Effect of Selected Luting Agents on the Retention of CAD/CAM Zirconia Crowns Under Cyclic Environmental Pressure.

OBJECTIVES: The aim of this study was to evaluate the retention strength of zirconia crowns luted with two types of resin cement under environmental pressure changes. MATERIALS AND METHODS: Thirty zirconia crowns were fabricated by using computer-aided design/computer-aided manufacturing (CAD/CAM) system and were cemented by Panavia F2.0 (PAN), hand-mixed RelyX Unicem (UNH), or auto-mix RelyX Unicem Aplicap (UNA) cements on the corresponding extracted human molars. The samples were randomly divided into three groups according to the cement type. After 3000 thermal cycles, the cemented crowns were subjected to 24 pressure cycles (0 to 5 atmospheres). The retention force (N) of the specimens was measured in a universal testing machine. To normalize the retentive force, the recorded force was divided by the surface area of each tooth for measuring the retentive strength (MPa). The mean retention strengths (and forces) of the groups were compared by using one-way analysis of variance (ANOVA) and Tukey's honest significant difference (HSD) test (α=0.05). The failure modes were also examined by using a stereomicroscope. RESULTS: The retention values related to the evaluated resin cements were significantly different; the UNA group showed the highest retention strength (6.45±0.35 MPa) followed by the UNH (4.99±0.47 MPa) and PAN (4.45±0.39 MPa, P<0.001) groups. The adhesive failure mode was predominant in all the groups. CONCLUSIONS: The choice of resin cements and their mixing methods, which lead to differences in porosity, may affect the retention strength of zirconia crowns.

The effect of aqueous media on the mechanical properties of fluorapatite-mullite glass-ceramics.

OBJECTIVES: To verify the effects of alternating thermal changes in aqueous media and chemical composition on mechanical properties of apatite-mullite glass-ceramics and to investigate concentration of ions eluted from glass-ceramics in aqueous media. MATERIALS AND METHODS: The glass compositions were from SiO2Al2O3P2O5CaOTiO2BaOZrO2CaF2 system. Glass-ceramics were prepared by heat-treating at 1100°C for 3h samples alternately immersed in water at 5 and 60°C. The 3-point bending strength (n=10) were determined using 3×4×25mm/bar and a universal testing machine, at a cross-head speed of 0.1mm/min. Vickers micro hardness were evaluated by applying a total of 15-20 indentations under a 100g load for 30s. Concentrations of ions eluted from glass-ceramics immersed in 60±5°C double distilled water were determined by ion chromatography. The toxicity of glass-ceramics was assessed by seeding the osteosarcoma cells (MG63) on powder for different days and their cell proliferation assessment was investigated by MTT assay. The data were analyzed using one way analysis of variance and the means were compared by Tukey's test (5% significance level). RESULTS: The highest flexural strength and hardness values after thermal changes belonged to TiO2 and ZrO2 containing glass-ceramics which contained lower amount of released ions. BaO containing glass-ceramic and sample with extra amount of silica showed the highest amount of reduction in their mechanical strength values. These additives enhanced the concentration of eluted ions in aqueous media. MTT results showed that glass-ceramics were almost equivalent concerning their in-vitro biological behavior. SIGNIFICANCE: Thermal changes and chemical compositions had significant effects on flexural strength and Vickers micro-hardness values.

Conventional versus implant-retained overlay dentures: a pilot study of masseter and anterior temporalis electromyography.

Implant-supported overlay dentures (ISODs) have been widely accepted among patients using conventional removable complete dentures (CRCDs). The present study aimed to comparatively study conventional and ISODs in terms of function and coordination of masticatory muscles using electromyograms. Included were 10 patients with ISODs (each with 2 implants in the intercanine area). The mean wave range (MWR) and frequency (MWF) of masseter and temporalis were recorded with (ISOD) and without (CRCD) ball attachments while maximum clenching on cotton rolls (cotton roll clenching), maximum intercuspal clenching (clenching), and unilateral gum chewing (chewing) using electromyography. Data were analyzed in SPAW using t-paired for matched groups and independent-sample t tests for unmatched ones. The MWF differences were not statistically significant with or without attachments (P > .05). Without attachments in place, the MWF of both masseter and temporalis muscles significantly decreased when patients clenched on cotton rolls (P = .01 and .02, respectively) and when chewing unilaterally (both P = .01). With attachments present, the right and left temporalis muscles did not show identical mean wave ranges while chewing (P = .01). Without attachments, this disharmony was seen in the left and right masseter muscles (P = .03). The MWR of masseter was higher in men while chewing with attachments (P = .02). Without attachments, the MWR of temporalis was higher in women while cotton roll clenching (P = .03) and chewing (P = .02). These findings are seemingly in favor of improved masticatory function and coordination in edentulous patients with the application of ISODs.

