Stress concentrations at the apex of pinned, implanted teeth.

Stress in the alveolus at the apex is reduced when the implant is held by a pin through the alveolar wall. This stress reduction is effected by transfer of part of the coronal force to the alveolar wall by the pin. Pin positions centrally located between the apex and the alveolar crest provide the greatest reduction of stress concentration in the alveolus at the apex. Since the bone is especially fragile near the alveolar crest, care must be taken when the pin is positioned in this region. Positioning the pin near the apex has the least effect on reducing the stress in the alveolus at the apex. Although no data were obtained relating to stress in the alveolar wall at points of pin penetration, results given here do indicate that from 7 to 30% of the intrusion component of the coronal force is transmitted to the alveolar wall by the pin. Additional research is needed to determine the effects of stress at the pin through the alveolar wall because of load transfer by the pin from the implant to the alveolar wall. The situation in the alveolar wall would be one of creation of a completely unnatural stress rather than reduction of an existing stress, as was the case at the apex. Whether the reduction of stress at the apex and the creation of stress at the pin through the alveolar wall are of physiological benefit is a question that must yet be answered.