New implant system - directly screw-retained single tooth crowns and the influence of crown material, sintering protocol and artificial aging on the bending moment.
Sonja Südbeck, Munich
While titanium abutments have long been considered the gold standard, various alternative abutment solutions have been developed in recent years. These include monoblock abutments, e.g. B. made of zirconium oxide, Hybrid abutments (titanium base and ceramic structure) as well as the concept of hybrid abutment crowns. The crown, which is manufactured in one piece, is glued directly to the titanium base. An alternative are implant systems without abutment or titanium base, e.g. B. the matrix system. Here the prosthetic restoration is screwed directly onto the implant. This solution promises – due to the prevention of excess luting material – a reduction in the risk of peri-implantitis as well as simplified access in the event of any complications. In addition, the time required for production and treatment is reduced.
The crown material used also plays a crucial role in the stability of the implant system. Due to their high strength and fracture toughness as well as biocompatibility and long-term durability, 3 mol% yttria-stabilized zirconium oxides (3Y-TZP) have become increasingly important in recent years. With the increase in the yttrium oxide content - third (5Y-TZP) and fourth (4Y-TZP) zirconium oxide generations - and the associated increased cubic phase, highly translucent materials were introduced. This development expanded the range of indications for zirconium oxide to include monolithic restorations in the visible range. The required layer thickness can be reduced. Even under high loads, there is no risk of chipping in the veneer. In addition, treatment with monolithic zirconium oxide restorations can be achieved through the use of chairside milling and High-speed sintering process Time can be saved.
Aim of the investigation
The aim of this in vitro study was to compare the bending moment of implants with directly screw-retained single-tooth crowns and implants with single-tooth crowns bonded to titanium bases. The influence of the crown material, the sintering parameters and thermo-mechanical aging on the bending moment should also be investigated.
Study design (CS: conventional sintering, HSS: high-speed sintering, CoCrMo: cobalt-chromium-molybdenum)
material and methods
240 test specimens were produced. 120 implants (n = 24 per material) were treated with directly screw-retained single-tooth crowns (Matrix Implants, TRI Dental Implants, Hünenberg, Switzerland) and 120 implants with single-tooth crowns that were previously bonded to a titanium base (Octa Implants, TRI Dental Implants).
The crowns were made of 3Y-TZP (Ceramill ZI CAM, Amann Girrbach, Koblach, Austria), 5Y-TZP (Ceramill Zolid fx, Amann Girrbach), 4Y-TZP (Ceramill Zolid HT+ white, Amann Girrbach) and a cobalt chrome Molybdenum (CoCrMo) alloy (Ceramill Sintron, Amann Girrbach), whereby 3Y-TZP, 5Y-TZP and CoCrMo were sintered conventionally, while 4Y-TZP was sintered conventionally (CS) and in a high-speed sintering process (HSS). .
In order to simulate the clinical situation after about five years, half of the test specimens were thermo-mechanically aged in the chewing simulator. All test specimens were then tested for breaking load at an angle of 30° and the bending moment was calculated. In addition, the fracture pattern of each test specimen was analyzed.
Left: Matrix implant (without titanium base), Right: Octa implant (with titanium base)
Results
Implant system
Initially tested, the matrix implants (without a titanium base) with zirconium oxide crowns showed higher bending moments than the Octa implants (with a titanium base) with zirconium oxide crowns. Octa implants supplied with CoCrMo showed higher bending moments. After aging, there was no difference in bending moments between the implant systems in any of the groups.
Material and sintering protocol
Regarding the materials, the highest initial bending moment values were observed for 4Y-TZP regardless of the implant system. For Matrix implants (without a titanium base) the lowest bending moments were measured for CoCrMo crowns and for Octa implants (with a titanium base) for 5Y-TZP_CS and 3Y-TZP_CS crowns. High-speed sintered restorations showed higher bending moments than conventionally sintered zirconium oxides for both implant systems. After the chewing simulation, no differences were observed between the different materials and sintering protocols.
Artificial aging
Thermo-mechanical aging led to a decrease in bending moment values in 70% of the groups.
Test setup to determine the bending moment at an angle of 30° (left) and bending moments of the matrix (without titanium base, blue) and the Octa (with titanium base, red) implants depending on the different crown materials before and after aging (right).
Fracture pattern
Matrix implants (without a titanium base) showed increased implant deformation after loading as part of the breaking load determination, while with Octa implants (with a titanium base) primarily a loosening of the crown in conjunction with implant deformation was observed. The cross-sectional images showed that crown loosening can be caused not only by screw failure, but also by crown fractures in the area of the interface (matrix implants) or fractures in the implant (octa implants), as the fracture can cause play in the interface.
a + b) Test specimen with complete crown fracture (top: Octa Implant, 5Y-TZP_CS; bottom: Matrix Implant, 5Y-TZP_CS).
c + d) Cross-sectional images of a loosened crown (top: Octa implant, 3Y-TZP_CS; bottom: Matrix implant, 4Y-TZP_HSS).
e + f) Cross-sectional images of a deformed implant (top: Octa implant, 4Y-TZP_HSS; bottom: Matrix implant 3Y-TZP_CS).
g) Cross-sectional image of a test specimen with a screw fracture after aging (matrix implant, CoCrMo).
The arrows mark the breaking points.
Conclusion
In summary, this study indicates that the mechanical stability of implants without a titanium base (directly screw-retained single tooth crowns) is generally sufficient for clinical use, as both implant systems showed comparable results. Consequently, the use of directly screw-retained single-tooth crowns (monolithic) on implants made from the materials studied appears to be a promising therapeutic option that can achieve excellent aesthetic results while reducing time and costs. The results also confirmed the previous positive findings on high-speed sintering processes and show that clinically comparable bending moments can be achieved with 5Y-TZP and 4Y-TZP as with 3Y-TZP.
However, since an in vitro study cannot completely reproduce in vivo conditions, there is a need to verify the results observed here in long-term clinical studies.
The results presented here are based on the following study: Südbeck S, Buser R, Reymus M, Hoffmann M, Edelhoff D, Stawarczyk B. A new implant system with directly screwed supra-constructions: Impact of restoration material and artificial aging on the bending moment. International Journal of Prosthodontics. In prep.