**Lecture 7: Digital Impressions** By Dr Cheryl Fu Acknowledgements to Dr Nedelcu and Dr Matsubara for slides # **Lecture 7: Digital Impressions** By Dr Cheryl Fu Acknowledgements to Dr Nedelcu and Dr Matsubara for slides **Learning Objectives** - Methods of digitalization - Benefits and disadvantages of intra-oral scanners - What is accuracy? - Clinical Protocols - Different scanners: intra-oral vs extra-oral No compulsory readings # **Learning Objectives** - Methods of digitalization - Benefits and disadvantages of intra-oral scanners - What is accuracy? - Clinical Protocols - Different scanners: intra-oral vs extra-oral - The underlying technologies that convert 2D images into 3D models. No compulsory readings **Digital Impression** --- **JPD** *THE JOURNAL OF PROSTHETIC DENTISTRY* **THE GLOSSARY OF PROSTHODONTIC TERMS** *Ninth Edition* --- **dental impression** \ˈdɛnˈtəl ˌɪmˈprɛʃən\ a negative imprint or a positive digital image display of intraoral anatomy; used to cast or print a 3D replica of the anatomic structure that is to be used as a permanent record or in the production of a dental restoration or prosthesis; syn IMPRESSION Figure showing a definition card for "dental impression" from The Journal of Prosthetic Dentistry, Ninth Edition, with branding from The University of Western Australia. # **Digital Impression Definition** --- **JPD** *THE JOURNAL OF PROSTHETIC DENTISTRY* **THE GLOSSARY OF PROSTHODONTIC TERMS** *Ninth Edition* --- **dental impression** \ˈdɛnˈtəl ˌɪmˈprɛʃən\ a negative imprint or a positive digital image display of intraoral anatomy; used to cast or print a 3D replica of the anatomic structure that is to be used as a permanent record or in the production of a dental restoration or prosthesis; syn IMPRESSION > [!info] Clarification > A **negative imprint** refers to a conventional impression using materials like PVS, which must be poured with stone to create a positive cast. A **positive digital image display** is what an intra-oral scanner creates directly, resulting in a 3D model without the need for an intermediate pouring step. **Impression** - **Aim of impression:** produce a dimensionally stable “negative” - Mould for an analogue model - Scanned with CAD/CAM model - Milled Model - 3D Printed Model Used not just for crowns. Have been increasingly used for other specialties. Including edentulous arches and orthodontic treatment. # **The Aim of an Impression** - To produce a dimensionally stable “negative” - Mould for an analogue model - Scanned with CAD/CAM model - Milled Model - 3D Printed Model Used not just for crowns. Have been increasingly used for other specialties. Including edentulous arches and orthodontic treatment. This record is then used to fabricate various dental prostheses, including: - ==Single indirect restorations (crowns, inlays, onlays).== - ==Fixed partial dentures (FPDs) or bridges.== - ==Removable partial dentures (RPDs).== - ==Complete dentures (for edentulous arches).== - ==Orthodontic aligners.== Workflow diagram showing Conventional and CAD-CAM pathways from Preparation to Insert, with steps including Impression, Scanning, Casting, Milling, Sintering, Manual Finishing, Veneering/Polishing. The CAD-CAM branch is circled in blue. **Benefits Vs Disadvantages** **Advantages** - Workflow improvements - Patient acceptance (gag reflex) - Time benefits - Financial advantages - Communication - Record keeping/storage **Disadvantages** - New skills - Digital confidence/mindset - Initial costs - Accuracy One-time payment **$29,050** Workflow: Tray selections + disinfection etc all need time. Additionally, the created digital impression is already a positive record (not a negative record like impression that needs to be poured up). Some manufacturers claim that you can achieve a full arch impression in less than 60 seconds with extensive experience! Record keeping. Many new scanners allow previous scans to be stored and compared against new scans. Potentially useful for patient education and monitoring changes, for example wear or erosion of teeth. # **Benefits Vs Disadvantages of Intra-oral Scanners** ## **Advantages** - **Workflow improvements:** The created digital impression is already a positive record, unlike a conventional impression that needs to be poured up. Tray selections, disinfection, etc., also require time in conventional workflows. - ==The lengthy disinfection process required for physical impressions can take approximately 15 minutes.== - **Patient acceptance (gag reflex):** Generally better tolerated by patients. - ==Allows for pauses during the scanning process without compromising the final result, unlike a setting silicone impression which would require a complete restart.== - **Time benefits:** Some manufacturers claim a full arch impression can be achieved in less than 60 seconds with experience. - **Financial advantages:** Despite initial costs, long-term savings can be realized. - ==While the initial investment is high (e.g., a Trios 5 costs ~$30,000 plus subscription fees), long-term savings are possible by eliminating costs for impression materials, trays, and physical shipping to the lab.