School type and oral conditions associated with school performance and absenteeism in adolescents: A multilevel analysis.

BACKGROUND: Investigations assessing how oral health status affects school performance and attendance considering individual and community variables are lacking. AIM: To analyze the association of school contextual factors and oral conditions with school performance and absenteeism in early adolescence. DESIGN: This cross-sectional study was carried out with 593 12-year-old students from 20 schools in Passo Fundo, a southern city in Brazil. The caregivers provided sociodemographic information by means of a questionnaire. Oral health status was clinically examined for dental caries and gingival bleeding. Students answered the CPQ11-14 questionnaire to assess the oral health-related quality of life (OHRQoL). Information on contextual factors was obtained from the schools' administrators. "School performance" was measured by Portuguese and Mathematic tests' scores, and "school absenteeism" by the number of school days missed. Descriptive statistics was conducted, followed by unadjusted and adjusted multilevel linear regression. RESULTS: At the individual level, low OHRQoL was associated with lower school performance and higher absenteeism. At the contextual level, students from private schools had higher school performance and lower mean of school days missed. CONCLUSIONS: The type of school and OHRQoL were associated with school performance and attendance of adolescents.

Assessment of the survival and success rates of lithium disilicate crowns after different surface finishing procedures: An in vitro study.

STATEMENT OF PROBLEM: Evidence is limited for the impact of clinical adjustments and polishing on the longevity of glazed lithium disilicate restorations. PURPOSE: The purpose of this in vitro study was to evaluate the influence of surface finishing on the survival and success rates of lithium disilicate restorations based on fatigue resistance and failure mode. MATERIAL AND METHODS: Lithium disilicate (IPS e.max CAD) maxillary premolar crowns (N=54) were cemented on a dentin analog. The restorations were divided into 3 groups: overglaze (OG), abrasion (GA), and abrasion and polishing (AP). The crowns were submitted to cyclic fatigue in 37 oC water at 100 N and 2 Hz in 2 lifetimes. The load was applied to the occlusal surface by using anatomic pistons to simulate a clinical tripod occlusal contact. After cycling, the crowns were examined for failure (cracking, chipping, or catastrophic fractures) under optical and scanning electron microscopy. Cracking was considered either a structural failure (success analysis) or a survival (clinical criteria - survival analysis). Data were analyzed by using the log rank Kaplan-Meier and Holm-Sidak tests (α=.05). RESULTS: Surface finishing had no influence on the structural integrity of lithium disilicate, with similar success rates (P=.720). The calculated survival rate was higher for AP than that for other groups (P=.028). Cracking was found for GA and AP crowns, mostly initiating from the external surface. Chipping occurred in all experimental groups, and AP crowns did not show catastrophic failures. CONCLUSIONS: Although surface treatments had no influence on the success of lithium disilicate, polishing showed a positive effect on the survival rate of the crowns based on the clinical implications of cracking (no need for replacement).

Influence of piston material on the fatigue behavior of a glass-ceramic.

STATEMENT OF PROBLEM: The lack of standardization regarding the loading piston material used in fatigue tests could limit the interpretation of study findings. PURPOSE: The purpose of this in vitro study was to evaluate the effect of the piston material on the fatigue behavior of a lithium disilicate glass-ceramic. MATERIAL AND METHODS: Plate-shaped, 1.2-mm-thick, lithium disilicate glass-ceramic specimens were cemented onto a dentin analog substrate with resin cement. The specimens were divided into 4 groups according to the piston material used in the fatigue test (n=30): metal, glass fiber-reinforced epoxy resin, ceramic, and human tooth. The fatigue test was performed in a mechanical cycling machine by using the boundary technique at 2 Hz in distilled water at 37 °C. The fatigue data were analyzed by using the Weibull distribution and a lifetime-inverse power law relationship. Failures were evaluated with fractography and transillumination. RESULTS: The Weibull modulus (ß) was similar among groups. The exponent of crack growth (n) was significantly greater for glass fiber-reinforced epoxy resin and tooth groups than for metal and ceramic; therefore, the probability of failure (Pf) of glass-ceramic specimens loaded by resin and tooth pistons depended more on load amplitude. Specimens tested with tooth showed the highest value of K (characteristic lifetime), which is an indication of greater survival. Radial crack was the only failure mode observed for all experimental groups. CONCLUSIONS: The piston material influenced the fatigue survival of the lithium disilicate glass-ceramic. The glass fiber-reinforced epoxy resin piston closely simulated the fatigue behavior induced by the human tooth on the evaluated glass-ceramic.

