Journal of Islamic Dental Association of IRAN
Volume:25 Issue: 3, 2013

Panoramic radiography is the preoperative imaging technique of choice for impacted mandibular third molar surgery. However، controversy exists regarding the ability of panoramic radiography in determining the relationship of the mandibular third molar roots with the inferior alveolar canal. This study aimed to assess the ability of panoramic radiography in determining the relationship of mandibular third molar roots with the inferior alveolar nerve (IAN) canal.

This diagnostic accuracy study was conducted on 100 panoramic radiographs that were evaluated by 5 oral and maxillofacial surgery residents. They offered their expert opinion on the relationship of third molars with the IAN canal based on panoramic radiographs. These perspectives were compared with the actual post-surgical findings. Kappa and weighted Kappa reproducibility tests were used for data analysis.

Among 100 understudy cases، physical contact between the mandibular third molar roots and the canal was not observed in 88 cases intra-operatively; while this relationship existed in 12 cases. The panoramic radiography had a diagnostic sensitivity of 83. 3%، specificity of 83%، positive predictive value of 40% and negative predictive value of 97. 3%. The overall accuracy was 85%. Kappa and weighted Kappa coefficients of reproducibility were 61% and 79%، respectively.

Panoramic radiography can be confidently used as the most reliable and commonly accessible imaging technique. Considering the obtained negative predictive value، panoramic radiography is capable of revealing the involvement of third molar roots with the IAN canal with 97. 3% accuracy. Panoramic radiography had a low diagnostic value in determining the morphology of roots.

The ability of DIAGNOdent (DD) for detection of occlusal caries under sealant and its reproducibility is a matter of question for dentists. The aim of this study was to evaluate DD values before and after the application of opaque fissure sealant (FS) and to determine the reproducibility of DD for detection of occlusal caries under sealant. This study was carried out on 42 extracted sound human premolar and third molar teeth. Two examinersassessed the deepest occlusal pit of teeth with DD Pen (Kavo، Germany). This evaluation was repeated one week later to assess DD reproducibility. Assessment with DD was also performed after acid etching and FS application. The results were recorded and analyzed using linear regression test and SPSS software. The intra-examiner reproducibility of DD was 75. 49% and 77. 56% for the first and second observers، respectively. The mean DD value after etching and FS therapy increased by 28 and 6 units، respectively. DD has high reproducibility making it suitable for the monitoring of occlusal caries. However، DD value is influenced by the opaque sealant and thus، it should not be used as the sole device for detection of caries under sealants.

Due to the widespread use of lateral cephalometric radiography especially in orthodontic therapy and orthognathic surgery، obtaining radiographs of high quality with the least amount of radiation exposure is of utmost importance. The aim of this study was to compare the absorbed dose of head and neck target organs in conventional and digital lateral cephalometric radiography. In this experimental study، RANDO phantom was used for absorbed dose estimation in thyroid، parotid، pituitary and submandibular glands، bone marrow and ocular lens. The phantom was exposed 60 times: 30 times with CRANEX Tome، Soredex and 30 times with CRANEX D، Soredex with standard exposure settings. TLD (GR-200) dosimeters were used to measure organ doses. A total of 69 TLDs were used with 9 TLDs for background radiation. T-test was used for statistical analysis. The mean absorbed dose of target organs was 0. 04±0. 005 mSv for conventional and 0. 01±0. 002 mSv for digital technique. The difference in absorbed dose in all target organs except for the thyroid gland (P=0. 08) between the two techniques of conventional and digital was statistically significant. (P=0. 01). Use of digital lateral cephalometric system causes a significant reduction in absorbed dose compared to the conventional film-screen system

