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S. Stübinger et al. (eds.)Lasers in Oral and Maxillofacial Surgerydoi.org/10.1007/978-3-030-29604-9_15
15. Laser Scanning in Maxillofacial Surgery
Capturing three-dimensional (3D) imaging is essential in the broad field of cranio-maxillofacial surgery. Laser scanners and stereophotogrammetry are more and more relevant for capturing (facial) soft tissues. For this purpose, a 3D laser scanning imaging system, using a nonhazardous laser, with a precise texture reproduction and in some models with colour capturing, can replace 3D imaging with radiation in many cases. This chapter gives an overview on the different applications of laser scanning in maxillofacial surgery. The following topics will be pointed out: the method of laser scanning; the laser scanning of plaster models, impressions and skull models; the laser scanning for oral surgical planning and for the assessment of facial swelling after oral surgery; the laser scanning of malformations; the laser scanning in facial aesthetics and epithetic procedures; and the laser scanning in orthodontic treatment and orthognathic surgery. 3D laser scanners are still commonly used, but recently other devices, often based on stereophotogrammetry or 3D camera systems, became often superior. Due to shorter acquisition times, these systems are less vulnerable to motion artefacts and, thereby, more suitable for capturing small children or less cooperative patients.
Laser scanningStereophotogrammetryPhotogrammetry3D imagingFacial aestheticsEpithetic proceduresOral surgeryMalformationsOrthodontic treatmentOrthognathic surgery
Once the machine is purchased for low cost, nowadays, short acquisition time and non-invasiveness are some of the advantages . Following the ALARA (as low as reasonably achievable) principle, radiation for 3D acquisition should be avoided whenever possible. Radiation reduction is essential because the radiation dosage accumulates throughout a subject’s lifetime. Publications, where dental X-rays and increased risk of intracranial meningioma  or computed topography (CT) imaging with possible influence to develop brain tumours or leukaemia [3, 4] were controversially discussed, lead to insecurity in patients. Magnetic resonance (MR) imaging would be another alternative to depict soft tissue, but the disadvantages prevail: long acquisition times and expensive and in the majority of magnetic resonance tomographs (MRT), the patient has to lie without moving. Therefore, due to gravidity, the soft tissue might be different to a sitting/standing position. Being able to offer a tool that allows 3D imaging without radiation is very helpful. A 3D laser scanning imaging system, using a nonhazardous laser, with a precise texture reproduction and in some models with colour capturing  can replace 3D imaging with radiation in large number of cases.
15.2 The Method of Laser Scanning
Below, the different usage of 3D laser scanning will be introduced: the scanning of plaster cast models and facial impressions, oral surgical interventions , orthognathic treatment and surgery , malformation, epithetic, aesthetics and facial movements [13–15]. Overlapping themes will be discussed depending on the aspect.
15.3 The Laser Scanning of Plaster Models, Impressions and Skull Models
The reliability of laser scanners in reproducing 3D objects has already been described , the accuracy and reproducibility having been tested on geometrical models and (facial/dental) plaster casts . The comparison of laser scanner and stereophotogrammetry for nasal plaster casts showed no significant differences between these two different techniques , whereas measurements on stone casts were somewhat smaller than values obtained directly from subjects (differences between −0.05 and −1.58 mm) . These findings were also detected by Holberg et al. . In their study, the accuracy of facial plaster casts and suitability for 3D mapping was investigated. From 15 adult volunteers, a facial alginate impression was taken. These impressions were poured with plaster resulting in facial plaster casts. The plaster casts and the probands’ faces were captured using a 3D laser scanner operating with structured light. They found – depending on the area of the face – deviations between 0.95 and 3.55 mm. Especially, soft tissue areas as lips, cheeks or tip of the nose as well as the lower face area showed marked differences. Areas with less soft tissue mass which could be shifted showed less deviations, e.g. forehead (1 mm) or nasal base (1.4 mm) .
