Fracture resistance of human root dentin exposed to calcium hydroxide intervisit medication at various time periods: an in vitro study.

The aim of this study was to evaluate the effect of calcium hydroxide on the fracture resistance of human root dentin at different time intervals. After root canal preparation, one hundred single-rooted premolar human teeth were randomly divided into two equal groups. After placement of calcium hydroxide paste within the canal, one group of teeth was divided into 5 subgroups and incubated for a period of 1 week or 1, 3, 6, or 12 months at 37°C and 100% humidity. The second group of teeth was also divided into 5 subgroups and incubated under the same conditions without placement of calcium hydroxide paste. After mounting the teeth in a Zwick test machine, the force required to break each tooth was determined. Data analysis was performed using the one- and two-way analysis of variance tests. The results demonstrated that the mean force needed to cause fracture differed significantly between the two groups during the first, third and sixth months of incubation (P = 0.001, P < 0.001 and P = 0.035, respectively), and the amount of force necessary for fracture was greater in the control group. Therefore, it would appear from this study that using calcium hydroxide as a long-term intracanal dressing showed a significant decrease in peak load at fracture when compared with the control groups at the end of the first, third and sixth months of treatment and would suggest that using Ca(OH)2 for periods longer than 1 month should be used with caution.

Change in elastic modulus of bovine dentine with exposure to a calcium hydroxide paste.

OBJECTIVE: To determine the effect of calcium hydroxide [Ca(OH)(2)] paste exposure on the elastic modulus of bovine dentine. METHODS: Dentine sections (4 mm x 4 mm x 1 mm) were obtained from freshly extracted bovine incisors and placed in dishes containing a 1-mm deep layer of Ca(OH)(2) paste or physiological saline as a control. An ultrasonic device was used to measure the sonic velocities of the longitudinal and shear waves, and the elastic modulus was calculated. Data were examined by analysis of variance followed by the Tukey H.S.D. test in order to compare different storage times. RESULTS: Exposure to Ca(OH)(2) paste significantly increased the mean elastic modulus of the dentine from 16.3 to 22.1 GPa. By contrast, the elastic modulus of the control dentine, which was exposed to physiological saline, remained constant. CONCLUSION: These results demonstrate that exposure to Ca(OH)(2) paste increases the elastic modulus of dentine, thereby making it more prone to fracture.

The Effect of Long-term Dressing with Calcium Hydroxide on the Fracture Susceptibility of Teeth.

INTRODUCTION: Calcium hydroxide has been widely used to treat immature teeth to achieve periodontal healing and to promote the formation of an apical barrier. However, retrospective clinical studies have shown a high incidence of cervical root fractures with long-term calcium hydroxide dressing. The alkalinity of calcium hydroxide has been suggested to weaken the root. In vitro studies using ovine teeth show conflicting results on fracture strength of dentine, although different commercial products may have influenced the results. The purpose of this study was to investigate the effects of 2 commercial products used in prior studies (Calasept Plus and UltraCal XS), as well as a new product (Calmix) that uses a nonaqueous vehicle that allows for a higher pH, on the fracture strength of dentine over time. METHODS: A total of 330 lamb incisor teeth were collected and the canals prepared so that 3 commercial calcium hydroxide products as well as a positive control of pure calcium hydroxide slurry that filled the root canal from the open apex and a negative control of saline was tested. The teeth were loaded until fracture with a universal testing machine at time points 0, 3, 6, and 9 months and the force to fracture was calculated. The data were analyzed with Friedman analysis of variance and Mann-Whitney t tests. RESULTS: No statistical differences were observed between the different calcium hydroxide products and the negative controls. CONCLUSIONS: Thin and fragile roots could be the cause of fracture rather than the calcium hydroxide dressing.

Dental abnormalities in rats after a single large dose of cyclophosphamide.

Delayed drug-related mortality in rats treated with a single high dose (75 mg/kg) of cyclophosphamide complicated experiments using this drug treatment. We observed that this delayed mortality was due to dental abnormalities including broken teeth, absent teeth, extra long teeth, and/or supernumerary teeth. These dental abnormalities developed about 140 days after treatment and, if left untreated, interfered with eating. Eventually, the untreated rats starved. Clipping their long teeth and feeding the rats powdered chow eliminated the deaths. Researchers should be aware that high doses of cyclophosphamide may result in dental abnormalities several months after the treatment.

A simple model for enamel fracture from margin cracks.

We present results of in situ fracture tests on extracted human molar teeth showing failure by margin cracking. The teeth are mounted into an epoxy base and loaded with a rod indenter capped with a Teflon insert, as representative of food modulus. In situ observations of cracks extending longitudinally upward from the cervical margins are recorded in real time with a video camera. The cracks appear above some threshold and grow steadily within the enamel coat toward the occlusal surface in a configuration reminiscent of channel-like cracks in brittle films. Substantially higher loading is required to delaminate the enamel from the dentin, attesting to the resilience of the tooth structure. A simplistic fracture mechanics analysis is applied to determine the critical load relation for traversal of the margin crack along the full length of the side wall. The capacity of any given tooth to resist failure by margin cracking is predicted to increase with greater enamel thickness and cuspal radius. Implications in relation to dentistry and evolutionary biology are briefly considered.

The effect of calcium hydroxide root filling on dentin fracture strength.

This in vitro study measured the effect of calcium hydroxide root filling on the microtensile fracture strength (MTFS) of teeth. A total of 40 extracted human disease-free permanent maxillary incisors were hand and rotary instrumented and vertically compacted with United States Pharmacopeia (USP) calcium hydroxide. The teeth were stored in a moist environment for 7, 28, and 84 days. As a control group, 10 teeth were vertically compacted with gutta percha and sealer. The MTFS of the teeth was measured (Mpa) using an Instron machine. Data were assessed statistically using an unpaired t-test (P value). The intracanal placement of calcium hydroxide weakened the MTFS of teeth by 13.9 Mpa per 77 days: an average of 0.157 MPa day-1. Between 7 and 84 days, the MTFS of the dentin was reduced by 43.9%. This difference was statistically significant (P < 0.05). A statistical difference (P < 0.05) was observed between the mean MTFS of the calcium hydroxide-filled dentin between 7 days (45.7 MPa) and 28 days (35.6 MPa) and also between 7 and 84 days (31.8 MPa). There was also a significant difference (P < 0.05) between the MTFS of the calcium hydroxide-filled dentin after 84 days (31.8 MPa) and the gutta percha-filled dentin (41.3 MPa) when used as a control root filling material. The weakening of the dentin by 23-43.9% following root canal filling with calcium hydroxide provides compelling evidence to re-evaluate the daily usage of this material in endodontic therapy.