Survival Rate and Esthetic Outcomes of 2-Piece Zirconia Dental Implants: A 1-Year Single Clinical Trial of Partially Edentulous Patients

For more than 40 years, titanium has been the primary material used in implant dentistry.¹  However, the search for alternatives has been spurred by esthetic concerns and the possibility of an allergic hypersensitivity reaction. The reflection of titanium through the mucosa may cause esthetic problems, mainly when thin mucosal phenotypes are present.²  Furthermore, at least among Europeans, there is a growing demand for metal-free alternatives.³ 

Ceramic implants, especially those made of zirconia, address these concerns, offering esthetic appeal and commendable mechanical properties.^4,5  In recent years, ceramic materials have emerged as a promising alternative to traditional titanium in the fabrication of endosseous dental implants. Specifically, yttria-stabilized tetragonal zirconia polycrystal (YTZP), commonly called zirconia, has gained prominence due to its remarkable mechanical stability.^6,7  This stability is attributed to zirconia’s unique ability to mitigate crack propagation by converting individual crystallites into a thermally stable allotrope, resulting in enhanced bending strength and fracture toughness. Coupled with its resistance to wear, chemical inertness, high biocompatibility, and reduced bacterial colonization, zirconia stands out as an optimal material for dental implants.^8,9 

Most recorded results concerning zirconia implants pertain to single-piece designs, primarily due to the complexities involved in integrating a screw-type connection with zirconia elements at the junction of the abutment and implant and the reduction of bone loss by eliminating the implant–abutment microgap and associated micromovements. However, single-piece implants are only helpful in situations in which immediate loading is possible, and their prosthetic adaptability is restricted.^8,10  The advent of 2-piece zirconia implants has shown encouraging results in both clinical studies and real-world applications.^11,12  Notably, the manufacturing landscape for zirconia implants is evolving with ceramic injection molding offering a cost-effective method for mass production. This technique capitalizes on the implant’s simultaneous molding and surface engineering, streamlining the production process.¹³ 

The decision to opt for 1- or 2-piece zirconia implants depends on individual cases as neither method has proven superior to the other.¹⁴  Therefore, the absence of clinical trials examining 2-piece zirconia implants highlights the need for further research. Consequently, this study examines the performance of 2-piece zirconia implants over a year, focusing on understanding their survival rate and related tissue parameters. The research hypothesis, informed by existing literature, posits that the survival rate of zirconia implants is comparable to that of titanium implants with an estimated survival probability of around 95%. Consequently, we anticipate that the performance and longevity of zirconia implants will align with that of titanium implants, which have been used for the past 40 years.

A prospective pilot trial was conducted at a single center within Department of periodontology, School of graduate dentistry, Rambam Health care Campus. The study was approved by the [redacted for peer review] ethics committee (RMB-0382-19) and registered at ClinicalTrials.gov (identifier NCT05105113). This study meets the current World Medical Association Declaration of Helsinki—Ethical Principles for Medical Research Involving Human Subjects. An independent statistician reviewed and approved the study design.

Participants were sequentially enrolled if they (1) were at least 18 years of age and provided written consent before treatment; (2) had a horizontal bone width of a minimum of 6 mm and (3) implant stability above 35 N during insertion; and (4) committed to adhering to the outlined schedule for clinical, radiographic follow-ups and maintenance visits.

Individuals were disqualified from the study if they met any of the following conditions: (1) smoked more than 10 cigarettes daily; (2) exhibited active periodontal disease evidenced by probing depths exceeding 5 mm, bleeding upon probing (BOP), or suppuration; (3) were noncompliant or did not provide consent; (4) had systemic contraindications to implant procedures, such as immunodeficiency or severe systemic diseases, or were on medications such as corticosteroids or bisphosphonates; (5) were pregnant; (6) had undergone radiation therapy in the head or neck region; (7) required bone or soft-tissue augmentation; or (8) exhibited parafunctional habits.

