A new technique to make transparent teeth without decalcifying: Description of the methodology and micro-hardness assessment

Abstract

Diaphanisation and other in vitro endodontic models (i.e., plastic blocks, micro-CT reconstruction, computerised models) do not recreate real root canal working conditions: a more realistic endodontic model is essential for testing endodontic devices and teaching purposes. The aim of this study was to describe a new technique to construct transparent teeth without decalcifying and evaluate the micro-hardness of so treated teeth.

Thirty freshly extracted teeth were randomly divided into three groups as follows: 10 non-treated teeth (4 molars, 3 premolars, 3 incisors; control group – G1), 10 teeth were diaphanised (4 molars, 4 premolars, 2 incisors – G2) and 10 teeth were treated with the new proposed technique (2 molars, 6 premolars, 2 incisors – G3). Vickers hardness tester (MHT-4 and AxioVision microscope, Carl Zeiss, 37030 Gottingen, Germany – load = 50 g, dwell time = 20 s, slope = 5, 50× magnification) was used to determine microhardness (Vickers Hardness Number – VHN). Statistical analysis was performed using the Intercooled Stata 8.0 software (Stata Corporation, College Station, TX, USA).

Only groups 1 and 3 could be tested for hardness because diaphanised teeth were too tender and elastic. Differences in enamel VHN 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 < 0.05); differences in dentine VHN were observed between G1 (mean 74.73; DS = 6.62; range 63.9–88.1) and G3 (mean 64.54; DS = 5.55; range 51.2–72.3) – (p < 0.05).

G3 teeth presented a slightly lower VHN compared to G1, probably due to some little structural differences among groups, and were dramatically harder than the diaphanised teeth. The described technique, thus, can be considered ideal for testing endodontic instruments and for teaching purposes.

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.