Measurements of surface scale changes in different denture base materials by stereophotogrammetric technique.

Background. This study aimed to evaluate the surface scale changes in the denture base material using different polymerization techniques, such as heat-cure/pressure polymerization system and injection molding technique with the stereophotogrammetric technique. The function of a complete denture is related to the adaptation of its base to the supporting areas. Proper adaptation of the base depends on the stability and retention of dentures. The surface scale changes of dentures during processing and in service are of great importance since they affect the denture base material's fit. Methods. This study focused on the use of a computer-assisted stereophotogrammetric method for measuring changes in the volume of three different denture base resins of an edentulous maxillary ridge. A stone master model simulating the shape of an edentulous maxillary arch was used to prepare three groups of denture base resins. The stereophotographs were evaluated to determine the surface scale differences of maxillary jaws. Results. The results showed no significant differences between the denture borders for three denture base materials (P > 0.05). Conclusion. In the evaluation made using this technique, no significant difference was found in the different polymerization techniques in terms of surface scale changes for three denture base materials. Stereophotogrammetry, especially the digital stereophotogrammetric technique, has several useful research applications in prosthodontics.

The accuracy of the prediction models for surface roughness and micro hardness of denture teeth.

The paper aimed to compare the performance of artificial neural network (ANN) model with the results of in vitro experiments. For these experiments, maxillary molars of four different denture teeth were subjected to tea, coffee, cola, cherry juice, distilled water. Vickers microhardness and surface roughness values were measured. Subsequently, ANN model for the prediction of microhardness and surface roughness of different denture teeth were examined. A back-propagation ANN has been used to develop a model relating to the amount of microhardness and surface roughness. The independent variables of the model are distilled water, tea, filtered coffee, cola, cherry juice, time and denture teeth. Microhardness and surface roughness were chosen as the dependent variables. According to the results, a neural network architecture having one input layer with ten neurons, two hidden layers with six neurons, one output layer with two neurons and an epoch size of 48 gives better prediction. Prediction models for dental materials could also be supportive for in vitro studies.

Effect of atmospheric plasma versus conventional surface treatments on the adhesion capability between self-adhesive resin cement and titanium surface.

PURPOSE: The aim of this study was to evaluate the effects of atmospheric plasma (APL) versus conventional surface treatments on the adhesion of self-adhesive resin cement to Ti-6Al-4V alloy. MATERIALS AND METHODS: Sixty plates of machined titanium (Ti) discs were divided into five groups (n=12): 1) Untreated (CNT); 2) Sandblasted (SAB); 3) Tribochemically treated (ROC); 4) Tungsten CarbideBur (TCB); 5) APL treated (APL). SEM analysis and surface roughness (Ra) measurements were performed. Self-adhesive resin cement was bonded to the Ti surfaces and shear bond strength (SBS) tests, Ra and failure mode examinations were carried out. Data were analyzed by one-way analysis of variance and chi-squared test. RESULTS: The lowest SBS value was obtained with CNT and was significantly different from all other groups except for APL. The ROC showed the highest SBS and Ra values of all the groups. CONCLUSION: It was concluded that the effect of APL on SBS and Ra was not sufficient and it may not be a potential for promoting adhesion to titanium.

Effect of toothbrushing on color changes of esthetic restorative materials.

PURPOSE: The aim of this study was to evaluate the effects of various drinks and toothbrushing on the color changes of esthetic restorative materials used in pediatric dentistry. MATERIALS AND METHODS: Forty specimens were prepared from each of three restorative materials (compomer [Dyract AP], glass ionomer cement [Ionofil Molar AC, Voco], composite resin [Filtek Z 250]). Specimens were divided into four groups for immersion in three different staining solutions (cherry juice, cola, chocolate milk) and distilled water. Each group was subdivided into brushing and non-brushing groups. The specimens in the brushing subgroups were brushed with toothpaste once a day using an electric toothbrush. Color was measured using a colorimeter, and color changes were calculated between baseline and 1, 7, 30, 60 days. Data was analyzed using Kruskal-Wallis, Mann-Whitney U, Wilcoxon, and Wilcoxon Signed Rank tests. RESULTS: All the solutions evaluated yielded color changes, and these changes were significantly greater for composite resin than for glass ionomer cement or compomer (p < 0.006). Brushing significantly decreased the color changes of restorative materials (p < 0.004). CONCLUSION: Brushing significantly influenced the color stability of esthetic restorative materials. The results of this study also showed that glass ionomer cements and compomers had higher color stability than composite resins. CLINICAL SIGNIFICANCE: The color stability values after brushing may better reflect the discoloration of the esthetic restorative materials. Any color stability study model should consider the effects of toothbrushing that can remove the adsorbed colorants. The results of this study also showed that glass ionomer cements and compomers can be used in anterior restorations of children with their higher color stability than composite resins.

