Evaluation of Shear Bond Strength Between Denture Teeth and 3D-Printed Denture Base Resin

An in vitro evaluation of bond strength and failure behavior between 3D-printed cobalt-chromium alloy and different types of denture base resins

OBJECTIVES

This study aimed to evaluate the shear bond strength and failure behavior between cobalt-chromium (Co-Cr) alloy and different types of denture base resins (DBRs) over time.

METHODS

Seventy-two disk-shaped specimens (8 mm in diameter and 2 mm in thickness) were manufactured using a selective laser melting technology-based metal 3D printer. Three types of DBRs were used: heat-cure (HEA group), cold-cure (COL group), and 3D-printable (TDP group) DBRs (n = 12 per group). Each DBR specimen was fabricated as a 5 mm × 5 mm × 5 mm cube model. The specimens of the TDP group were manufactured using a digital light processing technology-based 3D printer. Half of the DBRs were stored in distilled water at 37 °C for 24 h, whereas the remaining half underwent thermocycling for 10,000 cycles. Shear bond strength was measured using a universal testing machine; failure modes were observed, and metal surfaces were evaluated using energy dispersive spectrometry.

RESULTS

The shear bond strength did not differ between the DBR types within the non-thermocycled groups. Contrarily, the TDP group exhibited inferior strength compared to the HEA group (P = 0.008) after thermocycling. All three types of DBRs exhibited a significant decrease in the shear bond strength and an increased tendency toward adhesive failure after thermocycling.

CONCLUSIONS

The bond strength between 3D-printable DBRs and Co-Cr alloy was comparable to that of heat-and cold-cure DBRs before thermocycling. However, it exhibited a considerable weakening in comparison to heat-cure DBRs after simulated short-term use.

CLINICAL SIGNIFICANCE

The application of 3D-printable DBR in metal framework-incorporated removable partial dentures may be feasible during the early phase of the treatment. However, its application is currently limited because the bond strength between the 3D-printable DBR and metal may weaken after short-term use. Further studies on methods to increase the bond strength between these heterogeneous materials are required.

In Vitro Analysis of Bonding and Wear Properties of 3D Printed Denture Tooth Materials

PURPOSE

While additive manufacturing (3D printing) has recently enhanced removable prosthodontics, the properties of new 3D printed materials are not well understood. This study aims to elucidate the physical properties of these materials, focusing on bonding to a 3D printed denture base material and wear resistance.

METHODS

For denture tooth-denture base bonding analyses, the same denture tooth material (Premium Teeth, Formlabs) was used with three denture base-bonding group assignments (n=6 each group) bonded using three protocols: Group A1 was bonded with Lucitone Digital Print-3D Denture Base using the Lucitone Fuse System (Dentsply), Group A2 with Formlabs Denture Base using the Formlabs Denture Base Bonding System, and Group A3 with Formlabs Denture Base using the Ivoclar Ivotion Bonding System (Ivoclar). Specimens were made according to the ISO-TS-19736-2027 standard. A 3D printed tooth mimicking a central incisor was bonded to the denture base and subjected to a palatal load at the incisal region at 90° from the long axis of the tooth until failure. The fracture surface was examined at 10× magnification. ANOVA with α=0.05 was used to determine statistically significant differences. For wear analysis, the same denture base material and bonding system (Lucitone Digital Print-3D Denture Base/Lucitone Fuse System, Dentsply) was used with four denture tooth material group assignments (n=8 each group): Group B1 used Formlabs Premium Teeth, Group B2 used SprintRay High Impact Denture Teeth, Group B3 used Lucitone Digital IPN Premium Tooth, and Group B4 used Ivotion Polymethyl Methacrylate (PMMA) Milled Teeth (Ivoclar). A premolar denture tooth bonded with the denture base was subjected to a chewing simulation cyclic loading of 1,200,000 cycles. Sample failures, vertical wear, and volume loss were documented. ANOVA with α=0.05 was used to determine statistically significant differences.