== - **Communication:** Facilitates easier collaboration with labs and other professionals. - **Record keeping/storage:** Many new scanners allow previous scans to be stored and compared against new scans. This is potentially useful for patient education and monitoring changes, for example, wear or erosion of teeth. - ==Digital scans can be stored securely in the cloud, eliminating the need to store bulky physical casts for the legally required period (e.g., 5-7 years).== - ==This allows for quantitative monitoring of dental conditions like bruxism or erosion by superimposing scans taken years apart to precisely measure changes.== ## **Disadvantages** - **New skills:** Requires learning new techniques and workflows. - **Digital confidence/mindset:** Requires a shift in clinical approach. - ==The price of the scanner, software subscriptions, and required high-performance laptops represents a significant financial barrier.== - ==Some experienced clinicians may be resistant to changing their established, reliable conventional workflows.== - **Initial costs:** Significant upfront investment (e.g., a one-time payment of **$29,050**). - **Accuracy:** While generally high, it can be a concern, especially in specific clinical situations. <html> <table> <tr> <th>Issues</th> <th>Conventional Impressions</th> <th>Intra-oral (non-digital) Impressions</th> <th>Technical Efficiency</th> <th>Clinical Efficiency</th> <th>Weather</th> <th>Applications</th> <th>Other relevant issues</th> </tr> <tr> <td>Patient related</td> <td>May provoke undesirable response from patients (e.g. gag reflex, unpleasant taste, etc.)</td> <td>Some intra-oral scanning can make this difficult to use in patients with small mouths, limited opening or tori</td> <td>Harder for inexperienced or unskilled to achieve ideal outcomes</td> <td>Clinical risk variable for multiple reasons (e.g. required time, appointments, adaptation)</td> <td>Setting environment (e.g. mobile clinics, domiciliary appointments) problematic for traditional impressions e.g. longer setting time</td> <td>Impressions—requiring disinfection to be transported physically (some flexibility required to address clinical application)</td> <td>Impressions susceptible to damage before models poured</td> </tr> <tr> <td>Quality of Outcome</td> <td>Accuracy and success of final result highly influenced by the ability of the operator to manage soft tissues, technique, environment, and access</td> <td>Software and hardware still developing and may have errors</td> <td>Longer processing time, multiple appointments, more rounds to achieve final outcomes</td> <td>Digital outcomes more predictable with training</td> <td>Digital impression—cloud sharing—less impacted by temperature or humidity</td> <td>Intraoral scanning— easier for digitally facilitated workflows; less suitable in some prosthodontic applications (e.g. long spans, multiple prepped teeth)</td> <td>Compression of soft tissues (e.g. during border moulding functional impressions) important e.g. removable prosthetics</td> </tr> <tr> <td>Responsibility</td> <td>Lab may be allocated responsibility for poor result from unclear instruction, poor impressions which can delay treatment</td> <td>Digital errors can be detected early e.g. real time or from same screen (scanning technique or software issues)</td> <td>Lab can be made more accountable for case planning and design of appliance by using same digital files</td> <td>Lab has better visibility of scanned data</td> <td>N/A</td> <td>Lab can impact final restoration if designing</td> <td>Well designed systems—can allocate responsibility to either party</td> </tr> <tr> <td>Trust in the Technology</td> <td>Some clinicians feel more confident with conventional impressions— more familiar</td> <td>Some clinicians do no believe in software results being accurate</td> <td>Hardware-software interactions, user confidence, errors in scan interpretation may affect real time decision making</td> <td>Simplifies verification process</td> <td>N/A</td> <td>Some resistance from older clinicians</td> <td>Compatibility, file types, data loss if not synced properly</td> </tr> <tr> <td>Activity/response time</td> <td>Time required for materials, costs, risk of damage from poor stone models</td> <td>Digital editing saves time, avoid mistakes or retakes. Labs receiving scans in real time can improve final result outcomes</td> <td>Less lag during consults, creates visible documentation</td> <td>Less time spent processing errors and retakes</td> <td>Improved logistical and appointment planning and case completion time for patients</td> <td>File sharing and tracking of treatment stage</td> <td>Digital files accessible over appointments—improved debugging of lab issues</td> </tr> </table> </html> # **Detailed Comparison: Conventional vs. Intra-oral Impressions** <html> <table> <tr> <th>Issues</th> <th>Conventional Impressions</th> <th>Intra-oral (non-digital) Impressions</th> <th>Technical Efficiency</th> <th>Clinical Efficiency</th> <th>Weather</th> <th>Applications</th> <th>Other relevant issues</th> </tr> <tr> <td>Patient related</td> <td>May provoke undesirable response from patients (e.g. gag reflex, unpleasant taste, etc.)