Midline denture base strains of glass fiber-reinforced single implant-supported overdentures.

STATEMENT OF PROBLEM: The fracture incidence of implant-supported overdentures is more frequent in the area of attachment because of stress concentration and denture deformation in this area. How E-glass fiber reinforcement can address this problem is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the influence of unidirectional E-glass fiber reinforcement on the mid-line denture base strains of single implant-supported overdentures. MATERIAL AND METHODS: An experimental acrylic resin cast was constructed with a single implant placed in the mid-line area and a ball attachment screwed to the implant. Twenty-four experimental overdentures were constructed and divided into 4 groups: group AP fabricated from autopolymerizing acrylic resin without fiber reinforcement, group APF fabricated from autopolymerizing acrylic resin with unidirectional E-glass fiber reinforcement running over the residual ridge and the ball matrix, group HP fabricated from heat-polymerized acrylic resin without fiber reinforcement, and group HPF fabricated from heat-polymerized acrylic resin with unidirectional E-glass fiber reinforcement running over the residual ridge and the ball matrix. A biaxial rosette strain gauge was attached to the incisor areas of each overdenture above the attachment level (Ch1, Ch2) and to a multichannel digital strain meter. A static vertical load of 100 N was applied to the first molar area bilaterally by using a universal testing device during strain measurement procedures. The differences in the mean strain and deflection values among the investigated groups were evaluated for statistical significance using 1-way analysis of variance (ANOVA) with the Tukey post hoc multiple comparison (α=.05). RESULTS: The type of acrylic resin did not have a statistically significant effect on the mean strain values among groups (P=.350), while the reinforcement did significantly affect them (P<.001). The interaction between reinforcement and acrylic resin was not statistically significant (P=.552). Both strain gauge channels in group APF and group HPF recorded significantly lower strain values by almost 50% than those of group AP and group HP (P<.05). CONCLUSIONS: Unidirectional E-glass fiber reinforcement placed over the residual ridge and implant attachment significantly reduced denture base strains and deformation of single implant-supported overdentures.

Fatigue resistance of a simulated single LOCATOR overdenture system.

STATEMENT OF PROBLEM: The incidence of fracture in a single-implant overdenture base increases in the region adjacent to the fulcrum implant. PURPOSE: The purpose of this in vitro study was to evaluate the effect of bidirectional woven electrical glass (E-glass) fiber reinforcements on the fatigue resistance of a simulated single LOCATOR-retained overdenture. MATERIAL AND METHODS: Test specimens with a centrally positioned metal housing for a LOCATOR stud attachment were fabricated from autopolymerizing acrylic resin. Specimens for the control group were fabricated without glass fiber reinforcements. The 4L group specimens had 4 layers of E-glass fiber weaves and were divided according to the fiber location into the following 3 subgroups: 4L-A with 4 fiber layers above the metal housing; 4L-N with 4 fiber layers adjacent to the metal housing; and 4L-A+4L-N with 4 fiber layers above and 4 fiber layers adjacent to the housing. Specimens were stored in distilled water for 1 week at 23 °C before cyclic fatigue testing at 10 000 cycles by using a staircase approach (n=12). The results were analyzed with 1-way ANOVA and the Tukey multiple comparisons post hoc analysis (α=.05). A 2-way ANOVA (α=.05) was conducted to detect the effect of fatigue cyclic loading and the position of the fiber layers and their interaction on the fatigue resistance. RESULTS: The results of the investigated compressive fatigue limits for the test groups were 190 ±15.9 N for the control group, 265 ±15.9 N for the 4L-A subgroup, 220 ±15.9 N for the 4L-N subgroup, and 275 ±15.9 N for the 4L-A+4L-N subgroup. A nonsignificant difference was found for creep values between the control group and reinforced subgroups (P>.05). The postfatigue flexural strength values in the 4L-A and 4L-A+4L-N subgroups were significantly higher than those in the control group (P<.001) and the 4L-N subgroup (P=.004 and P=.005). However, no significant difference was found in postfatigue flexural strength between the control group and the 4L-N subgroup (P=.828). CONCLUSIONS: Placing 4 layers of bidirectional E-glass fiber weaves above the metal housing can increase the fatigue resistance and the postfatigue flexural strength of single LOCATOR-retained overdentures.

