Influence of different surface treatments on microshear bond
strength of repair resin composite to two CAD/CAM esthetic
restorative materials
M.M. Wahsh
a,*
, O.H. Ghallab
b aDepartment of Fixed Prosthodontics, Faculty of Dentistry, Ain Shams University, Cairo, Egypt b
Operative Dentistry Department, Faculty of Dentistry, Ain Shams University, Cairo, Egypt
Received 22 April 2015; revised 27 May 2015; accepted 1 June 2015 Available online 26 June 2015
Abstract
Objective: The aim of this in vitro study was to evaluate which surface treatment and adhesive type might provide the most predictable microshear bond strength results of repair resin composite to lithium disilicate ceramic and a newly introduced resin nanoceramic (RNC).
Methods: A total of thirty six slices were prepared out of resin nanoceramic (Lava Ultimate) and lithium disilicate (IPS e.max CAD ceramic blocks) with dimensions of 14123 mm (n¼18 for each material). The slices were divided into three main groups according to surface treatment: Control group (CN) received no treatment, group (DB) roughened with diamond bur and group (CJ) silica coated with Cojet system. Each group was subdivided into two subgroups according to the type of adhesive system used for repair: Subgroup (MH): Treated with Monobond plus and Heliobond adhesive system and subgroup (SBU): treated with Single bond universal adhesive system. The adhesives were applied according to the manufacturers'instructions. Five transparent microtubules were adjusted on each substrate slice and then repair resin composite (Tetric Evoceram, shade A3) was applied and light cured (n¼15 for each subgroup). After 24 h storage in distilled water, microshear bond strength (mSBS) was measured for each specimen of tested groups.
Results: Lava Ultimate RNC showed statistically significant highermSBS compared to IPS e.max lithium disilicate ceramic. The use of diamond bur in conjunction with Monobond plus and Heliobond adhesive system showed highermSBS compared to all tested groups.
Conclusions: The effect of different surface treatments on themSBS to the repair resin composite is material dependent. Com-bination of the abrasive action of diamond bur and adhesive with separate silane treatment modalities had a synergistic influence on mSBS of the repair resin composite under the current circumstances.
©2015, Hosting by Elsevier B.V. on behalf of the Faculty of Dentistry, Tanta University.
Keywords:Lithium disilicate; Resin nanoceramic; Repair; Surface treatments; Microshear bond strength
*Corresponding author. 196 Elyasmeen, 14th district, Sheikh Zayed, Egypt. Tel.:þ20 1001500587.
E-mail addresses:mmwahsh2@gmail.com(M.M. Wahsh),omaimaghallab@asfd.asu.edu.eg(O.H. Ghallab). Peer review under the responsibility of the Faculty of Dentistry, Tanta University.
http://dx.doi.org/10.1016/j.tdj.2015.06.001
1687-8574/©2015, Hosting by Elsevier B.V. on behalf of the Faculty of Dentistry, Tanta University.
ScienceDirect
Tanta Dental Journal 12 (2015) 178e184
1. Introduction
One of the goals of restorative dentistry is to pro-vide functional and esthetic restorations. Ceramics are widely used clinically as indirect restorations because of their proved long lasting physical and mechanical properties. Varieties of all ceramic materials and sys-tems are available in the market for laminate veneers, inlays, onlays and all ceramic crowns[1e3].
Lithium disilicate-based glass ceramics are of the valuable advances in CAD/CAM technology. Unfor-tunately, ceramics have an inherent weakness due to their brittleness. Under occlusal forces or during cementation, fracture or chipping of the material can occur specially if there was an internal defect or inadequate thickness[4,5].
Recently, 3M ESPE introduced a new CAD/CAM RNC material (Lava Ultimate™ brand) to the dental market. The material is neither a resin nor a pure ceramic; it's a mixture of both but mainly consists of ceramic. Lava Ultimate as a RNC and in terms of material science, it belongs to the resin composite category[6]. It is devel-oped as nanomer particles which are monodisperse, non-aggregated and non-agglomerated nanoparticles. Lava Ultimate contains two types of nanomers; silica of 20 nm diameter, and zirconia of 4e11 nm diameter. The new material is claimed to combine the merits of high flexural strength, fracture toughness, resiliency, durability and esthetics. The material is available as highly heat cured blocks through a controlled manufacturing process; thus, the firing step after milling is eliminated. It can be chair-side machined or in the dental lab [7]. The literature is short of knowledge regarding RNC, thus it is in the focus of this study.
