Growth factors and metabolic markers in cord blood: relationship to birth weight and length.

Low birth weight and length for gestational age are associated with a high risk of short stature and metabolic syndrome in adulthood. The mechanisms that link prenatal growth to adult stature and metabolic syndrome have not yet been entirely clarified. The aim of our study was to evaluate the relationship between standardized anthropometric measures at birth and insulin-like growth factor (IGF)-I, IGF-II, insulin, adiponectin, and non-esterified fatty acid (NEFA) cord blood levels in the general population. One hundred fifty-eight random newborn subjects (77F, 81M) from Genoa, Italy, were analyzed. Anthropometric parameters were measured and standardized according to standard Italian tables. Insulin values were treated as categorical, since in several cases the results fell below detection cut-off. Mean birth weight was 3,214.23∓488.99 gr and mean length was 49.82∓2.17 cm. Females had higher mean IGF-I (p=0.04), and were more likely to have insulin values either <2 μU/ml or >4.5μU/ml (p= 0.04) compared to males. Weight and length SD scores (SDS) were higher in subjects with elevated insulin levels (p=0.002). A moderate correlation was found between weight and IGF-II (r=0.354). Multivariable analysis demonstrated that standardized birth weight was associated with IGFII and insulin values. Our data highlight the importance of IGF-II in fetal growth and suggest that gender differences should be taken into consideration when evaluating prenatal growth.

New radiopaque acrylic bone cement. II. Acrylic bone cement with bromine-containing monomer.

Bromine-containing methacrylate, 2-(2-bromopropionyloxy) ethyl methacrylate (BPEM), had been used in the formulation of acrylic radiopaque cements. The effect of this monomer incorporated into the liquid phase of acrylic bone cement, on the curing parameters, thermal properties, water absorption, density, compression tests and radiopacity was studied. A decrease of maximum temperature and an increase of the setting time were observed with the addition of the bromine-containing monomer in the radiolucent cement composition. Adding BPEM in radiolucent acrylic bone cements composition results in the decrease of glass transition temperature and increase of its thermal stability. Acrylic bone cements modified with bromine-containing comonomer are characterized by polymerization shrinkage lower than the radiolucent cement. Addition of bromine-containing comonomer in radiolucent acrylic bone cement composition determines the increase of compressive strength. Acrylic bone cements modified with bromine-containing comonomer proved to be radiopaque.

Restoration of non-carious cervical lesions Part II. Restorative material selection to minimise fracture.

OBJECTIVE: It is still largely unknown as to what material parameter requirements would be most suitable to minimise the fracture and maximising the retention rate of the restoration of cervical non-carious lesions (NCCL). The present paper, as a first of its kind, proposes a radical approach to address the problems of material improvement, namely: numerical-based, fracture and damage mechanics materials optimisation engineering. It investigates the influence of the elastic modulus (E) on the failure of cervical restorative materials and aims to identify an E value that will minimise mechanical failure under clinically realistic loading conditions. METHOD: The present work relies on the principle that a more flexible restorative material would partially buffer the local stress concentration. We employ a "most favourable" parametric analysis of the restorative's elastic modulus using a fracture mechanics model embedded into finite element method. The advanced numerical modelling adopts a Rankine and rotating crack material fracture model coupled to a non-linear analysis in an explicit finite element framework. RESULTS: The present study shows that the restorative materials currently used in non-carious cervical lesions are largely unsuitable in terms of resistance to fracture of the restoration and we suggest that the elastic modulus of such a material should be in the range of 1GPa. We anticipate that the presented methodology would provide more informative guidelines for the development of dental restorative materials, which could be tailored to specific clinical applications cognisant of the underlying mechanical environment.

Restoration of non-carious cervical lesions Part I. Modelling of restorative fracture.

