Article

Clinical Performance and Bonding Mechanism of ThreeResin Adhesives

Kun Wu

Department of Gastrointestinal Surgery, TheAffiliated Huai’an No.1 People’s Hospital of Nanjing Medical University,Huai’an 223300, China;drKunwu@163.com

Received: 6 January 2021; Accepted: 28 March2021; Published:2April 2021

Abstract: Juxtaposed surfacescould be bond to achieve marginal sealing and adhesive of interfacebetween different kinds of substrate. Therefore, the purpose of the current study is to investigate the bonding strength of threecommon resin adhesives after bonding and polymerization, and to evaluate thebonding effect.PanaviaTM-F resin adhesive, Rely 3M EPSEresin adhesive, and Kerr NX3 resin adhesive were used to prepare modules (10 ×10 × 3 mm³). The glass permeable ceramic was made into a rectangularcomponent (10 × 10 × 10 mm³), ensuring all surfaces to be smooth.Three kinds of different adhesives were bonded to surface of theglass-infiltrated ceramic. Tensile tests, compression tests and shear testswere performed on different adhesives after cold and hot cycles tocomprehensively evaluate the differences in the clinical properties ofadhesives.After testing, the surface hardness of KerrNX3 resin adhesive was the highest among the three, andless affected by water storage. The tensile strength and compressive capacityof Kerr NX3 resin were much stronger than those of the other two adhesives.After cold and hot cycles,Kerr NX3 resin was 39% higher than PanaviaTM-F resin and 15% higher than Rely 3M EPSE resin. Scanning Electron Microscopy(SEM)observations of morphology and failuresurfaces of three adhesives showed that the repairing effect of Kerr NX3 resinwas the best and the bonding strength was the highest. Compared with thePanaviaTM-F and Rely 3M EPSE resin, the bonding strength of Kerr NX3 resin wasthe highest with best repairing effect.

Keywords: bonding strength; compressiontest; resin bonding; shear force; surface-dimensional hardness, tensile test

1. Introduction

Dental caries, also known astooth decay or cavities, remains a major health concern worldwide [1]. In elderly people, edentulism is an importantindicator of dental caries and a ‘final marker of disease burden for oralhealth’[2]. In thetreatment of dental caries, prosthodontics is a unique dental profession thatcombines aesthetics, philosophy and sciences, including reversible andirreversible treatments [3]. Wearresistance is one of the most important properties for choosing dentalrestorative materials[4]. Thewear properties of restorative materials are very complicated, which areaffected by a variety of factors, including wear of polymer matrix, loss offiller by failure of its bond with the matrix, shear of filler particle,cohesive failure through matrix, and exposure of air bubbles [5]. Glassceramic is a relatively common dental material that is used as dental inlay,onlay, crown or other structures to fix dental problems [6]. However, it has been stated that while ceramicmaterials are resistant to compressive forces,they are susceptible to tensile stresses and more prone to fracturethan composite materials [7]. In addition,etching silica-based ceramics with hydrofluoric acid produce insolubleby-products consisting of silica fluoride salts on the surface, and theremaining by-products can disrupt the bond strength of the resin [8]. Today, the utilization of new materials has made itfeasible to fabricate all-ceramic prosthodontic restorations with superioresthetics [9].

