Showing papers in "Journal of Prosthodontics in 2010"

Bonding to Zirconia Using a New Surface Treatment

Abstract: Purpose: Selective infiltration etching (SIE) is a newly developed surface treatment used to modify the surface of zirconia-based materials, rendering them ready for bonding to resin cements. The aim of this study was to evaluate the zirconia/resin bond strength and durability using the proposed technique. Materials and Methods: Fifty-four zirconia discs were fabricated and divided into three groups (n = 18) according to their surface treatment: as-sintered surface (control group), airborne-particle abrasion (50-μm aluminum oxide), and SIE group. The zirconia discs were bonded to preaged composite resin discs using a light-polymerized adhesive resin (Panavia F 2.0). The zirconia/resin bond strength was evaluated using microtensile bond strength test (MTBS), and the test was repeated after each of the following intervals of accelerated artificial aging (AA): thermocycling (10,000 cycles between 5 and 55◦C), 4 weeks of water storage (37◦C), and finally 26 weeks of water storage (37◦C). Silver nitrate nanoleakage analysis was used to assess the quality of zirconia/resin interface. A repeated measures ANOVA and Bonferroni post hoc test were used to analyze the data (n = 18, α = 0.05) Results: There were significant differences in theMTBS values between the three test groups at each of the test intervals (p < 0.001). AA resulted in reduction in the bond strength of the as-sintered and the particle-abraded groups (5.9 MPa and 27.4, MPa, respectively). Reduction in the bond strength of these groups was explained by the observed nanoleakage across the zirconia/resin interface. The bond strength of the SIE specimens was stable after completion of AA (51.9 MPa), which also demonstrated a good seal against silver nitrate penetration across the zirconia/resin interface. Conclusion: SIE established a strong, stable, and durable bond to zirconia substrates. Conservative resin-bonded zirconia restorations are now possible using this new technique. The introduction of zirconia-based materials to the dental field broadened the design and application limits of all-ceramic restorations. As a result of the unique mechanical properties of zirconia framework materials, three- or four-unit-fixed partial dentures (FPDs) are no longer the safe limit for the construction of all-ceramic restorations. Combined with CAD/CAM technology, the fabrication of extensive zirconia restorations became a simple and an accurate procedure.1 Chemical bonding is the basic fundamental for minimally invasive dentistry where the retention of the restoration mainly depends on adhesion to the tooth structure instead of retentive features made in the preparation.2 Additionally, it reduces microleakage, tooth sensitivity, and the possibility of recurrent decay.3 Patients have a preference for methods that can spare the reduction of their sound abutment teeth and would welcome

Clinical Success of Zirconia in Dental Applications

Abstract: The application of ceramic materials for the fabrication of dental restorations is a focus of interest in esthetic dentistry. The ceramic materials of choice are glass ceramics, spinel, alumina, and zirconia. Zirconia was introduced into dentistry in the 1990s because of its good mechanical and chemical properties and is currently being used as a material for frameworks, dowels, implants, abutments, and orthodontic brackets. Many in vitro studies about zirconia use have been published, but clinical long-term studies are very important. This article presents data regarding the incidence of clinical success and complications of zirconia in these dental applications. Clinical studies published to date seem to indicate that zirconia is well tolerated and sufficiently resistant.

A review of failure modes in teeth restored with adhesively luted endodontic dowels.

Abstract: Purpose: Previous clinical studies indicated loss of retention between dowel and tooth was a major cause of failure for passive endodontic dowels. Advances in luting cement technology may have improved the retention of dowels. The purpose of this systematic review was to determine the clinical failure modes for dowel/core/crown restorations luted using resin-based cements that are either self-etching or used in conjunction with a bonding agent. Materials and Methods: PubMed was searched for English language, peer-reviewed clinical research following restorations for 2 years or longer. For inclusion, a study group must have followed more than 50 permanent teeth restored using a dowel luted withresincementandabondingagent.Furthermore,morethan80%oftherestorations must have received a nonresin crown. Results: Fifteen studies met the inclusion criteria and reported a total of 187 failures from 3046 restorations. The commonly reported causes of failure were dowel debonding (37% of all failures and primary cause in 8 of the 17 reporting study groups) and endodontic lesions (37% of all failures and primary cause in 6 of the 11 reporting study groups). Conclusions: Loss of retention remains a major mode of failure even for passive, nonmetal dowels luted by resin cements with a bonding agent. The exact nature and underlying causes of debonding have not been adequately investigated.

Investigation of mechanical properties of experimental Bis-GMA/TEGDMA dental composite resins containing various mass fractions of silica nanoparticles.

