Selecting the Right Intraoral Scanner to Transform Your Practice

The most substantial differences in IOSs are in the accuracy of the intraoral optical impressions (IOIs) generated. Accuracy of IOIs can be determined based on two variables: trueness and precision.⁵ Trueness dictates how close a measurement is to the actual dimension of the object being scanned, while precision indicates the consistency of scan measurements. These differences arise primarily because of variations in the way the IOI is generated and digitally stored: stereolithography (STL) file format versus object (OBJ) or polygon (PLY) file formats.⁶

The STL file format generates a 3D representation of an object being scanned by creating an approximate meshwork of the scanned 3D object. This approximate meshwork consists of small, adjoining, nonoverlapping triangles; however, as an "approximation," this meshwork allows for deficiencies in trueness.⁶ This limitation can be an especially important factor when considering the recreation of something as critical as a finish line for a fixed restoration. STL digital impressions are said to be comparable to traditional impressions for simple fixed prosthodontic cases, such as single-unit crowns and small bridges spanning one to four units. However, substantial deficiencies in scan accuracy present when utilizing IOIs encoded in the STL file format for restorations spanning five units or more.⁷ Additionally, IOIs stored in STL format do not encode any information about the surface texture or color of the object being scanned; this may be an important limitation to consider if one of the practice goals is to use the IOS for 3D printing definitive restorations.

IOSs that utilize the newer file formats OBJ and PLY allow for the acquisition of higher-quality and more accurately encoded digital models.⁶ These digital models are created using a "precise mesh" by utilizing tessellation with polygonal facets, freeform curves, and freeform surface patches. For comparison, the highest-resolution STL scan is still significantly lower resolution than the lowest-quality scan encoded in the OBJ and PLY file formats. Additionally, IOIs stored in OBJ and PLY formats encode information about color and surface texture of an object being scanned. This allows for very accurate, multicolor 3D printing, as opposed to monochromatic printing alone offered by the STL file format.

The ability to manipulate scans and alter them at a later time is heavily dependent on whether the IOI is "open" or "closed" format. IOSs that store files in the STL file format are considered closed systems, and the files are extremely difficult to alter after a scan is acquired. OBJ and PLY file formats are considered open, meaning that the files can be readily imported into most CAD software and easily modified at a later date, which might allow for collaborative workflows and modification of designs at a subsequent time.

The speed of scan acquisition is another important consideration when comparing IOSs.^6,8 IOSs that generate IOIs with smaller file sizes (STL) allow for more rapid scan acquisition. Larger, more accurate OBJ- and PLY-generated IOIs store more information and, therefore, require more time for scan acquisition. This might be a critical factor when treating pediatric patients where time and the duration of patient compliance may be extremely limited.

Ergodynamics and hardware features are additional considerations. Pediatric patients and patients with limited mouth opening might require an IOS with a smaller tip size.^9,10 Antifog and wireless wand capabilities are also factors when assessing patient demographics, patient cooperation, and office setup.

Sterilization versus disinfection-only capabilities should also be weighed when selecting an IOS. According to the Centers for Disease Control and Prevention, sterilization and prevention of cross-contamination is best achieved through steam sterilization using an autoclave.¹¹ Most IOSs do not have detachable tips and only allow for disinfection of the scanning unit using CaviCide^™ and/or isopropyl alcohol. However, some IOSs now offer a detachable tip that can be used from 20 to 300 times depending on the manufacturer and autoclaved for sterilization.^1,2 This may be a particularly important consideration for offices with a high volume of patients or immunocompromised patient populations and in the COVID-19 era where disease transmission is a major threat to anyone in the office.¹²

The volume of patients leads to additional considerations about calibration requirements. All IOSs require routine maintenance and calibration to function properly.¹³ Calibration demands increase as IOS use increases and if the machine is frequently being transported from one location to another within the dental office. If calibration is neglected, scans can become compromised, which may jeopardize final restorative outcomes. Most manufacturers require manual calibration of the IOS through the use of a calibration tool, which involves an operator physically connecting the IOS to the calibration tool and manually cycling through several steps to achieve effective calibration. A recent development, however, involves technology that allows for autocalibration through the manufacturer's server, which could be an important benefit in high-volume dental practices, practices in which the machine will be transported, or where delegation of calibration responsibilities can potentially lead to neglect of this critical task.

There is no simple answer as to which IOS is the "most ideal." Dental providers must first assess their ultimate goals for obtaining an IOS, the types of procedures they will be performing, and the demographics of the population being treated. From there, they can begin to determine which model may best suit their needs.

Ilser Turkyilmaz, DMD, PhD
Clinical Professor, Department of Prosthodontics,
New York University College of Dentistry,
New York, New York

Samantha Lakhia, DDS
Resident, Post-Graduate Prosthodontics, Department of Prosthodontics, New York University College of Dentistry, New York, New York

Lisa R. Antonoff, DDS
Clinical Associate Professor, Department of Prosthodontics,
New York University College of Dentistry,
New York, New York

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