III. Periodontal ligament

E. CLINICAL CONSIDERATIONS

E.  Clinical considerations

1.    The thickness of the periodontal ligament varies from 0.1 to 0.4 mm with a mean of around 0.2 mm.

2.     The ligament is thicker in functioning than in non-functioning teeth, and in areas of tension than in areas of compression (see table below):

Comparison of periodontal width of functioning and non-functioning teeth in an adult male
(Adapted from Kronfeld, R. , 1931)

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                                                     Premolar in heavy function    Premolar in light function          Molar out of function

Mean width of PDL at coronal
        end of alveolus                                         0.35 mm                                 0.14 mm                           0.10 mm

Mean width of PDL in middle
        of alveolus                                                0.28 mm                                 0.10 mm                           0.06 mm

Mean width of PDL at apical
        end of alveolus                                         0.30 mm                                 0.12 mm                           0.06 mm

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3.     The ligament cells are capable of remodeling the ligament and adjacent bone when functional forces are altered or the ligament is damaged.

4.     The periodontal ligament plays a key role in protecting the tooth from being resorbed by the normal remodelling process that affects the adjacent alveolar bone.

5.     Excessive forces can cause localized necrosis (cell death) of the ligament by cutting off the normal blood supply to the cells. This situation immediately results in stoppage of remodeling at the affected site.  Therefore, orthodontic tooth movement is no longer possible.  Repair occurs via emigration of cells from adjoining vital periodontal ligament.  In the event the ligament continuity is not restored, localized resorption and ankylosis may occur.

6.     Accidentally exfoliated teeth can be replanted.  Complications include external root resorption and ankylosis if portions of the ligament are permanently damaged. These can be minimized by avoiding excessive handling of the torn ligament prior to replantation.

7.     Appropriate therapy can halt progressive destruction of the periodontal ligament by periodontal disease and can result in repair of periodontal defects.

8.     The periodontal ligament is unique among the periodontal tissues, in that it contains precursor cells for the production of the entire attachment apparatus of the tooth, i.e. cementum, periodontal ligament and bone.  By using biologically compatible barriers, the therapist is able to promote the ingrowth of these cells into damaged sites where a new periodontal attachment is needed.  This therapeutic principle is known as guided tissue regeneration.

9.     Current research on growth factors and cytokines is aimed at promoting the ingrowth of specific cell types into a wound, while keeping out undesirable cell types.

University of Pennsylvania and Temple University © 1999. All rights reserved. Created: May 8, 1999  Revised: URL: Max A. Listgarten: Comments to author: max@listgarten.com (Technical Support: Center for Dental Informatics: Heiko Spallek)