Evaluation of Shade Reproducibility and Mechanical Properties of Preshaded and Manually Shaded Monolithic Zirconia.

OBJECTIVES: This study aimed to investigate the effect of manual coloring of blank monolithic zirconia blocks of four materials on their shade reproducibility, flexural strength, and surface roughness as compared with preshaded blocks of the same material. METHODS AND MATERIALS: Eight disc-shaped specimens (diameter=12mm; height=2mm) and eight bar-shaped specimens (25×2×2 mm) were milled from the shaded and non-shaded blocks of the four zirconia systems: Ceramill, Kerox, White Peaks, and Dental Direkt. In total, 128 specimens were fabricated. The non-shaded specimens of each system were coloured according to A2 shade. The surface roughness (Ra) was measured using a contact profilometer. Color difference was calculated according to the CIEDE2000 formula. The bar-shaped specimens were loaded to fracture following three-point bend testing at 1 mm/minute crosshead speed. Data were analysed following one-way analysis of variance (ANOVA), and the Tukey post-hoc test (p=0.05). RESULTS: Manual-coloring affected the surface roughness, color difference, and flexural strength of three materials in comparison to their preshaded blocks (p<0.05). White Peaks was not affected (p>0.05). Ra values ranged from 1.1-1.9; three materials were not affected (p>0.05). Kerox preshaded blocks were the smoothest (p<0.05) but became the roughest once colored (p<0.05). White Peaks and Dental Direkt materials had preshaded blocks matching the A2 guide-tab (p>0.05). DE was perceptible and unacceptable for the preshaded and manually shaded blocks of all materials tested (ΔE>1.8). While manual coloring reduced flexural strength of Ceramill and Dental Direkt (p<0.05), flexural strength was retained by Kerox and White Peaks (p>0.05). CONCLUSIONS: White Peaks was not affected by the coloring technique. Coloring had negative effects on Ceramill flexural strength and color reproducibility.

Surface characteristics and microbial adherence ability of modified polymethylmethacrylate by fluoridated glass fillers.

BACKGROUND: The current study objectives were to evaluate the influence of fluoridated glass fillers loading on the surface roughness, wettability, and adherence of candida and bacteria with and without saliva presence to a polymethylmethacrylate (PMMA) denture base material surface. METHODS: Four concentrations of fluoridated glass fillers were added to PMMA: 1%, 2.5%, 5% and 10% by weight pre-polymerization and 0% was the control. Discs of each concentration were fabricated (n = 5 for each variable). Surface roughness (Ra ) was measured using atomic force microscopy (AFM). Wettability was assessed by measuring the contact angle of a sessile drop of water. Specimens were incubated with Candida albicans, or Streptococcus mutans with and without saliva coating. Adherence was presented as a percentage of the colonized surface area, counted using an optical microscope at x100 magnification. RESULTS: The 10% group showed significantly greater roughness than the control and 1% groups; however, no significant differences in contact angle values were detected. The microbial adhesion was inversely proportional to the fluoridated glass fillers concentration where 10% concentration significantly decreased candidal and bacterial adhesion compared to others. Saliva coating significantly decreased microbial adhesion. CONCLUSIONS: It was concluded that fluoridated glass fillers could decrease microbial adhesion to acrylic denture base without adversely affecting surface properties.

Fluoride release, recharge and flexural properties of polymethylmethacrylate containing fluoridated glass fillers.

BACKGROUND: The purpose of this study was to investigate the effect of fluoridated glass fillers on fluoride release, recharge and the flexural properties of modified polymethylmethacrylate (PMMA). METHODS: Specimens of PMMA denture base material with various loading of fluoridated glass fillers (0%, 1%, 2.5%, 5% and 10% by weight) were prepared. Flexural properties were evaluated on rectangular specimens (n = 10) aged in deionized water after 24 hours, 1 and 3 months. Disc specimens (n = 10) were aged for 43 days in deionized water and lactic acid (pH 4.0) and fluoride release was measured at numerous intervals. After ageing, specimens were recharged and fluoride re-release was recorded at 1, 3 and 7 days after recharge. RESULTS: Samples containing 2.5%, 5% and 10% glass fillers showed significantly (p < 0.05) greater levels of fluoride release compared with the control and 1% glass fillers specimens. All experimental specimens exhibited fluoride release in both media. The flexural strength of specimens decreased in proportion to the percentage filler inclusion with the modulus of elasticity values remaining within ISO Standard 1567. CONCLUSIONS: The modified PMMA with fluoridated glass fillers has the ability to release and re-release fluoride ion. Flexural strength decreased as glass filler uploading increased.

The effect of laser irradiation on retention of full cast crowns.

The objective of this work was to determine the effect on the retention force of full cast crowns cemented on short tooth preparations after preparation of dentine with an erbium, chromium: yttrium scandium gallium garnet (Er, Cr:YSGG) laser at different sub-ablative power settings. Thirty teeth were prepared for full cast crowns using a milling machine. The surface area for all preparations was measured. The surfaces of the preparations were irradiated with 0 (control), 0.25 and 0.75 W laser. The crowns were cemented with self-cure resin cement and tested for retention on a Hounsfield Tensometer machine. The 0.75 W power setting produced the highest failure load value (346.2 +/- 86.1 N) and was significantly higher than the other groups. There were no significant differences between the 0.25 W and 0 W control groups

Prevalence of temporomandibular disorders' signs and symptoms and chewing ability in patients with prosthodontic prostheses.

