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Silicate cements prepared with mechanical mixers
Silicate cements prepared with mechanical mixers
Joseph Rubinstein, D .D .S ., Highland Park, III.
Silicate cements mixed with a W ig-L-B u g mechanical amalgamator had a higher compressive strength than those mixed by hand. Mechanical mixing reduced the setting time but increased the working time of the cements. Mechanical mixing provides uniform mixtures within a frac tion of a minute. There is no waste of powder. Use of the glass slab and spatula is eliminated.
The introduction of the mechanical amal gamator for the mixing of amalgam alloys with mercury has led to a more uniform amalgamation from one mix to another.1 It also has made it possible to reduce the mercury: alloy ratio, thus resulting in an amalgam restoration with increased ini tial strength.2 It was felt that a mechanical mixer could be used in the preparation of other dental materials as well. Brauer and Dickson3 examined the properties of mechanically mixed silicate cements at a standard consistency. This study was undertaken in order to compare the behavior of silicate cements at different powder: liquid ratios when mixed by hand and with the mechanical mixer. PR O C E D U R E
Four brands of silicate cements and cor responding liquids were purchased from
a dental supply house. They, together with the code letters, purchasing date, batch numbers and shades, are listed in Table 1. Six bottles of powder of the same brand and shade were emptied into a square-sided jar and mixed by rotating horizontally for two hours at the rate of 25 rpm. Six bottles of the corresponding liquid were emptied into a clean glassstoppered bottle. Small amounts of pow der, ranging in weight from 1.2 to 1.8 G m ., were placed in gelatin capsules4 large enough to accommodate these quantities. Unless otherwise specified, the prepa ration of the specimens was carried out at a temperature of 2 1 ° C. ± 2 ° C. and a relative humidity of 55 ± 4 per cent. The specimens were stored in an oven with a relative humidity approximating 100 per cent at 3 7 ° C. T h e temperature was con trolled by means of a thermostat. T h e humidity was produced by placing wick material around the walls of a glass cabi net inside the oven. W ater stored in con tainers at the bottom of the oven supplied the moisture through the wick material. In one series of experiments, the pow ders, ranging in weight from 1.2 to 1.8 G m ., were mixed on a glass slab with 0.4 cc. of liquid. T h e liquid was meas ured in calibrated syringes. One half of the total mass of powder was drawn into the liquid and spatulated for 15 seconds. One half of the remaining amount of powder was incorporated during the next 15 seconds. T h e remaining one fourth
RUBINSTEIN . . . VOLUME 65, SEPTEMBER 1962 • 25/311
portion was mixed into the already pro duced powder: liquid combination for 15 seconds. Then the whole mass was spatulated for the remaining 15 seconds in accordance with the method described in the American Dental Association Specifi cation No. 9 for dental silicate cement.® Quantities of 0.5 ml. of these mixed but unset cements were pressed between two flat plates until the specimens were 20 mm. in diameter. They were then tested for solubility and disintegration as de scribed in the American Dental Associa tion Specification No. 9 for dental silicate cement.5 Specimens were also prepared in brass rings which were approximately 5 m m . high and 9 m m . across the internal di ameter. These specimens were used to test the setting time of the silicate cements. A mold, 12 mm. high and 6 m m . in diameter, was employed to prepare the specimens for the compressive strength tests. A t the onset of this investigation, the specimens were prepared in split metal molds. Later on, Teflon6 was used to facilitate the separation of the speci mens from the molds.7 N o significant dif ference could be observed between the results obtained from the specimens pro duced in split metal molds and those in which Teflon was used to separate the silicate cements from the molds. Th e compressive strength, the solubil ity and the setting time of the cements
T a b le 1 •
were tested according to the methods de scribed in the American Dental Associa tion Specification No. 9 for dental silicate cement.5 In a second series of experiments, 0.4 cc. of liquid was added to the content of each gelatin capsule. T h e capsules were closed without the inclusion of a pestle and vibrated in a W ig-L -B u g me chanical amalgamator8 for 5, 10, and 20 seconds. The mixtures were then removed from the capsules and tested in the same fashion as the specimens mixed by hand. It soon became apparent that a 5-second vibration did not always mix the liquid with the powder, particularly at increased powder : liquid ratios. Therefore, mixing for five seconds was discontinued and no data are reported. In order to ascertain the influence of the pestle in the capsule on the heat pro duction in the silicate cement mixture, the temperature in the capsule was measured before and immediately after mechanical mixing. U pon conclusion of the tests, the shades of the mechanically mixed specimens were compared with the corresponding shades of the manufacturers’ shadeguides. R E S U L T S A N D D IS C U S S IO N
It was noted that the incorporation of a pestle into the capsule increased the tem perature of a mixture containing 1.6 to
M aterials investigated
Product
M a n u fa ctu re r
C ode le tte r
Purchase date
Batch no.
Shade
S. S. W h ite Filling p orce la in im proved
S. S. W h ite Dental M a nu f. C om pany
A
Dec. I960 Feb. 1961 A p ril 1961
20154173 11954099 32959294
20
De Trey's Synthetic P orcelain Im proved
L. D. Caulk C om pany
B
Dec. 1960 Jan. 1961 M a y 1961
25835 A 696 A 697
20
D urodent Enamel
O scar S ch a efer
C
A p ril 1961 M a y 1961
B 11 B 12 B 13
22
A ch a tite
V ivadent C o rp .