Abstract: Purpose: Mechanical properties of dental composite resins need to be improved in order to enhance their performance for applications in direct restorations. Application of nanoparticles in this field is a recent development. The aim of this study was to investigate the mechanical properties of experimental composites containing various mass fractions of silica nanoparticles.Materials and Methods: Experimental composites were composed of a visible-light-curing monomer mixture (70 wt% Bis-GMA and 30 wt% TEGDMA) and silica nanoparticles of a size ranging from 20 nm to 50 nm modified with γ-methacryloxy propyl trimethoxy silane (γ-MPS) as reinforcing filler. The composites were classified into four groups according to their filler mass fractions ranging from 20% to 50%. Following the same preparation procedure, a conventional composite was also fabricated consisting of a mass percentage of 60% silica fillers having particle sizes ranging from 10 μm to 40 μm in the same organic matrix, which served as control. Ten specimens were prepared of each experimental group and also of the control. Fracture toughness was measured using single-edge notched bend (SENB) specimens. Specimen fracture surfaces were mounted on aluminum stubs with carbon cement, sputter-coated with gold and examined under scanning electron microscopy (SEM). Flexural strength was evaluated through a standard three-point bending test and Vickers microhardness test was performed to investigate the hardness of the samples.Results: Filler mass fraction had a significant effect on composite properties. Fracture toughness, flexural strength, and hardness of composites at filler mass fraction of 40% of silica nanoparticles were (mean ± SD) 1.43 ± 0.08 MPa.m, 149.74 ± 8.14 MPa, and 62.12 ± 3.07 VHN, respectively; relevant values for composites at 50% mass fraction of silica nanoparticles were 1.38 ± 0.07 MPa.m, 122.83 ± 6.13 MPa, and 70.69 ± 3.67 VHN, respectively, all of which were significantly higher than 1.07 ± 0.06 MPa.m, 104.61 ± 8.73 MPa, and 52.14 ± 4.02 VHN of the control, respectively (Tukey's multiple comparison test; family confidence coefficient = 0.95). Measured values for composites at 20% mass fraction of silica nanoparticles were 0.94 ± 0.06 MPa.m, 103.41 ± 7.62 MPa, and 42.87 ± 2.61 VHN, respectively; relevant values for composites at 30% mass fraction of silica nanoparticles were 1.16 ± 0.07 MPa.m, 127.91 ± 7.05 MPa, and 51.78 ± 3.41 VHN, respectively.Conclusions: Reinforcement of dental composite resins with silica nanoparticles resulted in a significant increase in the evaluated mechanical properties in comparison with the conventional composite. The filler mass fraction played a critical role in determining the composite's mechanical properties.

Color Stability of Denture Acrylic Resins and a Soft Lining Material Against Tea, Coffee, and Nicotine

Abstract: PURPOSE The purpose of this study was to investigate the effect of four solutions [saliva (control group), saliva+tea, saliva+coffee, saliva+nicotine] on the color of different denture base acrylic resins (heat-polymerized, injection-molded, autopolymerized) and a soft denture liner. MATERIALS AND METHODS Twenty specimens from each type of test material were prepared (2.5 mm diameter, 2 mm thickness). Five specimens from each test material (heat-polymerized, chemically polymerized, injection-molded acrylic resin, soft denture reliner) were stored in each solution in 37 degrees C in a dark environment. Colorimetric measurements were done on the 1st, 7th, and 30th days. Color differences among specimens immersed in saliva (control group), and staining solutions were evaluated over time. Data were statistically analyzed with one-way analysis of variance (ANOVA) (alpha= 0.05). ANOVA was followed by Tukey test to find which groups differed from each other. RESULTS Significant color shifts occurred in heat-polymerized and injection-molded acrylic resins in coffee and in soft liner in nicotine over time (p 1). The color shift of soft liner in nicotine was significantly different than that of the remainder of the test materials in nicotine (p 0.05). CONCLUSIONS The effect of staining solutions on the color of each test material in each session was perceivable by the human eye (DeltaE > 1); however, the color shifts of all test materials were clinically acceptable (DeltaE < 3.7) except for soft liner in nicotine, which was not clinically acceptable over time. Therefore, minimizing drinking of such beverages and use of tobacco, particularly when soft liner is applied, may be advantageous for denture wearers for long-term color stability.

The Effect of Denture Cleansing Solutions on the Retention of Pink Locator Attachments: An in Vitro Study

Abstract: Purpose: To evaluate the changes in retention of pink Locator attachments after exposure to various denture cleansers. Materials and Methods: Six groups (20 pairs each) of pink Locator attachments (3.0 lb. Light Retention replacement patrix attachments) were soaked for the equivalent of 6 months of clinical use in the following solutions: Water (control), Polident Regular, Efferdent, 6.15% sodium hypochlorite (NaOCL, 1:10 dilution), Polident Overnight, and Cool Mint Listerine mouthwash. A universal testing machine set at a crosshead speed of 2 in/min was used to perform one pull. The peak load-to-dislodgement was recorded to reflect changes in the retention of the Locator attachments after soaking. Data were analyzed by one-way ANOVA followed by Tukey's Honestly Significant Difference test. A p≤ 0.05 was considered significant. Results: Denture cleansing solutions significantly affected the retentive values of pink Locator attachments (F = 344.3, p≤ 0.0001). Cool Mint Listerine mouthwash increased the retentive values of the attachments (51.10 ± 5.31 N) when compared to the control group (45.25 ± 3.49 N). There was no significant difference in the retentive values of attachments soaked in Polident Regular or Polident Overnight when compared to the control group. Efferdent caused a small reduction in the retentive values (40.81 ± 2.56 N) and most importantly, diluted NaOCl caused a large reduction in the retentive values (7.83 ± 2.50 N) of pink Locator attachments. In addition, Cool Mint Listerine mouthwash caused blue discoloration of the Locator attachments, and NaOCl caused whitening and softening of the pink Locator attachments. Conclusion: Cool Mint Listerine and Efferdent's small effect on the retentive values of the Locators might be clinically unimportant; however, NaOCl caused a large reduction in the retentive values of the attachments. Because of their effect on retentive values and on the color of the Locator attachments, NaOCl and Cool Mint Listerine are not recommended. These results should be interpreted clinically with caution, realizing that different results may be obtained when fatigue stress during function and multiple pulls (in vivo) are combined with the chemical action of denture cleansers.

