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Influence of enamel biomineralization on bonding to minimally invasive CAD/CAM restorations

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Influence of enamel biomineralization on bonding to minimally invasive CAD/CAM restorations

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Content Influence of Enamel Biomineralization on Bonding to
Minimally Invasive CAD/CAM Restorations

Clarisa Amarillas Gastélum

A Thesis Presented to the
FACULTY OF THE HERMAN OSTROW SCHOOL OF DENTISTRY
UNIVERSITY OF SOUTHERN CALIFORNIA

In Partial Fulfillment of the Requirements for the Degree
MASTER OF SCIENCE
CRANIOFACIAL BIOLOGY

Advisor: Sillas Duarte, Jr

December 2016

1
Table of Contents

List of Tables 3
List of Figures 4
Chapter 1 – Microtensile Bond Strength of a CAD/CAM ceramic-reinforced polymer
to Cervical Enamel 5

Abstract 6
Part 1: Introduction 7
Part 2: Materials and methods 9
2.1 Microtensile Bond Strength (μTBS) Evaluation 12
2.2 Statistical Analysis 12
2.3 Scanning Electron Microscopy (SEM) Analysis 12
2.4 Polarized Light Microscopy 13
Part 3: Results 14
3.1 Microtensile Bond Strengths 14
3.2 Scanning Electron Microscopy 18
3.3 Polarized Light Microscopy 21
Part 4: Discussion 24
Part 5: Conclusion 29
References 30

2
Chapter 2 – Wettability of Dental Adhesives on Cervical Enamel 34
Abstract 35
Part 1: Introduction 36
Part 2: Materials and methods 38
2.1 Statistical Analysis 41
Part 3: Results 42
Part 4: Discussion 48
Part 5: Conclusion 53
References 54

3
List of Tables
Chapter 1 – Microtensile Bond Strength of a CAD/CAM ceramic-reinforced polymer
to Cervical Enamel 5

Table 1: Enamel surface treatment 10
Table 2: Restorative materials used 11
Table 3: Results of three-way ANOVA of the data from the samples assessed 14
Table 4: Mean Bond Strength Values in MPa, Standard Deviation and statistical results 14
Table 5: Failure mode percentages obtained for each group 16
Chapter 2 – Wettability of Dental Adhesives on Cervical Enamel 34
Table 1: Adhesive systems used 39
Table 2: Results of three-way ANOVA of the data from the samples assessed. 42
Table 3: Mean contact angles values and Standard Deviation obtained for each group 43

4
List of Figures
Chapter 1 – Microtensile Bond Strength of a CAD/CAM ceramic-reinforced polymer
to Cervical Enamel 5

Figure 1: Illustrates mean strength values in MPa and standard deviation for each groups 15
Figure 2: Illustrates failure mode percentages obtained for each group after 24 h 16
Figure 3: Illustrates failure mode percentages obtained for each group after artificial aging 17
Figure 4: Field-emission SEM depicting fractured bonded interface of cervical enamel etched with 35%
phosphoric acid after aging 18
Figure 5: Field-emission SEM depicting fractured bonded interface of cervical enamel etched with 15%
hydrochloric acid after aging 18
Figure 6: Field-emission SEM depicting fractured bonded interface of middle third enamel etched with
35% phosphoric acid after aging. 19
Figure 7: Field-emission SEM depicting fractured bonded interface of middle third enamel etched with
15% HCl acid after 24h 19
Figure 8: Field-emission SEM depicting fractured bonded interface of prepared middle third enamel
etched with 35% phosphoric acid after 24h 20
Figure 9: Field-emission SEM depicting fractured bonded interface of middle third enamel sandblasted
and etched with 35% phosphoric acid after 24h 20
Figure 10: Polarized light microscopy depicting intact cervical tooth structure. 21
Figure 11: Polarized light microscopy depicting etched surface of cervical etched with 35%
phosphoric acid. 21
Figure 12: Polarized light microscopy depicting etched surface of cervical etched with 15% HCl acid. 22
Figure 13: Polarized light microscopy depicting sandblasted and etched surface of cervical etched with
35% phosphoric acid. 22
Figure 14: Polarized light microscopy depicting prepared etched surface of cervical etched with 35%
phosphoric acid 23
Chapter 2 – Wettability of Dental Adhesives on Cervical Enamel 34
Figure 1: illustrates the results presented in table 3 for the contact angles measured in the moment
of the application (at 0s). 44
Figure 2: illustrates the for the contact angles measured after 20 seconds of application (at 20 s). 45
Figure 3: Contact angle OptiBond FL 46
Figure 4: Contact angle Scotchbond Universal 46
Figure 5: Contact angle Clearfil SE 47
Figure 6: Contact angle Single Bond 47
5

Chapter 1

Bonding Efficacy of CAD/CAM Ceramic Reinforced Polymers
to Aprismatic Enamel

6
Abstract

Objective: The purpose of the study was to compare microtensile bond strengths between
cervical enamel and middle third enamel using different surface treatments and a universal
adhesive with previous etching with phosphoric acid.

Materials and methods: Sixty-four extracted molars were assigned into one of the eight
experimental groups: Intact cervical enamel etched (CEE), intact cervical enamel sandblasted
and etched (CESE), intact enamel etched with hydrochloric acid (CEHE), prepared cervical
enamel etched (PCE), Intact middle third enamel etched (MEE), intact middle third enamel
sandblasted and etched (MESE), intact middle third etched with hydrochloric acid (MEHE), and
prepared middle third enamel etched (PME). Sectioned teeth were bonded to customized
CAD/CAM ceramic-reinforced polymer blocks (Lava Ultimate, 3M/ESPE). The samples were
tested after 24 h or after 20,000 thermocycles. Teeth were sectioned with a cross-section of 0.8
± 0.2 mm2 and fractured at a crosshead speed of 1 mm/min. The data were submitted to 3-way
analysis of variance (ANOVA), followed by Tukey’s HSD post hoc test (α=.05). Additionally, the
enamel etching pattern was investigated using scanning electron microscopy and polarized light
microscopy.

Results: Statistical analysis showed significant differences among different enamel sites
(P<.001). No statistical difference was found between surface treatments (p = 0.301) or
moments (p = 0.556). Statistically higher bond strength was found for cervical enamel (40.70 ±
10.1 MPa) compared to middle third enamel (36.63 ± 11.3 MPa).

Conclusion: Cervical enamel and middle third enamel can result in similar bond strength by
proper surface treatment of enamel.

7
1. Introduction

Enamel is composed of both a mineral and an organic phase. The mineral phase is
mainly comprised of an apatitic calcium phosphate providing enamel´s hardness.
1
Extracellular
matrix proteins such as amelogenin, ameloblastin, enamelin, and amelotin, regulate its
formation throughout enamel biomineralization.
2
Amelogenin prevails as the most
predominant structural protein and is responsible for the formation and orientation of enamel
crystallites.
3
Thickness of enamel varies according to the region where it is located. For maxillary
central incisors at the cervical third (1mm above the cemento-enamel junction - CEJ) the
average is 0.31mm, 0.54mm in the middle third (3mm above the CEJ) and 0.75mm at the incisal
third (5mm above the CEJ).
4
Molars on the other hand measure from 0.18 - 0.77mm at the
cervical third (1.8mm above the CEJ), 0.46 – 1.43 at the middle third (2.5 above the CEJ), and
1.13-2.37mm at the occlusal third (1mm cervically from the cusp tip).
5

The most superficial layer of enamel usually referred to as “prismless” or “aprismatic”
enamel has been previously studied.
6-9
In 1959 it was described by Gustafson as a nearly
homogenous layer produced by compression of the prisms during the final stages of
amelogenesis.
7
Aprismatic enamel is most frequently located in the cervical region and usually
measures 15-30μm at its widest point. Histologically, it presents a different crystallite pattern
than prismatic enamel; since it is parallely oriented to a line perpendicular to the striae of
Retzius as they reach the enamel periphery.
6

Aprismatic enamel has also been categorized into four different types: “false prismless”
enamel which has enamel prisms bended at the subsurface; “moderate prismless” enamel that
has unclear prism boundaries throughout; “essential prismless” which contains no prism
structure at all; and the “complex prismless” enamel that shows a mixture of the “essential
prismless” with the “moderate and/or false prismless” type.
8

Overall, enamel formation is a complex process that takes years in order for every
enamel crystallite to be formed and arranged in such a manner that a structure with such
toughness is created. Until now it is unable to regenerate in the human mouth and substituting
8
it with different materials is a difficult task. For this reason, the ultimate goal should be to
maintain it for as long as possible.
For esthetical reconstructions of anterior teeth, veneers preparations provide more
enamel preservation than crown preparations. Formerly, it was thought that veneer
preparation depths had to remain up to 0.7mm in thickness. Consequently, enamel was
removed and dentin would sometimes be exposed.
4, 10
Nowadays, advances in modern
technology and dental materials have allowed for minimally invasive dental restorative
techniques. Minimal or no-preparation techniques, that relies exclusively on bonding, have
been introduced.
11
Highly conservative techniques provide the great advantage of preservation
of tooth structure and thus the reliability of bonding to enamel tissue.
12

Nevertheless, there are challenges when conservative treatments are done that may be
a threat to their long term effectiveness. These include understanding the limitations of each
restorative material, the technique sensitivity of adhesive procedures, as well as
comprehending distinct tooth structures in order to determine what surface treatment is
optimal.
Resin-enamel bond strengths can vary depending on the region: occlusal, middle, or
cervical thirds.
13
Furthermore, tensile strength of enamel is dependent on the prismatic
orientation.
14
It is important to understand this anisotropic structure in order to determine the
appropriate adhesive technique to consequently achieve better bond strength.
Therefore, the objective of this study was to examine the microtensile bond strength of
cervical enamel compared with middle third enamel, as a function of time and enamel surface
treatment. The null hypothesis to be tested was that (1) there would be no significant
difference in microtensile bond strength between enamel sites; (2) there is no difference in
bonding with different surface treatments of enamel; and (3) aging does not affect microtensile
strength.

