Etiology
The pulp calcifications can arise due to:

pulp degeneration
increasing age
circulatory disturbances within the pulp
long standing local irritants such as dental caries, pulp-capping procedures, healed tooth fractures, tooth injury restorations and periodontal diseases
orthodontic tooth movements
transplantation of teeth
traumaIt is shown that pulp stone occurring in adolescents is significantly associated with carious and/or restored teeth, which suggests a causative relationship of chronic pulp irritation to pulp stone formation. A defence reaction in the pulpodentinal complex may be triggered by caries and microleakage around restorations which lead to pulp calcifications. The formation of pulp stone may have a similar mechanism as the tertiary dentine formation near the irritated odontoblasts. Apart from that, with aging, the pulp decreases in size due to the deposition of secondary or tertiary dentine. This subsequently results in favourable conditions for the formation of pulpal calcifications. The other reported etiologic factors also include:

idiopathic factors
consumption of fluoride supplements
hypervitaminosis D
a possible genetic predisposition such as dentinogenesis imperfecta and dentinal dysplasia

Types/classification
Pulp stones can be classified based on different location and structure. Based on location, they can classified into free, embedded and adherent pulp stones. Free pulp stones are found within the pulp tissue and is the most common encounter. The size vary from 50μm in diameter to several millimetres and may occlude the entire pulp chamber. Embedded pulp stone is fully embedded in dentine and most commonly found in the apical portion of the root. Adherent pulp stones are attached to the wall of pulp space but not fully enclosed by dentine.
Besides cardiovascular disease, other disease such as end stage renal disease, Marfan syndrome, Ehlers-Danlos syndrome, Calcinosis universalis, tumoral calcinosis  are also discovered to be in association with pulpal calcifications.Several genetic diseases such as dentin dysplasia and dentinogenesis imperfecta are also accompanied by pulpal calcifications and hence, Marfan syndrome was suspected to be in association with pulp stones due to abnormal dentin formation, leading to the increased frequency of pulpal calcifications in these individuals. Another theory suggests that individuals with Marfan syndrome have connective tissue dysplasia or vascular defects which in the case of tooth pulp, endothelial rupture of the pulp arterioles will lead to hemorrhagic areas in the pulp. It was proposed that these hemorrhagic areas in the pulp will induce mineralization within the pulp. Prevalence
Pulpal calcifications can be developed throughout the life and prevalence rates from 8–9% in worldwide population had been reported in studies. It was also found that pulpal stones occurred most frequently over the fourth decade, in advancing age. Generally, pulp stones are more frequent to be found in maxillary teeth compared to mandibular teeth. A study in Australia resulted higher occurrences of pulp stones in molars as opposed to premolars, and first molars as opposed to second molars. First molars which were restored and/or with caries showed a higher incidence of pulp stones as compared to intact, unrestored first molars. Clinical implications
Pulp stones generally do not have significant clinical implications as they are usually not a source of pain, discomfort or any form of pulpitis.