Effect of Resin Cement Mixing Method on the Retention Strength of a CAD/CAM Zirconia Crowns.

Several treatments have been suggested to improve the retention of zirconia-based restorations luted with different cements. Resin cements are believed to improve crown retention under certain circumstances. The aim of the present study was to examine the effect of three cements with different mixing methods on the retention of CAD/CAM zirconia crowns. Thirty extracted human molars were randomly divided into three groups and prepared for all-ceramic crowns (6° taper, 4-mm height and a 1.2 mm rounded shoulder finish line). A zirconia crown (Tizian CAD/CAM) was fabricated for each tooth. The crowns were air-abraded using airborne particles, adjusted, and cemented to the corresponding tooth with one of the following cements: Panavia F2 (PAN group), RelyX Unicem (UNH group) or RelyX Unicem Aplicap (UNA group). After 3,000 rounds of thermal cycling, retention was measured using a specific retentive jig and a universal testing machine. The retention strength was measured by dividing the retention force by the surface area of each tooth. The means of the pull-out test results for each group were compared using analysis of variance and Tukey's HSD test (α = 0.05). The mode of failure was examined using a stereomicroscope. The mean retention value was 6.45 (0.34) MPa for the UNA group, 4.99 MPa (0.47) for the UNH group, and 4.45 (0.39) for the PAN group; the differences among the three test groups were significant. A mixed failure was observed in 83.3 % of specimens, while no cohesive failure occurred in the crowns. Within the limitations of the present study, of the three tested cements, Relyx Unicem Aplicap cement was associated with the highest retention force for Tizian zirconia crowns.

Comparative Microflora Assessment of Natural Sulci vs. Deep and Shallow Implant Sulci in Partial Edentulousness.

The main cause of peri-implantitis and crestal bone resorption is bacterial infection. The present study aimed to comparatively assess the microbiological parameters in sulci around teeth and crowns supported by dental implants and also compare microbiological parameters around deep and shallow implant sulci. In this cross-sectional study, 34 partially edentulous patients with a total of 72 implants (22 deep vs. 50 shallow sulci) were included. Excluded were the patients with compromised systemic and periodontal health or smoking habits. All Implants (ITI) were at least 6 month in place covered by definite prostheses. Samples of gingival sulci were taken around teeth and implants with paper points and transported in Stuart Transport Medium. Samples were cultured and examined by dark field microscope to determine the microorganisms. Data were evaluated statistically in SPSS (v11.5) using chi-square test. Cocci G+, Cocci G-, Prevotella, Porphyromonas gingivalis, Bacteroid fragilis and Fusobacterium were found. The relative frequency of P. gingivalis was significantly higher in deep implant sulci compared to shallow implant sulci (p = 0.044) and natural sulci (p = 0.009). B. fragilis was also significantly more isolated from the deep implant sulci compared to shallow implant sulci (p = 0.001) and natural sulci (p = 0.064). Within the limitations of the present study, it may be concluded that peri-implantitis is more likely in deep sulci compared with shallow sulci in partial edentulousness.

One-year clinical and radiographic assessment of fluoride-enhanced implants on immediate non-functional loading in posterior maxilla and mandible: a pilot prospective clinical series study.

OBJECTIVE: The functional, esthetic, and psychological problems of 3-6 months of edentulousness and also discomfort of two-stage surgery might cause many patients to avoid implant-supported restorations. Therefore, the immediate non-functional loading protocol might be of value. METHODS: Twenty Astra Tech implants, 11-13 mm in length and 3.5-4 mm in diameter, were placed in maxillary and mandibular posterior sites of 10 healthy patients (two for each) with adequate alveolar bone. Temporary prostheses were relieved of all centric and eccentric contacts. Functional permanent prostheses were fabricated 13 weeks postoperatively. Clinical and radiographic examinations (including the implant stability quotient [ISQ]) were carried out immediately after implantation and 3, 6, and 12 months postoperatively. RESULTS: A 100% success rate was observed within 1 year. The plaque and bleeding indices, and pocket-probing depths did not show a significant change throughout the study. The ISQ values after implant insertion, and 3, 6, and 12 months later were respectively 76.6 ± 6.57, 77.6 ± 10.54, 81.8 ± 6.8, and 82.43 ± 3.7. The increase was statistically significant (P=0.004) according to the Freidman test. The ISQ values measured after the implant insertion were significantly different from those measured in the sixth and 12th postoperative months (P<0.008) according to the Wilcoxon signed-ranks test. The mean crestal alveolar bone resorption values in the third, sixth, and 12th postoperative months were 0.4 ± 0.55, 0.48 ± 0.37, and 0.48 ± 0.21 mm, respectively; and the change in marginal alveolar bone loss was not significant according to the Freidman test. CONCLUSION: Within the limitations of this pilot study, non-functional immediate loading might meet the expectations of both the patients and clinicians.

