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Adhesive cementation: the key for clinical longevity

Adhesive cementation: the key for clinical longevity

We are living in the Esthetic Dentistry era, where virtually all the posts, materials, courses and symposia are dedicated to it, directly or indirectly. We are caught up in thoughts like what composite and/or ceramic should I use? Is it better to have the teeth bleached before I start the treatment? Which lab technician should I work with? FAQ valid and fundamental concerns in the preparation of a ideal restorative treatment, but another question still remains, and this procedure is often neglected or underestimated in its importance and complexity: the adhesive cementation.

The adhesive cementation is a complex procedure, that has several steps that require knowledge of different materials and devices. A failure in this phase of the rehabilitation treatment can result in failure of the entire restoration process, no matter how beautiful and “natural" the result was, and surely will result in a great dissatisfaction and frustration not only yours but mainly the patients, who have been waiting anxiously for the treatment. So that you have the knowledge and the more precise understanding of what is being exposed, we suggest the reading of some posts already published here in Opalini, ok?

At first we have to know the adhesive systems, self-etching, universal, simplified... easy, isn’t it?! No, it's not! Knowing these materials is important not only for them to be properly applied, but their indication for each procedure. However, I do not need to talk about the different adhesives and its features n this post, because this was already addressed in an unique way by my great friend Rafael Ratto de Moraes, in the post “What are universal adhesives?” Only a few considerations remain on the total etching adhesives.

Total-etch adhesives are those that require the etching step (usually with 35-37% phosphoric acid) prior to the application of the adhesive system. These systems have two forms of presentation, one being the two-bottle adhesives, that contain the primer agent with more hydrophilic monomers, for better interaction with demineralized dentin, and the adhesive or bond itself, containing a higher concentration of hydrophobic monomers to form a hybrid layer more resistant to hydrolysis. The other form of presentation of these adhesives is simplified. These adhesives have hydrophilic and hydrophobic monomers, the primer and the bond, mixed in the same bottle, which makes its application simple and quick [1].

The second step for an efficient cementation is the knowledge of dental ceramics. What type of ceramic was used in each treatment? Is it a glass ceramic? Polycrystalline? Enhanced? Acid sensitive? Acid resistant? A lot to know, isn’t it?!?! All these details are important, since depending on the type of ceramic used, the surface treatment and the cement, among other things, will be determined. Considering this, I recommend the reading of the post “Not only of beauty live the ceramics”, from these great guys, Raphael Monte Alto and Leandro de Moura Martins.

When working with crowns and inlays/onlays, we have a thicker piece as they  are often restoring a large tissue loss. Thus, one of the first decisions we have is: will we use dual cure adhesive resin cement? When we perform the polymerization through the ceramic, the blue light emitted by the curing unit can be reduced up to 70% [2] and this implies in significant reduction of the cement conversion rate [2], which may compromise the entire restorative procedure. The dual cure cements are not only light cured, but also chemically cured, which is important for situations where we have a reduction of the light emitted by the curing unit.

We have already chosen the cement, now we have to look at the ceramic piece: is it acid sensitive or acid resistant? Let's start by the acid sensitive! If you are working with a feldspathic ceramic you have to know that the etching time is longer (60s) with 10% hydrofluoric acid, this way we can create micro-retentions and provide better retention of resin system and indirect restoration [3]. If using an enhanced ceramic (either lithium disilicate or leucite) we need to reduce this etching time to 20s using 5% or 10% hydrofluoric acid, this way obtaining the necessary retentions. After etching with hydrofluoric acid, there is the formation of a residue layer on the ceramic which can be removed using 35-37% phosphoric acid for 60 seconds, improving the union. Ok, preparation of the pice done, right?!?! Not really, we need to treat the ceramic surface with silane. This promotes the union between the inorganic and the organic parts, allowing the union between these substrates, in other words, it promotes the union of the ceramic with the adhesive/resin cement system. After the silane, the use of an adhesive system in the piece is recommended, in order to obtain a higher union between the piece and the cement [3]. This is not required, but your results will be better with the use of adhesive!!

However, beware of the adhesive to be used! Remember when I warned about the adhesive systems, we must know them to accomplish success in indirect restorative procedures. In this case, it is better not to use simplified adhesive systems, as these have a slight incompatibility with dual cure resin cements [4], which makes the union of the piece with these adhesives is more fragile. 

Finally, we should perform the conditioning of the tooth structure, and the adhesive procedure is similar to that performed for direct restorations, with one small detail: the polymerization of the adhesive!!!!!! For crowns and onlays, curing the adhesive prior to the crown placement can occur, but the adhesive layer must be very, very thin. If you are afraid, there are no problems in carrying out the polymerization of the adhesive along with the polymerization of the cement after the placement of the ceramic piece, which by the way, is the recommended procedure.

