scholarly journals In Vitro Fracture Strength of Teeth Restored with Lithium Disilicate Onlays with and without Fiber Post Build-Up

2018 ◽  
Vol 6 (3) ◽  
pp. 35 ◽  
Author(s):  
Nicola Mobilio ◽  
Alberto Fasiol ◽  
Francesco Mollica ◽  
Santo Catapano
Keyword(s):  
Fracture Strength ◽  
Failure Modes ◽  
Mechanical Performance ◽  
Lithium Disilicate ◽  
Fiber Post ◽  
Chi Square ◽  
Human Teeth ◽  
Group A ◽  
Group B

To our knowledge there is no data about the mechanical performance of indirect restoration adhesively cemented on teeth without an adequate build-up to provide the correct geometrical configuration. The aim of this study was to compare the fracture strength of human teeth restored with lithium disilicate onlays, with and without fiber post build-up. Methods: Twenty human mandibular molars were horizontally sectioned and divided into two groups (n = 10). No treatment was applied in group A. Teeth in group B were endodontically treated, built-up using fiber post and composite core and prepared with a circumferential chamfer providing a 1 mm circumferential ferrule. Lithium disilicate onlays were pressed and luted on teeth using dual-curing luting composite. Teeth were tested under static load. Failures were classified as restorable or not restorable. Failure loads were analyzed with one-way analysis of variance. Failure modes were compared using Pearson’s Chi-square tests. Results: The mean fracture loads were 1383.5 N for group A and 1286.3 N for group B. No difference was found (p = 0.6). Ninety per cent of fractures were classified as not restorable in both groups, with no difference (p = 0.8). Conclusions: For teeth restored with adhesive procedures and lithium disilicate onlays, the presence of build-up with fiber post to provide retention and resistance form does not influence the fracture strength.

scholarly journals Load-Bearing Capacity of Zirconia Crowns Screwed to Multi-Unit Abutments with and without a Titanium Base: An In Vitro Pilot Study

Materials ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3056
Author(s):  
Hadas Heller ◽  
Adi Arieli ◽  
Ilan Beitlitum ◽  
Raphael Pilo ◽  
Shifra Levartovsky
Keyword(s):  
Failure Modes ◽  
Load Bearing ◽  
Zirconia Crowns ◽  
Group A ◽  
Monolithic Zirconia ◽  
Loading Tests ◽  
Group B ◽  
Iso 14801 ◽  
Static And Dynamic Loading

The static and dynamic load-bearing capacities and failure modes of zirconia crowns screwed to multi-unit abutments (MUAs) with and without a titanium base (T-base) were determined. Thirty-six monolithic zirconia crowns screwed to straight MUAs torqued to laboratory analogs (30 Ncm) were assigned to two groups (n = 18). In group A, the zirconia crowns were screwed directly to the MUAs; in group B, the zirconia crowns were cemented to the T-base and screwed to the MUAs. All specimens were aged in 100% humidity (37 °C) for one month and subjected to thermocycling (20,000 cycles). Afterwards, the specimens underwent static and dynamic loading tests following ISO 14801. The failure modes were evaluated by stereomicroscopy (20×). There was an unequivocally similar trend in the S-N plots of both specimen groups. The load at which the specimens survived 5,000,000 cycles was 250 N for both groups. Group A failed mainly within the metal, and zirconia failure occurred only at a high loading force. Group B exhibited failure within the metal mostly in conjunction with adhesive failure between the zirconia and T-base. Zirconia restoration screwed directly to an MUA is a viable option, but further studies with larger sample sizes are warranted.

284 FERTILIZING CAPACITY OF BUFFALO (BUBALUS BUBALIS) SPERM CO-CULTURED WITH OVIDUCT EPITHELIAL CELLS

2010 ◽  
Vol 22 (1) ◽  
pp. 299 ◽  
Author(s):  
E. Mariotti ◽  
S. Di Francesco ◽  
M. De Blasi ◽  
C. Siniscalchi ◽  
M. V. Suárez ◽  
...  
Keyword(s):  
Production Efficiency ◽  
Penetration Rate ◽  
Bubalus Bubalis ◽  
Cleavage Rate ◽  
Chi Square ◽  
Chi Square Test ◽  
Group A ◽  
Group B ◽  
Bovine Oocytes

