Purpose: This study investigated the magnitude, direction, and temporal aspects of the force applied during instrumentation with a piezoelectric ultrasonic periodontal scaler, compared this force with recommendations in the literature, and assessed the influence of the profession (dentist or dental hygienist) and calculus hardness. Materials and Methods: The force applied by ten dental hygienists and six dentists during debridement of comparatively soft and hard artificial dental calculus with a piezoelectric ultrasonic scaler was recorded in-vitro. The total force and its components in three axes were statistically analysed. Results: During debridement of soft artificial dental calculus, the mean total force applied by dental hygienists was 0.34 N (± 0.18 N, range: 0.13 N to 0.59 N) and by dentists 0.28 N (± 0.33 N, range: 0.06 N to 0.95 N), and the total force exceeded 0.5 N approximately 23% and 14% of the time for dental hygienists and dentists, respectively. During debridement of hard artificial dental calculus, the mean total force applied by dental hygienists was 0.63 N (± 0.40 N, range: 0.28 N to 1.64 N) and by dentists 0.57 N (± 0.17 N, range: 0.34 N to 0.76 N); the total force exceeded 0.5 N more than half of the time for both professions. On average, dental hygienists applied 1.85x (p = 0.04) and dentists 2.04x (p = 0.06) higher force on hard than on soft artificial calculus. However, dental hygienists and dentists used similar forces during the debridement of both hard (p = 1.00) and soft (p = 0.26) calculus. Conclusion: The force applied during the debridement of hard artificial dental calculus was statistically significantly higher than during the debridement of soft artificial dental calculus. No statistically significant difference between dentists and dental hygienists was found. The force applied by both groups on soft and hard artificial dental calculus frequently exceeded recommended values.