Fatigue testing and microscopic evaluation of post and core restorations under artificial crowns

Effect of different ceramic systems on antagonist dental structure by microtomographic analysis

OBJECTIVES

This study aims to identify the two-dimensional and three-dimensional analyses and evaluate the loss of tooth structure in the tooth's different constituent elements and the ceramic antagonist's surface.

METHODS

In this study, three groups (n = 10) represented by different ceramic systems (lithium disilicate [GDis], lithium silicate reinforced with zirconia [GSil], and monolithic zirconia [GZir]) were evaluated. Each group obtained ten ceramic blocks and submitted them to the sintering/crystallization process. To carry out the wear test, healthy mandibular premolars were used as the specimens and the ceramic blocks as antagonists. The premolars were submitted to two-dimensional and three-dimensional analyses using a computerized microtomography (µTC) before and after the wear test. The wear test was performed with 30 N and 300,000 cycles load, with occlusion, laterality, and disocclusion movements.

RESULTS

The statistical analysis comparing the loss of two-dimensional tooth structure showed a statistically significant difference among all groups (p < 0.05). Statistical analysis comparing the percentage of loss of three-dimensional tooth structure showed a statistically significant difference between groups GDis and GSil and between groups GDis and GZir. However, when comparing GSil with GZir, no statistically significant difference was found. The qualitative analysis of the teeth showed that GDis showed considerable enamel loss and dentin exposure, GSil showed enamel wear with flattening the cusp without dentin exposure, and GZir showed minimal enamel wear without dentin exposure. In the qualitative analysis of ceramic antagonists, more significant wear of the ceramic material for GDis was observed, followed by the GSil and GZir groups, respectively.

SIGNIFICANCE

The use of the lithium disilicate should be cautious, restricting it to areas with lower masticatory forces. Areas of higher masticatory forces showed a large amount of antagonist wear, with dentin involvement. This can lead to dentinal hypersensitivity, risk of compromising patients' occlusion, by harming group disocclusion guides, causing pain and temporomandibular disorders.

Deterioration of direct restorative materials under erosive conditions with impact of abrasion and attrition in vitro

Objective

To compare the cumulative impact of sequential wear on mechanical properties and appearance of a composite resin (CR), Filtek Z250^®, a glass ionomer GI, Fuji IX GP^®, and a glass hybrid (GH), Equia Forte^®.

Material and Methods

Six equally sized specimens of each material were subjected to wear tests, i.e., simulation of brushing, chewing and acidic liquid exposure, mimicking at least 6 months of clinical exposure. Surface roughness, hardness, substance loss and degree of shade lightness were determined.

Results

Following wear tests, significant increase in surface roughness and decrease in hardness values were observed for all materials (p < .05). Significantly larger substance loss was found in Equia Forte^® specimens compared to Filtek Z250^® (p < .05), while that of Fuji IX^® exceeded the measurement capacity of the instrument. Opposite to the two other materials, the shade of Filtek Z250^® became darker.

Conclusions

Sequential wear exposure mimicking abrasion, erosion and attrition to products representing CR, GI and GH, caused weakening and change in appearance of the materials. The composite resin was the most mechanically resistant to the sequential wear.

Influence of Root Post Materials and Aging on Fracture Strength and Marginal Gap Quality of Ceramic Crowns-An In Vitro Study

