THE INFLUENCE OF INTER-IMPLANT DISTANCE ON BONE HEIGHT CHANGES FOR A THREE IMPLANT RETAINED MANDIBULAR TELESCOPIC OVERDENTURE

Introduction: Implant retained mandibular overdentures have improved patient satisfaction and quality of life for completely edentulous patients , that is why it has been the most successful treatment modality for the edentulous mandible. The optimum number of implants to retain an overdenture has been debatable, most studies have recommended installing two to four implants to retain an overdenture. Many authors have reported that three implant retained over denture will provide sufficient support and stability. Bars, studs, magnets, and telescopic coping are attachments to be used to retain mandibular overdentures, many factors should be considered during the selection of the most suitable attachment. Telescopic retainers have offered excellent retention with a splinting effect in addition to providing superior oral hygiene maintenance. One of the important criteria determining the success of an overdenture is the even distribution of stresses to the underlying implants as excessive loads may result in failure of the anchoring implants. Monitoring of bone height changes is therefore mandatory and is most commonly carried out by standardized peri-apical X- rays at different follow up intervals. The aim of this clinical trial is to investigate the effect of the inter-implant distance in a telescopic three implant retained overdenture on the amount of load transfer to the implants which is clinically interpreted by changes in bone height utilizing standardized peri-apical x rays.
Materials and methods: Fourteen completely edentoulous patients have been recruited from the outpatient clinic of the Removable Prosthodontic Department Cairo University. All recruited patients were seeking implant installation in the edentulous jaw to improve retention of their mandibular denture. Patients with contra-indication for implant placement were excluded from the study. All patients received three implants in the mandible in the canine region bilaterally and in the central incisor area, but the interimplant distance of the installed implants varied in the two groups of patients. In the first group of patients all implants were installed with an even interimplant distance of 40mm. While in the second group of patients an uneven distribution of implants with different interimplant distance, on the right side the implants in the canine area and central incisor region had an interimplant distance of 15mm, while on the left side the implant in the left canine region was installed at a 40mm from the implant at the central incisor area. Standardized peri-apical x rays were used to record changes in bone height for the three installed implants in the two groups of patients at the different follow up intervals; day of delivery, after 3 month follow up, after 6 month follow up and after 12 month follow up.
Results: In both groups of patients there has been a decrease in bone height for all implants after a 12 month follow up. In the first group of patients there was no statistically significant difference in the mean bone height changes between the three implants, but the implant in the mid line have shown the greatest changes in bone height followed by the implant in the left canine and the least was the implant in the right side. In the second group of patients there was no statistically significant difference between the two implants in the right side with a 15 mm interimplant distance, while a statistically significant difference in bone height changes was recorded for the implant on the left side with a 40mm interimplant distance showing the greatest changes in bone height followed by the implant in the mid line, and the least was the implant in the right canine. When comparing the mean bone height changes between the two groups of patients after a 12 month follow up, the second group of patients have shown a statistically significant decrease in bone height for all of the three implants, indicating more bone loss encountered in the second group of patients than in the first group.
Conclusion: The interimplant distance plays an important role in the transfer of stresses to the anchoring implants, as the interimplant distance increase so will the lever arm and eventually the moment falling on the implant will also increase, which will lead to bone height changes around the installed implants. All of the bone height changes in the present study after a 12 month follow up were within the physiological limit. Within limitations of this clinical trial it is recommended to install implants with an equal interimplant distance, and avoid implant installation with an increased interimplant distance. More researches with a larger sample size and longer follow ups are recommended to reach to definitive conclusions.