Fracture Resistance Of Group Research Articles

Evaluating the Effect of Different Intra-Orifice Barriers and Various Bleaching Agents on the Fracture Resistance of Teeth After the Walking Bleach Procedure: An In Vitro Study.

Objective This study aimedto evaluate the effect of three different commercially available intra-orifice barriers and bleaching agents on root canal-treated teeth. Materials and methods Forty-five freshly extracted single-rooted incisors, canine, and premolars were collected and stored in 10% formalin. Root canal procedures were performed on the extracted teeth and these were classified into three groups and three subgroups (n=5). Group 1: resin-modified glass ionomer cement (RMGIC); placed at the level of cemento-enamel junction (CEJ) and cured for 20 seconds. Group 2: BiodentinTM (Septodont Ltd., Saint Maur des Fausse´s, France); powder and liquid were mixed according to the manufacturer's instructions and placed at the level of CEJ, and waited for 15 minutes to set. Group 3: bulk-fill composite; placed at the level of CEJ. Group A was treated with 35% carbamide peroxide (Ultradent Opalescence 35% PF regular). Group B was bleached with 35% hydrogen peroxide (Pola Office). Group C,which was the control group, was treated with distilled water. The bleaching procedure was repeated once every seven days for a period of three weeks. After bleaching, every sample was sectioned 2 mm above the level of CEJ to remove the crown.Auniversaltesting machine (UTM) was used for the evaluation of the fracture resistance of teeth.Data were analyzed for significance by using analysis of variance (ANOVA) and further pair-wise comparison was performed by pos-hoc analysis. The level of significance was set at p<0.05 Results There was a significant difference between the fracture resistance of the three materials when bleached using distilled water (p<0.05). The fracture resistance of Group 3 was significantly greater than that of Group 2 and Group 1 (p<0.05). The difference in the fracture resistance between Group 1 and Group 2 was nonsignificant (p>0.05). Conclusion Walking bleach performed via bleaching agents 35% carbamide peroxide and 35% hydrogen peroxide leads to a reduction in the fracture resistance of endodontically treated teeth; 35% hydrogen peroxide causes more fracture resistance reduction than carbamide peroxide of the same concentration. The presence of intra-orifice barriers leads to greater fracture resistance and reinforcement of endodontically treated teeth that undergo the walking bleach procedure. Bulk-fill composite can be used as an intra-orifice barrier with good fracture resistance.

The Effect of Chloroquick on Fracture Resistance of Root Filled Teeth- An In-Vitro Study

Aim: To evaluate and compare the fracture resistance of endodontically treated teeth irrigated with different irrigating solutions under instron testing machine. Materials and Methodology: Hundred extracted, human, single rooted mandibular premolars, recently extracted from patients for orthodontic purpose were selected. All the teeth were decoronated upto a standardised length of 12 mm. All the teeth were then biomechanically prepared upto size F4 and chemomechanically irrigated with different combinations of irrigants : Group 1: Chloroquick, Group 2: 5% EDTA(ethylenediamine tetra acetic acid) and 2.5% NaOCl(so, Group 3: 17% EDTA and 2.5% NaOCl, Group 4: 5% EDTA, Chloroquick and 2% Chlorhexidine and Group 5: 17% EDTA, Chloroquick and 2% Chlorhexidine followed by insertion of F4 gutta percha cones and application of AH Plus 26 sealer. All teeth irrespective of the groups were stored at 370C and 100% relative humidity for 14 days to allow sealer to set and each group was subjected to instron testing machine to evaluate their fracture resistance. The force required to fracture each specimen was recorded in Newtons and data were analysed statistically using analysis of variance ( ANOVA) test and Post- Hoc Tukey test. Results: The mean fracture resistance of Group 5 was highest followed by Group 3, Group 1, Group 4 and Group 2. (Group 2&lt;Group 4&lt;Group 1&lt;Group 3&lt;Group 5). The mean fracture resistance of Group 5 was significantly higher than rest of the groups (P&lt;0.001) and also of Group 3 was significantly higher than other groups. Conclusion: In context to all the irrigating solutions used for chemomehanical preparation, Chloroquick and it’s combination with 17% EDTA and 2% Chlorhexidine showed higher fracture resistance.

