Zirconia Dental Implants: A Clinical, Radiographic, and Microbiologic Evaluation up to 3 Years Felix Brüll, DDS1/Arie Jan van Winkelhoff, PhD2/Marco S. Cune, DDS, PhD1 Purpose: To retrospectively evaluate the clinical performance of zirconia endosseous implants. Materials and Methods: Partially edentulous patients with adequate bone volume to fit yttria tetragonal zirconia polycrystal (Y-TZP) implants at least 3.5 mm wide and 8.0 mm long were included. Full-mouth probing pocket depth (PPDs) and percentage bleeding on probing (BOP) scores around teeth and implant(s) were assessed and compared. Marginal bone loss/gain relative to baseline was measured on intraoral radiographs, and the prevalence and quantities of seven periodontal bacteria were assessed around implants and teeth in the same patient. Results: Seventy-four consecutively treated patients with 121 zirconia implants (66 two-piece implants and 55 one-piece implants) were clinically evaluated after a mean observation period of 18 months. Three implants had failed and had been removed, for a cumulative implant survival rate of 96.5% (± 2.0%) after 3 years. The 118 surviving implants demonstrated healthy mucosal conditions, with low mean PPDs (1.8 ± 0.4 mm) and mean BOP scores (4.1% ± 4.2%). PPD and BOP were statistically significantly lower around implants than around teeth. BOP and PPD around implants and teeth were significantly correlated. Stable marginal bone levels were observed (mean bone loss of 0.1 ± 0.6 mm after 3 years). The frequency of isolation of all marker bacteria was similar at tooth and implant sites. Conclusion: Zirconia endosseous implants can achieve a 3-year implant survival rate in partially edentulous patients, similar to that of titanium implants, with healthy and stable soft and hard tissues. Int J Oral Maxillofac Implants 2014;29:914–920. doi: 10.11607/jomi.3293 Key words: clinical evaluation, dental implants, microbiology, peri-implant mucosa, zirconia
itanium (Ti) is generally recognized as the “gold standard” material for endosseous implants, but it has some drawbacks. For example, blueish-grey shimmering of the implant itself or the implant components may have esthetic ramifications in areas with thin overlying mucosal tissues or when the mucosa recedes over time.1 Also, although survival rates are high, peri-implantitis and peri-implant mucositis around Ti implants are observed in 28% to 56% and 80% of subjects, respectively.2 This raises general health concerns and jeopardizes the longevity of the restorations. From a biomechanical perspective, Ti provides relatively 1Department
of Fixed and Removable Prosthodontics, Centre for Dentistry and Oral Hygiene, University Medical Center Groningen, The University of Groningen, Groningen, The Netherlands. 2Department of Medical and Oral Microbiology, Centre for Dentistry and Oral Hygiene, University Medical Center Groningen, The University of Groningen, Groningen, The Netherlands. Correspondence to: Dr F.C.W.E. Brüll, UMC Groningen/ Centrum voor Tandheelkunde en Mondzorgkunde, Sectie Orale Functieleer, Gebouw 3212, kamer 206, A. Deusinglaan 1, 9713 AV Groningen, The Netherlands. Email: [email protected]
©2014 by Quintessence Publishing Co Inc.
