Effect of implant type on the stability of cantilever fixed dental prostheses: An in vitro study.

OBJECTIVES: To simulate the replacement of a premolar with an implant-supported cantilever fixed dental prosthesis (ICFDP) and how the fracture load is affected by implant type, positioning within the zirconia blank, and aging protocol. MATERIALS AND METHODS: Seventy-two ICFDPs were designed either within the enamel- or dentin layer of a 4Y-PSZ blank for bone-level and tissue-level titanium-zirconium implants. Fracture load was obtained on the cantilever at baseline (no aging) or after aging in a chewing simulator with the load applied within the implant axis (axial aging) or on the cantilever (12 groups with n = 6). A three-way ANOVA was applied (α = .05). RESULTS: A three-way ANOVA revealed a significant effect on fracture load values of implant type (p = .006) and aging (p < .001) but not for the position within the zirconia blank (p = .847). Fracture load values significantly increased from baseline bone level (608 ± 118 N) and tissue level (880 ± 293 N) when the implants were aged axially, with higher values for tissue level (1065 ± 182 N) than bone level (797 ± 113 N) (p < .001). However, when the force was applied to the cantilever, fracture load values decreased significantly for tissue-level (493 ± 70 N), while values for bone-level implants remained stable (690 ± 135 N). CONCLUSIONS: For ICFDPs, the use of bone-level implants is reasonable as catastrophic failures are likely to be restricted to the restoration, whereas with tissue-level implants, the transmucosal portion of the implant is susceptible to deformation, making repair more difficult.

Influence of aging of PEEK attachment inserts on the pull-off force of implant-retained overdentures - A laboratory study.

OBJECTIVES: The aim of the current study is to investigate the influence of mechanical stress as well as cleaning agents on the performance of various polyether ether ketone (PEEK) inserts for implant-retained overdentures (IOD). MATERIALS AND METHODS: Three different standard PEEK inserts were subjected to rapid artificial aging through storage in chemical denture cleaning agents (acetic acid, sodium hypochlorite, or sparkling denture cleaner) as well as demineralized water. The pre-aged PEEK inserts were then placed in unilateral IOD and subjected to 200,000 chewing loads (5 kg ~ 50 N), with 5000 thermal cycles (5/55°C), and 1100 removal/insertion cycles (vertical movement 2 mm). RESULTS: For all the PEEK inserts, the retention forces decreased significantly with an increasing number of mechanical load cycles and after exposure to all the cleaning agents. PEEK inserts aged by exposure to chemical cleaning agents showed a significantly higher decline in retention force than the inserts stored in water. Confocal laser scanning microscopy indicated that the decline in retention force might be caused by wear on the internal insert surface in contact with the patrix. CONCLUSIONS: Within the limitations of this study, it can be concluded that the application of chemical cleaning agents accelerates the decline in the retention forces of PEEK retentive inserts in IODs.

A new CAD/CAM tooth mobility simulating model for dental in vitro investigations.

OBJECTIVES: To validate a new tooth mobility simulating in vitro model for biomechanical tests of dental appliances and restorations. MATERIAL AND METHODS: Load-deflection curves for teeth in CAD/CAM models (n = 10/group, 6 teeth/model) of the anterior segment of a lower jaw with either low tooth mobility (LM) or high tooth mobility (HM) were recorded with a universal testing device and a Periotest device. All teeth were tested before and after different ageing protocols. Finally, vertical load capacity (Fmax) was tested in all teeth. RESULTS: At F = 100 N load, vertical/horizontal tooth deflections before ageing were 80 ± 10 µm/400 ± 40 µm for LM models and 130 ± 20 µm/610 ± 100 µm for HM models. Periotest values were 1.6 ± 1.4 for LM models and 5.5 ± 1.5 for HM models. These values were within the range of physiological tooth mobility. No visible damage occurred during ageing and simulated ageing had no significant effect on tooth mobility. Fmax values were 494 ± 67 N (LM) and 388 ± 95 N (HM). CONCLUSION: The model is practical, easy to manufacture and can reliably simulate tooth mobility. The model was also validated for long-term testing, so is suitable for investigating various dental appliances and restorations such as retainers, brackets, dental bridges or trauma splints. CLINICAL RELEVANCE: Using this in-vitro model for high standardised investigations of various dental appliances and restorations can protect patients from unnecessary burdens in trials and practice.

