In vitro validation of Digital Image Analysis Sequence (DIAS) for the assessment of the marginal fit of cement-retained implant-supported experimental crowns.

BACKGROUND: The replica technique with its modifications (negative replica) has been used for the assessment of marginal fit (MF). However, identification of the boundaries between prosthesis, cement, and abutment is challenging. The recently developed Digital Image Analysis Sequence (DIAS) addresses this limitation. Although DIAS is applicable, its reliability has not yet been proven. The purpose of this study was to verify the DIAS as an acceptable method for the quantitative assessment of MF at cemented crowns, by conducting statistical tests of agreement between different examiners. METHODS: One hundred fifty-one implant-supported experimental crowns were cemented. Equal negative replicas were produced from the assemblies. Each replica was sectioned in six parts, which were photographed under an optical microscope. From the 906 standardized digital photomicrographs (0.65 µm/pixel), 130 were randomly selected for analysis. DIAS included tracing the profile of the crown and the abutment and marking the margin definition points before cementation. Next, the traced and marked outlines were superimposed on each digital image, highlighting the components' boundaries and enabling MF measurements. One researcher ran the analysis twice and three others once, independently. Five groups of 130 measurements were formed. Intra- and interobserver reliability was evaluated with intraclass correlation coefficient (ICC). Agreement was estimated with the standard error of measurement (SEM), the smallest detectable change at the 95% confidence level (SDC95%), and the Bland and Altman method of limits of agreement (LoA). RESULTS: Measured MF ranged between 22.83 and 286.58 pixels. Both the intra- and interobserver reliability were excellent, ICC = 1 at 95% confidence level. The intra- and interobserver SEM and SDC95% were less than 1 and 3 pixels, respectively. The Bland-Altman analysis presented graphically high level of agreement between the mean measurement of the first observer and each of the three other observers' measurements. Differences between observers were normally distributed. In all three cases, the mean difference was less than 1 pixel and within ± 3 pixels LoA laid at least 95% of differences. T tests of the differences did not reveal any fixed bias (P > .05, not significant). CONCLUSION: The DIAS is an objective and reliable method able to detect and quantify MF at ranges observed in clinical practice.

Evaluation of the frequency and temperature dependence of the dynamic mechanical properties of acetal resins.

The purpose of this study was to evaluate and compare the dynamic mechanical properties of two acetal resins (different colored samples of the same resin), an autopolymerized reline resin, and a heat-polymerized denture base resin. Measurements were obtained in two conditions, the frequency- and temperature-dependent conditions, using a dynamic viscoelastometer. The acetal resins exhibited lower loss tangent values than the autopolymerized reline resin and heat-polymerized denture base resin. With respect to temperature dependence, all of the materials displayed stable viscoelastic properties in the temperature range found in the oral environment. The acetal resin had both a glass transition temperature and a melting point, whereas the autopolymerized reline resin and heat-polymerized denture base resin had only glass transition temperatures. The results of this study suggest that acetal resin displays elastic properties when compared with the other 2 materials.

Mechanical Properties and Simulated Aging of Silicone Maxillofacial Elastomers: Advancements in the Past 45 Years.

PURPOSE: To identify and discuss the findings of publications on mechanical behavior of maxillofacial prosthetic materials published since 1969. METHODS: Original experimental articles reporting on mechanical properties of maxillofacial prosthetic materials were included. A two-stage search of the literature, electronic and hand search, identified relevant published studies up to May 2015. An extensive electronic search was conducted of databases including PubMed, Embase, Scopus, and Google Scholar. Included primary studies (n = 63) reported on tensile strength, tear strength, and hardness of maxillofacial prosthetic materials at baseline and after aging. RESULTS: The search revealed 63 papers, with more than 28 papers being published in the past 10 years, which shows an increased number of publications when compared to only 6 papers published in the 1970s. The increase is linear with significant correlation (r = 0.85). Such an increase reflects great awareness and continued developments and warrants more research in the field of maxillofacial prosthetic materials properties; however, it is difficult to directly compare results, as studies varied in maxillofacial prosthetic materials tested with various silicone elastomers being heavily investigated, standards followed in preparing test specimens, experimental testing protocols, and parameters used in setting simulated aging conditionings. CONCLUSION: It is imperative to overcome the existing variability by establishing unified national or international standards/specifications for maxillofacial prosthetic materials. Standardization organizations or bodies, the scientific community, and academia need to be coordinated to achieve this goal. In the meantime and despite all of these theoretically significant alternatives, clinical practice still faces problems with serviceability of maxillofacial prostheses.

