Effect of preparation design on fracture strength of compromised molars restored with direct composite resin restorations: An in vitro and finite element analysis study.

STATEMENT OF PROBLEM: More data are needed on the influence of preparation design on the fracture strength, failure type, repairability, and polymerization-induced cracks of molar teeth restored with direct composite resin restorations. PURPOSE: This in vitro and finite element analysis study investigated the effect of different preparation designs on fracture strength, failure type, repairability, tooth deformation, and the formation of polymerization-induced cracks of compromised molars restored with direct composite resin restorations. MATERIAL AND METHODS: Human molars (n=64) were randomly assigned to 4 different preparation designs: undermined inlay (UI), extended inlay (EI), restricted overlay (RO), and extended overlay (EO). The teeth were restored using direct composite resin and subjected to artificial thermomechanical aging in a mastication simulator, followed by load-to-failure testing. Three-dimensional (3D) finite element analysis was conducted to assess tooth deformation. Polymerization-induced cracks were evaluated using optical microscopy and transillumination. The fracture strength data were analyzed using a Kruskal-Wallis test, while the failure mode, repairability, and polymerization cracks were analyzed using the Fisher exact test (α=.05). RESULTS: All specimens withstood thermomechanical aging, and no statistically significant difference in fracture strength was observed among the 4 preparation designs (P>.05). The finite element analysis showed differences in tooth deformation, but no correlation was observed with in vitro fracture resistance. The RO and EO groups presented significantly more destructive failures compared with the UI and EI groups (P<.01). The RO group had significantly fewer repairable failures than the UI and EI groups (P=.024). A correlation was found between higher frequencies of repairability and higher tooth deformation. A significant correlation between the increase in microfractures and preparation design was observed (P<.01), with the UI group exhibiting a higher increase in microfracture size compared with the EO group (P<.05). CONCLUSIONS: No influence of preparation design on the fracture strength of compromised molars restored with direct composite resin restorations was evident in this study, but the failure mode of cusp coverage restorations was more destructive and often less repairable. The finite element analysis showed more tooth deformation in inlay preparations, with lower stresses within the root, leading to more reparable fractures. Since cusp coverage direct composite resin restorations fractured in a more destructive manner, this study suggests that even a tooth with undermined cusps should be restored without cusp coverage.

Shrinkage-induced cuspal deformation and strength of three different short fiber-reinforced composite resins.

OBJECTIVE: The aim of this study is to assess the shrinkage-induced cuspal deformation and strength of large MOD restorations using three different short fiber-reinforced composite resins (SFRC). MATERIALS AND METHODS: Twenty-seven typodont teeth #30 (Columbia) received a standardized slot-type preparation (5-mm by 5-mm depth and bucco-palatal width). Three types of SFRCs (everX Posterior, everX Flow, and a 50/50 mixture of both materials) were used with the Optibond FL bonding system. The intercuspal distance of each specimen (n = 9) was measured after preparation, immediately after restoration and at 3, 18, and 24 h. Each specimen was then subjected to simulated mastication (30° angulation with cyclic loading of buccal cusp at 5 Hz), starting at 100 N with 100 N increase every 100 cycles until fracture. Failure mode was determined as re-restorable versus nonrestorable failures. Cusp deformation data were analyzed by two-way repeated measures ANOVA and the fracture performance by Kaplan-Meier survival analysis. RESULTS: Shrinkage-induced cuspal deformation ranged from 27-34 microns (immediately) to 33-43 microns (24 h). The largest deformations were observed for everX Flow and the 50/50 mixture (up to 43 microns at 24 h), which also demonstrated the lowest average strength (1456 to 1511 N). everX Posterior demonstrated the least amount of shrinkage-induced cuspal deformation (27 microns, up 33 microns at 24 h) and the higher average strength (1744 N). everX Flow tended to demonstrate more repairable partial fractures while everX Posterior induced mainly catastrophic failures. CONCLUSIONS: Large direct MOD restorations were most favorably restored with everX Posterior (less shrinkage, higher strength) at the expense of failure mode. everX Flow induced more friendly failure modes but more shrinkage-induced cuspal deformation. CLINICAL SIGNIFICANCE: When a low-cost restoration must be chosen, EverX Posterior will significantly improve the performance but not the failure mode of directly layered restorations. Because of its increased shrinkage values, everX Flow is best indicated as a limited liner to cover the IDS layer and improve geometry for semi-(in)direct restorations.

Effect of thickness and CAD-CAM material on fatigue resistance of endodontically treated molars restored with occlusal veneers.

