Repairing fractured metal-ceramic restorations using tribochemical impregnation

The fracture of the ceramic from a metal-ceramic restoration may often lead to an emergency attendance, because of compromised appearance or because the fractured restoration had rough margins, which were traumatizing the soft tissues. Causes of such fractures include, trauma (occlusal or physical), unsupported ceramic (which could be extrapolated to poor laboratory design), and/or insufficient rigidity in the metal substructure of the crown. It could be expected that the latter would be a cause of an early fracture, while the other causes could occur at any time in the life of the crown. Previous methods of attempting repair of such restorations used so-called chemically-active resins, an example of which was 4-methacryloxyethyl trimellitate anhydride (4-META).¹ It is the aim of this short paper to describe a method of repairing fractured metal-ceramic restorations using the Cojet (3M ESPE) system.

This system is based upon the Rocatec laboratory system (3M ESPE, Germany) which has been in use since 1989 for bonding resin composite to metal surfaces. It relies on sandblasting the metal surface with 30 microns aluminium oxide particles modified with silicic acid at a pressure of 0.25 MPa at a distance of 1cm (Cojet sand in the intra-oral kit).² This causes a tribochemical (heat) reaction at the metal surface, with spot heating of up to 1,000 °C, causing silica particles to be impregnated into the surface to a depth of 15 microns. This enables the surface to be treated with the silane solution which facilitates bonding to a resin-based material, with a resin-based opaquer also being included. The intra-oral version of this system is known as Cojet (3M ESPE).

In the illustrated case report, a 35 year-old woman presented following trauma, having lost ceramic from two metal-ceramic crowns (Figure 1). The patient's medical history included bulimia during her teenage years, which led to her upper anterior teeth receiving metal-ceramic crowns as a ‘treatment’ for excessive toothwear. Clinical examination indicated that the crown margins were intact, so it was decided that a repair using Cojet should be attempted.

The shade of the crowns was taken, and the defective crowns were isolated with rubber dam. The patient was provided with a nosepiece and protective eyewear. The exposed metal surfaces and surrounding ceramic were sandblasted using an intra-oral sandblaster filled with Cojet Sand, then with silane, the Cojet opaquer, ESPE-Sil (both 3M ESPE) and then resin composite. The repair was finally finished and polished using abrasive discs and impregnated rubber points (Figure 2).

While long-term reports of the success of such treatment are sparse, one review reports positive findings,³ and it may be considered that the trauma to the hard dental tissues is substantially less when the technique described above is utilized, when compared with the removal of the crowns and their replacement. In short, repair is always worth a try!