2024 Volume 24 Issue 2 Pages 13-17
Purpose: The purpose was to investigate the effect of simulated intra-oral temperature and humidity variations on dentin bonding performance of resin luting agents.
Methods: A self-cure resin luting agent (Super-Bond C&B, SB) and dual cure type resin luting agents (Panavia V5, PV; RelyX Ultimate, RU; Estecem II, E2) were used. The PV, RU, and E2 groups were divided into two sub-groups; light cured (LC) and self-cured (CC). Specimen preparation was performed at room temperature (LAB), supragingival finish line (SUP), and subgingival finish line (SUB) simulation occurred in a thermostatic device (31 ± 2℃/93 ± 3%). The SUB specimens were stored in water 10 s after bonding. Shear bond strength (SBS) values were measured and analyzed using Dunn's test with Bonferroni correction (P = 0.05).
Results: The bonding performance of SB was stable under all the environmental conditions. In contrast, the SBSs of PV, RU, and E2 significantly decreased in SUP and SUB (P < 0.05). The SBSs of PV, RU, and E2 were reduced in CC (except for PV/LAB).
Conclusion: The bonding performance under the three environmental conditions were resin luting agent dependent. SB provided the highest SBS regardless of the bonding environments. Light irradiation strongly influenced the bonding performance of the dual cure resin luting agents.
The bonding performance of resin luting agents has improved since their introduction to clinical dentistry, owing to continual technological innovations. For indirect restorations, dentists are no longer required to include mechanical retention form in preparations as bonding materials have greatly improved the retention of restorations. This has resulted in the ability to preserve as much intact tooth tissue as possible [1].
Generally, laboratory-based bond tests are routinely performed at room temperature and 50% relative humidity using extracted teeth. To date, little information has been reported about the bonding performance of resin luting agents to dentin under simulated intra-oral temperature/humidity conditions [2,3,4,5]. The clinical factors affecting dentin bonding performance, such as saliva, blood, dental calculus, and biofilm should be eliminated or reduced where possible such that bonding procedures are able to ensure clinical success of bonding restorations. Intra-oral temperature and humidity is considerably higher than that typically used in laboratory tests. Variations in temperature and humidity have been shown to impact bonding performance [2,4,5,6,7,8].
In the clinical situation, bonding often cannot be performed under ideal conditions and differs greatly from the conditions generally used for testing in the industrial evaluation environment. The bonding between dentin and restorative materials in the oral cavity can be very challenging, particularly for restorations in the molar region.
Therefore, an intra-oral environment replicating temperature and humidity was simulated using a thermostatic box in this study. The bonding procedures were performed in this environment to investigate the effect of simulated intra-oral temperature and humidity variations on dentin bonding performance of resin luting agents. The null hypothesis was that dentin bonding performance of resin luting agents was not influenced by variations in temperature and humidity. Implementing moisture control measures is therefore necessary when using such dual-cure resin luting agents for the luting agentation of posterior restorations.
Four commercially available resin luting agents were used in this study (Table 1, 2). A self-cure resin luting agent, Super-Bond C&B (SB, Sun Medical, Moriyama, Japan) is activated with the catalyst, tri-n-butyl borane (TBB, Sun Medical). Dual cure type resin luting agents, Panavia V5 (PV, Kuraray Noritake Dental, Tokyo, Japan) , RelyX Ultimate (RU, 3M-ESPE, St. Paul, MN, USA) and Estecem II (E2, Tokuyama Dental, Tsukuba, Japan) were used. For PV and E2, the associated primers for each resin luting agent were used according to the manufacturer's instructions. For RU, a one-step dentin bonding agent, Scotchbond Universal (3M-ESPE) was applied according to the manufacturer's instructions without light curing.