Porcelain Fracture Resistance of Screw-Retained, Cement-Retained, and Screw-Cement-Retained Implant-Supported Metal Ceramic Posterior Crowns

Abstract: Purpose: The purpose of this in vitro study was to compare the porcelain fracture resistance between screw-retained, cement-retained, and combined screw-and cement-retained metal-ceramic (MC) implant-supported posterior single crowns; and to investigate the effect of offsetting the occlusal screw-access opening on porcelain fracture resistance of screw-retained and cement-retained MC implant-supported posterior single crowns.Materials and Methods: Forty standardized MC molar-shaped restorations were fabricated. The 40 restorations were divided into four groups (SRC, SRO, CRP, and CSC) of 10 specimens each. Group SRC: screw-retained, screw-access hole placed in the center of the occlusal surface; Group SRO: screw-retained, screw-access hole placed 1 mm offset from the center of the occlusal surface toward the buccal cusp; Group CRP: cement-retained, zinc phosphate cement was used; Group CSC: cement-retained with a screw-access hole in the center of the occlusal surface. The screw-retained restorations and abutments were directly attached to 3i implant fixtures embedded in acrylic resin blocks. Subsequently, all test specimens were thermocycled and vertically loaded in a universal testing machine at a crosshead speed of 2 mm/min until fracture. Mean values of load at fracture (in N) were calculated in each group and compared with a one-way ANOVA and Tukey's Studentized test (alpha = 0.05).Results: Mean values of loads required to fracture the restorations were as follows (N): Group SRC: 1721 +/- 593; Group SRO: 1885 +/- 491; Group CRP: 3707 +/- 1086; Group CSC: 1700 +/- 526. Groups SRC, SRO, and CSC required a significantly lower force to fracture the porcelain than did the CRP group (p < 0.05).Conclusion: The cement-retained restorations showed significantly higher mean fracture loads than the restorations having screw-access openings in their occlusal surface. The position of the screw-access hole within the occlusal surface did not significantly affect the porcelain fracture resistance.

Reducing the Incidence of Denture Stomatitis: Are Denture Cleansers Sufficient?

Abstract: Purpose Candida albicans is the predominant oral yeast associated with denture stomatitis. With an increasing population of denture wearers, the incidence of denture stomatitis is increasing. Effective management of these patients will alleviate the morbidity associated with this disease. The aim of this study was to examine the capacity of four denture cleansers to efficiently decontaminate and sterilize surfaces covered by C. albicans biofilms. Materials and methods Sixteen C. albicans strains isolated from denture stomatitis patients and strain ATCC 90028 were grown as mature confluent biofilms on a 96-well format and immersed in Dentural, Medical Interporous, Steradent Active Plus, and Boots Smile denture cleansers according to the manufacturers' instructions or overnight. The metabolic activity and biomass of the biofilms were then quantified, and scanning electron microscopy (SEM) used to examine treated biofilms. Results Dentural was the most effective denture cleanser, reducing the biomass by greater than 90% after 20 minutes. Steradent Active plus was significantly more effective following 10-minute immersion than overnight (p Conclusions This study showed that denture cleansers exhibit effective anti-C. albicans biofilm activity, both in terms of removal and disinfection; however, residual biofilm retention that could lead to regrowth and denture colonization was observed. Therefore, alternative mechanical disruptive methods are required to enhance biofilm removal.

Relationship between oral health-related quality of life, satisfaction, and personality in patients with prosthetic rehabilitations.

Abstract: Purpose: This study investigated the relationship between oral health-related quality of life, satisfaction with dentition, and personality profiles among patients with fixed and/or removable prosthetic rehabilitations. Materials and Methods: Thirty-seven patients (13 males, 24 females; mean age 37.6 ± 13.3 years) with fitted prosthetic rehabilitations and 37 controls who matched the patients by age and gender were recruited into the study. The Dental Impact on Daily Living (DIDL) questionnaire was used to assess dental impacts on daily living and satisfaction with the dentition. The Oral Health Impact Profile (OHIP) was used to measure self-reported discomfort, disability, and dysfunction caused by oral conditions. Oral health-related quality of life was assessed by the United Kingdom Oral Health-Related Quality of Life (OHQoL-UK) measure. Moreover, the NEO five-factor inventory was used to assess participants’ personality profiles. Results: Prosthetic factors had no relationship to the DIDL, OHIP, and OHQoL-UK scores. Patients with the least oral health impacts had better oral health-related quality of life (p= 0.023, r =–0.37), higher levels of total satisfaction, and satisfaction with appearance, pain, oral comfort, general performance, and eating (p < 0.05, r =–0.79, –0.35, –0.59, –0.56, –0.58, and –0.50, respectively). Patients with better oral health-related quality of life (QoL) had higher total satisfaction, satisfaction with oral comfort, general performance, and eating (p < 0.05, r = 0.34, 0.39, 0.33, and 0.37, respectively). Patients with lower neuroticism scores had less oral health impact (p= 0.006, r = 0.44), better oral health-related QoL (p= 0.032, r =–0.35), higher total satisfaction, satisfaction with appearance, pain, oral comfort, and eating (p < 0.05, r =–0.58, –0.35, –0.33, –0.39, and –0.35, respectively). Conclusion: Patients’ satisfaction with their dentition and prosthetic rehabilitations has positive effects on oral health-related QoL and oral health impacts and improves patients’ daily living and dental perceptions. Neuroticism might influence and predict patients’ satisfaction with their dentition, oral health impacts, and oral health-related QoL. Satisfaction with the dentition might predict a patient's level of neuroticism.

Conversion degree of indirect resin composites and effect of thermocycling on their physical properties.

Abstract: Univ Zurich, Dent Mat Unit, Ctr Dent & Oral Med, Clin Fixed & Removable Prosthodont & Dent Mat Sci, CH-8032 Zurich, Switzerland

Effects of abutment screw coating on implant preload.