Comparison of tensile bond strength of ball attachments made of different materials to root canal dentin after chewing simulation.

BACKGROUND: Debonding of ball attachments is one of the complications that annoy teeth supported overdenture wearers. The polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) polymers are widely applied in the dental field. The purpose of the current study was to compare the tensile bond strength of ball attachments made of such materials and the commonly used titanium ones after 5 years of overdenture insertion and removal (5000 cycles) in addition to chewing simulation (1,200,000 cycle). METHODS: Extracted mandibular canines (N = 60) were randomly allocated into three groups and received ball attachments; titanium (group TI; N = 20), PEEK (group PE; N = 20), PEKK (group PK; N = 20). In each group, the samples were divided into two subgroups whereas tensile bond strength was measured pre aging (T0; n = 10) and post aging (T1; n = 10). Tensile bond strength was measured by the Pull out test using the Universal testing machine. Failure mode analysis was determined by examination of the samples' surfaces under 65X stereomicroscope. The resulting data followed normal distribution and the significance level was set at (α = 0.05). RESULTS: One Way Anova showed statistically significant difference between the three groups (P < .00001). PostHoc Tukey test showed statistically significant difference between the groups TI and PE, TI and PK and no statistically significant difference between the groups PE and PK. Paired t test showed statistically significant difference in the tensile bond strength pre and post aging in each group. CONCLUSIONS: PEEK and PEKK ball attachments could be concluded to have a higher tensile bond strength compared to the titanium ones when bonded to root dentin. Tensile bond strength of such attachments may decrease with aging as well. Clinically, the higher tensile bond strength may have a lesser rate of debonding and thus reduced patient apprehension.

Fracture load of 3D printed PEEK inlays compared with milled ones, direct resin composite fillings, and sound teeth.

OBJECTIVE: The objective of this in vitro study was to investigate fracture load, fracture types, and impact of chewing simulation of human molars restored with 3D printed indirect polyetheretherketone (PEEK) inlays and compare these with milled indirect PEEK inlays, direct resin composite fillings, and sound teeth. MATERIALS AND METHODS: A total of 112 molars with form congruent class I cavities were restored with (n = 16/group) 3D printed indirect PEEK inlays via fused layer manufacturing (FLM): (1) Essentium PEEK (ESS), (2) KetaSpire PEEK MS-NT1 (KET), (3) VESTAKEEP i4 G (VES), (4) VICTREX PEEK 450G (VIC), (5) milled indirect PEEK inlays JUVORA Dental Disc 2 (JUV), and (6) direct resin composite fillings out of Tetric EvoCeram (TET). Sound teeth (7) acted as positive control group. Half of the specimens of each group (n = 8) were treated in a chewing simulator combined with thermal cycling (1.2 million × 50 N; 12,000 × 5 °C/55 °C). Fracture load and fracture types of all molars were determined. Statistical analyses using Kolmogorov-Smirnov test and two-way ANOVA with partial eta squared (ηp2) followed by Scheffé post hoc test, chi square test and Weibull modulus m with 95% confidence interval were computed (p < 0.05). RESULTS: ESS and TET demonstrated the lowest fracture load with a minimum of 956 N, whereas sound molars showed the highest values of up to 2981 N. Chewing simulation indicated no impact (p = 0.132). With regard to Weibull modulus, KET presented a lower value after chewing simulation than JUV, whereas TET had the highest value without chewing simulation. All indirect restorations revealed a tooth fracture (75-100%), direct resin composite fillings showed a restoration fracture (87.5%), and 50% of the sound teeth fractured completely or had cusp fractures. CONCLUSIONS: All 3D printed and milled indirect PEEK inlays as well as the direct resin composite fillings presented a higher fracture load than the expected physiological and maximum chewing forces. CLINICAL RELEVANCE: 3D printing of inlays out of PEEK via FLM provided promising results in mechanics, but improvements in terms of precision and esthetics will be required to be practicable in vivo to represent an alternative dental material.

