Evaluation and restoration of endodontically treated posterior teeth

Radiographic assessment of the quality of post and core restorations performed by general dental practitioners in Saudi Arabia

Background

Dentists utilize various techniques and materials for post and core restoration of endodontically treated teeth, which remains a noteworthy health concern and can be addressed through interdisciplinary strategies to enhance outcomes. Therefore, this study aimed to evaluate the technical quality of the residual gutta-percha (GP) and posts by analysing the periapical radiographs of endodontically restored teeth.

Methods

A total of 594 periapical digital radiographs were evaluated for tooth type, post material, post shape, design, diameter, length, residual GP, GP length, GP tapering, GP homogeneity, and final restoration. Frequency distribution and cross-tabulation of the variables were performed.

Results

Maxillary molars had the highest frequency of restorations, including posts, accounting for 27.4 %, followed by maxillary premolars (25.4 %) and maxillary anterior teeth (19.2 %). The prefabricated metallic posts were most commonly used (81.0 %), among these, 50.4 % were screwed posts. Tapered posts were the most commonly used (65.6 %). The percentage of posts with an acceptable length was 58.2 %. The most commonly used posts exhibited a width of one-third of the root diameter, accounting for 87.0 %. Suitable GP lengths were observed in 61.1 % of the restorations, and 62.8 % demonstrated adequate GP homogeneity. The findings of this study revealed that crown restoration accounted for 42.6 % of the studied sample.

Conclusions

The technical quality of the remaining GP after restoration was comparable to that of previous epidemiological investigations. However, the technical quality of the post was deemed suboptimal.

Quality of post and core placement by final year undergraduate dental students

The success of endodontic restoration of badly compromised teeth depends on the quality of post and core placement and the extra-coronal restoration. Ensuring that students place posts to acceptable quality standards is therefore essential. The aim of this study was to radiographically evaluate post placement by final year undergraduate dental students and to identify any predictors of performance. Two hundred retrospectively and randomly selected posts placed by sixth year students were evaluated radiographically. Data on student gender; number and quality of radiographs; periapical pathology; tooth location; root canal treatment quality; amount of remaining gutta percha; gap between gutta percha and post; post-to-root width; crown-to-root ratio; and types of core material and crowns were recorded. Four criteria were used to grade post placement quality: (i) amount of remaining gutta percha; (ii) gap between gutta percha and post; (iii) post width to root ratio; and (iv) crown-to-root ratio. Assessments were scored to produce final grades. Data are presented using descriptive statistics and the chi-squared test was used to investigate whether student gender or tooth location were associated with final grade. Post and core quality was acceptable in most cases (97.5% were graded as adequate), with no differences in quality between male and female students nor according to tooth location (anterior, premolar, and molar). Just over half of radiographs were adequate quality (53.5%), while just under half were assessed as less than adequate (46.5%) due to cone cutting, overlap, shortening or elongation, although this did not affect formal assessment of post quality. General outcomes of post and core placement by undergraduate students were good, with few errors that might affect the prognosis and long-term survival of treated teeth. Providing undergraduate dental students with clear guidelines on when and how to take radiographs throughout the procedure may improve the quality of post and core treatment and reduce the risk of multiple unnecessary radiographic exposures. From the clinical perspective, although dental students generally place high quality posts and cores, it remains important to monitor the quality and performance of post placement as this determines the survival of compromised teeth.

Push-Out Bond Strength of Resin-Modified Glass Ionomer Cement and Flowable Composite Luting Systems on Glass Fiber Post of Root Canal

Background: Posts that have been properly fitted can withstand torsion forces and so provide better retention. The push-out bonding strength of glass fiber posts to the root canal was evaluated using resin-modified glass ionomer cement (RMGIC) and flowable composite (FC). Method: Forty single-rooted maxillary central incisors were used in the study. The samples were randomly divided into two groups of 20 teeth each. The crown-down procedure was used to clean and shape the pulp area. A Tenax fiber trans Coltene whaletene post was used by both groups. The first group utilized FC (Filtek Z 350 3M ESPE) to coat the post, whereas the second group used RMGIC (Rely X 3M ESPE). The specimens were cross-sectioned after 24 h. Specimens were cross-sectioned four millimeters thick into coronal and middle parts using a sectioning machine, yielding 40 specimens per group. The strength of the bond between the luting cement and the posts was measured using push-out bond strength testing. We loaded the components at a cross speed of 0.5 mm/min on a universal testing machine until the bond failed. Results: The FC group had a 4.80 N push-out bond strength, whereas the RMGIC group had a 7.11 N push-out bond strength. Conclusion: FC’s mean push-out bond strength score is lower than RMGIC’s.

Cone beam computed tomography analysis of residual dentin thickness after virtual post placement in the palatal roots of maxillary first molars

STATEMENT OF PROBLEM

In endodontically treated maxillary first molars, post space preparations in the palatal roots can compromise the residual dentin thickness (RDT) and increase the risk of perforations or root fractures. This can be attributed to the direction of the buccopalatal curvature that cannot be viewed with conventional 2D imaging.

PURPOSE

The purpose of this clinical study was to investigate the RDT of palatal roots following the placement of digital post analogs of different diameters positioned at various distances from the radiographic apex by using cone beam computed tomography (CBCT).