Between 2021 and 2022, a single surgeon (HZG) placed 9 2-piece tissue levels of YTZP implants (TAV Dental, Ltd.) (Figure 1) in 8 patients. All implants had a diameter of 4.1 mm and a length of 10 or 12 mm. Before surgery, patients were administered preoperative antibiotics, either 2 g of amoxicillin or 600 mg of clindamycin. Once the flaps had been raised, drilling was carried out per the manufacturer’s guidelines using all available drill diameters, followed by implant insertion. The implants were placed about 1.8 mm supra-crystally (tissue-level implants), and healing abutments were placed. Postoperative instructions included antibiotics (amoxicillin 1500 mg per day or clindamycin 600 mg per day for 1 week), analgesics, and rinsing twice daily with chlorhexidine 0.2%. Sutures were removed after 1 week.

Following a 3-month osseointegration period for both the upper and lower jaws, conventional impressions were taken using polyether (Impregum NF, 3M ESPE, Seefeld, Germany). Based on these impressions, dental molds were created and then scanned. Utilizing this scanned information, all-ceramic crowns were designed and fabricated from lithium disilicate (IPS e.max CAD blocks, Ivoclar Vivadent) using the Cerec AC system from Sirona (Figure 2).

Plaque accumulation and mucosal inflammation parameters were measured by the same calibrated examiner (DR) at 3 time points—3, 6, and 12 months—and included the following:

• Plaque index, according to Sillness and Löe (1964), is measured on the buccal and lingual surfaces. The scoring ranges from 0 (no plaque) to 3 (heavy plaque accumulation).

• Gingival index, according to Löe and Stillness (1963), is measured on the buccal and lingual surfaces. Scoring ranges between 0 (absence of inflammation) and 3 (severe inflammation: marked redness, hypertrophy, and tendency toward spontaneous bleeding).

Other clinical parameters were recorded by the same examiner (DR) after 3 and 12 months:

• Peri-implant pocket depth (PD) was measured from the mucosal margin to the bottom of the probable pocket using a graduated manual periodontal probe (PCP-UNC 15, Hu-Friedy, Chicago, IL). Four sites per implant were evaluated (mesiobuccal, midbuccal, distobuccal, and midlingual).

• BOP in 4 sites (mesiobuccal, midbuccal, distobuccal, and midlingual) was evaluated dichotomously with either the presence or absence of bleeding within 30 seconds following probing.

• Recession depth was measured from the implant–abutment interface to the mucosal margin at the midbuccal aspect using a graduated manual periodontal probe (PCP-UNC 15, Hu-Friedy). In cases with a mucosal margin coronal to the implant shoulder, it was considered to be 0.

• Soft tissue color and soft tissue texture were based on the pink esthetic score, according to Fürhauser (2005), to assess the soft tissue esthetics around the dental implants (0 = clear difference, 1 = slight difference, 2 = no difference).

Peri-apical X rays were captured using the Planmeca Intra X-ray unit with an intraoral sensor set at 63 kV, 8 mA, and 0.064 s, combined with the XCP-DS FIT Universal Sensor Biteblock (Dentsply, Lancaster, PA). The implant’s width served as a calibration reference for the radiographs. The bone level was measured as the distance from the top edge of the implant to the first point of bone contact on both the mesial and distal sides of the implant with 1.8 mm being deducted from this measurement. This was achieved using the Planmeca Romexis image analysis software (version 3.8.1.R, Planmeca OY, Helsinki, Finland). All radiographic evaluations were conducted twice by a single examiner (JH), who was calibrated. Measurements were performed immediately after implant insertion, after 3 months (before implant loading), and at 12 months.

Two repeated evaluations were performed to assess the consistency of the observer’s measurements. The discrepancies between these measurements were analyzed using point estimates and a 95% confidence interval. The outcomes for the radiographic evaluations were as follows: mesial side difference of d = 0.11 mm (95% CI 0.033–0.18), P = .006, and distal side difference of d = -0.004 mm (95% CI -0.083–0.075), P = .914.

