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.
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.
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.
Emeritus Professor of Orthodontics, University of Manchester, UK.