Trueness and fitting accuracy of maxillary 3D printed complete dentures.

Purpose The trueness and fitting accuracy of complete dentures (CDs) manufactured digitally from wax dentures have not been investigated yet. This study evaluated the trueness and fitting accuracy of maxillary CDs manufactured using computer-aided design technology.Methods CD bases were manufactured from fully edentulous maxillary casts using a milling machine and three three-dimensional (3D) printers (two stereolithography apparatus (SLA) and one digital light processing (DLP)). 3D printing was performed using an SLA printer with eight build support angles (0° to 315°). As a control, a CD base was conventionally fabricated using a heat-polymerized PMMA resin. After the tissue surfaces of the casts and the cameo surfaces of all the CD bases were scanned, their STL data were superimposed with a best-fit alignment. The deviations of all the CD bases were evaluated using data-matching software.Results The milled CD bases showed higher trueness and fitting accuracy compared with the 3D-printed and conventional bases. SLA showed a higher fitting accuracy than DLP. The best support angles for the fitting accuracy were 45° and 225°. The fitting accuracy of the SLA 3D-printed CD bases with an angle of 45° was comparable to or slightly higher than that of conventionally fabricated bases.Conclusions The milled CD bases showed an excellent fitting accuracy. The SLA-printed CDs demonstrated a clinically acceptable fitting accuracy.

Analysis of plaque microbiota and salivary proteins adhering to dental materials.

OBJECTIVES: Plaque causes oral diseases and aspiration-pneumonia in the elderly. It is not known whether pellicle-like attached salivary proteins and microbiota on dental materials are identical to those on teeth. The purpose of this study was to determine the properties of salivary proteins and microbiota that attach to dental materials. METHODS: Eight subjects wore removable oral splints with pieces of pure-titanium, cobalt-chromium alloy, silver-palladium-copper-gold-alloy, denture-base-resin, and hydroxyapatite for 24 h. The bacteria that adhered to each material were analyzed using 16S rRNA sequencing simultaneously. Each material sample was then immersed in pooled saliva, and the attached proteins were collected. Salivary proteins were analyzed using MALDI-TOF/MS, and high molecular weight proteins were identified using peptide mass fingerprinting. RESULTS: Among the dental materials, the α- and ß-diversity of adherent flora were similar. The bacterial species that adhered easily to materials were Streptococcus sp. oral taxon 058, Neisseria mucosa, Gemella haemolysans, and Rothia dentocariosa. Regardless of material, the peaks or spots of attached salivary proteins had similar patterns, containing functioning proteins such as anchoring receptors for early colonizers. CONCLUSIONS: There were no significant differences in microbiota and protein adherence in hydroxyapatite compared to the dental materials. Therefore, similar microbiota was determined to have formed on the similar pellicle-like proteins. In our study, the characteristics of plaque adhesion on both hydroxyapatite and dental materials were clarified. Based on this study, the creation of new methods of inhibiting plaque adhesion to prevent aspiration-pneumonia and oral infections can be undertaken.

Fitness accuracy and retentive forces of additive manufactured titanium clasp.

PURPOSE: Laboratory and clinical assessment of cast titanium dentures were reported, little is known about additive manufacturing (AM) frameworks. This study evaluated in vitro AM titanium alloy clasps for clinical use. METHODS: After scanning the stainless steel dies to simulate the first molar, an Akers clasp was designed by CAD. AM clasp specimens were manufactured using laser sintering and AM machines from CP titanium grade 2 (CPTi), Ti-6Al-4V (Ti64), and Ti-6Al-7Nb (Ti67) powders. As controls, cast titanium clasps were conventionally made with same three titanium alloys. After nondestructive inspection and surface element analysis, surface roughness, fitness accuracy, initial retentive forces, and changes in retentive forces were measured. RESULTS: Although few porosities and little contamination of AM clasps were confirmed, the AM clasp arm and tip indicated slightly worse fitness accuracy as compared to cast clasps. The initial retentive forces of all titanium clasps showed appropriate retentive forces within the acceptable ranges, AM clasps tended to have lower decreases in retentive forces with up to 10,000 insertion/removal cycles as compared to those of the cast clasps. CONCLUSIONS: AM titanium clasps would be acceptable for clinical use similar to that of cast titanium clasps.

