Jui-Ting Hsu

Detection of Permanent Three-rooted Mandibular First Molars by Cone-Beam Computed Tomography Imaging in Taiwanese Individuals

This study determined the prevalence of permanent three-rooted mandibular first molars and their morphology among a Taiwanese population by using cone-beam computed tomography (CBCT). Images from 744 patients were screened to obtain 123 samples for this study. All permanent mandibular first molars were evaluated in axial sections from the pulpal floor to the apices of the roots to determine the number of roots. The interorifice distances from the distolingual (DL) canal to the mesiobuccal (MB) and distobuccal (DB) canals were also estimated. The prevalence of permanent three-rooted mandibular first molars was 33.33%, with a bilateral incidence of a symmetrical distribution of 53.65%. There was a significantly greater incidence of three-rooted teeth on the right side of the mandible than on the left, but gender did not show a significant relationship with this variant prevalence.The mean interorifice distances from the DL canal to the DB, MB, and ML canals of the permanent three-rooted mandibular molars were 2.7, 4.4, and 3.5 mm, respectively. The high prevalence of the DL root in permanent mandibular first molars among the Taiwanese (Chinese) population and estimations of the interorifice distance of such teeth might be useful for successful endodontic treatments.

Bone Strain and Interfacial Sliding Analyses of Platform Switching and Implant Diameter on an Immediately Loaded Implant: Experimental and Three-Dimensional Finite Element Analyses

BACKGROUND Strain gauge analysis and finite element (FE) simulations were used to estimate the bone strain and micromovement at the bone-implant interface (BII) for platform switching and different diameters of a single, immediately loaded mandibular implant. METHODS Four models were created, including 5-mm-diameter implants assembled with abutments that were 5 or 4 mm in diameter on bonded (delay-loading treatment) and contact (immediate-loading treatment) BIIs; a model with an implant diameter of 3.75 mm was also analyzed. Vertical and lateral loads of 130 N were applied to all models. RESULTS During lateral loading, the strains were highly concentrated on one side of the mandible in the experimental and validation FE models. Bone strains were reduced by <10% when platform switching was used compared to no platform switching. However, increasing implant diameter decreased the surrounding bone strain significantly. The sliding and gap distances at the BII did not differ significantly among all models considered. CONCLUSIONS Bone strain was reduced more by increasing the diameter of the implant than by using platform switching in the immediately loaded implant. However, neither a wide implant nor platform switching reduced micromotion at the BII for enhancing implant stability.

Variations in bone density at dental implant sites in different regions of the jawbone

The survival rate of dental implants is markedly influenced by the quality of the bone into which they are placed. The purpose of this study was to determine the trabecular bone density at potential dental implant sites in different regions of the Chinese jawbone using computed tomography (CT) images. One hundred and fifty-four potential implant sites (15 in the anterior mandible, 47 in the anterior maxilla, 55 in the posterior mandible, and 37 in the posterior maxilla) were selected from the jawbones of 62 humans. The data were subjected to statistical analysis to determine any correlation between bone density (in Hounsfield units, HU) and jawbone region using the Kruskal-Wallis test. The bone densities in the four regions decreased in the following order: anterior mandible (530 +/- 161 HU, mean +/- s.d.) approximately equal anterior maxilla (516 +/- 132 HU) > posterior mandible (359 +/- 150 HU) approximately equal posterior maxilla (332 +/- 136 HU). The CT data demonstrate that trabecular bone density varies markedly with potential implant site in the anterior and posterior regions of the maxilla and mandible. These findings may provide the clinician with guidelines for dental implant surgical procedures (i.e., to determine whether a one-stage or a two-stage protocol is required).

Effect of Screw Fixation on Temporomandibular Joint Condylar Prosthesis

PURPOSE The objective of the present study was to evaluate the effect of the number of screws on the stress and stability of the temporomandibular joint (TMJ) condylar prosthesis and on the strain distribution in the bone. MATERIALS AND METHODS Three-dimensional, finite element models of the mandible and a TMJ condylar prosthesis with fixations involving different numbers of screws in 8 configurations were established to investigate the effect of the number of fixed screws on the stress and stability of the implant and strain in cortical and cancellous bone. RESULTS The simulations showed that increasing the number of screws beyond 3 only slightly enhanced the implant stability and reduced the implant stress. The position of the inserted screws significantly affected the strain distributions in cortical and cancellous bone tissues. CONCLUSIONS The results of our study have shown that 3 staggered screws can provide optimal implant stability and bone stress and strain distributions in a TMJ condylar prosthesis.

Initial stability and bone strain evaluation of the immediately loaded dental implant: an in vitro model study

OBJECTIVES The aim of this study was to evaluate the effects of cortical bone thickness and trabecular bone elastic modulus on the strain in the bone surrounding an immediately loaded implant. We also examined the correlations between bone structure and the following indices of primary implant stability: insertion torque value (ITV), Periotest value (PTV), and implant stability quotient (ISQ). MATERIAL AND METHODS The ITV, PTV, and ISQ were measured in 24 artificial jaw bone models representing cortical bone with four thicknesses (0, 1, 2, and 3 mm) and trabecular bone with four elastic moduli (137, 47.5, 23, and 12.4 MPa). Two loading conditions were applied (force of 130 N applied vertically and at 45° laterally), and the strains in the crestal region were measured by rosette strain gauges with a data acquisition system. RESULTS When the cortical bone thickness and the elastic modulus of trabecular bone decreased, the bone strains increased by 10.3-52.1% and 39-73.1%, respectively, for vertical loading and by 35-62% and 42.4-56.2% for lateral loading. The cortical bone thickness has a stronger correlation (R(2) =0.95-0.71) with ITV, PTV, and ISQ than the elastic modulus of trabecular bone (R(2) =0.89-0.59). CONCLUSIONS The initial stability at the time of implant placement is influenced by both the cortical bone thickness and the elastic modulus of trabecular bone; however, these parameters are not totally linearly correlated with ITV, PTV, and ISQ. The placement of an immediately loaded implant in cases with thin cortical bone and/or weak trabecular bone can induce extreme bone strains and may increase the risk of implant failure.

Biomechanical simulation of various surface roughnesses and geometric designs on an immediately loaded dental implant

Experiment with rapid prototyping technique and validation finite element model was performed to evaluate the biomechanical behavior of an immediately loaded mandibular implant. Also, 18 finite element models of six implant designs and three surface roughnesses with anisotropic bone material properties were analyzed to compare the bone stresses and the sliding at the bone-implant interface under a vertical or lateral force of 130N. The results show that bone stress (strain) of an immediately loaded implant is heavily dependent on the implant design and surface roughness. Improving the initial interfacial interlocking using a threaded implant has a higher priority than using cylindrical or step designs with a rough surface for an immediately loaded implant.

The assessment of trabecular bone parameters and cortical bone strength: A comparison of micro-CT and dental cone-beam CT

This study compared the capabilities of micro-computed tomography (micro-CT) and dental cone-beam computed tomography (CBCT) in assessing trabecular bone parameters and cortical bone strength. Micro-CT and CBCT scans were applied to 28 femurs from 14 rats to obtain independent measurements of the volumetric cancellous bone mineral density (vCanBMD) in the femoral head, volumetric cortical bone mineral density (vCtBMD) in the femoral diaphysis, cross-sectional moment of inertia (CSMI), and bone strength index (BSI) (=CSMI×vCtBMD). Five structural parameters of the trabecular bone of the femoral head were calculated from micro-CT images. A three-point bending test was then conducted to measure the fracture load of each femur. Bivariate linear Pearson analysis was conducted to calculate the correlation coefficients (r values) of the micro-CT, dental CBCT, and three-point bending measurements. The statistical analyses showed a strong correlation between vCanBMD values obtained using micro-CT and dental CBCT (r=0.830). There were strong or moderate correlation between vCanBMD measured using dental CBCT and five parameters of trabecular structure measured using micro-CT. Additionally, the results were satisfactory regardless of whether micro-CT or dental CBCT was used to measure the femoral diaphysis vCtBMD (r=0.733 and 0.680, respectively), CSMI (r=0.756 and 0.726, respectively), or BSI (r=0.846 and 0.847, respectively) to predict fracture loads. This study has yielded a new method for using dental CBCT to evaluate bone parameters and bone strength; however, further studies are necessary to validate the use of dental CBCT on humans.

