This study evaluated the mechanical properties of cold worked JIS type 2 titanium (compression ratio 39.7%) and their matching to the grades of the JIS mechanical properties. The study also evaluated the effect of heat treatment on mechanical properties at 450℃ for 60, 120, or 180 min. Additionally, the amount of released titanium immersed in 1% lactic acid solution was measured for pre- and post-cold working. The tensile strength, yield strength and hardness of cold worked JIS type 2 titanium were similar to those of JIS type 4 titanium. Elongation matched the JIS type 3. After heat treatment, the tensile strength, yield strength and hardness of cold worked titanium decreased, and the mechanical properties did not match those of the JIS type 4 titanium. However, specimens that were heated at 450℃ matched the JIS type 3 titanium regarding tensile strength, yield strength and elongation. On pre-cold working titanium, large and small crystal grains were clearly observed. On the other hand, on cold worked titanium, compressed crystal grains were observed overall as a fibrous structure. The amount of released titanium for pre-cold working was the maximum when specimens were heated at 450℃ for 60 min. In contrast, the amount of released titanium was not affected by the heating time for cold worked titanium. Before heat treatment, the amount of released titanium of the as-received specimen (before heat treatment) was not affected by cold working. It is concluded that implant materials fabricated with cold worked JIS type 2 titanium may be useful for improving corrosion resistance and mechanical properties.
Recently, multipotent stem cells have been studied as material for the regeneration of bone defects. In this study, we investigated the possibility of inducing craniofacial bone through osteogenesis from mouse embryonic stem(ES) cells. During development, the majority of the craniofacial skeleton is derived from cranial neural crest cells. ES cells were induced to differentiate into various cell types including neural precursor and neural crest cells using embryoid body(EB) formation. The differentiated cells in EBs were characterized by immunostaining using specific antibodies for neural precursors, Nestin and p75, and neural crest precursors, AP2α and Sox9. The results showed that the EBs contained Nestin or p75 positive cell masses and AP2α or Sox9 positive cells, indicating that ES cells could differentiate into neural crest cells through neural precursor cells during EB formation. Subsequently, these EBs were transferred to a tissue culture plate and grown in osteogenic medium. The differentiated cells were positive with Alizarin Red S staining and expression of osteoblast markers including Osteocalcin, Osteopontin, and Collagen type I were detected by RT-PCR. These results suggest that cranial osteoblasts are generated from mouse ES cells through induction of neural crest cells.
The biological safety and effectiveness of one-piece type thin HA sputter-coated implants (“thin HA implants”) were evaluated by implantation and mimic tests under the occlusal loading condition using beagle dogs. In the implantation test conducted under Good Laboratory Practice(GLP) standards, six thin HA implants and six titanium implants as controls were placed in the mandible bones of the dogs. All the thin HA implants remained in the mandibles at 2, 4 and 12 weeks after implantation. No changes in the general conditions of the dogs or dental X-ray observations were observed during the 12-week observation period. Insignificant differences in inflammation and bone formation around each implant were observed at 2 and 4 weeks. However, at 12 weeks the inflammation around the thin HA implants decreased, and bone formation increased much more than that of the titanium implants. In the mimic test, three gold alloy bridges were cemented on the six thin HA implants after six weeks of implantation. The general conditions of the dogs, blood and blood biochemical tests were normal during the six-month testing period after cementing the bridges. Oral inspection and dental radiographic observation did not reveal any abnormal changes. A proliferation of inflammation cells and growth of fibrous connective tissue were observed at a part of the gingival interface around the implants, however, the inflammation was slight. All of the six implants were fixed with the new bone without mobility and were functional during six months under the occlusal loading condition. These results demonstrated that the thin HA implants were biologically safe and stably functional under occlusal loading, the same as other commercial implants.
