Assessment of sagittal split ramus osteotomy rigid internal fixation techniques using a finite element method

Does adjunctive fixation in conjunction with miniplate affect condylar position and morphology after mandibular advancement through bilateral sagittal split ramus osteotomy? A retrospective 3-dimensional CT comparative study

To minimize condylar positional and morphological changes after mandibular advancement through bilateral sagittal split ramus osteotomy (BSSRO), surgeons add either a bicortical screw or a two-hole plate distal to the conventional single miniplate. Since there have been no previous studies investigating the effect of this combination, our study aimed to evaluate the short- and long-term effects of these adjunctive fixation methods (AFM) on condylar positional and morphological changes after mandibular advancement through BSSRO. This retrospective cohort study included consecutive patients with retruded mandibles who were treated in the Department of Orthognathic and TMJ Surgery at West China Hospital of Stomatology, Sichuan University. The patients were divided into two groups based on the primary predictor variable, which was the addition of AFM - either a single bicortical screw or a two-hole plate in addition to the single miniplate. The primary outcome variable was the condylar positional and morphological changes after mandibular advancement through BSSRO. Three-dimensional facial CT scans were obtained at three different time points (preoperatively - T0, 1 week postoperatively - T1, and 1 year postoperatively - T2) and analyzed using ITK-SNAP, 3D Slicer, and SlicerSALT software. Intergroup comparisons were conducted with an independent t-test, with a p-value of <0.05 considered significant. Correlations between the variables were estimated by Pearson correlation. The study comprised 51 patients (32 females, 19 males; mean age 25.13 ± 4.24 years), involving a total of 81 condyles (21 unilateral and 60 bilateral). There was a significant difference in long-term condylar displacement in favor of AFM along with a single miniplate (p < 0.001). The bicortical screw group recorded less condylar displacement than the two-hole plate group horizontally (0.11 mm vs 0.22 mm) and sagittally (0.03 mm vs 0.17 mm), but more vertically (0.85 mm vs 0.03 mm). Bone formation associated with AFM occurred on all condylar surfaces, compared with only three surfaces in the single miniplate group. The adjunctive method in addition to the single miniplate fixation method showed less condylar displacement and more bone apposition after mandibular advancement through BSSRO. The follow-up duration variable was the only significant determinant for volumetric changes in the condyle.

The effect of different hybrid rigid internal fixation techniques on the postoperative stability following a mandibular advancement using a bilateral sagittal split ramus osteotomy: A retrospective three-dimensional comparative study

OBJECTIVE

To three-dimensionally evaluate post-operative mandibular stability following bilateral sagittal split ramus osteotomies between hybrid and non-hybrid rigid internal fixation techniques.

MATERIALS AND METHOD

Seventy adults with skeletal class II deformity who underwent bilateral split sagittal osteotomy with mandibular advancement were included. Patients were divided into four groups based on their fixation techniques: hybrid technique (HT) groups I, II, and IV received a 4-hole 2 mm miniplate with either a bicortical screw (BS), additional 2 mm 4-hole miniplate, or two-hole miniplate, while non-HT group III received a 4-hole 2 mm miniplate with four mini-screws (MS). Measurements were taken pre-operatively (T0), immediately postoperatively (T1), and ≥1 year after surgery (T2) using 3D Slicer software.

RESULTS

Age, sex, and follow-up period did not correlate significantly with postoperative relapse or stability. Significant differences were observed in the advancement on the right side between groups II, III, and IV and on the left side between groups I, III, and IV. However, the type of surgical intervention showed no significant effect on postoperative relapse and stability. All groups of fixations showed satisfactory stability with irrelevant relapse (< 2 mm or 2°).

CONCLUSION

The study demonstrated satisfactory and comparable stability among different fixation groups on patients undergoing mandibular advancement following bilateral split sagittal osteotomy. The results highlighted the importance of considering the degree of advancement when planning orthognathic surgery and managing postoperative outcomes.

A finite element analysis of stress distribution with various directions of intermaxillary fixation using orthodontic mini-implants and elastics following mandibular advancement with a bilateral sagittal split ramus osteotomy

OBJECTIVE

This finite element analysis (FEA) aimed to assess the stress distribution in the mandible and fixation system with various directions of the intermaxillary fixation (IMF) using mini-implants (MIs) and elastics following mandibular advancement with a bilateral sagittal split ramus osteotomy (BSSRO).