Assessment of Fracture Resistances of Endodontically Treated Teeth Filled with Different Root Canal Filling Systems.

Background:The motive of endodontic therapy is cleaning, shaping, and subsequently obturation. This study assessed different root canal filling systems in terms of fracture resistances of endodontically treated teeth.Methodology:This study was conducted on eighty single-rooted permanent mandibular incisor teeth which were divided into five groups: Group I was negative control; Group II was positive control; Group III comprised of gutta-percha/AH Plus; Group IV comprised of Thermafil/AH Plus; and Group V Resilon/Epiphany SE. Universal testing machine measured fracture resistance.Results:The mean fracture resistance in Group I was 458.6 ± 112.4 N, in Group II was 214.8 ± 104.6 N, in Group III was 428.6 ± 108.2 N, in Group IV was 388.2 ± 126.2 N, and in Group V was 334.8 ± 102.7 N. The difference found to be statistically significant (P < 0.05). Intergroup comparison showed a statistically significant difference (P < 0.05) between Groups I-II, I-V, II-III, and II-IV.Conclusion:The authors found that lateral condensation performed with AH Plus sealer and gutta-percha and the Thermafil technique were the highest among all other methods.

The Effects of Various Restorative Techniques on the Fracture Resistance of Pulpotomized Permanent Premolars.

Aim This study aimed to evaluate the effects of various restorative techniques on the fracture resistance of pulpotomized premolars with mesioocclusodistal (MOD) cavities treated with mineral trioxide aggregate (MTA) or calcium enriched mixture (CEM) cement. Materials and Methods One hundred and eight sound extracted maxillary premolars were randomly assigned to nine experimental groups (n = 12). The teeth in group 1 did not receive any preparation. Class II MOD cavities were prepared in the other experimental groups. In groups 2, 4, 6, and 8, tooth-colored MTA was used for pulpotomy. In groups 3, 5, 7, and 9, CEM cement was used for pulpotomy. Groups 2 and 3 were left unrestored. Groups 4 and 5 were restored with amalgam. Groups 6 and 7 were restored with a conventional composite resin, and groups 8 and 9 were restored with bulk-fill giomers. Fracture resistance was measured, the fracture pattern of each specimen was assessed, and the results were statistically analyzed. Results The fracture resistance of group 1 was significantly higher than those of the other groups (p < 0.05). The fracture resistance of group 2 (MTA + amalgam) was statistically lower than those of all experimental groups (p values < 0.05) except groups 3, 4, and 5 (p values > 0.05). No statistically significant differences were found between the groups restored with amalgam, conventional composite resin, and bulk-fill giomer (groups 4, 5, 6, 7, 8, and 9) (p values < 0.05). The highest rate of mode 1 fracture (restorable fracture) was observed in group 1 followed by groups 8 and 9. Conclusion No significant differences were found among the fracture resistances of the restored teeth using various restorative techniques. Bulk-fill giomers followed by conventional composite resin were better able to prevent unfavorable fractures compared to amalgam. Therefore, they seem to be more reliable for the restoration of pulpotomized teeth with MOD cavities.

