Relationship of Margin Design for Fiber‐Reinforced Composite Crowns to Compressive Fracture Resistance

Purpose: Fiber‐reinforced composite restorations provide excellent esthetics; however, little is known regarding the influence of margin design on marginal fit and fracture resistance for this type of crown. This study evaluated the effect of variations in tooth‐preparation design on the marginal fit and compressive fracture resistance of fiber‐reinforced composite crowns. Materials and Methods: Three metal dies with a total convergence of 5° and different margin designs (0.5‐mm light chamfer, 1.0‐mm deep chamfer, and 1.0‐mm shoulder) were prepared. Sixty standardized crowns (FibreKor) were made on duplicated base metal alloy dies (n = 20 for each margin design). Marginal fit was stereoscopically evaluated by measuring the distances between each of the four pairs of indentations on the crowns and on the dies. The specimens were then subjected to a compressive fracture‐loading test using a universal testing machine. The data were analyzed with one‐way analysis of variance (ANOVA) followed by Ryan‐Einot‐Gabriel‐Welsch multiple‐range test (α= 0.05). Results: Analysis of marginal fit and fracture resistance disclosed a statistically significant difference for tooth‐preparation design (p < 0.001). The marginal adaptation of preparations with the 0.5‐mm light chamfer (66.2 μm) and 1.0‐mm deep chamfer (69.7 μm) was significantly better than preparations with a shoulder finish line (92.8 μm) (p < 0.001). The fracture strength of the preparations with the 0.5‐mm light chamfer (15.8 MPa) and 1.0‐mm deep chamfer (15.1 MPa) was significantly greater than those of the preparations with the 1.0‐mm shoulder (13.7 MPa) (p < 0.001). Conclusions: Marginal fit of fiber‐reinforced crowns was adversely affected by tooth‐preparation design. The marginal gaps were greater for the shoulder margin specimens than in the light or deep chamfer margin specimens; however, the fracture strength of the chamfer margin specimens was greater than that of the shoulder margin specimens.     

Effect of Fiber Post and Cusp Coverage on Fracture Resistance of Endodontically Treated Maxillary Premolars Directly Restored with Composite Resin

IntroductionThere are different reinforcement methods in restoring root-filled teeth. The aim of this in vitro study was to evaluate the effect of fiber post and cusp coverage on fracture resistance of endodontically treated maxillary premolars directly restored with composite resin.MethodsSeventy-five maxillary premolars were divided into 5 groups (n = 15). Except for the control group (intact teeth), in other groups mesio-occlusodistal (MOD) cavities were prepared after endodontic treatment. In the groups with cusp coverage, both buccal and lingual cusps were reduced up to 2 mm. Then specimens in the experimental groups were prepared as follows: composite resin restoration without post and cusp capping, composite resin restoration without post but with cusp capping, composite resin restoration with post but without cusp capping, and composite resin restoration with post and cusp capping. After finishing and polishing, the specimens were stored in distilled water at 37°C for a week. Subsequent to thermocycling and exertion of compressive forces parallel to the long axes of the teeth at a strain rate of 2 mm/min, data were analyzed by using one-way analysis of variance and χ² test.ResultsThere were no significant differences in fracture resistance between the groups (P = .057). However, χ² test showed statistically significant differences between the groups in failure mode (P < .001). The highest number of favorable fractures was observed in the control group (intact teeth).ConclusionsRoot-filled maxillary premolars, restored with direct resin composite with or without fiber post and cusp capping, had similar fracture resistance under static loading.     

