Effect of Cement Space on Retention of CAD/CAM PMMA Provisional Crowns

doi:10.13701/j.cnki.kqyxyj.2021.04.011

Abstract

Abstract: Objective: To explore the effect of cement space on the retention of CAD/CAM PMMA provisional crown. Methods: Five first premolars extracted for orthodontics were selected and prepared according to the standard of full crown tooth preparation. Intraoral scanner (CS3600) and Exo-cad software were used to complete the design of full anatomical PMMA crown. The samples were divided into 6 groups according to the setting of cement space. Among them, the cement space within the finish line 2 mm was 0 μm, and the cement space above the finish line 2 mm was set to 20 μm, 40 μm, and 60 μm, respectively, which were named as group 0-20, group 0-40, and group 0-60. The cement space within the finish line 2 mm was 20 μm, and the cement space above the finish line 2 mm was set to 20 μm, 40 μm, and 60 μm, respectively, which were named as group 20-20, group 20-40, and group 20-60. PMMA full crowns were made by chair side milling machine (n=5, N=30). The marginal suitability and stability of the restoration were evaluated by tactile-visual evaluation. The edge gap was measured by stereo zoom microscope. The retention force was detected by tensile test with a universal testing machine. The data were analyzed by SPSS 19.0 statistical software. Results: With the setting of different cement space parameters, the average marginal gap of the CAD/CAM PMMA crowns (P＜0.001) met the clinical requirements. Among them, the average marginal gap of group 0-20 was the largest (83±6) μm, and the mean marginal gap of group 20-60 was the smallest (37±5) μm (P<0.05). There was a negative correlation between marginal gap and cement space. There was significant difference in the retention of PMMA full crown with different cement space parameters. Among them, the retention force of group 20-20 was the highest [(61±6) MPa] and group 0-60 was the lowest [(39±5) MPa]. Conclusion: The retention and stability of CAD/CAM PMMA full crown restoration can achieve satisfactory results when the cement space is set to 20-20 μm.

Key words: computer aided design/computer aided manufacture, cement space, marginal gap, poly(methyl methacrylate), provisional restoration

LUO Youcheng, ZHAO Jian, YANG Shuang, WU Zhe. Effect of Cement Space on Retention of CAD/CAM PMMA Provisional Crowns[J]. Journal of Oral Science Research, 2021, 37(4): 325-329.

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