How home bleaching agents affect the color and translucency of CAD/CAM monolithic zirconia materials.

To assess the effect of 10% carbamide peroxide (CP) and 6% hydrogen peroxide (HP) home bleaching agents on the translucency and color of monolithic zirconia. Ninety disc specimens were fabricated (diameter, 10 mm) from multi-layered (ML), ultra translucent multi-layered (UTML), and super translucent multi-layered (STML) zirconia blocks at three thicknesses (0.4,1,1.5 mm) (n=5). The samples were divided into two subgroups, which were treated with 6% HP (45 min per day) or 10% CP (8 h per day) for 14 days. The color of specimens was measured before bleaching (T0) and after bleaching on the third (T3), seventh (T7), and 14th (T14) day. Color (∆E) and translucency (TP) changes were calculated. The thickness varieties used in the samples and the bleaching agent types used created statistically significant differences only in TP and ∆E00, respectively (p<0.05). Bleaching agents can affect TP and ∆E. Patients who have zirconia restorations should be careful when using home bleaching agents.

The effect of adjustment and finishing procedure on roughness, strength, and phase transformation of monolithic zirconia.

OBJECTIVE: To evaluate the effect of adjustment and finishing procedures and thermal aging of monolithic zirconia on the surface roughness, phase transformation, and flexural strength. MATERIAL AND METHODS: One hundred disk-shaped monolithic zirconia specimens were randomly divided into 5 groups: control, received only glazing; group Gr, was grinded; group GrP, was grinded and polished; group GrG, was grinded and re-glazed; group GrPG, was re-glazed after grinding and polishing. Half of the each group were stored in distilled water for 24 h and the remaining were thermocycled for 5000 cycles. Topographic evaluations were done with profilometer and scanning electron microscope. Phase changes were assessed through X-ray diffractometer. The biaxial flexural strength test was calculated by universal test machine. Statistical analysis was performed by using two-way ANOVA and Tukey multiple comparison test (p < 0.05). RESULTS: Group Gr showed statistically higher surface roughness and flexural strength values than the other groups (p < 0.001). However, no significant differences were observed between finishing groups (p >0.05). Phase transformation was occurred in all groups but the differences were not statically significant (p >0.05). Artificial aging had no effect on surface roughness, flexural strength, and phase transformation (p >0.05). CONCLUSION: Surface roughness significantly increased after grinding, but finishing procedure approximated it to the control group. Glazing after grinding decreased the flexural strength, but polishing did not. Zirconia polishing system may be an alternative to re-glazing for monolithic zirconia. CLINICAL RELEVANCE: Polishing is one of the most effective finishing procedures that can improve the physical properties of the material without damaging its mechanical properties.

Effect of staining and bleaching on the microhardness, surface roughness and color of different composite resins.

BACKGROUND: There are studies that examined the effect of staining on the surface properties of composite resins, using different solutions and bleaching applications. However, the effect of both staining and bleaching on the same composite specimens is an issue that needs to be investigated. OBJECTIVES: The aim of this study was to investigate the surface microhardness, roughness and color changes (ΔE) of 2 different composite resins after staining and bleaching. MATERIAL AND METHODS: A microhybrid and a nanohybrid composite were used in the study. One hundred and fifty specimens were prepared from each composite. The specimens were divided into 5 groups and stained for 30 days with tea, coffee, cola, red wine, or distilled water (control). Subsequently, each group was divided into 3 subgroups. Each subgroup received a 14-day application of Opalescence™ Boost, Opalescence PF or VivaStyle® Paint On Plus bleaching materials. The color as well as surface microhardness and roughness of all specimens were determined at baseline, after staining and after bleaching. Data was analyzed using the repeated-measures analysis of variance (ANOVA) and the Bonferroni method. RESULTS: A statistically significant decrease was observed in the surface microhardness of the microhybrid composite specimens after bleaching (p < 0.05).The highest ΔE values were observed in the red wine groups for both composite resins. CONCLUSIONS: Staining and bleaching may affect surface properties and color, depending on the type, filler and matrix content of the composite resin.

