Chamfer Margin Research Articles

Fracture resistance of ultratranslucent multilayered zirconia veneers with different facial thicknesses.

To assess the fracture resistance of computer-aided design and computer-aided manufacturing (CAD/CAM) ultratranslucent multilayered zirconia (5Y-YZP) veneers with varying facial thickness. Sixty translucent zirconia veneers were designed and milled using a chairside CAD/CAM system for maxillary central incisors. The butt joint incisal veneer tooth preparations consisted of 1.00 mm incisal reduction, 0.40 mm chamfer margin, and three different facial reductions; 0.50, 0.75, and 1 mm, respectively. The ceramic veneers were cemented to printed resin dies and subjected to thermal cycling. Subsequently, the restorations were loaded with compressive loading force, and fracture occurrences were recorded. Scanning electron microscope (SEM) images of the fractured specimens were captured. The fracture resistance varied among the veneers with different facial thicknesses. Ultratranslucent zirconia veneers with a facial thickness of 1.00 mm exhibited the highest fracture resistance values (742.15 N), followed by those with 0.75 mm facial thickness (673 N). Minimally invasive veneers with 0.50 mm thickness displayed similar fracture resistance as thicker veneers with 0.75 mm. However, veneers with 1.00 mm thickness displayed the highest values. SEM fracture patterns for 0.50 and 0.75 mm display similar and fewer crack lines than 1.00 mm veneers. RESEARCH HIGHLIGHTS: Minimally invasive zirconia veneers exhibit similar fracture resistance to thicker veneers.

Effect of preparation design and endodontic access on fracture resistance of zirconia overlays in mandibular molars: An in vitro study.

To evaluate the fracture resistance of zirconia overlays, considering various preparation designs and the presence of endodontic access. Ninety translucent zirconia (5Y-PSZ) overlay restorations were divided into six groups (n = 15/group) based on different preparation designs, with and without endodontic access: chamfer margin 4mm above the gingival level without (group 1) and with endodontic access (group 2); margin 2mm above the gingival level without (group 3) and with endodontic access (group 4); overlay with no chamfer margin without (group 5) and with endodontic access (group 6). Restorations were bonded to mandibular first molar resin dies, and the groups with endodontic access were sealed with flowable resin composite. All restorations underwent 100,000 cycles of thermal cycling between 5°C and 55°C, followed by loading until fracture. Maximum load and fracture resistance were recorded. ANOVA with Tukey post-hoc tests were used for statistical comparison (α < 0.05). Fracture resistance significantly varied among overlay designs with and without endodontic access (p < 0.001), except for the no-margin overlays (groups 5 and 6). Overlays with a 2mm margin above the gingival margin with endodontic access (group 4) exhibited significantly higher fracture resistance compared to both the 4-mm supragingival (group 2) and no-margin (group 6) designs, even when compared to their respective intact groups (groups 1 and 5). There were no significant differences between the no-margin and 4-mm supragingival overlays. The more extensive zirconia overlay for mandibular molars is the first choice since the 2mm margin above the gingival level design withstood considerable loads even after undergoing endodontic access. A no-margin overlay is preferred over the 4-mm supragingival design as it preserves more tooth structure and there was no outcome difference, irrespective of endodontic access. Caution is warranted in interpreting these findings due to the in vitro nature of the study.

Impact of Auxiliary Features on Retention of Short Dental Crowns: An In-Vitro Analysis of Box and Groove Preparations.

BACKGROUND Several auxiliary features have been proposed to achieve sustainable retention for short-prepared dental crowns; however, achieving retention is challenging. This study aimed to assess the impact of increased total occlusal convergence and auxiliary preparation factors like box and groove on the retention form of short tooth preparations. MATERIAL AND METHODS Eighty resin machine-milled dies with a height of 3 mm and a deep chamfer margin of 1 mm were prepared to mimic the short-prepared molar. Initially, 2 teeth were prepared following the guidelines, and the total occlusal convergence was kept at 10° and 20°, respectively. Auxiliary features such as the proximal box and buccal groove were prepared on separate 20° dies. Eighty dies were prepared with 10 samples each for 10°, 20°, 20° with proximal box and 20° with buccal groove for zirconia (n=40) and metal crowns (n=40). Cementation was done with glass ionomer luting cement, and a pull-off test was conducted. Data were analyzed using one-way analysis of variance and post hoc fisher least significant difference test (P<0.05). RESULTS The highest mean was observed in the proximal box group with the metal crown (14.59), and the lowest in the group with 20° zirconia crowns (9.12). Within groups, the highest retentive values were found for the 20° taper with proximal box preparation; the lowest was for the 20° taper group. CONCLUSIONS Within the study limitations, it could be concluded that incorporating a proximal box or buccal groove in short tooth preparations with an increased total occlusal convergence improved retentive values.

