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Vacuum-mixed silicate cements
Vacuum-mixed silicate cements acid gel matrix. This condition can be observed
Harvey W . Lyon, DDS, PhD Louella J. Cosca, DMD, Chicago
readily by pressing a small amount o f freshly m ixed cem ent betw een tw o glass slides until a thin film is form ed. W hen view ed m icroscopically, a myriad o f bubbles, ranging in diameter from 5(n to 80/x can be seen in the translucent matrix (F ig. 1 ). These observations were noted b y Paf-
Silicate powder and liquid can be mixed me chanically in a vacuum atmosphere to m ini mize the porosity of the silicate cement gel m atrix induced by the use of conventional m ix ing methods. Until the effect of the elim ina tion of porosity on the properties of silicate cements has been determined, however, the clinical use of vacuum-mixed silicate cements is not advised or recommended.
During the past 25 years, m uch attention has been given to the refinement o f the chemical, physical, and physiologic properties o f silicate
fenbarger4 and he recom m ends that extrem e care be used during the mixing procedure to minimize the am ount o f entrapped air in the mix. H e further says that, “ T hey (air b u bbles) cannot be co n veniently eliminated as they w ould be if m ixed in a vacuum .” R ecently, we have been com paring the sub surface penetration depths o f various coating agents and their subsequent efficacy in the pre vention o f syneresis or im bibition o r both in freshly prepared, conventionally m ixed silicates. Exam ination o f ground, polished sections at 30 X
or higher magnifications revealed severe
cements. A lthough classified as a permanent re
pitting and cratering on flat surfaces and at line angles, primarily the result o f the exposure of
storative material, the durabilty o f silicate cem ent
entrapped air bubbles during the polishing p ro
seems to range from 6 months in som e patients to several decades in others.1 Some properties
cedure. It should be noted that the sm ooth sur face o f a porous silicate restoration is virtually
contribute tow ard the inadequacies o f silicate ce ment and seem to defy significant im provem ent;
free o f pits and craters after rem oval o f the
namely, relatively low levels o f crushing strength and surface hardness, a tendency toward a rapid
as a result o f the finishing procedures, the porous voids being exposed b y the abrasive action o f p o l ishing disks and strips.
rate o f dissolution, and a lack o f resistance to surface stains.2' 3
matrix strip. Surface pitting and roughness occu r
To
com bat porosity,
we
have
developed
a
O ne unexplored and unevaluated factor that may contribute to the presence o f these inade
simple inexpensive technic w hereby the silicate p ow der and liquid are m ixed m echanically in a
quacies is the induced porosity o f the gel matrix.
vacuum
C onventional mixing procedures, hand spatula-
relatively free o f voids and appears highly trans
tion or m echanical mixing, m ake it im possible
lucent. T he efficacy o f vacuum -m ixed procedures
to prevent entrapment o f air bubbles in the silicic
is apparent in a com parison o f Figures 2 and 3.
atmosphere,
and the resulting m ix is
129
Fig. 1 ■ Silicate cem ent m ixed by hand sp a tu la tio n fo r 4 0 seconds; film thickness, 80«. D iam eters of bubbles range from 3ft to 7 0 m. Each d ivision represents 10/i
T echnic Disposable glass vials or other appropriate containers with volumes of 1, 2, or 3 ml. are fitted with self-sealing rubber stoppers after the addition of a preweighed amount of silicate powder. A 26-gauge needle is adapted to a va cuum source; it is then inserted through the stop
Fig 2 ■ Silicate cem ent m echani c a lly m ixed in d e ntal a m a lg a m ato r fo r 15 seconds in nonvacuum a t mosphere. D iam eter and num ber of bubbles are s im ila r to those in h a n d -s p a tu la te d m ixes. Each d iv i sion represents 10 m
130 ■ J A D A , V o l. 75, Ju ly 1967
per, and air is removed from the interstices of the powder particles and the container. Dispos able tuberculin syringes are used to inject a pre cise volume of phosphoric acid through the self sealing stopper while the container is still con nected to the vacuum source. After the injection, the two needles are withdrawn, and the container is transferred to a mechanical amalgamator and mixed for 10 to 15 seconds. The container is then
..
