Bone repair in mandibular body osteotomy after using 2.0 miniplate system--histological and histometric analysis in dogs

Abstract

The objective of this study was to evaluate the bone repair along a mandibular body osteotomy after using a 2.0 miniplate system. Nine adult mongrel dogs were subjected to unilateral continuous defect through an osteotomy between the mandibular 3rd and 4th premolars. Two four-hole miniplates were placed in accordance with the Arbeitgeimeinschaft für Osteosynthesefragen Manual. Miniplates adapted to the alveolar processes were fixed monocortically with 6.0-mm-length titanium alloy self-tapping screws, whereas miniplates placed near the mandible bases were fixed bicortically. At 2, 6 and 12 weeks, three dogs were sacrificed per period, and the osteotomy sites were removed, divided into three thirds (Tension Third, TT; Intermediary Third, IT; Compression Third, CT) and prepared for conventional and polarized light microscopy. At 6 weeks, while the CT repaired faster and showed bone union by woven bone formation, the TT and IT exhibited a ligament-like fibrous connective tissue inserted in, and connecting, newly formed woven bone overlying the parent lamellar bone edges. At 12 weeks, bone repair took place at all thirds. Histometrically, proportions of newly formed bone did not alter at TT, IT and CT, whereas significantly enhanced bone formation was observed for the 12-week group, irrespective of the third. The results demonstrated that although the method used to stabilize the mandibular osteotomy allowed bone repair to occur, differences in the dynamics of bone healing may take place along the osteotomy site, depending on the action of tension and compression forces generated by masticatory muscles.

Figure 1

Stabilization of the bone fragments using two four-holes miniplates in an iatrogenic osteotomy made between the 3rd and 4th premolars.

Figure 2

(a,b) Conventional and (c–f) polarized light microscopy of histological sections of (a,c,e) the Tension Third (TT) and (b,d,f) the Compression Third (CT) at (a,b) 2, (c,d) 6, and (e,f) 12 weeks. (a) TT at 2 weeks showing the inner surface of the lingual cortical with areas of active bone resorption (arrow) and initial endosteal reaction. (b) The inner surface of the lingual cortical in the CT at 2 weeks supports an exuberant endosteal reaction characterized by woven bone trabeculae (*) overlying a previously resorbed parent, lamellar bone. (c) TT at 6 weeks showing a transient ligament-like connective tissue formation at the osteotomy site, with collagen fibre bundles (arrow) inserting into newly-formed woven bone as Sharpey fibres. (d) The osteotomy site exhibits union of the bone edges by woven bone (*) in the CT at 6 weeks. (e,f) Bone repair in the (e) TT and (f) CT at 12 weeks is characterized by parallel-fibred bone (*), a transitional stage between woven bone and lamellar bone. (a–f) Arrowheads indicate the osteotomy margins. Mallory’s trichrome. Scale bar = 200 μm.

Figure 3

(a) Light microscopy of the Intermediary Third (IT) at 6 weeks showing a focal area of chondrocytic differentiation in an exuberant periosteal reaction at the lingual cortical (arrow). (b) High magnification of the dotted area in (a) showing a partial replacement of cartilage by bone tissue. Mallory’s trichrome. (a) Scale bar = 800 μm and (b) 200 μm.

Figure 4

(a) Light microscopy of the Intermediary Third (IT) at 12 weeks showing a ligament-like formation at the osteotomy site, which was in continuity with the periodontal ligament associated with a cross-sectioned tooth root. (b) High magnification of the dotted area in (a) showing a pattern of tissue repair resembling the organization of periodontal supporting tissues. Arrowheads indicate the osteotomy margins. Mallory’s trichrome. (a) Scale bar = 800 μm and (b) 200 μm.

Figure 5

Percentage of newly formed bone in the osteotomy site at the Tension Third (TT), Intermediary Third (IT) and Compression Third (CT) at 2, 6 and 12 weeks.