Relevance of in vitro tests of adhesive and composite dental materials, a review in 3 parts. Part 1: Approval requirements and standardized testing of composite materials according to ISO specifications

The first part of this three-part review on the relevance of laboratory testing of composites and adhesives deals with approval requirements for composite materials. We compare the in vivo and in vitro literature data and discuss the relevance of in vitro analyses. The standardized ISO protocols are presented, with a focus on the evaluation of physical parameters. These tests all have a standardized protocol that describes the entire test set-up. The tests analyse flexural strength, depth of cure, susceptibility to ambient light, color stability, water sorption and solubility, and radiopacity. Some tests have a clinical correlation. A high flexural strength, for instance, decreases the risk of fractures of the marginal ridge in posterior restorations and incisal edge build-ups of restored anterior teeth. Other tests do not have a clinical correlation or the threshold values are too low, which results in an approval of materials that show inferior clinical properties (e.g., radiopacity). It is advantageous to know the test set-ups and the ideal threshold values to correctly interpret the material data. Overall, however, laboratory assessment alone cannot ensure the clinical success of a product.

Teat anatomy affects requirements for udder preparation in Mediterranean buffaloes

The present study was conducted to assess the interrelation between teat anatomy and machine milking in dairy buffaloes raised in Switzerland. A 3-min pre-stimulation induced milk ejection before cluster attachment in most cases and caused an optimal milk removal during machine milking. In an additional experiment, longitudinal cross-section ultrasound was obtained before and after a 3-min pre-stimulation. Teat wall thickness, teat diameter, cisternal diameter and teat canal length were evaluated. It was observed that 3-min pre-stimulation dramatically reduced teat canal length whereas all the other anatomical parameters remained unchanged. The vacuum needed to open the teat canal was also measured before and after a 3-min pre-stimulation by using a special teat cup with only the mouthpiece of the liner remaining on the top of the teat cup (no liner, no pulsation). Without pre-stimulation but after wetting the teat canal by stripping one squirt of milk out of the teat, no milk could be withdrawn with a vacuum up to 39 kPa. However, after pre-stimulation, milk flow occurred in all buffaloes at a vacuum between 16 and 38 kPa. In the last experiment, the teat tissue was examined in slaughtered buffaloes and compared with teat tissue of cows. No difference was noted in histological sections and teat canal length was similar in cows and buffaloes. Proximal to the teat canal, the teat did not pass into an open cistern but the lumen was collapsed. In conclusion, buffaloes need to be well pre-stimulated because the tissue above the teat canal provides additional teat closure before milk ejection. Therefore, milk can only be obtained after pre-stimulation.