An evaluation of localized debonding between fibre post and root canal wall by finite element simulation

AIM

To investigate the effect of localized bonding defects between fibre post and root canal wall on the stress distribution in the radicular dentine.

METHODOLOGY

A tooth restored with a fibre post together with the alveolar bone were axisymmetrically modelled. A total of four models with localized debonding at the post to canal wall interface in different locations were analysed: Model A: perfect bonding layer over the entire interface; Model B: debonding at the cervical 1/3 of the interface; Model C: debonding at the mid 1/3; and Model D: debonding at the apical 1/3. A tooth restored without using a post was also included as the control (Model E). A load of 50 N was applied to the top of the full veneer cast crown at angles of 0, 15, 30, and 45 degrees with the tooth's longitudinal axis. The stress distribution across the fibre post and root dentine was compared.

RESULTS

Higher stresses were generated in the radicular dentine as a function of the load angle. The differences in the stress distribution were negligible between the four models and virtually the same as that for model E (control).

CONCLUSIONS

In this simulation, localized debonding at the fibre post to root canal wall interface, regardless of its location along the post, had little effect on the stress distribution in the root dentine.

Stimulation of alkaline phosphatase activity by ascorbic acid and suppression by 1,25-dihydroxycholecalciferol in rabbit craniofacial chondrocytes in culture

To clarify the role of vitamins D and C in chondrocyte hypertrophy of craniofacial cartilage, we have studied cultured chondrocytes from rabbit mandibular condylar cartilage (MCC), sphenooccipital synchondrosis (SOS) and nasal septal cartilage (NSC) under conditions in which these cells mature into hypertrophic chondrocytes. In cultures of MCC- and SOS-chondrocytes, alkaline phosphatase (ALPase) activity started to increase on day 9 at confluence and the cessation of cell division, and reached a maximum on day 18. The degree of the increase of ALPase activity on day 18 was higher in MCC-chondrocytes than in SOS-chondrocytes. ALPase activity was very low level in NSC- and CGC-chondrocytes. Ascorbic acid induced a marked increase in ALPase activity in MCC-, SOS-, NSC- and CGC-chondrocytes. The ALPase activities in MCC- and SOS-chondrocytes with 50 micrograms/ml ascorbic acid were 2.5-times those in its absence. Those in NSC- and CGC-chondrocytes were 10 times and 20 times, respectively. When chondrocytes were cultured with 10% charcoal-treated serum, ALPase activity decreased less than that in cultures with 10% normal serum in MCC-, SOS-, NSC- and CGC-chondrocytes. Treatment of 1,25-(OH)2D3 for 9 days from days 4 to 13 in MCC-chondrocytes and for 14 days from days 4 to 18 in SOS-, NSC- and CGC-chondrocytes inhibited ALPase activity dose-dependently at the concentrations of 10(-12) M to 10(-8) M in MCC- chondrocytes, 10(-10) M to 10(-8) M in SOS- and CGC-chondrocytes, 10(-11) M to 10(-9) M in NSC-chondrocytes. These findings suggest that 1,25-(OH)2D3 and ascorbic acid may be involved in the control of cartilage growth and terminal differentiation.

[Individual indirect bonding technique (IIBT) using set-up model]

There has been much progress in Edgewise Appliance since E.H. Angle. One of the most important procedures in edgewise appliance is correct bracket position. Not only conventional edgewise appliance but also straight wire appliance & lingual appliance cannot be used more effectively unless the bracket position is accurate. Improper bracket positioning may reveal much problems during treatment, especially in finishing state. It may require either rebonding after the removal of the malpositioned bracket or the greater number of arch wire and the more complex wire bending, causing much difficulty in performing effective treatments. This made me invent Individual Indirect Bonding Technique with the use of multi-purpose set-up model in order to determine a correct and objective bracket position according to individual patients. This technique is more accurate than former indirect bonding techniques in bracket positioning, because it decides the bracket position on a set-up model which has produced to have the occlusal relationship the clinician desired. This technique is especially effective in straight wire appliance and lingual appliance in which the correct bracket positioning is indispensible.