Finite element modeling of an intact and cracked mandibular second molar under quantitative percussion diagnostics loading.

STATEMENT OF PROBLEM: Quantitative percussion diagnostics (QPD) has been devised to nondestructively evaluate the mechanical integrity of human teeth and implants, the mechanical integrity of the underlying bone, and the presence of cracks, but the mechanism is not clearly understood. PURPOSE: The purpose of this study is to better understand the dynamic behavior of a tooth under conditions consistent with QPD by focusing on physiologically accurate 3D finite element models of a human mandibular second molar with surrounding tissues. MATERIAL AND METHODS: Finite element analysis (FEA) was used to study the force response of dental structures measured by the sensor in a QPD handpiece. A defect-free (intact) and a cracked tooth model containing a vertical crack involving enamel, dentin, periodontal ligament, bone, and the QPD percussion rod were used for this purpose. Different crack gap spaces were studied for comparison. The FEA model was validated with clinical QPD data for a second mandibular molar containing a vertical crack that subsequently had to be extracted. The location and size of the vertical crack was determined once the tooth was extracted. RESULTS: The present FEA results exhibited features consistent with those of corresponding clinical data, thus verifying the model. An examination of the relative acceleration of the crack faces with respect to each other revealed that an oscillation between the crack surfaces results in secondary peaks in the QPD energy return response compared with that of an intact tooth. CONCLUSIONS: The present FEA modeling can generate simulated QPD results that exhibit established distinguishing characteristics in clinical QPD data for intact and cracked second mandibular molars. The model results also give insight into how QPD detects the presence of cracks and show that the oscillation of crack surfaces can produce the multipeak QPD results for a cracked molar observed clinically.

An evaluation of quantitative percussion diagnostics for determining the probability of a microgap defect in restored and unrestored teeth: A prospective clinical study.

STATEMENT OF PROBLEM: Current dental diagnostics are image based and cannot detect a structural microgap defect such as a crack in a tooth. Whether percussion diagnostics can effectively diagnose a microgap defect is unclear. PURPOSE: The purpose of the present study was to determine from a large multicenter prospective clinical study whether quantitative percussion diagnostics (QPD) could detect structural damage in teeth and whether a probability of its presence could be provided. MATERIAL AND METHODS: A nonrandomized prospective and multicenter clinical validation study with 224 participants was performed in 5 centers with 6 independent investigators. The study used QPD and the normal fit error to determine whether a microgap defect was present in a natural tooth. Teams 1 and 2 were blinded. Team 1 tested teeth scheduled for restoration with QPD, and Team 2 disassembled the teeth aided by a clinical microscope, transillumination, and a penetrant dye. Microgap defects were documented in written and video formats. Controls were participants without damaged teeth. The percussion response from each tooth was stored on a computer and analyzed. A total of 243 teeth were tested to provide approximately 95% power to test the performance goal of 70%, based on an assumed population overall agreement of 80%. RESULTS: Regardless of the collection method, tooth geometry, restoration material used, or restoration type, the data on detecting a microgap defect in a tooth were accurate. The data also reflected good sensitivity and specificity consistent with previously published clinical studies. The combined study data showed an overall agreement of 87.5% with a 95% confidence interval (84.2 to 90.3), beyond the 70% predetermined performance goal. The combined study data determined whether it was possible to predict the probability of a microgap defect. CONCLUSIONS: The results showed that the data on detecting microgap defects in a tooth site were consistently accurate and confirmed that QPD provided information to aid the clinician in treatment planning and early preventative treatment. QPD can also alert the clinician of probable diagnosed and undiagnosed structural problems via the use of a probability curve.

Ten-year retrospective study of the effectiveness of quantitative percussion diagnostics as an indicator of the level of structural pathology in teeth.

