Viscoelastic Properties of Human Facial Skin and Comparisons with Facial Prosthetic Elastomers.

Prosthesis discomfort and a lack of skin-like quality is a source of patient dissatisfaction with facial prostheses. To engineer skin-like replacements, knowledge of the differences between facial skin properties and those for prosthetic materials is essential. This project measured six viscoelastic properties (percent laxity, stiffness, elastic deformation, creep, absorbed energy, and percent elasticity) at six facial locations with a suction device in a human adult population equally stratified for age, sex, and race. The same properties were measured for eight facial prosthetic elastomers currently available for clinical usage. The results showed that the prosthetic materials were 1.8 to 6.4 times higher in stiffness, 2 to 4 times lower in absorbed energy, and 2.75 to 9 times lower in viscous creep than facial skin (p < 0.001). Clustering analyses determined that facial skin properties fell into three groups-those associated with body of ear, cheek, and remaining locations. This provides baseline information for designing future replacements for missing facial tissues.

Effect of Superhydrophobic Coating and Nanofiller Loading on Facial Elastomer Physical Properties.

Facial prosthetics are currently constructed of materials that are far from optimal; superior materials with a "skin-like" feel are required. In this study, the property changes brought about by the consecutive additions of hydrophobic- and uncoated nano-SiO2 to polydimethylsiloxane (PDMS) are assessed, and the alterations are compared with those observed for conventional submicron SiO2-filled materials. In sequence, 0%, 0.5%, 5%, 10%, and 15% by weight of each filler type were successively added to vinyl-terminated PDMS. Tensile, tear, Durometer hardness, translucency, and viscoelastic properties were assessed, and hardness and translucency were further measured after 3000 h of outdoor weathering. The results showed that 15% coated nano- SiO2-filled PDMS materials given the highest tensile strength, elastic modulus, storage modulus, loss modulus, tear strength, and durometer hardness (p < 0.05), whereas 15% submicron coated SiO2-filled materials displayed the highest failure strain and translucency parameter (p < 0.05). Only 10%- and 15%-filled submicron SiO2 PDMS materials were altered by outdoor weathering; nevertheless, the increases were assessed to be too small to be clinically perceptible. As increased filler levels provided protection against solar radiation, heat, and moisture, only unfilled and 0.5%-filled PDMS formulations discolored from weathering. 15%-filled superhydrophobic-coated nano- SiO2-filled PDMS was found to produce the strongest, most tear-resistant, and least translucent materials, but it also produced materials with limited stretchability and high hardness, which were regarded to be downsides for creating a "skin-like" feel.

A Comparison of Efficiency and Material Wear of Diamond-Plated versus Ceramic Sharpening Stones.

Purpose: The purpose of this study was to compare sharpening efficiency and metal (carbon steel) removal from scalers using two types of synthetic sharpening stones: ceramic and diamond-plated. Previous research used scanning electron microscopy alone to measure instrument sharpness. Additionally, no research has been reported on the use of diamond-plated sharpening stones.Methods: Fifteen threaded, double-ended H6/H7 scalers were randomly divided into three groups of ten: control, ceramic stone, and diamond-plated stone. All cutting edges were dulled by scaling the surfaces of extracted molars. The cutting edges were then sharpened by a blinded examiner with the assigned stone until optimal sharpness was achieved using a test stick between sharpening strokes. The number of strokes needed to reach sharpness for each cutting edge was recorded. Four hundred sharpening strokes were then applied on each end using the assigned stone. The scaler ends were weighed before and after sharpening to determine amount of material loss in milligrams. Statistical analysis was performed using ANOVA followed by a Tukey-Kramer post-hoc test.Results: The diamond-plated sharpening stone removed significantly more metal (7.62 mg +/-0.38) than the ceramic stone (0.69 mg +/-0.06) (p<0.001), while there was no significant difference between the ceramic sharpening stone and the control. There was no significant difference between diamond-plated and ceramic stones in the number of strokes needed to sharpen scalers.Conclusion: While a similar number of strokes was needed to sharpen scalers with the diamond-plated or ceramic stone, the diamond-plated stone removed nearly 7 mg more metal than the ceramic stone using a standardized number of sharpening strokes, suggesting greater scaler longevity when using a ceramic sharpening stone.

