Effects of Phosphoric Acid Concentration and Etching

Duration on Enamel and Dentin Tissues of Uremic

Patients Receiving Hemodialysis: An AFM Study
Salah Hasab Mahmouda/Magda Elsayed Ahmedb/Khaled Mohamed Mahmoudc/
Mohammed El-Awady Grawishd/Ahmed Ragheb Zahere

Purpose: Using atomic force microscopy (AFM), the purpose was to investigate the effect of phosphoric acid
(H3PO4) concentration and etching duration on surface roughness (Ra) and micromorphology of enamel and den-
tin substrates of uremic patients receiving hemodialysis.
Materials and Methods: Sixty-three enamel and dentin slabs were prepared from 42 sound natural molars col-
lected from uremic patients under hemodialysis and mechanically polished up to 4000-grit roughness. Nine
slabs of each substrate were not etched (control group). The remaining slabs were divided into two experimental
groups (n = 27) according to etchant concentration (37% or 42%). In each group, 9 specimens were etched for
15, 30, and 60 s. The surface morphology of the control and test specimens was examined by AFM operated in
“contact” mode. The obtained Ra was subjected to statistical analysis.
Results: Statistical analysis showed that increasing the duration of acid application (irrespective of acid concen-
tration and type of substrate) significantly increased the amount of Ra. H3PO4 at a concentration of 42% was
more effective at producing Ra than was H3PO4 at 37% for all 3 application times. The Ra quantity produced by
H3PO4 at 42% was time specific, with 15 s being significantly less effective than 30 or 60 s. However, 60 s was
significantly better than 30.
Conclusion: The findings of this study support the use of 42% H3PO4 for etching uremic hard tooth tissues for
60 s.

Keywords: uremia, etchant concentration, etching duration, enamel and dentin, surface roughness.

J Adhes Dent 2012; 14: 215–221. Submitted for publication: 27.04.10; accepted for publication: 14.04.11
doi: 10.3290/j.jad.a22421

1955.9 Phosphoric acid (H3PO4) ranging in concentra-

T he clinically reliable bonding of resin composites
to the enamel surface became possible thanks to
the acid-etching technique introduced by Buonocore in
tion from 30% to 50% has been used for decades to
etch enamel in preparation for bonding resin-based
materials.3 Enamel etching creates microporosities and
increases the surface area. It increases surface wetta-
bility and, consequently, the spread and penetration of
a Professor and Head, Conservative Dentistry Department, Faculty of Den- resin adhesives.12 After polymerization of the bonding
tistry, Mansoura University, Mansoura, Egypt. Idea, hypothesis, experimental agent, a durable attachment to the enamel surface is
design, wrote manuscript.
b
achieved by the formation of tag-like resin extensions
Clinical Demonstrator, Conservative Dentistry Department, Faculty of Den-
tistry, Mansoura University. Performed the experiments in partial fulfillment into interprismatic and intercrystallite enamel micropo-
of requirements for a Master’s Degree. rosities.8,13 The micromechanical interlocking has been
c Lecturer, Urology and Nephrology Center, Faculty of Medicine, Mansoura considered as the predominant mechanism of bonding
University. Co-wrote manuscript, contributed substantially to discussion. resin composites to H3PO4-etched enamel.8,18 The bond
d Associate Professor, Oral Biology Department, Faculty of Dentistry, Man- strength of resin composites to acid-etched enamel
soura University. Co-wrote and proofread manuscript, consulted on and is typically in the range of 20 to 25 MPa and provides
performed statistical evaluation.
routinely successful retention of resin composites for a
e Professor, Oral Biology Department, Faculty of Dentistry, Mansoura Univer-
sity. Proofread manuscript, performed a certain test.
variety of clinical applications.19
Dentin bonding with the etch-and-rinse technique has
not been as predictable as enamel bonding, and to date,
Correspondence: Dr. S. H. Mahmoud, Conservative Dentistry Department,
Faculty of Dentistry, Mansoura University, Mansoura, Egypt. Tel: +2-010-023- bonding to dentin substrate remains both challenging and
0460, Fax: +2-050-226-0173. e-mail: salahmahmoud2010@yahoo.com problematic. Dentin is a complex hydrated biological com-

