Tensile Bond Strength of Three Custom-made Tooth-Colored Implant Superstructures to Titanium Inserts.

STATEMENT OF THE PROBLEM: Hybrid abutments are made of a titanium implant insert and a ceramic component. The tensile bond strength between the titanium implant insert and the ceramic component is not still clearly known. PURPOSE: This in vitro study aimed to compare the tensile bond strength of the titanium insert to ceramic components made of milled lithium disilicate, milled zirconia, and pressable lithium disilicate. MATERIALS AND METHOD: To standardize the shape and dimension of the ceramic components, a single computer-aided design/computer assisted manufacturing (CAD/CAM) superstructure was designed with Dental Designer software. Based on this model, CAD milled zirconia (Zr), CAD milled Lithium disilicate (CAD-LD) and heat-pressed lithium-disilicate (H-LD) superstructures were fabricated (n=10 per group). They were bonded to the titanium inserts by using self-adhesive resin cement. The prepared superstructure-titanium insert complexes (hybrid abutments) were screwed into the implants with 35 Ncm torque. The tensile bond strength of the ceramic superstructures to the titanium inserts were recorded by the universal testing machine with a crosshead speed of 2 mm/min. The data were analyzed by using one-way ANOVA and Tamhane post-hoc test (p< 0.05). RESULTS: The mean±SD of tensile bond strength was 328.50±30.4 N in CAD-LD, 257.30±23.8 N in H-LD, and 242.20±21.2 N in Zr groups. One-way ANOVA revealed the groups significantly different in terms of the tensile bond strength (p< 0.001). Tamhane post-hoc test showed a significant difference between the CAD-LD and the two other groups (p<0.001); however, no statistically significant difference was detected between the H-LD and Zr groups (p= 0.39). CONCLUSION: It can be concluded that the CAD-LD has higher bond strength to titanium insert compared with the H-LD and Zr groups. Therefore, they might be clinically more beneficial in high-esthetic areas.

Comparison of the Water Sorption and Solubility of Four Reline Acrylic Resins after Immersion in Food-Simulating Agents.

OBJECTIVES: Water sorption and water solubility adversely affect the mechanical properties and biocompatibility of the denture material. This study aimed to evaluate the water sorption and solubility of three direct hard reline acrylic resins and a heat-curing one after immersion in food-simulating agents. MATERIALS AND METHODS: This study was performed on four groups of samples (n = 10 per group). The samples were made of three direct hard reline acrylic resins (TDV Cold Liner Rebase, Tokuyama Rebase II Fast, GC Reline Hard) and a heat-curing one (Meliodent). Each group was divided into four subgroups (n = 10) to undergo 7-day immersion in distilled water, 75% ethanol/water, 0.02 N citric acid, and heptane. Water sorption and solubility were calculated according to Oysaed and Ruyter formula. The statistical analyses were done by using SPSS software (version 22). Kruskal-Wallis H Test and Dunn's test were used to detect any significant difference among the groups (P < 0.05). RESULTS: The median range of water solubility and water sorption values were -0.87-4.92 and 3.75-27.25 µg/mm3, respectively. The median solubility and sorption values of different resins differed significantly in the same solution (P < 0.05). Besides, immersion in different solutions caused significant differences in the median solubility and sorption values of each reline material (P < 0.05), except for Meliodent whose solubility was not significantly affected by different solutions (P = 0.16). CONCLUSIONS: Water sorption and solubility values of the tested hard reline resins were within the range of International Standards Organization 1567:1999. Given the low sorption and solubility values, these hard reline materials can be safely used in clinical situations.

Investigating possible correlation between condylar asymmetry and clinical dysfunction indices in patients with temporomandibular dysfunction using Cone-beam computed tomographic.

PURPOSE: Temporomandibular disorder (TMD) is a common problem in modern societies. Causes of TMD, as a consequence of condylar asymmetry index (CAI), are still a subject of controversy. The aim of the present study was to determine the possible correlations between the degree of condylar asymmetry and clinical dysfunction indices. MATERIALS AND METHODS: In this cross-sectional study, we used the Habets method to measure the CAI in 42 TMD patients. The participants' age and sex were matched in the control group. Patients were divided into mild, moderate and severe dysfunction groups based on Helkimo's clinical Di. The data were analyzed using Mann-Whitney U and Kruskal-Wallis tests. Also, the study attempted to assess the possibility of correlation between age and CAI. RESULTS: The CAI values of TMD patients were significantly higher than those of the control group (P = 0.001). However, CAI was not significantly different among TMD patients with different dysfunction index. There was no significant correlation between CAI and age (Spearman r = 0.655, P = 0.23). CONCLUSION: Based on the findings of the present study, patients with condylar asymmetry index are more susceptible to TMD. However, degree of the condylar asymmetry is not a criterion for TMD signs and symptoms.

