PubMed · 9002885
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M B Miller. 1995. Taking risks.. https://pubmed.ncbi.nlm.nih.gov/9002885/
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Biomaterials may initiate several and complex biological reactions in host tissues, and the cell-biomaterial interactions can determine the release of mediators including monocytes and lymphocytes chemotactic factors. The present work was aimed to investigate in vitro the macrophage biological reactions of a natural apatite obtained by heat treatment at 400 degrees C of bovine bone, compared to other ceramics usually used for dental and orthopedic applications, using synthetic apatite and three types of alumina as controls. Particles chemotactic activity and powders oxidative burst evidenced no monocyte macrophages sensitivity reaction for natural and synthetic hydroxyapatite powders at great granulometry (> 50 microm); data were confirmed by ultrastructural observations; electron microscopy analysis showed macrophages with the features of healthy cells in the presence of both natural and synthetic apatites while macrophages grown in the presence of alumina seemed to be negatively affected. In conclusion, among all ceramics tested, natural apatite displayed a good compatibility with living cells, being better tolerated than synthetic hydroxyapatite which in turn is better tolerated than alumina.
The resistances to sliding were studied as a function of five angulations (0 degrees, 3 degrees, 7 degrees, 11 degrees, and 13 degrees) using nine different couples made of stainless steel, single crystal sapphire, or polycrystalline alumina brackets against stainless steel, nickel titanium, or beta-titanium arch wires. After 22 mil brackets were mounted to fixtures and 21 x 25 mil arch wires were ligated with 10 mil stainless steel ligatures, the arch wires were slid through the brackets at 1 cm/minute in the dry state at 34 degrees C. The resistance to sliding was measured by one computer while five normal forces (nominally 0.2, 0.4, 0.6, 0.8, and 1.0 kg) were serially maintained by another computer. A second couple was prepared for each material combination with five normal forces that were each 0.1 kg less. Statistical fits of linear regressions were such that p <.001 for most tests. When couples were in the passive configuration at low angulations, all stainless steel wire-bracket couples once again had the least resistance to sliding. When the angulation exceeded about 3 degrees, however, the active configuration emerged and binding quickly dominated as the resistance to sliding increased over 100-fold. Under these conditions, the relative rankings among the materials transposed; couples of stainless steel had the most resistance to sliding, whereas, couples of the more compliant alloys, such as nickel titanium wire, had the least. Results suggested that the active configuration and subsequent binding emerged when no bracket clearance remained. This binding component increased in importance with angulation and was additive to the frictional component, that is, they followed the principle of superposition.
The overall resistance to accidental blows of the many ceramic brackets that are sold today has not been explored. Facing a similar diversity, the eyeglasses industry has chosen to standardize the testing of lenses by subjecting them to the drop of a steel ball. By slightly modifying this test, 10 brands of ceramic brackets were examined. In most cases, the findings coincided with those found by other authors when duplicating debonding. Thus, polycrystalline ceramics with bulkier structures and glazed surfaces were found to be more resistant to impact than the monocrystalline brackets, the loftier real "twins," and the less dense attachments. Protruding tie wings and bases were liabilities, and domed configurations seemed to deflect the blows. Bulkier "single" designs alone did not offer a guarantee of impact resistance when not accompanied by an appropriate microstructure and a smooth surface. The ceramic brackets most resistant to impact were found to be 20/20 by American Orthodontics and Fascination by Dentaurum. Medium resistance was displayed by Lumina by Ormco, Allure III and Allure by GAC, Transcend 2000 and Transcend by Unitek/3M; the last was not as good as the other four. The least resistant were Illusion by Ortho-Organizers, Intrigue by Lancer Orthodontics, and Starfire TMB by "A"-Co. Probably because of its real twin design, the last bracket lends itself to the highest probability for accidental breakage. Although resistance to impact and accidental debonding is desirable from the point of view of treatment, the advantage should be weighted against the chance of enamel fracture. Indeed a weak bracket attached with a soft adhesive may be preferable when the chance of an increased exposure to accidental blows is probable. In such cases, the ceramic may take the brunt of the force, instead of the tooth.