Load-bearing capacity of simulated Locator-retained overdenture system.

STATEMENT OF PROBLEM: Acrylic resin overdenture bases usually fracture because of stress concentrations at the area of the abutments. PURPOSE: The purpose of this study was to evaluate the reinforcing effect of bidirectional woven electrical glass (E-glass) fiber weaves with a different number of layers and different locations on the load-bearing capacity of simulated Locator-retained overdenture specimens. MATERIAL AND METHODS: Test specimens with a centrally located metal housing for a Locator stud attachment were fabricated from autopolymerizing acrylic resin (polymethylmethacrylate based) and reinforced with bidirectional woven E-glass fiber layers. The control group specimens were fabricated without fiber reinforcement. The 2L group had 2 layers of E-glass fiber weaves and was divided according to the fiber location within the specimens as follows: 2L-A subgroup with 2 fiber layers above the metal housing; 2L-N subgroup with 2 fiber layers adjacent to the housing; and 2L-A+2L-N subgroup with 2 fiber layers above and 2 fiber layers adjacent to the housing. The 4L group had 4 layers of E-glass fiber weaves and was divided according to the fiber location as follows: 4L-A subgroup with 4 fiber layers above the housing; 4L-N subgroup with 4 fiber layers adjacent to the housing; and 4L-A+4L-N subgroup with 4 fiber layers above and 4 fiber layers adjacent to the housing. Dry specimens were submitted to a 3-point static loading test, and the mean flexural strength, flexural modulus, and strain values were analyzed with 1-way ANOVA and Tukey post hoc tests (α=.05). Two-way ANOVA was conducted to detect the influence of the number and location of the reinforcing layers (α=.05). RESULTS: The results revealed a significant difference (P<.001) in flexural strength values between the control group (92.4 ±14 MPa) and the 2 subgroups, 4L-A (116 ±7.3 MPa) and 4L-A+4L-N (117.1 ±6 MPa), with a significant effect only from the number of the reinforcing layers (P<.001) and not the location (P=.153). No significant differences were found with flexural modulus (P=.195) and strain values (P=.174) among the tested groups. CONCLUSIONS: The load-bearing capacity of a Locator-retained overdenture can be significantly increased by placing 4 layers of bidirectional woven E-glass fiber weaves either only above the metal housing or in both locations above and adjacent to the metal.

Effect of different surface treatments on shear bond strength of autopolymerizing repair resin to denture base materials processed with different technologies.

PURPOSE: To evaluate the effect of chemical, mechanical, and combination surface treatments on the shear bond strength (SBS) of autopolymerizing repair resins to conventional heat-cured, computer aided design (CAD)-computer aided manufacturing (CAM) milled, and three-dimensionally (3D) printed denture base materials. METHODS: Specimens were fabricated and divided according to the surface treatment as follows: no surface treatment (control group), monomer treatment (monomer group), resin remover treatment (resin remover group), roughening with 180 FEPA grit abrasive paper followed by monomer treatment (180-grit plus monomer group), and air particle abrasion (air abrasion group). Autopolymerizing resin cylinders were attached before accelerated aging of the specimens in water at 100 °C for 16 h. The SBS was tested using a universal testing machine. Surface roughness was evaluated using a 3D optical profilometer. Scanning electron microscopy (SEM) and stereomicroscopy were used for surface analysis. Data was collected and analyzed using analysis of variance (ANOVA) and Kruskall-Wallis tests (α = 0.05). RESULTS: The denture base material and surface treatment significantly affected the SBS. The milled Temp Basic Tissue demonstrated the highest SBS values across all surface treatments, whereas the two 3D-printed denture base materials exhibited the lowest SBS values. CONCLUSIONS: The bond strength of CAD-CAM-milled denture base resins to autopolymerizing repair resins is comparable to that of heat-cured resins. Surface roughening using air particle abrasion or 180-grit carbide paper can enhance the bond strength of the autopolymerizing repair resin to 3D-printed denture base materials.

