Wear at the titanium titanium and the titanium zirconia implant abutment interface: A comparative in vitro study

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d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 1215 1220 Available online at www.sciencedirect.com jo u rn al hom epa ge : www.intl.elsevierhealth.

Kurt Erdelt b, Arndt Happe c, Florian Beuer b a Private Practice for Oral Surgery, Josef-Heilingbrunnerstr. 2, 93413 Cham, Germany b University of Munich, Department of Prosthodontics, Goethestr.

1 d e n t a l m a t e r i a l s 2 8 ( ) Available online at jo u rn al hom epa ge : Wear at the titanium titanium and the titanium zirconia implant abutment interface: A comparative in vitro study Michael Stimmelmayr a,b,, Daniel Edelhoff b, Jan-Frederik Güth b, Kurt Erdelt b, Arndt Happe c, Florian Beuer b a Private Practice for Oral Surgery, Josef-Heilingbrunnerstr. 2, Cham, Germany b University of Munich, Department of Prosthodontics, Goethestr. 70, Munich, Germany c University of Cologne, Department of Oral and Maxillofacial Plastic Surgery and Implantology, Kerpener Str. 62, Cologne, Germany a r t i c l e i n f o a b s t r a c t Article history: Received 18 January 2012 Received in revised form 25 July 2012 Accepted 14 August 2012 Keywords: Cyclic loading Fatigue testing Implant abutment Zirconia Titanium Objective. The purpose of this study was to determine and measure the wear of the interface between titanium implants and one-piece zirconia abutments in comparison to titanium abutments. Methods. 6 implants were secured into epoxy resin blocks. The implant interface of these implants and 6 corresponding abutments (group Zr: three one-piece zirconia abutments; group Ti: three titanium abutments) were examined by a microscope and scanning electron micrograph (SEM). Also the implants and the abutments were scanned by 3D-Micro Computer Tomography (CT). The abutments were connected to the implants and cyclically loaded with 1,200,000 cycles at 100 N in a two-axis fatigue testing machine. Afterwards, all specimens were unscrewed and the implants and abutments again were scanned by microscope, SEM and CT. The microscope and SEM images were compared, the CT data were superimposed and the wear was calculated by inspection software. The statistical analysis was carried out with an unpaired t-test. Results. Abutment fracture or screw loosening was not observed during cyclical loading. Comparing the microscope and SEM images more wear was observed on the implants connected to zirconia abutments. The maximum wear on the implant shoulder calculated by the inspection software was 10.2 m for group Zr, and 0.7 m for group Ti. The influence of the abutment material on the measured wear was statistically significant (p 0.001; Levene-test). Significance. Titanium implants showed higher wear at the implant interface following cyclic loading when connected to one-piece zirconia implant abutments compared to titanium abutments. The clinical relevance is not clear; hence damage of the internal implant connection could result in prosthetic failures up to the need of implant removal Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. Corresponding author at: Josef-Heilingbrunnerstr. 2, Cham, Germany. Tel.: ; fax: address: michael.stimmelmayr@med.uni-muenchen.de (M. Stimmelmayr) /$ see front matter 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

