Osseointegration of zirconia implants: an SEM observation of the bone-implant interface

Pre-implantation teriparatide administration improves initial implant stability and accelerates the osseointegration process in osteoporotic rats

PURPOSE

Osteoporotic individuals who have dental implants usually require a prolonged healing time for osseointegration due to the shortage of bone mass and the lack of initial stability. Although studies have shown that intermittent teriparatide administration can promote osseointegration, there is little data to support the idea that pre-implantation administration is necessary and beneficial.

METHODS

Sixty-four titanium implants were placed in the bilateral proximal tibial metaphysis in 32 female SD rats. Bilateral ovariectomy (OVX) was used to induce osteoporosis. Four major groups (n = 8) were created: PRE (OVX + pre-implantation teriparatide administration), POST (OVX + post-implantation administration), OP (OVX + normal saline (NS)) and SHAM (sham rats + NS). Half of rats (n = 4) in each group were euthanized respectively at 4 weeks or 8 weeks after implantation surgery, and four major groups were divided into eight subgroups (PRE4 to SHAM8). Tibiae were collected for micro-CT morphometry, biomechanical test and undecalcified sections analysis.

RESULTS

Compared to OP group, rats in PRE and SHAM groups had a higher value of insertion torque (p < 0.05). The micro-CT analysis, biomechanical test, and histological data showed that peri-implant trabecular growth, implants fixation and bone-implant contact (BIC) were increased after 4 or 8 weeks of teriparatide treatment (p < 0.05). There was no statistically difference in those parameters between PRE4 and POST8 subgroups (p > 0.05).

CONCLUSIONS

In osteoporotic rats, post-implantation administration of teriparatide enhanced peri-implant bone formation and this effect was stronger as the medicine was taken longer. Pre-implantation teriparatide treatment improved primary implant stability and accelerated the osseointegration process.

A Mapping Review of the Pathogenesis of Peri-Implantitis: The Biofilm-Mediated Inflammation and Bone Dysregulation (BIND) Hypothesis

This mapping review highlights the need for a new paradigm in the understanding of peri-implantitis pathogenesis. The biofilm-mediated inflammation and bone dysregulation (BIND) hypothesis is proposed, focusing on the relationship between biofilm, inflammation, and bone biology. The close interactions between immune and bone cells are discussed, with multiple stable states likely existing between clinically observable definitions of peri-implant health and peri-implantitis. The framework presented aims to explain the transition from health to disease as a staged and incremental process, where multiple factors contribute to distinct steps towards a tipping point where disease is manifested clinically. These steps might be reached in different ways in different patients and may constitute highly individualised paths. Notably, factors affecting the underlying biology are identified in the pathogenesis of peri-implantitis, highlighting that disruptions to the host-microbe homeostasis at the implant-mucosa interface may not be the sole factor. An improved understanding of disease pathogenesis will allow for intervention on multiple levels and a personalised treatment approach. Further research areas are identified, such as the use of novel biomarkers to detect changes in macrophage polarisation and activation status, and bone turnover.

Dental implants in large animal models with experimental systemic diseases: A systematic review

This systematic review aims to identify and discuss the most used methodologies in pre-clinical studies for the evaluation of the implementation of dental implants in systemically compromised pigs and sheep. This study provides support and guidance for future research, as well as for the prevention of unnecessary animal wastage and sacrifice. Preferred Reporting for Systematic Reviews and Meta-Analyses (PRISMA) was used as a guideline; electronic searches were performed in PubMed, Scopus, Scielo, Web of Science, Embase, Science Direct, Brazilian Bibliography of Dentistry, Latin American and Caribbean Literature in Health Sciences, Directory of Open Access Journals, Database of Abstracts of Reviews of Effects, and gray literature until January 2022 (PROSPERO/CRD42021270119). Sixty-eight articles were chosen from the 2439 results. Most studies were conducted in pigs, mainly the Göttinger and Domesticus breeds. Healthy animals with implants installed in the jaws were predominant among the pig studies. Of the studies evaluating the effect of systemic diseases on osseointegration, 42% were performed in osteoporotic sheep, 32% in diabetic sheep, and 26% in diabetic pigs. Osteoporosis was primarily induced by bilateral ovariectomy and mainly assessed by X-ray densitometry. Diabetes was induced predominantly by intravenous streptozotocin and was confirmed by blood glucose analysis. Histological and histomorphometric analyses were the most frequently employed in the evaluation of osseointegration. The animal models presented unique methodologies for each species in the studies that evaluated dental implants in the context of systemic diseases. Understanding the most commonly used techniques will help methodological choices and the performance of future studies in implantology.

Comparison of mechanical stability of mini-screws with resorbable blasting media and micro-arc oxidation surface treatments under orthodontic forces: An in vitro biomechanical study

INTRODUCTION

The aim of this study was to compare the primary stability of mini-screws with different surface treatments such as resorbable blasting media (RBM) and micro-arc oxidation (MAO) under in vitro orthodontic forces.

MATERIAL AND METHODS

Thirty-six self-drilling TiAl6V4-ELI grade 23 titanium alloy 1.6×8mm mini-screws were inserted into polyurethane foam blocks and divided into three groups according to surface properties: machine surface (MS), RBM-treated, and MAO-treated. An orthodontic force of 150g was applied to the mini-screws using NiTi coils. Maximum insertion torque (MIT) and maximum removal torque (MRT) were measured with a digital torque screwdriver during insertion and removal. For each mini-screw, stability measurements were made with the Periotest M device at day 0 and weeks 1, 2, 4, 8, and 12.

RESULTS

Significant differences in MIT were observed between all groups in pairwise comparisons (P<0.001) with the highest value in the MAO-treated group and the lowest in the MS group. The mean MRT values differed in all three groups (P=0.001). In pairwise comparisons of MRT, only the difference between MS group and RBM-treated group was significant. The highest value was observed in the RBM-treated group, while the lowest value was observed in the MS group. Periotest values were significantly higher in the MAO-treated group than the RBM-treated group at weeks 8 and 12. A positive significant correlation was found between MIT and MRT in all groups. No significant correlation was found between MIT, MRT and Periotest values in all groups.

CONCLUSION

RBM-treated group was significantly higher than the MS group in MIT and MRT values. According to Periotest values, RBM-treated group was found to be significantly more stable than the MAO-treated group at weeks 8 and 12. Therefore, RBM surface treatment was found to be more favourable than other surfaces to increase success rate in clinical applications.