Fracture Resistance of Chairside CAD/CAM Lithium Disilicate-reinforced Ceramic Occlusal Veneers With and Without Margin and Full Coverage Crowns.

The aim of this investigation was to compare the fracture resistance of chairside computer-aided design and computer-aided manufacturing (CAD/CAM) lithium disilicate-reinforced ceramic occlusal veneers with and without margin and traditional full coverage premolar crowns. A total of 60 chairside CAD/CAM lithium disilicate-reinforced ceramic (Amber Mill, Hass Bio) restorations were designed and fabricated with a chairside CAD/CAM system (CEREC Dentsply Sirona). The restorations were divided into three groups (n=20): 1) occlusal veneer with 1.0-mm uniform occlusal thickness and with chamfer margin; 2) occlusal veneer with 1.0-mm uniform occlusal thickness and without margin; and 3) full coverage crown with uniform occlusal thickness and gingival margin. Occlusal veneers and crowns were cemented with dual cured resin luting cement (Multilink, Ivoclar Vivadent) to printed resin dies, load cycled (5 million load cycles at 1 Hz with 275 N force), and then loaded until fracture. Load at break (LB) and peak load (PL) until fracture were recorded. Scanning electron microscope images of the tested restorations on the abutments were obtained. Fracture strengths were different depending on the design of the restoration. There was no significant difference in fracture strength between the two types of occlusal veneer (LB: 1132.45 N; PL: 1143.30 N for veneers with margin; LB: 1149.25 N; PL: 1219.05 N for veneers without margin). Full coverage crowns showed the lowest fracture resistance (LB: 936.26 N, PL: 976.42 N), which was significantly lower than both designs of occlusal veneer. The fracture resistance of the CAD/CAM lithium disilicate-reinforced ceramic restorations was influenced by the design. Occlusal veneers with and without margin displayed higher fracture resistance than traditional crowns.

MTA apical plug in non-vital permanent tooth with an open apex: A case report

Objective: This case report aimed to describe a case of a post-core-crown restoration in an anterior tooth that had been endodontically treated with a direct monobloc technique using a composite resin material. Methods: After root canal treatment on tooth 11, a post cavity was made in the root canal with a diameter of 1 mm and a length of 5 mm. The post cavity was then filled with dual-cure resin cement and light-polymerized. Next, the core build-up is carried out using the same material, and crown preparation is carried out with a circumferential chamfer margin. The crown was made with direct composite resin materials with the aid of a silicone key to create a palatal enamel wall and then proceeded with the bilaminar technique until the crown was finished. Results: Three months' follow-up showed that the restoration was still in good condition and could function optimally. Conclusion: Post-core-crown restoration using direct monoblock technique using composite resin material shows good results and is aesthetically acceptable after three months of follow-up.&#x0D; Keywords: Endodontically treated tooth, Post-Core-Crown, Monoblock

Comparative Effect of No Finish Line, Heavy Chamfer, and Shoulder Marginal Designs on the Fracture Resistance of Zirconia (Cercon) Ceramic Restoration: An In Vitro Study.

