Microhardness and Microleakage Assessment of a Newly Formulated Hydrophilic Nano-Sealant and a Flowable Nano-Composite: An In Vitro Study

Dental caries is one of the most prevalent chronic conditions worldwide, affecting all ages and influenced by lifestyle, socioeconomic and environmental factors [1,2]. While many developed countries report declining caries rates, developing nations face increasing prevalence due to high sugar consumption and inadequate fluoride exposure [3]. Occlusal pits and fissures although comprising only 12% of the tooth surface-are highly susceptible, accounting for up to 85% of carious lesions because of their complex morphology and plaque-retentive nature [4,5].

Pit-and-fissure sealants are a proven preventive measure, reducing caries risk by up to ninefold when effectively retained [6,7]. Their success depends on adequate penetration into fissures, adaptation to enamel walls and resistance to microleakage [8,9]. Moisture contamination during placement is a major cause of early sealant failure, making hydrophilic resin-based materials particularly valuable in settings where isolation is challenging [10].

A well-penetrated fissure sealant, in addition to providing sealant retention, is desirable in order to decrease caries development in the deep crevice. Additionally, a thoroughly infiltrated sealant protects against shear stresses caused by masticatory movements [11]. Advances in nanotechnology have led to the development of nano-filled sealants and flowable composites with potential improvements in mechanical performance and sealing ability [12-15]. This in vitro study aimed to compare the microhardness and microleakage of a newly formulated hydrophilic nano-sealant, a commercial hydrophilic sealant and a formulated flowable nanocomposite to determine their suitability for preventing pit-and-fissure caries.

This in vitro study was conducted in the Department of Public Health Dentistry, Saveetha Dental College and Hospital, India.

Sample Collection

Sixty extracted human mandibular third molars free from caries, cracks, restorations or developmental defects were included. Teeth with deep pits and fissures requiring sealant application were selected, cleaned with a prophylactic brush and stored in 2% thymol until use.

Grouping and Materials

Teeth were randomly assigned to three groups (n = 20 each):

• Group I: Newly formulated hydrophilic nano-sealant (experimental formulation)
• Group II: UltraSeal XT Hydro sealant (Ultradent Products Inc., USA)
• Group III: Formulated flowable nano-composite (experimental formulation)

Application of Sealant

Occlusal surfaces were etched with 37% phosphoric acid gel for 20 sec, rinsed with water and dried according to manufacturer or formulation protocol. Materials were applied to fissures and light-cured for 20 sec with an LED curing unit (1000 mW/cm² output) (Figure 1).

Figure 1: Tooth prepared for 3 different groups for microhardness, the etched samples on prepared surfaces and the 3 sealants of Group I- Newly formulated hydrophilic Nano-sealant, Group II- Ultra seal XT Hydro sealant and Group III- Formulated flowable nano-composite on the surfaces of the tooth.

Thermocycling

All specimens underwent 1500 thermocycles between 5°C and 55°C, with a dwell time of 15 sec.

Microleakage Evaluation

Specimens were coated with nail varnish except for a 1 mm window around the restoration margin, immersed in 0.5% basic fuchsin for 24 h, rinsed, sectioned buccolingually and examined under a confocal laser scanning microscope. Dye penetration was scored using Overbo and Raadal’s criteria (Figure 2).

Figure 2: Microleakage images of Group I, II, III

Microhardness Evaluation

A low-speed diamond cutting blade was used to split the tooth into two pieces following mesiodistal sectioning. The cured occlusal surface was polished flat and tested with a Vickers hardness tester (Figure 3) Using a 200 g load for 20s. Three indentations per specimen were averaged. (Figure 4).

Figure 3: Micro Vickers Hardness Tester

Figure 4: Microhardness images of Group I, II, III

Statistical Analysis

Data were analyzed using SPSS v23. Non-parametric data were summarized as median (IQR). Group comparisons used the Kruskal–Walli’s test (microhardness) and Chi-square test (microleakage). Significance was set at p<0.05.

Microleakage Assessment

Each group's average microleakage scores are displayed in Table 1, Group I (median 0.5 (0–1.0)) had significantly lower microleakage than Group III (median 1.5 [1.0–2.0]) (p = 0.032). Group II showed intermediate scores (1.0 [0.5–1.5]) with no significant difference from either Group I or III.