PURPOSE: To evaluate the influence of the thickness and type of computer-aided design and computer-aided manufacturing (CAD-CAM) material on the fatigue resistance and failure mode of endodontically treated teeth (ETT) restored with occlusal veneers (OV). MATERIALS AND METHODS: Seventy-five (N = 75) ETT were restored with Herculite XRV in the endodontic access. Five experimental groups (n = 15) were tested. Four groups had two different thicknesses (0.6-0.7 mm or 1.4-1.6 mm) and two different CAD-CAM materials: zirconia-reinforced lithium-silicate (LS/Celtra Duo) and composite resin (RC/Cerasmart). The fifth group (control) did not have occlusal veneers. All the specimens were subjected to accelerated fatigue (5 Hz frequency) with an occlusal load increasing up to 1800 N and 131,000 cycles. The number of cycles was recorded when the machine stopped or at the completion of the test. Fatigue resistance was analyzed using the Kaplan-Meier survival test (95% significance level, log-rank post hoc pairwise comparisons). The samples were categorized according to failure mode. The CAD-CAM materials were examined through scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). RESULTS: No differences were found between the thicknesses, regardless of the type of the CAD-CAM material. The thick LS OV outperformed the RC and control groups. The thin RC OV and control groups showed a higher percentage of repairable and possibly repairable failures than the other groups. LS was more homogeneous under SEM, and the EDS analysis detected Si and Zr, but not Li. CONCLUSIONS: A larger thickness did not improve the resistance of the CAD-CAM materials. Thick LS showed a higher cumulative survival rate to fatigue than the RC and control groups. The direct composite alone (control) survived similarly to the experimental groups, except for the thick LS.

Fatigue and failure analysis of restored endodontically treated maxillary incisors without a dowel or ferrule.

STATEMENT OF PROBLEM: Information on the survival and mode of failure of endodontically treated incisors without a ferrule and restored without dowels is lacking. PURPOSE: The purpose of this in vitro study was to compare the survival and failure mode of endodontically treated incisors without a ferrule and restored with bonded ceramic crowns and various composite resin foundation restorations without dowels with a control group with fiber dowels. MATERIAL AND METHODS: Forty-five decoronated endodontically treated bovine incisors without ferrule were divided into 3 experimental groups and restored with different adhesive foundation restorations without dowel: nanohybrid composite resin (Nd), bulk-fill composite resin foundation restoration (NdB), and fiber-reinforced bulk-fill composite resin (NdFR). A control group with conventional foundation restorations (glass-fiber dowel with nanohybrid composite resin foundation restoration without ferrule) (D) was included for comparison. All teeth were prepared to receive bonded lithium disilicate ceramic crowns luted with dual-polymerizing composite resin cement and were subjected to accelerated fatigue testing. Cyclic isometric loading was applied to the incisal edge at an angle of 30 degrees and a frequency of 5 Hz, beginning with a load of 100 N (5000 cycles). A 100-N load increase was applied each 15 000 cycles. Specimens were loaded until failure or to a maximum for cycles endured of 1000 N (140 000 cycles). Groups were compared by using the Kaplan-Meier survival analysis (log rank test at α=.05 and pairwise post hoc comparisons) and life table analysis for load-at-failure (followed by Wilcoxon pairwise comparison α=.05). RESULTS: All the specimens failed before 140 000 load cycles. Even though no statistically significant differences were found between the experimental groups without dowel (P>.127), the fiber-reinforced foundation restoration yielded the highest mean ±standard deviation cycles to failure (46 023 ±4326) compared with Nd (38 899 ±2975) and NdB (39 751 ±2998). NdFR, however, outperformed the foundation restoration with glass-fiber dowel (35 026 ±2687) (P<.05). Most failure in groups without dowel were restorable, while 100% of catastrophic failure (unrestorable) were found in the group with dowels. CONCLUSIONS: Based on the present in vitro study, dowels did not improve the performance of the adhesive restoration of endodontically treated incisors without a ferrule. The use of a short fiber-reinforced composite resin foundation restoration without a dowel was able to not only improve the resistance of the restorations compared with adhesive foundation restorations with dowels but also minimize catastrophic failures.

Significance of immediate dentin sealing and flowable resin coating reinforcement for unfilled/lightly filled adhesive systems.

