Clinical report

Titanium framework removable partial denture used for patient allergic to other metals: A clinical report and literature review

The properties of commercially pure titanium are better than those of cobalt chromium alloys in various ways. However, casting pure titanium is challenging because of its high melting point and chemical reactivity. Because of excellent mechanical strength, a titanium alloy, Ti-6Al-4V, has been commonly adopted, but the aluminum and vanadium ions released may be cytotoxic.

The purpose of the present study was to evaluate a new titanium alloy, Ti-7.5Mo, developed by the National Cheng Kung University for casting removable denture frameworks. The casting success rate, porosity, and guide plane or rest fit were compared among frameworks cast with Ti-7.5Mo alloy and pure titanium for 3 types of edentulism.

Ti-7.5Mo alloy and pure titanium were used to cast frameworks for Kennedy Class I and II and completely edentulous conditions, with 5 frameworks for each condition. Wax patterns of the frameworks were designed and fabricated by using computer-aided design and computer-aided manufacture (CAD-CAM) technology to ensure their geometrical consistency. They were then invested with aluminum oxide–based material and cast. The castings were examined with microcomputed tomography (μCT) for porosity, and fit was evaluated from the thickness of a vinyl polyether silicone material at the guide plane or the rest by using an optical microscope. The casting was determined to be successful if the frameworks were complete. The porosity and fit were statistically evaluated by using 2-way ANOVA (α=.05).

Using pure titanium, the casting success rate was 80%, with only 64% of the major connectors in the deficient castings being complete. The μCT images showed that the percentage of casting defects in Ti-7.5Mo castings was one-third of the pure titanium castings. Furthermore, internal voids were detected in the clasps of the pure titanium castings, while the Ti-7.5Mo castings had few defects in the minor connectors and no radiographically detectable defects in the clasps. The fit analysis demonstrated smaller gaps over both guide planes and rests in the Ti-7.5Mo castings.

Ti-7.5Mo alloy had better castability than pure titanium. Based on the results, Ti-7.5Mo alloy is suitable for dental casting and may provide better performance.

Cobalt chromium (Co-Cr) alloys possess beneficial mechanical properties because alloys, even in thin sections, can resist high mastication forces and exhibit an acceptable bond to the surface porcelain layer. Traditional manufacturing techniques of Co-Cr alloys such as casting have been replaced with newer fabrication techniques, such as milling, laser melting, and presintered milling. Despite scarce documentation, these new manufacturing techniques are being used to fabricate dental and implant constructions.

This in vitro study investigates the hardness, yield strength, elastic modulus, and microstructure of the most commonly used Co-Cr alloys for fixed prosthodontics based on manufacturing technique. In addition, this study investigates the effect of heat treatment on the mechanical properties and microstructure of these materials.

Five Co-Cr alloys were included (dumbbell and rectangular shaped) based on four manufacturing techniques: cast, milled, laser melted, and presintered milled. Commercially pure titanium grade 4 and titanium-6 aluminum-4 vanadium ELI (extra low interstitial) were included for comparison, and yield strength and elongation after fracture were evaluated. The specimens were tested for hardness using the Vickers test and for elastic modulus using a nondestructive impulse excitation technique. The microstructure of selected specimens was analyzed using focused ion beam-scanning electron microscopy (FIB-SEM) and energy dispersive X-ray spectroscopy (EDS).

The mechanical properties depend on the manufacturing technique used; the laser-melted and presintered Co-Cr specimens demonstrated the highest mechanical properties, followed by the milled and cast groups. Both the laser-melted and the presintered milled Co-Cr specimens showed smaller grain size compared with the cast and milled Co-Cr specimens. The titanium-6 aluminum-4 vanadium ELI demonstrated higher hardness and yield strength compared to commercially pure titanium grade 4. No major differences were observed for the selected materials regarding the mechanical properties and microstructural appearance after heat treatment.

The laser melting and presintered milling techniques produced higher mechanical properties compared with the cast and milled Co-Cr. These findings were confirmed through microstructural analysis with respect to the grain size, precipitation, and number of pores.

The resection and reconstruction of the vena cava is frequently needed in tumor resection. The goal of this study was to evaluate the performance of the magnetic compression anastomosis (MCA) device for fast nonsuture anastomosis of caval reconstruction with artificial blood vessel transplantation after resection in canines.