RESULTS

The fracture load to failure values for A1, A2, and A3 were 175±106 N, 167±46.3 N, and 183±48.9 N, respectively (p=0.95). Most failure characteristics were mixed, except one of A2 was cohesive and half of A3 was cohesive. For cyclic loading, B4 was the only group where all specimens failed within 1,200,000 cycles, while B1, B2, and B3 had four, three, and five sample failures, respectively. Vertical wear was 0.93±0.34 mm, 1.22±0.37 mm, 1.05±0.27 mm, and 0.37±0.02 mm for B1, B2, B3, and B4, respectively (p<0.01). Abrasion volumes were 9.5±3.7 mm³, 12.2±4.7 mm³, 10.6±3.5 mm³, and 2.2±1.3 mm³ for B1, B2, B3, and B4, respectively. Vertical height loss per chewing cycle (μm/cycle) was 0.0022±0.0019, 0.0030±0.0029, 0.0012±0.00005, and 0.0080±0.0050 for B1, B2, B3, and B4, respectively (p<0.01). Abrasion volume per chewing cycle (μm³/cycle) was 17650.8±9682.9, 27263.4±24746.8, 11836.5±4200.8, and 70436.8±73602.5 for B1, B2, B3, and B4, respectively (p=0.02).

CONCLUSION

The bonding strength and wear resistance of 3D printed denture materials vary by manufacturer. Formlabs Denture Base with Ivoclar Ivotion showed the highest fracture load, indicating superior bonding strength. In wear analysis, Ivoclar Ivotion PMMA Milled Teeth exhibited the least vertical wear and abrasion volume but had the highest failure rate under cyclic loading. While printed denture materials excel in bonding strength, their wear resistance may not be as good as milled denture teeth, highlighting the need to balance these properties in clinical applications.

Bonding Efficiency between Artificial Teeth and Denture Base in CAD/CAM and Conventional Complete Removable Dentures

A common challenge encountered with both traditional and digitally produced dentures involves the extraction of artificial teeth from the denture base. This narrative review seeks to present an updated perspective on the adherence of synthetic teeth for denture base materials, employing diverse methods. Dental technicians often employ chemical approaches and mechanical techniques (including abrasion, laser treatment, and abrasive blasting) to augment the retention of denture teeth. However, the efficacy of these treatments remains uncertain. In certain instances, specific combinations of Denture Base Resin (DBR) materials and artificial teeth exhibit improved performance in conventional heat-cured dentures following these treatments. The primary reasons for failure are attributed to material incompatibility and inadequate copolymerization. As new denture fabrication techniques and materials continue to emerge, further research is imperative to identify optimal tooth-DBR combinations. Notably, 3D-printed tooth-DBR combinations have demonstrated reduced bond strength and less favorable failure patterns, while utilizing milled and traditional combinations appears to be a more prudent choice until advancements in additive manufacturing enhance the reliability of 3D-printing methods.

Targeting bonding protocols to increase the bond between acrylic resin or 3D printed denture bases and prefabricated or 3D printed denture teeth

STATEMENT OF PROBLEM

The difference in chemical composition between denture base resin and denture teeth requires the development of bonding protocols that increase the union between the materials.

PURPOSE

The purpose of this in vitro study was to evaluate the impact of different bonding protocols on the bond between heat-polymerized and 3-dimensionally (3D) printed acrylic resin denture bases and acrylic resin prefabricated and 3D printed artificial teeth.

MATERIAL AND METHODS

Four types of artificial teeth were evaluated: prefabricated acrylic resin (VITA MFT) and 3D printed (Cosmos TEMP, PRIZMA 3D Bio Denture, and PrintaX AA Temp) bonded to 20×24-mm cylinders of heat-polymerized (VipiWave) and 3D printed (Cosmos Denture, PRIZMA 3D Bio Denture, and PrintaX BB Base) denture bases. Three bonding protocols were tested (n=20): mechanical retention with perforation + monomer (PT1), mechanical retention with perforation + airborne-particle abrasion with 50-µm aluminum oxide + monomer (PT2), and mechanical retention with perforation + Palabond (PT3). Half of the specimens in each group received 10 000 thermocycles and were then subjected to the bonding test at a crosshead speed of 1 mm/minute. The failure type was analyzed and scanning electron micrographs made. Additionally, surface roughness (Ra) and wettability (degree) were analyzed (n=15). ANOVA was used to evaluate the effect of the bonding protocol, and the Student t test was applied to compare the experimental groups with the control (α=.05). For type of failure, a descriptive analysis was carried out using absolute and relative frequency. The Kruskal-Wallis test was used to evaluate the surface changes (α=.05).

RESULTS

Among the protocols, PT3 with in Yller and PT2 with Prizma had the highest bond strengths of the heat-polymerized denture base and 3D printed teeth (P<.05). When comparing the experimental groups with the control, PT3 and PT2 had greater union with the 3D printed denture base + 3D printed teeth (in Yller), with no difference from the heat-polymerized denture base + prefabricated teeth in acrylic resin. The treatment of the 3D printed tooth surfaces affected the surface roughness of Prizma (P<.001) and wettability (P<.001).

