Restorative dentistry done digitally Schepke, Ulf
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Implementation and evaluation of some digital tools in contemporary implant dentistry
Ulf Schepke
University Medical Center Groningen University of Groningen
Nederlandse Vereniging voor Gnathologie en Prothetische Tandheelkunde / nvgpt.nl Nederlandse Vereniging voor Orale Implantologie / nvoi.nl
Dentsply Sirona Deutschland Dentsply Sirona Benelux
Gronings Tandtechnisch Laboratorium Noord Negentig, accountants Nobel Biocare
3M
ttmfl Gerrit van Dijk Straumann Zircon Vision Elysee Dental
Concept and Design: Lara Blackwood
Final Artwork: Maroesja Swart-Nijhuis, Puur*M Vorm & Idee Cover figure: Berend Blok
Printing: Gildeprint
ISBN: 978-94-6233-873-9 ISBN e-pub: 978-94-6233-874-6
© Ulf Schepke, 2018
ttmfl Gerrit van Dijk
Implementation and evaluation of some digital tools in contemporary implant dentistry
Proefschrift
ter verkrijging van de graad van doctor aan de Rijksuniversiteit Groningen
op gezag van de
rector magnificus prof. dr. E. Sterken en volgens besluit van het College voor Promoties.
De openbare verdediging zal plaatsvinden op woensdag 14 februari 2018 om 16:15 uur
door
Ulf Schepke
geboren op 12 februari 1979 te Kiel
Prof. dr. H.J.A. Meijer Prof. dr. G.M. Raghoebar
Beoordelingscommissie Prof. dr. A.J. van Winkelhoff Prof. dr. H. de Bruyn Prof. dr. G.J. Meijer
Sjoerd G. Bakker
Preface 09
CHAPTER 01
General introduction 11
CHAPTER 02 • PART A
Osseointegration of a zirconia implant: a case report and review 25
CHAPTER 02 • PART B
On the bulk degradation of yttria-stabilized nanocrystalline zirconia
dental implant abutments: an electron backscatter diffraction study 39
CHAPTER 02 • PART C
Phase transformation and fracture load of stock and CAD/CAM customized
zirconia abutments after 1 year of clinical function 57
CHAPTER 03 • PART A
Clinical bonding of Resin Nano Ceramic restorations to zirconia abutments:
a case series within a randomized clinical trial 79
CHAPTER 03 • PART B
Adhesive failure of Lava Ultimate and Lithium Disilicate crowns, bonded to
zirconia abutments: a prospective within-patient comparison 95
CHAPTER 03 • PART C
Fractography of clinically fractured, implant-supported dental
CAD/CAM polymer crowns 105
CHAPTER 04
Digital versus analog full-arch impressions for single-unit premolar implant
crowns: Operating time and patient preference 123
RESTORATIVE DENTISTRY DONE DIGITALLY
Implementation and evaluation of some digital tools in contemporary implant dentistry
patient-based outcomes in a randomized controlled clinical trial 135
CHAPTER 06
General discussion, recommendations and conclusions 155
Epilogue 163
Summary 167
Samenvatting 173
Zusammenfassung 179
Acknowledgements 185
Curriculum Vitae 195
My generation deals with a continuous transition from analog to digital workflows. I still keep my old personal letters, and at the dawn of e-mailing I even saved a hard copy of my most important electronic correspondence. However, today I find it disturbing not to be able to refer a patient by e-mail, and I cannot understand why some scientific journals still require a fax for certain correspondence.
As a dentist, I adhere to digitization as much as possible: I believe that patient records, storage of diagnostic information, treatment planning, and documentation of the treatment implemented should be organized digitally for various reasons.
Within all workflows in a dental office, many show crosslinks to other economic fields that might be easily adapted to the specific needs of the dental office. Manufacturers and all kinds of consultants, promoting various implementations, are willing to contribute to a healthy and successful dental office and to improving oral health care as a whole with their products.
