February 24, 2020

Does piezocision speed up first molar space closure? An RCT.

When the first molars are extracted, space closure may be difficult and take a fair amount of time.  But does piezocision speed up this tooth movement?  This new trial looked into this question.

Over the past few years, there has been a large amount of research into methods of speeding up tooth movement. Most of these studies have shown that vibration, mysterious lights and localised trauma do not have a clinically significant effect. This new study looked at the impact of localised trauma with piezocision on the rate of space closure of first molar spaces.  I thought that it was worth looking at this carefully because this is a complex tooth movement. It also evaluated the effect of localised piezocision on the rate of movement of only one tooth.

The Angle published this paper. A team from Jordan did the study.

Effect of piezocision on mandibular second molar protraction

Angle Orthodontist: Online advanced.  DOI: 10.2319/080419-511.1

What did they ask?

They did the study to answer the following question about first molar space closure;

“What is the effect of piezocision on the rate of mandibular second molar protraction”?

What did they do?

They did a randomised controlled trial.  The PICO was


Orthodontic patients aged 20-27 years old with Class I malocclusion who had at least one mandibular first molar extracted for longer than a year with a residual extraction space of >6mm.


Piezocision mesial and distal to the extraction space. They did this immediately before molar protraction.


Molar protraction without piezocision.


The primary outcome was the rate of molar protraction.  Secondary outcomes were the level of Interleukin in gingival crevicular fluid and duration of space closure.

They did a pre-prepared 1:1 allocation that was concealed from the operator using sealed envelopes.

When they enrolled a patient with bilateral absent first molars, they randomly allocated piezocison to the right or left side.  This introduced a split-mouth component to the trial. For patients with unilateral missing first molars, they assigned the patient to control or intervention.  The unit of analysis for the study was the tooth.

One operator treated all the patients. Space closure was done in 019X025 ss wires with a mesial force being applied from a TAD with a Ni-Ti spring delivering a 150g force.

They reviewed the patients every month and took an alginate impression to make study casts. These casts were scanned.  Then they measured from the mesial contact point of the second molar to a point representing the mini screw head constructed on the lower occlusal plane.

They did not mention whether the operator or the person recording the tooth movement was blinded to the treatment allocation.

They did a sample size calculation based on the number of teeth required for analysis.  This suggested that they needed 16 molars per group.

What did they find?

In the piezocision group, 21 molars received the intervention, and 18 were in the control group.

Both the control and the intervention group included 13 teeth from patients with bilateral and 9 teeth from those with unilateral absent molars.  They excluded 2 patients because of poor oral hygiene and miniscrew failure from the intervention group.

The mean rate of space closure was increased in the first two months for the piezocision group. However, when they reported the speed of space closure from the start of treatment to 5 months, this was 4.53 (SD= 0.4) mm/month for the piezocision group and 3.32 (SD=0.36) mm/month for the control group. The effect size was 1.21 (0.4) mm/month, with a 95% CI of 0.12 to -0.54.

The duration of space closure was 9.61 months for the piezocision group and 10.87 months for the control. This was a difference of 1.2 months (95% CI -2.09 to -0.42).  These confidence intervals are wide and almost include zero, this means that the level of uncertainty is high, and any difference could be small.

Their overall conclusion was;

“Although piezocision doubled the rate of space closure over the first two months after surgery, overall first molar protraction was increased by only 1 month”.

Importantly, they pointed out that this difference was not worth the invasive procedure.

What did I think?

In the past, I have been critical of studies that reported that interventions have an effect on the rate of tooth movement.  Indeed, I have been accused of bias in these blog posts.  I am going to apply the same high criteria for this study. Importantly, again this was a study that would have been improved if the journal had used the CONSORT guidelines.

I have the following concerns about this study.

Firstly, the study included a mixture of patients with bilateral and unilateral missing first molars.  Yet, the unit of analysis was the tooth.  This means that the trial is a mixture of split-mouth and per patient randomisation. I am not an expert statistician, but I suspect that there may be clustering issues in the analysis. It would have been preferable to randomise per participant, and the unit of analysis was the patient. The primary outcome would be the rate of tooth movement per patient.