Effect of gingival height of a titanium base on the biomechanical behavior of 2-piece custom implant abutments: A 3-dimensional nonlinear finite element study

STATEMENT OF PROBLEM

Titanium base (TiBase) abutments to restore an implant-supported single crown are available in different gingival heights, but information on the biomechanical effects of the gingival heights is lacking.

PURPOSE

The purpose of this nonlinear finite element analysis study was to evaluate the effects of TiBase gingival heights on the biomechanical behavior of custom zirconia (CustomZir) abutments and TiBase, including von Mises stress and maximum and minimum principal stress.

MATERIAL AND METHODS

TiBases with different gingival heights (0.5 mm, 1 mm, 1.5 mm, and 2 mm) with internal hexagon Morse taper connections were simulated in 3-dimensional models. The simulations (ANSYS Workbench 2020; ANSYS Inc) included the OsseoSpeed EV implant (Ø5.4 mm) (AstraTech; Dentsply Sirona), restoration, and surrounding bone in the mandibular first molar region. An occlusal force of 200 N was applied with a 2-mm horizontal offset toward the buccal side and a 30-degree inclination from the vertical axis.

RESULTS

High-stress concentration was observed in the uppermost internal connection area on the buccal side and the antirotational part of the titanium abutment on the lingual side in all models. CustomZir abutments with a shorter gingival height exhibited larger concentrated areas of volume average stress von Mises stress and higher magnitude of maximum and minimum principal stress compared with a taller gingival height.

CONCLUSIONS

A TiBase abutment with a taller gingival height reduced the fracture risk of a CustomZir abutment without increasing any mechanical risk.

In Vivo Biofilm Formation on Novel PEEK, Titanium, and Zirconia Implant Abutment Materials

The formation of biofilms on the surface of dental implants and abutment materials may lead to peri-implantitis and subsequent implant failure. Recently, innovative materials such as polyether-ether-ketone (PEEK) and its modifications have been used as abutment materials. However, there is limited knowledge on microbial adhesion to PEEK materials. The aim of this in vivo study was to investigate biofilm formation on the surface of conventional (titanium and zirconia) and PEEK implant abutment materials. Split specimens of titanium, zirconia, PEEK, and modified PEEK (PEEK-BioHPP) were manufactured, mounted in individual removable acrylic upper jaw splints, and worn by 20 healthy volunteers for 24 h. The surface roughness was determined using widefield confocal microscopy. Biofilm accumulation was investigated by fluorescence microscopy and quantified by imaging software. The surface roughness of the investigated materials was <0.2 µm and showed no significant differences between the materials. Zirconia showed the lowest biofilm formation, followed by titanium, PEEK, and PEEK-BioHPP. Differences were significant (p < 0.001) between the investigated materials, except for the polyether-ether-ketones. Generally, biofilm formation was significantly higher (p < 0.05) in the posterior region of the oral cavity than in the anterior region. The results of the present study show a material-dependent susceptibility to biofilm formation. The risk of developing peri-implantitis may be reduced by a specific choice of abutment material.

Conductive cross-section preparation of non-conductive painting micro-samples for SEM analysis

Scanning electron microscopy (SEM) is a common method for the analysis of painting micro-samples. The high resolution of this technique offers precise surface analysis and can be coupled with an energy-dispersive spectrometer for the acquisition of the elemental composition. For light microscopy and SEM analysis, the painting micro-samples are commonly prepared as cross-sections, where the micro-sample positioned on the side is embedded in a resin. Therefore, the sequence of its layers is exposed after the cross-section is polished. In common cases outside of cultural heritage, a conductive layer is applied on the polished side, but in this field, the measurements are mostly done in low-vacuum SEM (LV-SEM). Although the charging effect is reduced in LV-SEM, it can still occur, and can hardly be prevented even with carbon tape or paint. This work presents two conductive cross-section preparation methods for non-conductive samples, which reduce charging effects without impairing the sample integrity.

Early bone formation around immediately placed two-piece tissue-level zirconia implants with a modified surface: an experimental study in the miniature pig mandible

PURPOSE

To histologically examine early bone formation around transmucosal implants and to evaluate the influence of surface characteristics on early peri-implant bone healing using a miniature pig model. For this, commercially available dental implants with a rough zirconia (YTZP) surface were compared to surface-modified Ti control implants at 4 and 8 weeks after placement.

METHODS

Immediately following the extraction of six mandibular premolars, 20 two-piece, tissue-level, screw-shaped YTZP implants (Patent™ Standard Zirconia Implant ø4.1 × 11 mm) with a modified rough blasted before sintering surface were inserted in four adult miniature pigs. In addition, four titanium (Ti) tissue-level implants (Straumann® Standard RN ø4.1 × 10 mm Roxolid®) with a moderate surface (SLActive®), one per animal, were placed as control implants. A histological analysis was performed on the hard tissues after 4 and 8 weeks of transmucosal healing.

RESULTS

The results show a high rate of osseointegration of the test YTZP dental implants at 4 and 8 weeks following insertion. At 4 weeks, a bone-to-implant contact ratio (BIC) of 73.7% (SD ± 16.8) for the test implants (n = 10) and 58.5% for the first control implant was achieved. The second control implant had to be excluded from analysis. At 8 weeks, a BIC of 82.4% (SD ± 16.9) for the test implants (n = 9) and 93.6% (SD ± 9.1) (n = 2) for the control implant was achieved. No statistical difference was observed comparing 4 and 8 weeks YTZP data (p = 0.126).

CONCLUSIONS

The results indicate a predictable osseointegration of immediate zirconia implants with a modified YTZP implant surface and a high degree of BIC present at 4 weeks following insertion. After 8 weeks of healing both the zirconia implants and the Ti implants show a BIC indicating full osseointegration. Further studies involving a larger sample size with more time points are needed to confirm these results.

Contemporary Concepts in Osseointegration of Dental Implants: A Review

In a society highly conscious of esthetics, prosthetic rehabilitation of lost teeth with tissue-integrated implants has gained wide acceptance and demand by patients and clinicians. The backbone of these tissue-integrated implants is the biotechnical process of osseointegration. Although the concept has been introduced and discussed for ages, the deepening knowledge about its cellular and molecular mechanisms has led the researchers to borrow further into the factors influencing the process of osseointegration. This has aided in the hastening and improving the process of osseointegration by exploiting several, even the minutest, details and events taking place in this natural process. Recently, due to the high esthetic expectations of the patients, the implants are being loaded immediately, which demands a high degree of implant stability. Implant stability, especially secondary stability, largely depends on bone formation and integration of implants to the osseous tissues. Various factors that influence the rate and success of osseointegration can either be categorized as those related to implant characteristics like the physical and chemical macro- and microdesign of implants or the bone characteristics like the amount and quality of bone and the local and systemic host conditions, or the time or protocol followed for the functional loading of the dental implant. To address the shortcomings in osseointegration due to any of the factors, it is mandatory that continuous and reliable monitoring of the status of osseointegration is done. This review attempts to encompass the mechanisms, factors affecting, and methods to assess osseointegration, followed by a discussion on the recent advances and future perspectives in dental implantology to enhance the process of osseointegration. The review was aimed at igniting the inquisitive minds to usher further the development of technology that enhances osseointegration.

Finite element analysis to assess stress and deformation in bone with glass fiber-reinforced-poly-ether-ether-ketone, zirconia, and titanium implants

Objectives

Recently, zirconia ceramic and glass or carbon fiber-reinforced poly-ether-ether-ketone (PEEK) composites have been introduced as newer implant biomaterials. This study was done to evaluate stress and deformation in bone with glass fiber-reinforced (GFR)-PEEK, zirconia, and titanium implants.

Materials and Methods

A geometric model of mandibular molar replaced with implant-supported crown was generated. Implant of 12 mm length and 4.5 mm diameter was used in study. Finite element analysis models of implant assemblies of three materials GFR-PEEK, zirconium, and titanium were generated. 150 N loads were applied obliquely and vertically along the long axis of implant. Von Mises stresses and deformation generated were compared using ANSYS Workbench 17.0 and finite element software.

Results

All three implant assemblies, i.e., GFR-PEEK, zirconia, and titanium, demonstrated similar stresses and deformation in bone without significant difference.

Conclusion

It was concluded that GFR-PEEK and zirconia implants can be used as a substitute to titanium implants.

Finite element evaluation to compare stress pattern in bone surrounding implant with carbon fiber-reinforced poly-ether-ether-ketone and commercially pure titanium implants

Background:

Titanium allergy is a main reason for failure of dental implant. Hence, newer implant biomaterials have emerged such as zirconia and carbon or glass fiber reinforced poly-ether-ether-ketone (CFR-PEEK)-based materials. The aim of the present study was to compare the stress pattern in bone surrounding implant with CFR-PEEK and commercially pure titanium implant.

Materials and Methods:

Three-dimensional formal model of mandibular first molar partsubstituting with implant supported crown was generated. Implant with dimensions of 10 mm length and 4.3 mm diameter was used in this study. Finite element models of CFR-PEEK and commercially pure titanium implant assemblies were generated. A 100 Newton (N) force was implemented along the long axis and obliquely at 30° to the long axis of implant. Von Mises pressures generated in the bone surrounding implant were analyzed using ANSYS workbench 16.0 and other finite element software.

Results:

Similar stress distribution was detected in bone surrounding implant with CFR-PEEK implant and commercially pure titanium implant assembly under 100 N force applied vertically and obliquely.

Conclusion:

PEEK reinforced with carbon or glass fiber implants can be a viable alternative in individuals who are more of esthetic concern and who demonstrate allergy to metallic implants.

Clinical and histological comparison of the soft tissue morphology between zirconia and titanium dental implants under healthy and experimental mucositis conditions-A randomized controlled clinical trial

OBJECTIVES

To analyse the soft tissue morphology under healthy and experimental mucositis conditions comparing zirconia and titanium implants.

METHODS

Forty-two patients with two adjacent missing teeth received one zirconia (Zr) and one titanium (Ti) implant, with the mesial and distal position randomized. At 3 months, half of the patients were instructed to continue (healthy; h) and the other half to omit (experimental mucositis; m) oral hygiene around the implants for 3 weeks. Clinical parameters were evaluated before and after the experimental phase, and a soft tissue biopsy was harvested. Mixed model analyses were performed to analyse the data.

RESULTS

The plaque control record increased significantly for the two mucositis groups, reaching 68.3 ± 31.9% (mean ± SD) for Zr-m and 75.0 ± 29.4% for Ti-m (p < .0001), being also significantly lower for Zr-m than for Ti-m. Bleeding on probing remained stable in group Zr-m and amounted to 21.7 ± 23.6%, but increased significantly in group Ti-m (p = .040), measuring 32.5 ± 27.8%. The number of inflammatory cells and the length of the junctional epithelium did not significantly differ between the groups.

CONCLUSION

Both implants rendered similar outcomes under healthy conditions. Lower plaque and bleeding scores were detected for zirconia implants under experimental mucositis conditions. Histologically, only minimal differences were observed.

The Impact of EBM-Manufactured Ti6Al4V ELI Alloy Surface Modifications on Cytotoxicity toward Eukaryotic Cells and Microbial Biofilm Formation

Electron beam melting (EBM) is an additive manufacturing technique, which allows forming customized implants that perfectly fit the loss of the anatomical structure of bone. Implantation efficiency depends not only on the implant's functional or mechanical properties but also on its surface properties, which are of great importance with regard to such biological processes as bone regeneration or microbial contamination. This work presents the impact of surface modifications (mechanical polishing, sandblasting, and acid-polishing) of EBM-produced Ti6Al4V ELI implants on essential biological parameters. These include wettability, cytotoxicity toward fibroblast and osteoblast cell line, and ability to form biofilm by Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans. Obtained results indicated that all prepared surfaces exhibited hydrophilic character and the highest changes of wettability were obtained by chemical modification. All implants displayed no cytotoxicity against osteoblast and fibroblast cell lines regardless of the modification type. In turn, the quantitative microbiological tests and visualization of microbial biofilm by means of electron microscopy showed that type of implant's modification correlated with the species-specific ability of microbes to form biofilm on it. Thus, the results of the presented study confirm the relationship between such technological aspects as surface modification and biological properties. The provided data are useful with regard to applications of the EBM technology and present a significant step towards personalized, customized implantology practice.