When we work with polycrystalline ceramics, eg zirconia, we have a small problem: it can not be etched!!! So we have to use other methods to improve the union to this ceramic so that we can cement it the best way we can. We can ask our technician to perform the sand blasting to the internal part of the piece, and so we can cement them similarly to the aforementioned, with the exception of etching [5]. If our technician does not have the device for internal blasting, we can use metal primers, which allow a greater union of the resin systems to ceramics, providing better results [6]. It is important to highlight that, as this union is not as stable as the union of acid sensitive ceramics, procedures such as inlays/onlays should always be performed with acid sensitive ceramics, because these pieces depend almost exclusively on the adhesive union.

Well, we got to the ceramic veneers, contact lenses… as you prefere. A common feature of these terms is that this piece has a significantly smaller thickness than the crowns. We may think this way cementation is easier and is similar to that performed for the procedures already described. But it is not!

Veneers have a smaller thickness, and yes, we could in fact manage to cement them using dual cure resin cement. But the problem is that these cements have a lower color stability compared to light-cure cements [7, 8]. Over time, the dual cure resin cements tend to become more yellow. With the smallest thickness, this color change may influence the final color of the restoration, which would bring problems not at the time of the cementation, but after one or two years, with the color change of cemented restorations, that may cause discomfort and consequent dissatisfaction with the treatment. Thus, the difference for the proposed protocols, for example, feldspar and enhanced ceramics, is to use the light-cure cement instead of the dual cure resin cement. An important step of cementing thin veneers is that the adhesive layer should not be item that is to be priorly cured. Due to the fine adjustment of the piece, any thin layer can change the correct positioning of the piece. Finally, as well as inlays/onlays, never perform zirconia veneers, because, besides the esthetic that can be compromised, these pieces depend solely on the adhesive union.

I hope I was able to clarify your most frequent doubts on cementation of ceramic pieces, and that this complex and long subject is no longer a thorn in your shoes! A huge hug.

Adriano Lima

MS and PhD in Operative Dentistry – FOP-UNICAMP

Post doctoral in Biomaterials – Birmingham University -England

Professor of post-graduation courses at the University Paulista-UNIP/SP e works at his Private Practice in São Paulo

References

[1]    Pashley DH, Tay FR, Breschi L, Tjaderhane L, Carvalho RM, Carrilho M, et al. State of the art etch-and-rinse adhesives. Dent Mater 2011;27:1-16.

[2]    Moraes RR, Brandt WC, Naves LZ, Correr-Sobrinho L, Piva E. Light- and time-dependent polymerization of dual-cured resin luting agent beneath ceramic. Acta Odontol Scand 2008;66:257-61.

[3]    Soares CJ, Soares PV, Pereira JC, Fonseca RB. Surface treatment protocols in the cementation process of ceramic and laboratory-processed composite restorations: a literature review. J Esthet Restor Dent 2005;17:224-35.

[4]    Tay FR, Suh BI, Pashley DH, Prati C, Chuang SF, Li F. Factors contributing to the incompatibility between simplified-step adhesives and self-cured or dual-cured composites. Part II. Single-bottle, total-etch adhesive. J Adhes Dent 2003;5:91-105.

[5]    Amaral R, Ozcan M, Bottino MA, Valandro LF. Microtensile bond strength of a resin cement to glass infiltrated zirconia-reinforced ceramic: The effect of surface conditioning. Dent Mater 2005.

[6]    Cavalcanti AN, Foxton RM, Watson TF, Oliveira MT, Giannini M, Marchi GM. Bond strength of resin cements to a zirconia ceramic with different surface treatments. Oper Dent 2009;34:280-7.

[7]    Almeida JR, Schmitt GU, Kaizer MR, Boscato N, Moraes RR. Resin-based luting agents and color stability of bonded ceramic veneers. J Prosthet Dent 2015.

[8]    Ghavam M, Amani-Tehran M, Saffarpour M. Effect of accelerated aging on the color and opacity of resin cements. Oper Dent 2010;35:605-9.

My purpose is to help you gain autonomy through knowledge, facilitating the dentistry and communication. AND how do I do this?

I put myself in your shoed, I identify what is preventing you from being happy with your results and untie the knots by means of a simple and accessible language! I graduated from UNESP | Araçatuba; did my Master and PhD in Operative Dentistry at UNESP Araraquara | I am a Professor of Operative Dentistry at the Federal University of Pelotas | RS.

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