Abstract: Purpose: The aim of the present study was to investigate the effects of tungsten carbide carbon (WC/CTa) screw surface coating on abutment screw preload in three implant connection systems in comparison to noncoated titanium alloy (Ta) screws. Materials and Methods: Preload of WC/CTa abutment screws was compared to noncoated Ta screws in three implant connection systems. The differences in preloads were measured in tightening rotational angle, compression force, initial screw removal torque, and postload screw removal torque after 1 million cyclic loads. Preload loss percent was calculated to determine the efficacy of maintaining the preload of two abutment screw types in relation to implant connection systems. Results: WC/CTa screws provided 10° higher tightening rotational angle than Ta screws in all three connection systems. This difference was statistically significant (p < 0.05). External-hex butt joint implant connections had a higher compression force than the two internal conical implant connections. WC/CTa screws provided a statistically significantly higher compression force than Ta screws in all three implant connections (p < 0.05). Ta screws required statistically higher removal torque than WC/CTa screws in all three implant connections (p < 0.05); however, Ta screws needed statistically lower postload removal torque than WC/CTa screws in all three implant connections (p < 0.05). Ta screws had a statistically higher preload loss percent than WC/CTa screws in all three implant connections (p < 0.05), indicating that WC/CTa screws were superior in maintaining the preload than Ta screws. Conclusions: Within the limits of present study, the following conclusions were made: (1) WC/CTa screws provided higher preload than noncoated Ta screws in all three implant connection systems. (2) The initial removal torque for Ta screws required higher force than WC/CTa screws, whereas postload removal torque for Ta screws was lower than WC/CTa screws. Calculated Ta screw preload loss percent was higher than for WC/CTa screws, suggesting that WC/CTa screws were more effective in maintaining the preload than Ta screws. (3) Internal conical connections were more effective in maintaining the screw preload in cyclic loads than external-hex butt joint connections.

Human perception of dental porcelain translucency correlated to spectrophotometric measurements.

Abstract: Purpose: This study evaluated the relationship between instrumental measurements and subjective visual assessment of differences in dental porcelain translucency. Materials and Methods: Unshaded feldspathic porcelain was used with controlled amounts of tin oxide to create two groups of 12-mm diameter disks with incremental changes in opacity. Contrast ratio (CR = Yb/Yw) was determined with a spectrophotometer, and used as a measure of porcelain translucency (Group A = 0.20 to 0.40; Group B = 0.6–0.8). Within each group, there were 14 specimens with 11 CRs. Three observer groups (first year dental students, residents, faculty with >10 years of shade matching experience) were recruited to assess the translucency between porcelain disks under two lighting conditions (reflected light, transmitted light). Each subject's ability to distinguish between specimens of differing translucency was determined. Descriptive statistics and three-way ANOVA followed by a post-hoc Tukey-Kramer test were used to evaluate the translucency perception threshold (TPT) of subjects (α= 0.05). Results: The overall mean TPT (ΔC) was 0.07, while 50% of the subjects could perceive a 0.06 CR difference between porcelain specimens. Three-way ANOVA revealed a significant difference in translucency perception among the observer groups (p < 0.0001), whereas the main effects for porcelain opacity (p= 0.3038) and lighting condition (p= 0.0645) were not significant, and no significant interactions were found. Post-hoc Tukey-Kramer test indicated that the mean TPT observed in the faculty group (ΔC = 0.04) was significantly lower than those observed in student (ΔC = 0.09) and resident groups (ΔC = 0.08), while there was no significant difference between students and residents. Conclusions: The overall mean TPT of all subjects was 0.07, and 50% of the study population perceived a 0.06 CR difference in translucency. Increased shade matching experience (≥10 years) significantly improved the ability to perceive differences in translucency; however, neither the viewing condition nor porcelain opacity affected the perceived translucency threshold.

Influence of Surface Treatment on the Shear Bond Strength of Ceramics Fused to Cobalt–Chromium

Abstract: Universidade Federal da Paraiba (UFPB), Dept Restorat Dent, BR-58059900 Joao Pessoa, Paraiba, Brazil

A Six-Month Assessment of Oral Health-Related Quality of Life of Complete Denture Wearers Using Denture Adhesive: A Pilot Study

Abstract: Purpose: Edentulism and conventional complete denture treatment have been shown to have a negative impact on oral health quality of life (OHQoL). The use of an adhesive agent can provide an alternative to implant-supported prostheses. The objective of this study was to show that new complete dentures using a denture adhesive (DA) improve oral health-related quality of life. Materials and Methods: The oral health QoL of 143 patients was assessed after 3 months of wearing new complete dentures. Fourteen participants presented a low geriatric oral health assessment index (GOHAI) score and were included in this study and asked to use a DA. Oral health QoL and masticatory parameters were assessed at the beginning of the study, then at 3 and 6 months. Results: Significant improvements were observed in the scores obtained for each field of GOHAI (function, pain, discomfort, psychosocial); however, even after use of the DA, no statistically significant change in masticatory parameters was found. Conclusions: These results show that using a DA may improve subjects’ ability to manage conventional dentures and enhance their oral quality of life. A larger, prospective, multicenter study is subsequently needed to confirm these results.

