Frailty of Human Enamel in Dental Pieces with and without Fluorosis: An in Vitro Study

Hardness is considering an essential physiological property of human dental enamel. Much more serious is the fluorosis, teeth pieces are subject to extensive mechanical failures of the surface. Objective: To compare relationship between force and hardness (F-H) in samples of human dental enamel with and without fluorosis. Material and Methods: In vitro experimental study. Dental pieces of adult humans derived from extractions due to periodontal problems or orthodontic treatment were used. Teeth with fluorosis (n = 11) and without fluorosis (n = 11) were included (beta = 10% and alpha = 5%, maximum error admitted at simple size calculation). From each tooth, 4 blocks were cut, each of one catted parallel to respective tooth surface (vestibular, mesial, palatine-lingual, distal); those little pieces were included into acrylic resin and polished. A Vickers microhardness test was used, consisting in measuring the diagonal length of an indent left by indentation of a diamond pyramid with a given load into the sample material. The F-H relationship was measured with Spearman coefficient (Sp), adjusting by group (fluorosis: yes-no) and by dental surface (palatine/lingual, mesial, distal, vestibular); statistical significance level: p < 0.05. Results: F-H relationship showed statistically associated in the group of teeth with fluorosis (Sp = 0.774, p = 0.009) but not in the group without fluorosis (Sp = 0.249, p = 0.586). Adjusting by dental surface, F-H relationship was statistically significant in fluorosis group (Sp = 0.699, p = 0.024 in mesial side; Sp = 0.964, p = 0.001 in distal side; Sp = 0.701, p = 0.036 in palatine-lingual side and Sp = 0.617, p = 0.077 in vestibular side), but not in the group without fluorosis. Conclusion: Evidence suggested that F-H relationship was statistically significant only in dental pieces with fluorosis, suggesting that dental fluorosis involves a weakening of complete dental structure.