BACKGROUND: Immediate dentin sealing implies applying an adhesive system to dentin directly after tooth preparation, before impression. The technique is universal (inlays, onlays, veneers, crowns) and well documented clinically and experimentally. Different types of dentin bonding agents (DBAs) are available on the market. Major differences lie in the thickness of the hybrid layer and overlaying adhesive resin (filled vs. unfilled/lightly filled adhesives). OBJECTIVE: The objective of this work is to provide precise clinical instructions and present new experimental data about the bond strength of five DBAs (Optibond FL, Scotchbond MP, Single Bond Plus, Clearfil SE Bond, and Scotchbond Universal) used conventionally (dentin sealed at the time of restoration delivery) or with immediate dentin sealing, as well as with an additional flowable resin coating. METHODS: Seventy-five human molars were selected, restored/tested according the microtensile bond strength method. Fifteen groups (n=5) were obtained from the combination of the five DBAs and three application modes: delayed dentin sealing, immediate dentin sealing and immediate dentin sealing with flowable resin coating. RESULTS: It appears that immediate dentin sealing was confirmed to significantly improve the bond strength of all tested adhesives. The use of a flowable resin coating reinforcement after immediate dentin sealing increased the microtensile bond strength of all unfilled/lightly filled adhesives (from 233% of increase for ScotchBond MP, up to 560% for Clearfil SE Bond) and maintained the performance of the 3-step golden standard adhesive. Optibond FL used with (52.51 MPa) or without (54.75 MPa) additional flowable resin coating and Clearfil SE Bond (45.64 MPa) used with flowable resin coating provided the best results. CLINICAL SIGNIFICANCE: The original immediate dentin sealing (IDS) technique implies the use of a filled DBA. With unfilled/lightly filled adhesives, it is suggested to reinforce IDS with an additional flowable resin coating. This seems especially paramount to the performance of simplified adhesive systems to protect the thin bonding interface from oxygen inhibition and preserve IDS layer during predelivery cleaning of the preparation. The clinical reinforcement of unfilled/lightly filled IDS with flowable resin composite is encouraged for more predictable bonding.

Survival of extensively damaged endodontically treated incisors restored with different types of posts-and-core foundation restoration material.

STATEMENT OF PROBLEM: Which post-and-core combination will best improve the performance of extensively damaged endodontically treated incisors without a ferrule is still unclear. PURPOSE: The purpose of this in vitro study was to investigate the restoration of extensively damaged endodontically treated incisors without a ferrule using glass-ceramic crowns bonded to various composite resin foundation restorations and 2 types of posts. MATERIAL AND METHODS: Sixty decoronated endodontically treated bovine incisors without a ferrule were divided into 4 groups and restored with various post-and-core foundation restorations. NfPfB=no-ferrule (Nf) with glass-fiber post (Pf) and bulk-fill resin foundation restoration (B); NfPfP=no-ferrule (Nf) with glass-fiber post (Pf) and dual-polymerized composite resin core foundation restoration (P); NfPt=no-ferrule (Nf) with titanium post (Pt) and resin core foundation restoration; and NfPtB=no-ferrule (Nf) with titanium post (Pt) and bulk-fill resin core foundation restoration (B). Two additional groups from previously published data from the same authors (FPf=2mm of ferrule (F) and glass-fiber post (Pf) and composite resin core foundation restoration; and NfPf=no-ferrule (Nf) with glass-fiber post (Pf) and composite resin core foundation restoration), which were tested concomitantly and using the same experimental arrangement, were included for comparison. All teeth were prepared to receive bonded glass-ceramic crowns luted with dual-polymerized resin cement and were subjected to accelerated fatigue testing under submerged conditions at room temperature. Cyclic isometric loading was applied to the incisal edge at an angle of 30 degrees with a frequency of 5 Hz, beginning with a load of 100 N (5000 cycles). A 100-N load increase was applied every 15000 cycles. The specimens were loaded until failure or to a maximum of 1000 N (140000 cycles). The 6 groups (4 groups from the present study and 2 groups from the previously published study) were compared using the Kaplan-Meier survival analysis (log-rank post hoc test at α=.05 for pairwise comparisons). RESULTS: None of the tested specimen withstood all 140 000 cycles. All specimens without a ferrule were affected by an initial failure phenomenon (wide gap at the lingual margin between the core foundation restoration/crown assembly and the root). NfPfP, NfPt, and NfPtB had similar survival (29649 to 30987 mean cycles until initial failure). NfPfB outperformed NfPt and NfPtB. None of the post-and-core foundation restoration materials were able to match the performance of the ferrule group FPf (72667 cycles). In all groups, 100% of failures were catastrophic. CONCLUSIONS: The survival of extensively damaged endodontically treated incisors without a ferrule was slightly improved by the use of a fiber post with a bulk-fill composite resin core foundation restoration. However, none of the post-and-core techniques was able to compensate for the absence of a ferrule. The presence of the posts always adversely affected the failure mode.

Effect of platform connection and abutment material on stress distribution in single anterior implant-supported restorations: a nonlinear 3-dimensional finite element analysis.