Vol 14, No 3, 2012 215

Mahmoud et al

posite structure. Its microstructures and properties are MATERIALS AND METHODS
the principal determinants of many procedures in adhe-
sive dentistry.26, 34,41 It has been speculated that regional The roughness of enamel and dentin substrates ob-
differences in matrix content, density, tubules, smeared tained from patients with CRF receiving hemodialysis
surface, and various forms of dentin (eg, normal vs scle- was measured to monitor the change in morphology due
rotic) would result in complex, nonuniform acid etching of to etching the surface. Forty-two sound natural molars
dentin.35 Recent studies have shown that the interaction of extracted for periodontal reasons were collected from
the etchants with dentin could be limited by many factors uremic patients under maintenance hemodialysis. The
from both the substrate and the etchant itself. For example, teeth were obtained according to a protocol approved by
the buffering effect of hydroxyapatite could dramatically our Institutional Committee for Ethics of Research.
limit the acid reaction with dentin.10,38 Other dentin compo- Uremic patients were seeking help for their dental pain
nents, such as the smear layer and the collapsed collagen, at the Outpatient Dental Clinic, Faculty of Dentistry, Man-
may also act as a barrier that decreases the demineraliza- soura University. They had been referred from the Outpa-
tion rate.32,36,39 It was reported that the acids preferentially tient Clinic of Mansoura Urology and Nephrology Center.
penetrate along the dentin tubules31 and that penetration Those patients were under regular hemodialysis treatment
of intertubular dentin occurred at a lower rate.25 using a biocompatible membrane dialyzed with a volumetric
Chronic renal failure (CRF) is defined as a slow pro- machine using bicarbonate dialysate 3 times weekly for 4
gressive loss of kidney function over the span of years, hours each time (12 h/week). The average length of time
resulting in permanent kidney failure.16 The clinical signs that the patients had been receiving hemodialysis was 4.8
and symptoms of renal failure are collectively termed years. No patient had decompensated organs other than
uremia.17 Patients with CRF need dialysis or a kidney the kidney. They had serum creatinine above 7 mg/dl and
transplant to do the work of their failed kidneys.30 CRF creatinine clearance rate less than 10 ml/min; 20 patients
has well-documented effects on oral tissues, including were normotensive and 22 had controlled hypertension.
xerostomia, delayed tooth eruption, calcifications lead- All the collected teeth were subjected to thorough scal-
ing to obliteration of pulp chambers and canals, enamel ing (Varios 550, NSK Nakanishi; Kanuma, Japan) to get rid
hypoplasia, decreased caries rates, and altered salivary of both hard and soft deposits. All teeth were kept in 1%
pH levels.29 thymol solution at room temperature for 2 weeks. Their
In patients with CRF, characteristic changes are found roots were separated from the crowns at the cementoe-
in the dentin of erupted teeth analogous to those seen in namel junction.
bone.43 This finding was confirmed in an earlier study13
that recorded ultrastructural alterations in the dentin of Specimen Preparation
uremic patients. In this context, Mahmoud et al24 recently Enamel samples for analysis were obtained from 21
investigated the influence of uremia on the bonding of molars. The buccal surface of each molar was ground
resin composite using an etch-and-rinse adhesive to the flat using water coolant and a sequence of carbide pol-
dental tissue of uremic patients undergoing maintenance ishing papers (Struers; Cleveland, OH, USA) to create a
hemodialysis. In addition, they assessed the micromor- final surface polishing of 4000 grit. Using a water-cooled
phological etching pattern of uremic enamel and den- low-speed diamond saw (Buehler; Lake Bluff, IL, USA),
tin surfaces vs normal tooth substrates by AFM. They the polished enamel was cut vertically in the mesiodistal
reported that uremia adversely affects the bonding of direction parallel to the long axis, yielding 3 pieces of the
composite resin to enamel and dentin and confers an size 3 × 3 mm2. The polished surface was used for AFM
altered micromorphological etching pattern with reduced analysis.
Ra (surface roughness) values compared to normal tooth Dentin samples for analysis were obtained from the re-
substrates. These observations suggested that uremia maining molars by removing the occlusal third of the crown
interfered with the acid etching of enamel and dentin and using a low-speed saw (Buehler) and water coolant. The
compromised the optimum bond strength of resin com- surface of each specimen was then mechanically polished
posite to tooth structure and hence durability. Tradition- up to 4000-grit roughness using the same abrasive papers.
ally, etch-and-rinse adhesive systems have used H3PO4 to From the polished tooth, samples for AFM analysis were
condition enamel and dentin surfaces and to successfully obtained by making a section about 2 mm thick parallel to
create a strong, durable bond to resin-based materials. the polished surface using the low-speed saw. The polished
The incidence of end-stage renal disease is increas- surface of the sample was analyzed with AFM. A stereomi-
ing and patients receiving renal replacement therapy in- croscope (Nikon 88286; Tokyo, Japan) at 40X magnifica-
cluding hemodialysis, peritoneal dialysis, or kidney trans- tion was employed to select the samples without cracks or
plantation will comprise a growing segment of the dental structural defects. To remove polishing debris, specimens
patient population.14 In light of the increasing number of were placed in an ultrasonic cleaner (T1440D, Odontobra;
such patients who will present for dental care and their Ribeirão Preto, SP, Brazil) with distilled water for 10 min.
needs for esthetic restorations, this study used AFM to in- Sixty-three slabs were produced for each substrate.
vestigate the effects of H3PO4 concentration and etching Nine slabs were used as a control group (not etched). The
duration on the surface roughness and micromorphology remaining slabs of each substrate (n = 54) were assigned
of enamel and dentin substrates obtained from uremic to two equal groups of 27 slabs each according to the con-
patients receiving hemodialysis. centration of the H3PO4 etchant (37% or 42%). From each

