HM clasp exhibited better fitness accuracy and retentive forces. The possibility of clinically using HM clasps as well as conventional cast clasps can be suggested.

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It is well known that magnetic records of marine sediments are affected to a certain degree by early diagenesis, the extent and mode of which are controlled by depositional environments. In order to investigate variations in the effects of early diagenesis, we have analyzed 11 gravity cores estimated to be Holocene in age that constitute a depth transect off the southern coast of the Okhotsk Sea. The rock magnetic parameters have peaks produced by the presence of volcanic ashes, basaltic granules and/or relatively coarser-grained layers. The concentrationdependent parameters display characteristic trends of a rapid decrease within the homogeneous silty clay zone in the middle parts of the cores, assuming that the total amount of magnetic minerals decreases through early diagenesis at this interval. This decrease is found in all of the cores from the transect (from both near-shore and offshore sites). In near-shore sites where larger volumes of organic materials are supplied compared to offshore sites, the depth of the decrease in magnetic minerals is relatively shallow. These results imply that the presence of organic materials accelerates the pyritization through the bacterial reduction of ferric ion, thereby causing the decreases in magnetic minerals to become shallower.

In order to reveal the potential effects of early diagenesis on magnetic minerals in deep‐sea sediments, we studied early diagenetic zones and magnetic mineral characteristics of Lower Pliocene hemipelagic sediment samples from IODP Sites U1305, U1306, and U1307 on Eirik Drift, Labrador Sea. All samples analyzed were unlithified silty clay sediments recovered by a piston corer from depths down to 200 meters composite depth (mcd). Based on shipboard interstitial‐water geochemistry, we divided the sediment column from each site into six early diagenetic zones. Magnetite (Fe3O4) was present at all analyzed depths, whereas maghemite (γFe2O3) was found only above the iron reduction zone. We attribute this to associated changes in interstitial redox conditions, which induced preferential dissolution of maghemitized surfaces on magnetite grains. Mineral magnetic results indicate a general down‐hole change in mean grain size of magnetic minerals. At Site U1307, which has relatively low organic carbon contents, the diagenetic zones occur at greater depths than at the other studies sites. This suggests that interstitial oxygen levels at this site remained high enough to degrade organic matter through oxic bacterial activity, and that detrital magnetic minerals have been preserved even at depth.

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