Inlay-fixed partial dentures adhesively retained and reinforced by glass fibers: clinical and scanning electron microscopy analysis after five years

Biomechanical reinforcement by CAD-CAM materials affects stress distributions of posterior composite bridges: 3D finite element analysis

OBJECTIVES

This 3D finite element analysis study aimed to investigate the effect of reinforcing CAD-CAM bars on stress distribution in various components of a posterior composite bridge.

METHODS

A virtual model mimicking the absence of an upper second premolar was created, featuring class II cavity preparations on the proximal surfaces of the adjacent abutment teeth surrounding the edentulous space. Five distinct finite element analysis (FEA) models were generated, each representing a CAD-CAM reinforcing bar material: 3-YTZP (IPS. emax ZirCAD MO; Zr), lithium disilicate (IPS e.max CAD; EX), nano-hybrid resin composite (Grandio Blocs; GB), Fibre-reinforced composite (Trilor; Tri), and polyetheretherketone (PEEK). A veneering resin composite was employed to simulate the replacement of the missing premolar (pontic). In the FEA, an axial force of 600 N and a transverse load of 20 N were applied at the center of the pontic. Subsequently, maximum von Mises (mvM) and maximum principal stresses (σmax) were computed across various components of the generated models. Additionally, shear stresses at the interface between the CAD-CAM bars and the veneering resin composite were determined.

RESULTS

CAD-CAM materials with high modulus of elasticity, such as Zr and EX, exhibited the highest mvM stresses and shear stresses while transferring the lowest stress to the veneering resin composite in comparison to other materials. Conversely, PEEK demonstrated the lowest mvM stresses but produced the highest stresses within the veneering resin composite. There was a uniform distribution of mvM stresses in the remaining tooth structure among all groups, except for a noticeable elevation in the molar region of Zr and EX groups.

SIGNIFICANCE

Reinforcing CAD-CAM bar materials with a high modulus of elasticity, such as Zr and EX, may result in debonding failures at the connector sites of posterior composite bridges. Conversely, GB, PEEK, and Tri have the potential to cause fracture failures at the connectors rather than debonding.

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.

The effect of fiber insertion on fracture strength and fracture modes in endocrown and overlay restorations

Aim of this study was to determine the fracture strength and modes of endocrown and overlay restorations with/without fiber reinforcement on endodontically treated teeth. Sixty-five molar teeth were used: Group IN (intact teeth), Group E (endocrown), Group ER (endocrown + ribbond), Group O (overlay), Group OR (overlay + ribbond; n = 13). Ribbond (Seattle, WA) was inserted at the base of pulp chamber in Group ER and OR. All restorations were designed and produced by using computer-aided design and computer-aided manufacturing (Sirona Dental Systems, Bensheim, Germany) and Cerasmart (GC Corp. Kasugai, Aichi, Japan). All teeth were subjected to thermomechanical aging and fractured in a universal test device. Fractured surfaces were analyzed with a stereomicroscope (SMZ1000, Nikon, Japan). Data were analyzed with Welch's analysis of variance and Games-Howell test (p < .001). Group E showed significantly lower fracture strength values than other groups(p < .05). No statistically significant differences were found among the other groups(p > .05). Most of the unfavorable fractures were seen in Groups E and O. Overlay restorations showed higher fracture strength values than endocrown restorations. Although fiber insertion did not improve the fracture strength of the indirect restorations, it reduced the frequency of irreparable fracture mode. Overlay restorations and fiber application are more advantageous in preserving the durability of the endodontically treated teeth.

Load bearing capacity and Weibull characteristics of inlay-retained resin-bonded fixed dental prosthesis made of all-ceramic, fiber-reinforced composite and metal-ceramic after cyclic loading

PURPOSE

The objectives of this study were to evaluate the load bearing capacity of RBFDPs made of different materials after cyclic loading, and classify the failure types after loading.