However, it takes a medical professional to weigh all the various interests and concerns, both the presumed benefits and anticipated drawbacks that come along with new and supposedly improved materials and technical procedures. Thus, I believe that the medical professional should always be involved in implementing workflows that involve:
- Planning for treatment and diagnostics;
- Production and treatment implementation;
- Patient safety and evaluation.
Restorative dentistry is a complex and field-specific domain, and, in order to implement digital workflows from other domains, extended evaluation and adaptation by the actual dentist seems indispensable.
CHAPTER
01
General introduction
Restorative dentists and technicians have been early adopters of innovation. In the 1970s, Duret adapted the concept of Computer Aided Design/Computer Aided Manufacturing (CAD/CAM) from the airplane industry and introduced the third dimension into digital dental treatment planning.1 In 1987, Mörman developed the first full chairside CAD/CAM workflow with the production of inlays and onlays under the name “Cerec” (Chairside Economical Restoration of Esthetic Ceramics, figure 1).2 Since then, more and more three-dimensional digital workflows have been developed, adapted, and implemented in the field of restorative dentistry.
Figure 1
Cerec: Prototype, Type 1, Type 2 and Type 3. Pictures by courtesy of Dentsply Sirona
Bhambhani and colleagues (2013) classify digitization in prosthodontics according to the clinical aspect, laboratory procedures, the training of students, patient motivation, practice management, and dental research. The potential benefits include, but are not limited to, enhanced motivation for patients, improved communication, use of enhanced biomaterials, reduced chair time for the patient, and providing predictable results of the treatment.3
Planning
Based on the concept of informed consent, the patient and the restorative dentist should be able to make a shared decision about the treatment plan.4 Several 3D-digital diagnostic tools are available to achieve this kind of a communication platform, and can help to arrive at a successful, predictable, and safe treatment. Cone beam computed tomography (CBCT) data can be combined with digital
CHAPTER 01 and functional reconstruction of large maxillofacial defects6 but also in cases of complex implant
replacement of missing teeth. The virtual model visualizes anatomical structures and prospected reconstruction and can help to decide, for instance, whether augmentation procedures are beneficial or whether it is possible to compensate for the implantation axis by means of the future prosthetic construction.7
The wax-up made by the dental technician is a tool that simulates the final restorative treatment and has always played an important role as a communication tool for the dental technician, the dentist, and the patient,8 as well as serving as a diagnostic device.9 Once the simulation is accepted by the whole team (i.e., patient, restorative dentist, and technician), the wax-up can be transferred to the definitive restoration. Traditionally, the wax-up was manually created and used as a guideline for a try-in simulation (mock-up).
The digital workflow, however, is less time consuming, offers less asymmetry due to the digital mirror function,10 and, in combination with rapid prototyping, makes it possible to offer the patient different realistic designs to choose from, in one single appointment.11 Additionally, the digital wax-up can be easily and accurately transferred to the final restoration.12
Production
The digitally minded practitioner can choose from a variety of rapid prototyping or CAD/
CAM applications. More than a dozen different CAD/CAM polymers for semi-permanent use have been available for half a decade already,13 and there are now seemingly countless millable materials intended for permanent restorations. Relatively new dental CAD/CAM materials, such as polyaryletherketone, are gaining in popularity in the dental community,14 and modifications of traditionally hand-pressed glass-ceramics are also available and used as a CAD/CAM material without any loss in quality, while taking up significantly less working time for the dental technician.15 CAD/CAM polymers – sometimes referred to as “indirect composites” such as Lava Ultimate – are intended for permanent restorations and are becoming popular. Manufacturers are working on combining the mechanical properties of direct composites and indirect ceramic restorations, which makes this material class potentially very interesting for a broad range of indications.16
In his well-recognized review about the digital future of dental devices, Van Noort states: “The challenge for the dental materials research community is to marry the technology with materials that are suitable for use in dentistry. This can potentially take dental materials research in a totally different direction.”17
Production – zirconia
One of those marriages is the use of zirconia in restorative dentistry. Since the 1990s, a modification of pure zirconia has been successfully introduced to restorative dentistry due to its favorable biological, mechanical, and esthetic properties.18-21
Zirconia (ZrO2) is a tooth-colored oxide ceramic. It is supposedly as biologically friendly as titanium.
