Effect of different endodontic access preparations on the biomechanical behavior of lithium disilicate and resin nanoceramic onlay restorations: An in vitro and 3D finite element analysis study

STATEMENT OF PROBLEM

The effect of different sizes of endodontic access preparations on the performance of lithium disilicate glass-ceramic and resin nanoceramic onlay restorations is unclear.

PURPOSE

The purpose of this in vitro and 3D finite element analysis study was to assess the effect of a conservative endodontic access cavity and a traditional endodontic access cavity on the fracture resistance and stress distribution of lithium disilicate glass-ceramic and resin nanoceramic onlays.

MATERIAL AND METHODS

Sixty caries-free human mandibular molars were anatomically prepared for onlays and divided into 6 groups. After restoration with a lithium disilicate glass-ceramic (N=30) or resin nanoceramic (N=30), each material was further divided into traditional or conservative endodontic access cavity or intact tooth groups. After endodontic therapy and thermocycling, all specimens were submitted to a cycle fatigue test and then loaded until fracture. Failure type and location after debonding or fracture were classified and recorded. Furthermore, stress distribution in the 6 models was analyzed by using a finite element analysis software program. The data were compared by using a 2-way ANOVA test and the Tukey post hoc test (α=.05). The Weibull modulus and Weibull failure probabilities were also estimated for each group.

RESULTS

The lithium disilicate glass-ceramic onlays had lower fracture resistance values than the resin nanoceramic onlays in both the traditional and conservative endodontic access cavity groups (P<.05). The fracture resistance of the 2 materials for onlays with endodontic access was significantly lower than that for the intact restorations (P<.05). No significant difference was found between the fracture resistance of Lava Ultimate restorations with traditional endodontic access and conservative endodontic access, while the fracture resistance of EMAX restorations with traditional endodontic access was significantly lower than that of restorations with conservative endodontic access (P<.05). A higher percentage of irreparable fractures was found in the 3 resin nanoceramic restoration groups. The von Mises stresses were higher in the lithium disilicate glass-ceramic restorations than in the resin nanoceramic restorations with the same access cavities. The von Mises stresses in the tooth structure were higher with the resin nanoceramic restorations than with the lithium disilicate glass-ceramic restorations with the same access cavities.

CONCLUSIONS

An endodontic access cavity had more influence on the lithium disilicate glass-ceramic onlays than on the resin nanoceramic onlays, and a traditional endodontic access cavity significantly decreased the fracture resistance of lithium disilicate glass-ceramic onlays.

Fracture Resistance of Repaired 5Y-PSZ Zirconia Crowns after Endodontic Access

This study analyzed the fracture load before and after a chewing simulation of zirconia crowns that were trepanned and repaired using composite resin. Overall, 3 groups with 15 5Y-PSZ crowns in each group were tested. For group A, the fracture load of the unmodified crowns was evaluated. For group B, the crowns were trepanned and repaired using composite resin, also followed by a fracture test. For group C, crowns were prepared like in group B but received thermomechanical cycling before the final fracture tests. Furthermore, scanning electron microscopy (SEM) and X-ray microscopy (XRM) analysis were performed for group C. The mean fracture loads and standard deviation were 2260 N ± 410 N (group A), 1720 N ± 380 N (group B), and 1540 N ± 280 N (group C). Tukey-Kramer multiple comparisons showed a significant difference between groups A and B (p < 0.01) and groups A and C (p < 0.01). After ageing, surface fissures were detected via SEM, but no cracks that reached from the occlusal to the inner side of the crown were detected via XRM. Within the limitations of this study, it can be stated that trepanned and composite-repaired 5Y-PSZ crowns show lower fracture loads than 5Y-PSZ crowns without trepanation.

Outcome of Endodontic Treatment through Existing Full Coverage Restorations: An Endodontic Practice Case Series

INTRODUCTION

This case series assessed the outcome of nonsurgical endodontic treatment completed through retained full coverage restorations (FCRs) in a board-certified endodontist private practice. The number of cases completed by the first author was 153.

