Effect of surface pretreatment on the shear bond strength of glass ionomer-based and giomer fissure sealants: an in vitro study

2.1 Study design

An in vitro experimental design was used in the present study to evaluate the SBS of different fissure sealant materials applied with various conditioning methods. A total of 100 bovine teeth were selected as substitutes for human enamel due to their comparable structural properties. The study protocol was reviewed by the Yeditepe University Faculty of Dentistry Scientific Review Board (#609) and the Yeditepe University Local Ethics Committee for Animal Experiments (YULECAE) during its meeting on 21 May 2024. Based on Article 8 of the “Regulation on the Working Procedures and Principles of Animal Experiments Ethics Committees”, which states that procedures using dead animal tissue, slaughterhouse materials, or fetal waste fall outside the scope of ethical review, it was determined that this research did not require formal ethical approval. This official assessment was confirmed and documented by YULECAE. The study was, therefore, conducted under the assurance of compliance with institutional and national ethical guidelines for in vitro research using non-living animal-derived specimens. The experimental procedures were conducted between 22 April and 30 May 2025. To minimize selection bias, the teeth were randomly allocated to the study groups.

2.2 Materials used in the study

In this experiment, four different commercially available fissure sealant materials were used. Fuji TRIAGE® (#250311 GC Corp., Tokyo, Japan) is a glass ionomer sealant and surface protectant. Riva Protect® (#1212217A, SDI Limited, Bayswater, Australia) is a low-viscosity glass-ionomer-based sealant. BeautiSealant® (#032383, Shofu Inc., Kyoto, Japan) is a fluoride-recharging pit-and-fissure sealant formulated with Surface Pre-Reacted Glass (S-PRG) technology. Helioseal F Plus® (#Z07J2X, Ivoclar, Zurich, ZH, Switzerland) is a light-curing, resin-based fissure sealant that possesses fluoride-releasing properties. In the study groups that required primer pretreatment, all applications were made according to the manufacturer’s instructions (Table 1).

2.3 Determination of study groups and sample size

A power analysis was conducted using G*Power 3.1 software (Heinrich-Heine-Universität Düsseldorf, Düsseldorf, NRW, Germany) to determine the minimum sample size based on an effect size of 0.44 derived from the results of similar previous in vitro studies [16, 17], using an alpha error probability of 0.05 and a power of 0.80. The analysis indicated that at least nine samples per group were required. However, to ensure robust statistical analysis and account for potential experimental variability, the sample size was increased to 10 specimens per group (Table 2).

2.4 Preparation of the specimens

2.4.1 Storage and preparation of the tooth surfaces

One hundred bovine incisors were used in the study, chosen for their similarity to human enamel. The extracted teeth were stored in distilled water, and before testing, the samples were thoroughly rinsed with distilled water to remove any residue.

The crowns of the teeth were separated from their roots with the help of a precision saw (BUEHLER IsoMet® 1000, Buehler, Lake Bluff, IL, USA) and a diamond separator (A7354 Medium Grain 200, 0.17 mm Acurata®) under water cooling (Fig. 1). The mesial, distal, and incisal edges of the teeth were also separated from the tooth using a diamond separator with water cooling. Samples for the bond strength study were placed in an acrylic resin block to facilitate handling during testing. The specimens were then randomly assigned to four main material groups (n = 30 for experimental groups, n = 10 for control). Afterwards, the buccal surface of the tooth was polished with 600-, 800-, and 1200-grit sandpaper (English Abrasives and Chemicals Ltd., London) under running water. The flattened enamel surface was cleaned with ultrasonic cleaning to remove organic debris.

Fig. 1.The separation of the teeth from their roots using a precision saw (BUEHLER IsoMet® 1000) and a diamond separator (A7354 Medium Grain 200, 0.17 mm Acurata®) under water cooling.

2.4.2 Application of fissure sealants to tooth surfaces

The specimens in the FTA (Fuji TRIAGE + Acid), RPA (Riva Protect + Acid), BSA (BeautiSealant + Acid), and HF (Helioseal F Plus (Control)) groups were pretreated with 37% phosphoric acid for 30 seconds and rinsed with water. To ensure standardization, the same acid etchant was used across all applicable groups. After air-drying, the corresponding sealant was applied using a silicon mold with a 1.5 mm radius and 2 mm height. The BSA and HF groups were photo-polymerized using a LED (light-emitting diode) curing unit (Bluephase® N G4, Ivoclar, Schaan, Liechtenstein) (1200 mW/cm²) for 20 seconds in accordance with the manufacturers’ instructions.