In cases of fracture or chipping of ceramic restora-tions, intra-oral repair may be considered, preserving the restoration and the tooth[8]. The previously published literature reveals the merits of intra-oral repair as decrease the cost for the patient and lengthening the life span of the fractured restoration[2,9e12]. On the other hand, Tyas et al. stated that, the repair is considered as (patchwork dentistry) and it is not approved by the clinicians[13]. It also may lead to a weaker restoration [11]. At an earlier time, repair depended on macro me-chanical retention by preparing grooves or undercuts. Now, the available repair kits and systems depend on micromechanical and chemical bond through different surface treatments of the substrate creating an interme-diate interface[4].
Resin composite has the ability to bond via advanced adhesive systems capable of bonding composite to different substrates rather than enamel and dentin[14].
The bond strength of repair interface determines the longevity and serviceability of the restoration[15]. This bond integrity and durability depend on the type of repair composite as hybrid composite resins reported higher bond strength than micro filled composite resins[10]as well as the surface treatment used[4,8,15e17].
Numerous surface treatments are available for repair of lithium disilicate-based ceramics through micro-mechanical and chemical retention [18]. Micro-mechanical roughening of the substrate surface can be achieved by diamond bur, acid etching with hydrofluoric or phosphoric acid, air-borne particle abrasion (which promotes mechanical interlocking) with or without silane coupling agents and adhesive systems (which enhances chemical bonding with the repair composite) [8,11,16,19].
Cojet is a chair side tribochemical silica coating system, substrate surfaces are abraded with 30 mm AL2O3modified with silicon acid. The surface treatment using Cojet system may increase the bond strength of repair composite to ceramics[9,20,21]and resin nano-ceramics[22].
Silanes act as mediators promoting adhesion between inorganic and organic matrices through dual molecular reactivity and increase the wettability improving the contact angle between the ceramic and resin [2,3,9,18,21]. On the other hand, Sorensen et al., [23] considered that the use of silane coupling agent had insignificant effect on the bond strength for all ceramics used. Barghi[24], stated that, the silane coupling agents remain a weak bond. Furthermore, silane can be sub-jected to hydrolytic instability especially in humid conditions[10].
From all the previously mentioned, it is concluded that there is no a specific method to condition the ceramic substrate for repair with resin composite. Therefore, the aim of this study was to evaluate the effect of different surface treatments on the micro shear bond strength of repair resin composite to lithium disilicate-based ceramic and RNC using two adhesive bonding agents. 2. Materials and methods
2.1. Preparation of substrates
The materials'description, brand names, chemical composition, manufacturers, and Lot.numbers used in this study are listed inTable 1and are provided from the manuals of the manufacturers. All the steps were performed by the same operator following the manu-facturers'instructions. A total of thirty six slices were prepared out of Lava Ultimate and IPS e.max CAD
ceramic blocks using diamond discs under continuous water irrigation (n ¼ 18 for each material). The di-mensions of the slices were (14123 mm). The slices were polished in a circular motion using silicon carbide papers of grits 600 and 12001under continuous water irrigation, for 20 s each[12]. After the polishing procedures, the substrate surfaces were ultrasonically cleaned in distilled water for 30 s and then dried.
The IPS e.max CAD slices were placed in the Programat P300 ceramic furnace2 for crystallization firing cycle with a holding time of 10 min at 840C.
2.2. Samples grouping
For each material the 18 slices were randomly assigned into three groups according to surface treatment before repair (n ¼ 6). Group CN received no further treatment and served as the control group. The other two
groups received surface treatments through roughening with diamond bur (DB); and silica coating using Cojet system (SC). Each group was divided into two subgroups according to the adhesive system used (n¼3): Subgroup MH: Monobond plusþHeliobond2þTetricEvoCeram (Light-curing nano-hybrid composite)2; and subgroup SBU: Single Bond Universal adhesive1 þ TetricEvo Ceram (Light-curing nano-hybrid composite).2
2.3. Substrate surface treatments
Control group (CN) received no surface treatment. For the DB group the surface was ground using a medium grit abrasive diamond bur3using a high speed hand piece under copious airewater irrigation in one direction for 4 s on each surface[16]. And for the SC group the surface was air abraded using Cojet powder, through an intraoral air abrasion device4 at 90, at
Table 1
Information regarding the materials used in the study. Serial
no.