Peri-implant crevicular fluid (PICF) and gingival crevicular fluid (GCF) samples were collected from implants and contralateral teeth 12 months after implant placement. First, supragingival plaque was carefully removed using currets, after which the sample sites were isolated with cotton rolls. Four absorbent paper points no. 25 (Meta Biomed 270, Republic of Korea) were inserted into the base of the pocket around the implant and contralateral tooth for 30 seconds. Samples were wrapped in aluminum foil and stored at -20°C. Every sample was concealed before the laboratory test. The total IL-1β level in PICF was determined using a quantitative sandwich enzyme-linked immunosorbent assay (ELISA) kit (Human IL-1 beta/IL-1F2 Quantikine ELISA Kit DLB50 human Il-1b, biotechne, R&D Systems Inc., Minneapolis, MN) as described previously by Mayer et al.¹⁵  Briefly, filter papers were unwrapped and inserted into a sterile test tube containing 1.0 mL distilled water. The tubes were left to stand at room temperature for 30 minutes and then agitated every 5 minutes to facilitate extraction of the sample from the filter paper. A monoclonal antibody specific for IL-1β was precoated on a microplate. Standards and samples were pipetted into the wells, and the immobilized antibody bound the cytokine. After washing away any unbound substances, an enzyme-linked polyclonal antibody specific for IL-1β was added to the wells. The absorbance values were determined by using an ELISA reader at 450 nm. A standard curve was constructed using standards provided in the kit, and the cytokine concentration was calculated from this standard curve. The color intensity results were obtained using a microplate reader.¹² 

The study analyses were performed by independent statisticians using SPSS software version 25.0. Microsoft Excel (Microsoft Corporation) was used for data collection. Descriptive variables were presented with mean and standard deviation. Intragroup comparisons were performed over time using a Wilcoxon signed-rank test. Differences were considered significant at p < .05.

Eight subjects (6 females and 2 males) were recruited for this pilot study. The demographic data is shown in Table 1. The age of the participants ranged from 31 to 63 years with a mean of 40.8 ± 10.7 years. Two participants were current smokers (<10 cigarettes per day). Nine implants were included in the study, 2 in the mandible and 7 in the maxilla.

One implant failed 6 months after restoration. This implant was placed in the second mandibular molar. The patient arrived at the clinic with symptoms of a peri-implant abscess. The implant was mobile, and peri-implant bone loss was observed. The implant was removed from the jaw.

The clinical parameters are described in Table 2. The plaque index and gingival index were less than 1 for all the observatory times, and the mean pocket depth was 3.18 ± 1.28 mm at the 1-year follow-up. Soft tissue color and texture were 1.85 ± 0.38 and 1.88 ± 0.35 after 12 months with a nonsignificant change compared with 3 months.

Figure 3 demonstrates radiographic marginal bone level changes in the mesial and distal aspects. The zirconia implants were associated with a mesial mean bone loss of 0.65 mm (SD: 0.37) after 3 months and 0.91 mm (SD: 0.59) after 12 months. On the distal side, the values were 0.59 mm (SD: 0.37) after 3 months and 0.87 mm (SD: 0.4) after 12 months.

IL-1β was examined in the PICF and GCF of the contralateral tooth at 12 months. Results showed an average level of 24.86 pg/ml of IL-1β in the PICF and 22.68 pg/ml in the GCF. The difference between the sites was not statistically significant (p > .05) (Figure 4).

In this prospective pilot cohort study, we scrutinized the performance of 2-piece zirconia implants, primarily in the context of replacing individual missing teeth. A year postimplantation, the observed survival rate was 88.8%. This rate, especially after 1 year, is marginally lower than those reported in certain existing studies comparing ceramic and titanium implants.^13,14  The overall documented survival rates for zirconia implants, considering both types (1- and 2-piece), fluctuate between 87% and 95%. Considering a year of functional use, the average survival rate is 92%.^11,13,16,17 

Comparatively, a recent retrospective analysis highlights that zirconia endosseous implants potentially match titanium implants in terms of survival rate while preserving the health of soft and hard tissues alike.^18,19  Specifically, Brull et al²⁰  examined 121 zirconia implants (66 2-piece and 55 1-piece) placed in 74 subjects. After an average monitoring span of 18 months, they reported a robust implant survival rate of 96.5%. This aligns with the findings from the Cionca et al¹²  prospective study on 32 patients, in which they documented a cumulative survival rate of 87% after 1 year of loading with all failures attributed to aseptic loosening, which is a process of bone resorption due to a noninfectious cause. Variations in connection systems, implant designs, and implant manufacturing processes may cause discrepancies across the studies. The current study’s sample size is extremely small: just 1 implant failure out of 9.

