Journal of Dental Medicine

Erratum

S. Arami

NO Abastract ####

Evaluation and comparison of mesiodistal inclination of posterior teeth in skeletodentalclass II and class I

SMH. Hosseini

Background and Aims: The main purpose of orthodontic treatment is normal positioning of teeth in three dimensional plans, including the mesiodistal inclination. In this study, mesiodistal axial inclination of posterior teeth in skeletal class II was evaluated and compared with that of posterior teeth in skeletal class I.

Materials and Methods: Seventy-eight panoramic radiographs for subjects between 12 to 24 years old with skeletal class I and 78 panoramic radiographs for subjects between 12 to 19 years old with skeletal class II were selected. All of the subjects were in permanent dentition with no tooth missing, no tooth extraction, no impacted tooth, and no crowding in posterior teeth. Two reference lines were established over each radiograph: the upper one passing through the most inferior point of right and left orbits lower one passing through the right and left mental foramina. After that, the long axis of teeth was traced (the image of root canal in single-rooted teeth, mean image of buccal and palatal canals in upper premolars, mean image of mesial and distal canals in lower molars, and the image of palatal canal in upper molars.). The mean values for two skelotodental classes were analyzed using T-test.

Results: The results showed that there was significant difference between (P<0.05) mesiodistal axial inclination of teeth 15, 16, 17, 25, 26, and 27 in upper jaw in skeletal class II compared with that of the same teeth in skeletal class I, which was more mesially in skeletal class II. Mesiodistal axial inclination of teeth 36, 46, and 47 in lower jaw was more mesially in class II compared with that of the same teeth in class I. For other teeth there were no significant differences between two skeletodental classes (P>0.05).

Conclusion: The mesiodistal axial inclination of upper molars and second premolars and lower molars in class II was more mesially compared with that of the same teeth in class I.

Pre-implant linear tomography using film-screen and Photostimulable Phosphor Plate in mandible

M. Mirzaey

Background and Aims: Radiographic examination prior to implant placement is often complemented with tomography for location of vital anatomic structures and evaluation of bone volume. The aim of this study was to evaluate the accuracy of Photostimulable Phosphor Plate system with that of conventional film-screen in mandibular pre-implant linear tomography

Materials and Methods: In this test evaluation study, tomograms of 2 dry human mandibles were taken using the both film-screen and Photostimulable Phosphor Plate. 10 sites were selected in each mandible and marked with gutta-percha. Distance of superior border to the mandibular canal and the total height and width of mandible were measured on the tomograms and also on the mandibles after sectioning. The radiographic values were compared with real ones.

Results: After correction of tomographic values by the magnification factor of the unit, the mean of absolute differences with reality in linear tomography using film-screen and Photostimulable Phosphor Plate for height of mandible were 0.59mm (SD=0.54) and 0.65mm (SD=0.72), respectively. The mean of absolute differences with reality in linear tomography using film-screen and Photostimulable Phosphor Plate for width of mandible were 0.34mm (SD=0.33) and 0.31mm (SD=0.33), respectively. In localization of the mandibular canal, the mean of absolute differences with reality were 0.54mm (SD=0.30 ) and 0.52mm (SD=0.56) for linear tomography using film-screen and Photostimulable Phosphor Plate, respectively. In linear tomography using film-screen, 100% of measurements for localization of the canal, 80% of height and 95% of width were with in ± 1mm error limits. In linear tomography using Photostimulable Phosphor Plate, 75% of measurements for localization of the canal, 75% of height and 95% of width were within ± 1mm error limits. There was no significant difference between linear tomography using film-screen and Photostimulable Phosphor Plate in localizing the mandibular canal and height and width estimation (P>0.05).

Conclusion: The accuracy of linear tomography using film-screen and Photostimulable Phosphor Plate in height and width estimation and localization of the canal is within acceptable limits.

Evaluation of the effect of the ergonomic principles’ instructions on the dental students’ postures an ergonomic assessment

S. Yaghobee

Background and Aims: Musculoskeletal disorders in dentists due to abnormal postures may result in economic and health problems. To prevent these problems, the working posture of dental students should be assessed and corrected in dental procedures. This study determine these problems and the effect of training courses on them by Rapid Entire Body Assessment method (REBA).

Materials and Methods: The posture of 69 students were assessed by REBA before and after of the “Ergonomic principles in dentistry” course. The subjects which were used in the training course were based on the previous studies on this issue. The REBA scores were assessed by SPSS software using Paired T-test.

Results: The results showed that the students’ posture should be corrected. Postures of 94.2% of students were in moderate and high risk level which needed to be corrected. The worst working positions were during surgery, endodontic and pediatric dentistry procedures. Although the REBA scores before and after training course were statistically different (P<0.05), the training did not improve the posture of students remarkably.

Conclusion: The students’ working postures should be improved. One-day ergonomic principles course improved the working posture of students but it was not sufficient. More training and instructions are needed to have a good working position in dental procedures.

A scanning election microscopic study of the effect of primer on sealant penetration in saliva contaminated enamel

A. Pahlevan

Background and Aims: Moisture contamination of etched enamel during application of sealant is the most frequently cited reason for sealant failure. In previous studies, some hydrophilic bonding agents have been shown to bond to etched enamel after salivary contamination. The purpose of this study was to evaluate the enamelsealant interface following the use of primer on the saliva contaminated and/or moist etched enamel.