MATERIALS AND METHODS

Sound human mandibular first premolars and first molar pairs (N = 60 per tooth type, n = 10 per group) were randomly divided into six experimental groups to receive one of the following inlay-retained RBFDP types: RC: Resin composite only, DFRC: Direct E-glass fiber-reinforced composite (FRC), IFRC: Indirect E-glass FRC, LS: Lithium disilicate glass-ceramic, ZR: Yttria-stabilized tetragonal zirconia, MC: Metal-ceramic. Box preparations were made in abutment teeth using diamond burs followed by standardized ultrasonic burs. The teeth were conditioned employing an etch-and-rinse adhesive system and the indirect RBFDPs were cemented adhesively. The specimens were subjected to cyclic loading for x1.200.000 in distilled water alternating between 5 and 55 °C (Zurich Chewing Simulator). They were then loaded to failure from the occlusal surface in the Universal Testing Machine (cross-head speed: 1 mm/min). Failure types were classified as repairable or irreparable depending on the location and size. Data were analyzed using Welch and Tamhane's T2 post-hoc tests (α = 0.05). Weibull modulus for each group was calculated based on parametric distribution analysis of censored data for maximum fracture load.

RESULTS

Mean load bearing capacity (N) of Groups LS (1274 ± 270), ZR (1567 ± 363) and MC (1544 ± 787) were significantly higher than those of other groups (p < 0.05). RC, DFRC, IFRC (601 ± 130 - 819 ± 270) and MC did not show significant difference (p > 0.05). Weibull modulus (m) was the highest in Group LS (m = 5.3) followed by Group RC (m = 5.1). Other groups presented Weibull moduli ranging between 1.4 and 3.3. Only in Group ZR, 2 early debonding occurred during cyclic loading. While in this group predominantly irreparable failures (debonding with without tooth fracture) were observed (8 out of 10), all other groups presented mainly single or a combination of repairable failures (chipping in the veneering material). DFRC, IDRC and MC did not show any debonding from the abutment teeth.

CONCLUSION

Considering load bearing capacity, repairable failure types and Weibull moduli, lithium disilicate seem to be more durable than those of other material options for posterior inlay-retained RBFDPs. Due to early debondings and catastrophic irreparable failure types, zirconia RBFDPs should be indicated with caution in the posterior region.

Fifteen-year outcome of posterior all-ceramic inlay-retained fixed dental prostheses

OBJECTIVES

To evaluate the long-term clinical outcome of inlay-retained fixed dental prostheses (IRFDPs) made from lithium-disilicate glass-ceramic.

MATERIAL AND METHODS

Forty-five IRFDPs were placed in 42 patients (21 women, mean age 36.1 years and 21 men, mean age 42.0 years). The IRFDPs replaced 4 premolars and 19 first molars in the maxilla and 4 premolars and 18 first molars in the mandible. All teeth were prepared following a standardized protocol for ceramic inlay restorations. Five of the 45 FDPs were hybrid-retained restorations, i.e. one abutment tooth with an inlay retainer and one with a full crown retainer. All restorations were fabricated from heat-pressed lithium-disilicate ceramic (IPS e.max Press, Ivoclar Vivadent AG). The minimal size of the proximal connector was 16 mm² (4 mm × 4 mm in height and width) with a minimum occlusal ceramic thickness of 1.5 mm. Hydrofluoric acid etching (5%) and silane application was used for conditioning the bonding surfaces. Standard adhesive luting techniques were performed using a dentin adhesive and a resin composite. Standardized follow-up reports were performed annually. The survival rates were performed using the Kaplan-Meier analysis.

RESULTS

The mean observation period was 100 months (minimum 4, maximum 234 months). Thirty-three FDPs (73%) failed during the observation period and had to be replaced by other restorations. The Kaplan-Meier survival rate for IRFDPs was 57% after 5 years, 38% after 8 years and 22% after 15 years, while for hybrid-retained FDPs it was 100% after 5 years, 60% after 8 years and also 60% after 15 years.

