Tissue Response To Increased Occlusal Forces

Stages of Tissue Response

Tissue response occurs in three stages"1": injury, repair, and adaptive remodeling of the periodontium.

Stage I: Injury. Tissue injury is produced by excessive occlusal forces. The body then attempts to repair the injury and restore the periodontium. This can occur if the forces are diminished or if the tooth drifts away from them. However, if the offending force is chronic, the periodontium is remodeled to cushion ils impact. The ligament is widened «it the expense of the bone, resulting in angular bone defects without periodontal pockets, and the tooth becomes loose.

Under the forces of occlusion, a tooth rotates around a fulcrum or axis of rotation, which in single-rooted teeth is located in the junction between the middle third and the apical third of the clinical root (see Fig. 2-12). This creates areas of pressure and tension on opposite sides of the fulcrum. Different lesions are produced by different degrees of pressure and tension. II jiggling forces are exerted, these different lesions may coexist in the same area.

Slightly excessive pressure stimulates resorption of the alveolar bone, with a resultant widening of the periodontal ligament space. Slightly excessive tension causes elongation of the periodontal ligament fibers and apposition of alveolar bone. In areas of increased pressure, the blood vessels are numerous and reduced in size; in areas of increased tension, they are enlarged.'"

(¡renter pressure produces a gradation of changes in the periodontal ligament, starling with compression of the fibers, which produces areas of hyaliniza-tion.64*66 Subsequent injury to the fibroblasts and other connective tissue cells leads to necrosis of areas of the ligament.0Vascular changes are also produced: within 30 minutes, retardation and stasis of blood flow occur; at 2 to 3 hours, blood vessels appear to be packed with erythrocytes, which start to fragment; and between 1 and 7 days, disintegration of the blood vessel walls and release of the contents into the surrounding tissue occur."1 In addition, increased resorption of alveolar bone and resorption of the tooth surface occur1-44 (Figs. 24-3 and 24-4).

Severe tension causes widening of the periodontal ligament, thrombosis, hemorrhage, tearing of the periodontal ligament, and resorption of alveolar bone.

Pressure severe enough to force the root against hone causes necrosis of the periodontal ligament and bone. The bone is resorbed from viable periodontal ligament adjacent to necrotic areas and from marrow spaces, a process called undermining resorption.

The areas o! the periodontium most susceptible* to injury from excessive occlusal forces are the furcations.11

Injury to the periodontium produces a temporary depression in mitotic activity and the rate of proliferation and differentiation of fibroblasts, in collagen formation, and in bone formation/" 1 { These return to normal levels after dissipation of the forces.

Stage II: Repair. Repair is constants occurring in the normal periodontium, and trauma from occlusion stimulates increased reparative activity.

The damaged tissues are removed, and new connective tissue cells and fibers, bone, and cenientum are formed in an attempt to restore the injured periodontium d ig. 24-S). forces remain traumatic only as long as the damage produced exceeds the reparative capacity of the tissues.

When bone is resorbed by excessive occlusal forces, the body attempts to reinforce the thinned bony trabecule with new bone (Fig. 24-6). This attempt to compensate for lost bone is called buttressing bone formation and is an important feature of the reparative process associated with trauma from occlusion.28 it also occurs when bone is destroyed by inflammation or osteolytic tumors.

Buttressing bone formation occurs within the jaw (central buttressing) and on the bone surface (peripheral buttressing). In central buttressing, the endosteal cells deposit new bone, which restores the bony tra-beculae and reduces the size of the marrow spaces (see Fig. 24-6). Peripheral buttressing occurs on the facial and lingual surfaces of the alveolar plate. Depending on its severity, peripheral buttressing may produce a shelf-like thickening of the alveolar margin, referred to as lipping (Fig. 24-7; see also Fig. 24-3), or a pronounced bulge in the contour of the facial and lingual bone16'26 (see Chapter 23).

Cartilage-like material sometimes develops in the periodontal ligament space as an aftermath of the trauma.21 Formation of crystals from erythrocytes has also been shown.67

Stage III: Adaptive Remodeling of the Periodontium. II the repair process cannot keep pace with the destruction caused by the occlusion, the periodontium is remodeled in an effort to create a structural

Periodontal Ligament Formation

Fig. 24-3 Periodontal accommodation to lateral forces. A, Mandibular premolar B, Lingual surface, show ing new bone formation in response to tension on the periodontal ligament. Note the pale-staining osteoid bordered by osteoblasts and the incremental lines indicative of previous additions to the bone. C, Facial sur face shows compression of the periodontal ligament and osteoclastic resorption of the bony plate. Note the new bone formed on the external surface. This is peripheral buttressing bone, which reinlorces the resorb-ing facial plate. Note also that the buttressing bone has produced a bulge in the bony contour.

Fig. 24-3 Periodontal accommodation to lateral forces. A, Mandibular premolar B, Lingual surface, show ing new bone formation in response to tension on the periodontal ligament. Note the pale-staining osteoid bordered by osteoblasts and the incremental lines indicative of previous additions to the bone. C, Facial sur face shows compression of the periodontal ligament and osteoclastic resorption of the bony plate. Note the new bone formed on the external surface. This is peripheral buttressing bone, which reinlorces the resorb-ing facial plate. Note also that the buttressing bone has produced a bulge in the bony contour.

Widened Periodontal Ligament
Fig. 24-4 Trauma from occlusion at the root apex. Note bone resorption with prominent osteoclasis (arrows). The periodontal ligament (P) is widened as the result ol bone resorption, and the blood vessels are engorged. The root is shown at 0.

I he three stages in the evolution ol traumatic lesions have been differentiated histometrically by means of the relative amounts of periodontal bone surlace undergoing resorption or formation10dig. 24-8». Ihe injury phase shows an increase in areas ol resorption and a decrease in bone formation, whereas the repair phase demonstrates decreased resorption and increased bone formation. After adaptive remodeling ol the periodontium, resorption and formation return to normal.

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  • peter
    How does occlusal forces affect the periodontium?
    2 years ago
  • Haile
    How occlusal forces affect periodontal tissues?
    10 months ago

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