9

2. Materials and Methods

Sixty-four extracted caries-free molars with similar proximal flat surfaces were carefully
selected, cleaned, scaled and stored in 0.5% chloramine solution (Fisher Scientific, Pittsburg, Pa)
at 4
o
C.
Standardized enamel specimens were obtained from cervical and middle third of each tooth
using a precision low-speed diamond saw (IsoMet 1000; Buehler Ltd, Lake Bluff, Ill), under
distilled water cooling. Each tooth was divided in half to obtain buccal and lingual surfaces.
Cervical specimens were then obtained by first sectioning at cervical enamel junction (CEJ)
followed by a second section 3.0 mm coronally to obtain 8.0 x 3.0 mm rectangular specimens.
Middle third specimens were obtained by first sectioning 1.5 mm from cusp tips and a second
section 3.0mm apically to obtain 8.0 x 3.0 mm rectangular specimens.
Each tooth was cleaned with pumice with a prophylaxis cup at low speed for 10s.
Enamel specimens were then assigned into eight experimental groups (n=8): Intact cervical
enamel etched (CEE), intact cervical enamel sandblasted and etched (CESE), intact enamel
etched with hydrochloric acid (CEHE), prepared cervical enamel etched (PCE), Intact middle
third enamel etched (MEE), intact middle third enamel sandblasted and etched (MESE), intact
middle third etched with hydrochloric acid (MEHE), and prepared middle third enamel etched
(PME). After bonding the groups were further divided into two subgroups (n=4) to be tested
after 24 hours and after artificial aging (AA). The first subgroup was stored in distilled water at
37º C for 24h and the second subgroup was artificially aged by thermal cycling for 20,000 cycles
in distilled water at 5º C and 55º C (THE1100, SD Mechatronik, Feldkirchen-Westerham,
Germany). A description of the groups can be found on table 1.
CEE-24H, MEE-24H, CEE-AA, and MEE-AA groups were etched with 35% phosphoric acid
for 30s, rinsed with distilled water and dried.
15
CESE-24H, MESE-24H, CESE-AA, and MESE-AA
groups were airborne-particle abraded using 50-μm aluminum oxide for 10 s at a distance of 10
mm, rinsed with distilled water, and air dried then etched with 35% phosphoric acid for 30s,
rinsed with distilled water and dried. CEHE-24H, MEHE-24H, CEHE-AA, and MEHE-AA groups
were etched with hydrochloric acid (Icon-Etch) for 30s, rinsed with distilled water 30s and
10
dried. An ample amount of 99% Ethanol (Icon-Dry) was applied, left for 30s, and air dried. PCE-
24H, PME-24H, PCE-AA, and PME-AA groups were prepared 0.1 mm with a diamond bur at
high-speed, rinsed and dried; after etched with 35% phosphoric acid for 30s, rinsed with
distilled water and dried (Table 1). Subsequently adhesive was applied (Adper Scotchbond
Universal, 3M ESPE, St. Paul, MN, USA) 20s rubbing it against tooth surface, air dried for 5s until
adhesive didn’t move. (Table 1)
CAD/CAM ceramic-reinforced polymer restorations (Lava Ultimate, 3M/ESPE) were
fabricated for each enamel specimen. Then restorations were treated according to
manufacturer instructions (Table 2): cleaned with ultrasonic cleaner, then airborne-particle
abraded using 50-μm aluminum oxide for 10s at a distance of 10 mm, removed sand with
ethanol, and air dried. Next, a silane coupling agent was applied on the surface (RelyX Ceramic
Primer; 3M ESPE), allowed to evaporate for 60s, and air dry for 5s to evaporate the solvent.
CAD/CAM ceramic-reinforced polymer restorations were cemented to each tooth using a light-
cure resin cement over specimen (RelyX Veneer, 3M ESPE, St. Paul, MN, USA) under 1 kg weight
for 60s. Excess cement was removed with micro-brushes and each surface was polymerized for
60s with a light output of 1000 mW/cm
2
(Elipar S10, 3M ESPE).

TABLE 1. ENAMEL SURFACE TREATMENT
Group Restorative technique
CEE
(Intact Cervical Enamel
Etched)
Clean tooth with pumice, Rinse and dry, Etch with phosphoric acid 35%
for 30s, Rinse and dry, Apply Scotchbond Universal adhesive (as
described in table 2)
MEE
(Intact Middle Enamel Etched)
CESE
(Intact Cervical Enamel
Sandblasted and Etched)
Clean tooth with pumice, rinse and dry, air abrade for 10s, rinse and dry,
etch with phosphoric acid 35% for 30s, rinse and dry, apply Scotchbond
Universal adhesive (as described in table 2)
MESE
(Intact Middle Enamel
Sandblasted and Etched)
CEHE
(INTACT CERVICAL ENAMEL
ETCHED WITH HCL ACID
Clean tooth with pumice, rinse and dry, etch with hydrochloric acid for
30s, rinse and dry, apply ethanol, leave 30s and air dry, apply Scotchbond
Universal adhesive (as described in table 2)
11
MEHE
(INTACT MIDDLE THIRD
ENAMEL ETCHED WITH HCL
ACID)
PCE
(PREPARED CERVICAL
ENAMEL)
Clean tooth with pumice, rinse and dry, prepare 0.1 mm with diamond
bur, rinse and dry, etch with phosphoric acid 35% for 30s, rinse and dry,
apply Scotchbond Universal adhesive (as described in table 2)
PME
(PREPARED MIDDLE THIRD
ENAMEL ETCHED)

TABLE 2. RESTORATIVE MATERIALS USED
MATERIAL Composition (Lot) Manufacturer Instructions of use
Adper
Scotchbond
Universal
Bis-GMA; HEMA; water; ethanol; silane-
treated silica; decamethylene
dimethacrylate (10–MDP); 2-propenoic
acid, 2-methyl-, reaction products with
1,10-decanediol and phosphorous oxide;
polyalkenoic acid; dimethylamino-
benzoate(-4); Camphorquinone;
(dimethylamino) ethyl methacrylate;
methyl ethyl ketone; (Lot: 588249)
3M ESPE, St. Paul,
MN, EUA

1. etch phosphoric acid for 30 s,
rinse and dry
2. rub adhesive for 20 s and gently
air-dry for 5 s until it no longer
moves and the solvent has
evaporated completely
3. light cure 10 s
Lava
Ultimate
Resin Nano Ceramic 80 wt. % (65 vol %)
Urethane dimethacrylate (UDMA)
Bisphenol A polyethethylene glycol dither
dimethacrylate (Bis-EMA)
Silica (20 nm)
Zirconia (4-11nm)
3M ESPE, St. Paul,
MN, EUA

1. Ultrasonic cleaner (10 min x 2)
2. Air abrade 50 um Aluminum
Oxide at 2 bar (30 psi) and remove
sand with ethanol and air
RelyX
Ceramic
Primer
Ethyl alcohol, water,
methacryloxypropyltrimethoxysilane
(Lot:N479421 )
3M ESPE, St. Paul,
MN, EUA

1. Brush a layer of primer (Relyx
Ceramic Primer) on surface for 60s
2. Lightly air-dry surface for 5s to
evaporate solvent solvent
RelyX
Veneer
Bisphenol-A-diglycidylether
dimethacrylate (BisGMA) and triethylene
glycol dimethacrylate (TEGDMA) polymer.
Zirconia/silica and fumed silica fillers (Lot:
N711662 and N715150)

3M ESPE, St. Paul,
MN, EUA

1. Apply a thin layer of the
selected shade of RelyX Veneer
cement directly from the syringe
onto the bonding surface
2. Protect the cement from direct
operatory light exposure.
3. Remove the excess cement
from the margins using a blunt
instrument or dry brush
4. Light cure the labial, lingual,
interproximal and occlusal
surfaces for 30 s each.
12

2.1 Microtensile Bond Strength (μTBS) Evaluation
The bonded enamel specimens were sectioned with a precision saw (IsoMet 1000,
Buehler, Lake Bluff, IL, USA) parallel to the adhesive interface into slabs with a thickness of
0.8±0.1 mm. Each slab was attached to a phenolic ring and further sectioned perpendicular to
adhesive interface with a thickness of 0.8±0.1 mm to obtain sticks. The specimens were then
individually attached to a microtensile jig using cyanoacrylate glue (Zapit; Dental Ventures of
America, Inc, Corona, Calif)
16
. The sticks were tested for micro-tensile bond strength using a
universal testing machine (Instron 5965, Instron, Canton, MA, USA) with a 5 KN load cell at a
crosshead speed of 1 mm/min. The bonding interface of all sticks was measured with a digital
caliper (Mitutoyo digital calipers; Mitutoyo Corp., Kanogawa, Japan) with an accuracy of 0.001
mm to calculate the bonding area in square millimeters. Pre- testing failures or spontaneous
debonding were considered as 0 MPa. Failure modes of all sticks were classified as adhesive (A),
cohesive enamel (CE), cohesive restoration (CR) or mixed (M).

