Fracture resistance of endodontically-treated teeth restored using three root-reinforcement methods

AIM

The aim of this in vitro study was to compare the fracture resistance of endodontically-treated anterior teeth with their roots reinforced using three different restorative methods.

METHODS AND MATERIALS

Forty sound maxillary human central incisors were randomly assigned to four groups (n=10). The crowns of the teeth were removed at a level 2 mm incisal to the cementoenamel junction (CEJ). After root canal therapy, flared canals were simulated in three groups. In the first, second, and third groups the flared canals were reinforced with resin composite (RCO) (Clearfil DC Core Automix), two Reforpins (REF), and a resin cement (RCE) (Panavia F 2.0), respectively. In the fourth (DEN) group flared canals were not created. The same size fiber reinforced composite (FRC) posts were cemented with resin cement (Panavia F 2.0) in all groups. After post cementation and restoration of the teeth crown with a core build-up composite (Clearfil Photo Core), the roots of the teeth were embedded in acrylic resin blocks up to 1 mm below the CEJ. The samples were loaded in an Instron testing machine with a crosshead speed of 0.5 mm/min at a 45 angle to the long axis of the tooth on the palatal surfaces until failure occurred. Data were analyzed using the Kruskal-Wallis, Mann-Whitney, and Chi-square tests (p=0.05).

RESULTS

Significant differences were found between fracture resistance in all of the groups (P<0.05) with the exception being among the RCO and REF groups. The least mean value 230 (130) N and the highest mean value 830 (220) N were shown in the fracture resistance of the RCE and DEN groups, respectively.

CONCLUSION

Reforpin can be used as an alternative to resin composite for internal reinforcement of weakened roots according to the results of this study. For reinforcement of flared canals, fiber posts along with Reforpin or resin composite proved to have higher fracture resistance than resin cement. Non flared canals had the highest fracture resistance.

Tooth fracture associated with debonding a metal orthodontic bracket: a case report

Enamel damage from debonding metal brackets is relatively rare. The purpose of this case report is to demonstrate that the risk of enamel or dental crown fracture is present when removing metal orthodontic brackets. It is advisable to take appropriate preventive measures, including examination of the anterior teeth for enamel cracks, prior to treatment. Patients should be fully informed of the risks of orthodontic treatment. Without pretreatment diagnosis and documentation, it is difficult for the orthodontist to prove that the appearance of enamel cracks or enamel/tooth fracture is unrelated to orthodontics.

Fracture resistance of roots obturated with three different materials

OBJECTIVE

The aim of this study was to compare the fracture resistance of roots obturated with different materials.

STUDY DESIGN

Sixty root canals were instrumented and divided into 4 equal groups (n = 15 each). The root canals in group 1 were filled with AH26 sealer and gutta-percha, in group 2 with Resilon and Epiphany, and in group 3 with Ketac-Endo Aplicap and gutta-percha. Fifteen root canals had no obturation. The force required to fracture was recorded. The data was analyzed with analysis of variance and Duncan test.

RESULTS

The mean force of fracture for group 1 was significantly higher than for the other 3 groups (P < .05). There was significant difference between group 2 and group 3 (P < .05). Group 2 and group 3 were not significantly different from the control group (P > .05).

CONCLUSION

The use of AH26 + gutta-percha increased the fracture resistance of instrumented root canals compared with Resilon + Epiphany and Ketac-Endo Aplicap + gutta-percha.

Evaluation of the effect of different ferrule designs on the fracture resistance of endodontically treated maxillary central incisors incorporating fiber posts, composite cores and crown restorations

AIM

The purpose of this study was to evaluate the fracture resistance of endodontically treated maxillary central incisors restored with quartz fiber posts, composite cores, and crowns when different types of ferrule designs were incorporated.