桩核材料与纤维/树脂复合材料桩钉联合修复无髓牙的抗折性能研究

目的评价3种树脂类桩核材料与高强玻璃纤维/树脂复合材料(FRC)桩钉联合修复无髓牙的抗折性能。方法用FRC桩钉和3种经不同方法处理(热压和未热压)的树脂核(Artglass聚合体、Charisma复合树脂、AB组份复合树脂)联合修复离体无髓牙根,测试1300加载时的破坏载荷。结果Artglass聚合体组的抗折力最高(505.4N),经热压处理后强度明显提高(564.1N) ; Chari~复合树脂组经热压后脆性增加,强度降低(热压前后分别为411.3N和 315.3N); AB组份树脂组经热压后强度明显提高(热压前后分别为358.4N和423.4N)。实验中无1例出现桩钉折断和聚酷冠碎裂。结论不同桩核材料与FRC桩钉联合修复无髓牙的抗折力不同,其中Art乡ass聚合体组的抗折力最高,但是此3组的抗折力均超过了咀嚼过程中前牙的咬合力,树脂核与纤维/树脂复合材料桩钉联合修复无髓前牙残根可以满足临床需要。     

Survival Rates from Fracture of Endodontically Treated Premolars Restored with Full-coverage Crowns or Direct Resin Composite Restorations: A Retrospective Study

Introduction

The aim of the present study was to compare the survival rates against fracture of premolar endodontically treated teeth (ETT) restored with resin composite or crowns and to identify risk factors associated with the fracture.

Fabrication of Complete Denture Bases Reinforced with Polyethylene Woven Fabric

Incorporation of 5 layers of woven, high-modulus polyethylene fiber into acrylic resin denture bases produces substantial improvements in mechanical properties and dimensional changes. A modified split-pack technique has been developed using conventional dental-laboratory compression molding to accommodate multiple layers of woven fabric in complete denture bases. A recess formed in the resin by a spacer allows the reinforcement to be embedded in the denture base without exposing the fibers. Embedded fibers do not compromise the esthetics of complete dentures.     

Influence of Smear Layer Treatment on Resistance to Root Fracture in Tooth Restored with Epoxy Fiber Post

To evaluate the influence of complete smear layer removal by EDTA on the resistance of root fracture of tooth restored with fiber post. Twenty single rooted premolars with average root length 16 ± 1 mm were randomly divided into two groups of ten each. All teeth were obturated with guttapercha after root canal preparation, sectioned 4 mm above the cement-enamel junction. In group I, teeth root canals were etched with 37 % phosphoric acid, fiber post cemented with self adhesive resin cement. In group II, teeth radicular dentin was treated with 17 % EDTA, followed by fiber post cementation with dual cure resin cement. Coronal part of the teeth reestablished with posterior composite and NiCr full veneer coping along with 2 mm circumferential ferrule. Restored teeth were loaded with incremental force at 30° to the long axis of the root until fracture occurred. The data obtained was evaluated with paired sample T test to compare the fracture resistance between the test groups. Group I had the mean failure load of 1,883.70 N while group II had 1,622.80 N mean failure load. Paired sample T test showed statistically significant (p value = 0.033) failure load difference between the groups tested. Within the limits of this study, it may be concluded that: the complete removal of smear layer by EDTA found to have reduced the fracture strength of tooth roots restored with an epoxy fiber post.     

Resin Composite Core and Fiber Post Improved the Fracture Parameters of Endodontically Treated Maxillary Premolars with Wedge-shaped Cervical Lesions

