7.1 Digital Imaging

7.1.1 History

For years, 2D imaging modalities like panoramic, cephalometric radiography, and dental photography have been used routinely by orthodontists to do basic orthodontic diagnosis, treatment planning, and monitoring of case progress. Certain cases, though, would require 3D investigation, like impacted canines and TMJ pathology, and the only option for 3D imaging and analysis in the past was medical-grade Computed Tomography (CT), but the radiation dose associated with it was so high to justify its use by orthodontists, especially because of the age of the orthodontic patient population [1]. Details about the imaging technologies is given in Chap. 3. CBCT and its use in orthodontics will be touched upon briefly in this section.

7.2 Cone Beam Computed Tomography (CBCT)

The advancement in technology and the invention of Cone Beam Computed Tomography (CBCT) provided a great alternative to CT. Some of the key advantages of CBCT over CT are that CBCT has a relatively lower radiation dose and cost, a significantly smaller footprint, and the acquisition and reconstruction time is lesser. All this made CBCT gradually replace 2D imaging, particularly in cases with impacted teeth (Fig. 7.1) [2], eruption problems, root proximities, root resorption, TMJ issues, complex orthognathic surgery cases, and to locate and diagnose maxillofacial pathologic structures [3].

7.2.1 Additional Benefits of CBCT in the Orthodontic Practice

Apart from the additional advantages of CBCT for accurate diagnosis and treatment planning, CBCT data can be used to [1]:

1. 1.

   Design 3D guides for miniscrews placement which will help orthodontists avoid any damage to anatomical structures and reduce patient discomfort (Fig. 7.2) [4].

    
2. 2.

   Analyze and monitor airway volume (Fig. 7.3) [2].

    
3. 3.

   Monitor and study very accurately the skeletal and dental effects of rapid maxillary expansion or any treatment modality that expands the teeth transversely.

    

7.3 3D Facial Photography

Facial scanners provide a 3D topography of a patient’s facial surface anatomy, which when combined with digital study model and CBCT image will give a complete 3D virtual representation of the patient [3, 5].

Facial scan can be generated within seconds either with a facial scanning machine like the Vectra M3 (Fig. 7.4), Artec Eva, and Arc Bellus 3D (Fig. 7.5), or can be created from the same CBCT scan like Planmeca ProFace, or simply using a smart phone app like Bellus 3D face app.

Clinicians and dental labs can use the 3D face as an integral part of diagnostic, surgical, and restorative smile design planning to accelerate high-value case acceptance and clinician approval. It is also a highly effective tool for preoperative planning and postoperative comparisons and superimpositions [6].

7.4 4D Facial Photography

There are certain limitations to 2D which are well documented. Using videos, evaluation of the motion of facial muscles mainly during talking and smiling was undertaken with some benefits but the main drawback is again 2D capture.

For this purpose, the motion capture stereophotogrammetry has recently been introduced to overcome the errors obtained from 2D and 3D still photography. 4D imaging allows clinicians to gain information and treatment plan based on a patient’s facial animations and expressions rather than the static views. 3dMDface™ dynamic system (3dMD, Atlanta, GA) and 4D capture system (DI3D™, Dimensional Imaging, Glasgow) are examples of commercially available 4D imaging systems [6].

7.5 Digital Model Acquisition

7.5.1 Extraoral Scanners

7.5.1.1 History

The primary purpose of digital model was to allow for easier storage of patient’s study models. In the 1990s, Ortho CAD™ introduced digital model fabrication into dentistry. Ortho CAD™ was primarily a scanning center where stone models or PVS impressions were sent and processed into digital file that was downloaded to an orthodontist’s office network. This has significantly reduced the need for large physical storage areas. By 2014, digital models were commonly used for diagnostic purposes in 21–55% of the US orthodontic practices [7].

Extraoral (EO) scanners offer an indirect method of obtaining a 3D digital model. Components of an extraoral scanner include: (a) a chamber with a platform, (b) a laser light source, and (c) a digital camera. Laser or white light technology is used to scan the impression or plaster model. The scanner is usually used in a laboratory setting where the impression or model, and bite registration is placed inside the chamber on the platform and rotates 360° allowing different angles to be recorded by a specialized sensor that gathers reflected surface data points from the object.

In terms of precision and accuracy, some studies [8, 9] showed significant differences in mesiodistal widths, arch length measurement, and tooth size-arch length discrepancy (TSALD) analysis measurements when 3D scanned models are compared to plaster model measurements. This being said, 90% of the mean differences were less than 0.20 mm, verifying that the extraoral scanners are clinically acceptable. One reason for inaccuracies is that even with the use of rotational feature and multiple angle views during scanning, there are often undercuts in the impressions or models that are difficult to capture thus leading to inaccuracies in indirect scanning techniques.