Comparison of internal fit between implant abutments and cast metal crowns vs laser-sintered crowns.

AIM: A common problem related to cemented single crowns is the internal misfit, which may cause inadequate retention, especially when seated on the implant abutment. The aim of this study was to compare the internal fit of Co-Cr crowns using a traditional lost-wax casting technique from laser-sintered Co-Cr alloy crowns. MATERIALS AND METHODS: Twelve metallic crowns per each technique were fabricated. The effect of the thickness of cement, originated internal gap was evaluated. Crowns were cemented on the implant abutments with resin cement, and the internal fit of crowns was measured at five areas with an optical microscope. The data were analyzed, and the means were compared with a t-test (p<0.05). RESULTS: The internal gap width measurements for the laser-sintered group (min. 52.19 ± 11.61 µm and max. 140.01 ± 31.84 µm) indicated the presence of a significantly closed internal gap compared to the crowns obtained through the lost wax method (min. 65.50 ± 9.54 µm and max. 313.46 ± 48.12 µm). CONCLUSION: The fit of the metal crown likely varies with the fabrication technique. The use of techniques that enable the adjustment of crown parameters, such as the laser sintering technique, maintains the desired fit between casting and implant abutments. CLINICAL SIGNIFICANCE: This study investigated which technique affects the internal fit of cemented implant-supported crowns, comparing the use of lost wax casting and laser-sintered metal dental alloys. The results of this study indicate that the use of laser-sintered crowns can improve for crown accuracy.

Evaluation of retention of cemented laser-sintered crowns on unmodified straight narrow implant abutments.

PURPOSE: A common problem with cemented crowns is inadequate retention at the crown-abutment interface. The aim of this study was to compare the retention of new laser-sintered cobalt-chromium alloy crowns to the retention of cobalt-chromium alloy crowns fabricated with a traditional casting technique with and without an alloy primer. MATERIALS AND METHODS: Twenty-four metallic crowns per casting technique were fabricated, and surface roughness values were recorded with a profilometer. Alloy primer was applied to half the specimens, and all crowns were luted with resin cement. After 24 hours, specimens were subjected to tensile force application with a universal testing machine. The effect of the cement amount was evaluated with an analytic balance. The results were compared using the Kruskal-Wallis multiple-comparison test. The Spearman correlation was used to determine correlations between crown retention and cement weight. RESULTS: The laser-sintered crowns (2.72 µm) were rougher than conventionally cast crowns. The mean load to failure values were as follows: 455.10 ± 192.69 Ncm for conventional crowns, 565.52 ± 112.87 Ncm for conventional crowns with alloy primer, 534.78 ± 130.15 Ncm for laser-sintered crowns, and 678.60 ± 212.83 Ncm for laser-sintered crowns with alloy primer. Laser-sintered crowns (10.10 ± 2.15 mg) showed a significant difference in terms of cement weight compared with cast crowns. In addition, negative correlations were found for retention and cement weight between all groups, except for the laser-sintered group without alloy primer. CONCLUSIONS: Retentive forces were significantly higher for laser-sintered crowns than for conventionally cast crowns. An increase in the surface roughness and the application of alloy primers led to an increase in the adhesive bonding of resin cements to metal alloys. It was concluded that a reduction in cement weight improved retention.

Nanotechnology and dentistry.

