Application of modified alveolar ridge augmentation technique for horizontal bone augmentation in posterior mandibular region: Report of 3 cases

Abstract Three cases with severe horizontal bone deficiency on mandibular posterior region were committed by modified alveolar ridge augmentation. The therapeutic outcomes show that it is an effective methodology in cases with compromised horizontal bone.


| INTRODUCTION
Up until the present, dentition defects raised by endodontic and periodontal diseases are common concerns in clinical practices. Implant prosthodontics are shown with good masticatory efficiency, neglectable foreign body sensation, and do not damage the adjacent teeth as the traditional porcelain/ metal bridge prosthodontics. However, the alveolar bone resorption often occurs associated with the defect of dentition, this is ascribed to the fact that functional loading by intact dentition is the prerequisite for maintaining the bone structures, without effective stimulation by masticatory forces, alveolar bone is prone to atrophy resorption. 1 The resorption of alveolar ridge mainly occurs adjacent to three regions: periodontal membrane, periosteum of buccal-lingual bone plate, and within the marrow cavity at cancellous bones. 2 The buccal side of bone plate at mandibular posterior region is thinner than in lingual side, and the mandibular bone resorption always result in the insufficient bone quantity at horizontal direction. As an effective method for horizontal bone augmentation, the bone-splitting technique does not need autologous bone grafting; however, the surgical trauma of traditional bone splitting is still unneglectable and unexpected bone fractures are also shown to happen during the splitting surgery. 3 To overcome these disadvantages, we designed a modified bone-splitting technique, and applied them on 3 cases with insufficient bone width at mandibular posterior region, this paper will discuss these cases in detail and provide future perspectives for such modified technique.

| CASE 1
Case 1 was a 48-year-old female patient with no systemic diseases, the bilateral posterior tooth were loss (Figure 1), which seriously compromised the daily mastications. Clinical and radiology examination indicated that the bone quantity of maxillary and left mandibular regions is sufficient for implant placement; however, the bone width at right mandibular region is significantly limited, moreover, the residual alveolar crest shaped as a narrow blade. CBCT scanning revealed that 45, 46, and 47 were missing, the vertical height of alveolar | 2549 CHU et al.
bone was sufficient but the horizontal width of alveolar crest was merely 3-4 mm (Figures 2 and 3).

| Treatment plan
The modified bone-splitting technique with simultaneous GBR was planned at the posterior region of right mandible, and delayed implant placement was designed at 6 months after GBR. Conventional implant prosthodontics were designed for other missing teeth.

| Treatment procedures
After the disinfection and local anesthesia, the linear incision was proceeded along the "blade shaped" top of alveolar ridge by the piezosurgical blade (PIEZOSURGERY ® 3; Mectron S.p.A.) on the mesial-distal direction. At the mesial and distal ends of top incision, 2 incisions were proceeded perpendicularly, and another A horizontal incision was cut 10 mm parallel to the top incision, all these 4 incisions penetrated through the cortical bone to reach the cancellous bone and bone marrow ( Figure 4). Bleeding holes were prepared on the surface of the bone-splitting region. A 4-mm wide osteotome was inserted from the crestal incision and extended into the cancellous bone, the osteotome was gently pushed by bone suture(H-563; Holycon) ( Figure 10). Patients were instructed to use clindamycin and ornidazole for 7 days to prevent infections; the sutures were finally removed after 14 days.

| Therapeutic effect
Significant bone width increment was achieved by the combination of modified piezosurgery technique and simultaneous

| CASE 2
Case 2 was a 58-year-old woman without systemic disease. The 35, 36, and 37 were missing for the severe dental caries ( Figure 17). CBCT showed the edentulous region of 35, 36, and 37 had a "blade shaped" residual alveolar ridge which is significantly insufficient for conventional implant placements, the width of residual alveolar crest was merely 3-4 mm (Figures 18 and 19).

| Treatment plan
The modified bone-splitting technique with simultaneous GBR was planned at the posterior region of left mandible, and delayed implant placement was designed at 6 months after GBR.

| Therapeutic outcomes
A significant bone increment was obtained at the horizontal direction of implant site after the application of modified ultrasonic osteotomy technique. The average bone augmentation at the horizontal direction was approximately 2-3 mm.

| CASE 3
Case 3 was a 42-year-old female patient without systemic diseases. With 35, 36, and 37 lost for severe dental caries for over 10 year, the residual alveolar crest for such sites were shown as "blade shaped" (Figures 34-36).