</td> <td>Some intra-oral scanning can make this difficult to use in patients with small mouths, limited opening or tori</td> <td>Harder for inexperienced or unskilled to achieve ideal outcomes</td> <td>Clinical risk variable for multiple reasons (e.g. required time, appointments, adaptation)</td> <td>Setting environment (e.g. mobile clinics, domiciliary appointments) problematic for traditional impressions e.g. longer setting time</td> <td>Impressions—requiring disinfection to be transported physically (some flexibility required to address clinical application)</td> <td>Impressions susceptible to damage before models poured</td> </tr> <tr> <td>Quality of Outcome</td> <td>Accuracy and success of final result highly influenced by the ability of the operator to manage soft tissues, technique, environment, and access</td> <td>Software and hardware still developing and may have errors</td> <td>Longer processing time, multiple appointments, more rounds to achieve final outcomes</td> <td>Digital outcomes more predictable with training</td> <td>Digital impression—cloud sharing—less impacted by temperature or humidity</td> <td>Intraoral scanning— easier for digitally facilitated workflows; less suitable in some prosthodontic applications (e.g. long spans, multiple prepped teeth)</td> <td>Compression of soft tissues (e.g. during border moulding functional impressions) important e.g. removable prosthetics</td> </tr> <tr> <td>Responsibility</td> <td>Lab may be allocated responsibility for poor result from unclear instruction, poor impressions which can delay treatment</td> <td>Digital errors can be detected early e.g. real time or from same screen (scanning technique or software issues)</td> <td>Lab can be made more accountable for case planning and design of appliance by using same digital files</td> <td>Lab has better visibility of scanned data</td> <td>N/A</td> <td>Lab can impact final restoration if designing</td> <td>Well designed systems—can allocate responsibility to either party</td> </tr> <tr> <td>Trust in the Technology</td> <td>Some clinicians feel more confident with conventional impressions— more familiar</td> <td>Some clinicians do no believe in software results being accurate</td> <td>Hardware-software interactions, user confidence, errors in scan interpretation may affect real time decision making</td> <td>Simplifies verification process</td> <td>N/A</td> <td>Some resistance from older clinicians</td> <td>Compatibility, file types, data loss if not synced properly</td> </tr> <tr> <td>Activity/response time</td> <td>Time required for materials, costs, risk of damage from poor stone models</td> <td>Digital editing saves time, avoid mistakes or retakes. Labs receiving scans in real time can improve final result outcomes</td> <td>Less lag during consults, creates visible documentation</td> <td>Less time spent processing errors and retakes</td> <td>Improved logistical and appointment planning and case completion time for patients</td> <td>File sharing and tracking of treatment stage</td> <td>Digital files accessible over appointments—improved debugging of lab issues</td> </tr> </table> </html> **Record keeping** Comparison Slider and Revamped left panel interface showing dental scans # **Record Keeping** Intra-oral scanners offer powerful tools for longitudinal patient monitoring. - ==Software (e.g., from Trios) allows for the comparison of scans taken at different appointments (e.g., years apart).== - ==This enables **qualitative** visual comparison and, more importantly, **quantitative analysis**.== - ==The software can generate a color map highlighting areas of change:== - ==**Green:** No significant change.== - ==**Red/Blue:** Indicates areas of tooth wear (attrition, erosion) or other changes, allowing for precise tracking over time.== **Time** **The time efficiency of intraoral scanners: An in vitro comparative study** *Sebastian B.M. Patzelt DMD, Dr med dent¹,²,⁸⁹, Christos Lamprinos DDS², Susanne Stampf Dr rer nat³, Wael Att DDS, Dr med dent habil, PhD⁴* **Methods** The authors used three different intraoral scanners to digitize a single abutment (scenario 1), a short-span fixed dental prosthesis (scenario 2) and a full-arch prosthesis preparation (scenario 3). They measured the procedure durations for the several scenarios and compiled and contrasted the procedure durations for three conventional impression materials. # **Time Efficiency of Intraoral Scanners** ## **Study: The time efficiency of intraoral scanners: An in vitro comparative study** *Sebastian B.M. Patzelt DMD, Dr med dent¹,²,⁸⁹, Christos Lamprinos DDS², Susanne Stampf Dr rer nat³, Wael Att DDS, Dr med dent habil, PhD⁴* ### **Methods** The authors used three different intraoral scanners to digitize a single abutment (scenario 1), a short-span fixed dental prosthesis (scenario 2) and a full-arch prosthesis preparation (scenario 3). They measured the procedure durations for the several scenarios and compiled and contrasted the procedure durations for three conventional impression materials. > [!note] Measurement Details > Time was measured from the initial setup (tray selection or hardware setup) through the final step before shipping (disinfection for conventional, file finalization