How adjustment could affect internal and marginal adaptation of CAD/CAM crowns made with different materials

PURPOSERecently introduced hybrid and reinforced glass ceramic computer-aided design/computer-aided manufacturing (CAD/CAM) materials have been used for full-coverage restorations. However; the effect of adjustment and type of materials on internal and marginal adaptation are unknown. This study aimed to evaluate and compare the marginal and internal adaptations of crowns made of three different CAD/CAM materials before and after adjustment.MATERIALS AND METHODSOne acrylic resin maxillary first molar was prepared and served as the master die. Thirty-six restorations were fabricated using CAD/CAM system (CEREC Omnicam, MCXL) with three materials including lithium disilicate (IPS e.max CAD), zirconia-reinforced lithium silicate (Suprinity), and hybrid ceramic (Enamic). Internal and marginal adaptations were evaluated with the reference point matching technique before and after adjustment. The data were analyzed using mixed ANOVA considering α=.05 as the significance level.RESULTSThe effect of adjustment and its interaction with the restoration material were significant for marginal, absolute marginal, and occlusal discrepancies (P<.05). Before adjustment, Suprinity had lower marginal discrepancies than IPS e.max CAD (P=.18) and Enamic (P=.021); though no significant differences existed after adjustment.CONCLUSIONWithin the limitations of this study, crowns fabricated from IPS e.max CAD and Suprinity resulted in slightly better adaptation compared with Enamic crowns before adjustment. However, marginal, axial, and occlusal discrepancies were similar among all materials after the adjustment.     

Fatigue behavior and crack initiation of CAD/CAM resin composite molar crowns

Objective

The aim of this study was to evaluate long-term fatigue behavior using an in vitro step-stress accelerated life test (SSALT), and to determine the crack initiation point using in silico finite element analysis for computer-aided designed and manufactured (CAD/CAM) molar crowns fabricated from three commercial CAD/CAM resin composite blocks: Cerasmart (CS; GC, Tokyo, Japan), Katana Avencia Block (KA; Kuraray Noritake Dental, Niigata, Japan), and Shofu Block HC (HC; Shofu, Kyoto, Japan).

Fracture strength testing of crowns made of CAD/CAM composite resins

Purpose

The purpose of this study was to ascertain whether computer aided design/computer aided manufacturing (CAD/CAM) composite resin crowns have sufficient strength to withstand the bite force of the molar teeth. The null hypothesis was that the fracture strength of CAD/CAM composite resin crowns is lower than the average maximum bite force of the molar tooth.

In vitro analysis of durability of S-PRG filler-containing composite crowns for primary molar restoration

ObjectiveTo evaluate the reliability, maximum principal stress, shear stress, and crack initiation of a computer-aided design/computer-aided manufacturing (CAD/CAM) resin composite (RC) incorporating surface pre-reacted glass (S-PRG) filler for primary molar teeth.MethodsMandibular primary molar crowns fabricated by experimental (EB) or commercially available CAD/CAM RCs (HC) were prepared and cemented to a resinous abutment tooth using an adhesive resin cement (Cem) or a conventional glass-ionomer cement (CX). These specimens were subjected to a single compressive test (n = 5/each) and the step-stress accelerated life testing (SSALT) (n = 12/each). Data was evaluated using Weibull analyses and reliability was calculated. Afterwards, the maximum principal stress and crack initiation point of each crown was analyzed by finite element analysis. To evaluate bonding of EB and HC to dentin, microtensile bond strength (μTBS) testing was conducted using primary molar teeth (n = 10/each).ResultsThere was no significant difference between the fracture loads of EB and HC for either cement (p > 0.05). The fracture loads of EB-CX and HC-CX were significantly lower than EB-Cem and HC-Cem (p < 0.05). The reliability at 600 N for EB-Cem was greater than that for EB-CX, HC-Cem, and HC-CX. The maximum principal stress concentrated on EB was lower than that on HC. The shear stress concentrated in the cement layer for EB-CX was higher than that for HC-CX. There was no significant difference among the μTBSs of EB-Cem, EB-CX, HC-Cem, and HC-CX (p > 0.05).SignificanceThe crowns fabricated with the experimental CAD/CAM RC incorporating S-PRG filler yielded greater fracture loads and reliability than the crowns manufactured with commercially available CAD/CAM RC regardless of the luting materials. These findings suggest that the experimental CAD/CAM RC crown may be clinically useful for the restoration of primary molars.     