MATERIAL AND METHODS

A total of 122 deidentified CBCT data sets containing both maxillary permanent first molars were randomly selected from a private radiology practice. Digital parallel-sided post analogs were superimposed onto the CBCT coronal images at distances of 3 mm, 4 mm, and 5 mm from the radiographic apex and at a depth equal to the height of the anatomic crown (1:1 crown/post ratio). Post analogs of 0.9 mm, 1.0 mm, and 1.14 mm in diameter were matched with safety zone analogs representing 1 mm of circumferential RDT. The minimum RDT for each analog was determined and grouped into 3 categories: RDT≤0 mm, 0 mm<RDT<1 mm, and RDT≥1 mm. The statistical significance between post diameters and post depth was analyzed with the Friedman test and Conover post hoc test (α=.05).

RESULTS

Significant differences in RDT were found at all tested depths and diameters of post analogs (P<.001). Generally, the amount of RDT increased as the post length was reduced. Most teeth (>50.0%) had inadequate or no RDT. The depth of the post (P<.001) had a greater impact on RDT than the post diameter (P>.017). No similarities were found in the RDT between contralateral molars in 86.9% of the images.

CONCLUSIONS

The risk of insufficient RDT (<1 mm) after the placement of parallel-sided posts in the palatal roots of maxillary first molars is minimized if the post is inserted to a depth equaling the height of the crown compared with 3, 4, and 5 mm from the radiographic apex. The RDT of the palatal root of a maxillary first molar is not a reliable predictor of the contralateral palatal root RDT in the same patient.

Influence of elastic modulus mismatch between dentin and post-and-core on sequential bonding failure

PURPOSE

Clinical failures of teeth restored with post-and-core are critical issues for the survival of teeth and maintenance of oral functions. A tooth with post-and-core restoration is a complex structure. Cement adhesion is believed to be the weakest component, and breakage in this component leads to changes in stress distribution in the complex structure. The tested hypothesis was that cement breaking processes of prosthetic treated teeth were affected by elastic properties of post-and-cores.

METHODS

Finite element analysis focused on sequential adhesion failure between the dentin and cement; the penalty function method was used to analyze stress during each stage of bonding conditions. Failure patterns of adhesion and stress distribution within dentin under load of different materials of post-and-core was observed.

RESULTS

Although, an initial failure of cement was observed at the palatal crown margin regardless of the material. Different patterns of adhesion failure between dentin and post-and-cores were observed by different elastic properties of post-and-cores. Stress concentration was observed at the corresponding areas of interface between adhesion failure and continued elements using both post-and-cores.

CONCLUSIONS

Using failure criteria for cement adhesion, sequential changes of adhesion failure between dentin and post-and-cores were observed. Local stress concentrations leading to severe destruction of dentin were caused by not only materials of post-and-cores but their adhesive conditions to dentin. Nonlinear finite element analysis (FEA) using complex structure model which deals with alterations of interfacial condition between components could provide the simulation for the clinical failure of teeth restored with post-and-cores.

Intracanal Adaptation of a Fiber Reinforced Post System as Compared to a Cast Post-and-Core

BACKGROUND

The purpose of this study was to compare the adaptation of fiber reinforced composite post system and cast post-and-core.

METHODS

17 extracted human permanent maxillary central incisors were endodontically treated following the standard protocol. 17 fiber reinforced composite post had been fabricated and adapted to the prepared parallel root canals. A light body poly vinyl siloxane (EXAMIX NDS, Japan) impression material was inserted into the root canals followed by the post. A digital scale was used to measure the weight of the remaining material that filled the gap between the post and the canal wall. The adaptation was indicated by the weight difference before and after impression material insertion. The same procedures were repeated with 17 cast post-and-core in the same teeth specimens.

RESULT

The mean difference for the weight of the material within the group was statistically significant (P-value <0.001) with the value of 6.1mg(± 2.7mg) for cast metal post and 6.4mg(± 2.7mg) for fiber reinforced composite post. However, the mean difference was not statistically significant when compared with both materials (P-value>0.05).

CONCLUSIONS

Both cast post-and-core and fiber reinforced composite post systems showed similar adaptation to the canal.

Endodontic treatment of a C-shaped mandibular second premolar with four root canals and three apical foramina: a case report

This case report describes a unique C-shaped mandibular second premolar with four canals and three apical foramina and its endodontic management with the aid of cone-beam computer tomography (CBCT). C-shaped root canal morphology with four canals was identified under a dental operating microscope. A CBCT scan was taken to evaluate the aberrant root canal anatomy and devise a better instrumentation strategy based on the anatomy. All canals were instrumented to have a 0.05 taper using 1.0 mm step-back filing with appropriate apical sizes determined from the CBCT scan images and filled using a warm vertical compaction technique. A C-shaped mandibular second premolar with multiple canals is an anatomically rare case for clinicians, yet its endodontic treatment may require a careful instrumentation strategy due to the difficulty in disinfecting the canals in the thin root area without compromising the root structure.