Nanotechnology deals with the physical, chemical, and biological properties of structures and their components at nanoscale dimensions. Nanotechnology is based on the concept of creating functional structures by controlling atoms and molecules on a one-by-one basis. The use of this technology will allow many developments in the health sciences as well as in materials science, bio-technology, electronic and computer technology, aviation, and space exploration. With developments in materials science and biotechnology, nanotechnology is especially anticipated to provide advances in dentistry and innovations in oral health-related diagnostic and therapeutic methods.

Effect of at-home whitening strips on the surface roughness and color of a composite and an ormocer restorative material.

PURPOSE: Oxygenating agents like carbamide peroxide or H(2) O(2) are commonly used whitening agents. They have varying influence on the color and surface roughness of resin-based restorative materials and teeth. The aim of this study was to evaluate the effect of an at-home peroxide whitening agent applied through a whitening strip on the color and surface roughness of a nanofilled composite resin and an ormocer-based resin. MATERIALS AND METHODS: Disc-shaped (2 mm thick, 10 mm diameter) nanofilled resin composite (n = 10) and ormocer (n = 10) specimens were prepared. All specimens were treated with a whitening strip. Whitening procedures were performed applying a 6.5% hydrogen peroxide whitening strip (Crest White Strips Professional) for 30 minutes twice each day for a period of 21 consecutive days. During the test intervals, the specimens were rinsed under running distilled water for 1 minute to remove the whitening agents and immersed in 37°C distilled water until the next treatment. Surface roughness and color of the specimens were measured with a profilometer and a colorimeter, respectively, before and after whitening. Color changes were calculated (ΔE) using L*, a*, and b* coordinates. Repeated measures of variance analysis and Duncan test were used for statistical evaluation (α= 0.05). RESULTS: The average surface roughness of composite increased from 1.4 Ra to 2.0 Ra, and from 0.8 Ra to 0.9 Ra for the ormocer material; however, these changes in roughness after whitening were not significant (p > 0.05). Also, when two materials were compared, the surface roughness of restorative materials was not different before and after whitening (p > 0.05). L* and b* values for each material changed significantly after whitening (p < 0.05). ΔE values (before/after whitening) calculated for composite (11.9) and ormocer (16.1) were not significantly different from each other (p > 0.05). CONCLUSIONS: The tested whitening agent did not affect the surface roughness of either resin-based restorative material. Both materials became brighter after whitening. The behavior of the materials in the yellow/blue axis was opposite to each other after whitening. Each material had clinically unacceptable color change after whitening (ΔE > 5.5); however, the magnitude of the color change of materials was similar (p > 0.05). According to the results of this study, with the use of materials tested, patients should be advised that existing composite restorations may bleach along with the natural teeth, and replacement of these restorations after whitening may not be required.

Effect of bleaching agents and whitening dentifrices on the surface roughness of human teeth enamel.

OBJECTIVE: The aim of this in vitro study was to evaluate the surface roughness of human enamel bleached with 10% carbamide peroxide or 10% hydrogen peroxide bleaching agents at different times and also subjected to different superficial cleaning treatments. MATERIALS AND METHODS: One hundred and forty flat enamel samples were divided into 14 groups, Group 1-Group 14 (G1-G14). G1-G7 were treated with 10% carbamide peroxide and different dentifrices, G8-G14 were treated with 10% hydrogen peroxide and different dentifrices (G1 and G8: not brushed as control groups; G2 and G9: brushed with Ipana® toothpaste; G3 and G10: brushed with Clinomyn® toothpaste; G4 and G11: brushed with Moos Dent® toothpaste; G5 and G12: brushed with Signal® toothpaste; G6 and G13: brushed with Colgate® toothpaste; G7 and G14: brushed without dentifrice). A profilometer was used to measure average roughness values of the initial surface roughness and at each 7-day-interval. The bleaching was performed for 6 h a day and the surface cleaning treatment was performed 3-times a day, 2 min each time, for 4 weeks. The samples were stored in distilled water during the test period. RESULTS: Statistical analysis revealed significant differences in surface roughness values over time for all groups except G1 and G8 (not brushed). The results of the surface roughness of all groups were nearly the same. CONCLUSIONS: The bleaching with 10% hydrogen peroxide and 10% carbamide peroxide did not alter the enamel surface roughness, but when the bleaching treatment was performed combined with abrasive dentifrices, a significant increase in roughness values was observed.

