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

Shape optimization of a 2-unit cantilevered posterior resin-bonded fixed dental prosthesis

STATEMENT OF PROBLEM

The cantilevered resin-bonded fixed dental prosthesis (RBFDP) is a feasible and minimally invasive treatment option to restore a single missing tooth, especially when the missing tooth space is small (<7 mm) and cost-effectiveness is essential. However, its long-term survival needs to be improved by increasing its structural strength and interfacial adhesion.

PURPOSE

The purpose of this study was to improve the interfacial bonding and to enhance the structural strength of a 2-unit inlay-retained cantilevered RBFDP with a 2-step numerical shape optimization.

MATERIAL AND METHODS

A finite element model of a mandibular first molar with a second premolar pontic was constructed. A load of 200 N simulating the average occlusal force was applied on the mesial fossa of the pontic. In the first step, an in-house user-defined material subroutine was used to generate the cavity preparation. The subroutine iteratively changed the tooth tissues next to the pontic to composite resin according to the local stresses until convergence was achieved. In the second step, the subroutine was used to optimize the placement of fibers in the pontic by placing fibers in high-stress regions. To assess the debonding resistance and load capacity of the optimized and conventional designs, further analyses were conducted to compare their stresses at the tooth-restoration interface and those within the restoration.

RESULTS

Shape optimization resulted in a shovel-shaped cavity preparation and a pontic with fibers placed near the occlusal surface of the connector region. With the optimized cavity preparation only, the maximum principal stress within the restoration and the tooth structure was reduced from 639.4 MPa to 525.4 MPa and from 381.7 MPa to 352.8 MPa, respectively. With the embedded fibers, the shovel-shaped cavity preparation reduced the maximum interfacial tensile stress by approximately 70% (conventional: 189.6 MPa versus optimized: 57.0 MPa) and the peak maximum principal stress of the veneering composite resin by 45% (conventional: 638.8 MPa versus optimized: 356.5 MPa). The peak maximum principal stress was also reduced for the remaining tooth structure by approximately 30% (conventional: 372.2 MPa versus optimized: 253.1 MPa).

CONCLUSIONS

Shape optimization determined that a shovel-shaped retainer with fibers placed near the occlusal surface of the connector area can collectively reduce the interfacial and structural stresses of the 2-unit cantilevered fiber-reinforced RBFDP. This may offer a more conservative treatment option for replacing a single missing tooth.

Validation of a shape-optimized 2-unit cantilevered inlay-retained fiber-reinforced resin-bonded dental prosthesis

STATEMENT OF PROBLEM

Current designs of fiber-reinforced composite (FRC) resin-bonded fixed dental prostheses (RBFDPs) have a limited lifespan, failing mainly through veneer-fiber delamination, debonding, and fracture.

PURPOSE

The purpose of this in vitro study was to validate a new inlay-retained 2-unit cantilevered RBFDP with an optimized cavity and fiber layout proposed in a previous study by using simulated occlusal loading.

MATERIAL AND METHODS

Two groups of specimens (n=20), 1 with and 1 without glass fibers, were used to test the influence of the cavity design and that of the fiber layout on their load capacity, respectively. The specimens without fibers were directly cut from a resin-ceramic block by using a computer-aided manufacturing system, while those with fibers were manually fabricated with unidirectional glass fibers and composite resin in a silicone mold. The specimens with and without fibers were attached to abutments made of the same resin-ceramic with a cyanoacrylate-based adhesive and a resin-based dental cement, respectively. An increasing compressive load was applied on the mesial fossa of the premolar pontic until failure. Cracking in the specimens during loading was monitored with a 2-channel acoustic emission (AE) system.