D
A p ril 1961 M a y 1961
0930759 0930758
4
26/312 • THE JOURNAL OF THE AM ERICAN D ENTAL ASSOCIATION
T a b le 2 • Effect o f varying p ow d e r:liq u id ra tio on the compressive strength o f silicate cements Amount o f p o w d e r in 0.4 cc. o f liquid
Compressive strength when hand-m ixed
C om pressive strength when mixed m echanically fo r 10 seconds
Com pressive strength when mixed m echanically fo r 20 seconds
Cement Mean
M e a n dev.
M ean
M ean dev.
M ean
M ean dev.
Grams k g ./cm .2
k g ./ cm.2
kg./cm .2
1.2 1.3 1.4 1.5 1.6 1.7 1.8
1,360 1,420 1,660 1,760 1,900 1,650
45 42 55 34 39 27
1,390 1,460 1,760 1,930 2,020 2,070 1,840
63 48 56 39 43 22 31
1,430 1,470 1,800 1,940 2,050 2,100 1,780
59 72 49 27 35 19 23
1.2 1.3 1.4 1.5 1.6 1.7 1.8
1,410 1,450 1,590 1,720 1,900 1,740
64 39 22 45 37 28
1,440 1,510 1,680 1,960 2,040 2,110 1,790
49 46 84 39 53 37 33
1,480 1,550 1,740 1,960 2,060 2,140 1,890
44 38 54 27 38 42 39
1.2 1.3 1.4 1.5 1.6 1.7 1.8
1,290 1,350 1,480 1,590 1,750 1,680
61 55 35 48 27 48
1,320 1,460 1,540 1,700 1,810 1,810 1,740
74 69 39 45 32 45 44
1,330 1,490 1,620 1,750 1,890 1,930 1,750
38 72 69 63 47 22 39
1.2 1.3 1.4 1.5 1.6 1.7 1.8
1,340 1,380 1,490 1,690 1,840 1,640
54 48 61 48 35 34
1,390 1,470 1,550 1,760 1,910 1,990 1,820
45 74 69 23 44 42 35
1,480 1,550 1,710 1,800 1,950 2,050 1,910
59 62 34 33 51 29 30
1.8 Gm . of powder to 0.4 cc. of liquid by 8 to 10° C . during a 10-second or 20second vibration. W hen the same ratios were mixed in capsules without the pestle, the temperature rose not more than 3 ° C. after 10-second or 20-second vibration. Since the rise of temperature had a defi nite influence on the setting time o f the silicate cements, it was decided to pre pare all the mechanically mixed speci mens, which were tested for compressive strength, solubility and disintegration, and setting time, without the use of a pestle inside the capsules. Compressive Strength • The values ob tained from the compressive strength tests together with the mean deviations are shown in Table 2.
In general, the greater the amount of powder added to 0.4 cc. of liquid, the higher was the compressive strength. This has already been pointed out by Paffenbarger and co-workers.9 A t a certain powder: liquid ratio, however, apparently when all of the particles had not been chemically attacked, the silicate cements became weak, whether prepared by hand or mechanically. It is interesting to note that the speci mens mixed mechanically for 10 or 20 seconds were able to develop a higher compressive strength than the handmixed cements. T h e motions in a W ig -L Bug are such that they add a sideward movement to the back-and-forth vibra tions. This results in a more thorough contact between the two ingredients of
RUBINSTEIN . . . VOLUME 45, SEPTEMBER 1962 • 27/313
the mixture, as evidenced by the fact that the color streaks caused by the in corporation of a colored catalyst into a white rubber paste disappear faster if a sideward motion is intermingled with the back-and-forth spatulation. It is possible, therefore, that the mixing in the W ig -L Bug provides, through its motions, for the incorporation of an increased amount of powder into a given portion of liquid. This may explain why the silicate ce ments mixed mechanically for 10 to 20 seconds showed a higher compressive strength than the hand-mixed specimens, with the 20-second mix exceeding the 10second mix by a slight margin. Solubility and Disintegration • T h e re sults of the tests on the solubility and
distintegration of handmixed and m e chanically mixed cements are shown in Table 3. T h e solubility decreased as the amount of powder incorporated into the liquid increased. A t increased powder: liquid ratios, the amount of matrix in the sili cate mixture is reduced and, according to Paffenbarger and co-workers,9 this decreases the solubility of the silicate cements. T h e solubility reached a minimum, after which the silicate cements became more soluble. N o striking differences re garding solubility and disintegration could be observed between the hand-mixed and the mechanically mixed specimens. T h e maximum strength and the mini mum solubility of the mechanically mixed
T a b le 3 • Effect o f varying p o w d e n liq u id ra tio on the so lu b ility o f silicate cements Am ount o f p o w d e r in 0.4 cc. o f liquid
S o lu b ility when hand-mixed
S o lu b ility when mixed m echanically fo r 10 seconds
S o lu b ility when mixed m echanically fo r 20 seconds
Cement M ean
M ean dev.
M ean
M ean dev.
M ean
M ean dev.
