There has been controversy as to whether superstructures should be splinted or un-splinted when several implants are installed for restoring partial edentulous space. The purpose of this study was to examine the difference in stress distribution using 3-dimensional finite element models of splinted and un-splinted superstructures for implants installed in the mandibular posterior region.
Results indicated that there was little difference between splinted and un-splinted superstructures under loadings in the axial direction. Splinted superstructures showed smaller and more distributed stress under oblique loadings.
From the results of this study, it is suggested that splinted superstructures have biomechanical advantages over un-splinted ones when the inter ach relationship or implant installation angle is not favorable.
Periotest measures the mobility of an implant by using percussion, and Osstell measures the stability of an implant by applying resonance frequency analysis. Both of the measurement values are useful references to understand the implant condition of osseointegration. In some cases, it is decided to adopt an immediate load based on absolute values of measurements. However, there are few reports concerning effective factors on the measurement values. A resin model that can easily reproduce the same conditions of osseointegration was made. The influence was evaluated under various conditions of length of transducer (Osstell only), changing angle between the detector and distance of resin model,and changing the length of the implant fixture.
The following conclusions were obtained.
1. In the case of Periotest, the percussion direction and the length of fixture did not affect the measured values, and the measured values were stable.
2. In the case of Osstell, the length of transducer had the greatest effect on the value of ISQ. The ISQ values of F1L5.0 were higher than those of F1L8.5 (average difference was 4.0～13.9). The ISQ values of F1L8.5 decreased with angle between transducer and resin model (parallel, oblique angle and right angle), but those of F1L5.0 increased slightly. The length of implant fixture did not affect the ISQ values.
3. On the waveform of F1L5.0, a sub peak was observed on the left of the maximum peak wave more often while F1L8.5 showed almost typical Implant Stability Quotient (ISQ) waveforms.
4. Periotest values measured based on the center axis of the implant were better than Osstell values (ISQ) because Periotest values hardly depended on the direction and the measured values were stable.
5. It is possible to calculate the reproducible measurement value when the measurement conditions of Periotest and Osstell were controlled. However, an overall judgment based not only on a physical evaluation is necessary.
Objective: This study characterizes chondrogenic phenotype possibly emerging or being altered while in an in vitro osteogenic environment with titanium and tests the hypotheses that(1) the process of osseointegration involves a novel cellular mechanism of chondroblastic/chondrocytic phenotype as well as osteoblastic phenotype and that (2) the chondroblastic/chondrocytic phenotype can be modulated by the surface topography of the titanium.
Materials and Methods: Two types of commercially pure titanium disks, a machined surface and a rough surface by acid-etching (AE), were prepared. Osteoblastic cells derived from rat bone marrow stromal cells were inoculated with an osteogenic medium onto polystyrene surfaces and machined titanium or AE titanium disks in 12-well culture plates. The cells were harvested, and total RNA was extracted at day 1, 3, 7, 14, 21 and 28 of culture. The mRNA expression of osteoblastic and chondroblastic/chondrocytic genes was examined using the reverse transcriptase polymerase chain reaction. The morphology was evaluated using a scanning electron microscope and the elements were quantified using an energy dispersive spectroscope in the day 28 mineralized cultures.
Result: Bone-related gene expressions, such as type I collagen, osteopontin and osteocalcin, were more upregulated in the titanium cultures than in the polystyrene culture. Chondroblastic/chondrocytic gene expressions, including type II, IX and X collagen, were exclusively expressed on the titanium surfaces. Biglycan and Sox9 genes tended to be more upregulated on both the titanium surfaces compared with the polystyrene surface. Such differential expression and upregulated expression of type II collagen genes were enhanced more on the AE titanium surface than on the machined titanium surface. The polystyrene culture seemed to be a fibrous structure and the machined titanium culture seemed to be a thicker structure compared with the polystyrene culture,while the AE titanium culture seemed to be a smooth surface structure. More sulfurelement was detected on the AE titanium surface than on the machined titanium or polystyrene surfaces.
Conclusion: Culturing osteoblastic cells derived from bone marrow stromal cells on titanium with the osteoblastic inducing media remarkably upregulates or induces chondrogenic gene expression, and the surface roughness of titanium boosts the unique transcriptional modulation.
