Influence of cervical preflaring and root canal preparation on the fracture resistance of endodontically treated teeth.

BACKGROUND: Evaluate the fracture resistance of endodontically treated teeth after cervical preflaring and root canal preparation and to assess the volume of the root canal and the amount of remaining root dentin before and after cervical preflaring. METHODS: Forty-four mandibular incisors were selected using micro-CT scanning and distributed into 4 groups (n = 11) according to the instrument used for cervical preflaring: control group - no cervical preflaring; Gates Glidden - burs size #2 and #3; WXN - 25.07 Navigator instrument; and Easy - 25.08 ProDesign S instrument. Coronal opening was performed, and the canals were prepared with Wave One Gold Primary and filled with an epoxy-resin based sealer and gutta-percha cones. Micro-CT scans were performed before and after root canal instrumentation. All images were reconstructed and assessed for the thickness of mesial and distal root dentin at 3 mm and 5 mm from the cement -enamel junction and for the volume of cervical portion of the canal after preparation. Fracture resistance test was performed applying compressive loads at a crosshead speed of 0.5 mm/min, applied on the palatal aspect of specimens at 135° along the long axis of the tooth. The data were analyzed using ANOVA and Tukey's test (P = .05). RESULTS: Cervical preflaring and canal preparation reduced the dentin thickness (P < .05) and increased the canal volume (P < .05) in all groups at 3 mm an 5 mm. Cervical preflaring with Gates Gliden burs reduced the fracture resistance of endodontically treated teeth (P < .05). CONCLUSIONS: All instruments reduced the dentin thickness and increased the canal volume in the cervical at 3 mm and 5 mm. Gates Glidden reduced fracture resistance of mandibular incisors submitted to cervical preflaring, whereas NiTi instruments did not. CLINICAL RELEVANCE: Cervical preflaring assumes particular importance previously to the root canal preparation because it minimizes the occurrence of operative accidents, and permits more accurate determination of working length and the apical diameter.

Evaluation of fracture resistance in root canal-treated teeth restored using different techniques.

OBJECTIVE: This study aimed to evaluate the effects of different coronal restoration techniques on fracture resistance of root canal-treated mandibular premolars with mesio-occluso-distal (MOD) cavities. MATERIALS AND METHODS: A total of 105 mandibular premolars were selected and randomly distributed into seven groups (n = 15). MOD cavities were prepared except the control group. Root canal treatments were performed. Each tooth was embedded in acrylic resin. Groups were classified as follows; G1: intact teeth (control), G2: unfilled MOD cavity, G3: MOD + composite resin, G4: 10-mm-long fiber post + composite resin, G5: 5-mm-long fiber post + composite resin, G6: Ribbond in the occlusal surface + composite resin, and G7: horizontal fiber post + composite resin. Specimens were loaded using a universal testing machine until fracture occurs. Fracture loads were recorded and statistical interpretations were made (α = 0.05). RESULTS: In Groups 1, 6, and 7, the greatest fracture resistance was shown and there were no significant differences among these groups (P > 0.05). No significant differences were detected among the Groups 3, 4, and 5 (P > 0.05), whereas the fracture resistances of Groups 1, 6, and 7 were significantly greater than these three groups (P < 0.05). Group 2 had the lowest fracture resistance of all groups (P < 0.05). CONCLUSION: Usage of horizontal post or occlusal Ribbond usage increased the fracture resistance of root canal-treated premolars with MOD cavities.

Restorative material and loading type influence on the biomechanical behavior of wedge shaped cervical lesions.

OBJECTIVES: To evaluate the influence of restorative materials used on the rehabilitation of MOD cavities and loading type, on biomechanical behavior of wedge-shaped (WS) lesions in endodontically treated maxillary premolars. The investigation was conducted by 3D finite element analysis (FEA) and strain gauge test. MATERIALS AND METHODS: Six models were generated, with MOD cavities and endodontic treatment: A (MOD amalgam restoration), R (MOD composite restoration), AL (A + cervical lesion (L)), RL, ALR (A + cervical lesion restored with composite (LR)), and RLR. Each model underwent two compressive loading (100N): axial and oblique-45° angle to the long axis on the buccal cusp. The models were analyzed by von Mises criteria. For strain gauge test, 14 standardized maxillary premolars were treated according to the groups described for FEA. Two strain gauges were bonded on each sample submitted to compressive loading in a mechanical testing machine. RESULTS: A presented higher stress concentration and strain values than R. Oblique loading promoted highest stress concentration and strain rates for all groups. ALR and RLR presented similar stress-strain distribution pattern when compared to A and R. CONCLUSION: The interaction between MOD cavity restored with amalgam and oblique loading propitiated the highest stress concentration and strain values on cervical region and WS lesion. CLINICAL RELEVANCE: The MOD cavity restored with composite resin is a better option than amalgam to improve the biomechanical behavior of wedge-shaped lesion, avoiding dental failure. In addition, the occlusal interferences must be removed, allowing homogeneous contact distribution and preventing WS lesion progression.

