Bioactive materials improve some physical properties of a MTA-like cement.

One of the main disadvantages of MTA is its long setting time which could result in higher solubility and microleakage, producing a failed treatment. Studies have shown that the addition of bioactive glass may decrease the setting time. The aim of this study is to evaluate the compressive strength, setting time, solubility and radiopacity of a MTAlike experimental cement to which different percentage of wollastonite and bioactive glass are added. White MTA Angelus® was used as control; an experimental MTA-like cement (ExpC) was prepared using white Portland cement with 20wt% of Bi2O3; three wollastonite cement composites were prepared adding 10, 20 and 30wt% of wollastonite to ExpC, and three more adding the same proportions of bioactive glass. Compressive strength was tested according to ADA 30; radiopacity, setting time and solubility were tested according to ISO 6876. SEM observations of the surface were made after the solubility test. Compressive strength, setting time, solubility and radiopacity were reduced as the wollastonite increased; solubility increased with the addition of bioactive glass. The surfaces of MTA Angelus® and ExpC were smoother than Wollastonite and Bioactive glass groups. Addition of wollastonite and bioactive glass improved the physical properties of a MTA-like experimental cement, reducing the setting time with good solubility percentages, which would be an advantage in its clinical use.

Reducing within-subject variation in chewing cycle kinematics--a statistical approach.

OBJECTIVES: High levels of within-subject variability have limited the use of chewing cycle kinematics in the experimental and clinical context. The purpose of this study was to validate a new strategy for reducing within-subject variability in chewing cycle kinematics, based on the 10 most representative cycles from a chewing sequence. METHODS: This prospective study included 25 young subjects, with normal class I occlusions. An optoelectronic recording system was used to track chin movements of subjects chewing gum (2.5 g). Computer programs provided estimates for duration and movement as well as the 3D coordinates of the chin point. The total output files were further processed for selection of 10 representative cycles based on standard scores for total duration, excursive ranges in the lateral, vertical and antero-posterior directions. Multilevel modelling procedures were used to test for significant differences. RESULTS: There were no significant differences in cycle duration or excursions between the estimates for all cycles versus the 10 most representative cycles. Cycle shapes were very similar. There were no statistically significant differences in between-subject variances. All within-subject variances were smaller when using data from the 10 most representative cycles. The reduction of variance was approximately 33% for total duration and 75% for total 3D excursion. CONCLUSIONS: The results validate the pre-processing strategy that selects the 10 most representative cycles from a sequence without altering cycle duration, excursions or shape or affecting between-subject variation but reducing within-subject variation substantially.

Bolus size and unilateral chewing cycle kinematics.

The purpose of this study was to determine how bolus size alters the human chewing cycle. This prospective within-subject design evaluated chewing cycles of 38 young adults between 20 and 38 years of age (21 males and 17 females). An optoelectric jaw tracking system was used to record movements of the chin during unilateral (right sided) chewing of four randomly ordered bolus sizes (1, 2, 4 and 8 g) of gum. Using each subject's 10 most representative cycles, multilevel statistical procedures were used to evaluate jaw kinematics. The results showed that bolus size has no consistent effect on opening, closing or total cycle duration. Cycle excursions increased significantly with increasing bolus size. With increasing bolus sizes, chewing cycle excursions along the three axes increased 52-115%. The greatest differences between bolus sizes occurred when the jaw was changing direction (i.e. passing from opening to closing and from working to balancing sides). However, the increases were proportionate and the shape of the chewing cycle was maintained. In order to maintain cycle duration while increasing excursive ranges, jaw velocities increased significantly, with the greatest differences occurring at approximately 70% of opening and 30% of closing. We conclude that humans adapt to larger bolus sizes by increasing chewing cycle perimeter and by increasing cycle speed, while maintaining cycle shape and duration.