STATEMENT OF PROBLEM: Although various abutment connections and materials have recently been introduced, insufficient data exist regarding the effect of stress distribution on their mechanical performance. PURPOSE: The purpose of this study was to investigate the effect of different abutment materials and platform connections on stress distribution in single anterior implant-supported restorations with the finite element method. MATERIAL AND METHODS: Nine experimental groups were modeled from the combination of 3 platform connections (external hexagon, internal hexagon, and Morse tapered) and 3 abutment materials (titanium, zirconia, and hybrid) as follows: external hexagon-titanium, external hexagon-zirconia, external hexagon-hybrid, internal hexagon-titanium, internal hexagon-zirconia, internal hexagon-hybrid, Morse tapered-titanium, Morse tapered-zirconia, and Morse tapered-hybrid. Finite element models consisted of a 4×13-mm implant, anatomic abutment, and lithium disilicate central incisor crown cemented over the abutment. The 49 N occlusal loading was applied in 6 steps to simulate the incisal guidance. Equivalent von Mises stress (σvM) was used for both the qualitative and quantitative evaluation of the implant and abutment in all the groups and the maximum (σmax) and minimum (σmin) principal stresses for the numerical comparison of the zirconia parts. RESULTS: The highest abutment σvM occurred in the Morse-tapered groups and the lowest in the external hexagon-hybrid, internal hexagon-titanium, and internal hexagon-hybrid groups. The σmax and σmin values were lower in the hybrid groups than in the zirconia groups. The stress distribution concentrated in the abutment-implant interface in all the groups, regardless of the platform connection or abutment material. CONCLUSIONS: The platform connection influenced the stress on abutments more than the abutment material. The stress values for implants were similar among different platform connections, but greater stress concentrations were observed in internal connections.

Preheated restorative composite resin for luting ceramic laminate veneers: An optimized technique report.

Resin cements are traditionally used to lute ceramic laminate veneers due to their lower viscosity, which facilitates a fast restoration seating. However, resin cements have lower mechanical properties compared to restorative composite resins. Thus, restorative composite resin is an alternative luting agent with lower marginal degradation as a potential advantage for clinical longevity. This article presents an application of preheated restorative composite resin for adhesive luting of laminate veneers with a predictable clinical technique for seating and marginal quality. By addressing important factors that influence film thickness, the predictable presented workflow should overcome this major concern when luting with restorative composite resin, therefore enabling the benefits of using a restorative material with better mechanical properties without the drawback of higher film thickness. Considering the clinical evidence that the adhesive interface between the dental substrate and restoration is the weak link of adhesive indirect restorations, bonding the restoration with preheated restorative composite resins (PRCR) may provide an interface filled with a restorative resin material, presenting optimized mechanical properties. Key words:Resin cements, ceramic laminate veneers.

Effect of preparation design on fracture strength of compromised molars restored with lithium disilicate inlay and overlay restorations: An in vitro and in silico study.

PURPOSE: The objective of this study was to determine the influence of different preparation designs on the fracture strength, failure type, repairability, formation of polymerization-induced cracks, and tooth deformation of structurally compromised molars restored with lithium disilicate inlays and overlays in combination with Immediate Dentin Sealing (IDS). MATERIAL AND METHODS: Human molars (N = 64) were randomly assigned to four different preparation designs: Undermined Inlay (UI), Extended Inlay (EI), Restricted Overlay (RO), and Extended Overlay (EO). The teeth were restored using lithium disilicate partial restorations and subjected to thermomechanical fatigue in a chewing simulator (1,2 × 10 (Mondelli et al., 2007) cycles on 50 N, 8000x 5-55 °C), followed by load to failure testing. In silico finite element analysis was conducted to assess tooth deformation. Polymerization-induced cracks were evaluated using optical microscopy and transillumination. Fracture strengths were statistically analyzed using a Kruskal-Wallis test, while the failure mode, repairability, and polymerization cracks were analyzed using Fisher exact test. RESULTS: The propagation of polymerization-induced cracks did not significantly differ among preparation designs. All specimens withstood chewing simulator fatigue, with no visible cracks in teeth or restorations. Fracture strength was significantly influenced by preparation design, with restricted overlay (RO) showing higher fracture strength compared to extended inlay (EI) (p = .042). Tooth deformation and fracture resistance correlated between in vitro and in silico analyses). UI exhibited a statistically less destructive failure pattern than EO (p < .01) and RO (p = .036). No statistically significant influence of the preparation design on repairability was observed. Groups with higher repairability rates experienced increased tooth deformation, leading to less catastrophic failures. CONCLUSIONS: The preparation design affected the fracture strength of compromised molars restored with lithium disilicate inlays and overlays, with significantly lower fracture strength for an extended inlay. The failure pattern of lithium disilicate overlays is significantly more destructive than that of undermined and extended inlays. The finite element analysis showed more tooth deformation in the inlay restorations, with lower forces in the roots, leading to less destructive fractures. Since cusp coverage restorations fracture in a more destructive manner, this study suggests the undermined inlay preparation design as a viable option for restoring weakened cusps.

Socket shield technique: Stress distribution analysis.

