The Effect of Motivational Interviewing on Oral Hygiene Behavior in Patients With Fixed Orthodontic Appliances: A Randomised Clinical Trial
Phase: NA
Conditions: Motivational Interviewing, Oral Hygiene, Orthodontic Appliance Complication
Sponsor: Universidad Iberoamericana

The effect of motivational interviewing on oral hygiene behavior in patients with fixed 
orthodontic appliances: A randomised clinical trial 
Document type: Study protocol with SAP 
Authors : 
1. Henry Adames-Vargas1 
2. Paula Yunes Fragoso1 
3. Carlos Bienvenido Matuk Ruiz2 
4. Leandro Feliz-Matos1 
Department(s) and institution(s)  
1Biomaterials and Dentistry Research Center, Academic Research and Innovation Department, 
Universidad Iberoamericana, Santo Domingo, Dominican Republic. 
2Department of Statistics- Universidad Iberoamericana (UNIBE), Santo Domingo, Dominican 
Republic. 
Corresponding Author: 
Name: Henry Adames-Vargas 
Address: av. Francia 129, Gazcue, Santo Domingo, Dominican Republic. 
Phone numbers: +1809 689 4111. Ext; 1503 
Facsimile numbers: 
E-mail address: h.adames1@unibe.edu.do   
 
 
Document date: March 1st, 2021 
IRB approval: June 6th, 2017 
 
 
 
 
 

Objective 
To evaluate the effectiveness of motivational interviewing on improving oral hygiene behavior in 
patients with fixed orthodontics appliances. 
Materials and Methods 
The present study was designed as a parallel-group randomized clinical trial. The approval 
number provided by UNIBE’s Ethics Committee is CEI2017-06.  The research was performed 
following the Declaration of Helsinki of 2013.  
Sample and eligibility criteria 
A power analysis was carried out to determine the number of participants needed to achieve a 
Simplified Oral Hygiene Index (SOHI) significant interaction with the study groups when 
applying repeated measures ANOVA. The total number of completed patients needed to achieve 
power of 0.90 with an alpha (α) of 0.05, an effect size (f) of at least .25 was determined to be 36; 
taking into consideration a possible 10% attrition rate, 45 participants were recruited, consented 
and randomized to either the experimental or control group. 
Due to the matter that repeated measures ANOVA treats each measurement as a separate 
variable, and it's preferable to use listwise deletion, if one measurement is missing, the whole 
case gets dropped. For this reason and therefore the incontrovertible fact that the trial suffers 
attrition, the sample for the three measurements was reduced to 30 participants. 
The clinical trial was carried out at the Orthodontic Clinic of UNIBE's Postgraduate Unit, Santo 
Domingo, Dominican Republic, from June 2017 to November 2018. The established inclusion 
criteria were patients with 18-40 years old, systemically healthy, without active dental caries 
lesions or periodontal diseases, who were candidates for fixed orthodontic appliances. Smokers 
and pregnant patients were excluded. Participants were discarded if they decided voluntarily to 
abandon the study of the orthodontic treatment or if they didn’t attend to the periodical check-
ups. 
Randomization 
A simple randomization procedure was executed by the principal investigator to allocate the 
participants into one of the study groups. A computer-generated list of numbers was created 
using the software SPSS V21.0, with a 1:1.25 allocation ratio. The aforementioned researcher 
didn’t participate in the data recollection process.  

Two dentists were in charge of the study logistic. They enrolled and allocated the participants 
according to the order of arrival and following the list of random numbers.  A coding system was 
used as a concealment mechanism, which consisted of colored labels attached to the participants’ 
file. This system was only known by the logistics managers and the interviewer (the periodontist 
who provided OHI and MI). Thus, the participant and the evaluator (the periodontist who 
recorded the data) were masked. 
Study intervention 
The patients were invited to participate in the research in their first appointment with the 
orthodontic postgraduate dentist. Then, on the second appointment, the fixed orthodontic 
appliance was placed and the intervention began.  A questionnaire to collect sociodemographic 
information was administered by the interviewer.  
The interviewer was also in charge of providing oral hygiene instructions for both groups. All the 
participants received a G.U.M. kit with special orthodontic hygiene tools. Then, the patients of 
the experimental group received a motivational interviewing session. It is important to point out 
that the periodontist was trained and evaluated by two expert psychologists in MI, who also 
supervised the interviewer to ensure that the intervention was properly applied. Additionally, all 
the staff related to the research was also trained. 
Afterwards, the clinical parameters were measured by another periodontist. The primary 
endpoint with respect of the efficacy of MI was the Simplified Oral Hygiene Index (SOHI). 
Additional parameters were recorded, such as the Gingival Index (GI), Periodontal Probing 
Depth (PPD) and Bleeding on Probing (BoP), with the purpose of evaluating the periodontal 
stability.  
Monthly follow-up appointments were scheduled for the orthodontic check-ups to deliver a new 
G.U.M. kit, to reinforce the OHI and MI and to register the periodontal parameters. The 
important data for this research was the one recorded at baseline, three and six months after the 
intervention.  
Statistical analysis 
Mean SOHI, GI, PPD and BoP scores were compared between groups across three time points 
using repeated-measures mixed-model analysis of variance.  Tests for equality of variances and 
sphericity to check for homoscedasticity were performed due to the problem of sample attrition.  
Nevertheless, it was not found any violation to these assumptions in any of the variables included 

in the analysis.  SPSS software was used for all calculations (IBM SPSS 25th version). Due to 
the nominal level of measurement of the variable BoP, it was performed a chi-squared test for 
each three time points to check if there were any differences between the two experimental 
conditions.