Comparative fracture strength analysis of Lava and Digident CAD/CAM zirconia ceramic crowns

PURPOSE

All-ceramic crowns are subject to fracture during function. To minimize this common clinical complication, zirconium oxide has been used as the framework for all-ceramic crowns. The aim of this study was to compare the fracture strengths of two computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia crown systems: Lava and Digident.

MATERIALS AND METHODS

Twenty Lava CAD/CAM zirconia crowns and twenty Digident CAD/CAM zirconia crowns were fabricated. A metal die was also duplicated from the original prepared tooth for fracture testing. A universal testing machine was used to determine the fracture strength of the crowns.

RESULTS

The mean fracture strengths were as follows: 54.9 ± 15.6 N for the Lava CAD/CAM zirconia crowns and 87.0 ± 16.0 N for the Digident CAD/CAM zirconia crowns. The difference between the mean fracture strengths of the Lava and Digident crowns was statistically significant (P<.001). Lava CAD/CAM zirconia crowns showed a complete fracture of both the veneering porcelain and the core whereas the Digident CAD/CAM zirconia crowns showed fracture only of the veneering porcelain.

CONCLUSION

The fracture strengths of CAD/CAM zirconia crowns differ depending on the compatibility of the core material and the veneering porcelain.     

Comparison of shear bond strengths of different types of denture teeth to different denture base resins

PURPOSETo determine the shear bond strengths of different denture base resins to different types of prefabricated teeth (acrylic, nanohybrid composite, and cross-linked) and denture teeth produced by computer-aided design/computer-aided manufacturing (CAD/CAM) technology.MATERIALS AND METHODSPrefabricated teeth and CAD/CAM (milled) denture teeth were divided into 10 groups and bonded to different denture base materials. Groups 1–3 comprised of different types of prefabricated teeth and cold-polymerized denture base resin; groups 4–6 comprised of different types of prefabricated teeth and heat-polymerized denture base resin; groups 7–9 comprised of different types of prefabricated teeth and CAD/CAM (milled) denture base resin; and group 10 comprised of milled denture teeth produced by CAD/CAM technology and CAD/CAM (milled) denture base resin. A universal testing machine was used to evaluate the shear bond strength for all specimens. One-way ANOVA and Tukey post-hoc test were used for analyzing the data (α=.05).RESULTSThe shear bond strengths of different groups ranged from 3.37 ± 2.14 MPa to 18.10 ± 2.68 MPa. Statistical analysis showed significant differences among the tested groups (P<.0001). Among different polymerization methods, the lowest values were determined in cold-polymerized resin.There was no significant difference between the shear bond strength values of heat-polymerized and CAD/CAM (milled) denture base resins.CONCLUSIONDifferent combinations of materials for removable denture base and denture teeth can affect their bond strength. Cold-polymerized resin should be avoided for attaching prefabricated teeth to a denture base. CAD/CAM (milled) and heat-polymerized denture base resins bonded to different types of prefabricated teeth show similar shear bond strength values.     

Physical properties and wear behavior of CAD/CAM resin composite blocks containing S-PRG filler for restoring primary molar teeth

ObjectivesThis study aimed to develop computer-aided design/computer-aided manufacturing (CAD/CAM) resin composite blocks (RCBs) containing surface pre-reacted glass-ionomer (S-PRG) filler for primary molar teeth and evaluate their physical properties and wear resistance.MethodsExperimental CAD/CAM RCBs containing S-PRG filler for primary molar teeth (EB), a commercial CAD/CAM RCB (HC), two resin composites for primary teeth (BKP and BKZ) and one for permanent teeth (BⅡ) were used. Hardness tests, three-point bending tests, fracture toughness tests, and water absorption tests were conducted. Wear tests were conducted for these materials and stainless steel crowns (SSCs).ResultsThe Vickers hardness of EB was lower than that of HC (p < 0.05), and there was no significant difference among BKZ, BKP, and BⅡ (p > 0.05). After 1 week of water immersion, EB and HC showed greater flexural strength than the other materials (p < 0.05). EB showed greater fracture toughness than the other materials (p < 0.05). The water absorption of EB was lower than that of HC, BKZ, and BKP (p < 0.05), and greater than that of BⅡ (p < 0.05). Antagonist wear was significantly smaller in EB than in HC and BⅡ (p < 0.05), and significantly greater than in BKZ (p < 0.05). Antagonist wear could not be measured in SSC because of excessive wear that was out of range of the surface roughness tester.SignificanceThe CAD/CAM RCBs containing S-PRG filler for primary molar teeth developed in this study demonstrated adequate physical properties and wear performance, suggesting that they are suitable for restoration of primary molar teeth and could function in place of SSCs.     

