Benjamin Pliska

Prospective Graduate Students / Postdocs

This faculty member is currently not actively recruiting graduate students or Postdoctoral Fellows, but might consider co-supervision together with another faculty member.

Associate Professor

Research Classification

Research Interests

Sleep and Sleep Disorders
Oro-Dental Disorders
Facial growth and development
sleep medicine

Relevant Thesis-Based Degree Programs

Affiliations to Research Centres, Institutes & Clusters

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I am available and interested in collaborations (e.g. clusters, grants).
I am interested in and conduct interdisciplinary research.

Graduate Student Supervision

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.

A comparison of skeletal, dental changes in Class II patients treated with Invisalign? with Mandibular Advancement and Herbst appliance (2022)

Objectives: Align Technology Inc introduced the Invisalign with Mandibular Advancement (IMA) features in 2017, which has been reported to function similarly to a removable functional appliance for growth modification in Class II patients. The IMA appliance utilizes precision wings on the aligners to posture the mandible forward for Class II correction. There is a lack of literature comparing the skeletal and dental changes, as well as their relative contribution to the overall treatment effect between fixed functional appliances and this novel removable appliance. The objective of this study is to characterize the skeletal and dental changes of growing patients with Class II malocclusions treated with the novel Invisalign Mandibular Advancement (IMA) appliance and also the changes caused by a more traditional method of Class II treatment, the Herbst appliance.Methods: Consecutively treated patients with the Herbst appliance and with the IMA appliance from two orthodontic practices were compared using lateral cephalometrics taken at three different time periods: T1: Before treatment, T2: Immediately after the functional advancement stage with the MA or Herbst appliance, and T3: After completion of comprehensive treatment. The skeletal and dental changes across the three time periods (T1, T2, T3) were analyzed for each treatment group separately using paired t-test. A two-sided p-value of less than .05 was considered statistically significant.Results: After the advancement phase, significant forward movement of the mandible, lower molars, lower incisors, and restraining of the maxillary molars were achieved with either the removable IMA or the fixed Herbst appliance; however, these changes were greater for the Herbst appliance. By the end of comprehensive treatment, these changes persisted except for a slight forward movement of the upper molars. Invisalign MA had less proclination of the lower incisors when compared to the fixed Herbst appliance.Conclusion: The Invisalign MA appliance was effective at treating Class II malocclusions by a combination of both dental and skeletal treatment effects, consisting of repositioning the mandible and mandibular teeth forward and by restricting the forward movement of the maxilla and maxillary molars.

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3D facial morphology and risk of sleep disordered breathing in children (2020)

Introduction: Craniofacial morphology has been recognized as an important factor in obstructive sleep apnea (OSA) pathogenesis and pathophysiology. Stereophotogrammetry eliminates many of the limitations of traditional craniofacial anthropometric methods. Objectives: To utilize stereophotogrammetry to determine whether associations exist between 3D facial morphometric parameters of children aged 2-17 years, and their risk of sleep-disordered breathing (SDB) as evidenced by their Pediatric Sleep Questionnaire (PSQ) score. Additionally, to compare facial morphology of patients at high risk of SDB and those at lower risk. Methods: 180 patients from the Otolaryngology Clinic at BC Children’s Hospital were recruited for this cross-sectional study. 3D facial images were acquired using the 3dMD Face system, and linear and angular measurements were calculated. Patients’ SDB risk was evaluated using the PSQ. Linear regression models were used to determine associations between PSQ scores and patient demographic and facial morphometric variables. 3D morphometric analysis was performed to assess for differences in facial morphology in subjects at high risk for SDB (PSQ score ≥ 0.33) and those at lower risk (PSQ score
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A study of short-term skeletal, dental, and soft tissue effects of Class II malocclusions treated with Invisalign(R) with Mandibular Advancement Feature or Twin Block appliance compared with historical controls (2020)

