09 May 2023

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Traditional versus digital post and core fabrication: Which is more accurate?

Lara Figini

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The conventional method for making an endocanal post and its abutment consists in taking the traditional impression with special pastes and using wax or acrylic resin to duplicate the root canal in its anatomy and create an "analog" post which will later be transformed into dental alloy after casting using the lost wax technique.

This technique has been considered the gold standard for constructing posts and cores for decades as it allows clinicians to obtain a framework that best adapts to the shape of the canal and provides good retention and support for the crowns. However, one of its shortcomings is that it creates some discrepancies which eventually can lead to loss of retention and catastrophic radical fracture.

Another way to make a post and abutment is to use a prefabricated metal post or a fiber post, reducing the number of clinical and laboratory steps. However, using a fiber post introduces other issues, such as the difficulty of achieving optimal adhesion and lack of strength. Recently, new methods have been proposed for making posts and abutments using digital technology. To date, few studies have investigated the accuracy of digitally fabricated pins by comparing them with those made with conventional techniques.

Materials and methods

In an in vitro study, published in the Journal of Prosthodontics, the authors compared the accuracy of root canal posts and the respective abutments created with three different processing techniques:

• conventional direct,
• with mechanical milling, and
• with three-dimensional (3D) printing.

Thirteen extracted single-root central incisors were selected for the study.

Root canal treatment and tooth preparation for the crown were performed on all teeth. The preparation of the 11 mm post housing was performed for a predetermined width and length standardized for all specimens.

Root canal impressions were made on all teeth using a polyvinylsiloxane impression material. Each impression was then scanned three-dimensionally using an extra-oral laboratory scanner. The scanned impressions were then processed using 3Shape CAD software. The digital designs of the posts and cores were used to fabricate 3D printed and milled posts and resin models for the cores.

The same teeth were used to fabricate the post and abutment with the conventional technique (direct duplication of the root canal with a resin model). All posts were then scanned before being cast using a metal-based alloy.

The post and abutments were scanned in several stages for digital volume measurement using Geomagic Control software to determine accuracy.

Results

These three core and post fabrication techniques have shown different results in the various fabrication steps. The accuracy of the 3D printed resin model (26.89±11.09 mm3) was found to be lower than the milled resin model (28.20±11.41 mm3, p = 0.0002).

However, the dimensional stability of the 3D printed resin model before and after casting (0.56±0.95 mm3) was found to be higher than the milled resin model (0.79±0.89 mm3) and direct resin (2.51±1.38 mm3, p = 0.00002).

All three techniques showed a significant volume reduction after adjustment (p = 0.0002).

In the final phase, the ground metal post and the respective abutment fabricated with the three different techniques did not show statistically significant differences in terms of accuracy (p = 0.15).

Conclusions

From the data of this study, it can be concluded that the digitally fabricated posts and abutments have the same degree of accuracy as those fabricated using the conventional technique.

For more information: "The accuracy of post and core fabricated with digital technology."