In vitro biomechanical comparison of six different fixation methods following 5-mm sagittal split advancement osteotomies

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.

Influence of the mandibular plane and magnitude of the movement in sagittal split ramus osteotomy: an in vitro study

PURPOSE

The aim of this study was to evaluate fixation resistance in mandibular sagittal split ramus osteotomy in standardized polyurethane hemimandibles with two types of advancement (6 and 12 mm), with or without mandibular plane rotation, using a 2.0-mm plate/screw system.

METHODS

Seven groups were evaluated using a vertical compressive load in the first molar region, and the applied force in Newtons was recorded in 1 mm, 5 mm, and 10 mm displacements, as well as the maximum force.

RESULTS

There was a statistical intergroup difference and it was observed that increasing the advancement decreased fixation resistance with a single plate, and inserting an additional plate significantly increased osteosynthesis resistance.

CONCLUSION

In the 12 mm advancements, clockwise rotation proved to be more resistant when fixed with only one plate. By contrast, counterclockwise rotation was significantly more resistant in stabilizing the mandibular sagittal ramus osteotomy when two plates were used.

Assessment of Resorbable and Non-resorbable Fixation Systems in Sagittal Split Ramus Osteotomy: An In vitro Study

Objective

The internal fixation has been purpose of study for many years, but there is still no consensus on the best method of fixation in relation to resistance for bilateral sagittal split ramus osteotomy (BSSO) using plates. Therefore, the aim of this study was to assess five different methods of osteosynthesis using resorbable and non-resorbable plates and screws in simulated sagittal split osteotomy (SSO) of the mandibular ramus.

Materials and Methods

SSO was performed in 25 polyurethane synthetic mandibular replicas. The distal segments were moved forward 5 mm, and the specimens were grouped according to the fixation method: Inion resorbable plate, KLS resorbable plate, standard four-hole titanium miniplate (Medartis), two standard four-hole titanium miniplates (Medartis) and an adjustable titanium miniplate (Slider/Medartis). Mechanical evaluation was performed by applying compression loads to first molar using an Instron universal testing machine up to a 5 mm displacement of the segments. Resistance forces were obtained in Newtons (N), and statistical analysis was performed using the software R v. 3.5 with significance level of 0.05. Linear mixed models were used to compare the force required to move each type of plate.

Results

The results showed that the resistance of SSO was better accomplished using two titanium miniplates and KLS resorbable plate showed the least resistance. However, both titanium and resorbable plates behaved similarly in small displacements, which are most commonly observed in BSSO postoperative time.

Conclusion

It can be concluded that both resorbable and non-resorbable systems might offer suitable mechanical resistance in the procedures where there are no mechanical postoperative complications.

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.

Stability of fixation methods in large mandibular advancements after sagittal split ramus osteotomy: an in vitro biomechanical study

Sagittal split ramus osteotomy (SSRO) with large mandibular advancements is a common surgical procedure and could be indicated for patients with sleep apnoea. As a large variety of fixation methods is used for the stabilisation of SSRO, a biomechanical test model was used to analyse which fixation technique was most stable. For this in vitro study, 80 polyurethane hemimandibles with a prefabricated SSRO were used as substrates. Loads in Newtons were recorded at displacements of the mandibular incisive edge at 1mm, 3mm and 5mm. The samples were divided into two groups: mandibular advancements of 10mm and 15mm. In both groups, four fixation techniques were used: (A) one four-hole miniplate; (B) two four-hole miniplates; (C) one four-hole miniplate plus one bicortical screw; and (D) three bicortical screws in an inverted-L arrangement. In group 1, three bicortical screws resulted in the best stability, and in group 2, two miniplates resulted in the best stability. The use of two miniplates did not show significant differences between both groups. Other fixation methods showed more stability with 10mm advancements. This study therefore suggests that in SSRO with advancements exceeding 10mm, the use of two miniplates is the optimal means of providing rigid fixation.

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.

Biomechanical Analysis of the Forces Exerted during Different Occlusion Conditions following Bilateral Sagittal Split Osteotomy Treatment for Mandibular Deficiency

The bilateral sagittal split osteotomy (BSSO) technique is commonly used to correct mandibular deficiency. If the patient is exposed to excessive external forces after the procedure, occlusal changes or nonunion may occur. However, previous studies only focused on single external forces on the mandible and did not conduct relevant research on the forces exerted by different occlusion conditions. The main purpose of this study was to use finite element analysis methods to determine the biomechanics of four common occlusion conditions after BSSO surgical treatment. This study constructed a finite element analysis computer model of a miniplate implanted in the lower jaw. The structure of the model consisted of the mandible, miniplate, and screws. In addition, external forces were applied to the superficial masseter, deep masseter, medial pterygoid, anterior temporalis, middle temporalis, and posterior temporalis muscles to simulate the incisal clench, intercuspal position (ICP), right unilateral molar clench (RMOL), and right group function occlusion conditions. Subsequently, this study observed the effects of these conditions on the miniplate, screws, and mandible, including the von Mises stress values. The results showed that all of the different occlusion conditions that this study evaluated placed high stress on the miniplate. In the ICP and RMOL occlusion conditions, the overall mandibular structure experienced very high stress. The screw on the proximal segment near the bone gap experienced high stress, as did the screw on the buccal side. According to the present analysis, although the data were not directly obtained from clinical practice, the finite element analysis could evaluate the trend of results under different external forces. The result of this study recommended that patients without intermaxillary fixation avoid the ICP and RMOL occlusion conditions. It can be used as a pilot study in the future for providing clinicians more information on the biomechanics of implantation.