In vitro evaluation of a removable partial denture framework using multi-directionally forged titanium.

PURPOSE: This study evaluated the availability of multi-directionally forged (MDF) titanium (Ti) as a component of removable partial dentures (RPDs). MDF-Ti remarkably improved the mechanical properties of RPDs due to its ultrafine-grained structure. MATERIALS AND METHODS: The wear resistance, plaque adhesion, and machinability of MDF-Ti were tested. As controls, commercially pure (CP) titanium was used for wear, plaque adhesion, and machinability tests. For wear resistance, the volume losses of the titanium teeth before and after wear tests were evaluated. Plaque adhesion was evaluated by the assay of Streptococcus mutans. In the machinability test, samples were cut and ground by a steel fissure bur and carborundum (SiC) point. An unpaired t-test was employed for the analysis of the significant differences between MDF-Ti and the control in the results for each test. RESULTS: Wear resistance and plaque adherence of MDF-Ti similar to those of CP-Ti (P>.05) were indicated. MDF-Ti exhibited significantly larger volume loss than CP-Ti in all conditions except 100/30,000 g/rpm in machinability tests (P<.05). CONCLUSION: Although the wear resistance and plaque adherence of MDF-Ti were comparable to those of controls, MDF-Ti showed better machinability than did CP-Ti. MDF-Ti could be used as a framework material for RPDs.

Antimicrobial Activity of Protamine-Loaded Calcium Phosphates against Oral Bacteria.

Protamine is an antimicrobial peptide extracted from fish. In this study, we loaded protamine onto dicalcium phosphate anhydride (DCPA), a dental material. Protamine was loaded by stirring DCPA into a protamine solution. To explore the antimicrobial activity of the materials, we cultivated Streptococcus mutans on fabricated discs for 24 h. When S. mutans was cultivated on the discs under no sucrose conditions, the loaded protamine was not released, and the ratio of dead bacteria increased on the surface of P (125) DCPA (half of the saturated level of protamine (125 ppm protamine) was loaded). Aside from P (500) DCPA (saturated level of protamine was loaded), some protamine was released, and the number of planktonic bacteria in the supernatant decreased. Using medium containing 1% sucrose, the release of protamine was promoted from P (125) DCPA due to lowered pH. However, lowering of the pH decreased the antimicrobial activity of protamine. On the other hand, P (500) DCPA released protamine before the pH was lowered, and biofilm formation was inhibited. The loaded protamine expressed antimicrobial activity, both on the surface of the materials and in the surrounding environment. The interaction of loaded protamine with calcium phosphates could promote the application of protamine in the dental field.

Fitness and retentive force of cobalt-chromium alloy clasps fabricated with repeated laser sintering and milling.

PURPOSE: With computer-aided design and computer-aided manufacturing (CAD/CAM), the study was conducted to create a removable partial denture (RPD) framework using repeated laser sintering rather than milling and casting techniques. This study experimentally evaluated the CAM clasp and compared it to a conventional cast clasp. METHODS: After the tooth die was scanned, an Akers clasp was designed using CAD with and without 50µm of digital relief on the occlusal surface of the tooth die. Cobalt-chromium (Co-Cr) alloy clasps were fabricated using repeated laser sintering (RLS) and milling as one process simultaneously (hybrid manufacturing; HM). The surface roughness of the rest region, gap distances between clasp and tooth die, initial retentive forces, and changes of retentive forces up to 10,000 insertion/removal cycles were measured before and after heat treatment. The HM clasp was compared to the cast clasp and the clasp made by repeated laser sintering only without a milling process. RESULTS: The HM clasp surface was smoother than those of cast and RLS clasps. With the digital relief, the fitness accuracy of the HM clasp improved. The retentive forces of the HM clasps with relief and after heat treatment were significantly greater than for the cast clasp. HM clasps demonstrated a constant or slight decrease of retention up to 10,000 cycles. CONCLUSIONS: HM clasp exhibited better fitness accuracy and retentive forces. The possibility of clinically using HM clasps as well as conventional cast clasps can be suggested.