Materials'description Brand names Composition Manufacturer Lot. # 1 Indirect resin composite
blocks (CAD/CAM) (A3-LT)
Lava Ultimate blocks Resin Nano-ceramic composite; BisGMA/TEGDMA, Silica and zirconia fillers
3M, St. Paul, USA N389826
2 Lithium disilicate blocks (LT-A4/C14)
IPS e.max CAD blocks SiO2(57e80%), Li2O (11e19%),
K2O (0e13%), P2O5(0e11%), ZrO2
(0e8%), Al2O3(0e5%), MgO 90 e5%) and coloring oxides (0e8%)
Ivoclar, Vivadent, USA
R64456
3 Single component, light curing adhesive
Single Bond Universal Adhesive
Water, ethanol, HEMA, BisGMA, dimethacrylates, photoinitiator system and a methacrylate functional copolymer of polyacrylic and polyitaconicacids, MDP phosphate monomer and silane(26)
3M Deutschland GmbH, Germany
510450
4 Light-curing nano-hybrid composite (A3)
TetricEvoCeram Monomer: Dimethacrylates (17
e18% weight), barium glass, ytterbium trifluoride, mixed oxide prepolymer (82e83% Wt.)-Additional contents: additives, catalysts, stabilizers, and pigments (<1% Wt.)
Ivoclar, Vivadent, USA
N36895
5 One component primer Monobond Plus Alcohol solution of silane methacrylate, phosphoric acid, methacrylate and sulphide methacrylate. Ivoclar, Vivadent, USA N51095 6 Light-curing bonding resin
Heliobond Bis-GMA and triethylene glycol dimethacrylate (99%Wt.), catalysts and stabilizers (<1%)
Ivoclar, Vivadent, USA
N44963
7 Silicatized sand CoJet sand 30mm silica Alumina blast coating agent (Aluminum oxide:>97%, Amorphous silica:<3%)
3M Deutschland GmbH, Germany
499438
1
3M ESPE, St. Paul, USA.
2
Ivoclar, Vivadent, Liechtenstein.
3
Mani Dia-burs, Mani, Inc., Tochigi, Japan.
4
distance of 10 mm for 20 s, and pressure of 2.8 bar[4], rinsed for 10 s using air water spray and dried using oil/water free compressed air for 3 s. The untreated surfaces were marked using a permanent marker for the ease of identification.
2.4. Repair using Heliobond adhesive
Silane coupling agent (Monobond plus) was applied on the treated surfaces of the samples for 1 min using a brush. The plates were dried for 10 s with oil/water free compressed air. Adhesive resin (Heliobond) was applied using a brush, lightly thinned with compressed air. Light emitting diode curing unit5of high intensity 1500 mW/cm2 was used to cure the bonding agent for 20 s. The intensity of the light curing unit was checked using a radiometer before curing of each group.
2.5. Repair using Single Bond Universal adhesive
The adhesive was applied using a brush for 20 s, air-dried using oil/water free compressed air for 5 s and light cured for 10 s using the same light curing unit.
2.6. Application of the repair resin composite
Each substrate surface received 5 resin micro-tubules (n ¼15 in each subgroup). Small transparent microtubules were cut from polyvinyl tube with inner diameter 0.9 mm and height 1 mm. After curing of the previously mentioned adhesives, each micro-tubule was adjusted over the cured adhesive, filled with light-curing nanohybrid composite TetricEvoCeram (Shade A3) and light cured for 20 s.
2.7. Microshear bond strength (mSBS) testing
After 24 h storage in distilled water, the microtubules were sectioned to expose the composite micro-cylinders using sharp scalpel blade number 11. Excess adhesive around each micro-cylinder was scrapped out using the same surgical blade to limit the bonding surface area. The micro-cylinders were examined by a magnifying lens for any defects at the interface.
Each specimen with the bonded composite micro-cylinders was secured with tightening screws to the lower fixed compartment of Universal testing machine6 with a load cell of 5N. A loop prepared from an ortho-dontic wire (0.01400in diameter) was wrapped around the
bonded micro-cylinder assembly as close as possible to the base of the micro-cylinder and aligned with the loading axis of the upper movable compartment of the testing machine.
A shearing load with tensile mode of force was applied via the testing machine at a crosshead speed of 0.5 mm/min. The relatively slow crosshead speed was selected in order to produce a shearing force that resulted in debonding of the micro-cylinder along the substrate/adhesive interface. The load required for debonding was recorded in Newton and the data were recorded using computer software.7The load at failure (Newton) was divided by bonding area (mm2) to ex-press the bond strength in MPa. The results were collected, tabulated and statistically analyzed.