Osseointegration of zirconia implants, for example, is considered comparable to that of titanium implants, although human histological studies are scarce. In implant dentistry, it is not only predominantly used as a basic material for abutments but is also applied for implants. In a recent, comprehensive review by Cionca and colleagues (2017) on the current status of zirconia implants in the dental field, reasons for choosing zirconia instead of titanium implants, as derived from the literature, are listed. They include enhanced aesthetics with white zirconia and presumed sensitivity to titanium in susceptible patients – zirconia is supposedly less attractive to bacteria – along with patients’ preference for non-metallic dentistry in general.22
Transformation of single crystals from the tetragonal to the monoclinical phase (t-m transformation), introduced by stress, accompanies expansion of the crystal and inhibits micro-crack propagation.
This mechanism, also referred to as “transformation toughening,” makes this particular white material extraordinarily strong; it is irreversible at body temperature, which makes the process nonrecurring.23
However, zirconia is a demanding associate: Due to the advanced production process, computer-aided manufacturing is mandatory,24-28 and production inaccuracies can have severe clinical consequences.29 Low-temperature degradation (LTD) was identified as the main reason for the catastrophic failures of hip-ball prosthesis in 2001 and 2002.30 It is unclear whether such catastrophic changes can also occur with dental devices under clinical circumstances.31
Production – bonding to zirconia
Most applications of dental zirconia have to be bonded to a sub- or super-stratum with cement.
Another major issue in the liaison between zirconia and dental material technology is the adhesion at the cement-to-zirconia interface: Microtensile tests for various bonding strategies indicate bond strengths around 16 to 23 MPa.32,33 Whereas some reviews are critically pessimistic,32,34 other authors consider this to be acceptable bond strengths.33,35 All the reviews, however, focus on the interface between zirconia and the (adhesive) cement.32-36 The influence of the mechanical and chemical properties of the sub- or super-stratum on clinical bonding failures remains unclear but is of clinical relevance.
Production – impression-taking
Alghazzawi describes the advantages of CAD/CAM technology and outlines a digital future for the field of restorative dentistry, stressing the digital impression as the most easily accessible “future”
technology in the dental office.37
The list of the potential advantages of digital impression-taking is extensive. Analysis of the preparation is possible in real time, and direct assessment tools are available for the dentist. The area of interest can be scanned in intervals and also selectively repeated. The dentist transfers the digital model to the technician within seconds, and disinfection is not germane. No impression or casting material is needed, while the files can easily be stored without loss of quality.38,39 This is just to mention a few of the advantages.
But there are certainly also disadvantages to digital impression-taking. The learning curve for
handling the scanning device seems to be flat and certain scan paths have to be followed.40 Extra equipment and maintenance41 is needed, and the scanner itself is quite expensive. On top of that, the digital workflow might be limited due to incompatible software or even scan fees.39
But what about the quality of the digital impression? Most of the studies performed showed comparable or even better results in terms of accuracy for the digital workflow for single units and short-fixed dental prosthesis (FDPs);42-47 whereas some studies show better results for analogue workflow, especially for full arch impressions.42,48,49
Based on those studies, the practitioner can conclude that it is safe to use digital impression-taking for single unit restorations. Even though there are differences in the accuracy of the available scanning systems,50,51 all the systems tested generally deliver clinically acceptable results.52,53 The expected number of treatments, the time and the aim needed to take a digital impression, along with the patients’ preference, could play a central role in decision-making about whether to invest in a digital scanning device or not.