216 The Journal of Adhesive Dentistry

 Mahmoud et al

Table 1 Three way ANOVA for enamel and dentin surface roughness measurements

Source Sum-of-squares df Mean-square F-ratio p-value

Substrate 8853.63 1 11167.56 14082.37 < 0.0001

Concentration 84030.90 2 42015.45 66828.69 < 0.0001

Duration 52507.26 2 26253.63 41758.35 < 0.0001

Substrate × concentration 2388.71 2 1194.35 1899.71 < 0.0001

Substrate × duration 2360.62 2 1180.31 1877.37 < 0.0001

Concentration × duration 36997.30 4 9249.32 14711.74 < 0.0001

Substrate × concentration × duration 2710.19 4 677.54 1077.69 < 0.0001

Error 67.90 108 0.629

Total 3218120.64 126

group, 9 specimens each were etched for 15, 30, and details of the enamel and dentin structure and to avoid
60 s. Three treatment times were used: 1) recommended damaging the tip. Analysis of AFM images was per-
treatment time (15 s), 2) extended treatment time (60 s) formed using the Park Scientific Instruments software
and 3) selected treatment time (30 s, intermediate time package supplied with the AFM instrument.
to provide a link between recommended and extended
treatment time). The same treatment times were used Data Analysis
also for the group etched with 42% H3PO4. A three-way ANOVA followed by the pairwise Tukey’s
post-hoc test were conducted for Ra to determine if
Etching Procedures there was a significant difference among the groups.
For the first group of enamel and dentin specimens, The factors for the ANOVA tests were: 1) type of tooth
37% H3PO4 gel (Total Etch, Ivoclar Vivadent; Schaan, substrate 2) etchant concentrations and 3) treatment
Liechtenstein) was applied to the surface of the sub- times (recommended, selected, and extended). A p-
strate for the treatment times specified above. Enamel value < 0.05 was considered statically significant. All
and dentin specimens of the second group were etched analyses were performed with SPSS for Windows, ver-
for the same treatment times with a 42% aqueous solu- sion 17 (SPSS; Chicago, IL, USA).
tion of H3PO4 (prepared at the Organic Chemistry De-
partment, Pharmacy Faculty, Mansoura University). The
etched surface was then rinsed with an air-water spray RESULTS
and gently air dried to be examined immediately.
Phosphoric acid etchant changed the micromorphologi-
AFM Study cal appearance of uremic enamel and dentin surfaces
Specimens to be scanned were tested once with the independent of the type of tooth substrate, etching dura-
Digital Instruments Thermo microscope AFM (Autoprob tion, and the acid concentration compared to the control
cp; Santa Barbara, CA, USA) that was used to measure group. The three-way ANOVA revealed a significant differ-
Ra and microstructural changes. Scanning and imag- ence on uremic enamel and dentin Ra among the tested
ing were performed in the laboratory atmosphere under variables (p  <  0.0001) using 37% and 42% H3PO4 con-
controlled temperature and dry conditions. The basic centrations at the recommended, extended, and selected
operating principles have been reported elsewhere.13 treatment times, as well as vs the control (Table 1).
For this study, we used the contact mode, in which a Tukey’s post-hoc test for Ra revealed no statistically
sharp silicon nitride tip is scanned over the sample significant difference between the Ra of enamel speci-
surface with a very light force of about 7 to 10 N. The mens etched with 37% or 42% H3PO4 concentration at
specimens were mounted with cyanoacrylate adhesive 15 s compared to the control (p > 0.05). The Ra created
on a piezoceramic tube that provided three-dimensional by treatment of enamel specimens with 37% H3PO4 con-
movement of each sample with subnanometer accu- centration at 30 and 60 s was statistically significantly dif-
racy. As the specimen was scanned at constant force, ferent (p < 0.05) compared to that of enamel specimens
the three-dimensional motion of the piezoceramic tube treated with the same acid concentration at 15 s treat-
was recorded as an image and matched to the surface ment time. Meanwhile, there was a statistically significant
morphology. The 20-nm in-plane resolution of the AFM difference between Ra of enamel specimens etched with
is dictated by the radius of curvature of the tip, while 42% H3PO4 concentration at 30 s and 60 s etching times
the vertical resolution is 0.1 nm. AFM images were col- (p < 0.05) compared with that obtained with the same
lected at a very low scan rate of 1 Hz in order to obtain concentration at 15 s group (Table 2).

Vol 14, No 3, 2012 217

Mahmoud et al

Table 2 Tukey’s post-hoc test for enamel and dentin of enamel crystallites in close proximity to each other
surface roughness measurements without any specific orientation were observed, denoting
shallow surface pitting (Fig 1a). Enamel specimens etched
Acid con- Time Enamel Dentin with 37% or 42% H3PO4 for 15 s showed mild incipient
centration (s) Ra (nm) Ra (nm) changes compared to the control, with shallow micropo-
rosities represented by low Ra. Microtopographically, the
15 115.5 ±1.02a 141.7 ± 0.815a*
grain size and the depth of the enamel microporosities in-
37% 30 146.8 ± 1.97b 166.2 ± 0.948b* creased proportionally after 30- and 60-s etching with 37%
H3PO4 (Figs  1b and 1c). Moreover, 42% H3PO4 etching
60 168.9 ± 1.02c 182.9 ± 0.752c*
revealed more pronounced enamel microporosities and
15 120.6 ± 0.707a 147.8 ± 0.769a* depth profile after 30- and 60-s applications compared to
their counterparts after etching with 37% H3PO4 (Figs 1d
42% 30 185.8 ± 0.694d 197.3 ± 0.844d*
and 1e).
60 248.5 ± 0.740e 224.5 ± 0.634e* Tukey’s post-hoc test for Ra revealed no statistically
0 112.0 ± 0.959a 137.0 ± 0.527a*
significant difference in the dentin specimens etched with
Control
37% or 42% H3PO4 at 15  s compared to the control.
Values in same column with the same superscript letter are not statisti- The Ra created by treatment of dentin specimens with
cally different (p > 0.05).* Statistically significant compared with the
42% H3PO4 at 60  s was statistically significantly differ-
surface roughness of enamel. Ra: roughness average; nm: nanometer.
ent (p < 0.05) from the control and the other treatment
groups (Table 2).
Since all dentin specimens were taken horizontally,
The qualitative analysis of the AFM images of untreated the images showed dentin tubules, peritubular and in-
uremic enamel specimens showed surfaces with tightly tertubular dentin in cross section. The polishing routine
packed enamel rods and several shallow longitudinal used for the preparation of specimens produced a dentin
grooves appearing between enamel rods. Small grains surface covered by smear layer, characterized by uneven

