Effect of ferrule height and distribution on the fracture resistance of endodontically treated premolars

Objective

To evaluate the effect of varying ferrule height and distribution on the fatigue resistance and fracture strength of endodontically treated premolars.

Materials and Method

Thirty-two extracted human premolars were endodontically treated and prepared to receive all-ceramic crowns. Teeth were randomly divided into two groups. The occluso-cervical height was reduced to 2 mm and 4 mm for the 1^st and 2^nd groups, respectively. According to the ferrule distribution, samples in each group were randomly divided into two subgroups with inadequate ferrule on 1 or 2 proximal walls, respectively. Coronal tooth structure was built-up to 4 mm using a core build-up material retained by a fiber post. The CEREC system (Sirona) was used to design and mill lithium-disilicate crowns. All posts and crowns were cemented to their respective teeth using self-adhesive universal resin cement. All crowns were subjected to cyclic loading in a universal testing machine (Instron) (20-100N, 100,000 cycles, 20Hz). After fatigue, crowns were loaded to fracture. Fracture load data were analyzed using two-way ANOVA at α = 0.05.

Results

All crowns passed the fatigue testing without any signs of fracture or crack. Two-way ANOVA revealed a statistically significant effect of the number of missing walls (P < 0.05) on the fracture load, but not the ferrule height or the interaction terms. Samples with one missing wall showed higher fracture load in comparison to samples with two missing walls.

Conclusion

The number of missing walls, not the ferrule height, has a significant effect on the fracture load of the lithium-disilicate crowns restoring endodontically treated premolars.

The effect of a modified fluoride toothpaste technique on buccal enamel caries in adults with high caries prevalence: a 2-year clinical trial

OBJECTIVE

To evaluate the preventive effect of a "modified fluoride (F) toothpaste technique" on the incidence and progression of buccal/ lingual enamel caries among Saudi adults with high caries prevalence.

METHOD

Adults were randomly assigned to test and control groups. Test group patients were instructed to use the provided F toothpaste twice a day as follows: 1, use 2cm toothpaste; 2, brush for 2 min; 3, swish the toothpaste slurry around the teeth for about half a minute before spitting it out; and 4, no post-brushing water rinsing and no eating/drinking for 2hr. The patients in the control group (n = 57) were instructed to continue using their regular F toothpaste twice a day without any further instructions. The patients' compliance in the test group was assessed after 2 years.

RESULTS

Of 175 adults, 113 completed the study. The test group (n = 56) had a lower enamel mean caries incidence 0.56 (sd 1.04) than the control group (n = 57), 1.01 (1.00) (p < 0.05), with a preventive fraction of 44%. There was no difference regarding enamel caries progression or arrested caries. The caries incidence in the test group was higher in the subgroup of patients who rinsed with water post-brushing and who only brushed once a day (p < 0.05).

CONCLUSION

The "modified fluoride toothpaste technique", as practised over the 2 years in a Saudi population with high caries prevalence, had a preventive effect on the incidence of buccal/lingual enamel caries but not on the progression.