Fatigue resistance of polymeric restorative materials: effect of supporting substrate.

The objective of this study was to investigate the effect of mismatch between the elastic properties of substrate and restorative material on the fatigue resistance and stress distribution of multilayer structures. The tested hypotheses were that (1) both an indirect composite resin (IR) and a polymer-infiltrated ceramic network (PICN) would show a higher survival rate after cyclic loading when cemented to a substrate with a high elastic modulus (E); and (2) PICN structures would have higher survival rates than IR structures regardless of the supporting substrate. Blocks of PICN and IR were cut to obtain 1.0-mm-thick sections, which were cemented to substrates with different E values: c, core resin cement (low E); r, composite resin (intermediate E); and m, metal (nickel-chromium alloy; high E). The resulting 6 groups of specimens (n = 20 per group) were subjected to a cyclic fatigue test (106 cycles). Stress distribution was verified using finite element analysis, and the risk of failure was estimated. Fatigue data were analyzed using Kaplan-Meier and Holm-Sidák tests. The χ2 test was used to evaluate the type of crack. The groups IRc, IRr, and PICNm had the highest survival rates after cyclic loading and were statistically similar to each other. Their survival rates were significantly greater than those of the IRm, PICNr, and PICNc groups (P < 0.001), which were all significantly different from each other (P < 0.001). There was a significant relationship between the experimental group and type of crack (P < 0.001). Specimens cemented to core resin cement and composite resin substrates showed predominantly radial cracks, while those cemented to nickel chromium alloy had predominantly cone cracks. The risk of failure values revealed that PICN was more sensitive to the type of substrate than IR. PICN has greater fatigue-resistant behavior when cemented to a substrate with a high E value, while IR has superior performance when substrates with lower and intermediate E values are used.

Effect of substrate and cement on the final color of zirconia-based all-ceramic crowns.

OBJECTIVE: To evaluate the influence of the substrate and the cement on the final color of ceramic crowns. METHODS: Prosthetic crowns (framework + porcelain) were fabricated using two all-ceramic systems (YZ, 3 mol% yttria-stabilized tetragonal zirconia; IZ, alumina-based zirconia-reinforced glass-infiltrated ceramic) and a metal-ceramic system (MC; n = 8). Metal (M) and resin (R) were used as substrate abutments. For R substrate, crowns were evaluated as seated (R) and after cementation (R-C). CIELAB color coordinates were obtained using a dental spectrophotometer with D65 light illumination. CIELAB, CIEDE2000 (1:1:1) and CIEDE2000 (2:1:1) color difference metrics were used. Data were analyzed using 95% confidence intervals and compared to perceptibility (PT) and acceptability (AT) thresholds. RESULTS: The ∆Eab* , ∆E00 (1 : 1 : 1), and ∆E00 (2 : 1 : 1) values of the restorative systems evaluated using different substrates (M.R) were similar to the AT values of each metric. When non-cemented and cemented crowns were evaluated (R.R-C), MC had color difference values at PT and below AT; while YZ and IZ showed similar values to AT, for ∆Eab* and ∆E00 (1 : 1 : 1) metrics. CONCLUSION: The substrate and cement affected the final color of zirconia-based all-ceramic crowns, but the color differences corresponded to an acceptable match. CLINICAL SIGNIFICANCE: As both substrate and cement influence the final color of multi-layered ceramic prosthesis, dentists and dental technicians should understand the optical properties of dental ceramics to reproduce the natural appearance of dental structures and maximize the chance for excellent color matches.

Predictors of orthodontic treatment conclusion: A historical cohort study.