little resistance against wear and fretting.3 Submicron Ti particles, which could develop as a result of implant bending, induce the secretion of inflammatory cytokines in vitro.4,5 Recent studies have also raised concerns regarding potential hypersensitivity to Ti, which seems to occur in a limited number of susceptible patients.6–10 High-strength ceramics, particularly zirconia (ZrO2), may be an attractive alternative. With respect to the physical properties of a ceramic material, three factors are of importance: bending strength, fracture toughness, and Weibull modulus. Yttria tetragonal zirconia polycrystal (Y-TZP) is considered to be chemically inert and has a particularly high three-point bending strength (~1,200 MPa) and fracture toughness (KiC: ~6 to 10 MPa.m1/2).11 The Weibull modulus of commonly used Y-TZP ceramics lies in the order of magnitude of 12 to 20.12 Both bone and soft tissues respond favorably to YTZP.13,14 Animal experiments have shown that roughening a milled zirconia surface improves bone apposition and increases removal torque values.15,16 Comparable percentages of bone-implant contact for Ti and Y-TZP implants have been seen in animal studies.11 Y-TZP is white, which is esthetically advantageous and entails far better light dynamics than Ti.17 Of particular interest is the fact that medical devices, such as dental implants or implant components, can easily be
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milled according to individual specifications by means of a computer-aided design/computer-assisted manufacture production process. A recent consensus report stated that the clinical use of Y-TZP implants could not yet be recommended because of a lack of high-quality evidence11; in spite of this, several continuing education–labeled Y-TZP and/or U.S. Food and Drug Administration–approved implant systems are available on the market today. Indeed, the reported clinical experience with Y-TZP endosseous implants in the English language is limited to a small number of case reports from few different authors.18–22 However, Oliva et al reported on a case series of 100 one-piece coated and uncoated zirconia implants.23 Eventually, a group of acid-etched implants was added, and the studied population reached a total of 831 one-piece implants (CeraRoot, Oral Iceberg) in 378 patients.24 They observed 5-year survival rates of 93%, 94%, and 98% for the coated, uncoated, and acid-etched implants, respectively. No further clinical or radiographic data were reported. In another study that used another brand of Y-TZP implant (White-Sky, Bredent) in the premolar region only, a 2-year survival rate of 96% was reported, with a single implant fracture, for 21 implants in 16 patients.25 The present study aims to expand on the clinical experience gained with Y-TZP implants by reporting on clinical, radiographic, and microbiologic data from a patient cohort that was followed for up to 3 years.
MATERIALS AND METHODS This study was designed as a retrospective case series. Patients were treated consecutively at two practices specializing in implant dentistry.
Patient with sufficient bone volume to fit implants at least 3.5 mm wide and 8.0 mm long were included in the period between November 2004 and October 2010 and observed at regular checkup visits. No additional exclusion criteria were applied.
Implants and Surgical Procedure
The implants were milled from round, isostatically pressed, yttria-stabilized and cerium co-stabilized zirconia blanks (MKM Engineering) and subsequently air particle abraded prior to sintering (ZV – Zircon Vision). Surface roughness was characterized by average roughness (Ra) of 7.0 µm and mean roughness depth (Rz) of 40.3 µm. The implants were placed by experienced surgeons according to a standard surgical protocol. One-piece implants (type 1P, Fig 1a) or two-piece implants were
Fig 1a Y-TZP implant, type 1P.
Fig 1b Y-TZP implant, type 2P.
used (type 2P, Fig 1b). The former were fitted with a computer-aided design/computer-assisted glass-fiber abutment and post that was eventually cemented (Panavia F 2.0, Kuraray) and retained the definitive restoration. The implants were individually designed on the basis of the available local bone volume (Fig 2a), milled (Fig 2b), and subsequently sintered (Fig 2c). The minimal required amount of bone width surrounding the implants was 1 mm. This resulted in a wide variety of implant lengths and diameters, as well as shapes of the implant necks. Data on implant dimensions are provided in Tables 1 and 2. There was no restriction in the study design regarding the implant reception beds. The implants were either placed immediately into extraction sockets or into so-called healed sites. A minor flap elevation was performed. Drills with increasing diameter were used to prepare the implant sites. The final bur had a diameter 0.1 mm less than the diameter of the anticipated implant. The implants were placed with a ratchet at an insertion torque not exceeding 35 Ncm. The implants were loaded after a healing period. Implants were provided with either an all-ceramic single crown or served as abutments for a multiple-unit fixed partial denture and were restored with an all-ceramic restoration. Restorations were luted with resin cement (Panavia F 2.0, Kuraray).