Endocrowns: review

The ideal restoration of endodontically treated teeth (ETT) has been widely and controversially discussed in the literature. Prevention of healthy dental structure is essential to help mechanical stabilization of tooth-restoration integrity, increase the amount of suitable surfaces for adhesion and thus positively affect the long-term success. ETT are affected by a higher risk of biomechanical failure than vital teeth. With the development of adhesive systems, the need for post-core restorations is also reduced. Especially for restoration of excessively damaged ETT, endocrowns have been used as an alternative to the conventional post-core and fixed partial dentures. Compared to conventional methods, good aesthetics, better mechanical performance, and less cost and clinic time are the advantages of endocrowns.

The effect of type of restoration on the stress field developed in terminal abutments with severely reduced periodontal support and coronal structure

STATEMENT OF PROBLEM

Periodontally compromised teeth (PCT) that serve as terminal abutments (TAs) are often challenging depending on the post-and-core treatment, the type of partial fixed dental prosthesis (PFDP), and the periodontal support.

PURPOSE

The purpose of this study was to investigate the biomechanical impact of 3 types of PFDP supported by cast post-and-cores on PCT serving as terminal abutments.

MATERIAL AND METHODS

A 3-dimensional (3D) model of a human mandible was fabricated by using computed tomography (CT) images and parameterized in a computer-aided design (CAD) environment as follows: Right premolar preparation geometries were designed. The second premolar was assembled with 7-mm or 10-mm cast post-and-core models. Both premolar-models were designed to support single, splinted, or 1-unit cantilever splinted crowns. In each situation, their periodontium geometries were designed to be reduced by 10%, 50%, and 70%. All models were imported into a 3D finite element analysis (FEA) environment and loaded; von Mises stress values and distribution patterns were evaluated.

RESULTS

Insertion of the post primarily affected the apical areas of both the root and post; the type of PFDP and periodontal support mainly affected stress distribution. In patients with a normal periodontium, splinting the teeth did not contribute to their stress relief. By extending the post length, a stressful area close to the apex of the post was developed. Splinting mitigated the stress field of the coronal part of the 50% PCT (up to 98.9%); the 30% PCT experienced a substantial decrease (up to 215.9%) in stress in the radical part as well. The increase in the length of the post produced negligible stress-related differences in the apical part of the 50% PCT (0.2% to 2.6%). The use of the 7-mm post effectively relieved the radical part of the splinted 30% PCT. The magnitude of the stress on the radical part of post-restored PCT was considerably increased in the presence of a cantilever.

CONCLUSIONS

Splinted crowns supported by a 7-mm cast post-and-core are a favorable biomechanical approach for the restoration of PCT with severe loss of coronal structure. The use of a cantilever greatly aggravates the biomechanical response, especially of post-restored PCT.

Fracture resistance of teeth restored with cast post and core: An in vitro study

CONTEXT

Influence of luting agent, design of tooth preparation for cast posts on tooth resistance to fracture.

AIM

To evaluate fracture resistance of teeth restored with cast posts and cores with or without cervical ferrule and cemented with zinc phosphate, glass ionomer, or resin cement.

MATERIALS AND METHODS

Sixty single-rooted maxillary first premolars of similar sizes were selected. Biomechanical preparation and post space preparation for cast post was done for all samples and then they were divided into two groups (n=30). Cervical ferrule preparation was done for Group A, and Group B was prepared without any cervical ferrule. Both groups were further divided into three subgroups (1, 2, and 3; n=10) Cast posts for subgroups 1, 2, and 3 were cemented with zinc phosphate, glass ionomer, and resin cement, respectively. A shearing load was applied to indented buccal cusp of specimens at an angle of 45° in universal testing machine at a cross-head speed of 1 mm/min until fracture.

RESULTS

Specimens with ferrule (Group A) had significantly higher shear bond strength values (mean 1503.37 N) than specimens without ferrule (Group B) (mean 1052.09 N).

CONCLUSION

Inclusion of ferrule in tooth preparations for posts increased the fracture resistance regardless of the luting agent.

A rapid nondestructive method for root dentin moisture measurements: in vitro pilot study

Dentin moisture content is important in adhesive bonding and structural strength research; however, there is no rapid method available to assess dentin moisture without sample destruction. This study examined the use of a digital grain moisture meter to measure root dentin moisture in vitro. Extracted mandibular single-rooted teeth were sectioned at the CEJ. The moisture of the root dentin was measured at 6 measuring modes for different grains and repeated 5 times. Dentin weight changes before and after drying were measured to obtain control values. The control values were compared with machine readings. In conclusion, (1) each nondestructive measurement took less than 30 seconds, (2) 24 hours of storage at 37 degrees C and 100% humidity did not restore dentin moisture, and (3) 5 grain modes had a high validity and could be used for dentin moisture measurements.

