20 May 2020

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Silane incorporation into universal adhesives: A systematic review.

Edoardo Mancuso

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“Progress means simplifying” not complicating. Manufacturers have well understood this concept and have tried over the years to simplify adhesion clinical protocols to reach an optimal bonding, reducing the steps and the time required to achieves it. One of the attempts proposed in adhesive systems to reduced for clinicians the number of operative steps, is the addition of a silane coupling agent into universal adhesives.
This would render dispensable the additional step of silane application on ceramic. It is now well established that silane coupling agent is crucial for bonding of silica-based ceramics. It must be applied after the etching with hydrofluoric acid to provide long-term chemical bonding between adhesive resin monomers and the silica crystals of the ceramic.
However, efficacy of such coupling agent, when added to universal adhesives, should be further evaluated to better understand if it could be a viable option to increase the bonding ability of universal adhesives when bonding silica-based ceramics or if it is still necessary the additional step for silane application.  

A recently published systematic review, written by Dr. Laércio Almeida De Melo and his team, analyzed the current literature, aiming to compare bond strength of indirect restorations when using silane incorporated into universal adhesives or when applied separately.
From the literature analysis, some critical data emerged regarding the addition of silane into universal adhesives. For instance, the mixture of different components in the same bottle (i.e., MDP, BisGMA and silane) may influence silane coupling agent function, making its molecule instable in solution.
Moreover, high viscosity of universal adhesives may reduce the penetration of the coupling agent in the retentions created by the hydrofluoric acid on the ceramic surfaces. It is finally to add that the bifunctional molecule of silane most frequently used in dentistry has an optimal pH of employment ranging from 4 to 5. Hence, the higher acidity found in the bottle of universal adhesives as a consequence of the presence of MDP molecules, may cause an autocondensation reaction and early formation of the silane active form.   All in vitro researches included in the review have indeed demonstrated the better performance for surface treatment of glass ceramics using silane in a separate step. The results suggest that an additional pretreatment with silane provides a regular and functional layer for bonding between the resin monomers of cement and the ceramic.  

The article concludes suggesting that, the pretreatment of ceramic with hydrofluoric acid, followed by the application of universal adhesives containing silane, is not as efficient as the application of silane and adhesive separately. It is then important for clinicians, when working with glass-ceramic restorations, to take the time to follow all the steps needed to achieve an optimal adhesion.

For additional information: Efficacy of prostheses bonding using silane incorporated to universal adhesives or applied separately: A systematic review