Ethical approval and consent
Ethical approval was obtained from the East London and the City Local Research Ethics Committee prior to starting the study. Eligible participants were provided with verbal and written information, and signed consent was obtained prior to participation.
Statistical input advised that a sample size of 100 subjects to be assessed would be sufficient to provide a variety of traits from within the narrow spectrum of borderline malocclusions. Subjects were recruited from ‘New Patient’ Orthodontic Consultant Clinics held at the Royal London Hospital and examined by the chief investigator (NL). The following inclusion criteria were met:
A score of 3 in the dental health component of the IOTN:
Increased overjet greater than 3.5 mm but less than or equal to 6 mm, with incompetent lips (3a)
Reverse overjet greater than 1 mm but less than or equal to 3.5 mm (3b)
Anterior or posterior crossbites with greater than 1 mm but less than or equal to 2 mm discrepancy between retruded contact position and intercuspal position (3c)
Contact point displacements greater than 2 mm but less than 4 mm (3d)
Lateral or anterior open bite greater than 2 mm but less than or equal to 4 mm (3e)
Deep overbite complete on gingival or palatal tissues but no trauma (3f)
Absence of or only mild gingival pigmentation
Permanent dentition or in the late mixed dentition with only retained second deciduous molars
Unrestored or minimally restored dentition
The chief investigator (NL) attended a calibration course on the use of Occlusal Indices, which included the IOTN. Each participant’s DHC of the IOTN was recorded, and a single frontal intra-oral photograph and a set of study model impressions were taken.
Once the sample of 100 photographs had been gathered, they were rotated and cropped as necessary to ensure horizontal occlusal planes to make them consistent with each other. The photographs were set up in random order on a Microsoft Power Point slide show and clearly numbered so they could be easily identified and scored by individual judges. Each time the photographs were shown, the sequence was re-randomised to reduce the order effect.
A pilot study involving ten orthodontists, dentists and adult patients was undertaken to help determine the best layout for the questionnaire for the study. The questionnaire they filled out determined that judges preferred to view each photograph for 10 s to allow full appreciation of the photograph without it taking too long. They also provided feedback on the layout of the questionnaire to be used in the study.
An error study was incorporated into the main study by repeating every fifth photograph at the end of the slide show, thus increasing the total number of photographs from 100 to 120. The judges were unaware that their reproducibility was under scrutiny.
A questionnaire was created to determine whether, in the judge’s opinion, the malocclusions shown in each of the 120 photographs warranted treatment for reasons of ‘appearance’, with four tick-box options: definitely no; borderline no; borderline yes; definitely yes.
At no time were the judges given any information about the borderline nature of the malocclusions to be assessed or about occlusal traits.
Three panels of 25 judges were recruited:
The orthodontic panel (specialist orthodontic registrars, specialist orthodontists and consultant orthodontists from the orthodontic departments at The Royal London Hospital, Essex County Hospital, Guy’s Hospital and King’s College Hospital)
The dental panel (qualified dentists with no postgraduate orthodontic training or experience, including periodontists, prosthodontists, restorative consultants, implantologists and dentists with specialist interests from the paedodontic, restorative, oral and maxillofacial surgery, and oral medicine departments at The Royal London Hospital and Guy’s Hospital)
The lay group (any person who had not undergone any previous orthodontic treatment, whose children were not undergoing orthodontic treatment, whose occupation was not in the dental field and had no extensive dental knowledge, recruited from hospital outpatient departments, secretaries and radiologists at the Essex County Hospital).
Judges for each panel were selected by the chief investigator and identical instructions were given individually prior to grading the photographs in the slide show. Special precautions were taken not to inform the orthodontic and dental judges of the objective features or borderline nature of the photographs to avoid bias. The chosen independent judges were not involved with the study and had no prior knowledge of the study. They were chosen based on their relevant specialty (for the orthodontic and dental panels) and their non-involvement with the study. Once the slide show had started, assessments were carried out in silence and in a single sitting. The screen size, brightness and contrast were kept identical throughout to ensure the same conditions.
Data from the main study and scores from the error study were analysed by the Statistical Package for Social Sciences computer software (SPSS Inc., Michigan Avenue, Chicago, IL, USA), using means, Spearman’s correlation analysis, and kappa analysis. A statistician was consulted regarding study design, statistical analysis and interpretation of the results.