a b c

d e
Fig 1 (a) 3-D AFM contact mode image of the uremic enamel specimen prepolished with 4000-grit carbide abrasive paper showing
shallow microporosities for non-etched enamel. (b) 3-D AFM contact mode image of the uremic enamel specimen prepolished with
4000-grit carbide abrasive paper showing slight increase in the microporosities after etching with 37% H3PO4 for 30 s. (c) 3-D AFM
contact mode image of the uremic enamel specimen prepolished with 4000-grit carbide abrasive paper showing a marked increase
in the microporosities after etching with 37% H3PO4 for 60  s. (d) 3-D AFM contact mode image of the uremic enamel specimen
prepolished with 4000-grit carbide abrasive paper showing a pronounced increase in the microporosities after etching with 42%
H3PO4 for 30 s. (e) 3-D AFM contact mode image of the uremic enamel specimen prepolished with 4000-grit carbide abrasive paper
showing an even greater increase in the microporosities after etching with 42% H3PO4 for 60 s. For each image (a-e), image size is
5 μm x 5 μm, in-plane resolution is 20 nm, vertical resolution is 0.1 nm.

218 The Journal of Adhesive Dentistry

 Mahmoud et al

surface topography resulting from the debris covering the DISCUSSION

underlying dentin tissue. The polished, untreated uremic
dentin surface depicted in Fig 2a revealed a few nearly Successful adhesion to enamel and dentin is a funda-
obliterated dentin tubules with funnel-shaped peritubular mental requirement prior to the insertion of resin com-
dentin protruding slightly above the intertubular dentin posite materials.36 Based on the underlying strategy,
with the narrow portion of the funnel pointed inward. The contemporary resin-based adhesive systems can be
micromorphology of specimens etched with 37% or 42% classified as “etch-and-rinse” or “self-etching” systems.
H3PO4 for 15 s was comparable to the control, with no In the etch-and-rinse strategy, the tooth is first etched
apparent changes except for slight lumen widening of the (37% H3PO4) and rinsed off. This conditioning step is
few nearly occluded dentin tubules. followed by a priming step and application of the adhe-
Figure 2b shows the preferential attack of 37% H3PO4 sive resin, resulting in a conventional three-step applica-
etching after 30 s on the occluded dentin tubules and the tion procedure.
slight but remarkable changes on the peritubular dentin Phosphoric acid is the most commonly used acid condi-
with its raised margins. The acid attack begins in the per- tioner in operative dentistry, in both liquid and gel forms.27
itubular region as a few tubules readily open, exhibiting Commercial etchants are usually used for 30 to 60 s on
a funnel shape, while the intertubular region seems less enamel. Dentin should be etched for 10 to 15 s because
acid resistant after 37% H3PO4 etching for 60 s (Fig 2c). this dental tissue is more porous and contains less calci-
Figure 2d shows clear signs of 42% H3PO4 etching after fied structure. The solubility of the dental tissue can vary
a 30-s attack on the dentin tubule lumen, with a sub- depending on the surface of the tooth, type of the tooth,
sequent decrease in the intertubular dentin areas and and numerous other factors that differ from person to
a more irregular surface, as reflected in the increased person.2,26,34,35,41
Ra values. In contrast, after 60 s of etching, the dentin The literature contains reports that uremia produced
surface was completely free from the smear layer and the micromorphological changes of dentin11,13,43 and altered
dentin tubules were completely open, accompanied by the etching pattern of hard tooth substrates with reduced
even smaller areas of intertubular dentin (Fig 2e). surface roughness, which negatively influenced the bond-