METHODS AND MATERIALS

Sixty maxillary incisors were divided into six groups: Group 1 (control): teeth with root canal treatments having a full crown prosthesis; Group 2: teeth with a 2 mm circumferential ferrule; Group 3: teeth with a 2 mm ferrule only in the vestibular region; Group 4: teeth with a 2 mm ferrule only in the palatal region; Group 5: teeth with a 2 mm ferrule in the vestibular and palatal region, having cavities in both proximal areas; and Group 6: teeth with no ferrule. The teeth in the experimental groups were restored with quartz fiber posts-composite cores and full metallic crowns. All experimental teeth were subjected to an increasing compressive force with a crosshead speed of 1 mm/min, until fracture occurred.

RESULTS

The median fracture values of groups were as follows: Group 1: 574.4 N, Group 2: 472.4 N, Group 3: 474.3 N, Group 4: 480.7 N, Group 5: 463.1 N, and Group 6: 297.9 N. A statistically significant difference was found between Group 1 and Group 6 (p< 0.01).

CONCLUSION

It was concluded different ferrule designs did not have any influence on the fracture resistance of teeth with fiber posts. The results of this study indicate fiber posts can safely be used for their reinforcing properties. Furthermore, there is no significant change in the resistance of teeth with fiber posts regardless of which ferrule design is incorporated. The property of these types of posts is an additional advantage in clinical practice.

Biomechanical considerations for the restoration of endodontically treated teeth: a systematic review of the literature--Part 1. Composition and micro- and macrostructure alterations

The specific biomechanical alterations related to vitality loss or endodontic procedures are confusing issues for the practitioner and have been controversially approached from a clinical standpoint. The aim of part 1 of this literature review is to present an overview of the current knowledge about composition changes, structural alterations, and status following endodontic therapy and restorative procedures. The basic search process included a systematic review of the PubMed/Medline database between 1990 and 2005, using single or combined key words to obtain the most comprehensive list of references; a perusal of the references of the relevant sources completed the review. Only negligible alterations in tissue moisture and composition attributable to vitality loss or endodontic therapy were reported. Loss of vitality followed by proper endodontic therapy proved to affect tooth biomechanical behavior only to a limited extent. Conversely, tooth strength is reduced in proportion to coronal tissue loss, due to either caries lesion or restorative procedures. Therefore, the best current approach for restoring endodontically treated teeth seems to (1) minimize tissue sacrifice, especially in the cervical area so that a ferrule effect can be created, (2) use adhesive procedures at both radicular and coronal levels to strengthen remaining tooth structure and optimize restoration stability and retention, and (3) use post and core materials with physical properties close to those of natural dentin, because of the limitations of current adhesive procedures.

Dental trauma: restorative procedures using composite resin and mouthguards for prevention

AIM

The aim of this article is to describe a step-by-step protocol for emergency care of a patient with a dentoalveolar injury in the anterior region of the mouth as well as the fabrication of a mouthguard to prevent future trauma.

BACKGROUND

Dental trauma is one of the most serious oral health problems in active children and adolescents. Care of traumatized patients requires immediate initial emergency treatment followed by integrated procedures to restore damaged oral structures along with a subsequent trauma prevention strategy. Dentoalveolar injuries in the anterior region of the mouth are often characterized by tooth avulsion and coronal fracture. They are managed using procedures such as dental splinting, endodontic therapy with its unique characteristics, and restorative techniques to re-establish function and esthetics as well as protective mouthguards.

REPORT

A 16-year-old male presented with avulsion of his maxillary central incisors as a result of a direct, unintentional impact with an opponent during a basketball game. The teeth had been stored in physiological serum immediately following the injury and the patient received immediate care. On clinical examination, the right central incisor was fractured at the incisal third of the crown but no bone fractures were found. The teeth were reimplanted and splinted. The fractured right central incisor was restored following endodontic treatment and a mouthguard was fabricated for the patient.

