Bone mineral density and bone strength from the mandible of chronically protein restricted rats
Acta odontol. latinoam; 24 (3), 2011
Publication year: 2011
The present investigation was performed to assess the biomechanical repercussion of protein malnutrition imposed on rats between the 26th and 135th days of postnatal life on the mandible, which is not a weight-bearing bone but supports the loads related to the masticatory activity. Female Wistar rats aged 26 d (n=14) were placed on either a 4%-protein diet (ICN 960254, P4 group) or a 20%-protein diet (ICN 960260, P20 group) and killed 111 d later. Both body weight and length were recorded regularly. The mandibles were dissected and cleaned of adhering soft tissue. Mandibular growth was estimated directly by taking measurements between anatomical points. Areal Bone Mineral Density (BMD) was estimated using a bone densitometer (LUNAR DPX-L). Mechanical properties of the right hemimandible were determined using a three-point bending mechanical test to obtain the load/deformation curve and estimate the structural properties of the bone. Results were summarized as means ± SD. Comparisons between parameters were performed by Student's t test. A 75% reduction in body weight and a 32% reduction in body length were observed in P4 rats. Like body size, mandibular weight, length, height and area (index of mandibular size) were negatively affected by P4 diet, as was the posterior part of the bone (posterior to molar III). The anterior part (alveolar and incisor alveolar process) was not affected by age or diet. The "load capacity" extrinsic properties of the mandible (load fracture, stiffness, yielding point) were between 43% and 64% of control value in protein restricted rats. BMD was similar in both groups of animals.
Conclusion:
1) Chronic protein malnutrition imposed on rats from infancy to early adulthood reduces the growth of the posterior part of the mandible without inducing changes in the anterior part, which produces some deformation of the bone in relation to age-matched rats; and 2) the significant reduction of strength and stiffness of the mandible seem to be the result of an induced loss of gain in bone structural properties as a consequence of a correlative loss of gain in both growth and mass, yet not in bone material properties.
La investigación presente fue diseñada con el objeto de evaluar la repercusión biomecánica de la malnutrición proteica impuesta a ratas entre los días 26º y 135º de edad sobre la mandíbula (M), hueso que no soporta carga relacionada con el peso corporal sino con las fuerzas masticatorias. Ratas Wistar hembras de 26 d de edad (n=14) fueron alimentadas con dietas conteniendo 4% (grupo P4) (ICN 960254) o 20% (grupo P20) (ICN 960260) de caseína y sacrificadas 111 d después. Peso y longitud corporales fueron registrados regularmente. Las mandíbulas fueron disecadas y liberadas de tejido blando. Se realizaron mediciones entre diversos puntos anatómicos para estimar la morfometría del hueso. La Densidad Mineral Osea (DMO) fue determinada en un densitómetro LUNAR DPX-L. La M derecha de cada animal fue sometida al test de flexión a 3 puntos para obtener la curva carga/deformación y estimar las propiedades estructurales del hueso mandibular. Los resultados (X±DS) fueron analizados estadísticamente mediante test t de Student. El peso y la longitud corporales fueron menores en el grupo P4 que en el P20 (-75% y -32%, respectivamente). Longitud de la base, altura y área mandibular (índice del tamaño de M) fueron afectados negativamente por la dieta P4, lo mismo que la porción posterior de M (posterior al molar III). La porción anterior (procesos alveolar e incisivo) no fueron afectadas por dieta o edad. Todas las propiedades biomecánicas de M (carga de fractura, resistencia en fase elástica, límite elástico) fueron 43-64% menores en grupo P4 que en grupo P20. El valor de DMO fue similar en ambos grupos.