Mineral Trioxide Aggregate (MTA) has a high clinical success rate when used as the apical plug. The conventional method of using MTA as an apical plug is doneduring two treatment sessions. This study aimed to evaluate the possibility of complete filling of root canal with gutta percha and AH26 sealer immediately after the placement of MTA plug. A total of 88 single-rooted teeth were selected for this experimental study. The teeth were prepared and randomly divided into two groups of 40 each. Four teeth were considered as the positive control group and the remaining 4 as the negative controls. In group 1، MTA apical plug was placed، specimens were stored in saline solution for 24h and then filled with gutta percha and AH26 sealer. In the 2nd group، the roots were filled immediately after the placement of MTA. In the positive control group، the root canals were left unfilled and in the negative control group، root canals were filled with gutta percha and sealer. The specimens were then immersed in 1% methylene blue، demineralized in 5% nitric acid and cleared in methyl salicylate. Dye penetration was measured by a stereomicroscope in micrometer. T-test was used for statistical analysis. The mean dye penetration was 7813 μ m in the first and 9152 μ m in the second group. According to t-test، the 2nd group had significantly greater microleakage than the first group (P<0. 05). MTA needs to be exposed to moisture for final setting and root canal obturation must be delayed until complete setting of MTA.

Since the use of rotary nickel titanium instruments is an essential part of endodontic treatment، itis important to compare the root canal cleaning ability of these instruments. The aim of this study was to compare the amount of smear layer and debris remaining following the use of four rotary instruments: MTwo، Pro Taper، Race and BioRaCe. A total of120 mesiobuccal canals of extracted human first molars with apical root curvature of 10 ° to 20 ° were selected. Working length of all roots was 19 mm. The roots were randomly divided into four groups of 30 specimens. After the preparation of access cavity، the roots were instrumented using rotary instruments according to the manufacturer’s instructions. After each file، the root canal was irrigated with 2. 5%sodium hypochlorite. Then the roots were studied under scanning electron microscope. The smear layer and debris scoreswere evaluated by 2 endodontistsusing Schafer and Schlingemann classification. Kruskal -Wallis and Dunn tests were used for statistical analysis of results. The amount of smear layer produced by MTwo was lower than the other instrumentation techniques and it was significantly lower than that inBioRaCe system (p<0. 05). The amount of debris was also lower in the mentioned group but the difference in this respect between groups was not significant. BioRaCe system had the highest level of remained smear layer while Pro Taper had the highest amount of remained debris. Within the limitations of this study، it was revealed that MTwo instruments had greater capability of removing smear layer and debris than theBioRaCe system.

Several studies have evaluated the effect of microwave radiation on physical properties of acrylic resins. However، due to the recent introduction of heat-cure and cold-cure acrylic resins into the dental market and rapid popularity of cold-cure resins with less distortion in denture base، the present study sought to assess the effect of microwave disinfection on dimensional stability and flexural strength of two recently introduced heat-cure (Ivoclar) and cold-cure (FuturaGen) acrylic resins. In this laboratory study، acrylic models were fabricated of an edentulous maxillary model using Ivoclar and FuturaGen acrylic resins. Three reference points were marked on the model: two in the back and one in the front of the edentulous arch. These reference points were used for the measurement of dimensional stability in the anteroposterior and cross-arch dimensions. Ten specimens of each acrylic resin were not disinfected. Ten samples were subjected to two 3 min cycles of microwave disinfection with 600 watt power. Distances between the reference points were measured by a Profile Projector. To evaluate flexural strength، a metal mould measuring 64x10x3. 3 mm was used for the fabrication of resin specimens. Similar to what was done for dimensional stability testing، 10 specimens of each acrylic resin were not disinfected and 10 other samples were subjected to 3-point bending test after disinfection. Data were compared and statistically analyzed using Mann-Whitney U test. The mean difference in anteroposterior and cross-arch dimensions revealed that two cycles of microwave disinfection of Ivoclar and FuturaGen acrylic resins did not have a significant effect on their dimensional stability (P>0. 017). The mean and standard deviation of the flexural strength of FuturaGen acrylic resin before and after disinfection was 76. 86±16. 80 and 70. 18±8. 48، respectively. These values for Ivoclar acrylic resin were 85. 92±12. 23 and 81. 91±6. 59، respectively. Two cycles of disinfection with microwave did not cause a significant effect on flexural strength of the two understudy acrylic resins (P>0. 05). Two cycles of microwave disinfection had no negative effect on dimensional stability or flexural strength of FuturaGen and Ivoclar acrylic resins.

