Evaluation of fracture behavior in short fiber-reinforced direct and indirect overlay restorations.

OBJECTIVES: The aim was to assess how incorporating a short-fiber composite (SFC) core would affect the fracture behavior of direct and indirect overlays. Furthermore, to examine the relationship between the thickness ratio of SFC core to particulate-filled composite (PFC) veneering and the fracture-behavior of bilayered-structured restorations. MATERIALS AND METHODS: A total of 120 molars were used to create MOD cavities, with palatal cusps removed. Four different groups of direct overlays were then made (n = 15/group), all of which featured a SFC core (everX Flow) with varying thicknesses (0, 1, 4, and 5 mm), as well as a surface layer of PFC (G-aenial Posterior), with the overall thickness of the bilayered-structured restoration set at 5 mm. Additionally, four groups of CAD/CAM restorations were created (Cerasmart 270 and Initial LiSi Block), with or without 2 mm of SFC core reinforcement. Following the fabrication of these restorations, cyclic fatigue aging was carried out for a total of 500,000 cycles, with an applied maximum load (Fmax) of 150 N. Subsequently, each restoration underwent quasi-static loading until fracture. The fracture mode was subsequently evaluated using optical microscopy and SEM. RESULTS: There were no statistically significant differences (p > 0.05) observed in the fracture resistance of indirect overlays reinforced with a 2-mm SFC core compared to those made solely from restorative materials. Direct overlays constructed using plain SFC or with a 4-mm layer thickness of SFC core exhibited significantly higher fracture resistance values (2674 ± 465 and 2537 ± 561 N) (p < 0.05) when compared to all other groups tested, according to the statistical analysis ANOVA. CONCLUSIONS: The most effective method for restoring large MOD cavities was found to be direct restoration using SFC either alone or as a bulk core in combination with PFC composite. CLINICAL RELEVANCE: The use of SFC as bulk reinforcing base will significantly improve the loading performance of directly layered restorations.

Influence of short-fiber composite base on fracture behavior of direct and indirect restorations.

OBJECTIVES: The aim was to examine the influence of short-fiber composite (SFC) core on the fracture-behavior of different types of indirect posterior restorations. In addition, the effect of thickness ratio of SFC-core to the thickness of the veneering conventional composite (PFC) on fracture-behavior of bi-structured composite restorations was evaluated. MATERIALS AND METHODS: MOD cavities with removed palatal cusps were prepared on 90 intact molars. Five groups of direct overlay restorations (n = 10/group) were fabricated having a SFC-core (everX Flow) with various thicknesses (0, 1, 2, 3, 4 mm) and layer of surface PFC (G-aenial Anterior), remaining the thickness of the bi-structure restoration to be 5 mm. Four groups of CAD/CAM-made restorations (Cerasmart 270 and e-max CAD) were fabricated either with 2-mm layer of SFC-core or without fiber reinforcement. Intact teeth (n = 10) were used as control group. Restorations were statically loaded until fracture. Fracture patterns were evaluated visually. Data were analyzed using ANOVA (p = 0.05). RESULTS: With indirect overlay restorations, no statistically significant differences (p > 0.05) were observed in the load-bearing capacities between restorations reinforced by 2-mm SFC-core (bi-structured) and those fabricated from plain restorative materials. ANOVA displayed that direct overlay restorations made from 4-mm layer thickness of SFC-core had significantly higher load-bearing capacities (3050 ± 574 N) (p < 0.05) among all the groups tested. CONCLUSIONS: Restorations (direct/indirect) combining SFC-core and a surface layer of conventional material demonstrated encouraging achievement in reference to fracture behavior. CLINICAL RELEVANCE: The use of flowable short-fiber composite as reinforcing base with large direct and indirect restorations may result in more repairable failure.

Original and Repair Bulk Fracture Resistance of Particle Filler and Short Fiber-Reinforced Composites.

