3D digital models or E-models

Introduction

Digital or E-models ( Fig. 36.1 ) are the electronic substitute of physical orthodontic study models traditionally prepared in Plaster of Paris from alginate impressions of the dental and oral tissues. Consequently, the need to make impressions or maintain a plaster lab in dental office is eliminated. The process of E-models or digital models involved recording digital three-dimensional (3D) coordinates of the objects, that is teeth and gums using intra oral scanner. 3D scanning has been in extensive use in industry from huge scanners to tabletop size used in jewellery and technical small parts. Before the advent and popularity of intraoral scanners, digital models were prepared with either scanning the impression or plaster model, however, these methods are now outdated and not in use.

Image, AltText currently not available — Figure 36.1

There are essentially two different technologies in use to produce digital models:

1.
Intraoral scanners
2.
Impression/model scanners

The advancements in refining the scanning process and sophisticated software functions can produce E-models in a few seconds with a life-like accuracy.

The E-models are stored on the computer’s hard disc or in the cloud, which can be accessed like any other digital file. The models are viewed as 3D images on the screen, can be rotated and with segmentation each of the dental morphology can be viewed and examined in various views.

The E-models can be transported as graphic files from one orthodontist to another, to a lab, to the patients or stored in the cloud.

The advanced technology required to make digital models is available with an attached cost of scanners and maintenance of sophisticated equipment and digital data storage cost on a hard disc or a server or in the cloud ( Tables 36.1 and 36.2 ).

TABLE 36.1

Advantages of digital or E-models

1.
Digital models offer tremendous advantages not only easy and quick access but also share benefits of state-of-the-art sophisticated 3D technology and advanced software functions.
2.
Digital models offer a cost-effective solution for clinics to eliminate the production, storage and archiving expenses of physical plaster models.
3.
This technology enables dental offices to free up physical space and enhances the accessibility of online digital file storage, which is available 24 h a day.
4.
This digital file storage system allows companies to streamline their processes and improve efficiency by reducing the need for physical storage space.
5.
Digital models can be transported via Internet and accessed from any location, eliminating the geographic barriers of plaster models and paper files for multiple site practices thereby empowering professionals.
6.
Digital models enable seamless communication between dental professionals and patients, facilitating interdisciplinary treatment planning.
7.
Most digital model viewing software applications are equipped with analytical tools that facilitate teeth and arch length measurements. These tools provide an efficient and effective means of performing the measurements, which may otherwise be time-consuming and error prone.
8.
The inclusion of such tools in digital model viewing software applications is a testament to the technological advancements that have been made in the field, which have resulted in the development of highly sophisticated and precise software. This technology has not only revolutionised the way teeth and arch length measurements are taken, but it has also significantly contributed to enhancing dental practice and research.
9.
E-models provide a time-saving advantage by enabling direct measurement on the screen, thereby enhancing the efficiency of orthodontic diagnosis, treatment planning and patient education processes.
10.
The 3D virtual teeth model facilitates precise plotting of individual tooth movements throughout the entire course of treatment, enabling orthodontists to offer personalised care and achieve optimal results.

TABLE 36.2

Limitations of E-models

1.
Digital models depend highly on the scanning procedure, which should be performed with utmost care to ensure accurate representation of the teeth and surrounding tissues. Any abrupt movement or shaking of the hand while scanning or patient movement can lead to inaccurate results.
2.
Digital models lack the personal touch or feel of traditional study models made from plaster offer.
3.
Digital images can only be viewed on a computer or printed on paper, while the patient can see and feel traditional models.
4.
Storing information digitally including E-models puts it at risk of data loss although this issue has now been addressed with cloud computing.

Evolution of dental scanners

In recent times, virtual models have gained widespread acceptance ^, revolutionising clinical dentistry by virtually eradicating the need for plaster and impressions. The concept of scanning dental arches was first introduced by Duret in 1973. Subsequently, in 1999, OrthoCAD (Cadent, Carlstadt, NJ, USA) developed the first orthodontic scanning system, which was followed by E-models (Geodigm Corp., Chanhassen, MN, USA) in 2001.

The process of obtaining digital scans can be done in two ways: directly or indirectly. The direct method uses an intraoral scanner to capture 3D data inside the patient’s mouth, while the indirect method involves scanning alginate impressions and plaster models using a desktop scanner or computed tomography (CT) imaging technology to obtain digital models.

The introduction of the first 3D intraoral scanner by CEREC-1 (Siemens, Munich, Germany) marked a significant milestone in the field of dentistry. This technology employed an infrared camera and an optical powder, specifically titanium oxide powder, to create a 3D model of the teeth. However, with the rapid advancement of technology, recent scanners have eliminated the need for powder-based scanning methodology. The direct method, thus, presents numerous advantages over the previous method.

As such, the direct method has become the preferred choice for modern intraoral scanning. Not only does it eliminate the need for powdering, but it also provides faster and more accurate scanning capabilities. Additionally, the direct method is non-invasive, and therefore, more comfortable for patients. The advantages of the direct method are :

1.
Convenience and comfort of procedure.
2.
Suitable for patients with a gag reflex.
3.
Intraoral scanning is a suitable alternative for patients who are at risk of aspirating or experiencing respiratory distress during traditional dental impressions.
4.
Cleft lip and palate patients.

