Experimental design of FPD made of all-ceramics and fibre-reinforced composite

An overview of development and status of fiber-reinforced composites as dental and medical biomaterials

Fibr-reinforced composites (FRC) have been used successfully for decades in many fields of science and engineering applications. Benefits of FRCs relate to physical properties of FRCs and versatile production methods, which can be utilized. Conventional hand lamination of prefabricated FRC prepregs is utilized still most commonly in fabrication of dental FRC devices but CAD-CAM systems are to be come for use in certain production steps of dental constructions and medical FRC implants. Although metals, ceramics and particulate filler resin composites have successfully been used as dental and medical biomaterials for decades, devices made out of these materials do not meet all clinical requirements. Only little attention has been paid to FRCs as dental materials and majority of the research in dental field has been focusing on particulate filler resin composites and in medical biomaterial research to biodegradable polymers. This is paradoxical because FRCs can potentially resolve many of the problems related to traditional isotropic dental and medical materials. This overview reviews the rationale and status of using biostable glass FRC in applications from restorative and prosthetic dentistry to cranial surgery. The overview highlights also the critical material based factors and clinical requirement for the succesfull use of FRCs in dental reconstructions.

Mechanical properties of resin glass fiber-reinforced abutment in comparison to titanium abutment

Purpose:

So far, definitive implant abutments have been performed with high elastic modulus materials, which prevented any type of shock absorption of the chewing loads and as a consequence, the protection of the bone-fixture interface. This is particularly the case when the esthetic restorative material chosen is ceramic rather than composite resin. The adoption of an anisotropic abutment, characterized by an elastic deformability, could allow decreasing the impulse of chewing forces transmitted to the crestal bone.

Materials and Methods:

According to research protocol, the mechanical resistance to cyclical load was evaluated in a tooth-colored fiber-reinforced abutment (TCFRA) prototype and compared to that of a titanium abutment (TA), thus eight TCFRAs and eight TAs were adhesively cemented on as many titanium implants. The swinging that the two types of abutments showed during the application of sinusoidal load was also analyzed.

Results:

In the TA group, both fracture and deformation occurred in 12.5% of samples while debonding 62.5%. In the TCFRA group, only debonding was present in 37.5% of samples. In comparison to the TAs, the TCFRAs exhibited a greater swinging during the application of sinusoidal load. In the TA group, the extrusion prevailed, whereas in the TCFRA group, the intrusion was more frequent.

Conclusion:

The greater elasticity of TCFRA to the flexural load allows absorbing part of the transversal load applied on the fixture during the chewing function, thus reducing the stress on the bone-implant interface.

Effect of glass fiber incorporation on flexural properties of experimental composites

This study evaluated the effect of fiber addiction in flexural properties of 30 wt% silica filled BisGMA resin (FR) or unfilled Bis-GMA (UR). Ten groups were created (N = 10) varying the resin (FR or UR) and quantity of glass fibers (wt%: 0, 10, 15, 20, and 30). Samples (10 × 2 × 1 mm) were submitted to flexural strength test following SEM examination. Data were analyzed by two-way ANOVA, Tukey, and Student t-test (α = 0.05). Results for flexural strength (MPa) were FR-groups: 0% (442.7 ± 140.6)^C, 10% (772.8 ± 446.3)^ABC, 15% (854.7 ± 297.3)^AB, 20% (863.4 ± 418.0)^A, 30% (459.5 ± 140.5)^BC; UR-groups: 0% (187.7 ± 120.3)^B, 10% (795.4 ± 688.1)^B, 15% (1999.9 ± 1258.6)^A, 20% (1911.5 ± 596.8)^A, and 30% (2090.6 ± 656.7)^A, and for flexural modulus (GPa) FR-groups: 0% (2065.63 ± 882.15)^B, 10% (4479.06 ± 3019.82)^AB, 15% (5694.89 ± 2790.3)^A, 20% (6042.11 ± 3392.13)^A, and 30% (2495.67 ± 1345.86)^B; UR-groups: 0% (1090.08 ± 708.81)^C, 10% (7032.13 ± 7864.53)^BC, 15% (19331.57 ± 16759.12)^AB, 20% (15726.03 ± 8035.09)^AB, and 30% (29364.37 ± 13928.96)^A. Fiber addiction in BisGMA resin increases flexural properties, and the interaction between resin and fibers seems better in the absence of inorganic fillers increasing flexural properties.

