Influence of eccentric cyclic loading on implant components: Comparison between titanium and zirconia abutments.

The objective of this study was to investigate the effects of eccentric cyclic loading on implant components using the internal joint system with titanium and zirconia abutments. Abutments were made of either pure titanium (Ti group) or zirconia (TZP group). Cyclic loading test was conducted according to the specifications of ISO 14801. Loading condition was at 2 points assuming axial load and eccentric load. The reverse torque value reduced after the eccentric load and reduced more in the TZP group than the Ti group. Marginal gap changed after eccentric loading, and was greater in the TZP group. In the TZP group, changes in configuration were observed in the implant body, and Ti was detected on the abutment surface. From the above, the eccentric load may have worse effects than axial loads. It was suggested that the TZP group was clinically disadvantageous compared to the Ti group.

Applying intraoral scanner to residual ridge in edentulous regions: in vitro evaluation of inter-operator validity to confirm trueness.

BACKGROUND: The purpose of this study was to investigate the trueness of intraoral scanning of residual ridge in edentulous regions during in vitro evaluation of inter-operator validity. METHODS: Both edentulous maxillary and partially edentulous mandibular models were selected as a simulation model. As reference data, scanning of two models was performed using a dental laboratory scanner (D900, 3Shape A/S). Five dentists used an intraoral scanner (TRIOS 2, 3Shape A/S) five times to capture intraoral scanner data, and the "zig-zag" scanning technique was used. They did not have experience with using intraoral scanners in clinical treatment. The intraoral scanner data was overlapped with the reference data (Dental System, 3Shape A/S). Regarding differences that occurred between the reference and intraoral scanner data, the vertical maximum distance of the difference and the integral value obtained by integrating the total distance were analyzed. RESULTS: In terms of the maximum distances of the difference on the maxillary model, the means of five operators were as follows: premolar region, 0.30 mm; molar region, 0.18 mm; and midline region, 0.18 mm. The integral values were as follows: premolar region, 4.17 mm2; molar region, 6.82 mm2; and midline region, 4.70 mm2. Significant inter-operator differences were observed with regard to the integral values of the distance in the premolar and midline regions and with regard to the maximum distance in the premolar region, respectively. The maximum distances of the difference in the free end saddles on mandibular model were as follows: right side, 0.05 mm; and left side, 0.08 mm. The areas were as follows: right side, 0.78 mm2; and left side, 1.60 mm2. No significant inter-operator differences were observed in either region. CONCLUSIONS: The present study demonstrated satisfactory trueness of intraoral scanning of the residual ridge in edentulous regions during in vitro evaluation of inter-operator validity.

Wear properties of esthetic dental materials against translucent zirconia.

To clarify the influence of translucent tetragonal zirconia polycrystals (TZP) on wear properties of esthetic dental materials, two-body wear test was performed using translucent TZP as abrader specimen, and bovine tooth enamel (BTE), two resin composites including hybrid filler (CRH) and nano filler (CRN), two glass ceramics including leucite reinforced feldspar porcelain (POR) and lithium disilicate (LDC), or translucent TZP as substrate specimen. After the wear test, wear volume were determined from substrate specimen and surface roughness were measured from abrader specimen. In addition, Vickers hardness was measured and surface morphologies were observed after wear test using a scanning electron microscope. The wear volume of the esthetic dental material against translucent TZP was greater in glass ceramics (POR, LDC), smaller in resin composite (CRH, CRN) and BTE, and no wear in translucent TZP. Microstructures of the esthetic dental material may play a crucial role for wear behavior against translucent TZP.

Bone marrow stromal cells from low-turnover osteoporotic mouse model are less sensitive to the osteogenic effects of fluvastatin.

This study aimed to investigate the effects of fluvastatin on the differentiation of bone marrow stromal cells (BMSCs) into osteoblasts in senescence-accelerated mouse prone 6 (SAMP6) compared with that in the normal senescence-accelerated-resistant mouse (SAMR1) model. SAMP strains arose spontaneously from the AKR/J background and display shortened life span and an array of signs of accelerated aging, compared with control SAMR strains. The dose effects of fluvastatin were also evaluated. BMSCs were cultured with/without fluvastatin (0 µM, 0.1 µM, 0.5 µM, and 1.0 µM). WST-1-based colorimetry was performed to evaluate cell proliferation. To evaluate cell differentiation, gene expression levels of bmp2 and runx2 were determined by quantitative reverse transcription polymerase chain reaction (qRT-PCR), and protein expression levels were determined using enzyme-linked immunosorbent assay (BMP2) and immunofluorescence staining (BMP2 and Runx2). Alkaline phosphatase (ALP) activity assay and histochemical detection were determined; the effect of noggin, a BMP-specific antagonist, was examined using ALP histochemical detection. To assess for mature osteogenic marker, gene expression levels of bglap2 were determined by qRT-PCR and mineralization was determined by alizarin red staining. RhoA activity was also examined by Western blotting. In SAMP6, BMP2, Runx2 and Bglap2 mRNA and protein expressions were significantly increased by fluvastatin, and ALP activity was increased by BMP2 action. RhoA activity was also inhibited by fluvastatin. The concentration of fluvastatin sufficient to increase BMP2 and Runx2 expression and ALP activity was 0.5 µM in SAMP6 and 0.1 µM in SAMR1. In conclusion, the present study revealed that fluvastatin promoted BMSC differentiation into osteoblasts by RhoA-BMP2 pathway in SAMP6. BMSCs of SAMP6 are less sensitive to the osteogenic effects of fluvastatin than SAMR1.

