Modifying Existing Bone Volume
These involve manipulation of the existing native bone to facilitate expansion of the volume. Expansion can be achieved by any one of the following methods:
Ridge Expansion Osteotomy
Alveolar Ridge Split Technique
Alveolar Ridge Expansion by Osseodensification
These techniques eliminate the need for a second surgical site and facilitate implant placement simultaneously. If the bucco-lingual dimension of the edentulous ridge planned for implant is ≥3 mm but <6 mm, horizontal augmentation of the existing ridge can be performed using these approaches.32 Having ≥3 mm of bone at the site ensures presence of a cancellous core of bone which lends itself to expansion and distraction without fracture.32
Ridge Expansion Osteotomy techniques focus on slowly expanding the bone during implant osteotomy, thus increasing the horizontal dimension simultaneous with implant placement. This technique was first introduced by Summers et al in 1994 and the expansion was achieved by the use of special instruments called osteotomes.33 Expansion osteotomes are used with progressive increase in diameter until desired expansion is achieved and implants are inserted simultaneously. This approach not only helps create required bone volume to anchor the implant but also condenses bone laterally, thus improving bone quality surrounding the implants.34 Studies have shown bone width gain between 3.5 and 3.9 mm using this method.30
Alveolar Ridge Split (ARS) Technique, introduced by Nentwig et al. in 1986, involves splitting the ridge using chisels and mallets with / without inter-positional bone graft. Advantages such as possibility of simultaneous implant placement, avoiding donor site, reducing morbidity and shortening treatment time have all been associated with this approach.35,36 Modifications to this procedure have been made with the use of rotary and oscillatory instruments and surgical ultrasonics.36 Studies have shown that the overall implant survival rate was 97%, and the average gain in alveolar bone thickness was 3.8 mm, regardless of the type of surgical instruments used.36
A. Alveolar ridge split osteotomy at edentualous site using piezo inserts.
B. Implants placed in desired position simultaneously.
Distraction Osteogenesis can be used to reconstruct larger bone defects. It is a technique that involves repositioning a bony block segment to improve vertical dimension in select cases but may also be used to augment horizontally. To mobilize the bone block segment, two vertical and one horizontal cut is made into the bone.37 The segment is then moved to the desired position gradually and the bone is given time to heal, filling in the gaps.37,38 There is a latent period of 7 days to allow for initial soft tissue healing.38 Following this is the distraction phase in which the two pieces of bone undergo incremental separation at a rate of 0.5 to 1 mm per day and a consolidation phase of 6 to 12 weeks which allows the bone to regenerate.38 Distracting devices can be either intraosseous, within the bone, or extraosseous, attached outside the cortical bone.38 There are certain factors which limit the success of this procedure, such as a minimum of 6 to 7 mm of bone height must be present above vital structures such as nerves or sinuses.39 In addition, the defect size should be 3 to 4mm and should span at least 3 teeth.39 The adjacent teeth should not have large vertical defects, as these are used as reference points and may limit the amount of vertical gain achievable.38,39 A systematic review and meta-analysis by Zhao et al. showed that a vertical gain ranging from 4-20 mm and on average 7.92 mm could be achieved.40
Alveolar Ridge Expansion by Osseodensification is a more recent expansion technique developed by Huwais et al.41 in 2015 in which special drills, called Densah burs, were designed to cut in reverse. This method allows for bone preservation through slow plastic deformation of the native bone.41 Through reverse drilling of the special burs, autografting particles are formed and present along the inner surface of the osteotomy. This condensed autograft around the implant increases the bone density and the primary stability of the implant.41,42 Using the osseodensification technique, patients with an alveolar ridge width of 3-4 mm, 5-6 mm, and 7-8 mm, showed 75%, 27%, and 17% increase in bone width, respectively.42 Overall, the procedure has been shown to increase the bone width by 2- to 3-fold, and provides stability for implants, resulting in double the insertion torque.42