Mechanical behavior of posterior all-ceramic hybrid-abutment-crowns versus hybrid-abutments with separate crowns-A laboratory study.

OBJECTIVE: The purpose of this laboratory study was to evaluate the fatigue resistance, fracture resistance and mode of failure of posterior hybrid-abutment-crown vs. hybrid-abutment with separate crown, both bonded to short titanium bases. MATERIALS AND METHODS: Thirty-two titanium implants were embedded perpendicularly in auto-polymerizing resin. Implant-supported restorations simulating a maxillary first premolar were designed and milled using a CAD/CAM system and divided into 2 groups according to material (n = 16): zirconia (Z) and lithium disilicate (L). Each group was subdivided into two subgroups according to design (n = 8): hybrid-abutment-crown (ZS, LS) and hybrid-abutment with separate crown (ZC, LC). Each group was subjected to 1.2 million cycles of thermo-mechanical fatigue loading in a dual-axis chewing simulator at 120 N load. Surviving specimens were subjected to quasi-static loading in a universal testing machine. Mode of failure was determined under a low magnification optical microscope. RESULTS: During chewing simulation, 18.8% of zirconia and 43.8% of lithium disilicate restorations failed. The fracture resistance median values ranged from 3,730 N for group ZC, 3,400 N for group ZS, 1,295 N for group LS to 849 N for group LC. Group ZC had a statistically significant higher fracture resistance than groups LC and LS; however, it did not differ significantly from group ZS (p ≤ 0.05). Failures were seen in both titanium bases and ceramic superstructure. CONCLUSIONS: Zirconia and lithium disilicate hybrid implant-supported restorations with short (3 mm) titanium bases failed in a considerable number already during chewing simulation. Therefore, despite their high fracture strength the use in the posterior region should be considered critically.

In-vitro performance of CAD/CAM-fabricated implant-supported temporary crowns.

OBJECTIVES: The aim of this study was to investigate the in-vitro performance and fracture resistance of a temporary computer-aided designed and computer-aided manufactured polymethylmethacrylate (CAD/CAM-PMMA) material as implant or tooth-supported single crown with respect to the clinical procedure (permanently bonded/temporarily cemented). MATERIALS AND METHODS: Sixty-four crowns were fabricated on implants or human molar teeth simulating (a) labside procedure on prefabricated titanium-bonding base ([TiBase] implant crown bonded in laboratory, screwed chairside), (b) labside procedure ([LAB] standard abutment and implant crown bonded in laboratory, screwed chairside), (c) chairside procedure ([CHAIR] implant crown bonded to abutment), and (d) reference ([TOOTH] crowns luted on prepared human teeth). Crowns were made of a CAD/CAM-PMMA temporary material (TelioCAD, Ivoclar-Vivadent). For investigating the influence of fixation, half of the crowns were permanently (P) or temporarily (T) bonded. Combined thermal cycling and mechanical loading (TCML) was performed simulating a 5-year clinical situation. Fracture force was determined. Data were statistically analyzed (Kolmogorov-Smirnov test, one-way ANOVA; post hoc Bonferroni, α = 0.05). RESULTS: All restorations survived TCML without visible failures. Fracture results varied between 3034.3 (Tooth-P) and 1602.9 N (Tooth-T) [TOOTH], 1510.5 (TiBase-P) and 963.6 N (TiBase-T) [TiBase], 2691.1 (LAB-P) and 2064.5 N (LAB-T) [LAB], and 1609.4 (Chair-P) and 1253.0 N (Chair-T) [CHAIR]. Tested groups showed significantly (p < 0.001) different fracture values. Failure pattern was characterized by fractures in mesial-distal, buccal-oral, or mixed (mesial-distal/buccal-oral) directions, with differences for the individual groups. CONCLUSIONS: Temporary CAD/CAM crowns showed no different in-vitro performance but provided different fracture results that depended on cementation, screw channel, and type of abutment. CLINICAL RELEVANCE: All bonded and screwed PMMA crowns were in a range where clinical application seems not restricted.