for digital). **Time** The time efficiency of intraoral scanners: An in vitro comparative study **Results** The mean total procedure durations for making digital impressions of scenarios 1, 2 and 3 were as much as 5 minutes 57 seconds, 6 minutes 57 seconds, and 20 minutes 55 seconds, respectively. Results showed statistically significant differences between all scanners (*P* < .05), except Lava (3M ESPE, St. Paul, Minn.) and iTero with foot pedal (Align Technology, San Jose, Calif.) for scenario 1, CEREC (Sirona, Bensheim, Germany) and CEREC with foot pedal for scenario 2, and iTero and iTero with foot pedal for scenarios 2 and 3. The compiled procedure durations for making conventional impressions in scenarios 1 and 2 ranged between 18 minutes 15 seconds and 27 minutes 25 seconds; for scenario 3, they ranged between 21 minutes 25 seconds and 30 minutes 25 seconds. ### **Results** - **Key Finding:** Digital impressions were significantly faster than conventional methods. - Mean digital impression times were up to 5:57 for single abutments, 6:57 for short spans, and 20:55 for full arches. - Conventional impression times ranged from 18:15 to 30:25 across the scenarios. - There were statistically significant differences between all scanners (*P* < .05), except Lava and iTero for scenario 1, CEREC and CEREC with foot pedal for scenario 2, and iTero and iTero with foot pedal for scenarios 2 and 3. > [!success] Key Finding > A major portion of the time saved with digital workflows comes from **skipping the ~15-minute disinfection step** required for conventional impressions. Time **The time efficiency of intraoral scanners: An in vitro comparative study** *Schweizer R.M. Polychi DMD, Dr. med. dent.¹, A. M. Christos Lymperis DDS.¹ Suzanne Stumpf Dr. rer. nat.¹, Wael Ali DDS, Dr. med. dent habil., PhD.¹* **CONVENTIONAL** → [Impression] → [Model] → [Scan] → [Design] → [Milling] → [Delivery] **DIGITAL** → [Scan] → [Design] → [Milling] → [Delivery] Flowchart comparing conventional and digital dental workflows, highlighting time efficiency differences. ## **Digital vs. Conventional Workflow** *Schweizer R.M. Polychi DMD, Dr. med. dent.¹, A. M. Christos Lymperis DDS.¹ Suzanne Stumpf Dr. rer. nat.¹, Wael Ali DDS, Dr. med. dent habil., PhD.¹* - **CONVENTIONAL:** → [Impression] → [Model] → [Scan] → [Design] → [Milling] → [Delivery] - **DIGITAL:** → [Scan] → [Design] → [Milling] → [Delivery] > [!info] Digital Workflow Details > The digital workflow is more direct: Scan → Digital file (STL) → Instant email/portal transfer → Lab designs crown → Milling/Fabrication. This eliminates multiple intermediate steps and reduces opportunities for introduced error (e.g., from pouring a stone model). # Extra-oral scanners vs Intra-oral scanners **Extra-oral scanners** - Scans conventional impression or casts **Intra-oral scanners** - Direct scan of the oral structures Pinhole from confocal microscope works to reduce scattered unfocused light to increase accuracy 12 # **Extra-oral vs. Intra-oral Scanners** ## **Definitions** - **Extra-oral scanners:** Scans a conventional impression or a physical cast. - **Intra-oral scanners:** Performs a direct scan of the oral structures. Pinhole from confocal microscope works to reduce scattered unfocused light to increase accuracy. **Extra-oral scanners** - Structured light scanners project a grid or other parallel scan pattern on the scan object. The distortions of the scan patterns are captured by the camera and processed by the software Diagram illustrating structured light scanning with labels: projector, illumination, object, camera, camera image ## **Extra-oral Scanner Technology** - Structured light scanners project a grid or other parallel scan pattern on the scan object. The distortions of the scan patterns are captured by the camera and processed by the software. **Extra-oral vs Intra-oral scanners** Definitive restorations which were made based on intraoral digital impressions demonstrated significantly smaller marginal openings (from 86.09 μm ± 61.46 μm to 88.95 μm ± 54.46 μm) than those which were fabricated based on laboratory scanning procedures (143.29 μm ± 100.71 μm) Others found no difference **Which one is better? Mixed literature.** Lab based scanners are scanning a cast (which is not the original site). Impression 99% accurate. Then you pour up or scan the impression. Compounding errors. Extra-oral scanners still allow records keeping. Allow CAD/CAM techniques on supplied physical models. ## **Comparative Accuracy** - **Key Finding:** The literature is mixed, but some studies show intra-oral scans can be more accurate. - One study found definitive restorations from intraoral digital impressions had significantly smaller marginal openings (86.09 μm to 88.95 μm) compared to those from laboratory scanning (143.29 μm). - Other studies found no difference. - **Consideration:** Lab-based scanners scan a cast, which introduces potential compounding errors from the impression and pouring stages. However, extra-oral scanners still allow for digital record keeping and CAD/CAM workflows from physical models. > [!warning] Compounding Errors > A potential reason for this difference is that