IAtured epithelium has a genetically programmed regenerative a migty that allows it to reestablish its integrity

BOX 4-]

Causes of Tissue Damage

Causes of Tissue Damage
Causes of Tissue Damage

through proliferation, migration, anda process known as contact inhibition. In general, a free edge of. epithelium continues to migrate (by proliferation of germinal epithelial cells that advance the free edge forward) until it
comes into contact with another free edge of epithelium, where it is signaled to stop growing laterally.

Although it is theorized that chemical mediators (released from epithelial cells that have lost contact with other. epithelial cells circumferentially) regulate this process, no definitive evidence for this is yet available. Wounds in which only the surface epithelium is injured
(i.e., abrasions) heal by proliferation of epithelium across the wound bed from the epithelium contained in rete pegs and adenexal tissues. Because epithelium does not normally contain blood vessels, the epithelium in
wounds in which the subepithelial tissue is also damaged proliferates across whatever vascularized’ tissue bed is available and stays under the portion of the superficial blood clot that desiccates (i.e., forms a scab) until it
reaches another epithelial margin. Once the wound is fully epithelialized, the scab loosens and is dislodged.

An example of the rarely detrimental effect of the process of contact inhibition controlling epitheiiiUization occurs when an opening is accidentally made into a maxillary sinus during tooth extraction. If the epithelium of both the sinus wall and the oral mucosa isinji),red, it
begins to proliferate in both areas. In this case. the. first. free epithelial edge the sinus epithelium may contact is . oral mucosa, thereby creatsng an oroantral fistula (i.e., anepithelialized tract between the oral cavity and the maxiIIary sinus).

The process of reepithelialization (i.e., secondaryepithelialization) is sometimes used tberapeuticaUy.  oral and maxillofacial surgeons during certain prepares thetic surgical procedures in which aan area of ordel mucosa is denuded of epithelium (i.e., unattached gingiva and then left to epithelialize by adjacent epithelium  (l.e., attached gingiva) creeping over the wound bed.

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