GWAS of Post-Orthodontic Aggressive External Apical Root Resorption Identified Multiple Putative Loci at X-Y Chromosomes

Genetic polymorphisms linked to extreme postorthodontic external apical root resorption in Koreans

BACKGROUND

External apical root resorption (EARR) is a common undesirable outcome of orthodontic treatment, this study aimed to identify genetic polymorphisms associated with the susceptibility to extreme orthodontic-induced EARR in a Korean population using extreme phenotype analysis sampling.

METHODS

Genomic DNA was isolated from the saliva of 77 patients who underwent orthodontic treatment involving two maxillary premolar extractions. The patients were divided into two groups based on EARR values measured on periapical radiographs: The significant resorption group (SG, EARR ≥ 4 mm) and the normal group (NG, EARR < 2 mm). In the NG group, patients with EARR < 1 mm were named the non-resorption group (NonG). Targeted next-generation sequencing was performed using the screened single nucleotide polymorphisms (SNPs), and firth logistic regression analysis was used to determine genetic associations with EARR. Haplotype-based association analysis was performed for specific SNPs.

RESULTS

SNPs related to genes TNFSF11, TNFRSF11B, WNT3A, SFRP2, LRP6, P2RX7, and LRP1 were found to be significantly associated with severe EARR (p < 0.05, pre-Bonferroni correction p-values). Additionally, the haplotype CCA of rs17525809, rs208294, and rs1718119 P2RX7 had a higher frequency in the SG group.

CONCLUSION

Extreme phenotype analysis has identified eleven SNPs related to genes TNFSF11, TNFRSF11B, WNT3A, SFRP2, LRP6, P2RX7, and LRP1 that are associated with severe root resorption in the Korean population. These findings will contribute to the development of predictive diagnostic tools for identifying severe root resorption that may occur during orthodontic treatment.

Under pressure-mechanisms and risk factors for orthodontically induced inflammatory root resorption: a systematic review

BACKGROUND

The application of orthodontic forces causes root resorption of variable severity with potentially severe clinical ramifications.

OBJECTIVE

To systematically review reports on the pathophysiological mechanisms of orthodontically induced inflammatory root resorption (OIIRR) and the associated risk factors based on in vitro, experimental, and in vivo studies.

SEARCH METHODS

We undertook an electronic search of four databases and a separate hand-search.

SELECTION CRITERIA

Studies reporting on the effect of orthodontic forces with/without the addition of potential risk factors on OIIRR, including (1) gene expression in in-vitro studies, the incidence root resorption in (2) animal studies, and (3) human studies.

DATA COLLECTION AND ANALYSIS

Potential hits underwent a two-step selection, data extraction, quality assessment, and systematic appraisal performed by duplicate examiners.

RESULTS

One hundred and eighteen articles met the eligibility criteria. Studies varied considerably in methodology, reporting of results, and variable risk of bias judgements.In summary, the variable evidence identified supports the notion that the application of orthodontic forces leads to (1) characteristic alterations of molecular expression profiles in vitro, (2) an increased rate of OIIRR in animal models, as well as (3) in human studies. Importantly, the additional presence of risk factors such as malocclusion, previous trauma, and medications like corticosteroids increased the severity of OIIRR, whilst other factors decreased its severity, including oral contraceptives, baicalin, and high caffeine.

CONCLUSIONS

Based on the systematically reviewed evidence, OIIRR seems to be an inevitable consequence of the application of orthodontic forces-with different risk factors modifying its severity. Our review has identified several molecular mechanisms that can help explain this link between orthodontic forces and OIIRR. Nevertheless, it must be noted that the available eligible literature was in part significantly confounded by bias and was characterized by substantial methodological heterogeneity, suggesting that the results of this systematic review should be interpreted with caution.

REGISTRATION

PROSPERO (CRD42021243431).

Orthodontic root resorption

External apical root resorption (EARR) is one of the most frequently reported iatrogenic side effects of orthodontic movement. Nevertheless, no robust and unequivocal scientific evidence is yet available in the literature regarding the clinical and biological factors that trigger EARR. The purpose of the present position paper is to provide clinicians, residents, and investigators a summary of our current understanding about root resorption caused by orthodontic tooth movement, based on up-to-date available scientific evidence. Morphological, structural, biomechanical, and biological differences account for predisposing the apical third to EARR compared to other root surfaces during orthodontic treatment. In addition, a relevant number of patient and treatment-related factors increase risk of EARR. The main patient-related factors are reviewed and discussed: genetic factors, tooth anatomy, demographic factors, malocclusion factors, previous endodontic treatment, medical history, short root anomaly. Similarly, the influence of treatment-related factors are analyzed with regard to the effect of: biomechanical factors, type of orthodontic appliance, adjunctive therapies to accelerate tooth movement, early treatment, maxillary expansion, teeth extractions, the duration of treatment and the amount of apical displacement. Clinical management of EARR from pre-treatment records to the monitoring strategy as well as recommendations for the post orthodontic-treatment period are presented as a guide for the clinician. Despite years of studies, we still do not fully understand EARR, but the future is promising. True three-dimensional imaging with higher resolution and low radiation, and predictive tools towards an earlier detection without radiographs, will mark future developments in the field of EARR in orthodontics.

Genetic variation involved in the risk to external apical root resorption in orthodontic patients: a systematic review

OBJECTIVE

To perform a systematic review/meta-analysis to elucidate the scientific basis for the association between genetic variations and risk of external apical root resorption (EARR) in orthodontic patients.

MATERIALS AND METHODS

Four databases (PubMed, Web of Science, Scopus, LILACS) were electronically searched until November 22, 2020, followed by manual and gray literature search. Case-control or cross-sectional studies that evaluated genes involved in the susceptibility of orthodontic patients to EARR were eligible. Two reviewers applied the inclusion and exclusion criteria, extracted qualitative data, as well as assessed methodological quality using instrument proposed for genetic studies. For synthesis results, narrative and quantitative data (meta-analysis) were performed. The certainty of the evidence was tested using the GRADE Working Group approach.

RESULTS

Of 201 articles in total, 16 studies were included in the review. Of these, 11 presented moderate and 5 of high methodological quality. In the narrative analysis, from 16 studies, 15 studies (10 genes) showed a significant association with EARR and 9 studies were included in the meta-analysis. Only the polymorphism rs208294 in P2RX7 (dominant model) was associated with EARR (OR = 0.52, 95%CI = 0.29-0.95, p = 0.03) and presented a very low certainty of the evidence.

CONCLUSION

Narrative analyses of individual studies demonstrated an association of many genes. The number of studies for each genetic variation was very low, and methodological heterogeneity between the studies was observed. Quantitative analyses (meta-analysis) could only show an involvement for P2RX7 (rs208294) in the risk of orthodontic patients to EARR at a very low certainty of evidence. (CRD42018085411).

CLINICAL RELEVANCE

The knowledge regarding the molecular aspects involved in the etiology of EARR will allow orthodontists to use a personalized treatment and early diagnosis of risk patients. This systematic review demonstrates that more studies are necessary to unravel the role of genetic variation for patients' risk to EARR during orthodontic tooth movement.