Effect of a new restoration technique on fracture resistance of endodontically treated teeth

The aim of the study was to investigate the effect of a new fiber-reinforced composite restoration technique on fracture resistance in endodontically treated premolars. Eighty sound extracted human mandibular premolars were assigned to four groups (n = 20). Group 1 did not receive any treatment. In groups 2, 3 and 4, the teeth received root canal treatment and a mesio-occluso-distal cavity preparation. Group 2 was kept unrestored. Group 3 was restored with a dentin bonding system and composite resin. In group 4, a piece of polyethylene ribbon fiber was inserted into the groove in a buccal to lingual direction during the restoration of teeth with dentin bonding system and composite resin. After finishing and polishing, the specimens were stored in 100% humidity at 37 degrees C for 24 h and placed at an angle of 45 degrees to the long axis of the tooth and subjected to compressive loading in a universal testing machine at a crosshead speed of 0.5 mm min(-1). The load necessary to fracture the samples was recorded in Newton (N) and submitted to Kruskal-Wallis anova and Mann-Whitney U-test. The fracture strength of the teeth reinforced with a combination of polyethylene fiber and composite resin were not significantly different than those that were restored with only composite resin (P > 0.05). However, most of the failure modes of the reinforced teeth were limited to the level of the enamel, while the other three groups showed fractures generally at the level of the dentin, cemento-enamel junction or more below (P < 0.05). Therefore, polyethylene ribbon fiber-reinforced composite resin restorations seemed a more reliable restorative technique than traditional composite restorations for extensive cavities.

Effect of thickness of cavity wall on fracture strength of pulpotomized primary molar teeth with class II amalgam restorations

AIM

This was to evaluate the effect of different thicknesses of cavity walls on fracture strength of pulpotomized primary molar teeth with class II amalgam restorations.

METHODS

80 carious extracted human primary molar teeth were selected for pulpotomy preparation. The teeth were divided into four groups. Mesio- or disto-occlusal (20 teeth) and mesio-occluso-distal (20 teeth); cavities were prepared in both first and second primary molar teeth. Each group was divided into two subgroups of ten teeth according to the thickness of their walls (1.5 or 2.5 mm). After restoring teeth with amalgam, all groups were stored in distilled water at 37 degrees C for seven days. They were then thermo cycled 1,000 times between 5 degrees to 55 degrees C. The specimens were then subjected to a compressive axial load in a universal testing machine at a crosshead speed of 0.5 mm min(-1). The t-test was used for statistical analysis.

RESULTS

Mean fracture resistances of the first and second molar teeth were 975.5 +/- 368.8 and 1049.2 +/- 540.1, respectively. In the first molars, fracture resistance of 2-surface cavities was significantly more than 3-surface cavities (p=0.001), but this difference was not statistically significant in second molars. In second molars, fracture strength in 2- and 3-surface cavities with a 2.5 mm thickness in the walls was more than those with 1.5 mm thickness. However, in first molars this difference was only statistically significant in 3-surface cavities (p=0.045).

CONCLUSIONS

The fracture strength in pulpotomized primary molar teeth with amalgam restorations was high, more than maximum bite forces in primary teeth, even in extensive 3- surface cavities.

In Vitro Evaluation of Five Core Materials

PURPOSE

This in vitro study determined the fracture strength of five core materials supported by two different endodontic dowels. Diametral tensile strength and microhardness of the three resin composite core materials used in this study were also tested.

MATERIAL AND METHODS

The fracture strength study used one lanthanide-reinforced flowable resin composite (Ti-Core Auto E), one titanium- and lanthanide-reinforced composite (Ti-Core), one lanthanide-reinforced composite (Ti-Core Natural), and two metal-reinforced glass ionomer core materials (Ketac Silver and GC Miracle Mix). Two types of dowels were used: a multitiered, split-shank threaded dowel with a flange (#1 Flexi-Flange) and one without a flange design (#1 Flexi-Post). The specimens were divided into ten groups. Each tooth/dowel and core specimen was placed in a special jig at 45 degrees and subjected to a load by a universal testing machine. The diametral tensile strength and the microhardness of the three resin composite core materials were measured by a universal testing machine and Barcol hardness tester, respectively. All test groups contained ten specimens.

RESULTS

The fracture strength value of the resin composite core materials was significantly larger ( p < 0.0001) than those for the metal-reinforced glass-ionomer core materials. Analysis of variance (ANOVA) also showed that the Flexi-Flange dowel interacted with Ti-Core and Ti-Core Auto E to significantly ( p < 0.0013) increase the fracture strength relative to the Flexi-Post. One-way ANOVA revealed that there were no significant differences between them in terms of diametral tensile strength. The Barcol hardness values of the composite core materials were statistically different ( p < 0.0001), with the Ti-Core the highest, followed by Ti-Core Natural, then Ti-Core Auto E.

CONCLUSIONS

Resin composite core material performed better than glass ionomer material in this in vitro study. The flowable composite core material performed about the same in terms of fracture strength and diametral tensile strength compared with nonflowable composites. Combined with certain core materials, the flange design increased the fracture strength of the tooth/dowel and core combination.

Survival time of cast post and cores: a 10-year retrospective study

OBJECTIVES

The aim of this retrospective, longitudinal study was to examine the survival time of custom-fabricated, cast post and cores and to evaluate, which covariates influence the risk of failures over a period of up to 10 years based on a large patient collective.

METHODS

The files of 565 patients, who had been fitted with a total of 802 custom-fabricated, cast post and cores using a standardised technique, were analysed. The following parameters were used in the evaluation: age of the post and cores, fabrication technique (direct, indirect), type of prosthetic restoration, location (upper, lower jaw), type of tooth (anterior, premolar, molar), number of root posts, luting material, post and core alloy and cause of failure. The survival probability was assessed using Kaplan-Meyer analysis. Cox regression was used to assess the risk of failure and identify possible covariates.

