Journal of Dental School, Shahid Beheshti University of Medical Sciences

Objective: Zirconia cores have limited light transmittance and data are scarce on light transmission through zirconia cores with and without the veneering ceramic.

Methods: In this in vitro study, Disc-shaped specimens (11.5 mm in diameter and 0.4 (0.05) mm in thickness) were fabricated of three types of zirconia namely Mamut, Heany and ZirkonZahn (n=5).  A disc-shaped specimen (11.5 mm in diameter and 0.65 (0.05) mm in thickness) of veneering ceramic (Cerabien ZR, Kuraray, Noritake, Japan) was also fabricated. The intensity of light transmitted through the zirconia specimens with and without the veneering ceramic was recorded using a light curing unit (LED, SDI Radii Plus, Australia) and its respective radiometer (LED Radiometer, SDI, Australia). Data were analyzed using repeated measures ANOVA and Tukey’s HSD test.

Results: A significant difference was noted in light transmission among different types of zirconia before and after veneering. After veneering, light transmission decreased in all specimens and the reduction in light transmission in Zirkonzahn group was significantly greater than that in Heany and Mamut groups (p<0.001).

Conclusion: Veneered zirconia systems have limited translucency and ceramic veneering significantly decreases light transmission through zirconia.

Objective: Adhesion of Lactobacillus acidophilus (L. acidophilus) to dental porcelain surface may lead to gingival inflammation and secondary caries. Surface roughness is among the factors affecting this adhesion. The purpose of this study was to evaluate the effects of four different  surface treatment methods on adhesion of L. acidophilus to dental porcelain.

Methods: Sixty specimens (3x10mm) were fabricated of Noritake porcelain and divided into 4 groups (n=15) treated with one of the following four surface finishing techniques:    1. Auto-glazing;

2. Over-glazing; 3. Polishing with Kenda kit and 4. No surface treatment (non-glazed specimens). Specimens were inoculated with bacterial suspension containing 1x106colony forming units per milliliter (CFU/mL) and L. acidophilus adhesion to the surfaces was evaluated using a spectrophotometer. Data were analyzed using one-way ANOVA and Tukey’s HSD test.

Results: The mean bacterial adhesion was 0.1440 (0.00429) to auto-glazed specimens, 0.0750 (0.00256) to over-glazed specimens, 0.1800 (0.00325) to polished specimens and 0.7064 (0.00408) to the non-glazed specimens. The differences in this regard among groups were statistically significant (p<0.001).

Objective: Bioactive glass 45S5 is a surface reactive glass-ceramic biomaterial, developed in 1969. BAG 45S5 with particle size of 20-60 nm has the ability of bone regeneration, broad spectrum antibacterial effect, repairs and replaces diseased or damaged bone. The aim of this study was to evaluate the antibacterial activity and determine MIC and MBC values of nano-BAG45S5 on Streptococcus mutans.

Methods: In this study the in vitro Antibacterial activity of polycrystalline and glass forms of nano- BAG 45S5 was evaluated. Bacterial susceptibility to test materials was examined by antibiogram test. Afterwards MIC and MBC assays were conducted via broth dilution, disc diffusion and colony count methods.

Results: Despite amorphous nano-BAG 45S5, poly-crystalline form had antibiogram negative test result. In broth dilution test, the optical absorbance of test dilution of 50mcg/ml and higher concentrations were equal to negative control’s optical absorbance and their inhibitory zone diameter were measured 10.0mm in disc diffusion test. No colony was observed on the culture media of test dilution of 200mcg/ml and higher concentrations.

Conclusion: Streptococcus mutans (ATCC 35668) is not susceptible to poly-crystalline nano- BAG45S5. Amorphous nano-BAG45S5 is bacteriostatic against Streptococcus mutans. MIC and MBC values for amorphous nano-BAG45S5 were 50 ppm and 200 ppm, respectively.

Objective: In dental treatments, use of carriers for targeted antibiotic delivery would be optimal to efficiently decrease microbial count. In this study, gentamicin was loaded into polylactic co-glycolic acid (PLGA) microspheres and its release pattern was evaluated for 20 days.

Methods: In this experimental study, PLGA microspheres loaded with gentamycin were produced  by the W/O/W method. The correct morphology of loaded microspheres was ensured using scanning electron microscopy (SEM). The rate of drug release from polymeric microspheres into the phosphate buffered saline (PBS) solution was measured during a 20-day period using spectroscopy. Data were analyzed using one-way ANOVA.

Results: SEM micrographs showed that the produced microspheres had smooth and nonporous surfaces and 30-micron diameter. Assessment of the pattern of drug release from the PLGA microspheres loaded with gentamycin revealed a burst release on day six followed by a  stable pattern of release until day 20.

Conclusion: Considering the biocompatibility of PLGA and optimal pattern of drug release, PLGA microspheres loaded with gentamicin can be successfully used for infection control and reduction of microbial count in dental treatments.