| Treatment plan
Ultrasonic piezosuegery induced bone splitting with simultaneous GBR was designed for this case, and followed by delayed implant placement.

| Treatment process
The same surgical procedure is performed at the site of surgery (35-37) (Figures 37-39). After the bone splitting, a Bio-oss bone substitution was placed into the surgical area (Figures 40 and 41), and two pieces of PRF and biological membrane (Haiao Heal-ALL, ZH-BIO) were finally applied to cover the GBR region (Figures 42,43). Other treatments and postoperative instructions were the same as in case 1 and 2 ( Figure 44 (Figures 46 and 47). The X-ray examination at 3 months after surgery indicated an ideally osseointegration and sufficient bone quantity at the implant-bone interface (Figures 48 and 49).

| Therapeutic effect
The ultrasonic piezosurgery induced bone-splitting technique dramatically the bone quantity at edentulous region, the horizontal bone quantity was augmented by 2-3 mm on average (Figures 50 and 51).

| DISCUSSION
To date, various clinical techniques are available for bone regeneration at cases with compromised bone quantity, which include the guided bone regeneration (GBR), onlay grafting, distraction osteogenesis, and bone splitting. GBR is a widely applied and thoroughly investigated technique since its invention, 4 it has the advantages of lower surgical trauma, and easier to be handled, also is shown with comparatively high success rate; however, the mere application of GBR may result in severe postoperative bone resorption, as Arunjaroensuk 5 found, this may relate to compromised bone strength and quantity. The onlay bone grafting was shown with a high success rate, and the autologous grafted bone is resistance to future resorption. 6 However, this technique has severe disadvantages such as aggravated postsurgical trauma, additional surgical area of bone donor sites. As Luca Cordaro et al 7 reported, when using heterogeneous bone grafting, the infection and other complications are more prone to occur. Distraction osteogenesis also have many advantages such as no need for autologous bone harvesting, a high proportion of new bone in the augmented area, and also makes it possible for the simultaneous soft tissue augmentation which guaranteed an excellent prosthodontic aesthetics. 8 But the F I G U R E 3 6 Residual bone crest (#35,#36,#37)

F I G U R E 3 7 The linear cortical incision by PIEZOSURGERY F I G U R E 3 8 Bleeding holes
disadvantage is that the size and direction of traction need to be repeatedly adjusted, which means additional times of surgery. In case of compromised bone width, thin implant is an alternative method for implant placement. 9 However, application of such implants are very limited with many restrictions, in severe bone atrophy cases even the thinnest implant cannot fulfill the criteria that buccal/lingual sides of residual bone should exceeded 1-1.5 mm.

