# Duration of fixed appliance treatment using 0.018-inch slot versus 0.022-inch slot brackets: a systematic review and meta-analysis

## TL;DR

This study compares the treatment duration and outcomes of two types of orthodontic brackets and finds no significant differences.

## Contribution

The study provides low-quality evidence that bracket slot size does not affect treatment duration or outcomes.

## Key findings

- No significant difference in treatment duration between 0.018-inch and 0.022-inch slot brackets.
- No significant differences in treatment quality or patient outcomes between the two bracket types.

## Abstract

The duration of fixed orthodontic appliance treatment is a major concern for both patients and clinicians. A lengthy treatment increases the likelihood of iatrogenic effects and burdens patient compliance.

The primary aim of this review is to compare the duration of orthodontic treatment between 0.018-inch and 0.022-inch slot brackets. Furthermore, the quality of treatment, iatrogenic effects, and patient perception will be explored as secondary outcomes.

An unrestricted comprehensive search was undertaken on six electronic databases updated up to May 2025. Moreover, ongoing and unpublished studies were searched on relevant sources. The reference lists of retrieved studies were screened for potential studies.

Only randomized clinical trials (RCTs) and prospective non-randomized studies (NRS) with parallel-arm design were selected for inclusion.

Study selection, bias assessment, and data extraction were performed independently by two reviewers, and inconsistencies were resolved by a third reviewer. Quantitative analyses were undertaken for comparable studies presented as a random-effects model along with its 95% confidence intervals (CI). Additional sensitivity and subgroup analyses were performed. The generated summary effect was evaluated using the GRADE approach.

Twelve articles involving nine unique studies (six RCTs and three NRS: 832 patients) met the inclusion criteria. The total duration of treatment did not differ between the bracket slot systems (standardized mean difference: −0.23; 95% CI: −0.68 to 0.23; I2: 24%; 4 studies; low level of evidence). Qualitative analysis revealed no significant differences between the 0.018-inch and 0.022-inch slot brackets regarding the quality of treatment outcomes, iatrogenic treatment effects, or patient-related outcomes.

Differences in reporting and clinical heterogeneity precluded meta-analysis for the secondary review outcomes.

Within the limitations of this systematic review, there is some low-quality evidence suggesting that bracket slot size does not significantly impact orthodontic treatment in terms of duration, treatment outcomes, or patient-centred variables.

PROSPERO CRD42019121569.