INTRODUCTION: The study investigated which patient and orthodontic treatment factors act as predictors for the conclusion of the ongoing treatment in a dental clinic of a specialization program in Orthodontics. METHODS: Data were collected from the records of patients treated from 1997 to 2015. Potential predictors for treatment conclusion were investigated: patient-related factors (PRFs) and treatment-related factors (TRFs). PRFs were sex, age, face balance, Angle malocclusion classification, open bite, denture, facial pattern, facial profile, buccal corridor, crossbite, maxillary deficiency, and sagittal mandibular behavior; and TRFs were therapeutic approaches, treatment modality, extractions, and Bolton discrepancy. The initial and final treatment dates were collected. Descriptive data analysis, univariate, and multivariate logistic regression were performed (5% significance). RESULTS: Of the 903 records, 561 patients were included in the study. It was demonstrated that starting the treatment at a young age (PRF) and the presence of crossbite (TRF) are predictive factors for the treatment conclusion. A vertical facial pattern (dolichofacial or brachyfacial) and a greater number of extractions for orthodontic reasons may contribute positively to the conclusion of the treatment. The frequency of treatment inconclusion was higher during the first 2 years of treatment (more than 50% of the patients that initiated the treatment). CONCLUSIONS: Young age at the beginning of treatment and the presence of crossbite malocclusion can increase the chance of treatment conclusion.

Effect of supporting substrate on the failure behavior of a polymer-infiltrated ceramic network material.

STATEMENT OF PROBLEM: Restorative materials are cemented on different types of substrates, such as dentin, metal, and glass-fiber posts with composite resin cores. PURPOSE: The purpose of this in vitro study was to evaluate the failure behavior after cycling fatigue of a polymer-infiltrated ceramic network material (PICN; VITA ENAMIC) cemented on different supporting substrates. MATERIAL AND METHODS: PICN plates (N=80) were obtained from computer-assisted design and computer-assisted manufacturing (CAD-CAM) blocks and cemented with a resin cement to 4 different supporting substrates (n=20): (1) human dentin (PICNDen); (2) dentin analog (PICNDenAn); (3) nickel-chromium alloy (PICNNiCr); and (4) composite resin plus fiberglass post (PICNRc). For comparison, the fracture behavior of a feldspathic ceramic (FelDenAn; VITABLOCS Mark II) and an indirect composite resin (ResDenAn; Opallis LAB Resin) cemented to the DenAn substrate was investigated (n=20). Thus, specimens were composed of the restorative material layer (1-mm thick) resin cemented (0.1-mm-thick layer) to a 2-mm-thick supporting substrate. All specimens were subjected to mechanical cycling (MC) using a pneumatic cycling machine (500 000 cycles, 2 Hz, 50 N). Specimens that did not fracture during cycling were tested under compression using a universal testing machine at a cross-head speed of 0.5 mm/min until the sound of the first crack was detected using an acoustic system. Failure data were statistically evaluated using Weibull distribution. Failures were classified as radial crack, cone crack, combined, and catastrophic fracture. RESULTS: All FelDenAn specimens were fractured during MC. Only 4 PICNRc specimens survived MC, so their fracture load data were not statistically analyzed. PICNNiCr showed the greatest characteristic load (L0) value, followed by ResDenAn. Groups PICNDenAn and PICNDen showed lower and similar L0 but statistically different Weibull modulus (m). There was a significant relationship between experimental group and failure mode (P<.001). FelDenAn and PICNRc had a higher frequency of radial cracks, whereas PICNNiCr failed from cone cracking. CONCLUSIONS: The supporting substrate influenced the failure behavior of PICN. When the substrate had a higher elastic modulus than the restorative material, better mechanical behavior was observed.

Fatigue Behavior of Crystalline-Reinforced Glass-Ceramics.

