A parathyroid adenoma is a benign tumor of the parathyroid gland. It generally causes hyperparathyroidism; there are very few reports of parathyroid adenomas that were not associated with hyperparathyroidism.A human being usually has four parathyroid glands located on the posterior surface of the thyroid in the neck. In order to maintain calcium metabolism, the parathyroid glands secrete parathyroid hormone (PTH) which stimulates the bones to release calcium and the kidneys to reabsorb it from the urine into the blood, thereby increasing its serum level. The action of calcitonin opposes PTH. When a parathyroid adenoma causes hyperparathyroidism, more parathyroid hormone is secreted, causing the calcium concentration of the blood to rise, resulting in hypercalcemia. Signs and symptoms
The first signs of a parathyroid adenoma and the resulting primary hyperparathyroidism can include bone fractures and urinary calculi such as kidney stones.Often, a parathyroid adenoma is diagnosed by an incidental finding on blood tests that reveal high calcium levels. Patients may not be experiencing any noticeable symptoms but could be producing excessive amounts of calcium and eventually experience problems later in life if untreated. However, if symptomatic, patients can experience: pain or discomfort in the joints, muscles, and abdomen; depression and mood changes due to the hormonal imbalance. ; constipation; exhaustion; and kidney damage. Genetics
Parathyroid adenoma can be associated with overexpression of the cyclin D1 gene. It is also associated with multiple endocrine neoplasia (MEN). Diagnosis
Hyperparathyroidism is confirmed by blood tests such as calcium and PTH levels.
Dens invaginatus (DI), also known as tooth within a tooth, is a rare dental malformation where there is an infolding of enamel into dentine. The prevalence of condition is 0.3 - 10%, affecting more males than females. The condition is presented in two forms, coronal and radicular, with the coronal form being more common. DI is a malformation of teeth most likely resulting from an infolding of the dental papilla during tooth development or invagination of all layers of the enamel organ in dental papillae. Affected teeth show a deep infolding of enamel and dentine starting from the foramen coecum or even the tip of the cusps and which may extend deep into the root. Teeth most affected are maxillary lateral incisors (80%), followed by maxillary canines (20%). Bilateral occurrence is not uncommon (25%). Signs and symptoms
Tooth affected by this condition has a higher risk of developing caries and periradicular pathology. The thin layer of the infolding enamel could be chipped off easily, providing entrance for microorganisms into the tooth canal. This can cause abscess formation, displacement of dental structures (i.e. teeth). Preventive measures should be taken. Cause
Cause of DI is unclear. However, there are several theories:

Infection
Trauma
Growth pressure of the dental arches during odontogenesis
Rapid proliferation of the internal enamel epithelium invades the underlying dental papilla

Diagnosis
During clinical examination, abnormally shaped tooth can be observed. Teeth with this condition can have a conical shape or deep pit on the lingual side or have an exaggerated talon cusp.