“A COMPARATIVE EVALUATION OF FRACTURE RESISTANCE OF BADLY MUTILATED ANTERIOR TEETH RESTORED WITH THREE DIFFERENT NOVEL POST CORE SYSTEM: AN IN VITRO STUDY”

Aim A study was aimed to compare the fracture resistance and the mode of failure of endodontically treated teeth reestablished with various fiber post-center frameworks. Method 60 extracted permanent maxillary central incisors selected and biomechanical preparation performed by Conventional step back technique and Obturated by manual lateral condensation technique with guttapercha using AH plus root canal sealer .Teeth randomly assigned into four experimental groups The access cavities were sealed with packable composite restoration.Crown preparation with shoulder of 1mm was prepared followed by reduction of crown high to 8mm from shoulder margin. The post space arrangement was finished with Peeso-Reamer up to number 4 size to a profundity of 10 mm. The fiber present was then applied on a stature of 4 mm over the tooth edge. Post was solidified with oneself fix glue tar concrete. The example with tempered steel square was mounted on an uncommon apparatus on a PC controlled Universal Testing Machine. The compressive burden was applied with 1 mm width, ball-finished steel compressive head at an edge of 130 to the long hub of the tooth. Result The results showed that the fracture resistance of group C (DT light post and Core Flo DC) was significantly higher than the other two groups. Group a (Control) had the least fracture resistance. Conclusion DT lightpost and Core Flo DT post-core system, making it one of the best combinations to be recommended for the treatment of badly mutilated teeth.

Fracture resistance of pulpotomized and composite-restored primary molars: Incremental versus bulk-fill techniques

The aim of this study was to assess the fracture resistance of pulpotomized primary molars restored with incremental and bulk-fill composite application techniques. In this in-vitro experimental study, 36 extracted primary molars were nonrandomly (selectively) divided into three groups of 12 each. All teeth underwent conventional pulpotomy treatment, and mesio-occluso-distal cavities were prepared in such a way that the buccolingual width of the preparation was two-thirds of the intercuspal distance, and the depth of the buccal and lingual walls was 4 mm. The teeth were then restored as follows: Group 1 (control) was restored with amalgam, Group 2 was restored with Tetric N-Ceram composite using the incremental technique, and Group 3 was restored with Tetric N-Ceram composite using the bulk-fill technique. The restored teeth were subjected to thermocycling and then underwent fracture resistance testing in a universal testing machine at a crosshead speed of 1 mm/min. Fracture resistance of groups was compared using the one-way ANOVA and Tukey's honestly significant difference test. The mean fracture resistance was 1291.47 ± 603.88 N in the amalgam, 1283.08 ± 594.57 N in the Tetric N-Ceram incremental, and 1939.06 ± 134.47 N in the Tetric N-Ceram bulk-fill group. The difference in this regard between Group 3 and Groups 1 and 2 was statistically significant (P = 0.019 and P= 0.035, respectively). Bulk-fill composite is recommended for reinforcing the remaining tooth structure after the primary molar pulpotomy procedure. Time-saving characteristics of this material are clinically important for reducing appointment time for children.

Effect of Glass Fiber Post Diameter on Fracture Resistance of Endodontically Treated Teeth

Objective: To determine the fracture resistance of endodontically treated teeth restored with three different diameters of glass fiber posts and metal-ceramic crowns. Material and Methods: Thirty human maxillary canines were selected and subjected to root canal therapy. The teeth were randomly divided into three groups of glass fiber posts with 1.4 mm diameter (Group I), 1.6 mm diameter (Group II), and 2.0 mm diameter (Group III). The teeth were restored with metal-ceramic crowns and subjected to the compressive load applied at 45° angle to the longitudinal axis until fracture. The mode of failure was determined. Data were analyzed using ANOVA, followed by Tukey's post hoc multiple comparisons test (p<0.05) . Results: The mean fracture resistance of groups I, II and III was 574 ± 91.2 N, 617 ± 85.21 N and 467 ± 99.43 N, respectively. No significant difference was noted between groups I and II, while the fracture resistance was significantly different between groups I and III (p<0.05) and groups II and III (p<0.05). No case of post fracture alone occurred in any group . Conclusion: The diameter of glass fiber posts can affect the fracture resistance of teeth. Based on the results, increasing the diameter of the post up to 1.6 mm may increase the fracture resistance of root, although excessive diameters are not recommended.