Oxygen saturation and perfusion index from pulse oximetry in adult volunteers with viable incisors.

OBJECTIVE: Evaluation of pulp vitality is an important diagnostic procedure in dentistry. Conventional techniques for measurement of pulp vitality, including thermal stimulation, electrical stimulation, or direct dentin stimulation, are frequently associated with false positive or false negative results. Recently, oxygen saturation from pulse oximetry has been utilized in the evaluation of pulp vitality. Perfusion index (PI) data calculated from photoplethysmography have been widely used to evaluate peripheral perfusion. The combination of oxygen saturation and PI may aid in the accurate measurement of pulp vitality. We aimed to investigate the baseline values of oxygen saturation and PI using pulse oximetry in adult volunteers. MATERIAL AND METHODS: Fifteen adult volunteers with viable incisors were tested. To measure PI, a fabricated oxygen sensor was applied to an incisor without a pulp lesion while oxygen saturation was simultaneously measured in the finger. Oxygen saturation and PI were continuously measured with customized software. The normal reference values of oxygen saturation and PI were obtained by analyzing the recorded data. RESULTS: Pulse oximetry showed relatively stable, objective, and accurate oxygen saturation results. The tooth oxygen saturation ranged from 97% to 100%. The PI ranged from 0.3% to 0.5%, and PI and oxygen saturation showed relatively consistent values across subjects. CONCLUSIONS: Although there are some limitations to our study, these results may prove useful for detecting teeth with impaired vitality and non-invasively differentiating between necrotic and vital pulp.

External root resorption during orthodontic treatment in root-filled teeth and contralateral teeth with vital pulp: A clinical study of contributing factors.

INTRODUCTION: There is a lack of research to support the belief that root canal treatment can be considered for stopping or decreasing external apical root resorption (EARR). There is conflicting evidence as to whether root-filled teeth are more or less likely to experience EARR after orthodontic treatment. The purpose of this study was to compare the degree of EARR of root-filled teeth with that of contralateral teeth with vital pulp after fixed orthodontic treatment. METHODS: The study sample consisted of 35 patients aged 25.23 ± 4.92 years who had at least 1 root-filled tooth before orthodontic treatment. Digital panoramic radiographs of each patient taken before and after orthodontic treatment were used to measure the EARR. The Student t test for matched pairs and the Pearson correlation analysis were applied. RESULTS: The mean EARR values were 0.22 (0.14, 0.35) for root-filled teeth and 0.87 (0.59, 1.31) for contralateral teeth with vital pulp, indicating significantly less EARR for root-filled teeth compared with the contralateral teeth with vital pulp after orthodontic treatment. EARR was influenced by the patient's age, treatment duration, treatment type, and periapical pathosis, but not by tooth type and sex. CONCLUSIONS: Root-filled teeth appear to be associated with significantly less EARR than are contralateral teeth with vital pulp. This study suggests that the possible complication of EARR in root-filled teeth may not be an important consideration in orthodontic treatment planning, and root canal treatment can be considered for stopping or decreasing EARR when severe EARR occurs during orthodontic treatment.

Mechanical weakening of devitalized teeth: three-dimensional Finite Element Analysis and prediction of tooth fracture.