CONCLUSION

With the design used in the current, study lithium-disilicate ceramic IRFDP had a high clinical failure rate and cannot be recommended for regular clinical use.

Comparison of Load-Bearing Capacities of 3-Unit Fiber-Reinforced Composite Adhesive Bridges with Different Framework Designs

Background

The aim of this study was to investigate and compare the load-bearing capacities of three-unit direct resin-bonded fiber-reinforced composite fixed dental prosthesis with different framework designs.

Material/Methods

Sixty mandibular premolar and molar teeth without caries were collected and direct glass fiber-resin fixed FDPs were divided into 6 groups (n=10). Each group was restored via direct technique with different designs. In Group 1, the inlay-retained bridges formed 2 unidirectional FRC frameworks and pontic-reinforced transversal FRC. In Group 2, the inlay-retained bridges were supported by unidirectional lingual and occlusal FRC frameworks. Group 3, had buccal and lingual unidirectional FRC frameworks without the inlay cavities. Group 4 had reinforced inlay cavities and buccal-lingual FRC with unidirectional FRC frameworks. Group 5, had a circular form of fiber reinforcement around cusps in addition to buccal-lingual FRC frameworks. Group 6 had a circular form of fiber reinforcement around cusps with 2 bidirectional FRC frameworks into inlay cavities. All groups were loaded until final fracture using a universal testing machine at a crosshead speed of 1 mm/min.

Results

Mean values of the groups were determined with ANOVA and Tukey HSD. When all data were evaluated, Group 6 had the highest load-bearing capacities and revealed significant differences from Group 3 and Group 4. Group 6 had the highest strain (p>0.05). When the fracture patterns were investigated, Group 6 had the durability to sustain fracture propagation within the restoration.

Conclusions

The efficiency of fiber reinforcement of the restorations alters not only the amount of fiber, but also the design of the restoration with fibers.

Fracture behavior of single-structure fiber-reinforced composite restorations

Objective: The applications of single-structure fiber-reinforced composite (FRC) in restorative dentistry have not been well reported. This study aimed to clarify the static mechanical properties of anterior crown restorations prepared using two types of single-structure FRC. Materials and methods: An experimental crown restoration was designed for an upper anterior incisor. The restorations were made from IPS Empress CAD for CEREC (Emp), IPS e.max^® CAD (eMx), experimental single-structure all-FRC (a-FRC), Filtek™ Supreme XTE (XTE), and commercially available single-structure short-FRC (everX Posterior™) (n = 8 for each material) (s-FRC). The a-FRC restorations were prepared from an experimental FRC blank using a computer-aided design and manufacturing (CAD/CAM) device. A fracture test was performed to assess the fracture load, toughness, and failure mode. The fracture loads were vertically applied on the restorations. The surface micromorphology of the FRC restorations was observed by scanning electron microscopy (SEM). The data were analyzed by analysis of variance (p = .05) followed by Tukey's test. Results: s-FRC showed the highest mean fracture load (1145.0 ± 89.6 N) and toughness (26.2 ± 5.8 Ncm) among all the groups tested. With regard to the micromorphology of the prosthetic surface, local crushing of the fiberglass was observed in s-FRC, whereas chopped fiberglass was observed in a-FRC. Conclusions: The restorations made of short-FRC showed a higher load-bearing capacity than those made of the experimental all-FRC blanks for CAD/CAM. The brittle-like fractures were exhibited in the recent dental esthetic materials, while local crushing fractures were shown for single-structure FRC restorations.

Longevity of fiber-reinforced composite fixed partial dentures (FRC FPD)-Systematic review

OBJECTIVES

to assess FRC FPDs longevity through systematically reviewing contemporary clinical evidence. Population investigated comprised patients requiring replacement of a single missing anterior/posterior tooth. Intervention was FRC FPDs. No control/comparison selected. Outcome was longevity of FRC FPDs. The focus question was: 'What is the longevity of FRC FPDs used to replace one anterior or posterior tooth in patients?'