2 1216 d e n t a l m a t e r i a l s 2 8 ( ) Introduction The function of titanium dental implants for replacing teeth in the oral cavity is well documented [1]. Due to high implant survival and success rates, the esthetic outcome has become a main focus of interest in esthetically sensitive areas [2,3]. However, the use of standard titanium abutments may compromise the appearance of tissue color in the esthetic zone [4 6]. This occurs, when the soft tissue thickness is 2 mm or less [7]. Hence, all-ceramic abutments have been introduced in 1991 to avoid discoloration at the cervical margin [8]. These alumina abutments were fabricated of densely sintered highly purified 99.5% aluminum oxide ceramic cores [9,10]. Low fracture resistance of these alumina abutments [11] lead to the development of a ceramic implant abutment which was bonded to a custom titanium or gold alloy abutment [5,12,13]. In 1997 Wohlwend introduced the first one-piece zirconia abutment [14], produced of 3-yttrium-stabilized tetragonal zirconia polycrystals. The fracture resistance of these zirconia abutments was about twice as high compared to alumina abutments [11]. Clinical studies showed the suitability of zirconia abutments in the oral cavity for single tooth replacement in the anterior and premolar region [5,13] and short span fixed dental prosthesis (FDP) [15]. However, zirconia is about 10 times harder than titanium [12] and nowadays there is concern, if zirconia abutments can damage the titanium interface of implants during function. Only a few articles argue with this subject. Yuzugullu analyzed the implant abutment interface of zirconia and alumina abutments in comparison to titanium abutments [16]. He measured the implant abutment microgap after dynamic loading with help of scanning electron microscopy. The titanium abutment revealed an increased microgap of 3.47 m in comparison to alumina (1.82 m) and zirconia abutments (1.45 m) at the palatal site. Hence, the mean measurement values at different measurement sites were not statistically significant. Brodbeck discussed the component wear between the implant and the abutment. If an abutment screw loosens between an all-ceramic abutment and a titanium implant platform, significant damage may occur to an external hex implant. This pilot study showed only the wear area and damage of the external hex, unfortunately the amount of wear was not evaluated [12]. At the moment only one pilot study measured the wear at the titanium zirconia implant abutment interface with help of scanning electron microscopy [17]. Therefore this study was performed to measure the wear of the interface of titanium implants connected with one-piece zirconia and titanium abutments. It was hypothesized that the wear of the interface following cyclic loading was higher when connecting the implants to one-piece zirconia abutments. 2. Materials and methods Six implants (Screwline Promote 3.8/13 mm; Camlog Biotechnologies, Wimsheim, Germany) were embedded perpendicularly in a self-curing resin block (DPC-Laminierharz LT 2, Duroplast-Chemie Vertriebs GmbH, Neustadt/Wied, Germany) with an edge length of 2.5 cm 1.5 cm 1.5 cm. The Young s modulus of the resin material was 3450 MPa, corresponding to Type III cancellous bone [18]. The implant shoulder was 2 mm above the resin, to mimic oral conditions with minimal bone loss Abutment fabrication Respectively three customized identical one-piece zirconia and titanium abutments (Prototypes, Camlog Biotechnologies) were fabricated with a height and width of 10 mm and a 30 angled occlusal plate like described by Steinebrunner et al. [19]. To have identical contact wear during cyclic loading, the titanium abutments were provided with mm chamfer preparations for zirconia crowns (Lava, 3M Espe, Seefeld, Germany). The abutments were mounted on lab analogs (Camlog Biotechnologies) with lab screws and the titanium abutments and the zirconia crowns were sandblasted with aluminum oxide (Hasenfratz, Assling, Germany) to increase adhesion. A grain size of 105 m and 1 bar pressure were applied for the titanium abutments, 50 m grain size and 1 bar pressure for the zirconia crowns. The titanium abutments were coated with Metal Primer (Alloy Primer, Kuraray, Osaka, Japan), the zirconia crowns with Ceramic Primer (ClearFil Ceramic Primer, Kuraray, Osaka, Japan) and luted with a composite resin (Panavia 2.0 F, Kuraray, Osaka, Japan) [20]. The polymerization was performed for 3 min with a high-power polymerization device (Dentacolor XS, Heraeus Kulzer, Hanau, Germany) Pre loading SEM and CT analysis Prior to connecting the abutments to the implants scanning electron micrographs (SEM) (Supra 40VP, Zeiss GmbH, Oberkochen, Germany) were taken with a magnification of 400 at the cam-groove where the maximal loading force was planned to be applied during artificial aging (Figs. 1a and 2a). Also 3D-Computer Tomography (CT) micrographs (METRO- TOM 1500, Zeiss GmbH) were made of the interface of the implants and the abutments to serve as baseline. Reference marks were placed on the resin blocks and the abutments to identify the maximal loading area during SEM and CT micrographs. Following the one-piece zirconia and the titanium abutments were secured to the implants with a new titanium screw and torqued to 20 N cm, as recommended by the manufacturer Dynamic loading All six specimens were fixed in a loading platform of a fatigue testing machine (CS-4, SD Mechatronic GmbH, Feldkirchen- Westerham, Germany) [21]. The cyclic fatigue test was applied to each abutment with a round stainless-steel stylus with a diameter of 4 mm. The stylus was placed 3.5 mm outside the center of the abutment on the angled area. The dynamic loading contained an additional horizontal shifting of 2 mm to the center of the abutment to induce a bending moment at the implant abutment interface [19]. A force of 100 N was applied for 1,200,000 cycles at a frequency of 1.2 Hz. The loading speed