Evaluation of flexible three-dimensionally printed occlusal splint materials: An in vitro study.

OBJECTIVE: To evaluate and compare the mechanical properties, water sorption, water solubility, and degree of double bond conversion of three different commercially available three-dimensional (3D) printing resins used for the fabrication of flexible occlusal splints. METHODS: A digital printer was used to generate specimens from the evaluated splint materials (KeySplint Soft, IMPRIMO LC Splint flex, and V-Print splint comfort). The specimens were equally divided and tested either dry or after water storage at 37 °C for 30 days. A three-point bending test was used to assess flexural strength, elastic modulus, and fracture toughness. A two-body wear test was performed using a dual-axis chewing simulator. Water sorption and water solubility were measured after 30 days. The degree of double bond conversion was determined by FTIR-spectrometry. All data for the evaluated properties were collected and statistically analyzed. RESULTS: Both material and storage conditions had a significant effect on the flexural strength (P < 0.001), elastic modulus (P < 0.001), fracture toughness (P < 0.001), and wear (P < 0.001). The highest water sorption was noticed with IMPRIMO LC Splint flex (1.9 ± 0.0 %), while V-Print splint comfort displayed the lowest water solubility (0.2 ± 0.0 %). For the degree of conversion, it was statistically non-significant among the different materials (P = 0.087). SIGNIFICANCE: Different flexible 3D-printed splints available in the market displayed variations in the evaluated properties and clinicians should consider these differences when choosing occlusal device materials. Among the tested flexible splint materials, KeySplint Soft had the greatest flexural strength, elastic modulus, fracture toughness, wear resistance, and degree of conversion. It also showed the lowest water sorption.

Effect of Surface Polishing on Physical Properties of an Occlusal Splint Material for Additive Manufacturing under Protection Gas Post-Curing Condition.

The aim of this study was to evaluate the effect of surface polishing as well as the post-curing atmospheres (air and nitrogen gas) on the physical properties of an occlusal splint material for additive manufacturing. Flexural strength, flexural modulus, Vickers hardness number (VHN), degree of carbon double bond conversion (DC), water sorption (WSP), and water solubility (WSL) were evaluated. Surface polishing significantly affected the evaluated properties. Regardless of the post-curing atmosphere, flexural strength, flexural modulus, VHN, and DC showed significantly higher values for the polished specimens when compared with the unpolished ones, while WSP and WSL were significantly lower for the polished specimens. Unpolished specimens post-cured at nitrogen gas showed significantly higher VHN and DC values. However, the effect of the post-curing at a nitrogen gas atmosphere was non-significant in polished specimens. The current results suggested that surface polishing plays a role in the physical properties of the evaluated occlusal splint material and can enhance all the evaluated properties regardless of the post-curing atmosphere. Meanwhile, the post-curing at a nitrogen gas atmosphere can enhance the VHN and DC but its effect is confined only to the surface layers, which can be removed during surface polishing.

Mechanical Properties Evaluation of Three Different Materials for Implant Supported Overdenture: An In-Vitro Study.

