Cross-sectional assessment of apical dye penetration following clinical simulation of various endodontic techniques.

This study compared apical leakage in mesial roots of mandibular molars that resulted from three different instrumentation/obturation techniques performed in a simulated clinical setting: hand instrumentation by nickel-titanium files followed by cold lateral condensation of gutta-percha/sealer; rotary instrumentation followed by the Microseal system of obturation with softened gutta-percha; and rotary instrumentation followed by obturation with the Thermafil system. Lateral condensation generally was measured superior to the Thermafil method for preventing apical dye penetration while no consistent statistical differences were seen between the lateral condensation and Microseal groups.

Effect of estrogen deficiency on skeletal and alveolar bone density in sheep.

BACKGROUND: This study provides a longitudinal assessment of changes in alveolar and skeletal bone mineral density (BMD) in ovariectomized animals. METHODS: Following ovariectomy (OVX) (n = 6) or sham-operation (n = 6) intraoral radiographs were made at 4-month intervals and serum 17-beta-estradiol, osteocalcin, and interleukin (IL)-6, urinary deoxypyridinium, and salivary IL-6, deoxypyridinium, and osteocalcin concentrations were evaluated. Twelve months after surgery, animals were sacrificed and the mandible and radius/ulna removed. Bones were sectioned and radiographed. Mean BMD and cortical thicknesses were calculated from each region. RESULTS: OVX animals had a progressive decrease in serum 17-beta-estradiol, increased serum osteocalcin and IL-6, urinary deoxypyridinium and salivary IL-6, osteocalcin and deoxypyridinium (P < 0.001), suggesting that they were becoming osteoporotic. The BMD of the radius/ulna and mandibular alveolar bone was significantly reduced in OVX animals (P < 0.05 and P < 0.001, respectively). Reduced alveolar bone BMD became evident in OVX animals 6 months after surgery and became more severe during the subsequent 6 months. Alveolar crestal height was also significantly reduced in OVX animals (P < 0.001). These biochemical and density changes preceded a significant reduction in serum 17-beta-estradiol, which occurred between 4 and 8 months following surgery. CONCLUSIONS: Serial measurements of alveolar BMD predicts loss of skeletal BMD in OVX sheep. Changes in alveolar BMD precede estrogen deficiency, suggesting that early signs of reduced BMD may be detected in peri-menopausal women. The presence of biomarkers of bone metabolism within saliva and their correlation with reduced BMD suggests that saliva could be used as an adjunct screening method for assessment of skeletal bone density.

Structure, metallurgy, and mechanical properties of a porous tantalum foam.

This study evaluated a porous tantalum biomaterial (Hedrocel) designed to function as a scaffold for osseous ingrowth. Samples were characterized for structure, Vickers microhardness, compressive cantilever bending, and tensile properties, as well as compressive and cantilever bending fatigue. The structure consisted of regularly arranged cells having struts with a vitreous carbon core with layers of CVI deposited crystalline tantalum. Microhardness values ranged from 240-393, compressive strength was 60 +/- 18 MPa, tensile strength was 63 +/- 6 MPa, and bending strength was 110 +/- 14 MPa. The compressive fatigue endurance limit was 23 MPa at 5 x 10(6) cycles with samples exhibiting significant plastic deformation. SEM examination showed cracking at strut junctions 45 degrees to the axis of the applied load. The cantilever bending fatigue endurance limit was 35 MPa at 5 x 10(6) cycles, and SEM examination showed failure due to cracking of the struts on the tension side of the sample. While properties were variable due to morphology, results indicate that the material provides structural support while bone ingrowth is occurring. These findings, coupled with the superior biocompatibility of tantalum, makes the material a candidate for a number of clinical applications and warrants further and continued laboratory and clinical investigation.

Use of x-ray photoelectron spectroscopy and cyclic polarization to evaluate the corrosion behavior of six nickel-chromium alloys before and after porcelain-fused-to-metal firing.