The overall in vitro embryo production efficiency in buffalo is hampered by the poor IVF efficiency. The aim of this work was to evaluate whether the fertilizing ability of buffalo sperm is improved by the presence of bovine oviductal cells (BOEC) during IVF. Because of limited availability of buffalo oocytes, this was assessed by heterologous IVF. Bovine oviducts were obtained at a local abattoir from cows that were in the preovulatory phase of a normal estrous cycle. BOEC recovered from 5 oviducts as previously described (Gualtieri and Talevi 2000 Biol. Reprod. 62, 1754-1762) were pooled and plated in 100 μL drops of TCM-199 + 10% FCS, 100 U mL-1 penicillin, 100 μg mL-1 streptomycin and 0.25 μg mL-1 amphotericin B under mineral oil. Medium was changed every 48 h up to Day 6, when cell confluence and cilia activity were optimal. On day of IVF the medium was removed from the drops and replaced with TALP supplemented with 0.2 mM penicillamine, 0.1 mM hypotaurine, and 0.01 mM heparin (IVF medium). Frozen-thawed sperm from an IVF-tested buffalo bull, treated by Percoll gradients, were used for all IVF groups (2 × 106 sperm mL-1). In vitro-matured bovine oocytes (n = 409), over 3 replicates, were distributed in 4 fertilization groups: (A) IVF medium alone (control); (B) BOEC monolayer + IVF medium; (C) sperm preincubated for 6 h in IVF medium; and (D) sperm preincubated for 6 h with BOEC + IVF medium. After 20 h of coincubation at 38.5°C and 5% CO2 in air, putative zygotes were denuded, washed, and cultured in SOF medium. Forty-eight hours after IVF, cleavage rate was evaluated, and cleaved and uncleaved oocytes were fixed in 60% methanol and stained with DAPI for nuclei examination under fluorescence microscope. Data were analyzed by chi-square test. Although cleavage rate was not different among groups (46.2, 55.8, 50.0, and 50.0% for A, B, C, and D, respectively), the monospermic penetration rate increased (P < 0.01) in group B (79.3%) compared with group A (69.6%), with intermediate values in groups C (75.2%) and D (76.0%). Interestingly, the percentage of advanced embryos (>4 cells) was higher (P < 0.01) in groups C and D (47.9 and 37.1%, respectively) than in group A (12.1%), whereas group B (21.0%) was only different from group C. We demonstrated that the fertilizing capacity of buffalo sperm, evaluated as oocyte penetration rate after heterologous IVF, is enhanced by the presence of BOEC. This suggests that IVF of buffalo oocytes on BOEC monolayer may improve the IVF efficiency in buffalo. The higher incidence of advanced embryos in both groups with preincubated sperm may be accounted for by an earlier accomplishment of capacitation, leading to anticipated oocyte penetration. However, because the penetration rate in these groups was not improved compared with the control, we hypothesize that sperm viability may have decreased and hence that shorter incubation times should be tested in further studies.

An in vitro Evaluation of Radicular Penetration of Hydrogen Peroxide from Bleaching Agents During Intra-Coronal Tooth Bleaching with an Insight of Biologic Response

2011 ◽  
Vol 35 (3) ◽  
pp. 289-294 ◽  
Author(s):  
Divya Sharma ◽  
Sanjay Sharma ◽  
SM Natu ◽  
Satish Chandra
Keyword(s):  
Root Resorption ◽  
Tooth Bleaching ◽  
Sodium Perborate ◽  
Human Teeth ◽  
External Root Resorption ◽  
Biologic Response ◽  
Group A ◽  
Group B ◽  
Almost All

Objectives: External root resorption is the complication of intra-coronal bleaching done with 30% H2O2alone or mixed with sodium perborate but not with sodium perborate mixed with water. The study was done to comparatively evaluate the H2O2 leakage from three H2O2 liberating bleaching agents. Study design:Fifty one single rooted human teeth were used. After root canal therapy gutta percha was removed below cemento-enamel junction. Three bleaching agents: sodium perborate mixed with water , sodium perborate mixed with 30% H2O2 and 30% H2O2 alone were used. Teeth without defect , with cervical root defect and with mid root defect constituted group A, group B and group C. According to various bleaching agents groups were subdivided into subgroup 1, 2 and 3. H2O2 leakage was measured with the help of spectrophotometer. Results: Almost all teeth showed H2O2 leakage. It was maximum in B1 followed by C1, B2,A1, A2, C2, B3, A3 and C3. Conclusion: Sodium perborate mixed with water was found to be the best bleaching agent.

