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ABSTRACT: This three-dimensional finite element analysis first described stresses distribution in loaded posterior fixed partial dentures, then compared the influences of bone height, abutment roots number and pontic length on their displacements. Twelve mandibular (three to five unit) FDPs integrating periodontal ligaments were designed. Stresses were localized in connectors and cervical areas of abutments near the edentulous span. The main FDPs' displacements consisted of vertical translation increasing with low bone height. FDPs underwent simultaneously an anteroposterior displacement (about ten times smaller) towards the weakest abutment side. Splinted abutments affected this anteroposterior displacement. Span length was associated with small beam deflection.
The European journal of prosthodontics and restorative dentistry 12/2009; 17(4):157-63.
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ABSTRACT: This study investigated the mechanical behaviour of tooth-implant fixed partial dentures by three-dimensional Finite Element Analysis. Titanium implants of various length and diameter were rigidly connected to a premolar either by two connected ceramic crowns or by a three unit Fixed Partial Denture. The implant acted like the fulcrum of an orthodontic device inducing tooth intrusion. Bone stresses appeared around the neck of the implant. Implant and abutment's stresses were meaningfully less intense with high diameter and low span. Implant length was a less influencing parameter. The use of wide-bodied implants is recommended in selected cases of short-span fixed partial dentures.
The European journal of prosthodontics and restorative dentistry 09/2009; 17(3):98-104.
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ABSTRACT: This three dimensional Finite Element Analysis study investigated stress distribution and intensity in implants restored with cemented or screwed crown. Two parameters varied: interarch space and abutment height. Highest stresses occurred at the cervical area in all models. Stresses increased mainly with vertical interarch space highness, and secondarily with abutments shortness. From a mechanical point of view, bone and prosthetics components supporting cemented crowns were not as solicited as with screwed crowns.
The European journal of prosthodontics and restorative dentistry 07/2009; 17(2):90-4.
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ABSTRACT: Short implants present superior failure rates for everybody.
The aim of this theoretic study was to assess to what extent implant length and bicortical anchorage affect the way stress is transferred to implant components, the implant proper, and the surrounding bone.
Stress analysis was performed using finite element analysis. A three-dimensional linear elastic model was generated. All implants modeled were of the same diameter (3.75 mm) but varied in length, at 6, 7, 8, 9, 10, 11, and 12 mm (Brånemark System, Nobel Biocare AB, Gothenburg, Sweden). Each implant was modeled with a titanium abutment screw and abutment, a gold cylinder and prosthetic screw, and a ceramic crown. The implants were seated in a supporting bone structure consisting of cortical and cancellous bone. An occlusal load of 100 N was applied at a 30 degrees angle to the buccolingual plane.
With the selected model and bone properties, the coronal cortical anchorage was dominating, and the bone stress concentrated to that area.
The maximum bone stress was virtually constant, independent of implant length and bicortical anchorage. The maximum implant stress, however, increased somewhat with implant length and bicortical anchorage.
Clinical Implant Dentistry and Related Research 02/2003; 5(4):254-62. · 3.53 Impact Factor
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ABSTRACT: Following endodontic therapy, teeth need to be protected, particularly in the cervical region, where the majority of fractures occur. The likelihood of a fracture depends on the condition of the crown and the type of reconstruction performed.
This simulation study was designed to compare the effect of different corono-radicular reconstruction methods on stress transmission to dental tissues.
The study software performed stress analysis of complex structures by finite element analysis. Seven 3-dimensional models were created, each representing a tooth embedded in a bony medium. The following parameters affecting corono-radicular restoration were studied: 2 levels of coronal destruction, core materials, post materials when present, and absence of post. The 2 levels of coronal tissue loss were (1) total tissue loss of the coronal dentin and (2) partial tissue loss of the coronal dentin with 2-mm surviving dentin walls. Teeth with 2 different levels of tissue loss (first study parameter) were reconstructed by 4 different techniques: nickel chromium (NiCr) cast post and core, NiCr post and composite core combination, carbon fiber post and composite core combination, and composite restoration without post. A NiCr crown covered each of the models and received a 30 degrees oblique occlusal load at a constant intensity of 100 N. The software computed the stresses (local tensile stress inducing cracks and compressive stress) for each of the models, comparing maximum intensity observed, localization, and concentration.