Effect of Veneering Techniques on Color and Translucency of Y‐TZP

Abstract: Purpose: This study compared the color parameters and total luminous transmittance of disc specimens by different veneering techniques in order to examine the effect of veneering technique on esthetics of yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) all-ceramic restorations Materials and Methods: Thirty disc specimens (10-mm diameter, 050 ± 001 mm thick) were fabricated of IPS emax ZirCAD core material, and ZL1 IPS emax ZirLiner (010-mm thick) was layered The specimens were randomly divided into three groups (n = 10/group) Group ZP (fully anatomical technique) was veneered 060 mm by heat-pressing IPS emax ZirPress fluorapatite glass-ceramic ingots; Group ZC (traditional layering technique) was veneered 060 mm by condensing and sintering IPS emax Ceram low-fusing nano-fluorapatite veneering porcelain; Group ZPC (cutback technique) was veneered by partially pressed ingots and subsequently layered 030 mm with veneering porcelain Color parameters (L*, a*, b*) and total luminous transmittance (τ) of zirconia core discs and core and veneer specimens were measured with ShadeEye NCC dental colorimeter and spectrophotometer, respectively Color saturation (C*ab) and color difference (ΔE) were calculated using color difference formula One-way analysis of variance (ANOVA) combined with a Tukey multiple-range test were used to analyze the data (α= 005) Results: As to ZP, ZPC, and ZC groups, the value of a* increased (−135 ± 007, −064 ± 006, −036 ± 005, respectively) (p < 005); b* decreased (2701 ± 007, 2548 ± 011, 2328 ± 025, respectively) (p < 005); and C*ab decreased (2704 ± 008, 2549 ± 011, 2328 ± 025, respectively) (p < 005) L* value and total luminous transmittance were highest in ZP group (8753 ± 048, 164 ± 003, respectively), and lowest in ZPC group (8214 ± 018, 147 ± 001, respectively) (p < 005) Conclusions: Y-TZP all-ceramic restoration veneered by fully anatomical technique was the most transparent and lightest, while restorations veneered by cutback technique were the least translucent and the darkest

Effect of Extraoral Aging Conditions on Color Stability of Maxillofacial Silicone Elastomer

Abstract: PURPOSE: Maxillofacial prostheses require enhancement or replacement due to deterioration in their color during service. The purpose of this study was to investigate color stability of pigmented and nonpigmented maxillofacial silicone elastomer exposed to different human and environmental aging conditions. MATERIAL AND METHODS: One hundred and twelve disk-shaped silicone (TechSil S25, Technovent, Leeds, UK) specimens were prepared and equally divided into pigmented (using intrinsic rose-pink skin shade, P409, Principality Medical, Newport, UK) and nonpigmented categories of seven groups (n = 16; 8 pigmented and 8 nonpigmented): dark storage (control) (group 1), sebum solution storage (group 2), acidic perspiration storage (group 3), light aging (group 4), natural outdoor weathering (group 5), silicone-cleaning solution (group 6), and mixed conditioning of sebum storage and light aging (group 7). Conditioning periods (groups) were 6 months (groups 1, 2, 3, 5), 360 hours (groups 4, 7), and 30 hours (group 6). Color change (?E) was measured at the start and end of conditioning. In addition, for groups 1, 2, and 4, ?E was measured at fixed intervals of 30 days, 15 days, and 30 hours, respectively. Data were analyzed with one-way analysis of variance (ANOVA), Dunnett's-T3 post hoc, and independent t-tests (p 3). Within the nonpigmented category, specimens stored in the dark for 6 months (group 1) exhibited high ?E (6.17), which was greater (p 3.0, range from 3.48 to 9.89 for pigmented and 3.89 to 10.78 for nonpigmented) when subjected to six of the seven extraoral aging conditionings used in this study. Inherent color instability of nonpigmented facial silicone elastomers primarily contributes to the color degradation of extraoral facial prostheses. Sebaceous skin secretions along with daylight radiation cause the greatest perceivable color change to the silicone and pigment used in this study.

Efficient resource use in simplified complete denture fabrication.

Abstract: Purpose: Conventional dentures will remain the only treatment available to most edentulous people for the foreseeable future. In this study, we compared the efficiency of two methods of making complete conventional dentures—the traditional academic standard (T) and a simplified technique (S) used in private practice. We have previously shown that they produce similar levels of patient satisfaction and denture quality. Materials and Methods: Data were gathered during a randomized controlled clinical trial of 122 subjects from initial examination until 6-month follow-up. For this report, the direct costs of providing one set of conventional complete dentures by T or S techniques were estimated. All materials used were recorded and their cost was calculated in Canadian dollars (CAN$). The costs of fabrication in an outside laboratory were added. Clinician's labor time was recorded for every procedure. Between-group comparisons for each clinical procedure were carried out with independent t-tests. The number of patients in each group who needed postdelivery treatment was compared with Chi-square tests. The effect of group assignment and of treatment difficulty on outcomes was analyzed with multiple regression analysis. Results: The mean total cost of the T method was significantly greater than S (CAN$166.3; p < 0.001), and clinicians spent 90 minutes longer (p < 0.001) on clinical care. The difficulty of the case had no significant influence on outcomes. Conclusions: The results indicate that the S method is the more cost-efficient method and that there are no negative consequences that detract from the cost savings.

Analysis of masticatory cycle efficiency in complete denture wearers.

