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Fracture strength of Class II amalgam restorations condensed over protective bases
Fracture
strength
condensed
over
of Class II amalgam protective
restorations
bases
Dioracy Fonterrada Vieira, D.D.S., D.L., M.S.D.,* Josh Mondelli, D.D.S., D.L.** Faculdades de Odontologia, Skio Paulo and Bauru, Sa’o Paulo, Brazil
and Universidade
de
A
protective base, serving as a substitute for dentin, guards the pulp against thermal, electrical, chemical, and mechanical injury. In addition, a medicated base promotes the formation of reparative dentin. All bases should possess sufficient strength to resist the forces of condensation of dental amalgam or gold foil’; in addition, they must resist the stresses of mastication. The most important physical requirement of a base is its ability to resist condensation forces.” A cement base needs to resist more than 170 p.s.i. to preclude fracture and displacement resulting from condensation3 Zinc oxide and eugenol cement (ZOE) lacks the necessary strength when compared to zinc phosphate cement in Class I and II amalgam restorations.‘+ The recommendation that two or more layers of varnish be applied to cavity walls has added another factor to base techniques.” When tested, the varnish failed to alter the strength of cylindrical specimens of amalgam.7 A previous report discussed pertinent factors which relate to the physical problems of protective bases5 The class of preparation, the size of the cavity, and whether or not the line angles are created in dentin relate to the physical needs of a base. The views in that report agreed with earlier discussions of this problem.P. :’ Calcium hydroxide, protected with zinc oxide and eugenol cement (ZOE), may suffice for small bases, but larger areas require zinc phosphate cement, These concepts and other clinical practices have, in part, been investigated. and the results are described in this report. MATERIALS
AND
METHOD
All tests were made in cobalt ing a Class II cavity preparation *Professor **Associate 166
and
Chairman,
Professor
and
chromium dies of a lower right first molar contain(Figs, 1, 2, and 3) .:, The preparation conformed
Department Chairman,
of Dental Department
Materials, of Operative
SF%o Paulo. Dentistry,
Bauru
Volume Number
30 2
Fracture
strength
of
A
/
,’
Fig. 1. Occlusal
(A) and proximal
A’ Fig. 2. (Top) the
(B) aspects
B’
Occlusal view in a longitudinal
same dies
amalgam
of dies 2 section
Fig. 3. Proximal
of dies 2
167
B
of die 1.
C’
(A), 3 (B), and 4 (C). (A’, B’, and C’).
aspect
restorations
(Bottom)
Schematic
view
of
(A), 3 (B), and 4 (C).
to standard operative procedures. lo, I1 The dies represented one preparation which requires no base and three variations which required bases. The base materials were: ZOE with 0.4 per cent zinc acetate, * Fynal cement,? Dycal,? zinc phosphate cement,$ and copalite varnish.§ These served as base materials and were used in “Pharmakopea,
Brazil,
South
America.
tL. D. Caulk $S. S. White
Company, Milford, Del. Dental Mfg. Company, Philadelphia,
§Cooley
Cooley,
and
Houston,
Texas.
Pa,
168
Vieira
and
Mondelli
A’
B'
Fig. 4. (Top) Pulpal walls and dies 2 (A), 3 (B), and 4 (C). section (A’, B’, and c’).
mesial
and
(Bottom)
C'
distal axial angles rebuilt with base materials for Schematic view of the same dies in a longitudinal
combinations conforming to clinical practice. The amalgam restorations were made of fine-cut alloy.* All materials were manipulated according to the manufacturers’ recommendations. Die 1 contained a cavity preparation which required no protective base (Fig. 1). The cavity was restored in two ways. One cavity preparation received three coats of varnish. Each layer was applied after the previous one had dried. The amalgam restoration was condensed over the varnish. The other cavity preparation received the amalgam restoration without the varnish. This was the control. Die 2 simulated a tooth with deep caries on the pulpal wall. The mesial and distal axial walls were sound. The base was inserted only on the pulpal wall (Figs. 4, A, and 5, A). A small step on the buccal and lingual walls established the thickness of the bases in all dies. After insertion of the base, all the preparations were the same as in die 1 (Fig. 1) The bases inserted in all dies (Nos. 2, 3, and 4) were made up of: three coats of varnish followed by zinc phosphate cement followed by three coats of varnish; zinc phosphate cement alone; 0.1 mm. of Dycal covered with zinc phosphate cement : and 0.1 mm. of ZOE covered with zinc phosphate cement. Die 3 simulated a tooth in which caries involved the mesiopulpal line angle. The bases replaced the mesioaxial wall and part of the pulpal wall (Figs. 4, B, and 5, B). Die 4 simulated a tooth with deep caries in which the pulpal and both axial walls required restoration with a base (Figs. 4, C, and 5, C) . After the bases had set, an amalgam restoration was condensed into the cavity. The size of all restorations was standardized by a matrix. Five restorations were made for each variation of base and time. After the designated time of one or 24 *L.
D. Caulk
Company,
Milford,
Del.
Volume Number
Fracture
30 2
Fig.
5. Same
as Fig.
4 seen from
Table I. Mean values conditions studied?
(kgf”)
the proximal
and standard
strength
amalgam
of
surfaces
for
deviations
dies 2 (A),
restorations
3 (B),
age
I hour No.
Conditions
1
z’$
4 (C).
for all experimental Specimen
Die
and
169
24 hours S.D.8
X
1
S.D.
1
With varnish No varnish
151.6 219.0
9.0 9.3
307.4 353.8
3.9 21.8
2
Zinc phosphate Zinc phosphate + Dycal Zinc phosphate + ZOE Varnish + zinc phosphate
+ varnish
212.8 196.0 193.2 146.8
11.7 15.6 15.8 13.1
332.0 304.2 315.8 247.8
6.1 18.7 24.4 30.5
3
Zinc phosphate Zinc phosphate + Dycal Zinc phosphate + ZOE Varnish + zinc phosphate
+ varnish
201.6 162.4 188.4 149.6
5.9 20.5 12.5 5.3
331.0 295.2 274.4 251.2
17.9 15.6 22.4 16.7
4
Zinc phosphate Zinc phosphate + Dycal Zinc phosphate + ZOE Varnish + zinc phosphate
+ varnish
195.0 112.6 125.0 119.8
6.0 9.7 21.9 10.3
295.6 178.0 159.0 194.8
10.7 7.3 10.6 10.8
“1 kgf
=
2.2 pounds.
tClass
II
amalgam
restorations
with
forces
applied
on the main
lingual
fossa.
$Mean. §Standard
deviation.
hours, the restorations were subjected to progressively greater stress on the central fossa of the amalgam restoration up to the point of fracture. The stress was applied with a Universal testing machine at a speed of 0.5 mm. per minute. The resultant data were subjected to analysis of variance. When indicated, the Tuckey test was applied for contrast. RESULTS Table I presents the mean value for each experiment. The results are expressed in the metric system. The results of subjecting the data to analysis of variance (Tables II and III) conformed to the existing information that the 24-hour amal-
170
Vieira
Table
II. Analysis Source
and
“Significant
for fracture Degrees freedom
(cavity-base)
force data
of
I
Sum of squares
13 1 13 112 139
1 Mean
287,751.69 383,987.32 33,186.68 25,879.60 730,805.29
square
1
22,134.75 383,987.32 2,552.82 231.07
Variance*
95.79 1,661.78 11.05
at the level of 0.1 per cent.
tCavity-base
Table
of variance
of variation
Combination be Interaction? Residue Total
J, Prosthet. Dent Auqust, 19i:i
Mondelli
Y age
III. Means
for fracture
force
according
to specimen
age
Specimen age Fracture
force
Table IV. Means base material
1 hour
24 hours
170
274
(kpf 1
for fracture
force
(kgf)
of combinations
Die Base material
l
None
I
of cavity shape and
No.
