Enhanced Lip-Contour During Facial Scan for 3D DSD and Implant Planning: A Blue Screen Approach Open Access

The rapid development of stereophotogrammetric imaging systems has permitted the use of digital technologies for the 3-dimensional (3D) prediction of dentofacial esthetics.^1–4  This image acquisition method captures several images of the patient's region of interest from multiple angles simultaneously; therefore, the potential introduction of error due to patient movement is reduced. Stereophotogrammetric imaging systems evaluate the coordinates of facial landmarks with excellent reproducibility and high precision.⁵  However, distortion could be introduced in anatomical areas with occlusion of illumination, such as the oral fissure, nostrils, and palpebral fissure. This primarily occurs at the image reconstruction stage since these areas differ considerably from the easier-to-capture flatter surfaces, such as the tragion and nasion region.^6–8 

Digital dental technologists can proceed with a 3D digital smile design (DSD) or a prosthetically driven implant planning after determining the relation of the standard tessellation language (STL) file from the intraoral scanner (IOS) to the 3D facial image from the extraoral scanner.⁹  This is a critical step to plan an accurate bone reduction for extensive implant-supported fixed reconstructions. However, the dentition and 3D facial image data must accurately reproduce the lip–tooth relationship in the computerized-assisted design software. This clinical report describes a face-scanning technique for 3D esthetic analysis and restorative-driven implant placement planning. The technique, which uses a customized silicone matrix and is aided by blue-screen technology, aims to capture a more accurate lip record.

A male patient presented to the hospital's dental clinic, reporting considerable esthetic problems and wishing to replace his maxillary screw-retained implant-supported fixed complete denture. After several options were presented, the patient decided to replace the implant-supported fixed complete dental prosthesis with a new prosthesis. Therefore, the patient agreed to evaluate a 3D esthetic analysis to improve his satisfaction with the future oral rehabilitation by understanding his expectations and potential esthetic limitaitons.^10,11 

1. The maxillary and mandibular dental arches were recorded using an IOS system (TRIOS; 3Shape A/S).

2. The 3D digital diagnostic casts with the intermaxillary relationship were obtained (Figure 1a), and the 3D digital images (Figure 1b) were exported in STL file format [file A].

3. Silicone putty (Coltene Rapid, Coltene/Whaledent, Inc) was added to the buccal surface of the visible teeth and gingiva (Figure 2a). The patient was instructed to repeatedly contract his orofacial muscles, for example, by protruding the lips and lifting the corners of the mouth,¹²  to reduce the excess material adding volume onto the cheek's buccinator muscle laterally and onto the orbicularis oris muscle anteriorly. The silicone's cameo surface was smoothened to prevent the scanning light from being obstructed by surface irregularities (Figure 2b).

4. The patient was scanned extraorally with a 3D face scanner (FaceSCAN^3D Scientific Photolab 60 Hz; 3D-Shape). The face was scanned in a dynamic position (ie, smiling) with a silicone matrix (Figure 3a). The 3D face image was exported and saved as an object file (ie, .obj) [file B].

5. The 3D face with silicone matrix image was imported into quality control software (Geomagic Control X; 3D Systems). The contour between the lips' vermilion border and the silicone matrix was outlined (Figure 3b). The silicone area was deleted, and the new image was saved (Figure 3c) [file C].

6. The 3D facial image file [file C] was superimposed using the maxillary arch file [file A].¹³  A new silicone key was fabricated, and a printed facebow for maxillary occlusal plane registration, which consisted of a horizontal bar with 5 scattered balls acting as scan bodies, was added (Figure 4a). The silicone key was scanned with the facebow (AutoScan-DS-EX, Shining 3D) and superimposed with file A using common references (eg, the buccal aspect of anterior teeth). Then, the dentition and facebow 3D objects were combined into a new file [file D] (Figure 4b). Step 4 was repeated, adding the facebow to the silicone matrix (Figure 4c). This file was exported as a new file [file E] (Figure 4d), and it was superimposed with file C using common references (eg, buccal surfaces). Then, a file was generated by combining the face and facebow 3D objects [file F]. File F was superimposed onto file D by superimposing the shared surfaces of the facebow 3D object. Lastly, the dentition and facial 3D objects were merged (Figure 4e).

