Mechanical properties of contemporary composite resins and their interrelations.

OBJECTIVE: To characterize a spectrum of mechanical properties of four representative types of modern dental resin composites and to investigate possible interrelations. METHODS: Four composite resins were used, a microhybrid (Filtek Z-250), a nanofill (Filtek Ultimate), a nanohybrid (Majesty Posterior) and an ormocer (Admira). The mechanical properties investigated were Flexural Modulus and Flexural Strength (three point bending), Brinell Hardness, Impact Strength, mode I and mode II fracture toughness employing SENB and Brazilian tests and Work of Fracture. Fractographic analysis was carried out in an SEM to determine the origin of fracture for specimens subjected to SENB, Brazilian and Impact Strength testing. The results were statistically analyzed employing ANOVA and Tukey post hoc test (a=0.05) while Pearson correlation was applied among the mechanical properties. RESULTS: Significant differences were found between the mechanical properties of materials tested apart from mode I fracture toughness measured by Brazilian test. The latter significantly underestimated the mode I fracture toughness due to analytical limitations and thus its validity is questionable. Fractography revealed that the origin of fracture is located at notches for fracture toughness tests and contact surface with pendulum for Impact Strength testing. Pearson analysis illustrated a strong correlation between modulus of elasticity and hardness (r=0.87) and a weak negative correlation between Work of Fracture and Flexural Modulus (r=-0.46) and Work of Fracture and Hardness (r=-0.44). Weak correlations were also allocated between Flexural Modulus and Flexural Strength (r=0.40), Flexural Strength and Hardness (r=0.39), and Impact Strength and Hardness (r=0.40). SIGNIFICANCE: Since the four types of dental resin composite tested exhibited large differences among their mechanical properties differences in their clinical performance is also anticipated.

Clinical effectiveness of two agents on the treatment of tooth cervical hypersensitivity.

PURPOSE: To investigate the desensitizing ability of a one-bottle bonding agent and a glutaraldehyde-based HEMA formulation on sensitive tooth cervical areas for a period up to 9 months. METHODS: The sample consisted of 40 patients with cervical hypersensitivity. Three sensitive teeth per patient were treated; one received One-Step (one-bottle bonding agent), the other Gluma Desensitizer (glutaraldehyde-based agent) and the third distilled water (control group). The hypersensitivity level was determined before, immediately after the desensitizing session, at 8 weeks, and 9 months post-treatment. Measurements of sensitivity were determined by the patient's response to tactile and air-blast stimuli. A verbal rating scale was used and scored as follows: 0, no discomfort; 1, discomfort but no severe pain; 2, severe pain during simulation; 3, severe pain after simulation. The results were subjected to statistical analysis by Kruskal-Wallis test (a=0.05). RESULTS: Both treatment procedures resulted in reduction of hypersensitivity to both stimuli, for up to 9 months. No significant differences were recorded between One-Step and Gluma Desensitizer at immediate and 8-week examinations, whereas Gluma Desensitizer produced lower hypersensitivity than One-Step at the 9-month assessment. In general, a lower level of reduction was found for the 9-month interval compared to the 8-week hypersensitivity score for both agents tested. A placebo effect was observed with water treatment, ranging from 4.7 to 27.5% reduction of hypersensitivity.