In vitro performance and fracture resistance of CAD/CAM-fabricated implant supported molar crowns.

OBJECTIVES: The aim of this study is to investigate the performance and fracture resistance of different CAD/CAM ceramic and composite materials as implant- or tooth-supported single crowns with respect to the clinical procedure (screwed/bonded restoration). MATERIALS AND METHODS: One hundred twenty crowns were fabricated on implants or human molar teeth simulating (a) chairside procedure ([CHAIR] implant crown bonded to abutment), (b) labside procedure ([LAB] abutment and implant crown bonded in laboratory, screwed chairside), and (c) reference ([TOOTH] crowns luted on human teeth). Four materials were investigated: ZLS (zirconia-reinforced lithium silicate ceramic; Celtra Duo, Degudent: polished (P)/crystallized (C)), RB (resin-based composite; Cerasmart, GC), and RIC (resin-infiltrated ceramic; Enamic, Vita-Zahnfabrik). LiS (lithiumdisilicate; Emax CAD, Ivoclar-Vivadent) served as reference. Combined thermal cycling and mechanical loading (TCML) was performed simulating a 5-year clinical situation. Fracture force was determined. Data were statistically analyzed (Kolmogorov-Smirnov test, one-way ANOVA; post hoc Bonferroni, α = 0.05). RESULTS: One crown of ZLS_C[LAB] (1,200,000 cycles) and RB[CHAIR] (890 cycles) failed during TCML. Fracture values varied between 977.7 N(RB) and 3070.4 N(LiS)[CHAIR], 1130.6 N(RB) and 2998.1 N(LiS)[LAB], and 1802.4 N(ZLS) and 2664.3 N(LiS)[TOOTH]. Significantly (p < 0.003) different forces were found between the materials in all three groups. ZLS_C, RIC, and RB showed significantly (p < 0.014) different values for the individual groups. CONCLUSIONS: Partly ceramic and resin-based materials performed differently on implant or tooth abutments. The insertion of a screw channel reduced the stability for individual crown materials. Insertion of the screw channel should be performed carefully. CLINICAL RELEVANCE: All restorations were in a range where clinical application seems not restricted, but insertion of a screw channel might reduce stability of individual materials.

Fracture Resistance of Molar Crowns Fabricated with Monolithic All-Ceramic CAD/CAM Materials Cemented on Titanium Abutments: An In Vitro Study.

PURPOSE: To assess the fracture resistance of single-tooth implant-supported crown restorations made with different CAD/CAM blocks. MATERIALS AND METHODS: Thirty-six titanium abutments were put on dental implant analogs (Mis Implant). For each of three test groups (n = 12/group), implant-supported, cement-retained mandibular molar single crowns were produced. Crowns were made of lithium disilicate glass (LD) IPS e.max CAD, feldspathic glass ceramic (FEL) Vita Mark II, and resin nano-ceramic (RNC) Lava Ultimate. The crowns were cemented with self-adhesive resin cement RelyX Unicem 2. After chewing cycling, crowns were tested to failure in a universal testing machine. Fracture values were calculated as initial (F-initial) and maximum fracture (F-max). RESULTS: The study groups were ranked, in order of having highest value, (LD > FEL) > RNC for F-initial load value and (LD > RNC) > FEL for F-max load value. This demonstrated that there was no parallel change in the F-initial and F-max values presenting the fracture resistance of specimens. CONCLUSIONS: There was no accordance between the F-initial and F-max values of the LD, RNC, and FEL after chewing simulation with thermocycling resembling 5 years of clinical functional use. LD had the highest fracture resistance during the fracture test. RNC had low fracture resistance; however, it had considerably high fracture resistance during the fracture test. FEL had considerably low fracture resistance values.

In vitro comparison of implant- versus gingiva-supported removable dentures in anterior and posterior applications.

