Boon Ching Tee

Effect of bone thickness on alveolar bone-height measurements from cone-beam computed tomography images.

INTRODUCTION Cone-beam computed tomography (CBCT) has been used to assess alveolar bone changes after rapid palatal expansion. The purpose of this study was to investigate the accuracy of alveolar bone-height measurements from CBCT images with varied bone thicknesses and imaging resolutions. METHODS Eleven maxillary specimens from 6-month-old pigs were measured for alveolar bone height (distance between drilled reference holes and alveolar crests) at 6 locations with a digital caliper, followed by CBCT scanning at 0.4-mm and 0.25-mm voxel sizes. Buccal alveolar bone of these locations was then reduced approximately by 0.5 to 1.5 mm, followed by CBCT rescanning with the same voxel sizes. The CBCT images were measured by using 3-dimensional software to determine alveolar bone height and thickness in buccolingual slices by independent, blinded raters. The specimens were subsequently cut into buccolingual sections at reference-hole levels, and direct bone height and thickness were measured from these sections. Intrarater and interrater repeatability and the differences between CBCT and direct measurements were assessed. RESULTS Excellent intrarater (intraclass correlations, r = 0.89-0.98) and good interrater (r = 0.64-0.90) repeatability values were found for alveolar bone-height measurements from the CBCT images. Before alveolar bone reduction, the thickness was much greater than the CBCT voxel size (0.4 mm), and bone-height measurements from the CBCT images were 0.5 to 1 mm more than the direct measurements (paired t tests, P <0.017 at most locations). After bone reduction, the thickness at the subcrest 1-mm level was near or below the CBCT voxel size (0.4 mm), and bone-height measurements from the CBCT images were 0.9 to 1.2 mm less than the direct measurements (paired t tests, P <0.017 at most locations). These measurement inaccuracies were substantially improved by decreasing the CBCT voxel size to 0.25 mm. CONCLUSIONS Alveolar bone-height measurements from conventional clinical 0.4-mm voxel size CBCT images might overestimate alveolar bone-height loss associated with rapid palatal expansion.

Factors affecting the accuracy of buccal alveolar bone height measurements from cone-beam computed tomography images

INTRODUCTION The reasons for inaccuracies in alveolar bone measurement from cone-beam computed tomography (CBCT) images might be multifactorial. In this study, we investigated the impact of software, the presence or absence of soft tissues, the voxel size of the scan, and the regions in the jaws on buccal alveolar bone height measurements in pigs at an age equivalent to human adolescents. METHODS Marker holes, apical to the maxillary and mandibular molar roots, and mesiodistal molar occlusal reference grooves were created in 6 fresh pig heads (12 for each jaw), followed by CBCT scans at 0.4-mm and 0.2-mm voxel sizes under soft-tissue presence and soft-tissue absence conditions. Subsequently, buccolingual sections bisecting the marker holes were cut, from which the physical alveolar bone height and thickness were measured. One blinded rater, using Dolphin (version 11.5 Premium; Dolphin Imaging, Chatsworth, Calif) and OsiriX (version 3.9; www.osirix-viewer.com) software, independently collected alveolar bone height measurements from the CBCT images. Differences between the CBCT and the physical measurements were calculated. The mean differences and the limit of agreement (LOA, ±1.96 SD) for every jaw, voxel-size, soft-tissue, and software condition were depicted. Each measurement was then assessed for clinical inaccuracy by using 2 levels of criteria (absolute differences between CBCT and physical measurements ≥1 mm, or absolute differences between CBCT and physical measurements ≥0.5 mm), and the interactions between soft-tissue and voxel-size factors for every jaw and software condition were assessed by chi-square tests. RESULTS Overall, the mean differences between the CBCT and the physical measurements for every jaw, voxel-size, soft-tissue, and software condition were near 0. With all other conditions kept equal, the accuracy of the maxillary CBCT measurements was inferior (larger limit of agreement ranges and higher frequencies of clinical inaccuracy) to the mandibular measurements. The physical thickness of the maxillary alveolar crestal bone was less than 1 mm and significantly thinner than the mandibular counterparts. For every jaw and software condition, the accuracy of measurements from the 0.2-mm soft-tissue presence CBCT images was consistently superior (smaller limit of agreement ranges and lower frequencies of clinical inaccuracy) to those from the 0.4-mm soft-tissue presence, the 0.4-mm soft-tissue absence, and the 0.2-mm soft-tissue absence images; all showed similar accuracies. Qualitatively, the soft-tissue absence images demonstrated much brighter enamel and alveolar bone surface contours than did the soft-tissue presence images. CONCLUSIONS At an adolescent age, the buccal alveolar bone height measured from the maxillary molar region based on 0.4-mm voxel-size CBCT images can have relatively large and frequently inaccurate measurements, possibly due to its thinness. By using 0.2-mm voxel-size scans, measurement accuracy might be improved, but only when the overlying facial and gingival tissues are kept intact.