PURPOSE: To evaluate the fatigue behavior of two crystalline-reinforced ceramics: leucite-reinforced (VL) and lithium disilicate-based (VD) glass-ceramics. MATERIALS AND METHODS: Bar-shaped specimens (16 × 4 × 1.2 mm) were produced for each ceramic using prefabricated CAD/CAM blocks. For each group, 30 specimens were subjected to a three-point flexural strength test in a universal testing machine. For VL and VD, 36 and 41 specimens were subjected to a cyclic fatigue test, respectively. The cyclic fatigue test was performed with a pneumatic mechanical cycling machine (1 Hz; 37°C distilled water). Specimens were tested at two stress levels for each preset lifetime (103 and 104 cycles for VL; 104 and 105 cycles for VD) following the boundary technique. Fractography was performed with a scanning electron microscope. Data were analyzed with Weibull analysis. RESULTS: There were significant differences among groups for characteristic strength (σ0 ) and Weibull modulus (m), as the confidence intervals did not overlap. The VD group presented the highest values of σ0 , but the lowest Weibull modulus. Both groups showed a reduction of approximately 60% of the initial flexural strength (σf ) after cycling for 104 cycles. For VD tested in fatigue, there was no degradation of σf when the number of cycles was increased from 104 to 105 . The VL group showed an 18% decrease in σf when the number of cycles increased from 103 to 104 . Flexural strength values estimated for a 5% probability of failure were 36 MPa for VL and 55 MPa for VD, after 104 cycles. CONCLUSION: Both glass-ceramics showed similar strength degradation (60%) after a lifetime of 104 cycles, despite their distinct mechanical properties. Mechanical cycling in humid conditions proved to be an important factor for the degradation of the mechanical properties of crystalline-reinforced glass-ceramics.

A literature review on the new polymer-infiltrated ceramic-network material (PICN).

OBJECTIVES: Ceramics and composites are the most used materials for dental application. Recently, the characteristics of both were combined on the called "polymer-infiltrated ceramic-network" (PICN). The aim of this review is to report the behavior of PICN, comparing the findings that may support the correct clinical application. OVERVIEW: The PICN material is a structure with a sintered ceramic matrix infiltrated with a polymer matrix. Studies evaluated this material microstructure and composition, mechanical properties and adhesive behavior. The most cited mechanical properties are flexural strength, compressive strength, elastic modulus, Weibull modulus, hardness, fracture toughness and fatigue resistance. Most studies compared PICN with feldspathic porcelain, lithium disilicate glass-ceramic, lithium silicate, zirconia-reinforced glass-ceramic, leucite reinforced glass-ceramic, polycrystalline alumina and zirconia. Other studies evaluated a similar material (a nanoceramic resin). CLINICAL SIGNIFICANCE: The mechanical properties of the PICN are equivalent to the properties of nanoceramic resins, lower to lithium disilicate glass ceramic and superior to feldspathic porcelain. Yet, the findings suggest a highly resistant material to degradation at low loads (close to physiological situation) when cemented on a substrate.

Effect of screw-access hole and mechanical cycling on fracture load of 3-unit implant-supported fixed dental prostheses.

STATEMENT OF PROBLEM: The effect of screw-access holes and mechanical cycling on fracture resistance of 3-unit screw-retained zirconia-based implant-supported fixed dental prostheses (ISFDPs) is unknown. PURPOSE: The purpose of this in vitro study was to evaluate the effect of screw-access holes on the maximum fracture load (Lf) of 3-unit ISFDPs fabricated with the same abutment design for screw (s)-retained and cement (c)-retained with either a metal- or zirconia-based framework, testing the hypotheses that ISFDPs with screw-access holes have the lowest Lf and that mechanical cycling decreases the Lf of screw-retained ISFDPs. MATERIAL AND METHODS: Models with fiberglass bases with 2 implants were fabricated. Special abutments were designed to allow for both s- and c-retained ISFDPs. The study considered the type of framework (s-retained metal-based and s-retained zirconia-based), fixation (s and c), and aging (a) with mechanical cycling, resulting in the following experimental groups (n=12): c-retained metal-based ISFDP; s-retained metal-based ISFDP (Ms); s-retained zirconia-based ISFDP aged by mechanical cycling (Zsa); and s-retained metal-based ISFDP aged by mechanical cycling (Msa). All ISFDPs were porcelain veneered and subjected to compressive load to failure. Fracture load data were statistically analyzed using 1-way ANOVA and Tukey range tests (α=.05). Fractography was used to evaluate the fracture surfaces. RESULTS: Cement-retained ISFDP (Zc and Mc) showed the greatest Lf values (P<.001). Zs prostheses showed higher Lf values than those for Ms. Aging significantly decreased the Lf of Zsa but had no effect on Msa. Chipping was the failure mode most frequently found. Only Zs and Zsa ISFDPs showed catastrophic failures. CONCLUSIONS: ISFDPs with screw-access holes showed lower Lf values, regardless of the framework type. Mechanical cycling affected the Lf of screw-retained zirconia-based ISFDPs.