RESULTS

The average survival time of the post and cores was 7.3 years. The cumulative failure rate was 11.2%. The most common complication was loss of retention of the post and cores. High-gold-content posts had a lower risk of failure than posts made from semi-precious alloy. The type of restoration fitted had a significant influence on the survival probability.

CONCLUSIONS

Post and cores custom-fabricated using a standardised fabrication technique have a good long-term prognosis. The most common cause of failure is loss of retention. The durability of posts with low friction at the try-in stage cannot be compensated for by using glass ionomer cement as the luting material.

The effect of fibre insertion on fracture resistance of root filled molar teeth with MOD preparations restored with composite

AIM

To evaluate the effect of using flowable composite with or without leno woven ultra high modulus polyethylene fibre reinforcement on fracture resistance of root filled mandibular molars with mesio-occlusodistal (MOD) preparations.

METHODOLOGY

Sixty sound extracted human mandibular molars were randomly assigned to five groups (n = 12). Group 1 did not receive any preparation. From groups 2 to 5, the teeth were root filled and MOD preparations were created. Group 2 remained unrestored. Group 3 was restored with a dentine bonding system (DBS; SE Bond, Kuraray, Japan) and composite resin (CR) (AP-X; Kuraray). In group 4, flowable composite resin (Protect Liner F; Kuraray) was used before restoring teeth with CR. In group 5, leno woven ultra high modulus polyethylene ribbon fibre (Ribbond, Seattle, WA, USA) was inserted into the cavities in a buccal to lingual direction and the teeth were then restored with DBS and CR. After finishing and polishing, the specimens were stored in 100% humidity at 37 degrees C for 1 day. Compressive loading of the teeth was performed using a universal testing machine at a crosshead speed of 0.5 mm min(-1). The mean load necessary to fracture the samples were recorded in newtons (N) and were subjected to analysis of variance (ANOVA) and Tukey post-hoc test.

RESULTS

The mean load necessary to fracture the samples in each group were (in N): group 1: 1676.75 +/-154.63(a), group 2: 376.51 +/- 37.36(b), group 3: 733.23 +/- 133.33(c), group 4: 786.48 +/- 145.34(c), group 5: 943.63 +/- 121.15(d). There were statistically significant differences between the groups annotated with different letters.

CONCLUSIONS

(i) Use of flowable composite resin under composite restorations had no effect on fracture resistance of root filled molar teeth with MOD preparations, (ii) use of polyethylene ribbon fibre under composite restorations in root filled teeth with MOD preparations significantly increased fracture strength.

Residual dentin thickness in mesial roots of mandibular molars prepared with Lightspeed rotary instruments and Gates-Glidden reamers

OBJECTIVE

We sought to measure the residual dentin thickness (RDT) in the mesial roots of mandibular molars after instrumentation with Lightspeed and Gates-Glidden rotary instruments. Study design Thirty extracted, untreated human mesial roots of mandibular molars were separated from the distal roots and embedded in clear polyester resin. The roots were cut horizontally at 1, 4, and 7 mm short of the anatomic apex. The diameter of each mesiobuccal canal was measured by using a stereo measuring microscope at each level in the buccolingual and mesiodistal directions. The dentin thickness was measured in each level in the mesial, distal, buccal, and lingual directions. Sections were reassembled with a muffle. The canals were enlarged to the working length with Lightspeed rotary instruments, of which the average size used was a No. 50 file. The coronal third was flared with No. 2 Gates-Glidden reamers. Slices were separated again, and the RDT and canal diameters were measured.

RESULTS

The minimal measured RDT after instrumentation at the 1-, 4-, and 7-mm levels was 0.70 +/- 0.28 mm, 1.04 +/- 0.18 mm, and 1.09 +/- 0.19 mm, respectively. The average diameter of the canals after instrumentation at the 1-, 4-, and 7-mm levels was 0.50 +/- 0.04 mm, 0.52 +/- 0.05 mm, and 0.74 +/- 0.08 mm, respectively. The canal diameter did not exceed one third of the root diameter at all levels.

CONCLUSIONS

Root canal preparation of mandibular mesial roots with Lightspeed instruments to No. 50 in the apical third and Gates-Glidden reamers to No. 2 in the coronal third does not significantly decrease the RDT.

Effect of different filling materials in combination with intraradicular posts on the resistance to fracture of weakened roots

The preservation and restoration of severely weakened pulpless teeth is a difficult and relatively unpredictable procedure. This study evaluated the resistance to fracture of experimentally weakened bovine roots internally reconstructed with different filling materials in combination with prefabricated post compared with restored roots that were relatively intact. The roots of 75 mandibular bovine incisors with similar bulks were selected. Of these, 60 were internally prepared to standardized dimensions, thereby simulating weakness. All roots were filled with different restorative materials. The specimens were submitted to the fracture resistance testing with the application of a tangential compressive loading at an angle of 135 degrees in relation to the long axes of the roots. Results indicated statistically significant differences in relation to the root conditions. Weakened roots were less resistant to fracture than were controls. The roots restored with the resin cement demonstrated the lowest fracture resistance values, but statistically significant differences were observed only when compared with those restored by the resin-modified glass-ionomer cement. Resin-modified glass-ionomer cement, polyacid-modified resin composite and resin composite behaved similarly without statistically significant differences among them. None of the materials evaluated were capable of achieving the fracture resistance recorded for unweakened controls.

