Failure cement/metal

CM - Cement/Metal failure failure at the primer to metal interface. For one coat adhesives, this is failure at the adhesive to metal interface. 

Cement/metal (CM) failures usually indicate a problem with metal preparation or application of adhesive. They are characterised by the appearance of bare metal in the bonded area of the part. Common causes of CM failure include poor metal preparation, i.e., the presence of contamination on the metal before application of adhesive, insufficient dry film thickness of primer, failure to properly agitate the adhesive to achieve a uniform dispersion prior to application, environmental attack (salt, water) on the primer/metal interface, dry spray of primer on to the metal (which does not allow the primer to... 

In many cases, combinations of the above failure modes appear on the same part. For instance, a failed part may show some R failure, as well as RC and CM failure. Steps must be taken to increase the proportion of R failure while reducing the other, unwanted failure modes. Bond failures are usually given in terms of the percent of the bonded area that contains a certain failure mode. For example, a failed part with the designation 65R, 15RC, 20CM means that in the bonded area, 65% of the bond surface shows failure in the rubber, 15% shows rubber/cement failure, and 20% shows cement/metal failure. 

The material in use as of the mid-1990s in these components is HDPE, a linear polymer which is tough, resiUent, ductile, wear resistant, and has low friction (see Olefin polymers, polyethylene). Polymers are prone to both creep and fatigue (stress) cracking. Moreover, HDPE has a modulus of elasticity that is only one-tenth that of the bone, thus it increases the level of stress transmitted to the cement, thereby increasing the potential for cement mantle failure. When the acetabular HDPE cup is backed by metal, it stiffens the HDPE cup. This results in function similar to that of natural subchondral bone. Metal backing has become standard on acetabular cups. 

M = failure at the interface between the primer cement and the metal. 

RC failure at the polyurethane cement interface CP failure at the cover cement primer interface CM failure at the metal primer interface R failure in the polyurethane... 

Teeth with decayed regions have traditionally been restored with metals such as silver amalgam. Metallic restorations are not considered desirable for anterior teeth for cosmetic reasons. Acrylic resins and sihcate cements had been used for anterior teeth, but their poor material properties led to short service life and clinical failures. Dental composite resins have virtually replaced these materials and are very commonly used to restore posterior teeth as well as anterior teeth [Cannon, 1988]. 

One of the principal reasons for failure of the adhesion bonds is a specific adsorption reaction of the medium with the material to be cemented at the boundary with the adhesive. There is an adsorption substitution of adhesive-substrate bonds by medium-substrate bonds. Surface structural defects that are present in each solid are the first to be subjected to adsorption. It is to be expected that the probability of appearance of such defects is higher at an interface of two materials with different properties. The rate of penetration of the medium along the polymer-substrate interface frequently substantially exceeds the rate of diffusion of the medium in pure polymer [212]. Adsorption substitution of the polymer macromolecules by water molecules on the metal surface explains the low water resistance of such adhesive-bonded joints as fluoroplastic-steel or polyethylene-steel [34]. The adhesion strength, which decreases during hold-up of adhesive-bonded joints in water, is frequently reestablished after the joints are dried [213]. 

---