How oral environment simulation affects ceramic failure behavior.

STATEMENT OF PROBLEM: Investigating the mechanical behavior of ceramics in a clinically simulated scenario contributes to the development of new and tougher materials, improving the clinical performance of restorations. The optimal in vitro environment for testing is unclear. PURPOSE: The purpose of this in vitro study was to investigate the failure behavior of a leucite-reinforced glass-ceramic under compression loading and fatigue in different simulated oral environment conditions. MATERIAL AND METHODS: Fifty-three plate-shaped ceramic specimens were produced from computer-aided design and computer-aided manufactured (CAD-CAM) blocks and adhesively cemented onto a dentin analog substrate. For the monotonic test (n=23), a gradual compressive load (0.5 mm/min) was applied to the center of the specimens, immersed in 37ºC water, using a universal testing machine. The initial crack was detected with an acoustic system. The fatigue test was performed in a mechanical cycling machine (37ºC water, 2 Hz) using the boundary technique (n=30). Two lifetimes were evaluated (1×106 and 2×106 cycles). Failure analysis was performed using transillumination. Weibull distribution was used to evaluate compressive load data. A cumulative damage model with an inverse power law (IPL) lifetime-stress relationship was used to fit the fatigue data. RESULTS: A characteristic failure load of 1615 N and a Weibull modulus of 5 were obtained with the monotonic test. The estimated probability of failure (Pf) for 1×106 cycles at 100 N was 31%, at 150 N it was 55%, and at 200 N it was 75%. For 2×106 cycles, the Pf increased approximately 20% in comparison with the values predicted for 1×106 cycles, which was not significant. The most frequent failure mode was a radial crack from the intaglio surface. For fatigue, combined failure modes were also found (radial crack combined with cone crack or chipping). CONCLUSIONS: Fatigue affects the fracture load and failure mode of leucite-reinforced glass-ceramic.

How does the piston material affect the in vitro mechanical behavior of dental ceramics?

STATEMENT OF PROBLEM: Variables involving the indication, manufacturing, and clinical use of ceramic restorations make the standardization of in vitro studies a challenge and raise questions as to the clinical validity of the resulting data. PURPOSE: The purpose of this in vitro study was to assess the effect of piston material on the fracture behavior of ceramics tested under compressive load. MATERIAL AND METHODS: Two ceramics were evaluated: a lithium disilicate-based glass-ceramic (D) and a feldspathic porcelain (P). Plate-shaped ceramic specimens (1.5-mm thick) were adhesively cemented onto a dentin analog substrate. The specimens from each ceramic were divided into 4 groups according to the piston material (n=20): metal (M) (stainless steel), composite resin (R) (NEMA-G10, fiber-reinforced epoxy resin), ceramic (C) (lithium disilicate-based glass-ceramic), and human tooth (T) (canine). A gradual compressive load (0.5 mm/min) was applied to the center of the specimen with a universal testing machine. The test was performed in 37°C distilled water, and the initial crack was detected by using an acoustic system. The fracture load values (N) were statistically analyzed with the Kruskal-Wallis and Dunn tests (α=.05). A finite element analysis (FEA) was also performed. RESULTS: Piston material had no influence on fracture load and failure mode of ceramic D. Ceramic P showed higher fracture load values when loaded with the composite resin piston. Ceramic P showed more combined failures (cone crack and radial crack) than D. The FEA showed a distinct stress distribution for R piston on P. Pistons C and T resulted in similar stress distribution, fracture load, and failure mode for both ceramics. CONCLUSIONS: The effect of piston material on the ceramic fracture behavior depends on the ceramic being evaluated.

Influence of surface finishing on fracture load and failure mode of glass ceramic crowns.

