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Volumetric proportioning techniques for irreversible hydrocolloids: a comparative study

1986; Elsevier BV; Volume: 112; Issue: 6 Linguagem: Inglês

10.14219/jada.archive.1986.0099

1943-4723

C. Wayne Caswell, Ann Sue von Gonten, Thomas R. Meng,

Anatomy and Medical Technology

I rreversible hydrocolloids, as well as m any o th e r den tal m aterials, are p ro ­ portioned volumetrically by dentists. T h e A m e r ic a n D e n ta l A s s o c ia t io n specifies that an accurate weight-to-w ater ratio should be stated by the m anufactur­ ers o f irreversible hydrocolloids. This a rti­ cle repo rts the findings o f a laboratory study conducted to evaluate th ree vol­ um etric m ethods used to dispense irrever­ sible hydrocolloids; to com pare I he results w ith th e m a n u f a c tu r e r s ’ s u g g e s te d weights; and to determ ine w hether a p re ­ ferred technique o f p roportion ing the m a­ terials volumetrically could be identified. T h e w ater-pow der ratio in irreversible hydrocolloid m ixing is crucial fo r accurate im pression. T h e physical an d handling properties o f an irreversible hydrocolloid m ix ture can be changed by altering the pow der con ten t while holding the w ater conten t constan t.1'6 Skinner and Pom es1 stated tha t the strength o f the final im­ pression decreased if the w ater-pow der ratio was incorrect. S k inner and o thers2,6 rep o rted that too m uch o r too little water in com parison with pow der content will not allow the irreversible hydrocolloid to m eet standard requirem ents. A change in handling properties was rep o rted by Wilson and Sm ith3 and Skin­ n e r an d P hillips,6 who show ed th a t a change in w ater-pow der ratio altered gela­ tion time. R udd and o thers4,5 stated that the handling properties could be changed by a m ix ture tha t is too thick o r too thin. A m ix ture tha t is too th in causes the m aterial to ru n (Fig 1), and a m ixture that is too thick causes the m aterial to becom e grainy and to flow im properly (Fig 2). A variation in the w ater-pow der ratio causes the m ate­ rial to set too fast o r too slow, which makes m anipulation difficult.3,6 D im ensional stability o f irrev ers ib le hydrocolloids can be im proved if the con­ stant w ater-pow der ratio recom m ended by the m anufactu re r is follow ed.1,7,8 I t has been rep o rted that the scoops provided by th e m a n u fa c tu re r a re in a c c u ra te fo r m e asu rin g bulk p o w d er.4,5 H a m p so n 9 recom m ends th a t the pow der be m ea­ su red on a balance. Koski10 and R udd and o th e rs4,5 recom m end that, to contro l the variables, the pow der should be weighed before it is packaged (Fig 3). Less variation occurs in m anipulative anti physical p ro p ­ erties when alginate is p ropo rtioned by weight ra th e r than by volume. A lthough p ropo rtion ing the m aterial by