Effect of splinting material type and location on resistance against deflection force of splinted periodontally compromised teeth with hypermobility.

This study aimed to evaluate the effect of splinting material type and material location on the force resistance of splinted periodontally compromised teeth with hypermobility. Extracted teeth including the target tooth (maxillary second premolar) and its adjacent teeth were placed into the alveolar sockets of a dental arch model via artificial periodontal ligaments made of elastic impression material. Three different experimental models with varied target tooth mobility including Periotest® values (PTVs) of 20, 30, and 40 were fabricated (named models #20, #30, and #40, respectively). For each experimental model, the force resistance of tooth splinting was tested using the following four materials: everStick PERIO (glass fiber reinforcement: GFR), FORESTAFLEX (braided stainless steel: BSS), Ortho-FlexTech (stainless steel chain: SSC), and Super-Bond (MMA-based resin cement: MRC). The evaluated measures were the PTV after tooth splinting and the required load to cause tooth displacements of 0.05 mm and 0.10 mm in the vertical and lateral directions, respectively. The splinting material type and material location as well as the original PTV of target the tooth significantly affected all the evaluated measures (p < 0.001). MRC revealed the significantly highest force resistance of tooth splinting regardless of material location in each experimental model and was followed by GFR. The PTVs of splinted teeth were comparable to those of adjacent anchor teeth in models #20 and #30 when using GFR, while that was comparable in model #40 when using MRC. Meanwhile, the load causing certain tooth displacement showed a similar tendency to previous-reported data with healthy teeth in model #20 when using GFR, while that showed a similar tendency in models #30 and #40 when using MRC. Overall results concluded that splinting material type and location play a role in the resistance against the deflection force of splinted periodontally compromised hypermobile tooth. It was noted that MRC provided the highest resistance against the deflection force of splinted teeth regardless of material location whereas GFR maintained the physiologically considered tooth mobility.

Influence of Post-Core and Crown Type on the Fracture Resistance of Incisors Submitted to Quasistatic Loading.

The aim of this paper was to evaluate the fracture resistance and failure type of maxillary incisor teeth, rebuilt with various types of post-core restorations and full crowns made of either direct conventional particulate filler composite (PFC, G-aenial Anterior, GC, Tokyo, Japan) or indirect CAD/CAM restorations (composite Cerasmart 270 and glass ceramic LiSi Block from GC). One hundred (n = 10/group) central incisors were cut and divided into 10 experimental groups restored with different approaches. In approach A, teeth were restored with a core build-up composite (Gradia Core, GC) for a core and full crown of PFC. Approach B had teeth restored using composite core and prefabricated fiber posts, and a complete crown of either PFC or CAD/CAM. Approach C contained teeth restored with a core of short fiber-reinforced composite (everX Flow, GC) and prefabricated fiber posts, and a complete crown of either PFC or CAD/CAM. In approach D, the teeth had a core of short fiber-reinforced composite only, and a complete crown of either PFC or CAD/CAM restorations. The root canals were prepared, and when posts were used, they were luted with either a dual-cure resin cement (LinkForce, GC) or everX Flow. As the control, sound teeth (n = 10) were used. Restorations were quasi-statically loaded until fracture. Failure type was visually investigated. The interface between the fiber post and luting cement was investigated using SEM, before and after completion of the loading test. The data were analyzed by analysis of variance (p = 0.05) followed by Tukey's test. None of the restorative approaches restored the fracture load strength of intact teeth (p < 0.05). Restorations with additional fiber posts (Approaches B and C) had higher load-bearing capacity (p < 0.05) than restorations without fiber posts (Approaches A and D). Restorations that had short fiber-reinforced composite cores with or without fiber posts presented more repairable failures. Using short fiber-reinforced composite as post-luting and core build-up material with conventional fiber posts proved to be a promising method to strengthen severely damaged incisors.

Impact of multiple firings and resin cement type on shear bond strength between zirconia and resin cements.

