Considerations on Dental Implants Fixation

Transcription

1 MECAHITECH 1 Bucharest, September 21 Considerations on Dental Implants Fixation Conf. Sorin Kostrakievici *, As. Mircea Iulian Nistor *, S.l. Doina Bucur *, Medic Cristian Dobreci **, *Politehnica University of Bucharest, ** University of Medicine and Pharmacy ABSTRACT Considerations on dental implants fixation In the paper it is presented a testing bench and the tests done on the special fixing screws of the upperstructure of the metalic dental implants. Are expressed also conclusions on measurements and those resulting for the users and producers. INTRODUCTION In the nowadays dental practice one of the frequently used prosthetic methods consists in the use of metalic dental implants, also known as root implants (after NIH 1988). These implants implies a threaded body (fig.1) which is inserted in the mandibular or maxilar bone. On this artificially created root, after osseointegration is fixed, the upperstructure of the thooth manufactured in the dental laboratory in conformity with the anatomical structure of the dental element of the patient. The fixing element of the upperstructure is, in this case, also a special screw of M1.8 or M2 thread (depending of the manufacturing company. Fig.1 Root implant A implant with surface treated with Titanium plasma; B implant with surface treated with hydroxylapatite (TPS); C - implant with fine surface texture; D - implant with medium surface texture. 52

2 MECAHITECH 1 Bucharest, September 21 Fig. 2 Upperstructure fixing screw Root osseointegration needs 3 to 6 months, time during which its central threaded chanel is loaded up with different substances. Taking into consideration other substances used in the dental practice such as metronidazole gel, special dental adhesive, clorehexidine, etc., during the processes of threading into and out of the screw has been reported accidents by tearing it off which is a very serious case as the restoring of the implants is in general compromised. The objective of the paper has been to investigate the resistance of the fixing screw for different working hypothesis. Fig.3 Testing bench 1 - rack, 2 moment transducer IMADA HTG2-2N ( 2Nm), 3 IMADA interface, 4 computer display, 5 receiving part. 53

3 MECAHITECH 1 Bucharest, September The testing bench and procedure In order to check the different types of screws it has been manufactured a receiving part having 1 threaded seats (fig.2, position 5) from which five are M1.8 and five M2. The receivinf part is mounted on the rotating plate 1 of the testing bench. Above the plate is postioned the moment transducer 2 which is connected to the computer 4. By the rotation of the plate the special screw is treaded into the receiving part 5. The seats were treated initially with blood, metronidazole gel, special dental adhesive, clorhexidrine and the first seat was dried. The maximum clamping moment used was of 35Nmm as in the manufacturer documentation. The tested special screws were measured with a pasameter SUHL TGL 225. Table 1 Outer diameter deviation of the thread for the M2 screw Numărul probei Dimensiune nominală filet [mm] 1. M2 -,22 2. M2 -,2 3. M2 -,95 4. M2 -,92 5. M2 -,21 Abaterea de la dimensiunea nominală [mm] Table 2 Outer diameter deviation of the thread of the M1.8 screw Numărul probei Dimensiune nominală filet [mm] Abaterea de la dimensiunea nominală [mm] 1. M1,8 -,6 2. M1,8 +,4 3. M1,8 +,15 4. M1,8 -,92 5. M1,8 +,11 proba 1 uscata proba 2 clorhexidrina valoarea m om entului frecventa de 5 Hz frecventa 5 Hz Fig. 4 Tightening screw M2, dry Fig. 5 Tightening screw M2, with clorhexidrine 54

