Changes in condylar position and morphology after mandibular reconstruction by fibular flap with condyle preservation

doi:10.21203/rs.3.rs-1594185/v1

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Research Article

Changes in condylar position and morphology after mandibular reconstruction by fibular flap with condyle preservation

https://doi.org/10.21203/rs.3.rs-1594185/v1

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Journal Publication

published 26 Aug, 2023

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Objects

Changes in condylar position and morphology after mandibular reconstruction are important to aesthetic and functional rehabilitation. We evaluated changes in condylar position and morphology at different stages after mandibular reconstruction with condyle preservation.

Materials and Methods

A total of 23 patients who underwent mandibular reconstruction with fibular flap were included in this retrospective study. CT data of all patients were recorded before surgery (T0), 7 to 14 days after surgery (T1), and at least 6 months after surgery (T2). 5 parameters describing the condylar position and 4 parameters describing the morphology were measured in sagittal and coronal views of CT images. The association between clinical characteristics and changes in condylar position and morphology. A finite element model was established to investigate the stress distribution and to predict the spatial movement tendency of the condyle after reconstruction surgery.

Results

The condylar position changed over time after mandibular reconstruction. The ipsilateral condyles moved inferiorly after surgery (T0 to T1) and continually move anteriorly, inferiorly, and laterally during long-term follow-up (T1 to T2). Contrary changes were noted in the contralateral condyles with no statistical significance. No morphological changes were detected. No significant relationship between clinical characteristics and changes in condylar position and morphology. A consistent result was observed in the finite element analysis.

Conclusion

Condylar positions showed obvious changes over time after mandibular reconstruction with condylar preservation. Nevertheless, Further studies should be conducted to evaluate the clinical function outcomes and condylar position

Clinical relevance

These findings can form the basis for the evaluation of short-term and long-term changes in condylar position and morphology among patients who have previously undergone mandibular reconstruction by FFF with condyle preservation.

Condyle

Position

Morphology

Fibula

Mandibular Reconstruction

The mandible is the most important skeletal scaffold for the lower face which not only supports the facial contours but also maintains several oral functions such as chewing and vocalization[1, 2]. Mandibular defects, especially extensive defects caused by oncological resection, will lead to loss of function and facial deformity, which seriously affect the patient's life quality and physical and psychological health[2].

Since the introduction of the vascularized fibula free flap (FFF) by Hidalgo[3], its technique has undergone a series of refinements by reconstructive surgeons. Previous studies have shown that FFF has unique superiority in aspects of aesthetics and functional rehabilitation[2, 4, 5]. Therefore, many institutions now consider FFF the gold standard for the reconstruction of complex mandibular defects[6–8]. Additionally, computer-assisted surgery (CAS) has been adopted in the field of craniomaxillofacial surgery to improve the accuracy of surgery in recent decades. With the assistance of preoperative virtual surgery, 3D-printed cutting guides, and surgical Navigation system, CAS could facilitate the accurate harvest of transplanted bone grafts and avoid displacement of the mandible and condyle after reconstruction[9–12].

Although much effort has been devoted to the reconstruction of the mandible by FFF, little research to date has focused on tumor patients’ functional recovery, especially masticatory function, due to the greater concern over survival and recurrence. Previous reports have shown that CAS can enhance the precision of mandibular reconstruction and achieve preferable functional recovery[13–15]. However, several researchers found that, even in patients who had undergone CAS, the condyle may still show deviation, which could cause unstable occlusion and undesirable masticatory function[16–18]. Furthermore, Wang et al. [19] proposed that condylar positions showed obvious changes over time after mandibular reconstruction.

The finite element stress analysis method, which has been used for the first time in the study of oral biomechanics since 1973, has become an important method for predicting stress distribution characteristics because of its practical, effective, convenient, and non-invasive features[20–23]. In our study, finite element analysis was adopted to investigate the stress distribution and to predict the spatial movement tendency of the condyle after reconstruction surgery.

Hence, this study aimed to use different analytical methods to determine (1)how condylar position and morphology change over both short- and long-term; (2) how these changes of the condyle are affected by mandibular reconstruction in different settings; (3) what possible mechanical factors may contribute to these changes.

Patients

This retrospective study was conducted to evaluate the changes in condylar position and morphology after mandibular reconstruction. Patients were eligible who had undergone mandibular reconstruction from January 2018 to December 2020 at No.1 unit of oral and maxillofacial surgery department, Nanjing Stomatological Hospital of the Medical School of Nanjing University (Nanjing, China). This study protocol was approved by the institutional ethics committee (2018NL-027(KS)).

The inclusion criteria were (1) mandibular defect with condylar preservation; (2) sequential CT documentation; (3) a follow-up period of at least 6 months; and (4) no denture for the occlusal defects caused by the surgery. Patients with preoperative temporomandibular joint (TMJ) dislocation, postoperative unstable occlusal relation, and inconsistent occlusal position during CT scan were excluded from the study.

In our grouping strategy, patients were allocated to the study group receiving CAS or to the control group with conventional surgery. All patients in both the study and control group underwent surgery performed by the same chief surgeon in NO.1 unit of the oral and maxillofacial surgery department.

Surgical procedures

Major procedures included tumor resection, bone ﬂap harvest, and mandibular reconstruction. CAS was performed on all patients in the study group, including preoperative virtual surgery, real surgery, and postoperative accuracy analysis[14, 24, 25]. Patient-speciﬁc cutting and shaping guides and pre-bent surgical plates were designed and fabricated by UEG Medical (Shanghai, China). In the control group, all the operations were performed relying on the surgeon’s experience, including tumor resection, bone ﬂap harvest and shaping, and grafts fixation. In situ ﬁxation of the condylar head and ﬁbula in both groups was accomplished using reconstructive titanium plates and (or) mini plates according to the flap shaping method.

Data Acquisition

Patients’ gender, age, pathology, type of defect, and resection range were documented. The mandibular defect was reported according to the Brown classiﬁcation[26]. In the pre and postoperative accuracy analysis, the patient’s computed tomography (CT) data were used. CT scans were taken routinely by a spiral CT device (0.625mm slices) within 1 week before surgery (T0); 7 to 14 days after surgery (T1) to evaluate changes caused by surgery, and at least 6 months after surgery (T2) to assess long-term changes. Patients were instructed to bite their teeth together and stabilize their occlusion while the CT scans were taken. All patients were followed up for at least 6 months.

Parameters and measurement

The CT data were imported into Mimics software 20.0 (Materialise HQ, Leuven, Belgium) and Geomagic Studio 2013 (Geomagic®, Morrisville, North Carolina) for multiplanar reconstruction (MPR) and analysis. Various parameters were established to evaluate the condylar position and volume changes based on quantitative and qualitative measurements.

Initially, the Frankfort horizontal (FH) plane of all the CT images was adjusted perpendicular to the ﬂoor before the analysis. Then the condylar position was evaluated by two-dimensional images. The sagittal view, in which the condyle could be viewed with the widest transverse diameter, was selected as the reference view for measurement. The coronal plane image was selected by the same method.

Five parameters were established to evaluate the condylar position according to the methods proposed by Kamelchuk et al[27] and Tyan et al[28]. A sagittal plane image and an axial plane image were selected as the reference views for the measurement. In the sagittal view, point A and B were respectively deﬁned as the most prominent anterior and posterior aspect of the condyle. Point C was deﬁned as the most superior surface of the glenoid fossa. Line AA’, BB’, and CC’ were vertical to the line CA and CB, and FH plane respectively. The length of AA’, PP’, and CC’, representing the distance of anterior joint space (AJS), posterior joint space (PJS), and superior joint space (SJS) was measured (Fig. 1A). In the axial view, point F was deﬁned as the most superior surface of the glenoid fossa. Point D and E were respectively the contact point on the medial and lateral surface of the condyle with line FD and FE, which were tangent to the medial and lateral surface of the condyle respectively. Line DD’ and EE’, vertical to the line FD and FE, represented the distance of medial joint space (MJS) and lateral joint space (LJS) (Fig 1B).

Four parameters were established to describe the morphological characteristics according to the methods proposed by Hoppenreijs et al[29] and Kinzinger et al[30]. In the sagittal view, Y-axis was tangent to posterior border of the condyle neck with the connect point G. X-axis was drawn perpendicular to Y-axis through the broadest point K of condyle. Top of condyle (point N) is related to midpoint (point M) on X-axis. The length of GK and MN represented the condylar width (CW) and condylar height (CH) respectively (Fig. 2A). In the axial view, the distance between the most prominent medial point Q and the most prominent lateral point R represented the condylar length (CL) (Fig. 2B). In terms of the condylar volume (CV), the contralateral condyle was dissected at the level of the sigmoid notch from the 3D mandible model, whereas the ipsilateral side was dissected at the level of the highest point of the remaining condylar section if the sigmoid notch was resected. The CV of all patients’ bilateral condyles was also calculated by Rhinoceros 5.0 (Robert McNeel & Associate, Seattle, USA). These four parameters were only measured in the CT images of T1 and T2.

All measurements were repeated 3 times, and the mean value was used for statistical analysis.

After the measurements, the condylar position was calculated respectively as ln(PJS/AJS) and ln(MJS/LJS) based on the method proposed by Pullinger and Hollender[31]. The condylar positions were divided into 3 categories in both sagittal and coronal views based on the results. In sagittal view, 1) concentric if ln(MJS/LJS) was at least -0.25 to no greater than 0.25; 2) medial if ln(MJS/LJS) was less than -0.25; or 3) lateral if ln(MJS/LJS) was greater than 0.25; In coronal view, 1) concentric if ln(PJS/AJS) was at least -0.25 to no greater than 0.25; 2) posterior if ln(PJS/AJS) was less than -0.25; or 3) anterior if ln(PJS/AJS) was greater than 0.25.

Finite element analysis

In this study, Finite element analysis was adopted to simulate the occlusal process and predict the deviation of mandible and condyle due to the imbalance caused by the reconstruction surgery.

CT scan data of a patient from the CAS group were served as the pattern for reconstructing a 3D model in Mimics software (Fig. 3). We excised the tumor on the left side of the mandible to obtain the defective mandibular and design the fibular grafts, titanium plates, and rivets in 3-Matic software (Materialise, Leuven, Belgium) according to the postoperative 3D model. The articular disc was obtained by offsetting the condylar surface by 2 mm[32, 33].

The constructed model above is meshed in 3-Matic, where the non-fluid assembly is used so that the titanium rivets and the mandible, bone graft, and titanium plate in contact with it are co-noded. All surfaces of the model were first meshed using triangular slices with side lengths set to 0.5. Linear tetrahedral (C3D4) was used to mesh the skull, articular disc, mandible, teeth, implants, and rivets.

The material properties of the mandible were set by gray values of CT images to obtain cortical bone and cancellous bone referring to previous literature[34]. The mean CT value and bone density of the cortical bone were set to 1600 Hu and 1.73 g/cm³based on the reference value -1024 Hu and 0 g/cm³. The empirical formula proposed by Carter-Hayes and Zannoni[34] for density and elastic modulus was E=kρ³, k=4249 GPa (g/cm³) [21, 32, 35, 36]. All mechanical properties were set in Mimics software referring to the values in the previous studies (Fig. 4).

Table 1 Mechanical properties and Masticatory muscle forces set in Mimics software

Mechanical properties			Loading
Materials	Young's modulus (MPa)	Poisson's ratio	Muscles	Maximum force (N)
Bone grafts	7300	0.3	Superficial masseter	272.8
			Deep anterior masseter	73.8
Titanium rivets and plates (Ti6Al4V)	110000	0.3	Deep posterior masseter	65.8
			Anterior temporalis	308.0
			Posterior temporalis	222.0
			Medial pterygoid	240.0
Articular disc	44.1	0.4	Superior lateral pterygoid	38.0
Articular disc	44.1	0.4	Inferior lateral pterygoid	112.8

In this study, masticatory muscles were simulated as linear-elastic spring element- SpringA and added between the skull and mandible according to their anatomical location (Fig. 5). The stiffness values of springs were taken from the literature[37]: masseter muscle=16.35 N/mm, lateral pterygoid muscle=12 N/mm, medial pterygoid muscle=15 N/mm, and temporalis muscle=14 N/mm. The maximum muscle force was taken from the relevant research[38] (Table 1). The masseter muscle, medial pterygoid muscle, and temporalis muscle of the ipsilateral side were removed in this model due to the surgical resection of the corresponding mandible and soft tissue. The ligaments connected to the skull behind the mandibular condyles were also modeled as springs connected to the fixed point. A square was placed on the right molar to simulate food, and its elastic modulus and Poisson's ratio were set to 100 MPa and 0.4.

The contact between the condyle and the articular disc was set as frictionless contact in the model. The contact between the titanium rivets and the plates, the mandible, and the bone graft was bound. The contact was set as penalty contact both between the bone graft and the mandible and between the tooth and the simulative food. The top of the articular disc and the upper surface of the square were fixed in all degrees of freedom.

The final model was imported into ABAQUS (Dassault Systemes, Cedex, France) for subsequent finite element analysis.

Statistical analysis

Data were statistically analyzed using IBM SPSS Statistics 20.0 (IBM Corp, Armonk, NY). A systematic error was assessed using paired t-test, and the random error was calculated using the formula of Dahlberg. Continuous data were recorded as the mean with standard deviation (SD); comparisons were made using the two-sample t-test or one-way analysis of variance (ANOVA). Categorical data were recorded as the count with percentage; comparisons were made using the χ²test or Fisher’s exact test. All statistical tests were two-sided, and signiﬁcance was deﬁned as a P-value <0.05.

Demographics

The demographics and clinical characteristics are summarized in Table 2. A total of 23 patients were included in this retrospective research: 12 in the control group who received conventional surgery and 11 in the study group who received CAS. There was no difference between the two groups concerning age, sex, lesion type, Brown classification of the defects, extent of the masseter resection, or use of postoperative radiotherapy.

Table 2

The demographics and clinical characteristics of the patients.
Characteristic	Conventional group (n = 12), n (%)	CAS group (n = 11), n (%)	P-value
Age (years), mean ± SD	55.42 ± 12.62	49.55 ± 14.66	0.31
Sex			0.67
Female	5(41.7%)	3(27.3%)
Male	7(58.3%)	8(72.7%)
Lesion type			0.37
Benign	2(16.7%)	4(36.4%)
Malignant	10(83.3%)	7(63.6%)
Brown classification			0.16
I, II	11(91.7%)	7(63.6%)
III, IV	1(8.3%)	4(36.4%)
Masseter resection			0.41
Yes	8(66.7%)	5(45.5%)
No	4(33.3%)	6(54.5%)
Postoperative RT			0.68
Yes	8(66.7%)	6(54.5%)
No	4(33.3%)	5(45.5%)
CAS, computer assistant surgery. SD, standard deviation. RT, radiotherapy.

Changes In Condylar Position And Morphology

The distance of the TMJ space at different stages on bilateral condyles is shown in Fig. 5. Generally, the condylar position of both sides showed significant changes in both sagittal and coronal views at different stages, whereas that of the contralateral side did not change obviously over time. For describing the accuracy of the reconstruction, the TMJ space was compared between T0 and T1. Deviations were observed in the SJS (from 4.10 ± 1.20 to 4.82 ± 1.28 mm, P < 0.05) and the LJS (from 3.37 ± 0.85 to 4.05 ± 1.30 mm, P < 0.01)of the ipsilateral side.

In terms of the long-term positional changes, from T1 to T2, there was an obvious movement of the ipsilateral condyle. In the sagittal view, a prominent decrease in AJS (from 2.97 ± 0.77 to 2.29 ± 0.83 mm, P < 0.01) and a prominent increase in PJS (from 4.00 ± 1.40 to 4.67 ± 1.70 mm, P < 0.05) were detected. On the contralateral side, only the PJS showed an obvious decrease (from 3.12 ± 1.03 to 2.79 ± 0.97 mm, P < 0.05). The consistent results of an anterior movement of the ipsilateral side and a posterior movement of the contralateral side were presented in Fig. 5C. In the coronal view, only a remarkable decrease in LJS was detected on the ipsilateral side in the long term (from 4.05 ± 1.30 to 3.78 ± 1.07 mm, P < 0.01), indicating an overall lateral movement of the ipsilateral condyle (Fig. 5G). A contrary movement of the contralateral condyle was also observed in this research; however, the difference was not statistically significant. When evaluating the changes between T0 and T2, the ipsilateral condyle showed an obvious anterolateral and inferior movement, while the contralateral side showed a contrary movement with no statistical significance.

Figure 5 Changes of the condylar position at different stages. A-C In sagittal view, the ipsilateral condyle showed an anterior movement during long-term follow-up (P < 0.01), whereas the contralateral side showed a posterior movement. D The superior joint space of the ipsilateral condyle increased continually over time (P < 0.01). The contralateral side only showed an obvious decrease in the long term. E-G In coronal view, the ipsilateral condyle showed a lateral movement in the long term (P < 0.01).

The four parameters describing the morphological characteristic of bilateral condyles after mandibular reconstruction are shown in Fig. 6. As a result, no significant changes were detected in all four parameters of bilateral condyles after long-term postoperative follow-up. A consistent result was observed after the superimposition analysis of bilateral condyles by the best-fit algorithm in the Geomagic Studio software (Fig. 7).

In this retrospective study, an analysis of variance was adopted to evaluate the association between the clinical characteristics and the changes in condylar position and morphology from T1 to T2. However, there were no positive results yielded from the analysis (table. 3, Table 4).

Table 3

The association between the clinical characteristics and the changes in condylar position
Characteristic	\(\varDelta\)ln(PJS/AJS), mean ± SD	P-value	\(\varDelta\)ln(MJS/LJS), mean ± SD	P-value	\(\varDelta\)SJS, mean ± SD	P-value
Group		0.98		0.92		0.26
Conventional	0.50 ± 0.44		0.28 ± 0.45		0.95 ± 1.32
CAS	0.49 ± 0.27		0.29 ± 0.57		0.41 ± 0.82
Lesion type		0.80		0.57		0.22
Benign	0.46 ± 0.27		0.18 ± 0.75		0.20 ± 1.36
Malignant	0.51 ± 0.40		0.32 ± 0.40		0.86 ± 1.01
Brown classification		0.74		0.36		0.86
I, II	0.48 ± 0.36		0.34 ± 0.49		0.71 ± 1.26
III, IV	0.55 ± 0.42		0.10 ± 0.53		0.61 ± 0.32
Masseter resection		0.20		0.28		0.37
Yes	0.58 ± 0.39		0.39 ± 0.38		0.88 ± 1.15
No	0.39 ± 0.32		0.16 ± 0.62		0.45 ± 1.09
Postoperative RT		0.70		0.47		0.64
Yes	0.52 ± 0.36		0.22 ± 0.36		0.60 ± 1.19
No	0.46 ± 0.39		0.38 ± 0.68		0.83 ± 1.05
AJS, anterior joint space. PJS, posterior joint space. MJS, medial joint space. LJS, lateral joint space. CAS, computer assistant surgery. SD, standard deviation. RT, radiotherapy

Table 4

The association between the clinical characteristics and the changes in condylar morphology
Characteristic	\(\varDelta\)CH	P-value	\(\varDelta\)CW	P-value	\(\varDelta\)CL	P-value	\(\varDelta\)CV	P-value
Group		0.83		0.64		0.28		0.21
Conventional	0.06 ± 0.61		0.48 ± 0.96		0.27 ± 1.49		118.50 ± 258.16
CAS	0.02 ± 0.35		0.27 ± 1.09		-0.28 ± 0.70		2.26 ± 159.88
Lesion type		0.34		0.32		0.69		0.68
Benign	0.21 ± 0.37		0.74 ± 0.77		-0.16 ± 0.75		95.94 ± 260.92
Malignant	-0.02 ± 0.52		0.25 ± 1.07		0.07 ± 1.32		51.25 ± 211.69
Brown classification		0.54		0.17		0.35		0.88
I, II	0.08 ± 0.54		0.22 ± 0.96		0.13 ± 1.29		59.67 ± 233.52
III, IV	-0.08 ± 0.26		0.93 ± 1.07		-0.45 ± 0.63		74.55 ± 185.97
Masseter resection		0.27		0.57		0.12		0.82
Yes	-0.06 ± 0.58		0.27 ± 1.19		0.35 ± 1.41		53.45 ± 242.09
No	0.17 ± 0.34		0.52 ± 0.74		-0.44 ± 0.65		75.20 ± 200.07
Postoperative RT		0.57		0.65		0.70		0.57
Yes	-0.01 ± 0.54		0.46 ± 0.95		-0.07 ± 1.36		41.05 ± 230.87
No	0.12 ± 0.42		0.25 ± 1.14		0.13 ± 0.93		96.90 ± 211.02
CH, condylar height. CW, condylar width. CL, condylar length. CV, condylar volume. CAS, computer assistant surgery. SD, standard deviation. RT, radiotherapy

Mechanical Analysis And Prediction

The displacement nephograms of the finite element analysis in ABAQUS software are shown in Fig. 6. For both sides, the preserved mandible, bone grafts, and titanium plates all showed a resultant displacement towards the anterior, inferior, and medial sides (Fig. 6B-D). Consequently, the displacement of the whole mandible after the reconstruction manifested as a clockwise rotation respectively in sagittal, coronal, and axial views. The maximum displacement was observed in bilateral mandibular angles (3.657mm on the ipsilateral side and 3.762 mm on the contralateral side, Fig. 6E-G).

Studies show that the TMJ is rarely invaded by tumors of the body and superior ramus of the mandible[39–41]. Thus, surgeons always manage to preserve the condyle as possible so that the patient’s original mandible function can be largely restored. How to use the fibular flap and preserved condyle to reconstruct the mandibular is an arduous task for every surgeon. Owing to the rapid development of CAS technology, mandibular reconstruction has become more exercisable and accurate, and patients who suffered from mandibular defects could rehabilitate aesthetics. However, even in this circumstance, there could still be a change in condylar position after reconstruction, which might lead to TMJ pain, clicking, poor incisal opening, malocclusion, or bone resorption[16–19]. Much attention has been paid to the morphology of grafted fibular bones and the matching degree of the mandible after the operation. There is a lack of sufficient studies on condylar morphology and position to reveal the reasons for patients' unsatisfactory functional recovery after reconstruction. Therefore, this comprehensive study investigated changes in condylar position and morphology after mandibular reconstruction at different stages and in different clinical settings.

Based on the evaluation of the postoperative and long-term changes of the condylar positions, we found significant changes in both the conventional and the CAS groups. Condyles on the ipsilateral side showed an anteroinferior deviation after surgery and tended to move in the same direction continually during follow-up, whereas a contrary result was noted on the contralateral side without a statistical significance. Therefore, the conclusion consistent with previous studies that the condylar position would change indeed during the long-term postoperative recovery.

Regarding these results, it is not clear whether this consequence is due to the movement of the condyle itself or to a change in its morphology. Four morphological parameters were measured additionally in this study to address this issue. Finally, we observed no obvious changes in the morphology of bilateral condyles. The assumption that morphological changes led to the position changes is excluded.

Several studies have shown that resorption of the transplanted fibula is one of the reasons for the displacement[42]. However, more studies, which were based on at least 10-year follow-ups, concluded that the fibular flap was the most stable bone graft compared with the scapular and iliac crest[43–45]. We speculate that these postoperative changes may be caused by changes in patients’ occlusion and muscle mechanics, rather than the resorption of the transplanted fibula.