The Effect of Sintering Time on the Marginal Fit of Zirconia Copings.

PURPOSE: This study analyzed the effect of different sintering times on the marginal adaptation of zirconia ceramic copings. MATERIALS AND METHODS: Thirty copings of pre-sintered 3Y-TZP blanks were milled and subsequently sintered in a special furnace for three different durations (n = 10 per group). The sintering time was 1 hour, 15 minutes for IPS e.max ZirCAD, 4 hours 20 minutes for Speed ZrO2, and 7 hours 20 minutes for the conventional ZrO2 group. The marginal gaps of specimens were measured at 18 spots on the master die by employing a digital microscope. One-way ANOVA test compared the mean differences among the 3 groups (α = 0.05). RESULTS: The mean values for the marginal gap of the IPS e.max ZirCAD, Speed ZrO2 , and conventional ZrO2 groups were 41.06 ± 14.03, 43.03 ± 11.67, and 39.88 ± 15.23 µm, respectively. There was no statistically significant difference among the groups regarding the marginal gap. CONCLUSION: Different sintering times did not alter the marginal fit of the zirconia copings. The mean values of the marginal gap were within the clinically acceptable level for all three groups.

The Effect of Food-Simulating Agents on the Bond Strength of Hard Chairside Reline Materials to Denture Base Resin.

PURPOSE: To investigate the influence of food-simulating agents on the shear bond strength between direct hard liners and denture base acrylic resin. In addition, mode of failure was evaluated. MATERIALS AND METHODS: One hundred fifty cylindrical columns of denture base resin were fabricated and bonded to three types of hard reline materials (Hard GC Reline, Tokuyama Rebase II Fast, TDV Cold Liner Rebase). Specimens of each reline material were divided into five groups (n = 10) to undergo 12-day immersion in distilled water, 0.02 N citric acid aqueous solution, heptane, and 40% ethanol/water solution at 37°C. The control group was not immersed in any solution. The shear bond strength test was performed, and the failure mode was determined. Statistics were analyzed with two-way ANOVA and chi-square test (α = 0.05). RESULTS: Significant interaction was found between the hard liners and food simulating agents (p < 0.001). The shear bond strength of Tokuyama in 40% ethanol and TDV in heptane decreased significantly (p = 0.001, p < 0.001 respectively); however, none of the solutions could significantly affect the shear bond strength of Hard GC Reline (p = 0.208). The mixed failure mode occurred more frequently in Hard GC Reline compared with the other liners (p < 0.001) and was predominant in specimens with higher bond strength values (p = 0.012). CONCLUSIONS: Food simulating agents did not adversely affect the shear bond strength of Hard GC Reline; however, ethanol and heptane decreased the bond strength of Tokuyama and TDV, respectively. These findings may provide support to dentists to recommend restricted consumption of some foods and beverages for patients who have to use dentures relined with certain hard liners.

Bond strength of hard direct reline materials to heat-cured acrylic denture base after immersion in denture cleansers.

