Key points
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Vertical and horizontal augmentation of critically-sized alveolar ridge deficiencies come with numerous challenges.
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Sandwich osteotomy (inlay bone grafting) has shown promising results; however; its limitations make it a not-so-desirable technique in some situations where width deficiency is present.
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Using anatomic repositioning of the recipient site bone, it is possible to treat certain critical-sized bone defects in the posterior mandible that would otherwise require extraoral bone harvesting.
Abbreviations
| GBR | guided bone regeneration |
| IAN | inferior alveolar nerve |
| LPS | lingual pedicled segment |
| PSR | pedicled segmental rotation |
Background and objectives
Vertical and horizontal ridge augmentation procedures try to address the challenges posed by the inadequacies in alveolar bone dimensions to facilitate successful dental implantations. ,, Given the fact that a minimum of 2 mm of alveolar bone above the inferior alveolar nerve (IAN) is required for dental implantation, fully or partially edentulous atrophic posterior mandible can compromise the placement of standard-length (ie, >8 mm) dental implants. Numerous ridge augmentation techniques and procedures have been introduced and investigated over the years, all of which come with their unique set of challenges and restrictions: IAN transposition/lateralization and distraction osteogenesis carry the risk of mandible fracture and transitory or permanent neurosensory dysesthesia. Moreover, both the need for prerequisite minimum bone dimensions, and the reported insufficient bone gain, make these procedures unpopular. ,
Autogenous onlay bone grafting has long been considered the gold standard for atrophic posterior mandible augmentation and has often resulted in long-term dental implant success and survival rates similar to implants placed in native alveolar bone. , Despite its wide popularity, this technique can suffer from unpredictable donor site morbidity and undesirable amounts of graft resorption. In order to reduce the number of surgeries and their complications, the placement of short-length implants (ie, <8 mm) have also been proposed as a solution for atrophic posterior mandible rehabilitation; however, even though these implants have shown promising short-term success, the viability and long-term survival rates of these implants is far from ideal. ,,,,,,
Guided bone regeneration (GBR) procedures have gained a lot of attention in recent years due to their extremely creative techniques and materials; nonresorbable and/or resorbable natural-sourced or synthetic membranes, titanium meshes (prefabricated or computer aided design/computer aided manufacturing [CAD/CAM] customized), titanium-reinforced membranes (perforated or nonperforated), and others, combined with varied mixtures of autograft, allograft, and xenograft bone substitutes and/or bone blocks. As popular as these GBR-based techniques are, they also come with their own restrictions: surgical and healing complications (eg, mesh exposures, flap infections, and so on); challenges in maintaining a stable protective space; failed central vascularization; thick pseudoperiosteum connective tissues, among others. In addition, in some cases, even though the volume of the regenerated bone is acceptable, the quality and density of the regenerated site might not be proper enough to be able to lead to a healthy and long-term osseointegration with dental implants. Furthermore, the amount of vertical bone gain in GBR-based techniques is unpredictable and can vary from 2 to 8 mm from case to case. ,,
In 1966, Barron-Saint-Pasteur introduced an alveolar ridge augmentation technique called the segmental sandwich osteotomy with the intention of providing a better vascular connection. A horizontal osteotomy on the upper third of the posterior mandibular alveolar ridge is performed, the mobilized bone segment from the buccal side is raised, while the lingual soft tissue attachments are maintained. Then the gap gets filled with particulate bone materials and/or bone blocks ( Fig. 1 ). ,, Even though sandwich osteotomy is technically difficult, it eliminates the need for major autogenous bone grafts while also facilitating desirable bone regeneration since the grafted bone substitutes are surrounded by the native alveolar bone and periosteum on all sides of the augmented area. However, the sandwich osteotomy technique can only achieve vertical bone gain, and the height of the augmentation procedure is limited to the stretch extension of the soft tissue.
( A – I ) Conventional segmental sandwich osteotomy technique. ( A ) Vestibular access to the area with careful subperiosteal dissection around the inferior alveolar nerve area. Osteotomy lines are apparent in the figure for both simultaneous harvesting of the lateral ramus cortical plate and sandwich osteotomy in the deficient area. ( B ) Upward fracture of the osteotomized segment while keeping the lingual periosteum attached. ( C ) Fixation of the osteotomized segment with microplate and microscrews in the proposed height. ( D , E ) Allogenic bone blocks were impregnated in the L-PRF and inserted interpositionally and placed in the middle of the space between the 2 bone segments and was covered with bovine bone mineral and PRF. Soft tissue were closed in 2 layers without tension and interarch space were considered during the closure to avoid possible occlusal injury. ( F – I ) Six months surgical site reentry shows a remarkable bone regeneration within the osteotomized segment. After removing the fixation device, 2 regular dental implants have been placed.
