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Three-dimensional printing of surgical guides for mandibular distraction osteogenesis in infancy

Mao, Zhe, MD; Zhang, Na, MD; Cui, Yingqiu, MD*

Section Editor(s): Li., Yan

doi: 10.1097/MD.0000000000014754
Research Article: Diagnostic Accuracy Study
Open
SDC

Pierre Robin sequence (PRS) is a congenital malformation characterized by micrognathia, glossocoma, and mechanical obstruction of the upper respiratory tract. These deformities impair respiration, sleep, feeding, and swallowing, and can lead to malnutrition, stunted development, and death. Bilateral mandibular distraction osteogenesis, whereby the mandible and tongue root are extended outward, is the standard treatment to relieve upper airway obstruction in severe PRS. Accurate placement of the distraction device is essential but challenging, especially in infants, and requires the pre-operative fabrication of surgical guides based on CT images. Three-dimensional (3D) printing allows for the accurate recreation of objects from digitized models. We compared surgical efficacy and safety of bilateral mandibular distraction osteogenesis using 3D printed or traditionally fabricated surgery guides for treatment of infants with severe PRS.

During the period from 2014 to 2016, 22 patients with severe PRS were treated using either traditional or 3D printed surgery guides. We compared outcome measures of operations, including intraoperative bleeding, operation time, and postoperative complications.

The 3D printed surgery guide group demonstrated significantly shorter operation time (P <.05) as well as moderately shorter hospital stay and artificial ventilation time (∼1 day less). Furthermore, despite markedly younger average age of the 3D printed group (1.3 vs 3.5 months), there was no increase in postoperative complications using the 3D printed guides.

Three-dimensional printed surgery guides were used successfully for bilateral mandibular traction osteogenesis, and according to several outcome, parameters demonstrated superior efficacy and safety compared to traditional guides. Further research is warranted to extend the applications of 3D printed surgical guides for craniofacial surgery.

Guangzhou Women and Children's Medical Center, Guangzhou Medical University, Guangzhou, Guangdong, China.

Correspondence: Yingqiu Cui, Department of Oral and Maxillofacial Surgery, Guangzhou Women and Children's Medical Center, Guangzhou Medical University, Guangzhou, Guangdong 510120, P.R. China (e-mail: gzhtwang@163.com).

Abbreviations: 3D = three-dimensional, CT = computed tomography, PRS = Pierre Robin sequence.

The authors have no conflicts of interest to disclose.

This is an open access article distributed under the terms of the Creative Commons Attribution-Non Commercial License 4.0 (CCBY-NC), where it is permissible to download, share, remix, transform, and buildup the work provided it is properly cited. The work cannot be used commercially without permission from the journal. http://creativecommons.org/licenses/by-nc/4.0

Received October 18, 2018

Received in revised form February 1, 2019

Accepted February 9, 2019

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1 Introduction

Pierre Robin sequence (PRS) is a congenital condition first described by the French physician Dr Pierre Robin in 1923.[1] PRS normally involves micrognathia, glossocoma, mechanical obstruction of the upper respiratory tract, and feeding difficulty due to these malformations. The estimated prevalence of PRS is 1/3000, and the associated mechanical obstruction of the upper respiratory tract and feeding difficulties can lead to secondary symptoms like respiratory and sleep disorder, malnutrition, slow to negative increase in body weight during development, and early death in severe cases.[2] For children with severe PRS, surgical treatment normally includes bilateral mandibular distraction osteogenesis in which the mandible is extended outward, thereby moving the tongue in the anterior and inferior directions and relieving the respiratory tract obstruction for improved respiratory function, sleep, and swallowing.[3] Infants suffering from PRS are usually small and poorly developed with severe malnutrition. Therefore, accuracy, reduced intraoperative bleeding, and short operation times are critical for outcome.[4] Thus, the pre-operational preparation of surgery guides is very important.[5] Most of the surgery guides used for mandibular distraction osteogenesis are hand-made, and so may carry disadvantages like poor dimensional accuracy, easy deformation, and long processing time, that do not meet the requirements of clinical use. Three-dimensional (3D) printing has several advantages for this purpose, including digitalization, flexibility, and customization during the fabrication process, all of which may improve dimensional accuracy and reduce complications. Indeed, 3D printed surgical guides are widely used in related fields, including fabrication of medical models for pre-surgical diagnosis and training,[6,7] customized implants, and medical devices,[8–10] and 3D printed cell/tissue models for drug testing.[11,12] Three-dimensional models customized to the diseased body parts of individual patients can provide surgeons with direct perception of the disease condition and facilitate the design of a better surgical plan. The application of the 3D printing technique has the potential to effectively reduce surgical risks and enhance accuracy and treatment efficacy.[13] In this study, the preparation of 3D printed surgery guides and use in mandibular distraction osteogenesis are described and surgical outcomes compared to procedures using traditional manually fabricated surgery guides.

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2 Patients and methods

2.1 Research patients

This non-randomized, retrospective single-center study included patients undergoing bilateral mandibular distraction osteogenesis for severe PRS disease at our hospital. Surgical options are mainly reserved for infants with severe airway obstruction who do not respond to non-invasive interventions aimed at mitigating the need for tracheostomy. The 22 patients were randomly divided into 2 groups, a 3D printed surgery guide group (3D print group) with 10 patients and a traditional surgery guide group (control group) with 12 patients. Before surgery, patient conditions were analyzed and compared (Table 1). This grouping method was approved by the ethics committee. The patient's consent was signed by parents or caregivers.

Table 1

Table 1

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2.2 Preparation of surgery guides

All patients underwent computed tomography (CT) scanning before surgery. We transferred on mandibular structure to Mimics software for 3D modeling. For the control group, traditional surgery guides were prepared as follows. The 3D digital model of the mandible was transmitted to a 3D printer with STL data and printed. A wax model was handmade according to the printed model and the surgery guide was then made using bio-resin copying the wax model (Fig. 1). For the 3D print group, the 3D printed surgery guide was prepared as follows. A 3D model of the mandible was constructed by CT scanning data as described. Subsequently, the surgery guide model was designed by computer software and then fabricated of the same bio-resin using a 3D printer (Fig. 2).

Figure 1

Figure 1

Figure 2

Figure 2

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2.3 Surgery procedures

All surgeries were performed by the same group of doctors following routine procedures; the only difference was the method of surgical guide preparation. The surgical guides were sterilized before surgical. The patient was placed horizontally in the supine position. Under general anesthesia, submandibular incisions were made to expose the bone surface, the surgery guide was placed on the bone surface and wrapped around the mandibular angle, and we performed osteotomy along the guide line. After osteotomy, a nonabsorbable device was implanted with a vector like this along the mid-point of the condyle to the chin point, parallel to the surface of the jaw. (Figs. 3 and 4)

Figure 3

Figure 3

Figure 4

Figure 4

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2.4 Comparison of the surgery guide effect

Surgical outcomes and postoperative complications were compared between groups. Surgical outcome was assessed according to common indicators for PRS (Table 2) and common complications after bilateral mandibular traction osteogenesis (Table 3).

Table 2

Table 2

Table 3

Table 3

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2.5 Statistical analysis

Statistical analyses were performed using Excel 14.3.9 and SPSS. Continuous variables are expressed as mean ± standard error of the mean and categorical variables as proportions (%). Means of continuous variables were compared by the X test and proportions by the Y test. All tests were 2-tailed and a P <.05 was accepted as statistically significant.

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3 Results

There were no significant differences in birth weight (kg), gestational age (week), ratio of males to females, and incidence of palatal cleft between the control group and the 3D print group (all P >.05) (Table 1). Of preoperative factors examined, only age at operation differed, with control patients significantly older (P <.05), indicating that average patient condition for surgery was actually superior in the control group.

During surgery, the traction process went well for both groups, the bone formed well at the surgical site, and no infections or other complications occurred in the perioperative period (6 months). Surgery efficacy and safety were rated according to 5 indices, surgery time (minutes), bleeding amount (mL), time of post-surgical separation of the artificial airway (days), time of hospitalization (days), and time of post-surgical oral feeding (days) (Table 2). Surgery time was significantly shorter for the 3D print group than the control group (P = .023), while bleeding amount (mL), time of post-surgery separation of artificial airway (days), time of hospitalization (days), and time of post-surgery oral feeding (days) did not differ (P >.05). Time to post-surgical separation of the artificial airway and time of hospitalization showed a trend towards a shorter time period in the experimental group (P = .056).

