Fixed partial dentures: all-ceramics,fibre-reinforced composites and experimental systems

The aim of this in vitro study was to compare the fracture strength of three-unit FPDs (fixed partial dentures) and three-unit inlay FPDs after a simulated 5-year oral wearing period. The restorations were made of a pressable all-ceramic (Empress 2) and two specially designed, experimentally fixed partial dentures combining ceramics with dental composite. Three-unit FPDs and inlay FPDs were manufactured and were adhesively luted onto human molars. After thermal cycling and mechanical loading in an artificial environment, the fracture strength was determined. Zircon-based milled ceramic (Lava) three-unit FPDs were used as a control. The zircon ceramic and the fibre-based ceramic three-unit FPDs showed median fracture values between 1000 and 1400 N. For composite veneered zircon FPDs a fracture strength of about 800 N and for all-ceramic Empress 2 of about 350 N could be determined. The results for the inlay FPDs were between 1300 N and 1400 N for FRC/ceramic, 1000 N for zircon/composite and 500 N for all-ceramic restorations. The all-ceramic showed higher fracture resistance applied as inlay FPDs. The described hybrid techniques combining ceramics and composites could represent an interesting procedure for further investigations and, eventually, clinical implication.     

Bond strength of Gradia veneering composite to fibre-reinforced composite

This study investigated the shear bond strength of light-curing veneering composite resin to glass fibre-reinforced composite (FRC). Polymer pre-impregnated FRC reinforcement was further impregnated with dimethacrylate monomer resin. The light polymerized FRC substrate was ground and dimethacrylate intermediate resin was applied on the surface before the light-curing veneering composite. Adhesional behaviour of veneering composite to the initially light polymerized FRC substrate was compared with well-polymerized FRC substrate. The treatment time of FRC substrate by the intermediate resin for 5 s and 5 min were also compared. Shear bond strength of veneering composite to FRC was determined for dry and thermocycled specimens (n = 6). The analysis of variance (anova) revealed significant differences (P = 0.042) between the shear bond strengths when 5 s and 5 min intermediate resin treatment times were compared. The highest shear bond strength (21.0 MPa) for FRC substrates was achieved when the well-polymerized FRC substrate was treated for 5 min with the intermediate resin and stored dry before tests. Thermocycling reduced the shear bond strengths. The results of this study suggest that applying the intermediate resin increased the shear bond strength values of veneering composite to FRC with multiphase polymer matrix. It was also concluded, that the use of multiphase polymer matrix FRC can be polymerized to high degree of conversion without deferiorating the shear bond strength of veneering composite to the FRC.     

In vitro repair of all-ceramic and fibre-reinforced composite crowns

Shear bond strength between fibre reinforced composite and all-ceramic frameworks and veneering/repair composites was investigated after different surface treatments for evaluating the possibility of a repair. Then, 24 crowns were adhesively luted on human teeth and artificially aged. Repair quality was characterized by a loading to fracture test, where undamaged crowns were compared to repaired crowns. To simulate repeated damage, aging and repair, the procedure was performed three times for each crown. A combined silicate-silane treatment of the fibre-reinforced composite frameworks and the hydrofluoric acid etching of the ceramic showed good repair qualities and a sufficient fracture strength for clinical application.     

上颌中切牙种植体全瓷基台的计算机辅助设计

目的 探索建立上颌中切牙种植体全瓷基台计算机辅助设计(CAD)软件功能模块.方法 选择1副右上中切牙缺失、已行种植的工作模型,通过三维激光扫描,直接获取愈合基台(牙合)面、种植体-基台连接底座定位突、人工牙龈内壁(牙合)1/3部分、近远中邻牙以及对(牙合)牙表面三维数据.通过空间几何变换,间接获取种植体长轴、基台-底座结合平面数据.设计最终全冠,应用定向数据偏置等功能模块对全冠进行虚拟回切,设计基台龈上部分.最后应用基于边界曲率特征的双端扫掠曲面造型等功能模块设计基台穿龈部分.结果 建立了一条上颌中切牙种植体全瓷基台CAD路线,确定了三维图形学功能函数及其组合,实现了完整的设计流程.结论 初步建立了上颌中切牙种植体全瓷基台CAD软件平台.     