Background Because all-ceramic crowns are more aesthetic and biocompatible than metal-ceramic crowns, they have grown in popularity among patients and dentists. Poor finish line layout can result in restoration margin fracturing, hence, finish line arrangement is critical to maintaining the restoration's marginal integrity. The goal of this in-vitro study is to evaluate zirconia's resistance to fracture (Cercon) ceramic restorations with three marginal designs (no finish line, heavy chamfer, and shoulder). This study is important in contributing to the ongoing debate about the optimal finish line design for zirconia restorations. Methodology Three different finish lines, namely, biologically oriented preparation technique (BOPT) with a marginal width of less than 0.3 mm, heavy chamfer with a marginal width of up to 0.3 mm, and shoulder with a marginal width greater than 0.3 mm, were made on 10 extracted maxillary first premolar tooth to make 30 epoxy resin dies on which zirconia (Cercon) coping was done using CAD/CAM technology, and marginal discrepancies were measured using a three-dimensional scanner. All the copings were affixed to their respective dies using GIC luting cement, and fracture resistance was measured using a digital universal testing machine. Results The Kruskal-Wallis test revealed that the mean fracture resistance was more in the heavy chamfer finish line, followed by the no finish line (BOPT) and the shoulder finish line. No statistically significant difference was seen between the no finish line and the heavy chamfer finish line. There was a significant difference between the heavy chamfer and shoulder finish lines (p = 0.004). Conclusions To increase the biomechanical performance of posterior single zirconia restorations, heavy chamfer margins are indicated.

Evaluation of the Quality of Undergraduate Full Veneer Crown Preparations at a UK Dental Teaching Hospital.

To determine the quality of full veneer crown preparations produced by supervised undergraduate students at a UK dental teaching hospital. One hundred and eighty-five scanned digital dies between October 2019 and March 2021 were obtained. Using cross-sections in four planes, the total angle of convergence, abutment height, margin design and margin depth were evaluated. Statistical comparisons were made by plane, location, material-type, tooth-type, and inter- and intra-arch positions. Across all preparations the mean total angle of convergence was 24.8° ± 11.7°. and mean abutment height was 3.6 mm ± 1.0 mm. Mandibular and molar teeth were significantly more tapered (P ⟨0.001) and exhibited significantly shorter abutment heights (P ⟨0.001). Chamfer margins were the most frequently observed and mean margin depths ranged from 0.49-1.06 mm. The compliance to recommended taught parameters were 28.1%, 42.7%, 34.1% and 6.5% for total angle of convergence, abutment height, margin design and margin depth, respectively. The findings from this study suggest that compliance to taught parameters is poor, especially for molar teeth, and demonstrates the use of digital software in guiding future research and teaching.

An in vitro comparison of incisal preparation design on load-to-failure of ceramic veneers.

This in vitro study aimed to compare the load-to-failure values of two different ceramic veneers (IPS e.max Press [Ivoclar Vivadent] and Vintage lithium disilicate [LD] press [Shofu]) with incisal preparation designs under standardized conditions. Twenty-two intact extracted maxillary incisors were selected and divided randomly into two groups (n = 11). The veneer tooth preparation was standardized in both groups where a butt joint incisal preparation was done along with chamfer margin. Group 1 included veneers made from IPS e.max Press (Ivoclar Vivadent) and Group 2 included veneers fabricated from Vintage LD Press (Shofu). Veneers were luted to their respective abutment teeth using standardized bonding protocols and resin cement for both groups. Later, every specimen was loaded to failure utilizing a universal testing machine, and the outcomes were noted in Newtons (N). The mean load-to-failure value obtained for Group 1 (IPS e.max Press) was 1386.46 N while that obtained for Group 2 was 1777.07 N. Statistically significant difference was found in this intergroup comparison (P = 0.006). The load-to-failure value of Vintage LD Press veneers (Shofu) was greater than that of IPS e.max Press veneers (Ivoclar Vivadent).

Marginal Misfit of 3D-Printed (Selective Laser Sintered), CAD-CAM and Lost Wax Technique Cobalt Chromium Copings with Shoulder and Chamfer Finish Lines: An In-Vitro Study.

