Master of Dental Surgery
Prosthodontics
2013-2016
AECS MAARUTI COLLEGE OF DENTAL SCIENCES AND
RESEARCH CENTRE, BANGALORE
RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES
BANGALORE, KARNATAKA
Proforma for
Registration of Subjects for Dissertation
1. Name of the candidate and address:
Dr Ipsha Rani
I year M.D.S student
Department of Prosthodontics
A.E.C.S Maaruti College of Dental
Sciences and Research Centre
108, Tank bund road, Hulimavu,
BTM 6th stage, 1st phase,
Bannerghatta road, Bangalore – 76
2.Name of the institution
A.E.C.S Maaruti College of
Dental Sciences and Research Centre
Bangalore
3.Course of the study and the subject
Master of Dental Surgery (MDS)
Prosthodontics
4. Date of admission to the course
10-06-2013
5. Title of the topic
Effect of joining the sectioned implant prosthesis on the strain caused in simulated mandibular model
6. Brief resume of the intended work
6.1 Need for the study
Implant supported prosthesis has become a preferred treatment option over the past decade.Inimplant dentistry, a passive fit of the superstructure is important in order to obtain a favourable physiologic response. Unlike natural teeth, implants are rigidly fixed to the bone. An imperfect fit of the framework can induce unpredictable stresses to the implant and the surrounding bone.It is extremely difficult to construct a superstructure with passive fit, when the casting is large because the resultant casting shrinkage is substantial. The prosthesis is then sectioned in order to obtain a passive fit, which can later be joined by different techniques such as soldering, laser welding and arc welding . This study is done to evaluate the strain developed in the supporting structures on joining the sectionedprosthesis using various joining techniques.
6.2 Review of literature
6.2.1.Barbi C.L.F, Camarini T.E, Silva S.R, Endo H.E, Pereira R.J conducted this study to compare three different techniques of joining viz Gas torch brazing, laser welding, tungsten inert gas welding , Co-Cr superstructures by measuring the resulting marginal fit in a simulated prosthetic assembly. Stainless steel model was made. The model was composed of two precisely machined orifices, 15mm apart to lodge the abutment analogs [Mini abutment analogs]. Two implants [ Revolution implant ] of dimension 3.25mm x 10mm were placed 7mm from the center of each analog orifice and two stop screws on the buccal aspect of the model to allow for the exchange of abutment analog during scanning electron microscopy measurements. Forty-five cast bar [ cylindrical(blue) plastic bar] type superstructures [ Co-Cr blocks, kera 501 (Co 61%, Cr 30%, Mo 5.5%, Nb 1%, Fe< 1%, Si 0.4%, Mn< 0.5%) ] were fabricated on the model and the specimens were divided into three groups with 15 specimens in each group according to the joining methods used: conventional gas-torch brazing (G-TB), laser welding (LW), tungsten inert gas welding(TIG). Plastic cylinders with Co-Cr pre-machined base were screwed over the abutments analogs. A 10mm plastic bar was positioned 13mm parallel to the model surface with the assistance of the delinerator [ 1000N; Bio Art, Sao Carlos, Brazil] and joined to the cylinder with sticky wax [ Geo Sticky Wax, Germany ]. A transfer device for a closed-tray impressiom technique was then fixed to the implants. Plastic cylinders located to the left of the operator were marked with a drop of wax [ Kerr Corp, Orange, Calif ] that was used to aid the correct positioning of the specimen during sectioning, joining, and measuring procedure. Patterns were sprued and invested [Polidental, Cotia, Brazil ] and cast in a two stage procedure with Co-Cr alloy [Kera 501; EisenbacherDentalwaren ED GmbH, Germany ]. After divesting with tungsten carbide burs [FG 169-170; Beavers Dental, Canada ] the specimen were airborne abraded with 50 micron meter Aluminium Oxide and ultrasonically cleaned in an isopropyl alcohol. The specimen were manually screwed onto the abutment analogs in the metal model. Carborundum disks [Dura-thin Metal cutting Abrasive disc ] for gold and chromium alloys were used to section the specimen. In Group G-TB specimens space created after sectioning was filled with autopolymerizing acrylic resin. Then, the acrylic resin was removed with an ethanol flame. Flux [Fluxo fit, Brazil ] was applied and a Co-Cr solder was used as filler material. The assembly was preheated to 750 degrees and gas-torch brazed at 1180 degrees. Group LW specimens were joined using Nd:YAG laser welding device [Smark 500; Sisma, Italy ] with a wavelength of 1064 nm, pulse duration of 1.5 ms, pulse energy of 70 J and frequency pf 4 Hz. Group TIG specimens were joined using TIG welding device [ Plasma welding machine, Brazil ] having pulse of 5 ms and the depth of .3 nm. The cylinders on side A i.e operator’s left were then tightened to 10 Ncm and retightened 10 minutes later again to 10 Ncm with a electronic torque gauge [ DEA 028 Control unit; Nobel biocare, Sweden ]. The cylinder on side B was left untightened. All the assembly was then placed in a sputtering machine [Shimadzu IC-50, Kyota, Japan ] where they received an ultrathin coating of pure gold [ P/M Metal Powders Ltd, Brazil ]. The marginal gap reading were made with scanning electron microscope [Shimadzu SS 550; Shimadzu Corporation ], with x200 magnification on the buccal aspect in the three different position distal (D), mesial (M), central (C). The results showed that on side A in position D, there were no significant differences among groups, in position C the mean values were significantly different between groups G-TB and TIG ( P=.036 ) and in position M values were significantly different between Groups G-TB and LW ( P=.013 ). On side B in position D, significant difference could be observed between Groups G-TB and TIG ( P=.006), in position C, significant difference were found between groups G-TB and TIG (P=.001) and Groups LW AND TIG (P=.007) and in position M, significant differences were seen between groups G-TB and LW (P=.001 ) and Groups LW and TIG (P=.001). It was concluded, the method used for joining Co-Cr prosthetic structures had an influence on the passive fit. Structures joined by the tungsten inert gas method produced better mean results than did the brazing or laser method.