An introduction of biological performance of zirconia with different surface characteristics: A review

Zirconia (ZrO₂) ceramic is widely used in dentistry as a clinical dental biomaterial. In this review, we are focusing on and summarizing the biological performance of zirconia under different surface characteristics. We have included an initial tissue cell attachment study on zirconia and bacterial adhesion on zirconia. Our results suggest that surface modifications applied on zirconia may change the interfacial surface characteristics e.g. surface roughness, surface free energy, and chemistry of zirconia. The modifications also result in advanced biological performance of zirconia, including enhanced tissue cell attachment and reduction of bacterial adhesion. The recent laboratory research has provided many interesting modification methods and showed clinically interesting and promising outcomes. A few of the outcomes are validated and have been applied in clinical dentistry.

Design of dental implants at materials level: An overview

Due to the excellent restoration of masticatory function, satisfaction on aesthetics and other superiorities, dental implants represent an effective method to resolve tooth losing and damaging. Current dental implant systems still have problems waiting to be addressed, and problems are centralized on the materials of implant bodies. This review aims to summarize major developments in the field of dental implant materials, starting with an overview on structures, procedures of dental implants and challenges of implant materials. Next, implant materials are examined in three categories, that is, metals, ceramics, and polymers, their mechanical properties, biocompatibility, and bioactivity are summarized. And as an important aspect, strategies of surface modification are also reviewed, along with some finite element analysis to guiding the research direction of implant materials. Finally, the conclusive remarks are outlined to provide an outlook on the future research directions and prospects of dental implants.

Epithelial sealing effectiveness against titanium or zirconia implants surface

The aims of implant treatment now involve not only restoration of mastication function, but also recovery of esthetics. Currently, zirconia is widely used as an esthetic material for implant abutment. Therefore, it is very important to understand the efficacy of zirconia for epithelial sealing as an implant material. We compared the effects of materials on the sealing of the peri-implant epithelium (PIE) to titanium (Ti) or zirconia (Zr) implants, for application to clinical work. Maxillary first molars were extracted from rats and replaced with Ti or Zr implants. The sealing of the PIE to the implants was evaluated with immunohistochemistry observation and HRP analysis. The morphological and functional changes in rat oral epithelial cells (OECs) cultured on Ti or Zr plates were also evaluated. After 4 weeks, the PIE on the Ti and Zr implants showed similar structures. The Zr implants appeared to form a weak epithelial seal at the tissue-implant interface, and exhibited markedly less adhesive structures than the Ti implants under electron microscopic observation. In the in vitro experiments, decreased expression levels of adhesion proteins were observed in OECs cultured on Zr plates compared with those cultured on Ti plates. In addition, the cell adherence on Zr plates was reduced, while the cell migration was low on Ti plates. Zr is a better choice for an esthetic implant material, but needs further improvement for integration with the epithelial wound healing process around a dental implant. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2019.

Osteoclastogenesis Behavior of Zirconia for Dental Implant

Zirconia is worth studying as an alternative to dental titanium implants to overcome the disadvantages of titanium. This study investigated the surface characteristics of the zirconia implant material and osteoclastogenesis responses on the surface compared with titanium. Yttrium oxide-stabilized 5% tetragonal zirconia polycrystalline specimens were manufactured, and osteoclast-precursor cells were cultured and differentiated into osteoclasts on the specimens. Surface shape, roughness, and chemical composition were evaluated. After culturing, cell morphologies and differentiation capacity were analyzed using tartrate-resistant acid phosphatase activity (TRACP). mRNA of two critical transcription factors, nuclear factor of activated T-cells 1 (NFATc1) and c-Fos were measured, and protein levels of NFATc1 and c-Fos were investigated. The zirconia specimens had rhomboid-like shapes with smooth surfaces and exhibited no difference in surface roughness compared to the titanium specimens. Morphologies of differentiated osteoclasts on both materials were similar. TRACP activity on the zirconia showed comparable results to that on the titanium. The mRNA value of NFATc1 on the zirconia was higher than that on the titanium at day four. The protein level of c-Fos was expressed thicker on the zirconia when compared to the titanium at day two. The results of this study suggest that zirconia material provides adequate osteoclastogenesis behaviors for dental implant use.

Manual polishing of 3D printed metals produced by laser powder bed fusion reduces biofilm formation

Certain 3D printed metals and surface finishes may be better suited for canine patient specific orthopedic implants on the basis of minimizing potential bacterial biofilm growth. Thirty disks each of titanium alloy, stainless steel, and cobalt chromium alloy were 3D printed via laser powder bed fusion. Fifteen disks of each metal were subsequently polished. After incubation with a robust biofilm-forming methicillin-resistant Staphylococcus pseudintermedius isolate, disks were rinsed and sonicated to collect biofilm bacteria. Serial dilutions were plated on blood agar, and colony forming units were counted log (ln) transformed for analysis of variance. Interference microscopy quantified surface roughness for comparison to biofilm growth. Scanning electron microscopy on both pre- and post-sonicated disks confirmed biofilm presence and subsequent removal, and visualized surface features on cleaned disks. Significantly more bacteria grew on rough versus polished metal preparations (p < 0.0001). Titanium alloy had more bacterial biofilm growth compared to cobalt chromium alloy (p = 0.0001) and stainless steel (p < 0.0001). There were no significant growth differences between cobalt chromium alloy and stainless steel (p = 0.4737). Relationships between biofilm growth and surface roughness varied: positive with the rough preparations and negative with the smooth. Polished preparations had increased variance in surface roughness compared to rough preparations, and within disk variance predominated over between disk variance for all preparations with the exception of rough cobalt chromium alloy and rough stainless steel. Using scanning electron microscopy, bacterial biofilms tended to form in crevices. Overall, manual polishing of 3D printed surfaces significantly reduced biofilm growth, with preparation-specific relationships between surface roughness and biofilm growth. These results suggest that metallic implants produced by laser powder bed fusion should be polished. Further research will elucidate the optimal surface roughness per preparation to reduce potential biofilm formation and implant associated infection.

Custom-made root-analogue zirconia implants: A scoping review on mechanical and biological benefits

The aim of this study was to conduct a literature review on the potential benefits of custom-made root-analogue zirconia implants. A PubMed and ScienceDirect bibliographical search was carried out from 1969 to 2017. The increased interest in zirconia-based dental structures linked to aesthetic and biological outcomes have been reported in literature. Recent technological advances have focused on novel strategies for modification of zirconia-based surfaces to accelerate osseointegration. However, only a few studies revealed mechanical and biological benefits of custom-made root-analogue zirconia implants and therefore further studies should investigate the influence of different design and surface modification on the performance of such implants. Custom-made root-analogue zirconia implants have become a viable alternative to overcome limitations concerning stress distribution, aesthetics, and peri-implantitis induced by biofilms. However, further in vitro and in vivo studies on surface-bone interactions and mechanical behavior of zirconia should be evaluated to reduce clinical issues regarding mechanical failures and late peri-implant bone loss. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2888-2900, 2018.

