Recession in sites with inadequate width of the keratinized gingival An experimental study in the dog
Authors: Ericsson Ingvar , Lindhe Jan 
Published: December 2005

Abstract The present investigation was performed to assess the inflammatory response in gingival units subsequent to the placement of restorations with subgingivally located margins. 3 beagle dogs were used. Cotton floss ligatures were placed around the neck of the mandibular third and fourth premolars of all dogs. The ligatures were exchanged once a month during the first 6 months of experiment. When 40–50% of the height of the supporting tissues had been lost in an experimental periodontitis the ligatures were removed but the animals allowed to accumulate deposits for another 60 days. The inflamed periodontal tissues were subsequently excised using either an “apically placed flap” procedure or a “gingivectomy” procedure. In the flap procedure the main part of the keratinized gingiva was preserved while in the gingivectomy procedure the keratinized part of the gingiva was removed in toto. Following scaling and root planing the animals were during a maintenance period of 4 months placed on a program involving chlorhexidine application and mechanical tooth cleaning twice daily. On Day 0 a notch was prepared in the buccal surface of each root at the level of the gingival margin. Furthermore, steel bands were placed along the buccal surface of each root of the third and fourth premolars and secured with an apical margin at the level of 1 mm apical to the notch. The bands were cemented to the root surfaces by a cement. The dogs were allowed to accumulate plaque and calculus for 6 months. Towards the end of the study a clinical examination was performed to assess the position of the steel bands in relation to the notch and the gingival margin, the presence of subgingival plaque and the condition of the gingiva. The animals were subsequently sacrificed and specimens containing' the mandibular third and fourth premolars were harvested, fixed in formalin, decalcified and embedded in paraffin. The buccolingual sections of each root were cut with a microtome set at 4 μm and stained in hematoxylin and eosin. In the biopsies the distance between the gingival margin and the most apical cells of the junctional epithelium, the distance between the junctional epithelium and the margin of the bone crest and the distance between the notch and the gingival margin were assessed. In addition, the size of the infiltrated connective tissue was calculated using a morphometric test system.The results of the experiment revealed that the placement of a “restoration” in a subgingival position in gingival sites also allowed to accumulate plaque established conditions which promoted development of moderate to severe gingival inflammation. In experimental sites characterized by the presence of an “inadequate” width of the keratinized gingiva, the inflammatory reaction was almost always accompanied by loss of gingival tissue. It is suggested that the placement of restorations in a subgingival position in sites with a narrow zone or lacking keratinized gingiva may in the presence of subgingival plaque favor the apical displacement of the soft tissue margin.