Comparison of pain perception and autonomic stress response during dental anesthesia: a split-mouth randomized clinical trial of computer-controlled versus conventional local anesthetic delivery

Anxiety remains a primary barrier to dental care and is often triggered by injections. Although computer-controlled local anesthetic delivery (CCLAD) is used to mitigate distress, previous research has been limited by methodological shortcomings. This split-mouth randomized trial objectively evaluated the efficacy of CCLAD by standardizing the injection duration and using heart rate variability (HRV) to quantify autonomic stress. Thirty-eight patients requiring bilateral maxillary premolar extraction received buccal and palatal anesthesia. An experienced oral surgeon administered the injections using CCLAD or a conventional syringe with standardized injection durations to reduce flow-rate bias. Pain perception was subjectively measured using a visual analog scale (VAS). Simultaneously, the autonomic stress response was objectively quantified using HRV indices. Subjective VAS scores did not differ significantly between the CCLAD and the conventional syringe for either buccal (1.77 ± 1.72 vs. 1.64 ± 1.17; P = 0.916) or palatal (2.88 ± 2.28 vs. 2.68 ± 1.98; P = 0.850) administrations. However, regardless of the device used, palatal injections elicited significantly higher pain scores than buccal injections (2.78 ± 2.12 vs. 1.70 ± 1.46; P < 0.001). Similarly, linear mixed model analysis revealed no significant differences between devices regarding primary time-domain HRV indices, specifically RMSSD (coefficient = -0.11; P = 0.075) and SDNN (coefficient = -0.09; P = 0.107). However, linear mixed model analyses indicated a modest shift toward sympathetic dominance with the CCLAD, with a significantly higher heart rate (coefficient = 3.28; P < 0.001), and sympathetic nervous system index (coefficient = 0.45; P = 0.013), together with a lower parasympathetic nervous system index (coefficient = -0.38; P = 0.008). In both groups, the palatal phase triggered significantly higher autonomic reactivity than the buccal phase. Specifically, markers during palatal deposition reflected marked vagal withdrawal and sympathetic dominance, supported by significant changes in heart rate (coefficient = -2.72; P = 0.010) and the low frequency to high frequency ratio (coefficient = -0.23; P = 0.038). Our findings demonstrate no statistically significant difference in physiological stability between the CCLAD and a conventional syringe when injection durations are standardized. ClinicalTrials.gov identifier NCT07431801, date 20/02/2026. This is a retrospectively registered trial.