Background: To analyze through finite element analysis the stress distribution in peri-implant bone tissues, implants, and prosthetic components induced by the socket shield (SS) technique in comparison to other techniques used to treat tooth loss. Materials and Methods: A three-dimensional model of a superior central incisor crown supported by implant was modeled and three different placement conditions were simulated: SS - 2.0-mm-thick root dentin fragment positioned between the alveolar buccal wall and implant; heterologous bone graft (HBG) - bovine bone graft positioned the alveolar buccal wall and implant; and control (C) - implant fully placed in bone tissue of a healed alveolus. The model was restricted at the lateral surfaces of the bone tissue and the following loads were simulated: Both oblique (45°) loads of 100 N on the lingual surface of the crown (maximal habitual intercuspation) and 25.5 N on the incisal edge of the crown (tooth contact during mandibular protrusion) were simultaneously applied. Tensile stress, shear stress, compression, and displacement were analyzed in the cortical bone, trabecular bone, dentin root fragment, and bone graft; while equivalent von Mises stresses were quantified in the implant and prosthetic components. Results: Stress values of SS and HBG in the bone tissues were higher than C, while slight differences within models were observed for dentin root fragment, bone graft, implant, and prosthetic components. Conclusions: The SS technique presented the highest stress concentration in the peri-implant tissues.

Biomechanical behavior of different designs of hybrid abutment-restoration on the posterior crown: a finite element analysis.

This study aimed to evaluate the influence of material and crown design on the biomechanical behavior of implant-supported crowns with hybrid abutment (HA) through three-dimensional (3D) finite element analysis. The study factors were the type of material used as the mesostructure or crown (zirconia, lithium disilicate, and hybrid ceramic) and the crown design cemented to the titanium base (mesostructure cemented to the titanium base and a crown cemented on it (HaC); hybrid crown-abutment, the abutment and crown are manufactured as a single piece and cemented to the titanium base (HC); monolithic crown cemented on the titanium base and screwed to the implant (CS); and monolithic crown cemented on the titanium base (CC). Four 3D models were constructed using an implant with an internal connection, and an oblique load of 130 N was applied at 45° to the long axis of the implant. The models were evaluated using the von Mises stress for crown, abutment, screw, and implant and maximum principal stress for bone tissues. The lowest stresses occurred in the groups with a lower elastic modulus material, mainly hybrid ceramics, considered a material with greater resilience. The cemented crown group presented the lowest stress values. The stresses were concentrated in the cervical region of the crown at the titanium crown/base interface. Mesostructures made of materials with a higher elastic modulus exhibited a higher concentration of stress. The presence of a screw hole increased the stress concentration in the ceramic crown. Cemented ceramic crowns exhibited better biomechanical behavior than screw-retained crowns.

Influence of Chitosan 0.2% in Various Final Cleaning Methods on the Bond Strength of Fiberglass Post to Intrarradicular Dentin.

The purpose of this study was to analyze the influence of Chitosan 0.2% in various final cleaning methods on the bond strength of fiberglass post (FP) to intrarradicular dentin. Ninety bovine incisors were sectioned to obtain root remnants measuring 18 mm in length. The roots were divided: G1: EDTA 17%; G2: EDTA 17% + PUI; G3: EDTA 17% + EA; G4: EDTA 17% + XPF; G5: Chitosan 2%; G6: Chitosan 2% + PUI; G7: Chitosan 2% + EA; G8: Chitosan 2% +XPF. After carrying out the cleaning methods, the posts were installed, and the root was cleaved to generate two disks from each root third. Bond strength values (MPa) obtained from the micro push-out test data were assessed by using Kruskal-Wallis and Dwass-Steel-Critchlow-Fligner tests for multiple comparisons (α = 5%). Differences were observed in the cervical third between G1 and G8 (p = 0.038), G4 and G8 (p = 0.003), G6 and G8 (p = 0.049), and Control and G8 (p = 0.019). The final cleaning method influenced the adhesion strength of cemented FP to intrarradicular dentin. Chitosan 0.2% + XPF positively influenced adhesion strength, with the highest values in the cervical third.

Accelerated fatigue resistance of endodontically treated incisors without ferrule restored with CAD/CAM endocrowns.