scholarly journals Influence of Irrigation with NaOCl and Chlorhexidine on Microleakage

2015 ◽  
Vol 19 (1) ◽  
pp. 38-42
Author(s):  
Zoumpoulia Mylona ◽  
Christos Gogos ◽  
Nikolaos Economides
Keyword(s):  
Fisher Exact Test ◽  
Human Teeth ◽  
Fluid Filtration ◽  
Filtration Method ◽  
Exact Test ◽  
Group A ◽  
The Difference ◽  
Group B ◽  
Endodontic Sealers

SUMMARYBackground: Irrigation during endodontic therapy is required in order to remove debris, tissue remnants, microbes and smear layer. Sodium hypochlorite (NaOCl) and Chlorhexidine (CHX) are the most commonly used irrigants. Although they are reported to have good antimicrobial effects, both have limitations. Hence, a combination of NaOCl and CHX has been proposed to compensate for these limitations. However, this association forms a dense, orange-brown precipitate that stains walls of the pulp chamber. The aim of this study was to clarify in vitro if this precipitate affects the microleakage of endodontic sealers.Material and Methods: Extracted human teeth were used for this study. The teeth were cut at the height of the cervix and instrumented with NiTi rotary instruments. They were then divided into 2 experimental groups. In the first group (Group A) irrigations were performed with 2ml NaOCl 1%, 1ml EDTA 17% and 1ml CHX 0.2% and in the second (Group B) with 2ml NaOCl and 2ml CHX. Following this, they were obturated with gutta-percha and roth sealer. The microleakage was determined using a fluid filtration method. The measurements were repeated a month later. All analyses were performed using Fisher exact test.Results: Microleakage of Group A was lower than microleakage of Group B but the difference was not statistically significant.Conclusion: The precipitate that is formed by NaOCl and CHX did not affect microleakage of endodontic sealers.

scholarly journals Fracture Strength of Monolithic Zirconia Crowns with Modified Vertical Preparation: A Comparative In Vitro Study

2021 ◽  
Author(s):  
Marwah Ismael Abdulazeez ◽  
Manhal A. Majeed
Keyword(s):  
Fracture Strength ◽  
In Vitro Study ◽  
Fracture Load ◽  
Significant Difference ◽  
Zirconia Crowns ◽  
Group A ◽  
Monolithic Zirconia ◽  
Bonferroni Test ◽  
Group B

Abstract Objective The aim of this study was to evaluate the influence of different marginal designs (deep chamfer, vertical, and modified vertical with reverse shoulder) on the fracture strength and failure modes of monolithic zirconia crowns. Materials and Methods Thirty sound human maxillary first premolar teeth with comparable size were used in this study. The teeth were divided randomly into three groups according to the preparation design (n = 10): (1) group A: teeth prepared with a deep chamfer finish line; (2) group B: teeth prepared with vertical preparation; and (3) group C: teeth prepared with modified vertical preparation, where a reverse shoulder of 1 mm was placed on the buccal surface at the junction of middle and occlusal thirds. All samples were scanned by using an intraoral scanner (CEREC Omnicam, Sirona, Germany), and then the crowns were designed by using Sirona InLab 20.0 software and milled with a 5-axis machine. Each crown was then cemented on its respective tooth with self-adhesive resin cement by using a custom-made cementation device. A single load to failure test was used to assess the fracture load of each crown by using a computerized universal testing machine that automatically recorded the fracture load of each sample in Newton (N). Statistical Analysis The data were analyzed statistically by using one-way analysis of variance test and Bonferroni test at a level of significance of 0.05. Results The highest mean of fracture load was recorded by chamfer (2,969.8 N), which followed by modified vertical (2,899.3 N) and the lowest mean of fracture load was recorded by vertical (2,717.9 N). One-way ANOVA test revealed a significant difference among the three groups. Bonferroni test showed a significant difference between group A and group B, while a nonsignificant difference was revealed between group C with group A and group B. Conclusion Within the limitations of this in vitro study, the mean values of fracture strength of monolithic zirconia crowns of all groups were higher than the maximum occlusal forces in the premolar region. The modification of the vertical preparation with a reverse shoulder placed at the buccal surface improved the fracture strength up to the point that it was statistically nonsignificant with the chamfer group.

