Finite Element Analysis of MOD Prosthetic Restored Premolars

Transcription

1 Finite Element Anlysis of MOD Prosthetic Restored Premolrs LILIANA SANDU, FLORIN TOPALĂ, SORIN POROJAN School of Dentistry V. Beş University of Medicine nd Phrmcy 9 Revolutiei 1989 Blv., Timişor ROMANIA lilinsndu@gmil.com Astrct: Inlys nd onlys cn e used on premolrs requiring MOD restortion insted posterior composite resins or mlgm direct restortions nd offer durle lterntive. Becuse it is known tht MOD restortions my increse the susceptiility to frcture, it is importnt to ensure optiml performnce in selection of the dequte preprtion design to reduce stresses in teeth structures nd lso in the restortions. However, inlys nd onlys do not restore the originl strength of tooth tissues. The im of the study ws to determine, using finite element nlysis, the optiml shpes of metl nd cermics MOD restortions in premolrs in order to minimize the potentilly dmging effects of stress on teeth structures nd restortions. The study ws performed on n upper first premolr, using finite element nlysis. 3D models of mxillry first premolrs, prepred for MOD inlys nd onlys with different tpers were generted. The mesh structure of the solid 3D model ws creted using the computtionl simultion of Ansys finite element nlysis softwre. An occlusl lod of 200 N ws conducted, nd stresses occurring in the metl nd cermics inlys, onlys nd teeth structures were clculted. In the MOD onlys recorded mximl stresses were higher thn in the MOD inlys in the most cses. In the cermics restortions the stresses were higher thn in the cst metl. Regrding the prosthetic restortions mteril, in the cermics inlys nd onlys the stress vlues were higher. MOD inlys trnsferred more functionl stress to the teeth structures compred to the MOD onlys. Key-Words: premolr, MOD cvity design, cst metl restortion, inly, only, 3D model, stress nlysis. 1 Introduction Inlys nd onlys cn e used on premolrs requiring MOD restortion insted posterior composite resins or mlgm direct restortions nd offer durle lterntive. Becuse it is known tht MOD restortions my increse the susceptiility to frcture, it is importnt to ensure optiml performnce in selection of the dequte preprtion design to reduce stresses in teeth structures nd lso in the restortions. Inlys restore centrl cvities in teeth. Onlys restore one or more cusps nd my completely cover the occlusl surfces, resulting in fvorle distriution of stresses in teeth nd decresed risk of frctures. However, preprtion for onlys requires dditionl tooth reduction reltive to inly restortions [1, 2]. Becuse it is known tht MOD inlys my increse the susceptiility to frcture, it is importnt to ensure optiml performnce in selection of the dequte preprtion design to reduce stresses in teeth structures nd lso in the restortions [1]. Lrge restortions hve een considered the principl fctors to predispose tooth to frcture, nd dequte preprtion guidelines re importnt. Irrespective of the cvity preprtion design, preprtions weken teeth. To reduce loss of tooth tissue nd to improve iomechnicl results, inly nd onlys restortions re good tretment choices for extensive cvities in posterior teeth [3, 4]. Cst metl inlys nd onlys cn prove to e extremely long-lived restortions ecuse of the excellent mechnicl properties of the gold lloys. Cermic inlys re primrily composed of leucitereinforced cermics. The disdvntges of cermic re its hrdness, which is greter thn enmel, low frcture resistnce, nd low ftigue strength. The primry cuses of filure of cermic inlys re cohesive ulk frctures nd mrginl deficiencies. Cermic inlys mintin etter ntomic form of the surfce nd exhiit etter mrginl integrity, s well s stilize the wekened cusps etter thn composite resin inlys [5-12]. However, inlys nd onlys do not restore the originl strength of tooth tissues. Previous studies on strength of MOD prosthetic restored teeth could not resolve which restortion mteril provides greter strength nd mrginl integrity [13,14]. ISBN:

2 Mthemticl Methods nd Techniques in Engineering nd Environmentl Science Finite element nlysis (FEA) hs een widely employed in mny reserches to investigte the impct nd effect of dentl mterils nd restortive techniques on stress distriution. FEA is deemed s n effective tool to evlute the iomechnicl chrcteristics of these dentl restortive mterils nd systems, wherey the results crry significnt clinicl implictions [15,16]. Modern design nd vlution in order to otin n dequte strength involves numericl simultions. involves finding nd connecting djcent points in order to crete continuous surfces. Nonuniform rtionl B-spline (NURBS) is mthemticl model commonly used in computer ided design, mnufcturing nd engineering. 2 Purpose The im of the study ws to determine, using finite element nlysis, the optiml shpes of metl nd cermics MOD restortions in premolrs in order to minimize the potentilly dmging effects of stress on teeth structures nd restortions. Fig. 2. Volume of the premolr. 3D models of mxillry first premolrs, prepred for MOD inlys nd onlys with different tpers (etween 0 nd 10 degree from the cvity se to the surfce) were generted (Fig. 3). In the only cvity, cusps were reduced nd included in the preprtion. Inly nd only cvities designs were creted using literture dt. 3 Mterils nd Method Detiled three-dimensionl models re required to etter understnd the mechnicl ehvior of teeth structures nd prosthetic dentl restortions. The first step of the study ws to chieve 3D models in order to design nd nlyze teeth, metl nd cermics MOD inlys nd onlys. The study ws performed on n upper first premolr, using finite element nlysis. Surfces were modeled ccording with ntomicl dimensions. The nonprmetric modeling softwre (Blender 2.57) ws used in order to otin the shpe of root, enmel, dentin nd pulp structures (Fig. 1). Fig. 3. Volume of the prepred premolr nd the restortion:. inly,. only. Fig. 1. Premolr surfces modelled ccording to the ntomicl dimensions. The mesh structure of the solid 3D model ws creted using the computtionl simultion of Ansys finite element nlysis softwre (Fig. 4). The collected dt were used to construct three dimensionl models using Rhinoceros (McNeel North Americ) NURBS (Nonuniform Rtionl BSplines) modeling progrm. These points were used to extrpolte the shpe of the oject, process clled reconstruction (Fig. 2). Reconstruction ISBN:

3 Fig. 4. Mesh structure of the restored premolr:. with inly,. with only. An occlusl lod of 200 N ws conducted, nd stresses occurring in the inlys, onlys nd teeth structures were clculted. It ws pplied in 5 points: to the mesil nd distl mrginl ridge, nd uccl cusp (3 points). At ech selected loding point, lod of 40 N ws pplied perpendiculr to the surfce in tht point. In mking the finite element models, the chrcteristics of tooth structures, gold lloy nd cermics used for the restortions were entered into the computer progrm (Tle 1). Tle 1. Elstic properties of the isotropic mterils. Mteril/component Elstic modulus Poisson s rtio [GP] Dentin Enmel Gold Cermics Results nd Discussions For ll cvity designs nd restortion type, stresses in the restortion, enmel, nd dentin were evluted seprtely (Fig. 5). c Fig. 5. Von Mises equivlent stress vlues for:. restortion,. enmel, c. dentin (on only, in inly, me cst metl, cer - cermics). In the onlys recorded mximl stresses were higher thn in the inlys in the most cses. In the cermics restortions the stresses were higher thn in the cst metl. Stresses in the enmel were pproximtely 10 times lower in the teeth prepred for onlys, compred to the teeth prepred for inlys. Between the vlues for cermics nd cst metl restortions there were no significnt differences. In the dentin mximl stresses were lso similr for cermics nd cst metl restortions, for the sme preprtion design. Depending on the tper, they were higher for inlys or onlys, in the most cses for inlys. ISBN:

4 For teeth restored with cst metl inlys stresses were higher in enmel thn for those restored with cermic inlys. Regrding the restortions, in the cermic inlys the stress vlues were higher. In the dentin the stresses were more thn 10 times lower for oth type of inlys (Fig. 6, 7). Fig. 9. Von Mises equivlent stress vlues for cermic only. Fig. 6. Von Mises equivlent stress vlues for cst metl inly. The highest stress vlues were exhiited in the restortion in the most cses. Occlusl lod on n MOD restored tooth produces stress surrounding the contct res in the restortions nd in the enmel (Fig. 10). In the enmel stresses re locted round the contct res for inlys prepred teeth nd distriuted in the functionl cusp nd round the uccl cervicl re for the onlys prepred teeth. For onlys restored teeth the vritions for different tpers were smller thn for inlys restored teeth. Fig. 7. Von Mises equivlent stress vlues for cermic inly. Regrding the stresses in the only restored teeth vlues in enmel nd dentin were out 15 times lower thn in the restortions with no significnt differences etween the two structures. In the cermic onlys stresses were higher thn in the cst metl (Fig. 8, 9). Fig. 10. Von Mises equivlent stress in the cermic inly restored premolr. Regrding the distriution of stresses in dentin, they re locted in the cervicl res, round the teeth for ll cses (Fig. 11, 12). Fig. 8. Von Mises equivlent stress vlues for cst metl only. Fig. 11. Von Mises equivlent stress in the dentin of cermic inly restored premolr. ISBN:

5 Fig. 12. Von Mises equivlent stress in the dentin of cermic only restored premolr. 4 Conclusion Within the limittions of this study, the following conclusions were drwn: 1. In the MOD onlys recorded mximl stresses were higher thn in the MOD inlys in the most cses. In the cermics restortions the stresses were higher thn in the cst metl. 2. Regrding the prosthetic restortions mteril, in the cermics inlys nd onlys the stress vlues were higher. 3. MOD inlys trnsferred more functionl stress to the teeth structures compred to the MOD onlys. 4. The tper of the preprtions hd no significnt influence on the stress vlues for ll the studied cses. 4 Acknowledgements This work ws supported y CNCSIS-UEFISCSU, project numer PN II-RU TE_217/2010. References: [1] Shillingurg HT. Fundmentls of fixed prosthodontics. 3rd ed. Chicgo: Quintessence;1997. [2] S. Rosenstiel, M. Lnd, J. Fujimoto, Contemporry fixed prosthodontics, 3rd ed. Mosy, St. Louis, [3] B. Dejk, A. Mlotkowski, M. Romnowicz. Strength estimtion of different designs of cermic inlys nd onlys in molrs sed on the Tsi-Wu filure criterion. J Prosthet Dent 2007;98: [4] Fonsec RB, Fernndes-Neto AJ, Correr- Sorinho L, Sores CJ. The influence of cvity preprtion design on frcture strength nd mode of frcture of lortory-processed composite resin restortions. J Prosthet Dent 2007;98: [5] Dejk B, Mlotkowski A, Romnowicz M. Finite element nlysis of stresses in molrs during clenching nd mstiction. J Prosthet Dent 2003;90: [6] Gormn CM, McDevitt WE, Hill RG. Comprison of two het-pressed ll-cermic dentl mterils. Dent Mter 2000;16: [7] Mnhrt J, Schmidt M, Chen HY, Kunzelmnn KH, Hickel R. Mrginl qulity of toothcolored restortions in clss II cvities fter rtificil ging. Oper Dent 2001;26: [8] Mnhrt J, Chen HY, Neuerer P, Scheienogen-Fuchsrunner A, Hickel R. Threeyer clinicl evlution of composite nd cermic inlys. Am J Dent 2001;14,95-9. [9] Mehl A, Kunzelmnn KH, Folwczny M, Hickel R. Stiliztion effects of CAD/CAM cermic restortions in extended MOD cvities. J Adhes Dent 2004;6: [10] Bremer BD, Geurtsen W. Molr frcture resistnce fter dhesive restortion with cermic inlys or resin-sed composites. Am J Dent 2001;14, [11] Sores CJ, Mrtins LR, Pfeifer JM, Ginnini M. Frcture resistnce of teeth restored with indirect-composite nd cermic inly systems. Quintessence Int 2004;35: [12] St-Georges AJ, Sturdevnt JR, Swift EJ Jr, Thompson JY. Frcture resistnce of prepred teeth restored with onded inly restortions. J Prosthet Dent 2003;89: [13] Dlpino PH, Frncischone CE, Ishikirim A, Frnco EB. Frcture resistnce of teeth directly nd indirectly restored with composite resin nd indirectly restored with cermic mterils. Am J Dent 2002;15: [14] Shor A, Nicholls J, Phillips KM, Limn WJ. Ftigue lod of teeth restored with onded direct composite nd indirect cermic inlys in MOD clss II cvity preprtions. Int J Prosthodont 2003;16:64-9. [15] Ymnel K, Cglr A, Gulshi K, Ozden UA. Effects of different cermic nd composite mterils on stress distriution in inly nd only cvities: 3-D finite element nlysis. Dentl Mterils Journl 2009; 28(6): [16] Dejk B, Mlotkowski A. Three-dimensionl finite element nlysis of strength nd dhesion of composite resin versus cermic inlys in molrs. J Prosthet Dent 2008; 99: ISBN: