Fracture resistance assessment of endodontically accessed hybrid ceramic crowns repaired with two different protocols

Statement of the Problem: It is frustrating when the patient has recently placed an all ceramic crown and now has symptoms of irreversible pulpitis or necrosis and an endodontic treatment is indicated. Providing endodontic care through all ceramic crowns in situ is a challenge. Endodontic access through the restoration may weaken it and initiate micro cracks that may propagate resulting in failure. The best practice protocol to improve the fracture resistance of endodontically accessed and repaired all ceramic crowns cannot be identified based on the currently available scientific data. In addition, wider variations in repair protocols are worthy of further investigation.
Purpose: The aim of this in vitro study was to measure the fracture resistance of endodontically accessed Vita Enamic crowns repaired with two different protocols (direct composite and
ceramic plug).
Materials and Methods: Fifteen freshly extracted human mandibular molar teeth were used in this study. All teeth were mounted in epoxy resin blocks using a special device (parallelometer). Teeth were randomly divided into three groups of five specimens each according to the type of restoration as follows; Group I: Teeth restored with full coverage CAD/CAM Enamic crowns (control group), Group II: Teeth restored with full coverage CAD/CAM Enamic crowns, endodontically treated and repaired with direct composite, Group III: Teeth restored with full coverage CAD/CAM Enamic crowns, endodontically treated and repaired with CAD/CAM bonded enamic plugs. Teeth were prepared using a special milling machine. Cerec Premium SW 4.4 was used for the fabrication of crowns from hybrid ceramic Enamic blocks. Crowns were cemented using Rely X Ultimate dual-cure resin cement. For groups II and III, an access cavity was made at the center of the occlusal surface using a round-end diamond bur and copious amounts of water spray followed by root canal treatment. A thin layer of flowable composite material was placed at the base of the pulp chamber. For group II; the access cavity was filled with Filtek Supreme nanofilled composite. For group III; the access cavity was scanned then a ceramic plug filling the access cavity was designed using the Cerec Premium software and milled from Vita Enamic blocks. The ceramic plug was then cemented inside the access cavity using Rely X Ultimate resin cement. All the specimens were subjected to thermo mechanical aging in a chewing simulator for 150,000cycles. Fracture resistance was measured using a computer controlled universal testing machine. For each crown, a single static compressive load was applied along the long axis till fracture occurred. The load required to induce failure was recorded in Newton (N).Data were recorded, tabulated and statistically analyzed.
Results: The highest mean±SD values were recorded for group I (2027.64±294.24 N) followed by group III (1784.26±72.15 N) while the lowest mean±SD values were recorded for group II (1494.95±46.95 N). The difference between groups was statistically significant as indicated by ANOVA test (p=0.0017<0.05). Pair-wise Tukey’s post-hoc tests showed non-significant (p>0.05) differences between (group I and group III) and (group II and group III).
Conclusions : 1- The endodontically accessed hybrid ceramic crowns repaired with the novel protocol (ceramic plug) recorded high fracture resistance values. 2- The use of ceramic plug is a feasible alternative to the currently used composite repair protocol.