Dietary consistency and the midline sutures in growing pigs

Abstract

Objectives: The purpose of this study was to investigate the effects of reduced masticatory function on midline suture growth and morphology in growing pigs.

Setting and sample population: The sample was 20 pigs separated into two dietary groups and raised at the Department of Anthropology, Harvard University. Midline suture specimens were analyzed at the Department of Orthodontics, University of Washington.

Materials and methods: Ten farm pigs and 10 minipigs, all male, were randomly assigned to hard (n = 9) and soft-diet (n = 11) groups. Fluorochromic mineral labels were administered to document bone apposition, and the animals were killed after 12 weeks. Undecalcified sections of the interfrontal, interparietal, internasal, and intermaxillary sutures were evaluated for bone quantity and sutural thickness, interdigitation ratio and growth rate.

Results: Soft-diet pigs were characterized by a slower rate of weight gain and less bone than their hard-diet counterparts. Even after correction for weight gain, soft-diet pigs had reduced suture growth rate and thickness. However, no difference in interdigitation ratio was detected between dietary groups.

Conclusions: Restriction to a soft diet reduces midline suture growth and bone apposition in the growing pig.

Figure 1

A) Ventral and B) dorsal views of a pig skull, showing locations and dimensions of sutural samples. C and D are stained sections illustrating bone quantity scores from anterior internasal sutures from representative (C) soft and (D) hard diet animals. The ectocranial side is toward the top and the endocranial (nasal) side is towards the bottom of the figures. Values were assigned on a 0–3 scale at 4 locations for each specimen: ectocranial cortex, endocranial cortex, sutural cortex, and trabeculae. Calibration bars = 1 mm.

Figure 2

A) Toluidine stained and B) unstained coronal sections of an internasal suture illustrate the evaluation of morphology and suture growth rate. Suture thickness is represented by the vertical line in (A), while Interdigitation Ratio is the length of the left suture margin (wavy line) divided by the thickness. Suture Growth Rate (B) was calculated as the area between the label margin and bone front margin (shaded area) divided by the average length of the two margins, and then divided by the number of days since the last label (μ/day). Calibration bars = 1mm. Suture growth rate (SGR) for farm pigs is depicted in (C). SGR was significantly decreased in soft diet animals when all locations were considered together (p=0.002). Locations: IF - interfrontal, IP-interparietal, IN – internasal, IM - intermaxillary (A-anterior, M-middle, P-posterior).