How accurate is 3D modeling in dental applications

I’m a dental student, and we’re starting to use 3D modeling and printing more in our lab. I’m specifically wondering about the accuracy of the models we’re creating with intraoral scanners and then manipulating in CAD/CAM software before printing. We’re making things like study models, surgical guides, and even provisional crowns.

My concern is, how reliable are these models really? We’re talking about millimeters here, even microns in some cases. Are we getting a true representation of the patient’s anatomy, or are there significant distortions and deviations from reality? What are the typical error margins we should be expecting with different scanning technologies and printing materials?

Also, how much does the operator’s skill affect the accuracy? Is it easy to introduce errors during the scanning or design process? And what about the accuracy of fit? If we design a crown using a 3D model, how closely can we expect it to fit the patient’s tooth compared to a traditionally made crown? I need some hard numbers and maybe some comparisons between different systems if possible.

Answer

3D modeling in dental applications has reached a high level of accuracy, enabling a wide range of precise and predictable treatments. The accuracy depends on several factors, including the technology used for data acquisition (scanning), the software used for model creation, and the expertise of the dental professional involved.

Data Acquisition Methods and Their Accuracy:

• Intraoral Scanners: These devices capture the oral anatomy directly in the patient’s mouth. Modern intraoral scanners boast impressive accuracy, with some achieving resolutions down to a few microns (µm). Different generations and brands of scanners vary in their accuracy, but high-end models are generally considered very accurate for most dental applications. Accuracy can be affected by factors such as the presence of saliva, blood, or movement during scanning. Scanning strategies and proper training are critical to minimizing errors. In vitro studies have shown accuracy ranging from 5 to 50 µm for single-tooth scans and 20 to 100 µm for full-arch scans, but clinical accuracy can vary.
• Extraoral Scanners (Desktop Scanners): Used primarily for scanning impressions or dental casts. These scanners are typically more accurate than intraoral scanners due to the stable, controlled environment and the ability to scan materials with ideal optical properties. Desktop scanners often serve as a reference standard for validating the accuracy of intraoral scanners. Accuracy ranges from 5 to 20 µm are achievable under ideal conditions.
• Cone-Beam Computed Tomography (CBCT): A 3D imaging technique that provides detailed images of the bone and teeth. While essential for implant planning and assessing bone structures, CBCT images have lower resolution compared to intraoral or desktop scans when it comes to surface details. Accuracy ranges from 100 to 400 µm depending on the field of view, resolution, and reconstruction algorithms. Specific software is often used to segment the teeth from CBCT scans to create 3D models.
• Laboratory Scanners: Employed to scan dental impressions or gypsum models. These scanners offer high precision, making them suitable for producing intricate dental restorations.

Software and Model Creation:

• CAD/CAM Software: Dental CAD/CAM (Computer-Aided Design/Computer-Aided Manufacturing) software plays a vital role in creating precise 3D models from the scanned data. The software allows for the design of restorations, appliances, and surgical guides with high accuracy. The accuracy of the final model depends on the algorithms used for model reconstruction, the quality of the scanned data, and the user’s ability to manipulate and refine the design.
• Segmentation Software: Segmentation software is often used to isolate specific structures, such as teeth or bone, from 3D scans. The accuracy of segmentation can significantly affect the accuracy of the resulting 3D model. Manual segmentation is more time-consuming but may yield more accurate results than automated segmentation, especially in complex cases.
• Model Reconstruction Algorithms: The algorithms used to convert scanned data into a 3D model can affect the accuracy and smoothness of the model. Advanced algorithms minimize noise and artifacts, resulting in more accurate representations of the oral anatomy.

Applications and Accuracy Requirements:

The required accuracy for 3D modeling varies depending on the specific dental application:

• Restorative Dentistry (Crowns, Bridges, Veneers): High accuracy is crucial for achieving proper fit, occlusion, and aesthetics. Intraoral scanners and CAD/CAM systems are commonly used, and accuracy in the range of 20-50 µm is generally considered acceptable. Marginal fit of restorations is critically dependent on the accuracy of the 3D models.
• Implant Dentistry: Accurate 3D models are essential for planning implant placement, designing surgical guides, and fabricating implant-supported prostheses. CBCT scans are used to assess bone volume and density, while intraoral or desktop scans are used to create models of the teeth and soft tissues. Accuracy in the range of 50-100 µm is typically required for implant planning and surgical guide fabrication.
• Orthodontics: 3D models are used for diagnosis, treatment planning, and the fabrication of orthodontic appliances (e.g., aligners, retainers). Intraoral scanners are increasingly used to replace traditional impressions. The required accuracy is generally lower than in restorative dentistry, but precise tooth positioning is still important. Accuracy in the range of 50-150 µm is often sufficient.
• Surgical Guides: 3D-printed surgical guides based on 3D models are used to assist in precise implant placement or other surgical procedures. Accuracy is critical to ensure that the implants are placed in the planned position. The accuracy of surgical guides depends on the accuracy of the 3D models, the design of the guide, and the printing process.
• Complete Dentures: 3D printing is increasingly used to fabricate complete dentures. While the overall accuracy may not be as critical as for single-tooth restorations, precise adaptation to the edentulous ridges and accurate occlusal relationships are still essential.

Factors Affecting Accuracy:

• Scanner Technology: Different scanner technologies (e.g., confocal microscopy, structured light, laser triangulation) have varying levels of accuracy.
• Scanning Protocol: Proper scanning technique, including adequate overlap, angulation, and attention to detail, is essential for accurate data acquisition.
• Software Algorithms: The algorithms used for data processing, model reconstruction, and design can affect the accuracy of the final model.
• Material Properties: The materials used for 3D printing or milling can affect the accuracy of the final restoration or appliance.
• Operator Skill: The skill and experience of the dental professional or technician using the technology play a crucial role in achieving accurate results.
• Calibration and Maintenance: Regular calibration and maintenance of scanning devices and CAD/CAM equipment are essential for maintaining accuracy.

Conclusion:

3D modeling in dental applications has become remarkably accurate, offering numerous benefits in terms of precision, efficiency, and patient comfort. While accuracy is continuously improving with technological advancements, it’s important to recognize that the overall accuracy is a combination of the accuracy of the scanner, the design software, the fabrication method, and the clinician’s skill.