Background and Objectives: The aim was to compare the Misfit of 3D-Printed, Selective laser melting (SLM), milled (Computer aided design-Computer aided manufacture CAD-CAM) and Lost wax technique (LWT) fabricated Cobalt chromium (CoCr) alloy copings on shoulder (SH), radial shoulder (R-SH) and chamfer (CH) finish line configuration. Materials and Methods: Ninety resin, second maxillary premolar teeth were prepared for metal-ceramic crowns, equally divided into (n = 30) SH, R-SH and CH margin preparations. For each preparation design (SH, R-SH and CH), CoCr copings were prepared using SLM, CAD-CAM and LWT. This resulted in nine study groups with 10 CoCr copings each. The marginal misfit of specimens was assessed with a high-resolution digital microscope. Misfit was evaluated in vertical and horizontal dimensions in μm. Data were analyzed using ANOVA and a post hoc multiple comparisons test. Results: For vertical misfit, the highest was observed in SLM samples with chamfer margin (167.96 ± 24.1), and the least was shown by CAD-CAM samples with radial shoulder (58.8 ± 12.53). CAD-CAM and shoulder margins showed the least vertical misfit. For horizontal misfit, the maximum was observed in SLM samples with shoulder margin (137.94 ± 37.85) and the least by LWT samples with chamfer (89.38 ± 14.81). Chamfer margins and LWT samples showed the least horizontal misfit among the group samples. Fabrication technique and finish line design play a critical role in reducing the marginal misfit of CoCr copings. Conclusions: For vertical misfit, SLM copings showed poor outcomes compared to CAD-CAM specimens, however comparable outcomes to Cast specimens. SLM copings showed comparable horizontal misfit outcomes to CAD-CAM specimens and low misfit compared to Cast copings, respectively. Vertical misfit was low with shoulder margins, and horizontal misfit was better with chamfer marginal configuration.

Success of Feather Margin Preparation for Full Metal Prosthodontic Crowns in the Canine Teeth in 84 Pet and Working Dogs (2005-2017).

Medical and dental records of Veterinary Dental Specialties and Oral Surgery were searched to identify dogs that received full metal prosthodontic crowns on canine teeth, using a feather or knife edge preparation between 2005 and 2017. A total of 160 teeth in 84 dogs were included in the study. Current follow-up by telephone, electronic mail, or electronic messaging was conducted, in addition to thorough record review for in-person recheck examinations. Treatment was considered successful if the prosthodontic crown was in place and no further or additional injury to the tooth had occurred at the time of reexamination, owner contact, or patient death. Tooth fracture apical to the prosthodontic crown occurred in 2 (1.25%) cases, bond failure between the tooth and the cement or the cement and the crown occurred in a single case (0.625%), and one metal crown required replacement after 3 years due to wear (0.625%), for an overall failure rate of 2.5%. These results suggest that feather preparation of the margin is at least as, if not more, successful as the more commonly accepted and performed chamfer margin, and thus is a successful, practical and durable option for prosthodontic crown treatment in dog canine teeth.

Evaluation of the marginal fit of a CAD/CAM zirconia-based ceramic crown system.

To evaluate the marginal fit of zirconia (Zi) CAD/CAM crowns in terms of gap and overhang compared to lithium disilicate (LDS) computer-aided design crowns, as well as the effect of finish line design on marginal accuracy. Stone dies were acquired from two master metal dies (n = 20 each) with two different finish lines and were scanned to produce digital models. Ceramic crowns (ZS-Ronde Zi, KaVo and IPS e.max CAD LDS, Ivoclar Vivadent) were designed and milled on the resulting 40 dies: 10 Zi-shoulder, 10 Zi-chamfer, 10 LDSshoulder, and 10 LDS-chamfer. Marginal gap and overhang were evaluated at six designated margin locations. The data were obtained, and the influence of material and finish line on the marginal fit of crowns was assessed using two-way analysis of variance and Bonferroni multiple comparisons test (α = .05). Mean marginal gap and overhang on Zi crowns were 30 ± 14 μm and 79 ± 27 μm for the shoulder, respectively, and were 68 ± 34 μm and 104 ± 34 μm for the chamfer. The corresponding values for LDS crowns were 57 ± 22 μm and 74 ± 29 μm for the shoulder, and 62 ± 12 μm and 59 ± 27 μm for the chamfer. ANOVA revealed that the differences in marginal gap between the two materials were not significant (P > .05), but that the finish line effect and interaction were significant (P < .05). With regard to marginal overhang, significant differences were found between Zi and LDS crowns (P < .05), although the finish line geometries did not show any significant differences (P > .05). LDS crowns showed no differences between shoulder and chamfer margins for gap or overhang (P > .05), whereas significant differences were found in marginal gap between the Zi shoulder and chamfer margins (P lt; .005). In terms of marginal accuracy, shoulder margins produced smaller marginal gaps compared to chamfers for Zi CAD/CAM crowns.

