Journal of Dental School
Volume:30 Issue: 2, 2012

Use of bone substitutes and membranes is an increasingly popular technique to stimulate new bone formation for treatment of orthopedic disorders resulting from bone defects and deficits and has been accepted as a standard treatment modality. Considering the use of bovine fascia as an absorbable membrane, this study compared the rate of bone formation after using bovine fascia and a collagen membrane (Evolution) in a rabbit model. In this experimental study 4 male New Zealand rabbits with a mean weight of 2.5 kg were used. After anesthetizing, three bone defects with 8 mm diameter were created bicortically in the parietal bone of the animals. Two defects were covered randomly with bovine fascia or ''Evolution" membrane and one remained uncovered as the control. After 12 weeks the rabbits were sacrificed and the bone formation was determined histologically. The bone type, inflammation, necrosis and fibrosis were also compared in the three groups and the data was analyzed using Jonckheere-Terpstra test. Out of 4 bovine fascia specimens, half of them showed no bone formation, one showed 33%-36% bone formation and the remaining one showed more than 66% bone formation. Half of the defects covered by "Evolution" membrane showed no bone formation, and the remaining two showed bone formation of less than 33%. In the control group, half showed no bone formation, and the remainder of the samples showed bone formation of more than 66%. No statistically significant difference in terms of bone formation was found between the three groups. From the aspect of type of bone, bovine fascia samples showed the formation of woven and lamellar bone each in one sample, two specimens in "Evolution" membrane group showed lamellar bone and two specimens in the control group showed woven bone formation. The three groups had no significant differences with regard to bone type, inflammation, necrosis or fibrosis. The present study showed that bone regeneration occurred in the defects covered with bovine fascia, "Evolution" membrane and control group was similar without any significant difference. Thus, the bovine fascia can be used as an alternative for "Evolution" membrane to induce bone formation. However, neither bovine fascia nor the "Evolution" membrane could facilitate bone formation as well as the control group.

In the available all-ceramic systems the zirconia core is commonly fabricated as one layer with an even thickness, but the veneering porcelain has different thicknesses in different parts of the restoration and therefore, undergoes chipping and fracture more rapidly under masticatory forces. This study aimed at comparing the fracture load of all-ceramic crowns with 2 different zirconia core designs in Cercon system and in-vitro conditions. In the present experimental study, 10 metal dies of mandibular first molar were fabricated with NNB base metal alloy using lost wax technique. Ten standard zirconia cores were then fabricated with an even thickness of 0.5 mm using Cercon CAD/CAM System. Also, 10 more were fabricated in the customized form with a 1 mm labial collar and 2 mm lingual shoulder. Porcelain was applied on all samples by an expert technician using an index. The prepared crowns were placed on their respective dies and cemented with Panavia F resin cement and under the constant pressure of 25 N. Vertical compressive force was applied to the samples by means of a stainless steel ball at a crosshead speed of 0.5 mm/min using Universal Testing Machine until failure. Data were analyzed using student t test. Our study results demonstrated the fracture load of 1852.11±587.9 N for zirconia core crowns with standard core design and 3332.63±916.38 N for custom design crowns. Statistical analyses demonstrated that the fracture load was significantly higher for customized core designs than the standard design cores(P<0.0001). Considering the obtained results we can conclude that crowns with customized core design have a greater fracture resistance than those with standard design.

Precise knowledge regarding the topography of the tooth apex and location of the apical assessing the constriction are necessary for good and efficient root canal treatment and its long term prognosis. Since radiography is among the most commonly used methods for termination point, it is essential to be able to determine the exact location of apical constriction by radiography. The aim of this study is to evaluate the distance of apical constriction from anatomic and radiographic apices in extracted maxillary second premolars using clearing technique. It also compared the reliability of radiographic results with that of histologic findings. In this in-vitro experimental study, 50 extracted maxillary second premolars of patients presenting to various dental care centers in Tehran were selected. After cleaning and disinfecting the root surfaces and preparing the access cavity, 2% methylene blue was injected into the canals along with theuse of negative pressure. Then, demineralization and clearing process were done using 5% nitric acid and methyl salicylate. Samples were evaluated under stereomicroscope at X16 magnification. In order to evaluate the distance between apical constriction and radiographic apex, a #10 file was fixed at the apical constriction under the stereomicroscope.Covering the apices with sealer, radiographs were taken from all samples.The reliability of radiographic results was compared with that of histologic findings. The mean distance of apical constriction from the anatomic and radiographic apices was 0.9 and 1.05 mm, respectively. Sensitivity, specificity, positive and negative predictive values of radiographic results were 87.8%, 88.8%, 93% and 62%, respectively. The likelihood ratio for positive and negative radiographic results was 7.9 and 0.1%, respectively. The diagnostic odds ratio was 57.6% which is indicative of the acceptableaccuracy and validity of the radiographic results in assessing the distance of apical constriction from the anatomic apex. This study demonstrated that the distance of apical constriction from the anatomic and radiographic apices in the maxillary second premolars was approximately 1 mm and therefore, the process of cleaning, shaping and obturation should end at this point. This study emphasizes on the accuracy of radiographic findings and importance of having sufficient anatomic knowledge for achieving a good treatment outcome in a clinical setting.