128 CULTURE CONDITIONS AFFECT THE SEX RATIO OF IN VITRO PRODUCED BOVINE EMBRYOS

2013 ◽  
Vol 25 (1) ◽  
pp. 211
Author(s):  
M. De Blasi ◽  
M. Rubessa ◽  
G. Zullo ◽  
L. Boccia ◽  
V. Longobardi ◽  
...  
Keyword(s):  
Energy Source ◽  
Sex Ratio ◽  
Trisodium Citrate ◽  
Culture Conditions ◽  
Bovine Embryo ◽  
Bovine Embryos ◽  
Chi Square ◽  
Group A ◽  
Group B

Most systems for producing bovine embryos in vitro use glucose as an energy source despite putative toxic effects. Glucose has a selective embryotoxicity towards female embryos, due to the higher expression of the X-linked glucose-6-phosphate dehydrogenase gene (Kimura et al. 2005 Mol. Reprod. Dev. 72, 201–207). Recently, the replacement of glucose with citrate and myo-inositol in SOF medium supplemented with 5% bovine serum (BS) increased the percentage of female embryos (Rubessa et al. 2011 Theriogenology 76, 1347–1355). Serum also affects the sex ratio of in vitro-produced (IVP) bovine embryos, favoring the male gender (Gutierrez-Adan et al. 2001 Theriogenology 55, 1117–1126). The aim of this work was to evaluate the effect of glucose replacement with myo-inositol during in vitro culture, in the presence of either BS or BSA, on bovine embryo sex ratio. Abattoir-derived oocytes (n = 1164, over 4 replicates) were matured and fertilized in vitro as previously described (Rubessa et al. 2011). After 20 to 22 h of gametes co-incubation, zygotes were denuded and cultured for 7 days in SOF with: group A) 0.34 mM trisodium citrate + 2.77 mM myo-inositol + 5% BS (n = 287); group B) 0.34 mM tri-sodium citrate + 2.77 mM myo-inositol + 8 mg mL–1 BSA(n = 290); group C) 1.5 mM glucose + 5% BS (n = 302) and group D) 1.5 mM glucose + 8 mg mL–1 BSA (n = 285). Representative samples of blastocysts produced in each group (n = 96, 58, 99, and 70, respectively in groups A, B, C, and D) were sexed by PCR as previously described (Rubessa et al. 2011). Differences among groups in blastocyst yields were analyzed by ANOVA. The percentages of female embryos were analyzed by chi-square test. Blastocyst rates in group C were lower (28.1%) than those recorded in groups A, B, and D (35.9, 41.0 and 36.1%, respectively; P < 0.01). A higher (P < 0.05) percentage of female embryos was observed in group A (61.5%) compared to group C (45.5%), with intermediate values in groups B (51.7%) and D (60.0%). Therefore, the replacement of glucose with citrate and myo-inositol favored the development of female embryos in the presence of BS but was ineffective in the presence of BSA. Furthermore, when glucose was the energy source, a tendency to greater incidence of female embryos was observed when the medium was supplemented with BSA rather than BS (P = 0.06). As a small amount of glucose is present in the BS, we hypothesize an additional glucose-dependent toxic effect on female embryos in group C. However, we cannot rule out that other factors present in the BS may interact with the energy source, playing a role in determining the sex ratio. Furthermore, the shift in sex ratio in favor of males or females embryo can be due to a better development of embryo of one sex, or to the delayed development or degeneration of embryos of the other sex. In conclusion, these results suggest that manipulating the metabolic profile of the embryos during culture may have an impact on both blastocyst production and sex ratio.

scholarly journals Efficacy of Palatal Applications on Fracture Resistance of Reattached Maxillary Central Incisors: AnIn VitroStudy

2017 ◽  
Vol 2017 ◽  
pp. 1-5
Author(s):  
İhsan Yikilgan ◽  
Nagihan Guven ◽  
Cemile Kedıcı Alp ◽  
Emre Tokar ◽  
Ozgur Topuz ◽  
...  
Keyword(s):  
Fracture Strength ◽  
Fracture Resistance ◽  
Composite Resin ◽  
In Vitro Study ◽  
Plane Normal ◽  
Fixed Distance ◽  
Group A ◽  
Group B ◽  
Group D

