Effect of Repair Gap Width on the Strength of Denture Repair: An In Vitro Comparative Study

Effect of repair and surface treatments on the strength of digitally fabricated resin-based dental prostheses: A systematic review of in vitro studies

OBJECTIVE

This review investigated the current literature pertaining to the repairability of computer-aided design-computer-aided manufacturing (CAD-CAM) milled and three-dimensional (3D) printed resin-based dental prostheses (RBDPs) as well as the appropriate surface treatment for each repair material that will produce adequate repair bond strength.

DATA/SOURCES

PubMed, Web of Science, and Scopus databases were searched for published articles involving repair of CAD-CAM RBDPs between January 2010 and June 2023. Data were collected and analyzed to reveal the surface treatment effects, suggested repair materials, and strength of repaired RBDPs.

STUDY SELECTION

Out of 164 retrieved titles, 11 studies were included, of which five investigated the repair of 3D-printed RBDPs, three investigated the repair of CAD-CAM milled resins, and three investigated both materials. Additionally, of the included studies, seven investigated denture base resins, three studied provisional restoration resins, and one evaluated 3D-printed intraoral splints. Various surface treatments were suggested, with air-abrasive methods being the most commonly used. Different materials for resin repair were proposed and used, including auto-polymerized, reline, and composite resins. For 3D-printed resins, repair with Bis-acrylic/Bis-GMA composites improved repair strength.

CONCLUSION

Surface treatments positively affected the repair strength of conventional and milled RBDPs. However, challenges remain relevant to the repair of 3D-printed resins owing to composition mismatches and fabrication techniques. Therefore, further investigation is required to develop new 3D-printed resins.

CLINICAL SIGNIFICANCE

CAD-CAM milled resins have satisfactory repair strength, which increases with surface treatment. The repair of 3D-printed resins has proven challenging even with surface treatments. However, composite resins are the materials of choice.

Repair Bond Strength of Conventionally and Digitally Fabricated Denture Base Resins to Auto-Polymerized Acrylic Resin: Surface Treatment Effects In Vitro

Denture base fracture is one of the most annoying problems for both prosthodontists and patients. Denture repair is considered to be an appropriate solution rather than fabricating a new denture. Digital denture fabrication is widely spreading nowadays. However, the repair strength of CAD-CAM milled and 3D-printed resins is lacking. This study aimed to evaluate the effect of surface treatment on the shear bond strength (SBS) of conventionally and digitally fabricated denture base resins. One l heat-polymerized (Major base20), two milled (IvoCad, AvaDent), and three 3D-printed (ASIGA, NextDent, FormLabs) denture base resins were used to fabricate 10 × 10 × 3.3 acrylic specimens (N = 180, 30/resin, n = 10). Specimens were divided into three groups according to surface treatment; no treatment (control), monomer application (MMA), or sandblasting (SB) surface treatments were performed. Repair resin was bonded to the resin surface followed by thermocycling (5000 cycles). SBS was tested using a universal testing machine where a load was applied at the resin interface (0.5 mm/min). Data were collected and analyzed using ANOVA and a post hoc Tukey test (α = 0.05). SEM was used for failure type and topography of fractured surfaces analysis. The heat-polymerized and CAD-CAM milled groups showed close SBS values without significance (p > 0.05), while the 3D-printed resin groups showed a significant decrease in SBS (p < 0.0001). SBS increased significantly with monomer application (p < 0.0001) except for the ASIGA and NextDent groups, which showed no significant difference compared to the control groups (p > 0.05). All materials with SB surface treatment showed a significant increase in SBS when compared with the controls and MMA application (p < 0.0001). Adhesive failure type was observed in the control groups, which dramatically changed to cohesive or mixed in groups with surface treatment. The SBS of 3D-printed resin was decreased when compared with the conventional and CAD-CAM milled resin. Regardless of the material type, SB and MMA applications increased the SBS of the repaired resin and SB showed high performance.

Effect of repair methods and materials on the flexural strength of 3D-printed denture base resin

PURPOSE

The aim of this study was to evaluate the flexural strength of a 3D-printed denture base resin (Cosmos Denture), after different immediate repair techniques with surface treatments and thermocycling.