Cast erosion from the cleaning of debris after the use of a cast trimmer.

STATEMENT OF PROBLEM: Whether using tap water to rinse off debris will make a clinical difference to the surface detail of a gypsum cast is unknown. In addition, how best to remove debris from the cast is unknown. PURPOSE: The purpose of this in vitro study was to evaluate the efficiency of different methods of cleaning a gypsum cast after trimming and the effect of short-term exposure to tap water on the surface quality of the cast. MATERIAL AND METHODS: A die fitting American National Standards Institute/American Dental Association specification 25 (International Standards Organization specification 6873) for dental gypsum products was embedded in a Dentoform with the machined lines positioned at the same level as the occlusal surface of the posterior teeth. A flat plate was used to ensure that the plane of occlusion for the die was at the same position as the posterior teeth. Forty polyvinyl siloxane impressions of the Dentoform were made and poured with vacuum-mixed improved Type IV dental stone. Each cast was inspected for the accurate reproduction of the lines. The base of the 2-stage pour was trimmed with a cast trimmer with water, and surface debris was removed by rinsing by hand under tap water for 10 seconds, by brushing the cast with a soft toothbrush for 10 seconds, or by resoaking the cast and using a soft camel hair brush in slurry water for 10 seconds. The amount of debris was evaluated on a scale of 1 to 4, and the quality of the 20-µm line was evaluated on a scale of 1 to 4 under ×15 magnification. The nonparametric Kruskal-Wallis ranks test was used to identify significant differences among the different cleaning methods (α=.05). RESULTS: Results of the Kruskal-Wallis and Kruskal-Wallis Z-value tests demonstrated that all cleaning methods produced cleaner casts than were observed for uncleansed controls (P<.001), but no differences in debris removal were found among the different cleaning methods (.065≤P≤.901). The ability to see the quality of a 20-µm line (P=.974) was not statistically different among the groups. CONCLUSIONS: Rinsing the cast under flowing tap water and brushing, or hand washing under flowing tap water, or using a soft camel hair brush in slurry water for 10 seconds had no noticeable effects on the quality of a 20-µm line, and all 3 methods resulted in a clean cast.

Performance of self-reported measures for periodontitis in rheumatoid arthritis and osteoarthritis.

BACKGROUND: This study evaluates the performance of self-report against the reference standard of clinically defined periodontitis in patients with rheumatoid arthritis (RA) and osteoarthritis (OA) after accounting for factors associated with periodontitis. METHODS: Six self-report periodontitis questions were evaluated in patients with RA and OA. Questions were validated against a reference standard of severe and moderate-to-severe periodontitis based on full-mouth examination. Multivariable logistic regression was used to evaluate the performance of: 1) self-report alone; 2) age, sex, education, and smoking status; and 3) a combination of the above. Model performance was assessed using the c-statistic. Convergent validity of self-reported "bone loss/deep pockets" and "loose teeth" was assessed; associations of self-report with RA disease characteristics were explored. RESULTS: Self-report performed similarly in RA and OA, with individual question specificity for periodontitis ≥ 68% and sensitivity from 9.8% to 45%. Question-only models yielded c-statistics of 0.66 to 0.72, whereas risk factor-only models yielded c-statistics of 0.74 to 0.79. The highest-performing models incorporated both self-report questions and periodontitis risk factors, with c-statistics ≥ 0.79. Greater radiographic alveolar bone loss was observed among participants reporting "bone loss/deep pockets" (P < 0.001) and "loose teeth" (P < 0.001). Among patients with RA, "loose teeth," but not other self-report items, was associated with rheumatoid factor positivity (P = 0.047) and higher disease activity (P < 0.001). CONCLUSIONS: Patient self-report, when combined with other risk factors, performs well in identifying periodontitis among patients with RA and OA. Self-report questions related to alveolar bone loss exhibit excellent convergent validity in these patient subsets.

