Universal universe: a new generation of universal adhesives and resin cements

The rise of adhesive dentistry has paved the way for less invasive, more esthetic restorative treatments, and universal adhesives in particular have evolved in promising ways. While first generation dental adhesives had limited indications, were very technique sensitive, and required multiple steps and bottles, new universal adhesives support procedure simplification and standardization. These new materials are also much less technique sensitive, making it easier to achieve predictable results.

As a part of these efforts, and as one of the leading manufacturers of universal products, 3M recently introduced a new universal adhesive and a universal resin cement. These new products were reviewed from a Research and Development (R&D) and scientific perspective during a symposium titled “Universal Universe – a new generation of universal adhesives and resin cements” that took place on September 17, 2021, in Brussels, Belgium, as part of the Continental European Division of the International Association for Dental Research (CED-IADR) and the Scandinavian Division (NOF) Oral Health Research Congress. During the event, four dental experts discussed the market demand and science behind 3M’s next-generation materials, as well as their applicability to the modern dental practice.

WHY DEVELOP NEW UNIVERSAL PRODUCTS?

To set the stage, Dr. Christoph Thalacker, Lead Specialist Product Development at 3M Oral Care in Seefeld, Germany, revealed why a new universal adhesive and the company’s first universal resin cement for both self-adhesive and adhesive mode were necessary. While 3M’s first true universal adhesive – 3M™ Scotchbond™ Universal Adhesive, introduced in 2011 – remains a highly successful and clinically proven product, market research revealed that dental practitioners still had unmet needs. Dental practitioners expressed the desire to reduce inventory with a single resin cement that was easy to use and didn’t compromise bond strength. To meet these needs, 3M™ Scotchbond Universal Plus Adhesive and 3M™ RelyX™ Universal Cement were developed as a two-component system.
An optimized version of its predecessor, Scotchbond Universal Plus Adhesive:

•  Features a dentin-like radiopacity to reduce the risk of X-ray misdiagnosis and overtreatment
•  Bonds and seals caries-affected dentin to support minimally invasive dentistry and maximize preservation of natural tooth structure
• Achieves gold standard bond strength to glass ceramics without using a separate primer

Dr. Christoph Thalacker, Lead Specialist Product Development at 3M Oral Care.

As Dr. Thalacker explained, other radiopaque adhesives utilize radiopaque fillers that tend to settle at the bottom of the bottle and increase viscosity. Scotchbond Universal Plus Adhesive, on the other hand, achieves its dentin-like radiopacity through a novel, radiopaque resin that allows for a homogeneous, low-viscosity solution that does not need to be shaken before use. It features the same shear bond strength to caries-affected dentin as to sound dentin, and forms a distinct, well defined, void-free hybrid layer on both etched and unetched caries-affected dentin.1 In addition, several independent studies show an improved bond strength to glass ceramics.^3,7
The second of 3M’s new products, 3M™ RelyX™ Universal Resin Cement, may be used as a standalone product in self-adhesive mode, or in combination with Scotchbond Universal Plus Adhesive in adhesive mode. Bonding performance and other relevant features have been tested in internal and external in-vitro studies. Its most important features are summarized below and include improvements to the cement itself as well as an innovative syringe:

• Simplified workflow
• Easy excess clean-up
• Proprietary self-sealing syringe is more ergonomic and easier to clean
• Less waste (80% less cement waste and 50% less plastic waste per application compared to currently available standard automix systems)
• Excellent bond strength with or without additional adhesive
• Highly esthetic (4 color-stable, fluorescent shades)
• Improved radiopacity
• Optimal viscosity (not runny)

DOES THE NEW UNIVERSAL ADHESIVE RELIABLY BOND TO TOOTH STRUCTURE?

In his lecture “Laboratory Performance of a New Universal Adhesive to Tooth Tissue and Glass Ceramics,” Prof. Dr. Bart Van Meerbeek (Head of the Biomaterials Research Group, KU Leuven) presented the results of two studies examining the micro-tensile bond strength of Scotchbond Universal Plus Adhesive compared with its predecessor, Scotchbond Universal Adhesive. The first compared the two adhesives’ bonding performance on enamel, the second on dentin. The products were tested in both self-etch and total-etch modes, and bond strength was measured immediately (after one-week water storage) as well as after artificial aging (50k thermocycling).

Prof. Dr. Bart Van Meerbeek, Head of the Biomaterials Research Group, KU Leuven

On enamel, both systems performed equally well, with one exception: Scotchbond Universal Plus Adhesive outperformed Scotchbond Universal Adhesive in the etch-and-rinse mode before aging (immediate bond strength). Both universal adhesives performed better on enamel in total-etch mode, as some aging degradation was observed in self-etch mode. On dentin, both systems performed equally well in all conditions, etching and rinsing outperformed self-etching, and no aging degradation was detected.2

An analysis of the adhesive-enamel and adhesive-dentin interfacial interaction by transmission electron microscopy (TEM) revealed distinct, well defined, void-free hybrid layers on both enamel and dentin. These results indicate that it is possible to achieve a high-quality bond with Scotchbond Universal Plus Adhesive when bonding to tooth structure.