Production – CAD/CAM
Restorative dentistry has to deal with specific features, as compared to other industrial production workflows. Whereas Rapid Prototyping (RP) normally deals with Additive Manufacturing (AM), using inexpensive material to build up a prototype for visualization and testing purposes,54 every dental restoration is unique, and therefore is a prototype and final product at the same time. Traditionally, AM in restorative dentistry was limited to manufacturing a “mock-up,”11 and Computer Numerical Control (CNC) milling was used for the final restoration.55 However, additive techniques, often referred to as 3D printing, are catching up.56 Printable biomaterials are available,57 and, even though current expert opinion is still critical about the use of AM in restorative dentistry,58 some authors report excellent or even superior accuracy in AM objects compared to CNC-milled objects in vitro.59,60 Still, it is not just the material that matters. The CAD/CAM production process, whether or not associated with 3D acquisition to a full 3D Workflow in prosthodontics (figure 2),61 enables the restorative team to personalize the designated therapy by means of easily accessible restorations.
Individually designed CAD/CAM implant abutments, for example, are not necessarily more expensive than their stock counterparts (e.g., zirconia abutments from Dentsply Sirona: figure 3).
CHAPTER 01
Figure 2
3D Workflow, adapted from van der Meer61
Figure 3
Stock (ZirDesignTM, left) and CAD/CAM customized (AtlantisTM, right) zirconia implant abutments, both from Dentsply Sirona implants, Mölndal, Sweden after one year of clinical service
The question remains, however, whether the use of individualized abutments leads to measurably significant differences in clinical everyday life.
Evaluation – visualization of the invisible
Objective measurements are needed to evaluate whether the treatment performed has met the restorative goal, or whether or not degeneration of the result takes place over time. They support – together with clinical experience – successful aftercare, on the one hand, and produce comparable outcome measurements, on the other, thus helping develop evidence-based and predictable treatment concepts. In this sense, careful evaluation and diagnosis are similar.
Traditional assessment methods are practitioner-based, and, even though more or less objective assessment methods have been developed, it is often difficult to introduce them to clinical practice.62 Therefore, superimposing 3D digital models could be a promising addition to visual examination and assessing restorative treatment results.63
Currently, a beta version of a dental superimposing tool is already available (OraCheck by Cyfex).1*
Even volume changes can be calculated,64 and the performance seems comparable to the standard superimposing software.65 In theory, the application seems suitable for assessing clinical wear, but an accurate superimposing strategy for the individual tooth appears to be lacking, to date.
Aim and research questions
The restorative dentist has to deal with a dilemma: He/she needs to keep up with modern technology in order to be able to offer state-of-the-art care, but the dentist also needs to identify lasting and reliable tools from the vast amount of novelties offered by the industry. The general objective of the research presented is to assess some of those novel tools and materials to help the practitioner make a choice and create awareness of this dilemma.
For a systematic division, featured in the Introduction above, clustering was chosen for different technological innovations: 1) diagnostics and treatment planning, 2) production and treatment execution, and 3) patient safety and evaluation. This thesis focuses on a selection of digital production and treatment execution related to aspects of restorative dentistry, more specifically the field of oral implantology.
The following research questions are posed:
Can zirconia implant single-tooth replacements perform in a way comparable to the gold standard (titanium implants) in terms of bone to implant contact (Chapter 2a)?
Do zirconia implant abutments exhibit bulk and/or surface degradation after one year of clinical service (Chapters 2b and 2c)?
Do zirconia implant abutments show a decrease in strength after one year of clinical service (Chapter 2c)?
Is the standard procedure for bonding Lava Ultimate crowns to zirconia implant abutments efficient (Chapter 3a)?
Does the restorative material have an influence on the debonding rate of crowns bonded to zirconia abutments (Chapters 3b and 3c)?
Is there a difference in patient appreciation and chair time between digital and conventional
1* http://www.cyfex.com/en/dental
CHAPTER 01
impression-taking in implant dentistry (Chapter 4)?
Do customized zirconia implant abutments perform better than zirconia stock abutments after one year of clinical service (Chapter 5)?
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CHAPTER 01
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CHAPTER 01
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CHAPTER
02
Osseointegration of a zirconia implant:
a case report and review
• PART A •
This chapter is an extended version of:
Schepke U, Meijer GJ, Meijer HJ, Walboomers XF, Cune M.
