Mathematisches Modell und klinische Simulation transmittierter Bestrahlungsstärke bei Lichtpolymerisation durch moderne CAD/CAM-Komposit-Restaurationen

Butterhof, Maximilian (2022): Mathematisches Modell und klinische Simulation transmittierter Bestrahlungsstärke bei Lichtpolymerisation durch moderne CAD/CAM-Komposit-Restaurationen = Mathematical model and simulated clinical model for predicting transmitted irradiance during light curing through recent CAD/CAM resin composites. Dissertation, LMU München: Medizinische Fakultät

Abstract

Statement of problem: Pre-estimating the irradiance passing through a CAD/CAM composite restoration for properly curing a luting composite is challenging due to irradi-ance loss by reflection and the influence of various exposure conditions. Objective: To establish a mathematical model for predicting the true transmitted irra-diance through CAD/CAM resin-based composites (RBCs) and the clinically relevant trans-mitted irradiance that can be expected when luting a CAD/CAM restoration. The influence of irradiance, exposure distance, light curing unit (LCU) angulation and direction of polymeri-zation was analyzed when curing through specimens of different thicknesses. Methods: Seven modern CAD/CAM RBCs and one CAD/CAM glass-ceramic (control group) were sectioned and polished to plane-parallel specimens of 0.5 to 5 mm thickness (in 0.5 mm steps, n = 6, resulting in 432 specimens in total). Three of the CAD/CAM RBCs were additionally used to produce 45 crown-shaped specimens with fissure thicknesses of 1.0, 1.5 and 2.0 mm (n = 5). Irradiance of a violet-blue LED light curing unit (LCU) (power modes: Standard, High and Plasma) was measured with a spectrometer after passing through each specimen. 180 exposure conditions per crown were investigated by variation in LCU curing mode, angulation, exposure distance and direction. Material specific parame-ters were calculated based on linear regression of the measured irradiances. Data was com-pared based on comparison of 95% confidence intervals and using univariate ANOVA fol-lowed by Tukey HSD (α = 0.05). Results: The measured transmitted irradiance passing through the specimens de-creased exponentially for increasing specimen thickness. Significantly highest values of transmitted irradiance were measured for 0.5 mm thick specimens for all materials (p < 0.05). The decadic absorption coefficient for CAD/CAM-RBCs ranged from 0.292 mm-1 to 0.387 mm-1 while the control group (glass-ceramic) reached a significantly lower value of 0.283 mm-1. The reflection correcting factor for plane RBC specimens reached values from 0.117 to 0.177 (glass-ceramic: 0.178), resulting in a reflection ratio for plane-parallelly pol-ished surfaces from 12.6% to 18.4% (glass-ceramic: 18,5%). Significant difference between the RBCs and control group is noted, as the glass-ceramic offers a comparably high reflec-tion ratio and the significantly lowest absorption coefficient, overall resulting in the highest transmitted irradiances. The modified reflection correcting factor for the selected RBC crowns ranges from 0.305 to 0.337, which was significantly higher than the correction for plane specimens (0.136–0.177). The correction model enables the calculation of transmit-ted irradiances based on the obtained material parameters and for varying radiant emit-tance and restoration thickness. Exemplarily calculated for 2-mm increments, the model predicts a reduction of measurable transmitted irradiance compared to the incident irradi-ance by 80–89% for plane specimens and by 88–92% for crowns, thus the crowns offered an averaged 32% lower transmitted irradiance compared to plane specimens. For photo-polymerization, 8–12% of the LCU’s radiant emittance can be expected after passing through an RBC based crown of 2-mm fissure thickness. Transmitted irradiance decreases significantly with increasing exposure distance and decreasing incident irradiance. For tilt angles greater than 10°, transmitted irradiances are significantly reduced (–11% for 20°, –23% for 30°, p < 0.05). Significantly lowest transmitted irradiances were measured for ves-tibular curing direction (up to –15%, p < 0.02). Conclusion: A correction model can predict the transmitted irradiance after passing through a dental restoration as function of radiant emittance, restoration thickness and material specific parameters. The practitioner can be supported by this model to adapt ma-terial choice of dental restoration and adhesive system to the individual situation. Variation in exposure conditions shows significant negative effect on the transmission of light and should be limited.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: CAD/CAM Composite, Resin-based composite, Correction model, Light curing, Irradiance
• Themengebiete: 600 Technik, Medizin, angewandte Wissenschaften ; 600 Technik, Medizin, angewandte Wissenschaften > 610 Medizin und Gesundheit
• Fakultäten: Medizinische Fakultät
• Sprache der Hochschulschrift: Deutsch
• Datum der mündlichen Prüfung: 21. Januar 2022
• 1. Bericht­erstatter:in: Ilie, Nicoleta