6.2.2Tashkandi A.E, Lang R.B, Edge J.M conducted this study to evaluate the effect of length of cantilevered implant supported prosthesis on the strain development in bone. A segment of bovine bone was taken in which three 13mm self- tapping endogenous implants ( Branemark, Nobelpharma USA, Chicago ) were placed in straight line on the bone model 15mm apart. Strain gauges (EA-06-125 AD-120, Measurement group Inc, Raleigh, N. C ) were cemented to the surface of bone with methyl - 2 -cyanoacrylate resin (M-BOND 200 adhesive ) at six different locations: distal to the most posterior implant, anterior to the most posterior implant, in between the middle and most anterior implant, at the apex of posterior implant, at the apex of middle implant, at the apex of anterior implant. Abutments( SDCA 006, Nobelpharma, USA) were screwed onto the implant with 20Ncm torque using manual torque driver (DIA 250, Nobelpharma, USA). Cantilevered superstructure was fabricated over the abutment. Six loading locations were prepared with fine carborundum disc, starting at the centre of the most posterior implant and 5, 10, 15, 20, 25mm in a posterior direction to the intial loading position. Loading forces of 10 and 20 pounds were applied and each load was applied five times at each location. The results showed maximum strain that occurred under 20 lb load was statistically significantly different from that with 10 lb load. Analysis of strain that occurred at the six strain gauge revealed, regardless of the cantilever length used, a significantly greater strain was recorded at the bone surrounding the apex of the most distal implant.
6.2.3 Eskitascioglu G, Usumez A, Sevimey M, Soykan E, Unsal E conducted this study to evaluate the effect of loading at one to three different locations on the occlusal surface of a tooth on the stress distribution in an implant supported mandibular fixed partial denture and surrounding bone, using three dimensional finite element analysis. A three dimensional finite element model of a mandibular section of bone with missing second premolar and its superstructure,simulating A-2 type bone were used in this study. A bone block, 24.2 mm high and 16.3 mm wide representing the section of mandible in the second premolar region was modeled. A one piece 4.1 X 10 mm screw shaped dental implant system (Solid implant ) ( ITI; InstutStraumann AG, Waldenburg, Switzerland ) was placed at the region of missing premolar. Cobalt- chromium (Wiron 99; Bergo, Bermen, Germany ) was used as crown framework material and feldspathic porcelain was used for occlusal surface. Porcelain and metal thickness used in this were .8 to 2 mm. An averageocclusal force of 300 N was determined from literature. Vertical load were applied at one to three different locations; a load of 300 N on the tip of the buccal cusp; a load of 150 N on the tip of the buccal cusp and a load of 150 N at the distal fossa; a load of 100 N on the tip of buccal cusp, 100 N at the distal fossa and 100 N at the mesial fossa. The applied forces were static. Stress levels were calculated using Von Mises stresses Values. The analyses were performed on a Dell precision 420 Dual Pentium III 1GHz ( Dell, Austin, Tex ) using COS-MOS/ M software (version 2.5; structural Research and Analysis Corp, Santa Monica, Calif ). The results showed stress distribution within the implant and the abutment were concentrated at the neck of implant. Maximum stress values were 89.9 MPa , 64.16 MPa, 67.99 MPa for loading at one loacation, two locations, three locations respectively. Stress distribution within the framework for loading at one location were located on the buccal cusp (95.58 MPa ) and buccal cervical margin (59 MPa ); for loading at two location on the distal fossa (149MPa) and for the loading at thre locations were located on the distal fossa and the mesial fossa ( 97.15 MPa ). The maximum stresses on the occlusal surface were concentrated on the distal fossae ( 533 MPa ) for loading at two locations. The maximum stresses were located on distal fossae and mesial fossae ( 441 MPa ) for loading at three location and on buccal cusp ( 437 MPa ) for loading at one location. Results also showed maximum stresses were located within the cortical bone surrounding the implant and within the lingual contour of mandible. There was no stress within the spongy bone. Maximum stess values within the cortical bone surrounding the implants were 106.65 MPa, 99.01 MPa, 102.55 MPa for loading at one, two and three locations respectively. Maximum stresses within the lingual contour of mandible were 61.88 MPa, 64.05 MPa for loading at two and three locations respectively. There was no stress within the lingual contour of the mandible for loading at one location. It was concluded from this study that loading at one location induced higher stresses within the bone and the implant than loading at two and three loacations.