Clinical and Radiographic Evaluations
Probing pocket depths (PPDs) and bleeding on probing (BOP) were assessed by one of the authors (FB) at six sites around all teeth and implants (mesiobuccal, midbuccal, distobuccal, mesiopalatal, midpalatal, and distopalatal). A plastic periodontal probe with 0.25 N of calibrated probing force was used (Click-Probe, Kerr Hawe). PPD was measured in millimeters from the mucosal margin to the clinical pocket. Full-mouth mean The International Journal of Oral & Maxillofacial Implants 915
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Table 1 Lengths of Implants Placed Length
Table 2 Diameters of Implants Placed Fig 2a Designing of the implant.
< 4.0 mm
> 5.0 mm
of evaluation were compared with those seen at baseline (immediately after implant placement).
Fig 2b Milling of the Y-TZP implant.
Sterile paper points were used to sample the tooth and implant with the deepest pocket that was encountered. Detection and counting of the numbers of Aggregatibacter actinomycetemcomitans (Aa), Porphyromonas gingivalis (Pg), Prevotella intermedia (Pi), Tannerella forsythia (Tf), Parvimonas micra (Pm), Fusobacterium nucleatum (Fn), and Treponema denticola (Td) were performed using real-time polymerase chain reaction as described elsewhere.26–28
Fig 2c Y-TZP implant after sintering.
PPD values for teeth and implants were calculated. BOP values are presented as the percentage of sites around both teeth and implants that demonstrated bleeding. Digital intraoral long-cone radiographs were made and mesial and distal marginal bone levels were measured after calibration of the radiograph on the basis of the known length of the implant (Adobe Photoshop C3 extended). Mesial and distal marginal bone levels were averaged. Mean marginal bone levels at the time
The mean values for full-mouth PPD and percentage BOP for both implants and teeth were compared using the Wilcoxon matched-pairs signed rank test. Implant survival (failure) was defined as the presence (absence) of the implant at the time of the clinical visit (or the date the implant was lost). Kaplan-Meier survival statistics were used. Observation periods for the radiographic findings were grouped in years and data were compared with analysis of variance, with post hoc analysis when applicable. Pearson correlations were calculated between mean full-mouth PPDs, percentage BOP, and marginal bone loss. The levels of the seven marker bacteria associated with the teeth and implants were described and compared statistically. Nonparametric statistical
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Table 3 Mean Marginal Bone Loss Since Implant Placement (n = 118 Implants in 71 Patients) Mean loss (SD) (mm) Overall
1.2 to –2.0
0.9 to –0.9
0.9 to –0.9
1.2 to –0.8
F = 1.3; P = .28 (analysis of variance).
procedures were used for all comparisons (Wilcoxon matched-pairs signed rank test). All statistical computations were performed with standard statistical software (SPSS version 20, SPSS Inc). Statistical significance for all comparisons was set at P < .05.
Fig 3 (a) Intraoral situation immediately after placing the Y-TZP implant at the location of the right maxillary central incisor. (b) Radiograph after implant placement and provisionalization. The implant is protected by means of a provisional denture on the adjacent teeth. (c) After 3 months. The fiberglass post-andcore has been cemented and prepared prior to impression taking. (d) Final result.
RESULTS Seventy-four partially edentulous patients received a total of 121 Y-TZP endosseous implants (55 type 1P and 66 type 2P) in all regions of the maxilla and mandible. Sixty-seven percent were women, and the patients’ mean age was 51 years (range 18 to 72 years). Patients received one to eight implants each, which were placed with local anesthesia. Implants were loaded after a mean observation period of 4.6 months (range, 3 to 17 months; Fig 3). One hundred implants were restored with an all-ceramic single crown (82.6%) and 21 served as abutments for a multiple-unit fixed partial denture (17.4%). Three of the 121 implants in three patients (one type 1P and two type 2P) failed during the mean observation period of 18.4 months (standard deviation [SD] 10.4 months). The overall chance of implant survival after 3 years is estimated at 96.5% (standard error 0.2%). One implant never osseointegrated. Another implant lost osseointegration in a patient who received extensive bone augmentation, and the third implant fractured. No fiber-reinforced abutments loosened or fractured during the period of observation. In general, healthy periodontal and peri-implant conditions were seen (Fig 4). Mean full-mouth PPDs for teeth and implants were 2.1 mm (SD 0.4 mm; range, 1.4 to 3.0 mm) and 1.8 mm (SD 0.4 mm; range, 1.0 to 3.0 mm), respectively, representing a statistically significant difference (z-score = –3.4; P = .001). The mean full-mouth percentage BOP was 7.2% (SD 6.5%; range, 0% to 29.5%) for teeth and 4.1% (SD 4.2%; range, 0%
Fig 4 Healthy peri-implant mucosa around implants in the first and second premolar positions.
