Physical Assessment of Veneering Process on Lithiumdisilicate and Zirconia Ceramics

Objectives: This study characterizes the dental veneering process in combination with different substrates focusing on thermal and mechanical compatibility. Key properties analyzed include the modulus of elasticity (E-Modulus), coefficient of thermal expansion (CTE), surface wetting behavior at elevated temperatures and veneering resistance via scratch testing. Calculation of interfacial stress is related to scratch test results.
Methods: As veneering material, Initial IQ Lustre Pastes ONE (L-NFL; GC Corp.) was used. IPS e.max ZirCAD™ MO (3Y-TZP;Zirconia, Ivoclar) and IPS e.max CAD (LS2; Glass-ceramic, Ivoclar) were the substrates. Youngs modulus (EM) and Poissons ratio (ν) were measured via Resonant Ultrasound Spectroscopy. Coefficients of thermal expansion (CTE) and glass transition temperatures (Tg) were measured via push rod dilatometer (DIL)(L75 PT, Linseis). The contact angle (Θ) was analyzed on a heating stage microscope (EM 301 Hesse Instruments) at 800°C (LS2) and 930°C (3Y-TZP) respectively. Residual stress (σ) at the veneering interfaces were calculated for the 3Y-TZP/L-NFL and LS2/L-NFL systems. Scratch tests using a Rockwell C stylus measured the force required to penetrate veneer thickness (Lc3). Variations employed were: 3Y-TZP sand blasted (SB) and polished (P), LS2 sand blasted, polished, etched (E) and combination fired (CF).
Results: The following data were measured: LS2: EM=104.4 GPa; n = 0.236; CTE_100°-500°= 10.4 ppm; 3Y-TZP: EM=208,4 GPa; n = 0.281; CTE_100°-500° = 10.6 ppm; N-NFL: EM=78.4 GPa; n = 0.229; CTE_100°-500°= 7.5 ppm. Thereof we calculated a tensile stress in the glaze layer at the interface to LS2 (σ = 24.9 MPa) and 3Y-TZP (σ = 34.7 MPa). The results for Θ and Lc3 are listed in Table 1.
Conclusions: Polished 3Y-TZP exhibited higher residual stress and lower scratch resistance. LS2 performed better due to its chemical bonding ability with the veneering glass. Clinically, veneering is recommended on sand-blasted zirconia for non-load-bearing surfaces.