Assessment of the resistance to fracture of endodontically treated molars restored with amalgam

STATEMENT OF PROBLEM

Controversy exists concerning the preferred type of final restoration of endodontically treated molars regarding their resistance to fracture under occlusal load.

PURPOSE

The aim of this study was to assess the resistance to fracture of endodontically treated molars with various degrees of tooth structure loss restored with amalgam under simulated occlusal load.

MATERIAL AND METHODS

. The study teeth consisted of 90 noncarious, nonrestored molars stored in physiological saline solution. The teeth were endodontically treated and randomly divided into 9 experimental groups of 10 specimens each with various degrees of tooth loss, ranging from a conservative endodontic access to removal of all cusps. All teeth were restored with a standardized technique to their original contour with amalgam. Each specimen was mounted onto a specialized jig for loading at the central fossa at a 30-degree angle to the long tooth axis. The resistance to fracture, under continuous compressive force at a cross-head speed of 2 mm/minute, was applied by a universal testing machine and was recorded. One-way analysis of variance with Scheffé contrast was used to statistically compare the differences between the groups at significance level P<.05.

RESULTS

One-way analysis of variance showed that the group with a conservative endodontic access (1137.6 +/- 311.6 N) and the group with removal of all cusps (1261.4 +/- 195.1 N) presented a significantly higher resistance to fracture when compared with the other groups (P<.05). There was no significant difference in resistance to fracture under the simulated load between the other 7 groups, which ranged from 655.8 +/- 229.4 to 906.3 +/- 168.1 N (P>.05).

CONCLUSION

Within the limitations of this study, the endodontically treated molars with a conservative endodontic access or after removal of all cusps that were restored to their original contour with amalgam presented the highest resistance to fracture under a simulated occlusal load.

The effect of sodium hypochlorite irrigant concentration on tooth surface strain

The effect of root-canal irrigation with different concentrations of sodium hypochlorite (3%, 5.1%, 7.3% NaOCI) on the mechanical properties of teeth was investigated in vitro. Root canals of 13 extracted, human premolars, denuded of enamel, were prepared with nickel-titanium rotary instruments (Quantec) to a standard size by using saline irrigation. An electrical strain gauge was bonded to the cervical aspect of each tooth. The 10 experimental teeth were subjected to 5 successive, 30-minute periods of irrigation. The irrigants were used in the following order: (a) saline; (b) 3.0% NaOCI; (c) 5.1% NaOCI; (d) 7.3% NaOCI; (e) saline. Three control teeth were irrigated with saline only for all five periods. After each irrigation, the teeth were cyclically loaded to 110N while the surface strain was measured. Changes in strain of the test teeth after each irrigation regimen followed broadly similar patterns that were different from the control teeth. There was no difference, however, in the strain recorded after irrigation by the different irrigants within the experimental group.

Cast post and core foundation for the badly broken down molar tooth

BACKGROUND

This article addresses the difficult clinical problem of restoration of endodontically treated posterior teeth, where there is nothing left of the clinical crown.

METHODS

A step by step procedure, including instrumentation and materials and a new impression technique, is described in detail, with clinical photographs.

RESULTS

This technique results in the fabrication of a robust and extremely retentive post and core on which to place fixed prosthodontic restorations.

CONCLUSIONS

The author has placed over 600 restorations of this type over a five year period, without any reported failures. With the 'greying' of the population there are increased demands on dentists to restore structurally compromised teeth, and increasing expectations of the performance of these restorations. This technique is offered as a superior alternative to conventional post and core constructions methods.

Fabrication of direct fiber-reinforced posts: a structural design concept

As the clinician continues the quest for optimal functional and esthetic success of a tooth-restorative complex, the current selection of restorative materials and techniques may prove overwhelming. Although no single system provides the ideal restorative solution for every clinical circumstance, understanding of general design criteria and the components for the various post and core systems available allow the clinician to appropriately select the method and materials compatible with the existing tooth structure and desired result. This article provides a discussion of the various post and core systems, the methods and materials inherent in these systems, and general design principles. Using that basic information and clinical experience, the authors offer an alternative procedure for the rehabilitation of the intraradicular anatomy of the post-endodontic channel with a direct composite resin--the fiber-reinforced post and core system.

CLINICAL SIGNIFICANCE

Using improved restorative materials that stimulate the physical properties and other characteristics of natural teeth in combination with the proper design principles, the clinician can develop a tooth-restorative complex with optimal functional and esthetic results.

Radiographic measurement of residual root thickness in premolars with post preparation

A minimum thickness of 1 mm has been suggested for the residual root wall in post preparation. The objective of this paper is to evaluate the reliability of radiography when used to measure root thickness. In 106 upper first premolars with one and two root canals, post preparations were made with Peeso reamers to a depth in the root equal to the crown length. Bucco-palatal radiographs were taken of each tooth. The films were processed and projected with a magnification of x20. The smallest thickness of the mesial and distal walls of each root at the apical end of the preparation was measured and recorded. The teeth were then cut at the level of the measurement, and the smallest thickness of the proximal walls was measured using a microscope with a micrometric eyepiece. Fourteen percent of the teeth with one root canal and 27% of the teeth with two root canals could not be measured due to blurred radiographic contours. Variance analysis showed a highly significant difference (p < 0.001) when radiographic and anatomical measurements were compared. The radiograph showed greater thicknesses than were actually present and should not therefore be considered to be a reliable method for measuring residual thickness of tooth walls after post preparation.