The Effect of Laboratory Procedures and Repeated-glazing on Color of Metal-ceramic Restoration.

BACKGROUND: Routine laboratory procedures and repeated glazed effect the final color of metal-ceramic restorations (MCRs). Clinicians wonder if the color changes after routine laboratory procedures and repeated glazed is clinically acceptable or not. AIMS: The aim of this study was to determine the color changes of MCRs after routine laboratory procedures and then glazed for 1, 2, and 3 times. MATERIALS AND METHODS: Forty-five disc-shaped (10-mm diameter and 1-mm thickness) specimens were fabricated from Cr-Co metal-alloy. Bonding agent, first and second layer of shade A2 opaque porcelain (OP) were applied on the metal specimens. The color of specimens was measured with a spectrophotometer after each procedure and △E1, △E2, and △E3 values were calculated. Shade A2 feldspathic porcelain was applied (2-mm thickness) to all specimens. Glaze was applied on the porcelain for 1, 2, and 3 times and then, the color measured after each procedure and △E4, △E5, and △E6 values were calculated. Data were analyzed with one-way ANOVA and Duncan test (P < 0.05). RESULTS: △E1 that was obtained between the first layer of OP and bonding agent showed the greatest value. △E2 that was obtained between the second and first layer of OP showed the lowest value. After repeated glazed procedures, the final color of the specimens was changed; but, these changes were clinically acceptable (△E < 5.5). CONCLUSIONS: The routine laboratory procedures and glazed for 1,2, and 3 times is effect the color of MCRs; but, the color changes were clinically acceptable (△E < 5.5).

Evaluating the microleakage between dentin and composite materials.

BACKGROUND: For successful restoration, it is necessary to minimize the microleakage between dentin and the composite material. OBJECTIVES: The purpose of this study was to evaluate the microleakage of 2 different resin cements (self-adhesive and conventional) on dentin treated with acid, sodium hypochlorite (NaOCl), the acid-NaOCl mixture, the erbium-doped yttrium aluminum garnet (Er:YAG) laser, and their combination. MATERIAL AND METHODS: Seventy dentin specimens were divided into 7 groups (n = 10) according to the surface treatment. Then, the specimens were divided into 2 subgroups (n = 35) according to the resin cement used during cementation with prepared composite resin blocks 5 mm × 11 mm × 3 mm: self-adhesive resin cement or conventional resin cement. Microleakage was scored and recorded at the occlusal and gingival levels, along the resin-dentin interfaces. The data was analyzed with the use of univariate analysis of variance (two-way ANOVA) and the Kruskal-Wallis test for both resin subgroups. RESULTS: The obtained results revealed that self-adhesive resin cement and conventional resin cement showed similar microleakage. Etching with sodium hypochlorite, the Er:YAG laser, the acid-NaOCl mixture, and their combination resulted in microleakage comparable to that achieved in acid etching, which is the conventional method of surface treatment. CONCLUSIONS: Microleakage exhibited by self-adhesive resin cement was similar as in the case of conventional resin cement.

Comparison of temperature change among different adhesive resin cement during polymerization process.

PURPOSE: The aim of this study was to assess the intra-pulpal temperature changes in adhesive resin cements during polymerization. MATERIALS AND METHODS: Dentin surface was prepared with extracted human mandibular third molars. Adhesive resin cements (Panavia F 2.0, Panavia SA, and RelyX U200) were applied to the dentin surface and polymerized under IPS e.max Press restoration. K-type thermocouple wire was positioned in the pulpal chamber to measure temperature change (n = 7). The temperature data were recorded (0.0001 sensible) and stored on a computer every 0.1 second for sixteen minutes. Differences between the baseline temperature and temperatures of various time points (2, 4, 6, 8, 10, 12, 14, and 16 minute) were determined and mean temperature changes were calculated. At various time intervals, the differences in temperature values among the adhesive resin cements were analyzed by two-way ANOVA and post-hoc Tukey honestly test (α = 0.05). RESULTS: Significant differences were found among the time points and resin cements (P < 0.05). Temperature values of the Pan SA group were significantly higher than Pan F and RelyX (P < 0.05). CONCLUSION: Result of the study on self-adhesive and self-etch adhesive resin cements exhibited a safety intra-pulpal temperature change.