Grams Per cent
Per cent
Per cent
1.2 1.3 1.4 1.5 16 1.7 1.8
1.4 1.2 1.1 0.9 0.9 1.0
0.07 0.08 ■0.06 0.03 0.03 0.04
1.5 1.3 1.2 1.0 1.0 0.9 1.0
0.05 0.06 0.03 0.04 0.03 0.02 0.03
1.6 1.4 1.2 1.1 0.9 0.8 1.0
0.05 0.01 0.06 0.04 0.03 0.01 0.02
1.2 1.3 1.4 15 1.6 1.7 1.8
1.3 1.2 1.2 1.0 0.8 0.8
0.07 0.04 0.03 0.07 0.04 0.03
1.4 1.4 1.3 1.1 0.9 0.8 0.9
0.04 0.04 0.02 0.08 0.05 0.03 0.02
1.5 1.4 1.4 1.2 1.0 0.9 1.0
0.04 0.07 0.09 0.06 0.04 0.04 0.03
1.2 1.3 1.4 1.5 1.6 1.7 1.8
1.4 1.3 1.1 1.0 . 0.8 1.0
0.06 0.04 0.07 0.04 0.05 0.04
1.4 1.4 1.3 1.2 1.1 0.9 0.9
0.05 0.03 0.02 0.06 0.04 0.04 0.06
1.5 1.3 1.3 1.2 1.0 1.0 1.0
0.06 0.05 0.09 0.05 0.04 0.02 0.05
1.2 1.3 1.4 1.5 1.6 1.7 1.8
1.3 1.3 1.2 1.1 0.9 1.0
0.03 0.02 0.04 0.05 0.05 0.05
1.5 1.4 1.3 1.1 0.9 0.8 1.0
0.04 0.05 0.03 0.02 0.03 0.06 0.03
1.5 1.4 1.4 1.2 1.0 0.9 0.9
0.05 0.08 0.05 0.04 0.04 0.05 0.03
28/314 • TH EJO U R N AL OF THE AMERICAN DENTAL ASSOCIATION
Ta ble 4 • Effect o f varying p ow d e r:liq u id ra tio on the setting time o f silicate cements
Am ount o f p o w d e r in 0.4 cc. o f liquid
Setting tim e * when hand-mixed
Setting tim e * when mixed m echanically fo r 10 seconds
Setting tim e* when mixed m echanically fo r 20 seconds
Grams
Minutes
M inutes
Minutes
A
1.2 1.4 1.6 1.8
7 'A 6 4
6 41/2 4 3
5 4 31/2 214
B
1.2 1.4 1.6 1.8
7 6 4
7 4 /2 3 /2 3
6 4 3'/2 2'/2
C
1.2 1.4 1.6 1.8
7A 5'A A'A
6 /2 4 3'/2 2 'A
5 3'A 3 2
D
1.2 1.4 1.6 1.8
7 6 4
7 5 4'A 3
6 4 3 2
Cement
*Mean o f the results o f three tests.
cements occurred between the ratios of 1.6 to 1.8 Gm . of powder to 0.4 cc. of liquid. Setting T im e • Table 4 shows the aver age setting time with various powder: liquid ratios. T h e setting time of the specimens mixed mechanically for 20 seconds was shorter than the setting time of the ce ments mixed for only 10 seconds. Both the 20-second and the 10-second mixed ce ments set faster than the specimens pre pared according to the method described in the American Dental Association Spec ification N o. 9 for dental silicate cement.5 However, the fear that the mechanical mixing would produce excessive heat when carried out without the incorpora tion of a pestle into the capsule, thus dras tically reducing the setting time, was not substantiated. Caution seems appropriate when inter preting the observation that setting time of the silicate cements was reduced with the W ig-L -B u g. O n e of the primary pur poses in controlling the setting time is to
prevent the formation of a gel before the insertion of the cement into the pre pared cavity.10 Since the silicate cements can be mixed mechanically within 10 or 20 seconds instead of the one minute re quired by the Specification No. 9 for hand-mixing, the working time available for manipulation of the silicates is pro longed even though the setting time is slightly reduced. In addition, the setting time of the sili cate cements can be extended by cooling the mixing vehicle. A cooling device to increase the setting time of hand-mixed cements was used by Grünewald11 when he kneaded a sealed balloon containing the silicate cement mixture between his fingers under water. Table 5 shows the effect of cooling on the setting time of silicate cements mixed at a ratio of 1.7 G m . of powder to 0.4 cc. of liquid. Reduction of the temperature of the mixing vehicle from 21 ° C. to 10° C. extended the setting time for handmixed as well as mechanically mixed specimens. Cooling of the gelatin cap sule may be a means of producing a
RUBINSTEIN . . . VOLUME 65, SEPTEMBER 1962 • 29/315
silicate cement mixture with increased strength, low solubility, and retarded set ting time, provided the dew-point will permit the lowering of the temperature without precipitation capsules.
of water in the
Discoloration • N o discoloration of the mechanically mixed specimens could be noted when their shades were compared with the corresponding shades of the manufacturers’ shadeguides. Apparently, the cement was not contaminated during its manipulation in the W ig-L-Bug.
T a b le 5 • C om parison o f setting time o f cem ent A when mixed a t 21°C . and 10°C. a t a ra tio o f 1.7 Gm. o f p o w d e r to 0.4 cc. o f liquid 21 °C.
10°C.
