Effect of preheating nano‑hybrid and bulk‑fill composites with warm airstream on their microtensile bond strength to dentin

Effect of preheating nano‑hybrid and bulk‑fill
composites with warm airstream on their microtensile
bond strength to dentin

1. 1 Effect of preheating nano‑hybrid and bulk‑fill composites with warm airstream on their microtensile bond strength to dentin Journal of Conservative Dentistry and Endodontics, Nov 2023

2. Journal of Conservative Dentistry and Endodontics, Nov 2023 26:702-8. 2

3. Content 3

4. Introduction The durability of composite restorations depends on their bond strength to tooth structures. DRAWBACKS 4

5. Degree of conversion (DC) is also one of the important factor related to the properties of the composite resin. Increasing the degree of conversion (DC) without adversely affecting the marginal adaptation is highly important to optimize the properties of composite resins. 5

6. The majority of available studies on composite preheating have an in vitro design and utilize a warmer for preheating the composite resins. However, the time lapse between the removal of the composite from the warmer and its application in the cavity can affect the results. To counteract this temperature loss, this study evaluated an alternative strategy, using a warm airstream from a modified hair dryer after applying the resin material into the cavity, to keep the composite warmth during application until light-curing in order to increase restoration longevity. 6

7. Aim This study assessed the effect of preheating nano‑hybrid and bulk‑fill composites with warm airstream on their microtensile bond strength (MTBS) to dentin. 7

8. Material and methods 42 extracted premolars were selected Subgroup 1: Preheating of composite to 50°C in a commercial composite warmer Subgroup 2: Preheating of composite with warm airstream by using a modified hair dryer Subgroup 3: No preheating (room temperature composite) Group 1: Bonding to EverX Posterior bulk-fill composite Group 2: Bonding to Grandio nano-hybrid posterior composite Subgroup 1: Preheating of composite to 50°C in a commercial composite warmer Subgroup 2: Preheating of composite with warm airstream by using a modified hair dryer Subgroup 3: No preheating (room temperature composite) O cclusal surface of the teeth was reduced by 4 mm to ensure no enamel remaining 8

9. Material and methods 9

10. 10

11. 11

12. Schematic illustration of the acquisition of specimens for micro-tensile bond strength test

13. Specimen failure analysis 13

14. The Shapiro–Wilk test was applied to analyse the normality of data distribution, which showed normal distribution of data. One-way ANOVA followed by the Tukey’s test was used to analyse the effect of preheating on MTBS. The Fisher’s exact test was used to compare the frequency of different modes of failure. The level of statistical significance was set at 0.05 Statistical analysis 14

15. Result 15

16. Result 16

17. Stereomicroscopic assessment 17

18. SEM analysis 18

19. The study examined the effect of preheating two composite types (nano-hybrid Grandio and bulk-fill EverX ) on microtensile bond strength (MTBS) to dentin. Two preheating methods were used: a warm airstream and a conventional warmer. Discussion 19

20. Impact of preheating on Degree of Conversion (DC) : Preheating increases monomer mobility and vibration, improving cross-linking and DC. Higher DC strengthens the composite, improves mechanical properties, and reduces microleakage . Impact of preheating on Marginal Adaptation : Preheating reduces composite viscosity and improves its flowability, leading to better marginal adaptation in cavity preparations. However, excessive heating may increase polymerization shrinkage, which can lead to marginal gaps and compromised bond strength. 20

21. Grandio GC Ever X posteior Increment fill composite Bulk fill composite Nano hybrid composite Fibre reinforced composite Comparatively lower MTBS Comparatively Higher MTBS 87 wt % filler content 74 wt % filler content (lower filler content) Comparatively higher percentage of Bis-GMA Lower percentage of Bis-GMA Influence of Composite Type : EverX (bulk-fill composite) had higher MTBS than Grandio (increment-fill composite), especially in the warmer group. Bulk-fill composites, such as EverX , contain fewer free monomers after curing, contributing to better bond strength. 21

22. Challenges with Preheating at Higher Temperatures : Excessive preheating (above 50°C) in a warmer may increase polymerization shrinkage and stress thus reducing MTBS despite improving the physical properties of the composite . Stereomicroscopic and SEM images of the warmer group revealed cracks and defects , which likely resulted from increased polymerization stress. Previous Research Findings : Previous studies (e.g., Davari et al., Demirbuga et al.) showed that moderate preheating (37°C to 50°C) improved bond strength, but only if the composite was used immediately after heating. Temperature drops during transfer from the warmer can reverse the benefits of preheating, as seen in this study. 22

23. Critical appraisal They have not mentioned the modifications of the hair drier in detail. They have not mentioned the No. of Specimen used for Stereomicroscope analysis. More studies are needed to evaluate the long-term clinical implications of preheating methods, especially warm airstream techniques , on composite restorations. 23

24. Conclusion Preheating with a warm airstream significantly increased the MTBS of both composite types to dentin. Preheating with warmer to 50°C decreased the MTBS of both composite types, compared with the control group. 24