Fracture Strength Of Teeth Research Articles

Impact of endodontic access cavity design and thermo-cycling on fracture strength of root canal treated mandibular molar teeth

Aim: Aim of study is to evaluate the fracture resistance of the root canal treated Mandibular 1st and 2nd molar teeth with Conventional(TEC) access design and Truss(TREC) access design restored with composite resin and subjected to thermocycling. Method: 60 human 1st and 2nd molar (mandibular) teeth were randomly categorised into six (6) groups: CON (GroupI), TEC (GroupIII), TREC(GroupV) not subjected to thermocycling whereas CONTC (GroupII),TECTC(GroupIV) and TRECTC(GroupVI) subjected to thermocycling. Biomechanical preparation of the canals were done upto #F3 of Protaper gold rotary files (Dentsply) and obturated using gutta-percha points and restored using SDR bulk-fill composite(Dentsply). All samples were then subjected to thermo-cycling for 5000cycles between 15°C and 45°C for different time intervals and their fracture toughness tested under an Universal Tester with steel ball of diameter 5mm at a constant 1mm/min speed. Two-way and one-way ANOVA test employed for statistical analysis. Result: The fracture strength of teeth in TREC group had no notable variation with the control group (P>0.05) without thermocycling. Both TEC and TREC designs notably reduced the fracture toughness after thermocycling (P<0.05). The least fracture resistance was noted in TECTC group. Conclusion: TREC ought to increase the fracture resistance of root canal treated teeth after thermocycling.

Influence of Glass Fiber Post Design and Luting Cements on Ease of Post Removal and Fracture Strength of Endodontically Retreated Teeth: An In Vitro Study.

ABSTRACTAims and Objectives:The aim of this study was to evaluate the time needed to remove two types of glass fiber posts cemented with two different cements and removed with two different techniques and to evaluate the fracture strength of teeth after post removal.Materials and Methods:Root canal treatment was completed in 80 extracted single-rooted premolars and the teeth were decoronated. Following canal preparation, the roots were coated with polysiloxane impression material and embedded in acrylic resin cubes. The specimens were randomly divided into eight experimental groups (n = 10) based on the type of fiber post inserted: Reforpost (R) or Contec Blanco (C); luting cement: Multilink-N/self-etch (M) or G-Cem/self-adhesive (G); technique of removal: Peeso reamer (P); or ultrasonic (U). The posts were removed with respective technique under magnification and the time (in seconds) of post removal was determined. Following post removal, the fracture strength of the specimens was determined using a universal testing machine. The mode of failure was also determined. Data were analyzed by three-way analysis of variance (ANOVA), one-way ANOVA, Tukey’s post hoc test, t test, and correlation. Chi-square analysis was performed to compare the failure mode. Statistical significance was set at P < 0.05.Results:The post and cement types had an influence in post removal time (P < 0.05). There was no role of post or cement types on the fracture strength of teeth after post removal with either technique (P > 0.05). A weak negative correlation was found between the post removal time and fracture resistance for both Peeso reamer (r = –0.373) and ultrasonic (r = –0.177) techniques. Both techniques of post removal produced a majority of favorable failures (P > 0.05).Conclusion:The type of post and luting cement plays a significant role in ease of post removal by Peeso reamer or ultrasonic technique. Post-removal technique had no effect on the fracture strength of teeth. Parallel serrated fiber post luted with self-etch resin cements was difficult to remove as compared with parallel smooth surface post luted with self-etch or self-adhesive resin cement.

Fracture strength of teeth with coronal destruction after core build-up restoration with bulk fill materials.

This study aimed to evaluate the fracture strength and failure modes of different core techniques in teeth with simulated coronal destruction. Forty teeth were endodontically prepared and the specimens were divided into four experimental groups (n= 10) according to the core composition: Filtek One Bulk Fill-FOBF, Filtek Z350 XT-FZ350 (standard group), Filtek Bulk Fill Flow-FBFF, and LuxaCore Z-LCZ. CAD/CAM Monolithic zirconia crowns were obtained and cemented with RelyX U200. After storage in distilled water at 37°C for 48 h, the specimens were subjected to thermal cycling and to compressive strength mechanical tests. Statistical analyses (α= 0.05) were performed by non-parametric Kruskal-Wallis, Dunn post hoc, and Fisher's exact tests. No significant differences (p> 0.05) were observed among FOBF, FZ350, and FBFF (mean ranks=20.30, 12.20, and 23.20, respectively). LCZ (mean rank=26.30) produced results similar to those of FOBF and FBFF (p> 0.05) and higher than those of FZ350 (p= 0.042). The most frequent type of failure was irreparable, regardless of the experimental condition. The lowest percentages of reparable fractures were produced by FOBF group (10%). The use of bulk fill materials, including the "core-and-post" LCZ dual-cure resin composite, did not impair the fracture strength of endodontically treated teeth with coronal destruction. Resin composite bulk fill materials that can be used as a core-and-post cementation in an only stage are interesting, since they enable clinicians to work with one only material, and avoid several materials interfaces, technical sensitivity, and longer chair-time due to multistep procedures.

