Dear Satish,

generally speaking anchorage usually is measured with an inversed approach: One measures how much teeth move, and this is interpreted as "loss of Anchorage". In a controlled trial with one arm using anchorage reinforcement and one arm without anchorage reinforcement, the difference between those two would be the anchorage capacity of the reinforcement.

The classic approach to measure tooth movement would be to use lateral cephalograms. With the techniques published by Ricketts (1), Pancherz (2) or the structural superimposition by Björk (3) one could gather information about tooth movement and at the same time compensate for changes due to growth.

The units to estimate tooth movement would be anterior-posterior and vertical movement in millimetres and tipping in degrees.

However, the drawback of these techniques is that the measurements show quite high standard deviations,(4) and the differentiation between the left and the right side can be difficult.

Since the loss of Anchorage has three dimensions, one could use digital 3D models. Here, the superimposition technique is crucial in order to get correct results. Even with these techniques, one uses millimetres and degrees to describe tooth movement, but all three dimensions are covered. This is important since this has the potential to reveal differences in biomechanics.

We recently published one approach called RFD-superimposition.(5) There are other techniques, and the findings by Becker et al.(6) are interesting to read. Two things are essential to keep in mind:

1. The differences between the two models may not be too big. In growing individuals, this might not be a too long time. The shorter, the better.

2. All of these techniques aim to measure tooth movement in the maxilla only. How do we measure the mandible? Some approaches use the occlusal plane or the maxillary structures as a reference. However, the risk of errors still is significant. Maybe we have to go back to the structural superimposition...

References

1. Ricketts RM. A four-step method to distinguish orthodontic changes from natural growth. J. Clin. Orthod. 1975;9:208–15, 218–28.

2. Pancherz H. The mechanism of Class II correction in Herbst appliance treatment. A cephalometric investigation. Am. J. Orthod. 1982;82:104–13.

3. Björk A. Sutural Growth of the Upper Face Studies by the Implant Method. Rep. Congr. Eur. Orthod. Soc. 1964;40:49–65.

4. Lenza MA, Carvalho AA de, Lenza EB, Lenza MG, Torres HM de, Souza JB de. Radiographic evaluation of orthodontic treatment by means of four different cephalometric superimposition methods. Dental Press J. Orthod. 2015;20:29–36.

5. Ganzer N, Feldmann I, Liv P, Bondemark L. A novel method for superimposition and measurements on maxillary digital 3D models-studies on validity and reliability. Eur. J. Orthod. 2018;40:45–51.

6. Becker K, Wilmes B, Grandjean C, Drescher D. Impact of manual control point selection accuracy on automated surface matching of digital dental models. Clin. Oral Investig. 2018;22:801–10.

• There were no differences in anchorage loss between the two groups studied even though the source of anchorage was different. Therefore, the present results do not support the notion that one treatment strategy is superior to the other in terms of anchorage control. • The pattern of jaw growth was similar in both groups, with a higher growth expected unit in the Bioprogressive group because of an earlier treatment starting age. • Lower anchorage loss was matched by upper mesial movement of upper posterior teeth in both groups. Differential jaw growth was the most important component to molar correction.

mm

Clinically - comparing the molar relationship during treatment and pretreatment is only way to estimate anchorage Loss. It is measured in mm