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ORIGINAL ARTICLE
Year : 2022  |  Volume : 25  |  Issue : 3  |  Page : 255-260

Effects of C-factor on dentin bonding using various adhesive systems


1 Department of Cariology and Operative Dentistry, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University (TMDU), Yushima, Bunkyo-ku, Tokyo, Japan
2 Department of Dental Hygiene, Chiba Prefectural University of Health Sciences, 2-10-1, Wakaba, Mihama-ku, Chiba-city, Chiba, Japan

Date of Submission27-Mar-2021
Date of Acceptance14-Oct-2021
Date of Web Publication16-Mar-2022

Correspondence Address:
Dr. T Yoshikawa
Department of Cariology and Operative Dentistry, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University (TMDU), 1-5-45, Yushima, Bunkyo-ku, Tokyo, 113-8549
Japan
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_1364_21

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   Abstract 


Aims and Background: This study evaluated the effect of C-factor on the bond strength of a resin composite to floor and wall dentin using various adhesive systems. Materials and Methods: Four dentin substrates (flat wall, flat floor, cavity wall, or cavity floor) were prepared on human molars. Each specimen was restored with one of three adhesives; Clearfil SE Bond, Single Bond, or Clearfil tri-S Bond followed by buildup or filling using Z100 resin composite. The specimen was cut perpendicular to the bonded surface parallel to the floor or wall to obtain beams after light curing at 24,000 mJ/cm2. The microtensile bond strength to wall specimens or the cavity floor was determined. Data were analyzed. Results: All adhesive systems exhibited the highest bond strength to flat wall group (p < 0.05). The bond strength to the cavity group was significantly lower than that to the respective flat group regardless of the bonding system (p < 0.05). There was no significant difference in bond strength with Clearfil SE Bond and Clearfil tri-S Bond between the cavity wall and cavity floor (p > 0.05). Conclusion: The findings suggested that the strength of bonding to the cavity floor and cavity wall was affected by C-factor regardless of the adhesive system. Bonding to flat wall was higher than flat floor regardless of the adhesive system. Self-etching system provided uniform bond to the cavity wall and cavity floor dentin. However, total etching system reduced bond to the cavity floor than to the cavity wall.

Keywords: Bonding system, C-factor, dentin bonding, resin composite, shrinkage stress


How to cite this article:
Yoshikawa T, Arakawa M. Effects of C-factor on dentin bonding using various adhesive systems. Niger J Clin Pract 2022;25:255-60

How to cite this URL:
Yoshikawa T, Arakawa M. Effects of C-factor on dentin bonding using various adhesive systems. Niger J Clin Pract [serial online] 2022 [cited 2022 Aug 19];25:255-60. Available from: https://www.njcponline.com/text.asp?2022/25/3/255/339704




   Introduction Top


Resin composite polymerization results in volumetric shrinkage. Light-cured resin composites are usually polymerized from the resin surface near a light source.[1],[2],[3] Then, direction of polymerization contraction of the resin is toward the light. This shrinkage create gaps[1],[4],[5],[6],[7],[8] between the resin and the cavity walls or floors if the forces of polymerization contraction are stronger than the bond strengths. Such gaps may permit microleakage[1],[5],[8],[9],[10] and cause postoperative sensitivity.[9],[11] The magnitude of resin composite polymerization stress[12] is dependent upon the configuration of the cavity and it is therefore called the C-factor.[13],[14] The C-factor is the ratio of the bonded area to the unbonded area or free surface area. When the C-factor values increases, the resin composite bond and adaptation to the cavity wall shows a decrease.[6],[15],[16],[17],[18]

A number of studies have measured the resin composite bond strength to superficial flat dentin surfaces and the results indicated that bond strength was reduced during bonding to deep dentin.[15],[16],[19],[20],[21],[22] Both the cavity configuration and effect of the dentin depth may combine to result in lower bond strengths to the cavity floor as deeper cavities are prepared.[15],[16] Further, the resin composite bond to the cavity wall is influenced by the dentinal tubule orientation and location.[23]