Resin cement has been thepinnacle of direct esthetic restorations long since its discovery [10]. Resincement is most commonly composed of bisphenol A-glycidyl methacrylate (Bis-GMA) and other dimethacrylate monomers, a filler material such as silica and inmost current applications, a photoinitiator. A direct resin composite restoration based on resincement adhesives can protect the integrity of tooth substance and achieveesthetic restoration, which significantly contributes to the realization of minimallyinvasive dental treatments [11]. In order toimprove the aesthetic level of the final restoration, the resin compositeveneer must have certain physical strength and resistance to abrasion [12]. Self-adhesive resin cement Panavia^TM-F isa catalyst promoting the bonding of the ceramic [13]. Self-adhesive Rely 3M EPSE is proved to have moreadvantages in its aesthetic properties and strength [14]. In addition, the adhesive strength of Kerr NX3 resincement is relatively strong and can meet the clinical requirements [15]. There is evidence regarding the effect of thethickness of resin cements on the polymerization shrinkage stress [16,17],which showed that different types of resin cements play important rolesin cementing ceramic restorations [15]. However, in current literature, there are fewstudies that compare the bondingstrength and restorative effect of Panavia^TM-F, Rely 3M EPSE andKerr NX3. Therefore, in this study, the bonding strength and restorative effectof the above three resin cements were evaluated by measuring their tension,compression and shear strength.

2. Material and Methods

2.1. Materials

Each of 60 components (10 × 10 × 3 mm³) was prepared from three different adhesives (Kerr NX3,Panavia^TM-F and Rely 3M EPSE). The surface was demanded to be smoothand the surface roughness (Ra) with no more than 0.10 μm. Twenty components (10 × 10 × 10 mm³). Smooth surface were obtained from glass-infiltrated ceramic. Under a stereoscope, the surface structureof each component was uniform. According to the manufacturer's instructions, 20adhesivecomposites (10 × 10 × 13 mm³) were obtained from the three kinds of resin cementsbonding to the glass-infiltrated ceramics.

2.2. Grouping

The prepared Panavia^TM-F was designated asgroup A1; Rely 3M EPSE was designated as group A2; and Kerr NX3 was designatedas group A3. Besides, Panavia^TM-F bonding to glass-infiltratedceramic was selected as group B1; Rely 3M EPSE bonding to glass-infiltratedceramic was selected as group B2; and the Kerr NX3 bonding to glass-infiltratedceramic was selected as group B3.

2.3. Vickers Hardness (HV) Test

Each of five components wererandomly selected from group A1, A2 and A3 and independently immersed in distilled water for 24 h, 1 week, 2 weeks, 4weeks and 12 weeks. Then the HV value of each group was calculated.

2.4. Tensile Testing

Fivecomponents were randomly selected from group A1, A2 and A3. The components weresliced vertically along its longitudinal axis using low-speed sawin cooling water, to prepare a specimen with a length of 10 mm andcross-sectional area 3 × 3 mm². The micro-tensile bond strengthof each specimen was measured using a universal testing machine (UTM).Furthermore, 5 components were randomly selected from group B1, B2 and B3. Thenthe components were sliced vertically along its longitudinal axis usinglow-speed saw in cooling water, to prepare a specimen with a length of 13 mmand cross-sectional area 3 × 3 mm². The micro-tensile bond strengthof each specimen was tested using a UTM.

2.5. Compression Test

Fivecomponents were randomly selected from group A1, A2 and A3. The compressivestrength was measured using a UTM at a crossheadspeedof 1mm/min. Moreover, five components were randomly selected fromgroup B1, B2 and B3. The compressive strength was measuredusing a UTM and the parameter condition was consistent with group A.

2.6. Thermal-Cold Cycling and Shear Strength Testing

Each offive components were randomly selected from group A1, A2 and A3, which weresliced vertically along its longitudinal axis using a low-speed saw in coolingwater, to prepare a specimen with a length of 10 mm and cross-sectional area 5× 5 mm². Additionally, five monomers were randomly chosen from groupB1, B2 and B3. The specimen with a length of 13 mm and cross-sectional area 5 ×5 mm² was obtained by the same way. All specimens were placed in thethermal shock chamber. And the specimens from the six groups were immersed inwater bath and then were thermocycled at 5°C and 55°C for 5000 cycles, 60seconds for each cycle. Next, the shear strength of the samples was calculatedusing a UTM at a crossheadspeedof0.5 mm/min.