MATERIALS AND METHODS

A total of nine mandibular advancement models were set according to the position of the MIs (1.6 mm in diameter, 8 mm in length) and direction of the IMF elastics (1/4 inch, 5 oz). Major and minor principal stresses in the cortical and cancellous bones, von Mises stresses in the fixation system (miniplate and monocortical screws), and bending angles of the miniplate were analysed.

RESULTS

Compressive and tensile stress distributions in the mandible and von Mises stress distributions in the fixation system were greater in models with a Class III IMF elastic direction and a higher IMF elastic force than in models with a Class II IMF elastic direction and a lower IMF elastic force. The bending angle of the miniplate was negligible.

CONCLUSIONS

Stress distributions in the bone and fixation system varied depending on the direction, amount of force, and position of IMF elastics and MIs. Conclusively, IMF elastics in the Class II direction with minimal load in the area close to the osteotomy site should be recommended.

Finite element analysis of different internal fixation methods for the treatment of atrophic mandible fractures

The aim of this study is to evaluate different plate systems and contribute to revealing the most appropriate treatment option for severe atrophic edentulous mandible fractures. A total of 8 different types of rigid internal fixation methods, which were a 4-hole miniplate on the crest, a 4-hole miniplate on the basis, a 6-hole miniplate on the crest, a 6-hole miniplate on the basis, two 4-hole mini plates on both the crest and basis, two 6-hole mini plates on both crest and basis, a 6-hole reconstruction plate on the crest and a 6-hole reconstruction plate on the basis, were simulated. Stress analysis on plates and screws and the displacement between fragments were evaluated using finite element analysis. The lowest von Mises stress was observed on the basis plate in Group 6. The highest von Mises stresses were measured on the screws closes to the fracture line. Values exceeding the boundary conditions were observed only in Groups 3 and 4 under molar loading. The highest compressive stresses were measured in Group 1, and the lowest compressive stresses were measured in Group 6. Under molar loading, the highest displacement was observed in Group 3, and the lowest displacement was observed in Group 6. When all groups are evaluated in terms of stress distributions and stability, a 1.5 mm thick six-hole reconstruction plate can be a reliable method in the treatment of severe atrophic edentulous mandible fractures.

Three Different Fixation Modalities following Mandibular Setback Surgery with Sagittal Split Ramus Osteotomy: A Comparative Study using Three-dimensional Finite Elements Analysis

Background

The provision of sufficient stability after maxillofacial surgery is essential for the reduction of complications and disease recurrence. The stabilization of osteotomized pieces results in rapid restoration of normal masticatory function, reduction of skeletal relapse, and uneventful healing at the osteotomy site. We aimed to compare qualitatively stress distribution patterns over a virtual mandible model after bilateral sagittal split osteotomy (BSSO) bridged with three different intraoral fixation techniques.

Methods

This study was conducted in the Oral and Maxillofacial Surgery Department of Mashhad School of Dentistry, Mashhad, Iran, from March 2021-March 2022. The mandible computed tomography scan of a healthy adult was used to generate a 3D model; thereafter, BSSO with a 3mm setback was simulated. The three following fixation techniques were applied to the model: 1) two bicortical screws, 2) three bicortical screws, and 3) a miniplate. The bilateral second premolars and first molars were placed under mechanical loads of 75, 135, and 600N in order to simulate symmetric occlusal forces. Finite element analysis (FEA) was carried out in Ansys software, and the mechanical strain, stress, and displacement calculations were recorded.

Results

The FEA contours revealed that stress was mainly concentrated in the fixation units. Although bicortical screws presented better rigidity than miniplates, they were associated with higher stress and displacement readings.

Conclusion

Miniplate fixation demonstrated the most favorable biomechanical performance, followed by fixation with two and three bicortical screws, respectively. Intraoral fixation with miniplates in combination with monocortical screws can serve as an appropriate fixation arrangement and treatment option for skeletal stabilization after BSSO setback surgery.