AIM: To determine to which extent cavity preparation and each step of dentine removal in the process of root canal treatment (access cavity preparation and root canal enlargement) both individually and jointly contribute to the weakening of the tooth. METHODS: Numerical analysis using finite element method (FEM) of separate and combined influence of two-surface Class II preparation and root canal treatment was undertaken to evaluate the decrease in tooth strength. The influence of the two stages in root canal treatment, access cavity preparation and root canal enlargement, was also analysed separately and jointly. After each of these phases, the crown was restored with composite resin, and the FEA was performed only on restored teeth. To estimate the influence of all these procedures on tooth fracture resistance numerically, a Failure Index based on the maximum principal stress criterion (MPCS) was applied. Compressive and tensile stresses were analysed separately and corresponding Failure Indices were calculated. RESULTS: A two-surface resin composite restoration weakened the tooth by 23.25%. Nevertheless, the Failure Indices showed that this tooth was not likely to fracture even under high occlusal stress (710N). However, after access cavity preparation, the Failure Indices reached the point where, under high occlusal force that may occur in the posterior area, a tooth fracture occurred. The enlargement of root canals had an additional, but relatively small impact on tooth weakening, making the tooth even more susceptible to fracture. The combined influence of both cavity preparation and root canal enlargement led to weakening of 62.6% under a load of 710N, ultimately causing tooth fracture. CONCLUSION: The combined finite element method and the maximum principal stress analysis gave insight into the fracture mechanisms of teeth with two-surface composite restorations followed by root canal preparation. Removal of tooth tissue, despite its subsequent restoration with dental materials, weakened the tooth by changing the stress intensity and distribution through tooth structures. Access cavity preparation had the greatest influence on tooth strength whilst canal enlargement did not contribute to this process substantially.

Three-dimensional finite element analysis of endodontically treated teeth with weakened radicular walls restored with different protocols.

STATEMENT OF PROBLEM: The restoration of weakened roots with glass fiber posts (GFPs) remains a challenge. PURPOSE: The purpose of this study was to evaluate the stress distribution of endodontically treated teeth with weakened radicular walls restored with different protocols by 3-dimensional finite element analysis (3D-FEA). MATERIAL AND METHODS: The following 4 models of endodontically treated maxillary canines restored with metal ceramic crowns were simulated on the basis of computed microtomographic images to characterize the groups: GNW (control), a nonweakened root restored with a GFP; GW, a weakened root restored with a GFP; GDA, a weakened root restored with a direct anatomic GFP; and GIA, a weakened root restored with an indirect anatomic GFP. Loads of 180 N were applied to the lingual surface on the incisal third of the teeth at 45 degrees. The models were supported by a periodontal ligament and fixed in 3 axes (x=y=z=0). The von Mises stress (VMS) was calculated. RESULTS: All models exhibited VMS concentrations at the loading area and were distributed along the proximal surfaces of the root. The GFP exhibited a homogeneous stress distribution, and similar VMS distributions were observed in all of the reconstructive techniques. CONCLUSIONS: Similar stress distributions were observed in the endodontically treated teeth, regardless of root weakness and the reconstructive technique for the radicular walls.

Fracture resistance of compromised endodontically treated teeth restored with bonded post and cores: An in vitro study.

STATEMENT OF PROBLEM: It is unclear which post and core system performs best when bonded to severely compromised endodontically treated teeth. PURPOSE: The purpose of this study was to investigate the fracture resistance and mode of failure of severely compromised teeth restored with 3 different adhesively bonded post and core systems. MATERIAL AND METHODS: Thirty extracted endodontically treated maxillary anterior teeth were randomly divided into 3 groups, CPC, gold cast post and core; TPC, titanium prefabricated post/composite resin core; and FPC, quartz fiber reinforced post/composite resin core. All posts were adhesively cemented. All cores resembled a central incisor preparation with no remaining tooth structure above the finish line. Cast gold crowns were fabricated and cemented adhesively. The specimens were aged with thermocycling and cyclic loading. Two specimens per group were randomly selected for micro-computed tomographic imaging before and after aging. Failure was induced with a universal testing machine. The mode of failure was characterized by the interface separation. Data were analyzed with 1-way ANOVA (α=.05) followed by post hoc tests (Bonferroni). RESULTS: A statistically significant difference was found among the 3 groups (P=.002). CPC was significantly different than TPC (P=.008) or FPC (P=.003). The primary mode of failure for CPC and TPC was root fracture, and for FPC post debonding. CONCLUSIONS: Severely compromised endodontically treated teeth restored with bonded gold cast post and cores showed significantly higher fracture resistance.

Effect of ferrule location on the fracture resistance of crowned mandibular premolars: An in vitro study.