Solubility is among the negative characteristics of dental materials leading to structural degradation of cements and decreased longevity of restorations. The present study sought to assess the water sorption and solubility of FujiCem resin-modified glass ionomer (RMGI) and G-Cem self-adhesive resin cement in water and acid.

In this experimental study، 5 discs were fabricated from each understudy cement for solubility testing in lactic acid and 5 other disc-shaped specimens were made for evaluation of water sorption and solubility. Specimens were immersed in distilled water for 7 days and immediately weighed afterwards (M2). Discs were then transferred to a desiccator again to reach a constant weight of M3. Water sorption and solubility were calculated using the respective equations. For acid solubility testing، specimens were immersed in lactic acid for 24h. Independent t-test was applied for statistical analysis of results.

Solubility in distilled water was 0. 0000139±0. 0001μg/m3 for FujiCem and 0. 0000016±0. 000005μg/m3 for G-Cem (P=0. 480). Water sorption was 0. 0000197±0. 000234 for FujiCem and 0. 0000025±0. 00004 for G-Cem (P<0. 001). Acid solubility was 0. 0059414±0. 0016 for FujiCem and 0. 0039115±0. 0016μg/m3 for G-Cem (P=0. 348).

The two understudy cements had no significant difference in water or acid solubility but FujiCem RMGI showed greater water sorption than G-Cem self-adhesive resin cement.

Different techniques are employed for sealer placementinto the root canal system. The purpose of this study was to compare the percentage of voids following root canal obturation with gutta percha and AH26 sealer using four different sealer placement techniques.

In this laboratory experimental study، root canals of 50 mandibular second premolars were prepared using the step-back technique. The teeth were assigned to 4 experimental groups of 10 and one control group based on sealer placement technique. After sealer application and canal obturation with lateral condensation technique، specimens were horizontally cut into 3 mm slices. Sections were evaluated under a digital microscope at 150X magnification for void detection in apical، middle and coronal thirds. Kruskal Wallis and Bonferroni tests were applied to compare the percentage of voids between different groups.

No significant difference was found in void percentage in one-thirds or total sections between the four methods (P=0. 276).

Overall، no significant difference was noted in void percentage between the four techniques of sealer placement.

Restoration of deepdental caries without pulp exposure is usually challenging for dentists. In order to prevent pulp exposure and subsequent root canal therapy (RCT)، indirect pulp capping is usually performed. Stepwise excavation (SE) is a conservative method that canreduce the incidence of pulp exposure and maintain tooth vitality without the need for RCT. Considering the high prevalence of dental caries among the Iranian population، knowledge about this treatment modality canbe beneficial for dentists. Case report: A 23 year-old patient with three deep carious lesions presented toour dental clinic. The teeth had normal responses to thermal tests and percussion. Due tothehighrisk ofpulp exposure following conventional complete excavation of caries، stepwise excavation treatment was done. Three different lining materials (calcium hydroxide، MTA، CEM cement) were used to cover the remaining caries. The teeth were restored using posterior restorative glass ionomer (Fuji9، GC، USA). The teeth were followed weekly inthe first month and then every six months up to 30 months clinically and radiographically. At30-month follow-up، the teethdid not show any sensitivity to cold or percussion،had no spontaneous nocturnal painor irreversible pulpitis symptoms and did not need RCT; these signs were all indicative of asuccessful treatment.

Use of panoramic radiography in some cases is easier and more cost-effective than other radiographies. However، it has some limitations as well. Considering the importance of radiography in dentistry، the present study sought to assess the consistency of selection of panoramic radiography by general dentists in Tehranwith FDA guidelines during 2010-2011.

In this descriptive cross-sectional study، 500 general dentists were selected using randomized cluster sampling and evaluated by a questionnaire. The questionnaire asked for demographic data and had 27 questions regarding the selection criteria for panoramic radiography. Dentists had the following answer choices for each criterion: “Strongly leads to prescription”، “probably leads to prescription”، “has no effect on prescription”، “probably prevents prescription” and “strongly prevents prescription”. The answers were collected and descriptively analyzed. To evaluate the effect of different factors on dentists’ answers، binary logistic regression with enter method was used.