Bond strength of fibre-reinforced composite to the metal surface

The aim of this study was to measure push-out bond strength of gold alloy and pure titanium bars to dimethacrylate polymer-glass fibre composite. Metal bars were either left untreated, or sandblasted with 110 microm grain size aluminium oxide, pyrolytically silica-coated (Silicoater, Heraeus Kulzer) and silanized, tribochemically silica-coated, silanized (Rocatec, 3M-ESPE) and heat treated (100 degrees C/10 min), or tribochemically silica-coated and left unsilanized. Light-polymerizable opaque was applied on the metal surface and unidirectional glass fibres with Bis-GMA-PMMA monomer-polymer gel matrix was placed in contact to the bars and polymerized. Push-out test was performed for dry specimens and for those thermocycled (12.000 x55-5 degrees C). For titanium and gold alloy silica-coatings with the silane treatments resulted in the highest bond strengths. Values for titanium were somewhat higher than those for gold alloy. Silica-coating without silane treatment gave lower bond strengths but higher than that obtained with aluminium oxide sandblasting. The control specimens showed the lowest bond strength values. anova showed differences between the groups (P < 0.0001) whereas no significant differences between dry and thermocycled specimens were found. The results suggest that pyrolytical silica-coating with silane application resulted in highest bond strengths of dimethacrylate based fibre-reinforced composite to pure titanium and gold alloy.     

Bonding of fibre-reinforced composite post to root canal dentin

OBJECTIVE: The aim of this study was to determine bonding properties of two types of fibre-reinforced composite (FRC) posts cemented into root canals of molars. Serrated titanium posts served as reference. METHODS: Prefabricated carbon/graphite FRC posts with cross-linked polymer matrix and individually formed glass FRC posts with interpenetrating polymer network (IPN) polymer matrix were compared. The crowns of extracted third molars were removed and post space (diameter: 1.5mm) was drilled, etched and bonded. The posts were treated with dimethacrylate adhesive resin, light-polymerized and cemented with a dual-polymerizing composite resin luting cement. After thermocycling (6000x) the samples were cut into discs of thicknesses: 1, 2 and 4mm (n=12/group). Push-out force was measured by pushing the post from one end. Assessment of failure mode was made under a stereomicroscope (1, adhesive failure between post and cement; 2, cohesive failure of post-system; 3, adhesive failure between cement and dentin). RESULTS: The push-out force increased with increased height of dentin disc in all groups (ANOVA, p<0.001). In the 4mm thick dentin discs the individually formed glass FRC posts showed highest push-out force and the difference to that of the titanium posts was significant (ANOVA, p<0.001). The other differences were not statistically significant. None of the individually formed glass FRC posts showed adhesive failures between the post and the cement. CONCLUSIONS: Contrary to the other posts, there were no adhesive (post-cement) failures with the individually formed glass FRC posts, suggesting better interfacial adhesion of cement to these posts.     

Load bearing capacity of fibre-reinforced and particulate filler composite resin combination

OBJECTIVES: Longevity of particulate filler resin (PFR) is controversial for large restorations with high occlusal-stresses. The aim of this study was to reinforce PFR with fiber reinforced composite (FRC) and to evaluate the effect of thickness of FRC substructure and thickness of overlaying PFR, on the static load-bearing capacity of the material combination. METHODS: A total of 336 test specimens having a FRC substructure (short random or continuous bidirectional fibre orientation) and layer of restorative PFR were prepared for this study. In Group A, the specimens contained short random oriented fibres (length: 2-3mm) and in Group B, there were continuous bidirectionally oriented fibres. The specimens (n = 12/group) were polymerized with a hand light-curing unit and were either dry-stored or thermocycled before they were statically loaded with a steel ball until fracture, using a universal testing machine. RESULTS: Increase the volume fraction of the short random FRC versus the fraction of PFR, the load-bearing capacity of the specimen increased (p < 0.001). Short random FRC revealed significantly different behavior than the bidirectionally oriented FRC (p < 0.001). By combining the FRC layer of 0.5mm in thickness with a layer of 2.5mm of PFR gave load values of 1462N and 1196N, which were considerably higher than values for plain PFR of 3mm in thickness (782N and 729N). CONCLUSION: The results suggest that by adding a FRC substructure under the PFR, the load-bearing capacity of the material combination was increased.     