extra-oral scanning of a cast can **compound errors**. Any small inaccuracy in the original PVS impression is carried over and potentially added to by another layer of inaccuracy from the scanning process itself. Intra-oral scanners capture the source anatomy directly, avoiding this cumulative error. **Intra-oral scanners** **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 1. Triangulation 2. Confocal 3. Active wavefront sampling 4. Stereophotogrammetry *Figure 3. Determining distance to the object. (a) Triangulation: distance BC could be determined according to the formula BC = AC × sin C / sin (A + C). (b) Confocal: distance to the object is determined according to the focal distance. (c) AWS requiring a sensor and an off-axis that moves on a circular path around the optical axis and produces a rotation of interest points. (d) Stereophotogrammetry is a technology that generates files by algorithm analyzing numerous pictures.* 15 # **Intra-oral Scanner Technologies** *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 **Intra-oral scanners: Triangulation** Triangulation. Triangulation is based on a principle that the position of a point of a triangle (the object) can be calculated knowing the positions and angles of two points of view (Figure 3(a)). These two points of view may be produced by two detectors, a single detector using a prism, or captured at two different points in time. Idea is that we can figure out the exact position of an object if we know the relative angle and distance from 2 different points. However noise, lens distortion can lead to inaccuracies. If there is an error, this could get carried forward to other calculations. Used by sirona omnicam scanners 16 ## **1. Triangulation** - **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. **Intra-oral scanners: Confocal** Confocal. Confocal imaging is a technique based on acquisition of focused and defocused images from selected depths (Figure 3(b)). This technology can detect the sharpness area of the image to infer distance to the object that is correlated to the focal length of the lens. A tooth can then be reconstructed by successive images taken at different focuses and aperture values and from different angles around the object. The sharpness area is directly related to the dexterity of the operator who can generate motion blur and this technique also requires large optics that may lead to difficulties in clinical practice. Eliminates aberrant beams via pin hole. ## **2. Confocal Imaging** - **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. **Intra-oral scanners** 1. Triangulation 2. Confocal 3. Active wavefront sampling 4. Stereophotogrammetry **Active Wavefront Sampling (AWS)** – Active wavefront sampling refers to getting 3D information from a single lens imaging system by measuring depth based on the defocus of the primary optical system. Three sensors capture the clinical situation from different perspectives. With these three images captured simultaneously, 3D surface patches are generated in real time by means of proprietary image processing algorithms using the in-focus and out-of-focus information. Used by Lava chairside Oral scanner. **Stereophotogrammetry** – Stereophotogrammetry estimates all coordinates (x, y, and z) only through an algorithmic analysis of images. As this approach relies on passive light projection and software rather than active projection and hardware, the camera is relatively small, its handling is easier, and its production is cheaper. ## **3. Active Wavefront Sampling (AWS)** - **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.== **Intra-oral scanners** - Relatively obsolete technique of coating the intra-oral surfaces with an anti-reflective powder such as titanium dioxide As mentioned in earlier slides, the light is an important feature of how the scanners capture information. Which is why important to not use overhead light. Additionally, saliva etc may reflect unwanted light. The earlier generations of IOSs required some opaquers in the form of sprays or powders for accurate recording, which have inherent disadvantages, including patient discomfort, time consumption, and technique sensitivity ## **Surface Coating (Powder)** - 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.== Close-up comparison of dental or anatomical surface with highlighted areas indicating evaluation of accuracy **Accuracy** According to the International Organization for Standardization (ISO) 5725-1: - The term *trueness* refers to the closeness between the arithmetic mean of a big number of test results and the true or accepted reference value. - *Precision* is another term which is used widely for optical impressions. This term refers to how close several measurements of the same quantity are close to each other. - *accuracy* refers to the combination of trueness and precision Accuracy diagram with four target illustrations showing combinations of trueness and precision, labeled High Trueness High Precision, High Trueness Low Precision, Low Trueness High Precision, and Low Trueness Low Precision, with axes labeled TRUENESS and PRECISION. # **Accuracy in Digital Impressions** ## **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. > [!tip] Analogy > This is analogous to *validity* (trueness) and *reliability* (precision) in research. Target diagrams illustrating reliability, validity, precision, and accuracy **IOS accuracy** *“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) ## **Study: IOS Accuracy** *“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. A diagram illustrating the concepts of precision and trueness using target-like images; high/low trueness and high/low precision are labeled in quadrants Scanner comparison with labeled brain scan images from various devices including ATOS (reference scanner), 3M, CS3500, CS3600, DWIO, OMNI, PLAN, TRIOS, and IPR; used to demonstrate accuracy differences **Accuracy** Images by Dr Nedelcu Three labeled medical scan images (PLANSCAN, TRIOS, IMPRESSION) displayed side-by-side with numerical values above each. **Accuracy** Images by Dr Nedelcu Comparison of dental scan and impression images showing accuracy and visibility of the finish line: PLANCAN (7.560A), TRIOS (23.560A), and IMPRESSION (18.000A). Comparison of scan accuracy showing PLANSCAN (7.500μ), TRIOS (23.500μ), and IMPRESSION (16.000μ) with close-up textures **Accuracy** Three thermal imaging scans labeled PLANSCAN, TRIOS, and IMPRESSION with corresponding values 7.500Δ, 23.500Δ, and 18.000Δ. Images by Dr Nedelcu. **Accuracy** **Finish Line** *Images by Dr Nedelcu* **Results:** All IOS, except PlanScan, had comparable overall accuracy, however, FLD and 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, whilst PlanScan had overall low FLD and FLA, as well as lower general accuracy. IMPR presented high FLD, except in subgingival areas, and high FLA. Trios had the highest resolution by factor 1.6 to 3.1 among IOS, followed by IMPR, DWIO, Omnicam, CS3500, 3M, CS3600 and PlanScan. Tessellation was found to be non-uniform except in 3M and DWIO. Topographic variation was found for 3M and Trios, with deviations below +/- 25 µm for Trios. Inclusion of color enhanced the identification of the finish line in Trios, Omnicam and CS3600, but not in PlanScan. **Conclusions:** There were sizeable variations between IOS with both higher and lower FLD and FLA than IMPR. High FLD was more related to high localized finish line resolution and non-uniform tessellation, than to high overall resolution. Topography variations were low. Color improved finish line identification in some IOS. 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. *Summary of the paper that previous slides were taken from.* ## **Study: Finish Line Accuracy** *Images by Dr Nedelcu* *Summary of the paper that previous slides were taken from.* ### **Results** - 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. **Newer study** **Results** The TRIOS 5 intraoral scanner displayed the lowest deviation for precision (37.8 ± 4.53 µm) and trueness (54.9 ± 11 µm), followed by Medit i700 (precision 40.6 ± 4.17 µm, trueness 60.3 ± 10.9 µm), whereas the highest deviation (precision: 49.1 ± 8.31 µm, trueness: 72.3 ± 10.4 µm) was reported when Primescan intraoral scanner was used for recording impressions of full arch implants. When the 3 intraoral scanners were compared, a statistically significant difference was observed in terms of precision (*P*<0.005) and trueness (*P*<0.005). **Conclusions** 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. # **Comparative Study: TRIOS 5, Medit i700, and Primescan** *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). > [!info] 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). **Trios scanners** **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** The TRIOS 5 intraoral scanner displayed the lowest deviation values for precision (37.8 ± 4.53 µm) and trueness (54.9 ± 11 µm), followed by Medit i700 (precision: 40.6 ± 4.27 µm, trueness: 60.5 ± 10.9 µm), whereas the highest deviation (precision: 49.1 ± 6.31 µm, trueness: 72.3 ± 15.4 µm) was reported when Primescan scanner was used for recording impressions of full arch implants. When the 3 intraoral scanners were compared, a statistically significant difference was observed in terms of precision (P<0.005) and trueness (P=0.005). **Conclusions** 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. Figure 1: A small picture that requires more context, showing a device, possibly intraoral scanner, with labels or sparse text. ## **Conclusions** - 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. **ATOS Core** - Industrial scanner (Not an intra-oral scanner) - Can be accurate to 1um - Often used as a "reference" # **Reference Scanners: ATOS Core** - 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. . Diagram showing the scan protocol for digital scanners (Trios) with directional arrows for upper and lower dental arches. Scan protocol for upper and lower dental arches using Trios digital scanner, illustrated with directional arrows **Scan Pattern** Trios scan patterns all achieve similar results. 36 # **Scan Pattern** - Trios scan patterns all achieve similar results. The protocol used to scan the arch can impact accuracy. - ==Studies have shown that for some scanners, deviating from the manufacturer's recommended scan pattern can lead to a significant increase in error.