Stress-transferring mechanism at the bone-implant interface characterized by the direction and profile of interfacial stresses, which leads to more compressive and less shear stress, may clarify the biomechanical aspect of microthread dental implants.

No abstract

Objective:The aim of this study was to investigate the predictability of bone density at posterior mandibular implant sites using cone-beam computed tomography (CBCT) intensity values.Materials and Methods:CBCT cross-sectional images for 436 posterior mandibular implant sites were selected for the study. Using Invivo software (Anatomage, San Jose, California, USA), two observers classified the bone density into three categories: low, intermediate, and high, and CBCT intensity values were generated.Results:Based on the consensus of the two observers, 15.6% of sites were of low bone density, 47.9% were of intermediate density, and 36.5% were of high density. Receiver-operating characteristic analysis showed that CBCT intensity values had a high predictive power for predicting high density sites (area under the curve [AUC] =0.94, P < 0.005) and intermediate density sites (AUC = 0.81, P < 0.005). The best cut-off value for intensity to predict intermediate density sites was 218 (sensitivity = 0.77 and specificity = 0.76) and the best cut-off value for intensity to predict high density sites was 403 (sensitivity = 0.93 and specificity = 0.77).Conclusions:CBCT intensity values are considered useful for predicting bone density at posterior mandibular implant sites.

No abstract

The mechanism of traumatic bone resorption in the denture-bearing bone has not yet been established with regard to the osteoclastic activity in relation to the mechanical stimulus. The purpose of this study was to clarify whether osteoclast appearance in maxilla depends on the strain intensity, using the murine loading model. The maxillary palate of thirteen-week-old male C57BL/6 mice was subjected to continuous pressure of 2 kPa (low stimulation, n = 4) or 7 kPa (high stimulation, n = 4) for 30 min/day for 7 consecutive days, and the mice were sacrificed after the last loading. The control group underwent the same protocol without load (n = 4). An animal-specific finite element model was constructed based on morphology and characteristics obtained from the micro-CT data and used to calculate the strain intensity of the bone. The bone histomorphometric technique revealed significant reduction of cortical bone volume and significant increase of bone resorption parameters such as osteoclast number in the bone tissue under the loading contact in comparison to the control (p < 0.05). The osteoclasts were observed in the subsurface region adjacent to the loading contact and the peripheral region of the marrow space in the intracortical region of the cortical bone in the mouse maxilla in both stimulation groups. An average of more than 90 % of the osteoclasts was observed in the areas with strain intensity higher than 85.0μ strain for the high stimulation group. The result suggests that the osteoclastic resorption is location-dependent and is also sensitive to the local strain intensity.

Background The purpose of this study was to assess the effect of different exposure levels of a dental implant’s first thread on adjacent bone stress and strain using the finite element analysis method. Material/Methods Three-dimensional models of 2 threaded implants and abutments with a mandibular bone segment were constructed to represent the covered (C) and exposed models. In the exposed models, the implant was first placed in the bone, and rotated around its axis a quarter-turn each time to simulate 4 different levels of first thread exposure at the mid-lingual side: Upper Flank (UF), Thread Crest (TC), Lower Flank (LF), and Thread Root (TR) models. Oblique forces were applied and analysis was performed. Results Maximum compressive stress magnitude and distribution varied according to the exposed thread profile. In the exposed group, peak stress ranged from 136 MPa to 197 MPa in TC and LF models, respectively, compared to 141 MPa in C model. In LF, UF, and C models, peak stress was observed at the mid-lingual side of the crestal region, while in TC and TR models, peak stress shifted distally in accordance with thread profile. However, alveolar bone volumes which exhibited compressive microstrain levels within the physiological loading and maintenance windows were relatively close in all models. Conclusions Results suggest that the exposed thread profile influences stress and strain outcomes in the adjacent bone; however, this influence is only limited to a small region around the exposed thread.

Calvarial critical-size defect has been used to assess techniques and materials in the bone regeneration field. Previous studies utilized young adult rats with 3 months of age, which might not reflect the geriatric conditions. This study aimed to assess the dimensions of the calvarial critical-size defect in aged rats. Seventy-two rats in a randomized block design were allocated into a control young adult (11–12 weeks), and a test old group (22–24 months). Both groups were divided according to bone defect's size: 3 mm, 5 mm, and 7 mm defects, which were surgically created and followed for 4 and 8 weeks. Radiographic and histologic analyses were performed. Based on the results, additional groups with 4 mm defect size were added following the same protocols. Young groups yielded higher bone volumes, defect closure percentages, and density of newly formed bone. Closure of cranial defects was only observed in 3 mm defects in both age groups after 8 weeks; however, the 4 mm defect group demonstrated bony bridging after 8 weeks in young but not old rats. Results confirmed that 5-mm defect is considered a critical size for calvarial bone defects in young adult rats; however, 4 mm defect might be considered critical size for the aged rats after 8 weeks.

The aim of the present study was to compare visibility of the mandibular canal on cone beam computed tomography (CBCT)-based orthoradial and oblique slices at molar implant sites. CBCT images for 132 mandibular molar implant sites were selected for the study. After generating orthoradial and oblique slices, two observers evaluated the visibility of the mandibular canal using three-point scoring scale (1À3, good to excellent). Wilcoxon signed-rank test compared the visibility scores of the two slices. Both orthoradial and oblique slices obtained from CBCT had only very good to excellent mandibular canal visibility scores. At 114 mandibular molar implant sites, the visibility score was equal on both orthoradial and oblique slices. Although the visibility score was higher on orthoradial slices for 12 implant sites, the visibility score was higher for six implant sites on oblique slices and the difference was not significant. Therefore, the visibility of the mandibular canal was excellent and comparable on most of orthoradial and oblique slices obtained from CBCT images.