Bond strength of luting materials to ceramic crowns after different surface treatments.

The aim of present study was to evaluate the effect of different pre-treatments of alumina and zirconia copings on the bond strength of different luting materials. Pull out tests was performed on 60 alumina and 80 zirconia copings. Randomly selected, copings were divided in groups of i) un-treated alumina and zirconia copings, (n=20) ii) alumina and zirconia copings sandblasted with 50 or 110 microm alumina particles respectively (n=20), iii) zirconia copings treated with monolayer of glass pearls fused to the inner surface (n=20), iv) zirconia copings treated with silanized glass pearls (n=10). Zinc phosphate, Panavia 21 and VarioLink II were used for cementation. Pull out tests were done in an Instron universal testing machine with a speed of 0.5 mm/min and fracture loads was measured in N. Untreated zirconia copings cemented with zinc phosphate showed significantly higher bond strength values compared to those with sandblasted surfaces. No difference was seen between untreated alumina copings and those with sandblasted surfaces. Sandblasting decreased bond strength of zirconia and alumina copings. Glass pearls increased bond strength of zirconia copings, which was even better after silanization. Variolink II in combination with alumina gave significantly lower bond strength.

Bonding capacity in bone of HIP-processed HA-coated titanium: mechanical and histological investigations.

The main problems using plasma-sprayed hydroxyapatite (HA) as a coating material on metallic implants are its porosity, low fatigue strength, and weak adherence to the metallic substrate. To overcome these problems a new technique using hot isostatic pressing (HIP) has been developed for producing HA-coated titanium (Ti) implants. Specimens produced at a maximum temperature of 850 degrees C and a maximum pressure of 720 bar displayed a dense, glassy, 25-microns thick coating with small amounts of porosity and a mean surface roughness of 0.7 microns, as compared with 1.6 microns for sandblasted Ti. Twenty conical HA-coated (720 and 100 bar pressure) and 10 noncoated Ti implants were inserted through the cortex of the lower margin of the mandibles of sheep and allowed to heal for 60 days. Push-out tests for implants processed at 720 bar pressure showed substantially higher bone/implant bonding values than for sandblasted Ti implants. Histological studies indicated a direct contact and probably chemical bonding between bone tissue and the HA coatings. The area of contact was almost 3 times as large as for the Ti implants. The adherence of the 100-bar coating to the Ti surface was inferior to the 720-bar coating, as shown by the loosening of the coatings in several areas.

In vitro release of nickel and chromium from different types of simulated orthodontic appliances.

Five identical samples, each consisting of a fixed appliance, a headgear and a quad-helix for one-half of a dental arch, were immersed in 0.9% sodium chloride for 2 hours, 24 hours and 7 days. A control appliance was subjected to dynamic test conditions in a specially built "oral simulator" under similar test conditions. A significant release of nickel was detected from the quad-helix during the first two hours in static conditions, whereas during the following two periods significantly less nickel was released from the quad-helix than from the other appliances. The fixed appliance with simulated function showed a significantly higher cumulative release of nickel than the similar appliance in static conditions, 44.2 micrograms (SD 22.8) and 17.1 micrograms (SD 3.4). The total amounts of chromium released from the fixed appliance were significantly lower than those of nickel. No difference in the release of chromium was seen between the static and dynamic conditions. The results indicate certain differences in the amount and pattern of nickel release from different stainless steel orthodontic appliances in vitro. The release rate of nickel from dynamically loaded fixed appliances was found to be accelerated compared with that released under static conditions. Caution should be exercised when applying the results to the in vivo situation.

A novel miniature bite force recorder and its clinical application.

Solid state components were used to construct a miniature bite force recorder suitable for registrations in large study groups. A semiconductor was chosen as the sensory unit. The complete recording system included a power supply, the bite force recorder, a chart recorder and a millivoltmeter. Laboratory calibration tests were performed to screen the limitations of the recorder. Series of loads were applied in the range from 10 to 1000 N. Eight females and eight males, 20 to 25 years old, were asked to produce a succession of maximum bites at three second intervals for as long as possible. The bite force recorder was positioned between the first molars on the left side. The laboratory tests showed that loads in the range from 10 to 1000 N were recorded with an error less than four percent. In the clinical tests, the mean maximal bite force was 500 N ranging from 330 to 680 N. The number of maximum bites varied from 5 to 27. No statistically significant differences were observed between the sexes as regards the maximal bite force and the number of bites.