== - ==For the **Trios scanner**, studies found that different scan patterns did not have a significant effect on accuracy.== > [!tip] Best Practice > It is always recommended to follow the **manufacturer's specified scan pattern** to ensure optimal results. The recommended pattern for Trios is typically: occlusal surfaces → zigzag across the anteriors → opposite occlusal surface → lingual/palatal surfaces → buccal surfaces. **Digital vs Conventional Impressions** **Digital Versus Conventional Impressions in Fixed Prosthodontics: A Review** *Andrea Almeida, *Rene Garcia, DDS, PhD; **Helena Valério, DDS, PhD; ***Mircea Johnson, DDS, PhD; & Ute Kunkel, DDS, ** **Abstract** **Purpose:** To conduct a systematic review to evaluate the evidence of possible benefits and accuracy of digital impression techniques vs. conventional impression techniques. **Materials and Methods:** Reports of digital impression techniques versus conventional impression techniques were systematically searched for in the following databases: Cochrane Central Register of Controlled Trials, PubMed, and Web of Science. A combination of controlled vocabulary, free-text words, and well-defined inclusion and exclusion criteria guided the search. **Results:** Digital impression accuracy is at the same level as conventional impression methods in fabrication of crowns and short fixed dental prostheses (FDPs). For fabrication of implant-supported crowns and FDPs, digital impression accuracy is clinically acceptable. In full-arch impressions, conventional impression methods resulted in better accuracy compared to digital impressions. **Conclusion:** Digital impression techniques are a clinically acceptable alternative to conventional impression methods in fabrication of crowns and short FDPs. For fabrication of implant-supported crowns and FDPs, digital impression systems also result in clinically acceptable fit. Digital impression techniques are faster and can shorten the operation time. Based on this study, the conventional impression technique is still recommended for full-arch impressions. - Efficiency of digital vs conventional impressions: - Digital (248.48 ± 23.48 s) and conventional (605.38 ± 23.66 s) - But when completing a full arch impression, conventional impressions more accurate 37 # **Systematic Review: Digital vs. Conventional Impressions** *Digital Versus Conventional Impressions in Fixed Prosthodontics: A Review* *Andrea Almeida, *Rene Garcia, DDS, PhD; **Helena Valério, DDS, PhD; ***Mircea Johnson, DDS, PhD; & Ute Kunkel, DDS, *** ## **Abstract** - **Purpose:** To conduct a systematic review to evaluate the evidence of possible benefits and accuracy of digital impression techniques vs. conventional impression techniques. - **Materials and Methods:** Reports of digital impression techniques versus conventional impression techniques were systematically searched for in the following databases: Cochrane Central Register of Controlled Trials, PubMed, and Web of Science. A combination of controlled vocabulary, free-text words, and well-defined inclusion and exclusion criteria guided the search. - **Results:** Digital impression accuracy is at the same level as conventional impression methods in fabrication of crowns and short fixed dental prostheses (FDPs). For fabrication of implant-supported crowns and FDPs, digital impression accuracy is clinically acceptable. In full-arch impressions, conventional impression methods resulted in better accuracy compared to digital impressions. - **Conclusion:** Digital impression techniques are a clinically acceptable alternative to conventional impression methods in fabrication of crowns and short FDPs. For fabrication of implant-supported crowns and FDPs, digital impression systems also result in clinically acceptable fit. Digital impression techniques are faster and can shorten the operation time. Based on this study, the conventional impression technique is still recommended for full-arch impressions. > [!warning] Stitching Error > The primary limitation of current digital technology with full-arch scans is the accumulation of small inaccuracies over the long span, a phenomenon known as 'stitching error'. ## **Key Findings** - **Efficiency:** Digital impressions (248.48 ± 23.48 s) are significantly faster than conventional impressions (605.38 ± 23.66 s). - **Accuracy:** When completing a full arch impression, conventional impressions are more accurate. **Digital vs Conventional Impressions** Other studies have reached similar conclusions **Purpose** The purpose of this in vitro study was to compare the accuracy of 2 intraoral scanners, TRIOS 3 (TR) and CEREC Omnicam (OC). Accuracy was assessed from changes to reference distances defined along the complete arch of a reference cast including 3 precision balls and 3 prepared teeth. The local accuracy (trueness and precision) of the scanned surface of each prepared tooth was also assessed. **Results** The following mean absolute changes in distance were determined: ΔP₁P₂ TR: 78.4 μm, OC: 139.6 μm; ΔP₁P₃ TR: 24.7 μm, OC: 17.2 μm; ΔP₂P₃ TR: 68.6 μm, OC: 41.2 μm. The scanner did not have a statistically significant