Table 1: Chi-square test, *significant microleakage of Group I- Newly formulated hydrophilic Nano-sealant, Group II- Ultra seal XT Hydro sealant, Group III- Formulated flowable nano-composite, Overbo and Raadal score criteria

Microhardness assessment

The Kruskal Wallis Test revealed that Group II had a greater instantaneous mean microhardness value 15.1 (14.5–15.6) than Group I: 13.9 (13.3–14.4), Group III: 10.1 (9.6–10.8). Differences did not reach statistical significance (p = 0.061) (Table 2).

Table 2: Kruskal Wallis test, *not significant microhardness of Group I- Newly formulated hydrophilic Nano-sealant, Group II- Ultra seal XT Hydro sealant, Group III- Formulated flowable nano-composite, SD ‑ Standard deviation

Caracterisation

Primary preventative care is crucial in developing nations such as India, where children and adolescents account for over 40% of the population. Primary prevention removes the possibility of disease occurrence, making it the preferred method. It alleviates pain, suffering and incapacity, while also being widely accepted. For decades, pit and fissure sealants have been the most popular preventive tools. Preventive methods such as sealants may cost more than restoration materials like dental amalgam [16-18].

Microhardness and Microleakage

The newly formulated hydrophilic nano-sealant demonstrated significantly lower microleakage than the formulated flowable nano-composite, aligning with reports that hydrophilic resin sealants may perform better in fissure adaptation under moist conditions.

Microhardness differences among materials were not statistically significant, despite the commercial hydrophilic sealant showing the highest median value. Hardness is an indirect indicator of the degree of polymerization; lower values, as seen in the flowable composite, may suggest reduced wear resistance.

Sulimany et al. claims that they conducted a comparison between sealants that release fluoride and those that do not. After age, the VHN of the Embrace TM group increased significantly from 24.33±5.60 to 31.70±3.59 (p = 0.001), suggesting that the effect of aging differs depending on the kind of material, as per the interaction model between time factor and material type [19]. As per the findings of Gunasekaran et al. [20], a substantial difference (p<0.001) between the mean microhardness values of Group Aegis (4.40±0.46) and Group Ultraseal XT/Hydro (9.88±1.46).

Microleakage scores for Group I (Formulated Phosphorylated BisGMA sealant) were determined to be 30% for scores 0 and 1 and 20% for scores 2. Compared to groups II (Ultra seal XT Hydro sealant) and III (Formulated flowable nano-composite), which had mean scores of 0.86±0.25 and 0.63±0.45, respectively, group I (Formulated Phosphorylated BisGMA sealant) had a mean microleakage score of 1.3±1.16 higher. The thixotropic feature, sophisticated adhesive technology and hydrophilic nature of the sealant may be the cause. Some writers, like Babaji et al. [21] found no significant difference in microleakage between the flowable composite and fluoride-releasing pit and fissure sealants such as Tetric flow, Helioseal F and Enamel loc. In order to determine the effect of sealant viscosity and enamel or dentin bonding agent (DBA) on sealant microleakage, Mehrabkhani et al. [22] conducted the study and found there were no bonding subgroups and no discernible differences in the microleakage scores between the enamel and dentin bonding agents in either group. The low viscosity sealant showed less microleakage than the high viscosity sealant in both the DBA (P = 0.002) and NB (P = 0.041) categories. The results demonstrated that pit and fissure sealant microleakage was reduced by using a low viscosity sealant.

The experimental hydrophilic nano-sealant exhibited significantly lower microleakage than the experimental flowable nano-composite. Micro-hardness differences among tested materials were not statistically significant. Further research with larger samples, defined material composition and in vivo trials is necessary before clinical recommendations.

Limitations

Limitations inclues Material compositions for experimental formulations were undisclosed, limiting reproducibility. The study was underpowered for microhardness detection (p = 0.061 suggests possible type II error). In vitro conditions cannot fully replicate intraoral temperature, pH and mechanical stresses. Use of extracted third molars may not generalize to other tooth types.

Ethical Statement

Prior to its start, the study received ethical approval from the Saveetha Institute of Medical and Technical Sciences Scientific Review Board.

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