Excellent question. Following

Hi Bruno Costa,

It's an interesting problem in digitalized dental education. To transform the manual procedure into the digital procedure in partial removable denture (PRD) sketching evaluation, the evaluation criteria should be re-defined, confirmed, reproducible, and digitalized-able.

For the commercialized three-dimensional solutions, there are several closed dental CAD/CAM based solutions, customized by software manufacturers (3Shape AG, ExoCAD GmbH, and ) or packed by dental system manufacturers (Sirona Dental/ CEREC-education systems, or KaVo Dental education system). They are mostly involved with die/ stump preparation in Dentistry and Dental Technology educations. For partial removable dentures, there are solutions for dental laboratory manufacturing only. In my opinion, the 2D visually evaluation solutions improperly work, due to (1) limiting in overall field-of-view, (2) 2D distortion, (3) perspective visuality, and (4) image capturing techniques, devices, and procedures. So, if you are interested in 3D solutions, please refer to the following suggestion.

I will make your answer divided into these issues, as (1) hardware infrastructure, (2) digitalized PRD sketching evaluation criteria, (3) working procedure, and (4) recommended software (just for reference).

1. Hardware infrastructure:

Obviously, you need a 3D optic scanner. Due to the PRD sketching replication, the colour HD camera scanner is essential. The mono-colour (monotonic) IOS is not recommended, because of unable to detect the sketch features on digital impression data. There are two options, as:

a. Intraoral scanner (IOS): You can use colour HD scanners, such as TRIOS 3/4 (colour) (3Shape AG), or its other same specified colour IOS.

b. Extraoral scanner (EOS or desktop dental optic scanner): You can use colour HD camera scanners, having partial denture design support option.

2. Digitalized PRD sketching evaluation criteria (SEC):

Different to human perspectives and subjective assessment, the digitalized PRD SEC can do some defined and intuitive criteria only. The evaluation issues are digitalized-able, measurable, and reproducible in any industrial 3D CAD software, known as:

a. The proper insertion and undercut area of the sketched PRD: You can use the plane function to re-orientate (automatically) the denture through manually defining the 3-pointed occlusal plane, which is attached on the digital cast duplication. The undercut areas are easily detected in the top-illumination and shaded visual modes.

b. The proper positions and locations of the sketched PRD's rest, lingual/ buccal/ labial connectors: Directly implemented on the 3D CAD software, you can doublecheck and measure the distance between a student's work and evaluation reference at the critical landmarks or reference points.

c. The proper positions, locations, and dimension of the sketched PRD's retainers: Directly implemented on the 3D CAD software, you can doublecheck and measure the distance between a student's work and evaluation reference at the critical landmarks or reference points. The proper length of embracing part, retaining part, etc could be measured for evidence.

Please make your evaluation sheet with the intuitive criteria, on MS-Excel for scripting the results.

3. Working procedure:

The possible working procedure is proposed as followed.

Step 1. Preparation:

Before doing the digital evaluation, the 3D-registration (3D-superimposition) fiducials (or landmarks) should be clearly embossed on the casts. The number of fiducials is not less than 5 points, which are uniformly distributed over the cast area from the insertion view-angle, and not violated the sketching areas. All the fiducials are duplicated with the working cast by the duplication mould, before delivering to students (as working casts) and teachers (as evaluation reference cast).

Step 2. Scanning and digital impression modification (if needed):

- Scanned the evaluation reference cast with your ideal sketch first. Then, scan the student's work casts individually.

- Doublecheck the mesh (triangulation) density. Corresponded to the software and the computer's configuration, the decimation should be applied on the digital impressions to reduce mesh density, it needed. That should be maintained your accuracy needs! (^^ 50% decimation still works, due to the sub-millimetre accuracy of your evaluation! Just mention about the unit triangulation patch size or area).

The free software for re-meshing 3D models is recommended below:

## 1. Meshmixer (Autodesk): http://www.meshmixer.com/download.html

## 2. Meshlab (IST-CNR): https://sourceforge.net/projects/meshlab/files/latest/download

## 3. Blender (Blender.org): https://www.blender.org/download/Blender2.82/blender-2.82a-windows64.msi/

Step 3. 3D format conversion (if needed):

Some commercialized scanners do not support the open industrial 3D formats, such as *.stl, *.igs, *.ply, *.asc, etc. Contact with the scanner's distributor about the format conversion application, if it is supported and plug-in with the scanner system (scanner software). If not, we will use some third-party application, such as Cross Manager (Datakit), link: https://www.datakit.com/en/product_search.php

The conversion should be done, before importing into any industrial 3D CAD software.

Step 4. 3D Registration (Superimposition):

Import in paired the digital impressions of the evaluation reference cast and a student's work cast. Do the point-paired registration. Check the

Step 5. 3D measurement:

Directly implemented on the 3D CAD software, you can doublecheck and measure the distance between a student's work and evaluation reference at the critical landmarks or reference points. The output measurement is scripted into MS-Excel file, as mentioned above.

4. The recommended 3D CAD software:

Herein, two useful free software is recommended, as below:

## 1. PowerShape (Delcam PLC/ Autodesk Inc.): free trial for 30 days: https://www.autodesk.com/products/powershape/free-trial

## 1. Fusion360 (Autodesk Inc.): free for academic and student use: https://www.autodesk.com/products/fusion-360/students-teachers-educators

Hope that works for you!

Most grateful for your answer which was more of a well summarized course then a simple statement; most impressive. May I just follow up with two key points. My obvious difficulty (ignorance, actually) in the digital field has hindered my understanding on how exactly the evaluation of the acquired images would be graded within your proposition. Would the teacher have to go through the scanned images and do a comparison or would some type of algorithm be able to compare them in real time. What would you expect would be a reasonable time for the suggested process to be completed. I probably should have mentioned (sorry) that the 2D image of the design, such as the one in the example, would be standardized for each of the aspects of the student's work; not the whole drawing need be evaluated simultaneously. Would this make the task easier? Hope you will continue to contribute. Thank you.

great and excellent response. And you've got all the work done for a quick publication!!! I/We need this kind of educational digital guidance.

I think that before you learn to run, you have to crawl. If you scan the models, the software will do a proposal but the student needs to make an interpretation ofnwhat he is seeing and why that component is there. CAD CAM is the future and they will get there sooner than us because they are tech natives. But the only way you make them understand the basic concepts is the analog way. Make them use a surveyor. They don't have one?, make them buy a mechanical pencil with a 2 mm graphite lead to use as a substitute. Let the take cell pictures to send you, decide the mourh preparation needs and make them analyze the prosthetic ecuators for a better clasp selection. When you consider that they are ready to make the next step, introduce them to the digital workflows. In my humble opinion, the first steps are analog classical way especially if you don't have enough scanners or you can't assure the students are understanding and assimilating the purpose of the technology

I concur Mauricio but, and maybe this wasn't clear initially, the drawings to be evaluated are the result of a sequence of didactic procedures which started with surveying, choosing the components and personal evaluation by the student of his own work on the proposed case. After some six hours of lab time, he will submit his work for our appraisal. His progress and efficiency are at the heart of the need of the digital processing I am trying to offer since several limitations have made a personal and real-time supervision very difficult. Hope you can contribute. Thank you.