2 ---p
/
286
4 -
Zinc phosphate Zinc Varnish phosphate alone
+ Dycal
230
272 250
266 229
245 145
Zinc phosphate Varnish + zinc
+ ZOE phosphate
-. -
255 197
23 1 200
142 157
*Tuckey
+ varnish
1,
Critical (5 per
value cent)*
I I j / J
23.3
test.
gam restorations had greater strength than the l-hour restorations. The combination of cavity form and type of base was highly significant as was the interaction of age and cavity form. Table IV presents the mean fracture strength for the combinations of cavities and bases. The critical value for contrasts according to the Tuckey test is included also. The data in column 2 suggest that two layers of varnish weaken the restoration. An amalgam restoration condensed over a zinc phosphate base presented mean values which did not significantly differ from those of the same restoration without a base or varnish (Table IV). However, an amalgam restoration condensed over Dycal or ZOE under zinc phosphate cement showed a reduction in fracture strength, but this strength value was not significantly different than that of a similar restoration over a zinc phosphate cement base for die 2. The fracture strength of these bases was statistically less than that of the amalgam restoration for die 1 without the varnish but was not different than die 1 with varnish. When cavity varnish was interposed between the pulpal wall and the cement base and again between the cement base and the amalgam, there was a considerable decrease in fracture strength.
;$gFr “2” Table cavity
Fracture
strength
of
amalgam
V. Means for fracture force (kgf), corresponding shape, base material, and age of specimen Age 4 specimen (hours)
Base material
Die
restorations
to the interaction
No.
1 24
11.2 219 354
-
-
* -
alone
1 24
152 307
-
-
-
Zinc
phosphate
-
213 332
202 331
195 296
Zinc
phosphate
+ Dycal
1 24 1 24
-
196 304
162 295
113 178
Zinc
phosphate
+ ZOE
1 24
-
193 316
188 274
125 159
1 24
-
147 248
150 251
120 195
None Varnish
Varnish
+ zinc phosphate
“Tuckey
+ varnish
171
I31
of
Critical (5 per
value cent)*
36.7
test.
Results similar to those of die 2 occurred with dies 3 and 4. The layers of varnish tended to decrease the fracture strength of the amalgam restoration as did the Dycal and ZOE bases. Table V presents the means of fracture strength for the values of interaction involving the ages of the amalgam restorations, cavity forms, and bases used, as well as the critical values for contrast. The restorations with only varnish reduced the fracture strength of the l-hour and 24-hour specimens. For die 2, the fracture strengths of the restorations were similar for zinc phosphate cement, Dycal and zinc phosphate cement, and ZOE and zinc phosphate cement. This was true for the l-hour and 24-hour specimens. However, the triple of layer of varnish over both the pulpal walls and the zinc phosphate cement base considerably decreased the fracture strength of the restoration. For die 3, only the zinc phosphate cement base showed a high strength value. The combination of Dycal and zinc phosphate cement or ZOE and zinc phosphate cement decreased the fracture strength of the amalgam restoration. A greater decrease occurred with triple layers of varnish below and above a zinc phosphate cement base. Die 4 showed less fracture strength for all bases when compared with die 1. The results were independent of specimen age. These data cannot be applied directly to clinical practice; they may serve only for comparison, since in vitro results do not literally apply to clinical practice. DISCUSSION Obviously, deep cavities have less remaining dentin and require bases. The dentist must anticipate a decrease in fracture strength of amalgam in such teeth. In restorations similar to the modules presented in this report, those with double or triple bases tend to decrease the fracture strength of the amalgam. These results
172
Vieira
and Mondelli
J. Prosthet. De~rt Auqust. 1973
are not in agreement with an earlier report.’ The results do question the use of two or three layers of varnish in restorations with bases. Perhaps the varnish should be more sparingly used. Despite these findings, the use of a varnish or base should not be indicated fat physical purposes alone. In applying a base, the physical, chemical, and biologic. factors must be considered. The ultimate solution should be determined by all factors involved, and the resultant method should satisfy the greatest number of considerations. CONCLUSIONS
Zinc phosphate cement bases did not significantly decrease the fracture strength of Class II amalgam restorations. When used in combination with Dycal, ZOE, or cavity varnish, there was a tendency toward a decrease in fracture strength of the amalgam. This occurred mainly where the base restored the axiopulpal line angle. References
1. Virmani, 2. 3. 4.
5.