Osseointegration of a zirconia implant: a histologic assessment.
Int J Prosthodont. 2017 Jul/Aug;30(4):370-372.
Abstract
The aim of this study was to describe the histological and histomorphometrical features of a retrieved, functional zirconia endosseous implant in a human subject and relate the findings to information available from literature on osseointegration in other explanted zirconia and titanium implants in man.
A maxillary zirconia implant in a 52-year old male patient (Zv3, Wolfratshausen, Germany) was retrieved and prepared for light microscopic evaluation. It had functioned successfully without objective or subjective concerns for approximately two years.
Histological examination demonstrated that most of the screw threads were filled with bone, showing a uniform colour, which was in close contact with the zirconia surface. No intervening fibrous tissue layer was observed between implant and the surrounding bone. In the calcified tissue many large rounded osteoblasts and osteocytes were visible. Bone contact measurements measuring from the most coronal aspect until the lowest thread revealed a mean percentage of bone to implant contact of 55.8% (SD 3.8%). This is comparable to findings regarding retrieved implants in the literature, although these show a wide range.
The histological data are coherent with a well osseointegrated zirconia implant after 2 years of functional loading. This provides further evidence of the potential of zirconia to osseointegrate to a more or less similar degree as titanium implants in man.
Osseointegration of a zirconia implant:
a case report and review
Titanium (Ti) is seen as the ‘gold standard’ ground material for dental implants and has been widely and successfully used for decades. Nevertheless, it has some potential drawbacks, among which blue-greyish shimmering of the implant itself or implant components in cases of thin overlying mucosa.1 Also, the high prevalence of peri-implant mucositis and peri-implantitis is of concern.2 Titanium has relatively little resistance against wear and fretting. Submicron titanium particles that can evolve from implant bending, induce inflammatory cytokines secretion in vitro and are observed in soft tissues adjacent to sites with peri-implantitis.3,4 In addition, concerns regarding the potential hypersensitivity towards titanium were raised which however, was seen in only a limited number of susceptible patients.5 Therefore, some patients prefer a metal-free solution.
High strength ceramics such as Yttria-stabilized zirconiumdioxide (Y-TZP) could form an alternative for titanium as implant material. Y-TZP being white, entails better light dynamics, especially in cases with thin overlying mucosa. It can be milled according to individual specifications by means of a Computer Assisted Design and Computer Assisted Manufacturing (CAD-CAM) production process. Both bone and soft tissues respond favourably to Y-TZP.6 In a 3-year retrospective study clinical gingival parameters around zirconia implants compared to natural teeth demonstrated less bleeding and smaller probing pocket depths around the implants.7 However peri-implantitis and peri-implant mucositis were also reported for zirconia implants which did not always respond favourably to treatment either.8 In a recent systematic review 19 clinical studies with zirconia implants could be included. Most were biased because of methodological shortcomings, resulting in only a low evidence level. Nevertheless, the authors concluded that to date zirconia implants are inferior to titanium implants in terms of implant survival.9 This is in agreement with a consensus statement from a few years previously in which the use of Y-TZP implants was discouraged.10 Comparison of osseointegration between Y-TZP and Ti implants is almost exclusively done in animal studies. The results are consistent as comparable percentages of bone-implant contact between Ti and Y-TZP implants were reported in mandibles, maxillae and femur heads of rats, minipigs, dogs, rabbits and goats.11-22 In one study in goats, multinucleated giant cells were seen in association with zirconia and not with titanium implants, however, without a difference in the percentage of bone contact.23
The aim of this case report is to describe the histomorphometrical and histological features of a retrieved, functional zirconia implant in a human subject and relate the findings to the limited amount of information available from literature on osseointegration from other explanted implants.
