DISCUSSION.
Alveolar atrophy may present an anatomical limitation to the placement of endosseous implants. Many osseous augmentation techniques, including bone grafting, use of membranes for guided tissue regeneration,8–10 and RWP, have been used in the treatment of this problem. In these treatments, most techniques described placing implants with sufficient bone height (.10 mm) but insufficient width (,4 mm). The following are the benefits of the RWP compared with other methods:

1. the RWP allows the implant to be placed in a less invasive manner and avoids donor-site morbidity caused by bone grafting;
2. the RWP allows primary implant placement and significantly shortens the treatment time;
3. the RWP allows treatment of narrow ridge location within the context of a routine dental office procedure.

The split-crest technique, applied in the present case, was an RWP introduced by Simion et al. They showed that a preoperative ridge width between 1.5 mm and 3.0 mm had a postoperative ridge width gain between 1 mm and 4 mm after a healing period of six months.
Most RWPs associated with immediate implant placement have used expanded polytetrafluoroethylene membranes or polyglactin 910 mesh for guided tissue regeneration. Although the possible benefits of guided tissue regeneration have received considerable attention in previous studies, the use of a membrane always increases the risk of complications, such as infections, painful inflamed tissues, and disrupted wound healing. In addition, various studies have reported complication rates of 20% to 50% when using membranes. In RWPs associated with immediate implant placement, the primary wound closure is generally more difficult compared with that of a standard implant placement and the risk of membrane exposure increases because the natural crest is dramatically augmented. For these reasons, we treated five atrophy cases, including the present one, without the membrane technique. Subsequent wound healing and osseointegration of the implants were uneventful. Furthermore, the reason for successful regeneration surrounding the implant without the membrane technique may be attributed to the small size and tapered shape of the implant, which is a beneficial shape to gradually widen a split crest. Only a small percentage of fusiform defects are made by the splitting process. In a small percentage of defect cases, the membrane is not essential for bone regeneration.
In their study of RWPs, Duncan et al described a higher success rate with a cylinder implant compared with a screw implant because the cylinder type was tapped into position and was easier to use. The Endopore (Innova) implant system also uses a tapping method when placed into bone. In addition, its tapered implant shape is believed to be a factor for an increased success rate. These factors suggest that the Endopore (Innova) implant system may be more appropriate for ridge widening procedures associated with immediate implantation.

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