A comparison of two post systems under applied compressive-shear loads

Influence of size-anatomy of the maxillary central incisor on the biomechanical performance of post-and-core restoration with different ferrule heights

PURPOSE

The study aims to investigate the influence of the ferrule effect and types of posts on the stress distribution in three morphological types of the maxillary central incisor.

MATERIALS AND METHODS

Nine models were created for 3 maxillary central incisor morphology types: "Fat" type - crown 12.5 mm, root 13 mm, and buccolingual cervical diameter 7.5 mm, "Medium" type - crown 11 mm, root 14 mm, and buccolingual cervical diameter 6.5 mm, and "Slim" type - crown 9.5 mm, root 15 mm, and buccolingual cervical diameter 5.5 mm. Each model received an anatomical castable post-and-core or glass-fiber post with resin composite core and three ferrule heights (nonexistent, 1 mm, and 2 mm). Then, a load of 14 N was applied at the cingulum with a 45° slope to the long axis of the tooth. The Maximum Principal Stress and the Minimum Principal Stress were calculated in the root dentin, crown, and core.

RESULTS

Higher tensile and compression stress values were observed in root dentin using the metallic post compared to the fiber post, being higher in the slim type maxillary central incisor than in the medium and fat types. Concerning the three anatomical types of maxillary central incisors, the slim type without ferrule height in mm presented the highest tensile stress in the dentin, for both types of metal and fiber posts.

CONCLUSION

Post system and tooth morphology were able to modify the biomechanical response of restored endodontically-treated incisors, showing the importance of personalized dental treatment for each case.

Posts--when it all goes wrong! Part 1: case assessment and management options

Posts have been used for many years to retain restorations or cores for extra-coronal restorations in endodontically treated teeth.This article discusses the variety of post systems that are available and the incidence and reasons for failure of teeth that have been restored with posts. The treatment options available for the management of such failures are considered, in addition to the indications for both non-surgical and surgical management of endodontic failures. The attitudes of dentists and the perceived complications of attempting post removal are reviewed, along with the evidence to support the prevalence of complications.

CLINICAL RELEVANCE

Failure of post-retained restorations is a relatively frequent finding due to failure of the restoration itself or the endodontic treatment. It is therefore important to understand and be aware of the various treatment options available, their indications and associated risks.

Effect of eugenol-based root canal sealers on retention of prefabricated metal posts luted with resin cement

OBJECTIVE

This study evaluated the effect of two different eugenol-based root canal sealers on the retention of prefabricated metal posts luted with adhesive resin cement.

MATERIALS AND METHODS

Thirty prefabricated ParaPosts randomly divided among three groups of 10 each were luted into extracted single-rooted teeth with adhesive resin cement. Two of the groups had been obturated with Gutta-Percha and one of two eugenol-based root canal sealers (Endofil and Tubli-Seal), respectively. The third group was not obturated and served as the control. The forces required for dislodgment of posts from their prepared post spaces were recorded using a universal testing machine. Data were statistically analyzed using one-way ANOVA and Tukey's multiple range test was used to determine the mean differences.

RESULTS

Endofil and Tubli-Seal groups demonstrated significantly reduced retention compared to the unobturated (control) group (P < 0.05).

CONCLUSION

Eugenol-based sealers significantly reduced the retention of prefabricated posts luted with adhesive resin cement.

Resistance of three new esthetic post-and-core systems to compressive loading

STATEMENT OF PROBLEM

Despite their esthetic properties, the fracture resistance of newly introduced esthetic post-and-core systems has not been studied, restricting clinical use.

PURPOSE

The purpose of this study was to determine and compare the fracture resistances of 3 recently introduced esthetic post-and-core systems with a cast metal post and core using a clinically related test method.