PURPOSE: The aim of this study was to evaluate the effect of multiple firings on the bond strength between yttria-tetragonal zirconia polycrystals (Y-TZP) and 2 types of resin cements. MATERIALS AND METHODS: Sixty 3Y-TZP specimens (LAVA Frame Multi) were divided into 3 groups depending on the following firing procedures: (1) 2-firing cycles, (2) 5-firing cycles, (3) 10-firing cycles. Two samples from each group were investigated by using SEM to determine the morphological changes. All specimens were treated with 125 µm airborne-particle abrasion and the surface roughness of each specimen was measured. The specimens from each firing group were then further divided into 2 subgroups (n = 9) to apply 2 types of resin cement (MDP-free resin cement: RelyX Unicem-RU, and MDP containing resin cement: Panavia F 2.0-PA). The shear bond strength (SBS) test was performed and failure types of all the debonded specimens were classified by using a stereomicroscope as adhesive, cohesive, and mixed. The statistical analysis of surface roughness and SBS data were performed by using 1-way ANOVA and 2-way ANOVA followed by Tukey-HSD tests (α=.05). Failure modes were calculated as a percentage for each group. RESULTS: The bond strength of RU and PA to the specimens obtained with 2 firings were not statistically different from each other (P=.1). However, the SBS values of PA were found to be significantly higher than RU for the specimens obtained with 5 and 10 firing cycles (P=.001 and P=.02, respectively). Surface roughness analysis revealed no statistical difference between groups (P=.2). The SEM analysis of samples fired 5- and 10- times showed irregularities and boundary loss in zirconia grains, and empty spaces between zirconia grains. CONCLUSION: The bond strength of PA cement was higher than that of RU to the zirconia subjected to repeated firings (5 and 10 firing cycles). When zirconia is subjected to multiple firings, using MDP-containing resin cement can be recommended.

Effect of various polymerization protocols on the cytotoxicity of conventional and self-adhesive resin-based luting cements.

OBJECTIVES: This study evaluated the cytotoxicity of resin-based luting cements on fibroblast cells using different polymerization protocols. MATERIALS AND METHODS: Two conventional dual-polymerized (RelyX ARC, VariolinkN) and two self-adhesive resin cements (RelyX Unicem, Multilink Speed) specimens were polymerized using four different polymerization protocols: (a) photo-polymerization with direct light application, (b) photo-polymerization over ceramic and (c) resin nano-ceramic discs and (d) auto-polymerization. The specimens were then assigned to four groups to test cytotoxicity at 0, 1, 2 and 7 preincubation days (n = 5). MTT test was performed using NIH/3T3 fibroblast cells. Data were analysed using three- and one-way ANOVA. Multiple comparisons were made using Bonferroni post hoc test (p < 0.05). RESULTS: The highest cytotoxic values were recorded at day 2 for conventional resin cements and at day 0 for self-adhesive resin cements. Self-adhesive resin cements showed the most cytotoxic effect at the second day, while conventional resin cements presented immediate cytotoxicity. Auto-polymerized resin specimens and especially Multilink Speed demonstrated the most cytotoxic effect regardless of the preincubation time. Cytotoxicity of cements tested reached the lowest level at day 7. Interposition of ceramic or nano-ceramic restorative material did not significantly affect the cytotoxicity of tested luting cements (p > 0.05). CONCLUSIONS: Cytotoxicity of dual-polymerized resin cements was material-dependent and decreased gradually up to 7 days. Photo-polymerization plays an important role in reducing the cytotoxic effects. CLINICAL RELEVANCE: When luting ceramic or resin nano-ceramic restorations of which thickness does not exceed 2 mm, the level of cytotoxicity with the tested materials is not significant. Luting of restorative materials that do not allow for light transmission such as metal-fused porcelain, clinicians should be cautious in the use of dual-polymerized conventional resin cements as only auto-polymerization of resin cements takes place under such materials.

Angle of convergence of posterior crown preparations made by predoctoral dental students.

The aim of this study was to determine angle of convergence (AC) of posterior crown preparations made by predoctoral dental students at the University of Toronto. Ninety-one dies of students' crown preparations were digitally scanned with an in-Eos-Blue scanner (Sirona). Created images were virtually sliced at three similar locations of mesiodistal and buccolingual planes. Virtual protractor was used to determine AC of each section. Means and SDs were calculated, and data were statistically analyzed with ANOVA and student's t-test for operator's gender, experience, and tooth type. There were no significant differences among the groups except for AC of preparations grouped by tooth type (p<0.0001). The greatest mean mesiodistal AC was 26.4° found with mandibular molars, while the smallest was 16° found with maxillary premolars. ANOVA revealed significant difference in mean mesiodistal AC among groups (p<0.01). Also, greatest mean buccolingual AC was 25° found with mandibular molars, while the smallest was 20.8° found with maxillary premolars. ANOVA did not reveal significant difference in mean buccolingual AC among groups (p>0.05). Overall mean AC values were greater than ideal range of 2-5°; however, they were within ranges published for dentists/prosthodontists. Gender and experience had no significant effect on AC, but tooth type significantly affected AC.