Aim: the aim of this study was to compare the flexural strength and elastic modulus of three-dimensionally (3D) printed, conventional heat-cured, and high-impact implant-supported overdenture materials specimens. Materials and Methods: Thirty implant-supported overdenture materials specimens (bar-shaped, 65.0 × 10.2 × 5.1 ± 0.2 mm3) with one central hole were fabricated using 3D-printed, heat-cured conventional, and high-impact denture base resins (n = 10/group). Autopolymerizing acrylic resin was used to attach titanium matrix housings to the central holes of the specimens. A three-point bending test was conducted using a universal testing machine and a model analog with a crosshead speed of 5 mm/min. The indicative flexural strength and elastic modulus were recorded. Data were statistically analyzed using analysis of variance (ANOVA) and the Tukey tests at α = 0.05. Results: One-way ANOVA revealed a significant effect of denture base material on the flexural strength (p < 0.001) but not on the elastic modulus (p = 0.451) of the evaluated materials. The flexural strength of the 3D-printed specimens (95.99 ± 9.87 MPa) was significantly higher than the conventional (77.18 ± 9.69 MPa; p < 0.001) and high-impact ones (82.74 ± 7.73 MPa; p = 0.002). Conclusions: The maximum flexural strength was observed in the 3D-printed implant-supported overdenture material specimens, which might indicate their suitability as an alternative to the conventionally fabricated ones. Flexural strength and elastic modulus of conventional and high-impact heat-cured implant-supported overdenture materials specimens were comparable.

Effect of Nitrogen Gas Post-Curing and Printer Type on the Mechanical Properties of 3D-Printed Hard Occlusal Splint Material.

Although three-dimensional (3D) printing is clinically convenient to fabricate occlusal splints, it is still unclear how the post-curing method and the printer type can affect 3D-printed splints. This study aimed to evaluate the effect of stroboscopic post-curing at a nitrogen gas (N2) atmosphere versus post-curing in an air atmosphere, as well as the printer type (liquid crystal display (LCD) and digital light processing (DLP)) on the mechanical properties of a 3D-printed hard-type occlusal splint material. Flexural strength, flexural modulus, Vickers hardness number (VHN), fracture toughness, degree of double bond conversion (DC), 3D microlayer structure, water sorption, and water solubility were evaluated. The post-curing method significantly affected all evaluated properties except fracture toughness and 3D microlayer structure, while the printer type significantly affected all evaluated properties except flexural strength and flexural modulus. VHN and DC were significantly higher, and the smoother surface was noticeably obtained when printed by LCD printer and post-cured at an N2 atmosphere. The current results suggested that the post-curing method and the printer type would play a role in the mechanical properties of the evaluated material and that the combination of post-curing at an N2 atmosphere and LCD printer could enhance its mechanical properties and surface smoothness.

Effect of 3D Printer Type and Use of Protection Gas during Post-Curing on Some Physical Properties of Soft Occlusal Splint Material.

Despite the fact that three-dimensional (3D) printing is frequently used in the manufacturing of occlusal splints, the effects of the 3D printer type and post-curing methods are still unclear. The aim of this study was to investigate the effect of the printer type (digital light processing: DLP; and liquid crystal display: LCD) as well as the post-curing method with two different atmospheric conditions (air and nitrogen gas (N2)) on the mechanical and surface properties of 3D-printed soft-type occlusal splint material. The evaluated properties were flexural strength, flexural modulus, Vickers hardness (VHN), fracture toughness, degree of double bond conversion (DC%), water sorption, water solubility, and 3D microlayer structure. The printer type significantly affected all the evaluated properties. Flexural strength, flexural modulus, and fracture toughness were significantly higher when specimens were printed by a DLP printer, while VHN and DC% were significantly higher, and a smoother surface was noticeably obtained when printed by an LCD printer. The post-curing at an N2 atmosphere significantly enhanced all of the evaluated properties except water sorption, 3D microlayer structure, and fracture toughness. The current results suggested that the printer type and the post-curing methods would have an impact on the mechanical and surface properties of the evaluated material.

Two-body wear and surface hardness of occlusal splint materials.