6. 7. 8. 9. 10. 11.
R., Phillips, R. W., and Swartz, M. L.: Displacement of Cement Bases by Coildensation of Direct Gold, J. Am. Acad. Gold Foil Op. 13: 39-43, 1970. Phillips, R. W., Swartz, M. L., and Norman, R. D.: Materials for the Practicing Dentist. St. Louis, 1969, The C. V. Mosby Company. Chong, W. F., Swartz, M. L., and Phillips, R. W.: Displacement of Cement Bases by Amalgam Condensation, J. Am. Dent. Assoc. 74: 97-102, 1967. Hoppenstand, D. C., and McConnell, D.: Mechanical Failure of Amalgam Restorations With Zinc Phosphate and Zinc Oxide-Eugenol Cement Bases, J, Dent. Res. 39: 389-905. 1960. Vieira, D. F., and Mondelli, J.: Fracture Strength of Classes I and II Amalgam Restorations Condensed on Different Cement Bases, Estomat. and Cult., Bauru, 5: 28-42, 1971. Wallace, R. C.: How a Base Affects Fracture Resistance of Amalgam, J. Dent. Child. 31: 187-193, 1964. Eames, W. B., and Hollenback, G. M.: Cavity Liner Thicknesses and Retentive Characteristics, J. Am. Dent. Assoc. 72: 69-72, 1966. Phillips, R. W.: Cavity Varnishes and Bases, D. Clin. North Am. 9: 159-168, 1965, Phillips, R. W.: Recent Improvements in Dental Materials, J. Am. Dent. Assoc. 73: 8490, 1965. Stibbs, G. D.: Cavity Preparation and Matrixes for .4malgam Restorations, J. Am. Dent. Assoc. 56: 471-479, 1958. Strickland, W. D.: Amalgam Restorations for Class II Cavity Preparations, in Sturdevant, C. M.: et al: The Art and Science of Operative Dentistry, New York, 1968, McGraw-Hill Book Company, Inc., pp. 235-259. UNIVERSIDADE FACULDADE
DE SXo
POSTAL 9137 PAULO, BRAZIL SOUTH AMERICA CAIXA
SXo
PAULO
DE ODONTOLOGIA
strength
condensed
over
of Class II amalgam protective
restorations
bases
Dioracy Fonterrada Vieira, D.D.S., D.L., M.S.D.,* Josh Mondelli, D.D.S., D.L.** Faculdades de Odontologia, Skio Paulo and Bauru, Sa’o Paulo, Brazil
and Universidade
de
A
protective base, serving as a substitute for dentin, guards the pulp against thermal, electrical, chemical, and mechanical injury. In addition, a medicated base promotes the formation of reparative dentin. All bases should possess sufficient strength to resist the forces of condensation of dental amalgam or gold foil’; in addition, they must resist the stresses of mastication. The most important physical requirement of a base is its ability to resist condensation forces.” A cement base needs to resist more than 170 p.s.i. to preclude fracture and displacement resulting from condensation3 Zinc oxide and eugenol cement (ZOE) lacks the necessary strength when compared to zinc phosphate cement in Class I and II amalgam restorations.‘+ The recommendation that two or more layers of varnish be applied to cavity walls has added another factor to base techniques.” When tested, the varnish failed to alter the strength of cylindrical specimens of amalgam.7 A previous report discussed pertinent factors which relate to the physical problems of protective bases5 The class of preparation, the size of the cavity, and whether or not the line angles are created in dentin relate to the physical needs of a base. The views in that report agreed with earlier discussions of this problem.P. :’ Calcium hydroxide, protected with zinc oxide and eugenol cement (ZOE), may suffice for small bases, but larger areas require zinc phosphate cement, These concepts and other clinical practices have, in part, been investigated. and the results are described in this report. MATERIALS
AND
METHOD
All tests were made in cobalt ing a Class II cavity preparation *Professor **Associate 166
and
Chairman,
Professor
and
chromium dies of a lower right first molar contain(Figs, 1, 2, and 3) .:, The preparation conformed
Department Chairman,
of Dental Department
Materials, of Operative
SF%o Paulo. Dentistry,
Bauru
Volume Number
30 2
Fracture
strength
of
A
/
,’
Fig. 1. Occlusal
(A) and proximal
A’ Fig. 2. (Top) the
(B) aspects
B’
Occlusal view in a longitudinal
same dies
amalgam
of dies 2 section
Fig. 3. Proximal
of dies 2
167
B
of die 1.