PURPOSE: The present study aimed to investigate the resistance and failure mode of broken-down endodontically treated incisors without ferrule restored with CAD/CAM endocrowns. MATERIALS AND METHODS: Endodontically treated bovine incisors (N = 30) without ferrule were divided into two groups and restored with two types of CAD/CAM endocrowns: lithium disilicate (Eld) or resin nanoceramics (Erc). The preparations included a 4-mm-deep 'internal ferrule' and immediate dentin sealing. The samples were subjected to accelerated fatigue testing. Cyclic isometric loading was applied to the incisal edge at a 30-degree angle at a frequency of 5 Hz, beginning with a load of 100 N (5,000 cycles). A 100 N load increase was applied every 15,000 cycles. Specimens were loaded until failure or to a maximum of 140,000 cycles. Previously published data from the same authors regarding lithium disilicate crowns over post-and-core buildups without ferrule (NfPf), core buildups without post without ferrule (NfNpFR), and with a 2-mm ferrule (FNp) using the same experimental setup were included for comparison. Groups were compared using the Kaplan Meier survival analysis for cycles (log rank pairwise post hoc test comparisons at P = 0.05) and Life Table survival analysis for load at failure, followed by the Wilcoxon pairwise comparison at P = 0.05. RESULTS: All specimens failed before 140,000 load cycles. There was no statistically significant difference between the endocrown materials (Eld: 53,448 mean endured cycles; Erc: 52,397 mean endured cycles; P = 0.844). Endocrowns outperformed the group with lithium disilicate crowns on incisors without ferrule and post-and-core buildup (NfPf with mean endured 35,025 cycles), showed no statistical difference compared with the group with no-post fiber-reinforced composite resin core buildup (NfNpFR with 45,557 mean endured cycles), and had a lower survival rate compared with the group with ferrule (FNp with mean endured 73,244 cycles). Endocrowns generated a majority of non-catastrophic failures (with an advantage for Erc), while 100% of catastrophic failures were found in the group with a post. CONCLUSIONS: CAD/CAM endocrowns of nonvital incisors without ferrule improved the resistance and optimized the failure mode when compared with traditional bonded crowns with adhesive post-and-core and no-post buildups.

Different Treatment Modalities Using Dental Implants in the Posterior Maxilla: A Finite Element Analysis.

The objective of this study was to compare the biomechanical behavior of peri-implant bone tissue and prosthetic components in two modalities of treatment for posterior region of the maxilla, using short implants or standard-length implants associated with bone graft in the maxillary sinus. Four 3D models of a crown supported by an implant fixed in the posterior maxilla were constructed. The type of implant: short implant (S) or standard-length implant with the presence of sinus graft (L) and type of crown retention: cemented (C) or screwed (S) were the study factors. The models were divided into SC- cemented crown on a short implant; SS- screwed crown on the short implant; LC- cemented crown on a standard-length implant after bone graft in the maxillary sinus and LS- crown screwed on a standard-length implant after bone graft in the maxillary sinus. An axial occlusal loading of 300 N was applied, divided into five points (60N each) corresponding to occlusal contact. The following analysis criteria were observed: Shear Stress, Maximum and Minimum Main Stress for bone tissue and von Mises Stress for the implant and prosthetic components. The use of standard-length implants reduced the shear stress in the cortical bone by 35.75% and the medullary bone by 51% when compared to short implants. The length of the implant did not affect the stress concentration in the crown, and the cement layer acted by reducing the stresses in the ceramic veneer and framework by 42%. Standard-implants associated with cemented crowns showed better biomechanical behavior.

A three-dimensional finite element analysis of permanent maxillary central incisors in different stages of root development and trauma settings.

BACKGROUND AND OBJECTIVES: Differences in dental maturation may affect the prognosis and clinical management of traumatized teeth. However, evaluation of the outcomes of dental trauma to the tooth and support structures in an in vivo model involves major methodological and ethical implications. Thus, the aim of the present study was to perform a three-dimensional finite element analysis of permanent maxillary central incisors in different stages of root development under different trauma settings. METHODS: The study factors included two trauma conditions (B, buccal; I, incisal) on upper permanent central incisors showing three different stages of root development (CR, complete rhizogenesis; IRA; incomplete rhizogenesis in the apical third of the root; and IRM, incomplete rhizogenesis in the middle third of the root) to yield six models. The complete rhizogenesis model was obtained with a cone-beam computed tomography examination of an extracted tooth. The two incomplete rhizogenesis models were modeled on the basis of similar examinations of patients. Trauma was simulated by applying a 300 N static surface to surface load on the incisal edge or perpendicular to the buccal surface of the tooth. The displacement and equivalent von Mises (σvM) stress values were obtained for alveolar bone, periodontal ligament, apical papilla, and dentin for the quantitative analysis. A σvM color-coded scale was used for qualitative analysis. RESULTS: The force direction had a greater influence on the stress than the root-formation stage. Buccal forces resulted in higher stress concentration in the bone and periodontal ligament, especially in B-CR. Lower stress was found on the periodontal ligament as the root formation progressed (decrease of 8% from B-IRA to B-CR and 11% from B-IRM to B-CR). The incomplete rhizogenesis models showed higher σvM stress peak values in dentin in comparison with complete rhizogenesis (increase of 52% from B-CR to B-IRA and 56% from B-CR to B-IRM). CONCLUSIONS: Buccal forces yielded greater stress values regardless of the stage of rhizogenesis. Teeth with fully formed roots showed a higher stress concentration in the alveolar bone and periodontal ligament in comparison with immature teeth, with the latter presenting high stresses in the tooth crown.

Luting of inlays, onlays, and overlays with preheated restorative composite resin does not prevent seating accuracy.

