In cases of severe loss of alveolar bone in the area of maxillary molars, sufficient alveolar bone augmentation is required to ensure successful implant placement and maintenance of implants. According to a 2004 study by Simion et al., vertical bone loss in maxillary molar areas was divided into four categories [11]. Vertical ridge augmentation is considered when vertical bone loss is greater than 3 mm from the cementoenamel junction of adjacent teeth to the crestal bone. If the residual alveolar bone is less than 6 mm in height, sinus elevation is necessary. In 7 years of long-term observation when two bone grafts were performed simultaneously, the bone reaction of implants did not significantly differ from implants that had no grafting.
If only maxillary sinus elevation and sinus bone grafting are performed on vertically atrophied alveolar bone, the length of the prosthesis may be longer, producing a ratio of crown to implant greater than 1:1, increasing the load transferred to the structure of the alveolar bone and implant prostheses [12]. This makes it difficult for the implant to resist occlusal forces and reportedly increases the risk of alveolar bone resorption, fracture of the porcelain of the prosthesis, loosening of screws, etc. [13, 14]. On the other hand, other studies have shown that, even with a subpar ratio of crown to implant, there is no significant clinical difference in implant success [15, 16].
In this study, nine of the 33 implants were simultaneously placed with bone grafts. In 24 cases, implant placement was delayed after initial bone grafting. In cases of delayed implant placement, an average healing period of 4.3 months was allowed after bone grafting. Cowood et al. reported that, if residual alveolar bone is insufficient, bone grafting performed with delayed implant placement after 3–6 months of healing time could increase the success rate [17]. McGrath et al., on the other hand, stated that, if the implant is placed at the same time as the bone graft, the implant minimizes resorption of grafted bone material and reduces alveolar bone loss [18]. In this study, if the initial stability was judged to be sufficient based on residual bone mass and ISQ, the implant was simultaneously placed with bone grafts; the placement of implant was delayed if the residual bone mass was insufficient.
The success of bone grafting is more important than the choice of materials to operate. Exposure to postoperative infections, exposure to wound dehiscence, and increased adherence of bone and grafting materials were important points. Increased mobility of grafted materials or bony segments hinder re-vascularization, resulting in necrotic bone, making it difficult to incorporate with alveolar bone due to survival of only calcified materials [19, 20]. Therefore, surgery of soft tissue is also an important factor in bone grafting, requiring tension-free suturing. In this study, resorbable membranes were used in the lateral sinus opening to reduce the mobility of the bone grafting particles and induce superior adhesion during bone grafting after sinus elevation, and resorbable membranes and tissue adhesives were used to close the perforated sinus mucous membrane. According to Jensen et al., covering the barrier membrane at the lateral sinus opening after bone grafting in the maxillary sinus prevents soft tissue penetration and reduces the mobility of the bone grafting material, resulting in increased success of good bone formation and implants [21].
The material used in maxillary sinus grafting is most ideal when containing autogenous bone. However, the biggest disadvantage of autogenous bone is the limited amount due to few donor sites [22]. There are also reports of greater resorption than with other bone grafting materials and less predictability after surgery [23]. In this study, the block bone of the symphysis of the mandible was collected from two cases, and implant placement was delayed after bone grafting. In one instance, osseointegration failed and resulted in early implant failure. To compensate for the many disadvantages of autogenous bone grafting, autogenous tooth bone graft material (AutoBT®) was used in 11 examples in this study. The bone grafting material is used in powder or putty form by processing the teeth of the patient or their family. Autogenous tooth bone grafting material has excellent osteoinduction and osteoconduction capabilities, has no immunological rejection, and has exhibited excellent clinical results [24, 25].
Complications after surgery included eight cases of ecchymosis, four cases of exposure of the titanium mesh or barrier membrane, three cases of peri-implantitis, three cases of hematoma, and two cases of maxillary sinusitis. Ecchymosis is usually found in patients who have taken drugs that increase bleeding (anti-thrombotic agents), and it is estimated that resuming postoperative medications, even with a temporary suspension of medication, causes severe subcutaneous bleeding, pain, edematous swelling, and hematoma. In this case, short-term use of corticosteroids to prevent postoperative edema may be helpful. It is thought that, if vertical ridge augmentation is performed, the risk of exposure of the barrier or titanium mesh along with postoperative wound dehiscence is high, and resorption increases as the load on the immature bone continues. The use of antibiotics was extended in cases of chronic sinusitis or local infection, and infection control was accompanied by immediate incision, drainage, and daily wound dressing to eliminate complications without any major issues.
The success rate of implants in this study was slightly lower than other studies, at 81.8%, with many complications. Many other studies have shown an average healing period of 5 to 6 months before prosthetic loading of maxillary bone grafts. If vertical ridge augmentation is performed with sinus bone grafting, it is believed that two to three more months of healing time would be advantageous for early stability and success.
In this study, six implants failed to survive, three due to loss of osseointegration before loading. Two of the implants were presumed to exhibit failed osseointegration due to poor initial fixation of approximately 50 ISQ at fixture placement and poor bone quality. The other implant was carefully placed, deliberately removed, and then replaced. The three other failed implants were late failures after prosthesis function, with two of them failing due to repeated parafunction and fracture of the fixtures, while the other implant failed due to repeated peri-implantitis.
In this study, vertical loss of marginal bone was 0.20 ± 0.37 mm at the final observation, with no significant difference compared to studies where implants were placed without bone graft. No significant difference was estimated for the six failed implants that were removed before prosthetic functioning or within 1 year of loading and excluded from the analysis of marginal bone loss. Study by Urban et al. showed no significant difference in resorption of marginal bone around the implants or success rate of implants when comparing cases where only vertical ridge augmentation was performed and cases where vertical ridge augmentation and sinus bone grafting were simultaneously performed [26].
Although vertical resorption of grafted bone materials has shown a gradual increase over time, two-dimensional panoramic radiographs indicate that changes or distortions in the measurement process occur depending on anatomical structure and patients’ position, which will result in a large margin of error and difficulty in assessing reliability. It is believed that, due to the wide variation in the number of cases, it is likely to be difficult to judge reliable results. It is known that resorption of bone grafts occurs continuously for 1 to 3 years after surgery, and that bony changes occur at a minimum level after that [27, 28]. In the future, prospective studies with computed tomography (CT) images analyzing both the type and height of grafted bone materials and changes in the volume of the three-dimensional material will be required.
Also, bone grafts were done with a mixture of autogenous bone, xeno-grafts’ materials, autogenous tooth bone grafts (autoBT®; powder and block), and auto-block bone graft. The marginal bone loss may cause differences in the types of bone grafts materials, but the comparison of the bone grafts by type is difficult due to very small sample size on each methods. For the more accurate assessment and predictive treatment, randomized comparison studies of large sample size, and precise diagnosis will be required according to the condition of the maxillary sinus and the alveolar bone.