Leakage associated with load fatigue-induced preliminary failure of full crowns placed over three different post and core systems

Fracture resistance of endodontically-treated maxillary premolars restored with different type of posts and direct composite reconstructions: A systematic review and meta-analysis of in vitro studies

OBJECTIVE

To conduct a systematic review and meta-analysis to assess if the presence of an endodontic post may increase the fracture resistance of endodontically-treated maxillary premolars directly restored with composite.

METHODS

A comprehensive systematic literature search according to the PRISMA statement was conducted to assess in vitro studies including endodontically-treated maxillary premolars, restored with different type of posts supporting direct composite reconstructions. Two groups of meta-analyses were performed using fixed effects model and additional Trial Sequential Analysis (TSA) was carried out. Moreover, risk of bias was conducted and quality of evidence for any performed meta-analysis was assessed using Grading of Recommendations Assessment, Development and Evaluation (GRADE).

RESULTS

Twenty-four articles met the inclusion criteria and 13 studies also underwent quantitative evaluation. Fracture resistance of endodontically-treated premolars restored with fiber posts was significantly less than sound teeth (p value: < 0.00001), however endodontically-treated premolars with a fiber post provided an increase in fracture resistance when compared to equivalent teeth restored without post (p value: 0.003). TSA revealed high power of both meta-analyses. Moderate risk of bias was reported in 23/24 studies; only 1 study showed high risk of bias. GRADE system showed moderate strength of evidence due to the presence of a study with high risk of bias and to wide confidence intervals.

SIGNIFICANCE

Within the limitation of the present systematic review and meta-analysis, it can be concluded that endodontically-treated maxillary premolars restored with a fiber post and direct composite restoration demonstrated increased fracture resistance when compared to equivalent teeth without post.

A castor oil-containing dental luting agent: effects of cyclic loading and storage time on flexural strength

Favorable results in the use of castor oil polyurethane (COP) as pulp capping, membrane material, sealer, mouthwash and in bone repair, associated with the fact that Ricinus communis is not derived from petroleum and it is abundant in Brazil, encourage researches in the development of luting agents.

Influence of ferrule preparation with or without glass fiber post on fracture resistance of endodontically treated teeth

Objective

This study evaluated the effect of ferrule preparation (Fp) on the fracture resistance of endodontically treated teeth, restored with composite resin cores with or without glass fiber posts.

Material and Methods

Forty-four bovine teeth were sectioned 19 or 17 mm (2 mm ferrule) from the apex, endodontically treated and assigned to four groups (n = 11): Group 1: Fp and post; Group 2: Fp and without post; Group 3: without Fp and with post; Group 4: without Fp and without post. All specimens were restored with composite resin core and metal crown. Specimens were subjected to fracture resistance testing in a universal testing machine at a crosshead speed of 0.5 mm/min. The data were analyzed by two-way ANOVA and Tukey’s tests (α=0.05).

Results

The mean fracture resistance values were as follows: Group 1: 573.3 N; Group 2: 552.5 N; Group 3: 275.3 N; Group 4: 258.6 N. Significantly higher fracture resistance was found for the groups with Fp (p<0.001).

Conclusion

There was no statistically significant interaction between the "Fp" and "post" factors (p = 0.954). The ferrule preparation increased the fracture resistance of endodontically treated teeth. However, the use of glass fiber post showed no significant influence on the fracture resistance.

Tensile bond strength of cast commercially pure titanium dowel and cores cemented with three luting agents

PURPOSE

The purpose of this study was to compare the tensile strength of commercially pure titanium dowels and cores cemented with zinc phosphate or resin cements.

METHODS

Twenty-one extracted human canines were endodontically treated. The root preparations were accomplished using Largo reamers (10mm in depth and 1.7 mm in diameter). Acrylic resin patterns for the dowel and cores were made, and specimens were cast in commercially pure titanium (n=7) and divided in three groups: TZ-CP Ti dowels luted with zinc phosphate luting agent, TP-CP Ti dowels luted with Panavia F and TR-CP Ti dowels luted with RelyX U100. Tensile strengths were measured in a universal testing machine at a crosshead speed of 0.5mm/min. The results (N) were statistically analyzed by ANOVA and Tukey tests (α=0.01).

RESULTS

The ANOVA indicated that there were significant differences among the groups tested. A Tukey multiple comparison procedure was performed and revealed statistically significant higher retention values for the dowel luted with RelyX U100 when compared with zinc phosphate or Panavia F.

CONCLUSION

Cast commercially pure titanium dowels and cores fixed with RelyX U100 cement presented superior bond strength retention when compared to zinc phosphate and Panavia F.