The aim of this in vitro study was to evaluate the wear and surface hardness of nine materials for conventional manufacturing, subtractive milling, and 3D printing of occlusal splints, as well as to evaluate the differences in wear and surface hardness between rigid and flexible 3D-printed occlusal splint materials. Two-body wear and Vickers hardness tests were performed. The vertical wear depth and Vickers hardness values were statistically analyzed. Vertical wear depth and surface hardness values were statistically significant among the investigated materials (p<0.05). The lowest vertical wear depth was observed for the heat-cured resin (27.5±2.4 µm), PMMA-based milled material (30.5±2.8 µm), and autopolymerizing resin (36.7±6.3 µm), with no statistical difference (p<0.05). Flexible 3D-printed and CAD-CAM milled polycarbonate-based splint materials displayed lower surface hardness and higher wear than the PMMA-based materials. PMMA-based splint materials displayed the most consistent surface hardness and wear resistance regardless of the manufacturing technology.

Evaluation of the mechanical properties and degree of conversion of 3D printed splint material.

OBJECTIVE: To evaluate the effect of post-curing method, printing layer thickness, and water storage on the mechanical properties and degree of conversion of a light-curing methacrylate based resin material (IMPRIMO® LC Splint), used for the fabrication of 3D printed occlusal splints and surgical guides. METHODS: 96 bar-shaped specimens were 3D printed (Asiga MAX), half of them with a layer thickness of 100 µm (Group A), and half with 50 µm (Group B). Each group was divided in three subgroups based on the post-curing method used: post-curing with light emitting diode (LED) and nitrogen gas; post-curing with only LED; and non-post-curing. Half of the specimens from each subgroup were water-stored for 30 days while the other half was dry-stored (n = 8). Flexural strength and flexural modulus were evaluated. Additional specimens were prepared and divided in the same way for surface hardness (n = 96), fracture toughness, and work of fracture (n = 96). Five specimens were selected from each subgroup for evaluating the degree of conversion (DC). Data were collected and statistically analyzed with 1-way, 2-way ANOVA, and Tukey post-hoc analysis (α = 0.05). RESULTS: The 2-way ANOVA showed that the post-curing method and water storage significantly affected the investigated mechanical properties (P < 0.001). The 1-way ANOVA revealed a statistically significant difference among the tested groups on the investigated properties (P < 0.001). After water storage, the 100 µm subgroup post-cured with only LED showed higher flexural strength (51 ± 9) than the 50 µm and 100 µm subgroups that were post-cured with LED in addition to nitrogen gas atmosphere (38 ± 5, 30 ± 3) (p < 0.05). The 50 µm subgroup post-cured with only LED showed the highest significant flexural modulus values (1.7 ± 0.08) (p < 0.05). However, the 50 µm subgroup post-cured with LED plus nitrogen showed significantly higher surface hardness values (p < 0.05) among the investigated groups. The non-post-cured subgroups showed the lowest values, which were significantly different from the other subgroups (p < 0.05). CONCLUSION: The post-curing method, water storage, and printing layer thickness play a role in the mechanical properties of the investigated 3D Printed occlusal splints material. The combination of heat and light within the post-curing unit can enhance the mechanical properties and degree of conversion of 3D printed occlusal splints. Flexural strength and surface hardness can increase when decreasing printing layer thickness.

3D-Printed vs. Heat-Polymerizing and Autopolymerizing Denture Base Acrylic Resins.