CHAPTER 02 • PART A
Materials and Methods
A zirconia (Y-TZP) implant (dimensions 5 mm wide x 11 mm long) in a 52-year old male patient at the position of the first upper right molar (ZV3, Wolfratshausen, Germany) was damaged and unsalvageable as a result of an intubation procedure necessary for unrelated treatment in general anaesthesia. The proximal crown of a natural abutment tooth was also injured. The implant was immobile and had functioned successfully without objective or subjective concerns for approximately two years. After informed consent was obtained, it was carefully retrieved using a trephine drill at low speed and copious cooling, including approximately 1 mm of surrounding alveolar bone. The specimen was stored in a cool place and eventually fixed in buffered formaldehyde (pH 7.4) 10% for 24 hours and subsequently dehydrated in ethanol.
After embedding in methylmethacrylate, following polymerization, three non-decalcified, 10-µm-thick, longitudinal sections of the implants were prepared in a plane parallel to the long axis of the implant using a modified sawing microtome technique24 and subsequently stained with methylene blue and basic fuchsin.
Light microscopical evaluation of all sections was executed using an automated Axio Imager Z1 microscope (Carl Zeiss Micro Imaging GmbH, Göttingen, Germany) at 10x as well as 200x magnification and consisted of a complete morphological qualitative description and quantitative analysis of the hard tissue response.
Results
At the time of retrieval, after having raised a muco-periosteal flap, the implant appeared clinically healthy and was fully surrounded by alveolar bone. Characteristic histological sections are presented as figures 1a-b.
Histological examination demonstrated that most of the screw threads were filled with bone, showing a uniform colour, which was in close contact with the zirconia surface. No intervening fibrous tissue layer was observed between implant and the surrounding bone. In the calcified tissue many osteocytes were visible.
Bone contact measurements were performed, measuring from the most coronal aspect until the lowest thread. The mean percentage of bone to implant contact as seen in the 3 sections was 55.8%
(SD 3.8%), taken into consideration that coronally some alveolar bone seems to have been severed from the implant. This percentage of bone to implant contact lies in the same range of magnitude or perhaps somewhat less than the percentages of bone to implant contact that have been reported in literature regarding human histology around implants with a titanium or hydroxyapatite surface (table 1).
Figure 1a
Characteristic histological section showing intimate contact between the zirconia implant (gray) and the red colored adjacent bone (magnification 10x).
Figure 1b
Histological section; the depicted area (see framework in picture 1a) emphasizes the intimate contact between the zirconia implant (gray) and the red colored bone (magnification 200x). The vital bone is bounded by osteoblasts.
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Table 1 Studies involving human histology regarding dental implants in relation to the current study StudyNLocationTypeReason for RetrievalYears Bone to implant contact (%) Zirconia Nevins et al, 2011261MaxillaY-TZPPlanned0.5Not provided Kohal et al, 20162519MandibleY-TZPPeri-implantitis4.176.4% (range 58.1–93.7%,SD 9.7%) 3MaxillaY-TZPPeri-implantitis4.577.2% (range 73.6-81.9%,SD 4.3%) Current study1MaxillaY-TZP Fracture255.8% (SD 3.8%) HA-coated Dominici et al, 1997271MandibleHA-coatedPost-mortem375.3% Rohrer et al, 1999282 MaxillaHA-coatedPost-mortem347% Romanos et al, 2005293MandibleHA-coatedIn function0.580.6% Trisi et al, 2005302MandibleHA-coatedPost-mortem1037.6% Iezzi et al, 2007312MaxillaHA-coatedFracture abutment1428%-60% Iezzi et al, 2009321MandibleHA-coatedFracture 1577.6% (SD 5.1%) Coelho et al, 20103330Maxilla and mandibleHA-coatedProsthetic reasons0.2-1335%-95% Iezzi et al, 2013341MandibleHA-coatedPeri-implantitis1036.3% (SD 1.2%) Titanium Dominici et al, 1997271MandibleTiPost-mortem372.2% Rohrer et al, 1999285 MandibleTiPost-mortem765% Degidi et al, 20033511Maxilla and mandibleTiIn function10/1260%-65% Rocci et al, 2003362Class III / IV boneOxidized TiIn function 0.584.9% (SD 0.9%) 6Class III / IV boneOxidized TiIn function0.581.4% (SD 10.6%) Bolind et al, 200537216Maxilla and mandibleTiVarious reasons0.3-1675% Romanos et al, 20052916MaxillaTiIn function0.662.4% 10MandibleTiIn function0.466.8% Coelho et al, 20093823Maxilla and mandibleTiProsthetic reasons8-1362.2% Degidi et al, 2011399Maxilla and mandibleTiIn function0.159.9% Iezzi et al, 2012402MandibleTiAbutment fracture589.8% 1MaxillaTiAbutment fracture576.6% Iezzi et al, 2014418Maxilla and mandibleTiProsthetic/psychologic5-2294-100% Mangano et al, 2015421MandibleTiFracture547.2% 1MaxillaTiFracture10NR
Discussion
Little information is available with respect to the osseointegration of zirconia implants in humans. The best indication of their potential for osseointegration is obtained from animal studies or compromised situations (i.e. retrieval after peri-implantitis). Therefore, the current observations are of interest.