Influence of Margin Designs on Crack Initiation of High Translucency Monolithic Zirconia Crowns.

Zirconia crowns often crack at the margin. This study determined the loads and the times at which cracks are initiated in high-translucency monolithic zirconia crowns with different margin designs. A total of 90 crowns were fabricated from Zirconia blanks. The fabricated crowns had different margin thicknesses (light-chamfer, CL and heavy-chamfer, CH ) and collar heights (no-collar, NC ; low-collar, LC ; high-collar, HC ). They were grouped as CL NC , CL LC , CL HC , CH NC , CH LC , and CH HC (15 crowns/group). The crowns were seated on a metal model and loaded vertically through round end punch (Φ = 10 mm) at 0.2 mm/min crosshead speed until cracks began to be seen. Videos of the crack initiation were recorded at the rate of 50 frames/second. Load-initiated cracks and durability time were compared for significant differences using analysis of variance. The mean ± standard deviation values of load (N) and time (s) taken to initiate cracks were 3190 ±775, 212 ±47 for CL NC ; 2754 ±1109, 180 ±42 for CL LC ; 2887±832, 191±27 for CL HC ; 4082 ±896, 241 ±36 for CH NC ; 4180 ±1029, 220 ±28 for CH LC ; 4119 ±1124, 222 ±39 for CH HC . This indicates that the thickness of the margin has a significant influence on load-withstanding crack initiation capacity and durability time (p < 0.05). No significant impact of collar height was observed on either load-withstanding capacity or durability time (p > 0.05). No interaction was observed among these factors. Heavy chamfer margin provided a stronger zirconia crown than the light chamfer margin, but both of them were capable of withstanding crack-initiated load higher than the theoretical maximum masticatory force. The presence or absence of a collar did not have any impact on the crack initiation. Fabrication of zirconia crowns with either a heavy or light chamfer margin and with or without the presence of a collar should be generated by considering the relevant emergence profile.

Effect of Marginal Designs on Fracture Strength of High Translucency Monolithic Zirconia Crowns.

Introduction Monolithic zirconia is able to achieve certain aesthetic, but its durability in resisting fracture has been questioned, as fractures often originate from margins of restoration. This study determined fracture resistance of highly translucent monolithic zirconia crowns with different margin designs in terms of marginal thickness and collar height. Materials and Methods Zirconia blanks (Ceramill® Zolid HT+) were selected for the fabrication of zirconia crowns according to different designs, including varying margin thicknesses (light chamfer, CL; heavy chamfer, CH) and collar heights (no collar, NC; low collar, LC; high collar, HC), which resulted in CLNC, CLLC, CLHC, CHNC, CHLC, and CHHC groups (15 crowns each). The crowns were seated on a metal die and loaded vertically through round end punch (θ = 10 mm), contacting with inclined planes of cusp in a testing machine with crosshead speed of 0.2 mm/min until fracture. Videos with a rate of 50 frames/second were used to record fracture. Fracture load (N) and durable period (s) were compared for significant differences using ANOVA and Bonferroni test (α = 0.05). Results The mean ± sd of fracture load (N) and durable time (s) were 3211 ± 778 and 212 ± 47 for CLNC; 3041 ± 1370 and 188 ± 53 for CLLC; 2913 ± 828 and 192 ± 27 for CLHC; 4226 ± 905 and 245 ± 35 for CHNC; 4486 ± 807 and 228 ± 29 for CHLC; and 4376 ± 1043 and 227 ± 37 for CHHC. This indicated that marginal thickness had a significant influence on load-bearing capacity and durable time (p < 0.05). No significant impact of collar height was shown, either on load-bearing capacity or durable time (p > 0.05). No interaction between two factors was presented (p > 0.05). Conclusions Heavy chamfer margin provided stronger zirconia crown than light chamfer, but both were capable of withstanding fracture load higher than maximum masticatory force. Neither presence nor absence of collar indicated any impact on strength. Fabrication of zirconia crowns with either heavy or light chamfer margin and either presence or absence of collar, with the consideration of emergence profile, should be considered.