DATA

Randomised, non-randomised, controlled, prospective and retrospective clinical studies were included. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses were applied. The Overall Strength of Clinical Recommendation (OSCR) was assessed using the Strength of Recommendation Taxonomy system. Survival of FPDs was assessed using the Kaplan-Meier method. Analysis of FPD-survival according to location and occurrence of different failures was performed using Logrank and Chi-square testing.

SOURCES

PubMed, MEDLINE, and Web of Science databases were searched between January 2007 and December 2015.

STUDY SELECTION

Nine studies were included, involving placement of 592 FRC FPDs in 463 patients. Follow-up periods ranged between 2 months and 8 years. Kaplan-Meier overall survival probability was 94.5% (95%C.I: 92.5%-96.5%) at 4.8 years. There was no significant difference in survival probability of anterior versus posterior FRC FPDs (P=0.278). Veneering material fracture/delamination occurred significantly more than other types of failures (Ps<0.05). A meta-analysis could not be performed. OSCR was moderate.

CONCLUSIONS

FRC FPDs demonstrated high overall survival with predictable performance outcomes. However, long-term performance remains unclear.

CLINICAL SIGNIFICANCE

FRC FPDs are viable medium-term management alternatives for replacing single anterior or posterior teeth in patients.

Retrospective study on the 7.5-year survival of resin-bonded dental prostheses in single missing second premolar cases

Purpose:

The purpose of this study is to report retrospectively the clinical results of cast metal slot-retained resin-bonded fixed dental prostheses (RBFDPs) used in the restoration of single missing second premolar teeth, as this kind of prostheses provides acceptable clinical outcomes in a minimally invasive and esthetic treatment for the average patient requiring cheaper and faster treatment alternative for a single missing posterior tooth. However, the data present in the literature are scarce.

Materials and Methods:

Clinical follow-up was reported up to 7.5 years in nine different cast metal slot-retained RBFDPs patients of both genders between 21 and 49 years of age. Routine clinical controls were performed 6 and 12 months after treatment, followed by regular intervals every year afterward. The Kaplan–Meier survival estimation method was used to determine the overall and functional survival rates and times of the RBFDPs at the end of the observation period.

Results:

At the end of the follow-up, all of the RBFDPs were still functional with a mean follow-up of 6.7 years. The Kaplan–Meier estimation for the overall survival was calculated as 89% for up to 7.5 years with one failure due to debonding. The functional survival rate was 100% with the lowest and highest observation periods being 5.8 and 7.5 years, respectively.

Conclusions:

Within the limitations of this retrospective clinical study, it seems that the design and cementation regimen used for the RBFDPs presented can guarantee clinical success in the restoration of single missing second premolar teeth.

The effect of a fiber reinforced cavity configuration on load bearing capacity and failure mode of endodontically treated molars restored with CAD/CAM resin composite overlay restorations

OBJECTIVES

To evaluate the fracture strength and the mode of failure of endodontically treated molars restored with CAD/CAM overlays with fiber reinforced composite build-up of the pulp chamber.

METHODS

40 Devitalized molars were cut over the CEJ and divided into five groups (n=8). The pulp chamber area was filled with: group 0 (control), no resin build-up; group 1, hybrid composite build-up (G-aenial posterior, GC); group 2, as in group 1 but covered with 3 nets of bi-directional E-glass fibers (EverStickNET, Stick Tech Ltd.); group 3, a FRC resin (EverX posterior, GC); group 4, as in group 3 but covered by the bi-directional fibers. The crowns were restored with CAD-CAM composite restorations (Lava Ultimate, 3M ESPE). Maximum fracture loads were recorded in Newton and data were analyzed using Kruskal-Wallis test (p<0.05). Fragments were analyzed using SEM.

RESULTS

The mean static loads in Newton were: group 0: 2448 (546); group 1: 2817 (873); group 2: 2128 (952); group 3: 2429 (1091); group 4: 2577 (833). No significant differences were found between the groups (p>0.05). All specimens fractured in a catastrophic way, under the CEJ. The main crack evolved in the corono-apical direction. In groups 2 and 4 secondary fracture paths with apico-coronal direction were detected close to the bi-directional fibers' layer.