effect (P=.138) for distance, and the different distances differed significantly from each other (P<.001). Both scanners provided results acceptable for the fabrication of inlays and short-span FPDs. A complete-crown scan was more accurate than an inlay scan (P<.001). Accuracy and precision were better for TR than for OC (P<.001). **Conclusions** With maximum discrepancies of 192.5 to 294.6 μm across the dental arch, complete-arch scans cannot yet be recommended for the fabrication of long-span FPDs. # **Further In Vitro Study on Full-Arch Accuracy** Other studies have reached similar conclusions. ## **Purpose** The purpose of this in vitro study was to compare the accuracy of 2 intraoral scanners, TRIOS 3 (TR) and CEREC Omnicam (OC). Accuracy was assessed from changes to reference distances defined along the complete arch of a reference cast including 3 precision balls and 3 prepared teeth. The local accuracy (trueness and precision) of the scanned surface of each prepared tooth was also assessed. ## **Results** - The scanner did not have a statistically significant effect (P=.138) for distance, and the different distances differed significantly from each other (P<.001). - Both scanners provided results acceptable for the fabrication of inlays and short-span FPDs. - A complete-crown scan was more accurate than an inlay scan (P<.001). - Accuracy and precision were better for TR than for OC (P<.001). - ==The anterior teeth generally scanned more accurately than the posterior teeth in a full-arch scan.== ## **Conclusions** - **Key Finding:** Complete-arch scans cannot yet be recommended for the fabrication of long-span FPDs due to significant discrepancies across the arch (maximum discrepancies of 192.5 to 294.6 μm). Questions? Most important: How to use intra-oral scanners. What are good traits of intra-oral scanners? In Vivo Accuracy and Precision in Prosthodontics ROBERT NEDELCU # **Conclusion and Key Takeaways** Questions? Most important: How to use intra-oral scanners. What are good traits of intra-oral scanners? In Vivo Accuracy and Precision in Prosthodontics ROBERT NEDELCU - ==Digital impressions offer significant advantages in workflow efficiency, patient comfort, and record-keeping.== - ==**Accuracy**, a combination of **trueness** and **precision**, is the most critical factor for clinical success.== - ==While excellent for single units and short-span restorations, intra-oral scanners currently show limitations in **full-arch accuracy** due to the accumulation of stitching errors.== - ==Following the manufacturer's recommended **scan pattern** is crucial for achieving the best possible results.== [[F4 DigitalImpressions.pdf#page=1|F4 DigitalImpressions, p.1]] [[F4 DigitalImpressions.pdf#page=2|F4 DigitalImpressions, p.2]] [[F4 DigitalImpressions.pdf#page=3|F4 DigitalImpressions, p.3]] [[F4 DigitalImpressions.pdf#page=4|F4 DigitalImpressions, p.4]] [[F4 DigitalImpressions.pdf#page=5|F4 DigitalImpressions, p.5]] [[F4 DigitalImpressions.pdf#page=6|F4 DigitalImpressions, p.6]] [[F4 DigitalImpressions.pdf#page=7|F4 DigitalImpressions, p.7]] [[F4 DigitalImpressions.pdf#page=8|F4 DigitalImpressions, p.8]] [[F4 DigitalImpressions.pdf#page=9|F4 DigitalImpressions, p.9]] [[F4 DigitalImpressions.pdf#page=10|F4 DigitalImpressions, p.10]] [[F4 DigitalImpressions.pdf#page=11|F4 DigitalImpressions, p.11]] [[F4 DigitalImpressions.pdf#page=12|F4 DigitalImpressions, p.12]] [[F4 DigitalImpressions.pdf#page=13|F4 DigitalImpressions, p.13]] [[F4 DigitalImpressions.pdf#page=14|F4 DigitalImpressions, p.14]] [[F4 DigitalImpressions.pdf#page=15|F4 DigitalImpressions, p.15]] [[F4 DigitalImpressions.pdf#page=16|F4 DigitalImpressions, p.16]] [[F4 DigitalImpressions.pdf#page=17|F4 DigitalImpressions, p.17]] [[F4 DigitalImpressions.pdf#page=18|F4 DigitalImpressions, p.18]] [[F4 DigitalImpressions.pdf#page=19|F4 DigitalImpressions, p.19]] [[F4 DigitalImpressions.pdf#page=20|F4 DigitalImpressions, p.20]] [[F4 DigitalImpressions.pdf#page=21|F4 DigitalImpressions, p.21]] [[F4 DigitalImpressions.pdf#page=22|F4 DigitalImpressions, p.22]] [[F4 DigitalImpressions.pdf#page=23|F4 DigitalImpressions, p.23]] [[F4 DigitalImpressions.pdf#page=24|F4 DigitalImpressions, p.24]] [[F4 DigitalImpressions.pdf#page=25|F4 DigitalImpressions, p.25]] [[F4 DigitalImpressions.pdf#page=26|F4 DigitalImpressions, p.26]] [[F4 DigitalImpressions.pdf#page=27|F4 DigitalImpressions, p.27]] [[F4 DigitalImpressions.pdf#page=28|F4 DigitalImpressions, p.28]] [[F4 DigitalImpressions.pdf#page=29|F4 DigitalImpressions, p.29]] [[F4 DigitalImpressions.pdf#page=30|F4 DigitalImpressions, p.30]] [[F4 DigitalImpressions.pdf#page=31|F4 DigitalImpressions, p.31]] [[F4 DigitalImpressions.pdf#page=32|F4 DigitalImpressions, p.32]] [[F4 DigitalImpressions.pdf#page=33|F4 DigitalImpressions, p.33]] [[F4 DigitalImpressions.pdf#page=34|F4 DigitalImpressions, p.34]] [[F4 DigitalImpressions.pdf#page=35|F4 DigitalImpressions, p.35]] [[F4 DigitalImpressions.pdf#page=36|F4 DigitalImpressions, p.36]] [[F4 DigitalImpressions.pdf#page=37|F4 DigitalImpressions, p.37]] [[F4 DigitalImpressions.pdf#page=38|F4 DigitalImpressions, p.38]] [[F4 DigitalImpressions.pdf#page=39|F4 DigitalImpressions, p.39]]