Four to Four-and-a-Half Years Old

The Temporary corner incisors are replaced with permanent incisors, and the last two permanent molars appear on each side of the top and bottom jaw.

At around this time, the male horse starts to grow tushes. By five years old, a horse should have all its permanent teeth.

Six Years Old
The Flat tops of the teeth are called 'tables,' and it is the wear on the tables of the incisors of the lower jaw that is usually studied to determine how old a horse is.

By the time the horse is six years old, three main changes occur on the tables incisors. First, a dark hole called the infundibulum appears on the tables of the horse's corner incisors.

Second a dark brown line appears on the tables of the central incisors; this is called the dental  star. Third, the tables of the lateral incisors show an infundibulum which decreases in size, an between this and  the front of the tooth, a dental star will be found