A prospective clinical study to evaluate the performance of zirconium dioxide dental implants in single-tooth edentulous area: 3-year follow-up

BACKGROUND

Traditionally, dental implants have been made from titanium or titanium alloys. Alternatively, zirconia-based ceramic implants have been developed with similar characteristics of functional strength and osseointegration. Ceramic implants offer advantages in certain settings, e.g. in patients who object to metal dental implants. The aim of this study was to investigate the mid-term (36 months) clinical performance of a ceramic monotype implant in single-tooth edentulous area.

METHODS

This was a prospective, open-label, single-arm study in patients requiring implant rehabilitation in single-tooth edentulous area. Ceramic implants (PURE Ceramic Implant, Institut Straumann AG, Basel, Switzerland) with a diameter of 4.1 mm were placed following standard procedure and loaded with provisional and final prostheses after 3 and 6 months, respectively. Implant survival rate and implant success rate were evaluated and crestal bone levels were measured by analysing standardized radiographs during implant surgery and at 6, 12, 24 and 36 months.

RESULTS

Forty-four patients received a study implant, of whom one patient withdrew consent after 3 months. With one implant lost during the first 6 months after surgery, the implant survival rate was 97.7% at 6 months. No further implants were lost over the following 30 months, and 3 patients were lost to follow-up during this time frame. This led to a survival rate of 97.5% at 36 months. Six months after implant surgery 93.0% of the implants were considered "successful", increasing to 97.6% at 12 months and remaining at this level at 24 months (95.1%) and 36 months (97.5%). Bone loss was most pronounced in the first half-year after implant surgery (0.88 ± 0.86 mm). By contrast, between 12 and 36 months the mean bone level remained stable (minimal gain of 0.06 [± 0.60] mm). Hence, the overall bone loss from implant surgery to 36 months was 0.97 (± 0.88) mm.

CONCLUSIONS

In the follow-up period ceramic implants can achieve favourable clinical outcomes on a par with titanium implants. For instance, these implants can be recommended for patients who object to metal dental implants. However, longer term studies with different edentulous morphology need to confirm the present data.

TRIAL REGISTRATION

Registered on www.clinicaltrials.gov : NCT02163395 .

Comparative study of new bone formation capability of zirconia bone graft material in rabbit calvarial

PURPOSE

The purpose of this study was to compare the new bone formation capability of zirconia with those of other synthetic bone grafts.

MATERIALS AND METHODS

Twelve rabbits were used and four 6-mm diameter transcortical defects were formed on each calvaria. Each defect was filled with Osteon II (Os), Tigran PTG (Ti), and zirconia (Zi) bone grafts. For the control group, the defects were left unfilled. The rabbits were sacrificed at 2, 4, and 8 weeks. Specimens were analyzed through micro computed tomography (CT) and histomorphometric analysis.

RESULTS

The Ti and Zi groups showed significant differences in the amount of newly formed bone between 2 and 4 weeks and between 2 and 8 weeks (P<.05). The measurements of total bone using micro CT showed significant differences between the Os and Ti groups and between the Os and Zi groups at 2 and 8 weeks (P<.05). Comparing by week in each group, the Ti group showed a significant difference between 4 and 8 weeks. Histomorphometric analysis also showed significant differences in new bone formation between the control group and the experimental groups at 2, 4, and 8 weeks (P<.05). In the comparison of newly formed bone, significant differences were observed between 2 and 4 weeks and between 2 and 8 weeks (P<.05) in all groups.

CONCLUSION

Zirconia bone graft material showed satisfactory results in new bone formation and zirconia could be used as a new synthetic bone graft material.

Application of combined porous tantalum scaffolds loaded with bone morphogenetic protein 7 to repair of osteochondral defect in rabbits<sup/>

PURPOSE

Porous tantalum (PT) has been widely used in orthopaedic applications for low modulus of elasticity, excellent biocompatibility, and the microstructures similar to cancellous bone. In order to improve the biological activity of PT, biologically active factors can be combined with the material. The purpose of this study was to investigate if bone morphogenetic protein 7 (BMP-7) modifications could enhance the repairing of cartilage of PT in osteochondral defect in medial femoral condyle of rabbits.

METHODS

A cylindrical osteochondral defect model was created on the animal medial femoral condyle of and filled as follows: PT modified with BMP-7 for MPT group, non-modified PT for the PT group, while no implants were used for the blank group. The regenerated osteochondral tissue was assessed and analyzed by histological observations at four, eight and 16 weeks post-operation and evaluated in an independent and blinded manner by five different observers using a histological score. Osteochondral and subchondral bone defect repair was assessed by micro-CT scan at 16 weeks post-operation, while the biomechanical test was performed at 16 weeks post-operation.

RESULTS

Briefly, higher overall histological score was observed in the MPT group compared to PT group. Furthermore, more new osteochondral tissue and bone formed at the interface and inside the inner pores of scaffolds of the MPT group compared to PT group. Additionally, the micro-CT data suggested that the new bone volume fractions and the quantity and quality of trabecular bone, as well as the maximum release force of the bone, were higher in the MPT group compared to PT group.

CONCLUSIONS

We demonstrated that the applied modified PT with BMP-7 promotes excellent subchondral bone regeneration and may serve as a novel approach for osteochondral defects repair.

3D-printing zirconia implants; a dream or a reality? An in-vitro study evaluating the dimensional accuracy, surface topography and mechanical properties of printed zirconia implant and discs

PURPOSE

The aim of this study was to evaluate the dimensional accuracy, surface topography of a custom designed, 3D-printed zirconia dental implant and the mechanical properties of printed zirconia discs.

MATERIALS AND METHODS

A custom designed implant was 3D-printed in zirconia using digital light processing technique (DLP). The dimensional accuracy was assessed using the digital-subtraction technique. The mechanical properties were evaluated using biaxial flexure strength test. Three different build angles were adopted to print the specimens for the mechanical test; 0°(Vertical), 45° (Oblique) and 90°(Horizontal) angles. The surface topography, crystallographic phase structure and surface roughness were evaluated using scanning electron microscopy analysis (SEM), X-ray diffractometer and confocal microscopy respectively.