PURPOSE: To evaluate in vitro the vertical seating of computer-assisted design/computer-assisted manufacturing (CAD/CAM) composite resin inlays, onlays, and overlays luted with two different composite resins. MATERIALS AND METHODS: Sixty plastic typodont molars were prepared for medium-sized MOD inlays, anatomic onlays, and flat overlays (n = 20); 3-mm thick at the central groove with similar morphology (Cerec biogeneric copy). Restorations were milled using Lava Ultimate blocks, and included standardized hemispherical occlusal concavity for seating measurements with an electromechanic system (force = 30 N). Restorations were luted either with preheated composite resin (Filtek Z100) or dual-cure resin cement (RelyX Ultimate). Seating of restorations was first evaluated at try-in (baseline). Seating was reevaluated after airborne-particle abrasion (Step 1), after seating with luting agent (Step 2), and after light polymerization (Step 3). The Friedman test followed by the Wilcoxon post hoc test were used to compare the seating among steps, and the Kruskal-Wallis test followed by the Mann-Whitney post hoc test were used to compare the seating between luting agents at P < 0.05. RESULTS: Seating differences varied significantly from baseline (P < 0.0125). All restorations seated 3.85 µm (inlays) to 5.45 µm (onlays) deeper after airborne-particle abrasion (Step 1) (P < 0.007). Except for cement-luted inlays, the try-in position (±1 µm) was recovered following unpolymerized luting (Step 2). After polymerization (Step 3), onlays and overlays seated 2.9 to 3.9 µm deeper than during try-in (baseline) using Z100 (P < 0.005), and 7.0 to 7.3 µm deeper using RelyX (P = 0.005). Inlays luted with RelyX seated higher than during try-in (baseline), exactly 7.9 µm after Step 2 (P = 0.005), and 7.7 µm after Step 3 (P = 0.008). Luting with Z100 sustained the seating of inlays with no statistical difference when compared to baseline (P = 0.157). CONCLUSION: Airborne-particle abrasion significantly deepens the seating of CAD/CAM composite resin restorations, but the presence of unpolymerized restorative composite resin luting agent perfectly compensates for this discrepancy. Following polymerization, onlays and overlays seat deeper compared to inlays, especially when using RelyX. The latter, however, resulted in a slightly higher seating of inlays. CLINICAL SIGNIFICANCE: With the least variation compared to baseline seating (try-in), restorative composite resin used as luting agent resulted in the seating of CAD/CAM inlays, onlays, and overlays closer to baseline when compared to dual-cure resin cement.

Current options concerning the endodontically-treated teeth restoration with the adhesive approach.

Adhesive procedures have changed the way to restore endodontically treated teeth (ETT). It started with the shift from cast post-and-core to fiber post. The original focus on strength also shifted towards failure modes, revealing that catastrophic failures are still a concern when restoring endodontically-treated teeth even with fiber posts. As an alternative, postless approaches have been proposed in order to improve the chances of repair. The goal of this critical review is to present a survey of the current knowledge on adhesive approaches to restore endodontically treated teeth with and without extensive coronal tissue loss. The preservation of tooth structure of endodontically treated teeth is paramount. Partial versus full coverage of ETT, the role of the ferrule, the post type effect on catastrophic failures and postless alternatives as endocrowns and postless build-ups are reviewed. There is a consensus that the remaining tooth structure plays an important role in ETT survival, although the current literature still is contradictory on the influence of post type on root fractures as well as the benefits of avoiding a post or partially restoring a tooth. More clinical studies should be carried out with the modern postless adhesive alternatives to conventional approaches.

Biomechanical behavior of different designs of hybrid abutment-restoration on the posterior crown: a finite element analysis

Abstract This study aimed to evaluate the influence of material and crown design on the biomechanical behavior of implant-supported crowns with hybrid abutment (HA) through three-dimensional (3D) finite element analysis. The study factors were the type of material used as the mesostructure or crown (zirconia, lithium disilicate, and hybrid ceramic) and the crown design cemented to the titanium base (mesostructure cemented to the titanium base and a crown cemented on it (HaC); hybrid crown-abutment, the abutment and crown are manufactured as a single piece and cemented to the titanium base (HC); monolithic crown cemented on the titanium base and screwed to the implant (CS); and monolithic crown cemented on the titanium base (CC). Four 3D models were constructed using an implant with an internal connection, and an oblique load of 130 N was applied at 45° to the long axis of the implant. The models were evaluated using the von Mises stress for crown, abutment, screw, and implant and maximum principal stress for bone tissues. The lowest stresses occurred in the groups with a lower elastic modulus material, mainly hybrid ceramics, considered a material with greater resilience. The cemented crown group presented the lowest stress values. The stresses were concentrated in the cervical region of the crown at the titanium crown/base interface. Mesostructures made of materials with a higher elastic modulus exhibited a higher concentration of stress. The presence of a screw hole increased the stress concentration in the ceramic crown. Cemented ceramic crowns exhibited better biomechanical behavior than screw-retained crowns.