4 MECAHITECH 1 Bucharest, September 21 proba 3 gel metronidazol proba 4 adeziv valo area m o m en tu lu i frecventa de 5 Hz frecventa de 5 Hz Fig. 6 Tightening screw M2, metronidazole gel Fig. 7 Tightening screw M2, with adhezive proba 5 sange proba 1 uscata 5 5 valo a re a m o m en tu lu i valo a re a m o m en tu lu i frecventa de 5 Hz frecventa de 5 Hz Fig. 8 Tightening screw M2, with blood Fig. 9 Tightening screw M1,8, dry proba 2 clorhexidrina proba 3 gel metronidazol v alo are a m o m e n tu lu i v alo are a m o m e n tu lu i frecventa de 5 Hz frecventa de 5 Hz Fig. 9 Tightening screw M1,8, cu clorhexidrine Fig. 1 Tightening screw M1,8, with metronidazole 55

5 MECAHITECH 1 Bucharest, September 21 proba 4 adeziv proba 5 sange.5.5 valo area m o m en tu lu i frecventa de 5 Hz frecventa de 5 Hz Fig. 11 Tightening screw M1,8, with adhezive Fig. 12 Tightening screw M1,8, with blood proba 1 seria I maxim proba 1 seria II maxim frecventa de 5 Hz frecventa de 5 Hz Fig. 13 Tightening screw M2, dry, maximum Fig. 14 Tightening screw M2, dry, maximum moment moment According to the known relationship of torque screw: M t= Q[ d 2 /2 tg ( α + φ ) + µ 1 D m /2] (1) where: µ dry =,2, µ wet =,15, φ dry = arctg,2 = 11,399, φ wet = arctg,15 = 8,53, α = 3 it can be deduced the values of the tensile forces in the screw rods when they are maximum stressed: Q = 243,345 N for the M2 screw and Q = 483,5 N for the M1,8 screw (2) For the two screws the resulting efective tensile forces in the threaded ros are: σ t = 4Q / π d 1 ² = 136,19 N/ mm² şi σ t = 297,3 N/ mm². (3) 3. CONCLUSIONS In none of the tests was observed breaking any screw rod no matter of the material interposed between the screw and the receiving plate. Also have not noticed cracks in the structure of materials. 56

6 MECAHITECH 1 Bucharest, September 21 The conclusion here is clear that the tightening of these bolts wrench to the recommended value of 35 Nmm, there is no riskof breaking special screws. But producers are required to verify possible structural failure of the materials these being the only ones which could lead to accidental breakage of these screws. Even if tightening the screws at a maximum, possibly manually created with the special designed instruments for thightining in the dental office, the tensile stress values do not exceed allowable values, which justifies once again the claim that in the absence of structural defects breaking their material is excluded. During interventions, while working with them it is indicated to use dynamometric keys in order to eliminate any unpleasant event. BIBLIOGRAPHY [1]. Cranin A. Herman, Klein Michael, Simons Alan - Atlas of Oral Implantology 1993, Thieme Medical Publishers, New York [2]. Dumitriu Horia Traian - Parodontologie, EdiŃia a-iv-a, Editura ViaŃa Medicală Românească 26 [3]. Gehrke Peter, Brunner Jochen, Wolf Dietrich, Degidi Marco, Piattelli Adriano - Ziconium Implant Abutments: Fracture Strength and Influence of Cyclic Loading on Retaining- Screw Loosening, Quintessence International vol.37, nr.7, ianuarie 26 [4]. Karl Matthias, Rosch Silke, Friedrich Greaf, Taylor D. Thomas, Heckmann M. Siegfried Strain Situation after Fixation of Three-Unit Ceramic Veneered Implant Superstructures, Implant Dentistry, Vol. 14, nr. 2, 25 [5]. Kohal Ralf-J., Klaus Gerold, Strub Jorg R. - Zirconia-Implant-Supported All-Ceramic Crowns Withstand Long-Term Load: A Pilot Investigation, Clinical Oral Implant Research.17, 26 [6]. Rosenstiel, Land, Fujimoto - Contemporary Fixed Prosthodontics, 3-rd Edition, Ed. Mosby, 22 [7]. ISO 1481/23 Încercarea la oboseală a implantelor dentare. 57