MethodsA new technique to make transparent teeth without decalcifying: Description of the methodology and micro-hardness assessment
Introduction
New endodontic devices (i.e., ultrasonic instruments, irrigation systems, and Ni-Ti rotary instruments) need to be tested on experimental models, which should have three major characteristics: (1) the models should be transparent to observe the devices while working; (2) the models should be of the same hardness of a natural tooth to test the real device efficacy and safety; and (3) the models should resemble the complex nature of the endodontic system as much as possible to validate the device efficacy in a complex environment. Such a model would be useful for both research and teaching purposes (Dummer et al., 1991, Nassri et al., 2008).
For many years, diaphanisation procedures have been employed to make teeth transparent. Diaphanised teeth are useful to evaluate root canal anatomy or the filling of root canal systems; however, these methods require massive decalcification of the tooth, which considerably alter the chemical and physical characteristics of hard tissues, softening them and giving the tooth a rubber-like consistency. Such a technique makes the tooth transparent, which is soft/elastic and cannot be used to test new endodontic devices while working within the root canal (Sidow et al., 2000, Shivapathasundharam and Berti, 2000, Yamamoto et al., 2001, Venturi et al., 2003).
Many alternative techniques and models have been developed and used to evaluate endodontic instruments, some of which attempt to recreate tooth anatomy (models consisting of transparent plastic) (Dummer et al., 1991, Bedford-Roberts et al., 1997), while others evaluate the effect of endodontic instruments via complex and expensive techniques (micro-CT reconstruction or computerised models) (Necchi et al., 2008, Cheung and Cheung, 2008, Lee et al., 2014); however, plastic models, virtual models, and micro-CT reconstructions do not recreate the working conditions within a real root canal.
The aim of the present study was to describe a new histological procedure to make the dentine transparent without decalcifying it and without depriving it of its inorganic components and to evaluate the effect of this technique on hard tissues (enamel and dentine) micro-hardness. The study hypothesis was that mechanical characteristics (i.e., micro-hardness) of teeth treated with the new histological procedure should be comparable with that of non-treated teeth, since the new produce does not affect the tooth inorganic component.
Section snippets
Specimen preparation
Thirty teeth, freshly extracted for orthodontic or periodontal reasons (Table 1), were used for this study. After extraction, the teeth were cleaned with gauze and physiological solution and stored in a solution of 98% glycerol and 2% formalin until the start of the experiment. All patients signed an informed consent agreement. Teeth were randomly divided into the three following groups by a block randomisation sequence: Group 1 (G1), 10 natural non-treated teeth as the control group; Group 2
Results
Sample characteristics (age, tooth position and reason for extraction) are reported in Table 1. Only group G1 and G3 could be tested for hardness because the diaphanised samples were so tender and elastic that the indentation did not leave a reliable and, in certain cases, detectable sign, even when the Vickers diamond indenter was loaded with 5 g.
Differences in enamel VHI were observed between G1 (mean 304.29; DS = 10.44; range 283–321) and G3 (mean 318.51; DS = 14.36; range 295.5–339.2) – (p <
Discussion
Diaphanised teeth have been used for many years to study and teach the complexity of the endodontium (Hess et al., 1925), but even when the real anatomy is conserved, their consistency is far from that of real dentine and enamel: even if diaphanisation was used mainly to study morphology, some studies employed this technique to study dye and bacterial leakage of root filling and restorative materials, concluding that diaphanisation is a useful technique, but it cannot be considered as sensitive
Acknowledgements
We would like to thank Prof. Mariangela Aita, M.D., Ph.D., for her helpful suggestions in preparing and revising the manuscript.
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