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Current Research Directions and Results

Mechanisms of dentin hypersensitivity and development of its treatment materials

Research Goals:

  1. Mechanisms underlying dentin hypersensitivity.
  2. Development of effective treatment procedures for dentin hypersensitivity.
  3. Utilization of nanotechnology in developing highly reactive bioglass to achieve long-term treatment of dentin hypersensitivity.

Results:

  1. Mechanisms underlying dentin hypersensitivity: as high as 34%, considerably higher than the figures from overseas reports, of the Taiwanese public suffers from dentin hypersensitivity and these incidents increase with increasing age. Inappropriate brushing techniques and periodontic diseases are important causes underlying dentin hypersensitivity. (J Edodon 1997, 1998 & 1999; Chin Dent J, 1998)
  2. Utilization of laser combined with bioglass for the effective treatment of dentin hypersensitivity: we developed a low melting point, low particle size, and highly laser absorbing NSC bioglass (N2CS3-NC2S3-NS2) with SiO2 as the main ingredient, with additional Na2O and CaO. The NSC bioglass surface is liquid soluble and crystallizes as CaO-P2O5 and chemically bonds with dentin. The newly developed NCS bioglass, combined with 64% phosphoric acid and CO2 laser, forms a liquid glass that penetrates dentinal tubules as deep as 10 or several times moreμm. (Biomaterials, 2003; Chin Dent J, 2003&2004; Formosan J Med, 2003; Dent Mater, 2004)
  3. Utilization of DP bioglass on the treatment of dentin hypersensitivity: we developed a DP-bioglass that combines and sets with phosphoric acid at a 1:2 ratio without the need of laser. Our research shows that the concentration of phosphoric acid affects the setting product such that when DP-bioglass combines with more than 40% of phosphoric acid, Ca(H2PO4)2•H2O is the main crystallized product, whereas combined with less than 30%, CaHPO4•2H2O is the main product, and these compounds have low solubility and high stability. In addition, when DP-bioglass combines with more than 30% phosphoric acid, they seal dentinal tubules as deep as 20~60μm. DP-bioglass is biocompatible and has potential to be used as a practical treatment material for dentin hypersensitivity. (Dent Mater, 2005;Dent Mater J, 2005; J Endodon, 2007 Accepted )
  4. Utilization of sol-gel techniques in creating porous DP-bioglass in the treatment of dentin hypersensitivity: it was found that 8000℃ is a suitable temperature for the calcination and production of sol-gel DP-bioglass. Our research shows that nitric acid is the best catalyst in producing a complete chemical reaction, achieving a more ideal sol-gel DP-bioglass quality, with particle size ranging from 20~30 μm and pore size ranging from 200nm to 3μm. Combined with 30% phosphoric acid, it can penetrate dentinal tubules and achieve blocking effects by re-crystallization within 10 minutes, evidently a better performance than that of the traditional DP-bioglass. (Dent Mater J, 2007 Accepted)

 

Endodontic microsurgery and development of nano-size biomaterials for pulp tissue regeneration and repair

Research Goals:

  1. Establish safe and effective microsurgery and root-end preparation procedures.
  2. Develop ideal nano-biomaterials for pulp regeneration and repair.
  3. Understand the solubility and adjustments of calcium silicate bioceramics as an endodontic treatment material.
  4. Develop biomaterials that induce pulp-dentin tissue regeneration and understand its mechanism.
  5. Investigate the biocompatibility and mechanisms of nano-biomaterials for pulpal repair.

Results:

  1. Development of nano-biomaterials for pulp regeneration: using the marketed Mineral Trioxide Aggregate (MTA) as a reference, we developed a bioactive Calcium Silicate bioceramic (Calcium mics, CSCs) that has high pH, rapid setting time, good dentin sealing abilities, and easy handling characteristics. We also developed a Partial Stabilized Cement (PSC) to further shorten the setting time. Our analysis shows that the hydration product of CSC and PSC are mainly CSH and Ca(OH)2 in the nano-lattice structure. Their microscopic structures consist of mainly block-like crystals with scattered acicular crystals. When PSC is added to 5% CoO, hardness of the material is enhanced and setting time is significantly reduced. Its microscopic structure shows a compact but porous structure, beneficial for the attachment of periodontal ligament and growth of alveolar bone. Currently PSC has received patency in Taiwan, Japan, and the United States. (J Endodont, 2000 & 2001 & 2002&2003;J Mat Sci, 2000; Biomaterials, 2000, 2001 & 2002& 2004; J Biomed Mater Res; 2004)
  2. Hydration behavior and mechanism of calcium silicate bioceramic in endodontics: research shows that the hydration behavior of calcium silicate bioceramic and partial stabilized cement are very similar to that of the marketed material, Mineral Trioxide Aggregate (MTA). Microscopically, their hydration product shows mainly block-like crystals with scattered acicular crystal structures. Clinically, the hydration product of MTA provides adherence, at the same time the coating effect provided by the block-like crystals allow the material to gradually release Ca2+ and OH-, which can possibly attract bone tissue, inducing cementogenesis and dentinogenesis, thus possessing great potential in vital pulp therapy, retrograde filling, and repair of root perforations. Furthermore, our crystal analysis shows that the crystal product of Ca(OH)2 at 18 degrees can be a marker in assessing physical properties and biocompatibility of the materials. Alkaline conditions positively affects the hydration of calcium silicate bioceramic materials whereas acidic conditions not only inhibits the process of hydration, it also erodes the crystal product, decreasing the strength of the material. Our research also shows that Ca2+ plays a key role in the hydration and biocompatibility of MTA, and this result is published in J Den Res, 2007. When hydration of MTA takes place in an environment with EDTA, the released Ca2+ directly reacts with EDTA and the process of hydration is inhibited, and cell adherence is interfered. This indicates that biocompatibility of MTA is negatively influenced by EDTA. Our data and results served as the basis in hypothesizing the mechanism of MTA hydration behavior. (Biomaterials, 2003& 2004; J Biomed Mater Res; 2004; J Dent Res, 2007 Accepted)
  3. Assessment of the biocompatibility of pulp repair nano-biomaterials: our results show that the marketed MTA, compared to Super EBA, Glass Ionomer, IRM, and Amalgam, has superior biocompatibility, and possesses close to none cytotoxicity. When comparing our Calcium Silicate bioceramic and Partial Stabilized Cement with MTA, they also show no cytotoxicity and furthermore, show good cell adherence capability. When transition metals are added to PSC, cobalt oxide and chromium oxide groups show higher cytotoxicity, whereas the addition of zinc oxide shows cytotoxicity and cell mitotic ability comparable to those of MTA, indicating that PSC-Zn has good potential when used in pulp repair treatment. (Biomaterials, 2003; J Biomed Mater Res PartB, 2004; J Biomed Mater Res PartA, 2007)

