Filtek Victoria, Australia) (Figure 6). the specimens

Filtek TM Z250, (Figure 1) Scotchbond Universal Adhesive also known as
Single Bond Universal (Figure 2). G-bond plus (G-aenial bond); (Figure 3).
Hydrophobic resin coating; with or with-out, Heliobond (Figure 4).

 

Product name

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Composition

manufacturer

Batch number

FiltekTM
Z250 shade
A1

Bis-GMA, Bis-EMA,
TEGDMA, UDMA, zirconia, silica (82 wt%/60 vol%)

3M ESPE, USA

 
N636467

 
 
 
 
Single Bond Universal

1-Etchant: 32% phosphoric
acid, water, synthetic amorphous silica, polyethylene glycol, aluminum oxide
(Scotchbond Universal Etchant)

 
 
 
 
SBU, 3M ESPE, St.
Paul, MN, USA

 
 
 
 
 
N601958

2. Adhesive: phosphate
monomer, dimethacrylate resins, HEMA, methacrylatemodi- fied polyalkenoic
acid copolymer, filler, ethanol, water, initiators,
and silane

 
 
G-BOND
plus
(G- aenial)

Acetone, dimethacrylate, 4
methacry- loxyethyltrimellitate anhydride, phosphoric acid ester monomer,
silicon dioxide, photo initiator, distilled water Note: The manufacturer does
not recommend dentin conditioning with phosphoric
acid

 
 
GC
Corporation Tokyo, Japan

 
 
 
N1510051

 
Heliobond

 
bis-GMA,              TEGDMA,
initiators, stabilizers

Ivoclar Vivadent,
Schaan, Liechtenstein

 
U34134

 

Figure 1.

 

Figure 2.

Figure 3.

Figure 4.

 

1.1.  Specimen Preparation

A flat occlusal dentin surface was exposed in all teeth after
wet-grinding the occlusal enamel with a slow-speed water-cooled diamond disk
Isomet, Buehler Ltd., Lake Bluff, IL, USA. The exposed dentin surfaces were
further polished with wet #600-grit silicon-carbide paper for 60 s to
standardize the smear layer 20. The adhesive systems
were applied according to the respective manufacturer’s instructions, except
for G-bond Plus, for which the manufacturer 
does  not   recommend  
dentin   etching with phosphoric
acid. Furthermore, the respective manufacturers do not recommend the
application of Heliobond. Composite resin crowns were built up in two increments
of 2 mm each. Except for bulk fill composite

applied in one increment. Each increment was light-cured for 40 s using a
LED light-curing unit set at 1200 mW/cm2 (Radiical,
SDI Limited, Bays water, Victoria, Australia) (Figure 6).

 

the specimens were sectioned longitudinally in mesio- distal and
bucco-lingual directions across the bonded interface with a slow-speed diamond
saw (Isomet, Buehler Ltd., Lake Bluff, IL, USA) (Figure 7) to obtain resin–
dentin beams (Figure 9) with a cross sectional area of approximately 0.8 mm2
measured with a digital caliper (Digimatic Caliper, Mitutoyo, Tokyo, Japan).
(Figure 8) half of beams used for microtensile bond strength test and the other
beams used for nanoleakage evaluation.

Figure 5.

Figure 6.

Figure 7.

Figure 8.

Figure 9.

1.2.  Adhesive and Resin Composite Application

Regarding subgroup 1: (self-etching
mode) using G- bond plus (G-aenial): Apply using a micro brush. Leave
undisturbed for 10s after the end of application. Dry thoroughly for 5s with
oil free air under maximum air pressure. Use vacuum suction to prevent splatter
of the adhesive. Light cure for 10s. Then apply a very thin layer of Heliobond
with a micro brush on the dental surface. Apply air blower to achieve an
optimally thin layer. Light- cure for 10s. filtek TM Z250 composite resin
crowns were built up in two increments of 2 mm each. Each increment was
light-cured for 40s using a LED light-curing unit (Figure 6). Regarding subgroup 2: the same
technique used in subgroup 1 with one exception Heliobond will not applied. Regarding subgroup 3: (etch and rinse
mode) using the same etching gel(Figure 5) used in subgroup 3, then application
of G-bond plus (G-aenial), application of Heliobond adhesive as mentioned in
subgroup 2. Regarding subgroup 4: the
same technique used in subgroup 3 with one exception Heliobond will not
applied.

 

1.3.   Testing Procedures

For microtensile bond strength
(µTBS): the resin– dentin bonded beam was attached to resin–dentin bonded
beam holder (Figure 10) with tetric-flow flowable composite (3M adhesive) and
tested under tension (Model5565, Instron Co., Canton, MA, USA) (Figure 11) at
0.5 mm/min until failure. The µTBS values were calculated by dividing the load
at failure by the cross- sectional bonding area 18,19.
The µTBS values (MPa)  of all beams from
the same tooth were averaged for statistical
purposes.

