AI-Assisted Intraoral Stereophotogrammetry

3D Modeling Using Simple Intraoral Cameras: A Research Study

Research Abstract

Objective

To evaluate the feasibility of 3D modeling of 2 types of typodonts from video files using stereo photogrammetry technique assisted by AI technology.

Materials and Methods

2 types of typodont's mandibles were used, one with full teeth and the other one with 4 teeth removed. Video files were created using iPhone 15, commercially available intra oral cameras (IOC) Qawachh and Waldent 5 Megapixel Intraoral cameras. 5 scans were obtained from both arches using the 3 different cameras mentioned. Using the video files 3D models were generated by stereophotogrammetry technology using AI assistance. These 3D models were compared with the gold standard Desktop scanner produced 3D models.

Results

Reasonable high quality 3D meshes were generated by iPhone video files (92% overlap) followed by Waldent 5 Megapixel (90% overlap) and a lesser quality by Qawachh (85% overlap) intra oral cameras.

Conclusion

Video files from intraoral cameras can be successfully converted into 3D models with reasonable accuracy using stereophotogrammetry with AI assistance.

Impact on Clinical Use

If we can improve the accuracy even more in generating 3D models of intra oral structures using simple intraoral cameras, we will be able to use them in underserved areas because of the very low cost of this technology.

Introduction

The advent of CAD/CAM digital technology has transformed dental practices, particularly in the area of 3D modeling for diagnosis, treatment planning, and prosthesis fabrication. Traditional methods of creating physical impressions, though reliable, are increasingly being supplemented or replaced by digital solutions. Among these the latest intraoral scanners and desktop scanners have set the standard for generating accurate 3D representations of dental structures. However, these devices often come with significant cost, learning curve and training requirements, limiting their accessibility in many settings.

To address these challenges, this study explores the use of cost-effective alternatives, AI assisted stereophotogrammetry using simple dental cameras, for 3D dental modeling. Stereophotogrammetry relies on capturing overlapping 2D images to reconstruct detailed 3D models, while simple dental cameras provide a more affordable option for image acquisition. By leveraging the latest technology, the research aims to assess the feasibility of economically accessible solutions for dental professionals.

Ali Saghiri et al showed that 2D images from still pictures can be used to produce accurate 3D models of the mandible. However, they used ReCap photo a 3rd party software, which is no longer a freeware and also it is difficult to integrate it into routine workflow. Using our own AI algorithms, we were able to bypass this process.

Current Intraoral Scanning Technologies

Active Light Technology

The projected light can be red, white or blue light with different patterns such as a line, point or a projected mesh.

  • Surface reconstruction: Achieved by matching points of interest (POI) in the obtained images
  • POI detection: Works by detecting edges, strong curvatures or differences in gray intensity
  • Output: STL file with triangles and coordinates

Distance Calculation Methods

  • Triangulation technique: Position calculated by knowing two angles from different positions
  • Confocal focal technology: Uses the difference between focused and defocused images
  • Active Wavefront Sampling (AWS): Camera lens rotates around a point on the surface

Passive Light Technology

In passive light technology such as stereophotogrammetry, the estimate of all three coordinates is calculated through computer algorithms using software only. Algorithms are used in estimating the camera positions and generating a point cloud for 3D model creation.

Advantages
  • Lightweight, smaller and cheaper equipment
  • No specialized hardware for light projection
  • More accessible for widespread use
Limitations
  • Subject to optical principles (reflection, refraction, shadows)
  • Requires good lighting conditions
  • Dependent on surface texture for feature detection

Comparison of Technologies

Feature Hardware-Heavy IOS Software-Dependent Technology
Cost Up to $40,000 + maintenance fees Significantly lower (uses existing cameras)
Size/Weight Bulky (up to 1lb) Lightweight, smaller form factor
Training Required Extensive training, steep learning curve Minimal training, intuitive operation
Ecosystem Limited to specific vendor More flexible, device-agnostic

Materials and Methods

Typodont Models

The Ultrassist Typodont Teeth Model was chosen for this study due to its accurate representation of human dental anatomy and versatility in replicating clinical scenarios.

