Mechanical evaluation of new injection needles for dental anesthesia.

AIM: In this study Authors want to evaluate the static and dynamic flexural behaviour of innovative injection needles for dental anaesthesia comparing to the traditional needles. METHODS: Four kinds of innovative injection needles (Carpule Free Flow-Heraeus Kulzer), different for length and external diameter, have been evaluated in comparison with the traditional ones (Carpule-Heraeus Kulzer), dimensions being equal except for the internal diameter. Static stiffness tests (10 for each kind of needles, resulting in a totality of 80 tests) and fatigue bending test (10 for each kind of needles, each tested at 3 different bending angles, resulting in a totality of 240 tests) have been conducted following the ISO 9626 norms. The final comparison among the obtained data have been conducted using a one way statistical analysis of variance (ANOVA). RESULTS: After stiffness tests the Carpule Free Flow injection needles and the traditional ones showed the same static behaviour, resulting in statistical comparable values of mean deflection at the maximum load allowed by ISO norms tests, whereas the 0.4 mm external diameter showed a statistically significant difference because the Carpule Free Flow needles achieved lower deflection values. After dynamic bending tests at 20 degrees both needle types showed the same behaviour, whereas at 30 degrees bending the Carpule Free Flow injection needles showed a higher number of breaks comparing to normal type, up to a maximum value of breaks (10 out of 10) for the 0.4 mm external diameter needles. After 50 degrees fatigue bending tests the Carpule Free Flow needles came to the break point after lower number of cycles than the Carpule needles. CONCLUSION: This study pointed out that, among anaesthesia injection needles, the Carpule Free Flow needles not only showed better clinical characteristics but also a mechanical behaviour, both static and dynamic, statistically similar to traditional ones, according to international standards. After fatigue bending higher than 20 degrees, exclusively made in this research in order to simulate critical or extreme conditions, all analysed Carpule Free Flow needles have been broken after a lower number of cycles. It is concluded that it is recommended not to repeatedly bend this kind of needles at more than 90 degrees. At the end of this study it may be suggested that this kind of needles cannot be repeatedly bended at angles more than 90 degrees.

[Pulpal effects of etching in the use of direct attachments]. / Effetti pulpari della mordenzatura nell'utilizzo di attacchi diretti.

Recurring enamel etching was observed to value the effects on pulp response. Four teeth were extracted and analysed by O.M.; no cellular alterations were observed except a slight inflammatory alteration testified by congested vessels and presence of fibroblasts.

Mechanical performance of dental amalgam--composite interfaces.

Composite veneering of amalgam is the most aesthetical solution to extensive direct tooth restoration and is applied with success in specific clinical situations. An in-vitro technique has been used to evaluate the mechanical performance of one amalgam bonded to four different composites. The amalgam-composite interfaces were subjected to tensile stress and shear stress at break tests, using dumb-bell and sandwich specimens in a PC-controlled electronic dynamometer equipped with innovative grips. Mean values were higher for tensile stress than for shear stress. Further studies and clinical experimentation will be necessary to explore the question of long-term reliability.