Egyptian Dental Journal, 52, 81 : 87, January, 2006
THE EFFECT OF TOPICALLY APPLIED 1.23% ACIDULATED
PHOSPHATE FLUORIDE ON ZINC PHOSPHATE CEMENT
Sahar. A. Al-Zain *
ABSTRACT
Topically applied fluoride preparations play an important role in reduction of caries incidence. It
was found that the commonly used 1.23% acidulated phosphate fluoride (APF) gel has a deleterious
effect on different dental materials. The effect of the gel on zinc phosphate cement is still not
known. It is expected that 1.23% APF gel may affect the microstructure of the zinc phosphate cement.
Thirty Teflon rings were prepared. Zinc phosphate cement was mixed and loaded into the rings.
Excess cement material was removed and samples were stored in 20 ml of distilled water at 37°C for
24 hours. They were then equally divided into five groups. Samples of the control group were stored
in 20 ml of distilled water at 37°C for 24 hours. The other four groups received four times
application of 1.23% APF gel for 1, 4, 6 and 10 minutes at each application with an intermediate
washing and immersion in 20 ml of distilled water at 37°C for one hour between applications.
Samples were prepared for examination under the scanning electron microscope. Results showed
that as the application time of the gel is increased, more reaction products are formed on the surface of
the set zinc phosphate cement. These products mask and may protect the surface from erosion by the
acidic APF gel. However, more surface roughness is produced that may accumulate bacteria and affect
the gingival health.
INTRODUCTION :
Topical fluorides are capable of enhancing the
remineralization of partially decalcified tooth
structure. They also reduce dentinal sensitivity.
Three types of fluoride preparations have been ad-
vocated for professional applications: Acidulated
Phosphate Fluoride (APF), Stannous Fluoride
(SnF2) and Sodium Fluoride (NaF). The efficiency
of various topical fluoride preparations depends on
the local pH and concentration of fluoride. 1.23%
APF gels are used as topical fluoride treatments in
almost all dental offices because of their ease of
application and their clinical effectiveness. Different
application times of 1.23% APF gels (1, 4, 6 and
10 minutes) have been used. For adults at high risk
for caries development, office application of APF
gels at 6- month intervals or more frequently is
appropriate.1 However, one of the problems as-
sociated with the application of 1.23% APF gel is its
deleterious damaging effect on the different res-
torative materials like composite resins2'7, Glass
ionomer7'10 and porcelain
11"14. APF gels has the
ability to etch the inorganic substances incorporated
in those materials. Therefore, it is pos-
Assistant Professor and consultant, Department of Prosthetic Dental Sciences, College of Dentistry, King Saud University,
Riyadh, Saudi Arabia.
sible that the zinc phosphate cement film at mar-
gins of cast restorations is also adversely affected
by the acidic nature of the 1.23% APF gel.
The purpose of this study is to evaluate the ef-
fect of topical application of 1.23% APF gel on the
microstructure of the zinc phosphate cement at dif-
ferent application times using the Scanning Elec-
tron Microscope (SEM).
MATERIAL AND METHOD:
Thirty Teflon rings of 10mm internal diameter
and 2mm thickness were prepared. Each ring was
seated on a Mylar strip that was placed on a glass
slab. The powder of zinc phosphate cement (Fleck's
Cement, mizzy, INC. Cherry Hill, NJ) was weighed
on an electronic microbalance to insure proper
proportioning and consistency. Mixing was then
done at room temperature on a glass slab following
the manufacturer's directions and the cement was
loaded into the rings. They were again covered with
another Mylar strip and a glass slab to extrude excess
cement material and to create a uniform surface
texture. Excess cement material was then removed.
All samples were immersed in 20 ml of distilled
water at 37°C for 24 hours. The specimens were then
equally divided into 5 groups, each containing five
samples. Samples of the control group were stored
in 20 ml of distilled water for 24 hours. The other
samples were repeatedly exposed to 1.23%
acidulated phosphate fluoride (APF) gel (Butler,
Sunstar Inc, Chicago, IL. USA) for four different
application times (1, 4, 6 and 10 minutes). The
process of APF application was repeated for a total
of four times for each sample simulating two-years
exposure to prophylactic fluoride treatment (one
application/six months). Each application was
followed by washing with distilled water and sub-
sequent immersion in distilled water at 37°C for
one hour. After completion of A,PF application,
samples were then stored in 20 ml distilled water at
37°C for 24 hours. All samples were prepared, gold
coated and examined under a JEOL JSM-6360LV
(JEOL, Tokyo, Japan) scanning electron micro-
scope. The surface micromorphology of the sam-
ples were evaluated and compared.
