The effect of periosteal injury and masticatory micromovement on the healing of a mandibular distraction osteogenesis site

Abstract

Objectives: Surgical periosteal injury and masticatory loading are likely factors affecting the healing of a mandibular DO site. This study is aimed to characterize the healing features of an early-phase mandibular DO site and assess the effects of these factors.

Design: Eighteen 3-6-month-old miniature pigs received a right mandibular osteotomy and were distracted for 5 days (1 mm/day) and consolidated for 0, 1 or 2 weeks (Groups A, B and C, respectively). Bone formation, chondrogenesis and vascular structure of the distraction site were measured using histological methods and their changes with consolidation time were characterized. The effect of periosteal injury was assessed by comparing the more severely injured lateral side with the less disturbed medial side. The effect of masticatory loading was evaluated by relating the healing features to the interfragmentary micromovement caused by soft-diet mastication.

Results: With consolidation time, bone formation and chondrogenesis became stronger whilst vascular structure became more mature. Compared to the medial side, bone formation and chondrogenesis on the lateral side were significantly delayed in Groups A and B, but not in Group C, in which periosteal recovery had occurred. No difference was found for vascular measurements between the medial and lateral sides. In Group B, bone formation, but not chondrogenesis or vascular structures, tended to be negatively correlated with the magnitude of masticatory micromovement during the distraction phase.

Conclusion: The results suggest that periosteal injury inhibits early mandibular DO site healing, whereas micromovement from soft-diet mastication mechanics has a negligible effect.

Fig. 1

A) Specimen collection. Two blocks were from the superior (above the distractor) and two from the inferior (below the distractor) locations, respectively. The blocks closest to the hardware (hatched boxes) were processed with decalcification. The most superior and inferior blocks (filled boxes) were processed without decalcification (filled boxes). One block (clear box) was collected from the middle location (underneath the distractor) and processed either with or without decalcification (see text for details). All blocks were sectioned in a plane parallel to the distractor rod. B) Diagram of a typical section. Newly formed callus spicules were wavy and thin. The solid-line boxes indicate surface callus. The broken-line boxes indicate gap callus, M, medial region; I, interior region and L, lateral region.

Fig. 2

A) Mineralization measurement in undecalcified sections illustrated by periosteal callus. Mineral apposition rate was the average distance between the fronts of calcein (green label, line b) and alizarin complexone (red label, line a) divided by 3 days. Mineral advancement was the average distance between the old bone front (line c) and the new callus front (line a). B) Periosteal callus bone volume fraction (BV/TV) measurement in decalcified sections. A square 19×25 test grid was superimposed on the image. BV/TV was defined as the number of intersections hitting the callus bone divided by the number of intersections hitting the entire callus area (enclosed by broken white lines). C) Linear percentage of Col-II (+) matrix measurement shown on a decalcified section reacted for anti-Col II. The bone margins of the DO gap on both sides are indicated by solid lines (a). The portions of the margins in relation to Col-II (+) (brown color, arrows) are indicated by broken lines (b). Col-II linear percentage was defined as the total length of b divided by the total length of a. D) Assessment of vascular structures illustrated on an image of the interior gap site. Lectin immunohistochemistry was used to reveal endothelial cells (brown). The site of interest was defined as the distraction gap soft tissue (inside of the broken lines. Color thresholding was performed to dichotomize the image (not shown) for quantification of endothelial cell density (thresholded area divided by the total area of site of interest) and blood vessel lumen area density (total area of vessel lumens divided by the total area of the site of interest). Calibration bars, 500 μm.

Fig. 3

Distraction gap callus formation. The left space in each image is the distraction gap. A) Lateral and B) medial regions of a Group A distraction site. Note callus was mainly forming in the medial region and arose from the periosteal callus. C) Lateral and D) medial regions of a Group C distraction site. Note callus was forming in both medial and lateral regions and was from both periosteal callus and the old cortex. E) and F), Interior regions from different animals. E shows callus formation originating from old trabecular bone (arrowheads). F shows callus formation originating from periosteal callus (arrows) and growing towards the old bone surface (*). Calibration bars, 500 μm.

Fig. 4

Chondrogenesis in the interior region of the distraction gap of Group C animals. Cartilage matrix was revealed by alcian blue staining (blue) and Collagen II immunohistochemistry (brown). Broken lines indicate bone fronts.

Fig. 5

Vascular structures inside the distraction gap. Positive (lectin-stained) cells were thresholded and pseudocolored (orange). Broken lines indicate the borders between distraction gap soft tissue and bone matrix. Differences in background color are due to variation of white balancing between sections. A), Group A (no consolidation), B) Group C (2 weeks of consolidation). With consolidation time, blood vessel walls thickened while lumens shrank. Calibration bars, 100 μm.

Fig. 6

Periosteal condition and new bone formation. At the end of distraction (A and B), the lateral periosteum was not continuous (arrow heads) but the medial periosteum was intact (arrows). New bone formation was stronger at the medial surface. After two weeks of consolidation (C and D), the lateral periosteum (arrows) was repaired and new bone formation was catching up with the medial side. Calibration bars, 1000 μm