Introduction: The purpose of this retrospective cephalometric study was to compare short-term skeletal, dental, and soft tissue effects in Class II malocclusions treated with Invisalign® with Mandibular Advancement Feature (IMAF) as compared to Twin Block (TB) appliance, and age and gender matched historical controls.Methods: 64 Class II malocclusion patients received phase I treatment with IMAF or TB, 32 in each group. Comprehensive phase II treatment was then completed for 19 of the IMAF group with Invisalign® clear aligner therapy and 19 patients of the TB group with full fixed edgewise appliances (FEA). 32 longitudinal historical controls were age and gender matched to the IMAF sample. Lateral cephalograms were obtained and intraoral photographs reviewed before treatment (T1), immediately following end of the active advancement of phase I (T2), and at completion of comprehensive phase II orthodontic treatment (T3). Radiographs were randomly traced by a single investigator blinded to group allocation. ANOVA and Tukey tests were used for inter-group comparisons. Intraclass correlations, t-tests, Dahlberg’s error, and scatter plots were utilized for reliability testing. Results: After phase I treatment, both TB and IMAF decreased the ANB angle, facial convexity, and overjet significantly more than the controls. IMAF decreased the overjet through significant retraction of the upper incisor and protrusion of the lower incisor. IMAF also impeded the vertical eruption of the lower incisor. TB decreased the overjet via retraction and retroclination of the upper incisor and protrusion of the lower incisor. Following phase II comprehensive treatment both treatment groups decreased the Wits Appraisal and overjet significantly more than the control sample. The lower incisor was significantly proclined and protruded in the TB and FEA group, and the lower incisor significantly protruded in the IMAF and Invisalign® group. Only the TB and FEA group significantly decreased the facial convexity more than the control group.Conclusions: IMAF with Invisalign® treatment and TB followed by FEA are effective in correcting a Class II malocclusion. Treatment with IMAF may result in less proclination of the lower incisors compared to the TB appliance.

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Dental and craniofacial findings in prematurely born children with non-invasive ventilation: a pilot study (2020)

Objective: This prospective pilot study aims to evaluate the craniofacial complex of prematurely-born children. Subjects are in the 3 and 4.5 year old cohorts, and participate in the Neonatal Follow-Up Program of B.C. Women’s Hospital, Canada. The specific aims of this project are to:1. Characterize the complete primary dentition, 2. Relate the presence of enamel defects with premature birth and its associated therapies,3. Characterize the three-dimensional facial morphology,4. Correlate neonatal parameters to facial morphology, 5. Evaluate the feasibility for a full-scale longitudinal project,6. Determine the role of dentistry in the care or prematurely born children. Methods: Subjects had medical histories collected, underwent a dental screening, and had their facial features recorded with a stereophotogrammetric camera. Dental and medical data were analyzed, and software was used to landmark features on the face, and perform traditional morphometric analyses. Linear facial distances were compared to normative data of age-matched children born full-term.Results: 27 children had facial images collected, including 23 patients who also underwent oral screenings. With regard to oral screenings, all subjects had a complete primary dentition, 43.5% had enamel defects on at least one tooth surface, and the mean dmfs score was 2.35. No significant associations were found between enamel defects, birth parameters, and medical therapies. For facial images, the mean gestational age was 26.3 months, and mean duration for non-invasive ventilation was 84.5 days. Significant differences in facial distances were present in the midface and eye regions in comparison to normative data. No significant correlations were noted between these facial distances and birth parameters. Conclusion: This is the first study to examine the complete primary dentition of prematurely-born children. The presence of enamel defects is in the expected range from literature and larger studies are recommended to examine the location and pattern of these defects. Compared to age-matched control, significant facial differences were present. Further investigation exploring different contributing factors may be worthwhile to determine true correlations and causations, and the role of dentistry for prematurely born children. At B.C. Women’s Hospital, a longitudinal study incorporating dentistry and facial morphometrics is feasible in the NFUP.

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Three-dimensional facial morphology and the use of non-invasive ventilation in infants (2020)

Objective: The goal of this prospective cohort study is to characterize the three-dimensional facial morphology of preterm infants at 4, 8 and 18 months corrected age who are enrolled in the Neonatal Follow-up Program at B.C. Women’s Hospital in Vancouver, BC. The study also aims to determine the association of non-invasive ventilation (NIV) on facial morphology at 4, 8 and 18 months corrected age.Methods: Potential participants were screened for eligibility criteria during their 4, 8 and 18-month follow-up appointments. Infants eligible were imaged with a 3dMD surface-imaging camera and facial morphometrics were related to anthropometric birth data and NIV therapy received in the neonatal period. Results: The study successfully obtained 82 facial images on 74 patients for analysis. Of the 82 images, 16 images were taken of the 4-month cohort, 31 of the 8-month cohort, and 35 of the 18-month cohort. The average gestational age was 185 days, birth weight of 853 grams, birth length of 33 cm and head circumference of 24 cm. The average NIV therapy duration was 49 days and the average NICU stay of 104 days. Using traditional morphometric analysis and geometric morphometric analyses, the study found no statistically significant correlation between NIV therapy duration and anthropometric distances or face shape. Conclusion: The study found in neonates born preterm treated with NIV in hospital, NIV duration was not statistically correlated to any anthropometric distances. The results of this study may indicate that NIV therapy duration does not influence the facial shape of preterm children up to 18-months corrected age.