The design of and materials for prosthodontic abutments and posts have significant influences on the fracture resistance of restored teeth. This in vitro study compared the fracture strength and marginal quality of full-ceramic crowns as a function of the inserted root posts via simulation of a five-year period of use. Test specimens were prepared from 60 extracted maxillary incisors using titanium L9 (A), glass-fiber L9 (B), and glass-fiber L6 (C) root posts. The circular marginal gap behavior, linear loading capacity, and material fatigue after artificial aging were investigated. The marginal gap behavior and material fatigue were analyzed using electron microscopy. The linear loading capacity of the specimens was investigated using the Zwick Z005 universal testing machine. None of the tested root post materials showed statistically significant differences in marginal width values (p = 0.921), except in the case of marginal gap location. For Group A, there was a statistically significant difference from the labial to the distal (p = 0.012), mesial (p = 0.000), and palatinal (p = 0.005). Similarly, Group B showed a statistically significant difference from the labial to the distal (p = 0.003), mesial (p = 0.000), and palatinal (p = 0.003). Group C showed a statistically significant difference from the labial to the distal (p = 0.001) and mesial (p = 0.009). Linear load capacity reached mean values of 455.8-537.7 N, and micro-cracks occurred after artificial aging, predominantly in Groups B and C. Through the chosen experimental design, it was shown that the root post material and root post length had no influence on the fracture strength of the test teeth before or after artificial aging. However, the marginal gap location depends on the root post material and its length, which is wider mesially and distally and also tends to be greater palatinally than labially.

Abutments with reduced diameter for both cement and screw retentions: analysis of failure modes and misfit of abutment-crown-connections after cyclic loading

OBJECTIVE

The aim of this study was to analyze failure modes and misfit of abutments with reduced diameter for both cement and screw retentions after cyclic loading.

MATERIAL AND METHODS

Forty morse-taper abutment/implant sets of titanium were divided into four groups (N = 10): G4.8S-4.8 abutment with screw-retained crown; G4.8C-4.8 abutment with cemented crown; G3.8S-3.8 abutment with screw-retained crown; and G3.8C-3.8 abutment with cemented crown. Copings were waxed on castable cylinders and cast by oxygen gas flame and injected by centrifugation. After, esthetic veneering ceramic was pressed on these copings for obtaining metalloceramic crowns of upper canine. Cemented crowns were cemented on abutments with provisional cement (Temp Bond NE), and screw-retained crowns were tightened to their abutments with torque recommended by manufacturer (10 N cm). The misfit was measured using a stereomicroscope in a 10× magnification before and after cyclic loading (300,000 cycles). Tests were visually monitored, and failures (decementation, screw loosening and fractures) were registered. Misfit was analyzed by mixed linear model while failure modes by chi-square test (α = 0.05).

RESULTS

Cyclic loading affected misfit of 3.8C (P ≤ 0.0001), 3.8S (P = 0.0055) and 4.8C (P = 0.0318), but not of 4.8S (P = 0.1243). No differences were noted between 3.8S with 4.8S before (P = 0.1550) and after (P = 0.9861) cyclic loading, but 3.8C was different from 4.8C only after (P = 0.0015) loading. Comparing different types of retentions at the same diameter abutment, significant difference was noted before and after cyclic loading for 3.8 and 4.8 abutments. Analyzing failure modes, retrievable failures were present at 3.8S and 3.8C groups, while irretrievable were only present at 3.8S.

CONCLUSIONS

The cyclic loading decreased misfit of cemented and screw-retained crowns on reduced diameter abutments, and misfit of cemented crowns is greater than screw-retained ones. Abutments of reduced diameter failed more than conventional.

Impact of a Core Ferrule Design on Fracture Resistance of Teeth Restored with Cast Post and Core

Objectives. To investigate the influence of a contra bevel on the fracture resistance of teeth restored with cast post and core. Materials and Methods. Sixty plastic analogues of an upper incisor were endodontically treated and prepared with 6° internal taper and 2 mm of ferrule in order to receive a cast post and core. The prepared samples were divided into two groups (n = 30); the first group serves as control while the second group was prepared with an external 30° bevel on the buccal and lingual walls. All samples crowned were exposed to a compressive load at 130° to their long axis until fractures occurred. Fracture resistance loads were recorded and failure modes were also observed. Mann-Whitney test was carried out to compare the two groups. Results. Mean failure loads for the groups were, respectively, 1038.69 N (SD ±243.52 N) and 1078.89 N (SD ±352.21 N). Statistically, there was no significant difference between the two groups (P = 0.7675 > 0.05). Conclusion. In the presence of a ferrule and a crown in the anterior teeth, adding a secondary ferrule to the cast post and core will not increase the resistance to fracture.