a b c

d e
Fig 2 (a) 3-D AFM contact mode image of the uremic dentin specimen prepolished with 4000-grit carbide abrasive paper showing
a few nearly obliterated dentin tubules for non-etched dentin. (b) 3-D AFM contact mode image of the uremic dentin specimen pre-
polished with 4000-grit carbide abrasive paper showing slight opening of the occluded dentin tubules after etching with 37% H3PO4 for
30 s. (c) 3-D AFM contact mode image of the uremic dentin specimen prepolished with 4000-grit carbide abrasive paper showing a few
open dentin tubules with the less acid-resistant intertubular dentin after etching with 37% H3PO4 for 60 s. (d) 3-D AFM contact mode
image of the uremic dentin specimen prepolished with 4000-grit carbide abrasive paper showing a decrease in the intertubular den-
tin areas after etching with 42% H3PO4 for 30 s. (e) 3-D AFM contact mode image of the uremic dentin specimen prepolished with
4000-grit carbide abrasive paper showing that dentin tubules are completely open after etching with 42% H3PO4 for 60 s. For each
image (a-e), image size is 5 μm x 5 μm, in-plane resolution is 20 nm, vertical resolution is 0.1 nm.

Vol 14, No 3, 2012 219

Mahmoud et al

ing of resin composite to dental tissues.24 Thus, the cur- creased in patients receiving hemodialysis compared with
rent study aimed to assess the effect of different H3PO4 healthy volunteers.20 The pH and buffering capacity of
concentrations and etching duration on the surface rough- the unstimulated saliva was also increased in the hemo-
ness of uremic hard tooth tissues to determine the best dialysis patients.15,33 The salivary pH was significantly
H3PO4 concentration and the effective etching duration. more alkaline in children with CRF compared with a group
To the authors’ knowledge, the current study is the first of healthy controls.1 Consequently, uremia and its effect
quantitative and qualitative analysis of the acid-etching on salivary phosphorus level and composition render the
patterns produced by different H3PO4 concentrations enamel more acid resistant, which explains the decreased
and application times on uremic enamel and dentin sub- Ra after uremic enamel etching with 37% or 42% for 15
strates. This provides a unique opportunity to investigate s. Thus, increasing the H3PO4 concentration and etch-
a fundamental step of the etch-and-rinse adhesive strat- ing duration provided greater Ra and micromorphological
egy used in current adhesive clinical practice. changes compared to the control.
In this study, AFM was used for the quantitative and In the current study, the Ra value of dentin was sig-
qualitative analysis of etching patterns of uremic sub- nificantly greater when etched with 42% H3PO4 than with
strates. Compared to conventional microscopes, AFM 37% at 30 and 60 s. The authors attributed the difference
offers the advantage of studying samples at high resolu- to the lower pH of the H3PO4 solution compared to that
tion in the wet or moist condition. The AFM allowed sur- of H3PO4 gel, in addition to the absence of the thinning
faces in water or solutions to be imaged, and continuous agent. Perdigão et al28 reported that H3PO4 etchant gels
time-dependent surface changes were easily observed. with similar concentrations result in different depths of
AFM can also provide quantitative data regarding surface dentin demineralization. Wang and Spencer40 reported
roughness.42,44 that differences in etchant viscosity induced differences
Our ultra-morphological approach demonstrated that in dentin demineralization and interfacial structure. Mar-
37% H3PO4 gel and 42% H3PO4 solution affect the etch- shall et al25 reported that peritubular dentin etching rates
