In vitro evaluation of frictional forces between archwires and ceramic brackets.

The aim of this study was to evaluate the frictional force between orthodontic brackets and archwires. The differences in magnitude of the frictional forces generated by ceramic brackets, ceramic brackets with metal reinforced slot, and stainless steel brackets in combination with stainless steel, nickel-titanium, and beta-titanium orthodontic archwires were investigated. Brackets and wire were tested with tip angulations of 0 degrees and 10 degrees. Friction testing was done with the Emic DL 10000 testing machine (S?o José do Rio Preto, PR, Brazil), and the wires were pulled from the slot brackets with a speed of 0.5 cm/min for 2 minutes. The ligation force between the bracket and the wire was 200 g. According to the data obtained, the brackets had frictional force values that were statistically significant in this progressive order: stainless steel bracket, ceramic bracket with a metal reinforced slot, and traditional ceramic bracket with a ceramic slot. The beta-titanium wire showed the highest statistically significant frictional force value, followed by the nickel-titanium and the stainless steel archwires, in decreasing order. The frictional force values were directly proportional to the angulation increase between the bracket and the wire.     

Histomorphometric evaluation of the effect of bovine collagen granules on bone healing. An experimental study in rats

Collagen materials have been utilized in medicine and dentistry because of their proven biocompatibility and capability of promoting wound healing. The aim of the present experimental study was to perform a histomorphometric evaluation of the effect of bovine collagen granules on post-extraction alveolar wound healing in rats. Twenty male Wistar rats were submitted to bilateral extraction of the first lower molars under ketamine/xylazine anesthesia according to the technique previously described by Guglielmotti and Cabrini. Sterile Bovine collagen granules of approximately 80 +/- 10 microm (Membracel G, Lab. Celina, Buenos Aires) were hydrated with saline solution and placed into the right mesial socket (experimental side) with gentle pressure, completely filling the site. The contralateral sockets were considered as the control side. Sutures were not performed. After surgery neither special diet nor antibiotics were given. The rats were fed rat chow and water ad libitum. All the animals were killed on the 30th day following surgery by ether overdose. The jaws were dissected, radiographed, decalcified, and embedded in paraffin. Sections were obtained at the level of the first molar mesial socket in a buccolingual orientation and stained with hematoxylin-eosin. The trabecular area and volume density of trabecular bone were measured histomorphometrically. The trabecular area was greater in alveoli treated with collagen granules than in control alveoli (P<0.05). Values of volume density of trabecular bone were greater in experimental than in control sockets (P<0.05). This experimental study provides evidence for the use of bovine collagen granules as bone grafting material, as a therapeutic alternative to fill postextraction sockets.     

Biodistribution of a carborane-containing porphyrin as a targeting agent for Boron Neutron Capture Therapy of oral cancer in the hamster cheek pouch

Boron Neutron Capture Therapy (BNCT) is a bimodal cancer treatment based on the selective accumulation of 10B in tumors and concurrent irradiation with thermalized neutrons. The short-range, high-LET radiation produced by the capture of neutrons by 10B could potentially control tumor while sparing normal tissue if the boron compound targets tumor selectively within the treatment volume. In previous studies, we proposed and validated the hamster cheek pouch model of oral cancer for BNCT studies, proved that absolute and relative uptake of the clinically employed boron compound boronophenylalanine (BPA) would be potentially therapeutic in this model and provided evidence of the efficacy of in vivo BPA-mediated BNCT to control hamster oral mucosa tumors with virtually no damage to normal tissue. We herein present the biodistribution and pharmacokinetics of a lipophilic, carborane-containing tetraphenylporphyrin (CuTCPH) in the hamster oral cancer model. CuTCPH is a novel, non-toxic compound that may be advantageous in terms of selective and absolute delivery of boron to tumor tissues. For potentially effective BNCT, tumor boron concentrations from a new agent should be greater than 30 ppm and tumor/blood and tumor/normal tissue boron concentration ratios should be greater than 5/1 without causing significant toxicity. We administered CuTCPH intraperitoneally (i.p.) as a single dose of 32 microg/g body weight (b.w.) (10 microg B/g b.w.) or as four doses of 32 microg/g b.w. over 2 days. Blood (Bl) and tissues were sampled at 3, 6, 12, 24, 48, and 72 h in the single-dose protocol and at 1-4 days after the last injection in the multidose protocol. The tissues sampled were tumor (T), precancerous tissue surrounding tumor, normal pouch (N), skin, tongue, cheek and palate mucosa, liver, spleen, parotid gland and brain. The maximum mean B ratios for the single-dose protocol were T/N: 9.2/1 (12h) and T/Bl: 18.1/1 (72 h). The B value peaked to 20.7+/-18.5 ppm in tumor at 24h. The multidose protocol maximum mean ratios were T/N: 11.9/1 (3 days) and T/Bl: 235/1 (4 days). Absolute boron concentration in tumor reached a maximum value of 116 ppm and a mean value of 71.5+/-48.3 ppm at 3 days. The fact that absolute and relative B values markedly exceeded the BNCT therapeutic threshold with no apparent toxicity may confer on this compound a therapeutic advantage. CuTCPH-mediated BNCT would be potentially useful for the treatment of oral cancer in an experimental model.     

A quantitative method of measuring the microleakage of thermocycled or non-thermocycled posterior tooth restorations

This study quantified microleakage in restorations made with three packable resin composites-Solitaire, SureFil and P60; one hybrid resin composite-Z250 and an amalgam-Dispersalloy, with or without the thermocycling process. Sixty sound, freshly extracted human molars were sectioned mesiodistally, creating buccal and lingual blocks. One hundred blocks with the flattest surface were selected. Cylindrical cavities with a diameter of 1.85 +/- 0.05 mm and a depth of 1.5 mm were prepared with a special diamond bur. The blocks were randomly assigned to 10 test groups (n = 10): five restorative materials and two thermal stress groups (thermocycled groups at 3,000 cycles at 5 degrees C and 55 degrees C with a dwell time of one minute at each temperature, or non-thermocycled). After the thermocycling test, the samples were immersed in 2% methylene blue for 12 hours. The samples were ground and the powder prepared for analysis in an absorbance spectrophotometer. All the results were statistically analyzed by the Kruskal-Wallis test and the Mann Whitney test. For the non-thermocycled groups, the means (microg/ml) of microleakage were: Amalgam-4.279 (a); Solitaire-4.148 (ab); Z250-3.418 (abc); P60-3.184 (bc); SureFil-2.890 (c). For the thermocycled groups, the means were: Amalgam-7.572 (a); Solitaire-5.471 (a); Z250-4.330 (ab); P60-3.418 (bc) and SureFil-2.779 (c). Thermocycling analysis showed no significant differences between the thermocycled and non-thermocycled groups for each material tested. It was concluded that no test material prevented microleakage. Only SureFil and P60 showed leakage means significantly lower than amalgam, with SureFil showing lower leakage than Solitaire. P60 only showed lower leakage than Solitaire in the thermocycled groups and Z250 showed results similar to the others materials.