Effects of Er:YAG laser treatments on surface roughness of base metal alloys.

We investigated the effects of different Er:YAG laser treatments on the surface roughness of base metal alloys. A total of 36 specimens were prepared of two base metal alloys (Wiron 99, Bellabond plus). The surfaces of the specimens were standardized by gradual wet grinding with 320-, 600-, 800- and 1,000-grit silicon carbide paper for 10 s each on a grinding machine at 300 rpm. Specimens of each alloy were randomly divided into six groups (n = 6) comprising a control group (group C), a group sandblasted with Al(2)O(3) powder at 60 psi for 10 s through a nozzle at a distance of 10 mm (group S), and four Er:YAG laser (Fotona AT) treatment groups. The laser treatment groups were as follows: 500 mJ, 10 Hz, 100 µs (group 500MSP); 500 mJ, 10 Hz, 300 µs (group 500SP); 400 mJ, 10 Hz, 100 µs (group 400MSP); and 400 mJ, 10 Hz, 300 µs (group 400SP). Surface roughness measurements (Ra) were performed using a profilometer. The data were analysed by two-way ANOVA, and mean values were compared using Tukey's HSD test (α = 0.05). According to the two-way ANOVA results, the base metal alloys and interaction between base metal alloy and surface treatment were not statistically significant different (p > 0.05), the surface treatments were significantly different (p < 0.0001). For the two base metal alloy groups, no significant differences were observed among the control, 400MSP, and 400SP groups (p = 0.912), and these groups demonstrated the lowest Ra values. The highest Ra value was observed in group S (p < 0.05). Er:YAG laser treatment at 400 and 500 mJ/10 Hz is not an alternative method for surface roughening of base metal alloys.

Effects of air-polishing powders on color stability of composite resins

OBJECTIVES: The purpose of this study was to investigate the effect of different air-polishing powders on the color stability of different types of composite resin restorative materials. MATERIAL AND METHODS: Thirty cylindrical specimens (15×2 mm) were prepared for each of 7 composite resin restorative materials. All specimens were polished with a series of aluminum oxide polishing discs (Sof-Lex). The prepared specimens of each composite resin were randomly divided into 3 groups of 10 specimens each, for control (Group-C) and two air-powder applications (Group-CP: Cavitron Prophy-Jet; Group-PS: Sirona ProSmile prophylaxis powder). A standard air-polishing unit (ProSmile Handly) was used. All specimens were air-powdered for 10 s at 4-bar pressure. The distance of the spray nosel from the specimens was approximately 10 mm and angulation of the nosel was 90°. Specimens were stored in 100 mL of coffee (Nescafe Classic) for 24 h at 37°C. Color measurement of all specimens was recorded before and after exposure to staining agent with a colorimeter (Minolta CR-300). Color differences (∆E*) between the 2 color measurements (baseline and after 24 h storage) were calculated. The data were analyzed with a 2-way ANOVA test, and mean values were compared by the Tukey HSD test (p<0.05). RESULTS: According to the 2-way ANOVA results, composite resin restorative materials, air-polishing powders, and their interaction were statistically significant (p<0.05) For Aelite Aesthetic Enemal, Filtek Z250, Grandio, CeramX Mono, and Quixfil composite resin restorative materials, no significant difference was observed between Group-PS and Group-CP (p>.05) and these groups demonstrated the highest ∆E* values. For Filtek Silorane and IntenS, the highest ∆E* values were observed in Group-PS. The lowest ∆E* values for all composite resin groups were observed in Group-C. When comparing the 7 composite resin restorative materials, Aelite Aesthetic Enemal demonstrated significantly less ∆E* values than the other composite resins tested. The highest ∆E* values were observed in Quixfil. CONCLUSION: Except for Quixfil, all control groups of composite resins that were polished Sof-Lex exhibited clinically acceptable ∆E values (<3.7). Air-polishing applications increased the color change for all composite resin restorative materials tested. Composite restorations may require re-polishing after air-polishing.

Effects of air-polishing powders on color stability of composite resins.