Specimen preparation for shear bond strength testAn illustration of the specimen preparation protocol for the shear bond strength test is shown in Fig. 1. Bovine incisors were cut at the enamel-cementum junction using a diamond disk (Isomet, Buehler, Lake Bluff, IL, USA) to obtain the crown portion. The pulp tissue was then removed and the pulp chamber was closed with dental multi-purpose wax (Utility Wax, GC, Tokyo, Japan). The crown portion of the bovine tooth was placed in a plastic mold (25 mm diameter, 25 mm height) and embedded with a self-curing acrylic resin (Provista, Sun Medical). After curing, the labial enamel surface of bovine incisor was removed using an automatic grinder (Ecomet 3000, Buehler) under a stream of water to expose the dentin surface, which was then ground using #400-grit SiC abrasive paper (Fujistar, Okegawa, Japan) to prepare a standardized bonding surface. The bonding area was demarcated using a composite resin (CR) rod (2.3 mm in diameter) according to ISO TS16506 [9]. The CR rod was prepared by placing a resin composite (Clearfil AP-X, shade A2, Kuraray Noritake Dental) into a Teflon mold (2.3 mm in diameter, Togawa Mold & Die, Hino-Gamou, Japan), which was then light-cured with a light curing unit (DC BlueLEX Plus 1,000 mW/cm2, Yoshida, Tokyo, Japan), after which the surface was ground with #600-grit SiC abrasive paper (Fujistar).
| Product | Primer/Bonding agent | Composition | Lot | Resin luting agent | Composition | Lot | Abbreviation | |
|---|---|---|---|---|---|---|---|---|
| Common products | Super-Bond PZ Primer (Silane coupling agent) | Liquid A | MMA, phosphate monomer, others | SR1 | — | — | — | PZ |
| Liquid B | MMA, silane compound, others | SR1 | ||||||
| Super-Bond (Sun Medical, Moriyama, Japan) |
Teeth Primer | methacrylate (4-META), water, acetone, others | RM1F | Catalyst V | partially oxydized tri-n-butylborane, others | SM12 | SB | |
| Quick Monomer | MMA, 4-META, others | SM2 | ||||||
| Teeth Color (powder) | PMMA, others | SM2 | ||||||
| Panavia V5 (Kuraray Noritake Dental, Tokyo, Japan) | Tooth Primer | MDP, HEMA, hydrophilic aliphatic dimethacrylate, accelerators, water | 2S0015 | Paste (Universal) | Bis-GMA, TEGDMA, hydrophobic aromatic dimethacrylate, hydrophilic aliphatic dimethacrylate, initiators, accelerators, silanated barium glass filler, silanated fluoroalminosilicate glass filler, colloidal silica, silanated alminium oxide fill er, dl-camphorquinone, pigments | 2K0072 | PV | |
| RelyX Ultimate (3M-ESPE, St. Paul, MN, USA) | Scotchbond Universal | HEMA, Bis-GMA, water, ethanol, MDP, camphorquinone, silica fillers, stabilizers, other additives | 666963 | Paste (A1) | Bis-GMA, methacrylate monomers, silica, zirconia, inorganic fillers, camphorquinone, photoinitiators, stabilizers, various pigments | 3911226 | RU | |
| Estecem Ⅱ (Tokuyama Dental, Tsukuba, Japan) | Bondmer Lightless | Liquid A | acetone, phosphate monomer, Bis-GMA, TEGDMA, HEMA, MTU-6, others | 010 | Paste (Universal) | Bis-GMA, TEGDMA, Bis-MPEPP, silica-zirconia filler, peroxide, camphorquinone, others | H0157 | E2 |
| Liquid B | acetone, isopropanol, water, borate catalyst, peroxide, silane, others | 010 | ||||||
| Group | Tooth surface treatment material | Tooth surface treatment method |
|---|---|---|
| PZ | Super-Bond PZ Primer (A/B) | mix A and B solutions → apply → medium air drying using a three-way syringe |
| SB | Teeth Primer | apply for 20 s → medium air dry using a three-way syringe |
| PV | Tooth Primer | apply for 20 s → medium air dry using a three-way syringe |
| RU | Scotchbond Universal | apply for 20 s → gentle air drying for 5 s using a three-way syringe |
| E2 | Bondmer Lightless (A/B) | mix A and B solutions → apply → dry with medium pressure air using a three-way syringe |
| Group | Temperature (℃) | Humidity room temperature condition (LAB) (%) | Water injection after 10 s |