Bone Ingrowth and Initial Stability of Titanium and Porous Tantalum Dental Implants: A Pilot Canine Study

Purpose:To investigate if a dental implant system with a midsection covered by 3-dimensionally porous tantalum material would exhibit stability comparable with a traditional threaded titanium alloy implant system and whether bone would grow into the porous section. Methods:Three experimental and 3 control implants were placed in the individual mandibles of 8 dogs. Resonance frequency analysis assessed implant stability at 0, 2, 4, 8, and 12 weeks of healing. Histomorphometric and backscattered scanning electron microscopic analyses examined the presence of bone ingrowth into the experimental implant’s porous section and bone-to-implant contact along the titanium surfaces of both implants. Results:Implant stability did not significantly differ during 0 to 12 weeks of healing. Progressive tissue mineralization developed inside porous sections from weeks 2 to 12. Porous implants exhibited a combination of progressive osseointegration along their titanium surfaces and bone ingrowth inside their porous tantalum sections. Conclusions:Cortical and apical implant threads, combined with the porous section, were able to stabilize the experimental implant to the same degree as the fully threaded control implant.

Scaffold-Based Delivery of Autologous Mesenchymal Stem Cells for Mandibular Distraction Osteogenesis: Preliminary Studies in a Porcine Model

Purpose Bone regeneration through distraction osteogenesis (DO) is promising but remarkably slow. To accelerate it, autologous mesenchymal stem cells have been directly injected to the distraction site in a few recent studies. Compared to direct injection, a scaffold-based method can provide earlier cell delivery with potentially better controlled cell distribution and retention. This pilot project investigated a scaffold-based cell-delivery approach in a porcine mandibular DO model. Materials and Methods Eleven adolescent domestic pigs were used for two major sets of studies. The in-vitro set established methodologies to: aspirate bone marrow from the tibia; isolate, characterize and expand bone marrow-derived mesenchymal stem cells (BM-MSCs); enhance BM-MSC osteogenic differentiation using FGF-2; and confirm cell integration with a gelatin-based Gelfoam scaffold. The in-vivo set transplanted autologous stem cells into the mandibular distraction sites using Gelfoam scaffolds; completed a standard DO-course and assessed bone regeneration by macroscopic, radiographic and histological methods. Repeated-measure ANOVAs and t-tests were used for statistical analyses. Results From aspirated bone marrow, multi-potent, heterogeneous BM-MSCs purified from hematopoietic stem cell contamination were obtained. FGF-2 significantly enhanced pig BM-MSC osteogenic differentiation and proliferation, with 5 ng/ml determined as the optimal dosage. Pig BM-MSCs integrated readily with Gelfoam and maintained viability and proliferative ability. After integration with Gelfoam scaffolds, 2.4–5.8×107 autologous BM-MSCs (undifferentiated or differentiated) were transplanted to each experimental DO site. Among 8 evaluable DO sites included in the final analyses, the experimental DO sites demonstrated less interfragmentary mobility, more advanced gap obliteration, higher mineral content and faster mineral apposition than the control sites, and all transplanted scaffolds were completely degraded. Conclusion It is technically feasible and biologically sound to deliver autologous BM-MSCs to the distraction site immediately after osteotomy using a Gelfoam scaffold to enhance mandibular DO.

Increased variability of bone tissue mineral density resulting from estrogen deficiency influences creep behavior in a rat vertebral body

Progressive vertebral deformation increases the fracture risk of a vertebral body in the postmenopausal patient. Many studies have observed that bone can demonstrate creep behavior, defined as continued time-dependent deformation even when mechanical loading is held constant. Creep is a characteristic of viscoelastic behavior, which is common in biological materials. We hypothesized that estrogen deficiency-dependent alteration of the mineral distribution of bone at the tissue level could influence the progressive postmenopausal vertebral deformity that is observed as the creep response at the organ level. The objective of this study was thus to examine whether the creep behavior of vertebral bone is changed by estrogen deficiency, and to determine which bone property parameters are responsible for the creep response of vertebral bone at physiological loading levels using an ovariectomized (OVX) rat model. Correlations of creep parameters with bone mineral density (BMD), tissue mineral density (TMD) and architectural parameters of both OVX and sham surgery vertebral bone were tested. As the vertebral creep was not fully recovered during the post-creep unloading period, there was substantial residual displacement for both the sham and OVX groups. A strong positive correlation between loading creep and residual displacement was found (r=0.868, p<0.001). Of the various parameters studied, TMD variability was the parameter that best predicted the creep behavior of the OVX group (p<0.038). The current results indicated that creep caused progressive, permanent reduction in vertebral height for both the sham and OVX groups. In addition, estrogen deficiency-induced active bone remodeling increased variability of trabecular TMD in the OVX group. Taken together, these results suggest that increased variability of trabecular TMD resulting from high bone turnover influences creep behavior of the OVX vertebrae.