2.7. Scanning Electron Microscopy (SEM)

Five components were randomlyselected from group B1, B2 and B3 and were sectioned perpendicularly to thebonded surface to expose the adhesive interface to obtain 1 mm specimens. Thespecimens were subsequently wet-polished using 500 to 2000 grit waterproofabrasive paper. The ultrastructureof bonded surface in group B1, B2 and B3 were observed by SEM. Moreover, allspecimens were rinsed with distilled water and placed in an ultrasonic bath forseveral minutes and were dried by gentle blotting using absorbent paper (Kimwipes; Kimberly-Clark Professional,Roswell, GA, USA). After goldsputtering, the specimens were viewed using SEM. Next, specimens were selectedfrom group B1, B2 and B3 after the shear testing. The damaged surface of resincements bonding to glass-infiltrated ceramic was observed by SEM.

2.8. Statistical Analysis

All the data were processedusing SPSS 19.0 statistical software (SPSS Inc., Chicago, IL, USA). Thehomogeneity of variance was examined using the shear and bonding strength ofthe three resin composites. Statistical analysis was performed using analysisof variance test.Comparisons between paired groups wereperformed using Last Significant Difference (LSD) tests for two groups, and thedata were presented as mean ± standard deviation. A p value of < 0.05was considered statistically significant.

3. Results

3.1. Kerr NX3 Possesses Higher HV

Initially, HV test was adoptedto explore the HV of resin. As shown in Table 1,cement types and the water storage time hada significant effect on the HV. Specifically, the HV of components in the A1group was not affected by water storage time. Then, the HV of the components inthe A2 group was decreased after long-term water immersion. Furthermore, thecomponents in the A3 group showed significantly higher HV and were lessaffected by water storage time. p < 0.05 indicated statistically significant. These results demonstrated that HV of KerrNX3 is higher and less affected by water storage time.

Table 1. The Vickers hardness (HV) of Panavia^TM-F, Rely 3M EPSE and Kerr NX3

Notes: h, hour; w, week; HV, Vickershardness; ^*, p < 0.05 compared with Panavia^TM-F;^△, p < 0.05 compared with Rely 3MEPSE.

3.2. Kerr NX3 Possesses Increased TensileStrength

A UTM was employed to measuremicro-tensile bond strength. In addition, the side length of each sample wasmeasured by a vernier caliper and the cross-sectional area (mm²) wascalculated. The micro-tensile bond strength (MPa = N/mm²) wasderived by dividing the imposed force (N) at the time of fracture. The resultsof tensile testing showed that, compared with resin cements bonding toglass-infiltrated ceramic in group B1, B2 and B3, pure resin material in groupA1, A2 and A3possessed a better tensile strength.Moreover, the micro-tensile bond strength of the specimens in group A3 and B3were significantly higher than that in the other two categories of groups (allp < 0.05, Table2). Thus, tensile strength isbetter in Kerr NX3.

Table 2. The micro-tensile bond strengths of Panavia^TM-F,Rely 3M EPSE and Kerr NX3 in the six groups (n = 5)

Notes: A1, Panavia^TM-F; A2, Rely 3M EPSE; A3, Kerr NX3;B1, Panavia^TM-F bonding to glass-infiltrated ceramic; B2, Rely 3MEPSE bonding to glass-infiltrated ceramic; B3, Kerr NX3 bonding toglass-infiltrated ceramic;^*, p < 0.05 compared withA1 and B1; ^△, p < 0.05 as compared with A2 andB2; ^#, p < 0.05 compared with the pure resin materials in the homogeneous group.

3.3. Kerr NX3 Yields Increased CompressiveStrength

Compressive strength wasmeasured by compression test using a UTM. As shown inTable 3, a pairwise comparison for obtained data wasconsidered statistically significant (p < 0.05). Pure resin material in group A1, A2 and A3 showed ahigher compressive strength than resin cements bonding to glass-infiltratedceramic in group B1, B2 and B3； thespecimens in group A3 and B3 showed a higher compressive strength than that inthe other two categories of groups. All above results implied that Kerr NX3 hasbetter compressive strength.

