Journal of Dental Medicine

Facial prognathism, which is a problem in some orthodontic patients, is characterized by a number of cephalometric changes. Most clinicians use SNA angle in lateral cephalometric analysis to evaluate the amount of maxillary prognathism. Since SNA angle is not a reliable measurement for maxillary prognathism, and taking into account that the amount of prognathism changes in relation to cranial anatomy, according to Bjork it's better to measure the facial prognathism by the angle between anterior and posterior cranial base. According, two angles are recommended NSBa and NSAr.In this study 80 lateral cephalograms from three malocclusion groups, were studied and the amount of maxillary prognathism in relation to SNA and NSAr angles and their relationship to each other were measured.

The results were as follows:
1- Studying facial prognathism in relation to SNA and NSAr angles it was found that SNA angle is influenced by cranial base shape
2- The mean value of anterior and posterior cranial bases didn't show significant differences.
3- The mean value of SNA angle didn't show significant statistical difference in various malocclusion groups.
4- The correlation coefficient of ANB angle and wit's measurement is low.

Background and Aim: Achieving adhesion between restorative materials and dentin as a wet and dynamic surface is an important topic in restorative and especially in conservative dentistry. Adhesion of new dentin bonding systems depends on the formation of hybrid layer and micromechanical retention. Nevertheless, an ideal adhesive system has not yet been introduced .Recent studies reveal an increase in bonding stability when the collagen is removed from demineralized dentin surfaces. This study investigates the effect of collagen removal on the shear bond strength of four single bottle dentin bonding systems regarding their structural differences.

Materials and Methods: This experimental study was performed on 56 intact human premolar teeth. Smooth surfaces of dentin were prepared on buccal & lingual aspects of teeth, providing 112 dentin surfaces. The dentin surfaces were etched with 37% phosphoric acid for 15 seconds and then rinsed. The specimens were divided into 8 groups. Single bottle adhesive systems [Single Bond (3M), One-Step (Bisco), Prime & Bond NT (Dentsply), and Excite (Vivadent)] were then applied on the dentin surfaces of 4 groups using the wet bonding technique. In the other 4 groups, the demineralized dentin surfaces were treated with a 5.25% solution of sodium hypochlorite for one minute in order to remove the surface organic components. The adhesive systems mentioned before were applied to these 4 groups with the same wet bonding technique. A cylinder of Z100 (3M) dental composite with a 3 mm diameter and 2 mm height was placed on the adhesive covered dentin surface of all groups and light-cured (400 mW/cm2 ,40 sec on each side). The specimens were kept in distilled water at room temperature for one week and then thermocycled for 3000 times (5-55 oc). Shear bond strength of specimens was measured using an Instron (1495) universal mechanical testing machine with cross-head speed of 0.5 mm/minute and chisel form shearing blade. Data were analyzed by Two Way ANOVA and Tukey HSD tests with p<0.05 as the limit of significance.

Results: The mean & standard deviation of shear bond strengths (in Mpa unit) of all groups were as follows: One-Step = 19.60 1.83 One-step +H = 19.72 2.01 Single Bond =21.44 3.94 Single Bond +H =18.26 2.85 Prime&Bond NT=26.51 5.02 Prime&Bond NT+H =26.98 5.70 Excite =29.78 3.85 Excite +H =19.07 9.94 Analysis of the results revealed that the use of 5.25% sodium hypochlorite for one minute on the surface of demineralized dentin significantly decreased the shear bond strength of Excite and Single Bond (P<0.05). For Prime & Bond NT and One-Step, shear bond strength increased with this treatment but was not statistically significant (P>0.05).

Conclusion: Based on the results of this study, collagen removal from demineralized dentin surface caused a significant decrease in shear bond strength of alcohol & water/alcohol based bonding systems, while the bonding strength of the acetone based systems was not affected. Therefore, the effect of collagen removal on shear bond strength depends on the bonding system applied and its solvent type.

Background and Aim: Nowadays, esthetic dentistry has become an important part of modern dentistry. Bleaching is considered as a conservative, safe and effective way for treatment of discolored teeth. Although bleaching is commonly used on anterior teeth, the bleaching gel may come into contact with patient's former amalgam restorations and result in corrosive effects, dissolution of amalgam phases and increasing release of mercury. Mercury released from dental amalgam during mouthguard bleaching can be absorbed and increase the total mercury body burden. The aim of this study was to determine the amount of mercury released from Iranian and foreign brands of amalgams with spherical and admixed particles, polished and unpolished, after 16%carbamide peroxide gel application.

