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ePaper created 2017-11-09, 09:28:26 | version 1.38.0
| research partly combined with screw fracture/loosening. Failures concerning the abutment/ implant region around the screw, indicate that the con- necting design is crucial for clinical success. m o c . k c o t s r e t t u h S / a g i v d e N . A r e d n a x e A © l Additionally, a study by Neu- Additionally, a study by Neu- mann et al. (2014) compared the frac- mann et al. (2014) compared the frac- ture resistance of abutment retention ture resistance of abutment retention screws made of titanium, polyetherether- screws made of titanium, polyetherether- ketone (PEEK) and 30 per cent carbon fi- ketone (PEEK) and 30 per cent carbon fi- bre-reinforced PEEK, using an external hexag- bre-reinforced PEEK, using an external hexag- onal implant/UCLA-type abutment interface assembly.23 UCLA-type abutments were fixed to implants using tita- nium screws (group 1), polyetheretherketone screws (group 2), and 30 per cent carbon fibre-reinforced PEEK screws. They found that the titanium screws had higher fracture resistance, compared with PEEK and 30 per cent carbon fibre-reinforced PEEK screws. Screwing abutments can be the trend, but cementation on the other hand could be a simpler and less time-con- suming procedure as it is also shown in the study by Brüll et al. (2014).24 It is closer to the dentist’s basic education, resembles the procedure of cementing a post in natural endodontically treated teeth and requires no extra instru- ments. A combination of both screwing and cementing though, could make the procedure more complicated. More studies are required to determine the proper abut- ment material, cementation method and procedure. The restoration materials that will be used together with their limitations should be studied. Mostly fixed prosthetics on single crowns or small bridges have been presented. The fracture resistance of two-piece zirconia and titanium implant prototypes un- der forces representative of a period of five years of clin- ical loading was tested, during an in vitro experiment by Kohal et al. (2009).25 In this experiment the crown mate- rials had no influence on the fracture strength of the zir- conia implants. Still, in certain cases such as treating a patient with parafunctional chewing, a softer prosthetic material could be a wise choice. The need for further investigation on removable prosthetics on zirconia im- plants should be kept in mind, too. Peri-implantitis apical to the pocket epithe- apical to the pocket epithe- lium contains large propor- lium contains large propor- tions of plasma cells and lym- tions of plasma cells and lym- phocytes but also PMN cells phocytes but also PMN cells and macrophages in high and macrophages in high numbers.27, 28 Peri-implantitis numbers. though has hardly been re- though has hardly been re- ported on zirconia implants. ported on zirconia implants. Zirconia demonstrates a low Zirconia demonstrates a low affinity to bacterial plaque, affinity to bacterial plaque, small amounts of inflammatory small amounts of inflammatory infiltrate and good soft tissue inte- infiltrate and good soft tissue inte- gration. These properties might lower the risk gration. These properties might lower the risk for peri-implant diseases.1–3 This hypothesis is strength- for peri-implant diseases.1–3 This hypothesis is strength- ened by the results of the study conducted by Nasci- mento et al. (2014), where cast and polished titanium were presented with the highest incidence and total count of bacteria, while zirconia showed the lowest.29 Rosenberg et al. (1991) claimed distinct differences be- tween bacterial profiles of infected and overloaded titanium implants.30 The latter were characterised by the absence of motile rods, spirochetes and classical periodontopatho- gens, along with a predominance of Gram-positive organ- isms, similar to what is observed in periodontal health. These observations were supported by Quirynen and List- garten in 1990.31 Failures of zirconia implants due to bacte- ria, should be differentiated against those of technical rea- sons and the microbiota should be investigated. It should be kept in mind that bacterial cells have a net negative charge on the cell wall, although the magnitude of this charge var- ies from strain to strain. Especially on the Gram-negative bacteria, LPS as a major component of their cell membrane increases even more the negative charge.32 Titanium is also negatively charged, thus acting repul- sively to bacteria. This could be one of the reasons of success of titanium implantation in a contaminated en- vironment. Zirconia though has no electric charge. De- pending on the roughness and the hydrophilic surface of every zirconia implant system, contamination may be easier to occur and this could be a reason of early fail- ure when zirconia is implanted in a contaminated envi- ronment. Studies are needed to clarify whether the latter could affect the osseointegration result and what is the relative danger comparing to titanium. Local disinfection could minimise the risk in immediate implantation using the help of ozone and autologous plasma. Nutrition and food supplements could also be helpful, too. Peri-implantitis in titanium implants is a serious and underestimated problem involving millions of implants. The prevalence of peri-implantitis according to the re- view of Zitzmann and Berglund (2008) varies between 12 and 43 per cent of implant sites.26 Many aetiologi- cal factors have been implicated, bacterial contamina- tion among them. In peri-implantitis, the lesion extended Intolerance to titanium and genetic predisposition to inflammation has been introduced as an additional and independent risk factor (Odds Ratio 12 and Odds Ratio 6 respectively) for peri-implantitis.33 The authors propose a direct effect of the released microparticles of titanium on the immunological mechanism of the body that could possibly initiate peri-implantitis. Zirconia particles on the 10 implants 1 2017