Some Tubulites asked me about core techniques and impression taking for posterior root filled teeth so I thought I would illustrate these with some clinical examples. I am not viewing this as a scientific publication so will not be providing references but am happy to provide any if I put anything contentious in the text.

I am passionate about endodontics and about how we preserve tooth tissue with our restorations. I consider the following items mandatory for all molar endodontics and restorations.

1) Rubber Dam2) A tight gingival seal around the cavity throughout all endodontic and adhesive

procedures3) High powered magnification with excellent illumination (the ideal is a surgical

microscope)4) Ultrasonics for canal identification and access5) Copious irrigation with Sodium hypochlorite (let’s leave the discussions on

concentration and temperature for another day)6) EDTA solution for smear layer removal and access cavity preparation prior to

bonding (I also use citric acid for this purpose)

I know there are lots more ideal pieces for our armamentarium but let’s leave those for an endodontic discussion on another day. I am firmly of the belief that getting the above conditions right and providing a well-sealed coronal restoration will advance our endodontic success rate far in advance of any alternative rotary file type or cement system ever will.

As I have mentioned previously I view endodontics as a way of delaying the loss of a tooth for as long as possible and I aim to achieve this by a combination of close attention to detail when identifying and negotiating the canal system and by providing as complete a seal as possible with my coronal restoration. Cliff Ruddle says “endodontics is just glide path and access cavity; the rest is just detail”. That is true from an endodontist’s point of view but from the tooth’s point of view it wants a solid coronal seal or all of that work will be undone through micro-leakage and fracture.

For me the crucial stage of any root filling is the initial “investigation stage” when I remove the existing restoration and assess the viability of providing a new restoration. One of the quickest ways of assessing a tooth’s viability is to see if I can isolate it fully with rubber dam. If I can’t isolate it I can’t restore it in its current state. If we take the gum level as “ground floor”, I need that tooth raised up to a 1st or 2nd storey level before I can isolate it. If the cavity ends deep in the basement then this needs resolving before the root canal work can begin. I will use gingival electroquatery and retraction chord to isolate the cavity margin and then use standard total etch adhesive techniques to “raise” the walls of this cavity up to a 2nd storey level so I can isolate it fully and have a tightly sealed access cavity that will not allow any seepage from under the rubber dam.

Fig 1 Impossible to isolate Fig 2 Isolated and well sealed

Once the access cavity is correctly opened and the canal system exposed and identified under these conditions then root canal work is predictable and easily manageable by all GDPs with an interest in this type of work.

Once the root filling is in place it is all about providing ideal bonding conditions to give us a chance of creating an adhesive and reinforcing core that can seal and strengthen the tooth at the same time. It is essential that the GP is cut back to a radicualr level (my prefernce is to aim for an GP finish line at a subosseous level where this is achievable as this reduces the risk of microleakage through furcation canals). We stand no chance of achieving predictable dentine bonding if there is cement or debris lining the cavity walls, this all needs to be removed at this stage. For me once I have cut the GP back I treat the cavity as follows

1) Citric scrub (30% citric acid). EDTA is an acceptable alternative and has been shown to enhance dentine bonding in some studies

2) Air Abrasion3) Total etch technique with 37% phosphoric acid4) Very careful drying technique using paper points and cotton wool pledgets to avoid

dentine descication 5) Optibond Fl (2 bottle system)6) Universal Flo by GC7) Adhesive restorative material of your choice- either direct composite or FRC core

Fig3 Access cavity prior to filling Fig 4 Access cavity after GP filling- note identification of canal system note clean walls ready for bonding

This case presented as an undiagnosed fracture causing symptoms relating to an irreversible pulpitis. The tooth was only very minimally filled suggesting heavy occlussal loading so I chose an internal FRC core and full coverage cast gold overlay.

Fig 5 Case of mid line fracture Fig6 RCT for hyperaemic pulp

Fig 7 Access cavity ready for core Fig 8 FRC core and preparation for cast overlay

I often treat very damaged mouths with extensive periodontal and restorative issues. My aim is usually to keep the teeth functional and infection free for as long as possible but both the patient and I know we are keeping them in a holding pattern until such time as the teeth need removal. In these cases I will often limit the restoration to a direct FRC restoration and forego the use of a cuspal coverage cast overlay. Put simply teeth like these don’t fracture they “wobble” so the extra expense of the cast restoration can be avoided.

Fig 9 advanced bone loss Fig 10 Direct FRC completed as 1 visit procedure

Redoing screw posts in any teeth brings with it that bitter sweet knowledge that the post will come out easily but the root will be a weakened state. A direct adhesive core offers an opportunity to seal and internally reinforce the root although these patients are always warned of the reduced prognosis due to the presence of this type of post. In my opinion there is never a need to place a post of any type into a molar tooth. These teeth are loaded axially (or they should be) where as a post is used to resist lateral forces. There is always enough internal surface to bond to in the access cavity so no extra retention from a post is required.

Fig 11 Screw post and suboptimal root filling Fig 12 retreatment and adhesive core

A re-treatment case like this will usually require an investigation visit at which I will remove the crown first to assess the viability of long term restoration. I realise that this increases the cost of the procedure and acknowledge that it is possible to remove the post through an access cavity but no one wants to find out the tooth was a “dead duck” 12 months down the road; it is much better to find that out in the first 15 minutes of the investigation visit. The investigation visit has a “stand alone” fee that is pre-agreed with the patient and they know will stand if the tooth is found to be unrestorable. If however the tooth is treatable then we continue to the next stage and the money paid is included in the overall cost. This approach allows me to assess many teeth that have been dismissed as unrestorable by previous dentist without exposing me to the financial risk of not having a root filling to charge for at the end of the session. The case below is a good example of such a case.

Fig 13 Pre-op radiograph Fig 14 reasonable coronal tissue height

Fig 15 Finished result Fig 16 Six month review showing good initial healing

Where a cast restoration is required there is no doubt that the best conditions for impression taking are immediately after removal of rubber dam and any retraction chord that has been used for isolation purposes. If I am happy with the prognosis of the root filling I will prepare the core and take the impression at the RCT appointment. (If I have concerns over prognosis I will delay the cast restoration until I have seen signs of apical healing).

If I am redoing an existing crown I will have to work with the margins that exist and will try and refine them to give an ideal shape. Deep down I suspect that all technicians want from us is a clearly defined consistent margin that gives them enough room to work in. My guilty secret is the use of triple trays for single unit cases as they are so quick and easy to use and so well tolerated by patient. I have no great brand loyalty to any silicone impression paste so long as it has a rigid enough set in a reasonable time frame and vaguely palatable taste to the patient (Hunigum Heavy and Light Fast is my current flavour but they all do the job).

Fig 16 clearly defined (if rather generous) margins

Fig 17 Amalgam filling Fig 18 Clinically sound margins of cast restoration (at 5 year review)

As with all of dentistry there are many ways to restore a tooth and for all (or any) of the readers saying what’s wrong with an amalgam filling Nayyar Core- well probably nothing if it has a cast gold overlay over it. I used them for the first 14 years of my career and after making the decision to go amalgam free 7 years ago it is the only occasion when I ever miss it.

Fig 19 Amalgam Nayyar Core and Cast Gold Overlay

I would certainly hate for this to be side tracked in to an amalgam debate but would say that aesthetic overlays all require adequate bonding and we will not get this to any amalgam core present, nor to any glass ionomer core.

In my hands I have enjoyed good success using direct adhesive cores in combination, where appropriate, with cast cuspal coverage overlays. I am sure that this success rests on my ability to see clearly what I am doing under great magnification and illumination in a dry and isolated environment. To enjoy these conditions I need the right “Tools, Time and Training”. All of these cost and this is reflected in the fee. I try to ensure that in my practice “the result justifies the fee; never the fee justifies the result”.

I would welcome any tips or advice in return and will endeavour to answer any of the easier questions!

Ian Kerr

All cases completed by Ian Kerr at StoneRock Dental Care (except for the amalgam Nayyar core case which was completed at a previous practice and reviewed 5 years later in the view shown)