In vitro antibacterial activity and cytocompatibility of bismuth doped micro-arc oxidized titanium

Chemical manipulations of the implant surface produce a bactericidal feature to prevent infections around dental implants. Despite the successful use of bismuth against mucosal and dermis infections, the antibacterial effect of bismuth in the oral cavity remains under investigation. The aim of this study was to evaluate the antibacterial activities of bismuth compounds against Actinobacillus actinomycetemcomitans, Staphylococcus mutans, and methicillin-resistant Staphylococcus aureus (MRSA), and to investigate the antimicrobial effects of bismuth doped micro-arc oxidation (MAO) titanium via an agar diffusion test. Cell viability, alkaline phosphatase activity, and mineralization level of MG63 osteoblast-like cells seeded on the coatings were evaluated at 1, 7, and 14 days. The results demonstrate that bismuth nitrate possess superior antibacterial activity when compared with bismuth acetate, bismuth subgallate, and silver nitrate. The bismuth doped MAO coating (contained 6.2 atomic percentage bismuth) had good biological affinities to the MG63 cells and showed a higher antibacterial efficacy against Actinobacillus actinomycetemcomitans and MRSA, where the reduction rates of colony numbers is higher than that of the control group by 1.5 and 1.9 times, respectively. These in vitro evaluations demonstrate that titanium implants with bismuth on the surface may be useful for better infection control.

Effects of the 3D bone-to-implant contact and bone stiffness on the initial stability of a dental implant: micro-CT and resonance frequency analyses

This study investigated the effects of bone stiffness (elastic modulus) and three-dimensional (3D) bone-to-implant contact ratio (BIC%) on the primary stabilities of dental implants using micro-computed tomography (micro-CT) and resonance frequency analyses. Artificial sawbone models with five values of elastic modulus (137, 123, 47.5, 22, and 12.4 MPa) comprising two types of trabecular structure (solid-rigid and cellular-rigid) were investigated for initial implant stability quotient (ISQ), measured using the wireless Osstell resonance frequency analyzer. Bone specimens were attached to 2 mm fibre-filled epoxy sheets mimicking the cortical shell. ISQ was measured after placing a dental implant into the bone specimen. Each bone specimen with an implant was subjected to micro-CT scanning to calculate the 3D BIC% values. The similarity of the cellular type of artificial bone to the trabecular structure might make it more appropriate for obtaining accurate values of primary implant stability than solid-bone blocks. For the cellular-rigid bone models, the ISQ increased with the elastic modulus of cancellous bone. The regression correlation coefficient was 0.96 for correlations of the ISQ with the elasticity of cancellous bone and with the 3D BIC%. The initial implant stability was moderately positively correlated with the elasticity of cancellous bone and with the 3D BIC%.

A Comparison of Micro-CT and Dental CT in Assessing Cortical Bone Morphology and Trabecular Bone Microarchitecture

Objective The objective of this study was to evaluate the relationship between the trabecular bone microarchitecture and cortical bone morphology by using micro-computed tomography (micro-CT) and dental cone-beam computed tomography (dental CT). Materials and Methods Sixteen femurs and eight fifth lumbar vertebrae were collected from eight male Sprague Dawley rats. Four trabecular bone microarchitecture parameters related to the fifth lumbar vertebral body (percent bone volume [BV/TV], trabecular thickness [TbTh], trabecular separation [TbSp], and trabecular number [TbN]) were calculated using micro-CT. In addition, the volumetric cancellous bone grayscale value (vCanGrayscale) of the fifth lumbar vertebral body was measured using dental CT. Furthermore, four cortical bone morphology parameters of the femoral diaphysis (total cross-sectional area [TtAr], cortical area [CtAr], cortical bone area fraction [CtAr/TtAr], and cortical thickness [CtTh]) were calculated using both micro-CT and dental CT. Pearson analysis was conducted to calculate the correlation coefficients (r) of the micro-CT and dental CT measurements. Paired-sample t tests were used to compare the differences between the measurements of the four cortical bone morphology parameters obtained using micro-CT and dental CT. Results High correlations between the vCanGrayscale measured using dental CT and the trabecular bone microarchitecture parameters (BV/TV [r = 0.84] and TbTh [r = 0.84]) measured using micro-CT were observed. The absolute value of the four cortical bone morphology parameters may be different between the dental CT and micro-CT approaches. However, high correlations (r ranged from 0.71 to 0.90) among these four cortical bone morphology parameters measured using the two approaches were obtained. Conclusion We observed high correlations between the vCanGrayscale measured using dental CT and the trabecular bone microarchitecture parameters (BV/TV and TbTh) measured using micro-CT, in addition to high correlations between the cortical bone morphology measured using micro-CT and dental CT. Further experiments are necessary to validate the use of dental CT on human bone.