OBJECTIVES: Removable dentures with different denture teeth may provide different performance and resistance in implant and gingival situations, or anterior and posterior applications. MATERIALS AND METHODS: Two situations of removable dentures were investigated: gingiva (flexible) and implant (rigid) bearing. For simulating the gingiva/jaw situation, the dentures were supported with flexible lining material. For the implant situation, implants (d = 4.1 mm) were screwed into polymethylenmethacrylate (PMMA) resin. Two commercial (Vita-Physiodens MRP, SR Vivodent/Orthotyp DCL) and two experimental materials (EXP1, EXP2) were investigated in anterior (A) and posterior (P) tooth locations. Chewing simulation was performed, and failures were analyzed (microscopy, SEM). Fracture strength of surviving dentures was determined. RESULTS: Only EXP1 revealed failures during chewing simulation. Failures varied between anterior and posterior locations, and between implant (P:4x; A:7x) or gingiva (P:1x; A:2x) situations. Kaplan-Meier log-rank test revealed significant differences for implant situations (p < 0.002), but not for gingiva bearing (p > 0.093). Fracture testing in the implant situation provided significantly highest values for EXP2 (1476.4 ± 532.2 N) in posterior location, and for DCL (1575.4 ± 264.4 N) and EXP2 (1797.0 ± 604.2 N) in anterior location. For gingival bearing, significantly highest values were found for DCL/P (2148.3 ± 836.3 N), and significantly lowest results for EXP1/A (308.2 ± 115.6 N). For EXP1 + EXP2 + Vita/P and for EXP1/A no significant differences were found between implant- or gingiva-supported situations. CONCLUSIONS: Anterior and posterior teeth showed different material-dependent in vitro performance, further influenced by implant/gingiva bearing. While an implant in anterior application increased fracture strength of two materials, it decreased fracture values of 3/4 of the materials in posterior application. CLINICAL RELEVANCE: Survival of denture teeth may be influenced by material, oral position, and bearing situation.

Bending moments of zirconia and titanium implant abutments supporting all-ceramic crowns after aging.

OBJECTIVES: To test the fracture load and fracture patterns of zirconia abutments restored with all-ceramic crowns after fatigue loading, exhibiting internal and external implant-abutment connections as compared to restored and internally fixed titanium abutments. MATERIALS AND METHODS: A master abutment was used for the customization of 5 groups of zirconia abutments to a similar shape (test). The groups differed according to their implant-abutment connections: one-piece internal connection (BL; Straumann Bonelevel), two-piece internal connection (RS; Nobel Biocare ReplaceSelect), external connection (B; Branemark MkIII), two-piece internal connection (SP, Straumann StandardPlus) and one-piece internal connection (A; Astra Tech AB OsseoSpeed). Titanium abutments with internal implant-abutment connection (T; Straumann Bonelevel) served as control group. In each group, 12 abutments were fabricated, mounted to the respective implants and restored with glass-ceramic crowns. All samples were embedded in acrylic holders (ISO-Norm 14801). After aging by means of thermocycling in a chewing simulator, static load was applied until failure (ISO-Norm 14801). Fracture load was analyzed by calculating the bending moments. Values of all groups were compared with one-way ANOVA followed by Scheffé post hoc test (P-value<0.05). Failure mode was analyzed descriptively. RESULTS: The mean bending moments were 464.9 ± 106.6 N cm (BL), 581.8 ± 172.8 N cm (RS), 556.7 ± 128.4 N cm (B), 605.4 ± 54.7 N cm (SP), 216.4 ± 90.0 N cm (A) and 1042.0 ± 86.8 N cm (T). No difference of mean bending moments was found between groups BL, RS, B and SP. Test group A exhibited significantly lower mean bending moment than the other test groups. Control group T had significantly higher bending moments than all test groups. Failure due to fracture of the abutment and/or crown occurred in the test groups. In groups BL and A, fractures were located in the internal part of the connection, whereas in groups RS and SP, a partial deformation of the implant components occurred and cracks and fractures of the zirconia abutment were detected. CONCLUSION: The differently connected zirconia abutments exhibited similar bending moments with the exception of one group. Hence, the type of connection only had a minor effect on the stability of restored zirconia abutments. In general, restored titanium abutments exhibited the highest bending moments.