The aim of this work was to investigate the effect of two post-curing methods on the mechanical properties of a 3D-printed denture base material. Additionally, to compare the mechanical properties of that 3D-printed material with those of conventional autopolymerizing and a heat-cured denture base material. A resin for 3D-printing denture base (Imprimo®), a heat-polymerizing acrylic resin (Paladon® 65), and an autopolymerizing acrylic resin (Palapress®) were investigated. Flexural strength, elastic modulus, fracture toughness, work of fracture, water sorption, and water solubility were evaluated. The 3D-printed test specimens were post-cured using two different units (Imprimo Cure® and Form Cure®). The tests were carried out after both dry and 30 days water storage. Data were collected and statistically analyzed. Resin type had a significant effect on the flexural strength, elastic modulus, fracture toughness, and work of fracture (p < 0.001). The flexural strength and elastic modulus for the heat-cured polymer were significantly the highest among all investigated groups regardless of the storage condition (p < 0.001). The fracture toughness and work of fracture of the 3D-printed material were significantly the lowest (p < 0.001). The heat-cured polymer had the lowest significant water solubility (p < 0.001). The post-curing method had an impact on the flexural strength of the investigated 3D-printed denture base material. The flexural strength, elastic modulus, fracture toughness, work of fracture of the 3D-printed material were inferior to those of the heat-cured one. Increased post-curing temperature may enhance the flexural properties of resin monomers used for 3D-printing dental appliances.

Characterization of occlusal splint materials: CAD-CAM versus conventional resins.

AIM: The aim of this in vitro study was to assess the mechanical properties of five commercially available subtractive computer-aided design and computer-aided manufacturing (CAD-CAM) milled splint materials, as well as to compare them with conventional heat-polymerized and autopolymerizing resins used in the construction of conventional splints. MATERIAL AND METHODS: Five CAD-CAM milled (ProArt CAD Splint, Therapon Transpa, Temp Premium Flexible Transpa, Cast, and Aqua), one autopolymerizing (Palapress), and one heat-polymerized (Paladon 65) resin materials were evaluated. Flexural strength, E-modulus, Vickers hardness, fracture toughness, fracture work, water sorption, and water solubility were measured. Samples were evaluated after dry and water storage for 30 days at 37 °C. Data were collected and statistically analyzed. RESULTS: Under both storage circumstances, the flexural strength values of Paladon 65, Therapon Transpa, Temp Premium Flexible Transpa, and Aqua were statistically non-significant (P=0.055). The polycarbonate-based CAD-CAM material Temp Premium Flexible Transpa had the highest statistically significant values of the fracture toughness and fracture work (P<0.001). Moreover, it exhibited the lowest percentages of water sorption and water solubility among the investigated materials (P<0.001). All of the CAD-CAM materials exhibited dry elastic moduli greater than Palapress and lower than Paladon 65. One of the CAD-CAM materials, Cast, had the highest dry Vickers hardness value, which was non-significant when compared to Therapon Transpa (P=0.762). CONCLUSION: CAD-CAM polycarbonate-based splint materials exhibit higher fracture toughness and fracture work as well as lower water sorption and solubility than polymethyl methacrylate-based ones. The mechanical characteristics of the assessed CAD-CAM milled splint materials were not typically superior to those of the conventional heat-polymerized resin. However, some of them outperformed the autopolymerizing acrylic resin in terms of flexural strength, surface microhardness, water sorption, and water solubility.

Effect of specific retention biomaterials for ball attachment on the biomechanical response of single implant-supported overdenture: A finite element analysis.

PURPOSE: The purpose of this finite element analysis (FEA) was to evaluate the effect of specific retention biomaterials with different elastic modulus on the biomechanical response to the axial and off-axial biting loads of a mandibular midline single implant-supported overdenture (SIO) model. METHODS: Five 3-dimensional (3D) finite element models of an edentulous mandible with SIO were designed as follows: model M with a titanium retentive element for ball attachment, model P with a PEEK retentive element, model S with a silicone resilient liner retentive element, model T with a thermoplastic acrylic resin retentive element made from a CAD-CAM material, and model A with a polyacetal resin retentive element. Posterior bilateral vertical load (PV) at the 1st molar areas and anterior oblique load (AO) at the incisal edge of the mandibular central incisors at a 30-degree angle of 100 N were applied. Stress values were recorded. RESULTS: Stress values were higher for all models under (AO) loading than under (PV) loading. Model M recorded the highest stress values on the implant, its components, cortical, and cancellous bone under both loading conditions. Under (AO) loading condition, the ball abutment von Mises stress value in model S was almost 7 times lower than that of model M (19 and 130 MPa respectively) and the other 3 models (P, T, and A) (119, 121, and 120 MPa respectively). However, model S recorded the highest value of denture base stress at the attachment area. CONCLUSIONS: The elastic modulus of retention materials can affect stresses generated on the implant overdenture components and supporting structures.