The purpose of this study was to evaluate the effects of different palatal applications on fracture strength of the fractured anterior tooth. Sixty caries-free human maxillary incisors were used. Endodontic treatments of the teeth were performed. Then, the teeth were divided randomly into five groups (n=12). Crowns of all teeth in groups A–D were cut with diamond discs at a fixed distance of 3 mm from the incisal margin in a plane normal to the buccal surface. In all groups, coronal fragments were reattached to the remaining teeth by bonding with hybrid composite resin. After then, the teeth were restored to the following; group A, bonding and palatal laminate; group B, bonding and creation of a vertical groove; group C, bonding and creation of two slot grooves; group D, bonding only; and group E, intact tooth. It was lesser in group B than in groups C and E (p=0.007andp=0.006, resp.) and lesser in group D than in groups A, C, and E (p=0.002,p<0.001, andp<0.001, resp.). Within the limitations of this in vitro study, it can be concluded that methods employing palatinal laminate and small grooves are clinically feasible for the reattachment of tooth fragments to incisors.

scholarly journals Effect of Load Cycling on the Fracture Strength/Mode of Teeth Restored with FRC Posts or a FRC Liner and a Resin Composite

2018 ◽  
Vol 2018 ◽  
pp. 1-10
Author(s):  
Maria D. Gaintantzopoulou ◽  
Eleftherios T. Farmakis ◽  
George C. Eliades
Keyword(s):  
Glass Fiber ◽  
Fracture Strength ◽  
Root Canal ◽  
Failure Modes ◽  
Resin Composite ◽  
Fracture Load ◽  
Load Cycling ◽  
Group A ◽  
Root Fractures ◽  
Group B

The aim of the study was to comparatively evaluate the fracture strength and mode of root canal treated teeth restored with resin composites with and without posts. The lingual cusps of root canal treated first upper premolars (n = 10/group) were removed down to cervical enamel and restored with the following: group A: glass-fiber post (Glassix) followed by a particulate-filled composite resin (PFC, G-aenial posterior, 3 × 2 mm layers); group B: glass-fiber reinforced composite bulk fill liner (EverX posterior, 4 mm layer) with the PFC (2 mm layer). Specimens were immersed in H2O (1 w/37°C), then subjected to load cycling (50 N/0.2 Hz/200k cycles), and fractured under compressive loading. Failure mode was characterized by stereomicroscopy. Statistical analysis was performed by Mann-Whitney (load) and Chi-square (mode) at a = 0.05. No statistically significant differences (p = 0.273) were found in fracture load between median values of groups A (860 N) and B (1059 N). In group A, 60% of the specimens demonstrated catastrophic root fractures and 40% mixed crown fractures (tooth cusp and restoration), whereas in group B, no root fractures were found, and the failure modes were equally distributed between mixed fractures as above and fracture of the buccal cusp. These differences were statistically significant (p = 0.004). The combination of the glass-FRC bulk fill liner with the PFC diminished the catastrophic root fractures induced by FRC posts, at a similar or higher fracture load.

scholarly journals Effect of Die Spacer Thickness on the Microshear Bond Strength of CAD/CAM Lithium Disilicate Veneers

2021 ◽  
Vol 2021 ◽  
pp. 1-7
Author(s):  
Sherine Mohamed Farag ◽  
Mona Mohamed Ghoneim ◽  
Rania Reda Afifi
Keyword(s):  
Bond Strength ◽  
Failure Modes ◽  
Lithium Disilicate ◽  
Chi Square ◽  
Cad Cam ◽  
Chi Square Test ◽  
Group B ◽  
Post Hoc ◽  
Microshear Bond Strength ◽  
Die Spacer