Abstract: Sao Paulo State Univ, Dept Dent Mat & Prosthodont, UNESP, BR-16050050 Aracatuba, SP, Brazil

Influence of Material of Overdenture-Retaining Bar with Vertical Misfit on Three-Dimensional Stress Distribution

Abstract: Purpose: This study evaluated the effects of different bar materials on stress distribution in an overdenture-retaining bar system with a vertical misfit between implant and bar framework. Materials and Methods: A three-dimentional finite element model was created including two titanium implants and a bar framework placed in the anterior part of a severely reabsorbed jaw. The model set was exported to mechanical simulation software, where displacement was applied to simulate the screw torque limited by 100-μm vertical misfit. Four bar materials (gold alloy, silver-palladium alloy, commercially pure titanium, cobalt-chromium alloy) were simulated in the analysis. Data were qualitatively evaluated using Von Mises stress given by the software. Results: The models showed stress concentration in cortical bone corresponding to the cervical part of the implant, and in cancellous bone corresponding to the apical part of the implant; however, in these regions few changes were observed in the levels of stress on the different bar materials analyzed. In the bar framework, screw, and implant, considerable increase in stress was observed when the elastic modulus of the bar material was increased. Conclusions: The different materials of the overdenture-retaining bar did not present considerable influence on the stress levels in the periimplant bone tissue, while the mechanical components of the system were more sensitive to the material stiffness.

Effect of different cements on the biomechanical behavior of teeth restored with cast dowel-and-cores-in vitro and FEA analysis.

Abstract: Purpose: To test the hypothesis that the type of cement used for fixation of cast dowel-and-cores might influence fracture resistance, fracture mode, and stress distribution of single-rooted teeth restored with this class of metallic dowels. Materials and Methods: The coronal portion was removed from 40 bovine incisors, leaving a 15 mm root. After endodontic treatment and standardized root canal relief at 10 mm, specimens were embedded in polystyrene resin, and the periodontal ligament was simulated with polyether impression material. The specimens were randomly divided into four groups (n = 10), and restored with Cu–Al cast dowel-and-cores cemented with one of four options: conventional glass ionomer cement (GI); resin-modified glass ionomer cement (GR); dual-cure resin cement (RC); or zinc-phosphate cement (ZP). Sequentially, fracture resistance of the specimens was tested with a tangential load at a 135° angle with a 0.5 mm/min crosshead speed. Data were analyzed using one-way analysis of variance (ANOVA) and the Fisher test. Two-dimensional finite element analysis (2D-FEA) was then performed with representative models of each group simulating a 100 μm cement layer. Results were analyzed based on von Mises stress distribution criteria. Results: The mean fracture resistance values were (in N): RC, 838.2 ± 135.9; GI, 772.4 ± 169.8; GR, 613.4 ± 157.5; ZP, 643.6 ± 106.7. FEA revealed that RC and GR presented lower stress values than ZP and GI. The higher stress concentration was coincident with more catastrophic failures, and consequently, with lower fracture resistance values. Conclusions: The type of cement influenced fracture resistance, failure mode, and stress distribution on teeth restored with cast dowel-and-cores.

Implant‐Supported Obturator Overdenture for Extensive Maxillary Resection Patient: A Clinical Report

Abstract: This clinical report presents an implant-retained obturator overdenture solution for a Prosthodontic Diagnostic Index Class IV maxillectomy patient with a large oronasal communication and severe facial asymmetry, loss of upper lip and midfacial support, severe impairment of mastication, deglutition, phonetics, and speech intelligibility. Due to insufficient bone support to provide satisfactory zygomaticus implant anchorage, conventional implants were placed in the body of the left zygomatic arch and in the right maxillary tuberosity. Using a modified impression technique, a cobalt-chromium alloy framework with three overdenture attachments was constructed to retain a complete maxillary obturator. Patient-reported functional and quality of life measure outcomes were dramatically improved after treatment and at the two-year follow-up.

Relevant anatomic and biomechanical studies for implant possibilities on the atrophic maxilla: critical appraisal and literature review.

Abstract: Purpose: The purpose of this review was to highlight anatomic and biomechanical aspects of atrophic maxillae for implant possibilities. Materials and Methods: A MEDLINE electronic search of the years 1966 to 2009 was conducted with the keywords “atrophic,”“resorbed,”“edentulous,” and “maxilla.” Results: Twenty papers presented the following findings: (1) previous use of a removable prosthesis is a risk factor for resorption, with flabby tissues related to the severity of resorption; (2) implants in the reconstructed maxilla (≤5 mm) and supporting overdentures had a higher risk for bone loss based on the worse periimplant soft-tissue health observed; (3) bleeding on probing was found with pocket depths ≥5 mm in half of the zygomatic implants; (4) prevalence of bone septa is higher in atrophic maxillae, and changes on nasopalatine canal can reduce up to 44.4% of the full length of buccal bone plates; (5) female patients have less medullar bone quantity and connectivity than male patients; (6) transectioning of nutrient vessels is easier and accelerates resorption; (7) stress does not concentrate on maxillary sinus base cortical bone contiguous to trabecular bone; (8) splinted implants receive nine times less load than nonsplinted implants even under oblique loading; (9) implant stability quotient (ISQ) values for implants ranged between 60 and 65; (10) in vivo force transfer to implants is similar between fixed prostheses and overdentures; (11) inclined implants generate better biomechanical responses; (12) masticatory efficiency and bite forces improve in maxillectomized patients who receive obturators with milled bar attachments. Conclusion: Sound implant-supported choices for an atrophic maxilla must be made with a thorough understanding of its anatomic and biomechanical factors.

Influence of cusp inclination on stress distribution in implant-supported prostheses. A three-dimensional finite element analysis.

