Analysis of stress distribution of tooth restored with metal-ceramic crown covering abfraction lesion according to its finish line location under occlusal load / 대한치과보철학회지

PURPOSE: When the full veneer crown was treated in the tooth with abfraction lesion due to various causes, the prognosis of it may be compromised according to the location of the finish line, but there is few study about the location of its buccal finish line. The purpose of this study was to investigate the effect of location of the finish line of the full veneer crown on stress distribution of the tooth with abfraction lesion. MATERIALS AND METHODS: The two dimensional finite element model was developed to express tooth, surrounding tissue and full veneer crown. The stress distribution under eccentric 144 N occlusal load was analyzed using finite element analysis. The location of finish line was set just at the lower border of the lesion (Group 0), 1 mm (Group 1) and 2 mm (Group 2) below the lower border of the lesion. RESULTS: In the Group 0, von Mises stress was concentrated at the finish line and the apex of the lesion. Also, the stress at the bucal finish line propagated to the lingual side. In the Group 1 and Group 2, stress distribution was similar each other. Stress was concentrated at the apex of lesion, but the stress at the buccal finish line did not propagate to the lingual side. That implied decrease of the possibility of horizontal crown fracture. CONCLUSION: Full veneer crown alleviated the stress concentrated at the apex of the abfraction lesion, when the finish line of full veneer crown was set below the lower border of abfraction lesion.

Notice of duplicate publication

No abstract available.

Mechanical Properties of Blood-Mixed Polymethylmetacrylate in Percutaneous Vertebroplasty

STUDY DESIGN: Mechanical study of polymethylmetacrylate (PMMA) mixed with blood as a filler. PURPOSE: An attempt was made to modify the properties of PMMA to make it more suitable for percutaneous vertebroplasty (PVP). OVERVIEW OF LITERATURE: The expected mechanical changes by adding a filler into PMMA included decreasing the Young's modulus, polymerization temperature and setting time. These changes in PMMA were considered to be more suitable and adaptable conditions in PVP for an osteoporotic vertebral compression fracture. METHODS: Porous PMMA were produced by mixing 2 ml (B2), 4 ml (B4) and 6 ml (B6) of blood as a filler with 20 g of regular PMMA. The mechanical properties were examined and compared with regular PMMA(R) in view of the Young's modulus, polymerization temperature, setting time and optimal passing-time within an injectable viscosity (20-50 N-needed) through a 2.8 mm-diameter cement-filler tube. The porosity was examined using microcomputed tomography. RESULTS: The Young's modulus decreased from 919.5 MPa (R) to 701.0 MPa (B2), 693.5 Mpa (B4), and 545.6 MPa (B6). The polymerization temperature decreased from 74.2degrees C (R) to 59.8degrees C (B2), 54.2degrees C (B4) and 47.5degrees C (B6). The setting time decreased from 1,065 seconds (R) to 624 seconds (B2), 678 seconds (B4), and 606 seconds (B6), and the optimal passing-time decreased from 75.6 seconds (R) to 46.6 seconds (B2), 65.0 seconds (B4), and 79.0 seconds (B6). The porosity increased from 4.2% (R) to 27.6% (B2), 27.5% (B4) and 29.5% (B6). A homogenous microstructure with very fine pores was observed in all blood-mixed PMMAs. CONCLUSIONS: Blood is an excellent filler for PMMA. Group B6 showed more suitable mechanical properties, including a lower elastic modulus due to the higher porosity, less heating and retarded optimal passing-time by the serum barrier, which reduced the level of friction between PMMA and a cement-filler tube.

Evaluation of Osteoporotic Vertebral Bone and Disc Degeneration Induced by Malnutrition during Growth Period: Biomechanical and Histomorphometrical Study / 체질인류학회지

The aim of the present study is to analyze the generation of osteoporotic vertebral bone induced by malnutrition during growth period and analyze its effects for disc degeneration, based on biomechanical and histomorphometrical study. Mechanical and histomorphological characteristics of lumbar vertebral bones and discs of rats with calcium free diet (CFD) were detected and tracked by using high resolution in-vivo micro-computed tomography (in-vivo micro-CT), finite element (FE) and histological analysis. Twenty female Sprague-Dawley rats (6 weeks old, approximate weight 170g) were randomly divided into two groups (CFD group: 10, NOR group: 10). The CFD group was maintained on a refined calcium-controlled semisynthetic diet without added calcium, to induce osteoporosis. All lumbars (L1~L6) were scanned by using in vivo micro-CT with 35 micrometer resolution at 0, 4, 8 weeks to track the effects of CFD on the generation of osteoporosis. The results of morphological characteristics showed that BV/TV, Tb.Th, Tb.N in CFD group were significantly decreased over time (p<0.05), while those in NOR group were statistically increased over time (p<0.05) in the most lumbars (L1~L6). We also investigated the contrary tendency in Tb.Sp and SMI, compared to the above results in each group. In the simulated compression test using FE models, the structural effective modulus of CFD group significantly decreased (p<0.05), whereas that of NOR group was statistically increased, depending on the measuring time (p<0.05). The present study observed remarkable histological changes of nucleus pulposus and annulus fibrous by water loss in CFD group, compared with NOR group. These findings indicated that calcium insufficiency was the main factor in the generation of osteoporosis and it induced lumbar vertebral disc degeneration. This study is a valuable experiment to firstly evaluate osteoporotic vertebral bone and disc degeneration induced by malnutrition during growth period from a biomechanical and histomorphometrical point of view.