BACKGROUND: Immersion-type denture cleansers are commonly used for denture hygiene maintenance. Hence, it is crucial to investigate the effect of denture cleansing solutions on bond strength between direct reline materials and denture base resin. AIMS: This in vitro study aimed to determine the effect of denture cleansers on bond strength between direct hard reline materials and denture base resin. MATERIALS AND METHODS: Cylindrical columns of hard-liners (Hard GC Reline, TDV Cold Liner Rebase, Tokuyama Rebase II Fast) were bonded to heat-polymerized denture base resin. A total of fifty specimens were fabricated for each reline material and divided into five groups (n = 10): Group I (control): No solution was used; Group II: Specimens were stored in distilled water for 60 days; Groups III, IV, and V: Specimens were stored in distilled water for 60 days with daily immersion in either sodium hypochlorite, calgon + sodium hypochlorite, or dentipur tablet for 5 min. The shear bond strength was examined at a cross-head speed of 1 mm/min. Failure mode was evaluated by stereomicroscope. STATISTICAL ANALYSIS: Data were analyzed by two-way ANOVA and Chi-square test (α=0.05). RESULTS: The results showed no significant interaction between the direct hard-liners and denture cleansers (P = 0.119). Hard GC Reline had the highest bond strength, followed by Tokuyama Rebase II Fast, and then, TDV Cold Liner Rebase. No significant difference existed in bond strength between samples immersed in water and cleansers or between the cleansers themselves. Hard GC Reline had more mixed failure mode compared to TDV Cold Liner Rebase and Tokuyama Rebase II Fast. There was a significant correlation between mixed mode of failure and higher values of bond strength (P = 0.008). CONCLUSIONS: Within the limitations of the present study, denture cleansing solutions could not significantly influence the bond strength between hard direct liners and denture base resin.

The Effect of Sintering Program on the Compressive Strength of Zirconia Copings.

STATEMENT OF THE PROBLEM: Considering the limitations of conventional sintering of zirconium oxide (ZrO2) copings, shortening the sintering time can be proposed as an alternative method for making the copings. PURPOSE: This study aimed to assess the effects of sintering time on compressive strength of Yttria Tetragonal Zirconia Polycrystal (Y-TZP) copings. MATERIALS AND METHOD: Thirty copings of pre-sintered 3Y-TZP blanks were milled and sintered in a special furnace for three different durations (n=10 per group). The sintering time was 1 h 15 min for IPS e.max ZirCAD, 4 h 20 min for Speed ZrO2, and 7 h 20 min for the conventional ZrO2 group. The specimens were cemented on the brass dies by using conventional glass ionomer cement. The copings were vertically loaded until fracture by using a universal testing machine. The data were analyzed through one-way analysis of variance (ANOVA) and post hoc test to compare the mean differences of compressive strength yielded in three study groups (α=0.05). RESULTS: The mean ± SD of compressive strength value was (3617 ± 543.54) N for IPS-e.maxZirCAD group, (2663 ± 508.11) N for Speed ZrO2 group, and (1662± 466.71 N) for conventional ZrO2 group. There were statistically significant differences among compressive strength values of the tested groups (p< 0.05). The highest compressive strength values were obtained from the IPS e.max ZirCAD group. CONCLUSION: Within the limitations of this in vitro study, it can be concluded that compressive strength of the zirconia copings is affected by the sintering time. High compressive strength of zirconia copings can be obtained by shortening the sintering time.

The association between condylar bone changes revealed in cone beam computed tomography and clinical dysfunction index in patients with or without temporomandibular joint disorders.

OBJECTIVE: The aim of the present study was to compare cone beam computed tomography (CBCT) findings pertinent to patients with temporomandibular disorder (TMD) and patients without TMD (non-TMD), as well as to investigate the correlation between these findings and the clinical dysfunction index (Di). STUDY DESIGN: In this cross-sectional study, CBCT images of temporomandibular joints (TMJs) were evaluated for condylar bone changes in 84 patients with TMD. The patients were assigned a score using Helkimo's clinical Di, ranging from 1 to 25, and were thereafter subdivided into 3 groups based on the degree of Helkimo's Di. CBCT and clinical records of sex- and age-matched non-TMD patients were used as the control group. RESULTS: There was a significant difference in the prevalence of all types of bone changes between TMD and non-TMD groups (all P < .05), except for loose joint bodies. Furthermore, there was a significant correlation between the total amount of bone change and the Helkimo Di score (P < .001). CONCLUSION: Evaluation of CBCT images in the present study revealed significant differences between TMD and non-TMD condyles. There was also a significant relationship between the Helkimo clinical Di and the total amount of condylar bone change in patients with TMD.

Marginal and internal fit of metal copings fabricated with rapid prototyping and conventional waxing.