The specimens in the FTC (Fuji TRIAGE + Conditioner) group were pretreated with GC Cavity Conditioner (GC Corp. Japan) for 10 seconds and rinsed with water. In the RPC (Riva Protect + Conditioner) group, specimens were pretreated with SDI Riva Conditioner (SDI Limited Australia) for 10 seconds and rinsed with water. For the BSC (BeautiSealant + Conditioner) group, specimens were pretreated with BeautiSealant Primer (Shofu Inc., Japan) for 5 seconds and dried. All conditioning and priming steps were performed in strict adherence to the respective manufacturers’ instructions.

After air-drying, the inner lesion area, with a 1.5 mm radius, within the pretreated area was filled with the corresponding sealant using a 2 mm height silicon mold. The specimens in the BSC group were photo polymerized using a LED curing unit (Bluephase® N G4 Ivoclar Liechtenstein) (1200 mW/cm²) for 20 seconds. Fuji TRIAGE and Riva Protect are chemically cured (self-cure) glass ionomer materials; therefore, no light curing was applied to the FTN (Fuji TRIAGE (No pretreatment)) and RPN (Riva Protect (No pretreatment)) groups, following the manufacturers’ protocols.

In the FTN, RPN, and BSN (BeautiSealant (No pretreatment)) groups, no pretreatments were applied to the tooth surfaces. After preparation, the area of 1.5 mm radius was filled using the corresponding sealant using a 2 mm height silicon mold. The BSN group was photo-polymerized using a LED curing unit (Bluephase® N G4 Ivoclar Liechtenstein) (1200 mW/cm²) for 20 seconds.

The experimental design and distribution of the study groups are illustrated in the flowchart shown in Fig. 2.

Fig. 2.Flowchart of the experimental design and distribution of the study groups. FTA: Fuji TRIAGE + Acid; FTC: Fuji TRIAGE + Conditioner; FTN: Fuji TRIAGE (No pretreatment); RPA: Riva Protect + Acid; RPC: Riva Protect + Conditioner; RPN: Riva Protect (No pretreatment); BSA: BeautiSealant + Acid; BSC: BeautiSealant + Conditioner; BSN: BeautiSealant (No pretreatment); HF: Helioseal F Plus (Control); SBS: Shear Bond Strength; ISO: International Organization for Standardization.

2.5 Testing of shear bond strength

Prior to testing, all specimens were stored in distilled water at 37 °C for 24 hours to simulate the immediate oral environment. SBS testing was performed using a universal testing machine (Instron® 3345, Instron Corp., Norwood, MA, USA) equipped with a 500 N load cell. Each specimen was mounted in a custom jig to ensure stable positioning and precise force application. A chisel-shaped loading head was aligned perpendicular to the enamel-sealant interface, and a shear load was applied at a crosshead speed of 1 mm/min until failure occurred. To reduce potential bias, the operator performing the SBS testing was blinded to the specific study groups. The SBS was calculated by dividing this force by the bonded surface area (mm²), yielding values in megapascals (MPa). This method ensured standardized loading conditions and minimized variability across samples (Fig. 3).

Fig. 3.Shear bond strength (SBS) test setup performed using an Instron universal testing machine (Instron® 3345, Instron Corp., USA) equipped with a chisel-shaped loading head aligned perpendicular to the enamel-sealant interface.

2.6 Assessment of bonding failure categories

The mode of bonding failure was identified by the remaining sealant on the enamel surface, which was used to determine the bond failure location according to the Adhesive Remnant Index (ARI). The failure modes were categorized as “adhesive failure”, “cohesive failure”, or “mixed failure”. Adhesive failure was indicated by fractures at the contact between the enamel and the bonding agent or sealant. Cohesive failure was indicated when failure occurred primarily within the sealant. Mixed failure was observed when a portion of the sealant adhered to the enamel. Bonding failure categories were classified through examination under 25× magnification using a ZEISS OPMI® pico S100 microscope (Fig. 4).