CONCLUSIONS

To increase the bond between Yller 3D printed denture base + 3D printed teeth, a bonding protocol including mechanical retention with perforation + Palabond or mechanical retention with perforation + airborne-particle abrasion with aluminum oxide + monomer is indicated. For the other materials tested, further bonding protocols need to be investigated.

Shear bond strength of ultraviolet-polymerized resin to 3D-printed denture materials: Effects of post-polymerization, surface treatments, and thermocycling

PURPOSE

The purpose of this study is to compare the shear bond strength of ultraviolet (UV)-polymerized resin to 3D-printed denture materials, both with and without post-polymerization. Moreover, the effects of surface treatment and thermocycling on shear bond strength after post-polymerization were investigated.

METHODS

Cylindrical 3D-printed denture bases and teeth specimens were prepared. The specimens are subjected to two tests. For Test 1, the specimens were bonded without any surface treatment or thermal stress for comparison with and without post-polymerization. In Test 2, specimens underwent five surface treatments: untreated (CON), ethyl acetate (EA), airborne particle abrasion (APA) with 50 μm (50-APA) and 110 μm alumina (110-APA), and tribochemical silica coating (TSC). A UV-polymerized resin was used for bonding. Half of the Test 2 specimens were thermocycled for 10,000 cycles. Shear bond strength was measured and analyzed using Kruskal-Wallis and Steel-Dwass tests (n = 8).

RESULTS

In Test 1, post-polymerization significantly reduced shear bond strength of both 3D-printed denture materials (P < 0.05). No notable difference was observed between the denture teeth and the bases (P > 0.05). In Test 2, before thermocycling, the CON and EA groups exhibited low bond strengths, while the 50-APA, 110-APA, and TSC groups exhibited higher bond strengths. Thermocycling did not reduce bond strength in the latter groups, but significantly reduced bond strength in the EA group (P < 0.001).

CONCLUSIONS

Post-polymerization can significantly reduce the shear bond strength of 3D-printed denture materials. Surface treatments, particularly APA and TSC, maintained bond strength even after thermocycling.

Artificial teeth obtained by additive manufacturing: Wear resistance aspects. A systematic review of in vitro studies

Wear resistance is one of the properties that must be considered for maintaining the long-term functionality of artificial teeth in dental prostheses. This property can be altered by the method of tooth fabrication, the material, the chewing force, and the relationship to the antagonist tooth. This systematic review evaluated the wear resistance of artificial teeth obtained by the additive manufacturing method and aims to answer the question, "Do artificial teeth for dental prostheses obtained by additive manufacturing show wear resistance similar to prefabricated ones?" The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Checklist guidelines were followed with a customized search in Scopus, PubMed/Medline, Embase, Science Direct, and Google Scholar databases on August 30, 2023. The inclusion criteria were artificial teeth for dental prostheses in acrylic resin by additive manufacturing and comparing the wear resistance with conventional prefabricated teeth, in vitro and English studies, without time restriction. And excluded if 1) do not make artificial teeth by additive manufacturing or that were metal or ceramic teeth; 2) clinical trials, animal studies, review articles, case reports, letters to the editor, short communication, book chapters; 3) another language that is not English. The selection was in two steps, reading the titles and abstracts, followed by reading the selected studies in full. The risk of bias analysis was performed with the adaptation of the quasi-experimental studies tool by Joanna Briggs Institute. Four hundred and twelve articles were found in the databases, after the selection steps and application of eligibility criteria, 6 articles were included for qualitative data analysis and presented low risk of bias. For teeth obtained by additive manufacturing, 2 studies reported lower wear resistance, 2 studies had higher resistance, and 2 similar compared to prefabricated ones. Additive manufactured teeth compared to prefabricated teeth show influences on wear resistance due to differences in material composition, relationship to the antagonist's tooth, applied force, chewing cycles, and processing methods.