The effect of ultrafast fiber laser application on the bond strength of resin cement to titanium.

The purpose of this study was to investigate the effect of ultrafast fiber laser treatment on the bond strength between titanium and resin cement. A total of 60 pure titanium discs (15 mm × 2 mm) were divided into six test groups (n = 10) according to the surface treatment used: group (1) control, machining; group (2) grinding with a diamond bur; group (3) ultrafast fiber laser application; group (4) resorbable blast media (RBM) application; group (5) electro-erosion with copper; and group (6) sandblasting. After surface treatments, resin cements were applied to the treated titanium surfaces. Shear bond strength testing of the samples was performed with a universal testing machine after storing in distilled water at 37 °C for 24 h. One-way ANOVA and Tukey's HSD post hoc test were used to analyse the data (P < 0.05). The highest bond strength values were observed in the laser application group, while the lowest values were observed in the grinding group. Sandblasting and laser application resulted in significantly higher bond strengths than control treatment (P < 0.05). Ultrafast fiber laser treatment and sandblasting may improve the bond strength between resin cement and titanium.

Influences of Fucoxanthin on Alveolar Bone Resorption in Induced Periodontitis in Rat Molars.

The aim of this study was to evaluate the effects of systemic fucoxanthin treatment on alveolar bone resorption in rats with periodontitis. Thirty rats were divided into control, experimental periodontitis (EP), and experimental periodontitis-fucoxanthin (EP-FUCO) groups. Periodontitis was induced by ligature for four weeks. After removal of the ligature, the rats in the EP-FUCO group were treated with a single dose of fucoxanthin (200 mg/kg bw) per day for 28 consecutive days. At the end of the study, all of the rats were euthanized and intracardiac blood and mandible tissue samples were obtained for biochemical, immunohistochemical, and histometric analyses. Fucoxanthin treatment resulted in a slight decrease in tumor necrosis factor-α, interleukin-1ß, and interleukin-6 levels and a significant decrease in oxidative stress index. It was observed that fucoxanthin caused a significant reduction in receptor activator of nuclear factor kappa-ß ligand (RANKL) levels and a statistically non-significant elevation in osteoprotegerin and bone-alkaline phosphatase levels. There were no significant differences in alveolar bone loss levels between the EP and EP-FUCO groups. This experimental study revealed that fucoxanthin provides a limited reduction in alveolar bone resorption in rats with periodontitis. One of the mechanisms underlying the mentioned limited effect might be related to the ability of fucoxanthin to inhibit oxidative stress-related RANKL-mediated osteoclastogenesis.

Effect of sealer coating and storage methods on the surface roughness of soft liners.

STATEMENT OF PROBLEM: A soft lining is applied under a removable prosthesis for various reasons. The porosity of the lining material may increase colonization by microorganisms and cause tissue inflammation. PURPOSE: The purpose of this in vitro study was to evaluate the effect of sealer coating on the surface roughness of soft lining materials under 4 different conditions. MATERIAL AND METHODS: A total of 125 specimens were prepared. One high-temperature silicone-based soft lining material and 2 room-temperature-polymerized soft lining materials (1 silicone-based and 1 methacrylate-based) were used. Twenty-five specimens of each room-temperature soft lining material were coated with 2 layers of surface sealer. Additionally, 5 specimens of each material were stored in either distilled water, Coca-Cola, denture cleanser, saliva, or air. The surface roughness was measured at baseline and after 1, 7, 14, and 28 days. Surface roughness values were analyzed with repeated measures analysis of variance, and the Bonferroni multiple comparison test was performed using time-dependent groups and storage methods. RESULTS: In the time-dependent groups, methacrylate-based sealer-coated soft liners exhibited a significant increase in roughness (1.74-2.09 µm, P<.001), and silicone-based sealer-coated soft liners exhibited a decrease in roughness, but it was not significant (2.16-2.02 µm, P>.05). Therefore, the sealer coating was not effective in reducing surface roughness. Among the time-dependent storage methods, the denture cleanser exhibited an almost significant increase in roughness (1.83-1.99 µm, P=.054). Coca-Cola and artificial saliva did not show a significant difference (P>.05). However, a significant decrease in roughness was found with distilled water (P=.02) and air (P<.001). CONCLUSIONS: Statistically significant differences in surface roughness were found among the different types of soft liners. The sealer coating had no significant effect, and denture cleanser slightly increased the surface roughness. Contrary to expectations, the roughness did not increase in all groups over time.