Figure 10.

Figure 11.

 

For
nanoleakage analysis: the beams were placed in an ammonical silver nitrate
solution in darkness for 24 h 21, rinsed thoroughly in
distilled water, and immersed in photo developing solution for 8 h under a
fluorescent light to reduce silver ions into metallic silver grains. Specimens
were polished with wet 600 grit Sic paper. Resin–dentin interface were analyzed with a
scanning electron microscope (Philips,
XL 30, Eindhoven, The Netherlands) (Figure 12), also analyzed using Energy
dispersive X-ray spectrometry (EDX Philips, XL
30 W/TMP, Eindhoven, The Netherlands) (Figure
12). The micrograph was taken in the center of the beam 22. The
mean NL (%) of all beams from the same tooth was averaged for statistical
purposes. Comparison between the twelve different subgroups was made using
four-dimensional mapping which was performed over 100 mm x 100 mm areas across
the resin-dentine bonded interface, these areas covered the adhesive layer. The
HL (hybrid), partially demineralized and un-affected dentine was visualized and
focused at 1000 x magnification. Amount of silver grains that was penetrated at
resin-dentin interface was calculated and statistically analyzed through energy
levels of EDX analysis 23.

adhesive type,
resin coating with Etch and rinse application mode. Figure 13: Column chart of
µ-tensile bond strength mean values for all composite groups as function of
adhesive type, resin coating with etch-&-rinse application mode

 

Table 2

 

Application mode (D)

Etch and rinse (D2)

t-test

Resin coating (C)

With (C1)

Without (C2)

P value

 

FiltekTM Z250 (A3)

21.3C±2.7

15.6C±2.9

0.0317*

ANOVA

P value

0.0002*

<0.0001*   Different letter in the same column indicating statistically significant difference (p < 0.05). *: significant (p < 0.05), ns: non-significant (p>0.05)

 

 

 

 

 

 

 

 

 

 

 

 

2.    Results

 

 

 

 

 

 

 

 

 

Figure 12.

Figure 13.

Interaction between
variables Self-etching application mode

with  Resin 
coating; it was found  that  FiltekTM  Z250

with heliobond
recorded the high statistically significant (P³0.05)
µ-tensile bond strength mean value as indicated by one way ANOVA followed by
pair-wise Tukey’s post- hoc tests.

without Resin
coating;
it was found that FiltekTM Z250

without heliobond
recorded the lower statistically significant (P<0.05) µ-tensile bond strength mean value as indicated by one way ANOVA followed by pair-wise Tukey's post-hoc tests. Resin coat vs. non-coated 2.1.   µ-Tensile Bond Strength (µ-TBS) Self-etching application mode: Table 1: Comparison of µ-tensile bond strength results (Mean±SD) between all composite groups as function of adhesive type, resin coating with self-etching application mode. Figure 12: Column chart of µ-tensile bond strength mean values for all composite groups as function of adhesive type, resin coating with self-etching application mode.   Application mode (D) Self-etching (D1) t-test Resin coating (C) With (C1) Without (C2) P value   FiltekTM Z250 (A3) 27.2C±2.1 14.6C±1.8 0.0001* ANOVA P value 0.0004* <0.0001*       Table 1           Different letter in the same column indicating statistically significant difference (p < 0.05). *: significant (p < 0.05), ns: non-significant (p>0.05)

 

Etch
and rinse application mode

Table 2: Comparison of µ-tensile bond strength results (Mean±SD)
between all  composite groups as  function of