Materials and Methods: This experimental in vitro study was performed on 256 Iranian and foreign amalgam samples with spherical and admixed particles. The provided samples were put in distilled water and classified according to the type of amalgam, shape of particles and quality of surface polishing. The test samples were placed in Nite White 16% carbamid peroxide gel and control samples were put in phosphate buffer (Ph=6.5) for 14 and 28 hours. The amount of released mercury was calculated using AVA-440 Mercury Analysis System (Thermo Jarrell Ash model SH/229) with cold-vapor atomic absorption. Data were analyzed using t-test, four way and three way ANOVA tests with P<0.05 as the level of significance.

Results: 16% Nite White carbamide peroxide gel caused a significant increase in amount of mercury released from amalgams in all groups (P<0.05). Mercury release from Iranian amalgam was higher than that from the foreign brands (P<0.05). There was no significant difference in mercury released from spherical and admixed amalgams (P>0.05). The amount of mercury released from Iranian and foreign amalgams was time dependent (P<0.05). Furthermore, the amount of mercury released from unpolished amalgams was higher than polished ones (P<0.05).

Conclusion: The present study indicated that exposure of amalgam to 16% Nite White carbamide peroxide  gel causes a significant increase in mercury release from the amalgam which is significantly influenced by the brand, exposure time, and surface polishing.

Background and Aim: Oral health is a sign of overall health. Sometimes fear of dental office deprives  patients from receiving proper care. This problem decreases the self-esteem of dentists and can also reduce health indices. Understanding anxiety factors may help solve this problem. The purpose of this study was to assess anxiety in patients undergoing treatment in dental offices in the city of Hamedan.

Materials and Methods: In this analytic cross sectional study patients above 9 years old and referred to general dental offices in Hamedan were randomly selected and surveyed with questionnaires in two stages. The first questionnaire included 17 standard items based on Dental Anxiety Scale (DAS) and screened anxious patients. Then 400 anxious patients were evaluated with a questionnaire of 64 items based on Corah scale. Data were analyzed by SPSS 13 with multivariate analysis of variance. P<0.05 was considered as the level of significance.

Results: Factors related to dental office environment with 31.1%, those related to personal imaginations with 19.4% and factor concerning office management and dental treatment each with 19.1% frequency showed to be most related to anxiety in patients. Improper rest-rooms (46.3%), blood stains in the environment (44.5%) and dirty dentist's gowns (43.8%) were reported to be the most prominent environmental factors. Among the factors originated from personal imaginations, the risk of disease transmission was accounted for the most justifiable source of anxiety (67.3%). Regarding factors concerning office management, dentist's nervous behavior (47.8%) and his carelessness to the patient (46.8%) were considered as the most significant anxiety sources. Extraction, injection and root canal therapy (48.3%, 44.5%, 44.3%) were the treatment related factors of higher importance respectively. Previous painful treatment experience (47.3%) and poor oral hygiene of the dentist (34.5%) were reported to be among the other justifiable anxiety sources. In all mentioned situations, variations in anxiety factors were significantly higher in women.

Conclusion: This study showed that the main cause of anxiety in patients undergoing treatment in dental offices in Hamedan is their personal imagination which is by far more obvious in women than men.

Background and Aim: A considerable percentage of failure in Endodontic treatments in maxillary molars is attributed to undiscovered second mesiobuccal canal (MB₂).There are different methods for discovering and accessing to this canal. The purpose of this ex vivo study was to compare the detection ability of three methods (direct look, fiberoptic loup and surgical microscope) to find MB₂ after troughing with ultrasonic.

Materials and Methods: In this experimental study, we selected 90 extracted maxillary molars (45 first and 45 second molars) in which after access cavity preparation MB₂ canal was not discovered by direct vision and endodontic explorer. They were divided into 3 groups (n=30). The dentinal shelf between mesiobuccal and palatal canals was eliminated by an endodontic ultrasonic tip (troughing). After that, first group was searched by direct vision, second group by a loup and fiberoptic light and third group by dental operating microscope. Data were analyzed, specificity and sensitivity were calculated.

Results: The results showed that 21%, 61%, and 92% of MB₂ canals after troughing was found by direct vision, fiberoptic loup, and surgical microscope, respectively.

Conclusion: Based on the results of this study, surgical microscope and loup with fiberoptic are preferred methods for discovering MB₂ canal. Troughing with ultrasonic can help find MB₂ canal in all methods.

Background and Aims: Freestanding fixed partial prosthesis is considered the first choice whenever possible. However, anatomical limitations for implants and other reasons may create situation in which it would be preferable to connect the implants to teeth. A biomechanical dilemma in a tooth/implant-supported system comes from dissimilar mobility. This disparity cause the bridge to function as a cantilever and a series of potential problems such as osseointegration loss, screw loosening arise. The aim of this study was to analyze the tooth-implant supported bridges in rigid/non-rigid connectors in cemented prostheses using finite element stress analysis.

