RESUMO
OBJECTIVES: Knowledge of the mechanical behaviour of root dentine can facilitate better understanding of spontaneous vertical root fracture (VRF), an age-related disease initiated mainly at the root apex. We tested the hypothesis that the biomechanical properties of root dentine change with ageing. METHODS: Sixteen human premolars were divided into "old" (17-30 years) and "young" (50-80 years) groups. The elastic modulus, nano-hardness, micro-hardness, elemental contents, tubular density/area of root dentine in cervical, middle and apical root regions were evaluated using atomic force microscopy-based nano-indentation, Knoop indentation, scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. RESULTS: The apical dentine showed a lower nano-hardness, a lower elastic modulus, a lower calcium content, a lower calcium-to-phosphorus ratio and a smaller tubular density/area than the cervical dentine in both age groups, whereas spatial differences in micro-hardness were observed only in old roots. Compared with young dentine, old dentine showed a greater hardness, a higher elastic modulus, a greater mineral content and a smaller tubular size in the cervical portion, whereas the age-induced changes in tubular density were insignificant. Finite element analysis revealed that due to its higher elastic modulus, old apical dentine has a higher stress level than young dentine. CONCLUSIONS: The intrinsic material properties of root dentine have spatial variations, and they are altered by ageing. The higher stress level in old apical dentine may be one reason, if not the most important one, why spontaneous VRFs are more likely to occur in the elderly population.
Assuntos
Envelhecimento/fisiologia , Dentina/fisiologia , Fraturas dos Dentes/fisiopatologia , Raiz Dentária/fisiologia , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Envelhecimento/metabolismo , Envelhecimento/patologia , Fenômenos Biomecânicos , Cálcio/análise , Dentina/química , Dentina/ultraestrutura , Módulo de Elasticidade , Análise de Elementos Finitos , Dureza , Humanos , Microscopia de Força Atômica , Microscopia Eletrônica de Varredura , Pessoa de Meia-Idade , Fósforo/análise , Espectrometria por Raios X , Estresse Mecânico , Ápice Dentário/química , Ápice Dentário/fisiologia , Ápice Dentário/ultraestrutura , Colo do Dente/química , Colo do Dente/fisiologia , Colo do Dente/ultraestrutura , Raiz Dentária/química , Raiz Dentária/ultraestrutura , Adulto JovemRESUMO
The objective of this study was to evaluate the influence of dietary naringenin (NAR) supplementation on physiological molar crestal alveolar bone (CAB)-cemento-enamel junction (CEJ) distances in young male albino rats. The effects of diets supplemented with 0.09%, 0.18%, 0.36%, and 0.72% NAR, at the expense of dextrose, were tested on 40 young rats, divided equally into five groups, for a period of 42 days. Rat skulls were defleshed, and CAB-CEJ distance was scored according to the modified method of Keyes and Gold. Data were analyzed using one-way analysis of variance, post hoc Tukey's test, and Spearman's (R(2)) correlation. P < .05 was used to reject the null hypothesis. NAR showed a statistically significant inverse dose-dependent relationship on CAB-lingual alveolar bone distance (P < .05). In all cases lingual CAB-CEJ distance was larger than buccal CAB-CEJ distance. Thus dietary NAR supplementation was shown to significantly reduce molar CAB-CEJ distance (P < .001-.05) during alveolar development in young male rats.