Accuracy and influencing factors of maxillary and mandibular repositioning using pre-bent locking plates: a prospective study.

In-house repositioning methods based on three-dimensional (3D)-printing technology and the use of pre-bent plates has been gaining popularity in orthognathic surgery. However, there remains room for further improvement in methods and investigations on clinical factors that affect accuracy. This single-centre, prospective study included 34 patients and aimed to evaluate the accuracy and factors influencing maxillary and mandibular repositioning using pre-bent locking plates. The plates were manually pre-bent on the 3D-printed models of the planned position, and their hole positions were scanned and reproduced intraoperatively with osteotomy guides. The accuracy of repositioning and plate-hole positioning was calculated in three axes with the set landmarks. The following clinical factors that affect repositioning accuracy were also verified: deviation of the plate-hole positioning, amount of planned movement, and amount of simulated bony interference. The median deviations of the repositioning and hole positioning between the preoperative plan and postoperative results were 0.26 mm and 0.23 mm, respectively, in the maxilla, and 0.69 mm and 0.36 mm, respectively, in the mandible, suggesting that the method was highly accurate, and the repositioning concept based on the plate hole and form matching was more effective in the maxilla. Results of the correlation test suggest that large amounts of bony interference and plate-hole positioning errors in the up/down direction could reduce mandibular repositioning accuracy.

A Novel Orthognathic Surgery With a Half-Millimeter Accuracy for the Maxillary Positioning Using Prebent Plates and Computer-Aided Design and Manufacturing Osteotomy Guide.

This retrospective study aimed to assess the accuracy of prebent plates and computer-aided design and manufacturing osteotomy guide for orthognathic surgery. The prebent plates correspondent to the planning model were scanned with a 3-dimensional printed model for guide design and used for fixation. Forty-two patients who underwent bimaxillary orthognathic surgery using computer-aided design and manufacturing intermediate splint with the guide (guided group: 20 patients) or with conventional fixation under straight locking miniplates (SLMs) technique (SLM group: 20 patients) were analyzed. A deviation of the maxilla between the planned and postoperative positions was evaluated using computed tomography, which was taken 2 weeks before and 4 days after the surgery. The surgery time and the infraorbital nerve paranesthesia were also evaluated. The mean deviations in the mediolateral ( x ), anteroposterior ( y ), and vertical directions ( z ) were 0.25, 0.50, and 0.37 mm, respectively, in the guided group, while that in the SLM group were 0.57, 0.52, and 0.82 mm, respectively. There were significant differences in x and z coordinates ( P <0.001). No significant difference in the surgery duration and paranesthesia was seen, suggesting the present method offers a half-millimeter accuracy for the maxillary repositioning without increasing the risk of extending surgery duration and nerve complication.

A 3-Dimensional Finite Element Analysis of Resected Mandibular Bone to Determine the Most Stable Implant Positions for a Fixed Prosthesis.

This study was conducted to determine the most secure implant positioning on the marginally resected mandible to support a fixed complete denture through finite element analysis. Three or 4 implants were placed at near, middle, or far positions from the resected margin in a simulation model with a symmetrical marginal defect in the mandibular symphysis. The height of the residual bone was 5, 10, or 15 mm. The 4 possible implant patterns for 3 or 4 implants were defined as (1) asymmetrically isolated position 1 to position 2, (2) asymmetrically isolated position 1 to position 3, (3) asymmetrically isolated with greater-length position 1 to position 2, and (4) 2 implants symmetrically positioned on each side of the defect. The von Mises stress in the resected and peri-implant bone with respect to the occlusal force was calculated. Initially, because the peri-implant bone stress around the isolated implant at the near position was greater than at the middle and far positions regardless of the residual bone height, the near position was excluded. Second, the von Mises stress in the resected bone region was >10 MPa when the isolated implant was at the far position, and it increased inversely depending on the bone height. However, the stress was <10 MPa when the isolated implant was placed at the middle position regardless of the bone height, and it was significantly lower compared with the far position and equivalent to the symmetrically positioned implants. Furthermore, the use of a greater-length implant reduced peri-implant bone stress, which was even lower than that of the symmetrically positioned implants. These results suggest that the asymmetrically positioned 3-implant-supported fixed denture, using a greater-length isolated implant, placed neither too close to nor too far from the resected margin, can be an effective alternative to the symmetrically positioned 4-implant-supported fixed denture.

Straight Locking Miniplate Technique Achieves Submillimeter Accuracy of Condylar Positional Change During Bimaxillary Orthognathic Surgery for Patients With Skeletal Class III Malocclusion.