STATEMENT OF PROBLEM: How the location of a ferrule affects the fracture resistance of endodontically treated mandibular premolars is unclear. PURPOSE: The purpose of this in vitro study was to compare the effect of ferrule location on the fracture resistance of endodontically treated mandibular premolars. MATERIAL AND METHODS: Seventy-two extracted human mandibular premolars were selected and divided into 6 test groups (n = 12) according to ferrule location: control group, GHT; endodontically treated teeth without endodontic posts and crowns, GCF; teeth with a 2 mm circumferential ferrule, GBF; teeth with a 2 mm buccal ferrule; GLF, teeth with a 2 mm lingual ferrule; GBLF, teeth with a 2 mm buccal and lingual ferrule; and teeth without ferrule, GWF. After glass fiber posts were cemented with a self-adhesive resin cement and foundation restorations were placed, NiCr crowns were luted to each prepared tooth. All specimens were quasistatically loaded at 30 degrees in a universal testing machine until fractured. Data were then analyzed with 1-way ANOVA, followed by multiple comparisons using the Tukey honestly significant difference test (α=.05). RESULTS: Mean ± SD failure loads for groups ranged from 791.1 ± 177.5 N to 1086.1 ± 181.1 N. One-way ANOVA revealed a statistically significant difference between the groups (P ≤ .05). However, no statistically significant differences were observed among groups (P > .05), except between GHT (control group) and groups GBLF and GWF (P = .025, P = .022). CONCLUSIONS: Within the limitations of this study, the location of the ferrule had no significant effect on the fracture resistance of endodontically treated mandibular premolars.

In vitro investigation on extensively destroyed vital teeth: is fracture force a limiting factor for direct restoration?

To evaluate the in vitro fracture load of extensively damaged vital teeth after either direct or indirect restauration, severe tooth substance loss was simulated for 96 molars. Subsequently, two cavities were prepared with little (design 1) or more substantial (design 2) residual tooth support. All molars were provided with a 2-mm ferrule design and then divided into 12 test groups based on their occlusal surface size. They were restored with composite or with either of two types of single crown (cast metal or milled zirconia). After thermal ageing (10,000 cycles at 6.5 and 60 °C), 1.2 million cycles of chewing simulation were applied (64 N). Maximum fracture load was determined with a loading angle of 45°. Statistical analysis was performed by use of Kaplan-Meier modelling, Student's t-tests, one-way anova, post hoc Tukey's HSD tests and linear regression analysis. Regarding mean fracture load without ageing, the indirect restorations outperformed composite (design 1: direct: 508 ± 123 N, indirect: 741 ± 248 N; design 2: direct: 554 ± 167 N, indirect: 903 ± 221 N). After artificial ageing, however, these differences were no longer significant (design 1: direct: 328 ± 189 N, indirect: 506 ± 352 N; design 2: direct 399 ± 208 N, indirect 577 ± 292 N). Instead, the fracture load of the aged composite restorations was comparable with that for zirconia (design 1) and cast metal (design 2) crowns. Fracture loads of direct composite restorations after artificial ageing might fulfil clinical requirements.

Fracture resistance of endodontically treated teeth restored with glass fiber posts of different lengths.

STATEMENT OF PROBLEM: Endodontically treated teeth are known to have reduced structural strength. Glass fiber posts may influence fracture resistance and should be evaluated. PURPOSE: The purpose of this study was to evaluate the influence of glass fiber post length on the fracture resistance of endodontically treated teeth. MATERIAL AND METHODS: Forty intact human maxillary canines were selected and divided into 4 groups, the control group consisting of teeth restored with a custom gold cast post and core, with a length of two-thirds of the root. Other groups received prefabricated glass fiber posts in different lengths: group 1/3, removal of one-third of the sealing material (5 mm); group 1/2, removal of one-half of the sealing material (7.5 mm); and group 2/3, removal of two-thirds of the sealing material (10 mm). All the posts were cemented with resin cement, and the specimens with glass fiber posts received a composite resin core. All the specimens were restored with a metal crown and submitted to a compressive load until failure occurred. The results were evaluated by 1-way ANOVA, and the all pairwise multiple comparison procedures (Tukey honestly significantly difference test) (α=.05). RESULTS: The ANOVA showed significant differences among the groups (P<.002). The Tukey test showed that the control group presented significantly higher resistance to static load than the other groups (control group, 634.94 N; group 1/3, 200.01 N; group 1/2, 212.17 N; and group 2/3, 236.08 N). Although teeth restored with a cast post and core supported a higher compressive load, all of them fractured in a catastrophic manner. For teeth restored with glass fiber posts, the failure occurred at the junction between the composite resin core and the root. CONCLUSION: The length of glass fiber posts did not influence fracture load, but cast post and cores that extended two-thirds of the root length had significantly greater fracture resistance than glass fiber posts.