Influence of Full Veneer Restoration on Fracture Resistance of Three Different Core Materials: An Invitro Study

AIMS AND OBJECTIVES

One of the factor which affects the strength of the tooth restored with core material is the property of the material. In clinical situation all such restored teeth are protected by crowns. This study evaluated the strength of different core materials on a compromised tooth structure after restoration with a crown.

MATERIALS AND METHODS

Seventy extracted intact human premolars were collected and mounted within a mould using auto-polymerizing resin. The teeth were divided in-to four groups - A, B, C and D. Each group contained 20 teeth except group A with 10 teeth. All the teeth were prepared for full veneer cast crown. Except for the teeth in group: A) extensive class-I cavities were prepared in the teeth of all the groups and restored with; B) composite resin, 3M EPSE Filtek P60; C) Silver reinforced glass ionomer, SHOFU Hi Dense XP and; (D) Resin reinforced glass ionomer, GC Gold Label light cure GIC. All the teeth were restored with cast-metal alloy and exposed to 1.2 million cycles of cyclic loading in a chewing simulator. Subsequently, the teeth that survived were loaded till fracture in the universal testing machine. Fracture loads and type of fractures were recorded.

RESULTS

All the specimens survived cyclic loading. The mean fracture strength of the silver reinforced glass ionomer was greater with and without crown (p<0.001). Statistical analysis for the mean fracture load of each specimen showed significant difference between the groups.

CONCLUSION

Under the condition of this study, core materials when restored with artificial crown had a significant increase in fracture resistance.

Bond strength between fiber posts and composite resin core: influence of temperature on silane coupling agents

This study evaluated the effect of air drying temperature and different silane coupling agents on the bond strength between glass fiber posts and composite resin core. The post surface was cleaned with alcohol and treated with different silane coupling agents, being three prehydrolyzed silanes [Silano (Angelus), Prosil (FGM), RelyX Ceramic Primer (3M ESPE)] and one two-component silane [Silane Coupling Agent (Dentsply)]. Two post-silanization air drying temperatures, 23ºC and 60ºC, were applied. A cylindrical plastic matrix was placed around the silanized post and filled with composite resin. Each bonded post provided 7 slices for push-out testing. Each slice was loaded to failure under compression at a cross-head speed of 0.5 mm/min. Data were analyzed by two-way ANOVA and Scott-Knott tests (α=0.05). Dunnett's test was used to compare the mean of the control group with that of each experimental group. Scanning electron microscopy (SEM) was used to evaluate the interface of the fractured slices. For the 23ºC air drying temperature, the use of RelyX Ceramic Primer resulted in significantly lower bond strength than the other silane coupling agents, while the bond strength with Silane Coupling Agent was the highest of all groups. Only with Silane Coupling Agent, the bond strength for the 23ºC air drying temperature was significantly higher than that for 60ºC air drying. In conclusion, the use of warm air drying after silane application produced no increase in the bond strength between the fiber-reinforced composite post and the composite core. The two-component silane produced higher bond strength than all prehydrolyzed silanes when it was used with air drying at room temperature.

Surface treatment of glass fiber and carbon fiber posts: SEM characterization

Morphology, etching patterns, surface modification, and characterization of 2 different fiber posts: Gfp, Glass fiber post; and Cfp, carbon fiber were investigated by SEM analysis, after different surface treatments. Thirty fiber posts, being 15 Gfp and 15 Cfp were divided into a 5 surface treatments (n = 3): C-alcohol 70% (control); HF 4%-immersion in 4% hydrofluoric acid for 1min; H(3) PO(4) 37%-immersion in 37% phosphoric acid for 30s; H(2) O(2) 10%-immersion in 10% hydrogen peroxide for 20 min; H(2) O(2) 24%-immersion in 24% hydrogen peroxide for 10 min. Morphology, etching patterns, surface modification and surface characterization were acessed by SEM analysis. SEM evaluation revealed that the post surface morphology was modified following all treatment when compared with a control group, for both type of reinforced posts. HF seems to penetrate around the fibers of Gfp and promoted surface alterations. The Cfp surface seems to be inert to treatment with HF 4%. Dissolution of epoxy resin and exposure of the superficial fiber was observed in both post groups, regardless the type of reinforcing fiber, H(2) O(2) in both concentrations. Relative smooth surface area was produced by H(3) PO(4) 37% treatment, but with similar features to untreated group. Surface treatment of fiber post is a determinant factor on micromechanical entanglement to resin composite core. Post treatment with hydrogen peroxide resulted strength of carbon and glass/epoxy resin fiber posts to resin composite core.