PURPOSE: The straight locking miniplate (SLM) technique is a straightforward method to accurately reposition the maxilla during bimaxillary orthognathic surgery. The present study evaluated the accuracy of the SLM technique in maintaining the condylar position during surgery without the use of a cutting guide. PATIENTS AND METHODS: The present prospective, single-center study was conducted at Yokohama City University between 2016 and 2017 and included patients with skeletal Class III malocclusion. The patients were divided into 2 groups according to the fixation method used for the mandibular segments. The mandibular segments were fixed with miniplates either manually (manual group) or using the SLM technique (SLM group). Computed tomography was performed before and 3 days after surgery to compare the condylar position. The bodily and rotational movements of the condyle were analyzed. RESULTS: The subjects were 18 Japanese patients (36 condyles) who had undergone bilateral set back surgery with Le Fort I osteotomy. The amount of bodily movements in the manual and SLM groups were 1.44 and 0.62 mm, respectively. The degree of rotational movement in the sagittal plane in the manual and SLM groups was 3.33° and 0.23°, respectively. The bodily and rotational movements in the SLM group were significantly smaller than those in the manual group (P < .05 and P < .01, respectively). CONCLUSIONS: These results suggest that use of the SLM technique reduces the risk of condylar positional changes to less than 1 mm during orthognathic surgery without the use of any complex devices or a cutting guide.

Effectiveness of subspinal Le Fort I osteotomy in preventing postoperative nasal deformation.

PURPOSE: This study sought to determine the effectiveness of subspinal Le Fort I osteotomy (SLFIO) in preventing nasal deformation, by analyzing changes in the nasal profile on three-dimensional computed tomography (3D-CT) images. PATIENTS AND METHODS: The participants were 39 Japanese patients with mandibular prognathism (6 men and 33 women) who underwent bilateral sagittal split ramus osteotomy and Le Fort I osteotomy with maxillary advancement: SLFIO was performed in 20 patients and conventional Le Fort I osteotomy (CLFIO) in 19 patients. All patients underwent modified alar base cinch suture, V-Y closure, and reduction of the piriform aperture. CT data acquired before and 1 year after the surgery were evaluated three-dimensionally with software to determine changes in the nasal profile. RESULTS: Changes in alar width, alar base width, nasal length, and nasofrontal angle were significantly smaller following SLFIO than following CLFIO, although there were no significant differences in nasal projection, nasal tip angle, or nasolabial angle between two procedures. CONCLUSION: SLFIO for anterior repositioning of the maxilla can prevent undesirable transverse soft tissue changes of the nose.

An accurate bimaxillary repositioning technique using straight locking miniplates for the mandible-first approach in bimaxillary orthognathic surgery.

Bimaxillary orthognathic surgery has been widely performed to achieve optimal functional and esthetic outcomes in patients with dentofacial deformity. Although Le Fort I osteotomy is generally performed before bilateral sagittal split osteotomy (BSSO) in the surgery, in several situations BSSO should be performed first. However, it is very difficult during bimaxillary orthognathic surgery to maintain an accurate centric relation of the condyle and decide the ideal vertical dimension from the skull base to the mandible. We have previously applied a straight locking miniplate (SLM) technique that permits accurate superior maxillary repositioning without the need for intraoperative measurements in bimaxillary orthognathic surgery. Here we describe the application of this technique for accurate bimaxillary repositioning in a mandible-first approach where the SLMs also serve as a condylar positioning device in bimaxillary orthognathic surgery.

U-shaped Osteotomy Around the Descending Palatine Artery to Prevent Posterior Osseous Interference for Superior/Posterior Repositioning of the Maxilla in Le Fort I Osteotomy.

In maxillary orthognathic surgery, superior repositioning of the maxilla is sometimes difficult, and removal of bony interference, especially around the descending palatine artery (DPA), is very time-consuming in cases of severe maxillary impaction. Posterior repositioning of the maxilla for removal of bony interference between the posterior maxilla and the pterygoid process is also technically difficult. Because the most common site of hemorrhage in Le Fort I osteotomy is the posterior maxilla, this bone removal is a source of frustration for surgeons in DPA injury. When the DPA is injured during bone removal and ligation is performed, aseptic necrosis of the maxilla may occur. Therefore, a simple and safe method for maxillary superior/posterior repositioning is required to remove osseous interference around the DPA. The authors describe here U-shaped osteotomy around the DPA to prevent posterior osseous interference for superior/posterior repositioning of the maxilla in Le Fort I osteotomy.

Vital staining of palatal soft tissue in horseshoe Le Fort I osteotomy for superior repositioning of the maxilla.

In maxillary orthognathic surgery, superior repositioning of the maxilla is sometimes difficult, and removal of the bony interference, especially around the descending palatine artery, is very time-consuming in cases of severe maxillary impaction. A useful method introduced for superior repositioning of the maxilla is horseshoe-shaped osteotomy combined with Le Fort I osteotomy (horseshoe Le Fort I osteotomy). However, injury to the palatal soft tissue during horseshoe-shaped osteotomy may cause aseptic complications of the maxilla. Therefore, a safe method is required to prevent such injury to reduce the risk for aseptic necrosis. We describe here vital staining of palatal soft tissue in horseshoe Le Fort I osteotomy for safer superior repositioning of the maxilla.