STATEMENT OF PROBLEM: Conventional dental diagnostic aids are only partially effective in diagnosing structural defects such as cracks in teeth. A more predictable diagnostic for structural instability in the mouth is needed. PURPOSE: The purpose of this clinical study with an increased population size was to evaluate the effectiveness of diagnosing structural instability by using the quantitative percussion diagnostics (QPD) system and to evaluate the influence of independent variables on the relationship between normal fit error (NFE) and observed structural instability found during the clinical disassembly of teeth. MATERIAL AND METHODS: Twenty-two participants with 264 sites needing restoration were enrolled in an institutional review board-approved 10-year retrospective clinical study. Each site had been tested with the QPD system before being disassembled microscopically with video documentation, and the clinical disassembly results were recorded on a defect-assessment sheet. The NFE data were separately recorded from the preexisting records. The classification of structural pathology based on the disassembly observations for each of the 264 sites was conducted by the clinical researcher (C.G.S.) who was blinded to the NFE values. RESULTS: The 264 sites from 22 patients were classified as 8 in the none group, 87 in the moderate group, and 169 in the severe group based on the disassembly findings. The NFE data for the sites were analyzed by using the predefined NFE cutoffs that were independently generated from the previous cumulative logistic regression and decision tree model. For the cumulative logistic regression, 235 out of 264 sites were correctly classified with an agreement of 0.89 (adjusted 95% CI: 0.83-0.95). The number of correctly classified sites for the decision tree model was 234, and the agreement was also 0.89 (adjusted 95% CI: 0.83-0.94). For both cumulative logistic regression and decision tree models, the overall misclassification rate was less than 20% for any restoration material or restoration type. Therefore, the overall performance of NFE classification was consistently good, regardless of restoration material or type. In addition, the sensitivity of the severe category was above 90% for any restoration material or type for the decision tree model. CONCLUSIONS: The QPD system was found to be a reliable diagnostic aid for classifying structural damage in the categories of none, moderate, or severe based on clinical disassembly findings under the clinical microscope and NFE values. Furthermore, it was determined that restoration type and restoration design were not significant factors in correlating structural pathology with NFE.

Quantitative percussion diagnostics as an indicator of the level of the structural pathology of teeth: Retrospective follow-up investigation of high-risk sites that remained pathological after restorative treatment.

STATEMENT OF PROBLEM: Structural damage may remain even after a tooth is restored. Conventional diagnostic aids do not quantify the severity of structural damage or allow the monitoring of structural changes after restoration. PURPOSE: The purpose of this retrospective clinical study was to provide an in-depth analysis of 9 high-risk sites after restoration. The analysis followed structural defects found upon disassembly, restorative materials used, therapeutic procedures provided, current longevity, and long-term quantitative percussion diagnostics (QPD) to monitor results. The hypothesis was that QPD can be used to quantify positive and negative changes in structural stability. MATERIAL AND METHODS: Sixty sites requiring restoration were part of an institutional review board-approved clinical study. Each participant was examined comprehensively, including QPD testing, at each follow-up. Long-term changes in normal fit error (NFE) values after restoration were evaluated according to a pathology rating system established in an earlier publication. Nine highly compromised sites were chosen for further analysis and monitored for an additional 6 years. RESULTS: Of the 9 high-risk sites (NFE>0.04), 7 sites improved and 2 sites deteriorated. Potential causes for each trend were documented. CONCLUSIONS: The data support the hypothesis that QPD can be used to monitor changes in structural stability after restoration. Knowledge of changes in advance of any symptoms allows further preventive or therapeutic intervention before serious structural damage can occur. Follow-up QPD indications of site improvement can also assure the clinician of the desired structural outcome.

In vivo study of the effectiveness of quantitative percussion diagnostics as an indicator of the level of structural pathology of teeth after restoration.

STATEMENT OF PROBLEM: Conventional diagnostic aids based upon imagery and patient symptoms do not indicate whether restorative treatments have eliminated structural pathology. PURPOSE: The purpose of this clinical study was to evaluate quantitative percussion diagnostics (QPD), a mechanics-based methodology that tests the structural integrity of teeth noninvasively. The study hypothesis was that QPD would provide knowledge of the structural instability of teeth after restorative work. MATERIAL AND METHODS: Eight participants with 60 sites needing restoration were enrolled in an IRB-approved clinical study. Each participant was examined comprehensively, including QPD testing. Each site was disassembled and microscopically video documented, and the results were recorded on a defect assessment sheet. A predictive model was developed for the pathology rating based on normalized fit error (NFE) values using data from the before treatment phase of the study published previously. Each restored site was then tested using QPD. The mean change in NFE values after restoration was evaluated by the pathology rating before treatment. The model was then used to predictively classify the rating after restoration based on the NFE values after treatment. The diagnostic potential of the rating was explored as a marker for risk of pathology after restoration. RESULTS: After restoration, 51 of the 60 sites fell below an NFE of 0.04, representing a greatly stabilized tooth site sample group. Several sites remained in the high-risk category and some increased in pathologic micromovement. Two models were used to determine severity with indicative cutoff points to group sites with similar values. CONCLUSIONS: The data support the hypothesis that QPD can indicate a revised level of structural instability of teeth after restoration.