d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 1215 1220 1217 Fig.

3 d e n t a l m a t e r i a l s 2 8 ( ) Fig. 1 SEM micrographs with a magnification of 400 of the implant interface connected with a one-piece zirconia abutment before (a) and after (b) cyclic loading. was 10 mm/s, the lifting speed 60 mm/s. In an unpublished pilot study a force of 120 N was applied to the abutments, however some of the one-piece zirconia abutments fractured during cyclically loading. Therefore the applied force was reduced to 100 N Post loading SEM and CT analysis After dynamic loading the abutments were disconnected and again SEM and CT micrographs were made of the interface of each implant and abutment. The SEM micrographs were taken with a magnification of 400 at the cam-groove where the maximal loading force was performed (Figs. 1b and 2b). These images allowed qualifying the wear. The three-dimensional CT data of the six implants produced before and after dynamic loading were superimposed with inspection software (VGStudio MAX 2.1, Volume Graphics GmbH, Heidelberg, Germany) and the value of wear of every implant interface, loaded with titanium or zirconia abutments, was calculated in m by the software. 3. Results No implant fracture, abutment fracture, zirconia titanium core connection loosening, abutment screw loosening or abutment screw fracture was noticed in any specimen during cyclic loading. Comparing the SEM micrographs before and after cyclic loading, more wear and damage on the implant interface was recorded when connected to one-piece zirconia abutments compared to titanium abutments (Figs. 1 and 2). Only minimal wear or abrasion was noticeable on the SEM image of the cam-groove loaded with a titanium abutment. The titanium chip as a result when producing the cam-groove (Fig. 2a) was flat pressure formed on the image after loading (Fig. 2b). On the SEM image of the cam-groove loaded with a one-piece zirconia abutment many scratches and undercuts vertical to the groove were identified. They show the deformation energy which is distributed to the material with the lower Young s modulus during cyclic loading. Also coiled furrows were seen on the implant shoulder and the cam-groove resulting from the micro rotational movement of the zirconia abutment (Fig. 1b). Fig. 2 SEM micrographs with a magnification of 400 of the implant interface connected with a titanium abutment before (a) and after (b) cyclic loading.

1218 d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 1215 1220 Table 1 Wear (in m) on the implant shoulder after disconnection of the abutments at the area of maximal loading force, calculated by the

3 Superimposed CT-micrographs of the implant interface connected with a one-piece zirconia abutment before and after cyclic loading. The inspection software calculated a median wear of 10.2 m (±1.