Abstract: Purpose The aim of this study was to assess the influence of cusp inclination on stress distribution in implant-supported prostheses by 3D finite element method. Materials and methods Three-dimensional models were created to simulate a mandibular bone section with an implant (3.75 mm diameter x 10 mm length) and crown by means of a 3D scanner and 3D CAD software. A screw-retained single crown was simulated using three cusp inclinations (10 degrees, 20 degrees, 30 degrees). The 3D models (model 10d, model 20d, and model 30d) were transferred to the finite element program NeiNastran 9.0 to generate a mesh and perform the stress analysis. An oblique load of 200 N was applied on the internal vestibular face of the metal ceramic crown. Results The results were visualized by means of von Mises stress maps. Maximum stress concentration was located at the point of application. The implant showed higher stress values in model 30d (160.68 MPa). Cortical bone showed higher stress values in model 10d (28.23 MPa). Conclusion Stresses on the implant and implant/abutment interface increased with increasing cusp inclination, and stresses on the cortical bone decreased with increasing cusp inclination.

Fabrication of an Orbital Prosthesis Using a Noncontact Three‐Dimensional Digitizer and Rapid‐Prototyping System

Abstract: Conventionally, fabricating a facial prosthesis requires complicated steps and sophisticated skills. Particularly, the facial impression can be uncomfortable for the patient and can cause compression because of the weight of the material. The new approach presented in this report could simplify the fabrication of facial prostheses using a noncontact three-dimensional digitizer and binder multinozzle inkjet printer, without computed tomography or making a conventional impression. Treatment time was reduced, and the patient expressed satisfaction after 6 months follow-up.

Resistance to wear of four matrices with ball attachments for implant overdentures: a fatigue study

Abstract: Purpose: The study evaluated in vitro the retention force and the wear resistance over simulated function of four matrix components of ball attachments for implant-retained overdentures. Materials and Methods: Four types of matrices for ball attachments were evaluated in a fatigue study simulating 5500 cycles of insertion and removal. The matrices used were (1) a Teflon matrix supported by a metal housing, (2) a titanium matrix, (3) a gold alloy matrix, (4) an O-ring matrix using the red color ring for medium retention. Dimensional changes of the ball attachments were investigated with a profilometer. Results: The Teflon matrices showed an increase of 27% in retention at 5500 cycles while the gold alloy matrices showed an increase of 50% in retention in the first 500 cycles and remained relatively stable up to 5500 cycles. On the other hand, titanium matrices and O-ring matrices exhibited progressive loss of retention ending with 68% and 75% of retention loss, respectively, at 5500 cycles. Dimensional analysis by profilometer revealed significant wear on the ball attachment only for titanium matrixes. Conclusions: Gold alloy and Teflon matrices showed the highest retention values without retention loss after 3 years of simulated function. Titanium and O-ring matrices presented a continuous loss of retention with the highest wear on the ball attachments when combined with the titanium matrix.

The position of the occlusal plane in natural and artificial dentitions as related to other craniofacial planes.

Abstract: Purpose: This study aimed at determining the most reliable ala-tragus line as a guide for the orientation of the occlusal plane in complete denture patients by use of cephalometric landmarks on dentate volunteers. Materials and Methods: Analysis was made for prosthodontically related craniofacial reference lines and angles of lateral cephalometric radiographs taken for 47 dentate adults. Variables were determined and data were analyzed using SPSS (SPSS, Inc., Chicago, IL). Results: Occlusal plane angle formed between the occlusal plane and Camper's plane had the lowest mean value in the angle formed with Camper's I, which represents the measure taken from the superior border of the tragus of the ear with a score of 2.1°. The highest was measured in the angle formed with Camper's III with a score of 6.1°, while the angle formed with Camper's II was 3.2°. The differences between the three planes in relation to the occlusal plane was significant (p < 0.001). Conclusion: The superior border of the tragus with the inferior border of the ala of the nose was most accurate in orienting the occlusal plane.

Variability of Mechanical Torque‐Limiting Devices in Clinical Service at a US Dental School

Abstract: Purpose: The purpose of this study was to measure the variability of torque produced by a population of mechanical torque-limiting devices in clinical service in a US dental school. The torque-limiting devices were divided into two categories according to their mode of action: toggle-type and beam wrenches. Proper action of these devices is essential for calibrated delivery of preload to implant prosthetic screws. Materials and Methods: Seventeen torque-limiting devices (35 Ncm) were obtained from graduate prosthodontic, predoctoral, and faculty practice clinics. Nine of these were toggle-type devices, and eight were beam-type wrenches. Torque from each wrench was measured using an MGT electronic torque meter. Wrenches were tested in two modes, slow (over 4 seconds) and fast (over 1 second). Results: Toggle-type torque wrenches produced a mean (± SD) torque of 38.1 ± 16.0 Ncm; beam-type wrenches produced 32.8 ± 1.1 Ncm. These results were not significantly different. When tested in fast mode (1 second), toggle-type wrenches produced 28.0 ± 9.6 Ncm; in the slow mode (4 seconds) they produced significantly more force, 36.6 ± 14.0 Ncm (p < 0.001). Beam-type wrenches produced 33.2 ± 1.1 Ncm and 32.8 ± 1.1 Ncm in fast and slow modes, respectively. Conclusions: Both types of wrenches tested were capable of producing accurate torque values; however, variability was higher in the toggle-type group. Some toggle-type torque wrenches in clinical service delivered unacceptably high torque values. It is recommended that clinicians calibrate toggle-type wrenches frequently. Torque wrenches should be activated slowly, over 4 seconds, when using a correctly calibrated toggle-type wrench.

