Luís Henrique Araújo Raposo

The effect of post, core, crown type, and ferrule presence on the biomechanical behavior of endodontically treated bovine anterior teeth

STATEMENT OF PROBLEM Unresolved controversy exists concerning the remaining coronal tooth structure of anterior endodontically treated teeth and the best treatment option for restoring them. PURPOSE The purpose of this study was to evaluate the effect of post, core, crown type, and ferrule presence on the deformation, fracture resistance, and fracture mode of endodontically treated bovine incisors. MATERIAL AND METHODS One hundred and eighty bovine incisors were selected and divided into 12 treatment groups (n=15). The treatment variations were: with or without ferrule, restored with cast post and core, glass fiber post with composite resin core, or glass fiber post with fiber-reinforced core, and metal- or alumina-reinforced ceramic crown (n=15). The restored incisors were loaded at a 135-degree angle, and the deformation was measured using strain gauges placed on the buccal and proximal root surfaces. Specimens were subsequently loaded to the point of fracture. Strain and fracture resistance results were analyzed by 3-way ANOVA and Tukey HSD tests (α=.05). RESULTS Ferrule presence did not significantly influence the buccal strain and fracture resistance for the ceramic crown groups, irrespective of core and crown type. Ferrule presence resulted in lower strains and higher fracture resistance in the metal crown groups, irrespective of core. The cast post and core showed lower strain values than groups with glass fiber posts when restored with metal crowns. CONCLUSIONS Core type did not affect the deformation and fracture resistance of endodontically treated incisors restored with alumina-reinforced ceramic crowns. The presence of a ferrule improved the mechanical behavior of teeth restored with metal crowns, irrespective of core type.

Effect of specimen gripping device, geometry and fixation method on microtensile bond strength, failure mode and stress distribution: Laboratory and finite element analyses

OBJECTIVES Innumerous modifications have been proposed for the microtensile test since its introduction; however, testing parameters are not often well described and wide variations in bond strength are commonly reported. The aim of this study was to evaluate the effect of the test specimens gripping device, specimen geometry and fixation method on microtensile bond strength, failure mode, and stress distribution when using an etch-and-rinse 2-step adhesive system bonded to human dentin. METHODS Resin-based composite bonded to occlusal dentin from 21 human molars was used to fabricate dumbbell- and stick-shaped test specimens which were divided into three groups: Di - dumbbell-specimens placed in a Dircks device; GeS - stick-specimens gripped in a Geraldelis device with Superglue; GeZ - stick-specimens gripped in a Geraldelis device with Zapit. Specimens were tested to failure in tensile mode and the failure mode was examined under stereomicroscopy and fracture initiation sites were verified by scanning electron microscopy and energy dispersive X-ray spectroscopy. Three-dimensional models of each device/specimen were created and finite element calculations were performed. RESULTS The effect of the gripping devices on the bond strength was not significant, unless the bond test areas were normalized. The failure mode was influenced by the type of device. Dircks device was less sensitive to human error than Geraldelis, and produced a more uniform stress distribution at the dumbbell specimen adhesive layer than did the Geraldelis device at the stick layer. SIGNIFICANCE Microtensile testing parameters can directly influence the results and consequently inter-study comparisons.

The effect of fiber post presence and restorative technique on the biomechanical behavior of endodontically treated maxillary incisors: an in vitro study.