Accurate and early detection of a carious lesioncan prevent its further extension. Therefore, capability to accurately diagnose carious lesions is a must-have qualification for dental graduates. The purpose of this study was to evaluate the ability of senior dental students of a dental university in detecting the presence and diagnosing the depth of proximal caries on a bitewing radiograph.

The present study was a diagnostic assessment and a total of 100 bitewing radiographs of optimal quality were randomly selected from patients’ files. Radiographs were separately observed by 30 senior dental students and 5 university professors from Shahid Beheshti School of Dentistry (in order to determine the gold standard) under similar conditions. The observers were asked to detect presence of carious lesions and diagnose its depth according to the set criteria and mark in the questionnaire. If 3 university professors unanimously agreed on presence or absence of caries, this opinion would be chosen as the gold standard of the study. In order to obtain reliability, radiographs were once again observed and evaluated one month later by the same 5 university professors and 11 students. Data were analyzed using SPSS software and Kappa values were analyzed and compared with t-test.

The mean Kappa value for 2 times observation was 0.777±0.065 among professors and 0.664±0.131 among students. According to Fleiss, this rate was excellent for 3 professors and 3 students. Diagnostic sensitivity, specificity, positive predictive value and negative predictive value of students in caries detection were 78.22%, 82.14%, 79.68% and 80.81%, respectively.

Diagnostic capability of students in differentiating carious lesions from healthy tissue was optimal and their reliability was not significantly different from the gold standard. Students were mostly able to detect the presence of carious lesions but there was an under-estimation about the depth of caries.

The relationship between IQ score and malocclusion is a subject that has been the focus of attention in the field of orthodontics. The present study aimed at determining the IQ score of patients with dentoskeletal malocclusions presenting to the Orthodontic Department of Shahid Beheshti Dental School during 2008-2009.

This descriptive cross-sectional study was conducted on 160 patients aged 12-18 yrs. who were receiving orthodontic treatment. A questionnaire was designed containing 3 sections of demographic characteristics, general information and orthodontic treatment. The questionnaire was completed by the patient and senior dental students and patients were asked to take the Cattell Culture Fair III IQ test on the computer and the obtained IQ score was recorded. Data were analyzed using linear regression analysis.

The mean IQ score of the understudy population was 98±16. IQ score had a significant correlation with level of education (P<0.001), age (P<0.001) and socioeconomic status (P<0.001). However, type of skeletal malocclusion and facial growth pattern were not correlated with the IQ score.

The obtained results showed no association between type of skeletal malocclusion or facial growth pattern and the IQ score.

The concept of tissue engineering holds huge promise for thefuture treatment of osseous defects. For bone tissue engineering, stem cells are applied on supporting scaffolds under controlled stimulation with growth factors. Scaffolds are provisional matrices for bone growth providing a specific environment for tissue development and favoring cellular attachment, growth and differentiation. To date, ceramics, polymers, and composite scaffolds have been widely used for bone tissue engineering in various in-vitro and animal studies. The objective of this article was to review the advances in jaw bone engineering from a scaffold material point of view. A review of literature was carried out by using Medline database and searching topics like “craniomaxillofacial tissue engineering”, “bone regeneration”, “scaffold”, “oral surgery”, “stem cell+ scaffold”, “xenograft” and “allograft”.Animal and human studies evaluating repair of craniomaxillofacial defects with scaffold and stem cells, were considered in this study. A total of 64 studies were evaluated. Based on the results of this literature review, although autogenous bone grafting has remained the preferred strategy for treatment of bone defects, rapid prototyping (RP) techniques do offer great opportunities to generate suitable scaffolds for bone tissue engineering in near future.

Sectional imaging modalities are accurate techniques for the identification and localization of the mandibular canal anatomy and variations. The aim of this study was to evaluate the mandibular nerve accessory branches. Existence of these variations may cause some difficulties in anesthesia and also in surgical procedures such as implant planning. Case: The authors report a rare crestal branching of right mandibular canal in a 49 year old male observed in cone beam computed tomography image. Although this anatomical variation is rare, it should be kept in mind.

In prosthetic reconstruction of maxillectomy defects, the weight of prosthesis is usually high due to the extension of prosthesis base into the surgical defect. In order to reduce the weight, this area should be formed hollow. This study describes a modified technique for hollowing out the obturator bulb to reduce its weight. Case: Our patient was a 56 year-old man with a completely edentulous maxilla. Due to an anaplastic carcinoma involving the palate and right alveolar ridge, a large segment of hard and soft palate and the whole right alveolar ridge were resected. After the surgery, the patient was unable to masticate or swallow and was not satisfied with the speech. The suggested treatment plan included fabrication of a complete denture along with a palatal obturator for the maxilla and a removable partial denture for the mandible. Silicone core method was used on the master cast for fabrication of the hallow bulb obturator.

Maxillary hollow bulb obturator prosthesis can greatly help in restoring functional capabilities of mastication, deglutition, and speech. Silicone core method on the master cast is a simplified approach for fabrication of the hallow bulb. This method helps to achieve a smooth surface in inner aspects of the bulb.