ABSTRACT:
 
 Introduction: The potential toxicity of silver nanoparticles (AgNPs) is becoming a more serious problem as interest in their uses in biotechnology and physiological effects grows. The toxicity of AgNPs was found to be dose and size dependent. Silver nanoparticles synthesis: Different routes lead to variable sizes, shapes, morphology, and even stability. Generally, these methods can be classified into three broad categories: physical, chemical, and biological (or green) synthesis. Aim: The aim of this work was to study the impact of oral administration of AgNPs on the mucous membrane and salivary glands of the tongue of albino rats. Material and Methods: Forty-six male albino rats were used in the present investigation. They were divided into the following groups: Group (1) (15 rats) they received 10mg/kg body weight AgNPs solution using curved metallic oro-pharyngeal tube for 21 days. Group (2) (15 rats) they were treated the same way as group 1 for 21 days then left for 1 month as a recovery period. Group (3) (16 rats) served as controls, subdivided into subgroup (3.1) (8) they received deionized water for 21 days. Subgroup (3.2) (8) they were treated the same way as subgroup 3.1 and then left untreated for one more month. Samples were examined under the light microscope for histological and immunohistochemical evaluation through PCNA labeling index where the number of PCNA positive cells were divided by the total cell number in the basal cell layer was estimated and treated statistically. Results: Examination of the tongue of the rats which were exposed to AgNPs solution revealed atrophic and degenerative changes of both the dorsal and ventral surfaces of the tongue as well as the lingual salivary glands. The examined tongues of the rats which were allowed a recovery period showed improvement in the histological picture. There was significant decrease in PCNA labeling index of the dorsal surface of the tongue of AgNPs treated group animals compared with control group as well as significant increase in PCNA labeling index of recovery group. Conclusion: Overexposure to AgNPs results in atrophic and degenerative effects. A one-month recuperation period can result in regeneration and an improvement in the histological appearance.