How to Choose an Appropriate EO Scanner

The different models differ mainly in resolutions and speeds. Accuracy of scans range from 15–200 microns, and speed for plaster model and impression scan range from 1 min 30 s to 7 min. Each scanner comes with a software that provides different features like digital storage of patient records, 3D cast analysis, and treatment planning features, such as tooth size measurements, landmark identification, arch length analysis, tooth segmentation, and evaluation of occlusion and occlusal contacts. Some software like Ortho analyzer feature sculpt and rebase applications with collision control, tooth movement simulation, superimposition of study models with photographs or DICOM data from CBCT images, and digital manufacture of appliances and restorations.

7.6 Intraoral Scanner

The intraoral scanner is an electronic device that emits a light source (which can be laser or structured) that captures the anatomical structures of the teeth and surrounding gum and creates a digital document of it in the form of 3D images (Fig. 7.6) [10]. This topic is covered in detail in Chap. 6.

7.6.1 Scanners in Orthodontics Today

7.6.1.1 Precision and Accuracy

Modern scanners’ precision is equal to or even better than alginate impressions converted to stone casts. One reason can be the elimination of error during impression taking and handling and the other reason is the elimination of error that can occur during pouring and manipulation in the lab. The less steps we have, the less error we get [6, 11].

7.6.1.2 Advantages

Digitally scanned occlusal records have several advantages over traditional study casts, in that they are [3, 6, 12]:

• Accurate and simple to produce.

• Easy to detect and correct defects immediately which reduces the time lost in retake due to impression inaccuracies and distortion.

• Cause minimal patient discomfort, mainly in patients with gag reflex or kids who are apprehensive towards impressions or their taste.

• Eliminate the need to maintain the materials required for conventional impressions.

• Minimize disinfection and cross-contamination issues.

• Avoid the storage problems of plaster casts, the possibility of breakage or misplacement.

• Easily shared worldwide without the need for packing and shipping, which will save on time and shipping cost.

• Immediately available chairside for analysis and viewing.

• Faster to start treatment planning and model analysis like arch length, arch width, and tooth size Bolton analysis in speedy and more accurate method.

• Can be used in various orthodontic software to perform virtual treatment plans within minutes as opposed to diagnostic wax up. One example is the iTero Element 5D by Align Technology that provides Invisalign result simulator feature in which within 1 min after a full scan of the mouth is performed, the patient can see an example of a possible result after orthodontic treatment (Fig. 7.7).

• Facilitates better communication with other professionals mainly in multidisciplinary cases that needs restorative planning.

• Perfect marketing tool as it facilitates virtual treatment objective (VTO) communication with patient, visualization of treatment outcome, and help the patient better understand the treatment process.

With an intraoral scanner, orthodontists report improved diagnosis and treatment planning abilities, increased case acceptance, faster records submission to insurance companies, fewer retakes, reduced chair time, reduced storage requirements, quicker lab turnaround times, improved appliance accuracy and fit, lower inventory expenses, and reduced treatment times [13].

7.6.1.3 Disadvantages

7.7 CBCT

The image of the dentition from CBCT can be used in certain cases, like (orthognathic surgery, dental impaction, and craniofacial syndromic cases) that require CBCT for diagnosis and treatment planning, or if the clinic adapted a protocol of replacing the 2D imaging (panoramic/cephalometric) by CBCT.

If one does acquire a CBCT scanned image, the CBCT images can be merged with the STL files from digital intraoral scans to create a 3D image of the dentition as well as the corresponding bone and root. This will allow the clinician to monitor the roots movement during treatment by retaking IO scans and superimposing them on the initial scan to monitor root movement [14]. The merged CBCT and STL files can also facilitate the creation of surgical guides, placement of temporary anchorage devices (TADs), and exposure of impacted teeth.

7.8 3D Printing

3D printing or additive manufacturing is a process of making three-dimensional solid objects from a digital file. It is the opposite of subtractive manufacturing, in which a block of material is carved away to form the object (as with milling units such as the chairside economical restoration of aesthetic ceramics, or CEREC).

7.8.1 History

In 1984, Chuck Hull developed 3D printing, also known as additive manufacturing, when he was using ultraviolet light to cure tabletop coatings. He established the 3D Systems Company in 1986 and created the first machine for rapid prototyping, which he called stereolithography (SLA) [15].

7.8.2 3D Printing Technologies

The most common technologies used for 3D printing today are stereolithography (SLA) and digital light processing (DLP) [16]. Some of the materials that are used in 3D printers are plastic, cobalt, nickel, steel, aluminum, and titanium. The print medium is either in liquid form or unwound from a spool.

7.9 Digitization and Direct Appliance Manufacture

Over the course of the past decade, the dental industry has been revolutionized by computer-aided design/computer-aided manufacturing (CAD/CAM) and 3D printing technology. Used in conjunction with intraoral scanning, 3D printing offers more efficiency in orthodontic practices and laboratories through fabrication of study models, aligners, acrylic and metal appliances, and indirect bonding trays. All this brought a new level of speed and ease to old procedures [13, 16].

The digitization process requires the dentition and soft tissues to be accurately captured by an intraoral scan or produced with a lab scanner from the impression tray/gypsum cast directly, allowing the acquired 3D data to be used to design and manufacture any type of appliance. The output from IO/EO scanners is usually saved in stereo lithographic (STL) format. Most software systems allow access to these files, enabling import and manipulation of the 3D data to design the appliance as desired.

7.10 Study Models

A rapidly advancing digital technology in orthodontics is 3D modelling and printing, prompting a transition from a more traditional clinical workflow toward an almost exclusively digital format. Digital models of the patient dentition and oral structures can be created either indirectly from a patient’s models or impressions using an extraoral scanner, or directly from the patient’s oral cavity using an intraoral scanner.

Most clinicians are satisfied with manipulating and analyzing digital models and will not request a printed 3D model for case study except in complex cases or in a teaching environment where it can be challenging to manipulate the digital models to discuss and explain treatment plans to students or patients [17] (Fig. 7.8).

7.11 Aligners

Clear aligner therapy (Fig. 7.9) with Invisalign introduced by Align Technology in the late 1990s led the way in using a virtual model, creating a virtual treatment plan (Fig. 7.10), and manufacturing appliances from digital models. Nowadays, many companies, like clear correct, 3 M™ Clarity™ Aligners, Eon aligners, and many others are offering the same service. The digital workflow of CAD/CAM and 3D printer will allow clinicians to design and create their own in-house aligners [3].

At this stage, however, aligners are still molded on individual printed models of every step in the sequence, which is a waste of 3D printed material, as thousands of tooth arches are printed daily in many orthodontic clinics and laboratories, without a stipulated regimen for disposal afterwards. Advancement in biocompatible 3D printing materials is expected to overcome this step in the very near future as it will allow the direct printing of aligners without the need for printed models.

Recently, digital smile design is being integrated with virtual aligners’ treatment plan software in order to plan the treatment based on the best smile for the patient.

7.12 Custom Brackets

7.12.1 Lingual Brackets

Customization of brackets started with lingual appliances over 15 years ago when Dr. Wiechmann created a fully customized lingual appliance Incognito (3 M Unitek, Monrovia, CA) (Fig. 7.11).

A virtual setup is created to achieve the treatment outcome, then fully customized brackets are digitally designed to fit the lingual surface of the teeth, then they are 3D printed in wax, and then cast in gold. The wires are then robotically bent to fit the individual arch form and to achieve the desired treatment outcome. The result is a fully customized lingual appliance with a low profile that closely mimics the lingual tooth surfaces, with a high degree of precision, and reduced tongue discomfort [18].

The orthodontist has the option to either do direct bonding of the brackets, due to the extended customized base, which permits clear-cut positioning on the tooth, or to do indirect bonding with the two-phase silicon bonding trays (Fig. 7.12) [18], which is the more time-saving option and will reduce the possibility of saliva contamination. This technology has overcome the many disadvantages that orthodontists faced with lingual braces like the substantially higher bracket loss compared to labial cases, the complexity and imprecision of indirect rebonding technique, the time-consuming finishing process, and the overall less quality compared to labial cases [19].

When accuracy in tooth positioning with a fully customized lingual orthodontic appliance, Incognito (3 M Unitek, Monrovia, CA), was studied it showed accuracy in achieving the goals planned at the initial setup, except for the full amount of planned expansion and the inclination at the second molars [20, 21]. Several other fully customizable lingual appliances have since been developed around the world and in popular use among orthodontists today, such as SureSmile (Orametrix, Inc., Richardson, TX), STb (Scuzzo-Takemoto bracket; Ormco, Orange, CA), in-Ovation L (Dentsply Sirona GAC, York, PA), and even self-ligating systems such as Harmony (American Orthodontics Corporation, Sheboygan, WI) and Alias (Ormco).

The newest fully customized lingual appliance today, INBRACE (Swift Health Systems, Inc., Irvine, CA), is a unique and innovative lingual orthodontic solution consisting of looped round arch wires (Fig. 7.13). The loops at the interproximal extend gingivally, allowing patients to floss freely and maintain a healthy periodontal condition.

7.12.2 Labial Brackets

CAD/CAM orthodontic appliances technology has also been utilized for labial appliances with the introduction of Insignia by ORMCO (Ormco, Glendora, CA, USA) as a system of customized labial appliances, which are then indirectly bonded.

The process begins by the clinician taking either a polyvinyl siloxane (PVS) impression or intraoral scan of the patient’s dentition, which is sent to Ormco^® for creation of digital models of the dental arches. The technicians then complete a virtual setup for ideal occlusion and arch form that is sent to the clinician for approval. The clinician can then manipulate the digital setup to achieve the intended individual tooth position, occlusion, smile arch, and arch form utilizing Ormco^®’s Insignia Approver software (Fig. 7.14). Once the clinician approves the treatment virtual setup, then they select their preferred bracket system [22, 23].

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