Our investigation included a critical measurement of bone loss on both the mesial and distal sides. More than 1 year after implant surgery, we observed a distal bone recession averaging 0.87 ± 0.4 mm. The mesial side exhibited a slightly more pronounced decrease, averaging 0.91 ± 0.59 mm. For context, a systematic review and meta-analysis by Elnayef et al⁴  documented an average marginal bone loss of 1.46 ± 9.57 mm associated with 2-piece zirconia implants. Correspondingly, Borges et al²¹  reported in their systematic review that marginal bone remodeling around zirconia implants resulted in average losses of 0.8 mm (95% CI: 0.60 to 1.00 mm) and 1.01 mm (95% CI: 0.72 to 1.29 mm) at 1 and 2 years after loading, respectively.

It is essential to notice that, according to several previous studies that examined tissue-level titanium implants, the average marginal bone loss during the first year was 0.2–0.61 mm, which is less than the results in our study.^22–25  Bone loss is generally found to be lower in 1-piece implants compared with 2-piece implants.^26,27  A systematic review comparing 1- and 2-piece titanium implants found no significant differences in marginal bone loss between the 2 options.²⁸ 

Interleukin-1’s role is paramount in the sphere of immune-inflammatory responses, essentially ensuring the maintenance of periodontal equilibrium. Elevated levels of the inflammatory cytokine interleukin-1 (IL-1) in the crevicular fluid around diseased implants play an important role in the pathogenesis and severity of peri-implantitis.²⁹  Over the years, myriad research undertakings have delved deep into understanding the intricate relationship between prevalent polymorphisms of IL-1 (specifically IL-1A and IL-1B) genes and the heightened risk factors associated with peri-implant ailments and implant failures. However, the verdict remains clouded with ambiguity. Notably, in the existing corpus of research, an endeavor had yet to be made to decipher the potential link between IL-1 and zirconia implants.³⁰  A previous study that examined 130 titanium implants found significantly higher levels of IL-1β in patients with peri-implant diseases such as mucositis (325.89 ± 235.17 pg/mL) and peri-implantitis (439.89 ± 182.67 pg/mL) compared with healthy implants (67.51 ± 62.9 pg/m).³¹ 

A focal point of our research revolved around analyzing the concentration of IL-1β levels in PICF and GCF samples extracted from the implants and control teeth. Surprisingly, the data amassed in the subsequent 12 months did not indicate any momentous deviations. Further, the ELISA results failed to draw any parallels with PD and BOP measurements. A similar absence of correlation was also evident between the marginal bone loss recorded during the subsequent monitoring phase and the 12-month ELISA results.

A notable limitation of this study is the small number of implants included in our analysis. This constraint might influence the perceived survival rates and serves as a primary restriction on the breadth of our research. Another challenge is the relatively short observation period. Unfortunately, long-term research in this field is still emerging with most studies chiefly centered on the 1-piece zirconia implant designs.^12,31,32 

During the research, we did not encounter any noticeable prosthetic complications. A common issue with zirconia implants is that the connecting parts can break. However, the 2-piece design usually makes it easy to swap out any broken parts.¹⁴ 

In summary, zirconia dental implants demonstrated minimal bone loss 1 year following their placement (0.6–0.9 mm) with a single implant failing to osseointegrate. However, given the limited sample size, this translates to an 88% survival rate at the 1-year mark.

The findings suggest that 2-piece ceramic implants may yield positive clinical results during the follow-up period. Their survival rates and bone loss metrics are on par with titanium and other ceramic implants. These implants may provide a viable and practical choice for individuals looking for metal-free options, especially those who prefer to avoid metal in their treatments. Extended studies encompassing various edentulous morphologies are required to validate the current data.

The study was approved by the Rambam Health Care Campus Ethics Committee (RMB-0382-19) and registered at ClinicalTrials.gov (identifier NCT05105113). The study was supported by TAV Dental Company, Ltd. Informed consent was obtained from all subjects involved in the study. The authors declare no conflict of interest. Author contributions are as follows: validation—Y.M. and E.M.; data curation—Y.M. and O.G.; writing original draft—Y.M. and L.K.; visualization—Y.M. and E.G.; software—O.G. and J.H.; investigation—D.R., J.H., and Z.G.; methodology—Z.G.; resource—H.Z.G.; conceptualization—H.Z.G.; supervision—H.Z.G.; writing, review, and editing—H.Z.G.