80 complete denture (CD) wearers participated in the quasi-experimental study. Two outcomes were: 1) oral health-related quality of life (OHRQoL) assessed using the Oral Impacts on Daily Performances index, and 2) masticatory performance, determined by a peanut particle size after 20-stroke mastication. Denture retention and stability were evaluated using the Chulalongkorn University (CU)-modified Kapur method to classify the CD into acceptable or unacceptable quality. Data were collected at 3-time points: 1) at baseline (T0), 2) after a 1-month trial of denture adhesive (DA) use (T1), at which time the participants decided whether to continue using DA, and 3) 1-month after continued or discontinued using DA (T2).

Participants The eligible participants were CD wearers randomly recruited from patients who visited the Prosthodontic clinic at the Faculty of Dentistry, Chulalongkorn University from 2015 to 2019. The inclusion criteria were patients who had worn removable maxillary and mandibular CDs for at least 6 months. The patients who wore a metal-based denture, had a history of DA use, had difficulty in responding to the interview, or were unwilling to follow the study protocol were excluded from the study.

Outcomes The primary outcome was OHRQoL determined using the Thai-version of Oral Impacts on Daily Performances index. The participants were interviewed whether they had difficulties in performing the following 8 daily activities: eat, speak, clean denture and mouth, sleep, smile, emotional stability, social contact, and carry out work or housework. The frequency and severity of each impact were rated using a five-point Likert scale, and their multiplication gave a condition-specific impact score. The overall oral impact score was the sum of all 8 activity scores. The prevalence of an oral impact was categorized into absence (score = 0) or presence of an oral impact (score > 0). The changes in oral impact score from T0 to T1 were categorized into 3 types: decreased (T0 score > T1 score), increased (T0 score < T1 score), and remained absent (T0 score = T1 score = 0).

The secondary outcome was masticatory performance assessed using the multiple sieve method of peanut mastication. The participants masticated 3 grams of roasted peanuts for 20 strokes in triplicate with a 15-minute resting interval between each test. The comminuted peanut particles were dried and sieved through 12 standard test sieves (Test sieve; Retcsh Technology GmbH) on a vibrating sieve shaker. A simple linear regression was plotted between the cumulative weight and diameter of each sieve test. The median peanut particle size (mm) was the sieve diameter through which 50% of the comminuted peanut particles passed. A smaller peanut particle size reflected a higher masticatory performance.

Intervention An external prosthodontist provided a cream-type DA (Polident®, GlaxoSmithKline, Ireland), and instructed the participants to use the DA cream once a day in the morning and use it throughout the day. They applied the DA onto maxillary and mandibular dentures on the tissue surface using a spot method. The participants had to remove the DA and clean the denture every day after the last meal by soaking and brushing the CD with liquid soap and a soft toothbrush under running tap water. Two gauze pads were used to remove DA from the denture and oral mucosa.

The OHRQoL, masticatory performance, and CD-quality were evaluated at 3-time points:

1. T0, at baseline before using the DA. The baseline information regarding the outcomes was evaluated. Then, the participants underwent a daily 1-month trial of DA use,
2. T1 (T0 + 1 month), after the 1-month trial period of DA use. The outcomes were evaluated with all participants using DA. The external prosthodontist asked the participants to choose whether they wanted to continue or discontinue using DA, and
3. T2 (T0 + 2 months), at 1-month after continuing or discontinuing DA use. At this time, some participants used DA during the outcome evaluations, while some did not, depending on the patient's decision on DA use.

A single-blind clinical trial protocol was created. One of the investigators (B.T.) performed the outcome assessment who did not notice whether the participants continue using DA.

Inclusion Criteria:

• Wear removable maxillary and mandibular complete dentures for at least 6 months.

Exclusion Criteria:

• Wear a metal-based denture
• Have a history of DA use
• Unable to respond to the interview
• Unwilling to follow the study protocol.

An external prosthodontist provided with a denture adhesive and knew who continued using denture adhesive.

Meanwhile, the outcome assessor did not notice whether the participants continue using denture adhesive