Journal of Islamic Dental Association of IRAN
Volume:26 Issue: 2, 2014

Cone beam computed tomography (CBCT) has attracted considerable attention as a new diagnostic imaging technique in dentistry. The aim of this study was to review its application in Endodontics. Electronic databases (MedLine, EMBase, Cochrane, Iran Medex, Science citation index, Scopus and Google scholar) were searched by the authors for articles published from 1999 to 2012. “CBCT imaging”, “Endodontics”, “vertical root fracture or VRF” and “periapical or PA lesions” were the searched key words. The assessment of PA lesions, healing process, tooth morphology, accessory canals, root curvature, traumatic injuries, internal and external tooth surfaces, root resorption, fracture lines specially vertical root fracture, perforations, broken instruments, over-extended filling materials, calcified canals, proximity and superimposition of roots and pre-surgical evaluation are the challenges that cannot be adequately addressed by conventional radiography. Cone beam computed tomography is a valuable imaging modality with minimal radiation exposure to the patient that provides maximal information for the clinician. It is going to be the front-line dental imaging modality in near future.

Dentin bonding agents are gradually replacing enamel bonding agents in the clinical setting. Considering the different properties of these two materials, their bonding strength to enamel may be different. The aim of this study was to compare the shear bond strength of composite restorations to enamel using dentin bonding and enamel bonding agents. In this experimental study, buccal surfaces of 24 freshly extracted primary and permanent teeth were polished by the polishing papers in order to obtain a piece of flat enamel 3 mm in diameter. After etching, rinsing and drying the surfaces, the specimens were divided into 4 groups. Enamel bonding (Margin Bond) was applied to the surfaces of 6 primary and 6 permanent teeth and Single Bond was applied to the surfaces of the remaining teeth. All teeth were cured. Composite resin (3mm in diameter and 4 mm in height) was applied to the prepared surfaces. Then, the specimens were thermocycled for 2000 cycles and the shear bond strength was determined using an Instron universal testing machine. The findings were analyzed by SPSS and two-way ANOVA. There was no significant difference in the mean shear bond strength of the two groups of primary and permanent teeth (P=0.518). Also, no significant difference was found between enamel and dentin bonding agents in primary and permanent teeth (P =0.17). The shear bond strength of composite to enamel was not significantly different between the primary and permanent teeth following the use of enamel or dentin bonding agents.

Marginal adaptation is important for long-term Successof full-coverage restorations. Thickness of core is one of the important factors influencing the marginal integrity.Thus, the aim of this studywas to evaluate the effect of different thicknesses of zirconia core on marginal adaptation of all-ceramic restorations. In this single blind in vitro study,a standard brass die7 mm in length and 5 mm in diameter was prepared with a classic chamfer finish line with 0.8 mm depthand 10 degrees of wall taper. Copings were made using the CAD / CAM system. We had three groupsof10 samples each.Group 1 with a zirconia thickness of 3.0 mm, group 2 with a thickness of 0.5 mm and group 3 with a thickness of 0.7 mm. Copings were then placed on the die and randomly numbered. The vertical gap in the margin was measured at 10 points using scanning electron microscopy (SEM). Data were collected. The mean and standard deviation values were calculated and ANOVA. was used for the comparison of the three groups. Tukey’s test was also applied. The gap in 0.3,0.5 and 0.7 mm thicknesses of zirconia before porcelain firing was 89.21± 28.90, 79.55 ± 39.32 and 40.813 ± 10.3 µ, respectively.The difference in marginal gap between the three groups was statistically significant (P=0.001).Tukey’s test failed to find a significant difference in marginal gap between 0.3 and 0.5 mm thicknesses(P=0.006).But, the difference between 0.3 and 0.7 mm (P=0.001) and also 0.5 and 0.7mm(P=0.001) was statistically significant. Based on the results, by increasing the thickness of the zirconia core marginal gap decreases in all ceramic restorations.