Postoperative complications were assessed by 7 parameters, local skin infection, nerve injury, tractor shedding, dental injury, accidental fracture, facial asymmetric deformity, and scarring (Table 3), none of which differed significantly between groups. However, age at operation was significantly younger in the 3D print group and surgeries were more complex, requiring a higher degree of surgical accuracy.

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4 Discussion

Mandibular distraction osteogenesis was first described by McCarthy in 1989 and has since become the most widely used and effective treatment for airway obstruction caused by PRS.[14] The aim is to lengthen the mandible, which in turn will move the tongue root forward, thereby relieving respiratory tract obstruction induced by glossocoma. Successful application has been demonstrated to improve respiratory function, sleep, and swallowing.[15] It is generally performed when body position change and other conservative treatments cannot improve respiration or help wean patients from artificial respiration.[16] However, mandibular distraction osteogenesis is a high-risk treatment when used in infancy as multiple postoperative complications may occur, such as permanent tooth injury, tractor fall off, fracture accidents, mandibular alveolar nerve injury, bone nonunion, infection, and scars[17] Moreover, the severity of these congenital malformations varies widely among patients, so pre-operational individualized planning is essential to improve surgery efficacy and reduce postoperative complications. Developments in computerized structural modeling have provided surgeons with a platform to facilitate individual surgical design, but application remains difficult during actual surgery.[18] In infants, the small size of the mandible necessitates highly precise operative design and procedures, and any minor error can lead to serious complications. The use of surgical guides helps greatly in surgery design.[19] However, traditional surgical guides fabricated manually often have poor accuracy. The development of 3D printing technology may help solve this problem. By 3D printing, the surgical guide is a reverse engineered product of the surgery design. In this study, 2 different manufacturing methods of surgical guides were compared. We found that 3D printing guide plate has obvious advantages, but the sample size of this study was small, and further enlargement of sample size is needed for comparison in the future.

Frequently used 3D printing techniques include fused deposition modeling (FDM), stereo lithography apparatus (SLA), selected laser sintering (SLS), and 3D spray (3DP). A wide range of materials can be used for 3D printing, including natural and synthesized polymers, metals, and ceramics.[20] Several processing methods can also be chosen for surgical guide synthesis, but the mechanical and biological properties will vary.[21] Choosing the optimal processing method and material composition involves many considerations. In this study, a bio-resin was used for 3D printing of surgical guides, and results demonstrated significant advantages compared to surgical guides made by traditional methods. The limitation of the investigation is the small sample size. In future studies, the sample size needs to be further expanded. So that whether this 3D printing method using bio-resin is sufficient for other clinical requirements requires additional evidence. Requirements of physical strength and dimensional accuracy vary according to operation site and surgical method. Further, the additional cost of fabrication must be balanced against clinical advantages. For different operation sites and techniques, a variety of raw materials and printing methods can be adopted for 3D printed surgical guides to lower synthesis costs while still meeting clinical requirements.

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5 Conclusions

Three-dimensional printed surgical guides have sufficient accuracy and physical strength to meet the clinical requirements of difficult mandibular distraction osteogenesis. With the help of 3D printed surgical guides, we were able to shorten operative time significantly. Prospective studies are required to confirm our findings. We hypothesize that choice of the appropriate 3D printing technique and materials can reduce synthesis costs while still fulfilling clinical requirements.

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Author contributions

Conceptualization: Na Zhang.

Data curation: Zhe Mao.

Formal analysis: Zhe Mao.

Project administration: Yingqiu Cui.

Resources: Na Zhang.

Supervision: Yingqiu Cui.

Writing – original draft: Zhe Mao.

Writing – review & editing: Yingqiu Cui.

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References

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Keywords:

3D print; bilateral mandibular traction osteogenesis; Pierre Robin sequence; surgery guide

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