2.8. Statistical analysis
Statistical analysis was performed using SPSS (version 21st edition).8Two-way ANOVA was used to evaluate the effect of material, treatment and their interaction on micro shear bond strength. One-way ANOVA followed by Tukey HSD Post hoc test were used to evaluate the effect of material with each treat-ment. Student TeTest was used to assess the effect of material within each treatment at P value¼0.05. 3. Results
Table 2showed that, both the type of material and the surface treatment applied had a statistically sig-nificant effect. Additionally, the interaction between them had a statistically significant effect.
Regardless of the surface treatment, Lava Ultimate RNC showed statistically significant higher microshear bond strength compared to IPS e.max lithium disilicate ceramic.
Regardless of the material used, the group (DBMH) showed statistically significant highermSBS compared to all treatment groups, except for group (CNMH), where the increase inmSBS was insignificant (Table 3). InTable 4, Lava Ultimate RNC, (DBMH) subgroup showed statistically significant higher mSBS value compared to (CJSBU) subgroup, and statistically non-significant with the other groups of treatments.
While for IPS e.max, (DBMH) subgroup showed statistically significant highermSBS value compared to other groups of treatments and statistically non-significant with (CNMH) group.
5
Radii plus, SDI dental limited, Australia.
6
Model LRX-plus; Lloyd Instruments Ltd., Fareham, UK.
7
Nexygen-MT Lloyd Instruments Ltd., Fareham, UK.
8
On comparing the two tested materials within each treatment, Lava Ultimate RNC subgroups (CNSBU), (DBSBU) and (CJSBU) showed statistically significant highermSBS values compared to the same IPS e.max subgroups.
There was no statistically significant difference be-tween the subgroups (CNMH), (DBMH) and (CJMH) for both tested materials.
4. Discussion
Replacement of defective restorations may not necessarily be the most practical solution because it weakens the tooth structure, in addition to further trauma to the pulp. Repair of a failed restoration, when possible and appropriate, offers many merits over replacement as:
reduced chair time, lower cost and ease of application [25,26].
The integrity of the bond between the substrate and the repair resin composite determines the clinical suc-cess of the ceramic repair system. This bond is achieved either by chemical or mechanical pre-treatment of the ceramic surface or by combination of both[19,25]. The selection of diamond burs in this study as a mechanical treatment to enhance the bond between repair resin composite and ceramics [28], as it is an easily appli-cable and cost-effective method for abrasive condi-tioning of the ceramic surface [1]. The surface roughening which result from Cojet system is thought to provide a large surface area for increased wettability, micro-retentive structure for micromechanical luting of the bonding material, thus enhancing the bond strength [8,25,28,29].
Single bond Universal adhesive system (SBU) used in this study, is claimed to have a unique chemistry containing silane coupling agent and MDP in addition to other components which allows the adhesive to chemically bond to glass ceramic surfaces without using a separate ceramic primer [30]. Ceramic repair system with separate silane step (Monobond plusþHeliobond adhesive) was also selected for the purpose of com-parison representing a commonly used repair modality. Tensile and shear bond strength tests are the most commonly used by the researchers to evaluate the adhesion properties of the adhesive systems. For evaluation of the bond strength between repair resin composite and ceramic surface, microshear bond strength test was used in this study as the specimens might be easily prepared[27]and to avoid the cohesive fracture on numerous samples[31].
Regarding the effect of surface treatment, the results of the current study revealed that the subgroups treated with (DBMH) showed higher statistically significant microshear bond strength value (12.4 ± 4.5 MPa) regardless of the material used. The use of diamond
Table 4
Means±SD values for the effect of treatment within each material and material within each treatment onmSBS in MPa.
Subgroup Resin nanoceramic Lithium disilicate CNMH 8.8±4.6ab B 12.2±3.7a A DBMH 12.6±6.0a A 12.6±5.0a A CJMH 8.8±3.6ab A 6.3±4.5b A CNSBU 9.7±6.9a A 2.5±1.3c B DBSBU 9.1±4.9ab A 2.4±1.7c B CJSBU 4.3±2.3b A 2.7±1.7c B
Means with the same subscript small letters in the same column and the same superscript capital letters in the same row are not statistically significant at P¼0.05.
Table 2
Two-way ANOVA for the effect of material, treatment and their interactions onmSBS in MPa.
Source Type III sum of squares df Mean square F Sig. Corrected model 2516.098a 11 228.736 14.113 .000 Intercept 10551.142 1 10551.142 651.007 .000 Material 277.107 1 277.107 17.098 .000 Treatment 1644.278 5 328.856 20.290 .000 Material*Treatment 598.080 5 119.16 7.380 .000 Error 2739.055 169 16.207 Total 15880.135 181 Corrected total 5255.153 180
a R squared¼.479 (Adjusted R squared¼.445).
