A simple guide to orthodontic miniscrews. Part 2: evidence of effectiveness and efficacy

How effective are temporary anchorage devices (TADs) in providing/reinforcing anchorage?

Following on from the history and success rate of TADs, evidence of effectiveness will be discussed here. Leaving clinical experience to the side for now, let’s first review the evidence. There has been a surge of good-high quality research on this topic. Below are consolidated summaries of important papers with relation to this topic.

Thiruvenkatachari et al. 2006: In this study posterior anchorage loss in the maxillary arch was compared between 2 groups (TADs and conventional molar anchorage) during canine retraction. Mean anchorage losses were 1.60 mm in the maxilla and 1.70 mm in the mandible when conventional anchorage was used; no anchorage loss occurred when TADs were used.

Ma et al. 2008: The aim of this study was to compare and evaluate the anchorage effectiveness of using either TADs or extraoral headgear. The maxillary incisors in the TADs group were significantly more retracted and intruded, while the lower incisors were more lingually inclined, than in the headgear group. There were differences in the final orientation of the occlusal plane between the 2 groups, something that we will elaborate on in future blogs of this series.

Upadhyay et al. 2008: In this randomised controlled trial (RCT), 30 patients requiring high anchorage after extraction of the maxillary first premolars were included. They were divided into 2 groups of 15 each. In the first group TADs were used for en-masse retraction; in the second group, conventional anchorage reinforcement was used. The maxillary first molars in the TADs group showed net distal movement of 0.55 mm, whereas in the conventional anchorage group a mesial movement of 1.95 mm was found. The differences were statistically significant. No anchorage loss was seen in either the horizontal or the vertical direction in the TADs group compared to conventional group.

Sharma et al. 2012: In this RCT, after maxillary canine retraction, mesial movement of upper first molars were compared between a transpalatal arch (TPA) group and a TAD group. The mean mesial movement of the first molars was 0.0 mm in the TAD group, whereas in the TPA group there was a mean forward movement of 2.48 mm. Absolute anchorage was therefore achieved in the TAD group in contrast to the TPA group.

Al-Sibaie and Hajeer 2014: In this RCT the authors compared treatment outcomes between the sliding en-masse retraction of upper anterior teeth supported by TADs and the two-step sliding retraction technique using TPAs. Following first premolar extraction, space closure was accomplished using either the en-masse technique with TADs or the two-step technique with TPAs. A bodily retraction of 4.42 mm of the upper anterior teeth was achieved in the TADs group, whereas upper anterior teeth retraction was achieved by palatal tipping in the TPA group.

Sandler et al. 2014: This RCT aimed to compare the effectiveness of TADs, Nance button palatal arches, and headgear for anchorage reinforcement in the treatment of patients requiring maximum anchorage. Compared with headgear, the average mesial movements of the maxillary molars were -0.09 to 0.62 mm with the Nance and -0.58 to -0.96 mm with TADs. The authors concluded that “there was no difference in the effectiveness between the 3 groups in terms of anchorage support. There were more problems with the headgear and Nance buttons than with the TADs”.

Becker et al. 2018: This meta-analysis looked at the efficacy of TADs in comparison with conventional devices (TPAs, headgear, Nance buttons, intrusion arches, and differential moments) in patients requiring en-masse retraction of anterior teeth. The weighted mean difference in anchorage loss between the 2 groups was - 2.79 mm in the horizontal plane favouring TADs over conventional devices.

Ganzer et al. 2018: This RCT compared the anchorage reinforcement of TADs and molar blocks. In the TADs group, the mean anchorage loss was 1.2 mm during levelling and alignment and no significant anchorage loss during space closure. In the molar block group, the mean anchorage loss was 1.4 mm during levelling and alignment and 2.4 mm during space closure. Molar block anchorage, therefore, could not be recommended for anchorage reinforcement.

Alharbi et al. 2019: This meta-analysis compared the effectiveness of TADs in reinforcing anchorage during en-masse retraction of anterior teeth to conventional anchorage appliances. Pooled data from 6 RCTs were analysed. Standardized mean difference of the anchorage loss between the two groups (TADs vs conventional anchorage) was 2.07 mm in favour of TADs. The level of quality of evidence was moderate.

Liu et al. 2020: In this meta-analysis, 12 studies were included. In the TADs group there was significantly less mesial movement of molars compared to conventional anchorage group (standardised mean difference of = -1.48 vs -2.25). There was no significant difference in the vertical movement.

Tian et al. 2020: In this meta-analysis, 3 RCTs and 5 controlled clinical trials (CCTs) were included. Meta-analysis showed a significant increase in anchorage preservation in the TAD group in both the maxilla and the mandible. There was also significant increase in the amount of canine retraction.

Complications associated with TADs placement will be discussed next.

For patients:

Bone screws are highly effective orthodontic appliances for providing temporary anchorage in orthodontic treatment. Their small size allows for placement in various locations in the mouth, such as the palate or the buccal region, to support tooth movement. Bone screws offer advantages such as improved control over tooth movement, reduced treatment time, and minimised need for patient compliance compared to traditional methods. Overall, bone screws have been shown to be a valuable tool in achieving successful orthodontic outcomes.