MATERIAL AND METHODS

Forty recently extracted caries-free maxillary central incisors were selected, sectioned, and their roots endodontically treated. The roots were then embedded in acrylic resin blocks and assigned to 4 experimental groups (n = 10). The cast metal (Wiron 99) post-and-core group (CMDC) served as the control. Three experimental groups consisted of a stainless steel post/composite-resin (Charisma) core group (SCOM), zirconium dioxide post/composite-resin (Charisma) core group (ZCOM), and zirconium dioxide post/ceramic (Cosmopost) core group (ZCER). The post spaces were prepared, posts were seated, cores were formed, and 40 post-and-core foundations were cemented into the roots. Following thermal cycling (5000 cycles between 5 degrees C and 55 degrees C with a dwell time of 30 seconds), a compressive load was applied to the inclined surface of each specimen at a 130-degree angle to the specimen long axes in a universal testing machine at a crosshead speed of 1 mm/min until failure occurred. Force to failure (N) was recorded. Data were analyzed with a 1-way analysis of variance and Bonferroni tests to determine the difference between the groups (alpha=.05). For pairwise comparisons among group mean values, P < .0083 indicated statistical significance and established the overall confidence level at 95%.

RESULTS

Groups CMDC (738.6 N +/- 10.2) and ZCER (710.2 N +/- 5.3) exhibited the highest resistance to fracture. The ZCOM group showed the lowest fracture resistance (450.3 N +/- 5.7). The fracture resistance of the SCOM group (565 N +/- 7.2) was lower than the CMDC and ZCER groups, and higher than the ZCOM group. The differences among the groups were significant (P < .001) except for CMDC and ZCER (P < .016).

CONCLUSION

Within the limitations of this study, the cast metal post/core and zirconia post/ceramic core foundations were found to be more fracture resistant than the zirconia post/composite-resin core and stainless steel post/composite-resin core foundations. Aside from its desirable esthetic properties, the zirconia post/ceramic core combination demonstrated high resistance to fracture.

In vitro evaluation of the retention of zirconia-based ceramic posts luted with glass ionomer and resin cements

The retention of zirconia-based ceramic posts (CosmoPost system) luted with glass ionomer and resin cements was evaluated. Thirty-two extracted, caries-free, unrestored teeth were selected and stored in chlorhexidine and water solution. The teeth were endodontically treated and randomly assigned to two groups (n=16). Each tooth was decoronated and prepared to a depth of 10.0 mm from root surface to receive a 1.4 mm diameter zirconium dioxide post. Each group had posts cemented with either glass ionomer cement (Fuji I) or resin cement (Variolink II). The post/teeth specimens were embedded in resin blocks and subjected to tensile testing. The tensile force required to dislodge the cemented posts in a tensile testing machine was recorded. The mean stress values of both groups were analyzed for statistical differences using ANOVA and Student's t-test. Significance level was set at 5%. Mean peak forces at failure (N) and standard deviation for the tested cements were the following: Fuji I = 121.8 (±17.4) and Variolink II = 228.1 (±36.8). Posts luted with the resin cement presented statistically significant higher tensile bond strength than those retained with glass ionomer (p<0.05). It may be concluded that zirconia posts cemented with resin-based cement (Variolink II) failed at statistically significant higher values compared to those cemented with glass ionomer cement (Fuji I). Regardless of the cement type, the posts failed adhesively at the cement/post interface when subjected to a tensile force.

Effect of core stiffness on the in vitro fracture of crowned, endodontically treated teeth

STATEMENT OF PROBLEM

Dentin and core materials that substitute for missing dentin are dissimilar materials. A core material with a lower elastic modulus may deform more under applied stress and therefore result in reduced stress concentration at the core/dentin junction.

PURPOSE

This in vitro study examined the effect of core stiffness on the fracture resistance and failure characteristics of a crowned, endodontically treated tooth under simulated occlusal load.

MATERIAL AND METHODS

Forty extracted human mandibular premolars were divided equally into 4 groups and prepared for posts and cast crowns as follows: group 1 = cast post and core, cast crown; group 2 = preformed metal post, composite core, and cast crown; group 3 = preformed metal post, amalgam core, and cast crown; and group 4 (control) = preformed metal post, no core, and cast crown. All prepared teeth had 2 mm of sound dentin on which the cemented crown rested. A continuous load (kg) was applied to the buccal cusp at a 30-degree angle to the long axis of each tooth at a crosshead speed of 2 mm/min until failure. Collected data were subjected to 1-way analysis of variance with the Welch modification to compare groups (P<.05).

