Objective. This study evaluated the marginal adaptation under cyclic loading of bulk-fill composite specimens prepared with a nanotheline gradient interlayer treatment. Methods. 78 specimens were divided into treated and untreated groups and stored in distilled water at 37 °C for 90 days prior to testing. Measurements were performed with a universal testing machine at a crosshead speed of 0.5 mm/min. Results. The treated group showed a 41% improvement relative to control (p < 0.02). Scanning electron microscopy revealed a more uniform interfacial layer in the treated specimens. Conclusions. Within the limitations of this in vitro study (2021), the nanotheline gradient interlayer treatment improved the marginal adaptation under cyclic loading of bulk-fill composite. Clinical significance. These findings may inform selection criteria for restorative materials in load-bearing posterior applications.
1. Introduction. Contemporary restorative dentistry increasingly relies on bulk-fill composite for indirect restorations. Despite widespread adoption, the long-term behaviour of the material-substrate interface remains incompletely characterised, particularly under the thermal and mechanical cycling that approximates intraoral service conditions.
2. Materials and methods. Specimens were sectioned to 12 × 2 × 2 mm and wet-polished through 1200-grit silicon carbide paper. The nanotheline gradient interlayer was applied in a single coat and allowed to dwell for 60 s before gentle air-thinning. Control specimens received no surface treatment. All groups were thermocycled for 10,000 cycles between 5 °C and 55 °C with a 30 s dwell time.
3. Results. Mean values differed significantly between groups by two-way ANOVA followed by Tukey post-hoc comparison. Weibull analysis indicated a higher characteristic strength in the treated group, with a modulus consistent with reduced flaw-population variability. No specimens failed prematurely during thermocycling.
4. Discussion. The improvement observed here is consistent with the hypothesis that the nanotheline gradient interlayer forms a compliant interlayer that redistributes stress away from the adhesive interface. This mechanism has been proposed for related silane chemistries, though direct spectroscopic confirmation was outside the scope of the present work.
5. Limitations. This was an in vitro investigation and does not account for salivary enzymatic degradation, dietary variation, or parafunctional loading. Randomised clinical evaluation would be required before the findings could inform practice.
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