F I G U R E 4 4 Suture the wound
Bone-splitting technique creates an affluent alveolar bone width by separating the bone plate into buccal and lingual sides, which can effectively increase the alveolar bone width with lower surgical trauma compared with onlay grafting, and the split buccal/lingual plates could act as frames for maintaining the stability of osteogenic cavity. However, as Simion et al 10 reported, due to the fact that the cortex of buccal bone plate is thick in the posterior mandible, it is easy to be fractured during bone splitting for the concentration of stress, thus developing a modified bone-splitting technique with less surgical trauma is necessary. GBR can provide space for osteoblasts by an absorbable membrane which prevents fibroblasts, thus bone tissue can be repaired. 11 PRF has been widely used in GBR process because of its role in promoting tissue regeneration. 12 PRF contains a variety of growth factors and cytokines including transforming growth factor-beta1 (TGF-β1), platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), interleukin (IL)-1β, IL-4, and IL-6. 13 In order to reduce the risk of bone plate fracture, infection and other complications in the F I G U R E 4 5 CBCT scanning 6 mo after the bone operation F I G U R E 4 6 Bone augmentation 6 mo later F I G U R E 4 7 Three Straumann implants installed process of bone splitting, 14 and meanwhile, to optimize the process of implantation surgery, the combination of modified bone splitting and GBR techniques can augment the bone width in surgical region safely and effectively. Mandible is composed of cortex bone and cancellous bone, bone marrow which is rich in blood supply is the majority composition of cancellous bones, moreover, compared with the cortex bones, the cancellous bones are more rapidly in self-reconstructing and healing. However, the elastic modulus of cancellous bone is shown to be significant lower than that of cortex bone. As a result, the cancellous bone is less likely to be fractured under deforming stress during the bone splitting.
Among the three cases reported in this paper, buccal/lingual sides of residual bone were <1.5 mm (class H-m according to Wang HVC classification), so an improved alveolar ridge augmentation technique was applied to augment the bone width at mandibular posterior region. 15 The first stage surgery involved bone splitting and GBR, then the implantion was operated after a 6-month healing period. After the bone splitting and GBR in the first stage of surgery, the jaw bone was healed and reconstructed to obtain bone augmentation. When the implant was implanted in the second stage, the alveolar bone width could be close to the unabsorbed. So that it could be easier for the second stage. To evenly distribute and induce the splitting stress, mesial and distal incisions were performed perpendicularly to the top incision, and an extra bottom incisions that parallel to the top incision was also applied to induce the splitting stress for safely buccal bone plate expansions. To improve the local blood supply of GBR region, several nourishing holes were drilled to penetrate the buccal bone plate into the cancellous bone region, and the continuity of cancellous bone structure is maintained during the expansion surgery. 16 These incisions were able to accurately penetrate cortical bone and achieve cancellous bone, by preoperative CBCT measurements and careful intraoperative manipulation. And the scale of ultrasonic bone scalpel provides necessary conditions for accurate cutting. Due to the favorable elastic modulus cancellous bone structures, they are shown to be firm and not easily to be broken during the bone splitting, moreover, to better support the osteogenetic cavity, bone substitutions were also placed between the split buccal-lingual bone plates, and excessive amount F I G U R E 4 8 CBCT scanning the day before final restoration F I G U R E 4 9 Final restoration of bone powder was placed on the buccal side to protect the bone plate against postsurgical resorption. After covering by the resorbable membrane and PRF respectively, the wounded region was closed tightly, which can prevent fibroblasts and provide a stable environment for the proliferation and differentiation of osteoblasts. In case 1, the PRF membrane was placed above the absorbable membrane because we were concerned at the beginning of the study that the surgical operation would create tension in the wound and cause poor soft tissue healing. As described above, PRF can promote soft tissue healing, so we tried to obtain soft tissue augmentation by it. 13 Through postoperative observation, we found that the soft tissue healed well and there was no obvious sign of cracking. So in case 2 we put the absorbable membrane on top of the PRF membrane to get more bone augmentation. To penetrate the cortical bone plates, ultrasonic piezosurgical instruments (PIEZOSURGERY ® 3, Mectron S.p.A.) were applied in these surgeries, with are shown with highly accuracy and lower surgical trauma during the bone incisions. 17 Compared with single-stage bone splitting which straightforwardly penetrate the cortical and cancellous bones, our methods applied the piezosurgical blade and osteotome to penetrate the cortical and cancellous bones, respectively, this will reduce the risk of surgical complications such as fractures and improve the accuracy during the bone-splitting surgery. The delayed implantation therapy in these cases provided the mandibles with affluent healing period and thus made it easy to control the position and direction of implant implantation under augmented bone quantity. Compared with an alternative threestage surgery therapy, our two-stage implant surgery can also reduce the number of surgeries, and thus reduces surgical trauma and financial burden for patients.
Combined with the GBR technique, the modified bone-splitting technique is shown to effectively fill the cleavage gap with sufficient bone substitutions, which provided osteogenic materials for future bone regeneration, and guaranteed a favorable initial stability for the future implant placement. 3 Through excessive bone substitutions transplanted, the postsurgical resorption will be effectively compensated, the above operations also follow the PASS principle of GBR bone grafting. 18 Clindamycin, a lincosamide antibiotic, is commonly used to treat gram-positive aerobic and anaerobic bacterial infections. 19 Ornidazole is a nitroimidazole which is an antibacterial and antiprotozoal drug used to treat anaerobic enteric protozoa. Also used in the treatment of prophylaxis susceptible anaerobic infections in dental and gastrointestinal surgery. 20 The risk of infection can be avoided by prophylactic use of antibiotics (clindamycin and ornidazole). Finally, all cases are indicated with ideal bone quantity after a period of healing time, and a robust and stable osseointegration is achieved at bone-implant interface.
Moreover, for fear of excessive economic burdens and extra surgical trauma by multiple surgeries, none of these 3 cases proceeded soft tissue transplantation and temporary prosthodontics for gingival induction remolding, etc This may limited the final aesthetic outcomes of the implant prosthodontics. In the future cases, we may combine the modified bone-splitting technique with the soft tissue transplantation to get a sufficient quantity in both soft and hard tissue for ideal implant prosthodontics.

| CONCLUSION
Modified bone splitting can take advantages of the favorable elastic modulus of cancellous bone, and reduce surgical complications such as trauma and fractures. A combination of piezosurgery and GBR techniques can reduce surgical injury and guaranteed an ideal outcome for GBR.