Effect of Reduced Occlusal Thickness with TwoMargin Designs on Fracture Resistance of Monolithic Zirconia Crowns.

Objectives The aim of this study was to compare the effects of two margin designs (shoulderless and slight chamfer) with two occlusal thicknesses on fracture resistance and failure mode of the monolithic zirconia crowns. Materials and Methods Forty nickel–chromium dies were duplicated from the previous two prepared teeth using a three-dimensional optical scanner. Nickel–chromium supporting dies were divided into two main groups ( n = 20) according to the type of margin design: group A, slight chamfer margin design and group B, shoulderless margin design. These groups were further divided into two subgroups according to the occlusal thicknesses (0.5 and 1 mm). The digital imaging of each die was done using a three-dimensional optical scanner, then zirconia blocks were milled by 5-axis machine. The crowns were cleaned by alcohol, air dried, and cemented by resin cement. Next, the crowns were subjected to 500 hot and cold cycles (30 seconds for each cycle). The samples were subjected to a static load until failure using an electronic universal testing machine and fracture resistance was recorded in Newton (N). Statistical Analysis Data were analyzed using the test of normality (Shapiro–Wilk test) and two-way analysis of variance (ANOVA) test. Results The highest mean fracture load was recorded by the shoulderless (1 mm occlusal thickness) subgroup (3,992.5 N), followed by shoulderless (0.5 mm occlusal thickness) subgroup (3,244.4 N), and the slight chamfer (1 mm occlusal thickness) subgroup (2,811 N). The lowest mean of fracture load was recorded by slight chamfer (0.5 mm occlusal thickness) subgroup (1,632.9 N). The two-way ANOVA test revealed a significant difference between the four subgroups. Regarding the fracture mode, the slight chamfer subgroups showed a severe fracture of the restoration while the shoulderless subgroups showed a fracture through the midline of the restoration. Conclusion Within the limitation of the comparative study, shoulderless margin design has a more favorable outcome than a slight chamfer design in all thicknesses. Although the restoration with reduced occlusal thickness has lower fracture resistance than 1 mm occlusal thickness, the 0.5 mm restorations still can tolerate occlusal forces.

Comparative evaluation of microleakage of conventional crowns and endocrowns using confocal laser scanning electron microscope – An in vitro study

Background and Aims: The purpose of this study was to compare the microleakage of conventional crowns and endocrowns using confocal laser scanning electron microscope. Materials and Methods: Thirty extracted human permanent mandibular molars were collected and sectioned parallel to the occlusal surface at 2 mm above the CEJ to deroof the pulp chamber. Endodontic treatment was performed. The gutta-percha was removed 1 mm below the orifice of each canal, and flowable resin composite was filled in the canals up to the level of the pulp chamber. Samples were then randomly divided into two groups with 15 teeth each according to the type of post endodontic restoration given – Group 1: conventional crowns and Group 2: endocrowns. In Group (1), teeth were restored with composite cores, wide circumferential deep chamfer margin (0.8 mm) was prepared at the CEJ and 2 mm from the occlusal surface, 1.5 mm were cut from the axial walls. In Group (2), preparation was performed by making a circular butt margin with a central retention cavity with rounded internal line angles. Impressions were made, crowns were fabricated, and cementation was done, followed by thermocycling. The specimens were coated with varnish up to 1 mm from the crown margins, placed in Rhodamine B dye for 60 h, rinsed thoroughly for 30 s, sectioned with hard tissue microtome and examined for microleakage. Statistical Analysis: Statistical analysis was accomplished with the Student t-test, and significance was predetermined at P Results: In this study, endocrowns (6.158) showed significantly low microleakage compared with conventional crowns (14.052). Conclusion: Endocrowns showed significantly lower microleakage.