Flexural strength and flexural modulus of fiber-reinforced, soft-liner retained implant overdenture.

PURPOSE: To compare the flexural strength and modulus of ball-soft liner­retained overdentures vs ballsocket­ retained overdentures, as well as to evaluate the effect of using glass fiber reinforcement on the mechanical properties of ball-soft liner­retained overdentures. MATERIALS AND METHODS: A total of 80 overdenture specimens were fabricated and divided equally into four groups (n = 20/group): specimens with a metal matrix (group 1); a silicone soft liner matrix (group 2); reinforced with one bundle of unidirectional Stick glass fiber placed above the silicone soft liner matrix (group 3); and reinforced with four weaves of bidirectional Stick Net glass fibers placed above the silicone soft liner matrix (group 4). Half of the specimens from each group were stored in water at room temperature (23°C ± 1°C) for 24 hours, while the other half were stored in water at 37°C for 30 days before being subjected to a static three-point loading test. RESULTS: After 1 day of water storage, the flexural strength and flexural modulus values of groups 1, 3, and 4 were not significantly different from each other (P = .788, P = .084), but were significantly higher than group 2 (P < .05). Water storage for 30 days significantly decreased the flexural strength of group 1 only (P < .001) and not the other three groups (P >.05). CONCLUSION: Overdentures retained with a metal matrix were not significantly different from those retained with a silicone soft liner matrix in terms of flexural strength and modulus after 30 days of water storage. Placing unidirectional and bidirectional glass-fiber reinforcement above soft liner matrices can increase the flexural strength of ball-soft liner­retained overdentures.

Characterization of the mechanical properties of CAD/CAM polymers for interim fixed restorations.

This study investigated some mechanical properties of five CAD/CAM materials used for the fabrication of provisional restorations and tooth segments for digitally fabricated dentures. The CAD/CAM blocks were sectioned into bars for flexural strength and elastic modulus testing (n=80), and for surface microhardness (n=80). Half of the specimens were water-stored for 30 days while the other half was dry-stored. Additional specimens were prepared for bond strength (n=40). A 2-way analysis of variance (ANOVA) was conducted to detect the effect of material and water storage (α=0.05). Statistical software (IBM SPSS Statistics v21; IBM) was used for conducting all analyses. Material type and storage significantly affected the flexural strength, flexural modulus and microhardness (p<0.001). The type of material did not have a significant effect on bond strength (p>0.05). The tested materials showed variation in their flexural properties and surface microhardness whereas their bonding properties with resin luting cement were similar.

Biomechanical aspects of reinforced implant overdentures: A systematic review.