Abrasion wear resistance of different artificial teeth opposed to metal and composite antagonists

One of the most important properties of artificial teeth is the abrasion wear resistance, which is determinant in the maintenance of the rehabilitation's occlusal pattern.

Effect of repeated torque/mechanical loading cycles on two different abutment types in implants with internal tapered connections: an in vitro study

OBJECTIVES

Internal tapered connections were developed to improve biomechanical properties and to reduce mechanical problems found in other implant connection systems. The purpose of this study was to evaluate the effects of mechanical loading and repeated insertion/removal cycles on the torque loss of abutments with internal tapered connections.

MATERIAL AND METHODS

Sixty-eight conical implants and 68 abutments of two types were used. They were divided into four groups: groups 1 and 3 received solid abutments, and groups 2 and 4 received two-piece abutments. In groups 1 and 2, abutments were simply installed and uninstalled; torque-in and torque-out values were measured. In groups 3 and 4, abutments were installed, mechanically loaded and uninstalled; torque-in and torque-out values were measured. Under mechanical loading, two-piece abutments were frictionally locked into the implant; thus, data of group 4 were catalogued under two subgroups (4a: torque-out value necessary to loosen the fixation screw; 4b: torque-out value necessary to remove the abutment from the implant). Ten insertion/removal cycles were performed for every implant/abutment assembly. Data were analyzed with a mixed linear model (P< or =0.05).

RESULTS

Torque loss was higher in groups 4a and 2 (over 30% loss), followed by group 1 (10.5% loss), group 3 (5.4% loss) and group 4b (39% torque gain). All the results were significantly different. As the number of insertion/removal cycles increased, removal torques tended to be lower. It was concluded that mechanical loading increased removal torque of loaded abutments in comparison with unloaded abutments, and removal torque values tended to decrease as the number of insertion/removal cycles increased.

A study of the fracture resistance of nyyar cores of three restorative materials

Despite the successful use of dental amalgam for coronal-radicular dowel and core build-up in endodontically-treated posterior teeth, newer materials offer many potential advantages over amalgam and have better patient acceptance. This study compared the fracture resistance of coronal-radicular restorations made from three different direct restorative materials. Sixty human premolars were selected, 45 of which were root treated and decoronated. Fifteen of these premolars were restored using amalgam, 15 with composite and 15 using resin-modified glass ionomer. The 15 unrestored teeth were used as a control group. All the teeth were mounted in acrylic within steel containers and subjected to compressive loading to failure on a universal testing machine. The force required to fracture each core specimen was recorded as well as the proportion of core lost due to failure. The results showed dental amalgam as having the highest fracture resistance (mean 1.93kN, sd 0.22) followed by resin-modified glass ionomer (mean 1.05kN, sd 0.20), sound tooth (mean 0.79kN, sd 0.20) and composite (mean 0.75kN, sd 0.11). The differences among all groups were significant. These results demonstrate that, although resin-modified glass ionomer is significantly weaker than amalgam, these restorations were stronger than unrestored teeth and failed at forces in excess of those encountered in normal mastication. Amalgam cores, along with resin-modified glass ionomer, tended to fail less catastrophically than the other materials and, given their strength, would remain the material of choice in situations where abnormally high forces are expected.