 

Nano-implantation technology in improving physical properties of Ni-Ti rotary instruments.

Research Goals:

  1. Fracture mechanism of Ni-Ti rotary instruments.
  2. Utilization of nano-implantation technology in improving physical properties of Ni-Ti rotary instruments.
  3. Investigation of the use of non-destructive testing on the cyclic fatigue of Ni-Ti rotary instruments.

Results:

  1. Analysis of the fracture mechanism of Ni-Ti rotary instruments: our analysis shows that once the instrument fractures, no matter what size or degree of taper, the distance between the fracture site and the instrument tip is on average within the apical 1/3 of the root, at 3 to 5mm. Statistically, the most frequent fracture incident takes place with 0.04 taper, size ISO25, and working length of 21mm. Under the electron microscope, almost 70% of the fractured instrument shows deformation, indicating excess torque that exceeds the flexibility limit, whereas the remaining 30% shows growth of fatigue lines, suggesting that cyclic fatigue is the underlying cause of instrument fracture. Furthermore, different bending angles and different alternating speeds show apparent difference in time required for fracture; when both increase, the time decreases. In applying pecking motion, different entry lengths and different alternating speeds show major difference in time required for fracture. The longer the entry length, the longer the time; the higher the alternating speed, the shorter the time. On the aspect of cycles required for fracture, alternating speeds do not influence the number of cycles significantly, yet when entry length increases or bending angle decreases, the number of cycles required for fracture increases. Therefore, to prevent fracture incidence of Ni-Ti rotary instruments, it is recommended that appropriate alternating speeds and continuous pecking motion are used. (J Endodont, 2002; Chin Dent J, 2001)
  2. Investigation of the use of non-destructive testing on the cyclic fatigue of Ni-Ti rotary instruments: our analysis shows that with increasing crack depth, stiffness shows increasing changes. Our studies also show that the direction and angle of instrument cracks are measurable. When simulating clinical use of Ni-Ti rotary instruments, we found the relationship between crack duration and depth of cracks in causing instrument fracture, and that growth of cracks leading up to fracture fatigue of Ni-Ti rotary files are measurable. Therefore non-destructive testing is a practical method to assess cyclic fatigue of Ni-Ti rotary instruments. (Dent Mat J, 2006; Chin Den Sci, 2004; J Dent Sci, 2006)
  3. Utilization of nano-implantation technology in improving physical properties of Ni-Ti rotary instruments: our analysis shows that, using thermal nitridation procedures and Plasma Immersion Ion Implantation (PIII) technology to transfer nitrogen to the surface of instruments, increases the surface hardness and cutting ability of Ni-Ti rotary instruments. Nitrogen could be successfully implanted into the surface of instruments as deep as 100nm, without affecting the original mechanical properties of the instruments. In comparing cutting abilities, abrasion resistance, cyclic fatigue resistance, and corrosion resistance of the processed vs. non-processed instruments, PIII processed Ni-Ti rotary instruments shows superior properties. PIII is the first in the world to be used on Ni-Ti rotary instruments. (Den Mat J, 2007; J Dent Sci, 2006)

Cover of the Journal

GRADUATE INSTITUTE OF CLINICAL DENTISTRY
Author: YL Lee, FH Lin, WH Wang, WH Lan, CP Lin
Topic:Effects of EDTA on the Hydration Mechanism of Mineral Trioxide Aggregate
Journal: JDR, June 2007; 86:534 -538

  • International Association of Dental Research Best Paper Award
    Author: Dr. HC Chen
    Topic: Development of a mesoporous biomaterial for treatment of dentinhypersensitivity.
  • International Association of Dental Research. Pulp Biology Student Research Award. Brisbane. Australia (2006)
    Author: Dr. Cen-Fang Dai
    Topic: Effects of TGF-b2 on human pulp cells and its signaling.