Polymerization behavior and thermal characteristics of two new composites at five temperatures: refrigeration to preheating.

PURPOSE: Heat of composite polymerization (HP) indicates setting efficacy and temperature increase of composite in clinical procedures. The purpose of this in vitro experimental study was to evaluate the effects of 5 temperatures on HP of two new composites. MATERIALS AND METHODS: From each material (Core Max II [CM] and King Dental [KD]), 5 groups of 5 specimens each were prepared and their total HPs (J/gr) were measured and recorded, at one of the constant temperatures 0℃, 15℃, 23℃, 37℃ and 60℃ (2 × 5 × 5 specimens) using a differential scanning calorimetry (DSC) analyzer. The data were analyzed using a two-way ANOVA, a Tukey's test, an independent-samples t-test, and a linear regression analysis (α=0.05). RESULTS: No polymerization reactions occurred at 0℃; then this temperature was excluded from statistical analyses. The mean HP of the remaining 20 KD specimens was 20.5 ± 14.9 J/gr, while it was 40.7 ± 12.9 J/gr for CM. The independent-samples t-test showed that there were significant differences between the HP of the two materials at the temperatures 15℃ (P=.0001), 23℃ (P=.0163), 37℃ (P=.0039), and 60℃ (P=.0106). Linear regression analysis showed statistically significant correlations between environment temperatures and HP of CM (R(2)=0.777). CONCLUSION: Using CM is advantageous over conventional composite because of its better polymerization capacity. However due to its high HP, further studies should assess its temperature increase in vivo. Preheating KD is recommended. Refrigerating composites can negatively affect their polymerization potential.

Effect of implants on maximum bite force in edentulous patients.

One of the main goals of prosthetic dentistry is to reconstruct the masticatory system. Replacing missing teeth by complete or partial denture is associated with decreased bite force and patient satisfaction. The aim of the present study was to measure the maximum bite force (MBF) and to evaluate patients' satisfaction from their conventional complete dentures and their mandibular implant-supported overdentures opposed by complete denture. In this cross sectional analytical descriptive study, seventy-five 45- to 65-year-old patients were divided into 3 groups wearing: (1) conventional complete dentures for up to 6 months; (2) conventional complete dentures for 10 years or more; and (3) complete maxillary dentures opposing mandibular implant-supported overdentures. Bite force was measured by means of electronic bite force measuring device with strain gauges. Three measurements were made on each side on the first molar region and the mean values were recorded. Patient satisfaction was also recorded using questionnaires. Results were analyzed by analysis of variance (ANOVA), t test, chi-square, and Pearson correlation test. The mean MBF for the first, the second, and the third group was, respectively, 5.65 +/- 1.46 kgf, 7.01 +/- 2.1 kgf, and 12.22 +/- 27 kgf. The difference between MBF in patients with overdentures and in patients with conventional complete dentures was statistically significant (P = .001). Patient satisfaction with mandibular implant-supported overdentures was recorded as "great." Results indicated MBF in the patients with mandibular implant-supported overdentures was significantly higher than that of patients with conventional complete dentures. This difference may indicate the important role of dental implants in the improvement of bite force and chewing efficiency and therefore patients' satisfaction.

Effect of macro-design of immediately loaded implants on micromotion and stress distribution in surrounding bone using finite element analysis.

OBJECTIVES: Macro-design influences the initial stability of implant and reduces micromotions. The aim of this study was to determine and compare micromotions and stress distribution in the bone around immediately loaded Maestro and Xive implants using finite element analysis. MATERIALS: In this experimental study, accurate, clear photos were prepared of Xive and Maestro implants 12 and 13 mm long and 4 and 3.8 mm in diameter, respectively, using a Nikon Digital Camera with a resolution 5.24-megapixels with 8x Optical Zoom and 4x Digital Zoom. After accurate measurements, 3-D models of the implants inside the lower mandible (D2) were processed in Solidworks Version 2003 environment and transferred into Ansys for finite element analysis. After loading of 500 N angled at 70 degrees from the horizontal plane, the micromotion of the implant and Von Misses stresses around the bone were measured. RESULTS: The measured micromotion in Maestro implant was 148 mum and that in Xive was 284 mum. Stress distribution in the bone surrounding Maestro implant was better than Xive, but maximum stress surrounding Xive implants (30 MPa) was lower than Maestro (33 MPa). CONCLUSION: Based on the results obtained in the present study, maximum micromotion in maestro was less than that in Xive implants. This finding can guarantee the application of maestro implants for immediate loading.