RESULTS

All the specimens without fiber reinforcement debonded from the abutments. Those using the optimized shovel-shaped cavity design had a mean ±standard deviation failure load (50.0 ±17.3 N) that was 193% higher than that of those with the conventional step-box design (17.1 ±6.2 N; P<.001). No significant difference was found between the groups for the mean number of AE events per specimen (step-box: 49 ±34 versus shovel-shaped: 63 ±34; P=.427), the mean amplitude of each event (58.4 ±1.3 dB versus 59.5 ±2.4 dB; P=.299), or the mean time to failure (283.2 ±122.3 seconds versus 297.5 ±66.7 seconds; P=.798). Between the groups of specimens with reinforcing fibers, the mean failure load of the conventional design was approximately half that of the optimized one. Again, no significant difference was found for the mean number of AE events per specimen (conventional: 28 ±18 versus optimized: 52 ±53; P=.248) or the mean amplitude for each AE event (64.9 ±4.2 dB versus 61.7 ±5.2 dB; P=.187). The connectors of 8 fiber-reinforced specimens with the conventional design fractured; the other 2 debonded from the abutments. Half of the shape-optimized fiber-reinforced specimens had fractured abutments, but the cantilevers remained intact, 4 specimens fractured at the connector, and only 1 debonded from its abutment.

CONCLUSIONS

The shape-optimized 2-unit cantilevered FRC RBFDP had a higher load capacity than the conventional design.

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.

Direct Fiber-Reinforced Interim Fixed Partial Dentures: Six-Year Survival Study

PURPOSE

Mechanical and optical studies of glass fiber composites have revealed great resistance and satisfactory bonds between the glass fibers and composite resins. This study aimed to evaluate the long-term survival of anterior and posterior direct glass fiber-reinforced composite (FRC) fixed partial dentures (FPD).

MATERIALS AND METHODS

Twenty-three patients (9 men, 14 women) aged 18 to 67 received 23 d-FRC-FPDs. The frameworks of the FPDs were unidirectional pre-impregnated glass fibers (ever Stick C&B). The retainers were inlay composite resin retainers (n1 = 19) and composite resin wings (n2 = 4). The FPD that used inlay retainers and composite resin wing retainers was called the hybrid design. The mean follow-up period was 4.91 years with 12-month check-ups performed by two independent operators. The survival rates of the glass fiber FPDs were determined.

RESULTS

Six-year survival rates for the two types of FPDs were 94.7% for the inlay retainer type versus 25% for the hybrid type, with a statistically significant difference (log-rank test χ² (1) = 11.422, p = 0.001). The inlay retainers were functional, with only one patient with a fracture line in the connector held by the glass fibers. Kaplan-Meier survival curves were drawn to show the difference between the two types of retainers.

CONCLUSION

According to the results of this study, these long-term interim FRC-FPD were resistant enough to allow mastication, minimally invasive and also esthetic, with inlay composite retainers as the better solution.

Covering of fiber-reinforced composite bars by adhesive materials, is it necessary to improve the bond strength of lingual retainers?

Objectives:

The objectives were to evaluate the shear bond strength (SBS) of fiber-reinforced composite (FRC) retainers when bonding them to teeth with and without covering the FRC bars using two different adhesive systems.

Materials and Methods:

Hundred and twenty extracted human maxillary premolars were randomly divided into eight groups (n = 15). FRC bars (4 mm length, Everstick Ortho^®, Stick Tech, Oy, Turku, Finland) were bonded to the proximal (distal) surfaces of the teeth using two different adhesives (Tetric Flow [TF, Ivoclar Vivadent, Switzerland] and resin-modified glass ionomer cement [RMGIC, ODP, Vista, CA, USA]) with and without covering with the same adhesive. Specimens were exposed to thermocycling (625 cycles per day [5–55°C, intervals: 30 s] for 8 days). The SBS test was then performed using the universal testing machine (Zwick, GMBH, Ulm, Germany). After debonding, the remaining adhesive on the teeth was recorded by the adhesive remnant index (0–3).