Outdoor weathering of facial prosthetic elastomers differing in Durometer hardness.

STATEMENT OF PROBLEM: Facial prosthetic elastomers with wide ranges in hardness are available, yet material weatherability is unknown. PURPOSE: The purpose of this study was to assess color, Durometer hardness, and tensile property changes after 3000 hours of outdoor weathering. MATERIAL AND METHODS: Unpigmented elastomers with Durometer hardness 5, 30, 50, 70, and A-2186 were polymerized into dumbbells (ASTM D412) and disks, 34 mm in diameter by 6 mm thick. Materials were subjected to outdoor or time passage environments for 3000 hours. CIELab color (n=5), Durometer hardness (n=5), and tensile mechanical properties (n=10) were measured at 0 and 3000 hours, and group differences were assessed by material and weathering condition (ANOVA/Tukey, α=.05). RESULTS: Except for A-2186, the mean Durometer changes for all materials were 1 unit or less, with no significant differences observed between time passage and weathered groups (P≥.05). Three-thousand-hour tensile mechanical property results demonstrated nonsignificant differences between time passage and weathered materials but significantly changed properties from immediately tested materials (P<.001). Outdoor weathering induced perceptible but acceptable color changes (1.7≤ΔE*≤2.6) for elastomers with Durometer hardness 5 and 30 and A-2186. CONCLUSIONS: With a few exceptions, outdoor weathering produced relatively small changes in color, Durometer hardness, or tensile properties compared with time passage.

Proposed shade guide for human facial skin and lip: a pilot study.

STATEMENT OF PROBLEM: Currently, no commercially available facial shade guide exists in the United States for the fabrication of facial prostheses. PURPOSE: The purpose of this study was to measure facial skin and lip color in a human population sample stratified by age, gender, and race. Clustering analysis was used to determine optimal color coordinates for a proposed facial shade guide. MATERIAL AND METHODS: Participants (n=119) were recruited from 4 racial/ethnic groups, 5 age groups, and both genders. Reflectance measurements of participants' noses and lower lips were made by using a spectroradiometer and xenon arc lamp with a 45/0 optical configuration. Repeated measures ANOVA (α=.05), to identify skin and lip color differences, resulting from race, age, gender, and location, and a hierarchical clustering analysis, to identify clusters of skin colors) were used. RESULTS: Significant contributors to L*a*b* facial color were race and facial location (P<.01). b* affected all factors (P<.05). Age affected only b* (P<.001), while gender affected only L* (P<.05) and b* (P<.05). Analyses identified 5 clusters of skin color. CONCLUSIONS: The study showed that skin color caused by age and gender primarily occurred within the yellow-blue axis. A significant lightness difference between gender groups was also found. Clustering analysis identified 5 distinct skin shade tabs.

Coverage error of commercial skin pigments as compared to human facial skin tones.

