Abstract
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 μm for group Zr, and 0.7 μm 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.
1
Introduction
The function of titanium dental implants for replacing teeth in the oral cavity is well documented . Due to high implant survival and success rates, the esthetic outcome has become a main focus of interest in esthetically sensitive areas . However, the use of standard titanium abutments may compromise the appearance of tissue color in the esthetic zone . This occurs, when the soft tissue thickness is 2 mm or less . Hence, all-ceramic abutments have been introduced in 1991 to avoid discoloration at the cervical margin . These alumina abutments were fabricated of densely sintered highly purified 99.5% aluminum oxide ceramic cores . Low fracture resistance of these alumina abutments lead to the development of a ceramic implant abutment which was bonded to a custom titanium or gold alloy abutment . In 1997 Wohlwend introduced the first one-piece zirconia abutment , produced of 3-yttrium-stabilized tetragonal zirconia polycrystals. The fracture resistance of these zirconia abutments was about twice as high compared to alumina abutments . Clinical studies showed the suitability of zirconia abutments in the oral cavity for single tooth replacement in the anterior and premolar region and short span fixed dental prosthesis (FDP) . However, zirconia is about 10 times harder than titanium 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 . 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 μm in comparison to alumina (1.82 μm) and zirconia abutments (1.45 μm) 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 . At the moment only one pilot study measured the wear at the titanium–zirconia implant–abutment interface with help of scanning electron microscopy .
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 . The implant shoulder was 2 mm above the resin, to mimic oral conditions with minimal bone loss.
2.1
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. . To have identical contact wear during cyclic loading, the titanium abutments were provided with 360° 1 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 μm and 1 bar pressure were applied for the titanium abutments, 50 μm 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) . The polymerization was performed for 3 min with a high-power polymerization device (Dentacolor XS, Heraeus Kulzer, Hanau, Germany).
2.2
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 (METROTOM 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.
2.3
Dynamic loading
All six specimens were fixed in a loading platform of a fatigue testing machine (CS-4, SD Mechatronic GmbH, Feldkirchen-Westerham, Germany) . 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 . A force of 100 N was applied for 1,200,000 cycles at a frequency of 1.2 Hz. The loading speed 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.
2.4
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 μm by the software.
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 . The implant shoulder was 2 mm above the resin, to mimic oral conditions with minimal bone loss.
2.1
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. . To have identical contact wear during cyclic loading, the titanium abutments were provided with 360° 1 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 μm and 1 bar pressure were applied for the titanium abutments, 50 μm 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) . The polymerization was performed for 3 min with a high-power polymerization device (Dentacolor XS, Heraeus Kulzer, Hanau, Germany).
2.2
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 (METROTOM 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.