STATEMENT OF PROBLEM: Given the limitations of conventional waxing, computer-aided design and computer-aided manufacturing (CAD-CAM) technologies have been developed as alternative methods of making patterns. PURPOSE: The purpose of this in vitro study was to compare the marginal and internal fit of metal copings derived from wax patterns fabricated by rapid prototyping (RP) to those created by the conventional handmade technique. MATERIAL AND METHODS: Twenty-four standardized brass dies were milled and divided into 2 groups (n=12) according to the wax pattern fabrication method. The CAD-RP group was assigned to the experimental group, and the conventional group to the control group. The cross-sectional technique was used to assess the marginal and internal discrepancies at 15 points on the master die by using a digital microscope. An independent t test was used for statistical analysis (α=.01). RESULTS: The CAD-RP group had a total mean (±SD) for absolute marginal discrepancy of 117.1 (±11.5) µm and a mean marginal discrepancy of 89.8 (±8.3) µm. The conventional group had an absolute marginal discrepancy 88.1 (±10.7) µm and a mean marginal discrepancy of 69.5 (±15.6) µm. The overall mean (±SD) of the total internal discrepancy, separately calculated as the axial internal discrepancy and occlusal internal discrepancy, was 95.9 (±8.0) µm for the CAD-RP group and 76.9 (±10.2) µm for the conventional group. The independent t test results showed significant differences between the 2 groups. The CAD-RP group had larger discrepancies at all measured areas than the conventional group, which was statistically significant (P<.01). CONCLUSIONS: Within the limitations of this in vitro study, the conventional method of wax pattern fabrication produced copings with better marginal and internal fit than the CAD-RP method. However, the marginal and internal fit for both groups were within clinically acceptable ranges.

A Comparison of the Marginal and Internal Fit of Cobalt- Chromium Copings Fabricated by Two Different CAD/CAM Systems (CAD/ Milling, CAD/ Ceramill Sintron).

STATEMENT OF THE PROBLEM: Marginal fitness is the most important criteria for evaluation of the clinical acceptability of a cast restoration. Marginal gap which is due to cement solubility and plaque retention is potentially detrimental to both tooth and periodontal tissues. PURPOSE: This in vitro study aimed to evaluate the marginal and internal fit of cobalt- chromium (Co-Cr) copings fabricated by two different CAD/CAM systems: (CAD/ milling and CAD/ Ceramill Sintron). MATERIALS AND METHOD: We prepared one machined standard stainless steel master model with following dimensions: 7 mm height, 5mm diameter, 90˚ shoulder marginal finish line with 1 mm width, 10˚ convergence angle and anti-rotational surface on the buccal aspect of the die. There were 10 copings produced from hard presintered Co-Cr blocks according to CAD/ Milling technique and ten copings from soft non- presintered Co-Cr blocks according to CAD/ Ceramill Sintron technique. Marginal and internal accuracies of copings were documented by the replica technique. Replicas were examined at ten reference points under a digital microscope (230X). The Student's t-test was used for statistical analysis. p< 0.001 was considered significant. RESULTS: Statistically significant differences existed between the groups (p< 0.001). The CAD/milling group (hard copings) had a mean marginal discrepancy (MD) of 104 µm, axial discrepancy (AD) of 23 µm and occlusal discrepancy of 130 µm. For CAD/ Ceramill Sintron group, these values were 195 µm (MD), 46 µm (AD), and 232 µm (OD). Internal total discrepancy (ITD) for the CAD/milling group was 77 µm, whereas for the CAD/Ceramill Sintron group was 143 µm. CONCLUSION: Hard presintered Co-Cr copings had significantly higher marginal and internal accuracies compared to the soft non-presintered copings.

The Comparison of Sorption and Solubility Behavior of Four Different Resin Luting Cements in Different Storage Media.

STATEMENT OF THE PROBLEM: Structural integrity and dimensional stability are the key factors that determine the clinical success and durability of luting cements in the oral cavity. Sorption and solubility of self-adhesive resin luting cements in food-simulating solutions has not been studied sufficiently. PURPOSE: This study aimed to compare the sorption and solubility of 2 conventional and 2 self-adhesive resin-based luting cements immersed in four different storage media. MATERIALS AND METHOD: A total of 32 disc-shaped specimens were prepared from each of four resin luting cements; seT (SDI), Panavia F (Kuraray), Clearfil SA Cement (Kuraray), and Choice 2 (Bisco). Eight specimens of each material were immersed in all tested solutions including n-heptane 97%, distilled water, apple juice, or Listerine mouth wash. Sorption and solubility were measured by weighing the specimens before and after immersion and desiccation. Data were analyzed by SPSS version 18, using two-way ANOVA and Tukey's HSD test with p≤ 0.05 set as the level of significance. RESULTS: There was a statistically significant interaction between the materials and solutions. The effect of media on the sorption and solubility was material-dependent. While seT showed the highest values of the sorption in almost all solutions, Choice 2 showed the least values of sorption and solubility. Immersion in apple juice caused more sorption than other solutions (p≤ 0.05). CONCLUSION: The sorption and solubility behavior of the studied cements were significantly affected by their composition and the storage media. The more hydrophobic materials with higher filler content like Choice 2 resin cement showed the least sorption and solubility. Due to their lower sorption and solubility, these types of resin-based luting cements are recommended to be used clinically.

