Giichiro Kawachi

Lateral bone augmentation with newly developed β‐tricalcium phosphate block: an experimental study in the rabbit mandible

OBJECTIVE To evaluate the biological effects of newly developed β-tricalcium phosphate (β-TCP) to improve lateral bone augmentation. MATERIAL AND METHODS Test samples (rod-shaped [RS]-blocks) were prepared through hydrothermal processing α-TCPs. As controls, commercially available β-TCPs (C-blocks; Osferion) were used. The blocks were placed onto the rabbit mandibles (n=5/group, mean: 4 kg). Samples were retrieved after 6, 12 and 24 weeks. Thereafter, the sections were evaluated for histological and histomorphometric analyses. The parameters set were: BV/TV (%): [(area of newly formed bone; area-NFB)/(whole measured area; WA)] × 100, BV+Imp.V/TV (%): [(area-NFB+area of remaining β-TCP block)/WA] × 100, N.Oc/I.Pm: (osteoclast number)/(entire β-TCP block perimeter; 100 mm). RESULTS BV/TV of the C-blocks (10.71 ± 3.39%) was significantly higher than the RS-blocks (3.5 ± 3.52%, P<0.05) at 6 weeks. At 24 weeks, the RS-blocks (23.66 ± 2.7%) showed significantly higher values than the C-blocks (13.23 ± 2.65%, P<0.001). The BV+Imp.V/TV of the RS-blocks was significantly higher than that of the C-block group (29.61 ± 5.84% and 19.13 ± 3.14%), maintaining high values between 6 and 24 weeks (44.16 ± 5.19% and 50.88 ± 4%, P<0.001). The N.Oc/I.Pm values were significantly greater in the RS-block group than in the C-block group throughout the observation period (P<0.05). CONCLUSIONS The newly developed β-TCP blocks presented subsequent replacement by newly formed bone, in conjunction with maintaining the external morphology.

Fabrication of βTCP foam using αTCP foam as a precursor by heat treatment

The present study reports the synthesis of βTCP foam with fully interconnecting pores based on phase transformation of αTCP foam precursor by employing heat treatment. First, the αTCP foam precursor was fabricated by sintering the ceramics slurry-coated polyurethane foam template at 1,500°C. The resultant αTCP foam was again heated below α,β transition temperature for an extended period of times. After heating at 800°C for 150 hours, 900°C for 100 hours and 1,000°C for 300 hours, βTCP foam was obtained. The compressive strength of βTCP foam was approximately 46 kPa and the porosity was approximately 93%. The long heating period as well as heating temperature were the key to the transformation of βTCP phase. βTCP foam could be an ideal bone replacement since the invasion of bone cells into the pores provides optimum bone growth or repair.

Regeneration of the periodontium for preservation of the damaged tooth.

The population of the world grows every year, and life expectancy tends to increase. Thus, long-term preservation of teeth in aged individuals is an urgent issue. The main causes of tooth loss are well known to be periodontitis, caries, fractures, and orthodontic conditions. Although implant placement is a widely accepted treatment for tooth loss, most patients desire to preserve their own teeth. Many clinicians and researchers are therefore challenged to treat and preserve teeth that are irreversibly affected by deep caries, periodontitis, fractures, and trauma. Tissue engineering techniques are beneficial in addressing this issue; stem cells, signal molecules, and scaffolds are the main elements of such techniques. In this review, we describe these three elements with respect to their validation for regeneration of the periodontium and focus particularly on the potency of diverse scaffolds. In addition, we provide a short overview of the ongoing studies of 4-methacryloxyethyl trimellitate anhydride/methyl methacrylate-tri-n-butyl-borane resin including calcium chloride or hydroxyapatite for periodontium regeneration.

Calcite Bone Substitute Prepared from Calcium Hydroxide Compact Using Heat-Treatment under Carbon Dioxide Atmosphere

The purpose of this study is to investigate whether calcite blocks with high mechanical property could be obtained for a short period from calcium hydroxide (Ca(OH)2) compact using heat-treatment under carbon dioxide (CO2) atmosphere. The Ca(OH)2 disks compacted with different pressure was heated at different temperature ranging from 200°C to 800°C for an hour under CO2 atmosphere. From the X-ray diffractometry, Ca(OH)2 converted into calcite along with the rise of the heating temperature. Small amount of unreacted Ca(OH)2 remained in samples heated at 600°C whereas samples treated at 800°C converted to calcite with very small amount of calcium oxide. The diametral tensile strength (DTS) value increased with the rise of heating temperature up to 600°C then decreased down to 800°C. Meanwhile, the porosity decreased with the rise of heating temperature up to 600°C then slightly increased up to 800°C. From the scanning electron microscope observation, grains grew bigger along with the rise of heating temperature. Intergranular space between grains decreased from 200°C to 600°C. The highest DTS value (14 MPa±1.3) at 600°C could be the result of lesser intergranular space due to sintering.

Fabrication of calcite blocks from gypsum blocks by compositional transformation based on dissolution–precipitation reactions in sodium carbonate solution

Calcium carbonate (CaCO3) has been used as a bone substitute, and is a precursor for carbonate apatite, which is also a promising bone substitute. However, limited studies have been reported on the fabrication of artificial calcite blocks. In the present study, cylindrical calcite blocks (ϕ6×3mm) were fabricated by compositional transformation based on dissolution-precipitation reactions using different calcium sulfate blocks as a precursor. In the dissolution-precipitation reactions, both CaSO4·2H2O and CaSO4 transformed into calcite, a polymorph of CaCO3, while maintaining their macroscopic structure when immersed in 1mol/L Na2CO3 solution at 80°C for 1week. The diametral tensile strengths of the calcite blocks formed using CaSO4·2H2O and CaSO4 were 1.0±0.3 and 2.3±0.7MPa, respectively. The fabrication of calcite blocks using CaSO4·2H2O and CaSO4 proposed in this investigation may be a useful method to produce calcite blocks because of the self-setting ability and high temperature stability of gypsum precursors.

Effects of Hydrothermal Treatment on Properties of Titanium Nitride Coating for Dental Implants

To improve surface hardness of dental implant made of pure titanium (Ti), titanium nitride (TiN) coating was introduced. However, studies revealed that TiN only showed osseointegration similar or inferior to that of Ti. Therefore it is necessary to improve the biocompatibility of TiN for dental implant coating. In the present study, TiN coating was prepared on pure Ti substrates and hydrothermal treatment was conducted to modify its surface properties. It was found that, TiN surface was partially oxidized after treatment and calcium (Ca) was successfully combined onto its surface. Surface morphology, roughness and hardness were not affected after treatments below 140°C and wettability was obviously improved.