Fig. 4.Representative images of bonding failure modes captured with a Zeiss OPMI Pico S100 microscope at magnification of 25×. (A) Cohesive failure (>80% of remaining sealant); (B) Mixed failure (20–80% of the remaining sealant); and (C) Adhesive Failure (<20% of remaining sealant).

2.7 Statistical analysis

The normality of the data was assessed using the Shapiro-Wilk test. One-way analysis of variance (ANOVA) and Bonferroni post-hoc tests were used for group comparisons of SBS (MPa) values. The Fisher exact and chi-squared tests were used to compare bonding failure categories. Statistical significance was defined as p < 0.05, with a 95% confidence interval (CI) reported.

3.1 Results of the shear bond strength tests

The mean and standard deviation of SBS values in megapascals (MPa) obtained in the subgroups according to the pretreatment methods, and the results of the intragroup and intergroup comparisons are given in Table 3. According to the one-way ANOVA test, the differences in SBS values across all pretreatment methods were statistically significant (p < 0.001). According to the Bonferroni post-hoc test, the comparison of the subgroups within the phosphoric acid application showed that the HF group values were significantly higher than those of the FTA, RPA, and BSA groups. It was also determined that the BSA values were higher than those of the FTA and RPA groups. The BSC subgroup showed significantly higher values than the FTC and RPC subgroups, which belonged to their respective conditioners. Finally, the comparison between no pretreatment specimens showed that the BSN subgroup values were significantly higher than those of the RPN and FTN subgroups.

Table 4 presents the mean and standard deviation of SBS values (MPa) for the subgroups by material group, along with the results of intragroup and intergroup comparisons. According to the one-way ANOVA test, the differences in SBS values across all material groups were statistically significant (p < 0.001). The intergroup comparisons with the Bonferroni post-hoc test showed that the FTA and FTC subgroups had significantly higher values than the FTN subgroup in the Fuji TRIAGE (GC®) material group. Similarly, in the Riva Protect (SDI®) material group, the RPA subgroup exhibited significantly higher values than the RPC and RPN subgroups, and the RPC subgroup also had higher values than the RPN subgroup. Also, among BeautiSealant (Shofu®) subgroups, the BSA subgroup showed significantly higher SBS than the BSC and BSN subgroups, and the BSC subgroup values were higher than those of the BSN subgroup.

3.2 Results of bonding failure categories

A statistically significant difference in the number and percentage of failures was found between subgroups in the no pretreatment group; in other words, failure types were not similar across all subgroups (p < 0.05). It was observed that, whereas the percentage of adhesive failures was highest, mixed failures were identified at the lowest level in the RPN group (52.9%, 7.7%, respectively) (Table 5).

A statistically significant difference was found between the number and percentage of failures of the subgroups in the Riva Protect (SDI®) group. In other words, failure types were not similar across all subgroups (p < 0.05). It was determined that 56.3% of adhesive fractures occurred in the RPN group, while 61.5% of mixed fractures and 100% of cohesive fractures were observed in the RPA group (Table 6).

4.1 Effect of surface conditioning and material type

The methodology of this study was carefully designed to evaluate the SBS of glass ionomer-based and giomer fissure sealants applied with various surface conditioning methods (phosphoric acid etching, polyacrylic acid conditioner, and no preparation) and to compare the findings with those of conventional resin-based sealants applied after phosphoric acid etching. This approach was selected in response to increasing interest in the clinical performance of newer bioactive sealant materials, particularly those containing surface-pre-reacted glass-ionomer (S-PRG) fillers. For example, Ogawa et al. [9] (2021) demonstrated that S-PRG-containing sealants significantly inhibited enamel demineralization around the sealant margins, highlighting the potential of these materials not only to provide physical sealing, but also to enhance preventive effects through ion release.

Furthermore, recent systematic reviews and clinical trials have underscored the versatility of high-viscosity glass ionomer cements in challenging clinical scenarios. Specifically, their hydrophilic nature renders them superior in treating partially erupted molars where effective moisture control is often unachievable [17]. Moreover, despite established concerns about retention rates relative to resin-based alternatives, contemporary studies suggest that the sustained fluoride release and chemical adhesion of GICs provide a caries-preventive effect comparable to that of resin-based alternatives [18].

