July 26, 2021

Space Closure: A matter of timing?

Several surgical approaches have been advanced in a concerted, high-tariff quest to avail of a regional accelerated phenomenon (RAP) and accelerate orthodontic treatment. These procedures range from invasive surgery to minimal insult. Unfortunately, the results from high-quality studies evaluating these interventions have typically yielded lukewarm results. It also seems that repeated intervention may be necessary to produce sustained surgical acceleration- a prospect that might not appeal to patients or providers and have a biological cost.

As we all know, extractions are regularly used to provide the necessary space to achieve orthodontic objectives. But when should we commence space closure? Should we extract immediately before initiating space closure to avail of a potential RAP and accelerate the space closure phase? Or should we extract earlier, permitting maturation and reorganisation in the area, and defer space closure and the use of the space?

This question has exercised me for some time as I continue to fixate on undertaking efficient treatment to a good standard while avoiding what I often regard as unproven ‘optional extras’ (doi: 10.25259/APOS_110_2020). I was therefore delighted to see this study published in APOS Trends. It is freely available online. A team from Karachi, Pakistan did this interesting trial.

 What did they do?

They conducted a split-mouth randomised controlled trial as follows:

Participants: Aged 15-29 years and having removal of first premolars as part of orthodontic treatment

Intervention: After initial alignment and engagement of a 0.017 x 0.025-inch NiTi wire, they extracted the maxillary first premolar randomly on one side (control group with healed site). Then they removed the contralateral first bicuspid 1 month later (intervention group with recent extraction site).

Eight days later, they stabilised the molars, and started individual retraction of the canines into the extraction site on a 0.017 x 0.025-inch stainless steel wire using NiTi closed coil springs.

Outcome: The rate of canine retraction over 1 month.

They took an alginate impression. Then they measured the distance from the distal surface of the canine to the mesial surface of the second premolar at the contact point using Vernier Calipers.

Thirty-five patients with a mean age of 17.6 ± 3.7 years took part in the trial. Three participants dropped out. The investigators used a sealed envelope system to conceal group allocation. The outcome assessor analysed the data blinded to group allocation.

What did they find?

The mean canine retraction rate in the control group was 0.75 ± 0.26 mm over the 1-month period, while for the recent extraction site, it was higher (1.17 ± 0.27 mm). This difference was statistically significant (P = 0.00). The mean canine retraction was also higher in males, although this was based on minimal data. Similarly, they found more efficient tooth movement in the younger cohort (15 to 22 years).

What did I think?

I liked this study as it addresses an important question and sheds further light on a means of accelerating tooth movement. Importantly, this does not involve an additional intervention (with all the imposition, risk and cost which that might bring). It is also the first randomised controlled trial on this topic. It, therefore, addresses a glaring gap in the literature. In addition, the write-up is clear and straightforward, and the methodology appears to be sound.

On the less positive side, I am not altogether clear on the statistical analysis undertaken, particularly given the split-mouth design. However, the observed difference between the groups does appear to be of potential relevance. It would, however, be interesting to see whether these early differences (over the first month of space closure) are sustained throughout space closure. A more prolonged follow-up would therefore be very instructive.

It would also be helpful to consider the nature of tooth movement that arose. It is conceivable that a more tipping rather than bodily movement may have occurred in the recent extraction group. A more detailed evaluation of this might therefore be of value. From a periodontal perspective, the potential harms associated with earlier space closure were not considered. There is evidence, for example, that earlier space closure may predispose to the formation of gingival clefts (doi: 10.1002/JPER.19-0376.). Nevertheless, this is an interesting study, which provides us with clinically applicable information.

What can we conclude?

Based on this small split-mouth study, fresh extraction sites may permit more efficient space closure. While the race to find the best tool to accelerate treatment will continue, this study provides another indication that the treating clinician remains the real and enduring catalyst. The power continues to lie within.

Have your say!

  1. Thanks for sharing! With the “hopes” of benefiting from the RAP effect in space closure I adopted this practice (as I am sure many others do) shortly after residency. In moderate to severe crowding extracting the premolar and within a week using segmental mechanics to retract the canine, or canine and 1st premolar into the extraction space with power thread generally on a 016 niti – until the canine was retracted enough to avoid any round tripping of the lower anterior teeth (most commonly use segmental on lower arch — especially with thinner attachment biotype). Have been really impressed with the space closure – can close all or majority of space in a couple months (Take lots of progress pics to document — but would be wise to scan, date and measure. However, “see” (would be a great study) a loss of post molar anchorage too. In mild to mod crowding — and excess ant flaring – L&A and then extract and retract anterior en masse – “seems” to be more efficient — but since that is all I do now — hard to compare. So many variable that influence. I am sure like others — I thought split mouth design would be great for some in office studies — but it is more common than I thought that we see variable rates of space closure — same techniques bilaterally — so it can call into question how accurate split mouth design is — especially with a smaller n.

  2. Or does the more recent extraction location and a measurement occlusal to the center or resistance, indicate increased tipping in the first month. (For whatever reason I hope for movement at the center of resistance, a center of roation at infinity,……usually)

    Glad you liked the study.

  3. Various ways that claim to reduce orthodontic treatment time seem to vary from disproven manufacturer/technique claims to moderately successful alternatives. Dental authorities continue to selectively punish individuals with an interest in this area as lawyers may overthink advertising regulation that suggest it is a claim of superiority. Is it that difficult to list the various approaches and state the current level of scientific verification for each one? Lawyers should not be barring the public from information that affects their choices.

  4. It seems to me that “RAP” is the antithesis of distraction osteogenesis – a bit like “reverse distraction osteogenesis”. Here’s my comparison of the phases of distraction osteogenesis with RAP phases (in parentheses);

    Phase I: Osteotomy (= Orthodontic extraction)
    Phase II: Latency (= Orthodontic control group with healed site)
    Phase III: Distraction (= Orthodontic retraction)
    Phase IV: Consolidation (= Orthodontic retention)

    Just a thought –

  5. I think that’s such an interesting point you raised MP re observing different rates of closure in the same mouth where same technique is used. Assuming force systems are actually similar ( we assume we activate at the same level in relation to location of application and magnitude), apart from differences in local anatomy, I can only think of occlusal interferences as a variable confounding movement 1 quadrant more / less than another. I (believe) that I see this even with aligner mechanics, despite the assumption aligners are removed only 2-4 hours daily, it appears that occlusion / mastication is a variable that may also be controlled (fixed bite plane) in follow-up research, as well as control (addition of subjects with no split mouth design as MP alluded ) and scanning instead of alginate. Imaging for root apex movement of allowed…wish list goes on! Seems logical to investigate effect of base-line mechanics before we throw in “optional extras!” Love it!

  6. Moving teeth into a newly created extraction site should increase the velocity of dental movements due to the cellular processes catalyzed by the act of tooth extraction, and the knowledge that the teeth moving into this space are bringing “their” alveolar bone with them. Superimposing orthodontic dental movement into a site of wound healing alters the balance of remodeling so that tooth movement will occur at a faster rate.
    I usually bond brackets and refer patients for dental extractions with fixed appliances in place (except for the prescribed teeth to be extracted), after which they return within 2 days for continuous archwire placement. I have found that this consistently reduces the time it takes to perform space closure.

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