In vitro assessment of polishing efficiency for additive-manufactured Co-Cr alloy clasps.

PURPOSE: The processes and methods of treating and polishing additive-manufactured (AMed) cobalt-chromium (Co-Cr) alloy clasps were assessed in vitro to determine their suitability for constant clinical use and the reduction of dental technician work. METHODS: AMed Aker clasps were fabricated by selective laser sintering of approximately 50 µm Co-Cr alloy powders. After the nodules and fins on the inner surface of the AMed clasps were removed and morphological correction was performed, a dental technician manually polished the clasps as a control. Four surface treatments, barrel finishing, shot peening, and wet and dry electropolishing, were performed to obtain smooth surfaces. In addition, hybrid manufacturing, which integrates repeated laser sintering and high-speed milling for one-process molding, was added to this study. After observing the treated surfaces using SEM and Hybrid Laser Microscope (HLM) the surface roughness, fitness accuracy, and retentive forces of the treated AMed clasps were measured, and their polishing efficiencies were compared. RESULTS: Similar to manual polishing, dry electropolishing yielded the smoothest surfaces in all treatments. The fitness accuracy of all clasp regions and treatment methods ranged from 80 to 140 µm, without significant differences among the treatment methods. All treated clasps showed acceptable retentive forces for clinical use, and hybrid manufacturing and wet electropolishing showed significantly higher forces. CONCLUSIONS: AMed Co-Cr clasps with all surface treatments could be clinically used if additional slight manual polishing was performed; however, each processing condition should be carefully selected.

Fabrication of mucocompressive splints for free gingival grafts via medical engineering in patients with reconstructed mandibles.

PURPOSE: Acquiring adequate attached mucosa is important in restoring masticatory function with a removable dental prosthesis or dental implant. In patients with inadequate attached mucosa, a free gingival graft (FGG) with a custom stent is used. However, it is challenging to apply the conventional method for fabricating a stent with a reshaped cast in patients with reconstructed mandibles because the reconstructed mandible has limitations due to a titanium mesh, skin flap, and unique bone morphology. In the present report, we have proposed a new design and fabrication process for a mucocompressive splint via medical engineering to acquire the attached mucosa for the prosthodontic treatment of reconstructed mandibles. METHODS: Three-dimensional (3D) craniomandibular models were reconstructed from a computed tomography dataset after mandibular reconstruction. The dentition region was replaced with highly precise scan data of the dental casts using a 3D scanner. The alveolar ridge mucosa and teeth were ideally designed using the 3D model while referring to the anatomical structures. The jig used to fabricate the working dental cast with artificial gum in real space was designed and fabricated using a 3D printer. The alveolar ridge was altered into a simulated configuration on the articulator using a jig. A mucocompressive splint was fabricated on an altered dental cast. The splint was immediately seated on the mandible without any major adjustments after the FGG. CONCLUSION: Adequate attached mucosa for the prosthodontic treatment of a reconstructed mandible was obtained by the pre-surgical fabrication of a mucocompressive splint through medical engineering.

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.

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.

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.

Clinical Usefulness of Mandibular Reconstruction Using Custom-Made Titanium Mesh Tray and Autogenous Particulate Cancellous Bone and Marrow Harvested From Tibia and/or Ilia.

The objective of this study was to evaluate usefulness of mandibular reconstructions using custom-made titanium mesh (Ti-mesh) tray and particulate cancellous bone and marrow (PCBM). Consecutive 21 patients who underwent mandibular reconstruction were enrolled in this study. They were 13 men and 8 women (mean age, 52.0 years). Virtual reality simulation was performed using computer software based on the preoperative computed tomography data. A 3-dimensional skull model was constructed using 3-dimensional printer. A tray was custom-made from Ti-mesh sheet bent to adapt to the model. After PCBM harvesting from posterior ilia and/or proximal tibia, the tray was fixed to the host bone. New bone formation and configuration of the reconstructed mandible were assessed radiologically. Complications were recorded in each patient during the follow-up period. Patients' satisfaction with postoperative facial contour was evaluated using visual analog scale (VAS score, range, 0-100). In 16 of 21 patients, excellent new bone formation was recognized and expected results were radiologically achieved. In 5 patients, new bone formation was insufficient. Causes of insufficient bone formation included postoperative infection in 2 patients, Ti-mesh tray fracture in 2 patients, and local recurrence of lower gingival cancer in 1 patient. To prevent a tray fracture, a double-layered Ti-mesh tray was useful. Mean VAS score on patients' satisfaction was 77.1. Our results comprehensively suggest that mandibular reconstruction using custom-made Ti-mesh tray and PCBM is clinically useful.

Computer assisted mandibular reconstruction using a custom-made titan mesh tray and removable denture based on the top-down treatment technique.