STATEMENT OF PROBLEM Unresolved controversy exists concerning the best technique for restoring endodontically treated teeth. Prefabricated posts have been recommended with some debate as a method of restoring pulpless teeth before placement of the final restoration. PURPOSE The purpose of this in vitro study was to evaluate the effect on the strain, fracture resistance, and fracture mode of endodontically treated human incisors of 4 types of restorations with or without glass fiber posts after thermal cycling. MATERIAL AND METHODS Ninety human maxillary central incisors were selected and divided into 1 control group and 8 treatment groups (n=10). The teeth were endodontically treated and received 2 large Class III preparations simulating coronal destruction. The teeth were then restored with or without glass fiber posts and by using 4 restorative techniques: direct composite resin, direct composite veneer, feldspathic ceramic veneer, or a feldspathic ceramic crown. After artificial aging by thermal cycling, the incisors were loaded at a 135-degree angle, and the strain was measured by using strain gauges placed on the facial and proximal root surfaces. Specimens were subsequently loaded to the point of fracture. Strain and fracture resistance results were analyzed by a 1-way and 2-way ANOVA, followed by the Tukey HSD and Dunnett tests (α=.05). RESULTS One-way analyses showed that the control group and the direct composite resin restoration with and without post groups presented significantly higher fracture resistance values (P<.001). Two-way analyses showed no significant differences for the post system. Proximal strain values were higher in the control and composite resin groups and lower in the feldspathic ceramic groups. CONCLUSIONS The presence of glass fiber posts did not increase the fracture resistance of endodontically treated incisors. Conservative composite resin restorations showed higher fracture resistance values.

Effect of different cements on the biomechanical behavior of teeth restored with cast dowel-and-cores-in vitro and FEA analysis.

PURPOSE To test the hypothesis that the type of cement used for fixation of cast dowel-and-cores might influence fracture resistance, fracture mode, and stress distribution of single-rooted teeth restored with this class of metallic dowels. MATERIALS AND METHODS The coronal portion was removed from 40 bovine incisors, leaving a 15 mm root. After endodontic treatment and standardized root canal relief at 10 mm, specimens were embedded in polystyrene resin, and the periodontal ligament was simulated with polyether impression material. The specimens were randomly divided into four groups (n = 10), and restored with Cu-Al cast dowel-and-cores cemented with one of four options: conventional glass ionomer cement (GI); resin-modified glass ionomer cement (GR); dual-cure resin cement (RC); or zinc-phosphate cement (ZP). Sequentially, fracture resistance of the specimens was tested with a tangential load at a 135 degrees angle with a 0.5 mm/min crosshead speed. Data were analyzed using one-way analysis of variance (ANOVA) and the Fisher test. Two-dimensional finite element analysis (2D-FEA) was then performed with representative models of each group simulating a 100 microm cement layer. Results were analyzed based on von Mises stress distribution criteria. RESULTS The mean fracture resistance values were (in N): RC, 838.2 +/- 135.9; GI, 772.4 +/- 169.8; GR, 613.4 +/- 157.5; ZP, 643.6 +/- 106.7. FEA revealed that RC and GR presented lower stress values than ZP and GI. The higher stress concentration was coincident with more catastrophic failures, and consequently, with lower fracture resistance values. CONCLUSIONS The type of cement influenced fracture resistance, failure mode, and stress distribution on teeth restored with cast dowel-and-cores.

Influence of Ferrule, Post System, and Length on Stress Distribution of Weakened Root-filled Teeth

INTRODUCTION The aim of this study was to evaluate the influence of a ferrule, post system, and length on the stress distribution of weakened root-filled teeth. METHODS The investigation was conducted by using 3-dimensional (3D) finite element analysis. A sound tooth and 8 3D models of a weakened root-filled central incisor were generated using computer-aided design/computer-aided manufacturing software. The models were created without a ferrule and with a 2.0-mm ferrule, restored with a relined glass fiber post or a cast post and core (Cpc), and 12.0- and 7.0-mm post lengths. Each 3D model was imported using ∗.STEP files to the finite element software for mesh generation. The models were subjected to 100-N oblique loading at the palatal surface, and the results were evaluated by von Mises criterion and maximum principal stress distribution. RESULTS Finite element analysis showed that the Cpc models showed elevated stress levels in the root canal regardless of the presence of a ferrule. Relined glass fiber post models showed homogeneous stress distribution to the dentin external surface similar to the sound tooth model. Without a ferrule, Cpc with a 7- or 12-mm length promoted high levels of tensile stress inside the root canal. CONCLUSIONS Ferrule presence promoted more satisfactory stress distribution to the roots. Post length influenced the stress distribution only for the models restored with a cast post and core. High levels of tensile stress inside the root canals were verified with a cast post and core, which should be avoided to rehabilitate weakened roots, mainly in the absence of a ferrule.