Influence of adhesive systems on bond strength between fiber posts and composite resin cores in a pull-out test design

The aim of this study was to evaluate the effects of post surface conditioning with adhesive systems on tensile bond strength between two composite resin core systems and FRP posts (ER DentinPost). Forty-eight posts were trimmed at the coronal part, and the upper part of 3 mm was covered with a standardized composite resin core build-up. Twenty-four posts were treated with the respective adhesive systems. Four groups were formed: G1 - ClearfilCore; G2 - Clearfil New Bond + ClearfilCore; G3 - MultiCore Flow; and G4 - AdheSE + MultiCore Flow. Mean (SD) bond strengths in MPa were 7.53 (0.89) for ClearfilCore and 8.08 (0.93) for New Bond + ClearfilCore; 5.80 (0.39) for MultiCore Flow and 5.92 (0.43) for AdheSE + MultiCore Flow. ClearfilCore achieved significantly higher bond strengths than MultiCore Flow (two-way ANOVA; p<0.0001). In conclusion, composite resin core materials exerted a significant influence on tensile bond strength, while adhesive systems did not significantly affect the results.

Bond strength between fibre posts and composite resin cores: effect of post surface silanization

AIM

To evaluate the tensile bond strength between two different composite resin cores and (Clearfil Core, MultiCore Flow) and fibre posts (DT Light Post), with and without silanization of the post surface.

METHODOLOGY

Forty fibre posts were shortened to a length of 15 mm. Specimens were then produced by covering the upper 3 mm of the posts with standardized composite core build-ups. The bonding surfaces of twenty posts were treated with silane coupling agent (Monobond-S). Four experimental groups were formed: G1: Clearfil Core; G2: Monobond-S + Clearfil Core; G3: MultiCore Flow; G4: Monobond-S + MultiCore Flow. Each post was positioned upright in a post centric device with moulds to ensure standardized shapes of the abutments. After tensile bond strength testing, the type of failure at the interface was determined. The results obtained were compared using an unpaired sample t-test.

RESULTS

The mean tensile bond strengths and standard deviations were [MPa] 10.08 +/- 0.92 for Clearfil Core, 10.47 +/- 1.05 for Clearfil Core + silane; 6.65 +/- 0.79 for MultiCore Flow and 6.91 +/- 0.83 for MultiCore Flow + silane. Statistical analysis revealed that Clearfil Core achieved significantly higher bond strengths than MultiCore Flow (P < 0.0001). Post silanization had no significant effect. All tested specimens had an adhesive failure mode.

CONCLUSION

Type of composite had a significant effect on tensile bond strength. Silanization of fibre post surfaces had no effect on core retention.

Treatment concepts for restoration of endodontically treated teeth: A nationwide survey of dentists in Germany

STATEMENT OF PROBLEM

Opinions concerning proper restoration of endodontically treated teeth (ETT) vary. A variety of techniques and materials for post-and-core restorations are available. The rationale for post placement performed by German dentists was unknown.

PURPOSE

The purpose of this study was to determine current opinions, applied techniques, and materials for the restoration of ETT in Germany.

MATERIAL AND METHODS

A nationwide questionnaire-based survey containing 18 multiple choice questions regarding treatment philosophies, favored post type, and materials for core foundations was mailed to 36,500 German general dentists. A total of 6029 questionnaires (16.5%) were returned. Data were evaluated in terms of the dentists' occupational experience and the frequency of post placement. Descriptive statistics were used to analyze the data.

RESULTS

Irrespective of their occupational experience, 52% of the surveyed dentists consider post placement for almost every postendodontic restoration of ETT. The majority of dentists (54%) believe that a post reinforces ETT. Cast posts and cores are used by 55% of all dentists, whereas 34% use prefabricated posts exclusively. Screw posts are the most popular prefabricated post type (47%). Composite resin (51%) is preferred for core foundation, followed by glass ionomer cements (GICs) (26%). Amalgam is seldom used (0.5%). Posts are placed primarily with zinc phosphate cement (51%), followed by GIC (38%).

CONCLUSION

The treatment philosophy of German dentists is not in complete agreement with recommendations found in the literature. The belief that a post would reinforce an ETT might explain the high frequency of post placements. Due to the partially inconsistent responses, it is difficult to derive a generalized treatment concept.

