Changes in Traditional Bolton’s Ratio with Various Extraction Combinations - An in Vitro Study
Premalatha Kanniyappan1, B. Saravanan2, E. Thulasiram3

1Premalatha Kanniyappan M.D.S., Reader, Department of Orthodontics, Tagore Dental College and Hospital, Chennai 600 015 2B. Saravanan, Associate Professor, Department of Orthodontics, Sree Balaji Dental College and Hospital, Bharath University, Pallikaranai, Chennai-600100 3E. Thulasiram, Post Graduate, Department of Orthodontics, Sree Balaji Dental College and Hospital, Bharath University, Pallikaranai, Chennai-600100  

Abstract: To obtain a good occlusion with the correct overjet and overbite. there should be an  harmony between the combined mesiodistal widths of maxillary and mandibular teeth. Extraction of premolars is routinely carried out in orthodontic treatment which changes the ratio of  inter arch tooth size relationship. Till date Bolton’s analysis remains the golden standard for predicting interarch tooth-size discrepancy.

  1. To investigate whether the extraction of four premolars as a requirement of orthodontic therapy is a factor in creating tooth size discrepancy
  2. To determine whether any tooth extraction combination creates more severe discrepancies.
  3. To investigate the reasons behind such discrepancies if determined due to any extraction combinations.
48 pretreatment models (30  Class I and 18 Class II) with  an ideal Bolton’s tooth size ratio of 91.3% ± 1 SD were taken and Bolton’s analysis -the overall ratio, anterior ratio and Bolton’s discrepancy was calculated.  Hypothetical tooth extractions were performed with the following combinations.
  1. All first premolars
  2. All second premolars
  3. Maxillary first and Mandibular second premolars
  4. Maxillary second and Mandibular  first premolars                                                                  and subjected  to Bolton’s analysis
Mesiodistal dimensions of all premolars were measured and the data is evaluated to find any variation between right and left sides or between the arches The Maxillary first and Mandibular second premolars extraction group produced the highest discrepancy followed by all first premolars extraction group. The all-second premolars extraction group produced the least discrepancy.  

Keywords: Bolton’s analysis; Mesio distal width; Anterior tooth ratio; Overall tooth ratio; Tooth size arch length discrepancy; Extraction combinations    

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