H and-mixed
3 1/2 minutes
5/2 minutes
M ixed m echanically fo r 10 seconds
3
4Vi minutes
M ixed m echanically fo r 20 seconds
2'A minutes
5.
minutes
4
minutes
T h e exposure of the liquid to the
environmental minimum.
influence
is
kept
at
a
C L IN IC A L S IG N IF IC A N C E S U M M A R Y A N D C O N C L U S IO N S
Although the portions of silicate cement and liquid used in the Specification tests are much larger than those used in clini cal application, the results seem to favor mechanical mixing over hand-mixing. T h e gelatin capsules containing the sili cate powder should be stored in a cool, dry place. They should be marked with the shade of powder which they contain. I f the amount of powder included in each capsule is known, the quantity of liquid
1. T h e compressive strength, solubil ity and disintegration, setting time, and discoloration of four brands of silicate cements were tested at varying pow der: liquid ratios when mixed by hand and with a W ig-L -B u g mechanical amal gamator.
sule. After mixing in the mechanical mixer for 10 or 20 seconds, the two portions of the capsule are drawn apart, and the mix is carried to the cavity with a clean carrier.
2. U p to a certain powder : liquid ratio, the compressive strength increased, and the solubility and disintegration de creased, for hand-mixed as well as me chanically mixed cements. 3. T h e mechanically mixed specimens reached a higher compressive strength than the hand-mixed cements, with the 20-second mix exceeding the 10-second mix by a slight margin. 4. Mechanical mixing reduced the set ting time but increased the working time of the silicate cements. Specimens mixed
T h e possible advantages of this proce dure to the dental practitioner are: 1. T h e consistency of the mix will re main the same for every operation. 2. There is no waste of powder as often occurs when placing it on a glass slab. 3. T h e mix is ready within a fraction of a minute. 4. Disposal of the gelatin capsule after use eliminates the burdensome cleaning of the glass slab and spatula.
mechanically for 20 seconds set faster than those mixed for only 10 seconds. Cooling of the gelatin capsules before mixing retarded the setting time. 5. A 5-second vibration did not al ways mix the liquid with the powder. 6. T h e manipulation of the silicate ce ments in the W ig-L -B u g did not affect their color. 7. In clinical application, the me chanically mixed silicate cements pro vided uniform mixtures within a fraction
necessary to produce a mixture rendering optimal properties can be predetermined. Thus, when the cavity is ready for the silicate cement, the required amount of liquid is added to the content of the cap
30/316 • THE JOURNAL OF THE AMERICAN DENTAL ASSOCIATION
of a minute. There was no waste of powder, and the use of the glass slab and spatula was eliminated. 1893 Sheridan Road
1. Skinner, E. W ., and Phillips, R. W . Science o f dental materials, ed. 5. Philadelphia, W . B. Saunders Co., I960, p. 391. 2. Skinner, E. W ., and Mîzera, G . T. The Eames amalgam condensation technic. D. Progress 1:13 O ct. I960. 3. Brauer, F. J., and Dickson, G. Effects o f mechanical mixing on silicate cements. Presented before the Inter* national Association fo r Dental Research, A tla n tic City, March 1957. 4. Manufactured by Eli Lilly Company, Indianapolis.
5. Paffenbarger, G. C ., and others. American Dental Association specification no. 9 fo r dental silicate ce ment; first revision, effective July I, 1950. J.A .D .A. 40:186 Feb. 1950. 6. Supplied by the E. J. DuPont DeNemours Com pany, C hicago. 7. McConnell, D., and Brawley, R. G. Compressive strength o f reinforced silicate cement. J. Pros. Den. 10:1092 Nov.-Dee. I960. 8. Made by the Crescent Dental M anufacturing Co., Chicago. 9. Paffenbarger, G . C .; Schoonover, I. C., and Souder, W . Dental silicate cements: physical and chemical prop erties and a specification. J .A .D .A . & D. Cosmos 25:32 Jan. 1938. 10. Skinner, E. W ., and Phillips, R. W . Science of dental materials, ed. 5. Philadelphia, W . B. Saunders Co., I960, p. 251. 11. Grünewald, A . H ., and others. Silicate cement method o f mixing in a closed container to prevent effect of exposure to atmosphere. J.A .D .A . 46:184 Feb. 1953.
Prevention of caries in the patient undergoing orthodontic treatment
Philip Levens, D .D .S ., M .S ., Clayton, M o .
T h e danger for the orthodontic patient of an increase in caries can be eliminated if the problem is handled properly. Before the beginning of orthodontic treatment, the patient should receive a complete dental check-up by the patient’s general practitioner. T h e patient should continue his regular periodic visits, to his general practitioner for examination of the ex posed surfaces of the teeth and for a prophylaxis. Orthodontic patients, espe cially, should reduce their consumption of refined sugar.
out certain hazards. O ne of these hazards can be an increase in the incidence of caries activity for the patient. This danger can be eliminated totally, however, if handled in the proper manner. Orthodontics should be thought of as a team effort, the members of the team consisting of the patient, the patient’s general practitioner, and the orthodon tist. W ith complete cooperation on the part of all members of the team, the dan ger of increased caries activity can be eliminated and the orthodontic treatment of the patient carried to a successful completion.
T h e importance of orthodontics to the dental and general health of an indi vidual cannot be denied ; however, ortho dontic treatment is not performed with
Caries can be defined as a disease of the calcified tissues of the teeth caused by acid resulting from the action of micro organisms on carbohydrates and charac terized by a décalcification of the inor ganic portion and accompanied by a
Joseph Rubinstein, D .D .S ., Highland Park, III.