Appropriateness of viscoelastic soft materials as in vitro simulators of the periodontal ligament

The periodontal ligament is a viscoelastic soft tissue that connects the tooth to the alveolar bone. This tissue should be simulated in numerical as well as in laboratory models. The mechanical properties of this tissue were previously determined ex vivo and in vivo. The aim of the study was to analyse the appropriateness of impression and reline materials used in dentistry to simulate viscoelastic behaviour of the periodontal ligament. Two reline [Durabase (Reliance Dental MFG, Co.) and Soft Liner (GC Corporation)] and two impression [President Plus (Coltene) and Prestige L (Vanini Dental Industry)] materials were examined in recovery and tensile relaxation tests. Recovery: This experiment simulated in vivo test. Roots of a pair of plastic maxillary premolar teeth were covered with each test material and embedded in acryl while maintaining the contact point. A 0·1-mm stainless steel strip, inserted at the contact point and maintained for 10 s, was used to tip the teeth. After removal, the tightness of dental contact point was measured over 30 min by determining the force needed to insert a 0·05-mm metal strip. Tensile relaxation: strips were elongated to 120%, 140% and 160% of their initial length and maintained at that length for 30 min. Two-phase decay function was applied. The results showed that elastic modulus and relaxation behaviour were significantly different between materials. Elastic modulus values were in the same range of those reported in the literature. However, the recovery values and behaviour showed that impression materials, especially President, are the materials of choice for this purpose because they simulated better the in vivo test.

Fracture strength of composite fixed partial denture using bovine teeth as a substitute for human teeth with or without fiber-reinforcement

This study evaluate the use of bovine teeth as a substitute for human teeth on fracture strength tests of composite fixed partial dentures (Cpd), with and without fiberglass reinforcement (Fg). Eighty teeth were selected, being 40 bovine incisors, 20 human premolars and 20 molars. Bovine incisors were ground to get a platform, simulating an occlusal surface of human molar. Teeth in pairs were embedded in polystyrene resin, simulating the periodontal ligament and divided in 4 groups: B-Cpd-Fg: bovine teeth restored with Cpd with Fg; B-Cpd-NFg: bovine teeth restored with Cpd without Fg; H-Cpd-Fg: human teeth restored Cpd with Fg; and H-Cpd-NFg: human teeth restored with Cpd without Fg. The Cpd were adhesively fixed and submitted to an axial compression load at the pontic center with a crosshead speed of 0.5 mm/min until fracture. Failure modes were assessed and classified. Data were subjected to two-way ANOVA and Tukey's HSD test (α=0.05). The tooth type had no influence on fracture strength and fracture mode. The inclusion of fiberglass increased significantly the fracture strength. The failure modes were more reparable in groups with fiber-reinforcement. Bovine teeth can be used as a substitute for human teeth in these types of fracture strength tests.

Comparison of load-bearing capacity of direct resin-bonded fiber-reinforced composite FPDs with four framework designs

OBJECTIVES

This in vitro study was aimed to compare the fracture resistance of directly fabricated inlay-retained fiber-reinforced composite (FRC) fixed partial dentures (FPDs) with four types of framework designs.

METHODS

Forty-eight directly fabricated inlay retained FPDs were made of FRC and particulate resin composite (everStick/Tetric flow and Ceram). Extracted human mandibular first premolars and first molars were as abutments. The following framework designs were tested: in the Group A (control group), the framework was made of two prepregs of unidirectional glass FRC; the Group B, two prepregs in pontic portion were covered with one layer of multidirectional fiber veil FRC; the Group C, the FRC prepregs were covered in pontic portion with four short unidirectional FRC pieces along the main prepregs; in Group D, one short unidirectional FRC prepregs were placed on the main prepregs in 90 degrees angle to the main framework. After thermal cycling, FPDs of each group (n=12) were randomly divided into two subgroups (n=6). Fracture test was performed at the universal testing machine (1mm/min) where FPDs were loaded from the occlusal direction to the occlusal fossa or to the buccal cusp. Failure patterns were observed with stereomicroscope. Median and 25%/75% percentile values were calculated and nonparametric analysis was performed.