Assure universal bonding resin is a modified cement with fluoride releasing property. It is claimed to provide adequate bond strength between the bracket and enamel in wet conditions; although more studies are required in this regard. This study compared the shear bond strength of Transbond XT and Assure universal bonding resin to dry and saliva-contaminated enamel in vitro. In this in vitro study, 60 extracted human premolars were selected and stainless steel brackets were bonded to enamel surfaces. Bonding of brackets to enamel surfaces was done using Assure universal bonding resin (dry condition), Transbond XT (dry condition) and Assure (saliva-contaminated condition). The shear bond strength of brackets to the enamel was determined by Zwick/Roell machine in three groups. Data were analyzed using one-way analysis of variance (ANOVA), and the Kruskal Wallis test. The mean shear bond strength of brackets to enamel surfaces bonded with Assure (dry condition), Transbond XT and Assure (saliva-contaminated condition) was 14.18±4.78 MPa, 16.13±5.49 MPa and 13.32±4.74 MPa, respectively (with no significant differences). Non-parametric Kruskal-Wallis test found no significant differences regarding the adhesive remnant index (ARI).(P=0.053).. Bonding of stainless steel brackets to enamel surfaces with Assure universal bonding resin provided adequate bond strength in dry and saliva-contaminated conditions. Thus, it may be used for bonding of orthodontic brackets to the enamel surfaces in the clinical setting.

Enamel wear is among the main disadvantages of ceramic restorations. Recently, use of full zirconia crowns without dental porcelain has been suggested. The aim of this study was to compare the effect of feldspathic porcelain and zirconia on the wear of natural teeth. In this experimental study, 22 zirconia specimens were fabricated; out of which, 11 specimens were polished and chosen as zirconia specimens while the remaining 11 were used to fabricate porcelain specimens. A total of 22 natural human teeth were also obtained. The natural teeth were photographed by a stereomicroscope in a fixed position and the distance from the cusp tip to a reference point was measured. Next, 11 teeth opposed zirconia and the remaining 11 opposed porcelain specimens in a chewing simulator and subjected to 120,000 masticatory cycles. The teeth were photographed again and the greatest difference between the before and after values ​​ was recorded. The mean (± standard deviation) wear rate was 153.8±95.68 and 306.3±127.74, in the zirconia and porcelain groups, respectively; and the two groups had a statistically significant difference in this respect (P=0.007). The mean wear was significantly lower in teeth opposing zirconia than in those opposing feldspathic porcelain.

If root fractures remain undetected, pulp necrosis will occur in 25% of cases leading to eventual tooth loss. The purpose of this study was to evaluate the diagnostic accuracy of digital phosphor plates using pseudo-color enhancement for detection of horizontal root fractures in single-rooted teeth. Eighty-two human single-rooted teeth were evaluated (41 with no horizontal fracture and 41 with horizontal fractures). Digital intraoral imaging plate system. (Digora® Optime PSP System, Soredex) was used to obtain 16-bit gray scale images. Five 16-bit images were obtained from each specimen and saved (one original and four with pseudo-color enhancement). Four observers evaluated the images twice with a 2-week interval. Accuracy, positive predictive value (PPV), negative predictive value (NPV), specificity and sensitivity for each observer and each image group were calculated. The diagnostic sensitivities were not significantly different among the five images (P absolute=0.125, P complete=0.170). But, statistically significant differences were found in the diagnostic specificity (P absolute=0.019, P complete=0.016) among the five views. Cool and Summer views had higher diagnostic specificity than Bone, Copper and Original views (P=0.025). Kappa and Weighted Kappa values showed statistically significant differences for intra- and inter-observer reliability in the five views (P=0.032). Both Cool and Summer views were suitable for detection of horizontal root fractures and had statistically significant differences with the original view

Luting cements are necessarily used to increase retention and enhance the marginal seal of fixed partial dentures (FPDs). In this study, the finite element method (FEM) was used to investigate the effect of different types of luting agents on stress distribution in the luting cement layer i n a three-unit implant-supported FPD. A three-dimensional (3D) FE model of a FPD was designed from the maxillary second premolar to the second molar teeth using CATIA V5R18 software, and analyzed by ABAQUS/CAE version 6.6 software. Three load conditions were statically applied to eight points in each functional cusp in horizontal (57.0 N), vertical (200.0 N) and oblique (400.0 N, θ=120°) directions. Five luting agents including glass ionomer, zinc polycarboxylate, polymer-modified zinc oxide eugenol (ZOE), composite resin and zinc phosphate were evaluated. The stress distribution pattern in the luting cement layer was almost uniform in all luting cements. In addition, the maximum von Mises stress in the luting cement layer (39.96 MPa) was at the cervical one-third of the palatal side of the second premolar when oblique force was exerted on zinc phosphate cement. Moreover, the minimum von Mises stress in the luting cement layer (0.41 MPa) was at the lateral side of the coronal one-third when the horizontal force was applied to the Polymer-modified ZOE cement. Likewise, the luting cement layers in the premolar tooth showed greater von Mises stress than that in molar tooth. The type of luting cement has no significant effect on the stress distribution pattern in the luting cement layer; however, von Mises stress values were different in various types of luting agents. USE of zinc phosphate cement is associated with more limitations.

