**6. Distraction osteogenesis**

*Oral and Maxillofacial Surgery*

bone gain [2, 49, 53].

**5.2 Transalveolar approach**

perforations. Separate windows can be prepared, if necessary. Healthy Schneiderian Membrane is usually 1 mm thick. Thickness of the sinus membrane should be examined and pathological conditions must be treated before the surgery if present. In the presence of active sinus infection, neoplasmic lesions, uncontrolled diabetes,

The augmented site is very well vascularized through surrounding sinus walls and Schneiderian Membrane, therefore it shows high success rates in terms of bone volume gain. Grafting is possible with various bone graft types. Graftless approach and grafting the site with highly degradable materials like collagen sponges or PRF is also possible but pneumatization of maxillary sinus and the required period for bone regeneration should be considered well enough before these approaches, since it's possible for membrane to collapse and decrease the

Comparing to lateral window approach, this technique is considered to be less invasive. It's indicated in cases with ≥6 mm residual bone height. In a retrospective clinical study by Rosen et al., implant survival rates were found to be higher where residual bone height is greater than 4 mm. This rate, which is 96% when the residual bone height is over 4 mm, decreases to 85.7% in the presence of bone height less than 4 mm [54]. In this approach, a pilot implant slot is created with a drill narrower than the final diameter of the implant. The pilot implant slot is prepared to a depth 1–2 mm from the sinus floor. Different osteotomes of increasing diameters and lengths are used to prepare the slot. It's recommended that the final osteotome has a diameter 0.5 mm less than the planned implant diameter. After the final osteotomy, dental implant is placed in the slot [49]. A group of researchers modified the technique by introducing bone grafts to osteotomy site before implant placement. This modification aims to increase bone amount between the implant and the sinus floor. However, Si et al. reported similar implant survival rates and no significant

recurrent chronic sinusitis this technique is contraindicated [5, 49].

difference between grafted sites and nongrafted sites [55].

*tip of the osteotome instrument for the prevention of the sinus membrane.*

There are various modifications of membrane elevation in transalveolar approach: antral membrane baloon elevation, hydraulic sinus lift, hydrodynamic ultrasonic cavitation sinus lift, trephine core sinus lift and osseodensification. Transalveolar approach is minimal invasive. Graft and membrane use is not compulsory with this technique and simultaneous implant placement is possible in eligible cases. On the contrary, full visualization of the surgical site is not possible

*Transcreastal osteotome technique used for the "closed sinus lifting" procedure. A bone graft was placed at the* 

**156**

**Figure 9.**

Distraction osteogenesis is based on creating two bone segments by controlled osteotomies and gradually separating the segments to induce bone regeneration mechanism in between. In the surgical procedure, after full-thickness flap elevation and proper visualization of the site, fixation plates are temporarily adapted to the cortical bone. In this way, borders of osteotomy is determined. Following osteotomies, the distractor is fixed in the final position. Mobility of the transport segment is checked, then the device is put to initial passive position. Post-operative activation period is divided into three phases: latency, distraction, consolidation [2, 46, 56].

*Latency:* This protocol takes 5 to 7 days for a proper soft tissue healing. Distractor is not activated during this period to reduce the risk of wound dehiscence.

*Distraction:* Following latency, the distraction is activated by turning activation key at a rate of 0.5–1 mm per day. Transport segment is distracted from native bone vertically. Duration of distraction period depends on amount of bone needed.

*Consolidation:* Once the distraction is finalized, maturation of newly formed bone between the segments is expected for 8–12 weeks. Then the device is removed and implants are placed [2, 46].

Distraction osteogenesis can provide a bone gain of 5–15 mm vertically. Therefore it's safely indicated in vertical bone atrophies up to 15 mm [46]. In two clinical studies comparing autogenous bone block grafting and alveolar distraction osteogenesis (ADO), Bianchi et al. reported more bone gain in ADO group where Chiapasco et al. controversially reported no significant differences between the outcomes [56]. The procedure's contraindicated in cases presenting a thin knife-edge crest and insufficient bone amount to allow adequate anchorage. Patient co-operation during the distraction period is critical, treatment procedure should be thoroughly discussed with the patient before the initiation [46]. It is also a technique-sensitive procedure, therefore it is recommended for experienced surgeons to practice [57].

There is no need for additional bone grafts and membranes with this technique. Gradual distraction helps soft tissue increase along with bone regeneration. There is minimal infection risk and resorption levels are low in the newly formed bone. In sites regenerated with distraction osteogenesis, implant survival rates are comparable with other techniques. Alveolar ridge is regenerated by it's own osteogenic and regenerative potential, therefore autogenous bone transplant is not needed in distraction osteogenesis. Functional and esthetic discomfort of distraction device in oral cavity remains as one of the disadvantages, though. A wide range of complications with a high incidence up to %76 is reported with distraction osteogenesis [2, 46, 58]. Chiapasco et al. stated 'change of distraction vector' as the most frequent complication. Premature consolidation, insufficient distraction, resorption of transport segment and fractures of native bone, the transport segment or the device is among the possible complications [59].