RESULTS

The printed implant was dimensionally accurate with a root mean square (RMSE) value of 0.1mm. The Weibull analysis revealed a statistically significant higher characteristic strength (1006.6MPa) of 0° printed specimens compared to the other two groups and no significant difference between 45° (892.2MPa) and 90° (866.7MPa) build angles. SEM analysis revealed cracks, micro-porosities and interconnected pores ranging in size from 196nm to 3.3µm. The mean Ra (arithmetic mean roughness) value of 1.59µm (±0.41) and Rq (root mean squared roughness) value of 1.94µm (±0.47) was found. A crystallographic phase of primarily tetragonal zirconia typical of sintered Yttria tetragonal stabilized zirconia (Y-TZP) was detected.

CONCLUSIONS

DLP prove to be efficient for printing customized zirconia dental implants with sufficient dimensional accuracy. The mechanical properties showed flexure strength close to those of conventionally produced ceramics. Optimization of the 3D-printing process parameters is still needed to improve the microstructure of the printed objects.

Thirty Years of Translational Research in Zirconia Dental Implants: A Systematic Review of the Literature

Thirty years of transitional research in zirconia (Zr) ceramics has led to significant improvements in the biomedical field, especially in dental implantology. Oral implants made of yttria-tetragonal zirconia polycrystals (Y-TZP) because of their excellent mechanical properties, good biocompatibility, and esthetically acceptable color have emerged as an attractive metal-free alternative to titanium (Ti) implants. The aim of the review was to highlight the translation research in Zr dental implants that has been conducted over the past 3 decades using preclinical animal models. A computer search of electronic databases, primarily PubMed, was performed with the following key words: "zirconia ceramics AND animal trials," "ceramic implants AND animal trials," "zirconia AND animal trials," "zirconia AND in vivo animal trials," without any language restriction. However, the search was limited to animal trials discussing percentage bone-implant contact (%BIC) around zirconia implants/discs. This search resulted in 132 articles (reviews, in vivo studies, and animal studies) of potential interest. We restricted our search terms to "zirconia/ceramic," "bone-implant-contact," and "animal trials" and found 29 relevant publications, which were then selected for full-text reading. Reasons for exclusion included the article's not being an animal study, being a review article, and not discussing %BIC around Zr implants/discs. Most of the studies investigated BIC around Zr in rabbits (30%), pigs (approximately 20%), dogs, sheep, and rats. This review of the literature shows that preclinical animal models can be successfully used to investigate osseointegration around Zr ceramics. Results of the reviewed studies demonstrated excellent %BIC around Zr implants. It should be noted that most of the studies investigated %BIC/removal torque under nonloading conditions, and results would have been somewhat different in functional loading situations because of inherent limitations of Zr ceramics. Further trials are needed to evaluate the performance of Zr ceramics in clinical conditions using implants designed and manufactured via novel techniques that enhance their biomechanical properties.

Success Rate of Two-Piece Zirconia Implants: A Retrospective Statistical Analysis

PURPOSE

About 10 years ago, one-piece zirconia implants were introduced to dentistry. The aim of the study was to evaluate the clinical success of two-piece zirconia implants regarding osseointegration using the manufacturers' warranty data.

MATERIALS AND METHODS

Over a period of 4 years (2010-2014), the data of warranty replacements of 15,255 sold Zeramex implants were evaluated retrospectively and blinded.

RESULTS

Three hundred forty-seven (2.2%) nonosseointegrated implants were sent back. Zeramex T showed an average success rate of 96.7%, whereas Zeralock implants exhibited an average success rate of 98.5%. Furthermore, Zeramex Plus implants exhibit an average success rate of 99.4% within the investigated period. Assuming, that 2% of the failed implants were unreturned, the above-mentioned values show no changes. Assuming 5% (10%) of unreturned nonosseointegrated implants, the average success rate of Zeramex T decreases from 96.7% to 96.6% (96.4%) and of Zeralock from 98.5% to 98.4% (98.4%), respectively. The success rate of Zeramex Plus implants remains unchanged at 99.4%.

CONCLUSION

The results of this study imply that two-piece zirconia implants show competitive success rates, improved from >96.7% to >98.5% over three product generations.

A systematic review of the clinical survival of zirconia implants

OBJECTIVES

The aim of this review was to evaluate the clinical success and survival rates of zirconia ceramic implants after at least 1 year of function and to assess if there is sufficient evidence to justify using them as alternatives to titanium implants.

MATERIALS AND METHODS

An electronic search in MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Clinical Trials (CENTRAL) databases was performed in April 2015 by two independent examiners to retrieve clinical studies focusing on the survival rate of zirconia implants after at least 1 year of function. Implant survival was estimated using the overall proportion reported in the studies with a Clopper-Pearson 95 % confidence interval (random effect model with a Der-Simonian Laird estimate).

RESULTS

Fourteen articles were selected out of the 1519 titles initially screened. The overall survival rate of zirconia one- and two-piece implants was calculated at 92 % (95 % CI 87-95) after 1 year of function. The survival of implants at 1 year for the selected studies revealed considerable heterogeneity.

CONCLUSIONS

In spite of the unavailability of sufficient long-term evidence to justify using zirconia oral implants, zirconia ceramics could potentially be the alternative to titanium for a non-metallic implant solution. However, further clinical studies are required to establish long-term results, and to determine the risk of technical and biological complications. Additional randomized controlled clinical trials examining two-piece zirconia implant systems are also required to assess their survival and success rates in comparison with titanium as well as one-piece zirconia implants.

CLINICAL RELEVANCE

Zirconia implants provide a potential alternative to titanium ones. However, clinicians must be aware of the lack of knowledge regarding long-term outcomes and specific reasons for failure.

Histological analysis of loaded zirconia and titanium dental implants: an experimental study in the dog mandible

OBJECTIVE

To assess whether or not peri-implant soft tissue dimensions and hard tissue integration of loaded zirconia implants are similar to those of a titanium implant.