The relatively higher SBS values observed for the giomer-based sealant (BeautiSealant), particularly when combined with phosphoric acid etching (BSA), underscore the evolving role of bioactive materials. Although phosphoric acid etching has traditionally been associated with resin-based sealants, our results indicate that it significantly maximizes the adhesion of giomer-based materials compared with their specific self-etching primers. This aligns with findings by Poggio et al. [19] (2021), who reported that phosphoric acid enhances micromechanical interlocking even in materials designed for chemical bonding.

Regarding glass ionomer sealants, our findings suggest that phosphoric acid may offer superior surface adhesion compared with conventional polyacrylic acid conditioning. This aligns with previous findings by Di Nicoló et al. [14] (2007) and Sidhu & Nicholson [20] (2014), who emphasized that phosphoric acid pretreatment facilitates better smear layer removal and improves micromechanical bonding. However, it is important to acknowledge a potential drawback: aggressive etching of glass ionomer cements may theoretically interfere with their chemical bonding mechanism by demineralizing the hydroxyapatite necessary for ionic exchange. Nevertheless, in the present study, the gain in micromechanical retention provided by phosphoric acid appeared to outweigh the potential loss of chemical adhesion.

4.2 Clinical implications

From a clinical standpoint, the comparison of bond strength values provides guidance for material selection. The findings of the SBS test indicated that the HF, BSA, and BSC groups demonstrated bond strength values generally considered acceptable for clinical use. These results are consistent with the minimum threshold of 6–8 MPa historically established by Reynolds (1975) [21]. While ISO standards define the testing methodology rather than specific performance thresholds, the “acceptability” of these values is supported by their alignment with effective enamel adhesion ranges reported in current literature. Although the bonding values observed in the remaining experimental groups were lower than these thresholds, they should be interpreted in the context of the geometric discrepancies between the standardized test protocols and the clinical indications for fissure sealants.

Consequently, the resin-based control group demonstrated the highest overall SBS, confirming that conventional etch-and-rinse systems remain the gold standard when optimal isolation is achieved. However, the giomer sealant presented a viable alternative with superior bonding performance compared with GICs. The findings suggest that when using giomer sealants, clinicians should prefer phosphoric acid etching over self-etching primers to maximize retention. However, glass ionomer sealants demonstrated lower bond strengths, particularly in no-pretreatment subgroups. This mirrors research by Prabhakar et al. [22] (2016) and Gunasekaran et al. [23] (2024), supporting the strategic use of GIC in moisture-compromised clinical environments where chemical bonding and fluoride release are prioritized over mechanical retention.

4.3 Bonding failure analysis

The occurrence of cohesive and mixed failure modes across several groups has clinical significance. Adhesive failures were predominant in groups with lower bond strengths, particularly in the glass ionomer groups without pretreatment, indicating that the interface was the weakest link. Conversely, cohesive and mixed failures were more frequent in groups exhibiting higher SBS values. These patterns imply that the bond interface is sufficiently strong to resist immediate detachment. Clinically, this suggests that even if partial debonding occurs under occlusal stress, residual material may remain within the fissures, potentially continuing to provide a physical barrier or bioactive protection against cariogenic challenges.

4.4 Study limitations

The present study has certain limitations that should be considered. First, the use of flattened enamel surfaces required for standardized shear bond strength testing (ISO 29022) does not reflect the complex geometry of natural fissures or the penetration capability of the sealants. The flat-surface model may have disadvantaged the GIC groups by excluding the penetration and locking factors that are critical to their performance in vivo [12, 16].

Second, this study evaluated immediate bond strength without subjecting the specimens to thermal cycling or long-term water ageing. Therefore, the findings represent immediate bond strength data. Future studies incorporating artificial aging are necessary to evaluate the long-term durability of the bond interface against hydrolytic degradation.

In this study, bovine incisors were selected as the substitute due to their availability and histochemical similarity to human enamel [24]. While this facilitates standardization and minimizes variability, future in vivo studies and long-term clinical trials are warranted to fully validate the clinical longevity of these materials under dynamic oral conditions.