Response of regenerative tissues to plaque: A histological study in monkeys
The aim of this study was to observe the histologic response of regenerated tissues to plaque following GTR. The researchers used eight adult monkeys. Bilateral mandibular lateral incisors of each monkey were randomly chosen as study areas (G1=0, no mobility, central incisors extracted).Two-walled (lingual and proximal) periodontal defects were created using a diamond bun The height of the defects was measured (bottom of the defect to crest of the lingual wall) at 5 mm (mesiodistal width=3 mm). Root surfaces were instrumented with curets, and a notch was placed at the bottom of the defect (reference point). Then 3-0 silk sutures were tied around the root surfaces and left in place for eight weeks, creating a chronic periodontal osseous defect. The defects then underwent GTR (e-PTFE membranes) . Tetracycline was given for five days. Membranes were removed after six weeks and biweekly plaque control was given. After healing for six months, 3-0 silk sutures were placed around the teeth (to the bottom of the pocket) to allow plaque accumulation for two or 10 weeks (every two weeks ligatures were checked and PI, GI, mobility, and PD were recorded). Contralateral healthy sites were used as controls. Ligatures were placed for two or 10 weeks without surgical procedures. Four monkeys were sacrificed after plaque accumulation for two weeks; the other four after 10 weeks. Tissue blocks were used for histological procedures. Sections were cut in the mesiodistal direction through the experimental roots. A grid-point intersection analysis was done to determine the percentage of inflamed connective tissue and vasculature in the area coronal to the alveolar bone. Osteoclasts were identified using a light microscope (in the coronal alveolar bone).
The researchers found that two weeks after ligature placement (in GTR) plaque was present and gingival margins were red and swollen (PI 2, PD 2 mm, mobility (II)). At 10 weeks all parameters increased (PI 2.75 ± .28, M.III). Gingival tissues were dark red and edematous (PD ~4 mm). In control sites, findings were similar. Histologically cementum and periodontal ligament regeneration was noted coronal to the reference point (notch). In two weeks postligature experimental sites, there was vascular proliferation and inflammatory cells. Well-demarcated connective tissue zones were present adjacent to the pocket epithelium. Epithelial proliferation was noted. There were inflammatory cells and vascular proliferation (not statistically significant). At 10 weeks no apical relocation of the junctional epithelium was found (prominent rete pegs). Inflammatory cells and osteoclasts were seen. In the control sites, proliferation and apical migration of junctional epithelium were noted. Lymphocytes and plasma cells were seen, but osteoclasts were not observed. No further increase in vasculature was noticed.
In conclusion, researchers found the newly regenerated bone (after GTR) might be more responsive to osteoclastic activity when plaque was allowed to form. Soft tissue responses were slower. Optimal plaque control must be strongly emphasized after GTR. [c.c.]
Ling L., Y. Lai, H. Hwang, and H. Chen, J Periodont, 65:781, 1994