Endodontik Giriş Kavitesi Şeklinin ve Akışkan Kompozit Uygulamasının Dişlerin Kırılma Dayanımı Üzerine Etkisi

Amaç: Çalışmanın amacı, azı dişlerinde oblik sırt korunarak açılan endodontik giriş kavitesinin ve akışkan kompozit kullanımının kırılma dayanımına etkisinin araştırılmasıdır. Gereç ve Yöntemler: Yüz on üst 1. büyük azı dişi 5 gruba ayrıldı. Grup 1 oblik sırtın korunduğu ve kaide olarak akışkan kompozitin (Filtek Supreme XT Flow; 3M ESPE, St. Paul, MN, ABD) uygulandığı dişler. Grup 2 oblik sırtın korunduğu ve akışkan kompozitin uygulanmadığı dişler. Grup 3 oblik sırtın kaldırıldığı ve akışkan kompozitin uygulandığı dişler. Grup 4 oblik sırtın kaldırıldığı ve akışkan kompozitin uygulanmadığı dişler. Grup 5 prepare edilmemiş dişler. Tüm dişlerin restorasyonları üniversal bir kompozit rezin ile tamamlandı. Maksimum kırılma dayanımları tek yönlü ANOVA ve Bonferroni testleri kullanılarak analiz edildi. Sonlu elemanlar stres analizi (SESA) için bilgisayar ortamında modeller oluşturuldu. Bulgular: En yüksek kırılma dayanımı hiçbir işlem uygulanmayan sağlam diş grubundadır (Grup 5). Grup 5, 1 ve 3 arasında istatistiksel fark bulunamamıştır (p>0,05). Akışkan kompozitin kullanılmadığı grupların kırılma dayanımı (grup 2 ve grup 4) akışkan kompozitin kullanıldığı gruplara (grup 1 ve grup 3) göre istatistiksel olarak anlamlı düşük bulunmuştur (p<0,001). SESA'da, grup 4 hariç grupların benzer stres dağılımı gösterdiği gözlendi. Grup 4'te stresin furkasyon bölgesine doğru yayılım gösterdiği gözlendi. Sonuç: Akışkan kompozit kullanımı ve oblik sırtın korunması dişlerin dayanımını artırmaktadır.

Effectiveness of the static-guided endodontic technique for accessing the root canal through MTA and its effect on fracture strength.

(1) To evaluate the effectiveness of the static-guided (SG) endodontics technique for accessing the root canal through the mineral trioxide aggregate (MTA) and (2) to evaluate the effect of this technique on the fracture strength of teeth. Thirty mandibular premolars were used in the present study. After standard coronal access cavity preparation, root canals were prepared up to size #80 to simulate an immature root apex. White MTA was placed approximately 3 mm below the cementoenamel junction (CEJ), as placed in regenerative endodontic procedures. After the MTA had set, the cavity was restored with a resin composite material. The teeth were randomly divided into two groups (n = 15). In the control group, the composite resin and MTA were removed without any guide. In the SG-access group, a cone beam computed tomography (CBCT) scan was performed, 3D-printed guides were designed and fabricated, and then the composite resin and MTA were removed with a guide. One inexperienced operator performed the removal of the composite resin and MTA in all groups. Pre- and post-operative periapical radiographs were taken. The mishaps and time to penetration to root canal were recorded. After that, the root canals were filled, and the access cavities were restored. The samples were subjected to a fracture strength test. Data were analyzed using Mann-Whitney U, independent samples of T test, and chi-square tests at 95% confidence level (P = 0.05). There were significant differences between the control and SG-access groups in terms of mishaps and time to penetration to the root canal through the MTA barrier (P < 0.05). The SG-access group required the shorter time as compared with the control group. Mishaps did not occur in the SG-access group. The SG-access group exhibited the significantly preserved fracture resistance of the teeth as compared with the control group (P < 0.05). Non-restorable failure occurred more frequently in the control group than in the SG-access group. Within the limitations of the present study, the SG endodontic technique yielded favorable results with respect to time, mishaps, and fracture strength. The static-guided endodontics technique may provide advantages to the clinician for MTA removal.

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.

The effect of glass fiber posts and ribbons on the fracture strength of teeth with flared root canals restored using composite resin post and cores

PurposeThis study evaluated the fracture strength and mode of failure of structurally compromised teeth with flared root canals restored using composite resin with four different systems. MethodsSixty endodontically treated bovine teeth were uniformly shaped to simulate human mandibular premolars with flared root canals. The roots were divided into four groups of 15 specimens each based on the type of restoration: composite resin core only (control), glass fiber post, cylindroid glass fiber ribbons, and glass fiber post and ribbons. All specimens were loaded until fracture occurred using a universal testing machine. Average fracture loads were compared with a one-way ANOVA and Tukey HSD test (α=.05). The modes of failure were observed and the Fisher exact test and Bonferroni correction were used for statistical analysis. ResultsThe fiber post and ribbon group (1035.70N) and the fiber ribbon group (881.77N) showed significantly higher fracture strength than the controls (567.97N) (p<.05). The fiber post and ribbon group also showed significantly higher fracture strength than the fiber post group (769.40N). Almost all specimens showed unrestorable root fractures (p<.008). The control group had a significantly higher ratio of core sectional fractures (p<.017). ConclusionsCylindroid glass fiber ribbons significantly increased the fracture strength of the composite resin post and cores in the case of the dentin within the thin root canal wall. Based on the results, this study recommends the combined use of glass fiber post and ribbons.

The effect of different restoration techniques on fracture strength of teeth with flared roots

The aim of this study was to investigate the effect of different restoration techniques on the fracture strength of roots with flared canals. The crowns of 50 extracted single-rooted human teeth were removed and the canals were flared. Five groups were created (n = 10): Group 1: ReforPost (Angelus) was luted using Clearfil SA Cement (Kuraray); Group 2: ReforPost and two accessory posts (Reforpin, Angelus) were luted with Clearfil SA Cement; Group 3: Restored with i-TFC post-core system (Sun Medical); Group 4: The thickness of the root-dentine was increased using composite resin (Clearfil AP-X, Kuraray) and cured with the help of Luminex. ReforPost was then luted; Group 5: Anatomic posts were created by relining ReforPost with Clearfil AP-X and then luted using Clearfil SA Cement. The cores were created with composite resin in all the samples. The crowns of sound teeth were prepared similar to a core (control, n = 10). The specimens were vertically loaded (1 mm/min), the force that was required to fracture each sample was recorded (N) and analyzed (One Way Anova, Tukey tests). No significant difference was found among the groups (p > 0.05). The roots restored by using accessory post and i-TFC post-core (Groups 2 and 3) indicated a 100% favorable fracture pattern. Ten percent of the root fractures were observed in other groups. All techniques saved the root structure and showed 80–100% favorable failure pattern. The use of i-TFC system in flared roots could be an alternative to anatomic, accessory, and prefabricated fiber posts.

Influence of post-thickness and material on the fracture strength of teeth with reduced coronal structure

Purpose:To evaluate the fracture strength of endodontically treated teeth with reduced coronal structure reinforced with glass-fiber posts and cast posts and core (nickel–chromium alloy) with different thickness.Materials and Methods:Forty maxillary central incisors were sectioned at 1 mm of the cementoenamel junction and endodontically treated. The teeth were divided into four groups (n = 10) and restored with cast post and core and glass-fiber posts with diameters of 1.5 mm and 1.1 mm. The fracture strength was evaluated using a Universal Testing Machine (Instron 1144) at 45° of angulation. The results were submitted to analysis of variance two-way and Tukey's test (P < 0.05). The failure mode was also evaluated.Results:Cast post and core were statistically superior to the glass-fiber posts with the self-post diameter (P = 0.001). When the self-post material was considered, no significant difference was observed between the two post-diameters (P = 0.749). The glass-fiber post-groups presented more fractures in the cervical third than the cast post and core groups.Conclusion:Teeth restored with cast post and cores present higher fracture strength than those reinforced with glass-fiber posts. An increased post-thickness does not increase the fracture strength. Glass-fiber posts lead to less severe fractures.

