Wolf tooth

Wolf teeth are small, peg-like horse teeth, which sit just in front of (or rostral to) the first cheek teeth of horses and other equids. They are vestigial first premolars, and the first cheek tooth is referred to as the second premolar even when wolf teeth are not present. Torbjörn Lundström in Sweden reported that about 45-50% of 25000 horses had wolf teeth. They are much less common in the mandible (lower jaw) than the maxilla (upper jaw) although mandibular wolf teeth are found very occasionally.
They do not have any deciduous precursors, but they may themselves be deciduous, as it is believed that they are often shed when the deciduous 2nd premolar is shed at around two and a half years of age. They may also be knocked out by the bit if particularly loose, and can certainly be extracted accidentally, either partially or whole, when routine equine dentistry is performed.
In size they are extremely variable from being small pegs only 3 mm in diameter to having roots up to 2 cm long. In a small number of cases they may be "molarized" with a distinct irregular rim of enamel. It is impossible to gauge the size of the root from an examination of the crown, except to say that if the crown is mobile it is very unlikely that there is a large intact root.
There is dispute as to the average time of eruption with different authors suggesting different times. All authors who have performed any type of rigorous study suggest that they erupt between birth and 18 months although most say 6–9 months.
Where there are two wolf teeth next to each other, it is very likely that one is a fragment of the deciduous 2nd premolar.
Blind wolf teeth.
Blind wolf teeth are wolf teeth that are present but may not have erupted through the gum. They may remain completely underneath the gingiva. A good rule that holds true in most cases is:
This is shown in the diagrams below where 106 and 406 are the second premolars according to the Modified triadan system and WT is the wolf tooth. The pink layer is the gum.
How wolf teeth might cause problems.
Normal wolf teeth without pathology are not inherently painful to a horse which does not have a bit in its mouth. Equally certain is that there are cases where wolf teeth do cause significant problems to horses because of their interaction with the bit.
There are four mechanisms which have been postulated by which wolf teeth may cause discomfort. It is probable that all four of these mechanisms are possible in different cases.
Assessing which wolf teeth should be removed.
There is a school of thought which says that all ridden horses' wolf teeth should be extracted, because if they are removed then they cannot cause problems, and it is not a major surgical procedure. With the wolf teeth removed, it is also easier to put in a proper bit seat. There is another school of thought which believes that wolf teeth should be assessed and removed when they are likely to be causing a problem. Very few vets or equine dental technicians subscribe to the belief that they are never a problem. Certainly it is useful to assess wolf teeth because some horse owners are reluctant to have them removed unless they are very likely to be causing problems. 
The following factors are useful in making an assessment: