The role of folded fibular flap in patients’ reconstruction of mandibular defects: a retrospective clinical study

This study has analyzed 41 patients with mandibular ameloblastoma who underwent a partial mandibulectomy and reconstruction by folding the free fibular flap. In the preoperative and postoperative (6 months and 24 months after surgery), the Quality of Life (QOL) of these patients was assessed by using the University of Washington Quality of Life Questionnaire (UW-QOL) and the medical outcome study short form-36 (SF-36) questionnaires. SPSS 20.0 statistical software was used to conduct statistical analysis on the base data of the two groups of patients. Independent sample t test was conducted for sf-36 and UW-QOL scores at two time points in each group. The SF-36 survey showed that body pain (54.54 ± 8.10), general health (55.27 ± 7.54), and health changes (58.29 ± 9.60) decreased significantly at 6 months after surgery, but the mean score at 24 months after surgery all exceeded the preoperational level. At 24 months after the surgery, the vitality (80.41 ± 3.74), social function (81.61 ± 4.07), emotional role (82.39 ± 4.07), psychological health (81.66 ± 4.37) and total score (704.00 ± 31.53) all returned to the preoperative level, which was statistically significant compared with 6 months after surgery. However, there was no significant difference compared with the preoperative level. The UW-QOL survey showed that chewing (56.68 ± 7.23), speech (54.54 ± 7.7) and taste (62.29 ± 10.15) have significantly changed at 6 months after the surgery, and the difference was statistically significant at 24 months after surgery. Saliva generation decreased slightly (80.76 ± 3.35) at 6 months after surgery, but quickly returned to the preoperative level (81.59 ± 4.06). The total score of the patients almost recovered to the preoperative level at 24 months after surgery. The folded the fibular flap can not only repair the defects of soft tissue and bone tissue, but also restore the height of the alveolar ridge to, avoid the imbalance of crown and root ratio after implantation and reduce the occurrence of peri-implant inflammation, so that a true functional reconstruction can be realized.

SF-36 survey results. The specific score of SF-36 is shown in Table 2. The Physical role decreased significantly after the surgery. Although there was a significant improvement in the 24 months after the surgery compared with the first 6 months after the surgery (t = − 5.134, p = 0.000), it still could not return to the preoperative level (t = 11.685, p = 0.003). Body pain (54.54 ± 8.10), general health (55.27 ± 7.54), and health changes (58.29 ± 9.60) decreased significantly at 6 months after surgery, but the mean score at 24 months after surgery all exceeded that before surgery.
At 24 months after the operation, vitality (80.41 ± 3.74), social function (81.61 ± 4.07), emotional role (82.39 ± 4.07), psychological health (81.66 ± 4.37) and total score (704.00 ± 31.53) all returned to the preoperative www.nature.com/scientificreports/ level, which was statistically significant compared with the 6 months after the operation, but there was no significant difference compared with the preoperative level.
UW-QOL survey results. The specific score of UW-QOL is shown in Table 3. The items with significant changes after 6 months were chewing (56.68 ± 7.23), speech (54.54 ± 7.7) and taste (62.29 ± 10.15), which have significantly improved at 24 months after the surgery and the difference was statistically significant. Saliva generation decreased slightly (80.76 ± 3.35) at 6 months after surgery, but quickly returned to the preoperative level (81.59 ± 4.06). There was no significant change in the swallowing function after the surgery, and the total score of the patients almost recovered to the preoperative level at 24 months after the surgery (t = 2.271, p = 0.402).

Discussion
The mandibular defects directly affect the facial features, masticatory and articulation functions of the patient 11 . This damage also restricts the daily life and social activities of the patients to different degrees, and indirectly affects the psychological state and social activities of the patients 12 . Traditional indicators for the evaluation of oral diseases do not consider the impact of diseases on the quality of life of patients. With the change of medical model, it has become a goal that surgeons pursue to ensure patients receive better QOL while prolonging the survival of tumor patients through medical intervention 13 .
With the constant improvement of the microsurgical technique, as well as 3D printing, the upgrade of free fibular flap surgical technique offers increasingly extensive applications in the repair of the mandibular defects 14 . It can repair not only bone tissue defects, but also soft tissue defects. When looking to repair the upper and lower jaw and adjacent tissue defects it is the tissue flap of choice. However, the biggest disadvantage when using the fibular flap is that the height is only 1.3-1.5 cm. Therefore, the height of the reconstructed mandible cannot meet the needs of implant repair. In addition, the mucosal scar on the surface of the single fibular is thick, which not only increases the difficulty of imprinting 15 , but also easily produces peri-implant inflammation (Fig. 1). Alternatively, the folded fibular flap perfectly restores the height of the alveolar ridge, avoiding the imbalance of the coronal root ratio in implant repair 16 . The thin crest mucosa reduces the incidence of peri-implant inflammation, which greatly improved the sample patient groups chewing function, language expression, and further increased the patient's confidence. All flaps of the selected cases in this group survived. This included the 2 patients presenting with flap crisis at 12-24 h after the operation which resulted in blocked venous reflux from poor drainage. The flap remained completely viable following efforts to improve drainage, which involved the removal of blood clots at the bottom of the mouth and microthrombus at the anastomosis 17 .  www.nature.com/scientificreports/ After fibular transplantation, more than 90% of the follow-up patients reported that the discomfort of lower limb pain, weakness, numbness and other discomfort gradually disappeared after 6 months, and the feeling and function of lower limb movement were basically normal, without affecting daily activities, which indicated that the flap resection of the donor area had almost no effect on the mobility of the patients.
The SF-36 results show that: (1) all functions of the patients recovered after the surgery, but the body still could not return to the preoperative level at 24 months after the surgery, the patients still felt slight discomfort in the lower limbs, itching in the scar, and even some patients still could not fully accept the fact that the fibular flap a.
(a) Imbalance of the coronal root ratio.  The mucosal scar on the surface of the single fibular is thick, which not only increases the difficulty of implanting and imprinting, but also easily produces peri-implant inflammation. (c) We can move the fibula upwards, but this may result in maxillofacial asymmetry. www.nature.com/scientificreports/ was placed in the maxillofacial region.
(2) body pain, general health and health changes decreased significantly after the surgery, which was related to the recovery of the lower limbs of the patients. With the further exercise of function and the restoration of implant teeth, the average score at 24 months after the surgery was higher than the preoperational level, and the difference was statistically significant. (3) physiological function, vitality, social function, emotional role, mental health and the total score decreased significantly at 6 months after the operation, which was significantly related to the surgical trauma and the self-discomfort of the patients, but recovered to the preoperative level at 24 months after the operation. UW-QOL results show that: (1) with the passage of time, the oropharyngeal function of the patients after the operation was significantly improved, especially after the implant was used to repair the dentition defect, the chewing and language of the patients were substantially changed. (2) some patients suffered from damage to the lingual nerve during the operation, postoperative tongue numbness and a decline in taste. This generally recovered 3 months following the operation. (3) since the submandibular gland of the affected side will be routinely removed during the operation, there will be a temporary decrease in the amount of saliva produced after the operation, but with the compensation of other glands, the patient's symptoms decreased significantly. Results from the survey indicate that the impact on swallowing as a result of this surgery is not significantly adverse.
Emotional factors are the most influential issues for cancer patients 12 . We found that while the patient recovered in terms of physiological function, social function and family status, the emotional status could not return to the normal level at 6 months after the surgery 18 . The low scores of patients in mental health are largely related to the psychological reality of patients' inability to accept jaw resection and their inability to adapt to changes in basic life functions such as speech and eating after surgery 19 . Patients are always worried about the recurrence of the tumor and the uncertainty of the future 20 , so they often experience symptoms such as irritability, fatigue, insomnia, pain, diarrhea and constipation [21][22][23][24] . This indicates that the emotional damage caused by the tumor to patients is more serious and long-lasting 25 . Patients think they are sicker than others and that their health is deteriorating 26 . Therefore, psychological and emotional rehabilitation treatment for patients is very important 27 . The psychological problems of cancer patients have aroused the attention of clinicians. While treating the patients' diseases, the patients should be taught about the disease knowledge before the operation to alleviate their fear and anxiety about the unknown. After the operation, the discomfort of the oral, maxillofacial and lower limbs should be diagnosed and treated in a timely manner, and the patients should be encouraged to actively participate in social activities. At the same time, the survey shows that the encouragement and support of family members play a vital role in the physical and mental health of patients, and the love from family members makes it easier for patients to recover from the trauma of the disease. Therefore, the patient's psychological discomfort and social disorder require not only the joint efforts of doctors and patients, but also the care and support of family members.
The surface of a single layer fibula is covered with thick scars and mucous membranes, which is prone to peri-implant inflammation. It is advised that peri-implantitis and mucositis after fibula repair were identified in 14.8% and 20.3% of surviving implants, respectively, at the 5-and 10-year follow-up 28 . The study also suggests that skin or connective tissue grafts seem to offer an aid to manage this problem. We have found in the clinic that the incidence of peri-implant inflammation after folding the fibula is relatively low. This is because the mucosa on the surface is thin, which facilitates the smooth neck of the implant to penetrate the gums and facilitates the self-cleaning of the implant neck. The 12-month clinical trials have shown that there is no significant difference between the restoration supported by a single short implant and the long implant 29,30 . Although the three-year clinical trial of 2018 supported the view mentioned above 31 , the seven-year clinical study of 2021concluded that the survival rate of short implants was significantly lower than that of conventional implants (87% vs. 100%) 32 . At present, there is no relevant research on the restoration of multiple missing teeth on the fibula. Therefore, we also need to make more efforts in the clinic to study whether the use of crown-to-root ratio in a single-layer fibula is not different from that of a folded fibula.
It is suggested that the folded fibula is the best repair and reconstruction plan for the defect of the middle part of the mandible, and it provides a good foundation for implant restoration 33 . Compared with the conventional one-strut fibula transplant, the "double-barrel" graft achieved more bone height and appreciably reduced the vertical distance to the occlusal plane. This technique creates better conditions for prosthetic rehabilitation. The folded fibula and iliac bone graft can better reconstruct the vertical height of fibula than vertical traction 34,35 .
The implant restoration after fibular transplantation is still in the exploratory stage. Therefore, the sample size is small, and the follow-up time is not long enough. In the subsequent research, we will also focus on the problems caused by peri-implant inflammation and crown-to-root ratio imbalance.

Materials and methods
Patients. Forty-one cases with mandibular ameloblastoma underwent partial mandibulectomy and repair www.nature.com/scientificreports/ were as follows: (1) preoperative design was carried out using 3D printing technology and digital technology, intraoperative resection of the diseased mandible was performed, and the fibular flap technique was used for reconstruction and repair at the same time.
(2) No serious complications after the operation. (3) No recurrence of the primary disease. (4) Implant repair was performed at 6-9 months after surgery. The observation period was longer than 24 months.
Sequential treatment steps. The CT data of the patient's maxillofacial region and legs which has been obtained before the surgery has been imported into Mimics Research 20.0 software (Belgium Materialise company, https:// www. mater ialise. com/) to complete the 3D reconstruction of the jaw. The scope of resection was clarified when the extent affected by tumor was determined, and then the digital technology was employed to simulate partial resection of the mandible. The mandible date of the healthy side was copied to the affected side by mirroring method and its position was adjusted appropriately. Then after importing the patient's fibula data, the fibula was cut and shaped according to the best shape of the defect area to be restored. Finally, a 3D head mold was printed, and the titanium plate was pre-bent on the head mold. The operation was carried out in two groups at the same time: one group received a partial mandibulectomy according to the lesion range, retaining the articular disc. The condyle was retained depending on the situation with work on the arteriovenous system carried out in the receiving area. In the other group, the Henry approach was adopted in the posterolateral part of the calf, and the fibular flap was made conventionally. Depending on the defect range, the skin island and fibular length of the free fibular composite flap and the required muscles were designed according to the preoperative digital design scheme. The fibular flap was fixed with a Swiss sinins AO 2.0 prefabricated titanium plate before the pedicle fracture. The branches of the peroneal artery and the external carotid artery were manually sutured with 8-0 Prolene line, and then the peroneal vein was anastomosed with the internal (external) jugular vein with a microvascular anastomosis device to reconstruct blood circulation. The Straumann implant system was used to implant 4.1 standard neck implants at the level of soft tissue through fixed points and stage by stage holes. The length was 10-14 mm and the smooth neck was located at the top of the alveolar crest. Porcelain crown restoration was carried out 3 to 4 months after implantation (Fig. 2).
Questionnaire and collection. SF-36 and UW-QOL are available in Chinese and have been validated for a Chinese population.
(1) SF-36 is a widely used QOL measurement tool to assess the impact of overall health status on QOL. This questionnaire has been used by scholars to evaluate the QOL of cancer patients in China. It mainly includes 9 aspects of physiological function, body pain, physical role, general health, vitality, emotional role, social function, health change and psychological health. The maximum score of each item is 100. The higher the score is, the better the status is.
(2) UW-QOL is a self-administered questionnaire that designed for patients with head and neck cancer. Internationally it is one of the most commonly used head and neck cancers QOL questionnaires in use. It includes pain, appearance, activity, entertainment, swallowing, chewing, language, mouth opening, taste, saliva, mood, anxiety, and overall well-being. The domains are scored on a scale ranging from 0 (worst) to 100 (best). Chewing, swallowing, speech, taste and saliva can be used to assess the patient's oral function.
Assessment methods. SF-36 and UW-QOL questionnaires were used in the survey, and a combination of doctor's examinations and questionnaire were adopted in the methodology. Before the operation, the survey (utilizing both types of assessment questionnaires were explained to the patients in full detail. The patients were then instructed to fill in the first questionnaire pre operation, with the second and third surveys to be filled in at 6-and 24-month post operation, respectively. A scoring manual provided by the designer of the questionnaire was used for scoring patient symptoms.
Statistical analysis. SPSS 20.0 statistical software was used to conduct statistical analysis on the base data of the two groups of patients. Independent sample t test was conducted for sf-36 and UW-QOL scores at two time points in each group.
Ethical approval. This study was conducted under the regulations and guidelines in accordance with institutional research ethics board at The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China (2012-KY-230) and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. All methods and experimental protocols were reviewed and approved by the research ethics board prior to initiating the study. Informed consent for participation and publication of the images has been obtained from all the participants.