The pedicled segmental rotation technique
The novel pedicled segmental rotation (PSR) alveolar ridge augmentation technique was first introduced by Khojasteh and colleagues in 2019 through a human case series. The PSR technique owes its justification to the 2 major limitations of conventional sandwich osteotomy: (1) inability in addressing the horizontal (bucco-lingual width) deficiencies and (2) interarch distance/length limitations that impact postsurgery prosthodontic treatments. A modification to the conventional segmental sandwich osteotomy technique, consists of a complete horizontal osteotomy to be kept at least 2 mm above the inferior alveolar nerve canal. The osteotomy line merged with 2 vertical osteotomy lines, 1 anterior and 1 posterior, which were designed to diverge (Smile Osteotomy). The piezoelectric surgery blade is a suitable choice for this area to prevent potential neural injury. The osteotomized bone segment was carefully fractured and mobilized upward to prevent soft tissue pedicle detachment. It was then rotated or flipped 90° toward the buccal side, so that the bucco-lingual width of the bone segment is now positioned vertically on top of the atrophic site ( Fig. 2 A-D ). A couple of long titanium screws will be inserted vertically to fix the mobilized bone segment to the remaining of the atrophic jaw underneath while keeping the insertion point at the lateral side of the canal. The gaps on all sides can be filled with particulate bone substitutes/materials. Moreover, this technique can be combined with and complemented by additional autogenous onlay bone grafting or IAN transposition to reach optimum regenerative outcomes both vertically and horizontally in complicated cases. The main advantage of the PSR technique compared to the conventional sandwich osteotomy technique is the fact that PSR can augment the atrophic jaw in both vertical and horizontal dimensions. Moreover, unlike the sandwich osteotomy technique, the height of the vertical augmentation in the PSR technique is not limited to or restricted by the stretch of the soft tissue but rather determined by the dimensions of the mobilized bone segment. The PSR technique can face challenging cases of severe vertical and horizontal alveolar atrophies (ie, C2 and C3 categories of bone deficiency according to the Khojasteh and colleagues’s 2013 classification) ; these complicated cases have a limited basal bone width (<5 mm) and no surrounding vertical bone walls. Such cases, if treated solely through autogenous onlay grafting, require a significantly bulky and wide cortical bone graft, such as lateral ramus cortical bone graft, which can cause numerous complications for patients. The previous case series by Khojasteh and colleagues consisted of 10 cases that had undergone PSR alone, or PSR combined with either onlay bone grafting or IAN lateralization/transposition ; the mean vertical bone gains were 7.13 mm, 7.80 mm, and 6.59 mm for the PSR alone, PSR + onlay bone grafting, and PSR + IAN lateralization/transposition groups, respectively. Some of the PSR procedure cases performed by Khojasteh and colleagues has been included in the following sections ( Figs. 3–12 ).
( A ) The initial dimensions of the atrophic site show a maximum height of 6 mm available for dental implantation. The orange line displays the surgical resection line in the PSR technique. ( B ) Complete horizontal resection of the upper third of the atrophic site. ( C ) The 90° flip/rotation of the pedicled segment and placement of fixation screws. By doing this, the available vertical height for dental implantation, 2 mm above the IAN, went from 6 mm to 11 mm. ( D ) A complimentary autogenous onlay bone graft is placed on the lingual side of the augmented site and fixed with horizontally-inserted titanium screws in order to reach optimum horizontal width.
( A – I ) Case #1 . ( A ) PSR alone. ( B ) Panoramic radiograph of a vertical defect in posterior mandible area. ( C ) Smile osteotomy in the posterior mandible was performed like sandwich inlay bone grafting technique. Keeping at least 2 mm of bone above inferior alveolar nerve is mandatory to avoid possible neurosensory injury. ( D ) The lingual soft tissue pedicle was stretched with mild tension with extreme care to not detach the segmentalized bone. ( E , F ) The upward fractured bone segment flipped 90° to a vertical position; care was taken to maintain the soft tissue pedicled on the lingual surface. The rotated segment fixed with three 12-mm endosteal microscrews in lateral 3rd of basal bone not penetrate the canal. ( G ) The augmented site, 4 months after surgery. ( H ) Panoramic radiograph of the augmented site. ( I ) Placement of dental implants.
( Adapted from Khojasteh A, Safiaghdam H, Farajpour H. Pedicled segmental rotation techniques for posterior mandible augmentation: a preliminary study. Int J Oral Maxillofac Surg 2019;48(12):1584–93. ∗Permission needed.)
(A-K) Case #2. Platelet rich in fibrin (PRF) combined with onlay bone grafting. ( A ) Panoramic radiograph of a combined vertical defect requiring horizontal and vertical bone augmentation. ( B ) Sagittal sections of the defect area, cone beam computed tomography (CBCT) imaging. ( C ) A vestibular access flap retracted without detaching the lingual mucoperiosteum to expose the anterior wall of the atrophic mandible. Smile osteotom lines with a piezoelectric surgery device were created. ( D ) The osteotomized segment was rotated with gentle force while lingual soft tissue pedicle keep attached. ( E ) The rotated segment fixed by 2 endosteal 12-mm microscrews in laterobuccal direction. ( F ) Lateral ramus cortical block was also harvested from the same surgical site by extending flap in retromolar area. Cortical harvested bone fixed to the lateral side of the rotated segment to increase the width for the proper future implant placement. Another piece of cortical bone block was fixed in the nonrotated segment to create a 3-dimension augmentation in deficient area. ( G ) The remaining gap was filled with bovine bone mineral. ( H ) Soft tissue healing, 6 months after surgery, showed normal healing sequence without any sign of dehiscence. ( I ) New vibrant regenerate bone was apparent in the whole rotated and block bone augmented area. The lateral ramus bone block that has been fixed to laterally to the rotated segment was also integrated and showed a 3-dimensional bone regeneration. ( J , K ) Placement of dental implants.
( Adapted from Khojasteh A, Safiaghdam H, Farajpour H. Pedicled segmental rotation techniques for posterior mandible augmentation: a preliminary study. Int J Oral Maxillofac Surg 2019;48(12):1584–93. ∗Permission needed.)
