INVESTIGATION TO THE ADHESIVE TITANIUM-TITANIUM CONJUNCTION IN A NEW DENTAL IMPLANT SYSTEM Jan-Dirk Reimers, Klaus Dilger, Stefan Böhm, IFS – Institute of Joining and Welding, Technical University Braunschweig, Langer Kamp 8, 38106 Braunschweig, Germany, Phone +49 531 391 7820, [email protected] H. Spiekermann, M. Augthun, K. Haselhuhn Klinik für Zahnärztliche Prothetik, Universitätsklinikum Aachen, Pauwelsstraße 30, 52074 Aachen, Germany, Phone +49 241 80 88240, [email protected] Introduction In close co-operation the IFS Braunschweig and the department for prosthetic dentistry of the university clinic Aachen researched the glue ability of titanium in a special dental implant system. Dental implants are used to replace lost natural teeth or to fix removable dentures and crowns and bridges. To realize a good absorption of the titan implant in the bone, until the first 3 to 6 month the implant system inserted in the bone has to be without load force on the implant. For that issue the implant body has to be separated into two parts, the implant in the bone (root) and the abutment on top of it (crown). Historically the solution for that was a screw conjunction. Abutment Crown / enamel Abutment with thread (1,2 mm) Abutment with plug connection Gum / Mucous membrane Dentin Bone Elastic fiber Suspension / root Implant Common system Recent system Implant with self–tapping thread TU Braunschweig TU Braunschweig Artificial dentures, dental implants – natural tooth Figure 1. scheme of the implant system Dental implants: structure of common and new system Figure 2. comparison between implant systems The new system is planed as displacement for conventionally screwed dental implant systems. Screwed systems are - due to the dynamic load forces in the normal use - vulnerable to relaxation of the tightening torque, the result is a reduced likelihood of survival of the abutment. In addition to this the medical treatment with multipart screwed systems is taking a long time for the dentist to fix the dental parts. A simple to use and structurally sustainable plug in system was build with the Heraplant SCI Implantsystem. The design of a long life time adhesive conjunction of the special plug in connector with its titanium-titanium joint is the task formulation of the following short pictured work. Experimental – technical lap shear specimens First the suitability in principle of different adhesives from the tooth-medical and the technical range for titanium was examined. TU Braunschweig T U B ra un sc h w eig Figure 3. Lap shear specimens, nitrated titan Figure 4. Shear strength of specimens 1 Independently of the implant system the fundamental influences on the gluing were examined here regarding to the compound strength, adhesion of the adhesive for the substrate and cohesion of the adhesive. The first part of the investigation was made with conventional shear strength specimens made of titanium plates, figure 3 is showing the specimens after measuring a dental adhesive system. Typical for all of the dental adhesive systems is an adhesive failure at the surface of the material. The systems are strong affected with oxygen inhibition and very impressionable on surface pretreatment. Over all the attainable shear strength is very low compared to several industrial adhesive systems, these systems reach up to 24 MPa. Dental adhesives and composites only reach up to 8-9 MPa. TU Braunschweig TU Braunschweig Shear strength of industrial and dental adhesives Figure 5. Lap shear test, different adhesives Screening of pretreatments for dental acrylics Figure 6. Lap shear strength, dental acrylic, titan But for the main focus - the long term stability of this joint – the important factor is the environmental condition in the human body. For this e.g. a storage of the compound in a medium similar to the salva and with increased temperature was arranged. All of the adhesives for an industrial use failed in this test, only the dental adhesives showed a decreasing holding force in the same time, after a longer time it failed as well (4 weeks). Figure 5 is showing the results after storage of only 1 week in the medium. The holding strength is very different, but the influence and course of ageing is almost the same. The surface pretreatment of the titanium with further different usual procedures was varied, figure 6. Here chemical surface treatments with acids and silane adhesion agents are used just as mechanical pretreatments, as blasting procedure, e.g. the Roccatec procedure was tested. The efficiency is obvious, but not long active. The ageing in fluid decreases the shear strength of the adhesive titanium joints in all kinds of dental used pretreatments. It is just a matter of time to lose adhesion in the joint. Experimental – dental implant specimens In the next step the special suitability of the implant system was examined regarding the glue ability. Here the same investigation parameters were taken to allow the direct comparability with the preliminary investigation. Instead of a lap shear test a tension test was proceeded, as shown in figure 7. Testtype: tension strength Testspecimens: original dental implants and abutments Focus: strength of the adhesive joint Mounting: with gimbal clamp and screwed locator Testequibment (Zwick 010) : Clamping distance: 5 mm Testspeed : 5 mm/min Test values: - maximum strength - maximum elongation TU Braunschweig Test of the different adhesives using the original implant system Figure 7. Test condition for implant system TU Braunschweig Preparation of the abutments sureface before glueing Figure 8. Sandblasting preparation of implant system 2 The surface pretreatment and the storage in the medium were the central points of investigation. The gluing e.g. took place in close support to the later conceivable procedure with the dentist. Whereby also restrictions had to be considered here by the special kind of the later use