For the long-term functioning of an implant,it is important that the established peri-implant bone is maintained. The formation and absorption of the bone are related to the microvasculature. Therefore, we investigated the sequential changes in bone percentage and vascular percentage around rough- and smooth-surfaced implants having the same structure and under occlusal loading. We additionally elucidated the implant that showed long-term functionality.
In this study, a rough-surfaced implant produced by blasting (BI) and a smooth-surfaced implant produced by machining (MI) were used.These implants were fixed in the molar part of the mandible of three monkeys and were maintained under non-loading conditions for 14 weeks. The implants were loaded after setting up a super-structure at 14 weeks following fixation. At 14 weeks under the non-loading conditions and at 1, 4, 12, and 24 weeks under the loading conditions, bone and microvasculature specimens were prepared by the plastic injection method and were observed under a scanning electron microscope. The bone percentage and the vascular percentage in the 500-μm area surrounding each implant were calculated using image processing software.
For each week, the bone percentage of MI was higher than that of BI. The former did not change during 0-12 weeks after the loading and decreased during 12-24 weeks. The latter did not change during 0-4 weeks after the loading, increased during 4-12 weeks, and decreased remarkably during 12-24 weeks. For each week, the vascular percentage of MI was higher than that of BI. The former did not change during 0-4 weeks after the loading,increased during 4-12 weeks, and did not change during 12-24 weeks. The latter did not change during 0-4 weeks, increased during 4-12 weeks, and increased further during 12-24 weeks.
From the result that the bone percentage of MI was higher than that of BI until 24 weeks after the loading, it was suggested that the peri-implant bone of MI was maintained for a longer time than that of BI.
The aim of this study was to reduce artifacts in microcomputed tomography (micro-CT) images caused by the beam hardening effects of X-ray. The micro-CT images were corrected in comparison with a human extracted tooth embedded in compensating material, dental plaster (CaSO4・1/2H2O), which was placed in an aluminum cylindrical container and not embedded. As a result, the artifacts of the micro-CT images were reduced by the compensating materials. It is considered that this phenomenon occurred because the low-energy X-ray parts were absorbed by the compensating material which has a high attenuation coefficient. The development of this method eliminated the problems caused by beam hardening effects when measuring bone mineral density (BMD), such as surrounding newly formed bone in dental implants, and also suggested the possibility of using the new methods for BMD by using micro-CT images.
Although ameloblastoma is a benign odontogenic tumor, its tendency to be slow growing, to infiltrate the bone, and in rare cases to recur, means the course of treatment is similar to that of malignant tumors. Often this results in an extensive surgical resection leading to functional and esthetic problems. Recovery of the masticatory function and form utilizing implant treatment is contingent on the provision of optimum placement for implants in the reconstructed mandible. This paper reports implant treatment for a 23-year-old man, based on two-stage bone grafting after a marginal mandibulectomy to remove a benign but partially invasive ameloblastoma. The treatment involved excision of the tumor, reconstruction of the mandible and restoration of the occlusion through a two-stage iliac block bone grafting procedure. For the first graft, autogenous bone material was harvested from the ilium. In the secondary procedure, eighteen months later, width and height around the alveolar ridge at the implant placement area were augmented with a partial thickness, block bone graft taken from the opposite side iliac crest and cortical plate, shaped into a saddle form. After a further twelve months, the patient received three implants in the second premolar and the first and second molar regions at the reconstruction site. A successful final outcome was achieved, with a three-year follow-up period showing satisfactory functional and cosmetic results.
We encountered a patient who developed multiple symptoms after insertion of a titanium implant at the site of the first molar of the right mandible at another hospital. Eventually, the implant was removed. The patient was a 57-year-old woman who received a titanium dental implant and then was diagnosed as having titanium allergy at a local clinic. She received antiallergy therapy with steroids, but it did not achieve symptomatic relief, so she was referred to our department. To assess the presence of titanium allergy, the patient underwent a patch test for titanium at the Dermatology Department of our hospital. The result was judged to be false-positive for allergy to titanium. Although the dermatologists concluded that she was not allergic to titanium considering the properties of the implant, the patient still strongly wished to have the implant removed. Therefore, we removed the implant on March 26, 2004, although there were no problematic clinical findings. As a result, her symptoms were markedly alleviated and no longer interfered with daily activities.