Accuracy of different impression materials in parallel and nonparallel implants.

BACKGROUND: A precise impression is mandatory to obtain passive fit in implant-supported prostheses. The aim of this study was to compare the accuracy of three impression materials in both parallel and nonparallel implant positions. MATERIALS AND METHODS: In this experimental study, two partial dentate maxillary acrylic models with four implant analogues in canines and lateral incisors areas were used. One model was simulating the parallel condition and the other nonparallel one, in which implants were tilted 30° bucally and 20° in either mesial or distal directions. Thirty stone casts were made from each model using polyether (Impregum), additional silicone (Monopren) and vinyl siloxanether (Identium), with open tray technique. The distortion values in three-dimensions (X, Y and Z-axis) were measured by coordinate measuring machine. Two-way analysis of variance (ANOVA), one-way ANOVA and Tukey tests were used for data analysis (α = 0.05). RESULTS: Under parallel condition, all the materials showed comparable, accurate casts (P = 0.74). In the presence of angulated implants, while Monopren showed more accurate results compared to Impregum (P = 0.01), Identium yielded almost similar results to those produced by Impregum (P = 0.27) and Monopren (P = 0.26). CONCLUSION: Within the limitations of this study, in parallel conditions, the type of impression material cannot affect the accuracy of the implant impressions; however, in nonparallel conditions, polyvinyl siloxane is shown to be a better choice, followed by vinyl siloxanether and polyether respectively.

The effect of various veneering techniques on the marginal fit of zirconia copings.

PURPOSE: This study aimed to evaluate the fit of zirconia ceramics before and after veneering, using 3 different veneering processes (layering, press-over, and CAD-on techniques). MATERIALS AND METHODS: Thirty standardized zirconia CAD/CAM frameworks were constructed and divided into three groups of 10 each. The first group was veneered using the traditional layering technique. Press-over and CAD-on techniques were used to veneer second and third groups. The marginal gap of specimens was measured before and after veneering process at 18 sites on the master die using a digital microscope. Paired t-test was used to evaluate mean marginal gap changes. One-way ANOVA and post hoc tests were also employed for comparison among 3 groups (α=.05). RESULTS: Marginal gap of 3 groups was increased after porcelain veneering. The mean marginal gap values after veneering in the layering group (63.06 µm) was higher than press-over (50.64 µm) and CAD-on (51.50 µm) veneered groups (P<.001). CONCLUSION: Three veneering methods altered the marginal fit of zirconia copings. Conventional layering technique increased the marginal gap of zirconia framework more than pressing and CAD-on techniques. All ceramic crowns made through three different veneering methods revealed clinically acceptable marginal fit.

Polyamide as a Denture Base Material: A Literature Review.

The purpose of this article was to review the biocompatibility, physical, and mechanical properties of the polyamide denture base materials. An electronic search of scientific papers from 1990-2014 was carried out using PubMed, Scopus and Wiley Inter Science engines using the search terms "nylon denture base" and "polyamide denture base". Searching the key words yielded a total of 82 articles. By application of inclusion criteria, the obtained results were further reduced to 24 citations recruited in this review. Several studies have evaluated various properties of polyamide (nylon) denture base materials. According to the results of the studies, currently, thermo-injectable, high impact, flexible or semi-flexible polyamide is thought to be an alternative to the conventional acrylic resins due to its esthetic and functional characteristics and physicochemical qualities. It would be justifiable to use this material for denture fabrication in some cases such as severe soft/ hard tissue undercuts, unexplained repeated fracture of denture, in aesthetic-concerned patients, those who have allergy to other denture base materials, and in patients with microstomia.  Although polyamide has some attractive advantages, they require modifications to produce consistently better properties than the current polymethyl methacrylate (PMMA) materials. Moreover, since there is a very limited knowledge about their clinical performance, strict and careful follow-up evaluation of the patients rehabilitated with polyamide prosthesis is recommended.