O
.if »
:
■* f
*
*
Fig 3 ■ Silicate cem ent m e ch a n i ca lly m ixed in d e ntal a m a lg a m a to r fo r 15 seconds under lig h t vacuum . Diam eters o f bubbles range from 3/u to 2 0 M. F urther reduc tio n in a ir bubble co n te n t could p robably be obtained by use o f h ig h er vacuum source. Each d iv i sion represents 1On
*,
-
O
o *
* # ** 0v © * **
10
20
3(9
,
40
.
50
niw+fflluii imlig iVyiinf placed on the platform of a vibrator for a seconds to consolidate the contents before vacuum is broken. T he initial setting rate be delayed by prechilling the container and liquid.
few the can the
Com m ents A lthough m echanical spatulation of silicate ce m ent m ixtures is an acceptable procedure and does not alter the essential properties of the m ix,3,512 we are n o t certain w hat effect the elimi nation of porosity will have on the general proper ties of this new m ixture. A lthough it is a wellknown fact that the elim ination of porosity from other dental m aterials resulted in im proved physi cal properties, we are concerned about such fac tors as dim ensional stability during the setting re action, residual phosphoric acid content, relative solubility, and m atching present color shades with tooth structure. Studies are being proposed to determ ine and com pare th e chem ical, physical, and clinical properties of vacuum -m ixed silicates with those prepared by conventional m ethods. We do not advise or recom m end the clinical use of vacuum -m ixed silicates until the chemical, physical, and physiologic properties have been determ ined.
From the research fa c ility , A m e rica n D ental Asso cia tio n , 211 E. C hicago A ve., Chicago, 6 0 6 1 1 , where D octor Lyon is senior research associate and d ire cto r and Doctor Cosca is a research assistant.
1. Paffenbarger, G. C. Silicate cem ent: an in ve stig a tio n by o group o f dentists under d ire ctio n o f the A .D .A . research fellow ship a t the N a tio n a l Bureau o f Standards. J A D A 2 7 :1 6 1 1 O ct., 1940. 2. Peyton, F. A ., and others. Restorative d e n ta l m a terials, ed. 2. St. Louis, C. V. M osby Co., 1964. 3. Phillips, R. W . Recent im provem ents in dental m aterials th a t the operative d e n tist should know. JA D A 7 3 :8 4 July, 1966. 4. P affenbarger, G. C .; Schoonover, I. C., and Souder, W ilm e r. Dental silica te cem ents: physical and chem ical properties and a sp e cifica tio n . J A D A 2 5 :3 2 Jan., 1938. 5. Brauer, F. J. M echanical m a n ip u la tio n o f silicate cements. JA D A 51 :7 1 3 Dec., 1955. 6. Rubinstein, Joseph. Silicate cements prepared w ith m echanical m ixers. JA D A 6 5 :3 1 0 Sept., 1962. 7. M cLendon, Huston. M echanical m ixin g o f silicate cements. Dent Asst. 3 2 :1 4 J u ly -A u g ., 1963. 8. Massler, M a u ry, and Barber, Dennis. M ore e f f i cie n t m ethod o f m ixin g silicate cem ent. J A D A 6 4 :7 2 4 M ay, 19 6 2 . 9. Berglars, G. K. M echanical m ixin g o f silica te ce ments, p a rt I. Dent Dig 7 0 :2 1 7 M ay, 1964. 10. Berglars, G. K. M echanical m ixin g o f silica te ce m ents, p a rt II. Dent Dig 7 0 :2 5 6 June, 1964. 1 1 . Phillips, R. W .; Swartz, M . L., and Chong, W . F. Properties o f silicate cements m ixed by hand and m e chanical means. J S C a lif D ent Assn 3 3 :2 3 9 M ay, 1965. 12. H o lze n do ro ff, L. C. Precision p ro p o rtio n in g fo r m echanically m ixed silicate cem ent. J Prosth D ent 1 6 :7 5 6 J u ly -A u g ., 1966.