Silicate cements mixed with a W ig-L-B u g mechanical amalgamator had a higher compressive strength than those mixed by hand. Mechanical mixing reduced the setting time but increased the working time of the cements. Mechanical mixing provides uniform mixtures within a frac tion of a minute. There is no waste of powder. Use of the glass slab and spatula is eliminated.
The introduction of the mechanical amal gamator for the mixing of amalgam alloys with mercury has led to a more uniform amalgamation from one mix to another.1 It also has made it possible to reduce the mercury: alloy ratio, thus resulting in an amalgam restoration with increased ini tial strength.2 It was felt that a mechanical mixer could be used in the preparation of other dental materials as well. Brauer and Dickson3 examined the properties of mechanically mixed silicate cements at a standard consistency. This study was undertaken in order to compare the behavior of silicate cements at different powder: liquid ratios when mixed by hand and with the mechanical mixer. PR O C E D U R E
Four brands of silicate cements and cor responding liquids were purchased from
a dental supply house. They, together with the code letters, purchasing date, batch numbers and shades, are listed in Table 1. Six bottles of powder of the same brand and shade were emptied into a square-sided jar and mixed by rotating horizontally for two hours at the rate of 25 rpm. Six bottles of the corresponding liquid were emptied into a clean glassstoppered bottle. Small amounts of pow der, ranging in weight from 1.2 to 1.8 G m ., were placed in gelatin capsules4 large enough to accommodate these quantities. Unless otherwise specified, the prepa ration of the specimens was carried out at a temperature of 2 1 ° C. ± 2 ° C. and a relative humidity of 55 ± 4 per cent. The specimens were stored in an oven with a relative humidity approximating 100 per cent at 3 7 ° C. T h e temperature was con trolled by means of a thermostat. T h e humidity was produced by placing wick material around the walls of a glass cabi net inside the oven. W ater stored in con tainers at the bottom of the oven supplied the moisture through the wick material. In one series of experiments, the pow ders, ranging in weight from 1.2 to 1.8 G m ., were mixed on a glass slab with 0.4 cc. of liquid. T h e liquid was meas ured in calibrated syringes. One half of the total mass of powder was drawn into the liquid and spatulated for 15 seconds. One half of the remaining amount of powder was incorporated during the next 15 seconds. T h e remaining one fourth
RUBINSTEIN . . . VOLUME 65, SEPTEMBER 1962 • 25/311
portion was mixed into the already pro duced powder: liquid combination for 15 seconds. Then the whole mass was spatulated for the remaining 15 seconds in accordance with the method described in the American Dental Association Specifi cation No. 9 for dental silicate cement.® Quantities of 0.5 ml. of these mixed but unset cements were pressed between two flat plates until the specimens were 20 mm. in diameter. They were then tested for solubility and disintegration as de scribed in the American Dental Associa tion Specification No. 9 for dental silicate cement.5 Specimens were also prepared in brass rings which were approximately 5 m m . high and 9 m m . across the internal di ameter. These specimens were used to test the setting time of the silicate cements. A mold, 12 mm. high and 6 m m . in diameter, was employed to prepare the specimens for the compressive strength tests. A t the onset of this investigation, the specimens were prepared in split metal molds. Later on, Teflon6 was used to facilitate the separation of the speci mens from the molds.7 N o significant dif ference could be observed between the results obtained from the specimens pro duced in split metal molds and those in which Teflon was used to separate the silicate cements from the molds. Th e compressive strength, the solubil ity and the setting time of the cements
T a b le 1 •
were tested according to the methods de scribed in the American Dental Associa tion Specification No. 9 for dental silicate cement.5 In a second series of experiments, 0.4 cc. of liquid was added to the content of each gelatin capsule. T h e capsules were closed without the inclusion of a pestle and vibrated in a W ig-L -B u g me chanical amalgamator8 for 5, 10, and 20 seconds. The mixtures were then removed from the capsules and tested in the same fashion as the specimens mixed by hand. It soon became apparent that a 5-second vibration did not always mix the liquid with the powder, particularly at increased powder : liquid ratios. Therefore, mixing for five seconds was discontinued and no data are reported. In order to ascertain the influence of the pestle in the capsule on the heat pro duction in the silicate cement mixture, the temperature in the capsule was measured before and immediately after mechanical mixing. U pon conclusion of the tests, the shades of the mechanically mixed specimens were compared with the corresponding shades of the manufacturers’ shadeguides. R E S U L T S A N D D IS C U S S IO N
It was noted that the incorporation of a pestle into the capsule increased the tem perature of a mixture containing 1.6 to
M aterials investigated
Product
M a n u fa ctu re r
C ode le tte r
Purchase date
Batch no.
Shade
S. S. W h ite Filling p orce la in im proved
S. S. W h ite Dental M a nu f. C om pany
A
Dec. I960 Feb. 1961 A p ril 1961
20154173 11954099 32959294
20
De Trey's Synthetic P orcelain Im proved
L. D. Caulk C om pany
B
Dec. 1960 Jan. 1961 M a y 1961
25835 A 696 A 697
20
D urodent Enamel
O scar S ch a efer
C
A p ril 1961 M a y 1961
B 11 B 12 B 13
22
A ch a tite
V ivadent C o rp .