C’
(A), 3 (B), and 4 (C). (A’, B’, and C’).
aspect
restorations
(Bottom)
Schematic
view
of
(A), 3 (B), and 4 (C).
to standard operative procedures. lo, I1 The dies represented one preparation which requires no base and three variations which required bases. The base materials were: ZOE with 0.4 per cent zinc acetate, * Fynal cement,? Dycal,? zinc phosphate cement,$ and copalite varnish.§ These served as base materials and were used in “Pharmakopea,
Brazil,
South
America.
tL. D. Caulk $S. S. White
Company, Milford, Del. Dental Mfg. Company, Philadelphia,
§Cooley
Cooley,
and
Houston,
Texas.
Pa,
168
Vieira
and
Mondelli
A’
B'
Fig. 4. (Top) Pulpal walls and dies 2 (A), 3 (B), and 4 (C). section (A’, B’, and c’).
mesial
and
(Bottom)
C'
distal axial angles rebuilt with base materials for Schematic view of the same dies in a longitudinal
combinations conforming to clinical practice. The amalgam restorations were made of fine-cut alloy.* All materials were manipulated according to the manufacturers’ recommendations. Die 1 contained a cavity preparation which required no protective base (Fig. 1). The cavity was restored in two ways. One cavity preparation received three coats of varnish. Each layer was applied after the previous one had dried. The amalgam restoration was condensed over the varnish. The other cavity preparation received the amalgam restoration without the varnish. This was the control. Die 2 simulated a tooth with deep caries on the pulpal wall. The mesial and distal axial walls were sound. The base was inserted only on the pulpal wall (Figs. 4, A, and 5, A). A small step on the buccal and lingual walls established the thickness of the bases in all dies. After insertion of the base, all the preparations were the same as in die 1 (Fig. 1) The bases inserted in all dies (Nos. 2, 3, and 4) were made up of: three coats of varnish followed by zinc phosphate cement followed by three coats of varnish; zinc phosphate cement alone; 0.1 mm. of Dycal covered with zinc phosphate cement : and 0.1 mm. of ZOE covered with zinc phosphate cement. Die 3 simulated a tooth in which caries involved the mesiopulpal line angle. The bases replaced the mesioaxial wall and part of the pulpal wall (Figs. 4, B, and 5, B). Die 4 simulated a tooth with deep caries in which the pulpal and both axial walls required restoration with a base (Figs. 4, C, and 5, C) . After the bases had set, an amalgam restoration was condensed into the cavity. The size of all restorations was standardized by a matrix. Five restorations were made for each variation of base and time. After the designated time of one or 24 *L.
D. Caulk
Company,
Milford,
Del.
Volume Number
Fracture
30 2
Fig.
5. Same
as Fig.
4 seen from
Table I. Mean values conditions studied?
(kgf”)
the proximal
and standard
strength
amalgam
of
surfaces
for
deviations
dies 2 (A),
restorations
3 (B),
age
I hour No.
Conditions
1
z’$
4 (C).
for all experimental Specimen
Die
and
169
24 hours S.D.8
X
1
S.D.
1
With varnish No varnish
151.6 219.0
9.0 9.3
307.4 353.8
3.9 21.8
2
Zinc phosphate Zinc phosphate + Dycal Zinc phosphate + ZOE Varnish + zinc phosphate
+ varnish
212.8 196.0 193.2 146.8
11.7 15.6 15.8 13.1
332.0 304.2 315.8 247.8
6.1 18.7 24.4 30.5
3
Zinc phosphate Zinc phosphate + Dycal Zinc phosphate + ZOE Varnish + zinc phosphate
+ varnish
201.6 162.4 188.4 149.6
5.9 20.5 12.5 5.3
331.0 295.2 274.4 251.2
17.9 15.6 22.4 16.7
4
Zinc phosphate Zinc phosphate + Dycal Zinc phosphate + ZOE Varnish + zinc phosphate
+ varnish
195.0 112.6 125.0 119.8
6.0 9.7 21.9 10.3
295.6 178.0 159.0 194.8
10.7 7.3 10.6 10.8
“1 kgf
=
2.2 pounds.
tClass
II
amalgam
restorations
with
forces
applied
on the main
lingual
fossa.