OBJECTIVE: As a typical non-carious cervical lesion, abfraction is a common clinical occurrence which requires restorative treatment in most patients. Nonetheless, the relatively poor clinical longevity of cervical dental used for restoring abfraction lesions has been a major concern of dentists and patients. The continuing loss of hard tissue and, in turn, the low retention of the restorative materials in situ motivates an in-depth exploration of the failure mechanism of the biomaterials involved. Despite considerable biomechanical relevance, conventional application of linear static finite element analysis (FEA) does not consider the fracture failure process, nor does it provide a quantitative predictive analysis for restorative design. This paper adopts a novel Rankine and rotating crack model to trace the fracture failure process of the cervical restorations. METHODS: In contrast to the existing linear FEA, this study presents a nonlinear fracture analysis in an explicit finite element framework, which involves an automatic insertion of initial crack, mesh updating for crack propagation and self contact at the cracked interface. RESULTS: The results are in good agreement with published clinical data, in terms of the location of the fracture failure of the simulated restoration and the inadequacy of the dental restoratives for abfraction lesions. The success of the proposed model also demonstrates the potential for the monitoring and prediction of mechanical failure in other brittle biomaterials in a clinical situation.

Mechanical evaluation of cervical glass-ionomer restorations: 3D finite element study.

OBJECTIVES: The aim of this paper was to investigate the influence of lesion shape and depth as well as the direction of occlusal loading on the mechanical response of cervical GIC restorations. METHODS: A finite element model of a lower first premolar was created. Both wedged and rounded lesions were then modelled with incremental depth after which the tooth was loaded at different angles. First principal stress (tension) was employed as an indicator of material failure, by contrasting our calculated stresses with the ultimate tensile strength of the GIC and known values of bond strength between material and tooth substrate. RESULTS: Obliquely loaded teeth exhibited significantly higher tensile stress in the cervical region of the restoration. For forces inclined at angles of 30 degrees and higher to the vertical tooth axis, the tensile stresses in the cervical margin of the restoration exceeded the ultimate material and bond strength. In contrast, lesion shape and depth have only a minor influence on tensile stress development. CONCLUSIONS: Lesion depth and shape are not of primary concern from a mechanical perspective for a restorative treatment decision. By contrast, occlusal diagnosis and subsequent re-adjustments of tooth contacts do form a critical part of the treatment of non-carious cervical lesions (NCCLs).

Modelling of fracture behaviour in biomaterials.

One of the most frequent causes of degradation and failure of quasi-brittle biomaterials is fracture. Mechanical breakdown, even when not catastrophic, is of particular importance in the area of biomaterials, as there are many clinical situations where it opens the path for biologically mediated failures. Over the past few decades the materials/biomaterials community has developed a number of numerical models, but only with limited incorporation of brittle failure phenomena. This article investigates the ability of a non-linear elastic fracture mechanics (NLEFM) model to reliably predict failure of biomaterials with a specific focus on the clinical settings of restorative dentistry. The approach enables one to predict fracture initiation and propagation in a complex biomechanical status based on the intrinsic material properties of the components. In this paper, we consider five examples illustrating the versatility of the present approach, which range from the failure of natural biomaterials, namely dentine and enamel, to a restored tooth, a three unit all ceramic bridge structure and contact-induced damage in the restorative layered materials systems. It is anticipated that this approach will have ramifications not only to model fracture events but also for the design and optimisation of the mechanical properties of biomaterials for specific clinically determined requirements.

Functional significance of strain distribution in the human mandible under masticatory load: numerical predictions.

A common feature of studies of mandibular morphology is the assumption that there is some functional relation between the form of the lower jaw and masticatory stress. It was noted that the local variation in cortical bone thickness in the mandibular corpus appears to be stereotypical among anthropoids. This occurs at sections under the molars, where the lingual cortical plate is thinner than buccal one. In this study we investigate and contrast the strain pattern along buccal and lingual surfaces of the mandibular corpus during mastication using a numerical model of a human mandible. We show that strain distribution differs in alveolar and mid-corpus segments of the mandible and that the latter develops an alternate pattern between the buccal and lingual aspects of the working and balancing sides of the jaw. We then relate the magnitude of these strains to Frost's mechanostat. Our results suggest that the cortical asymmetry of the human mandible is in fact not related to strain patterns generated during mastication.