2.2 Statistical Analysis
The statistical analysis was performed based on the data from microtensile bonding
strength in MPa. Kolmogorov-Smirnov test was used to evaluate the normality of the data
distribution. After confirming a normal distribution of the data (p=0.200), the homoscedasticity
assumptions of the tensile strength data were confirmed by the Levene test (p = 0.062). The
μTBS data were then statistically analyzed using analysis of variance with three-factors (three-
way ANOVA) and Tukey’s multiple comparison post-hoc test was applied to detect which means
differ from each other. The significance level for both testes was 5% (α = 0.05). The data were
analyzed using Microsoft Excel 2011 (Microsoft Office system 2011) and SPSS 20 (SPSS Inc.,
Chicago, Il, EUA).

2.3 Scanning Electron Microscopy (SEM) Analysis
Stick fragments of each group were chosen randomly and submitted to SEM for
interface analysis. The fragments were serially dehydrated with different concentrations of
13
ethanol (25%, 40%, 50%, 70%, 95% and 100%). Subsequently they were immersed in
hexamethyldisilizane (HMDS) (Electron Microscope Sciences, Fort Washington, PN, USA) for 10
mins, removed, and placed on filter paper under a vent hood until air dried at room
temperature for 24h.
17
Fragments were then mounted on stubs, gold sputter coated and
examined under field-emission scanning electron microscope (JSM-7001F, JEOL, Tokyo, Japan).
Illustrative images were taken of all groups.

2.4 Polarized Light Microscopy
Four additional extracted caries-free molars were carefully selected and stored in 0.5%
chloramine solution (Fisher Scientific, Pittsburg, Pa) at 4
o
C. Each tooth was cleaned with pumice
with a prophylaxis cup at low speed for 10s. Teeth were then assigned to one of the four
different surface treatments: intact cervical enamel etched with phosphoric acid, intact cervical
enamel sandblasted and etched, intact cervical enamel etched with hydrochloric acid and
prepared cervical enamel etched.
Half of the tooth was treated according to the different surface treatment while the other
side was left untreated. Teeth were cleaned two times in ultrasonic cleaner in distilled water for
15 mins. Each tooth was sectioned at the cervical enamel junction using a precision diamond
saw (IsoMet 1000; Buehler Ltd, Lake Bluff, Ill), under distilled water cooling. Followed by
another two to three 0.4mm slab sections. Each specimen was manually polished to a thickness
of approximately 0.2mm with 400-, 600, 800, 1000, and 1200-grit SiC abrasive papers (Carbimet
Paper Strips; Buehler Ltd, Lake Bluff, Ill) under running distilled water. Felt polishing pads with
0.05μm diamond paste (Buehler Ltd, Lake Bluff, Ill)) were used to complete polishing
procedure. Specimens were mounted in a glass slide with distilled water and examined under a
polarized optical light microscope (Omax; China), coupled to a camera (Omax 35140U3; China).
The slides were seen at 10X magnification and images were photographed and saved directly
onto computer.

14

3. Results

3.1 Microtensile Bond Strengths
Three-way ANOVA showed a significant difference between enamel site (cervical and
middle third enamel) (p < 0.001) and for the interaction between the treatment surface and the
enamel site (p=0.022). No significant difference was found on the μTBS among the different
surface treatments (p = 0.301) and moments (p = 0.556) (Table 3).

Table 3 – Results of three-way ANOVA of the data from the samples assessed.
Source S.S. D.F. Mean Square F Sig.
Corrected Model 4755.628 15 317.042 2.797 .000
Intercept 1323463.39 1 1323463.39 11673.758 .000
Moment 39.432 1 39.432 .348 .556
Surface treatment 415.160 3 138.387 1.221 .301
Location 1915.612 1 1915.612 16.897 .000
Moment * Treatment 497.305 3 165.768 1.462 .223
Moment * Location 69.605 1 69.605 .614 .434
Treatment * Location 11010.664 3 366.888 3.236 .022
Moment * Treatment * Location 509.818 3 169.939 1499 .213
Error 101693.612 897 113.371
Total 1522962.88 913
Corrected Total 106449.240

The results of the microtensile bond strength values, standard deviation and post-hoc
statistical results for the evaluated groups are presented in the Table 4.

Table 4. Mean Bond Strength Values in MPa, Standard Deviation and statistical results.
Surface treatment
24 hours Aged
Cervical Middle Cervical Middle
Etched H
3
PO
4
40.01±10.3
aA
(n= 61) 36.10±13.56
aA
(n= 31) 42.82±9.8
aA
(n= 75) 34.95±10.1
aB
(n= 46)
Sandblasted + H
3
PO
4
41.39±9.8
aA
(n= 60) 36.38±11.04
aA
(n= 48) 42.27±11.1
aA
(n= 60) 39.42±11.3
aA
(n= 54)
Etched HCl + ethanol 41.09±9.8
aA
(n= 66)

40.57±11.27
aA
(n= 58) 38.28±10.7
aA
(n= 53) 39.38±11.9
aA
(n= 60)
Prepared + etched H
3
PO
4
40.37±10.2
aA
(n= 58)

35.62±10.70
aA
(n= 71) 38.92±9.4
aA
(n= 76) 38.92±11.0
aA
(n= 36)

Cervical enamel bond strength varied from 40.01±10.3 (CEE) to 41.39±9.8 (CESE)

for 24h
and from 38.28±10.7

(CEHE) to 42.82±9.8 (CEE)

after aging. Additionally, middle third enamel
ranged from 35.62±10.70

(PCE) to 40.57±11.27

(MEHE) for 24h and from 34.95±10.1

(MEE)

to
15
39.42±11.3 (MESE) after aging. Nevertheless, no significant difference was found for both
cervical and middle third enamel groups when compared with different surface treatment or
time. (Figure 1)
Statistically higher bond strengths with a mean of 40.70 ± 10.1 MPa were found for
cervical third enamel compared to 36.63 ± 11.3 MPa of middle third enamel (p < 0.001).

Figure 1. Illustrates mean strength values in MPa and standard deviation for each groups

Failure modes varied between cervical and middle third enamel. CEE-24h displayed
83.6% adhesive failure modes; whereas MEE-24h had 48.4% adhesive, 32.3% mixed, and 19.4%
cohesive resin. Compared with CEME-AA, MESE-AA had a lower adhesive (51.9%) and higher
cohesive enamel (29.6%) failure mode. MEHE-24h and MEHE-AA presented 67.2% and 70%
adhesive failures respectively; in contrast with CEHE-24H and CEHE-AA which had 86.4% and
54.7% . The highest cohesive enamel failures were found for MEHE-24h (27.6%), CEHE-AA
(32.1%), and MESE-AA (29.6%). PCE-AA had the lowest adhesive failure mode of 50% and
0
5
10
15
20
25
30
35
40
45
Cervical Middle Cervical Middle
24 hours Aged
Etched Phosphoric Acid
Sandblasted + Etched
Etched HCl + Ethanol
Prepared + Etched
16
displayed 27.8% mixed and 22.2% of cohesive enamel. (Table 5). Overall, failure mode was
predominantly adhesive for both cervical enamel (75.64%) and middle third enamel (63.61%).
Table 5. Failure mode percentages obtained for each group

GROUP Adhesive Mixed CE
CEE-24H 83.6 9.8 6.6
MEE-24H 48.4 32.3 19.4
CESE-24H 85.0 11.7 3.3
MESE-24H 75.0 8.3 16.7
CEHE-24H

86.4

10.6

3.0
MEHE-24H

67.2

5.2 27.6
PCE-24H

72.4

6.9

19.0
PME-24H

67.6

16.9 15.5
CEE-AA 81.3 8.0 10.7
MEE-AA 67.4 15.2 17.4
CESE-AA 75.0 10.0 15.0
MESE-AA 51.9 18.5 29.6
CEHE-AA

54.7

13.2

32.1
MEHE-AA

70.0

18.3 11.7
PCE-AA

64.5

15.8

18.7
PME-AA

50.0

27.8 22.2

Figure 2. Illustrates failure mode percentages obtained for each group after 24 h

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
CEE-24H
MEE-24H
CESE-24H
MESE-24H
CEHE-24H
MEHE-24H
PCE-24H
PME-24H
Failure Mode at 24h
Failure Mode Adhesive Failure Mode Mixed Failure Mode CE
17

Figure 3. Illustrates failure mode percentages obtained for each group after artificial aging

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
CEE-AA
MEE-AA
CESE-AA
MESE-AA
CEHE-AA
MEHE-AA
PCE-AA
PME-AA
Failure Mode after aging
Failure Mode Adhesive Failure Mode Mixed Failure Mode CE
18
3.2 Scanning Electron Microscopy

Figure 4. Field-emission scanning electron microscopy depicting fractured bonded interface
of cervical enamel etched with 35% phosphoric acid after aging. (Magnification: X250) (CE:
cervical enamel, SU: Scot bond Universal, RC: resin Cement)