RESULTS:
Figure 1 (a & b) shows the
micro-morphology of the samples of the control
group. The surface of the set zinc phosphate cement
(ZPC) matrix is more or less smooth with areas of
cracks and small voids. There is an evidence of
many un-reacted irregularly shaped particles on the
surface of the set ZPC. There is a wide variation
in the shape and size of the incompletely dissolved
particles of zinc oxide overlaying the set cement
matrix. These particles are characterized by their
smooth surfaces and sharp and well-defined edges.
There are Small voids and cracks on the surface of
the set cement matrix.
Samples that received four times 1-minute
application of APF gel have lost the fine and
smooth characteristics of the set ZPC matrix and
the surrounding unreacted particles (Fig 2-a & b).
The surface particles vary in size and shape. Most
of them have smoother and flatter surfaces than
those of the samples of the control group. At many
areas, the particles are joined together. The surface
of the cement is rough due to the formation of re-
action products on it of varying sizes and shapes.
They partially mask the underlying set cement sur-
face. Voids and cracks are still evident.
Figure 3 (a, b & c) shows the
micro-morphology of the samples that received four
times 4-minute application of APF gel. The surface
particles are flattened more than those of the
previous groups. At many areas, the unreacted
cement particles are found adhering to each other to
form bundles that are overlaying the surface of the
set cement. The bundles have a characteristic
feature at this group of being narrow at their middle
area and widely separated at both ends giving them
a fan-shaped appearance. They have pitted surfaces
with rough edges. There is an evidence of formation
of globules precipitating on the surface of the set ce-
ment that completely mask the surface of the set
cement.
82 Sahar. A. Al-Zain E.D.J. Vol. 52. No. 1
THE EFFECT OF TOPICALLY APPLIED 1.23% ACIDULATED PHOSPHATE
Figure 4 (a, b &c) shows the
micro-morphology of the samples that received
four times 6-minute application of APF gel. The
surface particles are flattened more than those in
the previous group. They are condensed together
and adhere to each other. The fan-shaped structures
are still evident, but are more packed together than
the previous group. However, the globules that are
formed on the surface of the set cement is similar
to those seen in samples of the
4-minute application of APF gel.
Samples that received four times 10-minute
application of APF gel shows further flattening and
smoothening of the surface particles by the acidic
APF gel (Fig 5- a, b & c). The fan-shaped struc-
tures are not evident. The appearance of globules
that completely mask the surface of the set cement is
similar those of globules that are formed in the 4-and
6-minute APF application groups.
Fig l-a&b: Micromorphology of a sample of a control
group. Unreacted irregularly shaped cement par-
ticles of different sizes Cracks are evident. (Mag-
nification a: xlOO, b: x200)
Fig 2-a&b: Micromorphology of a sample that received four
times 1-minute 1.23% APF gel. Surface particles
have smooth surfaces. The reaction products par-
tially cover the set cement surface (Magnification a:
xlOO, b:x500)
83 E.D.J. Vol. 52. No. 1
(A) (A)
(B) (B)
(C)
Fig 3-a,b &c: Micromorphology of a sample that received four
times 4-minute 1.23% APF gel. Most of the unreacted
cement particles form fan- shaped bundles that have
pitted surfaces and rough edges. Globular reaction
products completely mask the set cement.
(Magnification a: xlOO, b: x500, c: x500)
(C)
Fig 4-a,b &c: Micromorphology of a sample that received
four times 6-minute 1.23% APF gel. More un-
reacted particles arc condensed and closely adhere
to each other. More flattening of the surfaces par-
ticles is evident. Globular reaction products are similar
to those seen in fig 3. (Magnification a: xlOO, b:
x500, c: x500)
E.D.J. Vol. 52. No. 1 Sahar. A. Al-Zain 84
(A)
(B) (B)
THE EFFECT OF TOPICALLY APPLIED 1.23% ACIDULATED PHOSPHATE
Fig 5-a&b: Micromorphology of a sample that received four times 10-minute 1.23% APF gel. Surface particles are further flattened and
are smooth. Globular reaction products are similar to those seen in fig 3 and 4. (Magnification a: xlOO, b: x500)
DISCUSSION:
When the zinc phosphate powder is brought
into contact with the liquid to begin the cement
mixing, wetting occurs and a chemical reaction is
initiated. The surface of the alkaline powder is dis-
solved by the acidic liquid resulting in the forma-
tion of a relatively insoluble zinc phosphate as fol-
lows:
3 ZnO + 2 H3Po4 + H2O —> Zn3(Po4)2 . 4H2O
Only the surface layers of the zinc oxide par-
ticles react, leaving unconsumed cores of residual
zinc oxide particles bound together by the phos-
phate matrix.15"18 The set cement is essentially a
hydrated amorphous network.15'16-18 It is very porous.15
In this study, there are unreacted irregularly shaped
particles with smooth surfaces and well-defined
edges on the surface of the zinc phosphate cement of
the control group. Because of the nature of the
cement and also due to preparation for Scanning
Electron Microscope (SEM) examination where the
residual moisture is removed, shrinkage of the
cement occurs which eventually leads to formation of
cracks and small voids. Trapped air bubbles during
cement mixing may also contribute to the formation
of small voids in the set cement.
