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.
Baastrups sign is an orthopedic and radiographic disorder that often occurs in elderly humans. It is characterized by enlargement of the posterior spinous processes of the lumbar spine, with normal intervertebral disc height and neuroforamina. The reason it is referred to as kissing spine is because the posterior spinous processes kiss and touch one another as the individual goes into lumbar extension, for example when flat on their stomach. The condition has been seen in humans,  canines, particularly with boxer breeds, and certain breeds of horses. This disorder is named after Christian Ingerslev Baastrup. Diagnosis
The salient feature of the disorder is the exuberant osteophytosis that occurs at posterior lumbar spinous processes. Osteophytes are coarse calcifications at the edges of bone that form due to repetitive stress and trauma. There is also atrophy and fatty replacement of paraspinal musculature, which can be detected by CT or MRI. Treatment
The malpositioning seen on radiography may not cause any symptoms at all. If there are related symptoms, however, therapeutic options include chiropractic care, physical therapy and nerve block injections. As a last resort, decompressive laminectomy may be attempted to relieve pain symptoms and remove the abnormally enlarged portions of bone. References


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