ing pattern of uremic hard tooth structure. The current increased with decreasing pH.
study showed that the uremic enamel surfaces generated In the present study, no significant difference was
using 37% H3PO4 gel at 30 s (selected time) and 60 s noted between the Ra of dentin specimens etched with
(extended time) are different from that generated at 15 s 37% H3PO4 gel or 42% solution and control specimens af-
and from non-etched uremic enamel. The mean enamel ter 15 s etching time. Previous studies13,24 reported that
surface roughness (Ra) created by applying a 37% H3PO4 the dentin of uremic patients undergoing chronic hemodi-
gel for 30  s (selected time) and 60  s (extended time) alysis exhibits significant ultrastructural alterations and
was significantly greater (p < 0.05) than that produced altered etching pattern with reduced Ra. This is similar to
by the same H3PO4 concentration when used for 15 s the results of the current study.
(recommended time). Legler et al22 showed a progressive When the acid-etching technique was introduced to den-
increase in surface roughness of enamel obtained from tistry, the standard enamel conditioning time was 60 s.
healthy individuals using a 37% H3PO4 solution for 15, Studies in the mid-1980s found that a reduction in enamel
30, and 60  s on 600-grit flat ground surfaces. Enamel etching time to 15 s did not significantly reduce the bond
etching with 42% H3PO4 at 60 s was the only treatment strength of a resin composite or orthodontic brackets
that produced the greatest surface roughness compared bonded to enamel.4,5 In the current study, extending the
to the other groups. H3PO4 etching time resulted in markedly higher Ra when
The consequences of progressive renal failure include 42% rather than 37% H3PO4 was used for both substrates.
an imbalance of calcium and phosphorus, which are nor- Sixty seconds was used for the extended treatment time
mally under the strict homeostatic control of the kidneys. in the current study, because it approaches the practical
The loss of metabolic control of calcium and phospho- time limit for this type of clinical procedure.
rus parallels the loss of renal function. Therefore, renal The relationship between the dentin Ra resulting from
failure-mediated phosphate retention plus dietary phos- an increased conditioning time and bond strength is ques-
phorus could lead to an increased phosphorus level in tionable. Brajdic et al7 showed that extending the condi-
salvia up to 10 to 11 mg/dl in contrast to a normal level tioning time of dentin may result in morphological changes
of 5 to 6 mg/dl.16 detrimental to resin infiltration into the demineralized sur-
The effects of saliva in protecting the teeth are well face and to the subsequent formation of an optimal hybrid
recognized. The chemical composition of saliva is criti- zone. However, Kimms and others21 did not find lower
cal for the way it performs its protective function.6,23 A bond strengths to dentin when extending the conditioning
numbers of studies have investigated the saliva content time to 60 s. The data obtained in this study support the
and flow rate in adults with CRF. Significantly greater use of H3PO4 at a 42% wt/wt concentration with a 60-s ap-
concentrations of salivary proteins, potassium, and so- plication time for conditioning uremic enamel and dentin
dium were observed in unstimulated saliva collected from when using etch-and-rinse adhesives for resin composite
adults undergoing hemodialysis compared with healthy bonding. Further investigations are still needed to better
volunteers.6 Other authors reported that the flow rate establish the relationship between increased Ra and ad-
of stimulated and unstimulated whole parotid saliva de- hesive efficacy.