Whatever the type of stress (tensile or compressive), the greatest stress was observed in the cervical region, regardless of the model. Only tensile stresses potentially responsible for fractures were compared. Cervical tensile stresses exceeded 230 Pa in the absence of a ferrule and were less than 140 Pa when a ferrule was present. In the absence of a ferrule, the NiCr composite/post combination generated greater cervical stress (254 Pa) than the cast post and core (235 Pa). Results with a ferrule showed 92 Pa for the NiCr composite/post combination and 90.5 Pa for the cast post and core. In the presence of a ferrule, the tensile stress intensities generated by the composite restoration with no root canal post (139 Pa) were 51% greater than those generated by the NiCr/composite combination and approximately 26% greater than those generated by the composite/carbon combination.
Within the limitations of this study, it was confirmed that all simulated reconstructed teeth were more subject to stress in the cervical region. The absence of a cervical ferrule was found to be a determining negative factor, giving rise to considerably higher stress levels. When no ferrule was present, the NiCr post/composite combination generated greater cervical stress than cast post and cores. Nevertheless, the peripheral ferrule seemed to cancel the mechanical effect of the reconstruction material on the intensity of the stresses. With a ferrule, the choice of reconstruction material had no impact on the level of cervical stress. The root canal post, the purpose of which is to protect the cervical region, was also shown to be beneficial even with sufficient residual coronal dentin. In the presence of a root canal post, cervical stress levels were lower than when no root canal post was present. Moreover, the higher the elasticity modulus, the lower the stress levels.
Journal of Prosthetic Dentistry 11/2002; 88(4):442-8. · 1.32 Impact Factor
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ABSTRACT: Four three-dimensional numerical models of a fixed partial denture were constructed, analyzed, and compared by means of the
finite element method. Each model consisted of three elements destined to compensate the loss of a first molar. The second
proemolar and the second molar were used as abutments. The connector surface was varied and then tested. A unidirectional
axial force was applied to the center of the occlusal surface of the pontic. For each model, we measured the strain undergone
by the connectors that link the pontic to each abutment. Results show that the strain measured in the mesio–distal direction
was much more significant than in any other direction. Strain originated on either side of the loading point, centrally located
on the cervical side of the pontic. The 0.15% strain threshold, beyond which rupture is possible, was only reached in one
model (connector surface = 3.3 mm2). Increasing both the height and the width of the connectors by 1 mm resulted in extending the surface by 3.3 to 7.95 mm2. Although the surface increased by 141%, the strain threshold was not reached. This first result indicates that extending
the surface of the connectors, which is less consistent with periodontal clinical requirements, is not necessary to ensure
resistance to rupture.
Clinical Oral Investigations 04/1998; 2(1):36-39. · 2.36 Impact Factor
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ABSTRACT: The aim of this study was to evaluate by finite element analysis the influence of the design of 3 different dental implants on micromovements, cervical shearing stress intensity, and stress distribution after occlusal loading.
The first investigated implant was a classical cylinder, the second was reinforced by 2 bicortical locking pins, and the third was an expanding dental implant. The parameters analyzed were the implant's geometry, the quality of the cancellous bone, and the orientation of occlusal loading.
It was found that initial stability of the locking pin implant was greater than the initial stability of the other investigated implant designs, regardless of the quality of cancellous bone and orientation of occlusal loading; in low-rigidity cancellous bone, under a horizontal load (500 N), decreasing displacement compared to those of the other investigated implants was 16 microm. The apical expansion and locking pin implants exhibited favorable behavior regarding the distribution and intensity of cervical shearing stresses; in low-rigidity cancellous bone, under horizontal load, decreasing cervical stresses compared with those of the cylindric implant were 10 MPa for the apical expansion implant and 150 MPa for the locking pin implant.
For the cylindric implant, stresses were concentrated in the neck region; for the apical expansion implant, stresses were evenly distributed from the neck to the apex of the implant. For the locking pin implant, stresses around the neck were moderate and appeared concentrated around the pins.
Initial stability of the pin implant was greater than that of the expanding implant, but the expanding implant showed the most favorable stress distribution.
The International journal of oral & maxillofacial implants 17(3):353-62. · 1.78 Impact Factor