Effect of dentin bonding and ferrule preparation on the fracture strength of crowned teeth restored with dowels and amalgam cores

STATEMENT OF PROBLEM

It is necessary to obtain an adequate bond at the core/dentin junction where the majority of failures occur. The effect of recently developed dentin bonding agents on the fracture resistance of endodontically treated teeth at the amalgam core/dentin junction is unclear.

PURPOSE

The purpose of this study was to evaluate the effects of 2 dentin bonding agents and a ferrule preparation on the fracture resistance of crowned mandibular premolars incorporating prefabricated dowel and silver amalgam cores.

MATERIAL AND METHODS

Sixty extracted mandibular second premolars were divided into 6 groups of 10 each. The coronal portion of each tooth was removed at the cemento-enamel junction (CEJ) in the first 3 groups. In the other groups, teeth were sectioned 1 mm above the CEJ to create a ferrule. After root canal preparations, prefabricated dowels (ParaPost) were placed. The first group served as a control and was tested without application of bonding agents and without incorporation of a ferrule design. In the second and third groups, respectively, an autopolymerizing adhesive (Superbond D-Liner) and a dual-polymerizing adhesive (Panavia F) were applied to tooth surfaces before restorative procedures. For the fourth (ferrule) group, no bonding agent was applied, but a 1-mm ferrule preparation was used. In the fifth (ferrule+D-Liner) and sixth (ferrule+Panavia F) groups, respectively, autopolymerizing and dual-polymerizing bonding agents were used in conjunction with the ferrule preparation. After amalgam core fabrication, Ni-Cr full cast crowns for each group were prepared and cemented. All specimens were stored in water for 1 week and thermal cycled 1000 times between 5 degrees and 55 degrees C. A compressive shear load was applied at an angle of 135 degrees to the crown, and the maximum load at fracture (N) was recorded. The data were analyzed with 1-way ANOVA and Tukey Honestly Significant Difference tests (alpha=.05).

RESULTS

Significantly higher fracture strength values were demonstrated for the ferrule+Panavia F (652.5 N), ferrule+D-liner (649.1 N) and ferrule (592.4 N) groups, respectively, than for the other groups. The next highest fracture strength values were found for the D-Liner (485.0 N) and Panavia F (486.3 N) groups. The control group (376.6 N) demonstrated the lowest fracture strength in all test groups (P<.001).

CONCLUSION

A ferrule preparation or a bonding agent designed for silver amalgam core-dentin bonding can each increase the fracture strength for teeth receiving cast crowns after endodontic therapy and dowel and amalgam core restorations.

Effect of an adhesive resin luting agent on the dowel-head retention of three different core materials

STATEMENT OF PROBLEM

A dowel-and-core restoration may fail due to failure at either the dowel-tooth or dowel head-core material interface. Long-term clinical success of a dowel-and-core restoration depends on retention of both the dowel to the tooth and the dowel head to the core material. Thus, strengthening of the dowel head-core interface is important.

PURPOSE

This study evaluated the retention between a prefabricated dowel and 3 different core materials with or without a dual-polymerized adhesive resin luting agent.

MATERIAL AND METHODS

Sixty prefabricated dowels (Gold Plated Anchorage Post) were divided into 3 groups (n=20) consisting of 1 of 3 core materials, amalgam (Standalloy F), light-polymerized resin composite (Clearfil Ray), or glass ionomer (Chelon-Silver). Each core group was divided into 2 subgroups (n=10), and a dual-polymerized adhesive resin luting agent (Panavia F) was applied to the dowel heads of 1 of these subgroups before application of the core material. The manufacturing procedure was standardized by using a plastic index (4.5-mm internal diameter and 5-mm height) and a custom-made dowel holder, which held the dowel head. Prepared specimens were stored in water at room temperature for 3 months and then loaded to fracture in a universal testing machine with a crosshead speed of 0.05 mm/min until failure. Bond strengths were recorded (MPa). Data were analyzed with 2-way analysis of variance (ANOVA) in a 2 x 3 factorial randomized design (alpha=.05). Afterward, core material differences were computed with 1-way ANOVA for both of the bonded and nonbonded groups. Post hoc multiple comparisons were made with the Dunnett C multiple range test.