This study aimed to determine the prevalence of temporomandibular disorders among patients wearing dental prostheses including complete and fixed partial dentures and to evaluate the chewing ability of those patients. Questionnaire and clinical examinations were used to assess those objectives. Fifty six percent of all examined subjects exhibited at least one sign or symptom of temporomandibular disorders while 8.0% bad moderate symptoms and 10% had severe symptoms. Patients with fixed partial dentures had a significantly higher prevalence of temporomandibular disorders signs than both complete dentures and dentate. The fixed partial denture group and dentate group exhibited significantly higher chewing ability than did the complete denture group. Therefore, the type of prosthesis correlated significantly with chewing ability.

The dimensional accuracy of four impression techniques with the use of addition silicone impression materials.

OBJECTIVE: The aim of this study was to assess the influence of impression technique selection on the dimensional accuracy of the produced casts. METHODOLOGY: Four impression techniques (single-stage, two-stage, monophase, and heavy/wash technique) were used to make addition silicone impressions of a phantom head maxillary jaw. The impression materials used were Aquasil, Extrude, and Imprint. Measurements on casts were made for the inter-abutment distances to assess dimensional accuracy. RESULTS: There was a significant difference (p < 0.05) for the anteroposterior distances with the single-stage technique. The crossarch distances were slightly increased compared with the master model for all techniques, but significant statistical differences were only recorded for the single-stage technique and the monophase technique. The monophase technique demonstrated irregular results. The heavy/wash technique showed no significant differences for all the measurements compared with the standard model. CONCLUSION: The results suggest that the selection of impression technique is an important factor that can affect the dimensional accuracy of the subsequent models which are used for indirect restorations.

Immediate resin-bonded bridgework: results of a medium-term clinical follow-up study.

A total of 21 immediate resin-bonded bridges were inserted under controlled and standardized clinical conditions and evaluated over a period of 35 months. During the evaluation period, two bridges debonded (9.5%). The debonded bridges were re-cemented successfully. This low incidence of debonding indicates that this simple alternative procedure for the immediate replacement of a single unsaveable tooth was satisfactory. The subjects included in this study expressed their satisfaction with this form of treatment.

Surface roughness and wettability of enamel and dentine surfaces prepared with different dental burs.

The aim of dental adhesive restorations is to produce a long lasting union between the restoration and the tooth structure. This bond depends on many variables including the geometry of the preparation and the type of bonding agent or luting cement. It is therefore suggested that the topography of the tooth surface may influence the wettability and the bonding quality of adhesive systems. This study measured the surface roughness and wettability of enamel and dentine after preparation with different dental burs. The mesial and distal surfaces of 15 extracted sound human premolar teeth were prepared with a tungsten carbide crown bur, a diamond bur and a tungsten carbide finishing bur and finished in enamel or dentin, respectively. The prepared surfaces were analysed with a surface profilometer and scanning electron microscopy (SEM). The contact angle of distilled water on each of the prepared surfaces was used as the measure of wettability. The differences in average surface roughness (Ra) were significant between the rotary instrument groups, as revealed by a two-way ANOVA test. No differences were detected between enamel and dentine surfaces prepared with the same type of dental bur. The smoothest surfaces were those completed with tungsten carbide finishing burs. The diamond bur preparations were intermediate in the roughness assessment and the tungsten carbide crown burs gave the roughest surfaces. There were no significant differences in the contact angle measurements for the various groups. It was concluded that the surface roughness of enamel and dentine prepared by different rotary instruments had no significant influence on the wettability of distilled water on these surfaces.

A microbiological investigation following the disinfection of alginate and addition cured silicone rubber impression materials.

The antimicrobial efficacy of four commercially available disinfectants (Haz-tabs, chlorhexidine, Virkon and C&J Algisept Spray) was investigated. It was shown that all were effective in decontaminating the impressions whilst those placed only in sterile water, used as a control, showed variable levels of bacterial growth. Moreover, alginate appeared to carry significantly higher numbers of bacteria than addition cured silicone rubber.

The effect of disinfecting alginate and addition cured silicone rubber impression materials on the physical properties of impressions and resultant casts.

Four commercially available disinfectants were tested and the dimensional stability and detail reproduction of impressions and their resultant casts were measured according to ANSI/ISO specifications. Results showed that alginate impressions immersed in chlorhexidine exhibited considerable dimensional change if not poured immediately. Moreover, alginate impressions soaked in a paraldehyde agent (Virkon) for more than 2 minutes produced casts of inferior surface quality whilst those sprayed and left in contact with phenol derivatives (C&J Spray) for 30 minutes resulted in casts which demonstrated statistically and clinically significant dimensional changes. Addition cured silicone impressions exhibited minimal dimensional change regardless of the disinfection regime employed and the resultant casts were accurate with acceptable surface quality.