Fracture resistance of endodontically treated premolars with fibre-reinforced composite restorations

This study investigated the fracture resistance and failure mode of endodontically treated premolars restored with a glass fibre-reinforced composite resin. Endodontically treated maxillary premolars were divided in 4 groups: group O: occlusal access opening restored with direct composite; group O+: as group O but with fibre reinforcement; group MOD: occlusal access opening and mesio-distal (MOD) cavity restored with direct composite; group MOD+: as group MOD but with additional fibre reinforcement. Pairwise comparisons of the fracture force among all groups was performed (95% confidence level). Fractures were classified in 4 groups depending on the type of fracture. Group O was the strongest (452.7N) and group MOD the weakest (292.4N). Fracture resistance was significantly different among all groups, except between groups O+ and MOD+. The majority of the unreinforced teeth displayed unfavourable fractures, while the reinforced teeth displayed more favourable fractures. The incorporation of glass fibre weakened endodontically treated but otherwise intact premolars; premolars with MOD restorations were stronger if reinforced with fibres. Fibre reinforcement led to more favourable fractures.     

The influence of electron beam irradiation on fibre-reinforced composite specimens

This study investigated whether glass fibre-reinforced composite (FRC) specimens can benefit from post-curing using electron beam irradiation. Twenty-four frameworks of the Vectris and 24 of the Stick glass fibre-reinforced system were veneered with their correspondent veneer materials. Eight specimens of both systems were post-cured using electron beam irradiation (3 x 33 kGy, 10 MeV). The specimens were fixed in a restrained-end apparatus and inserted in an artificial mouth. With the exception of controls (n = 8 each) all other groups were thermally cycled and mechanically loaded (TCML). Finally, all samples were loaded to fracture using a universal testing machine. In two of eight non-irradiated Vectris/Targis specimens facing fracture occurred during TCML. Irradiation avoided these failures. No Stick/Sinfony facing fractured. However, Stick frameworks showed considerable torsions. Post-curing with electron beam irradiation made Stick frameworks stiffer. The fracture load of irradiated Stick/Sinfony specimens reached 520 +/- 31 N; control (without TCML and irradiation) 396 +/- 14 N, TCML-group without irradiation 362 +/- 41 N. Irradiated Vectris/Targis had a fracture resistance of 575 +/- 57 N; the control 556 +/- 36 N and the TCML group without irradiation 383 +/- 51 N. This investigation demonstrated that different types of FRC systems could considerably benefit from electron beam irradiation. The reconstructions became stiffer and resisted higher load.     

Fracture resistance of reattached incisor fragments with mini fibre-reinforced composite anchors

Objectives

Fractured coronal fragments of incisors can be adhered to the remaining tooth with resin composite, but are prone to failure. This study explores whether mini fibre-reinforced composite (FRC) anchors increase fracture resistance of reattached fragments.

Methods

Forty-five extracted incisors were randomly divided into three groups. In Groups A and B coronal fragments were reattached to the remaining tooth, with additionally two anchors placed in Group B. In Group C resin composite buildups were made. Specimens were statically loaded until failure occurred. Failure modes were characterized as intact remaining tooth substrate (adhesive or cohesive failure of coronal fragment) or fractured remaining tooth substrate (fracture limited to enamel or extending into dentin).

Results

Mean fracture loads were 255 N (SD = 108 N) for Group A, 599 N (SD = 465 N) for Group B and 786 N (SD = 197 N) for Group C (values significantly different, all p values <0.05). Group A showed purely adhesive failures, while Groups B and C showed 73 and 53% fractures of remaining tooth substrate (p < 0.05).

Conclusions

Mini FRC anchors increase fracture resistance of reattached coronal fragments, but induce more remaining tooth substrate fractures.     

The shear bond strength of bidirectional and random-oriented fibre-reinforced composite to tooth structure

OBJECTIVES: The objective of this study was to evaluate the bond strength and fracture pattern of fibre-reinforced composite (FRC) with two different fibre orientations and matrix compositions to dentine and enamel. MATERIALS AND METHODS: Extracted human molars were used as substrates (enamel and dentine) with a standard acid-etch technique. Light-polymerizable FRC with two different interpenetrating polymer network matrices and random or bidirectional fibre orientations was applied to the substrate, together with the adhesive resin. As a control, particulate filler composite resin was bonded to the substrates. The substrate-composite specimens (n=10) were either stored in water for 24h or additionally thermocycled for 6000 cycles. The shear bond strength of composite to substrate was measured and the fracture surfaces were evaluated visually and with SEM. RESULTS: Three-way factorial analysis of variance highlighted significant differences according to the substrate type, storage condition and composite material (p<0.05). Dentine specimens showed a significantly lower range of bond strength values (8.8-15.0 MPa), compared with enamel specimens (14.0-23.0 MPa). The highest mean bond strength in dentine was 15.0 MPa obtained with bidirectional FRC, whereas the highest bond strength in enamel was 23.0 MPa obtained with random-oriented FRC. Thermocycling did not identify a significant effect on the dentine bond strength, but did identify a significant decrease in enamel bond strength values (p<0.05). Several cohesive failures were observed in the tooth structure with the control material, whereas no cohesive bulk fracture of the tooth was observed when a thin layer of FRC was placed at the interface. CONCLUSIONS: The addition of bidirectional or random continuous fibres did not show any significant improvement in bond strength values compared to control of particulate filler. However, the difference in the fracture patterns observed may have implications for clinical applications.     