Effects of different cavity designs on fracture load of fiber-reinforced adhesive fixed dental prostheses in the anterior region.

PURPOSE: To evaluate the fracture strength of inlay-retained, surface-retained, and cantilevered fiber-reinforced adhesively fixed dental prostheses (FRA-FDPs) in the anterior region. MATERIALS AND METHODS: Thirty-two sound human right central incisors and canines were divided into four groups. Test groups were as follows: group 1, both teeth had deep cavity preparation; group 2, both teeth had shallow cavity preparation; group 3, only the canine teeth had deep cavity preparation; group 4, no preparation was made on the abutment teeth. Lateral pontics were restored with FRA-FDPs. All restorations were subjected to fracture loading from the lateral pontic. The restorations were tested in a universal testing machine (LRX Material Testing Machine) with a crosshead speed of 1 mm/min. One-way ANOVA was used for statistical analyses. Fracture modes were examined visually. RESULTS: The highest (667.3 ± 90.4 N) and the lowest (409.3 ± 158.1 N) debonding values were found for groups 4 and 3, respectively. CONCLUSIONS: Different preparation designs (inlay-retained, surface-retained) had no significant effect on fracture strength of FRA-FDPs in the anterior region. However, a cantilever design exhibited significantly lower fracture strength. Delamination of the veneering composite was observed as the primary failure type after fracture tests.

Load-bearing capacity of fiber reinforced fixed composite bridges.

OBJECTIVE: The aim of this study was to evaluate the reinforcing effect of differently oriented fibers on the load-bearing capacity of three-unit fixed dental prostheses (FDPs). MATERIALS AND METHODS: Forty-eight composite FDPs were fabricated. Specimens were divided into eight groups (n = 6/group; codes 1-8). Groups 1 and 5 were plain restorative composites (Grandio and Z100) without fiber reinforcement, groups 2 and 6 were reinforced with a continuous unidirectional fiber substructure, groups 3 and 7 were reinforced with a continuous bidirectional fiber and groups 4 and 8 were reinforced with a continuous bidirectional fiber substructure and continuous unidirectional fiber. FDPs were polymerized incrementally with a handheld light curing unit for 40 s and statically loaded until final fracture. RESULTS: Kruskal-Wallis analysis revealed that all groups had significantly different load-bearing capacities. Group 4 showed the highest mean load-bearing capacity and Group 7 the lowest. CONCLUSION: The results of this study suggest that continuous unidirectional fiber increased the mechanical properties of composite FDPs and bidirectional reinforcement slowed crack propagation on abutments.

Tensile bond strength of a lithium-disilicate pressed glass ceramic to dentin of different surface treatments.

The effects of desensitizer, disinfectant, saliva, blood, and hydrogen peroxide on the tensile bond strength between adhesive and ceramic as well as between adhesive and dentin were examined. Sixty 7x3 mm pressed ceramic discs of IPS e.max were fabricated and randomly assigned to six groups of different dentin surface treatments (control, desensitizer, disinfectant, saliva, blood, and hydrogen peroxide). Representative samples of fractured specimens were observed by SEM (scanning electron microscopy). There were significant differences between the control group and saliva, blood, and hydrogen peroxide groups (p<0.05). However, there were no significant differences between any other dentin surface treatment groups (p>0.05). Results of this study suggested that only saliva, blood, and hydrogen peroxide influenced the tensile bond strength between dentin and ceramic.

Effect of ultrasonic agitation on bond strength of self-etching adhesives to dentin.

PURPOSE: The aim of this study was to evaluate the influence of ultrasonic treatment on the microtensile bond strength of self-etching adhesives to dentin. MATERIALS AND METHODS: Forty-two human molars were wet ground occlusally until dentin was exposed. Clearfil S3 Bond, Futurabond NR (one-bottle) and Clearfil SE Bond (two-bottle) self-etching bonding systems were used in this study. In control groups, bonding procedures were performed according to the manufacturers' instructions. In the experimental groups, bonding materials were applied with an ultrasonic scaler. When using Clearfil SE Bond, the ultrasonic device was used either during priming or the bonding stage. The composite was then built up to 5 mm in height. Each tooth was serially sectioned into rectangular beams. The beams were categorized also according to positional status as marginal or central. Beams were subjected to microtensile testing after 24 h of water storage. Failure modes were observed with a stereomicroscope and classified. Randomly selected tested beams from each group were examined with SEM. RESULTS: Three-factor ANOVA results indicated that the adhesive bonding system had a significant effect on bond strength (p < 0.001), whereas ultrasonic agitation and the position of the tested beam (marginal vs central) had no effect on bond strength (p > 0.05). Failure after the test was commonly due to adhesive breakdown associated with partial cohesive failure in the dentin. The mean (SD) microtensile bond strengths to dentin for S3 Bond, Futurabond NR, Clearfil SE Bond in the control group were 44.3 (11.7), 35.3 (12.0), 25.1 (8.8), resp, and in the ultrasonic group 39.3 (14.2), 31.3 (13.5), 35.5 (13.5) at priming and 32.6 (16.2) at bonding. CONCLUSION: Ultrasonic agitation during application of self-etching adhesives had no effect on bonding performance of the self-etching adhesive.