RESULTS

Failure loads for the 4 test groups were as follows: 98.1 +/- 34.6 kg (group 1), 94.4 +/- 41.8 kg (group 2), 105.5 +/- 18.6 kg (group 3), and 101.1 +/- 55.3 kg (group 4). No significant difference in failure load values was found among the 4 groups. The primary mode of failure (80%) in all groups was an oblique radicular fracture, either apical to the post or at the post level. Horizontal fracture of the root and post was found in groups 1, 2, and 3 (20%). Loosening of the crown, post, and core was found only in group 2(20%).

CONCLUSION

Within the limitations of this study, core stiffness did not affect the failure resistance of teeth restored with posts and cores and complete-coverage cast metal crowns. The dominant pattern of failure was unrepairable root fracture. Only the composite core exhibited repairable fractures.

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.

Effect of prefabricated metal post-head design on the retention of various core materials

Retention of various post heads to core restorative materials is an important factor in the selection of prefabricated post systems and restorative materials for the restoration of endodontically treated teeth. This study examines the retention of a post-core prefabricated system in relation to core material and post-head design. A total of 60 samples were prepared using two different post systems (ParaPost Plus (PP) and ParaPost Unity (PU), with amalgam, composite or glass-ionomer as one of the core materials. The samples were tested using the Instron testing machine. The PP was superior to the PU prefabricated post with respect to the retention of various core materials. Retention values in descending order of magnitude were found to be: composite, amalgam and glass-ionomer (significantly lower). The rhomboid serrated design of PP was superior in retention to the rounded smooth UP system. Composite material proved to be superior in retention, closely followed by amalgam, with glass-ionomer significantly less retentive.

Stiffness, elastic limit, and strength of newer types of endodontic posts

OBJECTIVES

To determine the stiffness, elastic limit, and strength of a selection of endodontic posts recently introduced onto the market.

METHODS

Endodontic posts of zirconia (Biopost, Cerapost), titanium (PCR), and carbon fiber (Composipost) were cemented in a brass block and loaded at an angle of 45 degrees in an Instron Testing Machine. From the recorded relationship between force and deflection the three mechanical properties were determined (n = 10 in each group).

RESULTS

The ceramic posts were very stiff and strong, with no plastic behavior. The PCR post was as strong as, but less stiff than, the ceramic posts. Composipost had the lowest values for stiffness, elastic limit, and strength of the posts investigated.

CONCLUSION

The posts under investigation differed significantly with respect to mechanical properties.

Esthetic restoration of endodontically treated teeth: factors that affect prognosis

Restoration of endodontically treated teeth involves a complex system of components and component interfaces designed to resist force. Dental materials, forces on teeth, clinical circumstances, and restorative design determine restoration success. A new classification evaluates number of canals, amount of remaining tooth surface, chamber space, canal quality, and canal orientation.

Retention of three endodontic posts cemented with five dental cements

STATEMENT OF PROBLEM

The retention of a post is believed to be a major factor in restoration survival. Therefore the cement with the greatest in vitro retention property should give the best performance for a restoration.

PURPOSE

This study compared retentive values of three posts (Flexi-Post, AccessPost, and ParaPost) cemented with five cements (Flexi-Flow, zinc phosphate, Advance, Duet, and Ketac-Cem) plus a control group that consisted of a Flexi-Post No. 2 dowel without cement.

MATERIAL AND METHODS

A total of 160 recently extracted human single-rooted teeth with crowns removed at the cementoenamel junction were divided into 16 groups of 10 samples. Post holes were prepared according to manufacturers' instructions. Posts were then cemented with one of the five cements. Each sample was placed into a specialized jig and on a tensile testing machine with crosshead speed of 0.638 cm/minute, applied until failure. A two-way analysis of variance and Newman-Keuls multiple range comparison tests were performed for all cemented groups. A one-way analysis of variance and a Student-Newman-Keuls multiple range comparison test were performed only for the groups with the Flexi-Post dowel, this included the no cement condition, with significant results if p < 0.05.