$Mean. §Standard
deviation.
hours, the restorations were subjected to progressively greater stress on the central fossa of the amalgam restoration up to the point of fracture. The stress was applied with a Universal testing machine at a speed of 0.5 mm. per minute. The resultant data were subjected to analysis of variance. When indicated, the Tuckey test was applied for contrast. RESULTS Table I presents the mean value for each experiment. The results are expressed in the metric system. The results of subjecting the data to analysis of variance (Tables II and III) conformed to the existing information that the 24-hour amal-
170
Vieira
Table
II. Analysis Source
and
“Significant
for fracture Degrees freedom
(cavity-base)
force data
of
I
Sum of squares
13 1 13 112 139
1 Mean
287,751.69 383,987.32 33,186.68 25,879.60 730,805.29
square
1
22,134.75 383,987.32 2,552.82 231.07
Variance*
95.79 1,661.78 11.05
at the level of 0.1 per cent.
tCavity-base
Table
of variance
of variation
Combination be Interaction? Residue Total
J, Prosthet. Dent Auqust, 19i:i
Mondelli
Y age
III. Means
for fracture
force
according
to specimen
age
Specimen age Fracture
force
Table IV. Means base material
1 hour
24 hours
170
274
(kpf 1
for fracture
force
(kgf)
of combinations
Die Base material
l
None
I
of cavity shape and
No.
2 ---p
/
286
4 -
Zinc phosphate Zinc Varnish phosphate alone
+ Dycal
230
272 250
266 229
245 145
Zinc phosphate Varnish + zinc
+ ZOE phosphate
-. -
255 197
23 1 200
142 157
*Tuckey
+ varnish
1,
Critical (5 per
value cent)*
I I j / J
23.3
test.
gam restorations had greater strength than the l-hour restorations. The combination of cavity form and type of base was highly significant as was the interaction of age and cavity form. Table IV presents the mean fracture strength for the combinations of cavities and bases. The critical value for contrasts according to the Tuckey test is included also. The data in column 2 suggest that two layers of varnish weaken the restoration. An amalgam restoration condensed over a zinc phosphate base presented mean values which did not significantly differ from those of the same restoration without a base or varnish (Table IV). However, an amalgam restoration condensed over Dycal or ZOE under zinc phosphate cement showed a reduction in fracture strength, but this strength value was not significantly different than that of a similar restoration over a zinc phosphate cement base for die 2. The fracture strength of these bases was statistically less than that of the amalgam restoration for die 1 without the varnish but was not different than die 1 with varnish. When cavity varnish was interposed between the pulpal wall and the cement base and again between the cement base and the amalgam, there was a considerable decrease in fracture strength.
;$gFr “2” Table cavity
Fracture
strength
of
amalgam
V. Means for fracture force (kgf), corresponding shape, base material, and age of specimen Age 4 specimen (hours)
Base material
Die
restorations
to the interaction
No.
1 24
11.2 219 354
-
-
* -
alone
1 24
152 307
-
-
-
Zinc
phosphate
-
213 332
202 331
195 296
Zinc
phosphate
+ Dycal
1 24 1 24
-
196 304
162 295
113 178
Zinc
phosphate
+ ZOE
1 24
-
193 316
188 274
125 159
1 24
-
147 248
150 251
120 195
None Varnish
Varnish
+ zinc phosphate
“Tuckey
+ varnish
171
I31
of
Critical (5 per
value cent)*
36.7
test.
