Subjective and photometric determination of bleaching outcomes.

OBJECTIVE: Subjective and objective measures were used to determine the relative efficacy of 10% and 35% carbamide peroxide gels in bleaching extracted human teeth. METHOD AND MATERIALS: Fifty-five teeth (premolars and molars) were sectioned longitudinally, and one-half of each tooth was assigned to group A (10%) and the other half to group B (35%). Prebleaching shades were evaluated subjectively by 5 experienced observers using standard shade tabs. Photographs were also taken with a calibrated digital camera. Luminosity, R, G, and B levels were determined with Photoshop software. The specimens were then bleached by either 10% or 35% carbamide peroxide, after which they were reexamined by the 5 observers and rephotographed. RESULTS: All bleached specimens were subjectively assessed as "lighter", but there was no perceived difference in final shade between groups. Objective measurement showed that the greatest spread in the 0 to 255 scales was in the B levels. Mean (and range) of pre- and postbleaching B levels and their differences, by group, were group A, 96.2 (76.5 to 117.1), 113.6 (87.7 to 129.1), difference 17.4, and group B, 95.4 (72.1 to 118.8), 110.5 (88.0 to 138.5), difference 15.1. Statistics were performed using paired t tests. These pre- and postbleaching differences were significant (P < .002). The difference between mean postbleaching B values was not significant (P = .479). The greatest change in luminosity occurred in initially dark teeth treated with 35% carbamide peroxide (P = .036). CONCLUSIONS: Subjective determinations suggest that the bleaching protocols tested were equally effective, but the objective measurements implied that the higher concentration of carbamide peroxide was more effective for darker teeth.

Effect of ultrasonic vibration on the retention of adhesively luted intra-radicular posts.

The aim of this study was to determine the effect of prolonged ultrasonic vibration on tensile force necessary to dislodge two different post types luted with an adhesive resin. Extracted human canine teeth were decoronated and root-filled. Either a ceramic or stainless steel intra-radicular post was luted into each root with resin-based cement. Half the samples in each group were randomly assigned to be subjected to ultrasonic vibration of the post (test group), the remaining samples did not receive vibration (control group). The tensile force required to dislodge each post was then determined in a universal testing machine. The mean force required to dislodge the stainless steel posts in the control group was 510.1N (SD 170.6) and in the 'treatment' group it was 539.5N (SD 163.3). For the ceramic posts in the control group the mean force was 447.8N (SD 165.5) and in the 'treatment' group it was 473.9N (SD 137.8). There was no statistical difference between the groups (p = 0.597). Within the limitations of this in-vitro study, the results cast doubt on the ability of application of ultrasonic vibration to displace/loosen intra-radicular posts luted with a resin-based cement.

Dentinal crack incidence following ultrasonic vibration to intra-radicular posts.

OBJECTIVE: To determine the incidence of dentinal cracks on the root-face of extracted teeth containing intra-radicular posts subjected to prolonged ultrasonic vibration. Design & Setting This in-vitro experiment, conducted at the University of Manchester, UK, used post type and ultrasonic vibration as dependent variables. MATERIALS AND METHODS: Forty canine teeth were decoronated and root-filled with gutta-percha and sealer. A parallel shaped post-space of 1.4 mm diameter and 10 mm depth was prepared in each root. The teeth were grouped into morphologically similar pairs, and for each pair one tooth was randomly allocated to receive a zirconium ceramic post, the other a stainless steel post. The pairs of teeth were randomly assigned to a control or to a test group. The root-face was examined for dentine cracks or fractures with direct vision and at 20x magnification with transillumination. Samples were then stored in sterile water for one week. Ultrasonic vibration was applied continuously for 30 minutes to the top of the posts in the test groups. All samples were then re-examined for dentine cracks or fractures. RESULTS: Following storage, no new cracks were evident for the control groups. Seven new cracks occurred in the test groups (following application of ultrasonic vibration), six of which were on the root-face of samples with ceramic posts. The difference in crack distribution between the two groups was significant (Fisher's Exact Test, p=0.029). CONCLUSION: Prolonged application of ultrasonic vibration to ceramic posts increased the incidence of root-face cracks.

Potential for temperature change during application of ultrasonic vibration to intra-radicular posts.

The aim of this study was to assess the potential for heat production when intra-radicular posts were subjected to ultrasonic vibration. Thirty zirconium ceramic posts and thirty stainless steel posts were luted into canine roots. Ultrasonic vibration was applied to the top of each post for thirty minutes and temperature change on the root surface was measured. The mean peak temperature rise from baseline was 18.7 degrees C. Post type had no influence on peak temperature. Temperature increase on the external root surfaces increased as the thickness of dentine between post and root surface reduced.