Effect of sodium hypochlorite on mechanical properties of dentine and tooth surface strain

AIM

The aim of this study was to test the null hypothesis that sodium hypochlorite irrigation of root canals does not alter the properties of dentine and contribute to the weakening of root-treated teeth.

METHODOLOGY

The effect of two concentrations (0.5%, 5.25%) of sodium hypochlorite (NaOCl) and saline on (i) the elastic modulus and flexural strength of machined dentine bars, and (ii) changes in strain of 'whole' extracted human teeth were evaluated. One hundred standardized plano-parallel dentine bars (> 11.7 x 0.8 x 0.8 mm) were randomly divided into the three groups, immersed for 2 h in the respective solutions and then subjected to a three-point bend test. Changes in strain of each of 10 teeth on cyclical nondestructive occlusal loading were measured using electrical resistance strain gauges bonded to the cervical aspects. Each tooth had its crown and enamel reduced and root canal prepared. These were irrigated sequentially in a series of four separate, 30-minute regimes; initial-saline, 0.5% NaOCl, 5.25% NaOCl and final-saline. The changes in strains after each irrigation regime were compared.

RESULTS

There was a significant decrease in elastic modulus of the dentine bars immersed in 5.25% NaOCl compared with the saline group (P < 0.01). There was also a significant decrease in flexural strength of the dentine bars in the 5.25% NaOCl group compared to both the saline and 0.5% NaOCl groups (P < 0.01). The strain data from the nondestructive tooth loading tests revealed significant increases in tensile strain between the initial-saline and the final-saline stages (P < 0.01). Significant increases in compressive strains were also found between initial-saline and 5.25% NaOCl; and between 0.5% NaOCl and 5.25% NaOCl stages (P < 0.01).

CONCLUSIONS

The null hypothesis was rejected, 5.25% NaOCl reduced the elastic modulus and flexural strength of dentine. Irrigation of root canals of single, mature rooted premolars with 5.25% NaOCl affected their properties sufficiently to alter their strain characteristics when no enamel was present.

Fracture strengths of three core restorative materials supported with or without a prefabricated split-shank post

PURPOSE

The aim of this study was to compare the fracture strengths of three restorative materials, a lanthanide reinforced composite (Ti-Core Natural), a silver amalgam (Tytin), and a hybrid glass ionomer (Advance), supported by either a multitiered, threaded split-shank post (Flexi-Flange) or with a dentin spur without a post.

MATERIAL AND METHODS

A total of 60 recently extracted single-rooted human teeth were divided into six groups of 10. All groups were stored at 100% humidity at room temperature for 1 week before testing. Each specimen was placed in a special jig at a 45-degree angle to the buccolingual axis and subjected to a load that was recorded in pounds and converted to Newtons on a universal testing machine, with a crosshead speed of 0.63 cm/minute until failure. Two-way analysis of variance followed by the Newman-Keuls pairwise multiple comparisons test were used to compare the results.

RESULTS

There was a statistically significant difference between core materials (p < 0.001), but not regarding post conditions. Ti-Core Natural material had a significantly larger mean failure threshold for fracture than either Tytin silver amalgam or Advance material and the letter two core materials (Tytin and Advance) do not differ from each other. There was no statistical difference between Ti-Core material supported by a post and Ti-Core material supported without a post.

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.

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.

The prosthodontic management of endodontically treated teeth: a literature review. Part III. Tooth preparation considerations

The final part of this literature review series presents guidelines for the optimal preparation of teeth to receive posts and cores.

Moisture content of vital vs endodontically treated teeth

The moisture content of vital and endodontically treated teeth was compared in matched pairs of contralateral human teeth extracted for prosthodontic reasons. Samples from each tooth were weighed then placed in an oven to remove the unbound water from the dentin. Weighing was carried out daily until a constant weight was achieved for three days. The moisture content was then calculated and expressed as a percentage of the initial sample weight. It was found that vital dentin had a moisture content of 12.35% whilst dentin from endodontically treated teeth had a moisture content of 12.10%. These results indicated that there was no significant difference in the moisture content between endodontically treated teeth and vital teeth.

The effect of post adaptation in the root canal on retention of posts cemented with various cements

This laboratory study compared the retention of prefabricated posts in well-fitting and loose-fitting post canals using different cement materials. Eighty-three human teeth were prepared for post placement. One of zinc phosphate cement, polycarboxylate cement, glass ionomer cement or resin cement was used to cement each post in place. A tensile force was applied to remove each post and the separation force was recorded. Posts cemented with the resin cement were the most difficult to dislodge. Posts cemented into loose-fitting canals exhibited greater resistance to dislodgment than posts cemented into well-fitting canals irrespective of the type of cements used.

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.

Are endodontically treated teeth more brittle?

