Prosthodontic treatment by implant-supported overdentures is effective for edentulous patients. The predictability and longevity of bar attachments connected to implant bodies are excellent for clinical results. In the past, cantilever length of bar attachments connected to implant bodies was often determined based on clinical experience and have not been well reported based on scientific basis. Hence, the objective of the present study is to establish the guidelines for ideal cantilever length in implant-supported overdentures using magnetic bar attachments using three-dimensional geometric analysis from the view point of biomechanics.
Seven patients with implant-supported overdentures which were supported by four implants between the mental foramina on edentulous mandibles participated.
Initially, we made silicone models that reproduced denture supporting tissues and bar attachments, and photographed these with certain specifications. Next, we examined (1) the length of cantilever necessary to support average occlusal force, (2) the distance from the most distal point of the cantilever to occlusal force by three-dimensional geometric analysis.
The average length of cantilever necessary to support average occlusal force in the second premolar was 3.2 ± 3.8 mm and in the first molar, 12.0 ± 5.8 mm. The average distance from the most distal point of the cantilever to occlusal force at the second premolar and first molar was 0.9 ± 0.5 and 12.0 ± 5.8 mm, respectively.
Cantilever is very effective in increasing the supporting ability to occlusal force, but it was necessary to require 12.0 mm at least to support occlusal force on the first molar only by bar-attachment with implants placed between mental foramens. So it is important that occulusal force at the molar should be supported by not only implants but also denture supporting tissues.

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The differentiation of mesenchymal stem cells (MSCs) into chondrocytes and osteoblasts is minutely regulated by bone morphogenetic proteins (BMPs) and various factors. There is no study describing the role of noggin in the differentiation from MSCs to chondrocytes or osteoblasts. We thus examined the effect of noggin on chondrogenesis and osteogenesis in a human cell line that expresses chondrocytic phenotypes, and the role of noggin in these processes. Noggin induces chondrogenic differentiation, and its repression induces osteogenic differentiation through BMP effects.
Noggin is reported to bind several BMPs and to inhibit their functions, but its exact role is not yet clarified. USAC cells usually show chondrogenic phenotypes and also have the potential to differentiate into osteoblasts and adipocytes under some circumstances. We investigated the effects of noggin on chondrogenic and osteogenic differentiation of USAC cells in vivo and in vivo.
After USAC cells were treated with noggin antisense oligonucleotide (As-Noggin) or noggin protein (rhNoggin), RT-PCR was performed to detect mRNAs of type I collagen (Col I), type II collagen (Col II), Cbfal, aggrecan (AG), Sox9 and osteocalcin (OC) on days 3, 7 and 14. Western blot analysis was done to detect Col II, BMP-2, BMP-4, Cbfal and OC proteins. Toluidine blue staining and immunostaining for Col II, BMP-2, Cbfal and OC were also performed.
As-Noggin induced the up-regulation of Col I and OC mRNA expression in USAC cells time-dependently, while it down-regulated the expression of Col II and AG mRNAs. As-Noggin stimulated BMP-2, Cbfal and OC production, but it reduced the production of Col II and BMP-4. Moreover, OC mRNA expression and BMP-2 production were down-regulated by the addition of rhNoggin. The same results were obtained by immunostaining. These results suggest that noggin may regulate chondrogenic and osteogenic differentiation through the production of BMP-2 and BMP-4.

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Orthodontically, we frequently encounter malocclusion cases accompanying impacted teeth. It has been reported that impacted teeth not only disturb the growth of the teeth, dentition, and jaw bone, affecting occlusal establishment, but also cause tooth root resorption in neighboring teeth when compressing their tooth roots.
In this study, the patient was a 13-year-2-month-old female at the time of the first examination, who visited our department with chief complaint that the maxillary right canine had not surfaced. As a result of examination, the patient was diagnosed as having Angle class I crowding with a completely impacted maxillary right canine and the absence of the mandibular left lateral incisor. An X-ray showed severe tooth root resorption in the maxillary right central incisor, and preservation of the tooth was considered impossible. Therefore, we extracted the maxillary right central incisor to achieve an eruption space for the maxillary right canine, and fenestration-traction of the maxillary right canine was performed. Thereafter, functional occlusion was established using multi-bracket appliances, and a good occlusal relationship was obtained.
However, since tooth root resorption in the neighboring maxillary central incisor had already been noted at the first examination, the maxillary central incisor, which is esthetically important, had to be extracted in this case. It was considered that if earlier treatment had been performed, tooth impaction could have been prevented, and unnecessary tooth extraction could have been avoided. Therefore, it was suggested that it is necessary to promote better treatment results by detecting impacted teeth earlier, and appropriately diagnosing their positional relationship.

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[in Japanese]

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