Dental Hypotheses

: 2021  |  Volume : 12  |  Issue : 4  |  Page : 189--192

Effect of the Resin-Based Adhesive Coating on the Shear Punch Strength of Aesthetic Restorative Materials

Najmeh Mohammadi1, Rafat Bagheri2, Lida Vaziri Borazjani1,  
1 Department of Pediatric Dentistry, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran
2 Department of Dental Material Sciences, Biomaterials Research Center, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran

Correspondence Address:
Rafat Bagheri
Department of Dental Materials, Shiraz Dental School, Shiraz University of Medical Sciences, Shiraz 43111


Introduction: This study aimed to investigate the effect of G-Coat Plus (GCP) on the shear punch strength (SPS) of conventional glass ionomer cements (CGICs) and resin composites (RCs). Materials and methods: In this experimental study, four groups of restorative materials (two CGICs (Equia Forte Fil and Fuji Bulk), and two RCs (Aura Bulk fil and Filtek Z250) were used. Twenty specimens were prepared for each material. GCP was applied on the first subgroup (n = 10). The specimens were stored in distilled water at 37°C, and SPS values were measured after 24 hours. Two-way analysis of variance and independent t test were used for data analysis. Results: RCs showed significant higher SPS values compared to the CGICs (P < 0.001). All materials tested showed increased SPS values after applying GCP (P < 0.05). Conclusion: Applying GCP significantly improves the SPS of tooth-colored restorative materials used in this study.

How to cite this article:
Mohammadi N, Bagheri R, Borazjani LV. Effect of the Resin-Based Adhesive Coating on the Shear Punch Strength of Aesthetic Restorative Materials.Dent Hypotheses 2021;12:189-192

How to cite this URL:
Mohammadi N, Bagheri R, Borazjani LV. Effect of the Resin-Based Adhesive Coating on the Shear Punch Strength of Aesthetic Restorative Materials. Dent Hypotheses [serial online] 2021 [cited 2022 Jan 23 ];12:189-192
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Full Text


Direct tooth-colored restorative materials including resin composites (RCs) and glass ionomer cements (GICs) have become popular in dentistry.[1] In clinical situations, characteristics such as biocompatibility, adhesion to the tooth structure, absence of marginal leakage, and acceptable mechanical properties are considered to choose an appropriate material.[2]

The RCs are usually preferred due to their color matching, desirable bonding, and less damage to the tooth structure.[3] However, some clinical failures of these materials have been reported.[4] Glass ionomer cement restoratives (GICRs) have been used in a wide variety of clinical applications.[5] Their key features are chemical bond to the enamel and dentin[6] and cariostatic function.[7] However, due to inferior mechanical properties, use of GICRs is limited to the nonstress bearing areas,[5] and the sandwich technique.[8]

Considerable efforts have been made to improve properties of GICRs.[8] Variety of surface-coating agents including petroleum jelly, cocoa butter, waterproof varnishes, and even nail varnishes has been used in the past.[9],[10],[11] However, the washed out of those coatings by the oral masticatory wear was reported.[5]

Recently, a nano-filled resin-based coating, G-Coat Plus (GCP; GC Co, Tokyo, Japan), was introduced.[9] GCP is a low-viscosity methyl methacrylate-based nano-filled resin that seals surface defects of the underlying material and protects it against abrasive wear and fracture.[3] The surface protection is important during initial days of GICRs maturation until peak strength is achieved.[12],[13]

Improvement of the mechanical properties of coated GICRs has been reported in previous studies.[5],[14] The study by Sukumaran and Mensudar exhibited increased mechanical strength of three different types of coated-GICs (Fuji II, Fuji IX, and Fuji II LC).[5] Bagheri et al. also found that coating significantly increased the flexural strength of conventional GIC (CGIC) of Fuji IX (GC Co).[3]

Although a recent study investigated the effect of GCP on the mechanical properties of RCs,[14] data about coated RCs are still limited. This study aimed to investigate the effect of GCP on the shear punch strength (SPS) of two types of CGICs and two types of RCs. The null hypothesis is that surface coating does not improve the SPS of restorative materials.

 Materials and Methods

Specimen preparation

In this experimental study, approved by ethics committee of Shiraz Dental School, a total of 80 specimens, in four groups [two CGICs of Equia Forte Fil (GC Co) and Fuji Bulk (GC Co) and two RCs of Aura Bulk fil (SDI, Bayswater, VIC, Australia) and Filtek Z250 (3M ESPE, St Paul, MN 55144-1000, USA)], were prepared.

Every group had two subgroups (n = 10): coated (GCP; GC Co) and uncoated. Disc-shaped specimens (10 mm diameter × 1 mm thickness) were prepared using plastic molds and cured by a LED unit (Radii plus LED; SDI). After removing the specimens from the molds, 1000, 1500, and 2000-grit silicon carbide papers were used to eliminate the excess material. Washing in an ultrasonic bath was performed between each grinding.

A thin coat of GCP was applied on the top surface of the specimens in the coating subgroups. Gentle air blowing for 5 seconds and light curing for 20 seconds were performed. All specimens were stored in distilled water at 37°C and tested after 24 hours.

Shear punch strength test

Gentle pressure of the restraining screw stabilized the specimen in the shear punch jig of the universal testing machine (Zwick/Roll Z020; Zwick GmbH & Co, Ulm, Germany) [Figure 1]. A flat-ended 3.2-mm diameter stainless steel rod at a crosshead speed of 1 mm/minute was used to penetrate the disc, and the maximum load was recorded. To calculate the SPS values in MPa the following formula was used:{Figure 1}

Shear punch strength (MPa) = N/π × D × T

where N is the applied force, D is the punch diameter (mm), and T is the thickness of the specimen (mm).


