EXPERT VIEW - Alain Souchet

Alain Souchet, Specialist Orthodontist in Mulhouse, France and President of EAS, discusses Clear Aligner Techniques and CBCT.
I would like to share some thoughts with EAS members about the subject of Clear Align Techniques and CBCT.

1) A CBCT scan is a necessary requirement: as an orthodontist, for all my treatment plans, I want to see:

- the crowns
- the roots of the teeth
- the gums
- the face and smile
- the roots of the teeth moving into the bone.

2) Why?

Avoid moving the roots of the teeth outside the bone and preclude fenestrations.

3) How?

- Panoramic radiographs and teleradiographs are a 2D world
- while orthodontics is a 3D world
- CBCT is a 3D visualization allowing us to see the complete tooth as one whole object (roots and crown) in the bone.

4) To see or not to see with CBCT

CBCT allows us to see:
- the roots
- the crown - but not in its entirety (dicom file)
- The maxillary and mandibular bones, and the skull.

CBCT does not allow to see:
- composite restorations of crowns
- the gums, very important for CAT

It is therefore necessary to incorporate the use of a CBCT with an Intra-oral scanner, in order to see all.

5) Technical aspects of matching CBCT and IOS scan

The CBCT’s output is a DICOM file, it must be converted into an STL file, segmenting all: teeth, bones, maxillary and mandible teeth.
- It is therefore necessary to associate the STL files of the teeth with the STL files of the crowns from the intraoral scanner. Note that composite teeth, for example, are not visible on the CBCT DICOM file.

With CBCT and teeth segmentation, the treatment plan integrates:
- the teeth with their roots
- the bones of the maxilla, the mandible and the face.

6) CAT and staging timeline with CBCT

- Simulations or treatment plans are visualized stage by stage (staging) on a timeline: e.g., 23 stages upper and lower = 23 aligners upper and lower.
- We can see all the teeth moving in the bone stage by stage, and roots moving inside the bone or outside: fenestrations.

7) CAT treatment Options with CBCT

Explanations
The roots are in the bone with the external limits of the corticals
Option 1: the roots remain in the bone between the 2 corticals
Option 2: the roots come out of the bone through the corticals
The algorithms of the software will be able to put alerts when the roots touch the corticals and/or cross them:
The doctor can decide which option is better: for example
- Upper arch expansion:
- Deep-bite Fig 1,2,3
- Lower incisors round tipping

8) Examples of doctor's choice with CBCT

- perfect alignment of crowns: we cannot see root fenestration if any without CBCT
- perfect alignment of roots in the bone is only visible with CBCT

Examples:
8.1 Upper arch expansion
- Children and teens (growth period)
With CBCT it is easier to see classic expansion of the maxillary arch in growth period with mixed dentition, aligning crowns and roots to the best and easier to check results.
- Adults (no bone growth): CBCT helps deciding small expansion or expansion with orthognathic surgery, and avoid fenestrations.

8.2 Deep-bite Fig 1,2, 3
- the axes of crown /root of the upper incisors are very bent or crooked:
- Option 1: with upper crowns aligned, correcting the deep bite with risk of roots moving out of the bone in the palatal area is big.
- Option 2: same with roots perfectly aligned and crowns of the upper incisors are misaligned. For instance, in case of prosthetic restorations (veneers) of decayed incisors.
It is the doctor’s decision to choose Option 1 or 2: obviously CBCT is a very big help.

8.3 CBCT Multidisciplinary cases with missing teeth:
- Periodontology
- Odontology
- Implants
- Restorative
- Orthognathic surgery
- etc.

9) Which aligners manufacturers offer CBCT integration?

- Dentsply SureSmile Aligners: CBCT is available
- 3D Predict Aligners: CBCT is available
- Biotech Dental Smilers: CBCT is available
- AirNivol: not sure
- Ormco Spark: Teeth library and CBCT available
- Align: rumours?
- Others?

10) Software

- 3 Shape
- CephX Orca dental: automatic CBCT segmentation https://cephx.com/cbct-segmentation/
- Bellus 3D Dental Pro

11) Virtual Patient

- the complete patient in 3D
- the middles deviated or not in relation to the frontal midline
- the obliquity of the occlusal plane: Cant
- the asymmetries
- to make a Smile Design, etc.

Conclusion:

The CBCT associated with an IOScan brings a real plus (+) to the treatments with aligners (CAT): to see the roots moving inside the bone.
The treatment plans and the CAT simulations are more realistic. We can see the complete teeth moving stage by stage (staging) in the timeline. Using a 3D image, we create a ‘virtual patient’ to allow for better diagnostic and treatment planning.

Fig 1,2,3, courtesy Dentsply Suresmile