IntroductionThe aim of this study was to evaluate the fracture resistance and fracture patterns of endodontically treated maxillary premolars with wedge-shaped cervical lesions restored with a resin composite core with or without a fiber post under nonaxial loading.MethodsSixty extracted human maxillary premolars with 2 root canals were randomly allocated into 4 groups (n = 15). Forty-five teeth were prepared with a wedge-shaped lesion at the buccal cervical area and root canal treatment. There were 3 restoration groups: no restoration, restoration with a resin composite core, and restoration with a resin composite core and a fiber post. Intact teeth served as the control group. All teeth were subjected to thermocycling and cyclic loading. A 45° compressive load was applied to the palatal plane of the buccal cusp until tooth fracture. The fracture resistance and facture patterns were analyzed using 1-way analysis of variance and the chi-square test (α = 0.05), respectively.ResultsThe no restoration group demonstrated the lowest fracture resistance and was significantly different from the other groups (P < .001). The intact teeth presented the highest fracture resistance, which was not significantly different from the restoration with a resin composite core and a fiber post group (P > .05). The failure patterns were significantly different between groups (P < .001). Most intact teeth fractured coronally to the cementoenamel junction level, whereas most teeth in the other groups fractured at the gingival margin of the cervical lesion.ConclusionsEndodontically treated maxillary premolars with wedge-shaped cervical lesions restored with fiber posts and a resin composite cores had a fracture resistance equivalent to intact teeth. However, their fracture patterns were not improved by the fiber post and a resin composite core.     

Bond Strength of Soft Liners to Fiber‐Reinforced Denture‐Base Resin

Purpose: This study evaluated bond strengths of four soft liners to fiber‐reinforced (FR) and unreinforced poly methyl(methacrylate) (PMMA) denture‐base resin. Materials and Methods: The autopolymerized denture‐base resin Palapress Vario (Heraus Kulzer GmbH, Hanau, Germany) was used as the substrate (15 × 15 × 5 mm³). The test group consisted of substrates reinforced with porous PMMA preimpregnated unidirectional glass fibers (Stick [StickTech, Turku, Finland]) (PMMA + FR group), and the control group was unreinforced acrylic resin (PMMA group) (n = 80 per group). One of four soft liners (Ufi Gel SC [Voco, Cuxhaven, Germany], Sofreliner Tough [Tokuyama Dental Corporation, Tokyo, Japan], Vertex SoftSil 25 [Vertex‐Dental B.V., Zeist, The Netherlands], and Eversoft [Dentsply Austenal, York, PA]) was placed and cured between two substrates using a polyethylene ring (10 mm inner radius, 3 mm height). Tensile bond strength tests (crosshead speed = 10 mm/min) were performed, and the results were analyzed using analysis of variance followed by Tukey's test (p= 0.05). Fracture surfaces were categorized as adhesive or cohesive‐mixed modes, and failure types were statistically analyzed using chi‐square test. Results: FR did not affect the bond strength results significantly (p > 0.05) except for Ufi Gel SC. Significant differences in bond strength were found among the reline materials (p < 0.001). FR specimens showed a significantly higher number of cohesive‐mixed fractures compared to unreinforced specimens (p < 0.05), except for plasticized acrylic‐based reline material (Eversoft [Dentsply Austenal]), which showed fewer cohesive‐mixed failures with FR. Conclusions: The choice of appropriate reline material system with FR acrylic resin is important for the soft liner/denture‐base polymer bond. Glass FR did not have a decreasing effect on the bond strength, except for Ufi Gel SC.     

The Effect of Three Composite Fiber Insertion Techniques on Fracture Resistance of Root-filled Teeth

The aim of this study was to evaluate the effect of three methods of fiber insertion on fracture resistance of endodontically treated maxillary premolars in vitro. Sixty extracted human maxillary premolars received endodontic treatment followed by mesioocclusodistal (MOD) cavities with 2.5 ± 0.2 mm thicknesses of buccal and lingual cusps at height of contour. The gingival cavosurface margin was 1.5 mm coronal to the cementoenamel junction (CEJ). Subsequently, the teeth were randomly divided into four groups. In the no-fiber group, the cavities were restored with composite, and in other groups, composite impregnated glass fibers were placed in the gingival, middle, and occlusal third surfaces of the cavities, respectively, and were restored similar to the no-fiber group. Subsequent to thermocycling and exertion of compressive forces, statistical analysis showed that the fracture resistance in the occlusal fiber group was significantly higher than that in other groups (p < 0.0005). In addition, the highest favorable fracture and the lowest cusp detachment rates were observed in the occlusal fiber group.