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Anelastic phenomena associated to water loss and collagen degradation in human dentin
No full textThis work describes the anelastic and dynamic Young modulus behaviour of human dentin from room temperature
up to 673 K. Human molars, extracted from individuals (males 55–70 years old) as part of their dental
treatment,were cut to obtain bar-shaped samples subsequently used formechanical spectroscopy experiments.
In addition, thermo-gravimetric analysis (TGA) has been performed to assess a possible weight loss occurring in
the same temperature range of mechanical spectroscopy tests.
A broad and asymmetric internal friction (Q−1)maximumat 500 K has been observed during the heating of the
as-prepared samples. This maximum is absent during the following cooling down to room temperature. It is
therefore due to the occurrence of an irreversible transformation in the sample. TGA shows a remarkableweight
loss in the same temperature range. This effect has been related to loss of fluids and degradation of collagen.
Another set of samples, previously kept for 36 h under a vacuum of 10−2 Pa, were submitted at room temperature
to test at increasing strain from 6×10−6 to 7×10−4. The results show transient and fully recoverable Q−1
increase and dynamic modulus (E) decrease.
The phenomenon has been ascribed to the breaking of weak H-bonds between polypeptide chains forming
the triple-helix with consequent increase of the mean length of vibrating chain segments
Mapping tooth mechanical properties by FIMEC tests
No full textDentin has different morphology near the enamel and in the inner part, resulting in mechanical properties progressive changing in correspondence of structure variation. In order to obtain a local mechanical characterization of dentin, FIMEC (Flat-top cylinder Indenter for mechanical characterization),1 an instrumented indentation technique, has been employed. FIMEC uses a cylindrical punch and permits local measurements of Young’s modulus E, yield stress Y, stress-relaxation and creep. The punch diameter (Φ = 0.5 mm) is much larger than the tubule size thus data are not so largely scattered as in micro- and nano-indentation tests but, at the same time, is small enough to guarantee a good resolution in mapping the mechanical properties in different tooth positions. More details about the FIMEC test and its application for measurements on human teeth can be found in Cappelloni et al. (2010)
Stress-based performance evaluation of osseointegrated dental implants by finite-element simulation
Full text linkIn this paper biomechanical interaction between osseointegrated dental implants and bone is numerically investigated through 3D
linearly elastic finite-element analyses, when static functional loads occur. Influence of some mechanical and geometrical
parameters on bone stress distribution is highlighted and risk indicators relevant to critical overloading of bone are introduced. Insertions both in mandibular and maxillary molar segments are analyzed, taking into account different crestal bone loss configurations. Stress-based performances of five commercially-available dental implants are evaluated, demonstrating as the optimal choice of an endosseous implant is strongly affected by a number of shape parameters as well as by anatomy and mechanical properties of the site of placement. Moreover, effectiveness of some double-implant devices is addressed. The first one is relevant to a partially edentulous arch restoration, whereas other applications regard single-tooth restorations based on non-conventional endosteal mini-implants. Starting from computer tomography images and real devices, numerical models have been generated through a parametric algorithm based on a fully 3D approach. Furthermore, effectiveness and accuracy of finite-element simulations have been validated by
means of a detailed convergence analysis
Three-dimensional finite-element analysis of osseointegrated dental implants
Full text linkIn this paper the biomechanical interaction between osseointegrated dental implants and bone is investigated by numerical simulations. The influence of some mechanical and geometrical parameters on bone stress distributions is highlighted and some risk-measures relevant to critical overloading are furnished. Load transfer mechanisms of several dental implants are analyzed by means of linearly elastic finite-element analyses, when static functional loads occur. For a given implant the variation of its performance with the placement is investigated, considering insertions both in mandibular and maxillary molar segments. The mechanical properties of the bone regions (cortical and cancellous) are approximated with those of a type II bone and the geometry of crestal bone loss after an healing period is modelled. Five commercially-available dental implants are analyzed, demonstrating as the optimal choice of an endosseous implant is strongly affected by a number of shape parameters as well as by anatomy and mechanical properties of the site of placement. Numerical results clearly proof as a given implant device exhibits very different performance on mandibular or maxillary bone segments, resulting in higher compressive stresses when maxillary placement is experienced. Finally, the effectiveness of several multiple-implant restorative applications is investigated. The first one is related to a partially edentulous arch restoration, based on a double-implant device involving a retaining bar. Other applications regard single-tooth restorations based on non-conventional devices consisting in a mini-bar supported by two mini endosteal implants, possibly reproducing the natural roots orientation of a multiple-root tooth
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