FiltekTM Z250;
it was found that group with Resin coating  recorded  statistically 
significant (P<0.05) higher µ-tensile bond strength mean value than groups without Resin coating as indicated by paired t-test Figure 14.   2.2.   For Nanoleakage Nanoleakage results (%) for all composite groups as function  of  adhesive  type,  application  mode  and  resin   coating are summarized in Table 3. Figure 15: Column chart of total nanoleakage mean values as function of application mode. Figure 16: Column chart of total nanoleakage mean values as function of resin coat application.   Table 3   Resin composite filling (A) FiltekTM Z250 (A3) Adhesive (B) G-bond plus (B2) Resin coating (C) With (C1) Without (C2) Application mode (D) Self-etching (D1) 7.6 61.03 Etch and rinse (D2) 9.28 11.81 Figure 15.   Figure 16. Regarding subgroup 1: Figure 17a: Backscattered electron image of SEM (a) and corresponding EDX spectrum (b) of the fractured surface of resin dentin beam side at a magnification 1000 x. Figure 17b: Element profile for Filtek TM Z 250 + G-Bond   plus  (self-etch   mode)   with hydrophobic  resin coating. Table 4: Amount of silver at energy  level  (L)  in  Figure 17a. SEM and EDX analysis Figure 17a; is a backscattered electron image of the morphology and surface composition of the resin-dentin beam side of the fractured surface of a specimen. The granules of silver depositions (b) in the hybrid layer of the resin dentin beam show that silver uptake was (7.59 wt %) in Table 4 at energy level (L).     Wt % At % O K 71.40 86.03 P K 16.59 10.32 ClK 02.57 01.40 AgL 07.59 01.36 CaK 01.85 00.89     Table 4 Figure 17a.   Figure 17b. Regarding subgroup 2: Figure 18a: Backscattered electron image of SEM (a) and corresponding EDX spectrum (b) of the fractured surface of resin dentin beam side  at  a  magnification  1000 x. Figure 18b: Element profile for Filtek TM Z 250 + G-Bond plus (self-etch mode) without hydrophobic resin coating. Table 5: Amount of silver at energy  level  (L)  in  Figure 18a. SEM and EDX analysis Figure 18a; is a backscattered electron image of the morphology and surface composition of the resin-dentin beam side of the fractured surface of a specimen. The granules of silver depositions (b) in the hybrid layer of the resin dentin beam show  that  silver  uptake  was  (61.03 wt %) in Table 5 at energy level (L).   Table 5   Element Wt % At % O K 12.22 36.80 P K 05.99 09.32 ClK 10.47 14.24 AgL 61.03 27.27 CaK 10.29 12.37   Figure 18a.     Figure 18b. Regarding subgroup 3: Figure 19a: Backscattered electron image of SEM (a) and corresponding EDX spectrum (b) of the fractured surface of resin dentin beam side at a magnification 1000 x.  Figure  18b:  Element  profile  for  Filtek  TM  Z  250 + G-Bond plus (Etch and rinse mode) with hydrophobic resin coating. Table 6: Amount of silver at energy level (L) in Figure 19a. SEM and EDX analysis Figure 19a; is a backscattered electron image of the morphology and surface composition of the resin-dentin beam side of the fractured surface of a specimen. The granules of silver depositions (b) in the hybrid layer of the resin dentin beam show that silver uptake was (9.28 wt %) in Table 6 at energy level (L).   Table 6   Element Wt % At % O K 43.81 66.51 P K 15.68 12.29 ClK 02.40 01.64 AgL 09.28 02.09 CaK 28.83 17.47 Figure 19a.   Figure 19b. Regarding subgroup 4: Figure 20a: Backscattered electron image of SEM (a) and corresponding EDX spectrum (b) of the fractured surface of resin dentin beam side at a magnification 1000 x. Figure 20b: Element profile for Filtek TM Z 250 + G-Bond plus (Etch and rinse mode) without hydrophobic resin coating. Table 7: Amount of silver at energy  level  (L)  in  Figure 20a. SEM and EDX analysis Figure 20 a; is a backscattered electron image of the morphology and surface composition of the resin-dentin beam side of the fractured surface of a specimen. The granules of silver depositions (b) in the hybrid layer of the resin dentin beam show  that  silver  uptake  was  (11.84 wt %) in Table 7 at energy level (L).   Table 7.   Element Wt % At % O K 46.61 69.75 P K 14.45 11.17 ClK 03.41 02.30 AgL 11.84 02.63 CaK 23.70 14.16   Figure 20a. Figure 20b.     3.    Discussion 3.1.   For Microtensile Regarding  the effect of  G-enial  bond plus (GBP),  is  a HEMA-free 1-step 4-MET-derived self-etch adhesive, with a pH 1.5 24. GBP is not recommended in ER mode on dentin. However, we decided to experimentally apply   GBP on phosphoric acid etched dentin, as some etching gels may inadvertently overflow  to  dentin  during  clinical procedures when selective enamel etching is used. GBP/SE resulted in statistically greater mean TBS compare to GBP/ER without HC, which validates the respective manufacturer's recommendation for not etching dentin, as well as, recently showed in the literature 24. Regardless of the application mode, GBP had the poorest performance even when coated with HC. These findings are in agreement with previous studies 25. Although Hanabusa et al. reported similar bond strengths for ER and SE strategies; they also reported low-quality hybridization in the ER mode for GBP, specifically a resin-infiltrated collagen network with signs of adhesive incomplete infiltration 25. The paradox is that, to reach the acidic pH that allows the self-etching capability, hydrophilic properties cannot be avoided. In fact, acidic self-etch formulations (low pH as in GBP) need more hydrophilic and acidic resins blends 26. The relatively low pH of 1.5 in GBP allows a more aggressive enamel and dentin demineralization 27, with less