In vivo study of the effectiveness of quantitative percussion diagnostics as an indicator of the level of the structural pathology of teeth.

STATEMENT OF PROBLEM: Conventional dental diagnostic aids based upon imagery and patient symptoms are at best only partially effective for the detection of fine structural defects such as cracks in teeth. PURPOSE: The purpose of this clinical study was to determine whether quantitative percussion diagnostics (QPD) provided knowledge of the structural instability of teeth before restorative work begins. QPD is a mechanics-based methodology that tests the structural integrity of teeth noninvasively. MATERIAL AND METHODS: Eight human participants with 60 sites needing restoration were enrolled in an institutional review board-approved clinical study. Comprehensive examinations were performed in each human participant, including QPD testing. Each site was disassembled and microscopically video documented, and the results were recorded on a defect assessment sheet. Each restored site was then tested using QPD. The normal fit error (NFE), which corresponds to the localized defect severity, was correlated with any pretreatment structural pathology. RESULTS: QPD agreed with clinical disassembly in 55 of 60 comparisons (92% agreement). Moreover, the method achieved 98% specificity and 100% sensitivity for detecting structural pathologies found later upon clinical disassembly. Overall, the NFE was found to be highly predictive of advanced structural pathology. CONCLUSIONS: The data from the present in vivo study support the hypothesis that QPD can provide the clinician with advance knowledge of the structural instability of teeth before restorative work begins.

An in vitro comparison of quantitative percussion diagnostics with a standard technique for determining the presence of cracks in natural teeth.

STATEMENT OF PROBLEM: The detection of cracks and fractures in natural teeth is a diagnostic challenge. Cracks are often not visible clinically nor detectable in radiographs. PURPOSE: The purpose of this study was to evaluate the diagnostic parity of quantitative percussion diagnostics, transillumination, clinical microscopy, and dye penetration. MATERIAL AND METHODS: Three independent examiners provided blind testing for the study. Examiner 1 transilluminated 30 extracted teeth and 23 three-dimensional copy replica control teeth and documented any visible cracks. Each tooth was then mounted in acrylic resin with a periodontal ligament substitute. Examiner 2 examined each specimen aided by the clinical microscope and transillumination and documented visible tooth cracks and fractures. Examiners 1 and 3 then independently tested all specimens with a device developed for quantitative percussion diagnostics. All visible cracks/fractures were removed with a water-cooled fine diamond rotary instrument. Crack visibility was enhanced by the use of a clinical microscope, dye penetrant, and accessory transillumination. This disassembly process was video documented/photographed for each specimen. One more quantitative percussion diagnostics testing was administered when the disassembly was complete. RESULTS: Quantitative percussion diagnostics crack detection agreed with the gold standard microscope and transillumination method in 52 of 53 comparisons (98% agreement). Moreover, the method achieved 96% specificity and 100% sensitivity for detecting cracks and fractures in natural teeth. When all tooth cracks were removed, quantitative percussion diagnostics indicated no further structural instability. CONCLUSIONS: Quantitative percussion diagnostics can nondestructively detect cracks and fractures in natural teeth with accuracy similar to that of the clinical microscope, transillumination, and dye penetrant. In addition, the method was able to reveal the presence of many cracks that were not detected by conventional transillumination.

Hydroxyl ion stabilization of bulk nanobubbles resulting from microbubble shrinkage.

HYPOTHESIS: The shrinkage of microbubbles that are less than about 50 µm in diameter is a well-known phenomenon that results from the surface tension. It has also been shown recently that hydroxyl ions have an extremely strong affinity for gas-water interfaces including bubble surfaces. A theoretical model is proposed that predicts bulk nanobubble stability in water, based on a force balance that results from the shrinkage of microbubbles. This model was designed to test the hypothesis that the surface tension of a shrinking microbubble can ultimately be balanced by the repulsion of the hydroxyl ions that initially adsorb onto the microbubble surface prior to shrinking. THEORY: The present model considers the forces due to ionic repulsion as microbubbles shrink under the surface tension. No special assumptions are required in the present model other than the recently reported strong affinity hydroxyl ions have to gas/water interfaces. The Debye-Hückel theory was used to determine the number of ions on the microbubble surface. FINDINGS: The results of this model predict a stable balance between the surface tension and the electrostatic repulsion of hydroxyl ions for nanobubble diameters less than 1100 nm. This predicted maximum in nanobubble size is shown to be consistent with experimental findings.

