Tetracycline as a marker in hard tissue research: effects on enamel formation in rat maxillary incisors

Abstract

Abstract— Tetracycline in low dose is often used as a marker in hard tissue research. A low dose effect on enamel formation has never been proven despite well known toxic reactions in enamel after higher doses. The purpose of the investigation was to evaluate enamel formation in maxillary incisors of rats given a single low dose of a tetracycline with low toxicity, commonly used in research. Eight young rats received an intraperiotonal injection of 2 mg oxytetracycline per 100 g. The rats were terminated after periods between 1 h until 5 days. Undemineralized ground sections were prepared and studied under fluorescence microscopy. Microradiograms were taken to study the degree of mineralization. A diffuse uptake was seen within enamel in areas corresponding to late secretory stage and incisally in maturing enamel with a low mineralization degree. Tendencies of enamel aberrations were seen in all rats. These appeared as splittings within the formed enamel. In conclusion, low toxicity tetracycline disturbs normal amelogenesis, even if administered in low doses. It should therefore be avoided in hard tissue research where enamel formation is studied.

Histological preparation of teeth and tooth growth

“…This compares with the studies by Fatani and Raja [8] who reported a rate of 0.015 mm/day, using radioautographs. The growth rate of the teeth in this study was also seen to be less in the presence of tetracycline which compares with Ranggard [11] who reported that even a single low dose of tetracycline (2 mg oxytetracycline per 100 g) caused a disturbance in normal amelogenesis in the rat incisor. The question then is "How does this affect the interpretation of the results when tetracycline is used as a histological marker for other studies?"…”

“…Fatani and Raja [27], using radioautographs, measured the thickness of dentine laid down per day as 0.015 mm. It is clear that the growth rate of teeth is effected by many factors, including age of animal [28,31], the physical properties of the diet [33], and medications [11]. In this study the mean growth of teeth was 0.010 mm/day during the period of tetracycline administration and 0.016 mm/day when no tetracycline was being administered.…”

“…Tetracyclines were introduced in 1948 as broad-spectrum antibiotics that may be used in the treatment of common infections in children and adults [25]. The use of low dose tetracycline as a histological bone marker has been well established since the 1960s with papers by Bevelander et al, [12], Ibsen and Urist [13], Faccini [14], Frost [15], and more recently by Ranggard [11], Engstrom [16], Sun et al, [17]. It was discovered that tetracycline is incorporated into hard tissues calcifying at the time of their administration and subsequently could be studied in undecalcified sections by fluorescence microscopy [12,14].…”

“…The use of low dose tetracycline as a histological hard tissue marker has been well established and allows clear evidence of continued hard tissue growth in experimental animals [11][12][13][14][15][16][17].…”

“…When ultraviolet (UV) light (450-490 nanometres [nm]) is applied to tetracycline-stained hard tissues, it exhibits a yellow Fuchsin Fluorescence. Hence tetracycline compounds are utilized in hard tissue research as a vital fluorescent dye for measuring the rate of hard tissue formation [11][12][13][14][15][16]. The tetracycline tends to remain incorporated into the newly formed hard tissue areas for some time after systemic administration [26].…”