Influence of Shoulder and Chamfer Margin Design on the Stress Distribution Pattern in Different All Ceramic Restorations by Three-Dimensional Finite Element Analysis

Purpose: The purpose of this study was to evaluate the influence of shoulder and chamfer margin design on stress distribution pattern in different all ceramic restorations.

Preparation Techniques Used to Make Single-Unit Crowns: Findings from The National Dental Practice-Based Research Network.

To: (1) determine which preparation techniques clinicians use in routine clinical practice for single-unit crown restorations; (2) test whether certain practice, dentist, and patient characteristics are significantly associated with these techniques. Dentists in the National Dental Practice-Based Research Network participated in a questionnaire regarding preparation techniques, dental equipment used for single-unit crown preparations, scheduled chair time, occlusal clearance determination, location of finish lines, magnification during preparation, supplemental lighting, shade selection, use of intraoral photographs, and trimming dies. Survey responses were compared by dentist and practice characteristics using ANOVA. Of the 2132 eligible dentists, 1777 (83%) responded to the survey. The top two margin configuration choices for single-unit crown preparation for posterior crowns were chamfer/heavy chamfer (65%) and shoulder (23%). For anterior crowns, the most prevalent choices were the chamfer (54%) and the shoulder (37%) configurations. Regarding shade selection, a combination of dentist, assistant, and patient input was used to select anterior shades 59% of the time. Photographs are used to communicate shade selection with the laboratory in about half of esthetically demanding cases. The ideal finish line was located at the crest of gingival tissue for 49% of respondents; 29% preferred 1 mm below the crest; and 22% preferred the finish line above the crest of tissue. Average chair time scheduled for a crown preparation appointment was 76± 21 minutes. Practice and dentist characteristics were significantly associated with margin choice including practice type (p < 0.001), region (p < 0.001), and years since graduation (p < 0.001). Network dentists prefer chamfer/heavy chamfer margin designs, followed by shoulder preparations. These choices were related to practice and dentist characteristics.

Effect of two Preparation Designs and Methods of Construction on the Fracture Resistance of Glass Ceramics Laminate Veneers

Purpose: To evaluate the effect of marginal finish line design and fabrication techniques on the fracture resistance of lithium disilicate laminate veneer. Materials and methods: A total of 24 veneers were designed, constructed, and divided into two main groups according to preparation design Chamfer 0.3 mm finish line (n=12) and, Chisel finish line (n=12). Each group was then divided into two subgroups according to the technique of veneer construction, veneers constructed by (CAD/CAM system) out of e max CAD blocks (n=6), and veneers constructed by (press on technology) using e max press ingots (n=6). then the veneers bonded to corresponding epoxy resin dies using resin cement. Finally fracture resistance test was done for all specimens using universal testing machine. Results: The highest fracture resistance values were recorded in the group of chisel marginal design fabricated by CAD/CAM technique. The lowest fracture resistance values were recorded in the group of 0.3mm chamfer margin design fabricated by Press technique. Regardless to margin design there was a significant difference between both processing techniques as indicated by two-way ANOVA test (p=0.0178 Press). Irrespective of material type it was found that margin design significantly influenced mean as indicated by two-way ANOVA test (p=0.0001 0.05). It was found that the Chamfer margin design recorded statistically significant higher fracture resistance mean value with CAD/CAM group (245.85±56.37N) than Press group (129.71±19.49 N) as indicated by unpaired t-test (P=0.002<0.05) Conclusions: The technique of fabrication of ceramic laminate veneer restorations has a crucial effect on its performance with the regard to fracture resistance. IPS e.max CAD could be considered as a valid restoration than IPS e.max press.