Evaluation of the fracture resistance of root filled thin walled teeth restored with different post systems

BackgroundRestoration of the teeth with extensive root canals with different post systems is a challenge for clinicians. Evaluation of these systems is important for clinical success. The aim of this study was to compare the fracture resistance and fracture mode of endodontically treated thin-walled teeth which restored with different post systems. MethodsEighty extracted and endodontically treated maxillary canines were divided into 4 groups (n = 20) and the thickness of the radicular dentin walls was reduced by using diamond burs. Each root was embedded in an autopolymerizing resin with a 0.25 mm layer of vinyl polysiloxane material to simulate the periodontal ligament. The subgroups were restored with one of the following post systems: only composite resin (Group 1), cast post (Group 2), glass-fiber post (Group 3), and I-TFC post (Group 4). The samples were subjected to a gradually increasing force (0,5 mm/min). The force required to fracture was recorded, and the data were analyzed with ANOVA, Tukey test's and Chi–Square test (p < 0.05). ResultsThe highest fracture resistance was recorded for Group 2, followed by the Group 3, Group 4, and Group 1. Differences in the fracture resistance of teeth were significant among the groups (p < 0.05). The fracture resistance of Group 4 was significantly different than the other tested post systems (p < 0.05). ConclusionsThe lowest fracture resistance was recorded for Group 1, but among all post systems, Group 4 had the lowest fracture resistance. The fracture mode of the fiber posts (Radix and I-TFC posts) would permit repair of the tooth.

In vitro comparison of the force required to fracture roots vertically following the use of two instrument retrieval systems

Objective: The objective of this study was to compare the force required to fracture the roots in a vertical direction following the use of two instrument retrieval systems. Introduction: A vertical root fracture is a longitudinal fracture of the root, extending throughout the dentin from the root canal to the periodontium. The fracture strength of teeth after the application of two systems used for instrument retrieval, i.e. ultrasonic (P5 Booster Company Irrisafe, Satelec ACTEON, North America) and instrument removal system (iRS Switzerland) was compared. Materials and Methods: Freshly extracted 60 maxillary central incisor teeth with straight roots and single canal were collected. The anatomical crowns of all the teeth were sectioned. The samples were cleaned and shaped with the crown down technique using Pro-Taper (DENTSPLY, Maillefer, USA) rotary instruments up to a size F2. The fracture of rotary file was deliberately induced by the pressure that was applied during rotary motion of F3 file. The samples were then randomly divided into three groups each having 20 teeth, i.e., Groups A, B, and C. Retrieval of separated file was performed in Groups B and C by means of Ultrasonic and Instrument retrieval system, respectively, while no retrieval of separated file was done in Group A. Each sample was then subjected to load by Instron testing machine until the sample got fractured. That load at the time of fracture of each sample was recorded. The data collected from all the samples were then subjected to statistical analysis using ANOVA and Tukey's HSD. Results: The results showed statistically significant difference among all the groups. The group in which no retrieval system was employed showed the best fracture resistance. The group in which ultrasonic removal system was used showed better fracture resistance as compared to the group in which iRS was used. The fracture resistance of Group A, Group B, and Group C ranged from 265.23–289.66, 114.67–135.66, and 70.56–97.56, respectively, with mean (± standard error) 277.60 ± 1.94, 124.65 ± 1.53, and 84.98 ± 1.76, respectively, and median 276.54, 123.95, and 85.78, respectively. Conclusion: According to the results of the present study, the difference between the force required to fracture roots vertically after removal of a fracture instrument with the ultrasonic and instrument removal system was statistically significant.