SUMMARY

The dentist must be knowledgeable about the most efficient and suitable treatment for each traumatic scenario in order to provide appropriate care for dental injuries. Coordinated multi-disciplinary action is fundamental in the successful treatment of these injuries. The dental mouthguard is an effective device for protecting the teeth and supportive structures during physical activities and must be part of the protective equipment used by athletes. It is the responsibility of the dental professional to make parents, trainers, and athletic associations aware of the risks associated with physical activities without orofacial protection; this should encourage the proper use of all protective devices to prevent dentoalveolar injuries that compromise oral functions, esthetics, and increase the cost of healthcare.

A comparison of the fracture resistance of core materials using different types of posts

OBJECTIVE

The purpose of this in vitro study was to determine the fracture resistance of 3 core materials (silver amalgam, resin composite, glass-ionomer cement) supported by 1 custom cast post (nickel-chromium alloy) and 2 prefabricated posts (Radix and Safix posts).

METHOD AND MATERIALS

A sum of 45 recently extracted single-rooted human incisors and canines were placed in 0.5% sodium hypochlorite. Before the experiments, the anatomic crowns of teeth were removed below the cementoenamel junction to obtain a standard root length. The roots were endodontically treated by the manual condensation method. The teeth were randomly divided into 9 groups with 5 samples per group. The posts were luted in the corresponding root canals with zinc polycarboxylate cement. Each core reconstruction was prepared with diamond instruments, and the height of cores formed was 6.0 mm. The tooth and post-core combinations were mounted in acrylic resin blocks. Each tooth and post-core combination was placed in a special jig at a 45-degree angle to the buccal/lingual axis and then subjected to a load on an electronic pull-tension-compression testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed using one-way analysis of variance.

RESULTS

The resistance to fracture for prefabricated posts was significantly higher for resin composite core than for the other post-core combinations (P <.001). For prefabricated posts, the composite core and amalgam core materials were significantly stronger than the glass-ionomer core material (P <.001). The differences between the core materials were statistically significant (P <.001).

CONCLUSION

The glass-ionomer core with custom post was the weakest post-core system, while the prefabricated posts (Safix and Radix) with resin composite and amalgam cores were the strongest post-core systems.

Restoring teeth with prefabricated fiber-reinforced resin posts

The use of fiber-reinforced resin (FRR) posts to restore endodontically treated teeth has gained popularity as an alternative to cast or prefabricated metal posts. This may be due to the two important characteristics of fiber posts: I) their modulus of elasticity, which is similar to that of dentin, and 2) their ability to be adhesively cemented. The following article will discuss these characteristics, clinical indications for FRR posts, as well as increased fracture resistance, adhesion to root dentin, and guidelines for placement.

LEARNING OBJECTIVES

This article reviews recent research on prefabricated fiber-reinforced resin (FRR) endodontic posts. Upon completing this article, the reader should: Understand clinical guidelines for the selection and cementation of FRR posts. Realize the importance of fracture resistance to the long-term performance of an endodontically treated tooth.

A comparative evaluation of the fracture strength of pulpotomized primary molars restored with various restorative materials

Sixty extracted primary molars were used in the study. After pulpotomy, these were divided into four groups on the basis of restorative materials to be used. Results showed that the Ormocer had the maximum fracture strength while the posterior Glass Ionomer Cement showed the least fracture strength among the various restorative materials used in the study.

Influence of beveling and ultrasound application on marginal adaptation of box-only Class II (slot) resin composite restorations

A laboratory study was performed to assess the influence of beveling the margins of cavities and the effects on marginal adaptation of the application of ultrasound during setting and initial light curing. After minimal access cavities had been prepared with an 80 microm diamond bur, 80 box-only Class II cavities were prepared mesially and distally in 40 extracted human molars using four different oscillating diamond coated instruments: (A) a U-shaped PCS insert as the non-beveled control (EMS), (B) Bevelshape (Intensiv), (C) SonicSys (KaVo) and (D) SuperPrep (KaVo). In groups B-D, the time taken for additional bevel finishing was measured. The cavities were filled with a hybrid composite material in three increments. Ultrasound was also applied to one cavity per tooth before and during initial light curing (10 seconds). The specimens were subjected to thermomechanical stress in a computer-controlled masticator device. Marginal quality was assessed by scanning electron microscopy and the results were compared statistically. The additional time required for finishing was B > D > C (p < or = 0.05). In all groups, thermomechanical loading resulted in a decrease in marginal quality. Beveling resulted in higher values for "continuous" margins compared with that of the unbeveled controls. The latter showed better marginal quality at the axial walls when ultrasound was used. Beveling seems essential for good marginal adaptation but requires more preparation time. The use of ultrasonic vibrations may improve the marginal quality of unbeveled fillings and warrants further investigation.