to 16.7%) for implants. Statistically significantly less bleeding was observed around implants (Z = –3.1, P = .002). There were moderately strong correlations between the full-mouth PPDs (r = 0.56, P < .003) and the percentage BOP (r = 0.47, P < .02) around implants and teeth in the same patient. Stable marginal bone levels were observed over time (Table 3). No statistically significant correlations between the amount of overall marginal bone loss, mean full-mouth PPDs, and percentage BOP around implants were observed. The percentage of patients presenting with detectable levels of the seven marker bacteria on implants and/or teeth are presented in Table 4. In almost all patients Fn was detected. Pm was found in the majority of the patients (81.8%). Aa and Td were both seen in two patients. Pg was found in 36.4% of the subjects. The International Journal of Oral & Maxillofacial Implants 917
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Table 4 Presence or Absence of Bacteria at Teeth and Implant Sites in 71 Patients Location
Implant only Neither
Both tooth and implant
Td 0 0 93.9% 6.1% 6.0%
Aa = Aggregatibacter actinomycetemcomitans; Pg = Porphyromonas gingivalis; Pi = Prevotella intermedia; Tf = Tannerella forsythia; Pm = Parvimonas micra; Fn = Fusobacterium nucleatum; Td = Treponema denticola.
Most often, species were detected simultaneously at tooth and implant sites, but detection in one or the other also occurred. The frequency of isolation of all of the marker bacteria was similar at tooth and implant sites, and no statistically significant differences were observed; nor were significant differences seen for the total bacterial load at implants and teeth.
DISCUSSION In vitro and animal studies have shown that zirconia (ie, Y-TZP) has potential, both biologically and biomechanically, as an alternative for Ti when used as the base material for endosseous implants.15,29–39 However, literature reviews have revealed that there are few data about their performance during routine clinical use. Consequently, application of Y-TZP implants in human subjects has not yet been recommended.11,40 Nevertheless, the Y-TZP implants (ZV3 – Zircon Vision) used in the present study have been used routinely since 2004. Some modifications have been introduced since then, leading to the present implant, as produced since 2009. The implants possess some unique features. Most noteworthy is that both the implant body and the permucosal part can be individually designed to fit local anatomical conditions. Production is fast because of the milling in the green phase, and there is no implant-abutment movement and gap that could cause leakage of harmful bacteria, as seen in conventional implant-abutment connections.41,42 The strength of the sintered material has been assessed preclinically. Bending strength was examined by means of three-point bending tests and averaged 1,274 MPa. Fracture toughness (KiC = 9 MPa.m1/2) and Weibull modulus (24.4) are favorable as well (personal communication, ZV3 – Zircon Vision). In the studied population (n = 74 patients, 121 implants) three implants failed, resulting in a cumulative implant survival rate of ~96% after 3 years. This is in reasonable agreement with survival rates found for titanium implants in the literature for partially edentulous situations.43 Patients with bruxism or who smoke
are often associated with compromised treatment outcomes but were not excluded from the present study. A severe unexpected adverse event was seen in one patient, who experienced implant fracture. The consequences were serious and necessitated surgical removal of the implant at the expense of additional patient discomfort. Fracture of Y-TZP implants has been described only occasionally in the literature. However, Gahlert et al reported a fracture percentage of another brand of Y-TZP implants (Z-Look3, Z-Systems) of ~8% (13/170) after 3 years; this occurred only with narrow implants (3.25 mm in diameter).44 All fractured implants were located in the anterior regions of the maxilla and mandible, making this result more worrisome, since occlusal forces tend to be relatively low in that region. The presumed mode of failure was mechanical overloading in all incidents. It was hypothesized that notches and scratches resulting from the postsintering roughening of the implant surface (sandblasting) induced local stress concentrations and initiated crack propagation.44 Oliva et al used another implant system (CeraRoot, Oral Iceberg).19 The Y-TZP implant used in the present study was roughened by means of a patented process during which the implants are sandblasted prior to sintering. Mechanical manipulation of already fully sintered surfaces is generally discouraged because it compromises the strength of the material. Implant fracture is a complication seldom seen with titanium implants, with a prevalence of 0.4% after 5 years.43 Titanium can bend 15% prior to fracture (modulus of elasticity of 100 to 105 GPa). The patients in the present cohort maintained a high level of oral hygiene and were generally in excellent periodontal condition, as reflected by the low full-mouth PPD values and percentage of BOP around teeth during their clinical examination. As in the majority of clinical studies dealing with the evaluation of dental implants and according to recommendations by some,45 the health of the peri-implant mucosa in the present study was monitored in the same way as around teeth. The values for mean full-mouth PPD and percentage BOP around the implants were significantly lower than those around teeth in the same patient.
