Dual surface modification of titanium

Abstract

Titanium has a wide range of use in dentistry, including removable and fixed prosthodontics due to its biocompatibility and other favorable properties. A widely used protocol is to first silica-coat the surface, followed by silanization before cementing it on the tooth with resin cement. This mechanism increases the longevity of dental prosthesis, however their adhesion degradation still is an issue for clinicians. Thus, there is a need for such a pretreatment protocol which enhances the said bonding mechanism. In the current PhD study, silica-coating, acid-etching, silanization are combined together to provide more durable bonding. The goal was to find a method which would enhance adhesion strength between a resin composite cement and titanium over a long period of time. For this laboratory study, dual surface modification methods. The specimens were silica-coated by using silica-coated alumina particles with a standard procedure and then acid-etched with different acids and acid blends. As a novel approach this pretreatment sequence was also used in the reverse order, i.e., acid-etching followed by silica-coating. SEM, EDX, AFM, XPS, high kinetic energy photoelectron spectroscopy (HIKE) and surface roughness profilometry analyses were carried out to observe and study the topography, surface chemistry, and surface roughness. Titanium surfaces were silanized with different silane primers, (i.e., surface modifiers to promote adhesion between inorganic and organic dissimilar surfaces) with a blend of 1.0 vol% 3-acryloxypropyltrimethoxysilane (ACPS) and 1,2-bis-(triethoxysilyl)ethane (BTSE) (an experimental silane primer blend), or commercially available Monobond™ Plus or Z-Prime Plus™. After silanization, resin composite cement stubs (mold enclosed) were bonded to the titanium specimens. The enclosed mold microshear bond strength tests (EM-µSBS) were carried out to evaluate the adhesion strength between the resin cement and titanium on 1 day, 1 week, 4 weeks, and 8 weeks. Optical microscopy was used to analyze the mode of failure. The results suggested that dual surface modification methods create various surface roughnesses on titanium specimens. However, roughness alone is not enough to provide durable adhesion. Presence of silica on the titanium surface before/after acid-etching plays an important role in forming a chemical bond between the resin cement and titanium. Titanium surfaces silica-coated before acid-etching exhibited lower EM-µSBS compared to the specimens acid-etched followed by silica-coating, upon ageing. The XPS and EDX analyses conferred with the EM-µSBS results suggesting that acid-etching followed by silica-coating leaves Si on the surface, which upon silanization provides strong adhesion. The XPS results indicated on the survey spectra that different species of Si (Si4+, Si3+, Si2+) and Ti (Ti4+, Ti3+, Ti2+, Ti0) were present when acid-etched with HF. Interactions of these species most probably play a role in adhesion between resin cements and titanium. The pilot HIKE study suggested that silanization is not homogenous on the surfaces, due to chemical shifts observed on the same surface. While, the thickness of commercial Monobond™ plus silane film was higher compared to the experimental silane blend film. In summary, a novel dual surface modification, silica-coating following acid-etching and silanization might be an interesting approach in adhesion promotion between resin cements and titanium.