لخّصلي

This in-vitro study was conducted to evaluate the effect of thermocycling in a coffee solution on surface roughness and color stability of two resin-based composite materials. Standardized cylindrical composite disc specimens with dimensions of 10 mm in diameter and 2 mm in thickness were prepared for evaluation.

Study Design (PICOTS)
The study population consisted of standardized composite disc specimens. The intervention group included Brilliant Everglow™ Nanohybrid Composite, while Filtek™ Supreme XT Nanofilled Composite served as the comparator. The primary outcome measure was surface roughness (Ra), and the secondary outcome was color change (ΔE). Measurements were obtained immediately after specimen preparation and after 5000 thermocycles in a coffee staining solution. All procedures were performed in an in-vitro laboratory setting following standardized protocols.

Specimen Preparation
A total of 40 specimens were fabricated from each composite material using a split Teflon mold. Mylar strips were placed on the upper and lower surfaces of the mold to ensure smooth, oxygen-inhibited-layer-free surfaces. Specimens were light-cured using an LED curing unit for 20 seconds at zero distance. Each specimen was assigned a unique identification code for tracking and analysis.

Finishing and Polishing
Finishing and polishing procedures were performed using the Sof-Lex™ XT sequential disc system. A standardized three-step polishing protocol was applied to all specimens under controlled speed and pressure conditions to minimize operator-related variability and ensure consistency.

Thermocycling Procedure
To simulate extrinsic dietary staining and oral aging conditions, specimens were immersed in a coffee solution and subjected to 5000 thermocycles between 5°C and 55°C, with a dwell time of 30 seconds at each temperature. This protocol corresponds to approximately six months of intraoral thermal fluctuations.

Surface Roughness Measurement
Surface roughness (Ra) values were measured using an Atomic Force Microscope (AFM). Three readings were obtained from each specimen, and the mean value was calculated to reduce measurement bias and enhance reliability.

Color Change Assessment
Color measurements were conducted using a spectrophotometer based on the CIE Lab* color system. Color difference (ΔE) was calculated using the standard formula: ΔE = [(ΔL)² + (Δa)² + (Δb)²]¹ᐟ². A ΔE value greater than 3.3 was considered clinically perceptible.

Statistical Analysis
Statistical analysis was performed using SPSS software (version XX). Descriptive statistics were calculated, and paired and independent t-tests were applied. Statistical significance was set at p ≤ 0.05.

This proposal outlines a rigorous in‑vitro investigation comparing the surface roughness and color change of a nanohybrid composite (Brilliant Everglow™) versus a nanofilled composite (Filtek™ Supreme XT) following thermocycling in a coffee staining medium.