Gender Differences in the Amount of Gingival Display During Smiling Using Two Intraoral Dental Biometric Measurements

Abstract: Purpose: The aims of this study were to compare gender differences in the width and length of the maxillary right central incisor and the horizontal and vertical overlap of the anterior teeth and to determine the relationships of these two intraoral dental biometric measurements with the amount of gingival display during smiling. Materials and Methods: A total of 61 men and 66 women were included in this study. For each participant, the gingival tissue display during smiling was judged to be either visible or not, and the maximum mesiodistal and incisogingival dimensions of the maxillary right central incisor were measured, along with the amount of horizontal and vertical overlap of anterior teeth using a digital caliper. Gender differences in these parameters and the relationship between subjects showing gingival display when smiling and the two intraoral dental biometric measurements were determined. Statistical analyses of data were performed using SPSS (V11) software. The mean scores for gender were calculated, and a Student's t-test was used to identify significant differences between both groups. Significance level was set to 0.05. Results: The age of the participants ranged between 23 and 52, with a mean of 33.47 ± 9.07 years. A relatively small percentage of the subjects (22.05%) displayed gingiva when smiling. More women displayed gingiva when smiling than men, with a 2:1 female:male ratio. Men exhibited significantly (p < 0.05) wider (8.76 ± 0.66 mm) and longer (10.28 ± 0.88 mm) central incisors compared to women (7.92 ± 0.72 mm; 9.27 ± 0.93 mm width and length, respectively). No gender differences were found in the width-to-length ratio. Subjects with gingival display had significantly more horizontal (4.28 ± 1.21 mm; p < 0.001), and vertical (3.52 ± 0.66 mm; p < 0.05) overlap of anterior teeth compared to those who did not display gingiva when smiling (2.40 ± 1.03 and 2.30 ± 0.93 mm, respectively). Conclusions: Significantly more women displayed gingiva in smiling. Men had significantly wider and longer central incisors. No differences were recorded between men and women relative to both the horizontal and vertical anterior tooth overlap. Subjects who displayed gingiva when smiling had more horizontal and vertical overlap of anterior teeth.

Opaque Layer Firing Temperature and Aging Effect on the Flexural Strength of Ceramic Fused to Cobalt-Chromium Alloy

Abstract: PURPOSE: To evaluate the effect of the opaque layer firing temperature and mechanical and thermal cycling on the flexural strength of a ceramic fused to commercial cobalt-chromium alloy (Co-Cr). The hypotheses were that higher opaque layer temperatures increase the metal/ceramic bond strength and that aging reduces the bond strength. MATERIALS AND METHODS: Metallic frameworks (25 x 3 x 0.5 mm(3); ISO 9693) (N = 60) were cast in Co-Cr and airborne-particle abraded (Al(2)O(3): 150 mum) at the central area of the frameworks (8 x 3 mm(2)) and divided into three groups (N = 20), according to the opaque layer firing temperature: Gr1 (control)-900 degrees C; Gr2-950 degrees C; Gr3-1000 degrees C. The opaque ceramic (Opaque, Vita Zahnfabrick, Bad Sackingen, Germany) was applied, and the glass ceramic (Vita Omega 900, Vita Zahnfabrick) was fired onto it (thickness: 1 mm). While half the specimens from each group were randomly tested without aging (water storage: 37 degrees C/24 hours), the other half were mechanically loaded (20,000 cycles; 50 N load; distilled water at 37 degrees C) and thermocycled (3000 cycles; 5 degrees C to 55 degrees C, dwell time: 30 seconds). After the flexural strength test, failure types were noted. The data were analyzed using 2-way ANOVA and Tukey's test (alpha= 0.05). RESULTS: Gr2 (19.41 +/- 5.5 N) and Gr3 (20.6 +/- 5 N) presented higher values than Gr1 (13.3 +/- 1.6 N) (p= 0.001). Mechanical and thermal cycling did not significantly influence the mean flexural strength values (p > 0.05). Increasing the opaque layer firing temperature improved the flexural bond strength values (p < 0.05). The hypotheses were partially accepted. CONCLUSION: Increasing of the opaque layer firing temperature improved the flexural bond strength between ceramic fused to Co-Cr alloy.

Effect of 180 days of water storage on the transverse strength of acetal resin denture base material.

Abstract: Purpose: Acetal resin has been used as an alternative denture base and clasp material since 1986. The manufacturers claim that acetal resin has superior physical properties when compared to conventional denture base acrylic resins. Limited information is available about transverse strengths of acetal resin. The purpose of this investigation was to compare transverse strengths of pink and white acetal resins to transverse strengths of conventional heat-polymerized polymethylmethacrylate (PMMA) resin in increasing durations of water storage. Materials and Methods: A transverse strength test was performed in accordance with International Standards Organization (ISO) specification No 1567. Twenty 65 × 10 × 2.5 mm3 specimens of each resin were prepared; five specimens of each resin group were subjected to three-point bending test after 50 hours, 30 days, 60 days, and 180 days of water storage in distilled water at 37°C. Experimental groups’ transverse strengths were compared by three-way ANOVA and Duncan's multiple range tests. Results: Transverse strength of PMMA denture base material was found to be in accordance with the requirements of ISO specification No 1567. Transverse strengths of white and pink acetal resin could not be calculated in this study, as white and pink acetal resin specimens did not break at the maximum applied force in the three-point bending test. Flexural strength of acetal resin was found to be within the ISO specification limits. As the water storage time increased, the deflection values of PMMA showed no significant difference (p > 0.05). Both the white and pink acetal resin showed significant increase in deflection as the water storage time was increased from 50 hours to 180 days (p < 0.05). Conclusion: The results of this study indicated that transverse strength values of PMMA were within the ISO specification limit. Water storage time (50 hours, 30, 60, and 180 days) had no statistically significant effect on the transverse strength and deflection of PMMA. Acetal resin suffered from permanent deformation, but did not break in the three-point bending test. Acetal resin showed significant increase in deflection as the water storage time was increased from 50 hours to 180 days. All materials tested demonstrated deflection values in compliance with ISO specification No 1567.