Additionally, hybrid layer formation is considered necessary for creating a strong bond between the resin and dentin.[24] However, the thickness of the hybrid layer is less important when the resin composite is bonded to a dentin substrate that is perpendicular to flat dentin,[23] and the bond strength between the resin and dentin is independent of the thickness of the hybrid layer.[25] The hybrid layer of the total etching system with phosphoric acid is thicker than that created by a self-etching adhesive system.[26],[27] However, the thick hybrid layer of the total etching system could not increase the resin composite bond strength to the cavity floor.[15],[16] Thus, we thought that it would be interesting to evaluate the bonding performance of various adhesive systems to a box-like Class 1 cavity wall and floor and flat wall and floor.

The purpose of this study was to test the hypothesis that the bond strength to walls and floors exhibits the same value, and the bond strength of resin composite to box-formed cavity floors and walls are reduced as a function of C-factor using various adhesive systems.


   Materials and Methods Top


Specimen preparation

The materials, components, manufacturers, batch numbers, and bonding procedures used in this study are listed in [Table 1]. This study protocol was approved by the Ethics committee of Tokyo medical and dental university (No. 725,2021/1). Forty-eight intact, erupted, non-carious third molars (eight teeth in each group) that were frozen immediately after extraction were used in this study. These molars were collected in accordance with our protocol No. 725, as approved by the appropriate institutional review board.
Table 1: Study materials

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The occlusal enamel was ground away [Figure 1]a and [Figure 2]a using a model trimmer under running water to expose a flat dentin surface, which was then wet-ground with #600 SiC paper. Box-form cavities (3 mm wide × 5 mm long × 2 mm deep) were prepared on the flat dentin surfaces [Figure 1]b and [Figure 2]b using a diamond point (#211, ISO #110 014; Shofu Co., Kyoto, Japan) with a copious water spray and were finished with a carbide steel bur (#600, ISO #071 012; Dentech Co., Tokyo, Japan). The walls of half of the cavities were then removed to make flat dentin floors (flat floor) and walls (flat wall) for bonding [Figure 1]c.
Figure 1: Preparation of a flat bonding substrate: Preparation of bonding substrate: (a) Extracted human tooth before prepartion: (b) Occlusal enamel was ground to expose flat superficial dentin, cavity 2mm deep; (c) Walls of cavity were removed to create a flat wall and flat floor. (d) Bonding substrates were restored with adhesive and composite, and specimens were sectioned perpendicular to the bonded surfaces; and each slab was cut into beams with a bonded area of approximately 0.9 mm2

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Figure 2: Preparation of a cavity bonding substrate: (a) Extracted human tooth before preparation: (b) Occlusal enamel was ground to expose flat superficial dentin, cavity 2 mm deep; (c) Cavities were restored with adhesive and composite; (d) Specimens were sectioned perpendicular to the bonded surfaces; and each slab was cut into beams with a bonded area of approximately 0.9 mm2

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The teeth were allocated to one of four groups: flat wall, flat floor, cavity wall, or cavity floor. Each specimen was restored with one of three adhesives: two-step self-etching system Clearfil SE Bond (SE, Kuraray Noritake Dental Inc., Tokyo, Japan), total etching system Single Bond (SB, 3M ESPE, St Paul, MN, USA) or one-step self-etching system Clearfil tri-S Bond. A Z100 resin composite (Shade A3; 3M ESPE) was then used to build on the flat surfaces (C-factor = 0.3) or fill in the cavities (C-factor = 3.1) [Figure 2]c. The resin composite was light cured at 600 mW/cm2 for 40 s (radiant exposure of 24,000 mJ/cm2) using an experimental quartz–tungsten halogen light curing unit (GC Corp., Tokyo, Japan) that was connected to a slide regulator and had a control system for lamp voltage and an adjustable light intensity, with a light tip diameter of 7 mm. The light tip-resin distance was 1 mm. The irradiance was measured using a curing radiometer (Model 100; Demetron Research Co., Danbury, CT, USA).