The effect of porcelain firing and type of finish line on the marginal fit of zirconia copings.

STATEMENT OF THE PROBLEM: Although all-ceramic restorations are broadly used, there is a lack of information concerning how their fit is affected by fabrication procedure and marginal configuration. PURPOSE: The purpose of this study was to evaluate the marginal fit of zirconia CAD/CAM ceramic crowns before and after porcelain firing. The influence of finish line configuration on the marginal fit was also evaluated. MATERIALS AND METHOD: Twenty standardized zirconia CAD/CAM copings were fabricated for chamfer and shoulder finish line designs (n=10). The marginal fit of specimens was measured on 18 points, marked on the master metal die by using a digital microscope. After the crowns were finalized by porcelain veneering, the measurements of marginal fit were performed again. The means and standard deviations were calculated and data were analyzed using student's t-test and paired t-test (α=0.05). RESULTS: There were significant differences between marginal fit of chamfer and shoulder finish line groups before and after porcelain firing (p= 0.014 and p= 0.000, respectively). The marginal gap of copings with shoulder finish line was significantly smaller than those with chamfer configuration (p= 0.000), but there were no significant differences between the two marginal designs, after porcelain firing (p= 0.341). CONCLUSION: Porcelain veneering was found to have a statistically significant influence on the marginal fit of zirconia CAD/CAM crowns. Both margin configurations showed marginal gaps that were within a reported clinically acceptable range of marginal discrepancy.

Effect of home bleaching on the mechanical properties of resin luting cements using Hertzian indentation test.

AIM: The aim of the present study was to determine the effects of immersion time and 10% carbamide peroxide treatment using a Hertzian indentation test after placing resin-based cements into 37°C distilled water, with and without 10% carbamide peroxide. METHODS: Disc-shaped specimens (10-mm diameter × 1-mm thick), were prepared from five resin-based cements; seT PP, Maxcem Elite, RelyX Unicem, Panavia F, and G-Cem. The specimens of each material were randomly divided into three groups of six. The study groups were bleached with 10% carbamide peroxide on one surface for 21 days for 2 h per day. Two control groups were kept in distilled water for either 24 h or 21 days. A load was applied to the center of the disc using a hard, steel ball. The load at the first crack was recorded. RESULTS: Significant differences were observed between the cements. seT PP showed the highest strength, and G-Cem the lowest. Differences between the treatment and control groups were statistically significant for all cements, except Panavia F. CONCLUSIONS: The effect of 10% carbamide peroxide treatment reduces cement strength, which could be important for patients undergoing bleaching who have crowns.

Evaluation of the effect of a home-bleaching agent on the surface characteristics of indirect esthetic restorative materials: part I--roughness.

BACKGROUND: Pressing esthetic demands of good looking make people undergo bleaching procedures. However, the effect of bleaching agents on esthetic restorative materials with different surface preparations has been poorly studied. AIM: The aim of this study was to examine the effect of a homebleaching agent (carbamide peroxide: CP 38%) on the surface roughness of the polished fiber reinforced composite (FRC), overglazed, autoglazed, or polished ceramic samples. MATERIALS AND METHODS: Twenty standardized cylindrical specimens were made of each of the following groups: over-glazed, autoglazed, polished porcelain and also FRC. The test specimens exposed to the CP 38%, 15 minutes, twice a day for 2 weeks according to the manufacturer's recommendation. Six samples from each group were selected randomly to form negative controls. Surface roughness measurements (Ra, micrometer) for baseline, test and control specimens were performed by use of a profilometer. Paired t-test, Mann-Whitney test, and Kruskal-Wallis test were used for statistical analyses. RESULTS: The data showed that bleaching with CP 38% significantly increased the surface roughness of all the test samples (p < 0.05). The type of surface preparation caused significant differences between the susceptibility of porcelain subgroups to bleaching (p < 0.05). The polished porcelain specimens showed the highest changes after bleaching. CONCLUSION: CP 38% significantly increases the surface roughness of the porcelains and FRC. The type of surface condition affects the amenability of the porcelain surface to the bleaching agent. Glazed porcelains were more resistant to roughness than the polished porcelains and also the composite. CLINICAL SIGNIFICANCE: Roughening of porcelain and FRC occur following bleaching procedure. No special surface preparation of indirect esthetic restorative materials can completely preserve these materials from adverse effects of bleaching agents.