15.4 The Laser Scanning for Oral Surgical Planning and for the Assessment of Facial Swelling After Oral Surgery
Jung et al. compared four intraoral scanners. One of them was a laser scanner (iTero; Cadent, Align Technology, San Jose, CA, USA). They compared the accuracy using models with buccal brackets and orthodontic wires where they found that the scanning results acquired by iTero were among the most reliable ones.
Buccal brackets and orthodontic wires were not clinically significant on the 3D image . The same scanner was used in a study, comparing different intraoral scanners as well as a lab scanner regarding the accuracy of scanbodies on dental implants. If computer-aided design or a computer-assisted manufacture process for implant prosthetics is requested, the digitization of the scanbodies is necessary. The precision of the intraoral scanners decreased with increasing distance between the scanbodies in contrast to the dental lab scanner. Independent of the increasing distance, a continuous precision was observed . All studies mentioned above were conducted with models. Lee et al. described the use of an intraoral laser scanner (iTero) for capturing the spatial position, surrounding tissue and a special scanning abutment of tooth implants in 36 patients. The acquired data were stored in STL format and used to produce a custom computer-aided design abutment and crown. Adjustments of contact and occlusion were required in six and seven patients, respectively, but the time for the adjustments was below 15 min . Another study, evaluating data from 100 patients, was published by San José V et al. . They were interested in comparing the reliability and accuracy of direct and indirect dental measurements using intraoral laser scanning (iTero), segmented cone beam computed tomography (CBCT) and a scanner for capturing plaster cast models. These results showed that both the iTero and the models segmented from CBCT are usable and accurate enough for dental measurements .
A different field is the evaluation of facial swelling after wisdom tooth removal. Before laser scanner and stereophotogrammetry became widely available , tape measurements were performed. Schultze-Mosgau et al. in their study about ibuprofen and methylprednisolone described how to measure the facial swelling by tape and ultrasound. They took distances from the lateral corner of the eye to the mandibular angle, from tragus to the outer corner of the mouth and from the tragus to the pogonion which they marked with a water-resistant pen . The use of an optical 3D scanner (FaceScan3D; 3D-Shape GmbH, Erlangen, Germany) for volumetric measurements of facial swelling is described by Rana et al. . They assessed the swelling after the use of different cooling mechanisms. For calculation of the volume, the patients were photographed while looking into a mirror with standard horizontal and vertical lines simulating a red cross marked on it. Harrison et al.  described the use of a laser scanner for the assessment of facial scanning. They evaluated a handheld laser surface scanner (FastSCANTM; Bruker Corporation, MA, USA) for the assessment of postoperative facial swelling. In their study, 20 patients were scanned before and 2 days after wisdom tooth removal. They detected the variability of the position as a source of inaccuracy. Otherwise, they found that the FastSCANTM is a simple, accurate and non-invasive method for the measurement of soft tissue volume changes.
15.5 The Laser Scanning of Malformations
Depending on the kind of malformation, a huge variety of 3D deviations to “normal” anatomy is seen. Just looking at cleft lip and palate patients, the cleft can vary widely. Lips with strong pouting and strong vermillion are seen, but it is also possible that the columella is short in combination with a severely contorted alar wing. Lip length differences also show a broad spectrum of variation, and so does the philtrum. For all of these variations, the non-cleft side (in unilateral clefts) is taken as the normal anatomy. The surgeon aims to establish anatomical symmetry as far as possible . The method of choice to perform the closure of the cleft varies between surgeons; therefore, a 3D tool for assessment of the surgical outcome is of high relevance in this field of maxillofacial surgery. It is also necessary to use standardized, reliable facial landmarks so a comparison is easier achievable. Literature about 3D facial landmarks is available [25, 26]. The identifications of landmarks need a certain amount of practice, but taking the same landmarks will show a learning effect and therefore higher accuracy in less time. For measurements, the patient’s presence is not necessary which is an advantage towards measurements taken directly/manually on the patient’s face.