One-Piece Zirconia Oral Implants for the Support of Three-Unit Fixed Dental Prostheses: Three-Year Results from a Prospective Case Series

Signs of in-vivo aging of zirconia from explanted dental implants with porous coating after several years in function

The present study investigated the in vivo aging of yttria-stabilized zirconia (YSZ) oral implants (ZiUnite®) removed after 37 to 181 months. These implants featured a porous zirconia surface to enhance osseointegration. They were placed in prospective clinical investigations and had to be explanted due to peri‑implant bone breakdown. Since no single clinical/non-clinical parameter or combination of parameters were found to influence the bone loss, we have assessed the extent of the in vivo aging, known as low temperature degradation (LTD), on five explants as a possible critical influencing parameter. This research represents, to the best of our knowledge, the first report on low-temperature degradation-induced tetragonal-to-monoclinic (t-m) transformation in clinically applied YSZ oral implants after up to 15 years. Using scanning electron microscopy (SEM) and focused ion beam (FIB)-SEM tomography, the analysis revealed significant surface t-m transformation, pronounced micro-cracking of the porous coating, and degradation. This extensive transformation and resultant volume expansion may have negatively impacted the bone-to-implant interface, contributing to clinical failure. Additionally, differently produced YSZ implants can exhibit varied behaviors, even with identical raw materials. The presented type of assessment of susceptibility to in vivo aging of oral implants could inspire the study protocol for other medical device systems. STATEMENT OF SIGNIFICANCE: This study is the first to document substantial t-m transformation of clinically used YSZ implants after up to 15 years in the oral environment. Extensive t-m transformation in the porous coatings at body temperature occurred rapidly, leading to microcracking and potential loss of cohesion with the implant bulk. The porous, cracked zirconia coatings were linked to brittle fractures in vivo and it is hypothesized that these changes possibly contributed to bone loss, loss of osseointegration and subsequent implant failures. The findings of such transformation underscore the potential clinical risks of these zirconia coatings leading to the mentioned changes. The present assessment method could serve as a valuable protocol model for investigating the in vivo aging susceptibility of other medical devices.

Five-Year Results of One-Piece Zirconia Oral Implants Supporting Three-Unit Fixed Dental Prostheses

OBJECTIVES

The purpose of the present prospective case series was to investigate the clinical and radiological outcome of one-piece zirconia implants fabricated from 3Y-TZP with a moderately roughened endosseous surface (Sa = 1.24 μm) to support three-unit fixed dental prostheses (FDP) after five years in function.

MATERIALS AND METHODS

Twenty-seven patients received a total of 54 implants in a one-stage surgery with immediate provisionalization. Peri-implant bone loss was assessed using standardized radiographs. Additionally, soft-tissue parameters were analyzed. Statistical analyses were conducted using linear mixed regression models and Wilcoxon Signed Rank tests (p < 0.05). All patients participated in an annual maintenance program.

RESULTS

Eighteen implants were lost up to the 5-year follow-up, resulting in a cumulative survival rate of 66.67%. The mean marginal bone loss of the remaining implants amounted to 1.89 mm. Probing depth, clinical attachment loss, and bleeding on probing increased from prosthesis insertion to the 5-year follow-up, while the plaque index showed no significant changes during the same period.

CONCLUSIONS

The investigated one-piece zirconia implant showed low survival rates as compared to previously reported survival rates of one-piece zirconia or two-piece titanium implants. Implant failure was attributed to peri-implantitis, leading to the necessity of implant removal. The implant is not commercially available.

Zirconia dental implants; the relationship between design and clinical outcome: A systematic review

OBJECTIVE

To evaluate the clinical outcome of different designs of zirconia dental implants.

DATA

This systematic review adhered to the PRISMA checklist and followed the PICO framework. The protocol is registered in PROSPERO (CRD42022337228).

SOURCES

The search was conducted in March 2023 through four databases (PubMed, Web of Science, Cochrane Library, and Google Scholar) along with a search of references in the related reviews. Three authors reviewed on title, and abstract level and analysed the risk of bias, and all authors reviewed on a full-text level.

STUDY SELECTION

Clinical studies excluding case reports for patients treated with different designs of zirconia dental implants were included. From a total of 2728 titles, 71 full-text studies were screened, and 27 studies were included to assess the risk of bias (ROBINS-I tool) and data extraction. After quality assessment, four studies were included, and the remaining 23 excluded studies were narratively described.

RESULT

The included prospective studies with moderate risk of bias reported success and survival rates of one-piece implants that ranged between 95 and 98.4 % with no difference between different lengths and diameters. The acid-etched roughened surface showed higher clinical outcomes compared to other surface roughness designs.

CONCLUSION

Promising 5-year clinical outcomes were found for one-piece zirconia implants with no difference between different diameters and lengths. Concerning surface roughness, better outcomes were found when using the acid-etched implant surface. However, due to the limited available studies, further high-quality clinical studies comparing zirconia one-piece and two-piece implants with different diameters, lengths, and surface roughness are needed.

CLINICAL SIGNIFICANCE

Based on this systematic review, under suitable clinical situations, the one-piece zirconia implants with diameters of 4.0 mm, 4.5 mm, or 5.5 mm and lengths of 8 mm, 10 mm, 12 mm, or 14 mm have similar promising clinical outcomes. Additionally, the acid-etched roughened implant surface may be preferable.

Clinical outcomes of zirconia implants: a systematic review and meta-analysis

PURPOSE

To assess the clinical outcomes of zirconia dental implants based on an updated systematic literature review.

METHODS

An electronic search was performed in three databases, last updated in June 2023, supplemented by hand searching. The eligibility criteria were clinical studies reporting patients rehabilitated with zirconia implants. The cumulative survival rate (CSR) of implants was calculated. A meta-analysis for marginal bone loss (MBL) under different follow-up times and a meta-regression assessing the relationship between mean MBL and follow-up were done.

RESULTS

Twenty-five studies were included (4017 implants, 2083 patients). Seven studies had follow-up longer than 60 months. 172 implants failed, after a mean of 12.0 ± 16.1 months (min-max 0.3-86.0), of which 47 early failures, and 26 due to implant fracture, the majority in narrow-diameter implants. The 10-year CSR was 95.1%. Implants with coronal part prepared by drills presented statistically significant lower survival than non-prepared implants (p < 0.001). Two-piece implants presented lower survival than one-piece implants (p = 0.017). Implants discontinued from the market presented lower survival than the commercially available ones (p < 0.001). The difference in survival was not significant between implants in maxilla and mandible (p = 0.637). The mean MBL fluctuated between 0.632 and 2.060 mm over long periods of observation (up until 132 months). There was an estimated MBL increase of 0.005 mm per additional month of follow-up.

CONCLUSION

Zirconia implants present high 10-year CSR and short-term low MBL. The review was registered in PROSPERO (CRD42022342055).

CLINICAL RELEVANCE

The clinical outcomes observed for zirconia dental implants are very promising, although these have not yet been extensively studied as titanium alloy implants.