The most traumatic treatment that can be performed on a live tooth is the preparation of the tooth for a crown; Preparing a tooth for a crown in a young patient 20-40 is the most detrimental. I have not placed a crown on a live tooth for a 20,20 or 40 year old in almost 25 YEARS.
If a crown is placed on a vital tooth in a young patient, the chance that the tooth lasts an entire life is very low while the probability of an implant is high. In my practice, the placement of a crown is the dental treatment of last resort, regardless of the age of the patient.
Notice what happened to the tooth when the mercury amalgam was removed. The entire cusp fell off because of expansion and contraction of the metal.
No healthy tooth structure was removed to restore either tooth. One or both of these teeth would have been crowns or onlays in other dental practices.
Do no harm.