RESULTS

Dowel-head retention values (MPa) of the tested core materials (mean +/- SD) from the highest to the lowest were as follows: bonded amalgam core, 296.1 +/- 108; bonded composite core, 284.3 +/- 38.3; nonbonded composite core, 177.0 +/- 53.7; nonbonded amalgam core, 128.5 +/- 35.0; bonded glass-ionomer core (GIC), 128.0 +/- 24.5; nonbonded GIC, 61.8 +/- 13.3. Two-way ANOVA revealed significant differences between the core material groups and between the bonded and nonbonded groups (P <.001). The interaction between the core material and bond variables was also significant (P =.018). One-way ANOVA revealed statistically significant differences between the bonded (P <.001) and also between the nonbonded core material groups (P <.001). Post hoc multiple comparisons showed that the dowel-head retention of the GIC was significantly weaker than the post-head retention for amalgam and resin composite, whether bonded or not.

CONCLUSION

Within the limitations of this study, the adhesive resin luting agent tested appeared to have a significant strengthening effect on the dowel-head retention of the core materials.

Fatigue resistance and structural characteristics of fiber posts: three-point bending test and SEM evaluation

OBJECTIVES

The aim of the present study was to assess the fatigue resistance of different types of fiber posts, and to observe their ultrastructure through scanning electron microscopy (SEM) before and after undergoing the fatigue test.

METHODS

Eight types of fiber posts were selected for this study. Easypost (Group 1), Para Post Fiber White (Group 2), FibreKor (Group 3), Ghimas White (Group 4), DT Light-Post radiopaque (Group 5), FRC Postec (Group 6), Luscent Anchors (Group 7), Snowpost (Group 8). Ten out of fifteen posts in each group were used for the fatigue test, and the other five were processed for SEM. A three-point bending machine, loading at an angle of 90 degrees and a frequency of 3 Hz was employed for fatigue testing. The test was carried out until two million cycles were completed or until fracturing of the post. SEM evaluation was performed using a three-step scale method to assess the fiber/resin ratio and fiber dimension.

RESULTS

The fatigue test showed statistically significant differences among the different posts. Groups 5 and 6 performed better than all the other groups, withstanding practically all the stipulated number of load cycles. All the other posts fractured before the end of the test. SEM observations of the surface integrity of the fiber posts showed that Groups 4-6 obtained better scores for both longitudinal sections and cross-sections.

SIGNIFICANCE

There was a large variation in the response of different kinds of fiber posts a fatigue resistance test. The absence of correlation between results of fatigue testing and parameters of structural integrity suggests that the latter mostly reflect random variations in the fiber post manufacturing process.

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.

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.

Effect of fatigue testing on core integrity and post microleakage of teeth restored with different post systems

The purpose of this study was to evaluate a new nondestructive test system, which could test concurrently fatigue and microleakage. Fifty, single-rooted teeth were restored with one of the following posts systems and a composite core: titanium ParaPost cemented with zinc phosphate cement; CosmoPost; C-Post; Esthetic C-Post; and FibreKor post, all cemented with resin cement. Samples were embedded and placed in a positioning jig. They were impacted at 45 degrees to the long axis of the tooth with a force of 55 N at a frequency of 3 Hz for a total of 100,000 impacts. After 60,000 impacts, samples were thermocycled. Core integrity and post microleakage were evaluated periodically throughout the 100,000 impacts. Samples showed no detectable displacement of any of the cores, but the metallic group showed a statistically significant increase in microleakage (p < 0.05) at the conclusion of the study compared with the nonmetallic groups.

Restoration of the endodontically treated tooth

It has been the purpose of this article to provide a rationale for the restoration of endodontically treated teeth. Treatment recommendations have been made in the areas of post design, placement technique, cements, core materials, and definitive restorations, based on a review of the clinical and laboratory data.

Influence of core buildup material on the fatigue strength of an all-ceramic crown

STATEMENT OF PROBLEM

Clinically relevant variables and testing methods have not been used to investigate the effects of core buildup materials on the strength of all-ceramic restorations.