OBJECTIVE: This study aimed to evaluate the original (OR) and repair (RR) fracture resistance of a semi-interpenetrating polymer network (semi-IPN)-based short fiber-reinforced composite compared to dimethacrylate-based composite materials by means of the V-notch test. METHODS AND MATERIALS: Circular specimens (5×2 mm) with a centrally machined 90° V-shaped notch were prepared. Four bulk fill (Filtek Bulk Fill, Venus Bulk Fill, TetricEvo Ceram Bulk Fill, SDR), three microfilled hybrid (GC-Anterior, GC-Posterior, Z250), one nanofilled (SupremeXTE), and two short fiber-reinforced (Alert, everX Posterior) composites were selected. EverX Posterior was the semi-IPN material. Specimens (n=12/group) were either dry or water stored for 7 and 30 days, respectively, at 37°C and then loaded in two-point load until fracture. One-half of each tested specimen was used for the repair procedure. Repairing surfaces were diamond-bur ground, etched, and treated with silane containing universal adhesive (Scotchbond Universal) before repair. RESULTS: Three-way analysis of variance revealed a significant statistical difference between the groups ( p<0.05). The fracture resistance of dry-stored groups was greater than that of water-stored groups. The highest OR was observed for dry-stored Alert (23.4 N/mm), which significantly deteriorated in water (17.4 N/mm) ( p<0.05). The highest RR was observed for everX Posterior (20.0 N/mm), which did not deteriorate in water significantly (19.0 N/mm) ( p>0.05). The everX Posterior preserved the specimens' integrity at the final fracture load (ductile fracture), whereas all other materials fractured into two halves at the interface (adhesive failure). CONCLUSIONS: The only material that provided enhanced repair strength that was close to the original cohesive strength of the material was everX Posterior. The endurance of repaired restorations can be improved by using semi-IPN-based filling material.

The degree of conversion of fiber-reinforced composites polymerized using different light-curing sources.

OBJECTIVES: Fiber-reinforced composites (FRC) with different polymer matrix compositions are available on the market. The aim of this study was to compare the degree of monomer conversion of FRC that contained either dimethacrylate resin matrix or semi-IPN resin matrix. In addition, the effect of different types of light-curing units and durations of light irradiation on the degree of conversion was evaluated. MATERIALS AND METHODS: Continuous unidirectional fibers impregnated with dimethacrylate or semi-IPN resin were compared. As control materials, a particulate filler composite resin and an unfilled resin were used. The materials were photopolymerized using various irradiation times and different types of light-curing units (quartz-tungsten-halogen with standard or turbo tip, light-emitting diode and plasma-arc). Degree of monomer conversion (DC%) was determined by FT-IR spectrometry. The infrared spectra were recorded at seven different time points after polymerization. RESULTS: ANOVA showed significant differences between the materials tested, and the curing units (P<0.05). The DC% of semi-IPN and dimethacrylate matrix FRC was not statistically different (P>0.05) compared to that of unfilled resin. Conventional quartz-tungsten halogen with turbo tip showed the highest DC% (69-72.3%), whereas the plasma-arc curing unit showed the lowest degree of conversion (47-62%). SIGNIFICANCE: Within the limitations of this study, it can be concluded that semi-IPN matrix of FRC did not show a difference in the degree of conversion compared to dimethacrylate resin FRC when quartz-tungsten or a light-emitting diode polymerization unit was used. The plasma-arc light-curing unit showed a lower degree of conversion with all materials compared to the light-emitting diode and quartz-tungsten-halogen lamps.

Fracture resistance of anterior, posterior and universal light activated composite restoratives.

This investigation measured the fracture resistance of a wide range of currently available light-activated-composite restoratives. Products intended solely for anterior use were tested together with universal materials and products intended for posterior application. All materials were handled according to manufacturers' instructions. For products evaluated in this investigation, universal and posterior materials yielded higher mean torque to fracture (T) values overall in comparison to the anterior products. One Microfilled and two Polyglas filled products designated for posterior application yielded relatively modest mean fracture resistance values.

PC controlled toothbrush/dentifrice abrasion machine.

A toothbrush/dentifrice abrasion machine was developed to use in dental research laboratory. The mechanism was designed as a hexagonal block driven by two stepping motors which move the mechanism in four directions. In order to control the stepping motors speed, position and direction commands or signals were generated by a software written in C Programming Language and then these commands were applied the stepping motor drives through parallel port of a personal computer. The toothbrush/dentifrice abrasion machine was finally used to measure different longevity of tooth brush. It was experimentally shown that the mechanism can be used for highly accurate position and speed applications.

