Since odontoblasts are present, a stimulus, such as caries, can trigger a biologic response. These defense mechanisms include the formation of sclerotic and tertiary dentin.In dentin from the deepest layer to the enamel, the distinct areas affected by caries are the advancing front, the zone of bacterial penetration, and the zone of destruction. The advancing front represents a zone of demineralized dentin due to acid and has no bacteria present. The zones of bacterial penetration and destruction are the locations of invading bacteria and ultimately the decomposition of dentin. The zone of destruction has a more mixed bacterial population where proteolytic enzymes have destroyed the organic matrix. The innermost dentin caries has been reversibly attacked because the collagen matrix is not severely damaged, giving it potential for repair. Sclerotic dentin
The structure of dentin is an arrangement of microscopic channels, called dentinal tubules, which radiate outward from the pulp chamber to the exterior cementum or enamel border. The diameter of the dentinal tubules is largest near the pulp (about 2.5 μm) and smallest (about 900 nm) at the junction of dentin and enamel. The carious process continues through the dentinal tubules, which are responsible for the triangular patterns resulting from the progression of caries deep into the tooth. The tubules also allow caries to progress faster. In response, the fluid inside the tubules brings immunoglobulins from the immune system to fight the bacterial infection. At the same time, there is an increase of mineralization of the surrounding tubules.
Ethinylestradiol/norethisterone (EE/NET), or ethinylestradiol/norethindrone, is a combination birth control pill which contains ethinylestradiol (EE), an estrogen and norethisterone (NET), a progestin. It is used for birth control, symptoms of menstruation, endometriosis, and menopausal symptoms. Other uses include acne. It is taken by mouth. Some preparations of EE/NET additionally contain an iron supplement in the form of ferrous fumarate.Side effects can include nausea, headache, blood clots, breast pain, depression, and liver problems. Use is not recommended during pregnancy, the initial three weeks after childbirth, and in those at high risk of blood clots. It, however, may be started immediately after a miscarriage or abortion. Smoking while using combined birth control pills is not recommended. It works by stopping ovulation, making the uterus not suitable for implantation, and making the mucus at the opening to the cervix thick.This combination pill was approved for medical use in the United States in 1964. It is on the World Health Organizations List of Essential Medicines. It is available as a generic medication. It is marketed under a large number of brand names. In 2020, it was the 45th most commonly prescribed medication in the United States, with more than 14 million prescriptions. See also
Mestranol/norethisterone
Oral contraceptive formulations
List of combined sex-hormonal preparations


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