RESULTS

Flexi-Post dowel with Flexi-Flow Natural cement obtained the highest retentive value (303.91 pounds). ParaPost dowel with Duet cement exhibited the lowest retention value (21.23 pounds). The Flexi-Post dowel demonstrated higher mean retention than AccessPost or ParaPost dowels, AccessPost dowel was higher than ParaPost dowel. Flexi-Flow cement had the highest overall mean retention followed, in decreasing order, by zinc phosphate, Advance, Ketac-Cem, and Duet cements.

CONCLUSIONS

Flexi-Post dowel was the most retentive post studied with values ranging from 303.91 pounds with Flexi-Flow Natural cements to 150.93 pounds without cement. Flexi-Flow cements had a higher overall mean retention than other cements studied.

Esthetic, biologic and restorative considerations in coronal segment reattachment for a fractured tooth: a clinical report

Reattachment of a fractured clinical crown involving minimal invasion of the biologic width can be accomplished without conventional ostectomy and crown lengthening so that satisfactory esthetics can be achieved. Adhesive techniques sometimes in conjunction with traditional mechanical retention, such as a post, can be used to reattach the fractured segment. An esthetic result can be obtained with a minimal number of procedures and cost to the patient.

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

Thirty-six maxillary central incisors were endodontically treated and restored with a post and core and cast crown. Three different post and core systems were evaluated. Restored teeth were fatigue-loaded until preliminary failure of the casting occurred as detected by a strain gauge bonded across the lingual margin of the cast crown. After preliminary failure, fatigue loading was continued for 100,000 load cycles with the crown margin exposed to basic fuschin dye. Teeth were then immersed in dye for 24 h, sectioned, and evaluated for leakage. There was no significant difference in the number of load cycles required to cause preliminary failure among the three post and core systems. Leakage occurred in all three groups, with no significant difference between groups. The occurrence of preliminary failure is clinically undetectable, yet it allows leakage between the restoration and tooth that may extend down the prepared post space.

Cyclic fatigue testing of five endodontic post designs supported by four core materials

PURPOSE

This pilot study examined the cyclic fatigue of five endodontic post systems (AccessPost, Flexi-Flange, Flexi-Post, ParaPost, and Vlock) with four core materials (Tytin silver amalgam, Ti-Core, Ketac-Silver and G-C Miracle Mix).

MATERIAL AND METHODS

In vitro cyclic fatigue was performed with a machine designed to simulate masticatory fatigue forces. An instantaneous force of 22.2 N (5 pounds) was applied to each post and core combination for a test configuration of 4,000,000 repetitions, or until failure occurred. The type of failure and number of repetitions at failure was recorded for each sample tested. Two-way analysis of variance (ANOVA) was used to compare groups.

RESULTS

All posts/core samples with Ti-Core composite and Tytin silver amalgam completed the test with no failures. All posts/core samples with Ketac-Silver material failed before the 4,000,000 test cycle configuration and all failures were core failures. All posts/core samples with G-C Miracle Mix material failed in a similar manner. Newman-Keuls multiple comparison test illustrated that, with this simulated fatigue test, Ti-Core material and Tytin silver amalgam were superior to both G-C Miracle Mix and Ketac-Silver materials.

Effect of different surface textures on retentive strength of tapered posts

STATEMENT OF PROBLEM

Tapered posts allow for the preservation of tooth substance in the fragile apical area and are advantageous in clinical situations where they conform to the root and canal configuration of endodontically treated teeth. However, their lower retention compared with passive parallel-sided or active threaded posts is a disadvantage.

PURPOSE

This study determined the retentive strength of tapered titanium posts with different surface textures and examined the effect of roughening dentinal walls of the prepared post space.