Figure 5. Field-emission scanning electron microscopy depicting fractured bonded interface
of cervical enamel etched with 15% hydrochloric acid after aging. (Magnification: X250) (CE:
cervical enamel, SU: Scotchbond Universal, RC: resin Cement)

19

Figure 6. Field-emission scanning electron microscopy depicting fractured bonded interface
of middle third enamel etched with 35% phosphoric acid after aging. (Magnification: X250)
(ME: middle third enamel, SU: Scotchbond Universal, RC: resin Cement)

Figure 7. Field-emission scanning electron microscopy depicting fractured bonded interface
of middle third enamel etched with 15% HCl acid after 24h. (Magnification: X250) (ME: middle
third enamel, SU: Scotchbond Universal, RC: resin Cement)

20

Figure 8. Field-emission scanning electron microscopy depicting fractured bonded interface
of prepared middle third enamel etched with 35% phosphoric acid after 24h. (Magnification:
X250) (ME: middle third enamel, SU: Scotchbond Universal, RC: resin Cement)

Figure 9. Field-emission scanning electron microscopy depicting fractured bonded interface
of middle third enamel sandblasted and etched with 35% phosphoric acid after 24h.
(Magnification: X250) (ME: middle third enamel, SU: Scotchbond Universal, RC: resin Cement)

21
3.3 Polarized Light Microscopy

Figure 10. Polarized light microscopy depicting intact cervical tooth structure. (Magnification:
10X) (EE: etched enamel, PE: prismatic enamel, DEJ: dentin-enamel junction; D: dentin)

Figure 11. Polarized light microscopy depicting etched surface of cervical etched with 35%
phosphoric acid. (Magnification: 10X) (EE: etched enamel, PE: prismatic enamel, DEJ: dentin-
enamel junction; D: dentin)
22

Figure 12. Polarized light microscopy depicting etched surface of cervical etched with 15% HCl
acid. (Magnification: 10X) (EE: etched enamel, PE: prismatic enamel, DEJ: dentin-enamel
junction; D: dentin)

Figure 13. Polarized light microscopy depicting sandblasted and etched surface of cervical
etched with 35% phosphoric acid. (Magnification: 10X) (SB: Sandblasted EE: etched enamel,
PE: prismatic enamel, DEJ: dentin-enamel junction; D: dentin)

23

Figure 14. Polarized light microscopy depicting prepared etched surface of cervical etched
with 35% phosphoric acid. (Magnification: 10X) (PE: Prepared enamel, DEJ: dentin-enamel
junction; D: dentin)

24
4. Discussion
Cervical enamel, which contains a high amount of aprismatic enamel, is able to have
similar or greater bond strength values to that of middle third enamel. Our results, therefore,
substantiate the rejection of the first null hypothesis that microtensile bond strength does not
differ between cervical and middle third enamel. Nonetheless, bonding efficacy to aprismatic
enamel was not affected by surface treatment neither artificial aging. Therefore, the second
and third null hypotheses were accepted.
Enamel is a complex structure. Even though it is mainly composed of hydroxyapatite
crystals, the structural complexity lies in the way HPa crystals are arranged three dimensionally.
Hydroxyapatite crystals can be organized into prisms and interprisms -which differ in the
orientation- being positioned parallel or perpendicular to the Retzius lines respectively.
18

Retzius lines and prism cross-striations are related to the development and growth of enamel.
In the former the incremental growth lines represent the layered apposition of enamel and
represent the position of the ameloblast layer at distinct times during amelogenesis. Likewise,
prism-striations are thought to reflect a daily pattern of enamel formation.
18, 19
Moreover, the
crossing of prism bundles known as decussation of enamel and the arrangement of these
prisms are accountable for the structural and mechanical anisotropy in enamel.
(20)
In addition
to prismatic enamel, aprismatic enamel is also found on the outer layer of enamel. Enamel
crystals in prismatic enamel present different orientation within each prism. Whereas, crystals
in aprismatic enamel are densely organized parallel to each other in one direction and almost
perpendicular to enamel periphery.
7, 21
Thus, showing a more negative birefringence when
examined under polarized light microscopy (Fig.10). Discrepancies in frequency and distribution
25
of aprismatic enamel have been found between different types of teeth and regions within the
same tooth.
22
Cervical enamel being one of the most common sites for aprismatic enamel to
be located.
6

It is assumed that middle third enamel provides higher bond strength than cervical
enamel.
23, 24
However, our present study shows that when proper surface treatment is
performed, cervical enamel may attain similar or higher bond strengths to that of middle third
enamel. Modification of the enamel surface can be obtained by several methods including: acid
etching, air-abrasion, or surface roughening, or a combination of them. Acid etching creates
microporosites by partially dissolving the surface apatite crystals that results in superior
dissolution of carbonate-rich crystal cores, forming void areas that allow intraprismatic
infiltration.
25
Likewise, acid etching increases surface area and reduces contact angle thus
increasing wettability of the adhesive systems into the enamel.
26, 27
Aprismatic enamel is more
acid resistant because of the parallel apatite crystals that are densely packed.
22
Thus, there is
no interprismatic organic substance where the acid can easily diffuse across to etch the prism-
like structure below. Acid etching of aprismatic enamel nevertheless can result in alteration of
the structure itself (Fig.11). Causing a less aggressive etching pattern, revealing a prism-like
structure.
28
Though different etching patterns can vary according to the aprismatic enamel
thickness. Moreover, thickness of prism-like structure can range from 76-198 µm.
5
This
structure includes “moderate” and “complex prismless” types which display indistinct circular
prisms and circular-like arcade prisms respectively.
8
These indistinct prism structures exhibit
particularly narrow prism boundaries and are present in the 15µm outer enamel surface. After
26
acid etching prism-like enamel microporosities are formed, a higher energy surface is produced
resulting in infiltration of the adhesive.
The technique used during etching is also important to expose the prism-like structures
into aprismatic enamel layers. Active application of the etchant has been demonstrated to help
in the removal of aprismatic enamel . Hence, mild etching patterns can be achieved by
uncovering the underlying prismatic enamel.
28
Furthermore, higher bond strengths of prismatic
enamel have been achieved by active application of a universal adhesive system after
phosphoric acid etching of the surface.
29, 30
Fresh acidic monomers present into universal
adhesive systems can also diffuse into deeper prismatic and interprismatic regions of the
etched surface generating greater enamel demineralization.
29, 30
This additional etching may
displace loose aprismatic island that remained in the etched enamel. The facts mentioned can
explain the adequate bond strengths observed in cervical enamel in the present study
.31

HCl acid is used as an erosive medium to remove natural caries lesion in preparation for
resin infiltration. It has been shown that the application of 15% HCl for 30s on intact enamel has
led to the removal in average of 15um of the superficial layer of enamel.
32
Furthermore,
removal of aprismatic enamel on deciduous teeth was found to be effective with the use of HCl
acid.
33
High demineralization and increase in surface roughness of enamel has also been shown
with 30s of HCl acid. Similar findings were obtained in the present study where removal of
aprismatic enamel was depicted. (Fig.12)
Other surface treatments such as air-abrasion of enamel surface followed by acid
etching with phosphoric acid, and tooth preparation were also tested. Air-abrasion may be used
as a surface treatment technique where aluminum oxide particles are driven against the
27
enamel surface by high air pressure in order to modify the surface by abrasion (Fig.13).
34
Thus,
an increase in surface roughness is observed and may contribute to the improvement of
wettability of adhesives
.35
Enamel surface preparation with air abrasion or tooth preparation
with a bur has shown to provide adequate bonding with different dental adhesive systems.
36

There is conflicted information in literature regarding bonding to roughened or intact enamel.
16, 37
Our results showed that roughening of enamel (by air-abrasion or bur) attained similar
bond strengths to all the other groups tested where the enamel surface was modified for
adhesion (Fig.14).
Alongside the micromechanical retention obtained by interlocking of the adhesive
within the microporosities in enamel, chemical bonding correspondingly plays an important
role in adhesion. The adhesive used in all specimens was a universal adhesive system (SU) that
contains 10-methacryloxydecyl dihydrogen phosphate (MDP). 10-MPD chemically bonds to
hydroxyapatite by interacting with calcium in the hydroxyapatite through nanolayering.
38-40

Resulting in a hydrophobic MDP- calcium salt layer that is believed to play a part in the
interfacial stability against hydrolytic degradation.
41
Additionally, SU includes polyalkenoic acid
that produces an ionic interaction between phosphate esther groups and calcium in
hydroxyapatite.
39
Thus, it is possible that chemical interaction assisted in bonding when using
the tested adhesive system.
Analysis of failure mode revealed that cervical third enamel groups had more adhesive
type of failure, whereas middle third enamel displayed cohesive and mixed failure modes.
Orientation of enamel prisms influences enamel bond strength and failure fracture mode.
13, 14,
23, 42
Cohesive failures are mainly exhibited when load is applied parallel to the long axis of the
28
enamel prisms whereas adhesive failures are seen when load is applied perpendicular to the
enamel prisms.
42
Interestingly, lower bond strength values were obtained from the parallel-
applied load and higher bond strength values for the perpendicular applied load.
42, 43
Thus, it
can be assumed that the middle third specimens obtained by horizontal sectioning exposed
parallel oriented prisms, which in turn produced lower bond-strength. Cervical enamel have
more densely packed HPa crystals that may influenced the bond strength observed when
compared to that of middle enamel. Nonetheless, enamel strength is dependent on prismatic
orientation.
14, 42, 43
Therefore, we can assume that in the present study the lower bond
strengths and further higher cohesive percentage of fracture failure mode obtained from
middle third enamel can be associated with the enamel prism orientation and applied load.
However, further studies are needed to prove this hypothesis.
Long-term success and durability of bonded restorations can be accomplished when
bonding to enamel.
11
Modification of enamel using different surface treatments will lead to
partial removal off aprismatic enamel and exposure of prism-like structures. Prism-like
structures are more susceptible for surface treatment that will provide improved permeation of
adhesive monomers among the HPa crystals and producing similar bond strength values to that
of middle third enamel. In addition to that, bonding efficacy to cervical enamel was not
affected by artificial aging. Further studies are suggested to evaluate bonding efficacy of
different adhesive systems to aprismatic enamel.

