months was 54.8% in male dentists and 36.3% in male pharmacists (P=.001). Logistic regression analyses, adjustmenting for occupation, age, body mass index (BMI), smoking, working years and working hours per week, revealed that there was a significant association between being a dentist and having low- back pain (OR=2.54, P=0.001).

 Conclusion: Dentistry as a profession in male gender is associated with low back pain, independent of age, body mass index (BMI), smoking, working years and working hours per week.