The 3D representation of dentofacial objects with well-defined contours is of value for accurate esthetic diagnosis and prognosis.^1–4,9  The integration of facial stereophotogrammetry acquisition and dental laser scan reproduction is well documented. Nevertheless, the deformation around the transition area between the lip vermilion border and dentition of the 3D object (due to an incomplete algorithmic image) introduces errors in the esthetic analysis (see Figure 5a).⁸  Although the distorted dentition region may be replaced with an undistorted one from the superimposition procedure (Figure 5b), little attention has been given to reproducing an undistorted lip contour.¹⁴  Local facial deformation in the stereophotogrammetric image causes deviations in the reproduced teeth–lip relationship (Figure 5b). To the authors' knowledge, there are no methods for recording the lip-teeth transition zone in extraoral canning. The dental industry is developing dynamic scanners to capture this hard-to-record zone from diverse angles better.

Silicone has been useful in several conventional clinical scenarios.^15–19  In the presented case, the distortion of the 3D image around the lip vermilion area due to illumination obstruction could be reduced with the silicone matrix emulating the blue screen principle (as well-known as, green screen or chroma key). This principle consists of a visual effect (ie, a postproduction method) for blending 2 video streams or illustrations dependent on color hues. As described here, this visual effect supports the compositing of 2 images through distinct color hues, providing a uniform cameo surface to capture a “complete” 3D image (Figures 2–4). A more reliable 3D reproduction can thus be obtained by superimposing a more accurate 3D stereophotogrammetric facial acquisition with the digitized dental arches (Figure 5c). This could be combined with other digital techniques to transfer the records to a virtual articulator.²⁰ 

Silicone putty was selected for the custom-made matrix for 3 reasons. First, it is mate, and its color distinguishes the lips' vermilion border. Thus, the 3D outline along the lips' vermilion border becomes easier to capture and define. Second, the putty can be manipulated and molded by patients' muscular compression from natural and exaggerated facial expressions. This reduces any tension on the labial and buccal soft tissues when of filling the vestibular aspect with putty. Finally, the putty is smoothed and provides a more regular surface to capture complete images with the laser scanner. Moreover, any other material with the above-listed characteristics could be used instead of silicone for the presented clinical technique.

Although the fabrication of the silicon matrix adds chair-time, the advantages mentioned above may justify its use for a partial-digital and more accurate workflow. It was observed that the silicone slightly displaced the lips buccally; however, the volumetric dimensions were not considerably altered. Thus, the esthetic analysis was not compromised. This can be further evidenced in the visual comparison between Figures 5c and d. It is expected that facial scanner technology will continue to improve, and as a result, the limitations regarding the anatomical areas lacking proper illumination will be minimized if not eliminated.

It should be considered that operator differences and patient cooperation can both lead to considerable distortion in the final silicone index produced. Nevertheless, a standardized method of incorporating a blue screen should be further developed.

This article describes a straightforward technique to avoid deformations in the lip fissure of 3D facial stereophotogrammetric objects. Image distortion caused by image incompletion could be avoided with the aid of a silicone matrix used as a blue screen. This technique advances esthetic analysis practice and prosthetically driven implant planning based on 3D facial image reproduction.

3D:

3-dimensional

DSD:

digital smile design

IOS:

intraoral scanner

STL:

standard tessellation language

Study supported by the Peking University School and Hospital of Stomatology grant (PKUSSNCT-19B11), the Peking University Stomatological Hospital Teaching Reform Project (2022-PT-06), the Key Health Projects of Science and Technology Development of Lanzhou (2021002), and the National Natural Science Foundation of China (82271039 and 82071171).[aa]