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Long-term periodontal changes during oral appliance treatment for sleep apnea (2019)

Background: 2 to 4% of estimated population within the age range of 30 to 60 years is diagnosed with obstructive sleep apnea (OSA). Contemporary management of OSA commonly involves continuous positive airway pressure (CPAP) or oral appliance (OAm) therapy. One of the side effects of long-term OAm wear is mesialization of mandibular dentition resulting in the proclination of mandibular incisors. Similar movement of incisors following orthodontic treatment has been associated with gingival recession.Purpose: The purpose of this retrospective, in-vivo, clinical and cephalometric observational study is to evaluate the periodontal changes associated with OAm treatment of 4.5 or more years, in individuals with OSA.Research Design: Patients consecutively treated between 2004 to 2014 at UBC Dental Sleep Clinic and an affiliated private practice were screened. Eligible subjects were followed up where periodontal exam was performed. A lateral cephalogram and impressions were also obtained. Clinical crown height was measured on study models. Periodontal exam included PSR (periodontal screening and recording), plaque index, gingival bleeding index, probing pocket depths and facial gingival margin thickness, in addition to clinical attachment level (CAL), recession and width of attached gingiva. Baseline (T1) and follow up (T2) data was compared.Results: A total of 21 patients (15 males, mean age 57.4±12.0 y.o) were enrolled, with a mean treatment length of 7.6±3.3 years (range = 4.5 to 14.3 years).At follow up all patients presented with good oral hygiene with mean plaque index of 0.4 and bleeding index of 4.1%. PSR data confirmed absence of active periodontal disease. For mandibular anterior teeth, mean probing depth was 1.4±0.5 mm, recession was -0.6±1.1 mm and CAL was 0.8±1.0 mm.Compared to baseline there was significant proclination of mandibular incisors (mean increase in IMPA of 5.1º) with the continued use of OAm. Clinical crown height did not change (mean increase of 0.01 mm) over the evaluated time period.Conclusions: The inclination of mandibular incisors increases significantly with the use of mandibular advancing oral appliance in OSA patients. The positional changes in these teeth was not associated with any measured evidence of increase in periodontal disease or increased clinical crown height.

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Mini-implant supported oral appliance for treatment of obstructive sleep apnea: a feasibility study (2019)

Introduction: Obstructive sleep apnea (OSA) is a major sleep breathing disorder characterized by repetitive obstruction of the upper airway during sleep leading to sleep fragmentation and oxygen desaturation. Mandibular advancing oral appliances (OAm) are an effective treatment for OSA but cause long-term dental changes, resulting in some patients stopping treatment. We hypothesized that a novel OAm which interfaces with orthodontic mini-implants (OMIs), instead of teeth, can avoid dental changes. This study aims to evaluate the effectiveness of a novel device; to suggest future design improvements; and to advance the understanding of design and anatomical factors that may contribute to successful treatment.Methods: The pilot trial included 3 non-obese adult OSA patients that were successfully treated with OAm. For each patient 4 OMIs were placed in the maxilla and 2 in the mandible, and an appliance was digitally designed and 3D printed based on patient anatomy. The appliance was tested on patients to evaluate viability of the design, retention, and patience experience. To evaluate the influence of anatomical factors, the dental records of 5 OSA patients were measured to determine the appliance design configurations at different amounts of titration and various OMI positions. Mathematical modelling was used to quantitatively approximate forces that would be exerted on the lower OMIs for different amounts of mandibular protrusion.Results: The appliance retention was deficient under the initial design configuration. A total of 24 OMIs were inserted. The overall OMI failure rate was 50.0%; 38.5% in the maxilla, and 63.6% in mandible. Model analysis showed optimal sidebar angulation was only achieved in a sample Class II division 2 malocclusion/non-extraction case at maximum titration. Quantitative force analysis revealed forces of up to 32.5N could be generated on the lower OMIs with the existing design configurations.Conclusion: Appliance design is limited by anatomical factors, OMIs location, and sidebar angulation. The overall appliance retention was deficient with a high OMI failure rate compared to previous orthodontic-based studies. Multiple individual OMIs may not be a suitable option to anchor the appliance. Conclusions should be taken with caution due to small sample size and high risk of bias.

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Craniofacial morphology and the use of neonatal non-invasive ventilation therapy (2018)

