With considerable improvement made in plastic materials in recent years, the fluid resin technique using reversible duplicating hydrocolloid has come to be applied clinically for the construction of removable denture prostheses. In view of the fact that, in the studies on the dimensional changes in the conventional fluid resin technique, only hardened plastic products have so far been the main consideration, and recognizing the vital necessity of going over the dimensional changes in the flasking mold, which represents an earlier stage of such products, the author has carried on these studies with the object of inquiring into the behaviours of the flasking mold of alginate and reversible hydrocolloid after flasking of wax denture.
The materials for experiments and the method applied may be outlined as follows: With two simple metal dies, large and small, used as models, alginate and reversible hydrocolloid were flasked respectively in the dies. Especially, hydrocolloid molds were taken at 2 time points, i.e. at the time point of early stage removal, which is a usual clinical practice, and at the time point of complete cooling removal. Measurements of dimensional changes on standing of the flasking mold under a 100% relative humidity environment and a water storage environment were made of outside diameter, inside diameter and occlusal surfaces, respectively, of metal die.
From the results obtained, the following conclusion was derived.
1. The measurements taken immediately after its removal from die under a 100% relative humidity environment showed a considerable contraction at occlusal surfaces of alginate mold, whereas only a small changes at other measuring points.
2. As for the dimensional changes on standing under a 100% relative humidity environment, outside diameter developed an expanding tendency, whereas inside diameter a contracting tendency, but occlusal surfaces showed only a small change.
3. As far as the alginate mold under a water storage environment is concerned, outside diameter developed a contracting tendency, whereas inside diameter an exdanding tendency, and the changes seen here were greater than those shown under a 100% relative humidity environment.
4. As for hydrocolloid mold under a water storage environnment, a swelling tendency due to imbibition could hardly be observed.
5. The difference in size of die did not have any great effect on dimensional changes. The aspect of dimensional changes, however, varied with the difference in surface area in the case of alginate mold under a water storage environment and with the difference in internal temperature at the time of its removal in the case of hydrocolloid mold removed at an early stage.
6. As for hydrocolloid mold, less dimensional changes were seen in the case of complete cooling removal than in the case of early stage removal under both environments of humidity and water storage.
7. It was found by comparing the dimensional changes on standing at various measuring points that less changes were seen in the order of alginate mold under water storage >alginate mold under humidity > hydrocolloid mold under humidity (early stage removal) > hydrocolloid mold removed after complete cooling under humidity (complete cooling removal) > hydrocolloid mold under water storage (early stage removal) > hydrocolloid mold removed after ccmplete cooling under water storage (complete cooling removal) environments, respectively.

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橋義歯ポンティックの基底面が, 顎堤粘膜におよぼす生物学的為害作用のうち, ポンティック基底面に付着するプラークによる細菌学的刺激の影響を調べるため, 実験的に種々の材料と形態のポンティックを有する橋義歯を口腔内に仮着した.一定期間仮着した橋義歯のポンティック基底面に付着するプラークを, 肉眼的および走査型電子顕微鏡によつて観察し, 同時に顎堤粘膜 に現れた反応を対比させ, 次のような知見を得た.
1. 橋義歯ポンティックの基底面には, 材料および形態を問わずプラークの付着が見られ, 完全自浄型ポンティックについても, 基底面におけるプラークの付着状態からみると, 自浄性は従来考えられているほど完全なものではなく, 今後の課題となるものと考えられた.
2. ポンティックの基底面を粘膜に接触させた場台および圧迫した場合, 短期間で基底面に付着するプラークの量は, 陶材およびレジンに比較すると, 白金加金および金銀パラジウム合金の金属類の方が多かった.
3. ポンティックの基底面を粘膜に接触させる場合, 無圧の状態で接触させるよりも, 軽く圧迫を加える方が基底面に付着するプラークの量は少ない傾向を示した.
4. ポンティック基底面が粘膜と接触している場合, そこに付着するプラークの量は, 顎堤粘膜の炎症反応の強さに影響を与えるものと考える.
5. ポンティックの基底面に付着するプラークの内容は使用材料に関係なく, ほとんど球菌, 桿菌および糸状菌の3種類の形態の細菌から成る.
6. ポンティック基底面に付着するプラークの形成機序は, 歯面におけると同様に, 最初糖蛋白と思われる薄膜が付着し, 初期においては球菌および桿菌を主とする細菌の集落が見られ, 日時の経過とともに様々な糸状菌の増殖が見られるようになつた.
7. 肉眼的にポンティッケ基底面に付着したプラーケの量が少ない場合には, 球菌および桿菌が主体を成していて, プラークの付着が多い場合には, 糸状菌が多く認められた.
橋義歯ポンティックの材料と形態については, また解明すべき多くの問題点が残されている.これらの問題を解明するために, 顎堤粘膜の反応についての客観的判定法を考案し, またポンティックの形態については, 今後, 基底面の粘膜に対する接触様式だけでなく, 歯間鼓形空隙の形態, ポンティック頬舌面の豊隆の形態などについても症例数を増やして追究を行い, 臨床に応用していきたいと考える.

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