6.2.4 Savadi C.R, Agarwal J, Agarwal S.R, Ranggarajan V conducted this study to evaluate the influence of implant surface topography and loading condition on the stress distribution in the bone surrounding the implant. A section of mandible of lower first molar region of a length 25.6 mm mesio-distally was taken from the CT scan and converted into three dimensional solid model using ANSYS version 8.0 software. A three dimensional model of endopore implant ( Innova corporation, Toronto ) of truncated root form with a 5 degree taper and dimension of 4.1 mm diameter and 12 mm length with a 1 mm smooth coronal region with a suitable abutment was generated. Except for the 1mm smooth coronal region, the rest of the surface of the implant was occupied by diffusion bonded microsphere surface and the implant was assumed to be placed in the region of first molar. Another implant of same dimension but with the smooth surface was also placed in the similar section of mandible for comparision. The section of bone containing implant with smooth surface was considered as model 1 and the one with porous surface topography as model 2. An axial load of 100 N, a non-axial load of 50 N from bucco-lingual direction and a non-axial load of 50 N from mesio-distal direction was directly applied onto the abutment. The model were analyzed by processor i.e solver and the results were displayed by post processor of finite element software ( ANSYS, version 8.0 ) in the form of color coded map using Von Mises Stress Analysis. The results showed irrespective of the model and loading condition, maximum stress was found in the cortical bone at the areas adjacent to the implant abutment junction. On axial loading stress values of 11.739 MPa and 13.674 MPa was recorded in model 1 and 2 respectively, while more uniform stress distribution was generated in model 2 as compared to model 1. During non axial loading, the stresses generated in model 2 ( 35.648 MPa ) were slightly higher as compared to model 1 (18.406 MPa ). On axial loading very low stress ( 6.669 MPa ) values were generated at the bone implant interface as compared to the stress values generated during non-axial loading ( 21 .631 MPa ). Irrespective of the loading condition and the type of model, the maximum amount of stress was generated in the implants directly on the point of application of load. Both the models exhibited much lesser values of stresses during axial loading when compared to stresses generated during non axial loading. It was concluded that porous surface topography appeared to distribute forces in a more uniform pattern around the implant and there was favourable distribution of stress and strain pattern during axial loading.
6.2.5 Himmlova L, DostalovaT, Kacovsky A, Konvickova S conducted this finite element analysis to evaluate influence of implant length and diameter on stress distribution. A three dimensional model was generated and solid cylinder shaped titanium implant with bioactive coating ( IMZ; Interpore International, Irvine, Calif; ITI Bonefit; InstitutStraumann, Waldenberg, Switzerland ) was placed into the molar region of the simulated mandible in vertical position. Implant model with a diameter of 3.6 mm and lengths of 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 17 mm, and 18 mm were used to investigate the influence of length as a factor. The influence of diameter was modeled by implants with a length of 12 mm and diameter of 2.9 mm, 3.6 mm, 4.2 mm, 5.0 mm, 6.0 mm and 6.5 mm. Implants were loaded with forces of 17.1 N, 114.6 N, and 23.4 N in a lingual, an axial, and a disto-mesial direction respectively at an angle of approximately 75 degrees to the occlusal plane and on the centre of the upper surface of the abutment at a distance of 4.5 mm from the upper margin of the bone. The results showed the maximum stress were located around the neck of the implant on the mesio-lingual rim of the bony socket.This location was identical for all implant lengths and diameters. The model for implant with the same length (12 mm) but different diameter indicated a marked influence of the implant on the stress in the simulated bone. Stress reduction continued to decrease for larger diameter. The implant with a diameter of 4.2 mm showed relative stress in the bone 31.5 % smaller than the reference implant ( 3.6 mm ). The use of an implant with a diameter of 6.5 mm resulted in reduction of stress values by almost 60%. The model for implant with the same diameter ( 3.6 mm ) but different lengths showed a relatively lower effect of length than diameter. For the 8 mm and the 17 mm long implants there was a difference of only 7.3%. it was concluded that increased implant diameter better dissipated the simulated masticatory force and decreased the stress around the implant neck, so from biomechanical perspective, the optimum choice was an implant with maximum possible diameter allowed by the anatomy.