Tensile bond strength measurement

The specimens were stored in water maintained at 37°C in the dark for 24 h, following which the restored floor/wall specimens were sectioned perpendicular to the bonded surfaces using a diamond saw (Isomet; Buehler Co., IL, USA) under copious water lubrication [Figure 1]d and [Figure 2]d). Each slab was cut into beams with a bonded area of approximately 0.9 mm2 using a diamond saw under copious water lubrication. The trimmed specimens were mounted on a μTBS jig (KDA Co. Ltd., Tokyo, Japan) with cyanoacrylate adhesive (Model Repair II Blue; Dentsply-Sankin Co., Tochigi, Japan) and stressed to failure under tension at 1 mm/min in a universal testing machine (EZ test; Shimadzu, Kyoto, Japan). Each specimen was then inspected using a scanning electron microscope (SEM) to determine the mode of fracture.

The bond strength to floor and wall dentin were statistically analyzed using the Bonferroni/Dunn test at a significance level of 5% using Stat View 5.0 software.

SEM observation of fractured surfaces

After the tensile bond test, each fractured dentin specimen was fixed in 10% neutral buffered formalin.[28] The dentin and composite paired specimens were then trimmed and placed on SEM stubs, coated gold-sputter, and observed using SEM (JSM-5310LV; JEOL, Tokyo, Japan) to microscopically assess the patterns of failure. The fractured surfaces were classified into one of four groups: interfacial failure, mixed failure, cohesive failure within the resin (adhesive layer or composite), and cohesive failure within the dentin.


   Results Top


Tensile bond strength

The tensile bond strength results are summarized in [Table 2]. The relative tensile bond strengths are summarized in [Table 3]. All adhesive systems exhibited the highest bond strength to flat wall group compared with the bond strength to the flat floor, cavity wall, and cavity floor (P < 0.05). The bond strength to the cavity wall group was significantly lower than that to the respective flat wall group regardless of the bonding system (P < 0.05). The bond strength to the cavity floor group was significantly lower than that to the respective flat floor group regardless of the bonding system (P < 0.05). The Single Bond showed significantly lower bond strength to the cavity floor than to the cavity wall (P < 0.05). However, there was no significant difference in bond strength with Clearfil SE Bond and Clearfil tri-S Bond between the cavity wall and cavity floor (P > 0.05).
Table 2: Mean tensile bond strength of the bonding system to the various substrates

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Table 3: Relative tensile bond strength percent of Flat floor/Flat wall, Cavity floor/Cavity wall, Cavity wall/Flat wall, and Cavity floor/Flat floor

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The bond strength to the flat wall using Clearfil SE Bond showed the highest bond strength for all groups, while the bond strength of Clearfil tri-s Bond to the cavity floor showed the lowest bond strength for all groups. Clearfil tri-S Bond provided significantly lower bond strengths for all groups than Clearfil SE Bond and Single Bond (P < 0.05). Clearfil tri-S Bond showed smallest relative tensile bond strength for Cavity wall/Flat wall and Cavity floor/Flat floor compared with other group (P < 0.05).

Failure mode

The failure mode results are summarized in [Table 4]. For the flat wall group, almost all specimens showed interfacial failure, regardless of the adhesive system used. Clearfil SE Bond specimens exhibited cohesive failure in the dentin except three specimens of the flat floor group, while Single Bind specimens showed interfacial failure except for two specimens, and Clearfil tri-S Bond specimens showed interfacial failure except for one specimen. For the cavity wall group, Clearfil SE Bond specimens exhibited mixed failure except for two specimens, while all Single Bind specimens showed interfacial failure, and Clearfil tri-S Bond specimens showed interfacial failure, mixed failure, and cohesive failure. For the cavity floor group, Clearfil SE Bond specimens exhibited mixed failure except for two specimens, while all Single Bond specimens showed interfacial failure, and Clearfil tri-S Bond specimens exhibited interfacial failure except for two specimens.
Table 4: Failure mode