Load-fatigue performance of gold crowns luted with resin cements

STATEMENT OF PROBLEM

Resin cements have gained popularity over the past few years because of their improved physical properties. There is a need to test these cements under fatigue loading, as there is growing recognition that fatigue testing is more clinically relevant than traditional monotonic static tests.

PURPOSE

This study investigated the load-fatigue performance of complete gold crowns cemented with 4 types of resin cement.

MATERIAL AND METHODS

Four resin cements (C & B Opaque [CBO], Calibra Esthetic [CE], RelyX Unicem [RU], and Panavia F [PF]) and a control, zinc phosphate cement (HY-Bond [HBZPC]) were tested. Fifty human maxillary premolars were prepared to an occluso-cervical dimension of 4 mm and a convergence angle of 20 degrees. Complete gold crowns were cast (Strator 3) and cemented with 1 of the 5 cements (n=10). A fatigue load of 73.5 N was applied at an angle of 135 degrees to the long axis of each tooth-crown specimen. Preliminary failure was defined as the propagation of a crack in or around the crown luting cement layer. The number of cycles to preliminary failure and the cement failure location were determined. Significant differences in cycles to preliminary failure were assessed by the nonparametric Kruskal-Wallis test, with follow-up Mann-Whitney tests (alpha=.05).

RESULTS

Group CE had the highest rank of cycles to preliminary failure, while HBZPC had the lowest cycles to preliminary failure. Group CE had a significantly higher failure cycle count compared to PF (P=.016), RU (P=.001), and HBZPC (P<.001), but was not significantly different from CBO (P=.112). There was no significant difference in the failure cycle count between RU and HBZPC (P=.070).

CONCLUSION

Not all tested resin cements had a superior fatigue life when compared with zinc phosphate cement. Of the 4 resin cement groups, Groups CE, CBO, and PF were significantly superior to HBZPC.

Periapical biomechanics and the role of cyclic biting force in apical retrograde fluid movement

AIM

To investigate the stress distribution pattern in the periapical region caused by biting forces and to study the role of cyclic biting loads on periapical fluid movement.

METHODOLOGY

In the first part, a digital photoelastic experiment was conducted to study stress distribution in the periapical region. In the second, 20 maxillary central incisors were selected and divided into three main groups: normal intact teeth (group 1), tooth specimens in which the root canal was enlarged and maintained wet (group 2), and tooth specimens in which the root canal was enlarged and maintained dry (group 3). The tooth specimens were placed in a polycarbonate support with a cavity filled with a sponge soaked in methylene blue solution to simulate a periapical defect with exudate. During testing, the specimens were placed in a water bath at 37 degrees C, and were loaded cyclically with a load of 20 N, at a rate of 72 cycles min(-1), to a maximum of 20,000 cycles. The specimens were then sectioned and evaluated for retrograde fluid movement using light microscopy. The data were analysed using one-way anova (post hoc tests).

RESULTS

Digital photoelastic experiments showed that the compression of teeth produced bending stresses in the periapical region. Testing with cyclic loads demonstrated retrograde fluid movement into the apical portion of the root canal and extraradicular region in all groups. There was a significant difference amongst the apical retrograde fluid movement displayed by different groups (<0.01). Group 2, in which the root canal was enlarged and maintained wet showed maximum retrograde fluid movement, whilst group 3, in which the root canal was enlarged and maintained dry showed the least retrograde fluid movement.

CONCLUSIONS

Biting forces would cause bending of the periapical bone and cyclic biting forces would contribute to retrograde fluid movement into the root canal space and extraradicular region.

Fatigue resistance of endodontically treated teeth restored with three dowel-and-core systems

STATEMENT OF PROBLEM

The successful restoration of endodontically treated teeth is enhanced by a crown design employing the ferrule effect. However, it is unclear which dowel-and-core system most effectively supports successful treatment.

PURPOSE

The purpose of this study was to compare the load fatigue resistance of 3 dowel-and-core systems.

MATERIAL AND METHODS

Fifteen endodontically treated maxillary central incisors were sectioned perpendicular to the long axis at a point 1.5 mm incisal to the cemento-enamel junction (CEJ). At the level of the CEJ, specimens were then prepared for crowns with 1-mm complete shoulder finish lines and 1.5 mm of axial wall height. The prepared teeth were divided into 3 groups (n=5) and restored with 1 of the following dowel-and-core combinations: Group CG, cast gold dowels and cores; Group TA, titanium alloy dowels (ParaPost XH) with composite cores; or Group FR, fiber-reinforced resin dowels (ParaPost FiberWhite) with composite cores. A dentin bonding agent (OptiBond Solo) was placed prior to the composite cores. Dowel-and-core castings and titanium alloy dowels were cemented with zinc phosphate cement. The fiber-reinforced dowels were cemented with a resin cement (ParaPost Cement). The crowns for all specimens were cast with an incisal notch for applying the fatigue load. The independent variable measured was the number of load fatigue cycles required to cause luting cement failure. The data were subjected to 1-way analysis of variance and the Student-Newman-Keuls test for 3 subsets (alpha=.05).