STATEMENT OF PROBLEM: Ceramic restorations often require adjustments using diamond rotary instruments, which damage the glazed surface. The effect of these adjustments on the fracture behavior of these restorations is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the influence of induced surface defects on the fracture load and mode of failure of lithium disilicate-based (LDS) glass ceramic restorations. MATERIAL AND METHODS: Premolar crowns were obtained from LDS computer-aided design and computer-aided manufacturing blocks (n=60) and glazed. The crowns were bonded to dentin analog dies and divided into 5 groups (n=12), as follows: glaze; abrasion (diamond rotary instrument 2135); abrasion and reglaze; abrasion and polishing (diamond rotary instrument 2135F, 2135 FF, and polishing devices); and polishing. The topography of the crowns was examined by scanning electron microscopy, and roughness was measured. A compressive load (0.5 mm/min) was applied by a piston to the center of the lingual cusp until fracture. The fracture load was recorded and data were statistically analyzed by ANOVA and the Tukey HSD test (α=.05). Fractured crowns were examined to determine the fracture origin. RESULTS: Polishing and/or reglazing resulted in lower roughness than for the abraded group (P<.05), which did not affect the fracture loads (P=.696). Catastrophic fracture with origin at the intaglio surface was the mode of failure for all the crowns. CONCLUSIONS: The experiment design successfully submitted the crowns to a clinical stress state, resulting in a clinically relevant failure. Reglazing or polishing were effective in reducing surface defects. Surface treatments had no effect on the immediate catastrophic failure of LDS crowns.

Effects of chrondro-osseous regenerative compound associated with local treatments in the regeneration of bone defects around implants: an in vivo study.

OBJECTIVES: The objective of this study was to evaluate the use of a chondroitin sulfate and glycosaminoglycan-based chrondro-osseous regenerative compound (CORC) with different local treatments for bone regeneration in dehiscence defects. The hypothesis is that CORC can enhance bone regeneration with or without local treatment. MATERIALS AND METHODS: Twelve mongrel dogs received four implants each in the right femur. Bony defects (4-mm height × 4-mm width) were created and locally treated as follows: reabsorbable membrane (Mem), hidroxyapatite (HA), hydroxyapatite covered with membrane (HA+Mem), or left untreated (Con). Six dogs received one pill of the CORC daily. After 90 days, the implants were retrieved, and histological sections were obtained. The height of bone formation, new bone area (NBA), and bone to implant contact (BIC) within the threads were evaluated to assess the effects of the use of CORC to promote bone regeneration in the defects. Results were statistically analyzed using ANOVA and Tukey's test with 5% significance level. RESULTS: CORC was not capable to increase the height of bone formation, NBA, and BIC. When the local treatments were analyzed regardless of the use of CORC, HA+Mem and Ha presented higher BIC and height of bone formation. There was no difference for NBA among the local treatments. CONCLUSIONS: The hypothesis was rejected since the use of CORC has not increased any of the parameters evaluated. CLINICAL RELEVANCE: Dehiscence-like defects can compromise soft tissue support and result in loss of periodontal health and implants. Hydroxyapatite can induce bone regeneration in the defects created. CORC in the formulation used in this study did not promote further bone regeneration in dehiscence-like defects.

Effect of the CAD/CAM Milling Protocol on the Fracture Behavior of Zirconia Monolithic Crowns.

Although advancements in CAD/CAM technology allow for more personalized treatments, it is not clear how modifications in the CAD/CAM milling process could affect the restoration surface conditions and their mechanical behavior. The objective of this study was to evaluate the effect of different CAD/CAM milling protocols on the topography and fracture behavior of zirconia monolithic crowns (3Y-PSZ) subjected to a chewing simulation. Monolithic 3Y-PSZ premolar crowns were milled using three protocols (n = 13) (slow (S), normal (N), and fast (F)). Crowns were cemented on a dentin analog abutment and subjected to mechanical aging (200 N, 2 Hz, 1,500,000 cycles, 37 °C water). Surviving crowns were subjected to compressive load test and analyzed using fractography. Fracture load data were analyzed with two-parameter Weibull analysis. The surface topography of the crowns was examined with a stereomicroscope and a 3D non-contact profiler. All crowns survived the chewing simulation. Crowns milled using the F protocol had the greatest characteristic fracture load, while crowns produced with the S protocol showed high Weibull modulus. Groups N and S had a more uniform surface and detailed occlusal anatomy than group F. The CAD/CAM milling protocol affected the topography and mechanical behavior of 3Y-PSZ monolithic crowns.