Biomechanical Evaluation of Seven Fixation Methods for Sagittal Split Ramus Osteotomy with Four Advancement Levels by Finite Element Analysis

Background

Mandibular sagittal split ramus osteotomy (SSRO) is a routine surgery to correct mandibular deformities, such as mandibular retrusion, protrusion, deficiency, and asymmetry. However, nonunion/malunion of the fragments and relapse caused by fixation failure after SSRO are major concerns. Rigid fixation to maintain postosteotomy segmental stabilization is critical for success. Additionally, understanding the biomechanical characteristics of different fixation methods in SSRO with large advancements is extremely important for clinical guidance. Therefore, the aim of the present study was to evaluate the biomechanical characteristics of different SSRO methods by finite element analysis.

Methods

SSRO finite element models with 5-, 10-, 15-, and 20-mm advancements were developed. Seven fixation methods, namely, two types of bicortical screws, single miniplate, dual miniplates, grid plate, dual L-shaped plates, and hybrid fixation, were positioned into the SSRO models. Molar and incisal biomechanical loads were applied to all models to simulate bite forces. We then investigated the immediate postoperative stability from four aspects, namely, the stability of the distal osteotomy segment, osteotomy regional stability, stress distribution on the mandible, and implant stress performance.

Results

The stability of the distal osteotomy segment and osteotomy region decreased when the advancement increased. All seven fixation methods displayed favorable biomechanical stability under minor advancement (5 mm). With large advancements, bicortical screws, dual miniplates, and grid plates provided better stability. The von Mises stress was concentrated around the screws close to the osteotomy region for the proximal segment for all fixation methods, and the von Mises stress on implants increased with larger advancements. With small advancements, five fixation methods endured tolerable maximum stresses of <880 MPa. A single miniplate and dual L-shaped plates generally suffered high stresses using larger advancements. The biomechanical characteristics were similar under molar and incisal loads.

Conclusions

The current study investigated the biomechanical properties of seven fixation devices after SSRO under molar and incisal loads. Generally, bicortical screws, grid plates, and dual miniplates provided better biomechanical stability using finite element analysis.

Biomechanical evaluation of seven fixation methods to treat pubic symphysis diastasis using finite element analysis

Background

Pubic symphysis diastasis (PSD) hinders the connection between bilateral ischia and pubic bones, resulting in instability of the anterior pelvic ring. PSD exceeding 25 mm is considered disruptions of the symphyseal and unilateral/bilateral anterior sacroiliac ligaments and require surgical intervention. The correct choice of fixation devices is of great significance to treat PSD. This study aimed to evaluate the construct stability and implant performance of seven fixation methods to treat PSD using finite element analysis.

Methods

The intact skeleton-ligament pelvic models were set as the control group. PSD models were simulated by removing relevant ligaments. To enhance the stability of the posterior pelvic ring, a cannulated screw was applied in the PSD models. Next, seven anterior fixation devices were installed on the PSD models according to standard surgical procedures, including single plates (single-Plate group), single plates with trans-symphyseal cross-screws (single-crsPlate group), dual plates (dual-Plate group), single cannulated screws, dual crossed cannulated screws (dual-canScrew group), subcutaneous plates (sub-Plate group), and subcutaneous pedicle screw-rod devices (sub-PedRod group). Compression and torsion were applied to all models. The construct stiffness, symphyseal relative micromotions, and von Mises stress performance were recorded and analyzed.

Results

The construct stiffness decreased dramatically under PSD conditions. The dual-canScrew (154.3 ± 9.3 N/mm), sub-Plate (147.1 ± 10.2 N/mm), and sub-PedRod (133.8 ± 8.0 N/mm) groups showed better ability to restore intact stability than the other groups (p < 0.05). Regarding regional stability, only single-plate fixation provided unexpected regional stability with a diastasis of 2.1 ± 0.2 mm (p < 0.001) under a compressive load. Under a rotational load, the single-crsPlate group provided better regional angular stability (0.31° ± 0.03°, p < 0.001). Stress concentrations occurred in the single-Plate, sub-Plate, and sub-PedRod groups. The maximum von Mises stress was observed in the single-plate group (1112.1 ± 112.7 MPa, p < 0.001).

