Malocclusion is a common condition in children and adolescents with a worldwide prevalence of 56%. It is estimated that approximately 30% of Swedish children and adolescents undergo orthodontic treatment at specialist clinics under Sweden’s free comprehensive dental care for children and young patients, with crowded and displaced teeth being one of the main reasons. One of the treatments used to align teeth is placing fixed appliances with brackets on the teeth. The beneficial effects of the treatment include well-aligned teeth and healthy, stable occlusion. However, every orthodontic treatment entails a risk of adverse effects such as external root resorption and pain. In recent decades, a technique that uses passive self-ligating brackets has gained in popularity. This technique is said to generate less frictional resistance, more physiological tissue response and reduced adverse effects compared to conventional techniques. According to a Cochrane report from 2021, the current evidence is sparse regarding fixed appliance treatment in general, and specifically for the treatment effect of passive self-ligating brackets compared to conventional bracket systems in the treatment of crowded teeth in children. 

Radiographic examinations before, during and after the treatment are recommended to monitor the risk of severe external root resorption. The recommendations given in textbooks and scientific articles are contradictive as different check-up intervals and radiographic modalities are recommended. Moreover, the grounds for the recommendations are weak, and due to radiation doses and the ALADA (“as low as diagnostically acceptable”) principle, it may not be justifiable for all patients. 

The CROWDIT (Crowded Displaced Teeth) project was started to decrease knowledge gaps concerning fixed appliance treatment of adolescents with crowded and displaced teeth, from the perspective of patients, clinicians and society. The overall aim of this thesis was to present a systematic, comprehensive evaluation of external apical root resorption and pain levels across various treatment phases during the orthodontic treatment of adolescents with crowded and displaced teeth. These evaluations were based on an RCT (Randomized Clinical Trial) consisting of treatments performed without extractions using either passive self-ligating or conventional bracket systems. 

The first study of the thesis was a systematic review aimed at evaluating the scientific evidence and identifying knowledge gaps concerning external root resorption. During the preparatory work for the systematic review, no appropriate tool was found to assess the risk of bias in studies of adverse effects associated with orthodontic treatment. For this reason, a tool was designed to assess that risk of bias.

The tool and its application in a systematic review identified knowledge gaps and highlighted issues concerning the planning, conducting and reporting of studies. Based on this new knowledge, a methodological study was carried out of reliability and agreement in root length measurements, and two randomized controlled trials were conducted investigating external apical root resorption and pain.

We expect that the outcomes of this thesis and the further studies planned as part of the CROWDIT project will decrease the knowledge gaps and that the results will be integrated into the national guidelines for orthodontic treatment. We anticipate that the outcomes will thereby influence future oral healthcare so that the treatment of adolescents with crowded and displaced teeth using fixed appliances will be supported by scientific evidence.

This thesis was thus based on the following studies:

Paper I: Development of a tool for assessing the risk of bias was developed and applied in a systematic review to answer the following questions:

·          What frequencies and severities of external root resorption have been reported?

·          Is frequency and severity of external root resorption related to the patient’s age, sex, malocclusion or type of appliance?

Paper II: A methodological study that aimed to investigate:

·          The inter-rater and intra-rater reliability and agreement for measurements of the root length of all teeth from incisors to molars using multiplanar reconstruction in CBCT examinations during different phases of orthodontic treatment in adolescents with fixed appliances.

Paper III: Originated from a multi-centre RCT that aimed to investigate: 

·          The frequency and severity of external apical root resorption identified through CBCT examinations obtained before treatment, after levelling of the teeth and insertion of the first 0.019 x 0.025 stainless steel archwire, and after treatment using either passive self-ligating or conventional fixed appliance systems. A further aim was to assess the results in relation to the most affected tooth groups, the time required for levelling, the duration of the 0.019 x 0.025 stainless steel archwire, total treatment time, differences in sex and initial irregularity of teeth.

·          The relevance of intermediate radiography for the early detection of severe or extreme external apical root resorption. 

Paper IV: Originated from a multi-centre RCT that aimed to investigate:

·          Self-reported pain levels across various treatment phases for patients using passive self-ligating or conventional bracket systems.

·          Pain levels in relation to sex, initial archwire dimension, intake of analgesics, degree of displacement of the anterior teeth and impact on everyday activities.

Key findings of Paper I:

·          External root resorption of ≥ 2 mm varied across studies by between 10% and 29% for maxillary incisors. 

·          Data concerning external root resorption as related to patients’ age sex, malocclusion, and type of treatment was contradictory

·          The quality of the evidence, evaluated according to the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) approach, was low due to study limitations, imprecision and inconsistency of study results.

Key findings of Paper II

·          CBCT using MPR is a reproducible method for measuring root length during different phases of orthodontic treatment. 

·          Root shortening of ≤ 2 mm measured by CBCT using MPR, for clinical or research purposes, should be interpreted with caution as it may represent a measurement error.

Key findings of Paper III

·          The mean external apical root resorption in mm for upper incisors was 0.20 in the passive self-ligating group and 0.51 in the conventional group, while the corresponding proportion of roots with clinically relevant EARR (≥ 2 mm) was 5.0% and 7.2% respectively.

·          None of the variables treatment time, sex or initial irregularity of teeth could significantly predict the mean external apical root resorption of the upper incisors.

·          It would appear that the relevance of intermediate radiographic examination is negligible for the early detection of severe external apical root resorption.

Key findings of Paper IV

·          Pain levels of 9 to 10 on a 10-point scale were reported from 21.8% of patients in the passive self-ligating group and 30.3% in the conventional group on the most painful day (NS). 

·          Statistically significant, lower mean pain scores and a lower intake of analgesics were reported in the passive self-ligating group than in the conventional group on the first days after bonding in both arches. 

·          After the insertion of the full-size stainless steel archwire, 40% of patients reported taking analgesics.

·          It was found that girls reported lower pain scores compared to boys.

Conclusions and clinical implications:There is a low quality of scientific evidence regarding external root resorption associated with orthodontic treatment with fixed appliances. 

Measurement of root length in CBCT images ia a reproducible method for measuring root length but measured values below 2 mm should be interpreted with caution as they may contain measurement errors.

The frequency and severity of external apical root resorption was generally low and similar for patients treated with passive self-ligating and conventional bracket systems.

Intermediate radiography may be avoided in an adolescent population with crowded teeth treated without extraction, which aligns with the ALADA principle and underlines the importance of individual indications for radiographic examinations and the minimization of radiation doses.

Patients treated with passive self-ligating brackets report lower pain levels and intake of analgesics compared to those treated with conventional bracket systems after treatment initiation. In general girls reported lower pain scores compared to boys.

It is important to inform the patients and their parents before treatment that pain levels are generally substantially high after bonding as well as after insertion of a full-size stainless steel archwire.