Effect of the crown, post, and remaining coronal dentin on the biomechanical behavior of endodontically treated maxillary central incisors.

STATEMENT OF PROBLEM: It is unclear how the amount of remaining coronal dentin and the type of post and core rehabilitation affect the strain, stress distribution, and fracture resistance of endodontically treated teeth. PURPOSE: The purpose of this study was to evaluate the effects of the type of post, type of crown, and the amount of remaining coronal dentin on the biomechanical behavior of endodontically treated teeth. MATERIAL AND METHODS: The investigation was conducted by using 3-dimensional finite element analysis and laboratory tests. Three-dimensional models of a maxillary central incisor were generated: without remaining coronal dentin, with 1.0 mm of remaining coronal dentin, with 2.0 mm of remaining coronal dentin, and restored with a glass-fiber post or a cast post and core in combination with a metal crown or an alumina-reinforced ceramic crown. The results were evaluated by using the von Mises criterion and Maximum Principal Stress. One hundred twenty bovine incisors were selected and divided into 12 treatment groups (n=10). Specimens were loaded at a 135-degree angle to perform strain measurements and were then loaded until fracture. The strain and fracture resistance results were analyzed with 3-way analysis of variance and the Tukey honestly significant difference test (α=.05). RESULTS: The alumina-reinforced ceramic crowns and metal crowns associated with a glass-fiber post showed a homogeneous stress distribution within the root. The cast post and core concentrated higher stresses at the post-dentin interface. Significant differences were found among the mean fracture resistance values for all groups (P<.05). The presence of 2.0 mm of coronal remnants resulted in lower strains and higher fracture resistance for both the metal and ceramic crowns. Roots restored with glass-fiber posts exhibited more favorable fractures. CONCLUSIONS: The presence of 2 mm of remaining coronal dentin improved the mechanical behavior of the endodontically treated maxillary incisors. Teeth restored with glass-fiber posts and composite resin cores showed a homogeneous stress distribution within the root dentin.

Effects of post core materials on stress distribution in the restoration of mandibular second premolars: a finite element analysis.

STATEMENT OF PROBLEM: Previous studies have not resolved the question as to which post and core combination optimizes the stress distribution within the post restoration and tooth. PURPOSE: The purpose of this study was to determine which post and core combination provides the most favorable stress distribution upon loading. MATERIAL AND METHODS: Three-dimensional models of teeth were created with the Ansys program to simulate different materials used for post and cores (Ti, NiCr, AuPd, zirconia, zirconia post/composite resin core, glass fiber post/composite resin core, and carbon fiber post/composite resin core) and metal ceramic crowns (nickel chromium alloy [Group NiCr] and gold palladium alloy [Group AuPd]). A force of 400 N was applied to the occlusal surface, and von Mises equivalent stress values were calculated. RESULTS: Carbon fiber post/composite resin core/metal ceramic crowns with NiCr alloy core had the highest stress values in the weakened root, tooth/post interface, and post. NiCr post/NiCr core/metal ceramic crowns with NiCr alloy core had the lowest stress values in the weakened root and post. The zirconia post and core had the lowest stress value in the tooth/post interface. CONCLUSIONS: A post material with a high elastic modulus led to lower stress in the weakened root (approximately 6%) and tooth/post interface (approximately 12%) and to higher stress in the post (approximately 5 times). A composite resin core led to higher stress in the weakened root (approximately 11% to 17%) and lower deformation in the tooth/post interface (approximately 17.5%) and post materials (approximately 24%). Group AuPd resulted in lower stress in the root and high stress in the post (approximately 4.5% to 7%) and affected the amount of deformation in posts with a composite resin core.

The effect of post material on the characteristic strength of fatigued endodontically treated teeth.