D
A p ril 1961 M a y 1961
0930759 0930758
4
26/312 • THE JOURNAL OF THE AM ERICAN D ENTAL ASSOCIATION
T a b le 2 • Effect o f varying p ow d e r:liq u id ra tio on the compressive strength o f silicate cements Amount o f p o w d e r in 0.4 cc. o f liquid
Compressive strength when hand-m ixed
C om pressive strength when mixed m echanically fo r 10 seconds
Com pressive strength when mixed m echanically fo r 20 seconds
Cement Mean
M e a n dev.
M ean
M ean dev.
M ean
M ean dev.
Grams k g ./cm .2
k g ./ cm.2
kg./cm .2
1.2 1.3 1.4 1.5 1.6 1.7 1.8
1,360 1,420 1,660 1,760 1,900 1,650
45 42 55 34 39 27
1,390 1,460 1,760 1,930 2,020 2,070 1,840
63 48 56 39 43 22 31
1,430 1,470 1,800 1,940 2,050 2,100 1,780
59 72 49 27 35 19 23
1.2 1.3 1.4 1.5 1.6 1.7 1.8
1,410 1,450 1,590 1,720 1,900 1,740
64 39 22 45 37 28
1,440 1,510 1,680 1,960 2,040 2,110 1,790
49 46 84 39 53 37 33
1,480 1,550 1,740 1,960 2,060 2,140 1,890
44 38 54 27 38 42 39
1.2 1.3 1.4 1.5 1.6 1.7 1.8
1,290 1,350 1,480 1,590 1,750 1,680
61 55 35 48 27 48
1,320 1,460 1,540 1,700 1,810 1,810 1,740
74 69 39 45 32 45 44
1,330 1,490 1,620 1,750 1,890 1,930 1,750
38 72 69 63 47 22 39
1.2 1.3 1.4 1.5 1.6 1.7 1.8
1,340 1,380 1,490 1,690 1,840 1,640
54 48 61 48 35 34
1,390 1,470 1,550 1,760 1,910 1,990 1,820
45 74 69 23 44 42 35
1,480 1,550 1,710 1,800 1,950 2,050 1,910
59 62 34 33 51 29 30
1.8 Gm . of powder to 0.4 cc. of liquid by 8 to 10° C . during a 10-second or 20second vibration. W hen the same ratios were mixed in capsules without the pestle, the temperature rose not more than 3 ° C. after 10-second or 20-second vibration. Since the rise of temperature had a defi nite influence on the setting time o f the silicate cements, it was decided to pre pare all the mechanically mixed speci mens, which were tested for compressive strength, solubility and disintegration, and setting time, without the use of a pestle inside the capsules. Compressive Strength • The values ob tained from the compressive strength tests together with the mean deviations are shown in Table 2.
In general, the greater the amount of powder added to 0.4 cc. of liquid, the higher was the compressive strength. This has already been pointed out by Paffenbarger and co-workers.9 A t a certain powder: liquid ratio, however, apparently when all of the particles had not been chemically attacked, the silicate cements became weak, whether prepared by hand or mechanically. It is interesting to note that the speci mens mixed mechanically for 10 or 20 seconds were able to develop a higher compressive strength than the handmixed cements. T h e motions in a W ig -L Bug are such that they add a sideward movement to the back-and-forth vibra tions. This results in a more thorough contact between the two ingredients of
RUBINSTEIN . . . VOLUME 45, SEPTEMBER 1962 • 27/313
the mixture, as evidenced by the fact that the color streaks caused by the in corporation of a colored catalyst into a white rubber paste disappear faster if a sideward motion is intermingled with the back-and-forth spatulation. It is possible, therefore, that the mixing in the W ig -L Bug provides, through its motions, for the incorporation of an increased amount of powder into a given portion of liquid. This may explain why the silicate ce ments mixed mechanically for 10 to 20 seconds showed a higher compressive strength than the hand-mixed specimens, with the 20-second mix exceeding the 10second mix by a slight margin. Solubility and Disintegration • T h e re sults of the tests on the solubility and
distintegration of handmixed and m e chanically mixed cements are shown in Table 3. T h e solubility decreased as the amount of powder incorporated into the liquid increased. A t increased powder: liquid ratios, the amount of matrix in the sili cate mixture is reduced and, according to Paffenbarger and co-workers,9 this decreases the solubility of the silicate cements. T h e solubility reached a minimum, after which the silicate cements became more soluble. N o striking differences re garding solubility and disintegration could be observed between the hand-mixed and the mechanically mixed specimens. T h e maximum strength and the mini mum solubility of the mechanically mixed
T a b le 3 • Effect o f varying p o w d e n liq u id ra tio on the so lu b ility o f silicate cements Am ount o f p o w d e r in 0.4 cc. o f liquid
S o lu b ility when hand-mixed
S o lu b ility when mixed m echanically fo r 10 seconds
S o lu b ility when mixed m echanically fo r 20 seconds
Cement M ean
M ean dev.
M ean
M ean dev.
M ean
M ean dev.