Comparison of two bond strength testing methodologies for bilayered all-ceramics.

OBJECTIVES: This study compared the shear bond strength (SBS) and microtensile (MTBS) testing methodologies for core and veneering ceramics in four types of all-ceramic systems. METHODS: Four different ceramic veneer/core combinations, three of which were feldspathic and the other a fluor-apatite to their respectively corresponding cores, namely leucite-reinforced ceramic ((IPS)Empress, Ivoclar), low leucite-reinforced ceramic (Finesse, Ceramco), glass-infiltrated alumina (In-Ceram Alumina, Vita) and lithium disilicate ((IPS)Empress 2, Ivoclar) were used for SBS and MTBS tests. Ceramic cores (N=40, n=10/group for SBS test method, N=5 blocks/group for MTBS test method) were fabricated according to the manufacturers' instructions (for SBS: thickness, 3mm; diameter, 5mm and for MTBS: 10 mm x 10 mm x 2 mm) and ultrasonically cleaned. The veneering ceramics (thickness: 2mm) were vibrated and condensed in stainless steel moulds and fired onto the core ceramic materials. After trying the specimens in the mould for minor adjustments, they were again ultrasonically cleaned and embedded in PMMA. The specimens were stored in distilled water at 37 degrees C for 1 week and bond strength tests were performed in universal testing machines (cross-head speed: 1mm/min). The bond strengths (MPa+/-S.D.) and modes of failures were recorded. RESULTS: Significant difference between the two test methods and all-ceramic types were observed (P<0.05) (2-way ANOVA, Tukey's test and Bonferroni). The mean SBS values for veneering ceramic to lithium disilicate was significantly higher (41+/-8 MPa) than those to low leucite (28+/-4 MPa), glass-infiltrated (26+/-4 MPa) and leucite-reinforced (23+/-3 MPa) ceramics, while the mean MTBS for low leucite ceramic was significantly higher (15+/-2 MPa) than those of leucite (12+/-2 MPa), glass-infiltrated (9+/-1 MPa) and lithium disilicate ceramic (9+/-1 MPa) (ANOVA, P<0.05). SIGNIFICANCE: Both the testing methodology and the differences in chemical compositions of the core and veneering ceramics influenced the bond strength between the core and veneering ceramic in bilayered all-ceramic systems.     

Structural optimization of the fibre-reinforced composite substructure in a three-unit dental bridge

IntroductionFailures of fixed partial dentures (FPDs) made of fibre-reinforced composites (FRC) have been reported in many clinical and in vitro studies. The types of failure include debonding at the composite-tooth interface, delamination of the veneering material from the FRC substructure and fracture of the pontic. The design of the FRC substructure, i.e. the position and orientation of the fibres, will affect the fracture resistance of the FPD.ObjectivesThe purpose of this study was to find an optimal arrangement of the FRC substructure, by means of structural optimization, which could minimize the failure-initiating stresses in a three-unit FPD.MethodsA structural optimization method mimicking biological adaptive growth was developed for orthotropic materials such as FRC and incorporated into the finite element (FE) program ABAQUS. Using the program, optimization of the fibre positions and directions in a three-unit FPD was carried out, the aim being to align the fibre directions with those of the maximum principal stresses. The optimized design was then modeled and analyzed to verify the improvements in mechanical performance of the FPD.ResultsResults obtained from the optimization suggested that the fibres should be placed at the bottom of the pontic, forming a U-shape substructure that extended into the connectors linking the teeth and the pontic. FE analyses of the optimized design indicated stress reduction in both the veneering composite and at the interface between the veneer and the FRC substructure.SignificanceThe optimized design obtained using FE-based structural optimization can potentially improve the fracture resistance of FPDs by reducing some of the failure-initiating stresses. Optimization methods can therefore be a useful tool to provide sound scientific guidelines for the design of FRC substructures in FPDs.     

