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Prosthetic suprastructure

Daily oral care should include thorough removal of biofilms and plaque adherent to the surface of teeth and prosthetic restorations. Implant restorations regularly feature an interface between abutment and prosthetic suprastructure (in two-piece implants) or between implant and prosthetic suprastructure (in one-piece implants), which is substantially larger than the implant/abutment interface (O’Mahony et al., 2000) and may serve as an additional retention site for microorganisms. Thus, large interfaces between abutment/implant and prosthetic restoration can hamper and complicate oral hygiene; thus—although no threshold has yet been defined—interfaces should be minimized. Moreover, supragingival positioning of the interface between abutment/ implant and prosthetic restorations has been recommended (O’Mahony et al., 2000).

Role of dental cement in biofilm formation on dental implants

Apart from the implant and abutments surfaces, the role of dental cements used for the luting of fixed crowns and bridges to implant abutments in the etiology and pathogenesis of periimplant infections has been highlighted by several groups during late 2000s and mid-2010s. In cemented restorations, several researchers have proven that if excess cement is not meticulously removed, periimplant infections are very likely to occur (Wilson, 2009; Linkevicius et al., 2013; Korsch et al., 2015a,b,c) (Fig. 5.7).

As the manifestation of periimplantitis differed markedly between few months up to several years after insertion of the restorations, it is likely that patient-specific factors substantially impact the pathogenesis of periimplant infections in patients with cemented implant restorations and excess cement. With regard to this aspect, the correlation between excess cement and the onset of periimplant inflammations appears to be particularly strong in patients with a history of periodontal disease (Pesce et al., 2015).

Regarding the processes involved in biofilm formation, it is likely that dental cements feature favorable conditions for the adhesion and proliferation of microorganisms. Some groups have investigated the adhesion of microorganisms to the surface of cements which are frequently employed for the luting of implant restorations in vitro. They discovered that temporary luting cements made from zinc oxide feature a low susceptibility to adhere oral microorganisms, whereas high levels of adherent streptococci and staphylococci were identified on the surface of definite luting cements, such as zinc oxide phosphate cement, glass ionomer cement, and resin cements. The authors attributed these observations to the lower surface roughness identified for the

Radiograph of an implant with periimplant bone loss resulting from excess cement

Figure 5.7 Radiograph of an implant with periimplant bone loss resulting from excess cement.

temporary cements (Winkler et al., 2014). An investigative clinical study identified extended biofilm formation on the surface of dental luting cements, which were placed subgingivally in modified healing caps. The authors failed to identify significant differences between the various cements regarding the extent of biofilm formation, yet authors showed that biofilm formation was significantly increased on the surface of the cements and on the surface of the cement-titanium interface in comparison to polished titanium (Papavasileiou et al., 2015). Although clinical studies on the effect of cements on periimplant tissues are rare, in 2015 a German group investigated clinical parameters such as suppuration, bleeding on probing and periimplant bone loss around dental implants with suprastructures luted with either a methacrylate- or a zinc oxide-based temporary cement. The authors showed that the clinical parameters were significantly worse in implants with restorations luted with the methacrylate-based cement (Korsch and Walther, 2015; Korsch et al., 2015b,c). These observations have been attributed to the more complex removal of excess resin cements, its lower viscosity in comparison to zinc oxide cement, the higher solubility of zinc oxide temporary cements in aqueous surroundings, and an antimicrobial effect of the eugenol included in zinc oxide temporary cements (Korsch et al., 2014). Moreover, increased biofilm formation on the surface of the resin cements in comparison zinc oxide cements has been discussed (Korsch et al., 2014), which is in agreement with the laboratory studies performed in this matter. Regardless of an excess of cement, Korsch et al. (2015a) identified an accumulation of periodontal pathogens, such as Tannerella, Treponema, and Porphyromonas species in the periimplant microbial community in patients with suprastructures luted with resin cement, whereas an abundant number of commensal oral bacteria, such as Streptococcus species, were identified in patients with suprastructures luted with zinc oxide temporary cements. However, it has also been highlighted that the presence of cement does not a priori induce a predictable shift in the microbial diversity of biofilms in implant sites (Obst et al., 2012). Nevertheless, although the existing scientific literature is scarce, the current data suggest that in cemented suprastructures on dental implants, temporary zinc oxide materials should be employed for the prevention of periimplant infections.

 
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