OBJECTIVES: It is unknown if present-day pigments used for intrinsic colouration of maxillofacial prostheses are representative of human facial skin tones. This study's purpose was to measure L*a*b* values of pigmented elastomers coloured by eleven skin tone pigments and determine coverage error (CE) when the pigments were compared to human facial lip and nose colour data. METHODS: 11 skin tone pigments were combined at 0.1%, 1% and 10% by weight with A-2186 elastomer (n=3). L*a*b* values were measured with a spectrophotometer and group means were used to calculate ΔE* colour differences with each L*a*b* value obtained for human nose and lip. Pigmented elastomer CEs were calculated for nose and lip. Results were compared to CEs for proposed shade guide colours obtained from clustering analyses of facial skin colours. RESULTS: L* values of pigmented elastomers generally were higher than those measured for nose and lip, whereas a* values were lower. CEs for pigmented elastomers were higher than those obtained from the proposed shade guide obtained from clustered skin measurements. CONCLUSIONS: Overall, the current commercial elastomers appeared to be too white and not red enough to adequately match the skin tones of the subject population. Adjustments must be made to the existing pigmenting system in order to adequately match the skin colours of the study population. CLINICAL SIGNIFICANCE: The creation of a shade guide and a collection of intrinsic pigments representing the realm of human facial skin colours would greatly decrease the time a patient must sit while the clinician is obtaining an acceptable colour match for the silicone to be used for processing the final prosthesis, thereby increasing both patient satisfaction and clinician productivity.

Human osteogenic protein-1 induces osteogenic differentiation of adipose-derived stem cells harvested from mice.

OBJECTIVE: Osteogenic protein-1 (OP-1) has been shown to stimulate undifferentiated cells to produce mineralized tissue. Adipose tissue is a rich source of undifferentiated cells for tissue engineering purposes. The purpose of this study was to investigate the effect of OP-1 on osteogenic differentiation of adipose-derived stem cells and the production of bony tissue in vitro. DESIGN: Adipose-derived stem cells (ADSCs) were isolated from inguinal fat pads of adult mice. Following cell expansion the cells were plated in 8-well chambered slides. The cells received one of four treatments: Group 1 cells were maintained in control medium, Group 2 cells were cultured in a common osteogenic medium, Group 3 cells were cultured in osteogenic medium supplemented with 250ng/mL of OP-1, and Group 4 cells were cultured with 250ng/mL of OP-1 added to control medium. Osteogenic differentiation of ADSCs was determined by estimating the number and size of mineralized nodules, and the amount of extracellular osteopontin secreted into cell culture medium. Mineralized nodule production was assessed at day 21 with von Kossa staining. Extracellular osteopontin release was measured after 8 and 21 days by enzyme-linked immunosorbant assay (ELISA). ANOVA/Tukey tests were used to identify differences among the four treatment groups for mineralized nodule production and osteopontin release (p0.05), which were significantly higher than the group incubated in cell growth medium only (p0.05). Linear regression analysis demonstrated a linear relationship was present between the presence of calcified nodules and the amount of osteopontin released (p

The effect of local simvastatin delivery strategies on mandibular bone formation in vivo.

Systemic simvastatin is known to reduce cholesterol and stimulate modest bone formation, but local surgical placement in polylactic acid domes causes robust bone formation and local swelling. A less invasive and more flexible injection protocol was studied to evaluate the bone-inducing effects compared to surgical implantation. Bone formation rate, short- and long-term bone augmentation histology, and mechanical properties were evaluated to characterize the new bone in a rat bilateral mandible model (test and control sides in same animal). Results demonstrated that multiple (3) injections of 0.5 mg simvastatin effectively reduced soft tissue swelling while preserving bone growth (60% increase of bone width at 24 days) compared to simvastatin dome placement (43% increase at 24 days). Compared to controls, bone formation rate was significantly higher on the simvastatin side, especially in the dome. Three-point bending tests revealed higher maximum force to fracture and stiffness at 24 days with simvastatin injections. Long-term evaluation showed that 55% of maximum new bone formed 24 days post-injection was retained at 90 days.

Mode I and Mode III fractures in intermediate zone of full-thickness porcine temporomandibular joint discs.