Of the understudy dentists، 44% were females and 56% were males with a mean age of 36. 84 yrs. Based on the results of regression analysis، panoramic radiography was prescribed by dentists in case of concerns regarding the carcinogenicity of radiation، good oral hygiene and for evaluation of growth and development before the age of 6 which are not in accord with the FDA guidelines. Also، for primary assessment of periodontal status، poor oral hygiene، disseminated pain، determination of alveolar crest height in the anterior region and pregnancy، panoramic radiography was prescribed by dentists which is completely in agreement with the FDA guidelines (P<0. 05).

Easy application of panoramic radiography and its accessibility were the reasons for its prescription in 55. 5% and 47. 6% of cases، respectively. Some reasons of prescription were in accord with the FDA guidelines while some others were in contrast to them.

Composite resins require time to complete their polymerization. This process usually reaches its maximum rate after 24 hours. On the other hand، immediately after restoration، water sorption results in hygroscopic expansion of composite resins and the mentioned two factors usually reachequilibrium after a week. Considering the effect of mentioned processes on the microleakage of composite restorations، the purpose of the present study was to evaluate the effect of finishing and polishing time on the mean microleakage of composite restorations. In this in-vitro experimental study، 60 sound human premolar teeth were selected. A standard Class V cavity was prepared measuring 1. 5 mm in depth، 3 mm in width and 2 mm in length on the buccal surface of each tooth and incrementally restored with composite resin. Next، the teeth were randomly divided into 4 groups. The teeth in groups 1، 2، 3 and 4 were finished and polished immediately، 15 min، 24 h and one week after storage in distilled water at 37°C، respectively. Specimens in each group were subjected to 500 thermal cycles. The teeth were then coated with adhesive wax and nail varnish and immersed in 2% fuchsin solution for 24h. The specimens were washed and each sample was longitudinally sectioned in half by a diamond saw. Both halves were evaluated in terms of dye penetration under a stereomicroscope at 28X magnification. For each sample، the section with greater degree of microleakage was selected. Kruskal Wallis test and Mann Whitney U test were used for data analysis with a 99. 1% confidence interval. The lowest mean microleakage was observed in the occlusal margin of group 3 teeth; while the highest mean microleakage belonged to the occlusal and gingival margins of teeth in group 2. A significant difference was noted between the 4 groups in occlusal margin microleakage (P<0. 009). However، no such difference was found in gingival margin. This study showed that the finishing and polishing timewas effective on the mean microleakage in the enamel margin of composite restorations. The best time of finishing and polishing was 24h after the restoration. Time of finishing and polishing had no effect on microleakage in dentin margins of restorations.

Estimation of the survival of dental materials is especially important when manufacturing new materials. Thermocycling can greatly help in this respect. The purpose of this study was to evaluate micro-shear bond strength of a nanofiller bonding with and without thermocycling in a newly invented device.

In this experimental study، human third molars were sectioned into 1. 5 mm slices after extraction and disinfection. Clearfil Tri-S nanofiller bond was applied to the dentin part of sections according to the manufacturer’s instructions. Clearfil AP-X composite resin was placed over the dentin using tubes with 0. 75 mm internal diameter and one mm height and light cured. Specimens were randomly divided into three groups and subjected to thermocycling in a newly invented device for zero، 3000 and 5000 cyclesbetween 5±2°C and 55±2°C. Micro-shear bond strength was measured by microtensile tester with a cross-head speed of 0. 5 mm/min. Obtained data were analyzed using one-way ANOVA. Tukey’s test was used for multiple comparisons with a 95% confidence interval.

The mean micro-shear bond strength after zero، 3000 and 5000 thermal cycles was found to be 19. 27±4. 56، 17. 00±6. 52 and 11. 58±4. 64 MPa، respectively. The reduction in bond strength between zero and 3000 thermal cycles was not statistically significant (P=0. 3) but this reduction between zero and 5000، as well as 3000 and 5000 cycles was statistically significant (P<0. 002 and P<0. 03، respectively).

Increase in number of thermal cycles for more than 3000 reduces the micro-shear bond strength of Tri-S bonding agent.