STATEMENT OF PROBLEM: Nickel-chromium casting alloys rely on a surface oxide layer for corrosion resistance to the oral environment. Porcelain-fused-to-metal (PFM) firing procedures may alter the surface oxides and corrosion properties of these alloys. Changes in alloy corrosion behavior affect metal ion release and therefore local and/or systemic tissue responses. PURPOSE: The aim of this study was to evaluate changes in alloy surface oxides and electrochemical corrosion properties after PFM firing. MATERIAL AND METHODS: The electrochemical corrosion behavior of 6 commercial nickel-chromium alloys was evaluated in the as-cast/polished and PFM fired/repolished states. Surface chemistries of the alloys were analyzed by x-ray photoelectron spectroscopy. RESULTS: Results indicated an increase in corrosion rates after PFM firing and repolishing for alloys containing 14% to 22% Cr and 9% to 17% Mo. This increase in corrosion rates was attributed to a decrease, caused by the PFM and repolishing process, in the Cr and Mo levels in the surface oxides of these alloys. The PFM firing and repolishing process did not alter the corrosion behavior of the alloys containing lower levels of Cr and Mo and/or Be additions in their bulk composition. These alloys exhibited low levels of Cr and Mo surface oxides in both test conditions. Si particles became embedded in the surfaces of the fired alloys during repolishing and may have contributed to the changes in surface oxides and the corrosion behavior of some alloys. CONCLUSION: The effects of PFM firing and repolishing on Ni-Cr dental casting alloy surface oxides and corrosion properties appear to be alloy dependent.

Evaluation of ergonomic dental stools through clinical simulation.

Work-related musculoskeletal pain occurs commonly within the dental community. Three stool designs were utilized in this study: a standard dental stool, a stool with dual arm supports, and a stool with dual arm supports and chest support. Electromyographic data from four muscle groups were collected on 13 clinicians during a simulated crown preparation procedure. Clinical simulation suggests that a potential musculoskeletal benefit to the clinician exists through utilization of dental stool designs which incorporate static arm supports.

Effect of camera angulation on adaptation of CAD/CAM restorations.

PURPOSE: A significant concern with computer-assisted design/computer-assisted manufacturing (CAD/CAM)-produced prostheses is the accuracy of adaptation of the restoration to the preparation. The objective of this study is to determine the effect of operator-controlled camera misalignment on restoration adaptation. MATERIALS AND METHODS: A CEREC 2 CAD/CAM unit (Sirona Dental Systems, Bensheim, Germany) was used to capture the optical impressions and machine the restorations. A Class I preparation was used as the standard preparation for optical impressions. Camera angles along the mesio-distal and buccolingual alignment were varied from the ideal orientation. Occlusal marginal gaps and sample height, width, and length were measured and compared to preparation dimensions. For clinical correlation, clinicians were asked to take optical impressions of mesio-occlusal preparations (Class II) on all four second molar sites, using a patient simulator. On the adjacent first molar occlusal surfaces, a preparation was machined such that camera angulation could be calculated from information taken from the optical impression. Degree of tilt and plane of tilt were compared to the optimum camera positions for those preparations. RESULTS: One-way analysis of variance and Dunnett C post hoc testing (alpha = 0.01) revealed little significant degradation in fit with camera angulation. Only the apical length fit was significantly degraded by excessive angulation. The CEREC 2 CAD/CAM system was found to be relatively insensitive to operator-induced errors attributable to camera misalignments of less than 5 degrees in either the buccolingual or the mesiodistal plane. The average camera tilt error generated by clinicians for all sites was 1.98 +/- 1.17 degrees.

Relationship between oral alveolar bone loss and aging among African-American and Caucasian individuals.

BACKGROUND: The periodontal attachment apparatus consists of the periodontal ligament, alveolar bone, cementum and supra-crestal connective tissue. They are interdependent and provide protection and support to the dentition. It is theorized that the integrity of the periodontal apparatus can be maintained throughout life by exercising comprehensive oral hygiene practices and routine dental care. Additionally, it appears to be unaffected by aging. As a consequence, the investigators performed a study to determine the effects of chronological aging on alveolar bone loss. OBJECTIVE: The present study was conducted to determine the relationship between oral alveolar bone loss, oral hygiene, and aging among African-American and Caucasian populations. METHODS: The population consisted of 229 individuals. There were 131 men and 98 women. With respect to race there were 89 African-Americans and 140 Caucasians. Oral examinations, oral hygiene and missing teeth determinations and bitewing radiographs were performed on all the individuals. Radiographs were digitized and measurements were made from the cementum/enamel junction to the alveolar bone crest. Measurements were made for both the maxillary and mandibular jaws. RESULTS: The results of the study showed a significant multiple linear regression model relationship between oral bone loss and aging. Oral hygiene was a factor, but contributed only slightly to the overall model. Race, gender and the number of missing teeth were not significant variables in the overall model. CONCLUSION: The results of this study suggest age-related alveolar bone loss.

Sensitivity of various radiographic methods for detection of oral cancellous bone lesions.

