It has been classically taught for decades in dental schools – sometimes dogmatically – that whenever a previously crowned tooth requires endodontic therapy that the appropriate restorative management is to remove the crown, to place a new core build-up after removing any previously replaced core materials to ensure the removal of caries, and then to re-prepare the tooth for a new crown.
In fact, this is still a very reasonable approach in many situations (a crown with questionable marginal integrity, esthetic compromise, fractured ceramic, poor function, questionable core visible through the access opening, etc.).
However, in light of what is now understood regarding the benefits of minimally invasive dentistry – and when applying ethical decision-making principles to multiple prescription dentistry – we should evaluate the possibility of adequately restoring endodontic access openings through similar techniques used for restoring screw-retained implant restoration access openings, especially when the existing crown is acceptable esthetically, functionally and physiologically.
Filling the void for easy access
Regardless of whether the access opening is for an implant screw or for endodontic access, a void needs to be created by some type of interim space filler if necessary. For implants, this filler protects the screw to enable future access. In endodontic therapy, the filler is used to facilitate subsequent access to the root canal orifices for medicaments and after obturation prior to separate definitive restorative management.
Various materials have been used for this purpose; most commonly, cotton pledgets have been used. In recent years, polytetrafluoroethylene (PTFE) tape, like common plumber’s tape, has become a common space filler in implant restorations.
Condensed into an access chamber, the tape provides a reasonably stable base over which to place a composite resin restoration that is not under significant occlusal function. It can easily be removed when necessary with a pigtail explorer and/or sharp spoon excavator. Since the interim restoration placed over the filler is what actually seals the system between therapeutic visits, the space filler serves no particular sealing or antibacterial purpose but rather is used to facilitate future access of the screw or root canal.
Protecting the root canal system between obturation and definitive restoration
Some endodontists place a glass ionomer seal over completed endodontic orifices, which prevents coronal microleakage of the obturation even if the interim restoration and filler dislodges.ii
When the endodontist places a glass ionomer seal over a freshly obturated endodontic chamber, PTFE provides an excellent interim filler that provides stability for the 3M Cavit interim restorative material. It is easy to remove since it tends not to stick to unset glass ionomer like cotton, which minimizes overplacement of interim restorative material that may require enlargement of the access opening and unnecessary tooth structure removal for complete removal of the Cavit.
Managing the pulp chamber through an existing crown
Assuming the existing crown on a tooth that has been treated with endodontics needs to be repaired because of one of the previously mentioned reasons, the interim access restoration and filler is removed under appropriate isolation, and the pulp chamber is evaluated for any residual caries preferably under magnification.
A caries detecting aid like Sable Seek by Ultradent Products can be valuable to identify caries and even vertical fractures that may compromise the prognosis of the tooth. At this time of reassessment after evaluating the chamber, there are several options for restoring the tooth that should be given ethical consideration:
- Remove the existing crown and core material and restore with either a new core and crown or a post/core and crown
- Restore the access opening only with a core
- Extract the tooth if deemed non-restorable due to pulpal floor fracture or other reasons
The choice of whether the glass ionomer seal is removed, if present, or left intact depends on the chosen restoration. For example, if there is sufficient reason to replace the existing crown, a post/core may need to be considered, in which case the glass ionomer seal would obviously need to be removed.
If, however, a direct restoration can be placed, then the question should be considered whether bonding to the existing pulp chamber or creating additional retentive features – such as creating an extension in to the root canal system with core material – would provide the best prognosis for the tooth and restoration complex. If no additional features are necessary, then the glass ionomer seal likely should be maintained to minimize the chance of contaminating the canal system.
Once the access chamber is refined for its appropriate restoration, the core build-up procedures may begin. Due to the need to bond to a variety of surfaces (deep dentin, possibly existing and mature core materials that may be metal or composite resin of either dual-cure or light-cured varieties, possibly metal crown substructure, a variety of ceramics, etc.) at depths deeper than the 2 mm that curing lights can reach vertically, a multi-use, chemically-cured or dual-cured resin (such as Amalgambond Plus by Parkelliii or 3M’s Scotchbond Universal with dual-cure activatoriv,respectively) should be used.
Etching should be based on the substance being etched. For this reason, it is advisable to build the restoration in phases: up to the apical junction of occlusal ceramic and then a second phase involving etching, silanating and bonding the internal walls of the ceramic access opening.
During the first phase of the restoration, an appropriate etchant for the bonding agent used is applied and rinsed (phosphoric acid 37% for typical resin bonding agents). This cleans older restorative materials and etches dentin for bonding.
Next, the dual-cured or chemically cured bonding agent is applied and allowed to cure, being cautious to avoid getting bonding agent on the occlusal porcelain access walls. A dual-cured core build-up material is then used to fill the chamber up to the apical aspect of the porcelain access and cured. The second phase of the endodontic access restoration is essentially the same as restoring an implant screw access opening.
Restoring the access opening
Once the foundation of the access opening has been established either with dual-cured resin in an endodontically treated tooth or with PTFE tape in a screw-retained implant restoration, the restoration of the access opening in both situations is the same. Under appropriate and adequate isolation to protect the tissues and prevent bonding contamination, the ceramic walls are air abraded with aluminum oxide and rinsed thoroughly.
Classically, hydrofluoric acid is carefully used to etch the internal walls to be bonded for 20 seconds (lithium disilicate) or 60 seconds (feldspathic porcelain) and then neutralized with a solution of sodium bicarbonate or a product like Ultradent's EtchArrest before thoroughly rinsing the access opening under high-speed evacuation.
Alternatively, one of several other products designed to prepare porcelain can be used, as long as you carefully follow the manufacturer’s instructions. Due to the unpredictable nature of bonding to zirconia, the access opening walls of an implant restoration can be glazed with feldspathic porcelain that can be predictably etched and bonded.
After adequate etching, which should leave the bonding surface frosty in appearance, a coupling agent like silane or a porcelain coupler containing silane is applied and dried after one minute. This is because water formation is a byproduct of silanation, which can compromise resin bonds to ceramic.
Incidentally, the inevitable overflow of these ceramic treatments also prepares the underlying resin foundation in the endodontically treated tooth for bonding of light-cure resin to dual-cure resin. Therefore, a light-cure resin bonding agent of choice may be used next over all surfaces to be bonded and cured appropriately. The silanation step may be skipped if the bonding agent of choice is Scotchbond Universal or a bonding agent containing silane and designed for bonding to ceramics.
Restoration of the occlusal surface is completed, finished and polished according to standard techniques. Of course, detail may or may not be paid to shade matching to the surrounding restoration. However, consideration should be given to the ease of future differentiation between surrounding porcelain and access restorative resin, which can be facilitated by using an off-color shade in non-esthetic areas with the patient's consent.
Alternatively, amalgam may be used to provide a simplified and durable core for endodontically treated teeth and over PTFE fillers in screw-retained implant restorations, but that is material for an entirely separate discussion ...
Restored and finished access opening can be matched closely to the surrounding ceramic in esthetic areas or off-color for easy identification. In the photograph above, a highly translucent material was used to enable deeper light curing and to make the access opening more recognizable since it is not in an esthetic area.
Access opening restoration steps
- Create a void for easy future access with PTFE tape or cotton
- Create a separate core build-up for endodontically treated teeth with a dual cure resin system
- Air abrade the ceramic walls of the access opening with aluminum oxide
- Etch the ceramic walls of the access opening with hydrofluoric acid and rinse thoroughly
- Silanate, apply bonding agent and cure (one-step or multi-step bonding system, per clinician preference)
- Restore with light-cure composite resin
- Finish and polish using standard techniques
- Monitor seal integrity indefinitely
Kevin D. Huff, D.D.S., M.A.G.D., is a diplomate of the American Board of Orofacial Pain. He is a member of Spear Visiting Faculty, a moderator on the Spear Talk online forum and a contributor to Spear Digest.
i K. Huff, C. Farah, M. Huff. Ethical Decision Making for Multiple Prescription Dentistry. General Dentistry. September/October, 2008. 538-547.
ii Rajakumar Vijay, R Indira. Effect of glass-ionomer cement as an intra-canal barrier in post space prepared teeth: An in vitro study. J Conserv Dent. 2009 Apr-Jun; 12(2): 65–68.
iii Hasegawa T, Retief DH, Russell CM, Denys FR. A laboratory study of the Amalgambond Adhesive System. Am J Dent. 1992 Aug;5(4):181-6. PubMed PMID: 1290605.