Student Presentation # 3 Biomechanics

Transcription

1 Student Presentation # 3 Biomechanics Anu Phogat Peter Ho 1

2 BIOMECHANICS OF DENTAL IMPLANTS 2

3 STRUCTURE OF TOOTH 3

4 INTERESTING FACTS According to the National Institutes of Health,by age 50, the average person has lost 12 teeth, and by 70, half of us are toothless altogether. In the days of imperial Rome, people hammered iron pegs in to replace missing teeth, and current technology is only slightly less grisly. How to solve tooth loss problem? 4

5 The Traditional Solution DENTURES A partial or complete set of artificial teeth for either the upper or lower jaw. Also called dental plate. The traditional solution to tooth loss. It is not not permanent and need to be replace or modify every once a while. 5

6 WHY IMPLANT??????????? More permanent than dentures The butt-joint method does not rely on neighboring teeth for support More natural looking than dentures 6

7 PROBLEMS ASSOCIATED WITH IMPLANTS Natural teeth and dental implants have differing degrees of mobility thus causing a potential biomechanical problem when connected by fixed bridgework. The clinical follow-up often discloses marginal bone loss around an implant neck probably due to high stress factors. An implant with a built-in compliance resembling the tooth mobility could be advantageous for stress distribution. So, how can we minimise stress????????? 7

8 STRESS EVALUATION In evaluation of the long-term success of a dental implant, the reliability and the stability of the implant abutment interface plays a great role. Abutment - tooth or teeth on either side of the mouth that support a fixed or removable bridge (used to support the replacement of the missing teeth). 8

9 DENTAL BRIDGES Because of fallen tooth/teeth, gaps created in the jaw, cause neighbouring teeth to move in. To avoid this, a dental bridge is placed in the gap. There are 3 main types of dental bridges- traditional fixed, resin bonded and cantilever. 9

10 Biomechanical effects. The bridges that are manufactured match the requirement to get custom overstructures but do not guarantee geometrical and dimensional tolerances. When a misfitting bridge is forced on the abutments, deformations may occur inducing a permanent preload at the fixture bone interface. Due to the bone remodelling mechanism, the preload induced by the strained bridge may cause fixture movements toward the direction that produces the decrease of the bridge strain. The greater the bridge misfit, the greater is the bridge strain and hence the preload. 10

11 MEASURING THE BRIDGE STRAIN Cartesian systems (CSs) of the two bridgeanchoring sites corresponding, in case of perfect fit, to those of the two abutments The four possible misfits include shifts or rotations of the CS2 as follows: bridge length error AX, bridge shear error AZ, bridge torsion error theta X and bridge bending error theta Y. 11

12 ERROR DEVICES Drawings of the shift (a) and rotation (d) error devices. The bridge to be mounted on the error devices has been instrumented with two strain gauges as indicated in the drawings (b) for bridge length error AX, (c) for bridge shear error AZ, (e) for bridge bending error theta Y and (f) for bridge torsion error theta X. 12

13 FEM MODELLING MODEL 1 3D model of half a bridge mounted on its abutment. Bridge length error between the abutment and bridge has been imposed at the gold screw-bridge surface by sequential steps of displacement in X direction. Loading conditions consist of five steps of displacement and, due to the fact that Model 1 represents only half a bridge, each step corresponds to one half of the displacement applied during the experimental tests. 13

14 FEM MODELLING contd.. It has been assumed that osseointegration at the bone implant surface has been completely achieved. MODEL 2 3D model of half a bridge connected by a gold screw to the titanium abutment which is connected by a titanium screw to the fixture inserted in a segment of cortical bone. The presence of the bone produces a compliant constraint to the fixture and hence the bridge length error causes a deformation both in the bridge and in the bone. This occurrence reduces the strain in the bridge in comparison with both the experimental situation and Model 1. 14

15 STRAINS MEASURED CORRESPONDING TO DIFFERENT TYPES AND VALUES OF BRIDGE MISFIT. 15

16 COMPARISON BETWEEN NUMERICAL AND EXPERIMENTAL DATA

17 STRESS DISTRUBUTION FOR BRIDGE LENGTH ERROR Ax=100 micrometers 17

18 LOCAL STRESSES Local stress: stress referred to each element local coordinate system. Local shear stresses may account for the failure of the fixture bone mechanical interface. Local normal stresses give information on the compression and tension produced in the bone that could be responsible for the bone remodelling process. 18

19 PRESENT RESEARCH Present studies reveal that strain development at the bone surrounding the implant cannot be removed completely. None of the investigated bridges revealed a truly passive fit without strains occurring. About 50% of the measured strains were found to be due to impression taking and model fabrication, whereas the remaining 50% were related to laboratory inaccuracies. Bonding bridge frames onto gold cylinders directly on the implants significantly reduces strain development. 19

20 The Butt-Joint system (Screw) Dental Implants The Ideal Replacement For Natural Teeth 20

21 General Implant Diagram A crucial factor that affects the outcome of implant treatment is the way occlusal forces are transferred to the bone-implant interface via the superstructure and the implant. 21

22 Implant Surgery 1. Place implant into jaw bone and let the bone grow around the implant for 3 ~ 6 months. 22

23 Implant Surgery 2. During growing time dentist will place a Flipper the false tooth to reserve a space for the crown tooth. 23

24 Implant Surgery 3. Finally the Crown is placed on top of the implant. Bone Grafting might need if you don t have enough bone. 24

25 Types of Screws Branemark Conical, Branemark Cylindrical, Astra Tech Conical, Astra Tech Cylindrical, ITI Solid Screw These are the ones going to be used in experiment. 25

26 Strain-gauged photoelastic model Biomedical sensors are placed around the neck to measure the stress and strain at the collar area A passage of polarized light through a model of an arbitrary geometric configuration and the generation of colored patterns, isochromatic fringes, are observed in the polariscope. Plexiglas 26

27 Vertical load Fringe Pattern The number of fringes indicates the stress or strain magnitudes, and the fringes being close to each other demonstrate higher stress concentrations at that region. 27

28 Oblique load Fringe Pattern Under oblique loading, stress magnitudes in the apical region of the implants were lower than those around the implant collars at the compression side. The isochromatic fringe orders in the collar region were the same for all designs under 100 N load. 28

29 Principle strains (compression) 29

30 Principle strains (Tension) 30

31 31

32 BIBLIOGRAPHY dex.html procedure.html Clinical Oral Implants Research Volume 15 Issue 2 Page April 2004 Implant design and interface force transfer R. Pietrabissa, R. Contro, V. Quaglini, M. Soncini, L. Gionso and M. Simion, Experimental and computational approach for the evaluation of the biomechanical effects of dental bridge misfit. J Biomech33 (2000), pp

33 Bibliography contd. Dinçer Bozkaya and Sinan Müftü,Mechanics of the tapered interference fit in dental implants Journal of Biomechanics, Volume 36, Issue 11, November 2003, Pages Salvatore Longoni, Matteo Sartori, Roberto Davide, A simplified method to reduce prosthetic misfit for a screwretained, implant-supported complete denture using a luting technique and laser welding, The Journal of Prosthetic Dentistry Volume 91, Issue 6, June 2004, Pages