Evaluation of fracture resistance and mode of failure of premolars restored with nanohybrid composite, ORMOCER and ceramic inlays

ObjectivesTo evaluate the fracture resistance and mode of failure of maxillary premolars restorations restored with nanohybrid Composite, ORMOCER and Ceramic Inlays. Materials and method100 extracted first maxillary premolar were collected. Samples were divided into five groups. Group I – Intact premolars, Group II –MOD cavities without restorations, Group III – MOD cavities restored with composite restoration, GROUP IV – MOD cavities restored with ORMOCER restoration and GROUP V – MOD cavities restored with ceramic inlays. All the samples were sent for the axial compression test under the universal testing machine. Fracture resistance and fracture modes were recorded. ResultHighest fracture resistance was achieved in Group V (1324.74±336.78) almost comparable to that of natural tooth (1381.07±259.36) (p<0.05), followed by Group IV (MOD cavities with ORMOCER restorations) (1082.27±351.27) (p<0.01) and least fracture resistance in Group III (MOD cavities with composite restorations) (778.35±100.25) (p<0.0001). Mode of fracture in Group IV and Group V are almost similar and In Group III 65% of the cases showed non-restorable fractures. ConclusionORMOCER fracture resistance along with other groups of clinically restorable fracture stand better than Nanohybrid composite. Clinical RelevanceBased on the present study, the dentist can utilize the ORMOCER material as a restoration material for the cavities of posterior teeth which is better in terms of fracture resistance and durability of the restoration when compare to nanohybrid composite.

In vitro fracture resistance of endodontically treated premolar teeth restored with a direct layered fiber-reinforced composite post and core

Methods for restoring endodontically treated teeth fall short of restoring the physiologic mechanical properties. Fracture of endodontically treated teeth is a common type of clinical failure. New treatment modalities or perfected versions of existing treatment concepts need to be tested to find a biomimetic solution. A novel method of restoring endodontically treated teeth is presented and compared in vitro with currently accepted restorative methods. Seventy-two extracted and endodontically treated maxillary premolar teeth were divided into six groups (n = 12) depending on restorative technique (Groups 1–6). Group 1: fiber-reinforced composite post (FRC), Group 2: direct layered short FRC post and core, Group 3: short fiber-reinforced obliquely layered composite restoration, Group 4: microhybrid composite restoration, Group 5: fiber-reinforced box, Group 6: control. Specimens were submitted to static fracture resistance test. Fracture thresholds and fracture patterns were evaluated. Group 6 exhibited the highest fracture resistance. Group 2 yielded the highest fracture resistance among the restored groups. The fracture resistance of Group 2 did not differ significantly from Group 6. Groups 1, 3, 4, 5 proved to be significantly different from the control group. There was no statistically significant difference among restored groups. Fracture patterns of tested groups were dominantly non repairable opposed to control groups mostly repairable fractures. Application of direct-layered short FRC post and core in endodontically treated premolars performed statistically similarly in the studied conditions as natural teeth. Therefore, it seems a promising alternative to current endo-restorative solutions. However, further testing is required.

Fracture Resistance of Endodontically Treated Maxillary Premolars Restored by Various Direct Filling Materials: An In Vitro Study.

The aim of this study is to compare the effect of various restorative materials on fracture resistance in maxillary premolars. Premolars (n = 64) with no restorations or cracks were selected. MOD cavities were prepared considering the buccolingual width to be equal to half of the intercuspal distance. The specimens were randomly divided into 8 groups, 8 specimens each: group A intact teeth, group B unfilled cavity, group C composite made by oblique layering technique, group D composite with 2 mm cusp coverage, group E bulk-filled posterior composite, group F glass-ionomer, group G amalgam, and group H composite with proximal boxes. The specimens were subjected to an axial compression load with the mean values of fracture resistance in group A: 1289 N, group B: 181.75 N, group C: 445.38 N, group D: 645.88 N, group E: 355.13 N, group F: 352.00 N, group G: 191.38 N, and group H: 572.00 N. There was no significant difference between groups B and G, between C and D, E, and F, and between group D and H. All other measurements were statistically significant. We conclude that composite restoration with cusp coverage is the most ideal nonprosthetic solution for endodontically treated teeth. Cusp coverage increases the fracture resistance compared to the conventional cavity design.

