Schulge (1987) classification, teeth falls into 5 categories according to the location of the tubercles 
Tubercle on the inclined plane of the lingual cusp
Cone-like enlargement of the buccal cusp
Tubercle on the inclined plane of the buccal cusp
Tubercle arising from the occlusal surface obliterating the central groove
Laus classification, divide teeth into groups according to their anatomical shapeSmooth
Grooved
Terraced
Ridged
Oehlers classification, teeth categorized depending on the pulp contents within the tubercle (histological appearance of the pulps were examined)Wide pulp horns (34%)
Narrow pulp horns (22%)
Constricted pulp horns (14%)
Isolated pulp horn remnants (20%)
No pulp horn (10%)
Hattab et al. classificationAnterior teeth
Type 1 - Talon, a well defined additional cusp that projects palatally and extends at least half the distance from the cementoenamel junction (CEJ) to the incisal edge
Type 2 - Semitalon, an additional cusp that extends less than half the distance from the CEJ to the incisal edge
Type 3 - Trace talon, prominent cingula
Posterior teeth
Occlusal DE
Buccal DE
Palatal DE/ Lingual DE

Management
If the tooth involved is asymptomatic or small, no treatment is needed  and a preventative approach should be taken. Preventative measures include:

Oral hygiene instruction
Scaling and polishing
Application of topical fluoride on reduced cusp
Application of fissure sealant
Frequent dental check-up, pay extra attention to fissures
Perform direct or indirect pulp capping in cases with pulpal extension, to try increase the rate of reparative dentin formation (but may result in obliteration of the canal)
Seal exposed dentin with microhybrid acid-etched flowable light-cured resin
Perform pulpotomy with MTA using a modified Cvek techniqueFor teeth with normal pulp and mature apex, reduce the opposing occluding tooth.
There is literature indicating that DE is an isolated anomaly. During the bell stage of tooth formation, DE may occur as a result of an unusual growth and folding of the inner enamel epithelium and ectomesenchymal cells of dental papilla into the stellate reticulum of the enamel organ. Diagnosis
Diagnosis of DE can be difficult when there is no signs and symptoms of necrotic or infected pulp. It is a challenging task to differentiate between a true periapical lesion and a normal periapical radiolucency of a dental follicle of an immature apex. Pulp tests (test results of immature teeth can be misleading, as they are known to give unreliable results)
Check and see if there is an elevated, flat wear facet on the occlusal surface of the tooth
Test cavity which has an absence of pain sensation and has an empty pulp chamber/ canal. Radiographs (usually periapical) - a V-shaped radiopaque structure could be seen superimposing on top of the affected crown. It could detect DE before tooth eruption. However, DE presentation on the radiograph can be quite similar to a mesiodens or a compound odontoma. Classification
The anterior DE tubercles have an average width of 3.5mm and length of 6.0mm, while posterior tubercles have an average 2.0mm in width and length of up to 3.5mm. If the cusp of Carabelli is present, the tooth associated are often larger mesiodistally and it is not uncommon that a DE involved tooth has an abnormal root pattern.There are 4 different ways to classify/ categorize DE involved teeth.