Blasting or etching? The surface pretreatment of silicate ceramic restorations prior to adhesive cementation is the focus of the study presented here. The influence of various blasting media on surface energy, roughness, and flexural strength was analyzed on 216 CAD/CAM specimens. The results show that certain blasting particles could represent an alternative to the risky hydrofluoric acid etching.
Silicate ceramics are in demand due to their aesthetic properties and minimally invasive treatment options and are often used for CAD/CAM-manufactured inlays, onlays, and veneers. For intraoral Attachment These restorations are traditionally etched with hydrofluoric acid. However, the use of hydrofluoric acid poses health risks for both the practice team and the patient and therefore requires increased safety measures.
Blasting the surface
An alternative to etching is blasting to roughen the surface. In dentistry, there are various types of blasting media that differ fundamentally in terms of their material, particle size, and particle shape. Factors such as blasting pressure, the distance of the blasting nozzle from the object, and the angle also have a decisive influence on the result. However, especially with brittle, low-strength materials (e.g., feldspar ceramics), there is a high risk of surface damage to the restoration with microdefects during the blasting process.
The superficial micro-defects can have a negative impact on the overall stability and must therefore be avoided by choosing the right parameters (blasting media, blasting pressure, distance and angle).
material and methods
For the study, 216 square test specimens were manufactured from silicate ceramic CAD/CAM blocks (VITA MARK II). The specimens were then sandblasted under standardized conditions at a distance of 10 mm, an angle of 45°, and a pressure of 0,5 bar (Figure 1). The control group consisted of one group in which the surface was conventionally etched with 9% hydrofluoric acid gel, and one group in which the surface was polished.
Results at a glance
Surface energy: Low surface energy leads to reduced wettability of the interior of the restoration with the luting adhesive, which results in reduced bond strength and can also negatively impact the mechanical stability of the restoration. However, after blasting with certain particles, similar values were observed as after etching with hydrofluoric acid.
Surface roughness: A higher roughness is advantageous for bonding because it allows for better mechanical anchoring of the bonding adhesive. Blasting with larger or more angular particles increased the surface roughness, with the use of aluminum oxide particles showing particularly good results.
Elasticity: According to DIN EN ISO 6872, ceramic restoration materials must exhibit a certain flexural strength depending on the indication. The interaction of the restoration material, pretreatment method, and luting material determines the stability of the restoration. By selecting specific particles, comparable strength values for etching could be achieved by blasting. However, it was found that not all particle types are equally suitable. Silicon oxide particles with a grain size of 100-200 µm resulted in lower flexural strength, which can be attributed to possible micro-damage to the surface.
Conclusion
The results of this study suggest that blasting with certain particle types is a promising alternative to hydrofluoric acid etching. Blasting offers similar mechanical advantages without the health risks associated with hydrofluoric acid. However, the particles must be carefully selected to ensure optimal results in terms of adhesion and long-term stability.
Further studies are needed to clarify the long-term effects of sandblasting on the clinical performance of silica ceramics.
Examination
The results presented here are based on the following study: Hoffmann M, Schmeiser F, Donmez MB, Meinen J, Stawarczyk B.
Surface Modification of Feldspathic Ceramic Used for Minimally Invasive Restorations: Effect of Airborne Particle Type on the Surface Properties and Biaxial Flexural Strength. Materials 2024, 17(15), 3777; https://doi.org/10.3390/ma17153777