|---|---|---|---|
| Room temperature conditions group (LAB) | 23 ± 2 | 50 ± 3 | — |
| Supragingival finish line assumption group (SUP) | 31 ± 2 | 93 ± 3 | — |
| Subgingival finish line assumption group (SUB) | 31 ± 2 | 93 ± 3 | yes |
Specimen preparation was performed under the following three conditions: room temperature (LAB), supragingival finish line (SUP), and subgingival finish line (SUB) (Table 3) [10]. For the LAB group, specimen preparation was performed using laboratory temperature/humidity condition (23 ± 2℃/50 ± 3%), which were confirmed using a temperature/humidity wireless probe (Saveris H2D, Matsuura Seisakusho, Tokyo, Japan). Regarding the SUP and SUB groups, specimen preparation was performed in a thermostatic device (MicroNIX, Kyoto, Japan), in which the intra-oral conditions were simulated to mimic the oral in the region of molar teeth (Fig. 2). The intra-oral temperature/humidity conditions (31 ± 2℃/93 ± 3%) were maintained using a humidifier (SH-OR30 WT, Topland, Shimada, Japan) and a thermo-hygrometer (AS-5648A, A&D, Tokyo, Japan) in the thermostatic device. Each resin luting agent was used in the thermostatic device according to the manufacturer’s instructions. For the CR rods, the ground surfaces were treated with a silane coupling agent (Super-Bond PZ Primer, Sun Medical) under the LAB condition, and then used in one of the three temperature/humidity conditions immediately before the bonding procedure. The CR rods were placed on the dentin surface with the resin luting agent. A 5 N weight was loaded on the CR rod and then the excess resin luting agent was carefully removed from the periphery of the rod. For the dual cure resin luting agents, the groups were further divided into two sub-groups; light cured (LC) and self-cured (CC). For the LC group, the resin luting agent was light cured with a light emitting diode (LED) light curing unit (DC BlueLEX Plus 1,000 mW/cm2, Yoshida) from two directions for 10 s each (total of 20 s). After fabrication of the bonded specimens, the specimens of the LAB and SUP groups were left for 30 min in each temperature/humidity condition and then stored in water. For the specimens of the SUB group, they were stored in water 10 s after the bonding operation was completed. All the specimens were stored in water at 37℃ for 24 h, and shear bond strength testing was performed using a universal testing machine (AG-IS, Shimadzu, Kyoto, Japan) at a crosshead speed of 1.0 mm/min. Number of the specimens was nine for each groups.
Same large and small letters indicate a significant difference was determined (Dunn's test with Bonferroni correction; P < 0.05).
| Group | CC / LC | LAB | SUP | SUB |
|---|---|---|---|---|
| SB | CC | 0 / 9 | 0 / 9 | 0 / 9 |
| PV | CC | 0 / 9 | 0 / 9 | 1 / 9 |
| LC | 0 / 9 | 1 / 9 | 0 / 9 | |
| RU | CC | 9 / 9 | 7 / 9 | 4 / 9 |
| LC | 1 / 9 | 0 / 9 | 0 / 9 | |
| E2 | CC | 0 / 9 | 2 / 9 | 0 / 9 |
| LC | 1 / 9 | 0 / 9 | 0 / 9 |
| Group | CC / LC | LAB A / M / C |
SUP A / M / C |
SUB A / M / C |
|---|---|---|---|---|
| SB | CC | 15 / 37 / 48 | 21 / 62 / 17 | 7 / 53 / 40 |
| PV | CC | 9 / 32 / 59 | 20 / 54 / 26 | 10 / 74 / 16 |
| LC | 17 / 47 / 37 | 17 / 64 / 19 | 15 / 70 / 15 | |
| RU | CC | 22 / 26 / 52 | 21 / 35 / 44 | 11 / 76 / 13 |
| LC | 13 / 70 / 17 | 11 / 80 / 9 | 10 / 82 / 8 | |
| E2 | CC | 13 / 68 / 19 | 13 / 74 / 13 | 8 / 80 / 12 |
| LC | 9 / 81 / 10 | 15 / 75 / 10 | 19 / 74 / 7 |
A: bonding failure; M: mixed failure including A and C; C: cohesive failure in resin luting agent
The fracture modes of the specimens after shear bond testing were examined using a digital microscope (VHX-900, Keyence, Kyoto, Japan) at ×50 magnification. The fracture morphologies were categorized into one of three types: bonding failure (A), cohesive failure in resin luting agent (C), and mixed failure including A and C (M).