MATERIALS AND METHODS

In six dogs, two one-piece zirconia implants (VC, ZD), a two-piece zirconia implant (BPI) and a control one-piece titanium implant (STM) were randomly placed. CAD/CAM crowns were cemented at 6 months. Six months later, animals were killed and histomorphometric analyses were performed, including: the level of the mucosal margin, the extent of the peri-implant mucosa, the marginal bone loss and the bone-to-implant contact (BIC). Means of outcomes variables were calculated together with their corresponding 95% confidence intervals.

RESULTS

In general, the mucosal margin was located coronally to the implant shoulder. The buccal peri-implant mucosa ranged between 2.64 ± 0.70 mm (VC) and 3.03 ± 1.71 mm (ZD) (for all median comparisons p > 0.05). The relative marginal bone loss ranged between 0.65 ± 0.61 mm (BPI) and 1.73 ± 1.68 mm (ZD) (buccal side), and between 0.55 ± 0.37 mm (VC) and 1.69 ± 1.56 mm (ZD) (lingual side) (p > 0.05). The mean BIC ranged between 78.6% ± 17.3% (ZD) and 87.9% ± 13.6% (STM) without statistically significant differences between the groups (p > 0.05).

CONCLUSIONS

One- and two-piece zirconia rendered similar peri-implant soft tissue dimensions and osseointegration compared to titanium implants that were placed at 6 months of loading. Zirconia implants, however, exhibited a relatively high fracture rate.

Zirconia in dental implantology: A review

Background:

Titanium has been the most popular material of choice for dental implantology over the past few decades. Its properties have been found to be most suitable for the success of implant treatment. But recently, zirconia is slowly emerging as one of the materials which might replace the gold standard of dental implant, i.e., titanium.

Materials and Methods:

Literature was searched to retrieve information about zirconia dental implant and studies were critically analyzed. PubMed database was searched for information about zirconia dental implant regarding mechanical properties, osseointegration, surface roughness, biocompatibility, and soft tissue health around it. The literature search was limited to English language articles published from 1975 to 2015.

Results:

A total of 45 papers met the inclusion criteria for this review, among the relevant search in the database.

Conclusion:

Literature search showed that some of the properties of zirconia seem to be suitable for making it an ideal dental implant, such as biocompatibility, osseointegration, favourable soft tissue response and aesthetics due to light transmission and its color. At the same time, some studies also point out its drawbacks. It was also found that most of the studies on zirconia dental implants are short-term studies and there is a need for more long-term clinical trials to prove that zirconia is worth enough to replace titanium as a biomaterial in dental implantology.

Zirconia Implants in Esthetic Areas: 4-Year Follow-Up Evaluation Study

Objectives. The aim is to evaluate the survival and success rates, as well as the marginal bone loss (MBL) and periodontal indexes of zirconia implants positioned in the esthetic jaw areas. Materials and Method. 13 patients were selected and 20 one-piece zirconia implants were used for the rehabilitation of single tooth or partially edentulous ridge in the esthetic jaw areas. Six months after surgery and then once a year, a clinical-radiographic evaluation was performed in order to estimate peri-implant tissue health and marginal bone loss. Results. The survival and success rates were 100%. The average marginal bone loss from baseline to 48 months after surgery was +2.1 mm. Four years after surgery, the median and the mode for visible Plaque Index and Bleeding On Probing resulted 1 whereas Probing Pocket Depth amounted to 3 mm (SD = ±0.49 mm). Conclusion. One-piece zirconia dental implants are characterized by high biocompatibility, low plaque adhesion, and absence of microgap that can be related to the clinical success of these implants even in the esthetic areas.

A Critical Review of Dental Implant Materials with an Emphasis on Titanium versus Zirconia

The goal of the current publication is to provide a comprehensive literature review on the topic of dental implant materials. The following paper focuses on conventional titanium implants and more recently introduced and increasingly popular zirconia implants. Major subtopics include the material science and the clinical considerations involving both implant materials and the influence of their physical properties on the treatment outcome. Titanium remains the gold standard for the fabrication of oral implants, even though sensitivity does occur, though its clinical relevance is not yet clear. Zirconia implants may prove to be promising in the future; however, further in vitro and well-designed in vivo clinical studies are needed before such a recommendation can be made. Special considerations and technical experience are needed when dealing with zirconia implants to minimize the incidence of mechanical failure.

An Overview of Zirconia Dental Implants: Basic Properties and Clinical Application of Three Cases

Due to the possible aesthetic problems of titanium implants, the developments in ceramic implant materials are increasing. Natural tooth colored ceramic implants may be an alternative to overcome aesthetic problems. The purpose of this article is to give information about the basic properties of dental zirconia implants and present 3 cases treated with two-piece zirconia implants. Two-piece zirconia dental implants, 4.0 mm diameter and 11.5 mm in length, were inserted into maxillary incisor region. They were left for 6 months to osseointegrate. Panoramic and periapical radiographs were obtained and examined for bone-implant osseointegration. During the follow-up period the patients were satisfied with their prosthesis and no complication was observed.

Two-piece zirconia implants supporting all-ceramic crowns: a prospective clinical study

Objectives

The aim of this prospective clinical study is to evaluate the safety and efficacy of a new all-ceramic implant system to replace missing teeth in partially edentulous patients.

Material and methods

Thirty-two partially edentulous, systemically healthy patients were treated with 49 two-piece zirconia implants (ZERAMEX® T Implant System). Zirconia abutments were connected with adhesive resin cement. Single-unit full-ceramic crowns were cemented. The cases have been followed for 588±174 days after loading (range 369–889 days). All patients have been re-evaluated 1 year after loading.

Results

The cumulative survival rate 1 year after loading was 87% implants. All failures were the result of aseptic loosening, and no implants were lost after the first year. The results of the other cases were good, and the patients were very satisfied. The cumulative soft tissue complication rate was 0%, the cumulative technical complication rate was 4% implants, the cumulative complication rate for bone loss >2 mm was 0%, and the cumulative esthetic complication rate was 0%. Including the data from 20 patients treated with an earlier version of the system, an over-all 2-year cumulative survival rate of 86% was calculated for a total of 76 two-piece zirconia implants supporting all-ceramic crowns in 52 patients.

Conclusions

Replacement of single teeth in the posterior area was possible with this new full-ceramic implant system. Failures were due to aseptic loosening.

