The arch forms they are a-changin’. But is this stable?

Today I want to bring to the table a rather worn and torn story about expansion and stability. We certainly have heard many times from our mentors that we should keep initial arch form without much alterations, but on the other hand, the market constantly urges us to try extra-wide arches, enjoy novel expanders, both tooth- and bone-borne, and by all means avoid extractions in most of the cases.

Many can’t resist the temptation. What should they expect in the long run? I decided to look at some evidence at hand.

Expansion with arch wires

First, I want to look at a retrospective study for which the authors collected data on 32 patients treated with 4 premolars extraction. 

Long-term stability of Class I premolar extraction treatment

Boley JC, Mark JA, Sachdeva RC, Buschang PH

Am J Orthod Dentofacial Orthop. 2003 Sep;124(3):277-87

doi: 10.1016/s0889-5406(03)00448-7

The authors’ goal was to evaluate long-term posttreatment changes using cephalograms and study models. All the patients were treated by one experienced operator.

The mean posttreatment time was 15 years. During this period, the intercanine width decreased 1.4 mm. Initially this distance had been increased 1.7 mm during the treatment. Importantly, the authors highlighted that these posttreatment changes occurred because of mesial molar movement rather than distal incisor movement. I think it is a valuable aspect to keep in mind taking into account a modern-day trend for mandibular molars distalization.

The authors found the alignment of the mandibular incisors 10+ years postretention quite satisfactory (irregularity index of <3.5 mm) and attributed this to “nonexpansion or minimal expansion treatment approach”. I couldn’t agree more.

Expansion with a jackscrew

Next, let’s look at a meta analysis on maxillary expansion in the mixed dentition. 

Maxillary expansion: a meta analysis

Schiffman PH, Tuncay OC

Clin Orthod Res. 2001 May;4(2):86-96. 

doi: 10.1034/j.1600-0544.2001.040205.x.

Two investigators participated in this study. They were blinded with respect to authorship, year of publication (search was limited by the period from 1978 to 1999), journal, and founding source.

The authors included into their analysis 12 papers. The average age of the patients was 10.8 years. The mean expansion right after the treatment was 6 mm. Only 4.89 mm was left after the retention period. Finally, in the long-term only 2.4 mm of expansion was reported to have remained. The authors reasonably pointed out the following: “this 2.4 mm of expansion remaining after more than a year or more of post-retention period was no greater than what has been documented as normal growth.”

They concluded: “Stability of maxillary expansion is minimal.”

Expansion via surgery

Another potential way to alter transverse dimensions is surgery. Here I want to look at a comprehensive long-term study undertaken at the University of North Carolina. 

The hierarchy of stability and predictability in orthognathic surgery with rigid fixation

Proffit, W.R., Turvey, T.A. & Phillips, C.

Head Face Med 3, 21, 2007

doi:10.1186/1746-160X-3-21

The records of 2264 patients who have had orthognathic surgery were analysed and thoroughly discussed. I think this illustration is a great summary of the authors’ findings:

The authors pointed out that 30% of the patents to whom the maxilla was widened had a relapse in expansion > 3mm across molars. Interestingly, the authors also found no significant differences between long term stability of expansion with osteotomy or SARPE.

So what?

Before deriving any clinical implications from the data above, let’s touch upon a question why. In my opinion, the explanation for the lack of stability of expansion could be narrowed down to a popular orthodontic saying “muscles always win”. More detailed reasoning you can find in a classic paper by William Proffit “Equilibrium Theory Revisited”

We need to appreciate that the waters around dentition has grown and not move teeth out of equilibrium zone. Does this mean that we should completely avoid expansion? No. We just have to keep our expansion rate at a reasonable level.

Here are the templates from 3M I use to evaluate initial arch form. No conflict of interest to declare.

In today’s orthodontic world, pro-expansionists’ voices are amplified by the marketing power of huge companies, while conservatives are barely heard. However, I think those with conservative views should not keep up reiterating simple truths. Strong statements come and go. Stable results stay for a lifetime.

2 comments

    • Hi Andrew, thanks for stopping by! I didn’t know this quote comes from Willian Osler. The variation I heard goes: “don’t be the first to jump on the bandwagon, but don’t be last in the parade either.” Whatever the wording is, I try to follow the message.

      Like

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