Adhesive systems are commonly used for restorative dental procedures. Solvent removal my be effective for increasing the microtensile bond strength of etch and rinse systems to dentin. The aim of this study was to evaluate the effect of solvent removal on microtensile bond strength of etch and rinse systems to wet and dry dentin. This in-vitro study was conducted on 40 intact human extracted third molars. A flat superficial dentin surface was exposed by wet abrasion. The specimens were randomly assigned to five groups. Two coats of the solvent-based (SB) and solvent-free (SF) adhesives were applied to dry (D) or rewetted (W) surfaces, under vigorous rubbing action after phosphoric acid etching according to the manufacturer’s instructions. The examined groups included: group one: adhesive with solvent on dry dentin, group two: adhesive without solvent on dry dentin, group three: adhesive with solvent on wet dentin, group 4: adhesive without solvent on wet dentin and group 5 (control group). After light curing (600mW/cm²/10 s), composite build-ups were constructed incrementally and specimens were stored in water (37 ° C/24 h). They were longitudinally sectioned in the “x” and “y” directions to obtain bonded sticks (1mm²) for immediate testing at a crosshead speed of 1 mm/min. The resultant bond strength was expressed for different fracture patterns. The microshear bond strength test was carried out in a Universal Testing Machine. The data were analyzed using two-way ANOVA. All statistical analyses were performed using SPSS version 2 software. P<0.05 was considered significant. The highest bond strength was achieved in group 1 and the lowest in group 4; but the differences among groups in this respect were not statistically significant. Within the limitations of this study, the results showed that presence of solvent was not essential to achieve high bond strength values to dry and wet dentin when applied vigorously.

Regenerative endodontics with the goal of replacing the lost dental tissues is developing fast. The aim of this study was to review the recent progressions, known limitations and advantages of regenerative treatments compared to other possible treatment modalities. We searched MedLine and PubMed systematically for articles published from May 2000 until May 2013 in English which were relevant to tissue engineering and regenerative procedures using the keywords “cell and tissue based therapy”, “regeneration”, “stem cell” and “tissue engineering”. More valid papers were chosen. Stem cells, growth factors and an appropriate scaffold are the three essential elements required for tissue regeneration. Revascularization is an ideal regenerative treatment, which uses a fibrin scaffold. This scaffold is made of peri-radicular stem cells, a clot and latent growth factors in dentinal walls. The clinical outcome of revascularization is complete root formation in a premature necrotic permanent tooth. Thus, revascularization is a realistic and worthwhile approach in patients with fair to good prognosis. Regenerative treatments with the aim of producing a completely formed permanent tooth are going to revolutionize dental science. Regeneration of a fully formed tooth is much more complicated than treatment of an open apex tooth and this issue requires further studies.

Preventing enamel demineralization around brackets is a concern for orthodontists. Fluoride releasing materials have been recommended to overcome this problem. The aim of this study was to evaluate the effect of incorporating nano-hydroxyapatite (NHA) into resin modified glass ionomer cements (RMGIC) on ceramic bracket debonding. In this experimental study, 80 human premolars were divided into 4 bonding groups as follows: group 1: Transbond XT (control group), group 2: Fuji II LC (RMGIC), group 3: 5% NHA added to RMGIC and group 4 10% NHA added to RMGIC. After enamel etching, ceramic brackets were bonded. The shear bond strength (SBS) and the adhesive remnant index (ARI) were calculated for each group. The data were analyzed using one-way ANOVA, Tukey’s post hoc HSD test and the Kruskal Wallis test. According to ANOVA, 10% NHA added to RMGIC had a significantly lower SBS compared to other groups (11.93±2.11) but no significant difference was found among the remaining groups. The mean SBS was 17.33±4.07 in group 1, 17.22±3.55 in group 2 and 16.56±2.59 in group 3. According to ARI, the predominant failure mode in RMGIC groups was cohesive. Resin modified glass ionomer cements containing 5% NHA can be as effective as composite resins for bonding ceramic brackets.