Background and Objectives: Progesterone and estrogen modify the bone metabolism directly related to the periodontium, this study aimed at answering the question whether fluctuations in the levels of these hormones or the use of their synthetic equivalents in modern contraceptives have a significant impact on the natural tooth mobility (TM) in its alveolus. Materials and Methods: Sixty healthy women who had never been pregnant and when interviewed reported either (1) having regular menstruations every 28–30 days or (2) taking oral two-phase two-ingredient hormonal contraceptives formed, respectively, groups M and S in the study. TM evaluated as the Periotest value (PTV) was checked in the menstruation, ovulation, and luteal phases of the menstrual cycle (group M) and on the days corresponding to the moment of the menstrual cycle in group S. Results: Although the PTV-s were within the limits of norm, the canines and the molars were always more stable than the other teeth. In group M, the TM was statistically comparable (p > 0.05) in the menstrual and ovulation phases, thus significantly increased (p < 0.001) in the luteal phase. The TM remained constant (p = 0.758) in all studies in group S. The results demonstrated that the canines and the molars in the luteal phase were significantly more mobile in group M than in group S (p < 0.001), although increased mobility of the teeth in group M affected the canines and the first molars to a significantly lesser degree than the other teeth. Conclusions: However, since women between 20 and 30 years old constitute the majority of ortho-dontic patients, possible determination of the optimum moment of force application in relation to the sex hormones cycle, namely, to its luteal phase, is clinically very promising.

Recently (Int.Journ.Mod.Phys. D27 (2018), 1847025) an interesting property of closed light rings in Kerr black holes has been noticed. We explain its origin and derive a slightly more general result.

Recently (Int. J. Mod. Phys. D 27 (2018) 1847025) an interesting property of closed light rings in Kerr black holes has been noticed. We explain its origin and derive a slightly more general result.