MATERIALS AND METHODS

Rectangular 3D-printed denture base resin (Cosmos Denture) specimens (N = 130) were thermocycled (5,000 cycles, 5℃ and 55℃) before and after the different repair techniques (n = 10 per group) using an autopolymerized acrylic resin (Jet, J) or a hard relining resin (Soft Confort, SC), and different surface treatments: Jet resin monomer for 180 s (MMA), blasting with aluminum oxide (JAT) or erbium: yttrium-aluminum-garnet laser (L). The control group were intact specimens. A three-point flexural strength test was performed, and data (MPa) were analyzed by ANOVA and Games-Howell post hoc test (α = 0.05). Each failure was observed and classified through stereomicroscope images and the surface treatments were viewed by scanning electron microscope (SEM).

RESULTS

Control group showed the highest mean of flexural strength, statistically different from the other groups (P < .001), followed by MMA+J group. The groups with L treatment were statistically similar to the MMA groups (P > .05). The JAT+J group was better than the SC and JAT+SC groups (P < .05), but similar to the other groups (P > .05). Adhesive failures were most observed in JAT groups, especially when repaired with SC. The SEM images showed surface changes for all treatments, except JAT alone.

CONCLUSION

Denture bases fabricated with 3D-printed resin should be preferably repaired with MMA+J. SC and JAT+SC showed the worst results. Blasting impaired the adhesion of the SC resin.

Effect of silicon dioxide nanoparticles on the flexural strength of heat-polymerized acrylic denture base material: A systematic review and meta-analysis

Objective

This study evaluated the influence of silicon dioxide (SiO₂) nanoparticles on the flexural strength of heat-polymerized denture base materials.

Background

Nanoparticles have been incorporated into the denture base materials in different proportions to enhance the mechanical properties. Recently, the incorporation of SiO₂ nanoparticles at low concentrations has shown promising outcomes.

Materials and Methods

Following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) protocol, this study was designed with the following focused question: “Does the addition of SiO₂ nanoparticles improve the flexural strength of heat-polymerized acrylic resins?” The inclusion criteria included in-vitro studies that assessed the flexural strength of SiO₂ nanoparticle-reinforced heat-polymerized acrylic denture base resins tested according to American Dental Association specifications. The database search involved articles published from 2005 to 2020 on PubMed/MEDLINE, Web of Science, Google Scholar, and Scopus using the following keywords: SiO₂, nanosilica, silica oxide, nanoparticles, denture base resin, acrylic resin, polymethyl methacrylate, PMMA, flexural strength, and mechanical properties.

Results

Among 167 studies, five papers fulfilled the inclusion criteria and were added for the data analysis and meta-analysis. Proportions of incorporated SiO₂ nanoparticles ranged from 0.25% to 15% and the reported flexural strength values for the reinforced acrylic resin ranged from 41.25 MPa to 124.56 MPa. The meta-analysis revealed no significant effect on the flexural strength between the unmodified and the SiO₂ nanoparticle-reinforced acrylic resin.

Conclusion

Therefore, No particular concentration of SiO₂ nanoparticles could be recommended for heat-polymerized denture base reinforcement.

Polymethylmethacrylate Incorporating Nanodiamonds for Denture Repair: In Vitro Study on the Mechanical Properties

OBJECTIVE

 This study aimed to evaluate the effect of nanodiamond (ND) addition to repair resin with repair gap modifications on the flexural and impact strength of repaired polymethylmethacrylate denture base.

MATERIALS AND METHODS

 Heat-polymerized acrylic resin specimens (N = 100/test) were prepared and sectioned to half creating two repair gaps: 2.5- and 0 mm with 45 degrees beveling. They were further divided into subgroups (n = 20) according to ND concentration (control, 0.25%ND, and 0.50%ND), thermocycling (500 cycles) was done to half the specimens in each subgroup. Flexural strength was tested using 3-point bending test and impact strength was tested by Charpy's impact test. Analysis of variance and post-hoc Tukey's tests were performed for data analysis (α = 0.05). Scanning electron microscope was employed for fracture surface analysis and ND distribution.

RESULTS

 Before and after thermocycling, the addition of ND significantly increased the flexural strength and elastic modulus in comparison to control group (p ˂ 0.001), while 0 mm repair gap showed insignificant difference between ND-reinforced groups (p ˃ 0.05). Regarding impact strength, ND addition increased the impact strength with 0 mm gap in comparison to control and 2.5 mm with ND (p˂0.001), while later groups showed no significant in between (p ˃ 0.05). Comparing thermocycling effect per respective concentration and repair gap, thermocycling adversely affected all tested properties except elastic modulus with 0 mm-0.25 and 0 mm-0.5% and impact strength with 2.5 mm, 2.5 mm-0.25%, 2.5 mm- 0.5% (p ˃ 0.05).

