Overdenture attachment selection and the loading of implant and denture-bearing area. Part I: In vivo verification of stereolithographic model

Preliminary to a study investigating the force transfer from osseointegrate d dental implants to the surrounding bone via various types of overdenture attachment, a stereolithographic model (SL-model) was constructed and compa red to an in vivo situation in order to confirm the validity of the modelin g technique for the planned measurements of implant strain and denture-bear ing area loading. The SL-model was generated using the patient's computer t omographic data and duplicated in a material of known elastic properties. T he model was fitted with sensors to measure strains in the peri-implant bon e and loading forces within the posterior mandibular bone, i.e. the denture -bearing area of the mandible. Special telescopic copings were constructed to measure implant strain in this model as well as in vivo. Using these cop ings under identical overdenture loading conditions, the strains measured a t the implants in vivo and in vitro were the same and never exceeded a tole rance of two standard deviations or a mean difference of -8.5% of the in vi tro value. This indicates that the model was reliable for the measurement o f implant strain. Denture-bearing area loading within the alveolar ridge ca nnot be measured in vivo. Instead, a method of extrapolating in vivo dentur e-bearing area loading figures from implant strain readings was developed a nd tested (better than 90% accuracy). These in vivo extrapolated figures we re then compared to in vitro readings under otherwise identical loading con ditions. The result indicated that the SL-model is reliable for measurement s of denture-bearing area loading with an error of 10 to 20%.