OBJECTIVES: The purpose of this study was to investigate the effect of different air-polishing powders on the color stability of different types of composite resin restorative materials. MATERIAL AND METHODS: Thirty cylindrical specimens (15×2 mm) were prepared for each of 7 composite resin restorative materials. All specimens were polished with a series of aluminum oxide polishing discs (Sof-Lex). The prepared specimens of each composite resin were randomly divided into 3 groups of 10 specimens each, for control (Group-C) and two air-powder applications (Group-CP: Cavitron Prophy-Jet; Group-PS: Sirona ProSmile prophylaxis powder). A standard air-polishing unit (ProSmile Handly) was used. All specimens were air-powdered for 10 s at 4-bar pressure. The distance of the spray nosel from the specimens was approximately 10 mm and angulation of the nosel was 90°. Specimens were stored in 100 mL of coffee (Nescafe Classic) for 24 h at 37°C. Color measurement of all specimens was recorded before and after exposure to staining agent with a colorimeter (Minolta CR-300). Color differences (∆E*) between the 2 color measurements (baseline and after 24 h storage) were calculated. The data were analyzed with a 2-way ANOVA test, and mean values were compared by the Tukey HSD test (p<0.05). RESULTS: According to the 2-way ANOVA results, composite resin restorative materials, air-polishing powders, and their interaction were statistically significant (p<0.05) For Aelite Aesthetic Enemal, Filtek Z250, Grandio, CeramX Mono, and Quixfil composite resin restorative materials, no significant difference was observed between Group-PS and Group-CP (p>.05) and these groups demonstrated the highest ∆E* values. For Filtek Silorane and IntenS, the highest ∆E* values were observed in Group-PS. The lowest ∆E* values for all composite resin groups were observed in Group-C. When comparing the 7 composite resin restorative materials, Aelite Aesthetic Enemal demonstrated significantly less ∆E* values than the other composite resins tested. The highest ∆E* values were observed in Quixfil. CONCLUSION: Except for Quixfil, all control groups of composite resins that were polished Sof-Lex exhibited clinically acceptable ∆E values (<3.7). Air-polishing applications increased the color change for all composite resin restorative materials tested. Composite restorations may require re-polishing after air-polishing.

Profilometer evaluation of the effect of various polishing methods on the surface roughness in dental ceramics of different structures subjected to repeated firings.

OBJECTIVE: To evaluate the changes in surface roughness of dental ceramics with various substances/instruments and polishing methods during the course of repeated firings. METHOD AND MATERIALS: Three types of dental ceramic (IPS Classic, Empress Esthetic, and Empress 2 [all by Ivoclar Vivadent]) were used to form three groups, respectively. The samples from the first group were subjected to glaze, the -second group to natural glaze, and the third group to mechanical polishing. As many as seven firings were performed on each sample, and surface roughness measurements of the samples were carried out at certain stages. Statistical evaluation was performed through repeated-measures ANOVA, and the Duncan test proved that the differences among the mean values were by no means a coincidence. RESULTS: The interaction among the substrates, the method used, and the time was statistically significant (P < .05). Mechanical polishing significantly increased surface roughness (P < .05), and the greater number of firings significantly decreased the amount of surface roughness (P < .05). CONCLUSION: In terms of surface roughness, the best method available is the glaze method and the best material is IPS Classic. The mechanical polishing process generates rough surfaces. Repeated firings should be avoided as much as possible because they have a destructive effect on the glaze layer and deform the surface.

The methods for the generation of smoothness in dental ceramics.

Occlusal corrections, acidulated phosphate fluoride applications, carbonated beverages, or air-powder abrasion procedures can roughen the surface of restorations. Once deteriorated, porcelain surfaces need to be repolished. These surfaces can be reglazed or polished through various intraoral and extraoral polishing kits. Although clinicians often seek studies on the effect of repeated firings on coherence between metal and ceramic, the color of the porcelain, fluorescence, microstructure, and brightness, only a limited number of studies are available in the literature. This article reviews the available literature and presents methods for generating a smooth surface and assessing surface roughness. It also discusses the differences between glazing and mechanical polishing, highlighting the importance of mechanical polishing of dental ceramics.