4 1218 d e n t a l m a t e r i a l s 2 8 ( ) Table 1 Wear (in m) on the implant shoulder after disconnection of the abutments at the area of maximal loading force, calculated by the inspection software. Implant Titanium abutments Implant Zirconia abutments # m # m # m # m # m # m Mean 0.7 m 10.2 m SD 0.3 m 1.5 m 4. Discussion Fig. 3 Superimposed CT-micrographs of the implant interface connected with a one-piece zirconia abutment before and after cyclic loading. The inspection software calculated a median wear of 10.2 m (±1.5 m) on the implant shoulder after disconnection of a one-piece zirconia abutment at the area of maximal loading force (Fig. 3). Compared to the titanium abutment the software calculated 0.7 m (±0.3 m) median wear at the implant shoulder (Fig. 4). The discrepancies of the wear caused by the two unequal abutments differed significantly (p 0.001; Levene-test). The wear on the six implants is shown in Table 1. Fig. 4 Superimposed CT-micrographs of the implant interface connected with a titanium abutment before and after cyclic loading. The wear of the titanium implant interface after cyclic loading connected to one-piece zirconia abutments was higher than connected to titanium abutments. Therefore the working hypothesis can be accepted. Comparing the SEM images a clear difference in wear and damage of titanium implants connected with one-piece zirconia versus titanium abutments was visible. However, the wear in this SEM images was not quantifiable. In this study only the cam grooves where the maximal loading force was applied were analyzed with the SEM. Hence, it is unknown whether more wear occurred in the compressive or tensile areas [17]. After consideration of the images of the superimposed CT micrographs, it seemed to be more wear at the implant shoulder and cam-groove where the maximal loading force was located. However, there was also wear on the opposite, tensile area visible. Klotz demonstrated nearly uniform titanium transfer around the entire surface of the zirconia abutment, though in this study an implant with an internal conical connection was used [17]. In the above mentioned study, the authors used an implant with an internal butt-joint connection with a flat implant shoulder. The different intern geometries induce different force distributions and therefore wear in different areas. Therefore studies to evaluate the wear of the implant abutment interface should be performed with different implant abutment interfaces under same conditions. Brodbeck described the wear of the hex of an implant with external butt-joint connection loaded with an all-ceramic alumina abutment. The wear resulted when micro movement occurred because of abutment screw loosening [12]. In this study scanning electron micrographs with a magnification of 35 were shown of an unused new implant with an external hex, and the same implants loaded with an alumina ceramic abutment and a titanium abutment. The wear on the implant loaded with the all-ceramic abutment was clearly seen; the corners of the hex were rounded and the top of the hex altered to a ring shape. The amount of wear was not evaluated [12]. Klotz measured the wear at the titanium zirconia implant abutment interface with help of scanning electron microscopy [17]. In this study the titanium transfer from the implant to the abutment was measured on the abutment and equated with the wear of the implant interface. The mean maximum wear with titanium abutments was m 2, with zirconia abutments m 2 [17]. The different values were statistically significant. In the present study the wear was measured directly at the implant interface.

