Nanomodification of mineral trioxide aggregate for enhanced physiochemical properties.

AIM: To analyse the physicochemical properties of a Nano white mineral trioxide aggregate (NWMTA) and compare it with white mineral trioxide aggregate (WMTA). METHODOLOGY: White mineral trioxide aggregate and NWMTA were prepared and mixed according to the manufacturer's instructions. Surface area of powder before hydration, setting time, X-ray diffraction and microhardness at pH values of 4.4 and 7.4 were evaluated by Brunauer-Emmett-Teller, ISO Specification no.6876, Vickers microhardness, and energy-dispersive X-ray spectroscopy equipped with X-ray colour (dot) map for both cements. anova and Mann-Whitney were used for statistical analysis at a significance level of 0.5. RESULTS: The mean ± SD of surface area and setting time were 1.8 ± 0.2 m(2) g(-1) and 43 ± 2 min for WMTA and 7.8 ± 1.2 m(2) g(-1) and 6 ± 1 min for NWMTA, respectively. Mean ± SD of Microhardness were 16 ± 2, 51 ± 1, 69 ± 1 and 81 ± 2 for WMTA at pH values of 4.4 and 7.4 and for NWMTA correspondingly. Numbers of open porosity over the surface were 88 ± 24 and 44 ± 13 for WMTA and NWMTA, respectively. Statistical tests revealed significant differences between the groups (P < 0.001) in surface area, setting time and surface hardness for both cements. Uniform distribution of strontium was only observed in NWMTA. However, other compounds were not significantly different. CONCLUSION: Increasing surface area of powder can reduce setting time and increase microhardness even at lower pH values after hydration.

A new approach for locating the minor apical foramen using an artificial neural network.

AIM: To develop a new approach for locating the minor apical foramen (AF) using feature-extracting procedures from radiographs and then processing data using an artificial neural network (ANN) as a decision-making system. METHODOLOGY: Fifty straight single-rooted teeth were selected and placed in a socket within the alveolar bone of a dried skull. Access cavities were prepared and a file was place in the canals to determine the working length. A radiograph was taken to evaluate the location of the file in relation to the minor foramen and further checked after retrieving the tooth from the alveolar socket. The location of the file tip was categorized into: beyond the AF (long), within the root canal (short) and just at the minor AF (exact). Each radiograph was used to extract relevant features using K-means, Otsu method and Wavelet protocol. Thirty-six extracted features were used for training and the rest were used for evaluating the multi-layer Perceptron ANN model. RESULTS: Analysis of the images from radiographs (test samples) by ANN showed that in 93% of the samples, the location of the AF had been determined correctly by false rejection and acceptation error methods. CONCLUSION: Artificial neural networks can act as a second opinion to locate the AF on radiographs to enhance the accuracy of working length determination by radiography. In addition, ANN can function as a decision-making system in various similar clinical situations.

Effects of three oral analgesics on postoperative pain following root canal preparation: a controlled clinical trial.

AIM: To compare the effects of single doses of three oral medications on postoperative pain following instrumentation of root canals in teeth with irreversible pulpitis. METHODOLOGY: In this double-blind clinical trial, 100 patients who had anterior or premolar teeth with irreversible pulpitis without any signs and symptoms of acute or chronic apical periodontitis and moderate to severe pain were divided by balanced block random allocation into four groups of 25 each, a control group receiving a placebo medication, and three experimental groups receiving a single dose of either Tramadol (100 mg), Novafen (325 mg of paracetamol, 200 mg ibuprofen and 40 mg caffeine anhydrous) or Naproxen (500 mg) immediately after the first appointment where the pulp was removed, and the canals were fully prepared. The intensity of pain was scored based on 10-point VAS before and after treatment for up to 24 h postoperatively. Data were submitted to repeated analysis of variance. RESULTS: At the 6, 12 and 24 h postoperative intervals after drug administration, the intensity of pain was significantly lower in the experimental groups than in the placebo group (P < 0.01). Tramadol was significantly less effective (P < 0.05) than Naproxen, and Novafen that were similar to each other (P > 0.05). CONCLUSION: A single oral dose of Naproxen, Novafen and Tramadol taken immediately after treatment reduced postoperative pain following pulpectomy and root canal preparation of teeth with irreversible pulpitis.

Effect of interfacial variables on metal-porcelain bonding.

