Tooth extraction will always cause bone loss in the extraction site.
When a tooth is removed, functional forces cannot be transmitted to the bone supporting that tooth. Bone loss occurs to conserve resources (to build and maintain bone at the same volume). This is a physiological (natural) phenomenon that keeps our bodies functioning efficiently.
There are techniques to reduce (but not prevent) bone loss (bone grafting) at the time of extraction. Bone grafting using artificial bone does not produce the same volume of native (a continuation of the patient's own jawbone) bone. The biggest advantage to maintaining the natural tooth is that the tooth maintains the surrounding bone and gum. Only tooth movement (through orthodontics i.e. braces) can grow native bone.
Native bone is the best foundation for an implant. Grafted bone is more unpredictable (it can resorb more quickly than native bone) which may cause longer term problems with an implant.
Once an implant has been surgically placed, the same rules of bone physiology and healing apply. All bone injuries (fractures etc) require at least 3-6 months for healing before loading. Therefore, the implant can only receive a crown (the part that is used for chewing) after this healing period.
Natural teeth that have been root-canal treated can be crowned immediately (if the symptoms have cleared up completely). If there are symptoms that require monitoring, a temporary crown may be placed for protection.