RESULTS

Compared with three other framework designs, the FPDs in Group D showed the highest resistance when loading to the occlusal fossa, with maximum load of 2,353.8N (25%/75%: 2,155.5/2,500.0) (p=0.000, 0.000, and 0.005 for compared with Group A, B, and C). The same group showed also higher resistance when loaded to the buccal cusp (1,416.3N (1,409.2/1,480.8)) if compared to the FPDs of the Group A and Group C (p=0.044, 0.010). In general the FPDs showed higher resistant to loading at the occlusal fossa (p<0.05).

CONCLUSIONS

This in vitro study showed that inlay-retained FRC FPD constructed with direct technique provided high fracture resistance. The framework design that provided support for the veneering composite of the pontic contributed to the highest load-bearing capacity even when loaded to the buccal cusp.

Optimum Design for Fixed Partial Dentures Made of Hybrid Resin with Glass Fiber Reinforcement by Finite Element Analysis: Effect of Vertical Reinforced Thickness on Fiber Frame

By means of finite element analysis, the optimal thickness of fiber framework placed in a fiber-reinforced composite bridge replacing the mandibular first molar was obtained. Test results demonstrated that more than 30% maximum principal stress was reduced by reinforcing with fiber framework in a thickness of up to 0.6 mm for 1.5-mm occlusal clearance. Indeed, maximum principal stress generated in lower embrasure of connectors was reduced from 107 MPa to 70 MPa by maximizing reinforcement effect.

Bonding of ceramic insert to a laboratory particle filler composite

The push-out bond strength of cylindrical ceramic inserts (CI) to particulate filler resin composite (VC) was evaluated in this study. Various surface treatments to improve the adhesion of CI to resin composite were tested. Additionally, the effect of fiber-reinforced composite (FRC) laminate encapsulation around CI was tested. Feldspathic porcelain CI with a diameter of 3.1 mm was bonded to VC. Adhesive resin was used for bonding. In group 1, no surface treatment of CI was done. In group 2, CI was encapsulated with a thin layer of woven glass FRC. In group 3, the surface of the CI was tribochemically silica coated and silanized. In group 4, the surface of the CI was grit-blasted with 50 microm aluminum oxide and etched with hydrofluoric acid. In group 5, the grit-blasted CI was encapsulated with a layer of FRC. The specimens (n = 6/group) were either dry stored or thermocycled in water (6000 x 5-55 degrees C). The push-out test was carried out with a universal material testing machine. The highest push-out strength was achieved in group 5 (20.4 MPa) and the lowest in group 2 (11.5 MPa). ANOVA revealed that both surface treatment and storage condition had a significant effect on push-out strength (p < 0.05). We conclude that the additional glass FRC encapsulation can be used to increase the bond strength of insert to composite.

Fibre reinforced composite dental bridge. Part I: Experimental investigation

This experimental investigation aims at revealing the mechanical behaviour and failure pattern of direct fibre-reinforced resin-bonded dental bridge with various designs. To evaluate the overall effects of some newly developed dental materials, in the experiment, genuine composite dental bridge specimens are prepared and tested. The ultimate load, stiffness and mode at the failure of the bridges are measured and compared with the design variations. A good agreement between test and some clinical observations is demonstrated. It is verified that the weakest region appears across the pontic-abutment interface in the composite bridges. This study suggests that the composite bridges reinforced by fibres and supported by adjacent teeth could be of a higher structural strength and stiffness; therefore would provide better clinical performances.

Fatigue resistance and stiffness of glass fiber-reinforced urethane dimethacrylate composite

STATEMENT OF PROBLEM

Retentive properties of cast metal clasps decrease over time because of metal fatigue. Novel fiber-reinforced composite materials are purported to have increased fatigue resistance compared with metals and may offer a solution to the problem of metal fatigue.

PURPOSE

The aim of this study was to investigate the fatigue resistance and stiffness of E-glass fiber-reinforced composite.