Cephalometric evaluation of maxillary complete, mandibular fixed-removable partial prosthesis: a 5-year longitudinal study.

Lateral cephalometric films were obtained from 10 subjects treated with maxillary complete dentures opposed to bar-supported mandibular removable partial dentures. The amount of bone resorption was determined following a 5-year period of denture use. In the maxilla, slight resorption was observed; a considerable amount had taken place in the mandible. Comparing the results of previous studies with the present one, it is suggested that bar-supported mandibular free-end saddle partial denture design has beneficial effects in terms of reduced bone resorption.

The strength of a heat-pressed all-ceramic restorative material.

A heat-pressed technique (IPS Empress, Ivoclar) has been described to construct single unit crowns, inlay/onlays and veneers using precerammed and precoloured glass-ceramic ingots. The aim of the study was to evaluate the strength of materials obtained using this technique. Strengths were determined by means of shell (disc rupture) tests. Seven groups of 10 specimens each were prepared with different combinations of core, incisal and glaze firing. Shell strength values of these seven groups varied between 167 +/- 18 and 81 +/- 9 MPa. After analysis, results showed that there was no statistical difference between groups when the core porcelain was in tension. However, there was a significant difference between those groups in which the lower surface was either core or incisal porcelain. The component thicknesses of the core and incisal materials did not change the strength of the complete specimen.

Influence of layer and stain firing on the fracture strength of heat-pressed ceramics.

Fracture strength (T = torque to initiate fracture; K(IC) = fracture toughness) and the fractography of heat-pressed leucite reinforced ceramic (IPS Empress, Ivoclar AG-Schaan, Liechtenstein) were analysed by the notched disc test technique and scanning electron microscopy methodologies. To determine the effects of additional firing schedules on the heat-pressed core ceramic, three groups of specimens were prepared. These groups were heat-pressed core, heat-pressed core and simulated stain firing, and heat-pressed core and simulated layer firing. Statistical analysis of both T and K(IC) values showed that there was no statistically significant difference between these three groups (P > 0.05). Scanning electron microscopy analysis of the fractured surfaces revealed that crack propagation occurred around some of the leucite particles and also partly and directly through other leucite particles.

Repair strength of heat-pressed ceramics.

The bond strengths of porcelain bonded to porcelain specimens using two different filled resin-based cements were compared by means of notched-disc test specimens. As a control group, unrepaired porcelain test specimens were fractured. Additionally, one group of broken half-repairs was achieved by applying a bonding agent only. The control test specimens had significantly higher fracture strengths (P < 0.05) than the specimens bonded with either bonding agent or resin-based cements. No difference between the resin-based cements was found (P > 0.05).

Microleakage of direct and indirect inlay/onlay systems.

The purpose of this in vitro study was to evaluate the microleakage of direct and indirect inlay/onlay systems. Two of the groups investigated have indirect applications only and consist of microfine composites. The other two groups of inlay/onlay systems have both direct and indirect applications and are hybrid composites. Standardized MOD preparations were cut in 60 extracted human premolars. One gingival margin was placed in enamel above the cementoenamel junction (CEJ) and the other was placed in dentine below the CEJ. The inlays were made and luted according to each manufacturer's recommendation. The restored teeth were thermocycled and immersed in a basic fuchsin solution for 24 h. Following the mesiodistal sectioning of the specimens, extent of dye penetration at the restoration-glass ionomer cement and tooth-glass ionomer cement interfaces were scored using a stereomicroscope. Both direct and indirect inlays showed substantial leakage at gingival-dentine margins. However, there was only superficial leakage at enamel margins. Comparing the overall indirect inlay systems, EOS inlay leaked the most (P < 0.05). Indirect Brilliant Dentin inlays showed a significantly smaller amount of leakage than the other inlay systems. SR-Isosit and Estilux Posterior C VS inlays provided a favourable marginal seal. In the case of Brilliant Dentin and Estilux Posterior C VS, indirect inlays leaked more than direct inlays. Generally, no significant difference was observed between the interfaces evaluated in microleakage performance.

The fracture resistance of dental materials.

A novel test procedure was developed that provides the basis for a standard plain strain fracture toughness test to evaluate fracture resistance of resin-based materials. This procedure utilizes a notched disc specimen. Using this technique, a new concept of Torque to initiate fracture (T)' was suggested. Also, fracture resistance can be assessed by means of critical stress intensity factor (K[IC]). Using this method, the fracture resistance of direct restorative materials, resin-based inlay/onlays and luting cements can be evaluated.

