Does sand blasting and acid etching affect the survival rate and removal and insertion torque of orthodontic miniscrews?

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Anchorage is an important consideration in the field of orthodontics, to prevent any unplanned and unwanted tooth movement. Controlling anchorage is essential for effective orthodontic treatment outcome. Miniscrews comprise the group of bone based anchor units referred to as Temporary Anchorage Devices (TADs). They are intended as a source of bone supported anchorage either as an independent source or as reinforcing anchorage. TADs are used in various tooth movements such as anterior retraction, protraction of posterior teeth, molar or posterior arch intrusion, molar distalization for Class II correction and anterior intrusion for deep bite correction. Other uses for TADs include uprighting molars, appliance anchorage, eruption of impacted teeth, assisting in tooth movement to shift maxillary and mandibular midlines, and as attachments for elastics in condylar fractures in young patients. The overall success rate of miniscrews varies from 60 to 91%. Several parameters that influence the stability of minicrews include gender, size,  screw mobilization time, loading of screw, location of the screw in the root, bone and in the gingiva. Loss of stability of micro implants leading to failure is a multifactorial problem. Failure to achieve good primary stability, poor quality cortical bone, overloading the miniscrew, angle of insertion, root impingement, root damage and poor oral hygiene are some of the reasons for failure of miniscrews. Surface topography might affect cell growth and orientation and surface treatment can increase the interdigitation between miniscrew and bone, and this phenomenon can be a possible solution for increasing the success rate of the miniscrews. Removal torque could also reflect the quality of the interface between miniscrew and bone, and can be used as a parameter in the evaluation of the Temporary Anchorage Devices.

The following article is one such article that has assessed the effect of sand blasting and acid etching on the stability and removal and insertion torque of orthodontic miniscrews.

“The effect of sandblasting and acid etching on survival rate of orthodontic miniscrews: a split-mouth randomized controlled trial”

Moghaddam SF, Mohammadi A, Behroozian A. The effect of sandblasting and acid etching on survival rate of orthodontic miniscrews: a split-mouth randomized controlled trial. Progress in Orthodontics. 2021 Dec;22(1):1-7.

doi: 10.1186/s40510-020-00347-z

What did this paper assess?

This paper evaluated the effect of surface roughening by sandblasting and acid etching on survival rate and removal and insertion torque of orthodontic miniscrews in a split-mouth study.

What was the protocol?

This was a single-blinded, split-mouth randomized clinical trial. Study population included 31 orthodontic patients (8 male, 23 female; mean age of 18.5 years) whose treatment plan included use of orthodontic miniscrews on both sides between the upper first permanent molar and the second premolar.

The treatment plan was en masse retraction of the upper six anterior teeth for all the included patients. Exclusion criteria included patients suffering from bone diseases like osteopetrosis, osteoporosis, or other systemic conditions that affects bone metabolism.

A pair of miniscrews were allocated for each patient. SAE( Sandblasted and Acid Etched) group miniscrew was given on one side and on the control side as received miniscrew was given. The side in which SAE or control miniscrew were placed, was decided by flipping a coin. The patients with the odd code in the registration list received SAE miniscrew in the left and even codes received it in the right.

Interventions

The sample included 62 miniscrews with the same shape and dimension (Dual-Top Anchor system, 1.6-mm diameter, 10-mm length, self-drilling style, Jeil Medical Co, Seoul, Korea) which was divided into two groups: the sandblasted acid-etched (SAE) and the control group. Miniscrews were blasted first with alumina particles of grain size 250 μm in the pressure of 4 MPa and then rinsed with acetone, 75% ethanol, and distilled water for 15 min in an ultrasonic cleanser, then were placed in 0.11 HF mol/l and 0.09 mol/l HNO3 solution in 25 °C temperature for 10 min. After etching, miniscrews were dried in an oven with 50 °C for 24 h; one of the SAE and control miniscrews were checked by a scanning electron microscope (SEM, Philips 515, Philips, Eindhoven, Netherlands) to confirm the sandblasting process.

The upper six anterior teeth were ligated on 19 × 25 stainless steel wire, and a traction force of about 250 g was applied with the use of a nickel-titanium (Ni-Ti) coil spring (Ormco, Orange, Calif) from the miniscrew to the canine, 6 weeks after insertion. Follow up was done in 3, 6, 10, and 14 weeks and then in 4 weeks interval, and the mobility of the miniscrews was checked. The failure was defined as the mobility of the miniscrews that precluded its clinical performance or more than 1 mm mobility. The percentages of the miniscrews of each group that were useful up to the end of the treatment were considered as success rate, and the time between insertion and failure point was considered as survival time.

What did the results show?

SURVIVAL RATE

  • The survival rate was 90.3% and 83.8% for the sandblasted and acid-etched(SAE) versus the control group, respectively. The difference in survival rate was not statistically significant (p=0.44).
  • Survival rate of miniscrews for the age group below 15 years was 66.66%  and above 15 years was 95.45% . Younger patients showed less survival rate (p=0.025) in both groups.
  • For males the survival rate was 93.75% and for females it was 84.78% and the difference between both the genders was not statistically significant (p=0.35) in both groups.
  • On both right and left sides the survival rate was 12.90% and it was not statistically significant (p=1) in both groups.

INSERTION TORQUE

The insertion torque for the SAE group was 5-30 Ncm and for the control group it was

5-25 Ncm. The difference between the groups was not statistically significant (p=0.83).

REMOVAL TORQUE

The removal torque for the SAE group was 10-30 Ncm and for the control group it was

5-10 Ncm. The difference between the groups was statistically significant (p=0.001)

Critical appraisal:

This was a single blinded study and so the clinician and outcome assessor knew the side of the SAE group due to its dull appearance and this could have possibly affected the results. The possible cytotoxity of the implants that were sandblasted could hinder the usage of this method to enhance stability. The procedure of sandblasting and acid etching would be a time consuming process.

Conclusion and scope for future studies:

Surface roughness of orthodontic miniscrews by sandblasting and acid etching had no influence on success rate of miniscrews but increased the removal torque significantly.

Splitmouth studies with larger sample size are needed to determine if surface treatment would have an effect on the success rate and the clinical performance of the miniscrews in different situations. Since these screws are in contact with the tissues after sandblasting and acid etching, the reaction of the tissues to these chemicals is an important factor and study of the histological section of these tissues is needed.

 

Contributors: Dr.M.Sureka, Dr.P.S.Haritha