The fracture resistance of a CAD/CAM Resin Nano Ceramic (RNC) and a CAD ceramic at different thicknesses

ObjectivesThis study aimed to investigate the influence of restoration thickness to the fracture resistance of adhesively bonded Lava™ Ultimate CAD/CAM, a Resin Nano Ceramic (RNC), and IPS e.max CAD ceramic. MethodsPolished Lava™ Ultimate CAD/CAM (Group L), sandblasted Lava™ Ultimate CAD/CAM (Group LS), and sandblasted IPS e.max CAD (Group ES) discs (n=8, Ø=10mm) with a thickness of respectively 0.5mm, 1.0mm, 1.5mm, 2.0mm, and 3.0mm were cemented to corresponding epoxy supporting discs, achieving a final thickness of 3.5mm. All the 120 specimens were loaded with a universal testing machine at a crosshead speed of 1mm/min. The load (N) at failure was recorded as fracture resistance. The stress distribution for 0.5mm restorative discs of each group was analyzed by Finite Element Analysis (FEA). The results of facture resistances were analyzed by one-way ANOVA and regression. ResultsFor the same thickness of testing discs, the fracture resistance of Group L was always significantly lower than the other two groups. The 0.5mm discs in Group L resulted in the lowest value of 1028 (112) N. There was no significant difference between Group LS and Group ES when the restoration thickness ranged between 1.0mm and 2.0mm. There was a linear relation between fracture resistance and restoration thickness in Group L (R=0.621, P<0.001) and in Group ES (R=0.854, P<0.001). FEA showed a compressive permanent damage in all groups. SignificanceThe materials tested in this in vitro study with the thickness above 0.5mm could afford the normal bite force. When Lava Ultimate CAD/CAM is used, sandblasting is suggested to get a better bonding.

Fracture Resistance of Premolar Teeth Restored with Silorane‐Based or Dimethacrylate‐Based Composite Resins

To restore posterior teeth using low-shrinkage composite to minimize microleakage. To compare the fracture resistance of mesio-occlusal-distal (MOD) cavity preparations restored with either low-shrinkage composite or with dimethacrylate-based composite in conjunction with cavity liners and without them. The null hypothesis of the study is that there are no differences in either fracture resistance or fracture mode between the silorane group and dimethacrylate groups with and without the use of cavity liners. Sixty maxillary premolars were divided into six groups of 10. MOD cavities were prepared in four groups: F: posterior composite (Filtek P60); GF: 0.5-mm Glass Ionomer (Fuji LC) + posterior composite; FF: 0.5-mm flowable composite (Filtek Supreme XT) + posterior composite; and S: low-shrinkage composite (Filtek P90). Negative (N) and positive (P) control groups consisted of unrestored and sound teeth, respectively. The specimens were thermocycled and loaded. Data were analyzed using analysis of variance, Tukey, and chi-square tests (α = 0.05). Groups FF (1643.09 ± 187/80 N) and GF (1596.80 ± 163/93 N) (p = 0.06 > 0.05) were statistically identical, although less than group P (1742/33 ± 110/08 N), but still demonstrated greater fracture resistance than the other groups. The fracture resistance of group S (1434/69 ± 107/62 N) was identical to GF and FF (p = 0.06 > 0.05). The fracture resistance of F (1353/19 ± 233/90 N) was less than GF and FF, and statistically identical to S (p = 0.87 > 0.05). Silorane-based composite showed a resistance to fracture similar to methacrylate-based composite restorations regardless of whether cavity liners were used. The findings of this study support the selection of silorane-based composite for the restoration of maxillary premolars with standardized Class II cavity preparations in order to strengthen the resistance to fracture to the same extent as do dimethacrylate composites using cavity liners or without them.

