these lost roots? Something had to be designed to maximize the intrabony portion of the metal of the implant to the minimal amount of bone that is usually available in areas where the teeth were missing for various lengths of time. Most of the designs of the blades contact more bone on only one of their surfaces than most of the roots of teeth contact when in bone. Secondly, where the tooth root contacts bone only on its outer surface, the blade contacts bone on two of its broad surfaces. Thirdly, the blades have openings to allow for regeneration of bone, which gives it further retention and in most instances there is much more alveolar bone flanking the blade buccally and lingually than there exists around natural teeth and acts as stronger butresses against lateral force displacements.

Nature made a mistake in having a minimum amount of bone flanking our teeth in both jaws labially and buccally and a maximum amount of bone flanking the teeth lingually and palatally where the bone is least needed. Thus, when teeth are lost periodontally they are lost at the expense of the labial and buccal plates of bone, rarely from the palatal or lingual plates. To potentiate this occurrence all concavities existing in both jaws exist on the buccal and palatal sides bringing the bone even closer to the teeth labially and buccally. The blade being so thin bucco-lingually allows a maximum amount of bone to flank it buccally and labially especially when the blade is inserted nearer to the lingual.

This does not mean that all those patients who are completely edentulous require implants. Many people are perfectly satisfied with removable prostheses. However, there are three basic types of people today who can only function with implants.

The first category are those patients who cannot have well fitted removable appliances fabricated because of extreme anatomical and morphological conditions due to loss of bone, high muscle attachments, dehiscencies of the mental foramina and mandibular canals.

The second type of patients are those who psychologically cannot tolerate covering the entire palate with a conventional denture or a lower removable prosthesis with a lingual bar and clasps involving often innocent teeth on the other side of the arch.

Thirdly, there are those patients exhibiting enough bone and healthy tissue to function well with removable dentures who visit their dentists and demand that either they insert implants or refer them to someone who will insert the implants so they can have fixed rather than removable prostheses.

I have never attributed a failure of any implant to electrogalvanic action, metal transfer, or rejection, other than to an improperly designed

xv