Investigation of Phase Transformation and Fracture Pattern as a Result of Long-Term Chewing Simulation and Static Loading of Reduced-Diameter Zirconia Implants.

While zirconia implants exhibit osseointegration comparable to that of titanium, concerns arise regarding low-temperature degradation and its potential impact on fracture strength. This study investigated the phase transformation and fracture characteristics of zirconia dental implants after aging through chewing simulation and subsequent static loading. The experimental setup involved 48 one-piece monobloc zirconia implants with diameters of 3.0 mm and 3.7 mm that had straight or angled abutments, with crown restorations, which were divided into six groups based on intraoral regions. The specimens underwent chewing simulation equal to five years of oral service, which was followed by static loading. Statistical analyses were performed for the data obtained from the tests. After dynamic and static loadings, the fractured samples were investigated by Raman spectroscopy to analyze the phase composition and micro-CT to evaluate fracture surfaces and volume changes. According to the results, narrow-diameter zirconia implants have low mechanical durability. The fracture levels, fracture patterns, total porosity, and implant fracture volume values varied according to the implant diameter and phase transformation grade. It was concluded that phase transformation initially guides the propagation of microcracks in zirconia implants, enhancing fracture toughness up to a specific threshold; however, beyond that point, it leads to destructive consequences.

Fracture Resistance of a Bone-Level Two-Piece Zirconia Oral Implant System-The Influence of Artificial Loading and Hydrothermal Aging.

Preclinical and clinical research on two-piece zirconia implants are warranted. Therefore, we evaluated the in vitro fracture resistance of such a zirconia oral implant system. The present study comprised 32 two-piece zirconia implants and abutments attached to the implants using a titanium (n = 16) or a zirconia abutment screw (n = 16). Both groups were subdivided (n = 8): group T-0 comprised implants with a titanium abutment screw and no artificial loading; group T-HL was the titanium screw group exposed to hydro-thermomechanical loading in a chewing simulator; group Z-0 was the zirconia abutment screw group with no artificial loading; and group Z-HL comprised the zirconia screw group with hydro-thermomechanical loading. Groups T-HL and Z-HL were loaded with 98 N and aged in 85 °C hot water for 107 chewing cycles. All samples were loaded to fracture. Kruskal-Wallis tests were executed to assess the loading/bending moment group differences. The significance level was established at a probability of 0.05. During the artificial loading, there was a single occurrence of an implant fracture. The mean fracture resistances measured in a universal testing machine were 749 N for group T-0, 828 N for group Z-0, 652 N for group T-HL, and 826 N for group Z-HL. The corresponding bending moments were as follows: group T-0, 411 Ncm; group Z-0, 452 Ncm; group T-HL, 356 Ncm; and group Z-HL, 456 Ncm. There were no statistically significant differences found between the experimental groups. Therefore, the conclusion was that loading and aging did not diminish the fracture resistance of the evaluated implant system.

Ex vivo investigation on the effect of minimally invasive endodontic treatment on vertical root fracture resistance and crack formation.

The evidence base on minimally invasive endodontic (MIE) treatment is limited. This study investigated the influence of MIE shaping on vertical root fracture (VRF) resistance and crack formation of root canal filled teeth. Human maxillary central incisors were randomized into six groups (n = 18, power = 0.9) and embedded in acrylic blocks with artificial periodontal ligaments. The root canals were either instrumented to size #40 and 0.04 taper (+MIE) or enlarged to ISO size #80 (-MIE). The canals were filled with cement-based (C) or adhesive resin-based (A) sealers in single-cone technique. The controls received no treatment or were left unfilled. After chewing simulation (staircase method, 25-150 N, 120,000×), the crack formation on the root surface was analyzed using stereomicroscope/digital imaging and classified (no defect, craze line, vertical crack, horizontal crack). Subsequently, the samples were loaded until fracture. The incidence of defects (56% vertical cracks) was not significantly different between the groups (p ≥ 0.077). VRF resistance was significantly higher in untreated teeth than in +MIE/C (p = 0.020) but did not significantly differ between the other groups (p ≥ 0.068). Minimal canal shaping did not reduce the risk of vertical root fracture and defects of root canal filled teeth.