IS A SEPARATE SILANE STILL NEEDED WHEN CEMENTING GLASS CERAMICS?

Scotchbond Universal Adhesive already contains silane, making it possible to omit the separate silane application step typically required when bonding to etched glass ceramics. However, the bond strength is still lower than the gold standard adhesion achieved with traditional silane primers such as 3M™ RelyX™ Ceramic Primer. For this reason, many dental practitioners continue to use a separate primer.

As Scotchbond Universal Plus Adhesive contains an optimized silane formulation, however, Prof. Van Meerbeek and his team posited that it may be possible to achieve the same bond strength to glass ceramics as multi-bottle adhesives plus silane primer. They explored this question by measuring the immediate and aged shear bond strength of the new adhesive to lithium disilicate (IPS e.max® CAD, Ivoclar Vivadent Inc.).³

The graphic below shows bond strengths obtained with different combinations of pretreated glass ceramic and different adhesives after aging.

After testing, they concluded that hydrofluoric acid etching is the most effective pretreatment and that Scotchbond Universal Plus Adhesive alone (without a separate primer) performs as well as Scotchbond Universal Adhesive pretreated with a ceramic primer.3 This confirms that a separate silane is no longer needed to achieve gold standard bond strength. Applying a separate ceramic primer with Scotchbond Universal Plus Adhesive, however, will lead to bond strength levels that exceed gold standard systems.

IS THE NEW UNIVERSAL RESIN CEMENT SUITABLE FOR FIBER POST CEMENTATION?

Debonding is one of the most frequently reported complications in endodontically treated teeth restored with fiber posts and an indirect restoration.⁴ According to Prof. Dr. Lorenzo Breschi (University of Bologna, Italy), these debonding issues may be due to the procedural complexity and technique sensitivity of cementation systems. Opting for a simplified approach involving self-adhesive resin cements that are less technique-sensitive and do not require any root canal pretreatment may help prevent these issues.

Prof. Dr. Lorenzo Breschi, University of Bologna, Italy.

A study conducted in 2009 confirmed that it is possible to opt for a simplified approach, and the most stable bond was achieved with a total-etch adhesive combined with a dual-cure cement.5 In order to assess the performance of the new universal resin cement used in the self-adhesive mode, Prof. Breschi and his team conducted an in-vitro study to investigate the push-out bond strength and nanoleakage of fiber posts cemented with RelyX Universal Resin Cement compared to several other self-adhesive or multi-step cementation systems. The bond strength was measured in the apical and coronal regions; tests were conducted at baseline and after twelve months (artificial aging).
In the push-out bond strength test, RelyX Universal Resin Cement performed equally well or better than other systems tested independent of the area (coronal versus apical). In addition, RelyX Universal Resin Cement outperformed other systems after artificial aging when used in self-cure mode, especially in the apical region. In all groups, mixed and adhesive failures at the cement-post interface were observed most often. Regarding nanoleakage, the new universal resin cement maintained stable results over time. Hence, the use of RelyX Universal Resin Cement in self-adhesive mode can clearly be recommended for fiber post cementation, as it offers reliable adhesion in the long term along with a simple cementation protocol.

Cross-section of a root with a cemented fiber post: Light micrograph showing the adhesive interface after silver particle staining to check for interfacial nanoleakage.⁸
P: Cross sectioned fiber post.
C: Cement
D: Dentin

DO THE PRODUCTS HANDLE WELL IN THE CLINICAL ENVIRONMENT?

This question was addressed by the chairman of the symposium, Prof. Dr. FJ Trevor Burke (University of Birmingham, UK), who presented the results of a recent PREP Panel evaluation.⁶ He stressed that RelyX Universal Resin Cement, used with or without Scotchbond Universal Plus Adhesive, handles very well in the hands of different dental practitioners. Among the features evaluated were the ease of dispensing, use and mounting of the mixing tips, viscosity, ease of excess clean-up, and overall satisfaction with the resin cement used in both application modes. The overall level of satisfaction was extremely high, which was also reflected in a recommendation rate of 100 percent.

Prof. Dr. FJ Trevor Burke, University of Birmingham, UK, chairman of the symposium.

CONCLUSION

The speakers of the symposium agreed that due to their beneficial features and promising performance in in-vitro studies and handling evaluations, both Scotchbond Universal Plus Adhesive and RelyX Universal Resin Cement seem to be very well suited for a wide variety of indications. Their universal applicability and simplified application protocols support dental practitioners who would like to streamline and standardize clinical procedures.