When evaluating the patients who accepted orthognathic surgery, their condyles showed movement in different directions. Previous research suggested that this might be affected by various factors, such as fixation methods, rotational movement of the distal segment, masticatory muscle tension, and the surgeon’s experience[46, 47]. However, these patients’ condyles tended to return to the preoperative position 3 months after surgery and remain stable during 1 year of follow-up[48]. A similar phenomenon was also observed among patients with a condylar fracture who may not undergo precise surgical condylar restoration[49]. We intended to evaluate the correlation between clinical characteristics and changes of condylar position by ANOVA, but no significant results were detected. Thus, further studies with a large cohort of patients are warranted to further evaluate this association.

Reasons for the different outcomes noted in this study are various. The most prominent one is that the reconstruction surgery breaks the balance of patients’ occlusion and neuromuscular environment. The radical surgery will not only resect the lesion location of the mandible and soft tissue but also lead to a defect of dentition. To the best of the authors’ knowledge, most patients suffer from lateral mastication or malocclusion which could result in the displacement of the condyle and even TMJ dysfunction[50]. On the other hand, most masticatory muscles were peeled off or even resected with the tumor during surgery, which disturbs the balance of the muscular system. Although most of the masticatory muscles are preserved in benign lesion cases, it requires time for muscles to reattach and rebalance in new positions. During this time, the oral and maxillofacial system remains in an unbalanced state. Moreover, in terms of malignant tumor patients whose part of total masticatory muscles are resected, the strength of residual muscles was not sufficient to maintain the condyles in the preoperative position[19]. In this study, we designed a finite element model of the mandible to simulate this unbalanced system based on the patient's real condition. The consistency between the prediction and actual measurement results suggested that the imbalance of the occlusal and muscular system was the main cause of the long-term changes of the condylar position. Nevertheless, a more precise finite element model, especially a dynamic one, is needed to accurately simulate the process of occlusal movements.

The TMJ is a complicated diarthrosis, and the condyle plays a vital role in TMJ function[41]. Previous literature has shown that whether the condyle is correctly restored in the articular fossa is a crucial indicator of better functional outcomes[51]. Indeed, the direct relationship between condylar position and clinical outcomes is far from established. Several researchers claimed an index, the minimal clinical important difference (MCID), should be emphasized and verified in this field[18]. Patients’ functional outcomes can be affected by various factors. Some scholars proposed that simultaneous implant denture restoration could accelerate the recovery of occlusion[52]. However, only some of the patients with benign lesions could be suitable for this treatment. According to our clinical experience, it still requires months for the healing of fibular grafts and gingivoplasty before denture restoration. There is also the hypothesis that radiotherapy might influence mandibular movements and TMJ function because of the formation of substantial scar tissue and the fibrosis of ligaments and muscles[53]. But it remained inconclusive because no valid evidence was found.

The findings of the present study showed obvious condylar positional changes after mandibular reconstruction using the free fibular flap with condylar preservation. The ipsilateral condyles moved anteriorly, inferiorly, and laterally during long-term postoperative follow-up. Contrary changes were observed in the contralateral condyles with no statistical significance. Further studies should be conducted to evaluate the clinical function outcomes and condylar position in patients with preserved condyles.

Conflict of interest

The authors declare that they have no competing interests.

Author Contributions

Haoliang Chen and Guowen Sun conceived the study design and contributed in manuscript revision. Yongheng Li contributed in the finite element analysis in this research. Haoliang Chen and Yawei Sun participated in data collection and statistical analysis. Xin chen, Yumei Pu, and Guowen Sun were the main surgeons of the operation in this research. All authors reviewed the manuscript.

Funding information

No funding was obtained for this study

Ethics approval and consent to participate

Ethical approval for this study was granted by the Ethics Committee of Nanjing Stomatological Hospital (2018NL-027(KS)). All procedures were executed strictly according to the tenets of the Declaration of Helsinki. Patient written consent was obtained routinely.

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Changes in condylar position and morphology after mandibular reconstruction by fibular flap with condyle preservation

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