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However, the differences were small, and the clinical significance of these differences is debatable. They compare favorably with the mucogingival findings reported from various clinical studies involving titanium implants.2 Marginal bone loss around implants in consecutive years was rare and fell within a clinically acceptable range. Occasionally, gain of marginal bone was observed, particularly in cases where implants were placed relatively soon after tooth extraction. The amount of bone loss was not correlated to the parameters related to the health of the soft tissues. The ability of conventional periodontal parameters to reflect (small differences in) the ankylotic-like implantto-bone response of dental implants remains a matter of debate.46 In a prospective case series study of Kohal et al, the implants showed a high risk of crestal bone loss of 2 mm during the first year after placement and therefore could not be recommended for clinical use. However, it is not clear whether the increased bone loss was a result of the implant material or other confounding factors such as geometry, surface, or mode of loading.47 In this study no differences were found in the prevalence and levels of several marker bacteria in implant and tooth sites. The low prevalence of Aa and Td reflected the good periodontal condition of the patients in this cohort. The prevalence of Pg was relatively high (36%) and exceeds the prevalence of this species previously observed in periodontally healthy carriers (10%) using the same detection technique.48 It should be noted that a significant number of the patients in the present study had previously suffered from periodontitis. Based on the microbial findings in relation to the clinical observations, one could speculate or hypothesize that zirconia submucosal biofilms can harbor periodontal pathogens such as Pg or Aa without provoking a host inflammatory process. The nature of this observation cannot yet be explained. Also, long-term periimplant health in this cohort has yet to be established. The present study is retrospective by nature, which has clear advantages but also obvious disadvantages. With regard to the former, in retrospective studies researchers must rely heavily on the accuracy of (patient) records that were never meant to serve as research material. It is difficult to control for bias and confounders in the absence of randomization (or blinding). Although the authors have made every effort to scrutinize the data, this may have introduced bias of some kind. As a consequence, the results should be interpreted with care and are, at best, hypothesis-generating. Nevertheless, they are promising and justify further studies. Better controlled, comparative clinical studies (Y-TZP versus Ti) or prospective case series are required to establish ideal indications, contraindications,
merits, and risks of Y-TZP implants. In these studies, biologic, esthetic, and economic parameters should be considered.
CONCLUSION When applied in partially edentulous situations by experienced surgeons in routine clinical practice, Y-TZP implants can achieve a 3-year implant survival rate similar to that of titanium implants, with healthy and stable soft and hard tissue conditions.
ACKNOWLEDGMENTS The authors express their gratitude to the dental offices at Betzl/Zeilmeir, München, and Winges, Bad Hersfeld, and to their staff, who granted unrestricted access to their patient charts and clinics. The participation of the patients in the clinical part of the study is greatly appreciated. This study was supported by a grant from ZV3 – Zirkon Vision and by the authors’ institutions. The authors declare that they have no conflicts of interest.
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