Results similar to those of die 2 occurred with dies 3 and 4. The layers of varnish tended to decrease the fracture strength of the amalgam restoration as did the Dycal and ZOE bases. Table V presents the means of fracture strength for the values of interaction involving the ages of the amalgam restorations, cavity forms, and bases used, as well as the critical values for contrast. The restorations with only varnish reduced the fracture strength of the l-hour and 24-hour specimens. For die 2, the fracture strengths of the restorations were similar for zinc phosphate cement, Dycal and zinc phosphate cement, and ZOE and zinc phosphate cement. This was true for the l-hour and 24-hour specimens. However, the triple of layer of varnish over both the pulpal walls and the zinc phosphate cement base considerably decreased the fracture strength of the restoration. For die 3, only the zinc phosphate cement base showed a high strength value. The combination of Dycal and zinc phosphate cement or ZOE and zinc phosphate cement decreased the fracture strength of the amalgam restoration. A greater decrease occurred with triple layers of varnish below and above a zinc phosphate cement base. Die 4 showed less fracture strength for all bases when compared with die 1. The results were independent of specimen age. These data cannot be applied directly to clinical practice; they may serve only for comparison, since in vitro results do not literally apply to clinical practice. DISCUSSION Obviously, deep cavities have less remaining dentin and require bases. The dentist must anticipate a decrease in fracture strength of amalgam in such teeth. In restorations similar to the modules presented in this report, those with double or triple bases tend to decrease the fracture strength of the amalgam. These results
172
Vieira
and Mondelli
J. Prosthet. De~rt Auqust. 1973
are not in agreement with an earlier report.’ The results do question the use of two or three layers of varnish in restorations with bases. Perhaps the varnish should be more sparingly used. Despite these findings, the use of a varnish or base should not be indicated fat physical purposes alone. In applying a base, the physical, chemical, and biologic. factors must be considered. The ultimate solution should be determined by all factors involved, and the resultant method should satisfy the greatest number of considerations. CONCLUSIONS
Zinc phosphate cement bases did not significantly decrease the fracture strength of Class II amalgam restorations. When used in combination with Dycal, ZOE, or cavity varnish, there was a tendency toward a decrease in fracture strength of the amalgam. This occurred mainly where the base restored the axiopulpal line angle. References
1. Virmani, 2. 3. 4.
5.
6. 7. 8. 9. 10. 11.
R., Phillips, R. W., and Swartz, M. L.: Displacement of Cement Bases by Coildensation of Direct Gold, J. Am. Acad. Gold Foil Op. 13: 39-43, 1970. Phillips, R. W., Swartz, M. L., and Norman, R. D.: Materials for the Practicing Dentist. St. Louis, 1969, The C. V. Mosby Company. Chong, W. F., Swartz, M. L., and Phillips, R. W.: Displacement of Cement Bases by Amalgam Condensation, J. Am. Dent. Assoc. 74: 97-102, 1967. Hoppenstand, D. C., and McConnell, D.: Mechanical Failure of Amalgam Restorations With Zinc Phosphate and Zinc Oxide-Eugenol Cement Bases, J, Dent. Res. 39: 389-905. 1960. Vieira, D. F., and Mondelli, J.: Fracture Strength of Classes I and II Amalgam Restorations Condensed on Different Cement Bases, Estomat. and Cult., Bauru, 5: 28-42, 1971. Wallace, R. C.: How a Base Affects Fracture Resistance of Amalgam, J. Dent. Child. 31: 187-193, 1964. Eames, W. B., and Hollenback, G. M.: Cavity Liner Thicknesses and Retentive Characteristics, J. Am. Dent. Assoc. 72: 69-72, 1966. Phillips, R. W.: Cavity Varnishes and Bases, D. Clin. North Am. 9: 159-168, 1965, Phillips, R. W.: Recent Improvements in Dental Materials, J. Am. Dent. Assoc. 73: 8490, 1965. Stibbs, G. D.: Cavity Preparation and Matrixes for .4malgam Restorations, J. Am. Dent. Assoc. 56: 471-479, 1958. Strickland, W. D.: Amalgam Restorations for Class II Cavity Preparations, in Sturdevant, C. M.: et al: The Art and Science of Operative Dentistry, New York, 1968, McGraw-Hill Book Company, Inc., pp. 235-259. UNIVERSIDADE FACULDADE
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