Failure behavior of zirconia crowns subjected to air abrasion with different particle sizes.

This study aimed to investigate the failure behavior of 3 mol.% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) prosthetic crowns air-abraded with aluminum oxide (AO) particles of different sizes. Ninety ceramic premolar crowns were produced with 3Y-TZP frameworks veneered with porcelain. Crowns were randomly divided into three groups, according to the size of the air abrasion AO particles (n = 30): (GC) untreated (control); (G53) 53 µm; (G125) 125 µm. Air abrasion was performed with 0.25 mpa pressure, 10-mm distance, for 10 s. Crowns were adhesively cemented to dentin analog abutments. Specimens were loaded in compression to failure, in 37oC distilled water, using a universal testing machine (n = 30). Fractographic analysis was performed using a stereomicroscope and SEM. The roughness of the crown's inner surface was evaluated using an optical profilometer (n = 10). Fracture load data were statistically analyzed with Weibull analysis and roughness data with Kruskal-Wallis (α = 0.05). GC had the lowest characteristic fracture load (L0), while G53 and G125 had higher and statistically similar L0 values. The Weibull modulus (m) was similar among groups. The failure modes observed were catastrophic failure and porcelain chipping. There were no differences between the roughness parameters for the experimental groups (p > 0.05). The size of the AO particles did not affect the fracture load and failure mode of 3Y-TZP crowns. Air abrasion with 53 µm and 125 µm particles resulted in a higher fracture load of ceramic crowns than the untreated group while maintaining their reliability and surface characteristics.

Optimization of Lithium Disilicate Glass-Ceramic Crowns: Finish Line, Scanning, and Processing Methods.

PURPOSE: To investigate the optimal combination of factors (finish line, scanning, and ceramic processing) to achieve the best values of both adaptation and fracture load for lithium disilicate crowns (LD). MATERIALS AND METHODS: Two abutment preparations, chamfer (C) and rounded shoulder (S), were produced with a dentin analog material and scanned with either extraoral (E) or intraoral (I) scanners. Images were processed using CAD software to design a premolar. Blocks of LD were milled using a CAD/CAM system (CAD). For the press technique (PRE), crowns were first 3D printed using a polymeric material, then heat-pressing protocol was performed. Design of experiments was used to plan four experimental groups (n = 10): CAD-CI, CAD-SE, PRE-CE, and PRE-SI. Two dependent variables were analyzed: adaptation, measured using the replica technique; and fracture load of the cemented crowns. Fractographic analysis was performed. Data were analyzed using ANOVA and regression statistical analyses. RESULTS: There was no significant effect of the scanning method and finish line on the gap thickness in the different regions. For the processing method, CAD resulted in larger gap thickness in the occlusal, axial angle, and marginal areas and a smaller gap in the axial area (P < .001). The investigated factors had no effect on the fracture load. Yet, PRE-CE was considered the optimum design because it achieved 100% of the desired fracture load (>1000 N) and 40% adaptation (< 200 µm). CONCLUSIONS: The optimum combination of factors for all-ceramic crowns is chamfer abutment preparation, extraoral scanning, and the press technique (combined with 3D printing). Int J Prosthodont 2023;36:e103-e118.

Effect of Aging on Fracture Load and Reliability of Cemented Glass-Ceramics.