Grams Per cent
Per cent
Per cent
1.2 1.3 1.4 1.5 16 1.7 1.8
1.4 1.2 1.1 0.9 0.9 1.0
0.07 0.08 ■0.06 0.03 0.03 0.04
1.5 1.3 1.2 1.0 1.0 0.9 1.0
0.05 0.06 0.03 0.04 0.03 0.02 0.03
1.6 1.4 1.2 1.1 0.9 0.8 1.0
0.05 0.01 0.06 0.04 0.03 0.01 0.02
1.2 1.3 1.4 15 1.6 1.7 1.8
1.3 1.2 1.2 1.0 0.8 0.8
0.07 0.04 0.03 0.07 0.04 0.03
1.4 1.4 1.3 1.1 0.9 0.8 0.9
0.04 0.04 0.02 0.08 0.05 0.03 0.02
1.5 1.4 1.4 1.2 1.0 0.9 1.0
0.04 0.07 0.09 0.06 0.04 0.04 0.03
1.2 1.3 1.4 1.5 1.6 1.7 1.8
1.4 1.3 1.1 1.0 . 0.8 1.0
0.06 0.04 0.07 0.04 0.05 0.04
1.4 1.4 1.3 1.2 1.1 0.9 0.9
0.05 0.03 0.02 0.06 0.04 0.04 0.06
1.5 1.3 1.3 1.2 1.0 1.0 1.0
0.06 0.05 0.09 0.05 0.04 0.02 0.05
1.2 1.3 1.4 1.5 1.6 1.7 1.8
1.3 1.3 1.2 1.1 0.9 1.0
0.03 0.02 0.04 0.05 0.05 0.05
1.5 1.4 1.3 1.1 0.9 0.8 1.0
0.04 0.05 0.03 0.02 0.03 0.06 0.03
1.5 1.4 1.4 1.2 1.0 0.9 0.9
0.05 0.08 0.05 0.04 0.04 0.05 0.03
28/314 • TH EJO U R N AL OF THE AMERICAN DENTAL ASSOCIATION
Ta ble 4 • Effect o f varying p ow d e r:liq u id ra tio on the setting time o f silicate cements
Am ount o f p o w d e r in 0.4 cc. o f liquid
Setting tim e * when hand-mixed
Setting tim e * when mixed m echanically fo r 10 seconds
Setting tim e* when mixed m echanically fo r 20 seconds
Grams
Minutes
M inutes
Minutes
A
1.2 1.4 1.6 1.8
7 'A 6 4
6 41/2 4 3
5 4 31/2 214
B
1.2 1.4 1.6 1.8
7 6 4
7 4 /2 3 /2 3
6 4 3'/2 2'/2
C
1.2 1.4 1.6 1.8
7A 5'A A'A
6 /2 4 3'/2 2 'A
5 3'A 3 2
D
1.2 1.4 1.6 1.8
7 6 4
7 5 4'A 3
6 4 3 2
Cement
*Mean o f the results o f three tests.
cements occurred between the ratios of 1.6 to 1.8 Gm . of powder to 0.4 cc. of liquid. Setting T im e • Table 4 shows the aver age setting time with various powder: liquid ratios. T h e setting time of the specimens mixed mechanically for 20 seconds was shorter than the setting time of the ce ments mixed for only 10 seconds. Both the 20-second and the 10-second mixed ce ments set faster than the specimens pre pared according to the method described in the American Dental Association Spec ification N o. 9 for dental silicate cement.5 However, the fear that the mechanical mixing would produce excessive heat when carried out without the incorpora tion of a pestle into the capsule, thus dras tically reducing the setting time, was not substantiated. Caution seems appropriate when inter preting the observation that setting time of the silicate cements was reduced with the W ig-L -B u g. O n e of the primary pur poses in controlling the setting time is to
prevent the formation of a gel before the insertion of the cement into the pre pared cavity.10 Since the silicate cements can be mixed mechanically within 10 or 20 seconds instead of the one minute re quired by the Specification No. 9 for hand-mixing, the working time available for manipulation of the silicates is pro longed even though the setting time is slightly reduced. In addition, the setting time of the sili cate cements can be extended by cooling the mixing vehicle. A cooling device to increase the setting time of hand-mixed cements was used by Grünewald11 when he kneaded a sealed balloon containing the silicate cement mixture between his fingers under water. Table 5 shows the effect of cooling on the setting time of silicate cements mixed at a ratio of 1.7 G m . of powder to 0.4 cc. of liquid. Reduction of the temperature of the mixing vehicle from 21 ° C. to 10° C. extended the setting time for handmixed as well as mechanically mixed specimens. Cooling of the gelatin cap sule may be a means of producing a
RUBINSTEIN . . . VOLUME 65, SEPTEMBER 1962 • 29/315
silicate cement mixture with increased strength, low solubility, and retarded set ting time, provided the dew-point will permit the lowering of the temperature without precipitation capsules.
of water in the
Discoloration • N o discoloration of the mechanically mixed specimens could be noted when their shades were compared with the corresponding shades of the manufacturers’ shadeguides. Apparently, the cement was not contaminated during its manipulation in the W ig-L-Bug.
T a b le 5 • C om parison o f setting time o f cem ent A when mixed a t 21°C . and 10°C. a t a ra tio o f 1.7 Gm. o f p o w d e r to 0.4 cc. o f liquid 21 °C.
10°C.
