Changes to Incisor Anteroposterior Angulation during Correction of Class II Malocclusion: Impact on Perceived Root Resorption as Analyzed from Conventional Radiography

  • Author / Creator
    Tieu, Long Dao
  • When camouflaging Class II malocclusions, there are often changes to both the maxillary and mandibular incisor angulations that can lead to artificial elongation and/or foreshortening of the dental image. OIEARR is a common result of orthodontic treatment and given the inherent limitations of 2D radiography, it would be beneficial to better understand how changes of tooth angulation can alter the perceived root lengths. With this knowledge, clinicians may be better equipped at recognizing cases of true root resorption as opposed to cases where the appearance of root resorption on the radiograph is due to an imaging foreshortening. This information can help clinicians identify teeth that need further imaging (periapical) to confirm/assess severity of root resorption and will also allow clinicians to make modifications to their treatment in an attempt to minimize the progression of root resorption. Research Question 1. Critically evaluate incisor OIEARR in patients undergoing non-surgical treatment of Class II Division I malocclusion by systematic review of the published data. a. Current evidence suggests comprehensive orthodontic treatment to correct Class II malocclusion results in increased prevalence of OIEARR, however given the fact that there was no RCT and only limited prospective data included in this SR, the findings should be considered with caution. i. Prevalence ranged between 65.6%-98.1% ii. OIEARR -Per patient – 65.6%-98.1% iii. OIEARR - Per tooth – 72.9%-94.2% iv. Majority of teeth experienced mild-moderate resorption with severe resorption being reported to be between 6.25-17.2% v. No Sex difference was reported vi. No evidence that either the Mx CI or LI more susceptible to RR vii. Weak to moderate positive correlation between Tx duration and RR viii. Weak to moderate positive correlation between AP apical displacement and RR 2. What is the prevalence of OIEARR over the course of treatment in a selected sample of patients treated with either the X-bow for Forsus? a. Prevalence per tooth 65.3% b. Prevalence per patient 98.6% 3. What is the severity of OIEARR over the course of treatment in a selected sample of patients treated with either X-bow for Forsus? a. Per tooth – None (34.7%); Mild (45.2%); Moderate (9.3%); Severe (11%) b. Per patient – None (1.4%), Mild (32.9%); Moderate (30%); Severe (35.7%) 4. Are the incisor length measurements determined from panoramic radiographs accurate and reliable when maxillary and mandibular incisor angulations are modified in a custom made typodont? a. Under experimental conditions, Md incisors appear to respond as expected when compared to theoretical model (assumption – teeth within focal trough) i. 10 degrees – 1.4% shorter ii. 20 degrees – 6.3% shorter iii. 30 degrees – 13.4% shorter iv. 40 degrees – 23.7% shorter v. 50 degrees – 34.6% shorter b. Mx Incisors are more difficult to say. At some angulations yes (80, 90), at others (50,60, 70, 100, 110) the answer isn’t clear c. Severe Resorption in clinical study was found in 11% of treated incisors and of the 25 patients with at least one tooth with severe RR, 20 of the cases were found on the Md arch 5. When several cephalometric variables are considered simulataneously over time, does sex and or treatment type affect the final outcome in a selected sample of patients treated with either X-bow or Forsus? a. No evidence of a Sex (p=0.840) difference in the overall pattern of cephalometric variables. b. No Evidence of a treatment type (p=0.395) difference in the overall pattern of cephalometric variables. c. Convincing evidence of a Time (p=0.006) difference in the overall pattern of cephalometric variables. d. Convincing evidence (p=0.019) that over the course of treatment OB was reduced by 1.79mm [1.66,1.92]. e. Convincing evidence (p=0.015) that over the course of treatment Y-Axis increased 1.3° [1.24,1.33]. 6. Additional Findings a. Shorter treatment length (p=0.037) with X-bow (24.18 months) compared to Forsus (30.17 months) b. Both compliance free Class II correction protocols (X-bow and Forsus) for the treatment of mild to moderate class II malocclusion appear to generate similar degrees of lower incisor proclination with similar variability. It appears than that foreshortening of the image on a panoramic radiograph due to proclination of lower incisors accounts for a small part, and the larger reason maybe due to the difficulties of accurately measuring the teeth due to distortion caused by the narrow focal trough size or superimposition.

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    Master of Science
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