The MCA device consisted of paired neodymium-ferrum-boron (Nd-Fe-B) magnetic rings that were coated with titanium nitride and embedded in a polypropylene shell. Artificial blood vessel transplantation procedure was performed in sixteen canines and then they were divided into 2 groups: MCA group (n = 8), in which the novel magnetic pinned-ring device was used, and the traditional manual suture group (n = 8). In situ artificial blood vessel anastomoses were performed in the inferior vena cava (IVC). The anastomosis time and anastomotic patency and quality were investigated through ultrasonographic scans, angiographic, gross observation, histological staining, and scanning electron microscopy at 24 weeks postoperatively.

The IVC anastomoses were reconstructed successfully in all canines and all animals survived. In the MCA group, the operation time for IVC anastomosis with artificial blood vessel was significantly shorter than that in the tradition manual suture group (P < 0.05). Vena cava angiography and ultrasound showed good blood patency. The scanning electron microscope showed the re-endothelialization was smooth and endothelial cells were arranged regularly at the anastomotic site. Histological examination confirmed that the MCA group was associated with infiltration of inflammatory cells compared with the manual suture group.

The MCA device combined with artificial blood vessels is applicable in reconstruction of large vessels after resection. The magnetic pinned-ring device offers a simple, fast, reliable, and effective technique for nonsuture artificial blood vessel anastomosis of caval reconstruction in canines, and the anastomosis is functionally better than the traditional sutured anastomosis.

Because of their inert character and desired biocompatibility, titanium implants have been universally accepted as safer alternatives to the conventional stainless steel orthopedic implants; however, recent emergence of type IV hypersensitivity reactions to titanium have included eczema, contact dermatitis, a prolonged febrile state, sterile osteonecrosis, and impaired fracture and wound healing. This report presents a patient with postoperative incision dehiscence and devascularization of surfaces in contact with titanium hardware after undergoing a double calcaneal osteotomy and a first metatarsal-cuneiform arthrodesis using titanium alloy implants. Titanium hypersensitivity was confirmed in this case through standard allergy patch testing by a board-certified immunologist. Complete healing occurred after diagnosis of the titanium allergy and hardware explant. To our knowledge, this is one of a few known allergies to titanium implants after foot and ankle surgery.

This study aimed to investigate the effects of selective laser melting (SLM), milling methods, and casting on the behavior of titanium clasp.

The clasp and its die simulating the molar were designed using 3D software. Clasp specimens were fabricated using SLM approaches (SLM Ti) and computerized numerical control (CNC) milling technology (Milling CPTi). Cast clasps of the same forms were also prepared as controls using titanium alloy powder (Cast Ti) and commercial pure titanium (Cast CPTi), following the conventional casting methods. The surface roughness and accuracy of clasps were analyzed. The changes in retentive force and permanent deformation were measured up to 10,000 insertion/removal cycles. One-way analysis of variance and Tukey’s test or Kruskal–Wallis H test were performed for data analysis and comparisons.

The Milling CPTi clasps had a smoother inner surface than the other groups (p < 0.05). The accuracy of the inner surface showed no significant difference among the groups, whereas that of the outer surface showed significant differences (p < 0.05). The SLM Ti clasp had significantly higher retentive forces than the other groups (p < 0.05), but it rapidly reduced after 2000 insertion/removal cycles until the fracture of all specimens was at 4000 cycles. The Milling CPTi clasps had more permanent deformation, but the rate of reduction of retentive force was only 9.5% (at 10,000 cycles).

Milling has the potential to replace casting for fabricating removable partial denture (RPD) titanium clasps. However, SLM should be further improved for fabricating RPD titanium clasps before clinical application.

We present the case of a patient who had experienced a fever of unknown cause for >7 months after surgical treatment for hallux valgus. A patch test revealed a positive reaction to a titanium alloy. All symptoms subsequently disappeared after we removed the implanted titanium screws. Histopathologic examination of the tissue surrounding the screws showed macrophage infiltration in the tissue. For >1 year after removal of the titanium screws, the patient's body temperature remained <37°C. These results support a diagnosis of titanium allergy in our patient. To the best of our knowledge, a long-term fever caused by an allergic reaction to mini-titanium screws of such a small size has not been reported. A review of 16 cases of titanium allergy reported in the published data confirmed that titanium allergy is extremely rare and that the clinical symptoms can vary. Titanium allergy should be suspected when a patient presents with a fever of unknown cause, delayed wound healing, dermatitis, or impaired fracture healing after internal fixation with titanium materials. A patch test for titanium or the lymphocyte transformation test could offer guidance for the clinical diagnosis of titanium allergy. Finally, we recommend that all patients should be asked whether they have a history of an allergy to any metal before surgery.