The attenuation of radiation by porcelain and its effect on polymerization of resin cements.

The influence of porcelain thickness and opacity on the polymerization of two dual activated (microfine and hybrid) and one light irradiated (hybrid) resin cements was assessed by hardness measurements. The surface microhardness values of the upper and lower surface of 1 mm thick resin cement specimens were determined. Specimens were polymerized using 40s irradiation beneath different thicknesses and opacities of porcelain discs. The results showed that increasing the thicknesses and opacity of the porcelain produced a statistically significant decrease in microhardness of the resin-based cements. The effect of attenuation is less for the microfine cement than for the hybrids. In the case of hybrid cements, the light activated material performed better than the dual activated cement.

Variables affecting the fracture toughness of resin-based inlay/onlay systems.

The fracture toughness of five different resin-based inlay/onlay materials was investigated by means of critical stress intensity factor (KIC) using the SEN three-point bending test procedure (BS 5447: 1977). KIC values were determined from specimens prepared by both the direct and indirect techniques. Tests were performed immediately, after 1 day, 1 month and 3 month time intervals. Also, fractured surfaces of specimens were observed using SEM photographs.

Mandibular guidance prostheses following resection procedures: three case reports.

Unilateral loss of mandibular continuity creates problems in prosthetic reconstruction. For dentate patients, palatal guide ramps or mandibular guide flange prostheses are indicated. Edentulous patients are much more difficult to retrain in mandibular movements, but complete dentures designed with stabilising occlusal contacts can be successful in compensating for the deviation. Three case reports are presented.

Evaluation of impression tray techniques in microstomic patients.

Three different methods of constructing impression trays for patients suffering from microstomia have been described. When sectional trays with connectors are designed, proper alignment of the sections is necessary for satisfactory results. Flexible trays, or even silicone putty without a tray, can be used for making preliminary impressions in these cases.

[Evaluation of stresses in different cingulum rest seats]. / Farkli singulum rest yuvalarinin kuvvet iletimi yönünden karsilastirilmalari.

Both lingual and incisal rest seats are used on anterior teeth. Lingual rest seats are preferred since they are more acceptable esthetically and located closer to the centre of rotation of the tooth. Lingual rest seats can be prepared directly on the abutment teeth as grooves, shoulders or may require restorations such as crowns, inlays and prefabricated rest seats to provide proper contour. In this study, the stress induced by two conventionally applied rest seats were compared with that of the U shaped rest seats which were recently induced. As a result it is found that more uniform stress distribution occurred in U and inverted "v" type rest seat designs.

[Analysis of stresses in modified resin-bonded cast fixed partial dentures]. / Modifiye metal destekli adhesif köprülerde kuvvet analizi.

In 1973, ROCHETTE introduced a periodontal splinting method that involved bonding of cast perforated retainers to the acid etched lingual surfaces of anterior teeth, using a resin. Nowadays, there have been a number of reports on the clinical performance of the adhesive bridges. The objective of this investigation was to photoelastically evaluate the forces exerted on the supporting structures of abutment teeth by modified resin-bonded cast fixed partial dentures. Four modified designs were tested and a traditional fixed bridge used as a control design. This study indicated that the resin bonded cast fixed partial denture with the lingual chamfer margin and mesial rest was the design to be chosen.

[Photoelastic stress analysis of fixed-removable partial denture which had bar and Ceka-Anchor attachment]. / Bar-Ceka-Anchor tutuculu sabit-hareketli bölümlü protezlerde fotoelastik kuvvet analizi.

In our study, we constructed fixed-removable partial prosthesis, which are supported by teeth and tissue for patients who exhibited extensive tissue loss. In these prosthesis the localization of the precision attachments on the bar and the stress conducted to the abutment teeth by changing the number of splinted teeth and inclination of the bar were compared with photoelastic analyses and the results were evaluated. The photoelastic material used was Araldite/B and its catalyst was HT 901 fitalic anhydrate. The models constructed with these materials were examined in photoelastic polariscope and fringes occurred due to the force applied were photographed and analyzed.