A few commercially available systems are listed in the following, although huge brands are available in the market.

1.
Lava, 3M ESPE, 3M Center, St. Paul, USA
2.
CS 3500, Carestream, Dental LLC, Atlanta, GA-30339, USA
3.
iTero, Align Technology Inc., Arizona 85281, USA
4.
PlanScan marketed by Planmeca, Helsinki, Finland
5.
Trios—by 3SHAPE A/S (Copenhagen, Denmark)
6.
CEREC AC Bensheim, Germany
7.
Lythos, Ormco Corporation, Brea, California, 92891 USA

Intraoral scanners/direct scanners

Intraoral scanners use the most advanced technology for 3D scanning of an object using either white light or laser light. The beam is projected on the teeth, which, when reflected, is captured back through a device. The reflection is converted into digital data through various technologies. Intraoral scanners employ a range of optical technologies, including confocal microscopy, optical coherence tomography, active and passive stereovision, triangulation, interferometry and phase shift principles. These cutting-edge technologies allow the scanner to capture tens or even hundreds of thousands of measurements per inch of the object, which, in conjunction with sophisticated algorithms, yield an accurate 3D depiction of the object’s form.

The intraoral scanners help the patient and orthodontist by providing flawless digital workflow in clinical practice, from scanning to virtual treatment planning and fabrication of appliances. iTero intraoral scanner operates on the principle of parallel confocal imaging to produce a powderless digital impression.

The iTero element scanner system consists of:

1.
High-definition multi-touch 19 in. display screen.
2.
Scanner sleeve:
- a.
  Blue protective sleeves protect the lens when not in use.
- b.
  Disposable sleeves for a single patient use.
3.
Wand:
- The video camera in the wand contains the laser light source, the focusing motor and analogue to digital converters.

The advanced iTero element scanner efficiently captures up to 20 scans per second, with an impressive scan capture time of 40–50 ms. When it comes to scanning the upper and lower arches and recording the bite, the average time taken is 11 min and 58 s, with a range of 6–18 min.

Steps for taking a complete scan with the hand-held scanner are given in Figs 36.2 and 36.3 .

Indirect scanners (impression/model scanners)

Indirect scanning methods are commonly utilised to generate 3D digital models from plaster or impression models. These methods employ a 3D scanner that comprises a light source, one or more cameras and a motion system with multiple axes. The purpose of the motion system is to position the scanned object in relation to the light source and camera(s). Impressions made with rubber base material are favoured over alginate impressions due to their superior accuracy and dimensional stability in a dry environment. The rubber base impressions can be transported to other facility like a lab at different location without losing their accuracy.

Desktop scanners ( Fig. 36.4 )

To make E-models, the orthodontist/laboratory uses 3D images recorded through a laser scanner. ^, This laser scanner uses a flashing white light, much like a video camera that digitally maps the teeth or plaster models into precise, high-resolution, 3D electronic records.

Few commercially available 3D desktop scanners are:

1.
Ortho Insight 3D (Motion View Software, LLC, Chattanooga TN, USA)
2.
R series, 3 Shape (Copenhagen, Denmark)
3.
Maestro 3D (AGE Solutions, Pisa, Italy)

3D scanners allow the scanning of study models without needing a base. The accompanying software programs will enable the creation of a virtual base from the 3D virtual base library ( Fig. 36.5 ).

CT-based scanner

In this method, the rubber base impressions and bite of a patient are transported in a special tray to an industrial scanner that works like a multidetector computed tomography (MDCT) scan of the skull. Highly sophisticated software functions are used to construct a 3D image of the dentition/oral structures. The artistic portion of the models is then superimposed for presentation and aesthetics. These models can be viewed from all possible views on the computer screen. ‘OrthoProof’ of Holland utilises this method. This service is commercially available in Europe, USA and Australia. E-models have dimensional accuracy, high resolution and life-like clarity.

Digital model orientation

An oriented digital model is necessary for repeatable measurements. In 3D space, X, Y and Z axes and origin (0, 0, 0) must be defined to quantify the changes in 3D.

Coordinate system

Choi and colleagues developed a coordinate system for a 3D virtual model. The X-Z horizontal plane is parallel to the occlusal plane constructed by the bilateral mesiobuccal cusp tips of the first molars and the midpoint of the central incisors and serves as the foundation of this system. The coordinate origin (0, 0, 0) is located at the junction of the incisive papilla and palatine raphe. The X-Y sagittal plane is perpendicular to the horizontal plane and includes the origin point and one arbitrary point on the mid-palatal suture. The Y-Z frontal plane is the section inclusive of the origin point and perpendicular to the sagittal and horizontal planes. This coordinate system utilises measuring points of the midpoint on the edge of the upper central incisors and the mesiobuccal cusp tips of the upper first molars. The system provides a clear and concise means of measurement for the 3D virtual model. It is essential to note that this system calls for accurate placement of the measuring points and careful consideration of the occlusal plane ( Fig. 36.6 ).

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3D digital models or E-models

Introduction

Evolution of dental scanners

Intraoral scanners/direct scanners