A simple sequential-binding model for calcium puffs.

Calcium puffs describe the transient release of Ca(2+) ions into the cytosol, through small clusters of 1,4,5-inositol triphosphate (IP(3)) receptors, present on internal stores such as the endoplasmic reticulum. Statistical properties of puffs, such as puff amplitudes and durations, have been well characterized experimentally. We model calcium puffs using a simple, sequential-binding model for the IP(3) receptor in conjunction with a computationally inexpensive point-source approximation. We follow two different protocols, a sequential protocol and a renewal protocol. In the sequential protocol, puffs are generated successively by the same cluster; in the renewal protocol, the system is reset after each puff. In both cases for a single set of parameters our results are in excellent agreement with experimental results for puff amplitudes and durations but indicate puff-to-puff correlations for the sequential protocol, consistent with recent experimental findings [H. J. Rose, S. Dargan, J. W. Shuai, and I. Parker, Biophys. J. 91, 4024 (2006)]. The model is then used to test the consistency of the hypothesized steep Ca(2+) gradients around single channels with the experimentally observed features of puff durations and amplitudes. A three-dimensional implementation of our point-source model suggests that a peak Ca(2+) concentration of the order of 10 muM at the cluster site (not channel) is consistent with the statistical features of observed calcium puffs.

Development of a stain shade guide to aid the measurement of extrinsic dental stain.

BACKGROUND: Accurate and reproducible assessment of extrinsic staining is pivotal to determining efficacy of some tooth whitening oral hygiene products. The aim of this study was: (1) to produce a stain shade guide to aid the in vitro and in vivo stain assessment (2) to assess intra- and inter-examiner reproducibility of stain assessment using the stain shade guide. METHOD: Using chlorhexidine and tea, perspex and acrylic teeth specimens were stained. The amount of staining on the perspex was measured with a spectrophotometer and the values obtained were assigned to the stained acrylic teeth, which were made into a stain guide. Using clinical photographs and a group of 10 volunteers, stain area and intensity were assessed using the stain guide and the recognized Lobene stain index by two examiners. The degree of intra- and inter-examiner reproducibility for these measurements were assessed using Cohen's kappa statistics. RESULTS: For both the clinical examination and use of photographs, intra-examiner reproducibility for stain intensity was improved when using the stain guide compared with the Lobene Index. Similarly, when assessing inter-examiner reproducibility, stain intensity kappa values were greater using the stain guide (kappa = 0.82) compared with the Lobene Index (kappa = 0.57). CONCLUSION: The findings of this study would suggest that the use of the stain guide could be of importance in the assessment of extrinsic dental stain.

Peri-implant bone reactions to immediately loaded implants. An experimental study in monkeys.

BACKGROUND: There are reports which demonstrate that immediately loaded splinted implants can be osseointegrated when they are placed in the anterior part of the lower jaw. The concept of immediate loading has not been well investigated in the posterior mandible. The aim of this study was to evaluate the bone reactions around immediately loaded implants placed in the posterior region of the lower jaw in the monkey model. METHODS: Six adult Macaca fascicularis monkeys were used in this study. A total of 36 implants were placed after extraction of the second premolars, first and second molars, and complete healing of the sockets. Three control (C) group implants were placed in one quadrant of the lower jaw of each monkey. After a delay of 3 months to allow osseointegration to take place, the implants were loaded for 1 month using temporary resin bridges and later for 2 months using metal splinted crowns. In the contralateral region of the lower jaw, 3 test (T) group implants were placed and loaded immediately with the same sequence as carried out for the C implants. Specimens were examined and evaluated histologically after sacrifice. RESULTS: All of the implants were osseointegrated. Compact, cortical bone in contact with the implant surface without any gaps or connective tissue formation was observed. CONCLUSIONS: It was concluded that immediately loaded, splinted implants can be osseointegrated with a similar hard and soft tissue peri-implant response as delayed-loaded implants in the posterior mandible.