Objective: Diagnosis of vertical root fractures (VRFs) is critical in endodontics; which most of the times occurs in endodontically treated teeth with root canal fillings such as gutta percha. Despite Cone Beam Computed Tomography (CBCT) has significantly enhanced image quality compared to digital radiography (DR) which aid the diagnosis, artifacts has remained as a problem in VRF detection. The aim of this study was to compare accuracy of CBCT and digital radiography system in vertical root fracture with presence and absence of gutta-percha.

Methods: In this experimental in vitro study, 60 premolar teeth were cut at the cementoenamel junction .The teeth were randomly divided into two groups; for one group root canal therapy was done and the roots filled with gutta-percha. The other group was the control one .At the first stage CBCT scan and digital radiography was done and subsequently, vertical root fractures were induced for all samples. Then all the teeth were scanned by CBCT and digital radiography system and three observer assessed CBCT images and digital radiographies for presence of vertical root fracture. ANOVA and weighted Kappa tests estimated the diagnostic accuracy values and inter-observer agreement.

Results: All values for CBCT were higher than Digital radiography except for absolute specificity and negative predictive value (p=0.409, p=0.053). In both imaging systems, there was no statistical difference between presence and absence of gutta-percha. (p=0.599, p=1.000, p=0.673, p=0.373).

Conclusion: Diagnostic accuracy of vertical root fracture was not influenced by presence or absence of gutta-percha. Additionally, CBCT imaging system had higher diagnostic accuracy in comparison of digital radiography.

Objective: Despite the advantages of esthetic posts, lack of studies on their fracture resistance has limited their clinical use. This study aimed to compare the effect of two types of esthetic posts namely zirconia and zirconia enriched glass fiber composite posts on fracture resistance of endodontically treated teeth against compressive forces.

Methods: This in vitro study was conducted on 20 mandibular premolar roots cut at the cementoenamel junction (CEJ). The roots were endodontically treated and randomly divided into 2 groups of 10. After post space preparation, in group 1 zirconia posts (CosmoPost, Ivoclar, Liechtenstein) and in group 2 zirconia enriched glass fiber composite posts (Ice Light, Danville, USA) were cemented in the roots using a dual-cure resin cement (Panavia F 2.0, Kuraray, Japan) according to the manufacturer’s instructions. The teeth were restored with composite resin cores (Lumiglass, RTD, France) using a prefabricated polyester matrix. After periodontal ligament (PDL) simulation by elastic polyether impression material (Impregum, 3M ESPE, USA), specimens were mounted in acrylic resin and subjected to 1195 Instron universal testing machine. Compressive load was applied at a 90° angle relative to the long axis of the teeth at a crosshead speed of 1mm/min  until fracture. Since the data were normally distributed, t-test was used for statistical analysis.

Results: The fracture resistance was 816.69 (120.89) N for zirconia posts and 843.76 (120.93) N for zirconia enriched glass fiber composite posts and these values were not significantly different (p=0.62). Fractures in group 2 were restorable.

Conclusion: The fracture resistance of zirconia and zirconia enriched glass fiber composite posts was not significantly different and both types of posts can be successfully used.

Objective: Considering the use of triple antibiotic paste (TAP) for root canal treatment of open apex teeth, this study aimed to assess the effect of TAP and calcium hydroxide (CH) on bond strength of composite to dentin.

Methods: This in-vitro study was conducted on 32 extracted human premolar teeth. After disinfection with 2% thymol solution, the enamel on the buccal surface of specimens was removed  to expose a smooth dentin surface parallel to the long axis of the teeth with approximately 19mm2 surface areas. Specimens were divided into three groups of 11, 10 and 11 specimens. In group one, TAP, in group two CH and in group three, saline solution were applied to dentin surfaces for 14 days. After removal of medicaments, composite cylinders were bonded to the dentin surfaces using a bonding agent. Shear bond strength was measured in an Instron machine at a crosshead speed of 1mm/min. Data were analyzed using one-way ANOVA.

Results: The highest mean bond strength belonged to the control group (14.4760 MPa) and the lowest belonged to the TAP group (11.5808 MPa). The mean bond strength in CH group was less than that of the control and higher than that of the TAP group (11.7834 MPa). However, the difference among the three groups was not statistically significant (p=0.327).

Conclusion: Use of medicaments such as CH and TAP has no effect on bond strength of composite to dentin.

Objective: Florid cemento-osseous dysplasia (FCOD) is a rare bone lesion that predominantly involves the women’s jaws in middle age. This condition is usually asymptomatic and has a benign course.

Case: This paper presents a rare case of FCOD in a white middle aged woman, which had affected mandible bilaterally and was diagnosed after tooth extraction and treated conservatively.

We believed tooth extraction was a contributing factor for outbreak of such a lesion in this susceptible patient.

Conclusion: For the asymptomatic patients, the best management consists of regular recall examinations with prophylaxis and reinforcement of oral hygiene to prevent periodontal diseases and tooth loss, but with accession of clinical signs and symptoms, surgical intervention is inevitable.