CONCLUSION

 ND addition combined with decreased repair gap improved the flexural strength, elastic modulus, and impact strength of repaired denture resin, while thermocycling has a negative effect on denture repair strength.

The impact of nanoparticles-modified repair resin on denture repairs: a systematic review

This study aimed to evaluate the effect of nanoparticles on the mechanical properties of acrylic denture repairs. The review was designed following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) guidelines. Database search was conducted involving articles published from 2000 to 2020 using the following keywords: PMMA/nanoparticles, denture repair/nanoparticles, and repair strength/nanoparticles. PubMed/MEDLINE, Embase, Google Scholar, Scopus, and EBSCOhost were used to find only those studies used repair resin reinforced with nanoparticles for denture repairs. Due to variations between nanoparticles types, sizes, and testing properties, the quantitative statistical meta-analysis couldn't be conducted. Therefore, a descriptive data analysis was applied. Out of 379 articles, 8 articles were included; three nanoparticles, zirconium oxide (nano-ZrO2), silicon oxide (nano-SiO2), and aluminum oxide (nano-Al2O3) nanoparticles were used as reinforcements to repair resin. Seven studies investigated the effects of 0.25-7.5 wt.% nano-ZrO2 on the mechanical properties of repaired denture bases and reported positive effects with high concentrations. Two studies study investigated 0.25-0.75 wt% nano-SiO2 and found that low % nano-SiO2 concentrations improved repair strength while, one study showed that 1 and 1.5 wt.% nano-Al2O3 increased the flexural strength. Although nanoparticles offer positive effects on the properties of denture repair, inadequate studies exist. Therefore, further investigations are required. Scientific field of dental Science: Prosthodontics.

Fibre-reinforced and repaired PMMA denture base resin: Effect of placement on the flexural strength and load-bearing capacity

OBJECTIVES

To measure the effect of placement of glass fibre mesh on the flexural strength and load bearing capacity of repaired polymethylmethacrylate (PMMA) denture base resin.

MATERIALS AND METHODS

A total of 150 heat-polymerised acrylic resin specimens were fabricated with dimensions of 5 × 30 × 50 mm for flexural strength testing. Specimens were divided into 5 groups according to repair width and placement of the fibre mesh. Three groups (n = 90) had a repair width of 20 mm (including the control group), and two groups (n = 60) had a narrower repair width of 16 mm. Fibre mesh was either embedded at the neutral (bottom of the repair area) or tension (top of the repair area) zone of the specimen when subjected to flexural strength testing. Half of the specimens from each group were subjected to artificial ageing by thermocycling (5 °C and 55 °C, 30s dwell time) for 10,000 cycles to stimulate 12 months in vivo. All the specimens were stored in distilled water at 37 °C for 24 h prior to testing. The flexural strength of the specimen was obtained by three-point bend testing, and data were statistically analysed using ANOVA and post-hoc analysis (SPSS; significance level p < 0.05). Probability of failure was calculated using Weibull analysis. Scanning electron microscopy analysis was used to identify the mode of failure.

RESULTS

Specimens repaired with the 20 mm fibre mesh placed in the tension zone showed the highest mean flexural strength (101.33 ± 12.66 MPa) with statistical significance (p = 0.05) to the other groups except for the specimens repaired with the 16 mm fibre mesh placed in the tension zone (p = 0.072). The highest Weibull modulus was found in the thermal cycling group of the specimens with 20 mm repair width repaired with the fibre mesh embedded at the neutral zone (10.01). The lowest Weibull modulus was found in the non-thermal cycling group of the control group (3.15).

CONCLUSION

Placing fibre mesh in the tension zone of a PMMA specimen significantly improved the flexural strength of the repair. Placing the fibre mesh in the neutral zone or the fibre mesh width was short of the lower support rollers resulted in no significant increase in flexural strength compared to the non-reinforced control group. Ageing via thermal cycling resulted in a decrease in flexural strength across all sample groups. This study highlights the importance of recognising the valid repair region and to have the mesh embedded in certain dimensions, otherwise it will have no significant contribution towards the repair and increase of flexural strength of the denture.

Effect of different surface treatments on surface roughness and flexural strength of repaired 3D-printed denture base: An in vitro study

STATEMENT OF PROBLEM

Information regarding three-dimensional-printed (3D-printed) dentures, especially when using the additive manufacturing technique, and the repair strength of this type of denture is sparse.