MATERIAL AND METHODS

Posts with four surface configurations (smooth, with and without grooves, and sandblasted, with and without grooves) were examined when cemented in extracted anterior teeth.

RESULTS

The smooth post showed the lowest retentive strength. Sandblasting the smooth post more than doubled its retentive strength. The retentive strength of both smooth and sandblasted posts could be further increased by the addition of circumferential grooves. Roughening the dentinal walls of the prepared post space increased the retentive strength of sandblasted posts with and without grooves even more.

CONCLUSIONS

These findings indicated that, when a tapered post is used, roughening the dentin canal wall, as well as sandblasting and grooving the post, can provide statistically significant additional resistance to dislodgment.

Four different core materials measured for fracture strength in combination with five different designs of endodontic posts

The purpose of this in vitro study was to determine the fractural load of four core materials supported by five post designs. This study was divided into 20 groups with 10 samples per group. Specimens were placed in a special jig at a 45-degree angle, and the fracture load values, in pounds, were obtained with the use of a universal testing machine. A 5 x 4 factorial design was used to assess and compare the fractural strength, and a two-way analysis of variance was used to determine whether the buccolingual, mesiodistal, and height dimensions differed across groupings. Mean fracture load values were obtained. Flexi-Post dowel/Ti-Core material at 277.1 pounds and ParaPost dowel/ Tytin silver amalgam at 277.3 pounds recorded the greatest mean values. These values were not statistically different. ParaPost dowel/Ketac-Silver material had the lowest mean value (49.6 pounds). For all posts Tytin silver amalgam and Ti-Core material were significantly stronger than Ketac-Silver and G-C Miracle Mix material. Ketac-Silver and G-C Miracle Mix materials did not differ from each other. Results indicated that Ti-Core composite material is at least as strong as Tytin silver amalgam.

Comparative study of two precision overdenture attachment designs

In this study two precision overdenture attachment designs were tested for retention--a nylon overdenture cap system and a new cap and keeper system. The new cap and keeper system was designed to reduce the time involved in replacing a cap worn by the conditions of the oral environment. Six groups were tested at two different angles and retentive failure was examined at two different angles (26 and 0 degrees). Failure was measured in pounds with a force gauge over a 2000 pull cycle. The amount of force required to remove caps for two overdenture caps and a replaced cap for the metal keeper system was determined. Two dependent variables were absolute force and relative force. Repeated measures analysis of variance (RMANOVA) was used to compare the between-subjects effects of cap and angle, and the within-subjects effect of pull. The results indicated a significant difference between cap types (p < 0.0001) with respect to the relative force required to remove the cap. There was no effect of angle. For absolute force, RMANOVA revealed a highly significant interaction between pull and cap (p < 0.0001). Thus, the way that force changed over pulls depended on which cap was used (no effect of angle). For relative force, RMANOVA revealed no interaction between pull and cap, but there was a main effect of cap type (p < 0.0001) (no effect of angle). The nylon cap design required less force for removal but showed more consistency in the force required over the course of the 2000 pulls when compared with the keeper with cap insert. The results obtained in this study were consistent with similar studies in literature.

Compressive characteristics of an internally threaded post system

PURPOSE

The effects of oblique compressive forces were evaluated for extracted teeth restored with posts of solid and internally threaded designs.

MATERIALS AND METHODS

A group of 25 roots was restored with crowns supported by Para-post dowels and pin-retained composite resin cores, and a second group was restored with gold copings cast to internally threaded stainless steel-post prototypes. Samples were then embedded in epoxy resin and loaded at 45 degrees until failure. Failure force and type were statistically analyzed to determine statistical difference (P < .05) between groups.

RESULTS

No statistical difference was shown between groups for either fracture force or type.

CONCLUSIONS

The internally threaded post system resisted oblique loading forces similarly to a solid post system.