Some studies reported the significant adverse
effect of the APF on other restorative materials.2-14
The application time of the APF gel have been rec-
ommended by manufacturers to be 1 min. How-
ever, some of the studies used a 4-minute application
time.3'5-7'8'19'20 Other studies used a topical
application of APF gel for 6 minutes.2-9'21 A
10-minute application time was also used by some
researchers.11'14 El-Badrawy & McComb19 and Yip et
al22 found that the application of 1.23% APF gel to
composite and glass ionomer cements for 4 minutes
resulted in increased surface roughness and
erosion of composite resin and glass ionomer ce-
ments. The low pH value affects the cement by
etching and eroding its surface. The APF has a ten-
dency to affect the inorganic substances incorporated
in the restorative materials. Therefore, it may affect
the zinc phosphate cement by etching both the
unreacted cement particles and matrix. However,
the globular reaction products that are formed on
the surface of the cement may inhibit etching and
erosion of ZPC. They may act as a barrier that
prevents damage of the cement by the acidic effect
of 1.23% APF gel. In this study, the 1-minute APF
application resulted in formation of reaction products
that are partially covering the set cement surface.
However, when APF application time is increased
more than 1 minute the cement particles
completely mask the underlying set cement surface.
The appearance of the globular prod-
E.D.J. Vol. 52. No. 1 85
(B) (A)
ucts is similar in the groups where APF was ap-
plied for 4, 6 and 10 minutes. Therefore, APF ap-
plication for 4, 6 and 10 minutes have the ad-
vantage of protecting the surface of the ZPC from
erosion by the acidic effect of the APF. On the other
hand, they may contribute to increased surface
roughness of the cement due to the formation of re-
action products on the surface of the ZPC. It was
found that colonization of bacteria may occur as a
result of surface roughness of the cement that is
produced by the acidic effect of the APF gel. 23-24
In
this study, the roughness that are produced by the
formation of the globules may harbor bacteria and
bacterial products which may initiate gingival
inflammation due to proximity of the margin of the
crown restoration to the gingival tissues.
In this study, as the APF application time is
increased, the surfaces of the unreacted particles on
the surface of the ZPC become flatter and smoother.
Some particles are joined together by the acidic
effect of the gel. The characteristic feature of sam-
ples at 4-minute APF gel application is the close
adherence of particles forming fan-shaped bundles
due to the increased exposure time to the acidic gel.
When the application time of APF gel is increased
to 6 minutes, the fan-shaped appearance is still ev-
ident, but the particles are more condensed together.
They closely adhere to each other and are packed
more than those of the samples of 4-minute APF gel
application. The samples in this study were placed
in distilled water for 24 hours after each APF
application. Consequently, any loose cement particles
were probably dislodged.
CONCLUSIONS:
Professionally applied 1.23% APF gel was found
to resulted in formation of reaction products on the
surface of the ZPC. At the 1-minute APF application,
the reaction products partially mask the surface of the
set cement. Whereas at the other groups receiving
APF for 4, 6 and 10 minutes, the globular reaction
products completely mask the underlying set cement
surface. Thus, they have the
advantage of protecting the cement surface from
further damage by the acidic APF. Therefore, they
inhibit cement erosion by the acidic APF gel. In ad-
dition, the globular structures may act as a reservoir
of fluoride that is beneficial in the oral environment.
However, they may result in a rough surface of the
cement which may accumulate bacteria.
Consequently, it may start the inflammatory process
of the gingival tissues due to the closed positioning of
the margin of the crown restoration to the gingiva.
Further studies on the effect of topical ap-
plication of the other fluoride preparations on the
zinc phosphate cement is needed.
