The Aggressive Shoulder Crown Preparation

Patient: 45 year-old male in excellent health

Chief Complaint: draining pus

Dental History: The patient previously had root canal treatment performed on the maxillary left first molar (#14). A routine radiograph was taken by his general dentist who noted periapical radiolucencies and an associated draining fistula on the buccal attached gingiva

Significant Findings (#14): Clinical examination normal periodontal probing depths with a draining buccal fistula, Periapical radiolucencies were noted over the MB and P roots. A large treaded post had been placed in the palatal canal

Pulp and Periradicular Diagnosis (#14): Previous root filling with an asymptomatic draining chronic periapical abscess

Treatment Prognosis: Good (#14)

Treatment Plan: Nonsurgical Endodontic Retreatment (#14)

Special Considerations of Performed Treatment:
It is not uncommon for teeth to be over-prepared for esthetic ceramic crowns. A deep shoulder preparation will invariably expose one of the mesiobuccal root canal systems on a maxillary molar. In this case, over-preparation in combination with a missed MB2 system likely contributed to the root canal failure.

Many dentists continue to think cores can be placed without aseptic isolation (i.e. no rubber dam). An additional failure vector is established when gutta percha is removed and a post is placed without adequate aseptic isolation. Placement of the core should be considered a key phase of the root canal treatment and performed immediately after filling the root canal system while rubber dam is placed.
The sequence of treatment steps were as follows:

First Treatment Visit (11/16/2020)

1. Removal of the temporary crown revealed the tooth to be over-prepared making rubber dam isolation difficult. Dycal was placed to prevent leakage with saliva and properly wall-off the MB line angle which had a deep shoulder into the MB1 canal system.

2. The post was removed and a previously untreated MB2 canal system was discovered. All previous root filling material was removed with chloroform and the root canal systems cleaned shaped and filled with calcium hydroxide.

3. A Cavit temporary was placed without a spacer (sponge or cotton) to prevent marginal leakage and sepsis. The frustration many dentists have temporizing a tooth between root canal treatment visits is failure of the temporary filling to “coronally seal”. There is no reason to place a spacer and it compromises the seal between visits.

This likely is one of the reason studies are equivocal showing the benefit of one-step versus two-step endodontic treatment. Two-visit root canal treatment especially on retreatment and necrotic cases would likely show enhanced benefits if the access was appropriately sealed without a spacer and if complete cleaning and shaping of all canals was performed before placement of calcium hydroxide. This is rarely practiced and not tradition.

Second Treatment Visit (12/15/2020)

1. The calcium hydroxide was removed with the aid of 90% trichloroacetic, the apical preparation was performed an EndoSequence BCS was placed in all canals due to large irregular, previously over-instrumented root apices.

2. A bonded composite core was placed utilizing the Dycal as a matrix, then the temporary crown was recemented with Cling2 temporary cement. Special care was taken to make sure the MB1 and MB2 canals at the shoulder margin had the orifices aseptically sealed and bonded (2mm deep).

A recall examination is scheduled for one year after treatment completion.

Key Learning Points:

1. It is very important to take time to meticulously seal off an over-prepared crown during root canal treatment.

2. The placement of the core should be performed as part of the root canal treatment and performed with aseptic control of a rubber dam, eliminating current and future coronal leakage.

3. A bioactive material such as EndoSequence BCS is a useful root filling material for ripped and over-enlarged apices. Bioceramics indefinitely release hydroxyl ions and are osteoconductive.