29
5. Conclusion
Cervical enamel can attain similar bond strengths to that of middle enamel, regardless
of the presence of aprismatic enamel. Proper surface treatment that exposes prism-like
structures within the enamel is essential to produce long-term bonding efficiency to cervical
enamel.

30
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on resin-enamel tensile bond strength. Dent Mater 1997;13(5):290-6.
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14. Carvalho RM, Santiago SL, Fernandes CA, Suh BI, Pashley DH. Effects of prism orientation
on tensile strength of enamel. J Adhes Dent 2000;2(4):251-7.
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electron microscopic evaluation of self-adhesive and self-etch resin cements to intact
and etched enamel. J Prosthet Dent 2008;100(3):203-10.
16. Perdigao J, Geraldeli S. Bonding characteristics of self-etching adhesives to intact versus
prepared enamel. J Esthet Restor Dent 2003;15(1):32-41; discussion 42.
17. Perdigao J, Lambrechts P, Van Meerbeek B, Vanherle G, Lopes AL. Field emission SEM
comparison of four postfixation drying techniques for human dentin. J Biomed Mater
Res 1995;29(9):1111-20.
18. Risnes S. Growth tracks in dental enamel. J Hum Evol 1998;35(4-5):331-50.
19. Li C, Risnes S. SEM observations of Retzius lines and prism cross-striations in human
dental enamel after different acid etching regimes. Arch Oral Biol 2004;49(1):45-52.
20. Bajaj D, Arola D. Role of prism decussation on fatigue crack growth and fracture of
human enamel. Acta Biomater 2009;5(8):3045-56.
21. A. Kakaboura LP. Bonding of Resinous Materials on Primary Enamel. Interfacial
Phenomena and Related Properties: Springer; 2005.
22. Whittaker DK. Structural variations in the surface zone of human tooth enamel observed
by scanning electron microscopy. Arch Oral Biol 1982;27(5):383-92.
23. Shimada Y, Kikushima D, Tagami J. Micro-shear bond strength of resin-bonding systems
to cervical enamel. Am J Dent 2002;15(6):373-7.
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restorations bonded to coronal and cervical enamel. Oper Dent 2005;30(4):468-73.
25. Hannig M, Bock H, Bott B, Hoth-Hannig W. Inter-crystallite nanoretention of self-etching
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27. Gwinnett AJ, Matsui A. A study of enamel adhesives. The physical relationship between
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Stages and Evolution of Dental Enamel Erosion. Braz Dent J 2016;27(3):313-7.
32. Meyer-Lueckel H, Paris S, Kielbassa AM. Surface layer erosion of natural caries lesions
with phosphoric and hydrochloric acid gels in preparation for resin infiltration. Caries
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33. Paris S, Dorfer CE, Meyer-Lueckel H. Surface conditioning of natural enamel caries
lesions in deciduous teeth in preparation for resin infiltration. J Dent 2010;38(1):65-71.
34. Powers J.M. T, W.H. Bond Strength to Enamel. Germany: Springer; 2005.
35. Marshall SJ, Bayne SC, Baier R, Tomsia AP, Marshall GW. A review of adhesion science.
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36. Sengun A, Orucoglu H, Ipekdal I, Ozer F. Adhesion of two bonding systems to air-
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37. Kanemura N, Sano H, Tagami J. Tensile bond strength to and SEM evaluation of ground
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39. Sezinando A, Serrano ML, Perez VM, et al. Chemical Adhesion of Polyalkenoate-based
Adhesives to Hydroxyapatite. J Adhes Dent 2016;18(3):257-65.
33
40. Fu B, Sun X, Qian W, et al. Evidence of chemical bonding to hydroxyapatite by
phosphoric acid esters. Biomaterials 2005;26(25):5104-10.
41. Yoshida Y, Yoshihara K, Hayakawa S, et al. HEMA inhibits interfacial nano-layering of the
functional monomer MDP. J Dent Res 2012;91(11):1060-5.
42. Munechika T, Suzuki K, Nishiyama M, Ohashi M, Horie K. A comparison of the tensile
bond strengths of composite resins to longitudinal and transverse sections of enamel
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Oper Dent 2003;28(1):20-7.

34

Chapter 2

Wettability of Dental Adhesives on Cervical Enamel

35
Abstract

Objective: The purpose of this study was to evaluate wettability of different adhesive systems
at 0s and 20s using distinct surface treatments on enamel.

Materials and methods: 48 extracted teeth were cut in half and assigned to 1 of the 4 groups:
cervical enamel etched (CEE), cervical enamel sandblasted and etched (CESE), enamel etched
with hydrochloric acid (CEHE), and prepared cervical enamel etched (PCE). Four adhesive
systems were used: Scotchbond Universal (SU), OptiBond FL (OFL), Clearfil SE (CSE) and Adper
Single Bond Plus (SB); OFL and CSE were also used without primer (OFLNP and CSENP).
Specimens were polished to a flat surface using 240-, 320-, 400-, 600 and 800-grit SiC abrasive
papers. Wettability was determined by contact angle using a goniometer at 0s and 20s. Contact
angle measurements were submitted to 3-way analysis of variance (ANOVA), followed by
Tukey’s HSD post hoc test (α=.05).

Results: Statistical analysis showed significant difference between adhesive systems, time and
surface treatment (p < 0.05). Highest contact angle was for SU followed by SB, CSE and lowest
for OFL. Primer significantly decreased contact angle for CSE and OFL. All groups, except SB
decreased contact angle after 20s. Treated enamel surfaces only etched presented higher
contact angle for SU, CSE, and CSENP.

Conclusion: Wettability of enamel is dependent of adhesive system, surface treatment and
time left after application. The use of primer increased wettability for both CSE and OFL.

36
1. Introduction

In 1805, Thomas Young was the first to examine contact angle and the equilibrium of a
drop resting on a solid surface under the action of surface tension. Contact angle is described as
the angle where a liquid-vapor interface meets a solid surface.
1
It quantifies the amount to
which a solid will be penetrated by the liquid.
2
Determined by cohesive forces of the liquid
molecules amongst themselves and adhesive forces between the liquid and solid.
3

When a drop has a contact angle over 90° it is said to be hydrophobic. This
demonstrates less spreading, reduced adhesiveness and low surface energy. On the other hand,
a drop with a smaller contact angle is hydrophilic. This suggests enhanced spreading, improved
adhesiveness, and higher surface energy.
Adhesive techniques rely on adhesive systems that have optimal wetting properties in
order to achieve better bond strength.
4
Stronger adhesion can be obtained with solutions that
have weaker cohesion and therefore produce low contact angle. In contrast, stronger cohesion
within the liquid reduces wetting and increases contact angle.
There are different factors that may affect contact angle such as: temperature, relative
humidity, surface roughness, and material homogeneity. Furthermore, surfaces that are
contaminated may affect wetting and hence produce higher contact angle compared with clean
surfaces.
5

In static contact angle measurements, an average value from a set of measures is
usually used. Moreover, dynamic measurements are made to measure contact angle over
time.
6
They can be used to evaluate the effectiveness of surfactants, such as primers and other
surface treatments. Molecules in primers contain functional groups that have an affinity for
adhesive materials called adhesion promoters.
4
Other factors that affect contact angle over a
period of time are evaporation, molecular relaxation, absorption, and adsorption.
Surface treatment of enamel is essential to achieve long-term success of adhesive
restorations. Acid etching is an important chemical treatment to improve adhesion. It is used as
a surface preparation step to modify morphology, chemistry and energetic characteristics such
as surface tension.

Acid-etched enamel surface has twice more surface energy than intact
37
enamel.
7, 8
Other surface treatments include air abrading and tooth preparation. However, only
few studies have shown the influence of enamel surface treatment on the wettability of
adhesives.
9

Contemporary adhesives can be categorized according to their mode of action into etch-
and-rinse, and self-etch.
10
These materials can be later subdivided into 5 main groups: 3-step
etch-and-rinse adhesives, 2-step etch-and-rinse adhesives, 2- step self-etch adhesives, 1-step
self-etch adhesives and multimode adhesives.
11 12

Adhesive systems have different compositions and consequently may vary in acidity and
viscosity. These amongst other previously discussed factors may influence the ability of the
adhesive to penetrate the enamel structure.
Therefore, the aim of this study was to evaluate the hydrophilicity of four adhesive
systems and to characterize the effect of distinctive surface treatments on enamel surface. The
null hypothesis tested was that (1) different types of adhesives had no significant influence on
hydrophilicity, and that (2) wettability of adhesives was not affected by different surface
treatments.