MATERIAL AND METHODS

Twelve cylindrical fiber-reinforced composite test cylinders (2 mm in diameter and 60 mm in length) were made from light-polymerized urethane dimethacrylate monomer with unidirectional, single-stranded, polymer preimpregnated E-glass fiber reinforcement. Six cylinders were stored in dry conditions and 6 in distilled water for 30 days before testing. Fatigue resistance was measured by a constant-deflection fatigue test with 1 mm of deflection across a specimen span of 11 mm for a maximum of 150,000 loading cycles. The resistance of the cylinder against deflection was measured (N) and the mean values of the force were compared by 1-way analysis of variance (alpha = .05). The flexural modulus (GPa) was calculated for the dry and water-stored cylinders for the first loading cycle. Scanning electron microscopy was used to assess the distribution of the fibers, and the volume percent of fibers and polymer were assessed by combustion analysis.

RESULTS

The test cylinders did not fracture due to fatigue following 150,000 loading cycles. Flexural modulus at the first loading cycle was 18.9 (+/- 2.9) GPa and 17.5 (+/- 1.7) GPa for the dry and water-stored cylinders, respectively. The mean force required to cause the first 1-mm deflection was 33.5 (+/- 5.2) N and 37.7 (+/- 3.6) N for the dry and water stored cylinders, respectively; however, the differences were not significant. After 150,000 cycles the mean force to cause 1-mm deflection was significantly reduced to 23.4 (+/- 8.5) N and 13.1 (+/- 3.5) N, respectively (P < .0001). Scanning electron microscopy highlighted fiber- and polymer-rich areas within the specimens and indicated that individual fibers were well impregnated with resin. The combustion analysis studies identified the fiber content to be 35.9 vol%.

CONCLUSION

The results of this study suggest that the fatigue resistance of the fiber-reinforced material examined was increased; however, the reduction in flexural modulus of fiber-reinforced composites may restrict their use where high rigidity is required, such as in removable partial denture clasps.

Effects of two preparation designs and pontic distance on bending and fracture strength of fiber-reinforced composite inlay fixed partial dentures

STATEMENT OF PROBLEM

Joint fractures observed in Targis/Vectris inlay adhesive fixed restorations may be related to the preparation design.

PURPOSE

This in vitro study investigated the effects of the proximal tooth preparation design and the pontic distance on the fracture strength and the amount of bending of fiber-reinforced inlay adhesive fixed partial dentures.

MATERIALS AND METHODS

Forty extracted premolars and 40 molars were embedded in a PMMA resin to represent a premolar and molar mesiodistal separation distance of 7 mm and 11 mm, respectively. Two preparation designs were used (proximal box and tub-shaped). The sample size was 10 for each group. Fiber-reinforced inlay adhesive fixed partial dentures were fabricated by use of the Targis/Vectris system and luted adhesively to the teeth with Variolink luting agent. A vertical force was loaded to the center of the fixed partial dentures at a crosshead speed of 1 mm/min. The initial bending (mm) prior to fracture was evaluated by measuring the distance the test rod moved from a 10 N preload to fracture. The differences in the mean fracture strength and the average amount of bending as a function of the preparation designs and pontic distances were compared by use of a 2-way analysis of variance (alpha=.05). The specimens were examined optically for the type of failure with a stereomicroscope. The fracture surface of the specimens was examined by scanning electron microscopy, and radiography was used to investigate the surface morphological features at the failure sites and to determine the fracture mode. A chi-square test was used to identify the differences in the debonding rates between the types of preparation designs and the pontic distance (alpha=.05).

RESULTS

The mean fracture strength and the standard deviation of the fiber-reinforced inlay retained adhesive fixed partial denture group was 1368+/-212 N for the 7-mm tub group, 885+/-109 N for the 11-mm tub group, 1779+/-317 N for the 7-mm box group, and 1336+/-281 N for the 11-mm box group. The fracture strength was significantly higher in the 7-mm pontic distance (P<.001) and for the box-shaped tooth preparation (P<.001). The amount of bending was significantly greater in the 7-mm pontic distance (P=.025) and the box-shaped tooth preparation (P=.002). Debonding was observed only in premolar teeth and tub-shaped design groups.

CONCLUSION

The box-shaped tooth preparation may be considered for restoration of a missing single posterior tooth with fiber-reinforced inlay adhesive fixed partial dentures.

