The root to crown concept in action
Peet J van der Vyver, Greg Flint and Martin Vorster present a pictorial guide to combining single file preparation systems with CAD/CAM workflows.
Indirect restorations are the restorative method of choice for most endodontically treated teeth that have lost substantial amounts of tooth structure. A core build-up with or without post placement may be required to supplement retention and resistance form.
Today, it is hard to envisage the laboratory fabrication of an all-ceramic restoration without the use of any CAD/CAM technology. The introduction of optical intraoral scanners allows for a complete digital workflow between dentist and laboratory.
A key benefit of digital impressions is that the scanned preparation can be immediately evaluated on the computer monitor. This permits any inadequacies to be corrected immediately. Digital acquisition also eliminates numerous manual processing steps in the dental practice: the selection of the impression trays; the mixing of the impression materials; waiting for the impression material to set; and the production of a plaster model, and registering a bite.
Fewer treatment and processing steps result in fewer sources of error and a more predictable outcome of the final result.
This article illustrates the workflow of a clinical case report of a maxillary premolar that required root canal treatment. As well as core build-up and placement of a new porcelain crown, using the latest materials and techniques.
Presentation and root canal treatment
A 45-year-old female patient presented with discomfort on her maxillary left first premolar. It had previously been restored with a lithium disilicate crown (Figure 1a). After removal of the original crown, extensive decay of the remaining tooth structure was evident (Figure 1b).
The decay was removed and the pulp exposed (Figure 1c), before a temporary crown was fabricated using a temporary crown and bridge material (Integrity, Dentsply Sirona) and temporarily cemented.
The temporary crown was accessed and an emergency root canal treatment was done. Length determination was determined using a Propex Pixi electronic apex locator (Dentsply Sirona) (Figure 2b) and confirmed radiographically (Figure 2c).
At a follow-up visit, a micro glide path was prepared with a size 10 K-File (Figure 3a) in the buccal and palatal root canal systems before the glide paths were expanded with a reciprocating Waveone Gold Glider instrument.
Root canal preparation was completed with a Primary Waveone Gold file before two primary Waveone Gold gutta percha points (Figure 3c) were used to confirm the cone fit radiographically.
After following a standard irrigation protocol, the two canals were obturated with the Primary Waveone Gold gutta percha points, AH Plus cement and the Calamus dual obturation system.
A post space was prepared in the palatal root canal. The access cavity and post canal space were cleaned with air abrasion using the bicarbonate soda in the Aquacare abrasion unit (Velopex). The canals and the access cavity were simultaneously etched with 36% phosphoric acid, before a mixture of Dentsply Sirona’s Prime & Bond Universal adhesive (Figure 4a) and self cure activator (Figure 4b) was applied according to the manufacturer’s instructions.
A fibre post (X-post no.2, Dentsply Sirona) (Figure 4c) was cemented using Core-X flow dual-cure core build-up material (Figure 4d), while the same material was used to build up the core inside the temporary crown.
Figure 5a shows a periapical radiograph of the root canal treatment after obturation and core build-up. The temporary crown was removed – Figure 5b illustrates the clinical result of the core build-up.
The margins of the crown preparations were improved by using diamond coated ultrasonic tips (Komet Dental). This was driven by an ultrasonic scaler before retraction cord was packed for gingival retraction (Figure 6a).
A digital impression was made using the Omnicam introral scanner on the Sirona Connect unit (Dentsply Sirona) of the preparation, antagonist and bite registration (Figure 6b). The temporary crown was modified and cemented with a non-eugenol temporary cement.
Sirona Connect software computed a virtual 3D model. The preparation margin was drawn in using the automatic margin detector (Figure 7a) before it was electronically submitted to the dental laboratory.
The biogeneric software then created a patient-specific restoration, with precise morphology of the restoration (Figure 7b).
The dental technician then made corrections to the proximal and occlusal contact points. In the milling preview, the position of the restoration within the ceramic block was viewed before the milling unit was activated to initiate the machining process (Figure 7c)
An Inlab MC X5 milling and grinding unit (Dentsply Sirona) (Figure 8a) was used to grind the crown from a shade A2 lithium disilicate block, before the laboratory completed the crystallisation firing cycle, polishing, staining and glazing stages (Figure 8b).
At the cementation appointment, the temporary crown was removed. The tooth preparation was cleaned with a slurry of pumice and water to remove any remnants of temporary cement.
The internal surface of the crown was etched with 9.5% hydrofluoric acid for 20 seconds, rinsed with water and air dried. A generous amount of silane coupling agent was applied to the etched internal surface of the crown. It was left undisturbed for 30 seconds before it was air-dried for 15 seconds.
The enamel and dentine of the tooth preparation was etched with 36% phosphoric acid for 15 seconds before it was rinsed with water and lightly air-dried. Prime & Bond Universal adhesive was applied to the etched tooth preparation and the etched and silanated internal surface of the crown before the solvent was evaporated using a light air stream from the three-in-one syringe.
Shade A2 of Calibra Ceram adhesive resin cement was dispensed into the crown before it was seated onto the tooth preparation.
The margins were light-cured for five seconds. Then, the excess cement removed before all the exposed margins were light-cured for 20 seconds.
The final, highly aesthetic, bonded crown demonstrated good contact points, anatomic contour and excellent marginal adaptation (Figures 9a and 9b).
The use of the Waveone Gold glider, a single reciprocating glide path instrument to expand the glide path, allowed for easy root canal preparation with the reciprocating Waveone Gold Primary file
Core build-up was achieved by using X-Post in combination with the Core-X flow dual-cure core build-up material. Because the Core-X flow dual-cure core build-up material can be used for post cementation and core build-up at the same time, it simplifies the procedure and saves valuable clinical time
Intraoral scanners allow clinicians to obtain very accurate digital impressions that can be sent to the laboratory to manufacture and to characterise the final shape and form to obtain a high level of aesthetics.
Reprinted with permission by International Dentistry – African Edition.
Van der Vyver PJ, Flint G and Vorster M (2019) A pictorial essay illustrating the root to crown concept using a single-file preparation system and CAD/CAM technology. Int Dent Afr Ed 9(3): 26-30.