Maiko Iwaki

Fabrication of titanium alloy frameworks for complete dentures by selective laser melting.

STATEMENT OF PROBLEM Casting difficulties have led to the limited use of titanium in dental prostheses. The selective laser melting system was recently developed to fabricate biomedical components from titanium alloys. However, the fabrication of a titanium alloy framework for a maxillary complete denture by selective laser melting has not yet been investigated. PURPOSE The purpose of the study was to fabricate thin titanium alloy frameworks for a maxillary complete denture with a selective laser melting system and to evaluate their hardness and microstructure. MATERIAL AND METHODS A cast of an edentulous maxilla was scanned with a dental 3-dimensional cone-beam computed tomography system, and standard triangulation language data were produced with the DICOM Viewer (Digital Imaging and Communications in Medicine). Two types of metal frameworks for complete dentures were designed with 3-dimensional computer-aided design software. Two titanium alloy frameworks, SLM-1 and SLM-2, were fabricated from these designs with the selective laser melting system. Plate-shaped specimens were cut from the central flat region of SLM-1, SLM-2, and as-cast Ti-6Al-4V (As-cast). Vickers hardness testing, optical microscopy, and x-ray diffraction measurements were performed. RESULTS Thin titanium alloy frameworks for maxillary complete dentures could be fabricated by selective laser melting. The hardness values for SLM-1 and SLM-2 were higher than that for the as-cast specimen. Optical microscopy images of the SLM-1 and SLM-2 microstructure showed that the specimens did not exhibit pores, indicating that dense frameworks were successfully obtained with the selective laser melting process. In the x-ray diffraction patterns, only peaks associated with the α phase were observed for SLM-1 and SLM-2. In addition, the lattice parameters for SLM-1 and SLM-2 were slightly larger than those for the as-cast specimen. CONCLUSIONS The mechanical properties and microstructure of the denture frameworks prepared by selective laser melting indicate that these dentures are appropriate for clinical use.

Effects of offset values for artificial teeth positions in CAD/CAM complete denture

Recently, computer-aided design/computer-aided manufacturing (CAD/CAM) technology has been applied to the field of removable complete denture prosthodontics. We developed a system for fabricating complete dentures applying CAD/CAM technology. In this system, artificial teeth were bonded to the recesses of a milled denture base. However, the offset values needed for the recesses are not known. The purpose of the present study was to evaluate the accuracy of bonded artificial teeth positions in 0.00 (control), 0.10, 0.15, 0.20, and 0.25mm offset recess groups. Four types of artificial teeth, upper left central incisor (UL1), upper left canine (UL3), upper left first premolar (UL4), and upper left first molar (UL6), were used. Each type of artificial tooth was arranged at regular intervals on the denture base model with the CAD software. These data were defined as the master data. The artificial teeth parts were subtracted from the denture base model by Boolean logic operations in order to make recesses, and the recesses were then offset in five values. Based on these denture base data, prepolymerized resin blocks were milled (n=3). After bonding artificial teeth on the milled denture base model, a cone beam computed tomography (CBCT) scan was performed to obtain scanned data. Deviations between the master data and the scanned data were calculated. Based on the results, the optimal offset values were found to be 0.15-0.25mm for UL1, 0.15 and 0.25mm for UL3, 0.25mm for UL4, and 0.10-0.25mm for UL6.

A randomized controlled trial of the different impression methods for the complete denture fabrication: Patient reported outcomes

OBJECTIVES To compare the effect of conventional complete dentures (CD) fabricated using two different impression methods on patient-reported outcomes in a randomized controlled trial (RCT). METHODS A cross-over RCT was performed with edentulous patients, required maxillomandibular CDs. Mandibular CDs were fabricated using two different methods. The conventional method used a custom tray border moulded with impression compound and a silicone. The simplified used a stock tray and an alginate. Participants were randomly divided into two groups. The C-S group had the conventional method used first, followed by the simplified. The S-C group was in the reverse order. Adjustment was performed four times. A wash out period was set for 1 month. The primary outcome was general patient satisfaction, measured using visual analogue scales, and the secondary outcome was oral health-related quality of life, measured using the Japanese version of the Oral Health Impact Profile for edentulous (OHIP-EDENT-J) questionnaire scores. RESULTS Twenty-four participants completed the trial. With regard to general patient satisfaction, the conventional method was significantly more acceptable than the simplified. No significant differences were observed between the two methods in the OHIP-EDENT-J scores. CONCLUSIONS This study showed CDs fabricated with a conventional method were significantly more highly rated for general patient satisfaction than a simplified. CLINICAL SIGNIFICANCE CDs, fabricated with the conventional method that included a preliminary impression made using alginate in a stock tray and subsequently a final impression made using silicone in a border moulded custom tray resulted in higher general patient satisfaction. TRIAL REGISTRATION UMIN000009875.