Table 3
Means±SD for the effect of different surface treatments regardless the materials used onmSBS in MPa.
Subgroup Symbol Mean±SD
DBMH A 12.4±4.5 CNMH AB 10.5±4.4 CJMH BC 7.5±4.2 CNSBU CD 6.1±6.1 DBSBU CD 5.7±5.0 CJSBU D 3.5±2.2
bur might present a more irregular and rough surface than those subjected to abrasion with silica coated particles (CJMH) (7.5 ± 4.2 MPa). This was in accordance with Phoenix and Shen [32], who stated that the mechanical interlocking has an effective in-fluence on the formation and maintenance of ceramic-to-resin bond[4].
For RNC material, the remarkable increase inmSBS value of (DBMH) subgroup (12.6±6.0 MPa) compared to the (CNMH) subgroup (8.8 ±4.6 MPa) proved the efficiency of created retentive surface with diamond bur that might have exposed the hydroxyl groups of RNC (high silica content) which was compatible with the silane. Thus it led to increase the wettability and resin impregnation of Heliobond adhesive into the micro-retentive areas [9,25]. While IPS e.max subgroups treated with (CJMH) (6.3 ± 4.5 MPa) and (CJSBU) (2.7 ± 1.7 MPa) showed statistically significant lower mSBS values compared to the subgroup treated with (DBMH) (12.6±5.0 MPa). This may denote that Cojet system could not roughen the surface to provide reliable bond strength between repair resin composite and ceramic. Silica coating is not the choice of treatment for silica-based ceramics [4,33]because the silica content of lithium disilicate ceramics is approximately (57e80%) as purported by the manufacturer, which does not need added silica coating as the integral silica content is adequate for the reliable chemical bond. Also Rathke et al.[34]found that the use of silica coating had no advantage over common bonding systems when used in repair of microhybrid composite.
However, Frankenberger et al.,[35]stated that, fa-tigue resistance of the repaired resin composite after using Cojet system or carbide burs used for roughening gave similar results. While Bouschlicher et al.[36]and Zaghloul et al. [29]reported better results when using Cojet system.
Regardless of the substrate material, the results of this study showed that all the groups treated with (SBU) adhesive system had significant lower mSBS values compared to the groups treated with separate silane step. Bonding to ceramic substrate seems to be dependent on the presence of silica on their surfaces. Silica which is well incorporated to the ceramic surface has a great affinity to silane coupling agent [3,4,27]. The decrease inmSBS values suggested that, the silane might not be effective to form siloxane bridges with the substrate surfaces[2,10,14,18,21]. In turn, it impaired the wetta-bility and resin impregnation leading to failure of bond. This may be due to the lower silane concentration in (SBU) than that of Monobond plus. There should be balance between the amount of the hydroxyl groups of
inorganic substrates exposed and the hydrolysable functional groups present in the silanes[37]. This bal-ance might have been lost, which might have led to the presence of unreacted hydrolysable functional groups with existence of weak siloxane bond. These results were in accordance with Zaghloul et al. [29] who showed that, the additional silanization step enhanced the chemical bonding to the exposed hydroxyl groups and wettability with the resin composite.
An overall comparison between the two ceramics repaired; Lava Ultimate RNC showed statistically higher significantmSBS values with the groups treated with (SBU) compared to the same treated groups of IPS e.max lithium disilicate ceramic. This may be due to the difference in micro-structure of the tested substrate materials. When treated RNC groups with (SBU) ad-hesive which contains MDP phosphate monomer that chemically reacts to zirconia in the RNC providing a higher bond specially after mechanical roughening of the latter's surface[6]. Borges et al.,[3]concluded that, the efficiency of the surface treatment is highly depen-dent on the composition of the ceramic substrate rather than the treatment itself. In addition to the different properties of flexural strength, resilience that might allow the RNC to have higher mSBS values before failure[6,8]. These findings suggested that, the effect of surface treatment onmSBS of repair composite to CAD/ CAM restoratives is material dependent.
5. Conclusions
Within the limitations of this study the following conclusions could be drawn for both tested materials:
1. The effect of surface treatment on mSBS of the repair resin composite is material dependent. 2. Combination of the abrasive action of diamond bur
and adhesive with separate silane treatment had a synergistic influence on mSBS of the repair resin composite under the current circumstances.
Disclosure statement
It is hereby stated that each author has no conflict of interest.
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