[Effect of composite restoration on the reinforcement of teeth]

OBJECTIVE

To determine the effect of composite restoration on reinforcement of weakened tooth structure and the possible mechanism.

METHODS

Sixty freshly extracted non-carious maxillary premolars were collected and divided into 6 groups with 10 specimen in each group. MOD cavities (buccolingual width: 2.8 to 3.2 mm; palatal cusp width: 2.0 mm; cusp height: 5.0 mm) were prepared individually. Group 1 was prepared and not restored (control). The other 5 groups were restored with silver amalgam alloy (group 2), Z250 without bonding (group 3), F2000 (group 4), Z250 (group 5) and Z350 nanocomposite (group 6) (3M ESPE) respectively. The fracture resistance of the tested teeth was determined by applying a vertical splitting load through a specially shaped steel rod at a crosshead speed of 1 mm/min. The data were analyzed by ANOVA.

RESULTS

The average fracture resistance of the 6 groups was: (245.29 +/- 39.49) N (group 1), (255.09 +/- 42.14) N (group 2), (267.34 +/- 31.56) N (group 3), (293.90 +/- 33.42) N (group 4), (337.81 +/- 32.63) N (group 5) and (349.08 +/- 32.93) N (group 6). There was no significant difference between the group 1, group 2 and group 3. The fracture resistance of group 4, group 5 and group 6 was higher than that of group 1 and group 2 (P < 0.05). Significant difference was noted between group 5 and group 3 (P < 0.01). The fracture resistance of group 4 was much lower than that of group 5 and group 6 (P < 0.01). No significant difference was found between group 5 and group 6.

CONCLUSIONS

The use of composite increased the fracture resistance of the tooth with an MOD restoration. This effect was related to the adhesive force, polymerization shrinkage stress and the elastic modulus of the composite.

Fracture resistance of the buccal cusps of root filled maxillary premolar teeth restored with various techniques

AIM

To compare the cusp fracture resistance of teeth restored with composite resins and two post systems.

METHODOLOGY

Eighty extracted single-rooted human maxillary premolars were randomly assigned to eight groups (n = 10). Group 1 (control) did not receive any preparation. From groups 2 to 8, the teeth were root filled and mesio-occluso-distal (MOD) cavities were prepared. Group 2 remained unrestored. Group 3 was restored with packable resin composite using a single-step adhesive. Group 4 was restored with packable resin composite using a single-step adhesive and a thin layer of flowable resin composite. Group 5 was restored with packable resin composite using a total-etch two-step adhesive. Group 6 was restored with ormocer resin composite using a total-etch two-step adhesive. Group 7 was restored with an endodontic glass fibre post and hybrid resin composite using a total-etch two-step adhesive. Group 8 was restored with an endodontic zirconium post and hybrid resin composite using a total-etch two-step adhesive. The teeth were then mounted in a universal testing machine, the buccal cusp loaded (30 degrees ) until fracture, and the data analysed statistically.

RESULTS

Group 1 had the greatest fracture resistance, and group 2 the poorest. Groups 5-8 had significantly greater (P < 0.05) fracture resistance than groups 3 and 4. No significant differences were found between groups 3 and 4, or amongst groups 5-8 (P > 0.05).

CONCLUSIONS

For root filled maxillary premolars with MOD cavities, adhesive resin composite restorations, with and without glass and zirconium posts, increased the fracture resistance of the buccal cuSPS. A total-etch two-step adhesive increased significantly fracture resistance more than a one-step adhesive. For the one-step adhesive, an additional layer of flowable resin composite did not enhance fracture resistance.