Relationships of Viscosity With Contact Hardness and Modulus of Bone Matrix Measured by Nanoindentation

Creep is an active form of time-dependent viscoelastic deformation that occurs in bone tissue during daily life. Recent findings indicate bone mineralization, which is involved in determining the elastic and plastic properties of bone matrix, can also contribute in controlling its viscoelastic property. Nanoindentation viscosity was used as a direct measure for the capacity of a material to resist viscous-like flow under loading. The objectives of this study were to examine (1) whether the nanoindentation viscosity obtained using the traditional viscoelastic Voigt model can describe creep response of bone matrix and (2) how the nanoindentation viscosity is related to contact hardness and elastic modulus. The Voigt model accurately described the creep behavior of bone matrix (r(2)>0.96, p<0.001). The nanoindentation viscosity had strong relationships with nanoindentation contact hardness (r(2)=0.94, p<0.001) and modulus (r(2)=0.83, p<0.001) independent of tissue ages of osteonal bone matrix. The strong positive relationships of nanoindentation viscosity with contact hardness and modulus can be interpreted as increases in the mineral portion of bone matrix may limit the interfibril motion of collagen while enhancing the mechanical stability of bone. We suggest that previous nanoindentation results can be reanalyzed to characterize the viscoelastic creep using the Voigt model.

Variability of Tissue Mineral Density Can Determine Physiological Creep of Human Vertebral Cancellous Bone

Creep is a time-dependent viscoelastic deformation observed under a constant prolonged load. It has been indicated that progressive vertebral deformation due to creep may increase the risk of vertebral fracture in the long-term. The objective of this study was to examine the relationships of creep with trabecular architecture and tissue mineral density (TMD) parameters in human vertebral cancellous bone at a physiological static strain level. Architecture and TMD parameters of cancellous bone were analyzed using microcomputerized tomography (micro-CT) in specimens cored out of human vertebrae. Then, creep and residual strains of the specimens were measured after a two-hour physiological compressive constant static loading and unloading cycle. Creep developed (3877 ± 2158 με) resulting in substantial levels of non-recoverable post-creep residual strain (1797 ± 1391 με). A strong positive linear correlation was found between creep and residual strain (r = 0.94, p < 0.001). The current results showed that smaller thickness, larger surface area, greater connectivity of trabeculae, less mean tissue mineral density (TMD, represented by gray levels) and higher variability of TMD are associated with increasing logarithmic creep rate. The TMD variability (GL(COV)) was the strongest correlate of creep rate (r = 0.79, p < 0.001). This result suggests that TMD variability may be a useful parameter for estimating the long-term deformation of a whole vertebral body. The results further suggest that the changes in TMD variability resulting from bone remodeling are of importance and may provide an insight into the understanding of the mechanisms underlying progressive failure of vertebral bodies and development of a clinical fracture.

Evaluation of cone-beam computed tomography in the diagnosis of simulated small osseous defects in the mandibular condyle.