Penetration of bonding resins into fibre-reinforced composite posts: a confocal microscopic study

AIM: To compare the penetration of two different bonding resins applied for different contact times, on glass reinforced-reinforced composite root canal posts showing an interpenetrating polymer network (IPN) or cross-linked polymer matrix. The research hypothesis was that the bonding resins were equally able to penetrate into the IPN post whereas less penetration was evident into the cross-linked post. In addition, the prolonged contact time of the bonding resin on the surface of post was assumed to increase the resin penetration. METHODOLOGY: A total of 36 posts, comprising 18 IPN posts (everStick Post) and 18 cross-linked posts (C Post Millennium) were divided into 12 groups of three posts. All posts had a diameter of 1.2 mm. Both bonding resins (Scotchbond Multi Purpose Plus and Stick Resin) were labelled with Rhodamine B for determination of the resin penetration into the post. After contact times of 1, 30 and 300 s the bonding resins were light cured for 60 s. Penetration of bonding resins into three sections of each post was measured by confocal scanning light microscope. The influences of post and type of adhesive resin on resin diffusion into the polymer matrix of the post were assessed by nonparametric methods. RESULTS: For C Post Millennium and for 1 s contact time, no penetration of bonding resins into the polymer matrix of posts occurred in any section of any post. For the everStick Post, penetration was always noted after 300 s contact (mean 22.8 microm) and nearly always after 30 s contact (mean 3.5 microm), with very little difference between the two adhesives. The degree of penetration into everStick Posts was invariably greater after 300 s contact than after 30 s (P < 0.001). Both sets of results were highly significantly greater than the zero penetration recorded using C Post Millennium or 1 s contact time (P < 0.001). CONCLUSIONS: The ability of bonding resins to penetrate into everStick Post with IPN polymer matrix may give the opportunity to establish a good link between fibre-reinforced composite posts, luting cements and composite cores.     

Treatment planning and smile design using composite resin.

Recent advances in dental materials and adhesive protocols have expanded the restorative procedures available to today's clinicians. Used in combination with proper treatment planning, these innovations enable dental professionals to provide enhanced aesthetic care that achieves the increasing expectations of their patients. Using a case presentation, this article will document the steps required to harmoniously integrate smile design, material selection, and patient communication that are involved in the provisional of aesthetic dental care. Learning Objectives: This article discusses the utilization of composite resin as a tool to enhance the patient's smile. Upon reading this article, the reader should: Become familiar with a smile-enhancing technique which can be completed in one office visit. Realize the benefits that intraoral composite mockups offer in terms of prototyping and confirming patient satisfaction.     

Static strength of molar region direct technique glass fibre-reinforced composite fixed partial dentures

The aim of this study was to determine static fracture force of fibre-reinforced composite (FRC) fixed partial dentures (FPD) with different retainer designs. The fabrication simulated the process to make directly made 3-unit maxillary molar FPD. Four types of retainers were tested (n = 5): conventional crown preparation (1.2 mm axially and 2.0 mm occlusally), slot preparation (3.5 mm high x 3.5 mm wide x 1 mm deep), no preparation with broad fibre abutment contact, and combination of the slot and broad fibre contact were performed. The FPD contained unidirectional E-glass FRC veneered with particulate reinforced composite. Dimensions of the FPDs were homogenized. FPDs were stored at 1 week 37 degrees C deionized water, thermocycled between 5 degrees C and 55 degrees C (5000 cycles, dwell time 10 s) and statically loaded to failure. The slot retainer design yielded the lowest mean load to initial and final failure (FF) (1284 and 1313 N, respectively), the crown retainer the highest mean load to initial failure at 1755 N, and the combination retainer resulted in the highest mean load to FF (1836 N) (anova, P < 0.001; Tukey multiple comparisons, 0.05 significance level). The results of this study suggest that the fabrication of direct FRC FPD does not necessarily require extensive preparation for the retainers.     

Influence of fibre position on the flexural properties and strain energy of a fibre-reinforced composite

The introduction of laboratory-processed composite systems and fibre reinforcement techniques have increased the possibilities for the prosthetic replacement of missing tooth tissues. Laboratory fabrication variables may significantly influence the properties of the final prosthesis. During the construction of a fibre-reinforced bridge it is necessary to place the fibre at some distance from the fitting surface of the restoration in the pontic region. No guidelines are available for optimal fibre placement in this respect. The purpose of this study was to assess the influence of placing ultra high molecular weight polyethylene (UHMWPE) fibre at five different distances from the tensile side of test samples on flexural properties and the strain energy stored within the dental composite. The results of this investigation showed that whilst moving the fibre reinforcement away from the tensile side by up to 1.5 mm led to a significant reduction in flexural strength, there was no significant decline in the increase in strain energy stored within the tested composite until this distance was exceeded.