BIOMECHANICAL REPERCUSSION OF PROTEIN MALNUTRITION ON THE RAT MANDIBLE

Keywords: bone biomechanics, protein malnutrition, growth, mandible          
OBJETIVES: The present investigation was performed to assess the biomechanical repercussion of protein malnutrition imposed to rats between the 26º and 135º days of postnatal life on the mandible, which is not a weight-bearing bone but supports the loads of the masticatory activity. METHODS: Female Sprague-Dawley 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 sacrificed 111 d later. Both body weight and length were registered 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. RESULTS: 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% reduced in protein restricted rats. BMD was similar in both groups of animals. CONCLUSION: 1) Chronic protein malnutrition imposed to 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 from protein restricted rats is apparently the result of a diminished bone mass and/or its spatial distribution, with maintenance of the biomechanical intrinsic properties of the bone. Supported by UBACYT O-005 and O-002.