Comparison of fatigue for three prefabricated threaded post systems

Post designs may have a direct effect on fracture resistance of endodontically treated teeth. This in vitro study compared the resistance of three prefabricated threaded post systems with lateral shearing forces. After endodontics were completed, prefabricated posts were inserted according to the manufacturer's instructions. A silver amalgam core was placed, and extracted human teeth were prepared to a standard size with a 1 mm gingival chamfer finished on sound dentino A cast was fabricated and cemented, and the specimens were thermocycled. The test samples were secured to an Instron testing machine and loaded until failure. Fracture patterns were recorded, fractured surface areas were measured, and compressive stresses were calculated. However, there were no statistically significant differences among threaded posts in each test group.

Comparison of the torsional forces at failure for seven endodontic post systems

Resistance to torsional forces is critical in restoration of endodontically treated teeth. Seven post designs (Flexi-Post, Flexi-Flange, Para-Post, AccessPost, World Post, Vlock, and Dentatus posts) were cemented in roots of natural teeth with zinc phosphate and Flexi-Flow cements, which resulted in 11 different groupings that were subjected to torsional forces in a clockwise direction. In addition, clockwise and counterclockwise torque was applied to the Flexi-Post and Flexi-Flange systems cemented with zinc phosphate and Flexi-Flow cements. A total of 150 samples were prepared, and groups for this study were: group 1, Flexi-Post/zinc phosphate clockwise and counterclockwise; group 2, Flexi-Post/Flexi-Flow clockwise and counterclockwise; group 3, Flexi-Flange/zinc phosphate clockwise and counterclockwise; group 4, Flexi-Flange/Flexi-Flow clockwise and counterclockwise; group 5, Para-Post/zinc phosphate clockwise; group 6, AccessPost/zinc phosphate clockwise; group 7, AccessPost/Flexi-Flow with grooved dentin clockwise; group 8, World Post/zinc phosphate clockwise; group 9, World Post/Flexi-Flow with grooved dentin clockwise; group 10, Vlock Post/zinc phosphate clockwise; and group 11, Dentatus post/zinc phosphate clockwise. Torsional forces for the groups ranged from 17 ounce-inches (Dentatus/zinc phosphate) to 81 ounce-inches (Flexi-Post/zinc phosphate). Flexi-Post and Flexi-Flange threaded posts exhibited statistically greater resistance to torsional forces. Analyses were computed with one-way and three-way analysis of variance followed by Duncan's multiple range test. Duncan's multiple range test indicated that Flexi-Post/zinc phosphate/clockwise was similar to Flexi-Post/Flexi-Flow/clockwise and that both had significantly higher torque levels than the other treatment conditions in the clockwise direction (p 0.0001). Dentatus/zinc phosphate/clockwise had significantly lower torque levels than the other treatment conditions (p 0.031).

Presentation of a new Flexi-Flange post system for clinical use

Advantages of a new post design, Flexi-Flange are described. It incorporates a split-shank parallel threaded post with a flange that seats into an occlusal countersunk dentine space. This case report describes placement of three Flexi-Flange posts in a first bicuspid, canine and central incisor. The Flexi-Flange system was designed to offer high retention of the post in the root, superior distribution of stresses on insertion and under function, and long-term resistance to metal fatigue.

Comparison of the photoelastic stress for a split-shank threaded post versus a threaded post

PURPOSE

This study compared the stress distribution during insertion and after cementation for two prefabricated endodontic posts, (1) a split-shank threaded post, and (2) a threaded post with no split in the shank.

MATERIALS AND METHODS

Three test blocks of photoelastic material were prepared with simulated endodontic canals for each group studied. Specimens were then photographed after insertion and cementation.

RESULTS

Minimal stresses were observed for the post with a split (group 1) throughout the length of the shaft, whereas asymmetric patterns of stresses for the post without a split (group 2) were present. Stress distribution for the post without a split were concentrated more apically rather than coronally.

CONCLUSIONS

The presence of a split reduces insertion and cementation stresses for this post system. The split also acts as a vent during the cementation of the post into the canal and minimizes stress concentration during cementation.