PURPOSE: Lithium disilicate (LD) and lithium silicate (LS) glass-ceramics may show a different acid etching behavior and mechanical integrity after aging. This study evaluated the influence of aging on the fracture load and reliability of glass-ceramics after different etching protocols. MATERIALS & METHODS: Specimens were fabricated and divided according to the etching time (10% hydrofluoric acid (HF) for 20s, 40s, and 60s). Etched surfaces were examined under microscopy. The ceramics were resin cemented to a dentin analog material. Samples were tested after 24 h (I) (n=20) or stored in 37°C water for 1 year (A)(n=20). A compressive load (0.1 mm/min) was applied to the samples until failure was detected by acoustic emission. The influence of aging on the fracture load (Lf) was tested by 2-way ANOVA and Tukey tests (α=0.05). The characteristic fracture load (L0) and Weibull modulus (m) values were calculated. RESULTS: LS etching for 20 s resulted in the highest immediate Lf, which was significantly decreased after aging (P≤0.05). Water-storage had no effect in this glass-ceramic Lf etched for 40 and 60s (P0.05). For LD, the etching time had no significant effect on the immediate and aged Lf (P0.05). The Lf was significantly reduced after aging (A) for LD (P≤0.05). Radial cracks were the predominant failure mode. Surface topography was more regular after lower etching times for LD, at after higher times for LS. CONCLUSIONS: After 1-year water-assisted aging, the evaluated etching times had no influence on the load-bearing capacity and structural reliability of resin-bonded glass-ceramics.

Fatigue and marginal adaptation of bulk fill restoratives: Effect of the layering technique and cavity dimension of extensively damaged teeth.

OBJECTIVES: To evaluate the effect of layering technique and cavity dimension on the fatigue behavior and marginal adaptation of bulk fill (BF) restorations in extensively damaged teeth. METHODS: Seventy-two premolars received class II cavities (MOD) followed by endodontic treatment. Half sample had 1/3 of their palatal cusp removed. Teeth were restored using three techniques: (I) incremental, with conventional resin composite (RC); (C) combined, using BF flow and RC, (B) bulk fill, with regular BF. Specimens were subjected to fatigue (80 N, 2 Hz, 37° C water) for 1 million cycles (n = 12). The test was interrupted every 250,000 cycles to evaluate tooth integrity, restoration fracture and adaptation using FDI criteria. Images of the proximal surfaces were obtained before and after the cycling to measure the gap. Restoration fatigue survival and success were analyzed using Weibull distribution and Maximum Likelihood Estimation. Gap thickness was analyzed with Kruskal-Wallis and Student-Newman-Keuls tests (α = 0.05). RESULTS: For the survival analysis, Weibull modulus (ß) and characteristic lifetime (η) were similar among groups. Yet, for the success analysis, in which only restorations that were free of technical complications were ranked as success, the bulk-fill technique resulted in higher ß, while the combined technique produced restorations with higher η, for teeth that had their cusp removed. C-technique also resulted in smaller gaps than I and B. SIGNIFICANCE: The effect of the layering technique on the success of restorations was dependent on the cavity extension. The combined technique favors the adaptation and the longevity of extensively damaged teeth.

Influence of different surface finishing protocols on the wear behavior of a lithium disilicate glass-ceramic.

PURPOSE: This study aims to evaluate the effect of different finishing protocols on the wear behavior of a lithium disilicate glass-ceramic. MATERIAL AND METHODS: Specimens were produced from lithium disilicate glass-ceramic prefabricated CAD/CAM blocks and divided into three groups, according to the surface treatment (n = 8): control; polishing; glaze. Ceramic specimens were subjected to wear test using a dual-axis chewing simulator. A 49 N load was applied in the axial direction combined with a lateral movement (1 mm path) using a lithium disilicate glass-ceramic spherical piston for a total of 106 cycles. Qualitative analysis of the wear surface was performed using an optical microscope. Quantitative analysis of surface roughness and volume loss was performed using a confocal microscope and a 3D-image editing software, respectively. Surface roughness and volume loss data were analyzed using Friedman's non-parametric statistical test for repeated measures and the Student-Newman-Keuls test (α = 0.050). RESULTS: There were statistical differences for surface roughness and volume loss of lithium disilicate glass-ceramic specimens in the different experimental conditions (P˂0.001). Control and polishing groups showed similar surface roughness and volume loss values for all testing times. Glaze group had greater wear volume after 103, 104 and 105 cycles. After 106 cycles, surface roughness and volume loss were similar among groups. For the piston, surface roughness was similar over time and among groups. CONCLUSIONS: A distinct wear behavior was found for glazed glass-ceramic specimens in comparison to control and polished specimens. The end of the simulation, the surface roughness and volume loss was similar for the groups.