Results

The search yielded 5 articles, of which 3 were included in the review.^{11, 34, 35} Two articles were excluded, because they did not report on dental implants of PEEK.^{36, 37}

Of the included articles, 2 reported on animal investigations^{34, 35} and 1 on an in vitro finite element study.¹¹

The aim of the 3-dimensional finite element study was to compare the stress distribution to the peri-implant bone in 4 distinct testing models consisting of either a titanium or a carbon fiber–reinforced PEEK (CFR-PEEK) implant, containing 30% carbon fibers to obtain an elastic modulus of 17.4 GPa similar to that of cortical bone,²⁷ each in combination with a titanium and a CFR-PEEK abutment, completed with a cemented artificial crown (Table 1).

The CFR-PEEK implants presented a higher load concentration in the cervical area and at the cortical bone than the titanium implants, whereas the titanium implants presented equivalent stress peaks in the cervical portion and a more homogenous load distribution throughout the whole implant body (Table 1).

The authors admit that the higher stress concentrations of the PEEK implant were not expected. A more homogenous stress distribution was intended to diminish stress peaks at the implant-bone interface. So, they conclude that the CFR-PEEK implant did not present any advantages in comparison to the titanium implant.

This material was also used for cylindrical implants in an animal experiment, which compared the bone-implant contact (BIC) and shear strength of 20 titanium-coated implants to 20 uncoated implants.³⁵ In this study 5 implants were inserted in each femur of 4 mongrel dogs, 5 uncoated on one side and 5 titanium-coated on the other side. After 4 and 8 weeks of healing, 2 dogs were sacrificed. Of each femur, 3 implants underwent pull-out testing to determine the mechanical integrity of the interface. The other 2 implants of each femur were reserved for intact histologic evaluation.

The coated implants showed significantly BIC values after a healing period of both 4 (P = .0014) and 8 weeks (P = .0261), whereas the BIC of both the uncoated and the coated implants generally decreased from 4 to 8 weeks. The shear strength for the uncoated implants was significantly higher after 4 (P = .0107) and lower after 8 weeks (P = .2496) (Table 2). The authors conclude that the addition of the titanium coating apparently increases the biocompatibility of the implant surface. Using the BIC ratio as a parameter for the grade of osseointegration, it can be stated that both CFR-PEEK implants (coated and uncoated) presented a desirable osseointegration in comparison to the BIC values of the titanium implants (40.91 ± 10.11%) of the second animal experiment³⁴ (Table 2). The aim of that study was to evaluate osseointegration of 1-piece zirconia vs titanium implants depending on their insertion depths after a healing period of 4 months due to a split-mouth design (submerged vs nonsubmerged healing). Therefore, the test implants made from zirconia and coated zirconia (covered by a calcium-liberating titanium oxide [TiO₂] sol-gel layer) were compared to a control implant made from titanium. Additionally, an experimental implant of PEEK was inserted. All implants had the same design, only differing in their biomaterials. In this study, the PEEK implants reached BIC rates of 26 ± 8.9%.

In neither of the 2 animal investigations were signs of inflammation or foreign body reactions observed.