Retentive properties of three post-core systems

The retention in root canals of Flexi-Posts, Para-Posts and Brasseler/Vlock-Posts was measured using tensile and compressive/shear forces. Forty-two extracted maxillary anterior teeth were embedded in self-curing acrylic resin and treated endodontically. Each root canal was prepared with the appropriate matching drills for the post-core system chosen. Each post-core was cemented in the canal with zinc phosphate cement. A tensile force was applied along the long axis of each tooth and the force needed to dislodge the post-core was recorded. There was no difference in retention between the small diameter posts, but the difference between the medium and the large diameter posts, however, was significant. In the medium diameter post group, the Flexi-Post was approximately twice as retentive as the other two post-core systems evaluated. In the second series of tests compressive/shear force was applied at an angle of 130 degrees to the long axis of the tooth. The retention difference between the small diameter posts was found to be statistically significant, Flexi-Posts being more retentive than Para-Posts and B/V-Posts.

Comparison of the retentive properties of two hollow-tube post systems to those of a solid post design

The retention of a post in a root is critical for the successful restoration of an endodontically treated tooth. This study compared the retention of two hollow-tube post designs (Access post and World post) cemented with zinc phosphate cement or a titanium-reinforced composite resin cement (Flexi-Flow cement with titanium) with that of the control Para-Post system, a solid post design cemented with zinc phosphate cement. The experiment was divided into 11 groups of 10 samples. Retentive values were measured with a universal testing machine and the data were recorded in pounds. A one-way analysis of variance was computed and included Duncan's multiple comparisons test, Tukey's Student range test, and Dunnett's test. Duncan's multiple comparison test and Tukey's test were inconclusive. Only Dunnett's test revealed a significant difference between group 5, Access post, grooved dentin with Flexi-Flow cement with titanium (mean of 89.7 lb), and the control, group 11, Para-Post dowel cemented with zinc phosphate cement (mean of 61.3 lb). All other groups exhibited similar results with retentive values that ranged from 62 to 76 lb.

The philosophies of dowel diameter preparation: a literature review

This article reviewed the literature regarding the diameter of dowels and identified three distinct philosophies of dowel space preparation. One group advocated the narrowest diameter for fabrication of a dowel to a desired length. Another recommended a dowel space with an apical diameter equal to one third of the narrowest dimension of the root at the terminus of the dowel. A third group advised that at least 1 mm of sound dentin should surround the entire surface of the dowel. A combination of the one third and 1 mm minimal philosophies yielded a practical guideline for dowel space preparation, particularly in aged teeth. Requiring a definite amount of tooth structure surrounding the dowel, while adhering to the one third proportion, indicated upper limits on both the diameter and length of the dowel. These calculated limits served as convenient starting points in selecting a specific style of dowel and assisted in determining whether additional measures are warranted to enhance dowel retention.

Effect of post design on resistance to fracture of endodontically treated teeth with complete crowns

The effect of post design on the fracture resistance of endodontically treated premolars restored with cast crowns was examined in vitro. The experimental model used cast posts and cores to test the effect of post design in a post-core system with identical rigidity. Samples loaded on an Instron testing machine until failure revealed that post design did not influence the fracture resistance of endodontically treated premolars restored with complete cast crowns. There was also no statistically significant difference between restored teeth with or without cast posts and cores.

Retention properties of a split-shaft threaded post: cut at different apical lengths

The retention of the post to the root of an endodontically treated tooth is critical for a successful restoration. Modification of the post length to accommodate a specific clinical situation is common. This study compared the retention of No. 1 and No. 2 Flexi-Post restorations shortened apically from 1 to 5 mm with that reported for full-length control No. 1 and No. 2 Flexi-Post dowels. The experimental material was divided into 10 groups with 10 samples in each group. Retentive values were recorded in pounds with a universal testing machine. Analysis of variance with a Tukey-Student range, multiple-comparison test showed no statistical differences from apical reductions of 1, 2, 3, and 5 mm including the full-length control Flexi-Post No. 1 system. With 4 mm of apical shortening statistically greater retention was recorded. No statistical differences resulted with apical reductions of 1 to 4 mm or with the full-length control Flexi-Post No. 2 system, but 5 mm of apical shortening caused significantly less retention.

