OBJECTIVE: To evaluate the effect of microwave polymerization and water-bath heat polymerization on accuracy and flexural strength of denture base resin. METHODS: Ten maxillary complete dentures were prepared and divided into microwave polymerization and water-bath heat polymerization groups according to random number table, with 5 dentures in each group. In the microwave polymerization group, the dentures were heated for 9 minutes with 40% firepower, natural cooled, the pressure of flasking at 4.5 kg/mm~2. In the water-bath heat polymerization group, the temperature increased from room to 70℃, sustained for 1.5 hours, then rise to 100℃ for 0.5 hour. The dentures were maintained at 25℃ thermostatic water bath for a week. The denture base, as well as standard cast was cut down at posterior border of the second molar. Dimensional accuracy between the posterior border of upper complete denture and standardized cast at five different positions was measured by digital microscope. Specimens with 64 mm× 10 mm×2.5 mm were made for measuring flexural strength.RESULTS: ①The posterior border gaps between the upper complete denture and standardized cast was (141±78) urn and (147±74) μm cured by microwave polymerization and water-bath heat polymerization, which has no statistical difference. The flexural strength of denture base resin cured by the microwave polymerization and water-bath heat polymerization was (81.60±14.04) MPa and (84.24±17.65) MPa, and there was no statistical difference (P > 0.05). CONCLUSION: There is no significantly difference in the accuracy and flexural strength cured by microwave polymerization and by water-bath heat polymerization, but the microwave polymerization takes shorter time than that by water-bath heat polymerization.

Objective:To analyze the safety and efficacy of ultrasound-guided needle-perc assisted retrograde intrarenal surgery (RIRS) in the treatment of small but complex renal calculi, and summarize our clinical experience.Methods:The clinical data of 36 patients with small but complicated renal stones treated by ultrasound-guided needle-perc assisted RIRS in Beijing Tsinghua Changgung Hospital from January 2020 to April 2022, were retrospectively analyzed. There were 25 males and 11 females. The average age was (54.7±6.1) years, and the body mass index (BMI) was (26.3±3.1) kg/m 2. The maximum diameter of the calculi was (1.8±0.7) cm. There were 28 patients without renal hydronephrosis before operation, 8 patients with mild to moderate renal hydronephrosis, 4 patients with caliceal diverticular stones, 32 patients with lower pole stones, 10 patients with ureteral stones, 6 patients with previous surgical history of ipsilateral kidney stones, and 3 patients with stones in the solitary kidneys. Patients were placed in oblique supine lithotomy position or prone split leg position (female). For lower pole stones or diverticular stones that were difficult to be handled by flexible ureteroscope, the needle-perc was used to puncture the stones in target calyx under ultrasound guidance. Holmium laser was then used to pulverize or fragment the calculi, and the flexible ureteroscope was used to remove or further pulverize the stone fragments. Perioperative indexes and postoperative complications were recorded, and stone-free rate was analyzed. Results:All 36 cases were successfully operated. The median operation time was 61.5(59.0, 66.8)min, with a median decrease in hemoglobin on the first postoperative day of 1.6(0.8, 2.0)g/ L, a median postoperative hospital stay of 1.5(1.0, 2.0)days, and a median needle-perc tract of 1(1, 2). The complications were recorded in 4 patients (11.1%), all of which were Clavien-Dindo grade I, including postoperative fever in 2 patients and analgesic use in 2 patients. The primary stone-free rate was 83.3% (30/36). The 6 patients with residual stones were treated by external physical vibration lithecbole on the 3rd to 7th day after surgery. After 1 month follow-up, residual stone expulsion were seen in 3 patients. Three patients with residual stones were followed up regularly. The final stone-free rate was 91.7% (33/36).Conclusions:Ultrasound-guided needle-per assisted RIRS is safe and effective in the treatment of small but complex renal calculi, with high postoperative stone free rate and low complication rate.