Stress-based performance evaluation of osseointegrated dental implants by finite-element simulation

In 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

In 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

Association of kidney disease measures with risk of renal function worsening in patients with type 1 diabetes

Background: Albuminuria has been classically considered a marker of kidney damage progression in diabetic patients and it is routinely assessed to monitor kidney function. However, the role of a mild GFR reduction on the development of stage 653 CKD has been less explored in type 1 diabetes mellitus (T1DM) patients. Aim of the present study was to evaluate the prognostic role of kidney disease measures, namely albuminuria and reduced GFR, on the development of stage 653 CKD in a large cohort of patients affected by T1DM. Methods: A total of 4284 patients affected by T1DM followed-up at 76 diabetes centers participating to the Italian Association of Clinical Diabetologists (Associazione Medici Diabetologi, AMD) initiative constitutes the study population. Urinary albumin excretion (ACR) and estimated GFR (eGFR) were retrieved and analyzed. The incidence of stage 653 CKD (eGFR < 60 mL/min/1.73 m2) or eGFR reduction > 30% from baseline was evaluated. Results: The mean estimated GFR was 98 \ub1 17 mL/min/1.73m2 and the proportion of patients with albuminuria was 15.3% (n = 654) at baseline. About 8% (n = 337) of patients developed one of the two renal endpoints during the 4-year follow-up period. Age, albuminuria (micro or macro) and baseline eGFR < 90 ml/min/m2 were independent risk factors for stage 653 CKD and renal function worsening. When compared to patients with eGFR > 90 ml/min/1.73m2 and normoalbuminuria, those with albuminuria at baseline had a 1.69 greater risk of reaching stage 3 CKD, while patients with mild eGFR reduction (i.e. eGFR between 90 and 60 mL/min/1.73 m2) show a 3.81 greater risk that rose to 8.24 for those patients with albuminuria and mild eGFR reduction at baseline. Conclusions: Albuminuria and eGFR reduction represent independent risk factors for incident stage 653 CKD in T1DM patients. The simultaneous occurrence of reduced eGFR and albuminuria have a synergistic effect on renal function worsening

Mapping tooth mechanical properties by FIMEC tests

Dentin 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)

Mapping tooth mechanical properties by FIMEC tests

Dentin 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)