The study had local NHS Research & Development approval, was approved by the South Staffordshire Local Research Ethics Committee and was conducted according to the guidelines outlined in the Helsinki Declaration. The present study was conducted in two separate, consecutive phases. In the first phase, conducted as part of an undergraduate student research elective project, the acceptability, reproducibility and validity of the scale was evaluated in a convenience sample of 68 patients attending Birmingham Dental Hospital for outpatient consultation clinics in the Oral Surgery department. Patients had been referred by General Dental Practitioners for consultations regarding TMJ problems or for third molar removal. After providing informed consent, patients were instructed in the use of the scale. A pilot study involving the first 13 patients revealed that careful instructions and practice with the clinician was needed for the patient to comfortably and accurately use the device. Based on these initial findings, an illustrated step-by-step guide was developed that was given to patients (available from the authors upon request). In addition to this, instructions on how to use the scale included practicing its use in front of a mirror.
Following this pilot phase, 55 consecutive patients were asked to make 4 repeated measurements of their mouth opening with the scale. For this purpose, they were provided with 4 scales and envelopes. In order to avoid bias by patients remembering their previous measurements, they were asked to place each scale in a provided corresponding envelope and seal it immediately after use. In addition, the numerical scale was masked using a marker pen. Patients were asked to leave at least 5 minutes between measurements. The fourth and final measurement was done in the presence of the investigator. The investigator noted the patients’ ability to locate the cardboard notch accurately on the lower incisors and to accurately position the scale on the upper incisors.
In order to assess the validity of the patients’ readings, the investigator measured a patient’s interincisal distance using a steel ruler both before and after the patient’s measurements. Finally, patients were then asked to record on a 5-point Likert scale how strongly they agreed or disagreed with the statements “I found this device easy to use” and “I would feel confident to record my mouth opening with this device every day over a week if needed”.
Following the evaluation of the use of the scale in this first phase, we used the scale in an ongoing clinical trial on third molar morbidity (NCT01145820). We present results for the first 80 patients enrolled in this study. Briefly, patients 18–65 years old of both genders, who required the surgical removal of a single impacted lower third molar where enrolled. Exclusion criteria included long-term anti-inflammatory medications, regular vitamin or mineral supplementation, pregnancy or lactation. Immediately following surgical removal of a single impacted lower third molar, patients were instructed in the use of the scale and asked to measure their mouth opening once during the evening of each postoperative day. The first reading was done on the day of surgery and then on each day during the postoperative week. Patients attended for follow-up appointments 2 days and 7 days after surgery.
A baseline recording of the interincisal distance was taken by the operating surgeon using a steel ruler immediately pre-operatively. This recording was repeated by the surgeon on post operative days 2 and 7 when the patient was asked to return to clinic for review. A diary of the patient’s daily recordings was also collected on day 7 at their final review appointment.
Summary statistics were calculated as appropriate. For the first phase of this study, paired t-tests were used to assess differences between the first and last measurements by patients and clinicians. To assess reproducibility of patients’ measurements, we calculated the intraclass correlation coefficient. Finally, to assess validity, the Pearson correlation coefficient was calculated comparing the first patient to the first clinician measurement, the final patient to the final clinician measurement, and finally, the mean of all patient measurements and the mean of all clinical measurements. For phase 2 of this study, summary statistics were calculated as appropriate. Pearson correlation coefficients were calculated to assess the validity of the patients’ measurements compared to the corresponding clinical measurements. These correlations were made between the clinician’s and patient’s measurements on day 2 and the clinician’s measurement at the final visit and the patient’s measurement recorded on the previous evening. All statistical tests were two-sided at α = 0.05 using a statistical software (STATA 11, Stata Corp, College Station, TX, USA).