PURPOSE

The purpose of this in vitro study was to assess the effect of different surface treatments on the surface roughness and flexural strength of repaired 3D-printed denture base.

MATERIAL AND METHODS

One hundred and twenty 3D-printed bar-shaped specimens were fabricated from acrylic resin and divided into 6 groups (n=20). The positive control group consisted of intact specimens. The other specimens were sectioned in half with a 1-mm gap. Except for the specimens in the negative control group, the remaining specimens were treated with erbium: yttrium-aluminum-garnet (Er:YAG) laser, airborne-particle abrasion, a combination of laser and airborne-particle abrasion, and bur grinding. All sectioned specimens were repaired by autopolymerizing acrylic resin and thermocycled after measuring their surface roughness with a profilometer. The flexural strength test was performed with a universal testing machine. One specimen of each group was inspected under a scanning electron microscope. The data were analyzed with ANOVA, followed by the Games-Howell post hoc test or the Kruskal-Wallis test followed by the Mann-Whitney test with Bonferroni adjustment.

RESULTS

The mean flexural strength of the PC group was significantly higher than that of all repaired groups (P<.001). All surface-treated groups showed significantly higher flexural strength (P<.05) and surface roughness (P<.004) than the negative control group. Bur grinding provided significantly higher flexural strength than other surface treatments (P<.001) and higher surface roughness than laser and airborne-particle abrasion plus laser (P<.001).

CONCLUSIONS

All surface treatments significantly increased the surface roughness and flexural strength, but none of them yielded a strength comparable with that of the intact group. Bur grinding provided the highest flexural strength.

Closed Repair Technique: Innovative Surface Design for Polymethylmethacrylate Denture Base Repair

PURPOSE

This study aimed to evaluate the repair strength of a newly introduced repair technique involving zero-gap repair width.

MATERIALS AND METHODS

A total of 36 rectangular prism specimens with dimensions of 64 × 10 × 3.3 mm were prepared from heat-polymerized acrylic resin. Nine specimens were kept intact. The other specimens were sectioned into halves and modified to create repair gaps of 2.5-mm beveled (2.5B) as control, 0-mm beveled (ZB), and 0-mm inverse bi-beveled (ZIBB). The ZIBB group was prepared with a V-shaped internal groove on both halves (repair tunnel), while the intaglio and cameo surfaces were kept intact except for two small holes at the cameo surface for repair resin injection. The 2.5B and ZB groups were repaired conventionally while the ZIBB group was repaired by injecting repair resin into the tunnel through one of the holes until excess material oozed from the other hole. Repaired specimens were thermally cycled at 5 and 55°C for 10,000 cycles with 1 min dwell time. A 3-point bending test was conducted using a universal testing machine for flexural strength and elastic modulus measurement. Kruskal-Wallis/Mann-Whitney tests and ANOVA/post hoc Tukey tests were applied for data analysis (α = 0.05).

RESULTS

The flexural strength of repaired specimens was substantially lower than that of intact specimens, and significant differences were present between repaired groups (p ˂ 0.05). ZB and ZIBB had higher flexural strength (p ˂ 0.001) and elastic modulus (p ˂ 0.05) than 2.5B. Among the ZB and ZIBB groups, ZB showed the highest flexural strength, and ZIBB had the highest elastic modulus.

CONCLUSION

The closed repair technique improved the flexural strength and elastic modulus of repaired acrylic denture base.

Influence of artificial aging and ZrO2 nanoparticle-reinforced repair resin on the denture repair strength

Background

The purpose of this study was to evaluate the effect of aging process on the tensile strength (TS) of repaired acrylic denture base using ZrO2 nanoparticles (nano-ZrO2)-reinforced autopolymerized resin.

Material and Methods

A total of 240 heat-polymerized acrylic resin specimens (n=10) were prepared and sectioned creating 2 mm-repair-gap. Autopolymerized acrylic resin, pure and modified with 2.5, 5, and 7.5wt% nano-ZrO2 were used for specimens repair. TS of repaired specimens were measured using the universal testing machine after water immersion at 37oC for 2, 7 and 30 days. At each time interval, half the immersed specimens underwent thermo-cycling aging process (5000 cycles at 5/55°C) before TS testing. One-way ANOVA and Tukey-Kramer multiple-comparison tests were used for data analysis at α=0.05.