Effects of cleansing methods on 3-D surface roughness, gloss and color of a polyamide denture base material.

OBJECTIVE: The purpose of this study was to determine the effects of two denture cleansing methods on 3-D surface roughness, gloss and color of denture base materials. MATERIALS AND METHODS: Thirty disks from nylon (Valplast) and 30 from heat-polymerized acrylic denture base material (Paladon 65) were made and 10 of each material were immersed in water (control), Val-Clean (peroxide cleanser) and Corega Extradent (peroxide cleanser) plus microwaving for a period simulating 30 days of daily cleansing. 3-D surface roughness, gloss and color parameters were measured before and after cleansing using an interferometric profilometer, a gloss meter and a colorimeter. The results were statistically analysed by regression, paired-t, Mann-Whitney and Kruskal-Wallis tests at α = 0.05 level of significance. RESULTS: The results showed significant differences at baseline in L* and b* parameters between materials (p < 0.01), with a significantly lower gloss (p < 0.05) and higher roughness (p < 0.05) for Valplast. After cleansing, Δϵ* was significantly greater in Valplast than Paladon 65 (p < 0.05). Gloss of both materials decreased significantly within the Corega Extradent plus microwave solution (p < 0.05), while roughness increased significantly only for Paladon 65 (p < 0.05). CONCLUSIONS: Valplast was found to have a significantly lower gloss and a higher roughness than Paladon 65 before cleansing. After cleansing, ΔE* increased more in Valplast than in Paladon 65, gloss of both materials decreased and roughness only of Paladon 65 increased within the Corega extradent plus microwaving method.

Dynamic mechanical thermal analysis of maxillofacial prosthetic elastomers: the effect of different disinfecting aging procedures.

In this study, dynamic mechanical thermal analysis was used to evaluate the changes that occurred in maxillofacial elastomers subjected to different disinfecting regimens. A commercial polydimethyl siloxane (PDMS) and an experimental chlorinated polyethylene (CPE) were treated with different disinfection procedures for a period that simulates 1 year of clinical service: microwave exposure (D1), hypochlorite solution (D2), neutral soap (D3), and a commercial disinfecting solution (D4). A fifth group was kept in dark storage as control. Dynamic mechanical thermal analysis tests operated in a fixed frequency (1 Hz) over a range of temperatures (-130°C to 20°C for PDMS, -60°C to 120°C for CPE). Loss modulus (G″), storage modulus (G'), and loss factor (tanδ) were recorded as a function of temperature. The obtained glass transition temperature (Tg) values were subjected to statistical analysis. Dynamic mechanical thermal analysis revealed changes in Tg values for both materials, which reflect the possible changes in their chemical and physical structure, after different disinfection procedures. The PDMS and CPE samples seem to have less dense structure maybe because of chain scission reaction that probably occurred during the disinfection procedures. According to statistical analysis, Tg values presented significant changes from the control samples among the different materials and disinfecting procedures. Microwave exposure and hypochlorite solution affect CPE significantly, whereas PDMS exhibited significant changes after being treated with a commercial antimicrobial agent, concerning changes that occurred in Tg. In all cases, Tg values were decreased compared with the untreated samples, which were stiffer, presenting higher Tg and G' values.

Tensile and microindentation properties of maxillofacial elastomers after different disinfecting procedures.

STATEMENT OF PROBLEM: Daily disinfection of maxillofacial prosthesis may reduce their service-life and lead to replacement. PURPOSE: The purpose of this study was to evaluate possible alterations in the mechanical behavior of two maxillofacial elastomers after application of four different disinfection procedures. MATERIAL AND METHODS: The materials tested were two maxillofacial elastomers, a commercially available polydimethylsiloxane (PDMS) and an experimental chlorinated polyethylene (CPE). Different disinfection procedures such as microwave exposure, hypochlorite solution, neutral soap and a commercially antimicrobial solution, were applied for a period which simulates one year of a real service life. Mechanical behavior was investigated through tensile and microindentation tests in various depths. Mathematical models were fitted to tensile curves. Alterations in tensile parameters (maximum stress, maximum strain, elasticity and viscoelasticity parameter) were subjected to two way ANOVA and Tukey's post hoc tests (α=.05). RESULTS: Most of the tensile parameters presented significant alterations among different disinfection procedures and maxillofacial materials which became also harder. Microwave exposure caused greater changes in PDMS and CPE elastomer whereas commercial antimicrobial solution and neutral soap did not significantly affect them. Microindentation and tensile tests revealed similar changes in materials' elastic modulus and hardness whereas the observed changes were greater into smaller depths. CONCLUSIONS: Tensile and microindentation properties of PDMS and CPE elastomers presented changes after disinfected with four different procedures. Changes in the surface of both materials were more intense than in the bulk of the materials. Microwave exposure affected most the two elastomers, so concerning the findings of this study is not recommended for the disinfection of the examined PDMS and CPE elastomers. Moreover, microwave exposure and hypochlorite solution caused greater changes in the surface (3µm) of CPE samples as indicated by microindentation results. PDMS affected less from the commercial antimicrobial agent and CPE from neutral soap, which seems to be the most suitable disinfection techniques.

Effect of different disinfecting procedures on the hardness and color stability of two maxillofacial elastomers over time.

OBJECTIVE: Disinfection procedures often cause deterioration in a maxillofacial prosthesis. Color and hardness alterations could lead to a replacement of the prosthesis. MATERIAL AND METHODS: An experimental chlorinated polyethylene (CPE) and a commercial polydimethyl siloxane (PDMS) sample were treated with four different disinfection procedures for a period which simulates 1 year of clinical service. The applied disinfection procedures included microwave exposure and immersion in three solutions, sodium hypochlorite, neutral soap and a commercial disinfecting soap. Shore A hardness (∆H) and color differences (∆E) were determined before and after each procedure. All data were analyzed by Two Way Analysis of Variance (ANOVA) and Tukey's post hoc tests at a level of α=0.05. RESULTS: The samples presented significant alterations in color and hardness after the different disinfection treatments. The color differences (∆E) were at least eye detectable in all cases and clinically unacceptable in most of the cases, with values ranging from 1.51 to 4.15 and from 1.54 to 5.92 for the PDMS and CPE material, respectively. Hardness was decreased after all the disinfection procedures in the PDMS, while for the CPE, a decrement was observed after disinfection with sodium hypochlorite and neutral soap and an increment after microwave exposure and the disinfection with a commercial antimicrobial agent. The PDMS samples presented greater alterations in color and hardness after disinfection with sodium hypochlorite solution, while the microwave exposure caused negligible effects. The CPE samples were affected most after disinfection when treated with neutral soap, and more slightly when disinfected with sodium hypochlorite solution. CONCLUSIONS: The disinfection procedures caused alterations in color and hardness of the examined materials. The most suitable disinfection procedure for the PDMS material is microwave exposure, while disinfection with sodium hypochlorite solution is not recommended. The CPE material is suggested to be disinfected with sodium hypochlorite solution and the use of neutral soap is not recommended. Comparing the two materials, the PDMS material is most color stable, while the CPE material presented fewer changes in hardness.

Effect of different disinfecting procedures on the hardness and color stability of two maxillofacial elastomers over time

Objective Disinfection procedures often cause deterioration in a maxillofacial prosthesis. Color and hardness alterations could lead to a replacement of the prosthesis. Material and Methods An experimental chlorinated polyethylene (CPE) and a commercial polydimethyl siloxane (PDMS) sample were treated with four different disinfection procedures for a period which simulates 1 year of clinical service. The applied disinfection procedures included microwave exposure and immersion in three solutions, sodium hypochlorite, neutral soap and a commercial disinfecting soap. Shore A hardness (∆H) and color differences (∆E) were determined before and after each procedure. All data were analyzed by Two Way Analysis of Variance (ANOVA) and Tukey's post hoc tests at a level of α=0.05. Results The samples presented significant alterations in color and hardness after the different disinfection treatments. The color differences (∆E) were at least eye detectable in all cases and clinically unacceptable in most of the cases, with values ranging from 1.51 to 4.15 and from 1.54 to 5.92 for the PDMS and CPE material, respectively. Hardness was decreased after all the disinfection procedures in the PDMS, while for the CPE, a decrement was observed after disinfection with sodium hypochlorite and neutral soap and an increment after microwave exposure and the disinfection with a commercial antimicrobial agent. The PDMS samples presented greater alterations in color and hardness after disinfection with sodium hypochlorite solution, while the microwave exposure caused negligible effects. The CPE samples were affected most after disinfection when treated with neutral soap, and more slightly when disinfected with sodium hypochlorite solution. Conclusions The disinfection procedures caused alterations in color and hardness of the examined materials. The most suitable disinfection procedure for ...

Patients' profiles and perceptions of complete dentures in a university dental clinic.

This study investigated factors associated with perceptions of complete dentures (CDs) among patients presenting at a university dental clinic. A retrospective chart review of all new edentulous patients presenting at the Athens University School of Dentistry Removable Prosthodontics Clinic between 1993 and 2002 (n = 2,526) was completed. More than half of CD-wearing patients were dissatisfied with their dentures at the initial visit. Dissatisfaction was correlated with current use of denture adhesives and less time spent edentulous and was more prevalent among females. Factors affecting patients? adaptation to and satisfaction with CDs should be considered at CD fabrication and follow-up.

Flexural and bond strengths of relined denture polymers assessed by four-point bending tests and Weibull analysis.

OBJECTIVES: The aim of this study was to (1) investigate the flexural strengths of three denture resins i.e. heat, photopolymerised and microwaved and how it was affected by relining with auto- and visible light-polymerised hard reliners, (2) investigate the bond strengths between denture resins and hard reliners and (3) interpret the results of both tests by utilising Weibull analysis. MATERIALS AND METHODS: Specimens (65 × 10 × 2.5 mm) from denture resins, relined and bonded combinations were tested using a four-point bending test in a universal testing machine and a crosshead speed of 5 mm/min. Ten specimens for each bulk resin and denture resin-reliner combination for a total of 150 were tested. RESULTS: Statistical analysis indicated significant differences between bulk materials (p < 0.001) and between reliners (p < 0.001) for flexural and bond strength tests. CONCLUSION: was concluded that (1) the four-point flexural strength was different between the denture base materials, (2) flexure strength between bulk and relined or between relined with autopolymerised and photopolymerised bases was different, (3) flexural strength among relined denture bases was different and (4) bond strengths among relined denture bases were different.

Attitudes and usage of denture adhesives by complete denture wearers: a survey in Greece and the Netherlands.

OBJECTIVE: To explore whether there are differences in usage of and attitudes towards denture adhesives among patients in two countries. BACKGROUND: There are no multi-country surveys concerning usage of and attitudes towards denture adhesives from complete denture wearers. MATERIALS AND METHODS: The survey took place in Greece and the Netherlands with a sample of 284 and 165 consecutive complete denture wearers, respectively, by using a 9-item prepared questionnaire. Statistical analysis relied on chi-square test at α = 0.05. RESULTS: In this survey, 26 and 20% of Greek and Dutch patients, respectively, had tried denture adhesive, but only 27% of them in Greece as well as in the Netherlands currently used it; 49% of the Greek and 45% of the Dutch participants rated the overall performance of adhesives as good. Between the two populations, no differences were identified in a majority of the research variables, except where 27% of Greeks answered that they did not know the existence of denture adhesives compared to none of the Dutch patients and when 90% of the Dutch contrary to 70% of Greeks reported that they did not need denture adhesives as they could manage their dentures well. CONCLUSION: The usage of and attitudes towards denture adhesives between the Greek and Dutch sample were similar with only two exceptions concerning the knowledge of existence and the need of using denture adhesives.

Optical properties of pigmented polydimethylsiloxane prosthetic elastomers: effect of "outdoor" and "indoor" accelerating aging.

OBJECTIVES: Optical properties of facial prosthetic elastomers undergo significant changes mainly due to aging. The resulting changes in their appearance are the main reasons of facial prosthesis' replacement. PURPOSE: The purpose of this study was to evaluate changes in the translucency parameter (TP) and color (ΔE*) of polydimethylsiloxane (PDMS) maxillofacial elastomers after exposure to 3 different aging conditions (time passage, accelerated "outdoor" aging, and accelerated "indoor" aging). MATERIALS AND METHODS: The PDMS prosthetic elastomers tested in this study were low- (LTV) and high-temperature vulcanized (Episil and Mollomed, respectively) in various shades. Color changes (ΔE*) and translucency parameter (TP) were determined in the CIE L*a*b* system using a tristimulus colorimeter. Data were subjected to 2-way analysis of variance followed by Tukey post hoc test. In addition, TP values were analyzed by paired t tests. The significance level of α = 0.05 was set for all tests. RESULTS: Translucency parameter values for most samples were significantly changed after aging, and ΔE* values were characterized as unacceptable. Both aging procedure and material type affected the changes that occurred. Moreover, dark-shaded samples of both silicone materials revealed significant changes in TP values before and after aging. ΔE* was not significantly different among the same material samples but had significant differences between the 2 materials (Episil and Mollomed). Time passage did not significantly affect TP values contrary to the other 2 accelerated aging procedures. Between outdoor and indoor aging, no significant differences were detected. CONCLUSIONS: Accelerated outdoor and indoor aging caused significant changes in ΔE* and TP values. Significant changes were also detected between material types.

Effect of time passage on some physical properties of silicone maxillofacial elastomers.

OBJECTIVES: Changes in color and other physical properties of silicone facial prosthesis are the main reasons for its replacement. The purpose of this study was to investigate the effect of time passage on some physical properties such as tensile strength, modulus of elasticity, elongation at break, tear strength, hardness, color stability, and contrast ratio (CR) of 2 silicone facial elastomers after being sealed in glass containers and kept in the dark for 1 year. MATERIALS AND METHODS: Specimens from 2 silicone elastomers (Silasto 30 and Premium 2) were made and stored in the dark. Tensile and tear strength tests were conducted according to International Organization for Standardization specification nos. 37 and 39, respectively, in a universal testing machine. Shore A hardness was measured according to the American Society for Testing Materials specification D 2240. Color changes (ΔΕ*) were determined in the CIE L*a*b* system using a tristimulus colorimeter, and CR also was calculated. Data were analyzed by paired and unpaired t-tests at a significance level of α = 0.05. RESULTS: Elongation at break, modulus of elasticity, and hardness were significantly changed, whereas changes in CR were observed only in 1 of the 2 elastomers. Tensile and tear strengths were not significantly changed for both of them. Within the limitations of this study, color changes (ΔΕ) were unacceptable. CONCLUSIONS: Most of the physical properties studied were significantly affected because of time passage. Mechanical and physical properties of silicone maxillofacial elastomers can be changed with time passage (natural aging in the dark). The average time of replacing a facial prostheses is 6 to 18 months; thus, it is important that the findings of this study covered a period of 12 months. Time passage seems to be a critical factor contributing to the overall deterioration of a silicone maxillofacial elastomer.

Effect of extraoral aging conditions on mechanical properties of maxillofacial silicone elastomer.

PURPOSE: The purpose of this study was to investigate the effect of extraoral human and environmental conditions on the mechanical properties (tensile strength and modulus, elongation, tear strength hardness) of maxillofacial silicone elastomer. MATERIALS AND METHODS: Specimens were fabricated using TechSil-S25 silicone elastomer (Technovent Ltd, Leeds, UK). Eight groups were prepared (21 specimens in each group; eight tensile, eight tear, five hardness) and conditioned differently as follows (groups 1 through 8): Dry storage for 24 hours; dry storage in dark for 6 months; storage in simulated sebum solution for 6 months; storage in simulated acidic perspiration for 6 months; accelerated artificial daylight aging under controlled moisture for 360 hours; outdoor weathering for 6 months; storage in antimicrobial silicone-cleaning solution for 30 hours; and mixed conditioning of sebum storage and light aging for 360 hours. The conditioning period selected simulated a prosthesis being in service for up to 12 months. Tensile and tear test specimens were fabricated and tested according to the International Standards Organization (ISO) standards no. 37 and 34, respectively. Shore A hardness test specimens were fabricated and tested according to the American Standards for Testing and Materials (ASTM) D 2240. Data were analyzed with one-way ANOVA, Bonferroni, and Dunnett's T3 post hoc tests (p < 0.05). Weibull analysis was also used for tensile strength and tear strength. RESULTS: Statistically significant differences were evident among all properties tested. Mixed conditioning of simulated sebum storage under accelerated artificial daylight aging significantly degraded mechanical properties of the silicone (p < 0.05). CONCLUSIONS: Mechanical properties of maxillofacial elastomers are adversely affected by human and environmental factors. Mixed aging of storage in simulated sebum under accelerated daylight aging was the most degrading regime. CLINICAL SIGNIFICANCE: Accelerated aging of silicone specimens in simulated sebum under artificial daylight for 12 months of simulated clinical service greatly affected functional properties of silicone elastomer; however, in real practice, the effect is modest, since sebum concentration is lower, and daylight is less concentrated.

Effects of storage in simulated skin secretions on mechanical behavior and color of polydimethylsiloxanes elastomers.

BACKGROUND: Among the deteriorations that occur in maxillofacial prosthesis due to exposure in various environmental factors, sebaceous oils (sebum) and perspiration are also responsible for several alterations. PURPOSE: Mechanical properties and color changes of 3 different medical-grade polydimethylsiloxanes were investigated in this study (Elastomer 42, Techsil 25, and M511), after immersion for 6 months in simulated sebum and perspiration at 37 °C. The purpose of this study was to determine the effects of storage in their physical properties. The null hypothesis investigated was that immersion time did not affect the measured properties. METHODS: Polydimethylsiloxane specimens were immersed in simulated perspiration and in sebum. Compression tests were conducted on a Zwick testing machine. Shore A hardness measurements were carried out in a CV digital Shore A durometer. Weight changes were measured, and color changes were determined in the CIELAB system, using a MiniScan XE spectrophotometer. Simple mathematical models were developed to correlate the measured properties with the immersion time. The data were analyzed by analysis of variance and Tukey multiple range test at a level of α = 0.05. RESULTS: Specimens immersed in simulated skin secretions became harder because of facilitation of the propagation of cross-linking reaction that probably occurred during aging of the polydimethylsiloxane samples, except for Elastomer 42, which seems to become more soft and ductile after immersed in sebum. Some weight increase was observed for the specimens immersed into the aqueous solutions, whereas for those immersed in sebum, weight loss was recorded, probably because of extraction of some compounds. The color change was higher for the specimens immersed in sebum than that corresponding to simulated perspiration. According to statistical analysis, all measured properties changed significantly after immersion in simulated perspiration and in sebum. Moreover, mathematical models reveal major alterations as well, which were introduced through their constants. Thus, the hypothesis investigated was rejected. CONCLUSIONS: Significant changes were observed in all the examined elastomers. The elastomers were aged for a period, which simulates 1.5 years of clinical service. Within the limitation of this study, concerning the mechanical behavior and mostly the color changes, sebum and perspiration greatly affect the examined elastomers.

Partial edentulism and removable partial denture design in a dental school population: a survey in Greece.

OBJECTIVES: To investigate the pattern of partial edentulism and the most frequent designs of cobalt-chromium removable partial dentures (RPDs), constructed at the Dental School of Athens, Greece. METHODS AND MATERIALS: Five hundred and fifty-three patients, between 42 and 81 years old, mostly males, treated by undergraduate dental students, were included. The survey was based on visual evaluation of master casts and work authorisation to dental technicians. Aspects examined were: Kennedy Classification, modification areas, major connectors, clasping, placement of rest seats and indirect retention. RESULTS: Kennedy Class I was the most common encountered in the maxilla (50.5%) and in the mandible (70%). The most frequent major connectors were the lingual bar (92.6%) and the U-shaped palatal strap (54%). The most common clasp was the Roach (69.2%) in Class I and Class II. In Class III and IV, the most common was the occlusally approaching clasp (55% and 70%). The most frequent location of the rest was mesial of abutment teeth. On the average, 39.5% of Class I RPDs and 58.6% of Class II RPDs had indirect retainers. CONCLUSION: A combination of the two major philosophies of RPD design (biomechanical and hygienic) was evident in the RPDs examined in our study.

Dynamic mechanical properties of a maxillofacial silicone elastomer incorporating a ZnO additive: the effect of artificial aging.

The main objective of the current study was to investigate the dynamic mechanical properties of a room-temperature vulcanizing silicone incorporating different fractions of zinc oxide (ZnO) after indoor and outdoor photoaging. Forty-eight samples were produced by adding different amounts of ZnO into a commercial maxillofacial silicone (EPISIL-E). The samples were divided into 4 groups containing 0.0, 0.2, 0.5, and 1 wt% ZnO additive, respectively. Samples were exposed to sunlight (subgroup 2), ultraviolet (subgroup 3), and fluorescence (subgroup 4) aging, whereas nonaged samples comprised the control subgroup (subgroup 1). Dynamic mechanical analysis was used to determine the storage modulus (E'), loss modulus (E″), and damping capacity (tanδ). General linear statistic model was conducted to evaluate the effects of aging, testing frequency, and composition on the dynamic mechanical properties of the silicone with the ZnO additive. Post hoc analysis was performed using Tukey test. Statistical analysis revealed a significant impact of composition on tanδ (P < 0.05). Aging influenced E' and E″ (P < 0.01). The combination of aging and composition had a significant effect on all dynamic properties (P < 0.01).

Screening of edentulous patients in a dental school population using the prosthodontic diagnostic index.

PURPOSE: The aim of this study was to classify a number of completely or partially edentulous patients who attended undergraduate clinics at the Dental School of Athens using the prosthodontic diagnostic index (PDI) to identify the complexity of the cases treated by the students. BACKGROUND: There is a scarcity of studies, concerning prosthodontic patients and screening them according to a classification system such as the PDI. MATERIAL AND METHODS: The survey was conducted on 181 patients who attended the clinics for treatment. The PDI categorised the patients into four classes (Class I-IV) according to the severity of certain diagnostic findings. RESULTS: From the 110 completely edentulous patients, 27 patients were in Class I, 21 in Class II, 15 in Class III and 47 in Class IV. From the 71 partially edentulous patients, two were in Class I, 17 in Class II, 29 in Class III and 23 in Class IV. CONCLUSION: Our results showed that the majority of patients were categorised in Class III (partially edentulous) and IV (completely edentulous). This indicates the need to introduce a proper screening tool, such as the PDIs, during the initial examination, to achieve a successful treatment.

Material properties of a maxillofacial chlorinated polyethylene elastomer stored in simulated skin secretions.

STATEMENT OF PROBLEM: Facial prostheses deteriorate in a service environment primary due to exposition to various environmental factors, including sebaceous oils (sebum) and perspiration. PURPOSE: This study investigated the physical properties of an experimental, facial prosthetic after immersion for 6 months in simulated sebum, and perspiration at 37 degrees C. MATERIAL AND METHODS: Chlorinated polyethylene (CPE) specimens were immersed in simulated perspiration as well as in sebum. Compression tests were conducted on a Zwick testing machine. Shore A hardness measurements were carried out in a CV digital Shore A durometer. Melting and glass transition temperatures were evaluated with a differential scanning calorimeter. Weight changes were measured and color changes were determined in the CIE LAB system using a MiniScan XE spectrophotometer. Simple mathematical models were developed to correlate the measured properties with immersion time. The data were also subjected to analyses of variance (ANOVA) and the Tukey multiple range tests at a level of alpha = 0.05. RESULTS: Specimens immersed in perspiration became harder due to facilitation of the propagation of cross-linking reaction that probably occurred during aging of the CPE samples. Some weight increase was observed for the specimens immersed into the aqueous solutions, whereas for those immersed in sebum, weight loss was recorded, probably because of extraction of some compounds. The color change was higher for the specimens immersed in sebum than that corresponding to simulated perspiration. CONCLUSIONS: The chlorinated polyethylene specimens aged for a period, which simulates 1.5 years of clinical service1, showed significant deformations in their physical properties.

Repeatability and interdevice reliability of two portable color selection devices in matching and measuring tooth color.

STATEMENT OF PROBLEM: There is a need to know how shade selection devices perform in matching and measuring tooth color, since these functions are usually evaluated independently and may present significant discrepancies. PURPOSE: The purpose of this study was to evaluate 2 devices which offer both functions to test the null hypothesis that they present no differences in their repeatability and interdevice reliability relating to the 2 functions. MATERIAL AND METHODS: Thirty-one extracted anterior human teeth were measured twice, with each of the devices (ShadeEye NCC and VITA EasyShade), by one investigator experienced and calibrated with both devices. L*a*b* values and shade matches to VITA Classical and Vitapan 3D-Master shade guide systems were determined for all teeth. Paired t tests and intraclass correlation coefficients (ICCs) were used to statistically analyze the data (alpha=.05). RESULTS: The results showed that L*a*b* values with VITA EasyShade were significantly higher than those with ShadeEye NCC (P<.01), with a mean difference of 10.01 Delta E units. Device repeatability ICCs for measuring tooth color ranged from 0.693 to 0.929, with significant differences between devices only with respect to parameter L* (P=.042). Intradevice ICCs for matching tooth color ranged from 0.714 to 0.894, with significant differences between devices only with respect to the VITA Classical shade system (P=.042). Interdevice ICCs for measuring tooth color ranged from 0.402 to 0.486, with no significant differences between L*a*b* parameters, while interdevice matching reliability ranged from 0.189 to 0.430, with no significant differences between shade systems (P>.05). CONCLUSIONS: All tooth color parameters were higher with the VITA EasyShade device. Measuring repeatability of the VITA EasyShade was higher than the ShadeEye NCC only for the L* parameter. Matching repeatability of the ShadeEye NCC was higher than the VITA EasyShade for the VITA Classical system. Interdevice measuring reliabilities were not different for the color parameters, but matching reliability of the VITA Classical system was higher than that of the Vitapan 3D-Master.