Materials and Methods: In this study four three-dimensional models were simulated by use of Solid works software. These models are: 1-RCCP: rigid connector between tooth and implant, 2-NRC CP1: non-rigid connector at mesial side of implant, 3-NRC CP2: non-rigid connector at distal side of second premolar, 4-NRC CP3: non-rigid connector at the middle of pontic, The stress values of four models loaded with vertical forces (150 N) were analyzed.

Results: The maximum stress concentration was located at the crestal bone around implant and stress distribution was more balanced around the teeth except in the model of NRCCP2. Stress distribution was imbalanced in non-rigid connection especially in the NRCCP1 model. The presence of non-rigid connector in bridge increases the stress values in suprastructure and transfers to the adjacent structures. Conclusion: The tooth-implant supported prosthesis should be considered as a valuable prosthetic option. It could be suggested that if tooth and implant abutments are to be used together as fixed prostheses supports, rigid connector is the choice because the prosthesis and implant possess the inherent flexibility to accommodate dissimilar mobility characteristics.

Background and Aims: There is not sufficient knowledge about the relationship between smoking and vertical bone loss in periodontal diseases. There are also important evidences which propose harmful effects of smoking on periodontal tissues including alveolar bone. The purpose of this study was to assess the relationship between smoking and prevalence and severity of vertical bone defects.
Materials and Methods: This case-control study consisted of 71 individuals with angular bone defects (case) and 69 individuals without angular bone defects (control) between 18 to 70 years old. People were selected by radiography, examining and filling up the questionnaire. Vertical bone defect was defined as interproximal bone resorption to the extent of ≥2mm with a clear angel towards the Mesial or Distal of root. Data were analyzed using SPSS software.
Result: The mean age of studied individuals was 37.14 years (±12.72). Among people with angular bone defects, 21.1% were light smokers and 25.4% were moderate-heavy smokers. There was a significant difference between smokers and nonsmokers in terms of smoking status and the chance of having angular bone defects (P=0.001). Simultaneous study of the effect of sex, age, brushing and smoking status showed that except sex, other variables have a significant effect on angular bone defects. The chance of having angular bone defects in light and heavy-moderate smokers was more than that in nonsmokers (adjusted OR=4.17 and adjusted OR=3.87, respectively).
Conclusion: These observations propose that smoking is related to increase in prevalence and severity of vertical bone defects. Smoking is considered as a potential risk factor for vertical periodontal bone loss.

  Background and Aims: The aim of this descriptive longitudinal study was to determine the type of teeth that were more prone in accidental bracket debonding and also to investigate the relationship between broken bracket bond and intervening factors such as age, type of malocclusion and sex.

  Materials and Methods: We used a pilot study to determine the correct sample size for this study. According to the pilot study which consisted of 20 records of patients, it was concluded that 576 patient’ records was needed. The mean time for a bracket before it fails was also measured using Kaplan-Meier method. Cox regression analysis was done to examine the effect of age, gender, and class of malocclusion on each tooth with broken bracket. Data were analyzed using the software SPSS 20.

  Results: Results showed that the percentage of unexpected broken bracket bond for each tooth varied and they were significantly related only in second premolars in both jaws with malocclusion that was different for each tooth (P=0.037, P=0.004).

  Conclusion: Maxillary second premolars and mandibular second premolars had the highest rate of unexpected broken bracket bond in CL II CL I malocclusion respectively. Age, gender and malocclusion had no effect on the unexpected broken bracket bond for other teeth.

Background and Aims: Trauma to the teeth is a common problem that occurs in children. Avulsion is the one of the most complex dental damages that if be untreated can cause multiple problems. Since many of dental traumas happen in school and school health teachers have main role in children treatments, the aim of this study was to evaluate the primary school health teachers’ knowledge regarding the emergency treatment of avulsed permanent teeth.

Materials and Methods: In this cross-sectional study, after consultation training of education, all of the health teachers of elementary schools in Hamadan were selected through census sampling method and were given the regulation questionnaire. After completing the questionnaire, information was collected using software SPSS19. The data was analyzed using Fisher Exact, Kolmogrov Smirnov test, Chi-square, One way, Levenes test and
T-test.

Results: 81 Health teachers were studied and the ratio of knowledge score of all of health teachers to a maximum knowledge score was obtained to be 43/1%. There was no significant relationship between the school health teacher knowledge and their work experiences and age (P=0.23-0.6), respectively. Average of knowledge score of who were educated was more than who were not educated previously (P<0.001).

Conclusion: Primary school health teachers' knowledge of dealing with Avulsion was not at a high level. Therefore, training on the dental trauma cases is quite essential for them.