No, you do not need a visa to travel to Mexico for dental implants if you are a citizen of the United States or Canada. Mexico allows Americans and Canadians to enter freely as tourists for stays up to 180 days, and this includes visiting for dental care. All you need is a valid passport and the simple tourist entry form you receive upon arrival by air or at the land border.
When you enter Mexico, the immigration officer will stamp your passport and give you permission to stay as a tourist. This is all that is required for dental treatment, whether you are coming for a quick three day visit for a crown or a longer stay for an All on X procedure. Just remember that although no visa is required, you must keep your entry document and passport safe because you will need them when you return to the United States or Canada.