While ceramic-to-metal bonding has been used in many applications, the actual chemical and physical factors leading to optimum bond strength are not well understood. In this work, several variables affecting the bonding between dental porcelain and a palladium alloy (85% Pd, 10% Cu, and 5% Ga) were investigated: 1) precoating the metal by sputtering various oxides before porcelaining; 2) peroxidation of the metal base before porcelaining; 3) porcelaining under reducing atmosphere; and 4) surface roughening at controlled levels before porcelaining. Using a modification of the push doughnut shear bond strength test to measure bond strength the following results were obtained. 1) Compared with standard "control" samples, the aluminum oxide precoated specimens showed a bond strength improvement of 46%, while the copper, manganese, and tin oxide precoatings exhibited smaller effects. 2) Preoxidation of the metal base led to pronounced bond strengthening (152%) by surface roughening as well as oxide formation. 3) Porcelaining under a reducing atmosphere severely reduced bond strength (88% lower than the controls) indicating the role of oxidation during the standard firing cycle. 4) Mechanical roughening of the surface by controlled amounts gave pronounced improvements with greater notch depth. Coarse roughening produced the highest bond strength improvements (486%).

In vivo wear. Part I: The Michigan computer-graphic measuring system.

Three-dimensional coordinate measuring machines for examining the quality of industrial castings were reviewed. The concept was modified and successfully converted to examine the minute geometric configurations of the surfaces of dental materials. The wear of composites has undoubtedly precipitated this perceptive, thorough study.

Effects of brackets and ties on stiffness of an arch wire.

Beam theory was used to evaluate the stiffness of a simulated orthodontic model as affected by the type of bracket, interbracket distance, type of ligature tie, and size of segment. For a given deflection, the model generated greater force (increased stiffness) as the beam constant (N) increased. N increased as interbracket distance increased. Metal ties were as rigid or more rigid than o-rings. Four bracket segments were more rigid than two-bracket segments when tied with o-rings but not metal ligatures. Values of N of Lewis and narrow twin brackets with metal ties were similar and greater than the N of wide twin and medium single brackets. Wide twin brackets were more rigid than others with o-rings.

Tensile strength comparison of presoldered and postsoldered joints.

Twenty half-dumbbell shaped rods were cast in a silverless gold-palladium alloy that contained a minimum of 42% fresh alloy and the rest once-melted alloy. Each pair of half-dumbbells was assembled and either presoldered or postsoldered using a vacuum-oven and a torch-soldering technique. There was no significant difference in the ultimate tensile strength values between the presoldered and postsoldered joints within the same technique group, but the torch-soldered joints for the same solder were significantly stronger (p less than .01). It was believed that slow heating and cooling has deleterious effects on the ultimate tensile strength joints (UTS) possibly because of the microstructural changes and the highly oxidizable content of the postsolder used. Another 15 samples cast using once, twice, and three-times remelted parent alloy were presoldered and postsoldered with the torch only. In each of these groups, specimens joined by presolder showed significantly higher strength than those joined by postsolder (p less than .02). Remelting the parent alloy affected the strength differences between the presoldered and postsoldered joints. It was assumed that on remelting, the nature of the parent alloy is changed because some original elements are volatilized and newly formed oxides dissolved into it. Because it contains copper, the postsolder is more affected by this contamination than presolder. The UTS of the parent alloy, as well as that of the presolder and postsolder, were also determined. As expected, the parent alloy possessed the highest strength and the postsolder, the lowest.

Castability of crown and bridge alloys.

A special saucer-shaped wax pattern was designed to evaluate the castability of five casting machines and four casting alloys. The casting machines used included one broken arm unit, one induction unit, one resistance unit, and two vacuum air pressure units. The alloys included one base metal alloy, two high-fusing noble metal alloys, and one type III gold alloy. Results of analysis of variance showed that at the 95% confidence level there was a significant difference among casting machines and alloys, the casting machines had a stronger effect on castability. No attempt was made to evaluate the fit quality of the castings with regard to surface roughness or porosity.

Measurement of resistance of amalgam mixes to condensation.

A method was designed to evaluate the resistance of amalgam mixes to condensation forces. For the purpose of classification with respect to the plasticity of amalgam, the optimum test condition was to apply 40 or 50 lb of static load at 30 sec after trituration.