Retentive properties of threaded split-shaft posts with titanium-reinforced composite cement

The retention of posts in tooth roots is vital to the success of the restoration. This study compared the retention of posts of various sizes and diameters cemented with a titanium-reinforced composite cement with that of posts previously reported cemented with zinc phosphate cement. Four groups made up of 10 samples each were used and retention values were compared using a universal testing machine. Two-way analysis of variance and the Newman-Keuls multiple range comparison test were performed. Larger diameter posts cemented with titanium cement had better retention than similar posts cemented with zinc phosphate cement. The statistical increase in retention for the larger size posts is probably the result of the deeper channels (threads) in the dentin and the higher cohesive strength for the titanium-reinforced composite resin.

Comparison of retentive properties of four post systems

This study compared the retention of posts in the root for various diameters (1.3 mm and 1.6 mm) of three prefabricated post systems (Unity, Filpost, and Brasseler) with that of the previously reported No. 1 and No. 2 Flexi-Post systems. The experiment was divided into three groups comprising 10 samples for each post system studied. In group 2, the Filpost system was cemented both with a resin cement and zinc phosphate cement. Retention values were obtained with a modified universal testing machine. The retention of 1.3 mm posts from most to least retentive was Flexi-Post (zinc phosphate) greater than Filpost (zinc phosphate) greater than Filpost (resin) greater than Brasseler (zinc phosphate), greater than Unity (resin). The retention of 1.6 mm posts from most to least was Flexi-Post (zinc phosphate) greater than Filpost (zinc phosphate) greater than Brasseler (zinc phosphate), Unity (resin) greater than Filpost (resin). The Filpost system achieved higher retention with zinc phosphate cement than it did with resin cement.

Fatigue behavior of direct post-and-core-restored premolars

Evaluation of long-term mechanical behavior of new types of restorations in clinical trials is time-consuming. A partial alternative can be found in experimental fatigue-testing, which simulates accelerated mechanical deterioration. The aim of this study was to determine the feasibility of using fatigue-testing of a complex dental restoration and to evaluate the mechanical fatigue behavior of premolar teeth restored with a titanium alloy post and an amalgam or composite core. Eighty-seven human upper premolar teeth were decoronated, embedded, and restored with a prefabricated post of 1 mm diameter. The teeth were randomly assigned to one of two groups corresponding with a core build-up of amalgam or chemically-cured core composite, respectively. Five to 21 days after restoration, the specimens were subjected to cyclic loading (frequency, 5 Hz), at an angle of 45 degrees to the long axis of the tooth. The boundary technique was used for determination of the mean fatigue strengths of the restorations at 10(4), 10(5), and 10(6) cycles, simulating up to 1-3 years of clinical functioning. Mean fatigue strength was expressed in percentage of initial strength: For 10(4), 10(5), and 10(6) cycles, the results were 66%, 58%, and 52%, respectively, for the amalgam and 62%, 62%, and 53% for the composite group. It is concluded that fatigue-testing of more complex systems is possible, if a suitable testing method is selected. The restorations showed a comparable strength reduction after 10(6) cycles of about 50% of their initial strength. The composite core build-up showed a behavior less predictable than that of the amalgam, which might be attributed to handling parameters.

Flexural and fatigue strengths of root canal posts

This study measured the flexural and fatigue strengths of root canal posts of different alloy, design, and diameter. Fixed posts were loaded up to a preset force and the number of loadings endured until fracture was recorded at each loading force. The flexural strength was defined as the maximum force a post could endure before fracture when loaded once. The fatigue strength was determined as the maximum force a post could endure when loaded 10,000 times. Both modes of strength were found to increase with increasing diameter. Aluminum posts had lower flexural and fatigue strengths than posts of titanium, stainless steel, and a Ag-Pd alloy, all of which had strength values of about the same magnitude. Among the investigated brands, Triax and Radix were stronger than the others at comparable diameters. The high strength of Triax may be explained by the design of the post, whereas a superior alloy may account for the high strength of Radix.