ORIGINAL ARTICLE

The Application of Rapid Prototyping Techniquein Chin Augmentation

Min Li Æ Xin Lin Æ Yongchen Xu

Received: 12 April 2009 / Accepted: 24 June 2009 / Published online: 30 July 2009

� Springer Science+Business Media, LLC and International Society of Aesthetic Plastic Surgery 2009

Abstract

Background This article discusses the application of

computer-aided design and rapid prototyping techniques in

prosthetic chin augmentation for mild microgenia.

Methods Nine cases of mild microgenia underwent an

electrobeam computer tomography scan. Then we per-

formed three-dimensional reconstruction and operative

design using computer software. According to the design,

we determined the shape and size of the prostheses and

made an individualized prosthesis for each chin augmen-

tation with the rapid prototyping technique.

Results With the application of computer-aided design

and a rapid prototyping technique, we could determine the

shape, size, and embedding location accurately. Prefabri-

cating the individual prosthesis model is useful in

improving the accuracy of treatment. In the nine cases of

mild microgenia, three received a silicone implant, four

received an ePTFE implant, and two received a Medpor

implant. All patients were satisfied with the results. During

follow-up at 6–12 months, all patients remained satisfied.

Conclusion The application of computer-aided design

and rapid prototyping techniques can offer surgeons the

ability to design an individualized ideal prosthesis for each

patient.

Keywords Computer-aided design � Rapid prototyping

technique � Microgenia � Chin augmentation

Microgenia is a kind of malformation of the lower face that

is caused by osteodysplasty of the chin with manifestation

as a small mental region and chin retraction. Recently,

people have been paying more attention to the shape of

their chin, and the number of patients desiring chin aug-

mentation has increased. The treatments for microgenia are

genioplasty and chin augmentation. Mild microgenia is

very common in our clinical practice. Plastic surgeons

often perform chin augmentation with a silicone or ePTFE

implant [1, 2]. In general, a surgeon evaluates a patient’s

microgenia by X-ray examination and then designs the

proper sized implant. During the operation, the surgeon

carves the implant using his clinical experiences to achieve

a satisfying outline. Even so, the surgeon can not get a

precise personalized prosthesis. To achieve a better result,

we used computer-aided design and a rapid prototyping

technique to design personalized chin implants preopera-

tively. With these two techniques, we prefabricate the

prosthesis mold as an intraoperative reference and get

satisfactory cosmetic results.

Materials and Methods

Clinical Data

There were nine female cases in this series ranging in ages

from 18 to 40 years. All cases presented with mild

microgenia and normal occlusion. All cases received chin

augmentation: three chose medical silicone implants, two

chose Medpor, and four chose ePTFE.

M. Li (&) � Y. Xu

Department of Traumatic and Aesthetic Surgery, Huangsi

Aesthetic Surgery Hospital, No. 9 Anwai Huangsi Street,

Beijing 100120, China

e-mail: elbert_lily@163.com

X. Lin

Department of Surgery, Unit 2, South Building, PLA General

Hospital, No. 28 Fuxing Road, Beijing 100853, China

123

Aesth Plast Surg (2010) 34:172–178

DOI 10.1007/s00266-009-9397-x

Three-Dimensional Reconstruction of Skull and

Prosthetic Model

All cases underwent a computer tomography (CT) scan of

the skull (C-150, Imatron, Hayward, CA, USA). Continu-

ous volume scanning was applied to collect imaging data

from the vertex of the cranial region to the mental region.

Scanning parameters were as follows: 130 kV voltage,

1.5 mm width, 216� angle of rotation, and 0.1 s exposure

time. All these data of slices were transferred to a com-

puter. Using 3DMsee (Gimmafei Technology Development

Co., Ltd., Beijing, China), three-dimensional reconstruc-

tion software, we abstracted the profiles of facies cranii and

soft tissue and got their vectorization diagrams. With these

data we were able to perform three-dimensional recon-

struction and get a stereo view of the facies cranii and soft

tissue (Figs. 1 and 2). In the same way, we scanned the

prosthesis and got its three-dimensional reconstruction

image. Then we performed the operational design and

simulation with the computer.

Operational Design and Simulation

We performed the operative design through computer-

aided three-dimensional reconstruction. First, we deter-

mined how long the mental region should be extended. We

measured the distance from the hairline to the glabella

(D1), from the glabella to the subnasal point (D2), and

between the subnasal point and the submentum (D3). The

difference between D3 and D1 or D3 and D2 was the

length of the chin extension (Fig. 3). Second, we had to

determine the thickness of the mental region. We marked

the nasal tip and lower lip, and extended the line from these

two points to the mental region. Then we measured the

vertical distance from this line to the pogonion; this was the

extended thickness of the mental region (Fig. 4). After that,

we simulated on the computer the implantation of the

Fig. 1 Three-dimensional reconstruction of skull

Fig. 2 Three-dimensional reconstruction of facial contour

Fig. 3 To determine how long the mental region should be extended,

the distances from the glabella to the subnasal point (D2) and from the

subnasal point to the submentum (D3) were measured. The difference

between D3 and D2 was the length of chin extension

Fig. 4 To determination the thickness of mental region, the nasal tip

and lower lip were marked and a line was extended from these two

points to the mental region. The vertical distance from this line to the

pogonion was the ideally extended thickness of the mental region

Aesth Plast Surg (2010) 34:172–178 173

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prosthesis into the mental region. In accordance with the

above measurements and aesthetic standards, we per-

formed the operative design, adjusting the location of

prosthesis implantation to keep the connection of the

prosthesis border and mandible natural and smooth

(Fig. 5).

Manufacture of Prosthetic Mold

Using the rapid prototyping technique, we transferred the

computer-aided design of the prosthetic implant to a rapid-

form machine and made the prosthetic mold (Fig. 6). From

it we can make individual silicone implants.

Operative Procedure

First we put the prosthetic mold into the mental region and

marked the central line and its designed location with

methylene blue according to the preoperative plan. Then

we started local anesthesia and made a V-shaped incision

in the gingival sulcus of the intraoral mucous membrane of

the lower lip, which was more than 0.5 cm away from the

gingiva. After incising the mucous membrane, submucosa,

and periosteum, we dissected the periosteum in the pre-

marked region as a plane with a detacher. It was extremely

important to control bleeding and place the prosthesis

under the periosteum in the mental region. Finally, the

Fig. 5 Computer simulation of the implantation of the prosthesis into

the mental region. a Anterior view of skull with prosthesis. b Lateral

view of skull with prosthesis. c Loxosis view of skull with prosthesis.

d Anterior view of face with prosthesis. e Delineation of mental

region with prosthesis. Yellow line marks the extended length of the

mental region

174 Aesth Plast Surg (2010) 34:172–178

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operational field was flushed with saline containing gen-

tamicin and the periosteum and mucous membrane were

sutured. We recommend pressure dressing for the opera-

tional field, a liquid diet for 3 days postoperatively, and

taking antibiotics orally for prophylaxis of infection.

Results

In our nine cases of mild microgenia, three received a

silicone implant, four received an ePTFE implant, and two

received a Medpor implant. All these prostheses were made

according to a preoperative design. Silicone implants can

be manufactured directly with the designed prosthetic

mold. However, Medpor and ePTFE implants had to be

carved to the shapes of the designed prosthetic molds. Each

prosthesis was implanted in accordance with the computer-

assisted preoperative design. Each operation resulted in a

satisfactory chin and facial shape (Figs. 7, 8, 9, 10, 11, 12,

13, 14, 15, 16, 17, 18) without complications. In the 6–12-

month follow-up, all patients were satisfied on the whole.

Fig. 6 a Anterior view of the

prosthetic model. b Dorsal view

of the recess of the prosthetic

model. c Anterior view of three-

dimensional reconstructed skull

model with prosthesis

Fig. 7 Preoperative front view of case 1

Fig. 8 Postoperative front view of case 1, six months after ePTFE

implantation

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Discussion

The mental region is an important part of the face. Its shape

and relative position with respect to the upper mandible

and nose directly affect their harmony and facial outlook.

Different from micrognathia, microgenia appears mainly as

the retraction of the mental region with normal, decreased,

or increased mandible length in the lengthwise direction.

McCarthy [3] classified microgenia into two categories:

normal occlusion and abnormal occlusion accompanied by

abnormal articulation. McCarthy et al. [4] had another

classification of microgenia according to the longitude

proportion of the vertical and sagittal mandible planes.

Type I included decreased sagittal length but normal ver-

tical length. Type II included decreased vertical length but

normal sagittal length. Type III had decreased sagittal and

vertical lengths. Type IV had decreased sagittal length but

increased vertical length. A short chin, mild mandibular

retraction, and microgenia with normal occlusion were all

indications for mental region augmentation. Silicone,

Fig. 9 Preoperative profile view of case 1

Fig. 10 Postoperative profile view of case 1, six months after ePTFE

implantation

Fig. 11 Preoperative front view of case 2

Fig. 12 Postoperative front view of case 2, six months after ePTFE

implantation

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ePTFE, and Medpor were optional filling materials. In

general, silicone and ePTFE implants did not need fixation

but Medpor implants had to be fixed with titanium nails.