RESULTS

The mean value+/-standard deviation for the cycles to failure for each group was: Group CG: 11,897+/-4080 load cycles, Group TA: 24,384+/-8231 load cycles, and Group FR: 50,696+/-7063 load cycles. Significant differences were found between all groups ( P<.05).

CONCLUSIONS

Fiber-reinforced resin dowels and bonded composite cores under fatigue loading provided significantly stronger crown retention than cast gold dowels and cores and titanium alloy dowels with composite cores under fatigue loading.

Effect of the diameter on Cu-Al post retention

This study compared the resistance to removal by traction of abraded cylindrical metal cast posts of Cu-Al (Goldent-LA). The posts had constant length (9 mm) and three different diameters (0.9, 1.3 and 1.7 mm), and were cemented with zinc phosphate cement. The crowns of 36 sound maxillary canines were sectioned, the roots were immersed in resin blocks and the root canals were endodontically treated. The teeth were divided into three groups to be prepared and standardized with the use of a parallelometer with the following burs: Group 1 - Largo n. 2; Group 2 - Largo n. 4; Group 3 - Largo n. 6. The posts were molded with chemically activated resin and after casting they were abraded and their dimensions were confirmed with a digital caliper. After cementation of the posts in the prepared root canals, the samples were kept at 37ºC in distilled water for 7 days and subsequently submitted to the traction test in a universal testing machine (Instron 4444). The results showed no statistical difference between the groups. Diameter variation (0.9 mm, 1.3 mm and 1.7 mm) in abraded cylindrical posts cemented with zinc phosphate did not affect resistance to removal.

An in vitro study evaluating the effect of ferrule length on fracture resistance of endodontically treated teeth restored with fiber-reinforced and zirconia dowel systems

STATEMENT OF PROBLEM

There are few published studies analyzing the effects of different ferrule lengths of endodontically treated teeth in relationship to newly developed fiber-reinforced and zirconia dowel systems.

PURPOSE

This in vitro study compared the effect of 3 different ferrule lengths on the fracture resistance and fracture patterns of crowned endodontically treated teeth restored with 4 different esthetic dowel systems.

MATERIAL AND METHODS

The crowns of 123 human maxillary canines were removed at the cementoenamel junction and the roots were endodontically treated. Three master tooth models were prepared to ferrule lengths of 1.0 mm, 1.5 mm, and 2.0 mm to produce 3 master analogs. Each root was embedded in autopolymerizing resin with a 0.2-mm layer of silicone impression material to simulate the periodontal ligament. Forty analogs of each master tooth, with ferrule lengths of 1.0 mm, 1.5 mm, and 2.0 mm were produced with copy-milling (Celay system). Each group was further subdivided into 4 groups of 10 specimens each and restored with 4 different esthetic dowel systems (quartz fiber, glass fiber, glass fiber plus zirconia, and zirconia). All dowels were luted with adhesive resin cement (RelyX ARC), restored with composite cores (Valux Plus), and Ni-Cr alloy (Wiron 99) complete crowns. All specimens were loaded at 130 degrees to the long axes in a universal testing machine at a crosshead speed of 1 mm/min until fracture. Fracture patterns were classified as failures above or below the incisal third of the roots. The data were analyzed with 2-way ANOVA and Tukey HSD tests (alpha=.05). A Fisher exact test was conducted for evaluation of the mode of failure (alpha=.05).

RESULTS

Mean failure loads (kg) for quartz fiber, glass fiber, glass fiber plus zirconia, and zirconia groups, respectively, with the 3 ferrule lengths were: 1.0-mm ferrule specimens: 98.09 +/- 2.90, 85.36 +/- 2.82, 80.24 +/- 1.88, 70.11 +/- 2.48; 1.5-mm ferrule specimens: 101.0 +/- 2.88, 87.58 +/- 2.83, 89.8 +/- 2.09, 82.71 +/- 2.14; 2.0-mm ferrule specimens: 119.5+/-1.78, 99.84+/-1.23, 98.6 +/- 1.64, 95.42 +/- 1.02. Teeth prepared with 2.0-mm ferrules demonstrated significantly higher fracture thresholds (P<.001). There were no significant differences in fracture patterns.