Influence of finish line design on the marginal fit of nonprecious metal alloy coping fabricated by 3D printing, milling and casting using CAD CAM

Background The marginal fit is one of the key factors for the clinical success of dental restorations. Ideal marginal adaptation can reduce gingival irritation and cement dissolution. After clinically examining over 1000 metal ceramic crowns, McLean and von Fraunhofer reported that marginal discrepancies up to 120 μm were acceptable. Other clinicians considered a marginal fit of 100 μm to be clinically acceptable for the longevity of the restorations. Aim/Hypothesis The purpose of this study was to examine the correlation between the finish line designs and the marginal adaptation of nonprecious metal alloy coping produced by different digital manufacturing methods. Material and Methods For fabrication of two master models with different finish lines, the master models were designed by 3-D designing software program based on the abutment preparation principle and titanium master models were milled by computer aided manufacturing. Nonprecious metal alloy copings were made respectively from each master model with three different methods, selective laser sintering (SLS), milling and casting by CAD CAM. 12 copings were made by each method resulting in 72 copings in total. The marginal fit was evaluated by measuring the gap between the cavosurface margin of the abutment die and the edge of the crown margin on mesial, buccal, distal and lingual site of each specimen. The measurement was conducted at 40 determined reference points along the circumferential margin with the confocal laser scanning microscope at magnification ×150. Results Mean values of marginal gap of laser sintered copings were 11.8 ± 7.4 μm for deep chamfer margin and 6.3 ± 3.5 μm for rounded shoulder margin and the difference between them was statistically significant (P < 0.0001). Mean values of marginal gap of milled copings were 53.9 ± 27.8 μm for deep chamfer margin and 48.6 ± 30.1 μm for rounded shoulder margin and the difference between them was not significant (P = 0.279). Mean values of marginal gap of casted copings were 18.8 ± 20.2 μm for deep chamfer margin and 33 ± 20.5 μm for rounded shoulder margin and the difference between them was significant (P = 0.0004). Meanwhile, the marginal fit depending on the manufacturing method was significantly different regardless of finish line design. Selective laser sintering group exhibited the best marginal adaptation among three manufacturing methods and digitalized casting group showed better marginal fit than milling group. Conclusions and Clinical Implications (i) The variation of finish line design influences the marginal adaptation of laser sintered metal coping and casted metal coping. (ii) Laser sintered copings with rounded shoulder margin had better marginal fit than deep chamfer margin. (iii) Casted copings with deep chamfer margin had better marginal fit than rounded shoulder margin. (iv) According to the manufacturing method, SLS system showed the best marginal fit among three different methods. Casting and milling method followed that in order.

Internal accuracy of digitally fabricated cross-arch yttria-stabilized tetragonal zirconia polycrystalline prosthesis.

ObjectiveThis investigation determined the internal precision of one-piece cross-arch yttria partially stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramic fabricated from two digital systems (Trios-3 and CS-3500) compared to traditional metal alloy casting.Materials and methodsA metal model consisting of four abutments (two canine and two molar) was used for one-piece cross-arch reconstruction. The metal abutments were computerized, prepared in a cylinder form possessing 5° taper and chamfer margin. Two digital approaches of computer-aided design and computer-aided manufacturing were used to fabricate one-piece cross-arch Y-TZP prostheses. The traditional lost wax technique was used to fabricate conventional cast prostheses with nonnoble metal alloys. Ten prostheses were constructed from each system. The preciseness of the prosthesis was evaluated at 22 positions for each abutment using a digital stereomicroscope. Analysis of variance (ANOVA) and Tukey’s method were determined for all pairwise differences at the 95% CI.ResultsThe means and SDs of internal accuracy of prostheses constructed from the traditional cast technique, Trios-3, and CS-3500 were 75.15±13.46 μm, 78.55±14.30 μm, and 82.43±16.32 μm, respectively. ANOVA revealed statistical significance for the internal accuracy of prostheses between the different techniques at different positions of each abutment. Preciseness of the Y-TZP prosthesis constructed from Trios-3 illustrated significantly better internal fit than that constructed from CS-3500 (p<0.05). Tukey multiple comparisons revealed that the Y-TZP prosthesis constructed from both digital systems displayed significantly less internal fit than the traditionally fabricated prosthesis (p<0.05).ConclusionThe one-piece cross-arch Y-TZP prosthesis constructed from Trios-3 demonstrated superior internal accuracy than that from CS-3500, but both slightly lower in accuracy than the traditional cast metal prosthesis. Nevertheless, the internal discrepancies of the Y-TZP prosthesis fabricated by both digital techniques were not beyond the range of clinical prestige and were convincingly precise to be recommended for one-piece cross-arch extensive reconstruction.