CONCLUSIONS

For the restoration of endodontically treated molars, the incorporation of FRCs did not influence the load-bearing capacity of the tooth-restoration complex. The SEM analysis showed a low ability of the bi-directional fibers net in deviating the fracture but this effect was not sufficient to lead more favorable fracture patterns, over the CEJ.

CLINICAL SIGNIFICANCE

The use of FRCs to reinforce the "core" of devitalized molars against vertical fractures under static loads seems useless when the thickness of the CAD/CAM composite overlay restoration is high.

A review of the success and failure characteristics of resin-bonded bridges

OBJECTIVES

This literature review was designed to assess and compare the success rates and modes of failure of metal-framed, fibre-reinforced composite and all-ceramic resin-bonded bridges.

MATERIALS AND METHOD

A Medline search (Ovid), supplemented by hand searching, was conducted to identify prospective and retrospective cohort studies on different resin-bonded bridges within the last 16 years. A total of 49 studies met the pre-set inclusion criteria. Success rates of 25 studies on metal-framed, 17 studies on fibre-reinforced composite and 7 studies on all-ceramic resin-bonded bridges were analysed and characteristics of failures were identified.

RESULTS

The analysis of the studies indicated an estimation of annual failure rates per year to be 4.6% (±1.3%, 95% CI) for metal-framed, 4.1% (±2.1%, 95% CI) for fibre-reinforced and 11.7% (±1.8%, 95% CI) for all-ceramic resin-bonded bridges. The most frequent complications were: debonding for metal-framed, resin-bonded bridges (93% of all failures); delamination of the composite veneering material for the fibre-reinforced bridges (41%) and fracture of the framework for the all-ceramic bridges (57%).

CONCLUSIONS

All types of resin-bonded bridges provide an effective short- to medium-term option, with all-ceramic performing least well and having the least favourable mode of failure. The methods of failures were different for different bridges with metal frameworks performing the best over time.

Fiber-reinforced resin coating for endocrown preparations: a technical report

Coronal rehabilitation of endodontically treated posterior teeth is still a controversial issue. Although the use of classical crowns supported by radicular metal posts remains widespread in dentistry, their invasiveness has been largely criticized. New materials and therapeutic options based entirely on adhesion are available nowadays, from direct composite resins to indirect endocrowns. They allow for a more conservative, faster, and less expensive dental treatment. However, the absence of a metal or high-strength ceramic substructure as in full-crown restorations can expose this kind of restoration to a higher risk of irreversible fracture in case of crack propagation. The aim of this case report is to present a technique to reinforce the cavity of an endodontically treated tooth by incorporating a fiber-reinforced composite (FRC) layer into the resin coating of the tooth preparation, before the final impressions of the cavity. This technique allows the use of FRCs in combination with any kind of restorative material for an adhesive overlay/endocrown.

Fixed partial dentures in an up to 8-year follow-up

Information on the longevity of fiber-reinforced composite fixed partial dentures (inlay FPDs) should be considered in the selection of materials, operative techniques and patient instructions related to prognosis and long-term cost-effectiveness.

Fracture resistance of short, randomly oriented, glass fiber-reinforced composite premolar crowns

The aim of this work was to determine the static load-bearing capacity of posterior composite crowns made of experimental composite resin (FC) with short fiber fillers and a semi-interpenetrating polymer network (IPN) matrix. In addition, we wanted to investigate how load-bearing capacity of surface composite resins was affected by substructures of fiber-reinforced composite (FRC) and FC, and by different curing systems. Five groups of crowns were fabricated (n=6). The crowns were either polymerized with a hand-light curing unit (LCU) or cured in a vacuum curing device (VLC) before they were statically loaded at a speed of 1mm min(-1) until fracture. Failure modes were visually examined. Data were analyzed using ANOVA. ANOVA revealed that crowns made from the FC had a statistically significant higher load-bearing capacity than the control PFC composite. Crowns with FRC substructure and PFC covering gave force values of 348N (LCU) and 1199N (VLC), respectively, which were lower than the values of FC composite. No statistically significant difference was found between crowns made from plain FC composite and those made from FC composite with a surface layer of PFC (P=0.892 and 1.00). Restorations made from short glass fiber-containing composite resin with IPN-polymer matrix showed better load bearing capacity than those made with either plain PFC or PFC reinforced with FRC substructure.