  • Complete Arch: Model featuring all 16 teeth intact
  • Partially Edentulous Arch: Model with four teeth removed (numbers 19, 20, 29, and 30)

Scanning Devices

  • iPhone 15: 48 MP camera capturing video sequences
  • QAWACHH 6 LED Professional Dental Intraoral Camera: 720p HD resolution with 6 LED lights
  • Waldent 5 Megapixel Intraoral Camera: USB-connected with 5 MP resolution
  • Desktop scanner: Shining 3D AutoScan-DS-EX Pro (gold standard for comparison)

Scanning Methodology

Lighting Conditions

All scans were performed under controlled ambient lighting at 1000 lux to ensure consistency.

Scanning Path

Systematic path beginning with occlusal surface, followed by buccal and lingual surfaces in a sequential manner.

Repeatability

Each typodont model was scanned five times with each device to evaluate consistency and accuracy.

Processing Pipeline

Video Acquisition

  • Lighting: 1000 lux ambient light
  • Angle/Distance: 10-15° angle, 2–3 inches distance
  • Scanning Path: Occlusal, buccal, and lingual surfaces systematically covered

Video to Image Conversion

  • Frame Extraction: Every 10th frame
  • Format Conversion: HEIC to JPEG
  • Resolution: 900 x 1600 pixels, 72 dpi

Image Preprocessing

  • Noise Reduction
  • Resolution Adjustment for efficiency
  • Detection of Overlapping Regions

3D Model Generation

  • Feature Detection/Matching: SIFT or ORB
  • Sparse Point Cloud Creation: Using SfM
  • Dense Point Cloud Generation
  • Mesh Generation and Texture Mapping

Model Refinement

  • Post Processing
  • Algorithm Optimization

Technical Implementation

The reconstruction process involved generating both sparse and dense point clouds to represent the 3D geometry of the scanned object.

Feature Matching

D = √∑(f₁ᵢ-f₂ᵢ)²

Where f₁ᵢ and f₂ᵢ are feature descriptors from two images.

Bundle Adjustment

E = ∑‖xᵢⱼ - PᵢXⱼ‖²

Where xᵢⱼ are observed 2D points, Pᵢ is the projection matrix for camera i, and Xⱼ are 3D points.

Texture Mapping

T(u,v) = I(x,y)

This ensured accurate surface details and high-quality visual output.

Computational Optimization

GPU-accelerated algorithms enhanced feature detection, point cloud generation, and mesh reconstruction, enabling efficient processing of large datasets.

Results and Discussion

Key Findings

92%

iPhone 15
Overlap with reference model

90%

Waldent 5MP
Overlap with reference model

85%

QAWACHH
Overlap with reference model

Optimal Conditions
  • 1000 lux ambient light is the optimal brightness for scanning
  • Grayscale images are better than color images for 3D model generation
  • 1080P images are optimal for 3D model generation
  • Higher resolution images did not offer any further advantage

AI Applications in Dental Imaging

AI has significantly helped in various steps of our process:

Current Implementation
  • AI-powered algorithms (SIFT and ORB)
  • Structure from motion and photogrammetry algorithms
  • Noise reduction and outlier filtering
  • GPU optimization for faster processing
  • Custom datasets trained using typodont models
  • Data augmentation for variations in lighting, angle, and reflections
Future Improvements
  • Generate synthetic variations of images to train models
  • Replace traditional algorithms with DL-based feature detection models
  • AI-enhanced photogrammetry using trained models for dental structures
  • Machine learning for mesh refinement
  • Trained supervised learning model for accuracy metrics
  • Utilization of CNNs, GANs, and reinforcement learning

Conclusion

This study demonstrates that video files captured with simple intraoral cameras can be effectively converted into accurate 3D models using stereophotogrammetry techniques enhanced by AI algorithms.

We believe that we can improve the accuracy to 99%+ by:

  • Using latest IOCs which can generate true 1080p images
  • Adapting standardized workflows to maintain optimal lighting and scanning paths
  • Using smaller tips with wide angle lenses in IOCs for posterior access
  • Implementing advanced AI techniques for feature detection and mesh refinement

The potential impact of this technology is significant, particularly for underserved areas where access to expensive dental equipment is limited. By providing a low-cost alternative for 3D modeling, this approach could democratize access to advanced dental care technologies.

Advanced 3D Modeling Research

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