Resumo O estudo teve como objetivo avaliar a influência do material e do desenho da coroa no comportamento biomecânico de coroas implanto-suportadas com pilar híbrido (AH) por meio da análise tridimensional (3D) de elementos finitos. Os fatores de estudo foram o tipo de material do HA ou coroa (zircônia, dissilicato de lítio e cerâmica híbrida) e o desenho da coroa sobre a base de titânio (mesoestrutura cimentada à base de titânio e coroa total cimentada em cerâmica; pilar e coroa fabricados em peça única cimentada à base de titânio; coroa monolítica cimentada sobre a base de titânio e aparafusada ao implante; e coroa monolítica cimentada à base de titânio). Quatro modelos 3D foram construídos e uma carga oblíqua de 130 N foi aplicada a 45° em relação ao longo eixo do dente. Os modelos foram avaliados utilizando a tensão de von Mises para a coroa, pilar, parafuso, implante e tensão principal máxima (tensão de tração) para o tecido ósseo. As menores tensões ocorreram nos grupos que apresentaram um material com menor módulo de elasticidade, principalmente a cerâmica híbrida, considerada um material com maior resiliência. Com relação às diferentes configurações, o modelo com coroa cimentada apresentou os menores valores de tensão. As tensões foram concentradas na região cervical da coroa na interface entre coroa e base de titânio. Mesoestruturas feitas de materiais com maior módulo de elasticidade exibiram maior concentração de tensões. A presença de um orifício para parafuso aumentou a concentração de tensão na coroa de cerâmica. As coroas cerâmicas cimentadas exibiram melhor comportamento biomecânico do que as coroas parafusadas.

Biomechanical Behavior of the Dental Implant Macrodesign.

PURPOSE: The aim of this study was to evaluate the influence of implant macrodesign when using different types of collar and thread designs on stress/strain distributions in a maxillary bone site. MATERIALS AND METHODS: Six groups were obtained from the combination of two collar designs (smooth and microthread) and three thread shapes (square, trapezoidal, and triangular) in external hexagon implants (4 × 10 mm) supporting a single zirconia crown in the maxillary first molar region. A 200-N axial occlusal load was applied to the crown, and measurements were made of the von Mises stress (σvM) for the implant, and tensile stress (σmax), shear stress (τmax), and strain (εmax) for the surrounding bone using tridimensional finite element analysis. The main effects of each level of the two factors investigated (collar and thread designs) were evaluated by one-way analysis of variance (ANOVA) at a 5% significance level. RESULTS: Collar design was the main factor of influence on von Mises stress in the implant and stresses/strain in the cortical bone, while thread design was the main factor of influence on stresses in the trabecular bone (P < .05). The optimal collar design able to produce more favorable stress/strain distribution was the microthreaded design for the cortical bone. For the trabecular bone, the triangular thread shape had the lowest stresses and strain values among the square and trapezoidal implants. CONCLUSION: Stress/strain distribution patterns were influenced by collar design in the implant and cortical bone, and by thread design in the trabecular bone. Microthreads and triangular thread-shape designs presented improved biomechanical behavior in posterior maxillary bone when compared with the smooth collar design and trapezoidal and square-shaped threads.

Biomechanical Effect of Prosthetic Connection and Implant Body Shape in Low-Quality Bone of Maxillary Posterior Single Implant-Supported Restorations.

PURPOSE: Dental implant macrogeometry parameters, such as the prosthetic connection and implant body shape, can influence the biomechanical behavior of the restoration. Using tridimensional finite element analysis (3D-FEA), this study evaluated the biomechanical behavior of two implant macrodesign parameters (prosthetic connection and implant body shape) in low-quality bone. MATERIALS AND METHODS: Four groups were obtained by the combination of external hexagon and Morse taper connections, and cylindrical and conical body shapes. Implants (4ø × 10-mm) with a microthread collar and triangular thread shape received a single abutment and monolithic zirconia crown on the maxillary first molar. Bone was constructed on the basis of cross-sectional images of the posterior human maxilla obtained by cone beam computed tomography. A 200-N axial loading was distributed on five points of the occlusal surface. Data were acquired as shear stress (τmax, in megapascals) and strain (εmax, in micrometers) in the cortical and trabecular bone. RESULTS: The external hexagon groups generated higher shear stress/strain values compared with Morse taper groups in the cortical bone, regardless of implant body shape. In the trabecular bone, the highest τmax and εmax values were observed in the Morse taper conical implant group (6.94 MPa and 21.926 × 10⁻4 µm, respectively), and the lowest values were observed in the external hexagon cylindrical implant group (4.47 MPa and 9.3155 × 10⁻4 µm, respectively). CONCLUSION: The magnitudes of shear stress and strain in the peri-implant region of low-quality bone was lower with the use of Morse taper connection and cylindrical implants compared with external hexagon connection and conical implants.