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A procedure is described for designing open-tubular liquid chromatographic (LC) columns with high resolving power, optimized for mass loadability. Large film thicknesses improve the loadability, but decrease the efficiency owing to the increased mass-transfer term. Normally an arbitrary upper limit of the magnitude of the contribution of the stationary phase mass-transfer term to the overall plate-height equation of about 20% is accepted. The present approach allows the real optimum value of the contribution of the stationary phase mass-transfer term to be calculated. The optimum was found to occur at about 50% in most instance. This corresponds to a plate height equation h = 2/ v + 0.12 v for k ′ = 3 instead of the expression for very thin films h = 2/ v + 0.08 v as advocated by Knox and Gilbert ( h = reduced plate height, v = reduced velocity; k ′ = capacity factor). The maximum column length is about 5 m for all phase systems with 3 · 10 5 theoretical plates, dead time of mobile phase 1000 s and 20 MPa pressure drop along the column. The mass loadability of an open-tubular LC column and a 21μm micropacked capillary were compared and were found to be in the same range. The optimization procedure uses known and established relationships, describing speed, efficiency and mass loadability in chromatographic systems. The calculations were carried out with a spreadsheet computer program.

In vitro enamel demineralization was studied in undersaturated calcium phosphate solutions containing fluoride in the concentration range 0–10 ppm. Depending on the fluoride concentration either erosi

Most of the fluoride acquired during topical applications will be released in the oral environment. This investigation deals with the effectiveness and retention of fluoride after different treatments of the enamel. The effect of acidified phosphated fluoride (APF) on sound, and etched, and neutral KF on etched enamel were investigated by studying the F profiles in the enamel after 0, 1, 2, 4 and 8 weeks exposure to running tap water. APF application on etched enamel showed the deepest fluoride penetration and retention. At 8 weeks the differently treated enamel samples were exposed to an artificial caries-inducing solution. The etched and subsequently APF-treated enamel showed least release of minerals.

Oral hygiene plays an important role in the prevention of caries. Therefore, when one is investigating the possible effects of acid etching on caries susceptibility, oral hygiene aspects and the supplementation of fluoride have to be considered. The objective of this investigation was to study the caries suceptibility of etched enamel surfaces in vitro. To simulate the in vivo situation, much attention was given to the influence of remineralization of saliva and fluorides. It was shown that etching and subsequently fluoridating and remineralization increases resistance of enamel against a caries attack.

The wear resistance of tooth enamel that had undergone eight different treatments regarding the bonding procedure has been investigated. In comparison to sound enamel, the outer 3 microns of the etched-surface enamel show a decreased wear resistance against toothbrushing in vitro. Remineralization, either direct or preceded by acidified phosphated fluoride (APF) application, did not improve the wear resistance. The prophylactic effect of the APF treatment of etched enamel is considerable and is not lost after the soft, outer surface layer has worn off.

Mineral loss and uptake in artificial enamel lesions was investigated by pH cycling: samples were subjected to a sequence of de- and remineralizing solutions. The ratio between de- and remineralization per day and the presence of fluoride in the remineralizing solution were varied among different experimental groups. Calcium, phosphate and fluoride uptake and loss were measured. The lesions were also studied with a hardness tester and micro radiography. The results show a difference in remineralization mechanism between continuously remineralized and pH-cycled samples (with respect to Ca/P ratios). With fluoride present, after some time, ‘arrested’ carious lesions are formed, which can hardly be further demineralized or remineralized. This is in agreement with clinical findings of remineralization in areas with fluoridation of the drinking water.

Three different dental luting agents (a polyalkenoate (glass-ionomer), a BIS-GMA-based material and a bipolyester adhesive) for crown and bridgework were investigated for shear bond strength between dental enamel, dentine and three types of casting materials (high gold, silver-palladium and non-precious alloys). The role of acid etching and sandblasting of the substrates was also investigated. A special apparatus was designed for this purpose. Adhesion to the non-precious alloys reached values as high as 30 MPa, while adhesion to precious alloys offered values approaching those with dentine, being in the order of 5–10 MPa. Acid etching of dentine decreased the adhesion, while the adhesion to enamel was promoted by acid etching. The results of this investigation indicated that the reliability of this testing device proved to be better than the tests described in other studies.