Fluoride-containing pastes for professional mechanical tooth cleaning (PMTC) have been frequently used during implant treatment. However, the influence of these pastes on the corrosion resistance of titanium implants is not well understood. The objective of this study was to clarify the influence of the pH of fluoride-containing paste on the corrosion resistance of commercially available pure titanium (cp-Ti).
Commercially available PMTC pastes with neutral pH (6.8-7.4) and different fluorine concentration (400-980 ppm), acidulated phosphate fluoride (APF) paste (APF 9000A, fluorine concentration:9000 ppm, pH=3.7), and experimental acidic NaF paste (NaF900A, fluorine concentration:900 ppm, pH=4.0) were applied to polished cp-Ti disks (grade 2). After storing the specimens at 37℃ for 3 days in a humid atmosphere, the color difference was measured, and optical microscope and scanning electron microscope (SEM) observations of the Ti disks were performed. In addition, the amounts of Ti dissolved into the pastes were evaluated.
Remarkable color differences were observed on the Ti disks coated with APF9000A and NaF900A pastes of ΔE＊ab=12.0(±2.3) and 8.8(±1.4), respectively. In contrast, negligible color differences were observed on the other specimens with ΔE＊ab ranging from 0.6 to 1.2. The optical microscopic and SEM observations revealed that the Ti disks coated with APF9000A and NaF900A pastes had roughened surface morphologies caused by pitting corrosion. In addition, noticeable amounts of Ti, 25.3(±6.2) and 8.6(±2.3) µg/cm2, from Ti disks coated with APF9000A and NaF900A pastes, respectively, were detected. Accordingly, the remarkable color differences of the APF9000A and NaF900A specimens were due to the roughening of the surface caused by corrosion of the Ti surface.
These results indicate that fluoride-containing pastes with low pH may reduce the corrosion resistance of titanium, and so great care is required when using these fluoride-containing pastes for PMTC.
The positional relationship between implant prosthetic crown designs made by the top-down method were measured on the basis of the remaining teeth and the actual defective part of the jawbone, to establish clinical guidelines for the surgical planning of dental implants and prosthetic therapy.
Cone-beam CT images were used to measure 469 sites in the mouths of 246 Japanese patients (133 males, 113 females;aged 26 to 83) who were diagnosed by CT scans during the period from April 2011 to July 2012. While referring to chair-side diagnosis and model diagnosis, cone-beam CT images were used to design appropriate prosthetic crown contours on the basis of the remaining teeth. In this study, appropriate continuity of the crown contour with the remaining teeth was taken as the criterion. The point of measurement was the center point between adjacent teeth in the curve formed by the row of teeth or the assumed position of the most posterior molar. At the measurement point, MPR images from a cone-beam CT scan that were both orthogonal to the row of teeth and parallel to the axis of the root of the mesial adjacent tooth were used to measure the labial or buccal displacement(mm) as the positional relationship between the position of the prosthetic crown design and the center of the defective part of the jaw.
The prosthetic crown design was positioned to the labial or buccal side of the center of the defective part of the jaw in the upper and lower anterior teeth and mandibular molars, as opposed to on the palatal side in the maxillary premolar area. In some cases, the position of the crown design in the maxillary molar area was the center of the jawbone or toward the palatal side.
In cases where there is insufficient amount of bone at the intended implant site for the prosthetic crown design, a bone transplant can be effective. Moreover, in cases where there is a distance between the planned implant position and the prosthetic position, it is possible to correct the tooth contour with a superstructure and abutment. However, bone transplantation is a highly invasive surgical procedure that often prolongs the treatment period. In addition, excessive over-contouring or angle revision with a superstructure and abutment can cause such problems as a dynamic burden on the implant body, breakage of the abutment or superstructure, or poor hygiene, and should accordingly be avoided.
For successful top-down treatment planning in dental implant therapy, it is imperative that the treatment be planned on the basis of a comprehensive diagnosis that takes into account the ideal crown contour and the anatomical features of the defective part of the jawbone.