While this may be an academic argument, my other concern is the method of measurement. I thought that there were several important problems.  Firstly, the TADS could have moved as they are not a stable structure. Secondly, the measurement from the mesial contact point of the second molar does not take tipping into account. Finally, they did not outline how they measured the duration of space closure.  Furthermore, the average time for space closure was 9 or 10 months. Yet they only measured the rate of space closure for five months.

Lastly, there was no mention of blinding of the operators or the person carrying out the measurement.  This puts the study at high risk of bias.

Final comments

I am sorry to point out so many critical issues with this trial. This is a study that would have benefitted from more critical reviewing and adherence to the CONSORT guidelines by the Journal. This would have improved the paper. Should you accept the findings? This is up to you and your interpretation of the article, which can be accessed under the Angle open access scheme.


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Have your say!

  1. When will people realise that creating empty premolar spaces is nonsense orthodontic planning. If an arch is crowded that tells us that the arch is too small. It does not mean the patient has too many teeth! To extract premolars and retract the other teeth, in most cases just as the facial complex is growing down and forwards, makes no sense and is known to relapse within a few years. Extraction orthodontics is not only unintelligent, it is tantamount to unethical.

    • These teeth were not extracted for orthodontic reasons. They needed to be extracted at least a year prior to the commencement of the study. The molars were protracted – a TAD was used.

      It is extremely rare to see narrow-minded arrogance exceed scientific understanding by such a large margin.

    • I suggest that you re read my post and perhaps the paper. The teeth were not extracted as part of orthodontic treatment. They were also not premolars!

      • My apologies for mis-reading this blog; I understand that it was referring mainly to first molars not first premolars. However, the creation of spaces, particularly large molar spaces, for whatever reason, creates a possible malocclusion and the argument is the same. Does one close the space (thereby reducing arch size and length) or does one maintain the space for future restoration?
        I know where I would put my money.

  2. Good to know some exotic treatments do not make much of a difference in treatment time. Wondering if you’ll look at the Ultrasound orthodontics from the Edmonton, Alberta, Canada company- Aevo System™ medical device.

  3. Noel Stimson, Interesting comment, seeing how this article described PROTRACTION of a second molar. Commenting on an article with out reading it first (or not really understanding the article), and then spewing multiple statements shown to be false by years of research speaks for itself.

  4. So True! Creating empty premolar spaces is totally nonsense orthodontic planning. As we have now discovered, all patients who have premolar extractions, will die!

    We must indeed address the cause of crowding…normal arch development does that. If only the arches can be “fully developed” to their genetic potential – but they can!

    A new procedure called Geno-expansion ® gently stimulates the hemi-maxillae and the hemi-mandible to slide away from each other thus creating room for teeth, tongue, tonsils etc. In some cases, there is adequate space for a second or third tongue. This in conjunction with Premolarogenesis® will allow us to meet the genetic potential of our hominid ancestors who had four premolars per quadrant.

    I agree with Dr. Stimson that premolar extraction is a brutal and medieval travesty akin to amputation. Do we remove limbs when we are trying to enhance function? No. After all, esthetics, function, stability, periodontal and TMJ health are not everything. Who is to say that Bimax. protrusion, lip incompetence, drooling, loss of attached gingiva, uncoupled incisors etc. are undesirable? One has to do a better job of explaining to patients why their appearance has worsened substantially – once they understand our concept of Atavistic© Orthodontics, they will leap on board like our primate ancestors. If malocclusion is a modern development, would harkening back to better times not surely resolve malocclusion by removing the cause? In the famous words of James Hetfield (father of down-picking) “ It’s all fun and games till someone loses an eye… then it’s just fun you can’t see.”

  5. Congratulations Noel! I believe you’ve written the most inane and absurd comment ever on Kevin’s page and you deserve an award. It seems you’re the editor of a group’s website http://www.jawache.com from which you appear to have 183 articles downloadable “research papers” provided by John Mew to support your ideas.

    Is this the same John Mew who wrote in a letter to the editor, (published in the AJODO, January 2009): “…We must not allow the present popularity of evidence-based orthodontics to blind us to obvious constant relationships.” In other words, it seems that data ain’t worth a crap if it conflicts with really uninformed, unintelligent and truly unethical claims. So, are Mew’s magical 183 worth a tinker’s damn? Perhaps, in an alternate universe. But there is a plethora of actual, unfiltered evidence that does not in any manner support the comments you’ve written.

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