Abstract:

Objective

To explore the impact of saliva and resonance cavities on the stability of prosthetic screws based on resonance frequency analysis.

Methods

Mandibular edentulous gypsum casts with screw-retained definitive fixed dental prostheses supported by 6 implants were used.The control group was placed in a standard indoor environment，while the experimental group was placed in a simulated oral environment with artificial saliva in a dental manikin.Different insertion torques were applied to the screws using a digital torque wrench，forming a parameter matrix related to screw stability.A tapping simulation was directly applied to the buccal side of the tested screw，and a pickup device was used to collect the acoustic signals.The resonance peak frequencies of these signals were extracted by using time-frequencydomain analysis based on short-time Fourier transform.The spectrograms of acoustic signal were plotted，and the coefficients of variation for each prosthetic screw at 15 N·cm were calculated for both groups.Bland-Altman analysis was used to evaluate the consistency of the resonance frequencies related to prosthetic screw stability in both groups.Pearson correlation analysis was conducted to investigate the relationship between prosthetic screw stability and corresponding resonance frequencies（α = 0.05）.

Results

The spectrograms of acoustic signal showed that both groups had energy concentration bands in the 7 to 9 kHz range，and as the insertion torque value decreased，the energy concentration band shifted left.The coefficient of variation results indicated that the resonance frequencies of the prosthetic screws in the experimental group at 15 N·cm ranged from（7 329±8）Hz to（8 400±8）Hz，with coefficients of variation ranging from 0.001 to 0.002.In the control group，the resonance frequencies ranged from（7 329±6）Hz to（8 463±11）Hz，with coefficients of variation ranging from 0.000 8 to 0.002.Pearson correlation analysis showed that a linear positive correlation between screw stability and resonance frequency in both groups（r=0.483 ～0.937，P＜0.001）and the correlation coefficient values for the same screw were similar.Bland-Altman analysis revealed that the normalized resonance frequencies in the experimental group ranged from 0.569 to 0.892，while those in the control group ranged from 0.585 to 0.881.The differences in resonance frequencies between the two groups were not statistically significant（t=-1.816 ～0.859，P＞0.05），with the absolute difference ranging from 0.001 to 0.016.

Conclusions

The moist and resonant oral environment did not have an adverse effect on the acoustic-vibration characteristics of implant prostheses based on tapping.Acoustic resonance frequency analysis showed good clinical prospects for reflecting the stability of the prosthetic screw.

Key words: Dental prostheses, Implant-supported, Prosthetic screw, Stability, Acoustic signal, Resonance frequency analysis