Materials and Methods: 40 extracted human incisors were selected. The enamel surfaces were etched for 20 seconds with an acid gel and rinsed for 30 seconds and dried until chalky surface was observed. Teeth were randomly divided into four treatment groups (n=10). Sealant (Deguseal mineral, Degussa) was applied on (1) etched enamel surface as a standard control group, (2) in conjunction with using primer material on moist etched enamel, (3) in conjunction with using primer material on salivary contaminated etched enamel, and (4) on wet contaminated etched enamel surface as a negative control group. Then, the specimens were observed with scanning electron microscopy (SEM) at ×1400 magnification. To evaluate the enamel resin interface, the number of resin tags was counted. Data were analyzed using one-way ANOVA.

Results: The results showed that primer used on moist enamel under sealant had no significantly difference in number and shape of tags in comparison with standard group (P>0.05). Application of primer on saliva contaminated enamel surface under sealant significantly reduced the number of tags and changed the shape and pattern of tags (P<0.001). Following application of sealant on contaminated and etched enamel alone, no resin tags formed.

Conclusion: Application of primer relatively reduced sensitivity to saliva contamination but the pattern was changed and number of tags reduced. Therefore, primer application might be useful whenever the isolation is not possible. However, it should be emphasized that restrict isolation in sealant therapy is recommended.

A three-dimensional finite element analysis of peri-implant bone stress and strain distributionin All-on-4 design

SH. Borghei

Background and Aims: The All-on-4 design with its significant advantages is an appropriate model in reconstruction of edentulous mandible. Evaluation of stress and strain distribution in this model is necessary for better judgment. The purpose of this FEA study was to measure stress and strain distribution on peri-implant bone in All-on-4 design in edentulous mandible.

Materials and Methods: Three dimensional finite element model of human mandible was simulated according to data from CT-Scan of a cadaver. The model of 4×13.5 mm Nobel Biocare implant was simulated. Posterior implants were inserted in 452 inclination and anterior implants were parallel and vertical. Implants were splinted with a titanium bar and an acrylic superstructure was then simulated around the bar. Vertical loads of 178 N and 300 N were applied at incisor and left first molar positions, respectively. After meshing, defining boundary conditions and materials properties, analysis was performed with the aid of ABAQUS.

Results: Maximum Von-Mises stress of 38.9 MPa during anterior loading was located in peri-implant bone of anterior implants but maximum strain was observed in peri-implant bone of posterior implants. In posterior loading, maximum stress (77.3 MPa) was in peri-implant bone of posterior implant which was next to the place of load insertion. Maximum strain was found in the same area.

Conclusion: During posterior loading, significant amount of strain was observed in peri-implant bone of posterior angulated implant. As a result, there was a possibility of resorption in this area. During anterior loading, detected stress and strain was absolutely favorable.

Finite element stress analysis of tooth-implant supported bridges in rigid/non-rigid connectors in cemented prostheses

HR. Rajati Haghi

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.

The effect of bovine demineralized bone matrix on regeneration of rabbit parietal bone defects

S. Aghazadeh

Background and Aims: The present study was designed for evaluation of bovine demineralized bone matrix (DBM) in healing process of bone defects and comparison of bovine DBM (xenograft) and human DBM (allograft) which is used clinically.

Materials and Methods: Seven male white New Zealand rabbits were used in this study. The incision was made directly over the midsagital suture of the parietal bone. Then 3 bicortical defects were created with trephine bur No.8 (8mm diameter). The defects were randomly filled with graft materials. One of the defects was left without any graft in all samples (as a control defect). The amount of bone formation was evaluated 3 months after surgery histopathologically. The data were analyzed using Friedman test, and when P-value was less than 0.05, the pair wise group comparison were performed by Wilcoxon (Boneferroni adjusted) test.

Results: Statistical analysis showed that there was a significant difference between bovine DBM group with control group (P=0.03). Furthermore, human DBM group was significantly different from control group (P=0.02). However, the difference between bovine DBM group and human DBM group was not statistically significant (P=0.87).

Conclusion: The results of this study showed the satisfactory bone healing in rabbit parietal bone defects filled with bovine DBM. The amount of healing in these defects was similar to bone defects which were filled with human DBM that is used clinically.

Prediction of mesiodistal width of unerrupted canines and premolars in South Iranian population by presenting new regression equations

SMM. Roeinpeikar

Background and Aims: Since there is a relationship between the tooth size and race, it seems that having statistical information about the tooth size in a society in which the orthodontic treatments are done, is very important. The aim of this study was to determine the relationship between the mesiodistal width of permanent incisors and first molars in both jaws with unerrupted permanent canine and premolars. New regression equations for prediction of the sum of mesiodistal width of canine and premolars were established.

Materials and Methods: A total of 715 dental casts (526 female, 189 male) were recruited from the department of orthodontics of Shiraz dental school and private offices of orthodontists for this cross sectional study. The greatest mesiodistal widths of all teeth were measured with digital caliper with accuracy of 0.01 mm. All data were analyzed with SPSS software and Pearson Correlation, independent T-test, paired sample T-test and multiple linear regression tests.

Results: Tanaka-Johnston equations and Moyer’s prediction tables had significant difference with mesiodistal dental width of south Iranian population, so new regression equations (based on incisors and first molars) for different jaws and sexes were presented in this study for south Iranian population. The best suggested regression is the regression that is based on all maxillary and mandibular incisors and first molars and has 12 variables. The suggested regression for prediction of maxillary canine and premolars based on the summation of mesiodistal width of all incisors and first molars in both jaws was Y=0.177X+4.227 and for prediction of mandibular canine and premolars was Y=0.188X+2.730, which a the greatest in r2 prediction of unerrupted teeth in comparison with the regressions based on incisors alone or incisors and first molars in one jaw.

Conclusion: Tanaka-Johnston and Moyer’s prediction tables are overestimated the actual size of south Iranian’s teeth width. So new regression equations based on incisors alone and incisors and first molars are suggested to increase the accuracy of space analysis in both jaws.