Surface conditioning of restorations

Whether zirconium oxide, alloy, polymer, or silicate ceramic – the correct surface conditioning is crucial for the quality of adhesive bonding. But which pretreatment is suitable for which material? An international study followed by expert consensus provides answers and summarizes them in 23 practical recommendations for dentistry and dental technology.

Surface conditioning for the adhesive bonding of dental restorations includes mechanical and chemical pretreatment steps. This study examines both methods and demonstrates their importance for secure and durable adhesive bonding.

Mechanical pretreatment is performed by corundum blasting, whereby abrasive particles, in practice usually aluminum oxide (25 µm to 250 µm), are blasted onto the restoration surface. A pressure of up to 1,2 MPa (only 0,1 MPa for zirconia) should be applied at a distance of 5–10 mm and an angle of 45° to the restoration. Depending on the particle size and applied pressure, the surface can be cleaned, enlarged, and its roughness profile modified. The resulting roughness is crucial for mechanical bonding and simultaneously improves wettability with adhesive systems. Additionally, chemical pretreatment with suitable adhesive systems is performed to ensure long-lasting bond strength. 

In general, restorations made of zirconia , alloys, PEEK, and polymers (PMMA, composites) should be treated with corundum blasting before cementation. The parameters must always be adjusted to the specific material, as improper application can impair flexural strength through microcracks and surface damage. For silicate ceramics, etching with hydrofluoric acid is currently considered the gold standard for surface preparation. Corundum blasting is being discussed as a possible alternative, as it can achieve a similar bond strength when applied correctly.

Since surface preparation varies considerably in practice, the aim of this study was to assess the knowledge and practical experience of the participants. Additionally, the importance of correct surface pretreatment is to be underscored by presenting recommendations from a panel of experts for general and material-specific workflows in the adhesive cementation of restorations. 

Survey Design

The findings presented here are based on an anonymous cross-sectional survey of 267 participants (dentists, dental technicians, and dental assistants) from Germany, Austria, and Switzerland, conducted from April to July 2023. The questionnaire comprised 47 questions on the pretreatment of restorations prior to cementation, cementation protocols, and participant demographics. Subsequently, a panel of 23 experts evaluated the results and developed 23 practice-relevant recommendations for the adhesive cementation of dental restorations.

What the survey shows

The results show that corundum blasting is widespread in practice: Almost all participants (96%) own a device, and over 94% stated that they use aluminum oxide. Over 87% of respondents have already gained practical experience with corundum blasting of aluminum oxide, and almost a quarter use it more than four times a day. At the same time, two-thirds (66%) stated that they had never received formal training. The majority (57%) base their parameter selection on their own experience. Manufacturer specifications and scientific evidence are mentioned less frequently. 

According to a survey, corundum blasting is most frequently used on zirconia (83%), followed by PMMA-based plastics (56%), alloys (55%), and indirect/semi-direct composites (54%). It is used significantly less often on silicate ceramics (28%).

In over half of cases (57%), the surface to be treated is not specially prepared beforehand; a third use steam, and 12% mark with a pencil or felt-tip pen. Around a quarter of the participants stated that the correct parameters for zirconia, polymer restorations, or alloys are unclear. Only 41% can imagine using corundum blasting on silicate ceramics as an alternative to hydrofluoric acid etching. Regarding whether a previously blasted restoration should be treated again after try-in, the participants were almost evenly split: 48% would repeat the corundum blasting, while 52% would not.

Among the dentists surveyed, 86% stated that they would conventionally cement a zirconia crown after provisional cementation with eugenol-containing cement. Universal adhesives were used for zirconia by 47% and for silicate ceramics by 59% of the dentists surveyed. Nearly 64% used an MDP-containing adhesive for zirconia, and 56% used a silane for silicate ceramics. Regarding both questions, approximately one in ten dentists indicated that the composition of the adhesive system was unclear to them. Three out of four participants (76%) expressed a desire for more training on this topic in their studies, apprenticeships, or continuing education.

23 recommendations of the expert panel

General

Availability

Access to a corundum blasting device is associated with a higher application rate prior to cementation and thus with better long-term restoration success. A suitable device should therefore be available in every dental practice and laboratory.

Training

Since scientifically sound parameter selection is related to experience, age, and targeted training, all users should be trained regularly.

Communication

Only slightly more than half of the study participants communicated whether and when corundum blasting is performed in the laboratory and practice. This increases the risk that restorations are blasted twice or not at all. A clear, ideally written, division of tasks is recommended.

Mark

To ensure that all surfaces of the restoration are treated evenly, it is recommended to mark them beforehand with a pencil or felt-tip pen. Connectors in multi-unit fixed dental prostheses should be specifically masked.

Preparation for corundum blasting

All relevant parameters should be taken into account when blasting with corundum: the type of abrasive, the pressure applied, the duration, the distance between the nozzle and the restoration, and the angle between the nozzle and the restoration.

Objective

Experts cite the following objectives of corundum blasting: increasing surface area, cleaning, improving wettability and thus the stability of the restoration. It also enables the efficient removal of investment material residue.

Safety

Using the device while seated allows for greater precision, especially with definitive restorations. The use of gloves is recommended for all professionals.

Cleaning

Cleaning protocols vary considerably according to a cross-sectional survey. If available, the manufacturer's recommendations for cleaning the equipment should be followed.

Parameter settings

The settings must be adjusted according to the specific material. Excessive pressure can cause microcracks, while insufficient pressure results in inadequate surface roughness. Both compromise long-term adhesion.

• Zirconium oxide: 50 µm aluminum oxide at 0,1 MPa
• Polymer restorations: 50 µm aluminum oxide at 0,1 MPa
• Alloys: 110 µm aluminum oxide at 0,2 MPa

Pre-treatments for the cementation of dental restorations

• Temporary fixing: If a zirconia restoration was previously provisionally cemented with eugenol-containing cement, most experts recommend conventional, non-adhesive cementation. However, corundum blasting alone is sufficient to remove polymerization-inhibiting eugenol components and thus enable reliable adhesive cementation.
• Cleaning of silicate ceramics: After etching with hydrofluoric acid, the literature recommends cleaning the silicate ceramic with phosphoric acid before silanization to remove etching residues and optimize the bonding surface.
• Phosphoric acid: Zirconia restorations that have been pretreated by corundum blasting must not be cleaned with phosphoric acid. This method prematurely occupies future bonding sites and thus impairs the bond strength.
• Universal adhesives: Universal adhesives are a viable option for adhesive cementation. However, dedicated restorative primers tend to exhibit higher and more durable bond strengths.
• Zirconium oxide: The choice of adhesive system directly influences long-term bond strength. For the adhesive cementation of zirconia restorations, the adhesive should contain MDP monomers.
• Silicate ceramics: For silicate ceramics, the adhesive should contain silane. A separate primer with silane and phosphate monomer can achieve a more durable bond than silane directly integrated into a universal adhesive.
• Try-on: Contamination with saliva or blood demonstrably impairs adhesion. Therefore, after the fitting, either re-blasting with corundum or the use of special cleaning products is recommended.
• Removed restorations: Experts agree that when restorations have detached, a second corundum blasting is mandatory to remove cement residue and create a new bonding surface.

Conclusion

Corundum blasting is well-established in practice and in the laboratory, but its application is often inconsistent. The consensus recommendations of the expert panel offer scientifically sound guidance for material-specific workflows and reliable adhesive bonding.