The facilitation of eruption of the second permanent molars to the space of the first permanent molar removes the burden of continuous restorative treatment.A favourable occlusion may be acquired following a well-planned treatment and this eliminates the need for fixed orthodontic appliances therapy. However, a comprehensive discussion of the possible need of orthodontic sequelae and treatment is important.Favorable eruption position of the second permanent molar may result if the first permanent molar is extracted when the child is at the age of between 8–10 years old. This is when the crown formation of the second permanent molar is complete and the mineralization of the bifurcation is commenced.Extraction of first permanent molars before 8 years old increases the chances of the unerupted second permanent premolar drifting distally. Extraction after the age of 10 years reduces the likelihood of the mesial movement of the second permanent molar in to the first permanent molar space and may result in tilting of the second permanent molar. Epidemiology
Since first recognised in the late 1970s, the condition has puzzled many people. It is thought to be a unique defect unlike other enamel disturbances e.g. fluorosis or amelogenesis imperfecta.Many prevalence studies have now been published from findings across the globe. However, there is a large amount of variation across the results of these studies. It is reported that the prevalence of MIH ranges from 3.6% to 40.2%  with an estimate of 14.2% of the global population suffering.
The definition of an ectopic pregnancy is a pregnancy outside the uterine cavity, not outside the uterus, as the interstitial pregnancy is still a uterine pregnancy. Diagnosis
Early diagnosis is important and today facilitated by the use of sonography and the quantitative human chorionic gonadotropin (hCG) assay. As in other cases of ectopic pregnancy, risk factors are:  previous tubal pregnancy, IVF therapy, tubal surgery, and a history of sexual infection. Typical symptoms of an interstitial pregnancy are the classic signs of ectopic pregnancy, namely abdominal pain and vaginal bleeding. Hemorrhagic shock is found in almost a quarter of patients. ; this explains the relatively high mortality rate. In pregnant patients, sonography is the primary method to make the diagnosis, even when patients have no symptoms. The paucity of myometrium around the gestational sac is diagnostic, while, in contrast, the angular pregnancy has at least 5 mm of myometrium on all of its sides. Ultrasonic criteria for the diagnosis include an empty uterine cavity, a gestational sac separate from the uterine cavity, and a myometrial thinning of less than 5 mm around the gestational sac; typically the interstitial line sign—an echogenic line from the endometrial cavity to the corner next to the gestational mass—is seen. MRI can be used particularly when it is important to distinguish between an interstitial and angular pregnancy. On average, the gestational age at presentation is about 7–8 weeks.