PURPOSE

The aim of this study was to evaluate the compressive strength of Optimal Pressable Ceramic (OPC) all-ceramic crowns supported by 1 of 3 different core materials and subjected to static or cyclic loading in air or water.

MATERIAL AND METHODS

A total of 135 human extracted third molar teeth were divided into 3 equal groups, and cores of amalgam, composite, and dentin (control) were fabricated. Complete crown preparations with a circumferential 90 degrees shoulder margin 1 mm deep were prepared to support complete crown restorations. Testing in compression was performed at a loading rate of 2.0 mm/min. Sixty teeth (20 with each type of core) were subjected to static loading, with equal numbers tested in air and water. The remaining 75 teeth (25 with each type of core) were subjected to cyclic loading in water. The compressive and diametral tensile strengths of 6 x 12-mm OPC cylinders also were tested in both air and water. The data were analyzed with 1-way analysis of variance followed by the Tukey multiple means comparison test (P<.05).

RESULTS

Analysis of the static fracture stress of OPC crowns indicated no significant differences among the core materials (values from testing in air and water, respectively: dentin core 22.7 +/- 4.5 MPa and 19.7 +/- 4.7 MPa; amalgam core 25.2 +/- 5.2 MPa and 21.6 +/- 6.3 MPa; and composite core 20.9 +/- 4.1 MPa and 18.7 +/- 4.9 MPa). Under wet conditions, static versus cyclic loading produced significantly different results for each of the core materials (dentin core 19.7 +/- 4.7 MPa vs. 9.5 +/- 1.5 MPa; amalgam core 21.6 +/- 6.3 MPa vs. 10.3 +/- 1.6 MPa; composite core 18.7 +/- 4.9 MPa vs. 13.3 +/- 3.2 MPa). A significant difference was observed for the solid compressive cylinders tested in water (793.8 +/- 280.1 MPa) versus in air (1473.6 +/- 527.4 MPa).

CONCLUSION

Within the limitations of this study, the mean compressive strength of OPC crowns tested in water was significantly different under cyclic versus static loading. No significant difference among the 3 core materials was found with respect to crown compressive strength.

In vitro fatigue resistance of glass ionomer cements used in post-and-core applications

STATEMENT OF PROBLEM

New glass ionomer cements exhibit better mechanical properties than their older counterparts. However, there is concern about their use as a core material in post-and-core applications.

PURPOSE

This in vitro study evaluated the fatigue resistance of 2 new glass ionomer cements, Shofu Hi-Dense and Fuji IX GP, and compared their mechanical behavior as a core material under masticatory load with a silver-reinforced glass ionomer (ESPE Ketac-Silver) and a silver amalgam (Cavex Avaloy LC).

MATERIAL AND METHODS

A total of 100 commercial plastic teeth were divided into 4 groups of 25 specimens each. Titanium posts were placed in the prepared root canals, and cores were built up in amalgam, silver-reinforced glass ionomer cement, and the 2 new glass ionomer cements. The post-and-core specimens were prepared for full cast metal crowns, which were fabricated and cemented with glass ionomer cement. Twenty specimens from each group were placed in a mastication simulator and cyclically loaded with a 400 N force for 1.5 million cycles. The 5 remaining specimens were used as controls. The specimens were sectioned and observed macroscopically and microscopically to determine the number of defects (alterations) in each material. Observed defects were verified with the Kruskal-Wallis test, and the 4 core materials were ranked with the Tukey multiple comparisons test.

RESULTS

The mean rank sum values of the defects were as follows: Cavex Avaloy LC Amalgam (16.75), Fuji IX GP (38.50), Shofu Hi-Dense (39.53), and ESPE Ketac-Silver (67.22). The amalgam alloy was significantly different (P< .05) from the others.

CONCLUSION

Under the conditions of this study, the 2 new glass ionomer cements used as core materials showed a higher number of defects than amalgam. These results suggest that their fatigue resistance may be inadequate for post-and-core applications.