Mechanical Properties of Blood-mixed PMMA in Percutaneous Vertebroplasty / 대한척추외과학회지

STUDY DESIGN: This is a mechanical study of polymethylmetacrylate(PMMA) mixed with blood as a filler. OBJECTIVE: We tried to change the properties of PMMA so that it is more suitable to use for percutaneous vertebroplasty (PVP). SUMMARY OF THE LITERATURE REVIEW: The mechanical changes by adding a filler into PMMA were expected to decrease the Young's modulus, the polymerization temperature and the setting time. These changes of PMMA were considered to be more suitable and adaptable conditions for PVP for treating osteoporotic vertebral compression fracture. MATERIALS AND METHODS: Porous PMMA was produced by mixing 2 ml (B2), 4 ml (B4) and 6 ml (B6)-blood as a filler, and the mechanical properties were investigated in comparison with regular PMMA(R) in view of Young's modulus, the polymerization temperature, the setting time and the optimal passing-time within the injectable viscosity (20~50N-needed) through a 2.8mm-diameter cement-filler tube. Porosity was inspected by performing microcomputated tomography (micro-CT). RESULTS: Young's modulus was decreased from 919.5 MPa (R) to 701 MPa (B2), 693.5 MPa (B4) and 545.6 MPa (B6) in each group. The polymerization temperature decreased from 74.2degrees C (R) to 59.8degrees C (B2), 54.2degrees C (B4) and 47.5degrees C(B6), respectively. The setting time decreased from 1065sec (R) to 624sec (B2), 678sec(B4) and 606sec (B6), respectively, and the optimal passing-time decreased from 75.6sec (R) to 46.6sec (B2), 65.0sec (B4) and 79.0sec(B6), respectively. The porosity increased from 4.2%(R) to 27.6%(B2), 27.5%(B4) and 29.5%(B6), respectively. A homogenous microstructure with very fine pores was seen on inspection of all the blood-mixed PMMAs. CONCLUSION: Blood mixed with PMMA was considered as an excellent filler that was easy to make and had good biocompatibility. The 6ml blood-mixed PMMA (B6) showed more suitable mechanical properties, including a decreased elastic modulus due to more porosity, less heating and a retarded optimal passing-time by the serum barrier, which diminished the friction between the PMMA and a cement-filler tube.

Effect of Whole Body Vibration on Trabecular Bone in OVX Rats / 체질인류학회지

Previous studies showed that whole body vibration could prevent bone resorption and stimulate new bone formation. The aim of this study is to detect and track effect of whole body vibration for osteoporotic bone of OVX rats. 12 Female rats were used and allocated into 5 group, CON, SHAM, WBV 17, WBV 30 and WBV 45. Rats except SHAM group were ovariectomised to induce osteoporosis. Rats in WBV groups were stimulated whole body vibration at magnitude of 1 mm(peak-peak) and frequency 17 Hz, 30 Hz and 45 Hz, repectively, for 8 weeks (20 min, 5 days/week). The 4th lumbar in rats were scanned at a resolution of 35 micrometer at baseline, before stimulation, and 8 weeks by In-vivo Micro-CT. To detect and track changes of morphological characteristics in lumbar trabecuar bone of rats, structural parameters were measured and calculated from acquiring images. In the results, changes of structural characteristics of WBV group were smaller than those of CON group. Loss of quantity of trabecular bone in WBV 45 was the least. In contrast, that in WBV 17 was the biggest. These results showed that reasonable whole body vibration beneficially affected osteoporotic bones. In addition to, whole body vibration was likely to be substituted partly for drug treatment.

Micro-CT Evaluation in Osteoporosis Model / 체질인류학회지

Osteoporosis is a major health-care problem for aging communities. And postmenopausal osteoporosis is a common disorder characterized by an increase in bone resorption relative to bone formation, generally in conjunction with an increased rate of bone turnover. Twenty female rats were used as rat model of osteoporosis. They randomly were divided into two groups: a normal control group, and calcium-free diet groups treated with bilateral ovariectomy. The animals were sacrified at 12 weeks after treatment. In the rats with osteoporosis, there was significant thining and loss of trabeculae, accompanied by a disconnection of trabeculae. And acid mucopolysaccharides were decreased in osteoporotic animals. In order to setup conditions of invivo micro-CT, proper anesthetic is ketamine (50 mg/kg) /xylazine (6 mg/kg). And proper breathing rate of experimental animals is 1.3~1.6/sec. Our finding suggest that bilateral ovariectomy and calcium-free diet induce decrease in thickeness of trabecular bone and decrease in acid mucopolysaccharide, therefore cause weakness of bone. And micro-CT imaging system is useful to evaluate trabecular bone. Anesthetic time, anesthetics and respiration rate also signify much in micro-CT imaging system.