StatisticsThe shear bond strength was obtained by calculating the mean values using the specimens that did not fail prior to testing. The shear bond strength was analyzed with Shapiro-Wilk normality test for each experimental group. Dunn's test with Bonferroni correction was performed in multiple comparisons for each experimental group.
Failure of specimens occurred prior to the shear bond strength test in some groups (pre-test failure) in this study. The pre-test failure rate was calculated by counting these fractured specimens.
The results of the shear bond strength test are shown in Fig. 3. The pre-test failure rates for the test group are listed in Table 4.
From the results of the shear bond strength testing for each resin luting agent, SB did not exhibit any significant differences in the bond strength among LAB, SUP, and SUB groups, providing consistently high dentin bond strengths. For PV, RU, and E2, the bond strengths significantly decreased in the SUP and SUB groups compared to the LAB group (P < 0.05). PV, RU, and E2 exhibited significantly lower bond strengths than SB in the SUP and SUB groups (P < 0.05).
For PV, the bond strength was not different between LC and CC in the LAB group, while those for CC significantly decreased in the SUP and SUB groups compared with LC (P < 0.05). For RU, pre-test failures occurred frequently in CC, resulting in the inability to measure the shear bond strength in the case of CC (Table 4). In the LC groups for PV, RU, and E2, there were no significant differences in bond strength among the LAB, SUP, and SUB groups (P > 0.05). For E2, there were no significant differences in shear bond strength with the presence/absence of light curing under the three different temperature/humidity conditions (P > 0.05).
Non-normal distribution of the shear bond strength value was indicated in the following four groups; PV/SUP/CC, RU/SUP/CC, RU/SUB/CC and RU/SUB/LC (P < 0.05).
Fracture mode analysisTable 5 shows the results of the fracture mode analysis of the debonded specimens after bond strength testing. For SB, mixed failure (M) was 37% in the LAB condition, and the rates increased to 62% (SUP) and 53% (SUB), respectively, while cohesive failure in resin luting agent decreased. For PV, the tendency of change of the fracture mode was same as described in SB. The tendency of decrease of the rate of cohesive failure in resin luting agent did not differ between LC and CC. For RU, mixed failures were more frequently observed in LC than in CC. For E2, the majority fractures were mixed failures regardless of the presence/absence of light polymerization.
Several studies reported that the humidity in the oral cavity can be over 90% during exhalation [3,10,11]. Other studies reported that the bond strength to dentin decreases when the environmental humidity reaches high levels [2,3,4,6,12].
In this study, the impact of the intra-oral environment on the bond strength of the four different resin luting agents to dentin was investigated by simulating the intra-oral environments using a thermostatic device. The results showed that the type of resin luting agent and the environment during the bonding procedures could strongly influence the adhesion. The bonding performance of SB to dentin was stable under all the environmental conditions used in this study. SB is a methyl methacrylate (MMA)-based self-cure type resin luting agent, and its polymerization catalyst, TBB, accelerates the polymerization behavior in the presence of moisture [13]. In contrast, the dual-cure resin luting agents, PV, RU, and E2, showed a decrease in the bond strengths when the bonding environment simulated the intra-oral conditions that may be observed in the molar region of the oral cavity (groups SUP and SUB). The current results demonstrated that the dual-cure type resin luting agents were affected by a humid environment, suggesting the need for measures to prevent a moist atmosphere during the bonding procedures in the clinical situation.
This study also demonstrated that the bonding performance of dual-cure resin luting agents to dentin was reduced without using light polymerization of the resin luting agent. These results are consistent with a previous study [14].
The bond strength of PV significantly decreased in the SUP and SUB groups compared to the LAB group, regardless of the presence/absence of the light curing. This was believed to be because the high-humidity environment negatively influenced the adhesion and intimate adaptation at the interface between the dentin and the primer/resin luting agent and/or the resin luting agent itself. However, PV exhibited a relatively high bond strength even when allowed to self-cure (group CC) [15,16].
