Edwin H Yen


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Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Fistula in cleft lip and palate patients (2018)

Introduction: The cleft lip and palate congenital malformation is a common condition, which poses a large burden of care on the young patients and their caregivers. The World Health Organization reported the prevalence of cleft lip with or without cleft palate to be 10 in 10,000 births in the United States and worldwide and 12 in 10,000 births in Canada (IPDTOC, 2011). Post-operative palatal fistula is frequently encountered after the surgical repair of a cleft lip and palate deformity. A wide range of fistula occurrence rates, have been reported in the literature with significant variability. After conducting a systematic scoping review of the cleft palate literature we found that high quality studies were needed in this field. Additionally there were very few Canadian studies available on this subject. We recognized the need to investigate the incidence of palatal fistula at British Columbia’s Children’s Hospital (BCCH) to be able to compare our rates with other centers worldwide. As a result of our research, we realized a gap in the literature, which was the lack of a standardized assessment protocol for the follow up of cleft lip and palate patients.Methods: A retrospective chart review was performed at British Columbia’s Children’s Hospital to examine the incidence of palatal fistula in children with non-syndromic clefts and to identify determinants associated with higher fistula rates.In preparation for the protocol development we conducted electronic database searches and contacted 13 major cleft centers worldwide.Conclusion: The systematic review concluded that the research mainly focused on surgeries and fistula-related risk determinants. The level of evidence was low and the quality was poor. No consistent pattern was detected between fistula occurrence and any of the studied risk determinants. The medical chart audit determined that almost a quarter of patients at BCCH presented with a palatal fistula. The significant risk determinants were severity of the cleft, less experienced surgeons, and the time period in which surgeries were performed. The structured protocol was developed and it will help facilitate data collection of cleft patients prospectively and prevent deficiencies in current medical reporting.

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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Effect of non-thermal plasma on the bond strength of orthodontic brackets to enamel : an invitro study (2015)

Objectives: Non-thermal plasma (NTP) has been used to modify enamel and dentin surfaces and improve the interfacial bonding of dental composite restorations. NTP is shown to cause super hydrophilic surface by decreasing the contact angle measurements and improve the quality of the adhesive - enamel and adhesive - dentin interface. We sought to determine the effects of NTP treatment on the bond strength of brackets to enamel. We investigated the application of NTP alone and in combination with phosphoric acid (PA) etching and assessed the outcomes after 24 hours and 1 month.Methods: 84 extracted pre-molars washed and disinfected were divided into 2 broad groups: No-treatment and Treatment group. No - treatment group consisted of 12 premolars on which orthodontic bracket bonding was performed without any surface - treatment except for polishing with pumice. Treatment group consisted of 72 premolars which were divided randomly into 3 main groups of 24 premolars each. These groups were Group 1: PA Etch (30s), Group 2: PA Etch (30s) + NTP (30s) and Group 3 NTP (30s). The bonded teeth were stored in water at 37° C and tested in shear mode after 24 hours and 1 month (n= 12). The fracture mode and adhesive remnant index were determined on de-bonded surfaces. SEM pictures were taken from enamel surfaces after each treatment. Results: During the first 24 hours of testing, SBS was maximum with Etch+ NTP and Etch treated group followed by NTP group ( P
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Changes in the occlusal curves secondary to serial sextractions compared to late premolar extractions and controls (2014)

Objectives: To determine the relationships between tooth tipping and occlusal curvature patterns in serial extraction (SE) cases versus late premolar extraction (LPE) cases and controls. Methods: Mandibular dental casts and cephalometric radiographs were collected from 90 subjects (30 Class I controls, 30 SE cases, 30 LPE cases) at 3 time points: baseline (T0) for controls and SE, after natural drift/pre orthodontics (T1) for controls, SE, and LPE, and after comprehensive orthodontic treatment (T2) for the SE and LPE groups. The casts were scanned and rendered as virtual models. 12 cusp tips (4 incisors and 2 first molars) were digitized and the occlusal curves were measured using Rhinoceros by fitting a sphere to the landmarks (least-squares method). Radiographs were digitized and the long axes of the central incisor, canine, and first molar were landmarked and related to palatal plane to determine the direction and amount of tipping. Results: The SE group differed significantly from the other two groups at T1, with smaller radii in 2/3 outcomes. From T0-T1, the SE group showed a tendency for the incisor and canine to tip distally, while the molar tipped mesially. From T1-T2, the SE group had smaller radii versus LPE and demonstrated mesial tipping of the incisor and canine angulations, with the molar tipping distally. Conclusions: SE cases tend to have steeper occlusal curves (smaller radii), post tooth drift and after orthodontic treatment as compared to the other groups. In general, orthodontic treatment, post SE, involved incisor and canine proclination, as well as molar uprighting. SE is unlikely to save more than 4-6 months of active treatment due to the time needed to correct the increased occlusal curvature that results from this procedure.

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Orthodontic treatment need of adolescents in Haida Gwaii, Canada (2013)

Introduction: The aims of the cross-sectional study were to determine the prevalence of malocclusion and orthodontic treatment need according to the Index of Complexity, Outcome, and Need (ICON) among schoolchildren of the Aboriginal Island Community of Haida Gwaii in Northwestern British Columbia, Canada.Methods: Out of 535 schoolchildren, 215 (90 boys and 125 girls) agreed to participate in the clinical examination. An examiner, trained in occlusal indices, assessed orthodontic treatment need in children employing the ICON score and the ICON complexity grade. In addition, a questionnaire was modified and used to measure the schoolchildren’s expectations of and self- perceived need for orthodontic treatment. Out of the 215 schoolchildren that were clinically examined, 192 were old enough to comprehend the questions in the questionnaire and were capable of completing the questionnaire without any assistance.Results: The mean age (N=215) was 12.9±2.8 years. Of the examined schoolchildren, 67% have Aboriginal ancestry (at least one parent is Aboriginal). The mean ICON score was 43.5±26.2. There were no statistically significant differences in ICON scores regarding gender (t-test, P=0.207), ethnicity (t-test, paternal ethnicity P=0.886 and maternal ethnicity, P=0.389), or school (ANOVA with Post Hoc Bonferroni Adjustment P=0.317). Overall, 43.7% of the schoolchildren needed orthodontic treatment (ICON > 43). Based on the ICON complexity, 31% of the schoolchildren had moderate to very difficult malocclusions to treat. Adolescents (N=192) with higher ICON complexity scores (more complicated malocclusions) felt a greater need for orthodontic treatment, for extractions, that treatment would give them confidence, and that they were willing to be treated either on island or off island (One way ANOVA with Post Hoc Bonferroni Adjustment, P
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