It is a bit difficult to tell from the picture but the tooth to which you are referring appears to be a baby tooth. If this is the case, it should fall out and an adult tooth should take its place. Also difficult to tell without an in person oral examination, but it appears that based on the picture and the age you have provided for Dexter, that there are retained baby teeth that should already have fallen out. If Dexter is truly unneutered and this is a procedure you plan on having done at some point, having those baby teeth manually pulled while under anesthesia will likely be in his best interest to avoid any significant dental problems while continuing to grow. Hope this makes sense.