Over erruption of lower anterior teeth is a problem common to "middle aged teeth". As anterior teeth wear they can compensate for the wear by slowly errupting. Teeth tend to 'want to remain' in contact with opposing teeth and can errupt until they meet them. As the lower teeth wear they become shorter and shorter and this can pose a problem to a restorative dentist. Patients with worn teeth desire longer teeth but often there is no room for the dentist to allow a lab technician to fabricate longer restorations.
Dentists have a number of different options that they can use to create this room, such as opening a patients bite (restoratively or orthodontically) or possibly sending a patient for crown leghtening surgury(removing supporting bone around a tooth in order to expose more tooth in the mouth)
Recently, I have been contemplating using Invisalign retainers to solve this issue, since in my experience Invisalign can predictably intrude lower anteriors about 1.5 mm. Many patients with worn lower anteriors that have extruded would be extremely pleased if their lower anteriors could be moved down (intruded) a little and then lengthened with bonding or bonded porcelain restorations. I look forward to trying this strategy out since it is less invasive and expensive than some of the other methods that I have previously employed to solve this esthetic problem.