Results:

The lowest mean SBS (standard deviation) was found in the TF group without covering with adhesive (12.6 [2.11] MPa), and the highest bond strength was in the TF group with covering with adhesive (16.01 [1.09] MPa). Overall, the uncovered RMGIC (15.65 [3.57] MPa) provided a higher SBS compared to the uncovered TF. Covering of FRC with TF led to a significant increase in SBS (P = 0.001), but this was not true for RMGIC (P = 0.807). Thermal cycling did not significantly change the SBS values (P = 0.537). Overall, eight groups were statistically different (ANOVA test, F = 3.32, P = 0.034), but no significant differences in bond failure locations were found between the groups (Fisher's exact tests, P = 0.92).

Conclusions:

The present findings showed no significant differences between SBS of FRC bars with and without covering by RMGIC. However, when using TF, there was a significant difference in SBS measurements between covering and noncovering groups. Therefore, the use of RMGIC without covering FRC bars can be suggested, which can be validated with in vivo studies.

Effect of different design preparations on the flexural and fracture strength of fiber-reinforced composite fixed partial dentures: an in vitro study

PURPOSE

To determine and compare the flexural and fracture strength of three-unit fiber-reinforced composite (FRC) fixed partial dentures (FPDs) using three abutment design preparations.

MATERIAL AND METHODS

The flexural and fracture strength of three-unit FRC FPDs were evaluated using three design preparations of the abutments (conventional full crown [group A], box-shaped [group B], and tub-shaped [group C]). Thirty three-unit FRC FPDs were fabricated (10 specimens per group) for the replacement of missing mandibular first molars and were adhesively luted to extracted human teeth. The flexural and fracture strength were determined using a universal testing machine with a steel loading pin of 20 mm diameter with a 3-mm-diameter hardened circular tip. Each specimen was evaluated under SEM to determine mode of failure.

RESULTS

Mean fracture strength for group A was 820.00 ± 56.51 N, group B was 536.94 ± 65.62 N, and group C was 501.24 ± 66.71 N. The highest mean flexural strength was found in group A (68.33 ± 4.71 MPa), followed by group B (44.74 ± 5.46 MPa) and lowest in group C (41.77 ± 5.56 MPa). The SEM evaluation showed partial or complete debonding of veneering composite from fiber framework, leaving intact fiber frameworks in all the specimens.

CONCLUSION

Full-coverage design had significantly higher flexural and fracture strengths than box and tub-shaped designs. Since both values were noted to be in the order of masticatory stresses, the full coverage design is a good alternative for the replacement of missing molar teeth; however, the framework veneering composite interface was the weakest phase of FRC FPDs, thus indicating that further improvement in veneering composite or fiber framework is needed to improve the compatibility of veneering composite with that of fiber framework for long-term clinical implications.

Single visit replacement of maxillary canine using fiber-reinforced composite resin

Missing a canine is of serious concern in social life of a patient in most of societies. While conventional fixed partial dentures and implant-supported restorations may often be the treatment of choice, fiber-reinforced composite (FRC) resins offer a conservative, fast and cost-effective alternative for single and multiple teeth replacement. This clinical report presents two cases where FRC technology was successfully used to restore canine edentulous area in terms of esthetic-cosmetic values and functionality.

In vitro validation of a shape-optimized fiber-reinforced dental bridge

OBJECTIVE

To improve its mechanical performance, structural optimization had been used in a previous study to obtain an alternative design for a 3-unit inlay-retained fiber-reinforced composite (FRC) dental bridge. In that study, an optimized layout of the FRC substructure had been proposed to minimize stresses in the veneering composite and interfacial stresses between the composite and substructure. The current work aimed to validate in vitro the improved fracture resistance of the optimized design.