Fracture Resistance of Repaired 5Y-PSZ Zirconia Crowns after Endodontic Access.

This study analyzed the fracture load before and after a chewing simulation of zirconia crowns that were trepanned and repaired using composite resin. Overall, 3 groups with 15 5Y-PSZ crowns in each group were tested. For group A, the fracture load of the unmodified crowns was evaluated. For group B, the crowns were trepanned and repaired using composite resin, also followed by a fracture test. For group C, crowns were prepared like in group B but received thermomechanical cycling before the final fracture tests. Furthermore, scanning electron microscopy (SEM) and X-ray microscopy (XRM) analysis were performed for group C. The mean fracture loads and standard deviation were 2260 N ± 410 N (group A), 1720 N ± 380 N (group B), and 1540 N ± 280 N (group C). Tukey-Kramer multiple comparisons showed a significant difference between groups A and B (p < 0.01) and groups A and C (p < 0.01). After ageing, surface fissures were detected via SEM, but no cracks that reached from the occlusal to the inner side of the crown were detected via XRM. Within the limitations of this study, it can be stated that trepanned and composite-repaired 5Y-PSZ crowns show lower fracture loads than 5Y-PSZ crowns without trepanation.

The Interaction Relationship of Aroma Components Releasing with Saliva and Chewing Degree during Grilled Eels Consumption.

The interaction perception between aroma and oral chewing during food consumption has always been a hot topic in exploring consumers' preferences and purchase desires. A chewing simulation system was set to find out the effect of key saliva components and chewing time on odorants released with grilled eel meat. Odor release did not always enhance with the degree of chewing, or the amount of saliva released. The breaking up of the tissue structure of the fish meat by the teeth encourages the release of odorants and the participation of saliva partially blocks this process. The release of pyrazine, alcohol, and acid compounds in grilled eel meat peaked within 20-60 s after chewing. Sufficient exposure of saliva to grilled eel meat will inhibit aromatic, ketone, ester, hydrocarbon, and sulfur compounds release. 3-methyl-2-butanol contributed to the subtle aroma differences that arise before and after eating grilled eel meat. Naphthalene, 2-acetylthiazole, 2-decenal, 2-undecanone, 5-ethyldihydro-2(3H)-furanone were the main odorants released in large quantities in the early stages of eating grilled eel and affected the top note. Consequently, the results provided the odorants information in aroma perception during grilled eel consumption and benefited the objective evaluation of grilled eel product optimization.

Impact of Contracted Endodontic Access Cavities on the Fracture Resistance of Endodontically Treated Teeth After Mechanical Aging by Simulated Chewing Forces.

INTRODUCTION: This in vitro study aimed to comparatively evaluate the fracture resistance of contracted endodontic cavities (CECs) versus traditional endodontic cavities (TECs) in mandibular molars after subjecting the samples to a chewing simulator. METHODS: A total of 24 freshly extracted human mandibular molars were included in the study. Teeth with intact crowns and mature root apices that were devoid of caries, attrition, restorations, and cracks were selected and randomly assigned to 3 groups (n = 8) as follows: Group 1: TECs, Group 2: CECs, and Group 3: intact teeth (control group). After endodontic treatment, the teeth were restored with EverX bulk-fill composite and layered occlusally with nanohybrid composite SolareX and subjected to a chewing simulator where 240,000 masticatory cycles were simulated, which translates to 1 year of clinical function. The teeth were then subjected to static loading in a universal testing machine and the maximum load to fracture and the pattern of failure (restorable/unrestorable) were recorded. Data were evaluated with analysis of variance and the Tukey post hoc test for multiple comparisons. RESULTS: The CEC group had higher fracture resistance when compared with the TEC group; however, the difference was not statistically significant. The fracture resistance of the samples in the control group was statistically higher than those in the experimental groups (P < .005). CONCLUSIONS: There was no difference observed in the fracture resistance of mandibular molars with TECs and CECs subjected to masticatory loading.

Effect of Simulated Mastication on Structural Stability of Prosthetic Zirconia Material after Thermocycling Aging.