Mandibular biomechanics and development of the human chin.

The development of the chin, a feature unique to humans, suggests a close functional linkage between jaw biomechanics and symphyseal architecture. The present study tests the hypothesis that the presence of a chin changes strain patterns in the loaded mandible. Using an anatomically correct 3-D model of a dentate mandible derived from a CT scan image, we analyzed strain patterns during incisal and molar biting. We then constructed a second mandible, without a chin, by 'defeaturing' the first model. Strain patterns of the second model were then compared and contrasted to the first. Our main finding was that chinned and non-chinned mandibles follow closely concordant patterns of strain distribution. The results suggest that the development of the human chin is unrelated to the demands placed on the mandible during function.

A finite element analysis of ferrule design on restoration resistance and distribution of stress within a root.

AIM: To analyse the effect of ferrule height upon the mechanical resistance and stress distribution within a root to explain variations in the pattern of root fracture. METHODOLOGY: An extracted, intact, caries free, maxillary right central incisor was scanned by laser and then reconstructed on a computer to produce a model of the tooth and associated periodontal ligament. A simulated post/core/crown restoration was constructed on conventional tooth preparations with various ferrules. The crown was loaded with a simulated 500 N force and the simulated displacement of components and the tensile and compressive stress within the tooth structure were recorded. RESULTS: Without a ferrule preparation, the simulated crown tilted to the labial and rotated distally. With increasing ferrule height the displacement and rotation of the crown reduced in conventional and crown-lengthening models with maximum reduction occurring when the ferrule height reached 1.5 mm. In ferrule models, higher levels of tensile stress developed in internal (by a factor of 8) and mid-root palatal (by a factor of 90) dentine at the cervical margin of the preparation. With an increase in ferrule height, the area of tensile stress within the palatal mid-dentine expanded towards the cervical margin. Similar patterns and stress values were recorded for the crown-lengthening models. CONCLUSION: The study confirms that a ferrule increases the mechanical resistance of a post/core/crown restoration. However a ferrule creates a larger area of palatal dentine under tensile stress that may be a favourable condition for a crack to develop. Crown-lengthening did not alter the levels or pattern of stress within compared with conventional ferrule preparations.

Mandibular stiffness in humans: numerical predictions.

The chin is a feature unique to humans. This study evaluates the effect of mandibular symphyseal design on biomechanical masticatory effectiveness as determined by structural stiffness and stress developed under flexural and torsional loading. A simple model of three symphyseal shapes (chin, flat symphysis and lingual buttress), was built to represent human, Neanderthal and higher primate symphyses and these were subjected to wishboning and torsional forces. Additionally, an anatomically detailed reconstruction was made of the CT scan of an actual human mandible, which was then also morphed into a chinless model. The results of a 3-D finite element analysis show firstly, that none of the three different symphyseal shapes is biomechanically more advantageous than the others for the given loading condition. Secondly, we show in a CT-derived model, that the presence of a chin does not confer significantly improved stiffness to torsional or flexural loading. These results indicate that the acquisition of a chin in modern humans is not related to the functional demands placed upon the mandible during mastication, but suggest that it may have developed in response to other biomechanical demands.

[Aspects of professional hygiene in dental technical laboratories]. / Aspecte de igiena profesionala in laboratoarele de tehnica dentara.

Investigations on hygiene and sanitary conditions in a laboratory for dental techniques consisted in physico-chemical determinations on microclimate (temperature, humidity, air currents), determination of dust particles (suspended and sedimented), determination of gases (CO, CO2, NO2, NH3, SO4(2-), chloride ions), and determination of microelements (Fe, Cu, Zn, Ni, Cd). In certain conditions the concentrations for dust, NO2, NH3, SO2(4-), chlorine and Cu were above the maximal accepted levels. Measures should be taken for the prevention and for the elimination of these noxious factors by implementing optimal hygienic conditions (heat, humidity, ventilation), by reducing gas emanations, by using protections equipment (mask, eyeglasses, gloves), and by periodic controls of the health status of dental technicians.