Evaluation of the effect of a home bleaching agent on surface characteristics of indirect esthetic restorative materials--part II microhardness.

BACKGROUND: The exponential usage of esthetic restorative materials is beholden to society needs and desires. Interaction between the bleaching agents and the esthetic restorative materials is of critical importance. AIM: This in vitro study has been conducted to evaluate the effect of a home bleaching agent, carbamide peroxide (CP) 38%, on the microhardness of the fiber reinforced composite (FRC), overglazed, autoglazed, or polished porcelain specimens. MATERIALS AND METHODS: For overglazed, autoglazed, polished ceramics and also FRC cylindrical specimens (n = 20 per group) were prepared. The specimens were stored in distilled water at 37°C for 48 hours prior to testing. Six samples from each group were selected randomly as negative controls which were stored in distilled water at 37°C that was changed daily. CP 38% was applied on the test specimens for 15 minutes, twice a day for 14 days. By using Knoop-microhardness tester microhardness testing for baseline, control and test specimens was conducted. Data were statistically analyzed using paired t-test, Mann-Whitney test, and Kruskal-Wallis test. RESULTS: Home bleaching significantly decreased the surface microhardness of all the test samples (p < 0.05), whereas the control groups did not show statistically significant changes after 2 weeks. The polished porcelain and polished composite specimens showed the most significant change in microhard-ness after bleaching process (p < 0.05). CONCLUSION: Although the type of surface preparation affects the susceptibility of the porcelain surface to the bleaching agent, no special preparation can preclude such adverse effects. CLINICAL SIGNIFICANCE: The contact of home bleaching agents with esthetic restorative materials is unavoidable. Therefore protecting these restorations from bleaching agents and reglazing or at least polishing the restorations after bleaching is recommended.

Correlation between articular eminence steepness measured with cone-beam computed tomography and clinical dysfunction index in patients with temporomandibular joint dysfunction.

OBJECTIVE: The purpose of this study was to investigate the correlation between articular eminence steepness and clinical dysfunction index (Di) in patients with temporomandibular joint dysfunction (TMD) using cone-beam computed tomography (CBCT). STUDY DESIGN: In this study, CBCT images of 60 temporomandibular joints in 30 patients with TMD were evaluated. The eminence inclination values were measured on CBCT images. Patients were subdivided into 3 groups based on Helkimo's clinical Di. The data were analyzed using Spearman's rho correlation coefficient test. RESULTS: The results of the present study did not confirm any significant differences in the values of articular eminence inclinations among the 3 groups (P value >.05). CONCLUSION: Based on the present study, there is no apparent relationship between the articular eminence inclination and the clinical Di in patients with TMD.

Comparison of temporomandibular disorders in Iranian dental and nondental students.

AIM: The aim of this study was to define the prevalence and severity of temporomandibular disorders (TMD) among Iranian dental and nondental students who attended Shiraz University of Medical Sciences. MATERIALS AND METHODS: The samples consisted of 200 subjects, 100 dental and 100 nondental students (equal distribution between males and females). Subjects ages ranged from 18 to 30 years (24.07 ± 2.93). A functional evaluation was performed using the Helkimo dysfunction index (Di). Data were evaluated by the Chi-square test. RESULTS: Among the total study population, 71% showed some degree of dysfunction. Prevalence ratio in dental students was 80%, while in nondental students was 62% (p > 0.05, odds ratio = 0.679). With respect to gender, women (80%) were more affected than men (62%). A significant relationship was found between gender and the occurrence of TMD (p > 0.05). CONCLUSION: A high prevalence of signs of TMD in Iranian university students was seen which was greater in dental students and women. CLINICAL SIGNIFICANCE: The results of this study showed that the prevalence of TMD among dental students and women was significantly higher than nondental students and men. These findings might be due to poor postural style or emotional stress during dental practice.