Table 1 Oral hypofunction assessment items and criteria

Chewing ability

• Color-changing chewing gum (Masticatory Performance Evaluating Gum XYLITOL, Lotte, Tokyo, Japan) was chewed for 1 min, and the change in color was determined by comparing it to a color chart (range: 1–5).

• Risk: 1, 2

• Normal: 3–5

Maximum occlusal pressure

• The sample was collected by biting a pressure-sensitive film (Dental Prescale II, GC Co., Ltd, Tokyo, Japan) with the maximum intercuspal position for 3 s.

• The collected films were analyzed using a a dedicated scanner (GT-X830, EPSON, Tokyo, Japan) and software (Bite Force Analyzer, GC Co., Ltd, Tokyo, Japan).

• Risk: < 500 N

• Normal: 500 N or higher

Number of remaining teeth

• Oral examination using a tongue depressor and penlight

• Risk: < 20

• Normal: 20 or more

Maximum tongue pressure

• Participants were asked to bite a JMS tongue pressure measuring instrument (TPM-02, JMS Co., Ltd, Tokyo, Japan) lightly and use maximum force to bite the balloon between the tongue and roof of the mouth for at least 7 s.

• A total of three trials were performed to determine the maximum value.

Criteria for 60–69 years old

• Risk: ≤ 30 kPa

• Normal: greater than 30 kPa

Criteria for Over 70 years old

• Risk: ≤ 20 kPa

• Normal: greater than 20 kPa

Oral dryness

• With the participants’ tongues out, an oral moisture checking device (Mucus, Life Co., Saitama, Japan) was placed perpendicular to the mucosa to measure it with a force of 200 g for 2 s.

• The average value of three consecutive measurements was used.

• Risk: < 27.0

• Normal: 27.0 or higher

Oral cleanliness

• Score for the oral cleanliness item on the Oral Health Assessment Tool

(0: Clean and no food particles or tartar in the mouth or dentures; 1: Food particles, tartar, or plaque in one to two areas of the mouth or small area of dentures or halitosis (bad breath); 2: Food particles, tartar, or plaque in most areas of the mouth or dentures or severe halitosis (bad breath)

• Risk: 2

• Caution: 1

• Normal: 0