Computer aided surgery (CAS) [5] has become a part of

clinical medicine. With the application of computer-assis-

ted image analysis and three dimensional reconstructions,

we can get more precise information than by traditional

methods. Also, model surgery based on a rapid prototyping

technique has become an important adjuvant to modern

surgery. Rapid prototyping techniques began at the end of

the 1980s. With the integration of computer-aided design,

computer-aided manufacturing, numerical control tech-

niques, laser techniques, and material science, surgical

operations can be performed in a more precise and

systematic manner. Recently, although CAS and rapid

prototyping techniques can be used in craniomaxillofacial

surgery, e.g., the rectification of congenital craniofacial

malformations (ocular hypertelorism, craniostenosis, first

and second branchial arch syndrome) and traumatic and

postoperative osseous defection, those techniques still had

limited application in cosmetic surgery. The improvement

of surgical accuracy is the inexorable trend in cosmetic

surgery, especially for those surgical operations associated

with filling materials such as rhinoplasty, chin augmenta-

tion and temporal augmentation. These operations depend

more on a rigorous and individual preoperative design

consistent with aesthetics than on a surgeon’s experience

Fig. 13 Preoperative profile view of case 2

Fig. 14 Postoperative profile view of case 2, six months after ePTFE

implantation

Fig. 15 Preoperative front view of case 3

Fig. 16 Postoperative front view of case 3, six months after Medpor

implantation

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and stereotyped feature. In our clinical practice, the rapid

prototyping technique was used to design individual pros-

thetic filling implants for the mental region. We designed

and prefabricated the mold for the prosthesis preopera-

tively using CAS and rapid prototyping techniques. Then

we carved the filling material following the predesigned

mold or directly used the silicone implant which was made

according to the predesigned mold. It simplified the oper-

ating procedure and shortened the operating time. In our

series, all patients underwent preoperative design accord-

ing to facial and mental aesthetics using computer-aided

three-dimensional reconstruction techniques. After deter-

mination of prosthetic size, shape, and location, we made

the personalized mold with the rapid prototyping tech-

nique. Then we carved and implanted the filling material

using the predesigned mold or directly used the silicone

implant which was made according to the mold. This

procedure was totally different from traditional operative

methods which depended on visual measurement and

experience. It not only shortened the operating time and

improved the accuracy of rectification, but also achieved

the best personal profile matching.

At present, this technique still has its limitations. For

example, implant materials such as Medpor and ePTFE

could not be sintered directly except for unitane, and with

the rapid prototyping technique we have to manufacture the

model for prosthetic material first and then trim the pros-

thetic material in accordance with the prosthetic mold. That

affects the accuracy of the rectification. Besides, the

computer-assisted designation could not picture the chan-

ges of soft tissue following osseous changes [6], i.e., when

designing chin filling, the effect on local soft tissue could

not be pictured. This means that the surgeon could not get

information on the result of the rectification. All these

limitations still need further research. We are sure that in

the future the rapid prototyping technique will be used

increasingly in medicine.

References

1. Guyuron B, Michelow BJ, Willis L (1995) Practical classification

of chin deformities. Aesthet Plast Surg 19:257–264

2. Stambaugh KI (1992) Chin augmentation: an important adjunctive

procedure to rhinoplasty. Arch Otolaryngol Head Neck Surg

118:682–686

3. McCarthy JG (1990) Plastic surgery. WB Saunders, Philladephia,

pp 1350–1332

4. McCarthy JG, Ruff GL, Zide MB (1991) A surgical system for the

correction of bony chin deformity. Clin Plast Surg 18:139–152

5. Li Y, Zhen Y (2007) Application of rapid prototyping in

craniofacial surgery. Chin J Aesth Med 16(9):1309–1311

6. Liu XJ, Gui L, Zhang ZY, Peng X, Liu C (2006) The application of

three-dimensional skull model in the treatment of craniofacial

malformation. Zhonghua Zheng Xing Wai Ke Za Zhi [Chin J Plast

Surg] 22(3):169–171

Fig. 17 Preoperative profile view of case 3

Fig. 18 Postoperative profile view of case 3, six months after

Medpor implantation

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