38
2. Materials and methods

Forty-eight extracted caries-free molars were carefully selected, cleaned, scaled and stored
in 0.5% chloramine solution (Fisher Scientific, Pittsburg, Pa) at 4
o
C. Standardized enamel
specimens were obtained from cervical third of each tooth using a precision low-speed
diamond saw (IsoMet 1000; Buehler Ltd, Lake Bluff, Ill), under distilled water cooling. Each
tooth was divided in half to obtain the flattest area. Specimens were then obtained by first
sectioning at the cervical enamel junction (CEJ) followed by a second section 3.0 mm coronally.
Each tooth was cleaned with pumice with a prophylaxis cup at low speed for 10s. Enamel
specimens were then assigned according to the surface treatment into 4 experimental groups
(n=12): Cervical enamel etched (CEE), cervical enamel sandblasted and etched (CESE), enamel
etched with hydrochloric acid (CEHE), and cervical enamel etched (PCE). Four adhesive systems
were used with each treatment surface group: Scotchbond Universal (SU), OptiBond FL (OFL),
Clearfil SE (CSE) and Adper Single Bond Plus (SB) (Table 1). Additionally, OptiBond FL and Clearfil
SE were used without Primer.
Cervical specimens were polished to a flat surface using 240-, 320-, 400-, 600-, and 800- grit
SiC abrasive papers (Carbimet Paper Strips; Buehler Ltd, Lake Bluff, Ill) under running distilled
water. Then completed by using felt polishing pads with 0.05-μm diamond paste (Buehler Ltd,
Lake Bluff, Ill). CEE groups were etched with 35% phosphoric acid for 30s, rinsed with distilled
water and dried. CESE groups were airborne-particle abraded using 50-μm aluminum oxide for
10 s at a distance of 10 mm, rinsed with distilled water, and air dried then etched with 35%
phosphoric acid for 30s, rinsed with distilled water and dried. CEHE groups were etched with
hydrochloric acid (Icon-Etch) for 30s, rinsed with distilled water 30s and dried. An ample
amount of 99% Ethanol (Icon-Dry) was applied, left for 30s, and air dried. PCE were prepared
0.1 mm with a diamond bur at high-speed, rinsed and dried; after etched with 35% phosphoric
acid for 30s, rinsed with distilled water and dried. Enamel treatment and bonding technique
was done according to manufacturer´s instructions with the exception of selective etching for
all specimens for 30s.
39
The sessile drop method was used to measure contact angle with an automated goniometer
(Ramé-Hart Model 290, Netcong, NJ, USA) using its corresponding software (Drop Image
Advanced Software for Windows). A 2 μl drop of adhesive was placed on the cervical enamel
specimen placed on a movable table using a calibrated micro syringe.
6
Measurements were
recorded at 0s and 20s after application of each droplet at room temperature. One or two
different locations of each specimen were used depending on flat area dimension. The static
contact angle was determined with the software with the half-angle method:

tan θ
1
= h/r à θ = arctan h/r

where r is radius and h is height of droplet.
13
The contact angle was obtained from both the
left and right ends using the vertex of the droplet against the solid surface.

Table 1. Adhesive systems used
GROUP Material Composition (Lot) Enamel Treatment
OFL
OptiBond FL
(Kerr, Orange, CA,
EUA)
Primer
2-hydroxyethyl methacrylate (10-30 wt.%), ethanol, 2-
[2(methacryloyloxy)ethoxycarbonyl]benzoic acid (10-30
wt.%), glycerol phosphate dimethacrylate (5-10 wt.%)
(Lot: 5422031)

Adhesive
2-hydroxyethyl methacrylate (10-30%), 3-
trimethoxysilylpropyl methacrylate (5-10 wt.%),
ytterbium trifluoride, 2-hydroxy-1,3-propanediyl
bismethacrylate (5-10 wt.%) alkali fluorosilicates(Na) (1-5
wt.%), Silicamorphous fumed (Lot: 5422032)
1. Apply etchant to enamel. Wait 30 s, rinse
for 10s and dry.
2. Apply OptiBond FL Prime (Bottle #1)
over enamel surface with a light scrubbing
motion for 15 seconds. Gently air dry for
approximately 5 seconds.
3. Apply OptiBond FL Adhesive (Bottle #2)
over enamel with a light scrubbing motion
for 15 seconds.
40
SU
Scotchbond
Universal
(3M ESPE, St. Paul,
MN, EUA)

Bis-GMA (15–25 wt.%); HEMA (15–25 wt.%); water (10–
15 wt.%); ethanol (10–15 wt.%); silane-treated silica (5–
15 wt.%); decamethylene dimethacrylate (10–MDP)
(5–15 wt.%); 2-propenoic acid, 2-methyl-, reaction
products with 1,10-decanediol and phosphorous oxide
(1–10 wt.%); polyalkenoic acid (1–5 wt.%);
dimethylamino-benzoate(-4) (<2 wt.%); camphorquinone
(<2 wt.%); (dimethylamino) ethyl methacrylate(<2 wt.%);
methyl ethyl ketone (<0.5 wt.%); silane (Lot: 588249)
1. Apply etchant to enamel for 30 s, rinse
for 10s and dry.
2. Apply Scotchbond Universal Adhesive to
the entire surface of the enamel and rub it
in for 20 seconds.
3. Gently air dry the adhesive for
approximately 5 seconds to evaporate the
solvent.
CSE
Clearfil SE
(Kuraray,
Kurashiki,
Okayama, Japan)
Self-Etching Primer
10-methacryloyloxydecyl dihydrogen phosphate (MDP),
2-Hydroxyethyl methacrylate (HEMA) (20-40 wt.%),
hydrophobic dimethacrylate, dl-Camphorquinone, N,N-
Diethanol-p-toluidine, water (Lot:A70012)

Bonding Agent
10-methacryloyloxydecyl dihydrogen phosphate (MDP),
bis-phenol A diglycidylmethacrylate (Bis-GMA) (25-40
wt.%), 2-Hydroxyethyl methacrylate (HEMA) (20-40
wt.%), hydrophobic dimethacrylate, dl-Camphorquinone,
N,N-Diethanol-p-toluidine, silanated colloidal silica (Lot:
A30018
1. Apply etchant to enamel. Wait 30 s, rinse
for 10s and dry.
2. Apply Clearfil SE primer for 30 s and dry
with mild air flow
3. Apply Clearfil SE bonding agent

SB
Adper Single Bond
Plus
(3M ESPE, St. Paul,
MN, EUA)

Ethanol (25–35 wt.%); silane treated silica 5-nm
(nanofiller) (10–20 wt.%); bis-GMA (10– 20 wt.%); HEMA
(5–15 wt.%); GDMA (5–10 wt.%); VCP (5–10 wt.%); water
(<5 wt.%); UDMA (<5 wt.%); diphenyliodonium
hexafluorophosphate (<1 wt.%); EDMAB (<1 wt.%) (Lot:
N753611)

1. Apply 35% phosphoric acid to enamel.
Wait 30 seconds, rinse for 10 seconds and
dry.
2. Immediately apply 2-3 consecutive coats
of adhesive for 15 seconds with gentle
agitation using a fully saturated applicator.
4. Gently air thin for 5 seconds to
evaporate solvent.

41

2.1 Statistical Analysis
The statistical analysis was performed based on the data from contact angle.
Kolmogorov-Smirnov test used to evaluate the normality of the data distribution. After
confirming a normal distribution of the data (p = 0.069), the homoscedasticity assumptions of
the tensile strength data were confirmed by the Levene test. The data were then statistically
analyzed using analysis of variance with three-factors (three-way ANOVA) and Tukey’s multiple
comparison post-hoc test was applied to detect which means differ from each other. The
significance level for both testes was 5% (α = 0.05).
The data ware analyzed using Microsoft Excel 2011 (Microsoft Office system 2011) and
SPSS 20 (SPSS Inc., Chicago, Il, EUA).

42
3. Results

Analysis of variance with three-factors was applied to evaluate if there were statistical
differences among the enamel surface treatments, bonding systems, and time that the contact
angles were measured, at 0 seconds and after 20 seconds.
Three-way ANOVA revealed a significant interaction among the three evaluated
variables (p=0.015) and all factors evaluated (p < 0.05) (Table 2).

Table 2 – Results of three-way ANOVA of the data from the samples assessed.
Source S.S. D.F. Mean Square F Sig.
Corrected Model 396997.43 47 8446.754 330.852 .000
Intercept 1453158.97 1 1453158.97 56918.962 .000
Surface treatment 999.795 3 333.265 13.054 .000
Adhesive system 293264.959 5 58652.992 2297.386 .000
Moment 77451.042 1 77451.042 3033.689 .000
Surface tx * Adhesive 6029.102 15 401.940 15.744 .000
Surface tx * Moment 463.994 3 154.665 6.058 .000
Adhesive * Moment 10231.505 5 2046.301 80.152 .000
Surface Tx * Adhesive * Moment 758.787 15 50.586 1.981 .015
Error 16492.583 646 25.530
Total 1900951.60 694
Corrected Total 413490.009 693
Sum of Squares (S.S.) and degree of freedom (D.F.).

