# The mechanical and optical properties of different transparent vinyl polysiloxane materials used for guided composite resin injection technique

## TL;DR

This study compares the mechanical and optical properties of transparent vinyl polysiloxane materials used in a dental restoration technique, finding that material choice and thickness affect performance.

## Contribution

The study provides a systematic comparison of mechanical and optical properties of VPS materials for guided composite resin injection, revealing correlations and thickness effects.

## Key findings

- ZHERMACK showed the highest mechanical properties, while DELIAN had the best optical properties across all thicknesses.
- Translucency and light irradiance decreased significantly with increasing material thickness for all VPS materials.
- Shore A hardness strongly correlated with compressive modulus (r = 0.93), and translucency with light irradiance (r = 0.96–0.98).

## Abstract

Vinyl polysiloxane (VPS) index is the most commonly used tool of guided composite resin injection (G-CRI) technique. Understanding the mechanical and optical properties of various transparent VPS materials is vital for determining optimal G-CRI parameters and identifying the best material. Still, existing literature on this topic is limited. This study aimed to compare the mechanical and optical properties of various VPS materials used for G-CRI technique, and to evaluate the effect of material thickness on optical properties.

Four transparent VPS materials (OKVD, DELIAN, HUGE, and ZHERMACK) were evaluated. Shore A hardness was measured on cylindrical specimens (Ø25 × 6 mm, n = 9) using a portable Shore durometer, and compression modulus was measured on specimens (Ø10 × 6 mm, n = 9) using a universal testing machine. For optical properties, cylindrical specimens (Ø12 mm, n = 5 per thickness) at five thickness (2, 4, 6, 8, and 10 mm) were fabricated. Translucency parameter was calculated from color measurements taken with a portable spectroradiometer against black and white backgrounds. Light irradiance transmitted through specimens was measured using a dental radiometer. Statistical analysis was performed using analysis of variance, and Pearson’s correlation was used to correlate the compressive modulus with Shore A hardness, and the light irradiance with translucency (α = 0.05).

The trend of changes in Shore A hardness and compressive modulus of VPS materials is consistent, with ZHERMARK > OKVD > DELIAN > HUGE. Both translucency and light irradiance decreased significantly with increasing thickness for all materials. DELIAN exhibited the highest optical properties across all thickness, while HUGE showed the lowest. Strong positive correlations were observed between Shore A hardness and compressive modulus (r = 0.93) and between translucency and light irradiance (r = 0.96–0.98).

Significant variations exist in the mechanical and optical properties of transparent VPS materials, with ZHERMACK exhibiting superior mechanical properties and DELIAN superior optical properties. The optical properties declined significantly with increasing thickness. Transparent VPS material with higher mechanical properties can enhance the restoration accuracy of G-CRI technique, while thicker index or that fabricated using lower translucent materials necessitate longer exposure times for complete polymerization. Additionally, compressive modulus and light irradiance can be predicted using Shore A hardness and translucency, respectively.