hydroxyapatite available for chemical interaction with the 4-MET, resulting in lower mean µTBS. If compared with the 10-MDP functional monomer, 4-MET is less hydrolytically stable 28, which also applies to the resulting 4-MET calcium complexes 29. The 4-MET functional monomer is not able to chemically interact with calcium in hydroxyapatite through nanolayering 29. The lack chemical bonding to calcium by 4-MET may have been responsible for the lower mean µTBS of GBP/SE compared to those of GBP/ER. Furthermore, GBP has acetone as organic sol-vent, which might contribute to a higher susceptibility to the degree of moisture in dentin 26. SBU is HEMA-containing adhesives (Figure 2), in opposition to GBP, which is a HEMA-free adhesive. HEMA is a hydrophilic monomer added to self-etch adhesives to enhance dentin wettability and monomer infiltration 30 and prevent hydrophobic monomer/water phase separation 31. The incorporation of poly-HEMA  in the polymer net-work enhances water uptake after polymerization 30, due to poly-HEMA hydrolytic degradation and elution of by-products during long-term storage 32. HEMA-containing adhesives are more hydrophilic and have higher water sorption 33. In long- term water storage, the reduction in the tensile strength of adhesives increases with their hydrophilicity, reducing their mechanical properties 34. The exclusion of HEMA within GBP composition has been suggested to have the potential of reducing the adhesive hydrophilic properties and, consequently, to avoid the decline in mechanical properties due to water sorption 32. Water sorption and ultimate tensile strength of HEMA-free adhesives do not significantly change with water storage 32. However, HEMA-free formulations do not produce bond strengths  as higher as those of HEMA-containing adhesives 35, which is in agreement with the results of our study.   3.2.   For Nanoleakage Regarding hydrophobic resin coating vs. non coating, in our study, HC resulted in greater mean µTBS of SBU/ER and GBP/SE. The thickness of the  adhesive  layer  may have increased 36 allowing the formation of a more densely packed hybrid layer with improved mechanical properties and nanoleakage characteristics. The HC also increased the mean µTBS of SBU/ER and GBP/SE, which may have been a result of enhanced adhesive layer hydrophobicity. The adhesive layer becomes less permeable to water movement, and less susceptible to water degradation 36. Coating with a hydrophobic layer may couple more un solvated hydrophobic monomers to the adhesive interface through copolymerization with the uncured adhesive surface, decreasing the relative concentration of retained solvent and unreacted monomers, thus enhancing the in situ degree of conversion. In our study, regarding SBU/ER and GBP/SE, exhibited the least amount of silver granules deposits at the bottom of the hybrid layer (6.9-7.6%). The performance of GBP improved after the application of HC. The GBP's inherent hydrophilic nature may have been reduced by HC allowing a higher in situ degree of conversion 37. However, we observed severe increase   of NL within the hybrid layer for GBP/SE, which may have been  a result of the hydrolysis of the phosphoric  acid ester monomer, which may have caused dentin demineralization over time. The instructions for use of GBP may have to be revised. The instructions for use  SBU clearly stated that this universal adhesive must be applied actively, with two consecutive coats. Active application 37,38, double application 39, and a greater infiltration time 40 are known to improve the performance of self-etch adhesives. The manufacturer of GBP recommends applying GBP passively, with 10 s of infiltration compared to 20 s for SBU, which may have adversely affected the interaction of GBP with dentin. GBP also resulted in higher nanoleakage with a water-tree pattern in the adhesive layer, characteristic of HEMA-free adhesives due to phase separation and residual water on the dentin surface 41. The dendritic pattern may also have been a result of phase separation. When we analyzed the NL results for ER and SE, we were unable to find a cause–effect relationship from the application of HC, as it occurred for µTBS. Some reductions were observed within groups with HC (SBU/ER, GBP/SE). NL may be more related to the adhesive infiltration and sealing capability. It is well known that the quality of the resin–dentin bonds is affected by the extent of resin infiltration into the exposed collagen 40,41. For ER, peritubular hybridization of the resin tags may not occur. For SE, the weakest zone in aged specimens is below the hybrid layer, due to poorer polymerization of the monomers within the bottom of the hybrid layer 42. These findings corroborate our NL pattern observations for both ER and SE modes. Even if resin hydrolysis may negatively affect the long-term bonding stability, collagen depletion may also occur due to enzymatic degradation. The activation of matrix metallo-proteinases (MMP's) is induced by adhesive chemical formulations on both mineralized and demineralized dentin, regardless of the bonding strategy 43. However, MMP's degradation is believed to be more destructive for ER hybrid layers than for mild SE hybrid layers, as SE adhesives bond to dentin with less demineralization 44.   4.    Conclusion An extra hydrophobic layer coating improved the immediate in vitro performance (µTBS and NL) of the universal adhesive systems that studied in SE mode. However, NL pattern is material-dependent and aging stability seems not to be related with the adhesive strategy.