Reconstructive materials and bone tissue engineering in implant dentistry.

Periodontal function for natural teeth and dental implants depends strongly on the mechanical integrity of the bone in the maxilla and mandible. Ongoing healthy bone remodeling around a natural tooth or implant is critical for longevity. Chemical factors that influence bone remodeling have been explored with the goal of enhancing the growth and maintenance of good quality bone. Less, but increasing, effort has been directed at understanding mechanical signals and factors, including those affected by implant/prosthesis materials that transmit loads directly to the surrounding bone. This article reviews research on the effects of synthetic materials and resulting mechanical stimuli on bone tissue engineering in dentistry.

Static stretch affects neural stem cell differentiation in an extracellular matrix-dependent manner.

Neural stem and progenitor cell (NSPC) fate is strongly influenced by mechanotransduction as modulation of substrate stiffness affects lineage choice. Other types of mechanical stimuli, such as stretch (tensile strain), occur during CNS development and trauma, but their consequences for NSPC differentiation have not been reported. We delivered a 10% static equibiaxial stretch to NSPCs and examined effects on differentiation. We found static stretch specifically impacts NSPC differentiation into oligodendrocytes, but not neurons or astrocytes, and this effect is dependent on particular extracellular matrix (ECM)-integrin linkages. Generation of oligodendrocytes from NSPCs was reduced on laminin, an outcome likely mediated by the α6 laminin-binding integrin, whereas similar effects were not observed for NSPCs on fibronectin. Our data demonstrate a direct role for tensile strain in dictating the lineage choice of NSPCs and indicate the dependence of this phenomenon on specific substrate materials, which should be taken into account for the design of biomaterials for NSPC transplantation.

Tissue engineering in dentistry.

Advances in tissue engineering provide an increased level of understanding of the mechanical and chemical stimuli that regulate tissue responses. Oral tissue engineering can be applied to recreate missing osseous or dental structures or correct orofacial deformities, changing the patient's smile, midfacial height, and the soft tissue drape. Biomechanical principles can also be applied to tissue engineering to enhance the bone/tooth or bone/implant functionality and long-term stability. Advancements are also being achieved in the area of biomimetics that will allow the creation of new biologic replacements for missing oral structures. The opportunity for bioengineering to charter the course of tooth regeneration is an exciting prospect and will improve the quality of life for patients for decades to come.

Stress relaxation behavior of tessellated cartilage from the jaws of blue sharks.

Much of the skeleton of sharks, skate and rays (Elasmobranchii) is characterized by a tessellated structure, composed of a shell of small, mineralized plates (tesserae) joined by intertesseral ligaments overlaying a soft cartilage core. Although tessellated cartilage is a defining feature of this group of fishes, the significance of this skeletal tissue type - particularly from a mechanical perspective - is unknown. The aim of the present work was to perform stress relaxation experiments with tessellated cartilage samples from the jaws of blue sharks to better understand the time dependent behavior of this skeletal type. In order to facilitate this aim, the resulting relaxation behavior for different loading directions were simulated using the transversely isotropic biphasic model and this model combined with generalized Maxwell elements to represent the tessellated layer. Analysis of the ability of the models to simulate the observed experimental behavior indicates that the transversely isotropic biphasic model can provide good predictions of the relaxation behavior of the hyaline cartilage. However, the incorporation of Maxwell elements into this model can achieve a more accurate simulation of the dynamic behavior of calcified cartilage when the loading is parallel to the tessellated layer. Correlation of experimental data with present combined composite models showed that the equilibrium modulus of the tessellated layer for this loading direction is about 45 times greater than that for uncalcified cartilage. Moreover, tessellation has relatively little effect on the viscoelasticity of shark cartilage under loading that is normal to the tessellated layer.

Analysis of percussion response of dental implants: an in vitro study.

The Periometer® quantitative percussion system was used to interrogate the interfacial stability of implants in vitro for comparison with X-ray computer tomography (CT) data. Selected implants were placed as per standard practice in bone stimulant polyurethane blocks. The dimensions of the surgical sites surrounding the implants were analyzed using X-ray computer tomography (CT) to determine the quality of support at the implant-bone interface. In particular, the misfit between the size of the surgical site and the corresponding implant was determined for each sample. The resulting average surgical site error from the CT scans was found to exhibit good agreement with the presence of irregularities found in the percussion data.

