A wide range of different surgical techniques are applied when placing implants under different preconditions. The summaries below show that one- and two-stage surgery, immediate placement in extraction sockets, bone augmentation and sinus lift can be successfully and predictably performed using the Astra Tech Implant System'".
Local sinus lift for single-tooth implant. I. Clinical and radiographic follow-up
Frequently patients seeking implant reconstruction to replace missing maxillary premolar and molar dentition require sinus augmentation to overcome problems related to inadequate bone height to the floor of the sinus. Typically this involves a large lateral window access for elevation of the Schneiderian membrane and grafting of the extra-sinusoidal space. For replacement of single missing premolars and molars such large access is neither necessary or practical.
Purpose: To present a local sinus elevation technique with autogenous bone in a 1-stage approach. And to present radiographic volume changes in the grafted area after 2 years.
Materials and Methods: Seven premolars and 11 molars requiring replacement in 20 systemically healthy patients, who reported no history of sinusitis, were undertaken using a local sinus lift. Standardized intra-oral radiographs were taken pre-operatively to confirm a bone height of >2 mm< 5 mm to the floor of the sinus.
Recipient sites were exposed through reflection of a full mucoperiosteal flap to allow a small circular window to be prepared over the sinus for access to elevate the Schneiderian membrane. At the same time an osteotomy was prepared through the crest of the ridge using a standard protocol for the insertion of a single Astra Tech OsseoSpeed'" 4.5 or 5.0 mm 0 implant. Implants were 13 mm to 17 mm in length and acted as a tent pole for the membrane. Bone was collected during lateral window and osteotomy preparation using a disposable Bone Trap" (Astra Tech) and this bone used to pack into the extra-sinusoidal space around the apex of the implants. A cover screw was placed and flaps repositioned and sutured for primary closure and submerged healing. Implants were exposed after 6 months and subsequently restored using conventional crown therapy. Follow-up radiographs were taken at exposure, and at 1- and 2-years post-op. Radiographs were digitized through image capture and evaluated using a picture analysis system to determine the total vertical bone height (VBHT) at each implant irrespective of the relation of the crest of bone to the implant.
Results: There was a 100% survival of all implants at the 2-year review. The mean baseline VBHT was 5.8 + 1.3 mm. Immediately after bone grafting and implant insertion the VBHT measured 13.0 + 1.8 mm. At the 1-year review VBHT measured 11.4 + 3.6 mm, while after 1.5 years of functional loading (2 years post-op) the VBHT measured 10.6 + 2.1 mm giving a net loss of mean loss of VBH of 3 mm over the 2-year period. The mean marginal bone level relative to the implant reference point was -0.83 + 0.77 mm suggesting the majority of change in VBHT occurred at the apical level within the graft. The changes in VBH were statistically significant from baseline to 1-year as well as from the 1- to 2-year follow-up, p < 0.01.
Discussion and Conclusions: The use of single-tooth implants is today considered the more conservative approach to tooth replacement when adjacent teeth are free of restorations. Unfortunately in the posterior maxilla placement is often made fraught by a pneumatized sinus limiting the available bone height. Historically for multiple implants the lateral window approach for sinus elevation and grafting has been employed while internal sinus tenting has also been presented in the literature, although this technique is more difficult to control with respect to preventing rupture of the membrane.
In the current study a localized lateral window-type technique is described at the same time as osteotomy preparation and implant placement. The need for implants longer than 13 mm remains open to debate and further research but for the purpose of the current study longer implants were utilized necessitating as much as 7-8 mm gain of vertical bone height. This was achieved by using bone collected at the time of surgery using a disposable Bone Trap", which proved most effective in the collection of the bone debris.
Nonetheless the volume of bone was not enough to completely fill the space under the tented membrane and it is proposed that this space has the potential to form new bone de novo under the elevated membrane. In this respect it was observed that when steep sinus walls exist close to the site of the implant, both elevation and tenting of the membrane as well as bone filling was more predictable. The loss of bone height was seen to occur around the apex and is likely due to sinus pressure bearing down on the graft. This might support the use of longer implants, which have been shown to give rise to higher survival rates in sinus grafted sites.
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