Fracture resistance of roots with thin walls restored using an intermediate resin composite layer placed between the dentine and a cast metal post

Thin-walled roots restored using conventional cast metal post-cores are at risk of fracture. Placing a thick intermediate layer of resin-based composite (RBC), sandwiched between the root dentine and a small-diameter metal post or dowel, may improve the fracture resistance of such roots. In this initial laboratory study, two similar groups each of six decoronated maxillary central incisor teeth were prepared with approximately 1.0 mm thick tapered root canal walls. Cast metal alloy post-cores and metal-ceramic crowns were fabricated and cemented for one group with, and for the other control group without, a thick intermediate layer of RBC. The mean force (N) to fracture the roots was 639.3 (SD 51.6) for the intermediate layer of RBC group and 360.8 (42.9) for the control group, P < 0.0001. These significantly different findings require clinical confirmation.

Influence of resin-based adhesive root canal fillings on the resistance to fracture of endodontically treated roots: an in vitro preliminary study

OBJECTIVE

The aim was to investigate the root reinforcing capability of the resin-based RealSeal.

STUDY DESIGN

In two groups (n=36) canals were instrumented with nickel-titanium rotary GTfiles or with hand K-files. Twelve teeth from each group were obturated with lateral compaction using either gutta-percha and AHPlus or RealSeal. The canals of twelve teeth of both groups were instrumented but not filled. Group 3 (n=12) acted as uninstrumented controls. The force required to fracture the roots was measured. ANOVA and Scheffé test were used for statistical analysis.

RESULTS

The intact roots were significantly stronger than both groups with instrumented and unobturated roots (P<.05). Between the roots of both groups obturated with RealSeal and the intact roots there were no significant differences (P>.05). The roots obturated with RealSeal were significantly stronger than those obturated with gutta-percha and AHPlus (P<.05).

CONCLUSIONS

An obturation with RealSeal significantly increases the fracture resistance of instrumented roots.

Role of alcohol in the fracture resistance of teeth

Healthy dentin, the mineralized tissue that makes up the bulk of the tooth, is naturally hydrated in vivo; however, it is known that various chemical reagents, including acetone and ethanol, can induce dehydration and thereby affect its properties. Here, we sought to investigate this in light of the effect of alcohol on the mechanical properties of dentin, specifically by measuring the stiffness, strength, and toughness of dentin in simulated body fluid and Scotch whisky. Results indicated that chemical dehydration induced by the whisky had a significant beneficial effect on the elastic modulus, strength, and fracture toughness of dentin. Although this made teeth more resistant to fracture, the change in properties was fully reversible upon rehydration. This effect is considered to be associated with increased cross-linking of the collagen molecules from intermolecular hydrogen-bonding, where water is replaced with weaker hydrogen-bond-forming solvents such as alcohol.

Resistance to fracture of roots filled with three different techniques

AIM

To compare the fracture resistance of roots filled with different materials.

METHODOLOGY

Thirty-four freshly extracted human maxillary central incisor teeth with similar dimension were selected. Crowns were sectioned at the cemento-enamel junction, and the length of the roots were adjusted to 13 mm. Following the preparation of the root canals and final irrigation with EDTA and saline, the 10 root canals in group 1 were filled with Resilon cones and Epiphany sealer, the 10 root canals in group 2 were filled with gutta-percha and AH 26 and the 10 root canals in group 3 were filled with gutta-percha and MCS Canal Sealer. All materials were used with a cold lateral condensation technique. Four root canals remained unfilled and were used as a control group. Tests for fracture strength were performed using a universal testing machine and a round tip that had a diameter of 4 mm. The force was applied vertically with a constant speed of 1 mm min(-1). For each root, the force at the time of fracture was recorded in Newtons. Results were evaluated statistically with ANOVA and Tukey Honestly Significant Difference (HSD) tests.