Fracture resistance of direct inlay-retained adhesive bridges: Effect of pontic material and occlusal morphology

This study evaluated the effect of a) pontic materials and b) occlusal morphologies on the fracture resistance of fi ber-reinforced composite (FRC) inlay-retained fixed dental prostheses (FDP). Inlay-retained FRC FPDs (N=45, n=9) were constructed using a) resin composite (deep anatomy), b) natural tooth, c) acrylic denture tooth, d) porcelain denture tooth and e) resin composite (shallow anatomy), as pontic materials. In addition resin composite beams were fabricated (N=30, n=10): i) 'circular', ii) 'elliptic I', and iii) 'elliptic II'. There was no significant difference between the fracture resistance of Groups a, b, c, and d (598, 543, 539, 509 N, respectively) (p>0.05) (One-way ANOVA). Fracture resistance of Group e (1,186 N) was significantly higher than those of other groups (p<0.05) (Tukey's test). No significant difference was found between Group i (1,750 N) and Group ii (1,790 N). Not the pontic material but the occlusal morphology affects the fracture resistance of FRC FDPs.

The Effect of Composite Fiber Insertion along with Lowshrinking Composite Resin on Cuspal Deflection of Root-filled Maxillary Premolars

The aim of the present study was to evaluate the effect of three methods of composite fiber placement along with siloranebased composite resin on cuspal deflection and fracture strength of root-filled maxillary premolars. Mesio-occluso-distal cavities were prepared in 60 extracted premolars subsequent to endodontic treatment. The remaining thickness of buccal and lingual walls at height of contour was 2.5 ± 0.2 mm and the gingival cavosurface margin was 1.5 mm coronal to cementoenamel junction. Subsequent to measurement of primary intercuspal distances, the teeth were randomly divided into four groups. In group 1, the cavities were only filled with Filtek Silorane composite resin. In the other three groups, preimpregnated glass fibers were placed at gingival, middle and occlusal thirds respectively, and the cavities were restored similar to the group 1. Cuspal deflection was recorded in micrometer using a stereomicroscope. Fracture strength of the samples was measured in Newton subsequent to thermocycling. Data was analyzed using Kruskal-Wallis, Mann-Whitney U, one-way ANOVA and post-hoc Tukey tests at a significance level of p < 0.05. The highest cuspal deflection was recorded in the group 1, and the difference between group 1 and other groups was significant (p < 0.001). Fracture resistance in group 4 was significantly higher than that in other groups (p < 0.001). In restoring root-filled premolars with siloranebased composite resins, cuspal deflection decreased with the use of preimpregnated glass fibers. Using preimpregnated glass fibers along with silorane-based composite resin may lead to better results in cuspal deflection and fracture resistance of endodonticallytreated maxillary premolars.

Effect of composite restoration on the reinforcement of teeth

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

Effect of bonded restorations on the fracture resistance of root filled teeth

To evaluate the fracture resistance of root filled maxillary premolars restored with different techniques. One hundred and twenty single-rooted maxillary premolar teeth were divided randomly into six groups of 20 teeth and subjected to the following procedures: group 1: intact teeth. Group 2: endodontic access cavities prepared. Group 3: MOD cavities were prepared, root canals were filled and no restoration was placed. Group 4: teeth were prepared as group 3 and restored conventionally with amalgam. Group 5: teeth were prepared as group 3 and restored with amalgam using a bonding material. Group 6: teeth were prepared as group 3 and restored with composite resin using the same bonding material. Teeth were embedded in acrylic resin and the loads for fracture strength were applied vertically with a constant speed of 1 mm min(-1). Data were evaluated statistically with anova and Tukey's tests. The mean force of fracture values were 1191.41, 599.86, 233.03, 494.72, 962.81 and 856.48 N for groups 1, 2, 3, 4, 5 and 6, respectively. The fracture resistance of group 5 was similar to group 1 (P > 0.05). The mean force at fracture of group 5 and group 6 was not significantly different. The fracture resistance of groups 5 and 6 was significantly higher than group 4 (P < 0.001). The group, restored with conventional amalgam, had the weakest resistance to fracture when compared with the bonded restorations. No statistically significant differences were found between the bonded amalgam and composite resin groups.