METHODS

All samples for the 3-unit inlay-retained FRC dental bridge were made with glass-fibers (FibreKor) as the substructure, surrounded by a veneering composite (GC Gradia). Two different FRC substructure designs were prepared: a conventional (n=20) and an optimized design (n=21). The conventional design was a straight beam linking one proximal box to the other, while the optimized design was a curved beam following the lower outline of the pontic. All samples were loaded to 400N on a universal test machine (MTS 810) with a loading speed of 0.2mm/min. During loading, the force and displacement were recorded. Meanwhile, a two-channel acoustic emission (AE) system was used to monitor the development of cracks during loading.

RESULTS

The load-displacement curves of the two groups displayed significant differences. For the conventional design, there were numerous drops in load corresponding to local damage of the sample. For the optimized design, the load curves were much smoother. Cracks were clearly visible on the surface of the conventional group only, and the directions of those cracks were perpendicular to those of the most tensile stresses. Results from the more sensitive AE measurement also showed that the optimized design had, on average, fewer cracking events: 38 versus 2969 in the conventional design.

SIGNIFICANCE

The much lower number of AE events and smoother load-displacement curves indicated that the optimized FRC bridge design had a higher fracture resistance. It is expected that the optimized design will significantly improve the clinical performance of FRC bridges.

Resin-bonded fiber-reinforced composite for direct replacement of missing anterior teeth: a clinical report

Missing anterior teeth is of serious concern in the social life of a patient in most of societies. While conventional fixed partial dentures and implant-supported restorations may often be the treatment of choice, fiber-reinforced composite (FRC) resins offer a conservative, fast, and cost-effective alternative for single and multiple teeth replacement. This paper presents two cases where FRC technology was successfully used to restore anterior edentulous areas in terms of esthetic values and functionality.

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.

Use of short fiber-reinforced composite with semi-interpenetrating polymer network matrix in fixed partial dentures

OBJECTIVES

The aim of this study was to determine the static load-bearing capacity of fixed partial dentures (FPDs) made of experimental composite resin (FC) with short fiber fillers and interpenetrating polymer network (IPN) polymer matrix.

MATERIALS AND METHODS

Experimental composite FC resin was prepared by mixing short E-glass fibers (3mm in length) of 22.5wt% and IPN-resin 22.5wt% with silane treated silica fillers 55wt%. Four groups of FPDs (3-unit) were fabricated (n=6); Group A: made from commercial composite resin (Sinfony dentin, 3M-ESPE, control), Group B: Sinfony and fiber-reinforced composite (FRC) substructure, Group C: made from FC, Group D: made from FC with 1mm surface layer of Sinfony. The bridges were polymerized with a hand-light curing unit for 40s then post-cured in vacuum curing device (Visio Beta) for 15min before they were statically loaded with speed of 1mm/min until fracture. Failure modes were visually examined. Data were analyzed using ANOVA (p=0.05).

RESULTS

ANOVA revealed that bridges made from experimental fiber composite had statistically significantly higher load-bearing capacity (2171N) (p<0.05) than the control restorations (1482N).

SIGNIFICANCE

Restorations made from short glass fiber containing composite resin with IPN-polymer matrix showed better load bearing capacity than in those made with conventional composites resin and similar with those reinforced with FRC-substructure.

Mechanical properties of woven glass fiber-reinforced composites

The aim of this investigation was to measure the flexural and compressive strengths and the corresponding moduli of cylindrical composite specimens reinforced with woven glass fiber. Test specimens were made by light-curing urethane dimethacrylate oligomer with woven glass fiber of 0.18-mm standard thickness. Tests were conducted using four reinforcement methods and two specimen diameters. Flexural strength and modulus of woven glass fiber-reinforced specimens were significantly greater than those without woven glass fiber (p < 0.01). Likewise, compressive strength of reinforced specimens was significantly greater than those without woven glass fiber (p < 0.01), except for specimens reinforced with woven glass fiber oriented at a tilt direction in the texture (p > 0.05). In terms of comparison between the two specimen diameters, no statistically significant differences in flexural strength and compressive strength (p > 0.05) were observed.