Lyon-C osca: V A C U U M -M IX E D
S ILIC A TE
CEMENTS ■
131
Harvey W . Lyon, DDS, PhD Louella J. Cosca, DMD, Chicago
readily by pressing a small amount o f freshly m ixed cem ent betw een tw o glass slides until a thin film is form ed. W hen view ed m icroscopically, a myriad o f bubbles, ranging in diameter from 5(n to 80/x can be seen in the translucent matrix (F ig. 1 ). These observations were noted b y Paf-
Silicate powder and liquid can be mixed me chanically in a vacuum atmosphere to m ini mize the porosity of the silicate cement gel m atrix induced by the use of conventional m ix ing methods. Until the effect of the elim ina tion of porosity on the properties of silicate cements has been determined, however, the clinical use of vacuum-mixed silicate cements is not advised or recommended.
During the past 25 years, m uch attention has been given to the refinement o f the chemical, physical, and physiologic properties o f silicate
fenbarger4 and he recom m ends that extrem e care be used during the mixing procedure to minimize the am ount o f entrapped air in the mix. H e further says that, “ T hey (air b u bbles) cannot be co n veniently eliminated as they w ould be if m ixed in a vacuum .” R ecently, we have been com paring the sub surface penetration depths o f various coating agents and their subsequent efficacy in the pre vention o f syneresis or im bibition o r both in freshly prepared, conventionally m ixed silicates. Exam ination o f ground, polished sections at 30 X
or higher magnifications revealed severe
cements. A lthough classified as a permanent re
pitting and cratering on flat surfaces and at line angles, primarily the result o f the exposure of
storative material, the durabilty o f silicate cem ent
entrapped air bubbles during the polishing p ro
seems to range from 6 months in som e patients to several decades in others.1 Some properties
cedure. It should be noted that the sm ooth sur face o f a porous silicate restoration is virtually
contribute tow ard the inadequacies o f silicate ce ment and seem to defy significant im provem ent;
free o f pits and craters after rem oval o f the
namely, relatively low levels o f crushing strength and surface hardness, a tendency toward a rapid
as a result o f the finishing procedures, the porous voids being exposed b y the abrasive action o f p o l ishing disks and strips.
rate o f dissolution, and a lack o f resistance to surface stains.2' 3
matrix strip. Surface pitting and roughness occu r
To
com bat porosity,
we
have
developed
a
O ne unexplored and unevaluated factor that may contribute to the presence o f these inade
simple inexpensive technic w hereby the silicate p ow der and liquid are m ixed m echanically in a
quacies is the induced porosity o f the gel matrix.
vacuum
C onventional mixing procedures, hand spatula-
relatively free o f voids and appears highly trans
tion or m echanical mixing, m ake it im possible
lucent. T he efficacy o f vacuum -m ixed procedures
to prevent entrapment o f air bubbles in the silicic
is apparent in a com parison o f Figures 2 and 3.
atmosphere,
and the resulting m ix is
129
Fig. 1 ■ Silicate cem ent m ixed by hand sp a tu la tio n fo r 4 0 seconds; film thickness, 80«. D iam eters of bubbles range from 3ft to 7 0 m. Each d ivision represents 10/i
T echnic Disposable glass vials or other appropriate containers with volumes of 1, 2, or 3 ml. are fitted with self-sealing rubber stoppers after the addition of a preweighed amount of silicate powder. A 26-gauge needle is adapted to a va cuum source; it is then inserted through the stop
Fig 2 ■ Silicate cem ent m echani c a lly m ixed in d e ntal a m a lg a m ato r fo r 15 seconds in nonvacuum a t mosphere. D iam eter and num ber of bubbles are s im ila r to those in h a n d -s p a tu la te d m ixes. Each d iv i sion represents 10 m
130 ■ J A D A , V o l. 75, Ju ly 1967
per, and air is removed from the interstices of the powder particles and the container. Dispos able tuberculin syringes are used to inject a pre cise volume of phosphoric acid through the self sealing stopper while the container is still con nected to the vacuum source. After the injection, the two needles are withdrawn, and the container is transferred to a mechanical amalgamator and mixed for 10 to 15 seconds. The container is then
..
