2007 年 20 巻 4 号 p. 644-650
Reports addressing the advantages of immediate and early implant placement in extraction sockets have been increasing in number. The majority of them, however, are centered on surgical procedures, and there have been few reports focusing on longitudinal implant stability. In this study, changes in bone levels on both mesial and distal aspects of each implant in an extraction socket were monitored radiographically for assessment of implant stability. During the period from May 2002 to October 2003, a total of 36 implants were placed in 30 healthy, non-smoking patients (7 males and 23 females). Average patient age at surgery was 51.0 years (range: 20 to 78 years). Of 36 implants, 27 were immediate and 9 were early implants. These implants were followed up for at least 3 years, including clinical and radiographic assessments at the time of implant placement, final restoration and each maintenance recall. Both immediate and early implants showed favorable clinical and radiographic findings at all recalls. In the 3-year follow-up period after final restoration, marginal bone resorption was found around every implant. However, in no case did the resorption reach the border between the smooth and SLA (Sand-blasted, Large-grit and Acid-etched) rough surfaces of the fixture. The bone resorption over time was evaluated by means of Tassay, and the results were compared in terms of immediate/early placement and insertion depth. The insertion depth was classified into 3 levels in reference to the adjacent alveolar crest (Level 1:the part of the implant fixture between the smooth/rough border and implant shoulder is placed at the alveolar crest; Level 2: the implant shoulder is level with the alveolar crest; and Level 3: the implant shoulder is placed below the alveolar crest). No significant difference in bone resorption was found between immediate and early implants. As for the bone resorption relative to insertion depth, significant differences were found between Level 1 and Level 2 (p＜0.01 at Year 1, 2 and 3)and between Level 1 and Level 3 (p＜0.01 at Year 1 and p＜0.05 at Year 2 and 3). In this study, implants placed at the insertion depth of Level 1 showed least bone resorption at all assessment periods, and the resorption after 3 years was within the biological dimensions like the natural dentition, thus a favorable long-term prognosis for this approach was indicated.