PURPOSE: The purpose of this systematic review was to investigate the effect of reinforcement on the mechanical behaviour of implant overdenture (IOD) bases and its cumulative biological effect on the underlying supporting structures (implants and the residual ridge). MATERIAL AND METHODS: The required documents were collected electronically from PubMed and Web of Science databases targeting papers published in English that focused on denture base reinforcement for IOD prostheses in order to recognize the principal outcomes of reinforcement on the mechanical and biological properties of overdentures. Such biological outcomes as: strains on implants, peri-implant bone loss, residual ridge resorption, and strain on the residual alveolar ridge. RESULTS: A total of 269 citations were identified. After excluding any repeated articles between databases and the application of exclusion and inclusion criteria, only 13 publications fulfilled the inclusion criteria. Three publications investigated the mechanical properties of fibre and/or metal-reinforced implant overdentures while another 3 articles investigated the effect of metal reinforcement on stress distribution and strains transmitted to the underlying implants. In addition, 3 in vitro studies investigated the effect of metal reinforcement on overdenture base strain and stresses. Stress distribution to the residual ridge and strain characteristics of the underlying tissues were investigated by 2 in vitro studies. Five clinical studies performed to assist the clinical and prosthetic maintenance of metal-reinforced IOD were included. Data concerning denture base fracture, relining, peri-implant bone loss, probing depth, and implant survival rates during the functional period were extracted and considered in order to evaluate the mechanical properties of the denture base, residual ridge resorption and implant preservation rates, respectively. CONCLUSION: The use of a denture base reinforcement can reduce the fracture incidence in IOD bases by enhancing their flexural properties and reducing the overdenture base deformation. Strains on the underlying supporting structures of overdenture prostheses including dental implants and the residual ridge can be decreased and evenly distributed using a metal reinforcement.

Effect of Implant Location on Palateless Complete Overdenture Retention: an In Vitro Study.

OBJECTIVES: The purpose of this in vitro study was to evaluate effect of implant location on initial retention values of palateless complete overdentures retained by four o-rings at different inter-implant distances. MATERIAL AND METHODS: Two standard acrylic models representing completely edentulous maxillary arches were used. Four single piece ball type implants were placed in each model. Models were divided into two groups according to the distance between anterior and posterior implants. Two canine implants with 32 mm inter-implant distance were placed in both models. In one model (G1), two posterior implants were placed in second premolar region away from canine implants by 14 mm on both sides, while in the other model (G2), the two posterior implants were placed in first molar region away from canine implants by 22 mm on both sides. Eighteen palateless complete overdentures were constructed for each model. Overdentures were retained by four o-rings. Initial axial (central), and para-axial (anterior, posterior, and lateral) retention values of overdentures were estimated and compared using a universal testing machine. RESULTS: Independent t-test revealed that implant location has a significant role in palateless complete overdenture retention with a level of significance set at P < 0.05. CONCLUSIONS: For in vitro simulated palateless implant overdentures retained by four o-rings, increasing the inter-implant distance between anterior and posterior implants is favourable for a more retentive prosthesis.

Clips vs Resilient Liners Used With Bilateral Posterior Prefabricated Bars for Retaining Four Implant-Supported Mandibular Overdentures.

The objective of this research was to clinically compare peri-implant tissue health of bar-clips vs silicone-resilient liners used with bilateral posterior bars for retaining 4 implant-supported mandibular overdentures. Thirty completely edentulous male patients (mean age, 65 years) were randomly assigned into 2 equal groups. Each patient received 4 implants in the canine and first molar regions of the mandible using a flapless surgical technique. Mandibular overdentures were immediately connected to the implants with bilateral prefabricated instant adjusting bars. According to the method of retention to the bar, 1 group was retained with clips (GI), whereas the other group was retained with a silicone-resilient soft liner (GII). Peri-implant tissue health was evaluated clinically in terms of plaque scores (MPI), bleeding scores (MBI), probing depth (PD), and implant stability (IS). MPI, MBI, and PD were measured at mesial, distal, buccal, and lingual surfaces of each implant. Evaluations were performed 2 weeks (T0), 6 months (T6), and 12 months (T12) after overdenture insertion. Implants of GI with clips demonstrated significant increase in plaque, bleeding, and PD scores compared with those of GII with silicone-resilient liner at all observation times. Implants in GI demonstrated a significant decrease in implant stability compared with those of GII at T6 and T12 anteriorly and at T12 posteriorly. Resilient liners are considered better than bar-clips when used with bilateral posterior bars for retaining implant-supported mandibular overdentures in terms of peri-implant soft tissue health. Bilateral posterior ready-made bars cannot be proposed as a promising design for supporting implant-assisted mandibular overdentures.