Biomaterials Adapted to Vat Photopolymerization in 3D Printing: Characteristics and Medical Applications

Along with the rapid and extensive advancements in the 3D printing field, a diverse range of uses for 3D printing have appeared in the spectrum of medical applications. Vat photopolymerization (VPP) stands out as one of the most extensively researched methods of 3D printing, with its main advantages being a high printing speed and the ability to produce high-resolution structures. A major challenge in using VPP 3D-printed materials in medicine is the general incompatibility of standard VPP resin mixtures with the requirements of biocompatibility and biofunctionality. Instead of developing completely new materials, an alternate approach to solving this problem involves adapting existing biomaterials. These materials are incompatible with VPP 3D printing in their pure form but can be adapted to the VPP chemistry and general process through the use of innovative mixtures and the addition of specific pre- and post-printing steps. This review's primary objective is to highlight biofunctional and biocompatible materials that have been adapted to VPP. We present and compare the suitability of these adapted materials to different medical applications and propose other biomaterials that could be further adapted to the VPP 3D printing process in order to fulfill patient-specific medical requirements.

A comparison of the shear bond strength between denture teeth and denture base resins manufactured either conventionally or with a 3D printer

STATEMENT OF PROBLEM

Limited information is available on the shear bond strength (SBS) between denture teeth and denture base resins fabricated using a stereolithography (SLA) 3-dimensional (3D) printer.

PURPOSE

The purpose of this in vitro study was to evaluate the SBS between denture teeth and the denture base resins produced with the conventional method and with a 3D printer.

MATERIAL AND METHODS

Conventional or 3D printed denture teeth were included in the study. The denture base resins were manufactured either conventionally or with a 3D printer. Four subgroups were tested: conventional teeth-conventional base resin (CT-CB), conventional teeth-printed base resin (CT-PB), printed teeth-conventional base resin (PT-CB), and printed teeth-printed base resin (PT-PB). The maxillary molars were combined with Ø5×2.5-mm-cylindrical denture base resin. Shear bond testing was performed by applying a parallel force to the denture teeth-denture base resin interface by using a blade-edge chisel with a crosshead speed of 1 mm/min until failure occurred. SBS and elastic modulus (EM) were recorded. One-way ANOVA followed by the Dunnett T3 post hoc test was used for the statistical analysis (α=.05). The failure modes of the specimens were also analyzed.

RESULTS

A statistically significant difference (P<.05) was found between the evaluated groups for the SBS and EM values. PT-PB showed the highest SBS value (15.4 ±2.7 MPa), and CT-PB showed the lowest (0.9 ±0.7 MPa). The PT-CB group showed the highest EM value (62.74 ±20.80 GPa), and the CT-PB group showed the lowest (29.46 ±28.40 GPa). The CT-CB and CT-PB specimens showed mostly adhesive failure; none of the PT-PB specimens showed adhesive failure.

CONCLUSIONS

Three-dimensional printing led to a better bond between the denture teeth and the denture base resin compared with the conventional method. Although these findings need to be supported by clinical studies, the use of 3D printers is appropriate in the production of denture teeth and denture bases.

Bond strength of CAD/CAM denture teeth to a denture base resin in a milled monolithic unit

Purpose Herein, the bond strength (BS) of denture teeth to a denture base resin in a milled monolithic unit was investigated and compared with those of 3D printed teeth to a 3D printed denture base and prefabricated teeth to a heat-cured acrylic resin before and after thermocycling.Methods Sixty specimens of a denture tooth attached to a cylindrical denture base were fabricated following ISO Standard 19736. Three fabrication techniques-3D printing, conventional compression molding, and milling using monolithic technology-were employed to mill teeth and denture base parts as a single unit. The BS was investigated before and after thermocycling. Data were statistically analyzed using the Kruskal-Wallis test with Bonferroni correction (α = 0.05).Results Before thermocycling, the mean BS of the milled group was significantly higher than that of the conventional group (P = 0.002). The 3D printed group showed no statistically significant difference from the milled (P = 0.051) and conventional (P = 0.824) groups. After thermocycling, although the mean BS values of the milled (P = 0.00) and 3D printed 
(P = 0.01) groups were significantly higher than that of the conventional group, there was no significant difference between them (P = 0.226). Only the BS of the conventional group was significantly reduced by thermocycling (P = 0.00).Conclusions The milled monolithic fabrication technique, which eliminates the need for a bonding step, offered a promising combination of high-precision digital fabrication and a significantly high BS. The BS of the conventional group significantly decreased after thermocycling.