Objective: A prospective cohort study with the overall objective to characterize the three-dimensional facial morphology of preterm infants over the course of the first 18 months of corrected age, participating in the Neonatal Follow-up Program of B.C. Women’s Hospital in Vancouver, BC. The specific aims of this project are to: 1. Characterize the three-dimensional facial morphology of a cohort of preterm infants at 4, 8 and 18 months of corrected age. 2. Determine the effects of the duration of NIV therapy on facial morphology at 4, 8 and 18 months of corrected age. 3. Evaluate the feasibility, time, adverse events, and minimum effect size to predict an appropriate sample size to improve study design prior to performance of a full scale longitudinal research project. Methods: To achieve this goal, infants reporting for follow-up at 4, 8 and 18 months of age corrected for prematurity will be screened for defined eligibility and imaged with a 3dMD surface-imaging camera, and facial morphometric parameters will be related to anthropometric data at birth and the specific characteristics of respiratory therapy received during the neonatal period or longer. Results: The study obtained 43 facial images: 10 images for the four-month cohort; 13 images for the 8-month cohort; 20 images for the 18-month cohort. The mean gestation age is 26 weeks, birth weight is 822 grams, birth length is 32.6 cm, and birth head circumference is 23.8 cm. The mean NIV therapy duration is 45 days and the mean NICU stay is 101 days. There was statistical significant negative correlation between intercanthal width versus duration of NIV therapy in the 4-month cohort. Conclusion: There were not any statistical significant correlations between the duration of NIV therapy and the linear distances measured in the transverse, vertical and anterior-posterior plane other than the intercanthal width. The duration of NIV therapy did not have any statistical significant correlation with measured facial angles and facial ratios. This pilot study was however not powered to detect a difference. There is overall positive feasibility for acceptability, demand, implementation, practicality, adaptation, integration and expansion of the research project.

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Reliability of upper pharyngeal airway assessment using dental CBCT (2017)

Introduction: Upper airway analysis is an often-cited use of CBCT imaging in orthodontics, however the reliability of airway measurements using this technology is not fully understood. The purpose of this study was to determine the intra-examiner and inter-examiner reliability of the complete process of volumetric and cross-sectional area assessments of the upper airway using CBCT imaging. Methods: Five examiners of varying levels of education and clinical experience performed manual orientation, slice and threshold selection, and measured nasopharyngeal, oropharyngeal, hypopharyngeal, and total upper pharyngeal airway volumes in addition to minimum cross-sectional area on the CBCT images of 10 patients. All measurements were repeated after 4-weeks. Intra and inter-examiner reliability was calculated using ICC and 95% CI. Results: Threshold selection showed poor intra and inter-examiner reliability, while minimum cross-sectional area showed moderate intra and poor inter-examiner reliability. Intra-examiner reliability of volumetric measurements varied based on the anatomical region assessed with ICC ranging from 0.747-0.976, and was worst for hypopharynx and best for the oropharynx. Inter-examiner reliability of volume measurements was generally lower, with ICC ranging from 0.175-0.945, and was worst for nasopharynx and best for the oropharynx. Conclusions: This study, for the first time, assessed the reliability of upper airway analysis with CBCT when all steps of image processing and measurement are performed by each examiner. Reliability improved with examiner experience, though was generally low for the hypopharynx and nasopharynx volumes and overall minimal cross sectional area. The oropharyngeal volume was the only parameter to have excellent intra-examiner and inter-examiner reliability.

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Effect of orthodontic treatment on the upper airway volume (2014)

Introduction: Currently, the influence of orthodontic treatment on the volume of the upper airway is not well understood. The aim of this study is to examine the effects of orthodontic treatment both with and without extractions on the anatomical characteristics of the upper airway in adults. Methods: For this retrospective study, the pre and post orthodontic treatment CBCT scans of adult patients treated at the UMN Division of Orthodontics between 2008 and 2012 were reviewed. From a pool of 1680 patient records, 74 patients met the eligibility criteria of the study and were included for further analysis. 3D imaging analysis software was used to segment and measure upper airway regions including the nasopharynx (NP), the retropalatal (RP) and retroglossal (RG) areas of the oropharynx, as well as total airway (TA). Coefficient of variation and the intraclass correlation coefficient were calculated. The Wilcoxon signed-rank test was used to compare volumetric and minimal cross-sectional area changes from pre (T0) to post (T1) treatment.Results: The reliability was high for all measurements with an ICC ≥0.82. Cephalometric analysis revealed no significant skeletal changes from T0 to T1. The T0 to T1 treatment changes for the upper airway for the extraction and non-extraction groups were as follows: TA: 1039.6 ± 3674.3mm³ vs. 1719.2.2 mm³ ± 4979.2, NP: 136.1 mm³ ± 1379.3 vs -36.5 mm³ ± 1139.8, RP: 412.7 mm³ ± 3042.5 vs. 399.3 mm³ ± 3294.6 , and RG 412.5mm³ ± 1503.2 vs. 1109.3mm³ ± 2328.6, respectively. The treatment changes for all airway regions examined were not significantly (p>0.05) different between the extraction and non-extraction groups. Similarly, changes in the minimum cross-sectional area were also not significantly different between the two types of treatment. Conclusions: Orthodontic treatment in adults does not cause clinically significant changes to the volume or minimally constricted area of the upper airway.

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