Influence of Surface Nano-Roughness on Osseointegration of Zirconia Implants in Rabbit Femur Heads Using Selective Infiltration Etching Technique

This study evaluates osseous healing of selective infiltration-etched (SIE) zirconia implants compared to as-sintered zirconia and titanium implants. Twenty implants of each group were inserted in 40 adult New Zealand white male rabbits. After 4 and 6 weeks, bone blocks containing the implants were retrieved, sectioned, and processed to evaluate bone-implant contact (BIC) and peri-implant bone density. SIE zirconia implants had significantly higher BIC and marginally higher bone density. The results suggest that selective infiltration-etched zirconia implant surface may improve implant osseointegration.

Evaluation of the success criteria for zirconia dental implants: a four-year clinical and radiological study

Objectives. The aim was to evaluate survival and success rates, soft tissue health, and radiographic marginal bone loss (MBL) of zirconia implants placed in the esthetic and posterior areas of the jaws and in association with multiple or single implant restorations after at least 6 months of definitive restoration. Material and Methods. 35 one-piece zirconium implants were utilized for single or partially edentulous ridges rehabilitation. All implants received immediate temporary restorations and six months after surgery were definitively restored. Every 6 months after implant placement, a clinical-radiographic evaluation was performed. For each radiograph, the measurements of MBL were calculated. Results. The results showed that the mean MBL at 48-month followup was 1.631 mm. The mean MBL during the first year of loading was not more significant for implants placed in the first molar regions than for those positioned in other areas. Moreover, no differences in marginal bone level changes were revealed for multiple and single implants, whereas MBL in the first year was observed to be slightly greater for implants placed in the maxilla than for those placed in the mandible. Conclusion. Zirconia showed a good marginal bone preservation that could be correlated with one-piece morphology and characteristics of zirconia implants.

A single-tooth, two-piece zirconia implant located in the anterior maxilla: a clinical report

It can be difficult to achieve a natural appearance in the anterior region with implant-supported restorations because metal components may show through the soft tissue. Zirconia implants, therefore, should be considered as an alternative treatment for improved esthetics. The goal of this clinical report was to evaluate a new 2-piece zirconia implant system for the maxillary anterior region. A 2-piece zirconia dental implant was placed in the maxillary left lateral incisor position and left in place for 6 months to osseointegrate. Panoramic and periapical radiographs were examined for bone-implant osseointegration. The plaque control record (PCR), bleeding on probing (BOP), and probing depth (PD) were measured after the cementation of the definitive restoration and a 6-month follow-up period. The PCR, BOP, and PD values were compared and the marginal bone level was also evaluated by making standardized periapical radiographs. The results showed that over the 6-month follow-up period, the marginal area was healthy and presented no bleeding on probing, no plaque accumulation, and no change in periimplant marginal bone level.

Zirconium, calcium, and strontium contents in magnesium based biodegradable alloys modulate the efficiency of implant-induced osseointegration

Development of new biodegradable implants and devices is necessary to meet the increasing needs of regenerative orthopedic procedures. An important consideration while formulating new implant materials is that they should physicochemically and biologically mimic bone-like properties. In earlier studies, we have developed and characterized magnesium based biodegradable alloys, in particular magnesium-zirconium (Mg-Zr) alloys. Here we have reported the biological properties of four Mg-Zr alloys containing different quantities of strontium or calcium. The alloys were implanted in small cavities made in femur bones of New Zealand White rabbits, and the quantitative and qualitative assessments of newly induced bone tissue were carried out. A total of 30 experimental animals, three for each implant type, were studied, and bone induction was assessed by histological, immunohistochemical and radiological methods; cavities in the femurs with no implants and observed for the same period of time were kept as controls. Our results showed that Mg-Zr alloys containing appropriate quantities of strontium were more efficient in inducing good quality mineralized bone than other alloys. Our results have been discussed in the context of physicochemical and biological properties of the alloys, and they could be very useful in determining the nature of future generations of biodegradable orthopedic implants.

Finite element stress analysis of Ti-6Al-4V and partially stabilized zirconia dental implant during clenching

OBJECTIVE

The purpose of this paper is to compare the differences in stress between Ti-6Al-4V and PS-ZrO(2) dental implant during clenching and whether these changes are clinically significant to limit the use of zirconia in oral implantology.

MATERIALS AND METHODS

The model geometry was derived from position measurements taken from 28 diamond blade cut cross-sections of an average size human adult edentulous mandible and generated using a special sequencing method. Data on anatomical, structural, functional aspects and material properties were obtained from measurements and published data. Ti-6Al-4V and PS-ZrO(2) dental implants were modelled as cylindrical structure with a diameter of 3.26 mm and length of 12.00 mm was placed in the first molar region on the right hemimandible.

RESULTS

The analysis revealed an increase of 2-3% in the averaged tensile and compressive stress and an increase of 8% in the averaged Von Mises stress were recorded in the bone-implant interface when PS-ZrO(2) dental implant was used instead of Ti-6Al-4V dental implant. The results also revealed only relatively low levels of stresses were transferred from the implant to the surrounding cortical and cancellous bone, with the majority of the stresses transferred to the cortical bone.

CONCLUSION

Even though high magnitudes of tensile, compressive and Von Mises stresses were recorded on the Ti-6Al-4V and PS-ZrO(2) dental implants and in the surrounding osseous structures, the stresses may not be clinically critical since the mechanical properties of the implant material and the cortical and cancellous bone could withstand stress magnitudes far greater than those recorded in this analysis.

Current findings regarding zirconia implants

PURPOSE

The present article aims to analyze the available clinical data on the survival and success rate of dental zirconia implants (ZI).

MATERIAL AND METHOD

Studies (2006-2011) listed in the bibliography were obtained by using the key words "zirconia, zirconium, implants, dental, clinical" and combinations of these in different databases and on the internet. These articles served as a basis for the article.

RESULTS

A total of 17 clinical studies were found, involving 1,675 implants and 1,274 patients. In 16 studies, one-piece implant systems were investigated. The survival rates for ZI range from 74-98% after 12-56 months, with success rates between 79.6-91.6% 6-12 months after prosthetic restoration. However, the design of most of the studies show considerable shortcomings, and only low evidence level.

CONCLUSION

The small number of studies and the limited period of observation permit only a qualified statement on the clinical success of ZI. The results available to date indicate that ZI are inferior to titanium implants (TI) with regard to survival and success rates. Well-conducted long-term studies are urgently needed to permit a meaningful assessment of the survival or success rates of ZI and a statement concerning their application as an alternative to TI.