Table 3. The compressive strength of Panavia^TM-F,Rely 3M EPSE and Kerr NX3 in the six groups

Notes: A1, Panavia^TM-F; A2, Rely3M EPSE; A3, Kerr NX3; B1, Panavia^TM-F bonding to glass-infiltratedceramic; B2, Rely 3M EPSE bonding to glass-infiltrated ceramic; B3, Kerr NX3bonding to glass-infiltrated ceramic; ^*, p < 0.05 ascompared with A1 and B1; ^△, p <0.05 as compared with the A2 and B2 groups; ^#, p < 0.05compared with the pure resin materials in the homogeneous group

3.4. Kerr NX3 Offers Shear Strength

Shear strength of Panavia^TM-F,Rely 3M EPSE and Kerr NX3 was measured by thermal-cold cycling and a UTM. Asshown in Table 4, the specimens in group A1 and B1 hadrelatively low shear strength. However, the specimens in group A3 and B3 showedsignificantly higher shear strength than that in the other two categories ofgroups, and there was significant difference between the homogeneous groups (p< 0.05), demonstrating that shear strength is higher in Kerr NX3.

Table 4. The shear strength of Panavia^TM-F,Rely 3M EPSE and Kerr NX3 in the six groups

Notes: A1, Panavia^TM-F; A2, Rely3M EPSE; A3, Kerr NX3; B1, Panavia^TM-F bonding to glass-infiltratedceramic; B2, Rely 3M EPSE bonding to glass-infiltrated ceramic; B3, Kerr NX3bonding to glass-infiltrated ceramic; ^*, p < 0.05 ascompared with A1 and B1; ^△, p <0.05 as compared with A2 and B2; ^#, p < 0.05 compared withthe pure resin materials in the homogeneous group.

3.5. Properties and Adhesive Strength Were Higher inKerr NX3

To explore properties and adhesivestrength of Panavia^TM-F, Rely 3M EPSE and Kerr NX3, SEM was used toobserve their morphology. As shown in Figure 1C,the bonding interface of Kerr NX3 bonding toglass-infiltrated ceramic was foundto be intact and without any voids, while the relatively large cracks, as well as long and dense resin tags were observed inPanavia^TM-F bonding to glass-infiltrated ceramic and Rely 3M EPSEbonding to glass-infiltrated ceramic. The results of interface damage wereshown in Table 5. The predominant failure mode of the threekinds of resin cements bonding to glass-infiltrated ceramic was quasi-cleavagefracture (53.33%) and only 26.67%samples showed adhesive failure. And the failure mode of the glassinfiltrated ceramics was the least, indicating that the cohesive force of thethree kinds of resin cements was lower than that of the glass-infiltratedceramic. In addition, Kerr NX3 showed no evidence of self-broken, whichindicated that better properties and adhesive strength may be possessed by KerrNX3.

Figure 1. Morphology of Panavia^TM-F, Rely 3M EPSE andKerr NX3 in the B1, B2 and B3 groups was observed by SEM.Notes: a, morphology of Panavia^TM-F; b,morphology of Rely 3M EPSE; c, morphology of Kerr NX3; the white arrowsindicated cracks and the black arrows indicated resin tags in Panavia^TM-F;the white letter C indicated the resin cement and the letters FP indicated theglass-infiltrated ceramics; the magnification of the SEM was ×500; B1, Panavia^TM-Fbonding to glass-infiltrated ceramic; B2, Rely 3M EPSE bonding toglass-infiltrated ceramic; B3, Kerr NX3 bonding to glass-infiltrated ceramic;SEM, scanning electron microscopy.