Does mineral trioxide aggregate reinforce the immature roots?

Dear Sir, I read with great interest the article entitled ‘Comparison of fracture resistance in root canals of immature sheep teeth after filling with calcium hydroxide or MTA’ by Andreasen et al. (1) published in your esteemed journal. I want to share few of my thoughts regarding this study. I appreciate the great work of the writers; however, in my opinion, this article has some technical errors: 1 As mentioned in the discussion, the reduction in fracture strength of teeth by long-term use of calcium hydroxide has been shown in the previous study of the authors (2). Therefore, the primary purpose of the present study was to evaluate the effect of MTA on fracture strength of teeth in comparison with calcium hydroxide. According to Table 1, the teeth in MTA group have greater fracture resistance; however, the small sample size of the study makes the differences statistically insignificant. With proper sample size, MTA may show reinforcing effect on the tooth (3, 4). This study may serve as a pilot for another study with sufficient sample size. 2 I have also a question about statistical analysis. Thedata of the study have been analyzed by the multiple t-tests; however, for comparing four groups, one-way analysis of variance (anova) followed by a proper post hoc test such as Tukey test is recommended assuming the normality of the data and homogeneity of variances. Why did the authors select multiple t-tests instead of anova? Comparing multiple groups by a series of independent sample t-tests is a type of ‘multiple testing’ (5). In this case, for comparing four groups of the study, a series of six independent samples t-tests is needed wherein the alpha (type I error) of 0.05 increases to 0.19 (1)(0.95)4). Therefore, the family error rate is much more than the alpha level defined in the statistical analysis (i.e., 0.05) (5). Contrary to the results of the study, anova shows that even the difference between calcium hydroxide and control group is not significant. I feel that this study can be more refined using sufficient sample size and proper statistical analysis.

Ex-vivo evaluation of the intrapulpal temperature variation and fracture strength in teeth subjected to different external bleaching protocols

This study evaluated the influence of bleaching protocols on intrapulpal temperature and fracture strength of the bleached teeth. Ninety maxillary incisors were assigned to 9 groups (n=10): G1: 35% carbamide peroxide (35% CP), G2: 38% hydrogen peroxide (38% HP), G3: halogen light, G4: LED-laser, G5: 35% CP + halogen light, G6: 38% HP + halogen light, G7: 35% CP + LED-laser, G8: 38% HP + LED-laser, and G9: no treatment (control). Pulp space was widened, a thermocouple was introduced through the apex up to the pulp chamber and the temperature was recorded (°C). The fracture strength (kN) was determined using an Instron machine. Data were analyzed by ANOVA and Tukey's test (p<0.05). The halogen light alone (1.10 ± 0.24) (G3) and associated with 38% HP (1.15 ± 0.30) (G6) produced the highest temperature increase, statistically different (p<0.05) from the other groups. G1 (0.15 ± 0.06) and G6 (0.19 ± 0.07) produced the lowest values, statistically different (p<0.05) from G5 (0.65 ± 0.49). The bleaching protocols increased the temperature, but no increment exceeded the critical value of 5.6°C. Neither 35% CP nor 38% HP or the light sources alone altered the fracture strength of the teeth.

Influence of adhesive system and bevel preparation on fracture strength of teeth restored with composite resin

The aim of this study was to evaluate the fracture strength of teeth with different cavosurface margin cavity preparations and restored with composite resin and different adhesive systems. Eighty premolars were randomly divided in 8 groups, as follow: G1- sound teeth; G2- MOD preparation (no restoration); G3- Adper Single Bond without bevel preparation (butt joint); G4- Adper Single Bond with bevel preparation; G5- Adper Single Bond with chamfer preparation; G6- Clearfil SE Bond without bevel (butt joint); G7- Clearfil SE Bond with bevel preparation; G8- Clearfil SE Bond with chamfer preparation. The adhesive systems were applied according to manufacturers' instructions. Composite resin (Filtek Z250) was incrementally placed in all cavities. After 24 h, the specimens were tested in a universal testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed statistically by ANOVA and Tukey's test (fracture strength) and Fisher's exact test (fracture pattern). The confidence level was set at 95% for all tests. Prepared and non-restored teeth showed the worst performance and G4 exhibited the highest fracture strength among all groups (p<0.05). In conclusion, all restorative treatments were able to recover the fracture strength of non-restored teeth to levels similar to those of sound teeth. Using a total-etch adhesive system with bevel preparation significantly improved the resistance to fracture.