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   Discussion Top


All adhesive systems showed significantly higher bond strength to the flat wall than to the flat floor group. Half of the Clearfil SE Bond specimens showed cohesive failure in the dentin in the flat floor group, while almost all exhibited interfacial failure for the flat wall group. This demonstrated that bond strength was affected by the mechanical properties of the dentin; i.e., the intertubular dentin dimensions. Bond strength was significantly higher with parallel tubules than with perpendicular tubules. The intertubular dentin had smaller dimensions in the floor than in the walls because the dentinal tubules were oriented almost parallel to the wall dentin. The hybrid layer is reportedly thinner in areas with parallel tubules.[23] This confirmed that resin–dentin bond strength is not affected by the hybrid layer thickness, which supports the findings of previous studies.[25] Half of the Clearfil SE Bond specimens also exhibited mixed failure to the flat floor, whereas almost all Clearfil tri-S Bond specimens showed interfacial failure. In contrast, nearly all specimens exhibited interfacial failure in the flat wall group for both bonding systems. Resin–dentin bond tests are usually performed on occlusal flat dentin surfaces of the molars. In this study, interfacial failure was observed not only for low-bond-strength specimens but also for high-bond-strength specimens, likely because of the resin bonding to parallel tubules on the dentin surface.

The bond strength to the cavity wall group was significantly lower than that to the respective flat wall group regardless of the bonding system. The bond strength to the cavity floor group was significantly lower than that to the respective flat floor group regardless of the bonding system. Clearfil SE Bond showed significantly higher bond strength to the cavity floor than that of Single Bond and Clearfil tri-S Bond. This suggested that the resin composite bond strength to the cavity wall was affected by C-factor.[15],[16],[18] Moreover, Clearfil SE Bond showed lower relative bond strength of the cavity wall/flat wall than that of the cavity floor/flat floor. These are thought to be related to differences in adhesive potential and in the thickness of the adhesive layer. Clearfil SE Bond has high bond potential and the thickness of adhesive resin layer has been shown to range from 40 μm to 200 μm.[29] This thick adhesive resin layer of Clearfil SE Bond was thus likely to absorb some of the shrinkage stresses that occurred during light curing of the resin composites.[30]

The one-step self-etching system Clearfil tri-S Bond resulted in significantly lower bond strength than the two-step self-etching system Clearfil SE Bond and Single Bond for all groups. One-step self-etching systems are more hydrophilic and water absorbent than two-step self-etching systems.[31] Evaporating water from the one-step adhesives is difficult, and even if evaporation is successful, water rapidly diffuses back from the bonded dentin into the adhesive resin.[32] This water sorption plasticizes polymers and increases solubility, and decreases modulus of elasticity[31] and mechanical properties of the polymers.[33] Therefore, the one-step self-etching system Clearfil tri-S Bond showed lower bond strength.

Single Bond showed significantly lower bond strength than Clearfil SE Bond to the flat wall and cavity floor. The Single Bond adhesive system uses a phosphoric acid etching agent. In the case of an etching agent, the bonding material may not fully infiltrate the collagen fibril network of the demineralized dentin. Failure of the resin to adequately penetrate the collagen network in deeply etched dentin will produce a porous zone at the hybrid layer base,[34] resulting in a weak porous hybrid layer zone that is susceptible to degradation of the resin–dentin bond.[35],[36] Conversely, the self-etching primer system appears to allow the bonding resin to completely penetrate the demineralized dentin.[26],[27] Thus, the self-etching primer system provides a high-quality resin-impregnated layer that contributes to a strong bond between the bonding system and tooth wall. The hybrid layer of Single Bond is about 2–6 times thicker than that of Clearfil SE Bond.[29] The quality of a hybrid layer, rather than quantity, is considered more important for obtaining a good resin–dentin bond.[26],[27] These findings are in agreement with an earlier study showing that the bond strength between resin and dentin was independent of hybrid layer thickness.[25]

Acknowledgements

This work was supported by a Grant-in-Aid for Scientific Research (C) No. 16591907, No. 22592115 from the Japan Society for the Promotion of Science.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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