Data were analyzed using SPSS, version 22 (IBM Corp, Armonk, NY, USA). Kolmogorov–Smirnov test was employed for assessing normality assumption of data. Two-way analysis of variance (ANOVA) was applied to investigate interactions between the materials and the coating. One-way ANOVA was used to compare different variables between the materials, and posthoc t test was performed to show significant differences in subgroup comparisons. The level of significance was set at 0.05.


The normality assumption was held in all cases. The mean SPS values and related standard deviations for all groups of the study are shown in [Table 1].{Table 1}

Results of two-way ANOVA indicated a statistically significant interaction between adhesive coating and the restorative materials (P < 0.001). Therefore, one-way ANOVA analysis was conducted and showed that the differences of the SPS values of the restorative materials with or without coating were significant (P < 0.001). No significant difference between two RCs was observed, but two CGICs showed statistically significant differences (P < 0.05) with higher SPS value for Fuji Bulk. Moreover, GCP significantly improved the SPS of all tested materials (P < 0.05).


SPS test is used to evaluate the effects of occlusal or incisal forces on the clinical properties of restorative materials.[15],[16],[17],[18] Performing this test, we polished the specimen to obtain flat parallel surfaces to be supported evenly while pressing the punch through it.[19] Furthermore, modified shear punch test jig with a screw clamp[19] was used for the present study. Hence, bending of the samples during application of the force is prevented.[20]

The GCP is recommended to improve the mechanical properties of restorative materials. Infiltration of GCP protects the materials against crack initiation, fills porosities, reinforces the materials, and inhibits the water movement across the restoration surface.[14],[21],[22],[23],[24],[25],[26]

Based on our results, GCP significantly increased the SPS values of all materials, so the null hypothesis is rejected. This could be related to the ability of GCP to provide a toughened laminated layer that disperses the mechanical stresses. Hence, adequate mechanical properties are sustained to endure forces.[5]

Similar to our results, other researches also showed improved mechanical properties (shear punch, fracture toughness, and flexural strength) of coated GICRs.[3],[5] Higher flexural strength of coated GIC of Fuji IX GP extra (GC) and micromechanical interlocking between the GCP and this material were reported.[12] Bagheri et al. also observed a significant increase in the fracture toughness of RMGIC (resin-modified glass ionomer cement) of Fuji II LC (GC Co, Japan) coated by GCP.[2]

Unlike our result, Pilo et al.[8] showed that coating decreased the SPS of three types of high-strength GICs: Ketac Molar (3M ESPE AG, Landsberg am Lech, Germany), Ionofil Molar AC (VOCO AC, Cuxhaven, Germany), and Fuji IX GP Fast (GC Co). Early exposure to water also increased the SPS of GICRs of Fuji IX GP Fast (GC Co), Ketac Molar, and Ketac Molar Quick (3M ESPE) in the study by Wang et al.[21]

The proposed explanation for these adverse effects may be the fact that surface coating interferes with the hydration process and strength increasing by the bound water.[19] Other reasons justifying the diversity of the results are different formulations of GICRs, diversity of the structure of the hardened materials, and various mechanical tests. Extended water storage time in some studies is another factor that affects the mechanical properties based on the composition and water sorption tendency.[22]

Fuji Bulk demonstrated higher SPS values than Equia Forte Fil in our study. Ultra-fine glass particles embedded in a stronger matrix having higher molecular weight polyacrylic acid is the probable reason for better results of Fuji Bulk.[23]

Based on our results, GCP application significantly improved the mean SPS values of RCs. Close to our results, applying GCP prevented microleakage and decreased possible replacement of nanohybrid composite restorations (Ceram-x, Dentsply Asia) in the clinical study by Kumar et al.[24]

However, Moghaddasi et al.[14] by evaluating other mechanical features reported no significant differences between flexural strength values of coated and uncoated specimens of Aura bulk fil (SDI), IPS Empress Direct (Ivoclar Vivadent, AG, Liechtenstein), Filtek Z250, and Filtek P60 (3M ESPE).

Two types of RCs demonstrated comparable SPS values in the present study. But microhybrid composite of Filtek Z250 having higher contents of inorganic fillers of zirconia and silica particles, exhibited better mechanical properties than that of nanohybrid composite of Aura Bulk fil in other studies.[3],[14]

Furthermore, GCP demonstrated better results in comparison with another coating of Fortify Plus in terms of decreasing microleakage of RC restorations (Clearfil Majesty ES‑2, Kuraray, Tokyo, Japan). The nano-sized filler particles in the matrix of GCP were considered as the cause of its excellence.[25]

According to the reported means of maximum occlusal bite force for different dentition stages (176 N in early primary stage, 240 N in late primary stage, 289 N in early mixed stage, 433 N in late mixed stage, and 527 N in the permanent dentition stage, respectively),[26] coated CGICs of Equia Forte Fil and Fuji Bulk can almost endure these forces up to the late mixed dentition. Considering other advantages of GICRs, they are suggested as suitable restorative materials in pediatric dentistry.

Although the results were in favor of applying GCP, only short-term performance of this coating was evaluated in this study. Therefore, further long-term clinical studies to determine the effect of occlusal wear or aging on the coated restorations are required.


Considering the limitations of this study, it was concluded that applying GCP significantly improved the SPS of restorative materials. RCs used in our study showed significant higher SPS values than CGICs.

Clinical significance

GCP is recommended to be applied on CGIC and RC restorations increasing the SPS of the materials in the first 24 hours of application.


The authors thank the Vice-Chancellery of Shiraz University of Medical Sciences for supporting this research (grant #15987). The authors also thank Dr Vosughi for contribution in statistical analysis.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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