Quartz 4

Intra-oral Scanner Technologies

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Review Article: Intraoral Scanner Technologies: A Review to Make a Successful Impression Raphael Richert,¹,² Gleb Guek,¹,² Laurent Veen,¹,² Gilbert Vigna,¹,² Stéphane Viennot,¹,²,³ Philip Kellner,¹,² Tom-Christopher Farges,¹,² Michel Fages,¹,² and Nicolas Doura²,³

There are four main types of technology used:

Note

This section provides background information and is not critical for examination purposes.

  1. Triangulation
  2. Confocal
  3. Active wavefront sampling
  4. Stereophotogrammetry

1. Triangulation[^16]

  • Principle: Based on the principle that the position of a point can be calculated by knowing its position and angle from two different points of view.

  • Mechanism: These two points of view may be produced by two detectors, a single detector with a prism, or captured at two different points in time. The distance to the object can be determined using trigonometric formulas.

  • ==Limitation: Prone to inaccuracies from optical noise and lens distortion, which can be compounded as the scanner builds the 3D model.==

  • Considerations: Noise and lens distortion can lead to inaccuracies that may be carried forward.

  • Used by: Sirona Omnicam scanners.

2. Confocal Imaging[^17]

  • Principle: A technique based on acquiring focused and defocused images from selected depths. It detects the sharpest area of an image to infer the distance to the object, which is correlated to the focal length of the lens.

  • Mechanism: A tooth is reconstructed by successive images taken at different focuses and apertures from different angles. A pinhole eliminates aberrant light beams to increase accuracy.

  • ==Example: Trios scanners.

  • Considerations: The technique is sensitive to motion blur from the operator and requires large optics, which can be difficult in clinical practice.

3. Active Wavefront Sampling (AWS)[^18]

  • Principle: Refers to getting 3D information from a single lens imaging system by measuring depth based on the defocus of the primary optical system.
  • Mechanism: Three sensors capture the clinical situation from different perspectives simultaneously. 3D surface patches are then generated in real time by proprietary algorithms using the in-focus and out-of-focus information.
  • Used by: Lava Chairside Oral scanner.

4. Stereophotogrammetry

  • Principle: Estimates all coordinates (x, y, and z) solely through an algorithmic analysis of images.

  • Mechanism: Relies on passive light projection and software rather than active projection and hardware.

  • Considerations: The camera is relatively small, its handling is easier, and its production is cheaper.

  • ==Disadvantage: The resulting images may not be as crisp or detailed as those from other techniques like confocal imaging.==

Surface Coating (Powder)[^19]

  • A relatively obsolete technique involved coating the intra-oral surfaces with an anti-reflective powder such as titanium dioxide.

  • Rationale: Light is a critical feature for how scanners capture information, so it’s important to control reflections from saliva or not use the overhead light. Earlier generations of IOSs required opaquing powders or sprays for accurate recording.

  • Disadvantages: Inherent disadvantages include patient discomfort, being time-consuming, and technique sensitivity.

  • ==Modern Scanners: Current-generation scanners are “powder-free” and do not have this requirement.==

Accuracy in Digital Impressions[^20][^21]

Defining Accuracy, Trueness, and Precision

According to the International Organization for Standardization (ISO) 5725-1:

  • Trueness: Refers to the closeness between the arithmetic mean of a big number of test results and the true or accepted reference value.
  • Precision: Refers to how close several measurements of the same quantity are to each other.
  • Accuracy: Refers to the combination of trueness and precision.

Analogy

This is analogous to validity (trueness) and reliability (precision) in research.

Study: IOS Accuracy[^22][^23]

“It is vital that IOS has an equally or higher accuracy and precision than conventional impressions. 3M and TRIOS had a higher accuracy than OMNI. IMPR overlapped both groups. However, the deviations are within a similar magnitude for arches up to ten units.” — Accuracy and precision of 3 intraoral scanners and accuracy of conventional impressions: A novel in vivo analysis method (Nedelcu et. al., 2018)

Accuracy is directly related to the resolution of the 3D model, which is determined by the number of triangles in the generated STL file mesh. More triangles = higher resolution and potentially higher accuracy.

  • ==Reference Scanner (ATOS): ~50,000 triangles.==
  • ==Trios: ~23,000 triangles.==
  • ==Omniscan: ~12,000 triangles.==
  • ==PlanScan: ~7,500 triangles.==

When comparing the clarity of the preparation margin (finish line), the Trios image was significantly crisper and more detailed, clearly showing the finish line, while the PlanScan image was blurry and made it difficult to identify the margin.

Accuracy Images by Dr Nedelcu

Accuracy

Study: Finish Line Accuracy[^24][^25][^26][^27][^28][^29][^30]

Images by Dr Nedelcu Summary of the paper that previous slides were taken from.

Results[^10]

  • All IOS, except PlanScan, had comparable overall accuracy; however, Finish Line Deviation (FLD) and Finish Line Angulation (FLA) varied substantially.
  • Trios presented the highest FLD, and with CS3600, the highest FLA.
  • 3M and DWIO had low overall FLD and low FLA in subgingival areas.
  • Trios had the highest resolution by a factor of 1.6 to 3.1 among IOS.
  • Inclusion of color enhanced the identification of the finish line in Trios, Omnicam and CS3600, but not in PlanScan.

Conclusions

  • Key Finding: IOS show significant variations in accurately capturing the finish line, especially in challenging subgingival areas, with some performing better or worse than conventional impressions (IMPR).
  • High finish line deviation (FLD) was more related to high localized resolution and non-uniform tessellation than to high overall resolution.
  • It is imperative that clinicians critically evaluate the digital impression, being aware of varying technical limitations among IOS, in particular when challenging subgingival conditions apply.

Comparative Study: TRIOS 5, Medit i700, and Primescan[^31]

Accuracy of 3 Intraoral Scanners in Recording Impressions for Full-Arch Dental Implant-Supported Prosthesis: An In Vitro Study Gonzalo Jara, Miguel Angel Llamas, Francisco M. Sánchez, David M. Cuesta, José M. Martínez, Jesús M. Gómez

Results

  • Key Finding: For full-arch implant impressions, TRIOS 5 was the most accurate, followed by Medit i700 and then Primescan.
    • TRIOS 5: Lowest deviation for precision (37.8 ± 4.53 µm) and trueness (54.9 ± 11 µm).
    • Medit i700: Precision 40.6 ± 4.17 µm, trueness 60.3 ± 10.9 µm.
    • Primescan: Highest deviation for precision (49.1 ± 8.31 µm) and trueness (72.3 ± 10.4 µm).

Potential Factor for Accuracy

Another factor contributing to Trios’s accuracy may be its larger scanning head. A larger field of view means the scanner needs to capture and ‘stitch’ together fewer images to create the full model. Fewer stitches can lead to fewer opportunities for stitching errors to accumulate.

  • A statistically significant difference was observed among the 3 scanners for both precision (P<0.005) and trueness (P<0.005).

Conclusions[^32]

  • TRIOS 5 intraoral scanner displayed the lowest deviation values for precision and trueness (more accurate), followed by Medit i700 and Primescan intraoral scanners.
  • However, deviation values of all scanners were within clinically acceptable limits.

Reference Scanners: ATOS Core[^33]

  • Industrial scanner (Not an intra-oral scanner).
  • Can be accurate to 1µm.
  • Often used as a “reference” for accuracy studies

Note

It is an industrial-grade, extra-oral scanner that is considered the ‘gold standard’ in research for evaluating the trueness of clinical intra-oral scanners.

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Graph View

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