Evaluation of the bond strength of different adhesive agents to a resin-modified calcium silicate material (TheraCal LC).

This study evaluated the bond strength of different adhesive agents to TheraCal LC and mineral trioxide aggregate (MTA) and examined the morphologic changes of these materials with different surface treatments. A total of 120 specimens, 60 of MTA Angelus (AMTA), and 60 of TheraCal LC, were prepared and divided into six subgroups according to the adhesive agent used; these agents included Scotchbond Multipurpose, Clearfil SE Bond, Clearfil Protect Bond, Clearfil S3 Bond, OptiBond All-in-One, and G-aenial Bond. After application of adhesive agents, Filtek Z250 composite resin was placed onto the specimens. Shear bond strengths were measured using a universal testing machine, followed by examination of the fractured surfaces. The surface changes of the specimens were observed using scanning electron microscopy. Data were compared by two-way analysis of variance. Although no significant differences were found among the bond strengths of different adhesives to AMTA (p = 0.69), a significant difference was found in terms of bond strengths of different adhesives to the TheraCal LC surface (p < 0.001). The total-etch adhesive system more strongly bonded to TheraCal LC compared to the bond with other adhesives. TheraCal LC bonded significantly more strongly than AMTA regardless of the adhesive agents tested. Resin-modified calcium silicate showed higher bond strength than AMTA in terms of the composite bond to these materials with different bonding systems. On the other hand, the highest shear bond-strength values were found for composite bonds with the combination of TheraCal LC and the total-etch adhesive system. SCANNING 38:403-411, 2016. © 2015 Wiley Periodicals, Inc.

In Vitro Evaluation of the Efficacy of Different Over-the-Counter Products on Tooth Whitening.

This in vitro study evaluated the whitening effect of four different over-the-counter products compared with a 10% carbamide peroxide (CP) bleaching gel. Specimens obtained from bovine incisors were stained in a tea solution and randomly divided into six groups according to the product used (n=10): CT: conventional toothpaste (negative control); CWT: Crest 3D White toothpaste; CWR: Crest 3D White mouth rinse; CWS: Crest 3D White strips; DW: Dazzling White (paint-on gel); and OP: Opalescence PF 10% CP (at-home bleaching gel, positive control). Over-the-counter products and 10% CP were used according to the manufacturer's recommendations. Color measurements were performed according to the CIELab system using spectrophotometer after staining, and after 4 and 8 weeks of the treatment procedure. The ∆E, ∆L, ∆a, and ∆b values were calculated. The data obtained were analyzed by repeated-measures ANOVA. Tukey's test for multiple comparisons was applied (p<0.05). All groups, except CWT, were effective in tooth whitening in comparison with conventional toothpaste. There was no significant difference in tooth whitening between CWT and CT (p=0.93). CWS, DW and OP groups presented significantly higher color changes than the CWR group. DW and CWS showed similar tooth whitening to OP.

In Vitro Evaluation of the Efficacy of Different Over-the-Counter Products on Tooth Whitening

This in vitro study evaluated the whitening effect of four different over-the-counter products compared with a 10% carbamide peroxide (CP) bleaching gel. Specimens obtained from bovine incisors were stained in a tea solution and randomly divided into six groups according to the product used (n=10): CT: conventional toothpaste (negative control); CWT: Crest 3D White toothpaste; CWR: Crest 3D White mouth rinse; CWS: Crest 3D White strips; DW: Dazzling White (paint-on gel); and OP: Opalescence PF 10% CP (at-home bleaching gel, positive control). Over-the-counter products and 10% CP were used according to the manufacturer's recommendations. Color measurements were performed according to the CIELab system using spectrophotometer after staining, and after 4 and 8 weeks of the treatment procedure. The ∆E, ∆L, ∆a, and ∆b values were calculated. The data obtained were analyzed by repeated-measures ANOVA. Tukey's test for multiple comparisons was applied (p<0.05). All groups, except CWT, were effective in tooth whitening in comparison with conventional toothpaste. There was no significant difference in tooth whitening between CWT and CT (p=0.93). CWS, DW and OP groups presented significantly higher color changes than the CWR group. DW and CWS showed similar tooth whitening to OP.

Este estudo avaliou o efeito branqueador de quarto produtos disponíveis comercialmente em comparação com um gel branqueador contendo 10% de peróxido de carbamida (PC). Amostras obtidas de incisivos bovinos foram tingidas numa solução de chá e distribuídas aleatoriamente em seis grupos, de acordo com o produto utilizado (n=10): CT: dentifrício convencional (controle negativo); CWT: dentifrício Crest 3D White; CWR: solução para enxague Crest 3D White; CWS: tiras branqueadoras Crest 3D; DW: gel branqueador Dazzling White e OP: Opalescence PF com 10% de PC (gel branqueador para uso doméstico, controle positivo). Os produtos comerciais e PC a 10% foram usados de acordo com as instruções dos fabricantes. Foram feitas medidas de cor com o sistema CIELab com espectrofotômetro, imediatamente após o tingimento, e após 4 e 8 semanas do tratamento. Foram calculados os valores de ∆E, ∆L, ∆a e ∆b. Os dados obtidos foram analisados por ANOVA para medidas repetidas. Foi aplicado o teste de Tukey para comparações múltiplas (p<0,05). Com exceção do Grupo CWS, todos os grupos foram efetivos para o branqueamento dental na comparação com o dentifrício convencional. Não houve diferença significativa no branqueamento dental entre CWT e CT (p=0,93). Os grupos CWS, DW e OP apresentaram mudanças de cor significativamente maiores que o grupo CWR. Os grupos DW e CWS produziram branqueamento similar a OP.

Comparison of the metal-ceramic bond after recasting and after laser sintering.

STATEMENT OF PROBLEM: Failure of the bond between metal and ceramic is common with metal ceramic prostheses. PURPOSE: The purpose of this in vitro study was to investigate how recasting affects the metal-ceramic bond strength for 1 base metal and 1 noble alloy compared with laser-sintered Co-Cr alloy by using a procedure based on ANSI/ADA Specification No. 38. MATERIAL AND METHODS: One laser-sintered (Co-Cr) and 2 metal (Co-Cr, Pd-Ag) alloys were used. Metal strips (25 × 3 × 0.5 mm) were obtained with 2 different methods: torch melting and laser sintering. Twelve alloy specimens were processed for each group. Vita VM13 porcelain layers (8 × 3 × 1.1 mm) were fabricated at the centers of the metal frameworks. Specimens containing 100% fresh alloy were used in the first casting group (control). Metal ceramic specimens were prepared for each alloy, and no new metal was added to the second and third castings. The findings were statistically analyzed and compared with a 2-way analysis of variance (ANOVA). RESULTS: The second casting of the noble alloy-ceramic specimen had the highest mean metal-ceramic bond strength in flexure. No significant differences were found between the laser-sintered Co-Cr and the Pd-Ag metal ceramic specimens after the first and third castings. CONCLUSION: All groups had adequate porcelain bond strength, except C2 (second casting of Co-Cr alloy) and C3 (third casting of Co-Cr alloy). Co-Cr alloy fabricated with new laser-sintering techniques is a promising alternative for metal ceramic restorations. Further research is needed before its use can be advocated in the dental laboratory.

Evaluation of the flexural strength of dual-cure composite resin cements.

The aim of this study was to evaluate of flexural strength of some adhesive resin cements. Three dual-cure composite resin cements (Nexus 3; Variolink II, Panavia F) were prepared. The manufacturer's mixing directions for the cements were followed. Adhesive resin cement was mixed, placed in the rectangular portion of the mold. Fifteen specimens were prepared for each cements. The cements were light-activated with light lamp for 40 s on both and top and bottom surfaces. The each cement specimens were divided into three groups according to time of storage and stored in distilled water for 24 h, 15, and 30 days. Total 45 specimens were stored at 37°C (98.6 0F) in distilled water for 24 h, 15, and 30 days prior to tests. The flexural strength was tested with a universal testing machine at a crosshead speed of 0.5 mm/min (0.02 in.) The maximum load was recorded as MPa. The results were analyzed by Analysis of Variance and Duncan test. The Panavia F resin cements content Bisphenol A was showed the highest flexural strength (80.80 MPa) (11.71 ksi) for 24 h. The lowest flexural strength was observed in Nexus 3 (51.00 MPa) (7.39 ksi). It was found significant interaction of material and time (p < 0.05). The types of cement and time of storage was statistically significant on the flexural strengths (p < 0.001).

Microtensile bond strength of resin cement to a feldspathic ceramic.

OBJECTIVE: The purpose of this study was to evaluate the microtensile bond strength of resin cement to a feldspathic ceramic after treating the surface with (a) hydrofluoric (HF) acid, (b) air abrasion, (c) Er:YAG laser irradiation, (d) Nd:YAG laser irradiation, and (e) HF acid etching after either air abrasion or laser irradiation. BACKGROUND DATA: It is unknown whether the laser application or its combination with another treatment method can be used as a tool to roughen the surface of a feldspathic ceramic in order to increase the bond strength between the resin cement and ceramic surface. MATERIALS AND METHODS: Forty feldspathic ceramic blocks (Ceramco(TM)) were prepared and divided into eight equal groups (n = 5) according to the following surface treatments: no treatment; etching with 9.5% HF acid; air abrasion with 50 µm Al(2)O(3); Er:YAG laser irradiation; Nd:YAG laser irradiation; air abrasion plus acid etching; Er:YAG laser plus acid etching; and Nd:YAG laser plus acid etching. After surface treatment, a silane-coupling agent and resin cement (Panavia F(TM)) were applied to each block. After storing for 24 h at 37°C and thermocycling between 5°C and 55°C for 1000 cycles, the microtensile bond strength of each specimen was measured. RESULTS: The highest bond strength was obtained from HF acid etching. HF acid etching after each laser irradiation significantly increased the bond strength (p < 0.05). However, HF acid etching after air abrasion decreased bond strength when compared to air abrasion alone. CONCLUSIONS: HF acid etching is the most effective surface treatment method for a feldspathic ceramic. However, laser irradiation with either the Er:YAG or Nd:YAG laser is not an adequate method for improving the bond strength of Panavia F. The laser application should be combined with HF acid etching.

An investigation of thermal changes of various permanent dental cements.

The aim of this study was to investigate and compare the temperature rises which occurred during the setting reactions of different permanent cements used to lute fixed partial prosthodontics. In this study, four cements were used. They were mixed in three different proportions: according to manufacturers' recommendations, at doubled powder ratio, and at doubled liquid ratio. With a thermocouple, the temperature rises which occurred during the setting reactions were measured. For each proportion, the measurement was repeated five times such that a total of 60 measurements were done for the four different cements. Data were analyzed using analysis of variance (ANOVA). ANOVA results showed that cement type and the interaction between cement type and the powder-liquid ratio were statistically significant factors (p<0.001). Similarly, the powder-liquid ratio was a statistically significant (p<0.01) factor. Among the dental cements tested, zinc phosphate cement showed the highest temperature rise during setting reaction, whereas glass ionomer cement showed the lowest.

Effects of different solutions on the surface hardness of composite resin materials.

In this study, the surface hardness of five light-cured composite resins were evaluated, namely: filled (Estelite), nanofil (AElite), unfilled (Valux Plus), hybrid (Tetric ceram), and Ormocer-based (Admira) composite resins. The microhardness values of composite specimens were measured at the top and bottom surfaces after 24 hours or 30 days of immersion in different solutions (tea, coffee, Turkish coffee, mouthwash, cola, and distilled water). Comparisons were made with univariate analysis of variance and Duncan's multiple range test. It was found that rough specimens of reinforced nano-hybrid composite material immersed in cola for 30 days had the lowest surface hardness (33.20), whereas rough specimens of hybrid composite material immersed in cola for 24 hours had the highest surface hardness (156.00). In both tea and coffee, the top surfaces tended to be harder than the bottom ones. In conclusion, the five different materials exhibited different hardnesses, and that the hardness values of composite materials were statistically different in different immersion solutions.

The investigation of solubility values,water sorption and bond strength of auto-polymerising and heat-polymerising acrylic resin materials.

In this study the solubility, water sorption and the bond strength of auto-polymerising and heat-polymerising acrylic resins were investigated. Two auto-polymerising and five heat polymerising acrylic resin materials were used for this study. Thirty-five specimens were prepared (50 mm in diameter and 0.5 +/- 0.01 in thickness) for water sorption and solubility tests. In order to examine bond strength, specimens were prepared in 2.5 x 10 x 64 mm dimensions. These specimens were repaired with QC and major repair acrylic. Some specimens were kept in distilled water for 50 hours, and others for 30 days. The strength of the bond was measured by a Pull-Compress device. As a result of the variance analysis; water sorption, solubility and the bond strength between acrylic resins were identified as statistically significant (P < 0.001). The water sorption of the major acrylic resin specimens were lower than the other materials (P < 0.001).

Evaluation of cobalt, chromium, and nickel concentrations in plasma and blood of patients with removable partial dentures.

This study assessed the plasma and blood concentrations of Cr, Co, and Ni among subjects using removable partial dentures. A comparison was made between subjects with and without RPD treatment history. Control group consisted of 10 healthy individuals without dentures. Concentrations of Cr, Co, and Ni in subjects' plasma and blood were measured with an atomic absorption spectrophotometer. Data were statistically analyzed by ANOVA, and multiple comparison test (alpha = 0.05) was used to identify significant differences between groups. RPD use had a significant effect on the concentrations of Cr (P < 0.001) and Ni (P < 0.05) in blood and plasma. As such, there were statistically significant differences between the control and study groups for the concentrations of Cr and Ni in blood and plasma. However, RPD use exhibited no significant effect on Co concentration in plasma. In conclusion, the use of removable partial dentures with metal frameworks led to an increase in the concentrations of Cr and Ni in both blood and plasma.

An investigation of pH changes of various cements.

OBJECTIVE: In this study, the time-related pH changes that occur in cements having different structures were observed. METHOD AND MATERIALS: Eight cements consisting of four permanent and four temporary cements were used. The materials were prepared according to manufacturers' instructions. The materials were used in 0.100 +/- 0.02-g increments, with the purpose of standardizing the effect of massive differences. The 80 total specimens, including 10 from each cement type, were prepared, and the pH value of the distilled water was measured at 3,10,30,60, and 120 minutes, and then again 24 hours later. RESULTS: Analysis of variance showed the relation between the kind of cement and its pH change during the course of the study was statistically significant. CONCLUSION: Though temporary cements indicated neutral pH from the beginning of the study, the acidity of the other cements changed with time and took values approximate to neutral pH within 24 hours.