OBJECTIVE: The purpose of this study was to determine the effectiveness in diagnosing cancellous bone defects of the following radiographic methods: conventional film, digitized film, enhanced digitized film, direct digital imaging, enhanced direct digital imaging, digital subtraction, and enhanced digital subtraction. STUDY DESIGN: Mechanical lesions of varying depths were generated beneath cadaver molar and premolar mandibular tooth roots. A portfolio of radiographic images of random types and lesion sizes was presented to 20 clinicians, and their diagnoses were evaluated. RESULTS: Positive identification of lesions was significantly improved by enhanced subtraction radiography over all other forms of radiography for the 4-mm lesions and was better than all forms except enhanced digital radiography and film for the 6-mm lesions. Subtraction radiography and enhanced subtraction radiography significantly reduced false positive diagnoses at all lesion sizes in comparison with the other radiographic methods except enhanced digital radiography at the 6-mm lesion size. CONCLUSIONS: For the methods evaluated, only subtraction radiography and enhanced subtraction radiography can significantly improve the clinician's diagnostic abilities for detection of oral cancellous bone lesions through increased rates for detection of existing defects and, even more importantly, through decreased rates of defect misdiagnosis.

The effect of amalgam overhangs on alveolar bone height as a function of patient age and overhang width.

The purpose of this study was to compare the effects of amalgam restorations with and without overhangs on alveolar bone loss via digitized radiographs for subjects of varying ages and overhang widths. The first phase of this study compared the alveolar bone loss among teeth with clinically acceptable two-surface amalgam restorations with a control surface on the same tooth. The second phase was similar to the first phase with the exception that it compared defective amalgam restorations (those containing amalgam overhanging approximal margins) with the control surface on the same tooth. The collected data showed a significant loss of alveolar bone as a result of amalgam overhang presence (P < 0.02). However, overhang width and patient age did not affect the significance of the detrimental effects of the amalgam overhangs. Overall alveolar bone height was seen to decrease with patient age, independent of amalgam restorations. Digital radiography was seen to be an accurate method for evaluating alveolar bone height changes due to the local environment created by overhanging amalgam margins.

Mercury release during autoclave sterilization of amalgam.

Natural teeth are an invaluable teaching tool for preclinical instruction in operative dentistry and endodontic techniques. Cavity preparation in teeth containing amalgam restorations is a realistic simulation of an often experienced clinical situation. As various pathogens are contained in saliva, teeth must be disinfected before use by students. The purpose of this study is to indirectly evaluate whether mercury vapor is released from amalgam restorations in such teeth during steam autoclave sterilization. Mercury vapor detection, sample mass changes and x-ray fluorescence data were collected from experimental steam autoclave sterilization of amalgam samples sealed in autoclave bags. All of the data showed evidence of mercury vapor generation coincident to steam autoclave sterilization. Mercury vapor levels within the room where amalgam was exposed to steam autoclave sterilization reached levels that constitute an unnecessary health risk to dental personnel. The volume of amalgam tested simulated that contained in 175 amalgam restored teeth. Initial venting of the autoclave chamber produced mercury vapor concentrations significantly in excess of OSHA vapor concentration ceiling levels. Thus, the use of a steam autoclave for sterilization of amalgam containing teeth for use in preclinical laboratory exercises may be harmful to personnel involved.

Optimization of glass-ceramic crystallization based on DTA exotherm analysis.

OBJECTIVES: Crystallization of glass-ceramics is traditionally achieved through a two-stage heat treatment consisting of an isothermal nucleation stage followed by an isothermal growth stage. A method for determining a more efficient heat treatment schedule for a glass-ceramic material using a thermal analysis technique is proposed. The goal of an optimized heat treatment schedule is the production of a glass-ceramic with a desired microstructure (number of crystals per volume) in the shortest amount of time. METHODS: The proposed method involves differential thermal analysis (DTA) to measure glass crystallization exotherm characteristics which are correlated with the population density of growing crystals, and therefore, to the effectiveness of any prior heat treatment. Traditional thermal processing parameters were investigated and optimized. A method for generating a more efficient heat treatment schedule composed of a series of increasing heating rates was also demonstrated. RESULTS: The thermal analysis method measured a significant effect upon the number density of crystals generated as a function of several experimental variables. Micrographs from samples crystallized with a more time-efficient heat treatment schedule were shown to have equivalent crystal number densities compared to those crystallized with a more time consuming, traditional schedule. SIGNIFICANCE: This work demonstrated that a rapid thermal analysis method was capable of measuring the relative effectiveness of heat treatment schedules to generate crystalline populations. A novel heat treatment schedule was developed based on progressive adjustment of processing heating rates to generate the maximum crystal population in the shortest amount of time.