Regarding RU, pre-test failures in the test specimens in CC were frequently observed in all the environmental conditions, indicating that light curing seems necessary to obtain reliable bonding to dentin. In addition, the bond strength of RU even with light polymerization significantly decreased when the humidity of the environment increased. This is probably due to an effect on the polymerization and wetting at the interfaces between dentin and the bonding (Scotchbond Universal)/the resin luting agent, and/or that of the resin luting agent itself in the humid environments [17].
The bond strength of E2 did not show any significant differences between LC and CC, suggesting that the polymerization initiator contained in E2 might contribute to the dentin bonding performance [18]. However, the bond strength of E2 exhibited a significant decrease in the high humidity environment of the SUP and SUB groups for both LC and CC. The bond strength of E2 in the LAB/LC group was lower than those of SB, PV, and RU.
The dentin bond strength of the dual-cure resin luting agents decreased in the high-humidity environment. Implementing moisture control measures is therefore necessary when using such dual-cure resin luting agents for the cementation of posterior restorations. Additionally, the results indicated that the light curing exhibited a strong influence on the dentin adhesion for the dual-cure resin luting agents. However, metal prostheses do not allow light transmission to the bonding interface. Tooth colored restoration materials, in general, possess some degree of translucency, however, zirconia-based prostheses have poor light transmittance. It was reported that the light transmission intensity decreases according to the increase of thickness of the restorative material [19]. The current results indicated that light irradiation is indispensable to improve the overall dentin bonding performance. However, a resin luting agent with a capability to provide stable and high bonding performance without light curing should be selected for clinical application.
The environmental conditions with high humidity to replicate what occurs in the oral cavity were simulated using a thermostatic device in this study. However, further investigations are needed to measure the intra-oral high-humidity environment clinically and then to evaluate the effect of the various moisture control measures used in clinical settings may influence bonding restoration placement and adhesion.
From the current results of this study, the following conclusions were drawn. A humid environment in the intra-oral environment was simulated using a thermo-hydrostat device. The bonding performance under the three environmental conditions were resin luting agent dependent. The dentin bond strength of SB provided high bond strengths regardless of the bonding environment. Light irradiation strongly influenced the bonding performance of the dual-cure type resin luting agents.
Moisture control measures are necessary when using dual-cure resin luting agents for the cementation of posterior restorations. Also, light curing exhibits a strong influence on dentin adhesion for the dual-cure resin luting agents.
Bis-GMA: bisphenol A-glycidyl methacrylate; Bis-MPEPP: 2,2'-bis(4-methacryloxy polyethoxyphenyl)propane; CC: self-cured; CR: composite resin; E2: Estecem II; EDGMA: ethylene glycol dimethacrylate; HEMA: 2-hydroxyethyl methacrylate; LAB: room temperature; LC: light cured; LED: light emitting diode; M: mixed failure; MDP: 10-methacryloyloxydecyl dihydrogen phosphate; MMA: methyl methacrylate; MTU-6: 6-methacryloyloxyhexyl 2-thiouracil-5-carboxylate; PMMA: poly(methyl methacrylate); PV: Panavia V5; RU: RelyX Ultimate; SB: Super-Bond C&B; SBS: shear bond strength; SUB: subgingival finish line; SUP: supragingival finish line; TBB: tri-n-butyl borane; TEGDMA: triethyleneglycol dimethacrylate; U: universal
Not applicable
Not applicable
This study was partly supported by a Grant-in-Aid for the Japan Society for the Promotion of Science (21K09924).
TW: conceptualization, investigation, methodology, data curation, formal analysis, visualization, and writing; HT: conceptualization, methodology, formal analysis, writing, review, editing, and supervision; MI: methodology, formal analysis, review, editing, and supervision; MB: formal analysis, writing, review and editing; TN: conceptualization, methodology, formal analysis, writing, review, editing, and supervision. All authors read and approved the final version of the manuscript.
1) HT*: hanemi@dent.asahi-u.ac.jp, https://orcid.org/0009-0000-4263-3621
1) TW: tokainext@me.com, https://orcid.org/0009-0005-6302-3837
2) MI: ikeda.csoe@tmd.ac.jp, https://orcid.org/0000-0003-2214-4980
3) MB: mfburr58@hku.hk, https://orcid.org/0000-0001-6419-6530
All data generated or analyzed during the current study are available from the corresponding author on reasonable request.
