Zongyang Sun

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.

Movement of temporomandibular joint tissues during mastication and passive manipulation in miniature pigs

Movement is an important aspect of the biomechanics of the temporomandibular joint (TMJ). To track the relative movements of TMJ components, radio-opaque markers were implanted in the left squamosal bone, mandible and retrodiscal tissue of miniature pigs. Medial-lateral (ML) and dorsal-ventral (DV) fluoroscopic records were made 8-10 weeks later during chewing and passive manipulation. Marker movements were digitized from the videotapes. During passive manipulation, the deformation of the lateral capsule was also measured with a differential variable-reluctance transducer. The results provide new details about porcine chewing pattern, which is distinguished by a regularly alternating chewing side. During masticatory opening, the mandible had a centre of rotation (CR) well inferior to the condyle and close to the angle. In contrast, the passive opening movement showed a higher CR location close to the condylar neck, indicating a different motion from masticatory opening. The retrodiscal tissue followed the movements of the mandibular condyle during both mastication and passive manipulation. The lateral capsule elongated during ipsilateral shifts and retrusion, implying a possible role in limiting such movements. These movement characteristics provide a useful reference for studies on the TMJ using pigs.

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.

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.

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.

The effect of periosteal injury and masticatory micromovement on the healing of a mandibular distraction osteogenesis site

OBJECTIVES Surgical periosteal injury and masticatory loading are likely factors affecting the healing of a mandibular DO site. This study is aimed to characterize the healing features of an early-phase mandibular DO site and assess the effects of these factors. DESIGN Eighteen 3-6-month-old miniature pigs received a right mandibular osteotomy and were distracted for 5 days (1 mm/day) and consolidated for 0, 1 or 2 weeks (Groups A, B and C, respectively). Bone formation, chondrogenesis and vascular structure of the distraction site were measured using histological methods and their changes with consolidation time were characterized. The effect of periosteal injury was assessed by comparing the more severely injured lateral side with the less disturbed medial side. The effect of masticatory loading was evaluated by relating the healing features to the interfragmentary micromovement caused by soft-diet mastication. RESULTS With consolidation time, bone formation and chondrogenesis became stronger whilst vascular structure became more mature. Compared to the medial side, bone formation and chondrogenesis on the lateral side were significantly delayed in Groups A and B, but not in Group C, in which periosteal recovery had occurred. No difference was found for vascular measurements between the medial and lateral sides. In Group B, bone formation, but not chondrogenesis or vascular structures, tended to be negatively correlated with the magnitude of masticatory micromovement during the distraction phase. CONCLUSION The results suggest that periosteal injury inhibits early mandibular DO site healing, whereas micromovement from soft-diet mastication mechanics has a negligible effect.

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.

Cell proliferation and osteogenic differentiation of growing pig cranial sutures

Bone growth at the cranial sutures relies on proliferation of osteogenic progenitor cells and/or differentiation of osteoblasts. The current study was undertaken to assess these events in relation to suture growth and fusion. A total of 21 pigs, divided into three age groups (0.5–1.5 months, 3–4 months and 5–7 months), were used for immunohistochemical evaluation of cell proliferation (BrdU) and osteogenic differentiation (Cbfa1/Runx2) in the interfrontal and interparietal sutures. Proliferation and osteogenic differentiation were both more prominent near the bone fronts than in the central zone. With age, both proliferation and osteogenic differentiation diminished. Proliferation ceased on the endocranial (dura mater) side by the age of 3–4 months. Proliferation on the pericranial side was accompanied by active bone formation and initiation of suture fusion from this side. In conclusion, (1) decreased suture bone growth with age reflects decreased cell proliferation and probably also osteogenic differentiation, and (2) suture fusion occurs from the pericranial side where activity remains relatively high.

Molecular Variations Related to the Regional Differences in Periosteal Growth at the Mandibular Ramus

Periosteal growth at human mandibular ramus is characterized by bone apposition at the posterior border and resorption at the anterior border. Molecular control of this regional variation is unclear. This study examined the expression of several molecules involved in bone apposition/resorption at these regions in vivo and in vitro. By using growing pigs as a model, the periosteal growth was assessed at the mandibular ramus by vital staining and histological observations. In parallel, periosteal tissues were harvested and pulverized for RNA and protein extraction. Periosteal cells were also isolated, expanded in osteogenic media, and subjected to a single dose of dynamic tensile strain (0, 5, or 10% magnitude at 0.5 Hz) to examine their responses to mechanical loading. Real‐time RT‐PCR and Western blot analyses were used to examine mRNA and protein expression from periosteal tissues and cultured cells. Histological observation confirmed an anterior‐resorption/posterior‐apposition pattern in the pig mandibular ramus. Both in vivo tissue and in vitro cells demonstrated greater mRNA expression of receptor activator of NF‐κB ligand (RANKL)/osteoprotegerin (OPG) ratio and bone morphogenetic protein 2 (BMP2) at the anterior region, while OPG expression at the anterior region was lower than the posterior region. In response to the application of a single dose of dynamic tensile strain, cultured periosteal cells appeared to change the expression profile of osteogenic markers but not that of RANKL/OPG and BMP2. These findings suggest that the unique regional variation of periosteal activity at the mandibular ramus is regulated by a differential expression of RANKL/OPG ratio (likely through differential induction of OPG) and BMP2. Anat Rec, 2010.