Conclusion

The dual-canScrew fixation device offers ideal outcomes to maintain stability and prevent failure biomechanically. The single-crsPlate and dual-Plate methods effectively improved single-Plate device to enhance regional stability and disperse stresses. The subcutaneous fixation devices provided both anterior pelvic ring stability and pubic symphysis strength.

Biomechanical assessment of different fixation methods in mandibular high sagittal oblique osteotomy using a three-dimensional finite element analysis model

With modern-day technical advances, high sagittal oblique osteotomy (HSOO) of the mandible was recently described as an alternative to bilateral sagittal split osteotomy for the correction of mandibular skeletal deformities. However, neither in vitro nor numerical biomechanical assessments have evaluated the performance of fixation methods in HSOO. The aim of this study was to compare the biomechanical characteristics and stress distribution in bone and osteosynthesis fixations when using different designs and placing configurations, in order to determine a favourable plating method. We established two finite element models of HSOO with advancement (T1) and set-back (T2) movements of the mandible. Six different configurations of fixation of the ramus, progressively loaded by a constant force, were assessed for each model. The von Mises stress distribution in fixations and in bone, and bony segment displacement, were analysed. The lowest mechanical stresses and minimal gradient of displacement between the proximal and distal bony segments were detected in the combined one-third anterior- and posterior-positioned double mini-plate T1 and T2 models. This suggests that the appropriate method to correct mandibular deformities in HSOO surgery is with use of double mini-plates positioned in the anterior one-third and posterior one-third between the bony segments of the ramus.

Comparison of bicortical, miniplate and hybrid fixation techniques in mandibular advancement and counterclockwise rotation: A finite element analysis study

OBJECTIVE

This study aims to evaluate biomechanical stability and stress distribution of five different fixation types with finite element analysis using 10-mm advancement with or without counterclockwise rotation of the mandible.

MATERIALS AND METHODS

After sagittal split osteotomy, 10-mm advancement was performed in the first group and 10-mm advancement and 10-degree counterclockwise rotation were performed in the second group. One miniplate (M-1), two-miniplate (M-2), one miniplate and a bicortical screw (H), l-shaped bicortical screw (B-1), and inverted l-shaped bicortical screw (B-2) systems were placed. Totally, 120 N force was applied to the models at a 45-degree angle from the lower edge of the symphysis.

RESULTS

The highest values on fixation were seen with miniplate, while the mean values were obtained with bicortical screw system. The highest values on bone were achieved using bicortical screws. One miniplate (M-1) showed both the highest and mean displacement. The highest values in counterclockwise-rotated models increased in all parameters, compared to non-rotated models.

CONCLUSION

In cases in which passive alignment between segments and adequate bone contact are ensured, inverted l-shaped bicortical screw, two-miniplate, or hybrid systems are recommended.

Biomechanical analysis in mandibular advancement and occlusal plane rotation with finite element analysis

We used finite element analysis to assess stress on the cortical bone and plate fixation system, as well as mandibular resistance after sagittal split ramus osteotomy with different mandibular advancements and rotations of the occlusal plane. Three-dimensional mandibular models were obtained, and 6mm and 12mm advancements were planned associated with linear, clockwise, and counter-clockwise rotation of the angle of the occlusal plane. Each model was then fixed with one or two 2.0mm system plates and secured with four monocortical screws. A total of 12 models were built and subjected to a vertical load in the lower central incisor ranging from 50N to 500N in 50N increments. Results showed that the 12mm advancement was associated with higher stress on the bone and plate surface. Additionally, the models fixed with two plates exhibited lower plate stress than those fixed with a single plate. Counter-clockwise rotation of the angle of the mandibular plane in the 6mm advancement caused more plate stress, which did not occur in the 12mm advancement. This analysis has shown that change in the occlusal plane in large mandibular advancements does not act as an additional stress factor. These findings can help to better understand the tensions on bone and plate surfaces in patients who need large mandibular advancements that are associated with a change in the occlusal plane, and will aid better surgical planning.

Which type of method shows the best mechanical behavior for internal fixation of bilateral sagittal split osteotomy in major advancements with clockwise rotation? Comparison of four methods

PURPOSE

The aim of the present study was to evaluate the four methods for bilateral sagittal osteotomy fixation.