Microbial adhesion and biofilm formation by Candida albicans on 3D-printed denture base resins

This study evaluated surface properties and adhesion/biofilm formation by Candida albicans on 3D printed denture base resins used in 3D printing. Disc-shaped specimens (15 mm x 3 mm) of two 3D-printed resins (NextDent Denture 3D+, NE, n = 64; and Cosmos Denture, CO, n = 64) and a heat-polymerized resin (Lucitone 550, LU, control, n = 64) were analyzed for surface roughness (Ra μm) and surface free energy (erg cm-2). Microbiologic assays (90-min adhesion and 48-h biofilm formation by C. albicans) were performed five times in triplicate, with the evaluation of the specimens' surface for: (i) colony forming units count (CFU/mL), (ii) cellular metabolism (XTT assay), and (iii) fluorescence and thickness of biofilm layers (confocal laser scanning microscopy). Data were analyzed using parametric and nonparametric tests (α = 0.05). LU presented higher surface roughness Ra (0.329±0.076 μm) than NE (0.295±0.056 μm) (p = 0.024), but both were similar to CO (0.315±0.058 μm) (p = 1.000 and p = 0.129, respectively). LU showed lower surface free energy (47.47±2.01 erg cm-2) than CO (49.61±1.88 erg cm-2) and NE (49.23±2.16 erg cm-2) (p<0.001 for both). The CO and NE resins showed greater cellular metabolism (p<0.001) and CO only, showed greater colonization (p = 0.015) by C. albicans than LU in the 90-min and 48-hour periods. It can be concluded that both 3D-printed denture base resins are more prone to colonization by C. albicans, and that their surface free energy may be more likely associated with that colonization than their surface roughness.

Adhesion of Conventional, 3D-Printed and Milled Artificial Teeth to Resin Substrates for Complete Dentures: A Narrative Review

BACKGROUND

One type of failure in complete or partial dentures is the detachment of resin teeth from denture base resin (DBR). This common complication is also observed in the new generation of digitally fabricated dentures. The purpose of this review was to provide an update on the adhesion of artificial teeth to denture resin substrates fabricated by conventional and digital methods.

METHODS

A search strategy was applied to retrieve relevant studies in PubMed and Scopus.

RESULTS

Chemical (monomers, ethyl acetone, conditioning liquids, adhesive agents, etc.) and mechanical (grinding, laser, sandblasting, etc.) treatments are commonly used by technicians to improve denture teeth retention with controversial benefits. Better performance in conventional dentures is realized for certain combinations of DBR materials and denture teeth after mechanical or chemical treatment.

CONCLUSIONS

The incompatibility of certain materials and lack of copolymerization are the main reasons for failure. Due to the emerging field of new techniques for denture fabrication, different materials have been developed, and further research is needed to elaborate the best combination of teeth and DBRs. Lower bond strength and suboptimal failure modes have been related to 3D-printed combinations of teeth and DBRs, while milled and conventional combinations seem to be a safer choice until further improvements in printing technologies are developed.

Orthodontic shear bond strength and ultimate load tests of CAD/CAM produced artificial teeth

OBJECTIVES

To investigate whether artificial CAD/CAM processed (computer-aided design/manufacturing) teeth could be a feasible option for the production of dental in vitro models for biomechanical testing.

MATERIAL AND METHODS

Disks (n = 10 per group) made from two different CAD/CAM-materials, one fiber-reinforced composite (FRC; Trinia, Bicon) and one polymethylmethacrylate-based resin (PMMA; Telio CAD, Ivoclar Vivadent), as well as bovine teeth (n = 10), were tested for their shear bond strength (SBS) and scored according to the adhesive remnant index (ARI). In addition, CAD/CAM-manufactured lower incisor teeth were tested for their ultimate load (F_u).

RESULTS

With regard to SBS, both PMMA (17.4 ± 2.2 MPa) and FRC (18.0 ± 2.4 MPa) disks showed no significant difference (p = 0.968) compared to bovine disks (18.0 ± 5.4 MPa). However, the samples differed with regard to their failure mode (PMMA: ARI 4, delamination failure; FRC: ARI 0 and bovine: ARI 1.6, both adhesive failure). With regard to F_u, FRC-based teeth could withstand significantly higher loads (708 ± 126 N) than PMMA-based teeth (345 ± 109 N) (p < 0.01).

CONCLUSION

Unlike PMMA-based teeth, teeth made from FRC showed sufficiently high fracture resistance and comparable SBS. Thus, FRC teeth could be a promising alternative for the production of dental in vitro models for orthodontic testing.

CLINICAL RELEVANCE

CAD/CAM-processed teeth made from FRC enable the use of standardized geometry and constant material properties. Using FRC teeth in dental in vitro studies has therefore the potential to identify differences between various treatment options with rather small sample sizes, while remaining close to the clinical situation.