The clinical performance of the particular implant type in the present study was described in a retrospective evaluation involving 74 patients, 121 implants, which observation time stretched up to 3 years. Implant survival was 96.5% with healthy peri-implant conditions, both clinically and radiographically.7 It is a 2-piece implant (figure 2) with a surface roughness with a Ra of 20-40 µm that is accomplished by blasting with zirconia grid before sintering (figures 3a-b).
Figure 2
Zv3 standard implant with a prepared glass fiber post (Wolfratshausen, Germany, bottom) and an implant with a personalized epi-gingival profile and unprepared glass fiber post (top).
The histological and histomorphometric data associated with the retrieved implant demonstrate a well osseointegrated, zirconia implant, concurrent with a healthy situation, ample bone to implant contact and no apparent signs of fibrous or granulomatous tissues adjacent to the implant after 2 years of clinical functional loading.
Comparison to literature is provided by the data from Kohal et al. who retrieved a relatively large number of zirconia implants. Peri-implantitis prompted their removal (n=22).25 The form as well as differences in surface characteristics makes comparison troublesome. They report compact bone at
CHAPTER 02 • PART A
the apical regions and state that the remaining bone that was attached to the implants contained a regular lamellar structure with osteons and osteocytes. Approximately 20% more bone to implant contact was observed compared to the present findings, despite the compromised condition that had required removal of the implants. This may be because of individual variation. However, the retrieved implants by Kohal et al were mostly mandibular implants for which a higher bone to implant percentage may be anticipated than for a maxillary implant. The current study evaluated only a single maxillary implant.
Figure 3a
REM image of the Zv3 implant surface.
Figure 3b
Detail of figure 3a, focused at the centre of the image.
In another study a female patient agreed to have a maxillary 2-piece zirconia implant (Ziterion, Ziterion GMBH) and to have it removed after 6 months for histological evaluation.26 It was not been functionally loaded. There were no signs of implant mobility. Both light microscopy and back scatter electron microscopy were performed. Histological analysis revealed close bone apposition with the combination of newly formed and native bone, with areas of mineralized bone contact to the implant surface as well as areas where bone marrow spaces were adjacent to the implant surface. No quantitative data with respect to the amount of bone-to-implant contact were presented and the authors state that they ‘expect it to be sufficient for clinical service, but not as strong as expected’.26 Information with respect to the implant surface was not provided in the article.
The human studies providing evidence of ossseointegration of titanium and HA-coated implants report a wide range of percentages of bone-to-implant contact and the data from the present study lie in that range (table 1).
The histological data presented in this case report are coherent with a well osseointegrated zirconia implant after 2 years of functional loading. It is concluded that the observations from the retrieved implant in this study provide further evidence of the potential of zirconia to osseointegrate to a more or less similar degree as titanium implants in man.
Acknowledgements
The work was supported by the authors’ institutions. The authors confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.
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