The aim of this study was to assess the critical energy required to induce flaw propagation in the temporomandibular joint (TMJ) disc when tensile and shear stresses were applied. J-integrals were measured for Mode I and III fractures because excessive tensile and shear stresses promote disc failure. Single edge notch (Mode I) and trouser tear (Mode III) specimens were constructed with flaws oriented parallel to the predominant anteroposteriorly oriented collagen fibers of the TMJ disc. Disks with and without an impulsive pre-load of 3 N s were studied to compare impact-damaged and healthy tissues. Results demonstrated that impulsive loading stiffened the tissues and significantly increased the Mode I fracture energy (J (IC)) but not Mode III (J (IIIC)) (p < or = 0.05). J (IC) and J (IIIC) values were similar for undamaged tissues, but J (IC) values were 2.3 times higher for impulsively loaded tissues (p < or = 0.05). This suggests that when flaws are introduced through impact, the TMJ disc responds by requiring more energy for tensile flaw extension. This research is a first step towards characterizing the mechanical microenvironment that initiates joint disease. This characterization is essential for successful integration of engineered replacement tissues for damaged TMJs.

Fracture toughness estimation for the TMJ disc.

J contour integral fracture toughness of the temporomandibular (TMJ) disc was estimated from a computational model based on fracture load data derived from experimental tests. The computational model involved a stress analysis of TMJ disc specimens with cracks oriented parallel and perpendicular to the primary collagen fiber axis within the intermediate zone of the disc. The results demonstrated differences occurred between crack orientations when an orthotropic model was used. Fracture toughness was much lower for a crack oriented parallel to the collagen fiber direction than that for a crack oriented perpendicularly. Thickness, crack size, and anisotropy ratio were observed as additional variables affecting the fracture toughness of the TMJ disc. Future model enhancements may be achieved by considering the poroviscoelastic nature of the TMJ disc.

Mechanical response of the porcine temporomandibular joint disc to an impact event and repeated tensile loading.

AIMS: To test for orthotropy in the stress-strain behavior of the temporomandibular joint (TMJ) disc under repeated physiologic loading before and after an impact event. METHODS: Two groups, each consisting of 10 discs, were subjected to repeated tensile cycling in the dorsoventral (group 1) and mediolateral (group 3) direction. Two additional groups, each consisting of 10 discs, had preconditioning in the form of a 1.18 N.s impulsive load before tensile cycling in either the dorsoventral (group 2) or mediolateral (group 4) direction. Physiologic loads of 1 to 3 N were cycled at 0.1 Hz, and stress-strain responses were recorded every cycle between 1 to 10 cycles, and then periodically at 50, 100, 500, 750, and 1,000 cycles. The properties of elastic modulus, residual strain upon unloading, and area contained within the hysteresis loop were measured. RESULTS: Dorsoventral loading produced 5-fold higher elastic modulus, 5-fold lower residual strain, and 5-fold lower hysteresis compared to mediolateral tensile loading (P < or = .001). Repeated loading effectively reduced the viscous response for all discs, as the elastic modulus increased while residual strain and hysteresis decreased. Impulsive loading caused elastic modulus to increase for dorsoventrally cycled discs, whereas hysteresis decreased for mediolaterally cycled discs (P < or = .05). CONCLUSION: The findings suggest that damage from the impact load may have increased the porosity of the extracellular matrix, which ultimately resulted in additional stress transfer to the collagen fibers during loading. Impulsive loads may be an important preconditioning factor in the fatigue failure of the TMJ disc in vivo.

Clinical ligation forces and intraoral friction during sliding on a stainless steel archwire.

The efficiency of tooth movement associated with some orthodontic mechanics can be compromised by friction between archwire and bracket. This study examined the effects of bracket ligation forces (F(N Ligation)) and mastication on friction when sliding a bracket along an archwire. Preliminary data from 5 orthodontists and 5 orthodontic residents characterized average tight and loose stainless steel F(N Ligation). These values were reproduced by a calibrated operator in a custom device used to estimate changes in the measurement of ex vivo and intraoral frictional forces, represented by mu(a), the apparent coefficient of static friction. Ten subjects chewed gum with the device in place to determine whether vibration eliminated friction when compared to ex vivo measurements. Nested analysis of variance and Tukey HSD tests determined the effects of ligation type and environmental variables. No significant differences (P >.01) were found between ex vivo and intraoral mu(a) values for tight and loose stainless steel ligation. Intraoral mu(a) values for elastic ligation were significantly greater than ex vivo mu(a) values (P

Clinical evaluation of two adhesive composite cements for the suppression of dentinal cold sensitivity.

STATEMENT OF PROBLEMS: Postoperative cold sensitivity after the cementation of indirect restorations with composite cements has been reported frequently but not scientifically documented. PURPOSE: This controlled clinical study was designed to simulate the dentin/composite cement interface immediately after cementation of a cast restoration. The desensitizing capabilities of a composite cement that contains a self-etching, dual-polymerizing resin adhesive system were compared with those of a composite cement that use phosphoric acid etching followed by a single-bottle, light-activated primer/resin-based adhesive. MATERIAL AND METHODS: The hypersensitive root surfaces of selected teeth were randomized to receive 1 of 3 treatments: coating with a self-etching adhesive (Linkmax) and its respective cement, coating with a conventionally etched adhesive (RelyX ARC) and its cement, or no treatment (negative control). The sample size was 22. Dentin sensitivity was ascertained with an accurate cold testing device that slowly decreased in temperature. Tooth sensitivity was measured both immediately and at 7 days after placement. Two-way analysis of variance and Fisher's least significant difference test (P<.05) were used to determine whether significant differences existed as a function of treatment type or time. RESULTS: Immediately after placement, the self-etching adhesive and its respective cement resulted in more suppression of cold sensitivity than no treatment (control); with Linkmax treatment, the temperature at which teeth responded was reduced by 8.4 degrees C. The conventionally etched adhesive and its cement reduced the temperature at which teeth responded by 9.4 degrees C. After 1 week, these temperature reductions were 7.0 degrees C and 4.3 degrees C, respectively. Untreated controls at the 2 intervals showed a mean decrease in sensitivity to cold of 3.6 degrees C and 4.1 degrees C. Statistical analysis showed type of composite cement to be a significant factor. CONCLUSION: Within the limitations of this study and in comparison to untreated control teeth, Linkmax treatment resulted in a significant reduction in tooth root sensitivity over 1 week (P=.02), whereas RelyX ARC did not (P=.066).

Small intestinal submucosa versus salt-extracted polyglycolic acid-poly-L-lactic acid: a comparison of neocartilage formed in two scaffold materials.

This study sought to compare differences in neocartilage produced over time from two types of resorbable scaffold materials. One material was entirely synthetic and contained a polyglycolic acid-poly-L-lactic acid matrix (PGA-PLLA). The second scaffold material was bioactive and consisted of a four-layered construct of porcine small intestinal submucosa (SIS). Disk-shaped scaffolds were seeded with canine chondrocytes and implanted into athymic mice for periods of 5, 8, 12, and 24 weeks. Constructs were examined microscopically, assayed for hydroxyproline (HP) and glycosaminoglycan (GAG) content, and collagen typed (I or II) at each time period. Creep indentation tests determined aggregate and shear modulus, permeability, and thickness. Results indicated that SIS maintained its thickness through the first 12 weeks, and then doubled by week 24. The 24-week tissue appeared chondroid-like and possessed high GAG content. Tissues derived from PGA-PLLA scaffolds were lower in HP content than SIS-derived tissues, but type II collagen was demonstrated only in PGA-PLLA-derived tissues at 24 weeks. Mechanical properties were not significantly different for any tissue over time (p > 0.05), but aggregate and shear modulus mean values were consistently higher for PGA-PLLA-derived tissues at nearly every time interval. This, coupled with the presence of collagen types I and II, suggested a more congruent solid phase may be forming within the extracellular matrix of tissues derived from PGA-PLLA scaffolds. Future study is necessary to compare these materials under simulated loading conditions.