Recent trends to improve the aesthetic properties-tooth-like color and translucency-of ceramic dental crowns have led to the development of yttria-stabilized zirconia (Y-TZP) materials with higher stabilizer content. These 5Y-TZP materials contain more cubic or t' phase, which boosts translucency. The tradeoff as a consequence of a less transformable tetragonal phase is a significant reduction of strength and toughness compared to the standard 3Y-TZP composition. This study aims at determining the durability of such 5Y-TZP crowns under lab conditions simulating the conditions in the oral cavity during mastication and consumption of different nutrients. The test included up to 10,000 thermal cycles from 5 °C to 55 °C "from ice cream to coffee" and a chewing simulation representing 5 years of use applying typical loads. The investigation of the stress-affected zone at the surface indicates only a very moderate phase transformation from tetragonal to monoclinic after different varieties of testing cycles. The surface showed no indication of crack formation after testing. It can, therefore, be assumed that over the simulated period, dental crowns of 5Y-TZP are not prone to fatigue failure.

Fibre-reinforced Cad/CAM post and cores: The new "gold standard" for anterior teeth with extensive coronal destruction?-A fully digital chairside workflow.

Objectives: Since one-third of persons suffer a dental trauma, treatment of anterior teeth using post and core (PC) is becoming important. In teeth with extensive destruction, cast PC (CPC) remain the "gold standard", even though they lead to aesthetic impairment and have a mismatching elastic modulus to that of dentin. Prefabricated fibre-reinforced posts have elastic modulus similar to that of dentin but the accuracy of fit and mechanical stability are worse. This study was aimed to evaluate the deviation and mechanical performance of fibre-reinforced CAD/CAM PC (FRPC) fabricated in a fully digital chairside workflow, compared to those of CPC. Methods: On 30 teeth, a PC preparation was conducted, and a conventional and digital post impression were taken with an intraoral scanner. Fifteen teeth each were treated with CPC and FRPC, respectively. The deviation was evaluated by superimposing the datasets of the digitalised stone models and digital post impressions. Decementation and root fracture during chewing simulation were analysed by microscopy and X-ray. Statistical analysis was performed by pairwise comparison and Kaplan-Meier analysis. Results: The median deviation for the "coronal", "middle" and "apical" were 14.5, 18.0 and 113.7 µm, respectively. The pairwise comparison for "coronal"/"middle" showed no significance (p = 0.465), whereas that for "coronal"/"apical" and "middle"/"apical" showed highly significant differences (p < 0.001). After chewing simulation, five decementations and two root fractures were detected for CPC. For FRPC, neither decementation nor root fracture were documented. Significance: Within the limitations of this study, FRPC performed significantly better than CPC.

Laboratory methods to simulate the mechanical degradation of resin composite restorations.

OBJECTIVES: This study reviewed the literature to identify in vitro approaches that have been used to simulate the mechanical degradation and fatigue of resin composite restorations. METHODS: A search for articles was carried out in 4 databases and included studies in which composite restorations were bonded to teeth and subject to cyclic loading. Articles were assessed for eligibility, and the following items were the extracted from the included studies: authors, country, year, materials tested, simulation device and details including load magnitude and frequency, number of cycles, type of antagonist, test medium, and temperature. Data were analyzed descriptively. RESULTS: The 49 studies included showed a high level of heterogeneity in methods, devices, and test parameters. Nineteen different simulation devices were used, applying loads varying between 30 and 2900 N, and frequencies varying between 0.4 and 12 Hz. The load and frequency used most often were ~ 50 N (63.3%) and 1.5-1.7 Hz (32.7%). The number of cycles varied between 10 K and 2.4 M, 1.2 M was the most prevalent (40.8%). The majority of studies combined cyclic loading with at least one additional aging method: static liquid storage, thermo-mechanical cycling applied simultaneously, and thermal cycling as a discrete aging step were the three most frequent methods. The overall evidence indicated reporting problems, and suggested a lack of clinical validation of the research methods used. SIGNIFICANCE: Validation studies, underlying clinical supporting data, and better reporting practices are needed for further improving research on the topic. Specific suggestions for future studies are provided.