in the mouth area. Of course only classified and FDA qualified dental adhesives are respected for the later use, but the comparison with the industrial adhesive was still an important valuation factor in the first examinations. TU Braunschweig TU Braunschweig Tensile strength of modified Durobond (sandblasted) Tensile strength of the acrylic Quickbond 5002 (sandblasted) Figure 9. Effect of ageing, dental adhesive Figure 10. Effect of ageing, industrial adhesive As we know from the overlap shear strength specimens the bonding strength is getting lost with the environmental influence we have to take care about. The implant system bonded with an industrial acrylic adhesive is showing this in figure 9. With the use of different pretreatments the effect is just getting a different order, but the loss of tensile strength is not stopped. A long term stability is still critical. But in cooperation with a dental adhesive the implant system shows an increase of holding force up to the double of magnitude. Average Shearstrength of implant system: Zugkraftt •~50 Mpa •no negative effect on ageing •10-20% increase of strength Scherzugbreite Überlapplänge Average Shearstrength of Shear specimens: 4-6 Mpa Weak adhesion Negative effect on ageing Zugkraft Circular Groove Effect of grooves for flow control of the adhesive TU Braunschweig Tensile strength of the implant system, different adhesives Figure 11. Effect of ageing and pretreatment TU Braunschweig Comparison: Shear test – Tensile strength of Implant System Figure 12. Comparison of test results The environmental effect of the dental adhesive in combination with the dental implant system is leading to an increasing of the tensile strength during ageing. It is increasing up to 20% and more. Figure 11 is showing the tensile strength diagram. The effect of increasing tensile strength of the implant systems is certifiable with all kinds of pretreatments and all kinds of acrylic dental adhesives. Only the completely not treated surface of the titanium, the just solvent cleaned surface, is showing a decreasing tensile strength. We suppose this affected by oxygen inhibition. Oxygen is trapped in the not mechanical cleaned surface and prevents the polymerization close to the surface. Discussion and Conclusion A requirement profile for adhesives and the pretreatment for a long term stability adhesive joint, cut to the special requirements in this implant system, appeared in the course of the investigation. Temporarily the results stand in the consonance with existing test results, but some aspects stand in the exact contrast to these [3] and draw a new picture for the use of adhesives in special kinds of bonding tasks 3 like the dental implant focus here. With the results of the work it is possible to design an adhesive joint witch is unattached from water and is not negative affected from ageing. But its neglecting fundamental effects of adhesive joints, the adhesion. The investigation of the durability of an adhesive system requires al aspects of adhesives, even the geometric aspects of the bonding parts. The main effect in this bonding task - implant system - is not, as supposed the chemical treatment of the surfaces to develop and promote the adhesion. As we know always from test specimens like from overlap shear strength measurements. The main effect is the geometric structure of the bonding task in tandem with the adhesive and its cohesion. Dental adhesives are characterized with a very high amount of filler, the polymeric backbone is very tough [2]. This is defecting the possibility to adhesion as we know, and we can see in the first part of the investigation. Adhesion promotion is than very important. Industrial adhesives in comparison are flexible which in general enhances the possibility of adhesion. The specific holding force of an implant system after 4 weeks is calculated with the possible area of adhesive bonding between 30 and 40 MPa. The adhesive is a dental adhesive which has theoretically only 6-8 MPa shear strength and at this time of ageing has absolutely no adhesion any more. The main difference in the ageing of this adhesive joint is accounted with the polymeric cohesion, not the adhesion. In combination with the geometric structure of the Implant system the adhesive is obstructing notches. In this case the adhesion is contrary to all knowledge before not important at all. The toughness of the polymer is the important factor. The principles of the joint were developed into a technical joint, the test showed comparable results. An environmentally not affected joint for “slot and key” conjunctions was designed, which showed strength of about 24 MPa at the first deHolding power of 20x20 mm sample: 12500 N (compareable to 24 Mpa) sign steps. Figure 13 is showing the structure. This joint is not effected by surface treatments, Technical joint prepared like titan implant surface contaminations, or environmental cirFigure 13. Experimental slot key joint cumstances, as we found out until know. TU Braunschweig Outlook Actually we investigate the load cycle fatigue of this adhesive bonded system. The system “Dental Implant” is for sure glueable in all terms of a durable bonding joint, safe procedure and good quality. In a clinical study the first 50 patients were operated successfully with this implant system. This is drawing a new picture for the use of adhesives and the construction of a joint in bad environments. Acknowledgements The authors want to thank the company Heraeus Kulzer for this great support and working relationship. References 1. 2. 3. Das Dental Vademekum, Deutscher Ärzte Verlag, 6. Auflage, 1997 Advanced Adhesive Dentistry, 3rd international Kuray Symposium, 3-4 December, 1999, ISBN, 88-87961-00-x Surface Preparation of Metals for High Temperature Bonding Applications, Kay Y. Blohowiak, Robert A. Anderson, Jacob W. Grob and Daniel McCray, Adhesion Society 2004, Wilmington 4