Influence of eccentric cyclic loading on implant components: Comparison between external joint system and internal joint system.

The purpose of this in vitro study was to investigate the influence of eccentric loading on implant components by measuring screw loosening and observing these components under several load positions and magnitudes. The external and internal joint system implants with butt joint connection were subjected to cyclic loading tests according to the specifications of ISO 14801. Load position was set at 0, 4, or 8 mm, and load was set at 100 or 300 N. On the external joint system, the reverse torque values decreased with distal shift in the loading position and an increase in magnitude of load, and abrasion and deformation on the anti-rotation device were observed. On the internal joint system, no large decrease in reverse torque was observed even though increasing the load position and load, however, abrasion and deformation on the anti-rotation device as well as fracture at implant/abutment connection were observed.

Translucency and flexural strength of monolithic translucent zirconia and porcelain-layered zirconia.

This study aims to investigate the effectiveness of monolithic translucent TZP with different colors and porcelain-layered TZP by evaluating their colors and strengths. Different mixing ratios of Zpex to Zpex-Yellow as translucent TZP, conventional opaque TZP (TZ-3YB-E) (Tosoh, Tokyo) as a control, and veneering porcelain (CERABIEN ZR, body porcelain, Noritake, Tokyo) with shade A3 as a typical shade. Disk-shaped specimens of 13 mm diameter and 1.5 mm thickness were prepared. These specimens were observed under reflected and transmitted light, and the translucency parameter (TP) values were measured. Strength was also evaluated with flexural strength in a biaxial bending test. The TP values of the monolithic TZP, Zpex100>Zpex70>Zpex50>TZ3YB, were larger in this order. The flexural strength of all the monolithic TZP showed approximately 1,000 MPa. It is suggested that colored translucent TZP is clinically useful when used as monolithic restorations.

Dental implant treatment after improvement of oral environment by orthodontic therapy.

A 57-year-old man presented with mesial inclination of the lower right first molar caused by untreated loss of the second premolar. The occlusal relationship was restored by dental implant treatment following improvement of the intraoral environment by orthodontic therapy. At his initial visit, the interdental spacing in the molar-premolar region was inadequate, as the first molar had mesially inclined into the extraction space of the second premolar. The patient had also lost the second molar and complained of masticatory problems on the right side. It was considered necessary to restore the second molar and improve the occlusal relationship with the first molar to recover occlusal function on the right side. After orthodontic therapy to correct the position of the mesially inclined tooth, occlusal restoration was carried out by dental implant treatment. The patient's clinical condition has remained excellent at over 5 years 2 months post-surgically and the patient is satisfied with the treatment outcome. The combination of dental implant treatment and orthodontic therapy were effective in improving the intraoral environment in this patient, indicating the efficacy of interdisciplinary treatment planning and practice.

Immediate implant placement in the maxillary central incisor region: a case report.

PATIENT: A 67-year-old female with root fracture of the maxillary central incisor underwent implant placement immediately after extraction, with the goal of shortening the treatment period. The superstructure was placed on the implant after a 4-month healing period. Review 5 years after implant loading revealed no clinical problems. DISCUSSION AND CONCLUSION: The treatment time was shortened effectively by the flapless immediate post-extraction placement procedure. Immediate post-extraction implant placement based on proper examination and diagnosis would reduce the patient burden.

Influence of width and depth of palatal vault on rigidity of palatal strap: a finite element study.

PURPOSE: The purpose of this study was to develop design criteria for palatal straps according to palatal shape. METHODS: The palatal shapes of 60 dentate maxillary stone casts were measured using a contact-type three-dimensional measuring instrument. Based on the average of the 60 palatal shapes, 5 three-dimensional finite element models (FE models) were constructed: a basic FE model, a wide palatal FE model, a narrow palatal FE model, a deep palatal FE model and a shallow palatal FE model. The FE models were simulated unilateral free-end saddle dentures with the maxillary left second premolar and first and second molars missing. The FE models included a denture base, two rests and a palatal strap. The mechanical properties of Co-Cr alloy, Ti-6Al-7Nb alloy and type IV gold alloy were given to the FE models. A vertical load of 50 N was loaded onto the occlusal surface of the left first molar. Vertical displacement of the distal edge of the denture base was then compared between models. RESULTS: Compared to the basic FE model, displacement in the wide FE palatal model and shallow palatal FE model was larger, and displacement in the narrow palatal FE model was smaller. The difference in displacement between the deep palatal FE model and basic FE model was small. CONCLUSIONS: With a wide and shallow palate, it is necessary to design a reinforced palatal strap. With a narrow palate, the anteroposterior width of the palatal strap can be narrower. With a deep palate, it is not necessary to change the palatal strap design according to the palatal shape.