H and-mixed
3 1/2 minutes
5/2 minutes
M ixed m echanically fo r 10 seconds
3
4Vi minutes
M ixed m echanically fo r 20 seconds
2'A minutes
5.
minutes
4
minutes
T h e exposure of the liquid to the
environmental minimum.
influence
is
kept
at
a
C L IN IC A L S IG N IF IC A N C E S U M M A R Y A N D C O N C L U S IO N S
Although the portions of silicate cement and liquid used in the Specification tests are much larger than those used in clini cal application, the results seem to favor mechanical mixing over hand-mixing. T h e gelatin capsules containing the sili cate powder should be stored in a cool, dry place. They should be marked with the shade of powder which they contain. I f the amount of powder included in each capsule is known, the quantity of liquid
1. T h e compressive strength, solubil ity and disintegration, setting time, and discoloration of four brands of silicate cements were tested at varying pow der: liquid ratios when mixed by hand and with a W ig-L -B u g mechanical amal gamator.
sule. After mixing in the mechanical mixer for 10 or 20 seconds, the two portions of the capsule are drawn apart, and the mix is carried to the cavity with a clean carrier.
2. U p to a certain powder : liquid ratio, the compressive strength increased, and the solubility and disintegration de creased, for hand-mixed as well as me chanically mixed cements. 3. T h e mechanically mixed specimens reached a higher compressive strength than the hand-mixed cements, with the 20-second mix exceeding the 10-second mix by a slight margin. 4. Mechanical mixing reduced the set ting time but increased the working time of the silicate cements. Specimens mixed
T h e possible advantages of this proce dure to the dental practitioner are: 1. T h e consistency of the mix will re main the same for every operation. 2. There is no waste of powder as often occurs when placing it on a glass slab. 3. T h e mix is ready within a fraction of a minute. 4. Disposal of the gelatin capsule after use eliminates the burdensome cleaning of the glass slab and spatula.
mechanically for 20 seconds set faster than those mixed for only 10 seconds. Cooling of the gelatin capsules before mixing retarded the setting time. 5. A 5-second vibration did not al ways mix the liquid with the powder. 6. T h e manipulation of the silicate ce ments in the W ig-L -B u g did not affect their color. 7. In clinical application, the me chanically mixed silicate cements pro vided uniform mixtures within a fraction
necessary to produce a mixture rendering optimal properties can be predetermined. Thus, when the cavity is ready for the silicate cement, the required amount of liquid is added to the content of the cap
30/316 • THE JOURNAL OF THE AMERICAN DENTAL ASSOCIATION
of a minute. There was no waste of powder, and the use of the glass slab and spatula was eliminated. 1893 Sheridan Road
1. Skinner, E. W ., and Phillips, R. W . Science o f dental materials, ed. 5. Philadelphia, W . B. Saunders Co., I960, p. 391. 2. Skinner, E. W ., and Mîzera, G . T. The Eames amalgam condensation technic. D. Progress 1:13 O ct. I960. 3. Brauer, F. J., and Dickson, G. Effects o f mechanical mixing on silicate cements. Presented before the Inter* national Association fo r Dental Research, A tla n tic City, March 1957. 4. Manufactured by Eli Lilly Company, Indianapolis.
5. Paffenbarger, G. C ., and others. American Dental Association specification no. 9 fo r dental silicate ce ment; first revision, effective July I, 1950. J.A .D .A. 40:186 Feb. 1950. 6. Supplied by the E. J. DuPont DeNemours Com pany, C hicago. 7. McConnell, D., and Brawley, R. G. Compressive strength o f reinforced silicate cement. J. Pros. Den. 10:1092 Nov.-Dee. I960. 8. Made by the Crescent Dental M anufacturing Co., Chicago. 9. Paffenbarger, G . C .; Schoonover, I. C., and Souder, W . Dental silicate cements: physical and chemical prop erties and a specification. J .A .D .A . & D. Cosmos 25:32 Jan. 1938. 10. Skinner, E. W ., and Phillips, R. W . Science of dental materials, ed. 5. Philadelphia, W . B. Saunders Co., I960, p. 251. 11. Grünewald, A . H ., and others. Silicate cement method o f mixing in a closed container to prevent effect of exposure to atmosphere. J.A .D .A . 46:184 Feb. 1953.
Prevention of caries in the patient undergoing orthodontic treatment
Philip Levens, D .D .S ., M .S ., Clayton, M o .
T h e danger for the orthodontic patient of an increase in caries can be eliminated if the problem is handled properly. Before the beginning of orthodontic treatment, the patient should receive a complete dental check-up by the patient’s general practitioner. T h e patient should continue his regular periodic visits, to his general practitioner for examination of the ex posed surfaces of the teeth and for a prophylaxis. Orthodontic patients, espe cially, should reduce their consumption of refined sugar.
out certain hazards. O ne of these hazards can be an increase in the incidence of caries activity for the patient. This danger can be eliminated totally, however, if handled in the proper manner. Orthodontics should be thought of as a team effort, the members of the team consisting of the patient, the patient’s general practitioner, and the orthodon tist. W ith complete cooperation on the part of all members of the team, the dan ger of increased caries activity can be eliminated and the orthodontic treatment of the patient carried to a successful completion.
T h e importance of orthodontics to the dental and general health of an indi vidual cannot be denied ; however, ortho dontic treatment is not performed with
Caries can be defined as a disease of the calcified tissues of the teeth caused by acid resulting from the action of micro organisms on carbohydrates and charac terized by a décalcification of the inor ganic portion and accompanied by a