STATEMENT OF PROBLEM: The biomechanical properties of post systems may become more important as the amount of remaining tooth structure decreases, thus different materials may influence the characteristic strength of fatigued endodontically treated teeth. PURPOSE: The purpose of this study was to assess the characteristic strength and probability of survival of endodontically treated teeth restored with different intraradicular post systems. MATERIAL AND METHODS: Forty human maxillary canines with similar root lengths were randomly divided into 4 groups (n=10): cast post and core, stainless-steel prefabricated post, carbon-fiber post, and glass-fiber post. Cores and metallic crowns were fabricated for all specimens. Restored teeth were exposed to mechanical fatigue (250,000 cycles) in a controlled chewing simulator. Each intact specimen was mounted in a special device and aligned at a 45-degree angle to the long axis of the tooth. A universal testing machine was used to apply a static load at a crosshead speed of 0.5 mm/min until specimen failure. The maximum value was recorded in newtons (N). Probability Weibull curves (2-sided 90% confidence bounds) were calculated for each group, and a probability of survival as a function of load at failure was plotted for the groups. RESULTS: A significantly higher characteristic strength was observed for groups carbon-fiber post (755.82 N) and cast post and core (750.6 N) (P<.05) compared with glass-fiber post (461.35 N) and stainless-steel prefabricated post (524.78 N) groups. All the roots in the cast post and core group demonstrated catastrophic fracture, whereas the remaining groups had no root fractures. CONCLUSIONS: Prefabricated posts made of glass fiber and stainless steel showed significantly lower characteristic strength and probability of survival than cast post and core, whereas crowns with carbon-fiber posts presented a single load similar to the fracture values of cast posts.

Influence of occlusal contact and cusp inclination on the biomechanical character of a maxillary premolar: a finite element analysis.

STATEMENT OF PROBLEM: Restoring teeth with large amounts of dentin loss is challenging, especially for posterior teeth with high cusps. However, strategies for reducing the lateral forces are based on clinical experience instead of than scientific evidence. PURPOSE: The purpose of this study was to analyze the biomechanical characteristics of maxillary premolars with different ferrule configurations and to investigate the influence of occlusal contact and cusp inclination on stress distribution with the finite element method. MATERIAL AND METHODS: Five numerical casts of a maxillary premolar were generated; each adopted 1 of the 5 coronal dentin configurations: i (access cavity with 4-mm dentin height) and ii to v (2-mm complete ferrule, 2-mm facial ferrule, 2-mm palatal ferrule, 2-mm proximal ferrule, and restored with a post and core, respectively). Both gold-alloy and glass-fiber posts were modeled. An oblique load of 200 N was applied to the top, middle, and bottom of the 45-degree facial cusps. The cusp inclination was remodeled to 60 degrees, followed by the application of a 200-N load to the top. The values of the maximum principal stress and von Mises stress were calculated to assess overload risk. RESULTS: When the top of 45-degree facial cusps was loaded, the maximum local stress concentration on dentin was found in teeth with a facial ferrule and restored with a gold-alloy post. When the middle of 45-degree facial cusps were loaded, the principal stresses of teeth with a complete ferrule, palatal ferrule, and proximal ferrule were similar to those of the access cavity teeth. In contrast, the principal stress of a tooth with a facial ferrule was close to that of the access cavity tooth after remodeling the facial inclination to 60 degrees. CONCLUSIONS: Maxillary premolars with only facial dentin remaining show higher local stress on root dentin. Altering the loading position and reducing the facial cusp inclination can reduce local stresses.

The effect of glass fiber-reinforced epoxy resin dowel diameter on the fracture resistance of endodontically treated teeth.

PURPOSE: To determine the effect of glass fiber-reinforced epoxy resin (FRC) dowels of different diameters on the failure load of endodontically treated teeth with different remaining dentine and reinforcing resin composite (RRC) thicknesses and the mode of failure in each group. MATERIALS AND METHODS: Fifty extracted intact human maxillary central incisors were decoronated 2 mm incisal to the buccal cementoenamel junction and endodontically treated. The teeth were randomly assigned to one of five groups (n = 10): group B, dowel space prepared with size 0 dowel drill/size 0 FRC dowel/no RRC; group W, size 1 dowel space/size 1 FRC dowel/no RRC; group R, size 3 dowel space/size 3 FRC dowel/no RRC; group WR, size 3 dowel space/size 1 FRC dowel/RRC; group BR, size 3 dowel space/size 0 FRC dowel/RRC. Ferrules of 2 and 0.5 mm were prepared at the facio-lingual and proximal margin respectively. All specimens were restored with a Ni-Cr crown, thermocycled and loaded at 135° from the long axis in a universal testing machine at a 0.5 mm/min crosshead speed until fracture. Data were analyzed using ANOVA followed by post hoc comparisons (Bonferroni) with α = 0.05. RESULTS: Mean failure loads (N) for groups B, W, R, WR, and BR were as follows: 1406 (SD = 376), 1259 (379), 1085 (528), 959 (200), and 816 (298). Significant differences were found between groups B and BR. Group B had the highest favorable failure mode. CONCLUSION: Within the limitations of this study, the use of a smaller FRC dowel and RRC is recommended rather than enlargement of dowel spaces to accurately fit larger FRC dowels, as the enlargement of dowel space may increase the risk of unfavorable failure.

Comparative evaluation of the fracture resistances of endodontically treated teeth filled using five different root canal filling systems.

AIM: The aim of this study was to compare the fracture resistances of teeth filled using different root canal sealers and rials. MATERIALS AND METHODS: One hundred and twenty single rooted mandibular human incisor teeth with single canals were divided into 5 experimental groups of 20 teeth with 2 control groups of 10 teeth each. After root canal shaping using K3 rotary instruments, root canals were filled as follows: Group 1: (-) control, Group 2: (+) control, Group 3: Gutta-percha/AH Plus, Group 4: Thermafil/AH Plus, Group 5: Resilon/Epiphany self-etch (Epiphany SE), Group 6: Gutta-percha/Epiphany SE ve Group 7: EndoREZ sealer/EndoREZ cone. After the root canal sealers set, the apical 4 mm. portions of the specimens were embedded in cold curing acrylic and a fracture resistance test was applied in a universal testing machine. The load at which fracture occurred was recorded for each group and statistically analyzed using one-way ANOVA and Tukey's honestly significant difference tests. RESULTS: Resilon/Epiphany SE ve EndoREZ sealer/EndoREZ cone groups had lower fracture resistances compared with the negative control group consisted of teeth without root canal shaping (P < 0.05). Gutta-percha/AH Plus, Thermafil/AH Plus and Gutta-percha/Epiphany SE groups showed similar fracture resistances (P > 0.05). The fracture resistance of the instrumented, but unfilled positive control group was significantly lower compared with (-) control, Gutta-percha/AH Plus, Thermafil/AH Plus (P < 0.01) and Gutta-percha/Epiphany SE (P < 0.05) groups. There were no significant differences between the fracture resistances of the Resilon/Epiphany SE and EndoREZ sealer/EndoREZ cone and positive control groups (P > 0.05). CONCLUSIONS: Root canal shaping procedures decrease the fracture resistance of teeth, and lateral condensation performed with AH Plus sealer and Gutta-percha and the Thermafil technique were found to be more successful.

Biomechanical impact of labiolingual diameter on endodontically treated anterior teeth with crown restoration under occlusal loading.

OBJECTIVE: To evaluate the effect of the labiolingual diameter and construction of an endodontically treated (ET) anterior tooth with crown restoration on stress distribution and biomechanical safety under occlusal loading. METHODOLOGY: Three-dimensional finite element models were generated for maxillary central incisors with all-ceramic crown restorations. The labiolingual diameters of the tooth, defined as the horizontal distance between the protrusion of the labial and lingual surfaces, were changed as follows: (D1) 6.85 mm, (D2) 6.35 mm, and (D3) 5.85 mm. The model was constructed as follows: (S0) vital pulp tooth; (S1) ET tooth; (S2) ET tooth with a 2 mm ferrule, restored with a fiber post and composite resin core; (S3) ET tooth without a ferrule, restored with a fiber post and composite resin core. A total of 12 models were developed. In total, two force loads (100 N) were applied to the crown's incisal edge and palatal surface at a 45° oblique angle to the longitudinal axis of the teeth. The Von Mises stress distribution and maximum stress of the models were analyzed. RESULTS: Regardless of the loading location, stress concentration and maximum stress (34.07~66.78MPa) in all models occurred in the labial cervical 1/3 of each root. Both labiolingual diameter and construction influenced the maximum stress of the residual tooth tissue, with the impact of the labiolingual diameter being greater. A reduction in labiolingual diameter led to increased maximum stress throughout the tooth. The ferrule reduced the maximum stress of the core of S2 models (7.15~10.69 MPa), which is lower compared with that of S3 models (19.45~43.67 MPa). CONCLUSION: The labiolingual diameter exerts a greater impact on the biomechanical characteristics of ET anterior teeth with crown restoration, surpassing the influence of the construction. The ferrule can reduce the maximum stress of the core and maintain the uniformity of stress distribution.

Effect of resin cements and aging on cuspal deflection and fracture resistance of teeth restored with composite resin inlays.