METHODS

In this study, 56 replicas of whole mandibles made of rigid polyurethane were used. After simulation of major advancement (11 mm) with clockwise rotation of the mandible (6^o) in relation to the occlusal plane, the bone segments were fixed with plates and screws of the 2.0-mm system on both the right and left sides: group I, double "H" plate; group II, two mini-plates; group III, "hybrid technique"; and group IV, three bicortical screws in the "inverted L" pattern. The mandibles were submitted to load on the central incisors and right first molar.

RESULTS

The mean value of group I was higher than those of groups IV and II in the displacement of 1 mm (F = 4.705; p = 0.010) with load on the incisor. The mean value of group III was higher than those of groups I and II in the displacement of 1 mm (F = 5.166; p = 0.007) and 3 mm (F = 5.166; p = 0.007). The mean value of group IV was higher than that of group II (F = 3.142; p = 0.044) with load on the molar.

CONCLUSION

Therefore, after the analyses, the hybrid technique was the one that showed the best results.

Three-Dimensional Finite Element Analysis of Different Plating Techniques for Unfavorable Mandibular Angle Fractures

The purpose of the current study was to assess the biomechanical behavior of 5 different fixation schemes for unfavorable mandibular angle fractures using the three-dimensional finite element analysis method. Five different miniplate fixation schemes were modeled for the fixation of unfavorable mandibular angle fractures. A double parallel miniplate (M1), which was placed at the halfway point of the mandibular angle height; a 1/3 superior-positioned miniplate (M2); a single miniplate (M3), which was placed at the halfway point of the mandibular angle height (1/2 middle-positioned); a 1/3 inferior-positioned miniplate (M4); and an X-miniplate which was placed at the halfway point of the mandibular angle height (M5). The lowest mechanical stresses were detected in the double miniplate model when compared with the other schemes, whereas 1/3 inferior-positioned miniplate had the highest stress and displacement values. The authors suggest that the double miniplate is an adequate rigid fixation technique, whereas the 1/3 inferior-positioned miniplate configuration should not be used in case of unfavorable mandibular angle fracture.

Cortical bone thickness of the mandibular canal and implications for bilateral sagittal split osteotomy: a cadaveric study

Preoperative delineation of the mandibular canal and surrounding cortical bone thickness is mandatory prior to bilateral sagittal split osteotomy (BSSO). The cortical bone thickness of 101 cadaveric mandibles was measured to define the mandibular canal. The mandibles were cut at the anterior ramus, at the third, second, and first molar, and at the premolar. The cortical bone thickness was measured between the mandibular canal and inferior border, buccal cortex, and lingual cortex at each cutting point. No difference was found between the right and left sides of the mandible, or between males and females, with one exception: males were found to have thicker inferior cortical bone at the premolar site than females. The implications for BSSO are: (1) for sagittal bone cutting, the maximum cutting depth of the buccal cortex at the ramus is 4.5mm, at the second and third molars is 6.5mm, and at the first molar is 5mm; (2) for vertical bone cutting at the first molar, the maximum cutting depth from the inferior border is 7.5mm. The measurement of cortical bone thickness from cadaveric mandibles provides useful preoperative information and confirms the results of computed tomography.

Comparative evaluation of the sliding plate technique for fixation of a sagittal split ramus osteotomy: finite element analysis

OBJECTIVE

This study evaluated the stress distribution of the sliding plate (SP) and conventional miniplate (CM) fixation techniques of a sagittal split ramus osteotomy (SSRO) using 3-dimensional (3-D) finite element analysis.

STUDY DESIGN

Four 3-D finite element models according to the number and shape of screw holes in the plate were simulated, and the von Mises stress was analyzed: SP with 2 round and 2 oval holes (SP-2 R2 O), SP with 2 round and 1 oval holes (SP-2 R1 O), CM with 4 round holes (CM-4 R), and CM with 3 round holes (CM-3 R).

RESULTS

The fixation technique with CM-4 R showed a better stress distribution than CM-3 R, which in turn showed better results compared to the 2 different SPs. SP-2 R2 O showed the worst stress distribution in the bone and fixation components.

CONCLUSIONS

The results suggest that the SP-2 R2 O technique increases the stress distribution of the plate and screws, which may reduce the stability of fixation after SSRO.