Fracture strength of teeth with flared root canals restored with glass fibre posts

To investigate the fracture strength and pattern of failure of teeth with weakened roots reconstructed by different procedures. In an in vitro study root posts were placed in 50 endodontically treated canines, divided into 5 groups (n=10) as follows: cast metallic post; glass fibre post with smaller diameter than the root canal; glass fibre post with smaller diameter than the root canal + glass fibre strips; glass fibre post with smaller diameter than the root canal + accessory glass fibre posts; anatomical post (glass fibre post with smaller diameter than the root canal, relined with low viscosity composite resin). Posts were luted with resin cement and the coronal portion of posts was constructed with composite resin. Metallic crowns were cemented on the posts. Specimens were submitted to compressive load in a universal testing machine. Fracture strength values of each group were compared. Fracture strength values were for Groups 1-5 respectively: 1087.06; 745.69; 775.41; 920.64; 876.12kgf, with significant differences between Groups 1 and 2 and between Groups 1 and 3 (p<0.05). Observed patterns of fracture were: Group 1 - 100% of roots fractured; Groups 2 and 4 - variable fracture modes; Group 3 - 60% of fractures occurred in the cervical root third; Group 5 - 50% of failures occurred in the coronal portion of the post. The fracture strength of teeth with cast metallic posts, teeth with anatomical posts or teeth with glass fibre posts combined with accessory posts was similar. All teeth restored with cast metallic posts presented fractures and were unfavourable to maintenance of the remaining tooth structure. Teeth with fibre posts (Groups 2 to 5) presented variable fracture modes; however, the maximum percentage of unfavourable fractures was 30%.

Effects of various periodontal ligament elastic moduli on the stress distribution of a central incisor and surrounding alveolar bone

Previous studies investigating the effects of core or post on the fracture strength of teeth often omitted the periodontal ligament (PDL) because its physical properties are difficult to reliably quantify. This study investigated the effects of various PDL elastic moduli on the stress distribution around a central incisor and surrounding alveolar bone using 3-dimensional finite element stress analyses. Four 3-dimensional finite element models of an upper central incisor and the dento-alveolar complex were established. Five models were constructed, including: no PDL, as well as a PDL with elastic moduli of 6.9 MPa, 68.9 MPa, and 1750 MPa. Two loading conditions were simulated, one with protrusive force and one with intrusive force. Protrusive loading was generated using a point force of 200 N at 45 degrees inclination to the longitudinal axis of the incisor applied on the lingual side. Intrusive loading was generated using a point force of 200 N applied perpendicular to the incisal edge. The absence of a PDL had detrimental effects on the surrounding bone, because the applied stress remained concentrated at the bone crest and cervical third of the root. A PDL with a lower elastic modulus, on the other hand, helped to alleviate the magnitude of stress throughout the surrounding bone and the bone crest, in particular, by distributing the stress deeper towards the apical region. The stress distribution at the crown was unaffected by variations in the PDL elastic modulus. PDL with a lower elastic modulus can help protect the alveolar bone crest from stress concentration.

Effect of thermal cycling on fracture strength and microleakage in teeth restored with a bonded composite resin.

Temperature variations in the clinical range may adversely affect bonded composite resin restorations. The aim of this study was to determine the effect of thermal cycling on fracture strength and microleakage in posterior teeth restored with bonded composite resin. Fourteen matched pairs of maxillary premolars were prepared with an MOD slot of uniform dimensions and restored with a posterior composite resin bonded to enamel and dentin (Scotchbond and P-30). One member of each pair was randomly assigned to an uncycled control group; the other to a test group which was cycled between 5° and 55°C. After cycling the test group, both groups of teeth were stained for microleakage with silver nitrate solution, then fractured by occlusal loading in a universal testing machine. The fracture strength of teeth in the groups was compared by Student's matched pairs t test, and microleakage was compared by the Wilcoxon signed-rank test. A significant decrease in fracture strength (P=0.02) of the thermal-cycled teeth was seen when compared with the control teeth. Extensive microleakage was found among both control and thermalcycled teeth. The results of this in vitro study suggest that variations in temperature in the clinical range may reduce the fracture strength gained with bonded posterior composite resins. Polymerization shrinkage may produce clinically significant microleakage even before thermal cycling of the teeth.