PURPOSE: To evaluate the influence of resin cements and aging on cuspal deflection, fracture resistance, and mode of failure of endodontically treated teeth restored with composite resin inlays. MATERIALS AND METHODS: Seventy-two maxillary premolars were divided into 6 groups: 1: sound teeth as control (C); 2: preparations without restoration (WR); 3: inlays luted with RelyX ARC (ARC); 4: inlays luted with RelyX Unicem (RLXU); 5: inlays luted with Maxcem Elite (MCE); 6: inlays luted with SeT (ST). Groups 2 to 6 received mesio-occlusal-distal preparations and endodontic treatment. Stone casts were made for groups 3 to 6. Composite resin inlays were built over each cast and luted with the resin cements. A 200-N load was applied on the occlusal aspect and the cuspal deflection was measured using a micrometer before and after 500,000 cycles of fatigue loading (200 N; 500,000 cycles). The specimens were then submitted to an axial load until failure. RESULTS: The median cuspal deflection (µm) and median fracture resistance (N) were calculated and statistically analyzed using Kruskal-Wallis and Mann-Whitney tests (p < 0.01). Values followed by the same letter represent no statistically significant difference. Cuspal deflection before cyclic loading: C = 3 µma; ARC = 4 µmab; RLXU= 5 µmab; MCE = 21 µmb; ST = 51 µmbc; WR = 69 µmc. Cuspal deflection after cyclic loading: ARC = 6 µma; RLXU = 19 µmab; MCE = 33 µmb; ST = 62 µmb. Fracture resistance in N: C = 1902a; ARC = 980b; RLXU = 670c; MCE = 533c; ST = 601c; WR = 526c. According to the Wilcoxon test, there was no statistical difference between the cuspal deflection before and after cyclic loading only for ARC (p = 0.015). There was a predominance of recovery fractures for the restored groups. CONCLUSION: Composite resin inlays luted with RelyX ARC maintained cuspal deflection stability and showed higher fracture resistance of the teeth than did inlays luted with the other cements tested.

Effect of resin-based materials on fracture resistance of endodontically treated thin-walled teeth.

STATEMENT OF PROBLEM: Composite resins are recommended for root reinforcement, but little information exists about self-adhesive resin cements that eliminate the acid etching and bonding steps. PURPOSE: The purpose of this study was to compare the fracture resistances of teeth restored with 2 different diameters of cast and fiber posts and to evaluate the effectiveness of increasing internal root thickness with 2 resin-based materials to reinforce thin-walled teeth. MATERIAL AND METHODS: Ninety maxillary incisors were endodontically treated and divided into 9 groups. In the first 4 groups, teeth were restored with tapered end cast (C1.3 and C1.7) and fiber (F1.3 and F1.7) posts of 1.3 and 1.7 mm diameters. In the other 5 groups, the root canals were enlarged to simulate the thin-walled teeth and restored with low viscosity composite resin with fiber posts of 1.3 and 1.7 mm diameters (LF1.3 and LF1.7), self-adhesive resin cement with fiber posts of 1.3 and 1.7 mm diameters (SF1.3 and SF1.7), and cast posts of 4 mm diameter that fit in post spaces (C4). Teeth were loaded to fracture at a 135-degree angle to their long axis. Data were analyzed with 2-way ANOVA and the Tukey HSD test (α=.05). RESULTS: Significant difference (P<.001) existed between the fracture resistances of the teeth restored with cast (C1.3, 588.4 ±72.7 N) and fiber (F1.3, 375.3 ±53.8 N) posts of 1.3 mm diameter; however, no significant difference was found between 1.3 and 1.7 mm post diameters. The teeth restored with the resin-based materials with fiber posts, groups SF1.3 (331.6 ±135.2 N), SF1.7 (535.7 ±134.4 N), LF1.3 (432.1 ±120.3 N) and LF1.7 (563.8 ±128.8 N), demonstrated fracture resistance values similar to or higher than those of the teeth restored with the fiber posts, groups F1.3 (375.3 ±53.8 N) and F1.7 (461.8 ±98.4 N). The parallel-sided cast posts C4 (799.8 ±228.9 N) of 4 mm diameter demonstrated the highest fracture resistance of all groups (P<.001). CONCLUSIONS: The fracture resistance of the teeth increased as the elastic modulus of the posts increased but was not affected by small diameter variations of the posts. The resin-based materials were able to preserve and reinforce the remaining tooth structures.