Results

Aging process for all groups showed significant differences in TS between unreinforced and nano-ZrO2 reinforced groups (p<0.05). Within immersed nano-ZrO2-reinforced specimens, 5% group immersed for 30-days showed the highest significant TS value (p<0.05). With regards to thermocycling, 5% group showed the highest TS values after 2-days and 30-days groups while after 7-days, significant differences were found between 2.5% group and 5% and 7.5% groups (p<0.05). SEM images analysis displayed the ductile fracture type for nano-ZrO2 reinforced groups.

Conclusions

In summary, 5.0%-nano-ZrO2 addition to repair resin showed an improvement in tensile strength of repaired acrylic resin with different aging processes. Key words:Acrylic resins, denture repair, tensile strength, thermocycling, water storage, zirconium oxide nanoparticle.

Effect of SiO2 Nanoparticles Addition on the Flexural Strength of Repaired Acrylic Denture Base

Objective  The objective of this study was to evaluate the effect of nano-SiO ₂ addition on the flexural strength (FS) of repaired acrylic denture base.

Materials and Methods  Heat-polymerized acrylic resin specimens were fabricated in dimensions of (65 × 10 × 2.5 ± 0.1 mm ³ ) and then sectioned and prepared, creating repair gap with butt (90 degrees) and bevel (45 degrees) repair surface designs forming two main groups according to joint design. Further subdivision was done into four groups ( n = 10) according to nano-SiO ₂ concentration: one unmodified group and three modified groups (0.25, 0.5, and 0.75 wt %) in the autopolymerized repair resin. Each pair of a specimen was assembled in a mold and repaired according to manufacturer’s recommendations.

Statistical Analysis  Three-point bending test was done to measure FS, followed by scanning electron microscope (SEM) examination for fracture surface analysis. Data were analyzed using ANOVA and Tukey’s post hoc test (α = 0.05).

Results  The addition of nano-SiO ₂ significantly improved FS of repaired acrylic resin in comparison to the unmodified group ( p ˂ 0.05). For butt joint, significant differences between nano-SiO ₂ reinforced groups were noticed ( p ˂ 0.05), while reinforced beveled groups did not differ significantly ( p ˃ 0.05). Bevel design remarkably increased FS compared with butt design per respective filler concentration. From the SEM images, improved FS was presented with a homogeneous distribution of nano-SiO ₂ within polymethyl methacrylate.

Conclusion  Nano-SiO ₂ addition to repair resin and 45 degree-beveled repair surface increased FS of repaired acrylic resin.

Comparative Effect of Glass Fiber and Nano-Filler Addition on Denture Repair Strength

PURPOSE

To evaluate and compare the effects of glass fiber (GF), Zirconium oxide nanoparticles (nano-ZrO₂ ), and silicon dioxide nanoparticles (nano-SiO₂ ) addition on the flexural strength and impact strength of repaired denture base material.

MATERIALS AND METHODS

Heat-polymerized acrylic resin specimens were fabricated. All specimens were sectioned centrally and beveled creating 2.5 mm repair gap except for 10 controls. Specimen grouping (n = 10/group) was done according to filler concentration of 0%, 0.25%, 0.5%, and 0.75% of auto-polymerized acrylic powder. Modified resin was mixed, packed in the repair gap, polymerized, finished and polished. Three-point bending test and Charpy type impact testing were done. Data were analyzed using one-way-ANOVA and Post-Hoc Tukey test (α = 0.05).

RESULTS

All additives significantly increased flexural strength and impact strength (p < 0.05). Within the modified subgroups, no significant differences were found for GF. Significant increase for nano-ZrO₂ and significant decrease for nano-SiO₂ as the concentration of additive increased were noted for both flexural strength and impact strength. Highest flexural strength was found with 0.75%-nano-ZrO₂ (69.59 ± 2.52MPa) and the lowest was found with 0.75%-nano-SiO₂ (53.82 ± 3.10MPa). The 0.25%-nano-SiO₂ showed the highest impact strength value (2.54 ± 0.21 kJ/m² ) while the lowest impact strength value was seen with 0.75%-nano-SiO₂ (1.54 ± 0.17 kJ/m² ).

CONCLUSION

Nano-filler effect was concentration dependent and its addition to repair resin increased the flexural and impact strengths. The incorporation of 0.75%-ZrO₂ or 0.25%-SiO₂ into repair resin proved to be a promising technique to enhance repair strength and avoid repeated fractures.