RESULTS

The mean force of fracture values was 1043 N, 967 N, 859 N and 517.5 N for groups 3, 1 and 2 and the control group, respectively. There was a significant difference (P < 0.01) between the experimental groups and the control group. No significant differences were found between the three experimental groups.

CONCLUSIONS

All the materials used in the present study reinforced the prepared root canals.

Fracture Strength of Endodontically Treated Teeth with Flared Root Canals and Restored with Different Post Systems

BACKGROUND

Many post systems are available to clinicians, yet no consensus exists about which one is better in restoring endodontically treated teeth.

PURPOSE

This study evaluated the fracture strength of teeth with flared canals and restored with two fiber-reinforced resin systems (glass fiber: FRC Postec [Ivoclar Vivadent, Schaan, Liechtenstein]; quartz fiber: D.T. Light-Post [Bisco Dental Products, Schaumburg, IL, USA]), and one custom cast base metal (Ni-Cr) post and core system.

METHODS

Thirty anterior teeth had their crowns removed below the cemento-enamel junction and were endodontically treated. The canals were prepared for post fixation, and the canal walls were flared using a taper diamond bur. The prepared roots were randomly divided into three groups according to the post system. All posts were cemented with an adhesive resin cement. For the fiber-reinforced resin posts, cores were built up using microhybrid composite. Metallic crowns were luted using zinc phosphate cement. Specimens were loaded at 45 degrees in a universal testing machine at a crosshead speed of 0.5 mm/min until failure. The mode of failure was classified as repairable or nonrepairable.

RESULTS

Teeth restored with cast posts had fracture strength twice that of teeth restored with resin posts. Fiber-reinforced resin posts failed at a compressive force comparable to clinical conditions, but all failures were repairable.

CONCLUSION

Fracture strength and mode of failure in anterior teeth with flared canals varied according to the type of post used to support a crown.

CLINICAL SIGNIFICANCE

Under the conditions of this study, cast posts are preferable to restore endodontically treated teeth with flared canals and no ferrule.

Fracture resistance of crowned incisors with different post systems and luting agents

This study evaluated the fracture resistance of crown-restored incisors with different post-and-core systems and luting cements. Fifty intact maxillary central incisors were randomly assigned to five groups of 10 teeth each. Group 1 was restored with fibre posts (Snowpost) luted with an adhesive composite resin cement (Panavia F). Group 2 was restored with titanium alloy posts (Parapost) luted with the resin cement, and Group 3 with titanium alloy posts and a glass-ionomer cement (Fuji I). Composite cores (Clearfil Photocore) were built up in groups 1, 2 and 3. Group 4 was restored with cast post-and-cores luted with the resin cement, and group 5 with the cast post-and-cores and the glass-ionomer-cement served as a control group. All teeth were restored with metal-ceramic crowns. After thermal stressing, the specimen was then secured in a universal testing machine. Fracture loads and modes were recorded. One-way ANOVA and a Tukey test were used to determine significant differences between the failure loads of groups. Chi-square test was conducted for evaluation of the fracture modes. The fracture loads of groups 1 and 2 were significantly higher than that of the control group (P<0.05). Group 1 had a significantly higher number of repairable fractures than the other four groups (P<0.001). Within the limitations of this study, the results suggest that fibre posts can be recommended as an alternative to cast and prefabricated metallic posts. Composite resin cement cannot significantly improve fracture resistance of metallic post and crown-restored incisors.

On material choice and fracture susceptibility of restored teeth: An asymptotic stress analysis approach

OBJECTIVE

The ultimate success or failure of a restored tooth is largely dependent on clinical management. Clinicians may choose from a number of restorative materials, different clinical techniques and cavity preparation procedures. The purpose of this study was to specifically examine aspects of the material choice holding other factors constant.

METHODS

The current paper adopts a fundamental result in the linear theory of elasticity on the singular stress distribution in a bi-materials wedge to analyze the fracture susceptibility of different materials used for the restoration of a tooth.