METHODS

All cases were performed following a standardized protocol for treatment and restoration depending on the type of FCR. Number of cases that showed up for 2- to 4-year follow-up was 127, with 83% recall rate. The age range of patients was 33-95 years, with mean age of 54.734 years. The mean recall time was 2.448 years. FCRs and their distribution were as follows: 4 anterior teeth, 14 premolars, and 109 molars. There were 103 nonsurgical root canal treatments and 24 retreatments. Patients who presented for recall had 74 porcelain fused to metal crowns, 17 zirconia crowns, 15 abutments of porcelain fused to metal bridges, 14 lithium disilicate crowns, 5 gold crowns, 1 full metal crown, and 1 gold onlay.

RESULTS

There were no endodontically related failures. Six cases failed; 3 were due to vertical root fractures, 1 was due to horizontal root fracture, and 2 were due to extensive recurrent caries causing restorative failure. The percentage of healed cases following the American Association of Endodontists outcome criteria adopted in 2004 with intact retained FCR was 95.3%.

CONCLUSIONS

The results suggest predictable favorable outcomes for nonsurgical endodontic treatment through FCR following the proposed protocol for diagnosis, treatment, and restoration.

Fracture strength of zirconia and lithium disilicate restorations following endodontic access

OBJECTIVES

To compare the fracture load of zirconia and lithium disilicate crowns prepared with endodontic access with fine and coarse diamond instruments.

MATERIALS AND METHODS

0.8 mm (3Y zirconia) or 1 mm (lithium disilicate) crowns were luted to resin composite dies with resin-modified glass ionomer (zirconia) or self-adhesive resin (lithium disilicate) cement. A 2.5 mm endodontic access hole was placed in each crown with fine (8369DF.31.025FOOTBALL) or coarse (6379 DC.31.023FOOTBALL) diamond instruments and restored with composite. A control group was prepared without access holes. Crowns were thermocycled for 10,000 cycles (5-55°C) and tested in compression with a steel indenter until failure (n = 8/group). A one-way ANOVA and Dunnett 2-sided test (alpha = 0.05) compared differences in fracture load between groups.

RESULTS

For zirconia, there was no statistical difference between the control group (2335 ± 160 N) and coarse diamond group (2345 ± 246 N); however, the fine diamond group (2077 ± 216 N) was significantly lower. For lithium disilicate, there was no statistical difference between the control group (2113 ± 183 N) and the fine (2049 ± 105 N) or coarse (2240 ± 118 N) groups.

CONCLUSIONS

3Y zirconia crowns became weaker when accessed with a fine diamond instrument. There was no negative effect of the endodontic access with bonded lithium disilicate crowns.

CLINICAL SIGNIFICANCE

Conservative endodontic access openings in high-strength ceramic restorations do not have a negative effect on their static fracture load. The coarse zirconia-cutting diamond rotary instrument is more efficient and has a less detrimental effect on the strength of the crowns than a fine diamond rotary instrument.

The effect of endodontic access preparation on the failure load resistance of a 3Y-TZP monolithic zirconia crown

The effect of endodontic access preparation on the failure load resistance of 3Y-TZP zirconia crowns was accomplished by preparing human molars and luting monolithic zirconia crowns with a self-adhesive resin cement. Besides the intact control, teeth received endodontic access preparations and then grouped (n = 12) into a positive control (no access repair), dentin core replacement only and complete access repair groups. Specimens were axially tested until failure with results of no significant difference between the failure load of intact controls and the complete access repair group. However, the positive control and dentin replacement only groups failed at significantly lower loads. Under the conditions of this study, there was no significant failure load difference between 3Y-TZP monolithic zirconia crowns with repaired endodontic access preparations to that evidenced by an unprepared control. Although this evidence is encouraging, caution is advised and definitive recommendations cannot be made until verified by clinical studies.