The authors’ experience in the medium term.
According to the current scientific literature, a prosthetically-guided approach should be the first choice for implant placement, even in case of horizontal/vertical alveolar bone resorption. In the last decade, different reconstructive techniques were described with the aim of restoring bone volume.
Among the available techniques, the authors widely experienced and achieved very satisfactory clinical outcomes with the “Edentulous Ridge Expansion” (E.R.E.), introduced by Dr. Bruschi and Scipioni in 1994.
This technique relies upon the healing potential of the spongy bone, associated with the elevation of a partial thickness flap to preserve the periosteum. The intra-bony gap is initially filled by a blood clot that turns into osteoid tissue in about 40 days. After about 90-120 days, the extracellular matrix progressively mineralizes and the osteoblasts mature into osteocytes.
In this technique, the preservation of an optimal trophism of the bone is paramount, leaving a thickness of at least 1-1.5 mm to the buccal bone; an extensive periosteal blood supply is required as well. This approach limits the risk of fenestrations, dehiscences or necrosis of the buccal bone during implant insertion and healing.
The E.R.E. technique is suitable in case of knife-edge alveolar ridges with at least a height of 10 mm and a width of 4 mm. Its main drawback is the risk of fracture during the displacement of the buccal bone plate; therefore, its predictability is not absolute. Such risk can be limited using a partial thickness flap, in order to ensure a better cortical blood supply in case of fracture.
If, on the one hand, a partial thickness flap is advisable, on the other hand, periosteal preservation does not allow to associate bone regeneration techniques that may be required during surgery, especially when a prosthetically-guided implant positioning is aimed. For this purpose, in recent years, the authors have developed a modified split-crest technique associated to a contextual guided bone regeneration (GBR), in order to compensate any dehiscence and/or fenestration, minimize the marginal bone loss and fill the gap between bone and implant. This approach is particularly important in the esthetic zone, where the stability of the buccal bone is critical for the success.
In a systematic review of the literature (Donos et al., 2008), the survival rate of implants placed in sites augmented with the split-crest technique ranged from 86.2 % to 100% after 12 months to 5 years in different studies. The success rate of the split osteotomy, measured as the achievement of adequate ridge dimensions for placement of implants, varied from 87.5% to 97.8% from 18 to 20.4 months post-loading, respectively.
The present article aimed at analyzing the clinical factors influencing the reliability of the split-crest technique as well as discussing its limits and rationale by the presentation of two clinical cases.
The technique: rationale and anatomic considerations
Comparing an atrophic ridge with its normal anatomy in sagittal view (Fig. 1), it can be noted that the bone volume is evidently resorbed, particularly on the buccal side. Differences in bone resorption rates between the buccal and lingual aspects are due to the greater amount of bundle-bone present on the buccal side of the alveolar ridge. The bundle-bone is strictly related to the presence of teeth, so a greater resorption rate occurs on the buccal aspect after tooth loss (Araujo & Lindhe 2005).
Frequently, in edentulous ridges an hourglass shaped alveolar process is found, due to the presence of an undercut at the base of the ridge. This anatomical peculiarity should not be underestimated in case of implants in the esthetic zone, as the drills can create fenestrations in the apical part of the implant site. Small fenestrations are not a big issue for osseointegration but can affect the achievement of optimal soft tissues esthetics, resulting in a grayish tissue transparency, particularly unpleasant in the anterior maxilla.