The most significant factor in the long term prognosis of a restored tooth is the preservation of a healthy periodontal attachment.
The best restorative margin is placed coronal to soft tissue. It is cleansable and can be maintained more easily.
The term “biologic width” denotes the combined connective tissue- epithelial attachment from the crest of the alveolar bone to the base of the gingival sulcus. This includes the width of supra-alveolar connective tissue fibres (average 1.07) and the junctional epithelium (average 0.97), which totals an average of 2.04 mm.
During placement of restorative margins, an additional 1-2 mm of sound structure coronal to the epithelial attachment is needed, hence the minimum distance between the alveolar crest and the restorative margin should be 3-4 mm (to allow a gingival sulcus of approx. 1 mm) This can be determined radio graphically.
Impinging on this width by a restoration will trigger loss of bone and epithelial attachment. An interproximal encroachment leads to osseous crater that will be unmanageable from oral hygiene standpoint.
The width of keratinized gingiva needed to maintain periodontal health and unaltered attachment levels is a controversial topic. The keratinized gingiva provides a protective fibre barrier against inflammation and attachment loss.
There is increasing evidence that periodontal health can be maintained in areas with minimal zones of keratinized gingiva as long as the patient can maintain the area and there are no restorations in the area of the gingival margin. When restorative procedures enter the gingival crevice, a minimum of 5 mm of keratinized tissue is required (2 mm of free gingiva and 3 mm of attached gingiva).
There are situations where we are forced to take the restorative margins sub-gingivally. When such conditions as fracture and caries force us to violate biologic width, periodontal surgery or crown lengthening procedures should be performed. Orthodontic extrusion or forced eruption is useful in the premolar and anterior region, where gingival width is important. When indicated, this procedure is to be completed before the restoration.
To conclude, the points to remember are:-
· To preserve biologic width and prevent attachment loss, restorative margins should be at least 3-4 mm from crestal bone.
· Sub gingival restorative margins should be properly contoured
· An adequate band of keratinized tissue is mandatory.
· Plan the treatment carefully and consider the benefits that periodontal surgery and orthodontic extrusion can provide.
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