Influence of methyl mercaptan at early setting stages on the properties of self curing addition silicone resilient denture lining materials

PURPOSE The aim of the present study was to clarify the influence of early setting conditions on the properties of self curing addition silicone resilient denture lining materials. METHODS Four auto-mix types of commercial self curing addition silicone resilient denture lining materials were used. Agar plates containing various concentrations of methyl mercaptan (MMP) were prepared and cylindrical specimens (10mm in height and 10mm in diameter) of silicone liners were set on the agar plate. The Shore A hardness of the agar-contacted surface of the specimen was measured at 0, 1, 7 and 28 days after stored in 37 degrees C water. The viscoelastic properties (instantaneous elastic modulus, coefficient of viscosity and permanent deformation) of two silicone liners, which showed a great decrease in the Shore A hardness by agar contact, were determined by a creep meter. RESULTS The Shore A hardness, coefficient of viscosity, and instantaneous elastic modulus deceased when the specimen was set on the MMP containing agar plate, but the permanent deformation of these specimens increased. CONCLUSION The exposure to MMP at the early setting stage influenced the properties of self curing addition silicone resilient denture lining materials.

The effect of new complete denture fabrication and simplified dietary advice on nutrient intake and masticatory function of edentulous elderly: A randomized-controlled trial

BACKGROUND & AIM Combination of new complete denture fabrication and tailored dietary counseling is necessary to improve nutrient intake of the edentulous elderly. However, there is no evidence on the effect of simple dietary advice combined with new complete denture fabrication on the nutrient intake of the edentulous elderly. The aim of this study was to clarify the combined effect of new complete denture fabrication and simple dietary advice, using a uniform pamphlet, on the nutrient intake and masticatory function of edentulous elderly. The null hypothesis was that there would be no difference in the nutrient intake and masticatory function between edentulous elderly patients provided with simple dietary advice and new complete dentures and those provided with new dentures alone. METHODS A double-blind, randomized-controlled, parallel clinical trial was performed on the healthy edentulous elderly who were required to fabricate a new pair of complete denture. The participants were randomly divided into two groups, and each group received different advice: the intervention group received simple dietary advice using a uniform pamphlet, whereas the control group received denture care advice. During the process of new complete denture fabrication, two 20-min one-on-one advice sessions were conducted by a dentist. The primary outcome of this trial was protein intake, which was calculated from the responses in the brief-type self-administered diet history questionnaire (BDHQ). Secondary outcome was masticatory function, which was measured with a color-changeable chewing gum and a test gummy jelly. Outcome assessment was conducted twice, at baseline and at 3 months post-treatment. RESULTS Among 70 participants who were randomized, 62 completed this trial. Protein intake in the intervention group significantly increased compared with that in the control group. Masticatory function was not significantly different between groups, but significantly increased at 3 months post-treatment compared with the baseline in both groups. CONCLUSION Simple dietary advice using a uniform pamphlet and a new complete denture fabrication increased nutrient intake and masticatory function of healthy edentulous elderly. CLINICAL TRIAL REGISTRATION NUMBER https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000020716 UMIN000017879.

Evaluating the influence of ambient light on scanning trueness, precision, and time of intra oral scanner

PURPOSE This study evaluated the influence of illuminance and color temperature of ambient light on the trueness, precision, and scanning time of a digital impression. METHODS Master data were acquired with a high-accuracy coordinate-measuring machine. The illuminance of ambient light was set at 0lux, 500lux, and 2500lux with a light-emitting diode (LED). Using a conversion filter, the color temperature was set at 3900 Kelvin (K) (yellow), 4100K (orange), 7500K (white), and 19,000K (blue). There were thus a total of 12 possible lighting conditions. The reference model was scanned five times under each condition by an intraoral scanner. Trueness was calculated as the mean difference between the master data and experimental data. Precision was calculated as the mean difference between the repeated scans in each test group. Statistical analysis was performed with two-way analysis of variance (ANOVA) and post hoc Tukeys multiple comparison test. The significance level was 0.05. RESULTS For trueness, the mean deviation was significantly lower at 500lux than at 0lux and 2500lux. At 500lux, the mean deviation was significantly lower at 3900K than at other temperatures. Regardless of the color temperature, the scanning time was significantly longer at 2500lux than at other illuminance levels. CONCLUSIONS The 3900K and 500lux condition is the most appropriate lighting condition for taking a digital impression. This condition is typical of clinical settings. High illuminance ambient light increased the scanning time.

Digital impression and jaw relation record for the fabrication of CAD/CAM custom tray

PURPOSE This article describes the protocol of a digital impression technique to make an impression and recording of the jaw relationship of edentulous patients for the fabrication of CAD/CAM custom tray using computer-aided design and manufacturing (CAD/CAM) technology. METHODS Scan the maxillary and mandibular edentulous jaws using an intraoral scanner. Scan the silicone jig with the maxillary and mandibular jaws while keeping the jig between the jaws. Import the standard tessellation language data of the maxillary and mandibular jaws and jig to make a jaw relation record and fabricate custom trays (CAD/CAM trays) using a rapid prototyping system. Make a definitive impression of the maxillary and mandibular jaws using the CAD/CAM trays. CONCLUSIONS Digitalization of the complete denture fabrication process can simplify the complicated treatment and laboratory process of conventional methods In addition, the proposed method enables quality control regardless of the operators experience and technique.