Mean contact angle measurements, Standard Deviation, and post-hoc statistical results
obtained for each group are displayed in Table 3.

43

Table 3 – Mean contact angles values and Standard Deviation obtained for each group
Time Adhesive system
Surface treatment
CEE CESE CEHE PCE

0 seconds
SU 86.47±3.6
aA
79.03±5.9
aB
76.99±6.4
aB
82.85±6.5
aAB

CSE 35.57±5.4
cdA
30.08±7.1
bA
35.66±6.4
bA
33.63±3.6
bA

SB 29.11±3.2
dA
34.37±6.7
bA
34.68±6.0
bA
29.19±4.6
bA

OFL 32.61±6.9
cB
29.74±5.9
bB
38.93±4.0
bA
34.44±6.6
bAB

CSENP 88.76±6.0
aA
81.82±6.1
aBC
76.15±5.5
aC
83.71±6.0
aAB

OFLNP 75.93±3.2
bB
75.38±4.0
aB
74.15±5.9
aB
88.48±5.1
aA

20 seconds
SU 64.70±5.1
aA
57.78±6.5
aB
55.74±3.2
aB
57.84±4.7
aB

CSE 21.84±5.9
dA
15.34±2.8
dB
15.41±1.8
eB
11.84±2.1
dC

SB 21.45±2.7
dB
27.68±7.5
cA
25.12±5.8
dAB
22.66±4.2
cAB

OFL 13.11±2.3
eA
15.54±6.2
dA
15.04±1.7
eA
12.97±2.0
dA

CSENP 56.99±5.2
bA
49.36±6.6
bB
48.26±2.7
bB
51.29±6.4
bB

OFLNP 49.97±4.1
cAB
47.16±3.3
bBC
44.04±4.4
cC
53.54±3.4
bA

Within the same vertical column, means with same superscript lower-case letters [comparing different adhesive system in each
moment (1 s or 20 s)] are not statistically different (P > 0.05). For each adhesive system, within the same horizontal row, means
with the same superscript upper-case letters (comparing different surface treatment) are not statistically different (P > 0.05).
There is statistical difference between the moments for all the groups evaluated (P > 0.05)

OFL and CSE displayed the lowest contact angle regardless of the surface treatment. OFL
ranged from 29.74±5.9

to 38.93±4.0

at 0s and from 12.97±2.0 to 15.54±6.2

at 20s (Fig.3).
Further, CSE varied from 30.08±7.1 to 35.66±6.4 at 0s and 11.84±2.1 to 21.84±5.9

at 20s.
Application of primer significantly reduced contact angle for both groups. Without the primer
OFLNP presented a higher contact angle of 74.15±5.9

to 88.48±5.1 at 0s and 44.04±4.4

to
53.54±3.4

at 20s. For CSENP it decreased from 76.15±5.5

to 88.76±6.0

at 0s to 48.26±2.7 to
56.99±5.2 at 20s (Fig. 5). SB presented slightly higher angles than OFL and CSE from 29.11±3.2

to 34.68±6.0

at 0s and from 21.45±2.7

to 27.68±7.5

at 20s (Fig.6). Whereas SU presented the
highest contact angle between all adhesives which ranged from 76.99±6.4

to 86.47±3.6

at 0s
and 44.04±4.4

to 53.54±3.4

at 20s (Fig.4).
44
When comparing surface treatments, CEE with SU, CSE, and CSENP presented a
statistically higher contact angle when compared with other surface treatments within the
same adhesive; 64.70±5.1, 21.84±5.9

, and 56.99±5.2

at 20s respectively. Moreover, the SB
group with CEHE showed a greater angle of 27.68±7.5 at 20s compared with the other
treatments. For the OFL group the highest angle was seen for the CEHE group for 38.93±4.0 at

0s. Additionally all of the groups statistically decreased after 20s.
Figures 1 and 2 are illustrate the data presented in the Table 2.

Figure 1 - illustrates the results presented in table 3 for the contact angles measured in the moment of
the application (at 0s).
0
10
20
30
40
50
60
70
80
90
CEE
CESE
CEHE
PCE
Surface treatment
Contact Angles at 0 s
SU
CSE
SB
OFL
CSENP
OFLNP
45

Figure 2 illustrates the results presented in table 3 for the contact angles measured after 20 seconds
of application (at 20 s).

0
10
20
30
40
50
60
70
80
90
CEE
CESE
CEHE
PCE
Surface treatment
Contact Angles at 20 s
SU
CSE
SB
OFL
CSENP
OFLNP
46

47

48
4. Discussion

The correlation between different adhesive systems and the degree of enamel
wettability has been determined in the present study. The infiltration of different dental
adhesives to enamel was dependent on the type of adhesive. The first null hypothesis was thus
rejected. Additionally, different enamel surface treatments coupled with the length of
application of dental adhesives in seconds played a significant role in the diffusion of dental
adhesives into enamel. Therefore, the second null hypothesis was also rejected.
In contrast to dentin, it was suggested that enamel mainly needs the application of a
hydrophobic material, since enamel’s composition has higher concentration of inorganic
content.
12, 14
However, in the present study the contact angle of both OFL and CSE decreased
more than 50% when applying the primer. Therefore, this important fact indicates that the
primer application is essential to increase the wettability of the bonding adhesive resin,
enhancing its permeation into the enamel. Meanwhile, OFL primer solution contains ethanol
that displaces residual moisture through evaporation. In addition to that, OFL primer contains
glycerol dimethacrylate (GDMA), which is a cross-linking responsible for the formation of a
polymer network.
15
GDMA presents the advantage of low viscosity and improved solubility in
water
.15
Thus, the main function of the primer is not only to promote permeation of the
hydrophobic monomers into the decalcified dentin, but also to etched enamel prisms.
16, 17

Conversely, when the primer was previously applied to etched enamel, OFL had the lowest
contact angle among all tested adhesives. This fact can be explained due to the fact that OFL
adhesive presents high percentage of HEMA monomer (10-30%), which enhances its
hydrophilicity.

The two-step self-etch adhesive tested (CSE) also benefited from the application of the
primer, resulting in similar contact angle of OFL. CSE self-etching primer is applied separately
followed by a solvent-free adhesive resin.

Functional monomers in CSE self-etching primer are
thought to act as etchants, permitting resin monomers infiltrate into the demineralized enamel
and chemically interact with hydroxyapatite (HPa) crystals.
18
Thus creating an acid-base
resistant zone by shielding the HPa crystals from acid attack.
18
Nevertheless, in the present
49
study, selective etching with 35% phosphoric acid was done in order to standardize all groups
since self-etching primers provide a shallower and less retentive enamel-etching pattern than
that of phosphoric acid etching.
11
Adding a preceding etching step has been demonstrated to
be beneficial for enamel when using two-step self-etch adhesives.
11, 19-21
Furthermore, both the
primer and the adhesive contain 10-MDP, which can generate chemical bonding. The 10-MDP
hydrophobic acidic monomer chemically bonds to hydroxyapatite of enamel.
17
It has been
described as the “adhesion-decalcification concept”, where first there is an ionic interaction of
the functional monomer followed by a ionic bond that is hydrolytically stable, resulting in a
calcium-monomer salt. Though, it has a lower chemical reactivity than dentin due to the
significantly higher crystallinity of enamel .
11, 22

The two-step etch-and-rinse adhesive (SB) tested showed lower contact angle compared
to SU and higher contact angle than that of OFL and CSE. Simplified two-step etch-and-rinse
adhesive combines the primer and the adhesive resin into a single solution. When a solvent is
added to a resin co-monomer, it decreases the adhesive´s viscosity and increases its wetting
characteristics.
.23
Solvents added in SB include approximately 25-35 wt.% of ethanol and less
than 5 wt.% of water.
24
Moreover, SB contains UDMA which despite its comparable molecular
weight to that of Bis-GMA, displays inferior viscosity properties.
17
Polyalkenoic acid is also
included in the composition of SB (5 to 10 wt.%). Polyalkenoic acid creates a chemical
interaction with hydroxyapatite (HAp) similar to the previously mentioned as the adhesion-
decalcification concept. Results from a previous study corroborate that carboxyl groups of
polyalkenoic acid replace the phosphate ion groups in HAp and chemically interact with
calcium
.25