CONCLUSION

Increasing the ferrule length of the endodontically treated teeth from 1 mm to 1.5 mm in specimens restored with quartz-fiber and glass-fiber dowels did not produce significant increases in the failure loads (P=.084, P=.119, respectively). No significant difference was detected between glass-fiber and glass-fiber plus zirconia dowels with 1.5-mm and 2.0-mm ferrules (P=.218, P=.244, respectively). However, fracture thresholds were higher for all 4 dowel systems when the specimens were prepared with a 2.0-mm ferrule length (P<.001).

Post placement and restoration of endodontically treated teeth: a literature review

The restoration of endodontically treated teeth is a topic that is extensively studied and yet remains controversial from many perspectives. This article reviews the major pertinent literature on this topic, with an emphasis on major decision-making elements in post placement and restoration of endodontically treated teeth. Recommendations are made for treatment planning, materials, and clinical practices from restorative and endodontic perspectives.

Stress-strain response in human dentine: rethinking fracture predilection in postcore restored teeth

In this study, the biomechanical perspective of fracture predilection in post-core restored teeth is investigated using computational, experimental, and fractographic analyses. The computational finite element analysis and the experimental tensile testing are used to evaluate the stress-strain response in structural dentine. The fractographic evaluations are conducted using laser scanning confocal microscopy and scanning electron microscopy to examine the topography of dentine from experimentally fractured specimens, and clinically fractured post-core restored teeth specimens. These experiments aided in correlating the stress-strain response in structural dentine with cracks and catastrophic fractures in post-core restored teeth. It was observed from these experiments that the inner dentine displayed distinctly high strains (deformations), while the outer dentine demonstrated high stresses during tensile loading. This implies that the energy fed into the material as it is extended will be spread throughout the inner dentine, and there is less possibility of local increase in stress at the outer dentine, which can lead to the failure of dentine structure. During post-endodontic restoration with increase in loss of inner dentine, the fracture resistance factor contributed by the inner dentine is compromised, and this in turn predisposes the tooth to catastrophic fracture.

Restoration of endodontically treated teeth

Endodontically treated teeth have lost substantial tooth structure as a result of previous restorations, dental caries, and the access preparation for the endodontic therapy. The topic of restoring these teeth is complex and controversial, and their long-term prognosis is directly connected to the quality of the final restoration. This article describes contemporary knowledge of the biomechanical principles related to the restoration of pulpless teeth and provides a critical review of currently available materials and methods.

Retrograde treatment in an extensive implant-tooth-supported reconstruction

Diagnosis and treatment of chronic apical periodontitis associated with an abutment tooth in an extensive tooth-implant-supported fixed prosthesis is reported. Careful, complete interpretation of clinical data was imperative because the periapical radiolucency presented around the apex of a vital tooth. A retrograde endodontic approach was used to prevent an adverse outcome to the complex rehabilitative treatment that had been performed over many years.

The ferrule effect: a literature review

LITERATURE REVIEW

A ferrule is a metal ring or cap used to strengthen the end of a stick or tube. It has been proposed that the use of a ferrule as part of the core or artificial crown may be of benefit in reinforcing root-filled teeth. A review of the literature investigating this effect is presented. The literature demonstrates that a ferrule effect occurs owing to the artificial crown bracing against the dentine extending coronal to the crown margin. Overall, it can be concluded that a ferrule is desirable, but should not be provided at the expense of the remaining tooth/root structure.

The effect of thermocycling on the fracture toughness and hardness of core buildup materials

STATEMENT OF PROBLEM

Thermocycling has been shown to cause surface degradation of many dental materials, but its effect on the fracture toughness and hardness of direct core buildup materials is unknown.

PURPOSE

This study was designed to determine the effect of thermocycling on the fracture toughness and hardness of 5 core buildup materials.

MATERIAL AND METHODS

Fifteen specimens were prepared from each of the following materials: Fluorocore, VariGlass VLC, Valiant PhD, Vitremer, and Chelon-Silver. American Standard for Testing Materials guidelines for single-edge notch, bar-shaped specimens were used. Ten specimens of each material were thermocycled for 2000 cycles; the other 5 specimens were not thermocycled. All specimens were subjected to 3-point bending in a universal testing machine. The load at fracture was recorded, and the fracture toughness (K(IC)) was calculated. Barcol hardness values were also determined. Data were analyzed with 1-way analysis of variance and compared with the Tukey multiple range test (P<.05). Pearson's correlation coefficient was also calculated to measure the association between fracture toughness and hardness.

