Discussion

Intraoral conditions (saliva pH, acidic drinks, bacterial plaque, etc.) interact with metals, increasing corrosion, a phenomenon that also affects titanium implants. Amongst other reasons, this is whereby patients increasingly request the use of materials free of metallic alloys. In response to this growing demand, zirconia implants are considered an alternative, due to their low reactivity.

In recent years, several implant manufacturers have investigated the behaviour of zirconia implants on hard and soft tissues. The characteristics of their biocompatibility, together with good osseointegration, make them clear candidates for clinical use in dentistry. One of the advantages of these implants is the absence of cracks (gap) between pillar and implant since they are made in a single block. (Bredent®, Straumman®). However, this feature implies the need to carve the pillars to achieve proper parallelisation.

Several studies have shown that zirconia implants present a similar healing pattern to titanium implants, both as regards the healing time and marginal bone stability. However, there is a controversy over the long-term stability of the bone-implant interface, which depends on several factors such as surface, composition and design of the implant. Other important factors to consider are the implant-stump-crown connection, as well as the composition of the restorative material and the occlusal load transmitted by the antagonist tooth.

In terms of the load-cushioning capacity of the prosthetic elements, the use of PEEK as a prosthetic structure on implants has increased in recent years. PEEK is a high-density thermoplastic polymer with a linear aromatic semi-crystalline structure that has exceptional physical and chemical properties as regards toughness, hardness and elasticity. Also, its low molecular weight, combined with the absence of metal, allows its use as excellent biocompatible prosthetic denture material.

PEEK has a modulus of elasticity (E-modulus 4 GPa) great overdenture implants compared to other conventional materials such as titanium (E-module 110 GPa) or zirconium dioxide (E-modulus 210 GPa).

In addition, the bending resistance of metal-ceramic restorations stands at around 400 to 600 Mpa., in contrast to new composite coatings that have a Vickers hardness of approximately 400 MPa and a bending capacity of 314 MPa. Conversely, zirconia is three times harder (1200 HV) and its resistance to bending is 1400 Mpa.

As a whole, all of these features mean that the use of materials of high rigidity will result in direct transmission of chewing forces to the zirconia implant. This potential overload could cause bone reabsorption around the implants. Some authors claim that this relation only exists in cases accompanied by a previous inflammatory process (of infectious origin), where bone loss would be accelerated.