RESULTS

Comparable results are reported for amalgam, gold alloys and ceramic materials. It is shown that due to a wide variety of mechanical properties the application of resin-based composites could lead to improved or less fracture resistance of the restored tooth.

SIGNIFICANCE

This variety in the mechanical properties for resin-based composites could be partially responsible for the contradictory evidences reported by different clinical studies. The present work contributes evidence from an analytical model to assist the restorative dentist in selection of an appropriate restorative material and guide the manufacturing companies on the preferred physical properties of newer designed materials.

Fracture behavior of structurally compromised non-vital maxillary premolars restored using experimental fiber reinforced composite crowns

PURPOSE

To study the fracture behavior of direct resin composite crowns with or without experimental fiber reinforcement.

METHODS

Clinical crowns of single-rooted maxillary premolars were cut off at the cemento-enamel junction. Canals were prepared with Gates Glidden drills up to size 4. No additional post-space preparations were made. Roots were embedded in acrylic and canal entrances were standardized (depth 2 mm, diameter 1.75 mm). Three groups of 14 samples were treated as follows: (1) custom-made glass FRC post (EverStick Post); fibers 5 mm deep in the canal, (2) similar post-system as (1) with incorporation of a new type of glass fiber fabric, (3) no fiber reinforcement (control). Posts were cemented with resin cement (Panavia F). Resin composite crowns (Filtek Z250) were made using an anatomically formed mold. Static load until fracture was applied using a universal loading device with a cylindrical bar (diameter 2 mm) with a crosshead speed of 5 mm/minute (loading angle: 30 degrees to the tooth long-axis). Failure modes were categorized as favorable and unfavorable failures.

RESULTS

There was no significant difference in mean failure loads among the four groups (P > 0.05). Favorable failures occurred significantly more often in Group 2 than in the other groups (P < 0.05). The results suggest that an incorporated glass fiber fabric does not affect the load-bearing capacity of resin composite complete crowns on structurally compromised and non-vital premolars. Incorporation of a glass fiber fabric, however, has a beneficial effect on the failure mode.

Effectiveness of a self-adhesive resin luting system on fracture resistance of teeth restored with dentin-bonded crowns

Laboratory studies have demonstrated satisfactory fracture resistance of all-ceramic crowns placed using a conventional resin-composite luting material and a dentine bonding system. This study investigated the fracture resistance of teeth restored with dentine-bonded ceramic crowns luted with a self-etching luting material. Standardized preparations were carried out on two groups of ten sound, unrestored, maxillary premolar teeth. Ceramic crowns were constructed, their internal surfaces etched and placed using two luting system combinations. Compressive fracture resistance was determined for each group using a Universal Testing Machine. Mean compressive fracture resistance of 890 (222) N and 760 (271) N were recorded for the RelyX Unicem Aplicap and Mirage groups, respectively. There was no significant difference in the mean compressive fracture resistance of the restored teeth in both groups (P<0.05). The failure modes were different for each cements with more severe (Mode V)failures associated with the Mirage group compared with the consistent Mode II failures associated with RelyX Unicem Aplicap. We conclude that the fracture resistance of dentine-bonded crowns luted with a self-adhesive resin-based luting material was no different from that of a conventional resin-based luting system. The fracture resistance of dentine-bonded ceramic crowns may be clinically satisfactory when a self-adhesive resin-based luting material is utilised.

Fracture resistance of weakened roots restored with a transilluminating post and adhesive restorative materials

STATEMENT OF PROBLEM

The increase in wall thickness of weakened roots using composite resins may increase the root resistance to fracture. However, little is known about the recently developed methods for intraradicular reinforcement of weakened roots.

PURPOSE

The purpose of this study was to determine the fracture resistance of experimentally weakened roots reinforced with composite resins, compared with conventional systems that use cast and prefabricated posts.