This study compared biomechanical properties (punch shear strength, toughness, hardness, and load to fracture) of 23 endodontically treated teeth (mean time since endodontic treatment: 10.1 yr) and their contralateral vital pairs. Analyses using paired t tests revealed no significant differences in punch shear strength, toughness, and load to fracture between the two groups. Vital dentin was 3.5% harder than dentin from contralateral endodontically treated teeth (p = 0.002). The similarity between the biomechanical properties of endodontically treated teeth and their contralateral vital pairs indicates that teeth do not become more brittle following endodontic treatment. Other factors may be more critical to failure of endodontically treated teeth.

Amalcore strength recovery following refilling of access preparations with amalgam

After endodontic treatment through an amalgam core, the recommended procedure is to replace the entire core. This study examined the strength achieved by restoring the access openings with dental amalgam and reported the type of failure during strength testing. Seventy-two Dispersalloy 8 x 8 mm cylindrical specimens were produced using controlled condensation pressures. The specimens were randomized in three groups: (1) controls, (2) 3 mm access preparations wetted with mercury-rich amalgam before restoration, and (3) 3 mm access preparations restored unwetted. The specimens tested for compressive strength were separated in two subsets. The unwetted group demonstrated significantly less strength than the control and wetted group (p less than 0.05), while the unwetted and wetted groups revealed significantly less strength than the control group (p less than 0.05). The mean diametral tensile strength recovery for the wetted and unwetted groups was 76% and 69%, respectively. The qualitative assessment of the fracture zones indicated that wetted specimens exhibited more fractures through the new amalgam core than the unwetted specimens (p less than 0.05). It would appear that amalgam refilling of access preparations through amalgam cores has clinical potential.

Tooth fracture in vivo and in vitro

The incidence, causes and methods of investigating tooth fracture are reviewed. This is a problem of increasing clinical significance, with many predisposing factors. Large restorations and extensive carious lesions tend to be associated with most fractures, with fracture incidence being higher in first permanent molars than other tooth types, especially in the lower jaw. Tooth anatomy influences fracture incidence, as does the functional force applied to cusps. Fracture risk in restored teeth may be reduced by cuspal coverage. Traditional tooth fracture investigations using destructive techniques provide valuable information; however, replica and nondestructive techniques are also of value.

Amalgam crown restorations for posterior pulpless teeth

Cast restorations are the usual technique chosen for the restoration of posterior pulpless teeth. Complex amalgam restorations are suggested as an alternative method of treatment, and several advantages are described. Techniques to provide sufficient retention and resistance form include the use of threaded pins, amalgapins, slots and grooves, amalgam in the pulp chamber, or canals, or both, and posts cemented within the canals. The practicing clinician is advised to become familiar with these retention techniques so that difficult retention situations may be treated effectively.

Vertical root fractures

In this study, I review, clinically and radiographically, 303 patients with 460 single or multirooted endodontically treated teeth. In all teeth, the therapy was performed by me with the use of final restoration of the crown with or without post and full cast crown coverage after treatment. The teeth were functioning for at least 3 years, without having received any other type of dental work since then. I evaluated the existence of vertical root fracture, the function of the teeth, the type of root canal therapy, the type and length of the post, and the type of retention of the post used in all 460 teeth. After statistical evaluation of the results, I found that 3.69% of the teeth had had vertical root fracture. Computer analysis, simple correlation hypothesis, and distribution method with 1 degree of freedom revealed significant correlation between vertical root fracture and the technique of instrumentation and obturation of the canal (p = 0.025), the length of the post (p = 0.05), and the existence of the post (p = 0.05). On the contrary, I found no correlation between root fracture and type of retention of the prefabricated post used with respect to the method of obturation.

Joint strength between two layers of different amalgam types condensed successively

The flexure strength of the joint between layers of different types of amalgam condensed consecutively one on to the other was evaluated in vitro. The data indicated no statistical differences in flexure strength between the combined samples (single composition spherical and lathe-cut eutectic amalgams) and the control (homogeneous lathe-cut eutectic amalgam).

The restoration of endodontically treated teeth. Part 3. Cores

The functions and features of cores in restorative dentistry and the importance of preserving sound tooth tissue are discussed. The experimental and clinical support for a perceived superiority of cast post cores is reviewed. It is suggested that there is a need to re-evaluate this viewpoint, particularly when restoring posterior teeth. The materials currently in use are briefly discussed as well as research relating to possible core/luting agent interactions.

Odontiatrogenic tooth fracture

While the awareness of vertical tooth fractures, whether incomplete or complete, is increasing, sufficient attention has not been paid to the manner in which the dentist may contribute to the occurrence of these fractures. This paper focuses on the most likely areas in which the practitioner can either misdiagnose the presence of a fractured tooth or where dental procedures contribute to fracture of the tooth structure. For this type of fracture the authors propose the term 'odontiatrogenic tooth fracture'.

The restoration of endodontically treated teeth. Part 2. Posts

Posts are normally used to aid core retention and to provide tooth support, although a significant minority question the use of posts in the latter role. A direct relationship is thought to exist between the quantity of sound tooth structure and tooth strength and care is required when preparing teeth to accept posts. Post configuration is of over-riding importance in determining retention and support and the effect on retention of small increases to post length should not be over emphasized. Because accurate post fit is important to maximize both retention and support, direct fabrication techniques using matched post/reamer systems are recommended.