Implant Dentistry Today No 14

Implant Dentistry Today 26 Implant Prosthesis: metal-free concept T he history of modern dental implantology begins with Professor Brånemark in 1965 when he put dental implants in different patients after discovering, by chance, the osseointegration property of titanium in 1952. This discovery is the basis for all implantology today. (1-5) The rehabilitation of one or more missing teeth, as well as a full mouth using dental implants, requires two fundamental parts: the intraosseous dental implant and the prosthesis or substitute for the missing teeth. The characteristic that changed the history of oral rehabilitation was the ability of titanium to bond to bone spontaneously (1-4) . Other metals had previously been tried, but without reaching the degree of osseointegration obtained with titanium. The titanium used in implantology varies according to the company, having different characteristics of purity, hardness, and biocompatibility depending on the type used. But in all cases, it has a high degree of biocompatibility. Although different authors have reported the possibility of suffering from allergy to titanium and/or corrosion of titanium due to the simple fact of being in contact with oral fluids (6-12) . This possibility or probability has been increased by the massive use of this rehabilitative technique, and has led to the search for alternatives to titanium as a material for dental implants. Some of the materials used as substitutes for titanium are zirconia (even though it is in the area of the metals in Mendeléyev’s table it has no characteristic of these, so several commercial companies supply them and their projection is very high due to their excellent biocompatibility and osseointegration) (13-16) or peek (polyether- ether-ketone) with little success so far, although the future is better as the companies manage to reduce the current problems of lack of osseointegration. (17-19) . Dental implants have evolved throughout history, but they have always maintained one characteristic (in 99% of implants) and that is to have a connection with the prosthesis. In the beginning, it was an external hexagonal connection, and later on internal connections have appeared. In all cases, the function is to retain the prosthesis. It is at this point that we focus on the possible problems that can appear due to the use of metals in the prosthesis, especially if we use non- noble metals. At the beginning of implantology, the metal used was gold or gold alloys (5) . For aesthetic reasons, resins and composites began to be used on the vestibular and occlusal sides, but these resins and composites were of poor quality, resistance, and aesthetics. For this reason, at the beginning of the 1990s, ceramics began to be used to improve the functional and aesthetic properties of prostheses (20) . A very different reason, the economic one, was the one that propitiated the change of the noble metals (gold or gold alloys) by non-noble metals for the use in the frameworks of the prosthesis (21) . The price of gold rose sharply at the end of 20th century and beginning of the 21st century, allowing a rapid increase in the use of non-noble metals. In all cases where a metal is used as a framework, it has to be covered by an aesthetic and functional material, such as resin teeth, composites, hybrid composites, ceramics, and zirconia. At this point, we will focus on metal framework. Non-noble metals, especially NiCr (Nickel-Chromium) and CoCr (Cobalt-Chromium) alloys have a physical and chemical characteristics that are totally different from gold alloys. We will divide them into corrosion, DNA allergies/mutations, and biomechanical behavior. Corrosion: Corrosion between two metals (titanium of the implant and non-noble metal of the prosthesis) is produced by an ion exchange between both (22) . The less noble the metal, the more likely it is that corrosion will occur in the implant- prosthesis-bone area. In other words, the more noble the metal (gold), less risk of corrosion. And among the non-noble metals, NiCr has a higher corrosive characteristic than CoCr (21-28) . There are also variables within CoCr: in cast frameworks (melted metal) the risk of corrosion is greater than if milling discs are used (29) . Prosthesis titanium can also cause corrosion with implant titanium, although this is very rare, (30,31) especially when the prosthesis titanium is of the same type as the implanted titanium. For this reason, it is important to use the prosthesis abutments provided by the commercial implant company since they usually use the same titanium alloy. When corrosion appears, it causes the liberation of microparticles around the peri-implant area, producing an inflammation, which will lead to a peri- implant bone loss (22, 23) . By Dr Oriol Canto-Naves . Private practice in Barcelona and Professor of the Universitat Internacional de Catalunya- Barcelona. oriolcanto@uic.es Dt. Angelo Di Franco, Brisbane: adi_franco@hotmail.com 3 Delta Dental supplies, QLD Australia. info@3deltadental.com Corrosion in the dental implant Angelo Di franco Oriol Canto-Naves Image of a buccal lichen produced by the metal of metal-ceramic crowns over implants.