INTRODUCTION In this study, we investigated the impact of defect size and scan voxel size on the accuracy of cone-beam computed tomography (CBCT) diagnoses of simulated condylar defects and assessed the value of orthodontic CBCT images typically scanned at lower settings (0.4-mm voxel size and full-size field of view) in diagnosing condylar erosion defects. METHODS Cylindrical holes simulating condylar defects with varied diameters (≤2, 2-3, and >3 mm) and depths (≤2 and >2 mm) were created in 22 fresh pig mandibular condyles, with defect number and size per condyle and quadrant randomly determined. With the soft tissues repositioned, 2 CBCT scans (voxel sizes, 0.4 and 0.2 mm) of the pig heads were obtained from an i-CAT unit (Imaging Science International, Hatfield, Pa). Reconstructed CBCT data were analyzed independently by 2 calibrated, blinded raters using Dolphin-3D (Dolphin Imaging and Management Solutions, Chatsworth, Calif) for defect identification and localization and defect diameter and depth measurements, which were compared with physical diagnoses obtained from polyvinyl siloxane impressions. RESULTS Identification and localization of simulated defects demonstrated moderate interrater reliability and excellent specificity and sensitivity, except for extremely small defects (both diameter and depth ≤2 mm) viewed with 0.4-mm scans, which had a significantly lower sensitivity (67.3%). Geometric measurements of simulated defects demonstrated good but not excellent interrater reliability and submillimeter inaccuracy for all defects. Receiver operating characteristic analyses demonstrated that the overall accuracy of diagnosing simulated condylar defects based on CBCT geometric measurements was fair and good for the 0.4-mm and 0.2-mm voxel-size scans, respectively. With the prevalence of condylar erosion defects in the patients considered, the positive predictive values of diagnoses based on 0.5-mm size (diameter or depth) cutoff points were near 15% and 50% for asymptomatic and symptomatic temporomandibular joints, respectively; the negative predictive values were near 95% and 90%, respectively. CONCLUSIONS When using orthodontic CBCT images for diagnosing condylar osseous defects, extremely small (<2 mm) defects can be difficult to detect; caution is also needed for the diagnostic accuracy of positive diagnoses, especially those from asymptomatic temporomandibular joints.

Mechanical strain at alveolar bone and circummaxillary sutures during acute rapid palatal expansion

INTRODUCTION Palatal expansion can potentially affect alveolar bone and circummaxillary sutures. In this study, we characterized their mechanical strain during acute expansion. METHODS Eight 3- and 6-month-old fresh pig heads received acute palatal expansion with hyrax expanders. Strain gauges were used to measure strain at the buccal alveolar bone of anchor and adjacent nonanchor teeth, and at maxillary-premaxillary, maxillary-zygomatic, and zygomatic-temporal sutures during expansion. Intermolar width changes were measured from dental casts. RESULTS Intermolar width increased less than expander activation, and the midpalatal sutures were only opened slightly. Alveolar bone strain increased linearly with expander activation and decayed by 20% to 30% during postactivation intervals. Compressive strain at anchor-tooth alveolar bone locations was directed occlusally and apically, related to tooth tipping, and significantly higher than that at nonanchor tooth locations. With expander activation, suture strains increased monotonically and tended to plateau. Suture strain magnitude was generally similar to physiologic (masticatory) strains reported in the literature. The dominant strain polarity was compression at the maxillary-zygomatic and zygomatic-temporal sutures, but there was tension at the maxillary-premaxillary suture. CONCLUSIONS In these pigs, palatal expansion can cause significant occlusal-apical compression at buccal alveolar bone and physiologic-level strains at circummaxillary sutures.

Alveolar ridge reduction after tooth extraction in adolescents: An animal study

OBJECTIVE The mechanism for tooth extraction induced residual alveolar ridge reduction (RRR) during adolescence is poorly understood. This study investigated the alveolar bone morphology, growth, resorption and functional loading at normal and extraction sites using an adolescent pig model. DESIGN Sixteen 3-month-old pigs were divided into two groups - immediate post-extraction (IE) and 6-week post-extraction (SE). The IE group received an extraction of one deciduous mandibular molar, immediately followed by a final experiment to record masseter muscle EMGs and strains from the buccal surface of the extraction and contralateral non-extraction sites during function (mastication). The SE group was given the same tooth extraction, then kept for 6 weeks before the same final functional recording as the IE group. Both groups also received baseline (pre-extraction) EMGs and fluorescent vital stains 10 and 3 days before the final functional recording. Immediately after the final functional recording, animals were euthanized and alveolar bone specimens from extraction and contralateral non-extraction sites were collected and used to analyse alveolar bone morphology, apposition and resorption based on fluorescent and hematoxylin and eosin stained histological sections. RESULTS At control sites (IE-extraction, IE-non-extraction and SE-non-extraction), the alveolar ridges grew gingivally and buccally. Bone formation characterized the buccal surface and lingual bundle bone, whereas resorption characterized the lingual surface and buccal bundle bone. The SE-extraction sites showed three major alterations: convergence of the buccal and lingual gingival crests, loss of apposition on the lingual bundle bone, and decelerated growth at the entire buccal surface. These alterations likely resulted from redirected crestal growth as part of the socket healing process, loss of tongue pressure to the lingual side of the teeth which normally provides mechanical stimulation for dental arch expansion, and masticatory underloading during the initial post-extraction period, respectively. CONCLUSIONS These data indicate that the initial phase of RRR in adolescents is a product of modified growth, not resorption, possibly because of decreased mechanical stimulation at the extraction site.