Interleukin-1 Beta (IL-1β) Gene Polymorphisms in Pre-Treatment Orthodontic Patients Exhibiting Short Root Anomaly (SRA)

Root resorption is a frequent unwanted occurrence during orthodontic treatment. Biological factors include the quantity of specific inflammatory mediators, growth factors, and hormones as well as an individual’s specific alleles for the genes encoding these mediators. Studies have shown an association between external apical root resorption (EARR) and the single nucleotide polymorphism (SNP) at +3954 of the IL-1β gene. Studies have also shown associations between chronic periodontitis and IL-1β gene polymorphisms in the region of +3954, -511 and -31. All previous studies to date, have evaluated genetic factors and root resorption in orthodontic patients in-treatment or post-orthodontic treatment. This study is novel in utilizing genomic DNA samples from buccal swabs of pre-treatment orthodontic patients to evaluate polymorphisms in the IL-1β gene at +3954, -511 and -31. Pre-treatment records were used specifically to determine if short roots (Short Root Anomaly) and selected IL-1β gene polymorphisms could be used to accurately assess a patient’s risk of root resorption prior to orthodontic treatment. Subjects were categorized as exhibiting normal root length or with short roots based upon the root morphology evident on 3D CBCT pre-treatment scans. The sample size consisted of 52 subjects; 26 subjects exhibiting short root anomaly and 26 subjects exhibiting root length within normal limits. Samples for DNA analysis were collected by scraping the inside of the cheek with 10 strokes of a sterile nylon bristle brush. Genomic DNA was obtained from these samples using the Puregene method (Gentra Systems, Minneapolis, Minn). PCR amplification of regions encompassing the +3954, -31 and -511 sites was followed by restriction endonuclease digestion using enzymes recognizing the polymorphic sites. Agarose gel electrophoresis was used to separate and identify bands specific to each allele and determine patient homozygosity and heterozygostiy for each polymorphic site. In our study, Hispanic and female patients showed a higher prevalence of SRA. There was no association identified between the IL-1β polymorphisms at -511 or -31 with SRA or normal roots. All of the patients in the SRA group exhibited the CC genotype for the IL-1β polymorphism at +3954. The presence of the CC genotype was statistically significant in the patients of Hispanic origin. There was no statistically significant difference between the presence of any specific genotype among Caucasian patients. The IL-1β +3954 CC genotype has been reported to increase the risk of root resorption by decreasing the IL-1β expression and consequently, decreasing alveolar bone resorption. In contrast, the CT genotype has been reported to increase IL-1β expression, possibly leading to decreased risk of root resorption by increasing bone remodeling. These findings from this study suggest that that there may be a genetic basis for Hispanic patients to be at a higher risk of root resorption compared to Caucasian patients. This study supports the idea that root resorption is multifactorial and multiple diagnostic measures (CBCT, DNA analysis) should be incorporated in the orthodontic records process to evaluate risk factors prior to starting any orthodontic treatment. Further studies can be designed to identify the patients who exhibit the IL- 1β +3954 CC genotype and follow these patients with regular radiographs and CBCT scans to evaluate root resorption during the course of orthodontic treatment