Advisory Committee Chair
Nathaniel C Lawson
Advisory Committee Members
Date of Award
Degree Name by School
Master of Science (MS) School of Dentistry
Background: The most common contaminant in the oral cavity is saliva. Many studies have shown that contamination with saliva negatively affects the strength of the resin-dentin bond. A literature review by Nair et al reported that 64.6% of studies on the topic show a detrimental effect of salivary contamination on adhesive materials. No published studies were found that thoroughly studied the effects of saliva contamination on RMGIs and resin cements with regards to crown retention rates. Objective: To study the effect of salivary contamination on crown retention strengths of RMGI and resin cements at various stages of bonding and in wet and dry environments. Methods: 100 extracted human mandibular premolars were centered in Teflon cylinders and embedded in auto-polymerizing acrylic resin. Occlusal surfaces of each specimen were ground flat on a model trimmer. Each specimen was fixed into a lathe for precise uniform reduction and prepared to uniform dimensions (20° total taper and 2 mm height) using a flat end taper diamond bur. Bonding surface areas of the prepared surfaces were calculated under 20X magnification using a Keyence digital microscope. The specimens were scanned using a digital scanner. Cylindrical copings were designed using 3Shape CAD design software. A 50μm cement gap was selected for each crown. The iv restorations were designed with a handle placed perpendicular to the long axis of the tooth which was used to attach a wire loop for debonding the crowns. The passive drool technique was utilized to collect unstimulated, whole saliva. In Part 1 of the study, two RMGIs, one Bioactive, one Self-adhesive Resin and one Adhesive Resin Cements were tested with and without dried salivary contamination. In Part 2a, one RMGI cement was tested with dried saliva and wet saliva contamination groups. In part 2b, one resin cement was evaluated with salivary contamination occurring before and after adhesive application and also with dried or wet saliva. The cement was applied to the copings according to manufacturer’s IFU. Crown retention was measured by placing the specimens in a universal testing machine. Specimens were loaded in tension at a crosshead speed of 1 mm/min until debonding; the debonding force (N) was recorded. Retention strength was calculated in MPa by dividing the debonding force (N) by the total bonding surface area of the preparation (mm2). Crown retention strength and force were analyzed with two-way ANOVA for Part 1 and one-way ANOVA for Part 2. Failure mode was examined under 20X on the Keyence digital microscope and classified in one of five categories: cement mainly on prepared tooth (over 75%), cement on both crown and tooth (between 25 and 75%), cement mainly on crown (over 75%), fracture of tooth without crown separation, or fracture of crown. Results: In part 1, two-way ANOVA comparing crown retention strength for cement type and contamination (clean and saliva contamination) showed no significant interaction (p = 0.394) between the two factors; however, the factor “cement type” was significant (p<0.001). In Part 2a, one-way ANOVA showed that there was significant difference (p<0.001) when cementing crowns with dried or wet saliva and in Part 2b, v one-way ANOVA showed that there was significant difference in crown retention strength when contamination occurred before adhesive application when compared to contamination after adhesive application. Conclusion: Salivary contamination has a significant effect on the crown retention strength of RMGI cements when cemented over wet saliva and for resin cements when contamination occurs before adhesive application.
Nizami, Bushra, "Effect of Saliva Contamination on Crown Retention Strengths of Resin and RMGI Cements" (2022). All ETDs from UAB. 563.