220 The Journal of Adhesive Dentistry

 Mahmoud et al

CONCLUSIONS 21. Kimmes NS, Barkmeier WW, Erickson RL, Latta MA. Adhesive bond
strengths to enamel and dentin using recommended and extended
treatment times. Oper Dent 2010;35:112-119.
Within the limitation of this study, it can be concluded 22. Legler LR, Retief DH, Bradley EL. Effects of phosphoric acid concentra-
that H3PO4 treatment of uremic enamel and dentin at tion and etch duration on enamel depth of etch: an in vitro study. Am J
Orthod Dentofacial Orthop 1990;98:154-160.
42% w/w appears to be much more effective than 37%
23. Lucas VS, Roberts GJ. Oro-dental health in children with chronic renal
w/w in terms of surface roughness. Increasing the treat- failure and after renal transplantation: a clinical review. Pediatr Nephrol
ment time with 42% H3PO4 produced greater surface 2005;20:1388-1394.
roughness compared to 37% H3PO4. Sixty seconds of 24. Mahmoud SH, Abdel kader Sobh M, Zaher AR, Ghazy MH, Abdelaziz KM.
Bonding of resin composite to tooth structure of uremic patients receiv-
H3PO4 treatment time of uremic enamel and dentin ap- ing hemodialysis: shear bond strength and acid-etch patterns. J Adhes
pears to be much more effective than 15- and 30-s treat- Dent 2008;10:335-338.
ment times for Ra. 25. Marshall GW Jr, Inai N, Wu-Magidi IC, Balooch M, Kinney JH, Tagami J,
Marshall SJ. Dentin demineralization: effects of dentin depth, pH and
different acids. Dent Mater 1997;13:338-343.
26. Marshall GW Jr, Marshall SJ, Kinney JH, Balooch M. The dentin
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