O
.if »
:
■* f
*
*
Fig 3 ■ Silicate cem ent m e ch a n i ca lly m ixed in d e ntal a m a lg a m a to r fo r 15 seconds under lig h t vacuum . Diam eters o f bubbles range from 3/u to 2 0 M. F urther reduc tio n in a ir bubble co n te n t could p robably be obtained by use o f h ig h er vacuum source. Each d iv i sion represents 1On
*,
-
O
o *
* # ** 0v © * **
10
20
3(9
,
40
.
50
niw+fflluii imlig iVyiinf placed on the platform of a vibrator for a seconds to consolidate the contents before vacuum is broken. T he initial setting rate be delayed by prechilling the container and liquid.
few the can the
Com m ents A lthough m echanical spatulation of silicate ce m ent m ixtures is an acceptable procedure and does not alter the essential properties of the m ix,3,512 we are n o t certain w hat effect the elimi nation of porosity will have on the general proper ties of this new m ixture. A lthough it is a wellknown fact that the elim ination of porosity from other dental m aterials resulted in im proved physi cal properties, we are concerned about such fac tors as dim ensional stability during the setting re action, residual phosphoric acid content, relative solubility, and m atching present color shades with tooth structure. Studies are being proposed to determ ine and com pare th e chem ical, physical, and clinical properties of vacuum -m ixed silicates with those prepared by conventional m ethods. We do not advise or recom m end the clinical use of vacuum -m ixed silicates until the chemical, physical, and physiologic properties have been determ ined.
From the research fa c ility , A m e rica n D ental Asso cia tio n , 211 E. C hicago A ve., Chicago, 6 0 6 1 1 , where D octor Lyon is senior research associate and d ire cto r and Doctor Cosca is a research assistant.
1. Paffenbarger, G. C. Silicate cem ent: an in ve stig a tio n by o group o f dentists under d ire ctio n o f the A .D .A . research fellow ship a t the N a tio n a l Bureau o f Standards. J A D A 2 7 :1 6 1 1 O ct., 1940. 2. Peyton, F. A ., and others. Restorative d e n ta l m a terials, ed. 2. St. Louis, C. V. M osby Co., 1964. 3. Phillips, R. W . Recent im provem ents in dental m aterials th a t the operative d e n tist should know. JA D A 7 3 :8 4 July, 1966. 4. P affenbarger, G. C .; Schoonover, I. C., and Souder, W ilm e r. Dental silica te cem ents: physical and chem ical properties and a sp e cifica tio n . J A D A 2 5 :3 2 Jan., 1938. 5. Brauer, F. J. M echanical m a n ip u la tio n o f silicate cements. JA D A 51 :7 1 3 Dec., 1955. 6. Rubinstein, Joseph. Silicate cements prepared w ith m echanical m ixers. JA D A 6 5 :3 1 0 Sept., 1962. 7. M cLendon, Huston. M echanical m ixin g o f silicate cements. Dent Asst. 3 2 :1 4 J u ly -A u g ., 1963. 8. Massler, M a u ry, and Barber, Dennis. M ore e f f i cie n t m ethod o f m ixin g silicate cem ent. J A D A 6 4 :7 2 4 M ay, 19 6 2 . 9. Berglars, G. K. M echanical m ixin g o f silica te ce ments, p a rt I. Dent Dig 7 0 :2 1 7 M ay, 1964. 10. Berglars, G. K. M echanical m ixin g o f silica te ce m ents, p a rt II. Dent Dig 7 0 :2 5 6 June, 1964. 1 1 . Phillips, R. W .; Swartz, M . L., and Chong, W . F. Properties o f silicate cements m ixed by hand and m e chanical means. J S C a lif D ent Assn 3 3 :2 3 9 M ay, 1965. 12. H o lze n do ro ff, L. C. Precision p ro p o rtio n in g fo r m echanically m ixed silicate cem ent. J Prosth D ent 1 6 :7 5 6 J u ly -A u g ., 1966.
Lyon-C osca: V A C U U M -M IX E D
S ILIC A TE
CEMENTS ■
131