Aim. The aim of this study was to compare the microshear bond strength of ceramic veneers with digital die spacer settings at 20, 40, and 100 µm. Materials and Methods. Eighteen milled lithium disilicate microdiscs (IPS e.max CAD, Ivoclar Vivadent) were divided into three groups (n = 6) according to their digital die spacer settings: group A = 20 µm, group B = 40 µm, and group C = 100 µm. Six randomly selected sound maxillary premolars received three microdiscs each. Each microdisc was 1 mm in diameter and 1 mm in height. The buccal surfaces of the premolars were prepared with a 0.5 mm depth in enamel. After cementation, the specimens were thermocycled for 2,500 cycles between 5 and 55°C. Microshear bond strength testing was performed using a universal testing machine until bonding failure. Failure modes were evaluated using a stereomicroscope. Statistical analyses included one-way ANOVA, Tukey’s post hoc test, and chi-square test with a 5% alpha error and 80% study power. Results. The mean microshear bond strength values were calculated in MPa for group A = 31.91 ± 12.41, group B = 29.58 ± 5.03, and group C = 13.85 ± 4.12. One-way ANOVA ( p ≤ 0.05 ) showed a statistically significant difference in microshear bond strength among the three groups. Tukey’s post hoc test showed significant differences between groups A and C ( p = 0.004 ) and between groups B and C ( p = 0.011 ). The failure modes were presented as cohesive, adhesive, and mixed failures. Chi-square test indicated that the failure mode distribution was not significantly different among the three groups ( p = 0.970 ). Conclusion. Higher digital die spacer settings decrease the microshear bond strength of CAD/CAM lithium disilicate veneers.

scholarly journals Comparative Evaluation of the Fracture Strength of Monolithic Crowns Fabricated from Different all-ceramic CAD/CAM Materials (an in vitro study)

2018 ◽  
Vol 11 (3) ◽  
pp. 1689-1697 ◽  
Author(s):  
Zainab M. Jassim ◽  
Manhal A. Majeed
Keyword(s):  
Fracture Strength ◽  
In Vitro Study ◽  
Lithium Silicate ◽  
Reinforced Composite ◽  
All Ceramic ◽  
Cad Cam ◽  
Group A ◽  
Group B ◽  
Group D

The objective of this in vitro study was to evaluate and compare the fracture strength of monolithic crowns fabricated from five different all-ceramic CAD/CAM materials (lithium disilicate, zirconia, reinforced composite, hybrid dental ceramic, and zirconia-reinforced lithium silicate) using single load to failure test. Forty sound human maxillary first premolar teeth extracted for orthodontic purposes were selected for use in this study. Teeth were prepared according to a standard protocol with 1 mm deep chamfer finishing line, 4 mm axial height with planer occlusal reduction and 6º total convergence angle. Teeth were then divided into five groups of eight teeth each according to the material used for the fabrication of the monolithic crowns as follow: Group A: Crowns fabricated from lithium disilicate (IPS e.max CAD, Ivoclar Vivadent), Group B: Crowns fabricated from zirconia (CEREC Zirconia, Dentsply Sirona), Group C: Crowns fabricated from reinforced composite (BRILLIANT Crios, COLTENE), Group D: Crowns fabricated from hybrid dental ceramic (VITA ENAMIC, VITA Zahnfabric), Group E: Crowns fabricated from zirconia-reinforced lithium silicate (CELTRA DUO, Dentsply Sirona). Teeth of all groups were then scanned with CEREC Omnicam digital intraoral scanner and the crowns were then designed using CEREC Premium software (version 4.4.4) and milled using CEREC MC XL milling unit. Post-milling, crowns of each group were subjected to either a firing procedure or to a polishing only according to the manufacturer's instructions of each material. The internal surfaces of the crowns of each group were then subjected to surface treatment according to the manufacturer's instructions of each material and the crowns were then cemented on their respective teeth using a universal dual-cured adhesive resin cement (Duo-Link Universal, Bisco Inc.). All teeth with the cemented crowns were then stored in deionized distilled water at room temperature for 24 hours before testing. All samples were then subjected to compressive axial loading until fracture in computer-controlled universal testing machine (Zwick Z010, Ulm, Germany) at a crosshead speed of 0.5 mm/min. The data were statistically analyzed using one-way ANOVA test and LSD test at a level of significance of 0.05. The results of this study showed that the highest mean value of fracture strength was recorded by Group B (2337.37), followed by Group C (1880.59), Group E (1404.49), Group A (1085.39) and Group D (767.06), respectively with statistically highly significant differences among the different groups (p<0.01). From the results of this study, it seems that the differences in the chemical composition and microstructure of the tested all-ceramic CAD/CAM materials may be responsible for the differences in the fracture strength of the fabricated crowns.

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