Table 5. The morphological observation of Panavia^TM-F,Rely 3M EPSE and Kerr NX3 in the B1, B2 and B3 groups by SEM (n = 5)

Notes: B1, Panavia^TM-F bonding toglass-infiltrated ceramic; B2, Rely 3M EPSE bonding to glass-infiltratedceramic; B3, Kerr NX3 bonding to glass-infiltrated ceramic; Type 1, cohesivefailures of resin cements; Type 2, failures of the glass-infiltrated ceramics;Type 3, adhesive failures of resin cements bonding to glass-infiltratedceramic; Type 4, quasi-cleavage fracture; SEM, scanning electron microscopy.

4. Discussion

Resin cements can determine thesuccess of fixed dental prostheses by bonding juxtaposed surfaces together toachieve marginal sealing and adhesive of interface between different kinds ofsubstrate, as well as adequate preservation and resistance [18]. Generally, two mechanical factors should be consideredas for the bonding of ceramics to the tooth: the adhesive forces at theresin-ceramic interface and at the resin-tooth interface [19]. One study showed that the resin cement combined withthe ceramic can significantly enhance the micro-shear bond strength [20]. This study was designed to investigate the bondingstrength and restorative effect of Panavia^TM-F, Rely 3M EPSE andKerr NX3, finding that Kerr NX3 may have higher bond strength values and betterrestorative effect than Panavia^TM-F and Rely 3M EPSE. The maincomponent of resin composite is the resin matrix and an inorganic filler,wherein the inorganic filler is uniformly dispersed in the resin matrix, andafter curing the resin composite essentially becomes a polymer compositereinforced by the inorganic filler; the resin composite matrix consists of aresin basis and the dilution monomers that are primarily methacrylate monomers [20]. Furthermore, Ishikiriamaet al. have reported that the degree of wear in NX3 is relativelysmall, indicating that the hardness of this material is higher than that of anaverage adhesive resin [21]. Lambade etal. also showed that Nexus NX3 has the highest shear strength [22]. In line with previous studies, it has been foundthat NX3 can solve the incompatibility problems during the bonding process andhas the highest bond strength and best restorative effect in this paper.

In this study, it was foundthat the HV of Panavia^TM-F was almost free from the impact of waterstorage, while the HV of Rely 3M EPSE changed more obviously after thelong-term water storage. The Kerr NX3 not only showed higher HV, but was alsoless impacted by water storage than Rely 3M EPSE. Water adsorption as well aspolymer chain hydrolysis and plastification can seriously affect the resincomposite in the mechanically mixed layer, thus causing the aging ofmorphologic integrity and affecting the bonding strength of resin [23]. Therefore, this study simulated the oral environmentand stored the resin cements in water to figure out whether the adhesivestrength of three resin composites would be affected. Moreover, Panavia^TM-Fwas a self-etching adhesive system that can be solidified by a dual mode ofoptical and chemical processes, thus providing excellent engineering featureswith wear resistances; [24]. Since Rely-XUnicem (3M EPSE) was a self-adhesive resin and the water storage could reducethe durability of self-adhesive bond strength by the slow degradation of theunprotected collagens, it indicated that 3M EPSE was more affected by waterstorage and decreased its adhesion strength [25,26]. Due to its unique amine free redox system, Nexus NX3was resistant to the acidic monomers in the air inhibition layer of the lightcured adhesive material so that the adhesive bonding strength increased,suggesting it was less impacted by water storage [22].

In summary, the tensiletesting, compression test, thermal-cold cycling and shear strength testing forthe three different resin cements showed that as compared to Panavia^TM-Fand Rely 3M EPSE, Kerr NX3 showed higher micro-tensile bond strength,compressive strength and shear strength, and less interface damage andquasi-cleavage fracture in the Kerr NX3 bonding to glass-infiltrated ceramics.However, there are still some limitations in this study. For example, theclinical efficacy of Kerr NX3 was not assessed in this study and hencerequiring further evaluation. And due to less evidences showing how theglass-infiltrated ceramic would be affected by Kerr NX3 resin cement, more advanced technology should be used forresearching the clinicalefficacy of Kerr NX3.

Funding: None.

Conflictsof Interest: The author declares no conflict of interest.

Copyright Statement

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