SU can be classified as a multi-mode adhesive that can be used as etch-and-rinse, self-
etch, and selective- etch technique for bonding to enamel or dentin.
26
For the purpose of this
study SU was used in the total-etch mode since it has shown higher enamel bond strengths.
18,
20, 26, 27
SU showed the highest contact angle among all adhesive system tested. SU has similar
components as the ones found in SB; however, their concentration is different in both
adhesives. For instance:

the concentration of Bis-GMA monomer is higher 15-25%wt to that of
SB. This hydrophobic monomer displays high reactivity, but accounts for high viscosity and low
50
water solubility.
15
Additionally, 1 to 5 wt.% of polyalkenoic acid is incorporated into SU.
Though, no chemical interaction was detected between polyalkenoic acid and HAp through
fourier-transform infra-red spectroscopy.
25
The lack of interaction may be associated to the
diverse polyalkenoic acid concentrations in the adhesive composition, since the degree of ionic
bonding between a polyalkenoic acid and HAp relies on the number of accessible carboxylic
groups.
25
SU contains the phosphate-based monomer 10-MDP as well as a high concentration
of the monofunctional resin monomer co-solvent HEMA (15-25%wt). Both HEMA and the
polyalkenoic acid copolymer seemingly compete with 10-MDP for the calcium coordination
sites on the surface of apatite crystallites.
28
The presence of HEMA in SU consequently
interferes with MDP from interacting chemically with HAp but does not completely inhibit it.
25,
29
Furthermore, although fillers are used to enhance the physical properties of adhesives, filler
may have a negative effect by reducing the penetration of the adhesive into the substrate.
Thus, the percentage of filler into an adhesive mixture is important to ensure adequate wetting
of the surface and infiltration of monomer
. 15
About 5-15% of silane treated silica particles are
incorporated in SU that may contribute to the higher contact angle of this adhesive.
Another factor to take into consideration to improve the contact angle of dental
adhesive is the evaporation of the solvents. Different types and amounts of solvent have
distinct vapor pressures and evaporation rates. SB contains 25-35 wt.% of ethanol and less than
5 wt.% of water while SU includes 10-15% ethanol and water respectively. Active application of
dental adhesives may promote the solvent to externally diffuse, because of the low vapor
pressure of water (23.8 mmHg at 25ºC) and ethanol (54.1 mmHg at 25ºC).
27
Ethanol has a
higher vapor pressure compared to water that allows better evaporation.
(4)
Water-alcohol
mixtures also known as “azeotropic” mixtures, infer the formation of hydrogen bonds between
water and ethanol molecules that accelerate desiccation when air-dried.
15
Evaporation of water
in the solvent may generate phase separation and thus increase viscosity.
30
Additionally, active
application of self-etch adhesives may improve enamel demineralization and hence resin
infiltration.
31
Though, when measuring contact angle for the present study, adhesives were left
undisturbed for 20s instead of air-dried. Consequently, evaporation of the solvents was not
accelerated.
51
The initial contact angles achieved at 0s for the adhesives are possibly related to the
initial viscosity with initial solvent content and its resulting wettability.
32
The second
measurement at 20s was taken in order to represent an average of the manufacturer’s
instructions to apply adhesive with agitation for 15s for SB and OFL, 20s for SU, and no
indications were disclosed for CSE. The contact angle decreased significantly for all groups after
20s. These results can be due to factors dealing with the physical–chemical characteristics of
both substrates and the chemical composition previously described.
Another factor that influences wetting of a solid by a liquid include the relative surface
free energy of the solid and the surface tension of the liquid. To achieve optimal wettability, the
surface free energy of enamel must be maximized. Phosphoric acid treatment increases the
enamel wettability and, hence, the surface free energy.
33, 34
Etching produces microporosities in
order to allow for the adhesive to penetrate via capillary attraction. The extent of penetration
will depend on the voids in the enamel into which the adhesive can flow. The depth of
penetration is known as “tag” length.
34
Wettability is additionally enhanced by the presence of
micro-surface roughness.
35
On the other hand, excessive roughness may obstruct the flow of
the adhesive and result in air voids being entrapped at the interface.
9
Selective etching with
phosphoric acid used in combination with self-etch adhesives may result in double conditioning
of the enamel surface due to the acidic monomers present in the adhesive;

and therefore
increase demineralization of enamel and enhance the superficial interaction with the
adhesive.
31
SU and CSE presented lower contact angle when air abrading, etching with HCl acid
and tooth preparation where used besides etching with phosphoric acid. This increase of
wettability can be explained by the increase of surface roughness achieved by the different
surface treatments. Preparation of enamel by the diamond bur provides roughness by giving
enamel the appearance of grooves as a result of the abrading effect of diamond facets.
9

Conversely, when attempting to preserve the integrity of enamel other methods are available
such as air-abrasion with aluminum oxide. Enamel air-abraded with 27 µm aluminum oxide
particles before acid etching has shown to result in greater roughness than intact enamel.
36, 37

Hydrochloric acid is rarely used as an etchant in adhesive systems because of its strong
acidity.
38
Nevertheless, it is used as an etchant in resin infiltration as a minimally invasive
52
treatment of white spot lesions. For the purpose of this study enamel was only etched actively
for 30s compared to manufacturer’s instructions of 120s. Exposure of hydrochloric acid on
enamel, has shown high demineralization and an increase in surface roughness of enamel even
at 30s.
39
The active application of 6.6% HCl acid has also presented a significantly decrease in
the microhardness of enamel that results in surface microwear of enamel.
40
Another study
obtained a result of an average enamel loss of 34μm after treatment with 15 % HCl for 120s.
38

Thus, we can assume that the decrease of contact angle for these groups might be due to
demineralization and further increase in surface roughness of enamel.
Significant differences were found amongst adhesive´s chemical composition and
surface treatments on enamel. Different factors play a role in defining wettability. Initial surface
energy of the substrate and surface tension of the adhesive is naturally provided by the intrinsic
chemical composition and polarity of each surface.
9
However, enamel surfaces may be altered
by different surface treatments such as etching, air abrading or tooth preparation in order to
change the surface energy and create roughness or irregularities.
9, 41
Consequently increasing
penetration of adhesive into the enamel substrate. Additionally, previous application of primer
on enamel significantly increases wettability of OFL and CSE adhesives. Enamel spreading is
time dependent and relies on the chemical features of the adhesive. However, active
application may increase infiltration of adhesives. High wettability that allows for increased
penetration of adhesives may be a substantial factor for improving long-term bonding efficacy
of enamel.

53
5. Conclusion

1. Different adhesive systems and further surface treatment of enamel have a significant
effect on wettability of adhesives.
2. Diffusion of adhesive into enamel increases with time.
3. Application of primer on enamel is critical to decrease contact angle of OFL and CLSE.

54
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Abstract (if available)

Abstract Chapter 1- Microtensile Bond Strength of a CAD/CAM ceramic-reinforced polymer to Cervical Enamel. ❧ Objective: The purpose of the study was to compare microtensile bond strengths between cervical enamel and middle third enamel using different surface treatments and a universal adhesive with previous etching with phosphoric acid. ❧ Materials and methods: Sixty-four extracted molars were assigned into one of the eight experimental groups: Intact cervical enamel etched (CEE), intact cervical enamel sandblasted and etched (CESE), intact enamel etched with hydrochloric acid (CEHE), prepared cervical enamel etched (PCE), Intact middle third enamel etched (MEE), intact middle third enamel sandblasted and etched (MESE), intact middle third etched with hydrochloric acid (MEHE), and prepared middle third enamel etched (PME). Sectioned teeth were bonded to customized CAD/CAM ceramic-reinforced polymer blocks (Lava Ultimate, 3M/ESPE). The samples were tested after 24 h or after 20,000 thermocycles. Teeth were sectioned with a cross-section of 0.8 ± 0.2 mm2 and fractured at a crosshead speed of 1 mm/min. The data were submitted to 3-way analysis of variance (ANOVA), followed by Tukey’s HSD post hoc test (α=.05). Additionally, the enamel etching pattern was investigated using scanning electron microscopy and polarized light microscopy. ❧ Results: Statistical analysis showed significant differences among different enamel sites (P<.001). No statistical difference was found between surface treatments (p = 0.301) or moments (p = 0.556). Statistically higher bond strength was found for cervical enamel (40.70 ± 10.1 MPa) compared to middle third enamel (36.63 ± 11.3 MPa). ❧ Conclusion: Cervical enamel and middle third enamel can result in similar bond strength by proper surface treatment of enamel. ❧ Chapter 2- Wettability of Dental Adhesives on Cervical Enamel. ❧ Objective: The purpose of this study was to evaluate wettability of different adhesive systems at 0s and 20s using distinct surface treatments on enamel. ❧ Materials and methods: 48 extracted teeth were cut in half and assigned to 1 of the 4 groups: cervical enamel etched (CEE), cervical enamel sandblasted and etched (CESE), enamel etched with hydrochloric acid (CEHE), and prepared cervical enamel etched (PCE). Four adhesive systems were used: Scotchbond Universal (SU), OptiBond FL (OFL), Clearfil SE (CSE) and Adper Single Bond Plus (SB)

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Asset Metadata

Creator Amarillas Gastélum, Clarisa (author)

Core Title Influence of enamel biomineralization on bonding to minimally invasive CAD/CAM restorations

School School of Dentistry

Degree Master of Science

Degree Program Craniofacial Biology

Publication Date 09/29/2016

Defense Date 09/06/2016

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag aprismatic enamel,cervical enamel,contact angle,microtensile,middle third enamel,OAI-PMH Harvest,wettability

Format application/pdf (imt)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Duarte, Sillas, Jr. (committee chair), Paine, Michael (committee member), Phark, Jin-Ho (committee member), Sartori, Neimar (committee member)

Creator Email clarisaa@usc.edu,clarisaag@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c40-308912

Unique identifier UC11213613

Identifier etd-AmarillasG-4842.pdf (filename),usctheses-c40-308912 (legacy record id)

Legacy Identifier etd-AmarillasG-4842.pdf

Dmrecord 308912

Document Type Thesis

Format application/pdf (imt)

Rights Amarillas Gastélum, Clarisa; Amarillas Gastelum, Clarisa

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the a...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus MC 2810, 3434 South Grand Avenue, 2nd Floor, Los Angeles, California 90089-2810, USA