PURPOSE: The purpose of this report is to propose a computer assisted mandibular reconstruction procedure, utilizing a custom-made Ti-mesh tray with particulate cancellous bone and marrow, and a removable denture. This procedure was based on the top-down treatment technique, and reviews the case of a representative patient with mandibular continuity defect. METHODS: The patient was a 74-year old female with a chief complaint of facial asymmetry and masticatory dysfunction. Due to gingival carcinoma, she underwent a segmental mandibulectomy on the left mandibule. On the VR space, using 3-D reconstructed computer tomography data, the residual right-side mandibular fragment was repositioned based on the condylar position and the occlusal relation. The mandibular fragment was then mirrored for a central sagittal plane. The position of the mirrored object was slightly arranged with the occlusal relation. Through the above operations, the landmark configuration, for the custom-made Ti-mesh tray as a virtual simulation model, was fabricated. On the physical model, we produced a custom-made Ti-mesh tray with a commercial Ti-mesh sheet. Surgical treatment was carried out using the tray. The denture pattern was designed by a dental technician on the VR space, fabricated using a 3D printer, and modified to create an impression tray with resin. Using the impression, the temporary removable denture was fabricated. CONCLUSIONS: We propose a computer assisted design for a custom-made Ti-mesh tray and a removable denture, based on the Top-down treatment concept. We feel this technique is advantageous in reconstructing functional occlusion, and in accurately regaining dental and facial esthetics.

Fabrication of crown restoration retrofitting to existing clasps using CAD/CAM: fitness accuracy and retentive force.

PURPOSE: A crown restoration engaged by a clasp as an abutment tooth for a removable partial denture (RPD) occasionally might be removed and eliminated due to secondary caries or apical lesions. However, if the RPD is clinically acceptable without any problems and refabricating the RPD is not recommended, the new crown must be made to retrofit to the existing clasp of the RPD. This in vitro study evaluated the conventional and CAD/CAM procedures for retrofitting crown restorations to the existing clasps by measuring the fitness accuracy and the retentive forces. METHODS: The crown restoration on #44 was fabricated with CP titanium and zirconium on the plaster model with #45 and #46 teeth missing to retrofit to the existing clasp using conventional thin coping and CAD/CAM procedures. The gap distance between the clasp (tip, shoulder, and rest regions) and the fabricated crown was measured using silicone impression material. The retentive force of the clasp was also measured, using an autograph at a crosshead speed of 50mm/min. The obtained data were analyzed by one-way ANOVA/Tukey's multiple comparison test (α=0.05). RESULTS: The CAD/CAM procedure caused significantly smaller gap distances in all of the clasp regions, as compared to the conventional procedure (p<0.05). The retentive force of the CAD/CAM crown was significantly higher than for the conventional one (p<0.05). CONCLUSION: When a crown restoration must be remade to retrofit an existing clasp, CAD/CAM fabrication can be recommended so that both appropriate fitness and retentive force are obtained.

The development and clinical application of novel connectors for oral appliance.

PURPOSE: Currently, over 40 different types of oral appliances (OA) are available to dentists to treat sleep disordered breathing. OA can be classified by mode of action or design. One of the major categories is tongue retaining device; the other is a mandibular advancement device (MAD). Each device, however, has its own particular drawbacks, the most common revolving around cost or inherent difficulties in the production process.In this present report, we will introduce a "movable" OA which does not disturb the physiologic function. This approach utilizes novel connectors that are both low in cost and involve a straightforward production procedure. METHODS: Our device is categorized as a MAD. The design of the appliance followed that of the cap clasp, and the undercut was set at 0.25 mm. The polyester sheet was pressed to casts via a pressure molding machine, and cut along the design line mentioned above. In our device, we converted a Co-Cr wire as a connector for the OA. From this we developed and applied 2 new connectors for the clinical setting that were low in cost and allowed for mandible movement. These are lingual-side and labial-side types. In this present study the rate of success was 75.5%; with a good response classified as an AHI with less than 5 events/h, or a 50% decrease in their pre-treatment AHI. The efficacy of our OA was equal to previous studies. CONCLUSION: In this present report, we could propose inexpensive novel connectors which do not disturb the physiologic function.

Investigation of trends and characteristics in patients with obstructive sleep apnea.

BACKGROUND: Oral appliance (OA) therapy for obstructive sleep apnea (OSA) has only been part of Japan's National Health care coverage plan since 2004. Subsequently, not enough time has passed to establish the medical trends and characteristics of OSA patients in Japanese Dental Hospitals. AIM: The aim of this study was to investigate the medical trends and the characteristics in patients with OSA who visited our clinic, and to compare our findings with previous studies. SETTING AND DESIGN: Epidemiological survey (retrospective study). MATERIALS AND METHODS: Two hundred and one patients were recruited at the Internal Medicine Division in the Tsurumi University Dental Hospital from February 2006 to December 2008, consecutively. Patients received a medical interview, and a detailed sleep analysis that included a polysomnography (PSG) to verify the exact nature of their condition. The efficacy of OA was assessed in 49 patients who wore an OA and underwent PSG. RESULTS: Of all subjects, 141 patients visited the Prosthodontic Division to receive OA therapy, 38 patients were treated or received a follow up examination in the Internal Medicine Division. The dropout rate was 10.4% in the all subjects, 17.0% in patients who visited the Prosthodontic Division. The male-to-female ratio was 3.3:1, 3.0:1 in patients who visited the Prosthodontic Division. In addition, females had a lower rate of OAS severity than males. In our patients, the major complication was hypertension and cardiac disease. The success rate of OA was 75.5%. CONCLUSION: This approach allowed us to reveal some of the trends and characteristics in our patients.