MATERIAL AND METHODS

Forty-eight maxillary incisors were divided into 6 groups (n = 8). The control group (C) used a conventionally prepared root canal filled with cast CuAl posts. Experimental groups had the root canals overprepared to weaken them and were restored as follows: CP, cast CuAl posts; LT, light-transmitting polymerization post (Luminex) + Tetric Ceram resin + prefabricated titanium post (PTP); LF, Luminex posts + Filtek Supreme resin + PTP; LZ, Luminex posts + Z100 resin + PTP; and LR, Luminex posts + Renew resin + PTP. All posts were cemented with a resin luting agent (C & B Cement). Specimens were subjected to compressive load (N) until fracture. Data were submitted to 1-way analysis of variance and the Dunnett test (alpha = .05).

RESULTS

There was significant difference (P < .01) between the conventionally prepared specimens and those filled with a cast post (C, 447.8 +/- 167.9) and the overprepared specimens and those filled with a cast post (CP, 212.8 +/- 62.4). No significant differences were found among the control specimens (447.8 +/- 167.9) and the weakened-roots filled with Luminex and composite resins LT (520.9 +/- 173.1), LF (479.9 +/- 214.9), LZ (391.6 +/- 173.6), and LR (333.0 +/- 112.2).

CONCLUSION

The use of composite resins in root canals reinforced the weakened roots during fracture resistance testing.

Fracture resistance of teeth restored with 2 different post-and-core designs fixed with 2 different luting cements: an in vitro study. Part II

OBJECTIVE

The purpose of this in vitro study was to investigate fracture resistance in teeth restored with cast posts and cores with and without ferrule and using 2 different luting cements.

METHOD AND MATERIALS

Forty intact extracted maxillary premolars were endodontically treated after their crowns were removed 2 mm from the cementoenamel junction. Specimens were embedded in acrylic resin blocks, in aluminum cylinders, 2.00 mm apical to the cementoenamel junction. Twenty specimens were ferruled. Within this group, half of the posts and cores were cemented with zinc phosphate cement, while the other half were cemented with resin cement. The same procedures were followed for the nonferruled group. The posts and cores were cast in gold alloy. Specimens were placed in a universal testing machine, and loads were applied at an angle of 45 degrees and a rate of 1 mm/min until the teeth fractured. Analysis of variance and Tukey tests were used for statistical analysis; level of significance was established at 5%.

RESULTS

There was no association between type of cement and cervical ferrule; ferruled specimens showed greater resistance than nonferruled ones, regardless of the cement used.

CONCLUSION

A 2-mm cervical ferrule improves fracture resistance of restored teeth, but the type of luting cement used does not seem to affect resistance.

Comparison of fracture resistance in root canals of immature sheep teeth after filling with calcium hydroxide or MTA

Thirty immature sheep incisor teeth were tested for their fracture resistance after various treatment modalities using calcium hydroxide (CH) or a mineral trioxide aggregate material (MTA) as a root filling. The incisors, having approximately 80% of their root growth completed, were removed from jaws of slaughtered sheep and divided into four experimental groups. The pulps were extirpated from all the teeth through the open apexes. (a) Saline group: the teeth were preserved in saline for 100 days at 6 degrees C. (b) CH group: the root canals were filled with CH and sealed apically with IRM and stored as above. (c) MTA group: the canals were filled with MTA and stored as above. (d) CH+MTA group: the canals were filled with CH and sealed with IRM. After 30 days, the CH was replaced with MTA and stored as above. At the end of the 100-day storage period, all teeth were embedded in plaster of Paris and tested for fracture strength at the cervical area in an Instron testing machine. The results showed a decrease in fracture resistance (a) of the incisors with CH in the root canals after 100 days of storage, compared to (b) teeth stored in intracanal saline and (c) teeth with 30 days of CH and then filled with MTA, and (d) those filled with MTA in the canals. In conclusion, when CH was kept in the canals of immature sheep teeth for only 30 days followed by root filling with MTA there was no significant decrease in strength of the root within an observation period of 100 days. This finding may be of importance in the decision of treatment plans for teeth with pulp necrosis and immature root formation.