In vitro evaluation of push-out bond strength of direct ceramic inlays to tooth surface with fiber-reinforced composite at the interface.

STATEMENT OF PROBLEM: Failure of a restoration, where a part of a ceramic inlay and/or a cusp is fractured, is a common clinical problem. The application of fiber-reinforced composites at the tooth-inlay interface may prevent undesirable fractures in dental restorations. There is little information regarding the effect of a fiber- reinforced composite layer on the push-out bond strength of ceramic inlays to tooth structure. PURPOSE: The purpose of this study was to compare push-out bond strengths of ceramic inlays to tooth structure using a layer of fiber weave-reinforced composite at the tooth interface with different adhesive systems. MATERIAL AND METHODS: Forty standardized occlusal, conically-shaped cavities, 5 mm in occlusal diameter, 3.5 mm in cervical diameter and 3.5 mm deep, were prepared in extracted human molars using a truncated cone-shaped diamond rotary cutting instrument, the dimensions of which corresponded with those of prefabricated ceramic inlays. The teeth were divided into 2 groups according to the adhesive system used. Solobond Plus was used as a total-etching system and Futurabond NR as a self-etching system. Preetched and silanized ceramic inlays were bonded to tooth structure with or without a layer of bidirectional fiber weave (StickTech). The groups without fiber-reinforced composite layer served as controls. The inlays were cemented with dual-polymerizing luting composite (Bifix QM) and light polymerized for 40 seconds from the buccal, lingual, and occlusal surfaces. Specimens were thermal cycled (6000 x 5 degrees -55 degrees C) and 3.5-mm-thick discs were prepared for the push-out test. The discs (n=10) were tested in a universal testing machine and pushed out with a cross-head speed of 1.0 mm/min. The data were analyzed with analysis of variance (ANOVA) (alpha=.05). Failure modes were analyzed using a stereomicroscope and SEM. RESULTS: Push-out mean bond strength (SD) values in MPa of direct ceramic inlays were: Solobond Plus (control): 9.7 (3.9), Solobond Plus with fiber-reinforced composite: 10.5 (5.0), Futurabond NR (control): 8.4 (2.5), Futurabond NR with fiber-reinforced composite: 8.6 (2.2). The differences between groups were not significant for either adhesive system or with the use of fiber-reinforced composite layer at the interface. Mixed failures were observed in the control groups, whereas in the fiber-reinforced composite layer groups, failures were mostly cohesive within the fiber layer. No cohesive fracture of the tooth was observed when a layer of fiber weave was placed at the interface. CONCLUSION: Within the limitations of this in vitro study, a fiber-reinforced composite layer at the bonding interface of ceramic inlay did not influence the push-out bond strength. Futurabond NR self-etching system and Solobond Plus total-etching system demonstrated similar push-out bond strengths.

Effect of accelerated restorative techniques on the microleakage of Class II composites.

PURPOSE: To assess the marginal seal of Class II resin-based composite restorations cured by a high intensity halogen light or a plasma arc light. MATERIALS AND METHODS: Class II cavities were prepared in extracted molar teeth with cervical margins located apical to the cemento-enamel junction. Cavities were restored with a posterior resin-based composite (Tetric Ceram) using either a two-increment or a bulk placement and cure restorative technique after application of bonding agent (Excite). Test parameters included light unit type/curing mode, application of flowable composite and restorative technique. After thermocycling, the teeth were immersed in basic fuchsin dye. Sectioned restorations were examined under a stereomicroscope (x 25) and extent of microleakage (mm) was recorded using an image analysis system. Data was analyzed by non-parametric statistical tests. RESULTS: No leakage was observed at the occlusal enamel margin of a nyrestoration. Median gingival leakage values for the different test groups ranged from 0.02-2.51 mm. Light unit type had a highly significant effect on leakage (P=0.0002). The highest leakage scores were recorded with the plasma arc light used in standard curing mode and the lowest with the halogen light in turbo-boost mode.