5 d e n t a l m a t e r i a l s 2 8 ( ) Therefore the CT micrographs before and after dynamic loading were superimposed with inspection software. The wear on the implant shoulder connected to a zirconia abutment was calculated by 10.2 m, nearly no wear (0.7 m) was calculated by the software when connecting the implant with a titanium abutment. As different methods of wear measurement were employed, the values of this study (10.2 m) and the study of Klotz ( m 2 ) cannot be compared. However, both studies found higher wear at the titanium implant interface after cyclic loading connected to one-piece zirconia abutments than connected to titanium abutments. This seems to be obvious if the stress distribution between the different components is analyzed. If implant and abutment are made from the same material (e.g. titanium), with the same Young s modulus, the deformation energy will be distributed between both components more or less equally. If one component is changed by a material with a different Young s modulus, the distribution of deformation energy changes. In this in vitro study the titanium abutment was replaced by a zirconia abutment with a higher Young s modulus. As a consequence the deformation energy is distributed to the material with the lower Young s modulus, that means to the implant [22]. If this wear has clinical impact and whether a titanium titanium interface would be favorable is unknown today. Further it is not clear, if the particulate titanium abraded from the implant interface can migrate from the interface to the soft tissue and create a tattoo of titanium particles in the periimplant gingiva [17]. Though one-piece zirconia abutments were placed especially in the esthetic zone [5,6], this could compromise the long-term esthetic outcome. Therefore it seems to be favorable to use zirconia abutments connected to titanium cores today [12]. As no disconnection of the zirconia to the titanium core of any specimen was detected in the study mentioned above, these abutments associate all advantages, like good esthetics, mechanical stability and titanium to titanium interface with nearly no wear. In unpublished studies these abutments show the same fracture strength than titanium abutments and can be placed also in the posterior regions. 5. Conclusion Within the limitations of this in vitro study, the following conclusions can be drawn: 1. The wear of the interface of titanium implants under cyclic loading is higher, when connected to one-piece zirconia abutments in comparison to titanium abutments. 2. No prosthetic failure (screw loosening, abutment loosening) were observed during cyclic loading, even though there was higher wear at the implant abutment interface when connected with one-piece zirconia abutments. 3. If two components with different material rigidity are in function, the deformation energy is distributed to the material with the lower Young s modulus. Acknowledgments We thank Camlog Biotechnologies AG for supporting this study by providing the tested implant components and the SEM and CT micrographs. Dr. Alain Denzer and Dr. Alex Schär helped to develop the study design. r e f e r e n c e s [1] Adell R, Eriksson B, Lekholm U, Branemark PI, Jemt T. Long-term follow-up study of osseointegrated implants in the treatment of totally edentulous jaws. The International Journal of Oral and Maxillofacial Implants 1990;5: [2] Al-Sabbagh M. Implants in the esthetic zone. Dental Clinics of North America 2006;50: , vi. [3] Furhauser R, Florescu D, Benesch T, Haas R, Mailath G, Watzek G. Evaluation of soft tissue around single-tooth implant crowns: the pink esthetic score. Clinical Oral Implants Research 2005;16: [4] Byrne D, Houston F, Cleary R, Claffey N. 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Esthetic high-strength implant abutments. Part II. Journal of Esthetic Dentistry 1993;5:63 8. [10] Prestipino V, Ingber A. Esthetic high-strength implant abutments. Part I. Journal of Esthetic Dentistry 1993;5: [11] Att W, Kurun S, Gerds T, Strub JR. Fracture resistance of single-tooth implant-supported all-ceramic restorations: an in vitro study. Journal of Prosthetic Dentistry 2006;95: [12] Brodbeck U. The ZiReal Post: a new ceramic implant abutment. Journal of Esthetic and Restorative Dentistry 2003;15:10 23, discussion 24. [13] Magne P, Magne M, Jovanovic SA. An esthetic solution for single-implant restorations type III porcelain veneer bonded to a screw-retained custom abutment: a clinical report. Journal of Prosthetic Dentistry 2008;99:2 7. [14] Wohlwend AS, Schaerer SP. The zirconium oxide abutment: an all ceramic abutment for esthetic improvement of implant superstructures. Quintessence of Dental Technology 1997;1: [15] Andersson B, Glauser R, Maglione M, Taylor A. Ceramic implant abutments for short-span FPDs: a prospective 5-year multicenter study. International Journal of Prosthodontics 2003;16: [16] Yuzugullu B, Avci M. The implant abutment interface of alumina and zirconia abutments. Clinical Implant Dentistry and Related Research 2008;10: [17] Klotz MW, Taylor TD, Goldberg AJ. Wear at the titanium zirconia implant abutment interface: a pilot study. The International Journal of Oral and Maxillofacial Implants 2011;26: [18] Rho JY, Ashman RB, Turner CH. Young s modulus of trabecular and cortical bone material: ultrasonic and microtensile measurements. Journal of Biomechanics 1993;26:111 9.

6 1220 d e n t a l m a t e r i a l s 2 8 ( ) [19] Steinebrunner L, Wolfart S, Ludwig K, Kern M. Implant abutment interface design affects fatigue and fracture strength of implants. Clinical Oral Implants Research 2008;19: [20] Rauscher O. Impression-free implant restorations with Cerec InLab. International Journal of Computerized Dentistry 2011;14: [21] Balfour A, O Brien GR. Comparative study of antirotational single tooth abutments. Journal of Prosthetic Dentistry 1995;73: [22] Saidin S, Abdul Kadir MR, Sulaiman E, Abu Kasim NH. Effects of different implant abutment connections on micromotion and stress distribution: prediction of microgap formation. Journal of Dentistry 2012;40:

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