Ceramic restoration repair: report of two cases

The esthetic and functional rehabilitation of patients with multiple missing teeth can be performed with several techniques and materials. Ceramic restorations provide reliable masticatory function and good esthetics. However, fracture can occur in some cases due to their brittle behavior. In some cases, the replacement of an extensive prosthesis is a problem due to the high treatment cost. In this paper, two cases are presented, in which fractures occurred in extensive metal-ceramic fixed partial dentures, and their replacement was not possible. Ceramic repair was chosen and the sequences of treatment with and without presence of the ceramic fragment are also discussed. The cases illustrate that, in some situations, fractured metal-ceramic partial dentures can be successfully repaired when prosthetic replacement is not a choice. Prosthodontists must use alternatives that allow a reliable repair to extensive metal-ceramic fixed partial dentures. Surface preparation of the ceramic with hydrofluoric acid in conjunction with a silane coupling agent is essential for a predictable bonding of composite resin. The repair performed with composite resin is an esthetic and functional alternative when extensive fixed partial dentures cannot be replaced.

Influence of different dentin substrate (Caries-affected, caries-infected, sound) on long-term μTBS

The aim of this study was to evaluate the μTBS in different dentin substrates and water-storage periods. Twenty-four dentin blocks obtained from sound third molars were randomly divided into 3 groups: Sound dentin (Sd), Caries-affected dentin (Ca) and Caries-infected dentin (Ci). Dentin blocks from Ca and Ci groups were subjected to artificial caries development (S. mutans biofilm). The softest carious tissue was removed using spherical drills under visual inspection with Caries Detector solution (Ca group). It was considered as Ci (softer and deeply red stained dentin) and Ca (harder and slightly red stained dentin). The Adper Single Bond 2 adhesive system was applied and Z350 composite blocks were built in all groups. Teeth were stored in deionized water for 24 h at 37 ºC and sectioned into beams (1.0 mm2 section area). The beams from each tooth were randomly divided into three storages periods: 24 h, 6 months or 1 year. Specimens were submitted to µTBS using EZ test machine at a crosshead speed of 1.0 mm/min. Failure mode was examined by SEM. Data from µTBS were submitted to split plot two-way ANOVA and Tukeys HSD tests (a=0.05). The µTBS (MPa) of Sd (41.2) was significantly higher than Ca (32.4) and Ci (27.2), regardless of storage. Ca and Ci after 6 months and 1 year, presented similar µTBS. Mixed and adhesive failures predominated in all groups. The highest µTBS values (48.1±9.1) were found for Sd at 24 h storage. Storage of specimens decreased the µTBS values for all conditions.

Influence of flexion angle of files on the decentralization of oval canals during instrumentation

The aim of this study was to evaluate the influence of the flexion angle of files on the decentralization of root canals during instrumentation. Fifteen lower incisors were instrumented with Protaper Universal files and radiographed in two directions (mesiodistal and buccolingual) before and after instrumentation with a #15 K-file in position for evaluating the flexion angle of files. The specimens were also scanned before and after instrumentation using micro-computed tomography to obtain the canal area and the distance from the center position of the file to the canal walls. Sections located 1.0 mm (end of the canal), 3.0 mm (apical third), 9.0 mm (middle third), and 15.0 mm (cervical third) from the apex were verified. After instrumentation, the flexion angles of files decreased by an average of 0.76º in the buccolingual direction and 1.92º in the mesiodistal direction (p < 0.001); the canal area increased by an average of 0.58, 0.37, 0.23 and 0.13 mm(2) from the cervical to the end of the root canal (p < 0.001). Non-instrumented areas were observed on the buccal and lingual walls, and effective action of files was determined on the mesial and distal walls. The sections from the end of the canal showed canal deviation toward the lingual wall, whereas the other sections showed deviation toward the buccal wall. The flexion angles of files influence the final shape of the root canal, resulting in file decentralization along the pathway of the canal.

Degree of conversion and bond strength of resin-cements to feldspathic ceramic using different curing modes

Abstract Resin cements have led to great advances in dental ceramic restoration techniques because of their ability to bond to both dental structures and restorative materials. Objective The aim of this study was to assess the performance of resin cements when different curing modes are used, by evaluating the degree of conversion and bond strength to a ceramic substrate. Material and Methods Three resin cements were evaluated, two dual-cured (Variolink II and RelyX ARC) and one light-cured (Variolink Veneer). The dual-cured resin cements were tested by using the dual activation mode (base and catalyst) and light-activation mode (base paste only). For degree of conversion (DC) (n=5), a 1.0 mm thick feldspathic ceramic disc was placed over the resin cement specimens and the set was light activated with a QTH unit. After 24 h storage, the DC was measured with Fourier transform infrared spectroscopy (FTIR). For microshear bond strength testing, five feldspathic ceramic discs were submitted to surface treatment, and three cylindrical resin cement specimens were bonded to each ceramic surface according to the experimental groups. After 24 h, microshear bond testing was performed at 0.5 mm/min crosshead speed until the failure. Data were submitted to one-way ANOVA followed by Tukey test (p<0.05). Scanning electron microscopy (SEM) was used for classifying the failure modes. Results Higher DC and bond strength values were shown by the resin cements cured by using the dual activation mode. The Variolink II group presented higher DC and bond strength values when using light-activation only when compared with the Variolink Veneer group. Conclusion The base paste of dual-cured resin cements in light-activation mode can be used for bonding translucent ceramic restorations of up to or less than 1.0 mm thick.

Effect of joint design and welding type on the flexural strength and weld penetration of Ti-6Al-4V alloy bars

STATEMENT OF PROBLEM Framework longevity is a key factor for the success of complete-arch prostheses and commonly depends on the welding methods. However, no consensus has been reached on the joint design and welding type for improving framework resistance. PURPOSE The purpose of this study was to assess the effect of different joint designs and welding methods with tungsten inert gas (TIG) or laser to join titanium alloy bars (Ti-6Al-4V). MATERIAL AND METHODS Seventy titanium alloy bar specimens were prepared (3.18 mm in diameter × 40.0 mm in length) and divided into 7 groups (n=10): the C-control group consisting of intact specimens without joints and the remaining 6 groups consisting of specimens sectioned perpendicular to the long-axis and rejoined using an I-, X30-, or X45-shaped joint design with TIG welding (TI, TX30, and TX45) or laser welding (LI, LX30, and LX45). The specimens were tested with 3-point bending. The fracture surfaces were first evaluated with stereomicroscopy to measure the weld penetration area and then analyzed with scanning electron microscopy (SEM). The data were statistically analyzed with 2-way ANOVA and the Tukey post hoc test, 1-way ANOVA and the Dunnett test, and the Pearson correlation test (α=.05). RESULTS Specimens from the X30 and X45 groups showed higher flexural strength (P<.05) and welded area (P<.05) than specimens from the I groups, regardless of the welding type. TIG welded groups showed significantly higher flexural strength than the laser groups (P<.05), regardless of the joint design. TIG welding also resulted in higher welded areas than laser welding for the I-shaped specimens. No significant differences were found for the weld penetration area in the X45 group, either for laser or TIG welding. SEM analysis showed more pores at the fracture surfaces of the laser specimens. Fracture surfaces indicative of regions of increased ductility were detected for the TIG specimens. CONCLUSIONS TIG welding resulted in higher flexural strength for the joined titanium specimens than laser welding. For both welding methods, X30- and X45-shaped joint designs resulted in higher flexural strength and welding penetration than the I-shaped joint design.