Fracture resistance of direct inlay-retained adhesive bridges: Effect of pontic material and occlusal morphology

Fatigue Resistance of Dissected Lower First Molars Restored with Direct Fiber-Reinforced Bridges—An In Vitro Pilot Study

The aim of this research was to evaluate the mechanical impact of utilizing different fiber-reinforced composite (FRC) systems to reinforce inlay-retained bridges in dissected lower molars with different levels of periodontal support. A total of 24 lower first molars and 24 lower second premolars were included in this study. The distal canal of all molars received endodontic treatment. After root canal treatment, the teeth were dissected, and only the distal halves were kept. Standardized class II occluso-distal (OD) (premolars) and mesio-occlusal (MO) (dissected molars) cavities were prepared in all teeth, and premolar–molar units were created. The units were randomly distributed among four groups (n = six/group). With the aid of a transparent silicone index, direct inlay-retained composite bridges were fabricated. In Groups 1 and 2, both discontinuous (everX Flow) and continuous (everStick C&B) fibers were used for reinforcement, while in Groups 3 and 4, only discontinuous fibers (everX Flow) were used. The restored units were embedded in methacrylate resin, simulating either physiological periodontal conditions or furcation involvement. Subsequently, all units underwent fatigue survival testing in a cyclic loading machine until fracture, or a total of 40,000 cycles. Kaplan–Meyer survival analyses were conducted, followed by pairwise log-rank post hoc comparisons. Fracture patterns were evaluated visually and with scanning electron microscopy. In terms of survival, Group 2 performed significantly better than Groups 3 and 4 (p < 0.05), while there was no significant difference between the other groups. In the case of impaired periodontal support, a combination of both continuous and discontinuous short FRC systems increased the fatigue resistance of direct inlay-retained composite bridges compared to bridges that only contained short fibers. Such a difference was not found in the case of sound periodontal support between the two different bridges.

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.

Short communication: Influence of restorative material and cement on the stress distribution of posterior resin-bonded fixed dental prostheses: 3D finite element analysis

The goal of this study was to compare the mechanical response of resin-bonded fixed dental prosthesis (RBFDP) made in zirconia, metal, lithium disilicate and composite resin cemented using resin cements with different elastic modulus. For the finite element analysis, a three-dimensional model of partial right maxilla was used to create a model with edentulous space in the second premolar and the cavity's preparation on the first pre-molar and first molar to receive a RBFDP. The model was imported to the analysis software in which they were divided into mesh composed by nodes (371,101) and tetrahedral elements (213,673). Each material was considered isotropic, elastic and homogeneous. No-separation contacts were considered between restoration/resin cement and resin cement/tooth. For all other structures the contacts were considered ideal. The model fixation occurred at the base of the bone and an axial load of 300 N was applied on the pontic occlusal surface. To simulate polymerization shrinkage effects on the cement, the thermal expansion approach was used. The displacement and maximum principal stress (in MPa) were selected as failure criteria. The prosthesis made in composite resin showed higher displacement, while in zirconia showed higher stress concentration. Tensile stress between restoration/cement, cement and cement/cavity was directly proportional to the restorative material's elastic modulus. The more rigid cement increases the tensile zones in the cement layer but decreases the stress between prosthesis and cement. The molar cavity showed higher stress concentration between restoration/cement than the preparation in the pre-molar tooth. The use of composite resin for the manufacturing of RBFDP increases the displacement of the set during the loading. However, it reduces the amount of stress concentration at the adhesive interface in comparison with the other materials.

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.

Load-bearing capacity of novel resin-based fixed dental prosthesis materials

To evaluate the influence of different materials on the load-bearing-capacity of inlay-retained fixed-dental-prosthesis (FDP). Ten types of FDPs were evaluated (n=7/group): Group PEEK: CAD-CAM polyetheretherketone (PEEK-TechnoMed), Group RC, made of discontinuous-fiber-composite (EverX Posterior); Group FRC1, made of discontinuous-fiber-composite (EverX Posterior) with two-bundles of continuous-unidirectional fiber-reinforced-composite (FRC) (Everstick C&B); Group FRC2, made of discontinuous-fiber-composite (EverX Posterior) with two-bundles of continuous-unidirectional-FRC (Everstick C&B) covered by two-pieces of short-unidirectional-FRC (Everstick C&B) placed perpendicular to the main-framework; Group FB, CAD-CAM fiber-block (Fibra-Composite Bio-C); Group PMMA, CAD-CAM polymethyl methacrylate block (Temp basic); Group RP, resin-paste; Group FRP1, made of resin-paste (G-Fix) with two-bundles of continuous-unidirectional-FRC (Everstick C&B); Group FRP2, made of resin-paste (G-Fix) two-bundles of continuous-unidirectional-FRC covered by two-pieces of short unidirectional-FRC placed perpendicular to the main-framework and Group exp-FRC, experimental CAD-CAM FRC. The bridges were statically-loaded until fracture. Fracture modes were visually examined. ANOVA revealed that significant differences were observed between FDP-materials (p<0.05). In addition, fiber addition to the framework significantly affected load-bearing-capacity (p<0.05).