RESULTS

Fluorocore had the highest thermocycled mean K(IC) and Valiant PhD the highest non-thermocycled K(IC). Chelon-Silver demonstrated the lowest mean K(IC) both before and after thermocycling. One-way analysis of variance demonstrated significant differences between conditions, and the Tukey test showed significant differences (P<.05) between materials for both conditions. Most specimens also showed significant hardness differences between conditions. Pearson's correlation coefficient indicated only a mild-to-moderate correlation between hardness and fracture toughness.

CONCLUSION

Within the limitations of this study, the thermocycling process negatively affected the fracture toughness and hardness of the core buildup materials tested.

Torsional resistance of crowns cemented to composite cores involving three stainless steel endodontic post designs

STATEMENT OF PROBLEM

There are no studies analyzing the effects of a crown in relationship to torsional resistance for a titanium-reinforced core material supported by a post.

PURPOSE

This study investigated the effects of post design on the torsional resistance of a crown supported by a titanium-reinforced composite core material (Ti-Core) and 3 endodontic posts (AccessPost, Flexi-Post, and ParaPost).

MATERIAL AND METHOD

Three groups of 10 specimens per group were studied. A total of 30 recently extracted human single-rooted (incisors) teeth with their crowns removed were used. Post holes preparations were created according to manufacturer's instructions. All posts were cemented using Flexi-Flow with titanium cement. Scotchbond Multi-Purpose bonding system was used as the bonding system for all groups. All cores were fabricated with Ti-Core with titanium core material with hard copper bands as the matrix. The Ti-Core core material was allowed to set for 1 hour. Metal crowns were fabricated and cemented with zinc phosphate cement. Specimens were placed in a special jig and a clockwise torsional force was applied. Torsional force was measured on a Lebow 1102-200 torque transducer and recorded on a Hewlett Packard 7015B X-Y recorder in inch x ounce. A 1-way analysis of variance (ANOVA) was used to test for statistical significance (P < .001).

RESULTS

The torsional values (inch x ounce) were AccessPost 77.2 +/- 30.3, Flexi-Post 162.2 +/- 51.2, and ParaPost 60.9 +/- 28.4. SNK and Scheffé comparison tests revealed that the Flexi-Post group had significantly greater resistance to torque loading than the AccessPost and ParaPost groups, which were statistically similar to each other.

CONCLUSION

Post design has an effect on torsional resistance of a crown supported by titanium-reinforced core build-up and post. The threaded split-shank design of the Flexi-Post dowel offers significantly greater resistance to torsional loading than the passive posts studied.

Foundation restorations in fixed prosthodontics: current knowledge and future needs

PURPOSE

The Ad Hoc Committee on Research in Fixed Prosthodontics established by the Academy of Fixed Prosthodontics publishes a yearly comprehensive literature review on a selected topic. The subject for this year is foundation restorations.

METHODS

Literature of various in vitro and in vivo investigations that included technical and clinical articles was reviewed to provide clinical guidelines for the dentist when selecting methods and materials for restoration of structurally compromised teeth. Topics discussed and critically reviewed include: (1) desirable features of foundation restorations, (2) foundations for pulpless teeth, (3) historic perspectives, (4) cast posts and cores, (5) role of the ferrule effect, (6) prefabricated posts, (7) direct cores, (8) foundation restorations for severely compromised teeth, (9) problems and limitations, (10) future needs, and (11) directions for future research.

CONCLUSION

This comprehensive review brings together literature from a variety of in vitro and in vivo studies, along with technique articles and clinical reports to provide meaningful guidelines for the dentist when selecting methods and materials for the restoration of structurally compromised teeth.

Effects of three bonding systems on the torsional resistance of titanium-reinforced composite cores supported by two post designs

STATEMENT OF PROBLEM

There are no studies that have investigated the effects of bonding agents on the resistance to torque of a composite core supported by a prefabricated post.

PURPOSE

This study investigated the ability of bonding agents to resist rational forces applied to titanium-reinforced composite cores supported by 2 post designs.

MATERIAL AND METHODS

Two post designs (AccessPost and ParaPost dowels) with titanium-reinforced core material and 4 bonding conditions (AllBond-2, ScotchBond Multi-Purpose, Tenure A&B, and without a bonding agent) were studied. A total of 80 specimens in 8 experimental groups were prepared and subjected to clockwise torsional forces until failure.

RESULTS

Torsional values ranged from 53.31 in. x oz (ParaPost/ScotchBond Multi-Purpose) to 72.31 in. x oz (AccessPost/ScotchBond Multi-Purpose). Two-way of analysis of variance failed to demonstrate a significant difference among posts or type of bonding system.

CONCLUSION

The use of a multistep bonding agent had no significant effect on the torsional resistance of a core supported by a passive endodontic post.