RelyX Unicem: We simply got lucky!

The development of 3M ESPE's latest luting cement, RelyX Unicem, was no accident according to Global Brand Manager, Dr Jürgen Sendelbach, but there was certainly a degree of luck involved.

"We definitely got lucky with the chemistry," explains Dr Sendelbach. "It sometimes happens that you get it right very early in the development phase and in the case of RelyX Unicem, the development time was a relatively short 3-4 years before extensive testing started."

Developed at 3M ESPE's European headquarters in Seefeld, outside Munich, Gemrnay, RelyX Unicem, in a nutshell, is the first self-adhesive universal resin cement that does not need any pre-treatment to achieve good bond strength between the tooth and any restorative material.

In essence, this is the Holy Grail of cement technology with the initially hydrophilic material bonding directly to the tooth. While a hydrophilic cement has been tried before - water absorption by the material over time lead to eventual failure of the restoration. RelyX Unicem succeeds because it becomes, in a kind of "intelligent switch", highly hydrophobic following polymerisation (by light or dark cure) with the key benefit to dentists being a considerable reduction in the number of steps in the application process.

According to Dr Sendelbach, the majority of dentists internationally still use zinc phosphate which is some 100 years old. "Even in highly developed countries like Germany, zinc phosphate is used in up to 60% of all cementations. They are reluctant to change," he explained. "They realise zinc phosphate is far from perfect, but they know all of its shortcomings and have learned to live with them.

"For the more progressive dentists, it is difficult for them to believe that they are going from up to 11 steps in a classical total etch resin cement to just three with RelyX Unicem."

With zinc phosphate, there is no chemical bond whatsoever. The cement fills the gap between the prepped tooth and the crown. It hardens and friction prevents it from being removed.

Resin cements provide a chemical bond but need various pre-treatment steps. The traditional etch, prime and bond is designed to prepare the hydrophilic tooth to accept the hydrophobic cement. The multiple steps present a potential for errors, however, when completed correctly, a very strong bond is obtained.

Etch roughens the enamel with phosphoric acid and decalcifies dentin. There is a chance of post-operative sensitivity if the tooth is etched for too long. It also removes the smear layer and can open up the dentin tubules.

Dr Sendelbach likens the necessity of a priming step in the procedure to that of soap when cleaning a greasy plate with water.

"Prime is like the detergent. It allows the hydrophilic tooth to have contact with the hydrophobic bond. In essence, it allows grease to react with water," he said.

Bond is the glue to stick the tooth to the cement. It glues the cement to the tooth and has a similar composition as the cement.

RelyX Unicem, conversely, removes the complex steps to prepare the tooth for cementation. Because of its initially hydrophilic properties, it flows easily on the tooth and new key ingredients react directly with the surface of the tooth structure. RelyX Unicem creates a chemical bond between the cement and the tooth and unlike most resin cements, it can also be used with metal restorations as it has true dual cure properties.

Polymerisation can be achieved through light cure for about 20 seconds or through dark cure within 5 minutes. The dual mode ensures reliable bond strength in areas below dark shade ceramics, metal crowns, posts, pins, etc. RelyX Unicem also releases fluoride and is easy to place.

According to Dr Sendelbach, there is essentially no chance of post-operative sensitivity with RelyX Unicem as it does not remove the smear layer and doesn't open the tubules.

"RelyX Unicem has a totally new and revolutionary chemistry. It is extremely challenging and complex scientifically, but very simple for the dentist to use. It's difficult to produce and aside from the patent protection we have in place, is difficult for others to copy.

"So far, the level of customer feedback we have received has been very positive and encouraging. There have been very few complaints or requests for help at our service centres compared to other newly introduced products. This is indicative of the ease of use of the product and its virtual lack of technique sensitivity.

"Essentially, we got rid of all the disadvantages and kept all the advantages. With RelyX Unicem, you truly only need one cement for virtually every indication."