Articles - Forum Implantologicum

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Feature Article

May 27, 2018 // 17 min read

Osseointegration of Zirconia Dental Implants: A Review of Preclinical Data

DOI: 10.3290/iti.fi.45663

Abstract

Background: Due to its advantageous physical, biological, and esthetic properties as well as its resistance to corrosion, zirconia as a biomaterial to replace missing tooth roots has been the focus of great interest and may become a reliable alternative to titanium implants.

Aim: To present and discuss the preclinical data available on osseointegration of zirconia implants placed in the jawbone.

Results: A great number of preclinical studies on zirconia implants with histologic and histomorphometric data are available. Zirconia implants were tested with different implant dimensions and designs, different surface treatments (e.g. machined, sandblasted, acid-etched, alkaline-etched, fusion-sputtered, selective infiltration-etched, powder injection molding, laser-treated, plasma-treated, microgrooved), in different species (i.e., rabbit, monkey, sheep, miniature pig, rat, dog) and different anatomical locations (i.e. tibia, femur, pelvis, maxilla, mandible), under different loading conditions, and with different observation periods (i.e. 1 - 56 weeks). Taken together, the bone-to-implant (BIC) values reported in the literature for zirconia implants placed in the jawbone range from 18% to 89% with many values in the order of 50% - 75%. All in all, most preclinical studies and reviews concluded that the BIC values did not reveal statistically significant differences between zirconia and titanium implants. Furthermore, most studies and most reviews come to the conclusion that modified zirconia surfaces have higher BIC values than machined ones.

Conclusions: Most preclinical studies and reviews conclude that zirconia and titanium implants have similar BIC values. Nevertheless, the survival and success rates of zirconia implants documented in clinical studies are dependent on the implant type/system and somewhat inferior to those of titanium implants. More solid, long-term clinical data on zirconia implants are needed and differences between implant systems and surgical procedures need to be evaluated.

Introduction

Since Brånemark et al. (Brånemark et al. 1969) provided evidence for direct bone apposition on the surface of titanium in the late 1960s, titanium has been the material of choice for dental implants due to its proven biocompatibility and superior mechanical strength and resilience. Different grades of purity exist (grades 1 to 4). Grade 4 titanium is most commonly used and studied in implant dentistry due to its mechanical strength and biocompatibility (Le Guehennec et al. 2007). Because of their high strength, titanium alloys such as Ti6Al4V and TiZr are also used for dental implants. Despite excellent clinical performance, there are reported limitations to titanium implants including visibility due to a gray hue, particle release as a result of increased surface roughness, ion leakage as a result of corrosion (Noronha Oliveira et al. 2018) and hypersensitivity to the biomaterial (Fage et al. 2016). These limitations may be the reason why alternatives to titanium implants are on the rise.

Zirconia (ZrO₂) may be one alternative to overcome the potential drawbacks of titanium. Due to its advantageous physical, biological, esthetic and corrosion properties (Chen et al. 2016, Cionca et al. 2017, Sivaraman et al. 2017), zirconia as a dental biomaterial for endosseous implants has been the focus of great interest in recent years. Although the mechanical stability of zirconia is increased by the addition of tetragonal polycrystals of yttrium (Y-TZP), wear and fracture of zirconia are still a concern (Chen et al. 2016, Cionca et al. 2017).

This review aims to present and discuss the data available from preclinical studies on osseointegration of zirconia implants placed in the jawbone with a focus on bone-to-implant contact (BIC). For clinical data on zirconia dental implants, readers are referred to recent reviews (Cionca et al. 2017, Depprich et al. 2014, Elnayef et al. 2017, Hashim et al. 2016, Pieralli et al. 2017). Although important to the long-term success of dental implants, soft tissue integration of zirconia will not be discussed in this review (for reviews, see Linkevicius & Vaitelis 2015, Sanz-Martin et al. 2018, Sculean et al. 2014)). Similarly, data from in vitro studies will also not be discussed in this review.

Fig. 1: Osseointegration of a titanium implant placed in the canine mandible

Fig. 2: Osseointegration of a titanium (A) and zirconia (B) implant after 6 weeks of healing and 4 weeks of loading in the canine mandible. Old bone (oB) and newly formed bone (nB) can be seen. Higher magnification shows bone apposition and an absence of multinucleated giant cells on the zirconia implant surface. A thick layer of newly formed bone (nB), osteoid (O), and osteoblasts (OB) is visible after 4 weeks of loading (C), whereas mature bone (mB) and bone marrow (mBM) indicate full maturation after 16 weeks of loading (D) (from Janner et al. 2017 with permission)

Fig. 3: Osseointegrated (A) titanium (Ti), (B) alumina-toughened zirconia (ZrO₂/Al₂O₃), and (C) zirconia (ZrO₂) implants after 4 weeks of healing and tissue integration in a miniature pig maxilla (from Chappuis et al. 2016 with permission)

Fig. 4: Higher magnifications of osseointegrated (A) titanium (Ti), (B) alumina-toughened zirconia (ZrO₂/Al₂O₃), and (C) zirconia (ZrO₂) implants after 4 weeks of healing and tissue integration in the maxilla of a miniature pig. Both new and old bone are present on and adjacent to the implants (from Chappuis et al. 2016 with permission)

Fig. 5: Histogram illustrating the percentage of bone-to-implant contact (%BIC) for titanium (Ti), alumina-toughened zirconia (ZrO₂/Al₂O₃), and zirconia (ZrO₂) implants after 4 and 8 weeks of healing in the maxilla of a miniature pig (modified from Chappuis et al. 2016 with permission)

Fig. 6: Graph illustrating the effect of implant surface modifications on the percentage of bone-to-implant contact (%BIC) for sandblasted (SB), sandblasted and acid-etched (SB-AC), and sandblasted and alkaline-etched (SB-AL) zirconia implants (modified from Saulacic et al. 2012 with permission)

Fig. 7: Multinucleated giant cells (arrow) on a micro-rough Ti6Al4V implant surface (from Saulacic et al. 2012 with permission)

Fig. 8: Multinucleated giant cells (arrows) in contact with (A) titanium (Ti), (B) alumina-toughened zirconia (ZrO₂/Al₂O₃), and (C) zirconia (ZrO₂) implants after 4 weeks of healing (from Chappuis et al. 2016 with permission)