Developing meaningful systematic review of CAD/CAM reconstructions and fiber-reinforced composites

OBJECTIVE

Clinical literature was examined for evidence supporting use of CAD/CAM reconstructions and fiber-reinforced materials.

MATERIALS AND METHODS

Potential evidence was identified via databases [PubMed; EMBASE (R) Drugs & Pharmacology; Center for Reviews and Dissemination, University of York; Cochrane Library], hand search of non-indexed literature, secondary reference searches, and personal contacts with clinical trial PI's. Search terms included: dental restorations; CAD/CAM; CEREC; LAVA; CERCON; Procera; inlay/onlay; dental prosthesis; fiber-reinforced composite (FRC).

RESULTS

Two randomized-controlled clinical trials were identified as examined in one Cochrane Collaboration review relevant to CAD/CAM inlays. One systematic review of 15 CAD/CAM inlay studies was examined. Six studies were identified of three commercial FRC endodontic posts and eight reported on FRC use for fixed denture prostheses. Fifteen ongoing prospective trials were identified studying CAD/CAM fabricated zirconia-based prostheses. A total of 76 papers were referenced including those related to use of in vitro measures as evidence.

CONCLUSIONS

Review of the Cochrane analysis raised concerns that typical RCT protocols may prove insufficient for stratification of confounding variables (patient, practitioner, material) when treatment outcomes are primarily prosthesis- or material-based (not patient-based, e.g., as in fracture). RCT designs are most straightforward when treatment outcomes are patient-based (e.g., soft tissue changes). When treatment responses are material-based, controls also become difficult to define and studies become tests of equivalency/superiority; where well-stratified cohort designs are likely preferred. Large numbers of independent cohort studies support the use of CAD/CAM ceramic inlay/onlay restorations and crowns but many complications inhibit the application of high-level systematic review. Except perhaps for fiber-based endodontic posts, the clinical FRC literature appears insufficient for expert review. Single in vitro measures cannot currently serve as evidence for clinical practice, except in limited cases of simple function (e.g., impression material accuracy). Batteries of in vitro measures are often applied during materials development but cannot substitute for clinical study.

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.

Fiber-reinforced composite substructure: load-bearing capacity of an onlay restoration

OBJECTIVE

To determine the static load-bearing capacity of composite resin onlay restorations made of particulate filler composite (PFC) with two different types of fiber-reinforced composite (FRC) substructures.

MATERIAL AND METHODS

Specimens were prepared to simulate an onlay restoration, composed of a 2 to 3 mm FRC layer as the substructure (short random and continuous bidirectional fiber orientation) and a 1 mm surface layer of PFC. Control specimens were prepared from plain PFC. The specimens were incrementally polymerized with a hand-light curing unit for 40 s and then post-cured in a light-curing oven for 15 min. The specimens were cemented on dentin substrate of extracted human molars using a standard adhesive resin cementation technique. The specimens (n=8/group) were water stored either for 24 h at room temperature or for 4 weeks at 37 degrees C before they were statically loaded until fracture using a universal testing machine. Failure modes were visually examined.

RESULTS

ANOVA revealed that all specimens with FRC substructures had higher values of static load-bearing capacity than those obtained with plain PFC (p<0.001). The load-bearing capacity of all the specimens decreased after water storage (p<0.001).

CONCLUSIONS

Restorations made from a combination of FRC and PFC showed better load-bearing capacity than those obtained with PFC alone.

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.