In vivo evaluation of quantitative percussion diagnostics for determining implant stability.

PURPOSE: To test in a rat model whether quantitative percussion diagnostics provide reliable, reproducible indications of osseointegration. MATERIALS AND METHODS: Titanium implants were placed in femurs of 36 Sprague-Dawley rats. Each animal was assigned to one of six groups defined by one of three time points (2, 4, or 8 weeks postplacement) and one of two treatments (matrix metalloproteinase [MMP] inhibitor GM6001 or control). Percussion testing was conducted three times per subject at implant placement and before sacrifice at one of the time points. For each time point, there was an experimental group that received daily intraperitoneal injections of GM6001, and a control group that received no MMP inhibitor. The percussion data consisted of loss coefficient (LC) values that characterize energy dissipation. Statistical analysis was performed on the LC values for the two animal groups using the paired Student t test to assess differences as a function of time, and the independent t test to compare mean LC for the study groups at sacrifice (α = .05). Histologic evaluation using the osteogenic CD40 protein marker was also performed. RESULTS: A nearly significant difference in mean LC at the 2-week time point was observed between the two treatments with the GM6001 group having the higher value (P = .053). There was a greater difference between the mean LC values for the 4-week GM6001 and control groups (P = .001). The histologic evidence for subjects in these two groups confirmed reduction of osteogenesis at the implant interface after administration of the MMP inhibitor. CONCLUSIONS: Lower control LC values relative to the GM6001 therapeutic group were observed, consistent with the effect MMP inhibition has on matrix remodeling at the implant bone interface. This finding in conjunction with histologic observations confirms that osseointegration can be monitored using percussion diagnostics.

Quantitative percussion diagnostics and bone density analysis of the implant-bone interface in a pre- and postmortem human subject.

PURPOSE: It has been hypothesized that a correlation exists between the density of surrounding cortical bone and the stability of an implant under percussion loading that can be used to quantify the implant's osseointegration. The purpose of the present research was to explore whether quantitative percussion testing of dental implants gives reasonable indications of the level of osseointegration that are consistent with bone configuration and its influence on osseointegration quality. MATERIALS AND METHODS: Data from percussion testing of a live human subject, obtained using the Periometer, were compared with corresponding bone density estimates from high-resolution computed tomography images and postmortem percussion probe data. RESULTS: The results confirm the hypothesis that the nature of an implant's response to percussion is determined by its cortical bone support. CONCLUSIONS: The findings suggest that the cortical bone supporting the crestal and apical regions of the implant is primarily responsible for structural stability.

Visualization of osseointegration of maxilla and mandible dental implants.

PURPOSE: We present a new, hybrid visualization method that can assist in assessing the degree of osseointegration of dental implants. METHOD: The method is based on radiographic imaging, three-dimensional (3-D) volume reconstruction, and color coding of bone density. It provides both a 3-D image of the titanium implant and the implant site, and a two-dimensional (2-D) profile of the lingual and buccal sides of the implant, exposing possible weaknesses in the supporting bone structure. The visualization procedure described here consists of 2-D cross-sectional CT imaging, 3-D gradient-based hardware-accelerated volume rendering using 3-D texture mapping, implant site extraction using 3-D selection of a 2-D cross-sectional, tri-linearly interpolated 2-D image, computation of a bone density profile and line integral along the implant, and 3-D hybrid rendering of the implant site and the derived bone density information in its anatomical context. This method has been demonstrated to be successful in enabling the mapping of information derived from virtual bone density measurements onto a geometric object, thus providing the necessary information to relate other information from mechanical testing or simulations to the respective site. RESULTS: A high-resolution scan of a cadaver was used as a reference data set. The hybrid view, a combination of 2-D density profile and 3-D color-coded density rendering, turned out to be very intuitive and easy to interpret. The 2-D view was also useful for relating standard 2-D X-ray imaging with enhanced 3-D imaging of bone density. On top of this, our image-based method was used for cross-validation of a mechanical testing method. It turned out that the results from mechanical testing of osseointegration were very well correlated with the results from our image-based 2-D and 3-D methods. CONCLUSIONS: Since these two methods work in completely different ways (mechanical vs. radiographic) and the results came out are the same, the results provide evidence that both methods for assessing the degree and location of osseointegration are valid. Further studies using additional scans on living subjects will be conducted to provide additional evidence. Cost-efficient X-ray imaging can be used to replace the simulated implant-aligned 2-D X-ray views that were obtained from a 3-D scan.