ACKNOWLEDGEMENT:
This study was funded by the Research Center
at College of Dentistry, King Saud University, Ri-
yadh, Saudi Arabia. The author acknowledge the
support of the Research Center.
REFERENCES:
1. Wei SHY, Yiu CKY. Evaluation of the use of topical fluo-
ride gel. Caries Res;27:29, 1993.
2. Kula K, McKinney JE, Kula TJ. Effect of daily topical flu-
oride gels on resin composite degradation and wear. Dent
Mater;13:305,1997.
3. Sousa EH, Consani S, De Goes MF, Sobrinho LC. Effect
of topical fluoride application on the surface roughness of
composites. Braz Dent J;6:33,1995.
4. Papagiannoulis L, Tzoutzas J, Eliades G. Effect of topical
fluoride agents on the morphologic characteristics and
composition of resin composite restorative materials. J
Prosthet Dent; 77:405,1997.
5. Soeno K, Matsumura H, Atsuta M, Kawasaki K. Effect of
acidulated phosphate fluoride solution on veneering
par-ticulate filler composite. Int J Prosthodont; 14:127,2001.
6. El-Sayed SM, Shereif AH, Farghaly A. Effect of fluoride
application on specular reflectance and stain potential of
unfilled and photocured microfilled resin veneering materials.
Egypt Dent J;40:813,1994.
7. El-Badrawy W, McComb D, Wood R. Effect of home-use
86 Sahar. A. Al-Zain E.D.J. Vol. 52. No. I
THE EFFECT OF TOPICALLY APPLIED 1.23% ACIDULATED PHOSPHATE
fluoride gels on glass ionomer and composite restorations.
Dent Mater;9:63,1993.
8. Dionysopoulos P, Gerasimou P, Tolidis K. The effect of
home-use fluoride gels on glass-ionomer, compomer and
composite resin restorations. J Oral Rehabil;30:683,2003.
9. Diaz-Arnold AM, Wistrom DW, Swift EJ. Toplical fluoride
and glass ionomer microhardness. Am J Dent; 8:134, 1995.
10. Neuman E, Garcia-Godoy F. Effect of APF gel on a glass
ionomer cement: An SEM study. J Dent
Child;July-August:289,1992.
11. Al Edris A, Al Jabr A, Cooley RL, Barghi N. SEM evaluation
of etch patterns by three etchants on three porcelains. J
Prosthet Dent;6:734,1990.
12. Demirhanoglu S, Sahin E. Effects of topical fluorides and
citric acid on overglazed and autoglazed porcelain sur-
faces. Int J Prosthodont;5:434,1992. 9
13. Kula K, Kula TJ. The effect of topical APF foam and other
fluorides on veneer porcelain surfaces. Pediatr Dent;
17:356,1995.
14. Canay S, Hersek N, Ertan A. Effect of different acid treat-
ments on a porcelain surface. J Oral Rehabil;28:95,2001.
15. Craig RG, O'Brien WJ, Powers JM. Dental Materials prop-
erties and manipulation. 6th ed.,114-118,St Louis, Mosby,
1996.
16. Craig RG, Ward ML. Restorative dental materials. 10th
ed.,173-183,St Louis,Mosby,1997.
17. McCabe JF, Walls AWG. Applied dental materials. 8th
ed., 226-229,Blackwell, 1998.
18. O'Brien WJ. Dental materials and their selection. 2nd ed.,
154-156,Quintessence, 1997.
19. El-Badrawy WA, McComb D. Effect of home-use fluoride
gels on resin-modified glass-ionomer cements. Oper Dent;
23:2,1998.
20. Soeno K, Matsumura H, Atsuta M, Kawasaki K. Influence of
acidulated phosphate fluoride agent and effectiveness of
subsequent polishing on composite material surfaces. Oper
Dent;27:305,2002.
21. Yap AUJ, Mok BYY. Effects of professionally applied topical
fluorides on surface hardness of composite-based res-
toratives. Oper Dent;27:576,2002.
22. Yip KH-K, Peng D, Smales RJ. Effects of APF gel on the
physical structure of compomers and glass ionomer ce-
ments. Oper Dent;26:231,2001.
23. Cehreli ZC, Yazici R, Garcia-Godoy F. Effect of 1.23 per-
cent APF gel on fluoride-releasing restorative materials. J
DentChild;September-October:330,2000.
24. Garcia-Godoy F, de Perez SL. Effect of fluoridated gels on a
light-cured glass ionomer cement: An SEM study. J Clin
Pediat Dent; 17:83,1993.
E.D.J. Vol. 52. No. 1 87