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.

Clinical evaluation of fiber-reinforced fixed bridges

BACKGROUND

This study evaluated the clinical performance of 39 light and heat polymerized fixed partial bridges made with a substructure of preimpregnated, unidirectional fiber-reinforced composite, or FRC, veneered with a hybrid particu late composite.

METHODS

The authors evaluated 22 extracoronal, full-coverage retainer prostheses and 17 intracoronal, partial-coverage retainer prostheses placed over a 37-month period. All substructures initially were fabricated with a low-volume FRC. The authors reevaluated this design after early failures occurred, leading to a substructure with a higher volume of FRC. All prostheses were assessed for surface integrity, anatomical contour, marginal integrity and structural integrity at several intervals.

RESULTS

The data show that survival was associated primarily with substructure design volume. When patients with severe parafunctional habits were excluded, the survival rate was 95 percent for prostheses made with a high-volume substructure (survival range, 2.77 to 4.30 years; mean +/- standard deviation survival, 3.75 +/- 0.4 years). Retainer configuration did not have a statistically significant influence on clinical survival. For all surviving prostheses, the authors observed few changes in any clinical parameters from baseline to 48 months. A loss of surface luster was observed in the majority of cases. Repairable surface defects were detected on two prostheses at 24 months. Scanning electron microscopic analyses indicated no exposed fibers on the occlusal surface and minimal wear.

CONCLUSIONS

This study shows that a unidirectional, preimpregnated FRC can be used successfully to make bridges of variable retainer designs that last up to four or more years when a high-volume substructure is used.

CLINICAL IMPLICATIONS

Short-span polymer prostheses made with particulate composite and unidirectional glass FRC can be used in certain clinical situations in which a metal substructure is not desired.

Stress distribution of inlay-anchored adhesive fixed partial dentures: a finite element analysis of the influence of restorative materials and abutment preparation design

STATEMENT OF PROBLEM

Indirect composite or ceramic fixed partial dentures (FPDs) have become an alternative to conventional metal-ceramic adhesive fixed partial dentures (AFPDs). Little information about the adequate restorative material and tooth preparation design for inlay-anchored AFPDs is available to the clinician.

PURPOSE

The purposes of this simulation study were: (1) to use 2-dimensional finite element modeling to simulate stresses at the surface and interface of 3-unit posterior AFPDs made with 6 different restorative materials, and (2) to investigate the influence of 3 different abutment preparation configurations on the stress distribution within the tooth/restoration complex.

MATERIAL AND METHODS

A mesio-distal cross-section of a 3-unit AFPD was digitized and used to create 2-dimensional models of the periodontal membrane, supporting bone, different restorative materials (gold, alumina, zirconia, glass-ceramic, composite, and fiber-reinforced composite), and different abutment preparation configurations (interproximal slots vs. 2-surface [MO, DO] vs. 3-surface [MOD]). A simulated 50-N vertical occlusal load was applied to the standardized pontic element. The principal stress within the restorative materials, stresses at the tooth/restoration interface, and surface tangential stresses at the level of the pontic were calculated in MPa from the postprocessing files and compared to each other.

RESULTS

All materials and tooth preparation design exhibited a similar stress pattern, with a definite compressive area at the occlusal side of the pontic, a tensile zone at the gingival portion of the pontic, and tensile stress peaks in the abutment/pontic connection areas. Among isotropic materials, standard non-reinforced composites exhibited better stress transfer and reduced tensile stresses at the adhesive interface than ceramics and gold. Optimized placement of the glass fibers within the composite resulted in similar stress distribution when tested in 2-surface abutment preparation configuration. There was no detectable influence of preparation design on the behavior of the pontic area. Among all 3 preparation designs, only the DO design exhibited almost pure compression at the interface.

CONCLUSION

Within the limitations of this simulation experiment, the composite materials tested demonstrated a resilient component that favored stress transfer within the tooth/restoration complex. Their clinical use, however, may be contraindicated due to insufficient strength and fracture toughness. The addition of extremely tough fibers to composites represents the most promising combination. Clinical trials are required to ensure that veneering composite can survive under clinical conditions.