Biomechanical evaluation of hybrid fixation method of sagittal split ramus osteotomy in mandibular advancement

PURPOSE

In this study, eight different fixation methods applied after sagittal split ramus osteotomy (SSRO) were compared experimentally.

MATERIALS AND METHODS

SSRO was performed to 48 sheep hemimandibles in eight groups of 6 each. Group A- a four hole standard miniplate; Group B- a four hole standard miniplate and one bicortical screw; Group C-a four hole locking plate; Group D-a four hole locking plate and one bicortical screw; Group E-a six hole straight miniplate; Group F-a six hole straight miniplate and one bicortical screw; Group G- a sliding plate, which was specifically designed for SSRO; Group H- sliding plate and one bicortical screw.

RESULTS

In terms of measured values of displacement, the highest degrees of displacement were observed in decreasing order in Groups G, C, A, and E. The least displacement values were detected in Groups H, F, D and B with values being very close to each other. For linear force applied up to 70N, 3 mm or higher displacement values were not seen in any fixation system.

CONCLUSION

According to the results of study, all systems are suitable for clinic usage. However, intermaxillary fixation or functional elastics may be needed for sliding plate systems during the healing period of hard tissue.

Fixation methods in sagittal split ramus osteotomy: a systematic review on in vitro biomechanical assessments

The aim of this systematic review was to assess the stability of rigid internal fixation (RIF) techniques in sagittal split ramus osteotomy (SSRO) based on in vitro biomechanical assessments, with particular interest in large mandibular advancements. In general, RIF methods can be divided into three groups: bicortical screws, miniplates, and a combination of the two. An electronic search of the PubMed, CINAHL, and Embase databases was performed, and studies published between January 2003 and March 2018 were screened for inclusion. Comparative studies with an in vitro experimental design, using biomechanical assessments to measure the stability of RIF methods in SSRO, were included. Of 104 unique studies identified in the initial search, 24 were included. Twenty-two of these 24 studies analyzed an advancement of the mandible of 7mm or less. The use of a single four-hole or six-hole miniplate was less stable than the use of bicortical screws, hybrid techniques, double miniplates, or grid plates. Two studies analyzed advancements of 10mm, for which two miniplates placed in parallel and a grid plate showed most stability. Although there was agreement between studies with regard to results, more biomechanical studies are required to quantify the stability of fixation methods in larger mandibular advancements.

Comparative study of biomechanical stability of resorbable and titanium fixation systems after sagittal split ramus osteotomy with a novel designed in-vitro testing unit

INTRODUCTION

Sagittal split ramus osteotomy (SSRO) is one of the most popular surgical procedures for correction of mandibular deformities. Several clinical and biomechanical studies exist in the literature which, comparing the stability of different osteosynthesis materials and techniques, were performed using two or three-point biomechanical test models. The aim of this study was to compare the stability of biodegradable and titanium materials for SSRO on one-piece polyurethane mandible samples which were fixed in a novel designed 6-point testing unit.

MATERIALS AND METHODS

16 polyurethane one piece replicas of human mandibles were used and bilateral SSRO were performed by the manufacturer according to Dal Pont modification. Mandibles were fixed with titanium and PLLA/PGA fixation materials. Displacement amounts were measured under loading forces using a non-contact extensometer, and strain values at the screws were recorded by strain gauges.

RESULTS

Bicortical titanium screws (Group 2) showed significantly lower displacement values, while bicortical PLLA/PGA screws (group 4) showed significantly higher displacement values at 40-360 N forces. (p < 0.05). The highest strain value was measured on screws that were inserted upright in a proximal segment near the osteotomy line.

CONCLUSION

To achieve more realistic results in biomechanical studies, test models should imitate jaw movements and test environments should be as similar as possible to physiological conditions. Newly designed six-point testing units will contribute to future biomechanical studies.

Mechanical evaluation of six techniques for stable fixation of the sagittal split osteotomy after counterclockwise mandibular advancement

We have evaluated the resistance to displacement of six stable methods of fixation of a sagittal split ramus osteotomy (SSRO) in the mandibular advancement with counterclockwise rotation. We tested 60 synthetic hemimandibles in six groups of 10 each: Group I - fixation with a straight four-hole 2.0mm miniplate; Group II - a straight six-hole 2.0mm miniplate; Group III - two straight 2.0mm four-hole miniplates; Group IV - an eight-hole 2.0mm (grid plate); Group V - a 2.0mm four-hole straight miniplate and 2.0×12mm bicortical screw; and Group VI - a straight four-hole 2.0mm locking miniplate. We applied a linear force in the region between the canine and the first premolar using a universal testing machine (EMIC- DL2000) with a loading cell of 10 KN. The loads at 1, 3, and 5mm displacement were recorded (N) and the data transmitted from the load cell to a computer. Results were analysed using analysis of variance (ANOVA) (p<0.001) and the Tukey post-test for comparison of the significance of the differences between the groups. For the three degrees of displacement, fixation with two straight 2.0mm plates and with the grid plate gave higher load values.