Fracture resistance of computer‐aided design/computer‐aided manufacturing‐generated composite resin‐based molar crowns

The aim of this study was to investigate whether different fabrication processes, such as the computer‐aided design/computer‐aided manufacturing (CAD/CAM) system or the manual build‐up technique, affect the fracture resistance of composite resin‐based crowns. Lava Ultimate (LU), Estenia C&B (EC&B), and lithium disilicate glass‐ceramic IPS e.max press (EMP) were used. Four types of molar crowns were fabricated: CAD/CAM‐generated composite resin‐based crowns (LU crowns); manually built‐up monolayer composite resin‐based crowns (EC&B‐monolayer crowns); manually built‐up layered composite resin‐based crowns (EC&B‐layered crowns); and EMP crowns. Each type of crown was cemented to dies and the fracture resistance was tested. EC&B‐layered crowns showed significantly lower fracture resistance compared with LU and EMP crowns, although there was no significant difference in flexural strength or fracture toughness between LU and EC&B materials. Micro‐computed tomography and fractographic analysis showed that decreased strength probably resulted from internal voids in the EC&B‐layered crowns introduced by the layering process. There was no significant difference in fracture resistance among LU, EC&B‐monolayer, and EMP crowns. Both types of composite resin‐based crowns showed fracture loads of >2000 N, which is higher than the molar bite force. Therefore, CAD/CAM‐generated crowns, without internal defects, may be applied to molar regions with sufficient fracture resistance.     

A possible risk of CAD/CAM-produced composite resin premolar crowns on a removable partial denture abutment tooth: a 3-year retrospective cohort study

Purpose

To evaluate the early performance of computer-aided design/computer-aided manufacturing (CAD/CAM)-produced composite resin crown (CAD/CAM composite crown) treatment on premolars, specifically, placement on a removable partial denture (RPD) abutment tooth, and the distalmost tooth in the dental arch, as possible clinical risk factors.

Developing meaningful systematic review of CAD/CAM reconstructions and fiber-reinforced composites

Objective: Clinical literature was examined for evidence supporting use of CAD/CAM reconstructions and fiber‐reinforced materials. Materials and methods: Potential evidence was identified via databases [PubMed; EMBASE (R) Drugs & Pharmacology; Center for Reviews and Dissemination, University of York; Cochrane Library], hand search of non‐indexed literature, secondary reference searches, and personal contacts with clinical trial PI's. Search terms included: dental restorations; CAD/CAM; CEREC; LAVA; CERCON; Procera; inlay/onlay; dental prosthesis; fiber‐reinforced composite (FRC). Results: Two randomized‐controlled clinical trials were identified as examined in one Cochrane Collaboration review relevant to CAD/CAM inlays. One systematic review of 15 CAD/CAM inlay studies was examined. Six studies were identified of three commercial FRC endodontic posts and eight reported on FRC use for fixed denture prostheses. Fifteen ongoing prospective trials were identified studying CAD/CAM fabricated zirconia‐based prostheses. A total of 76 papers were referenced including those related to use of in vitro measures as evidence. Conclusions: Review of the Cochrane analysis raised concerns that typical RCT protocols may prove insufficient for stratification of confounding variables (patient, practitioner, material) when treatment outcomes are primarily prosthesis‐ or material‐based (not patient‐based, e.g., as in fracture). RCT designs are most straightforward when treatment outcomes are patient‐based (e.g., soft tissue changes). When treatment responses are material‐based, controls also become difficult to define and studies become tests of equivalency/superiority; where well‐stratified cohort designs are likely preferred. Large numbers of independent cohort studies support the use of CAD/CAM ceramic inlay/onlay restorations and crowns but many complications inhibit the application of high‐level systematic review. Except perhaps for fiber‐based endodontic posts, the clinical FRC literature appears insufficient for expert review. Single in vitro measures cannot currently serve as evidence for clinical practice, except in limited cases of simple function (e.g., impression material accuracy). Batteries of in vitro measures are often applied during materials development but cannot substitute for clinical study.     

Fit of zirconia fixed partial denture: a systematic review

Summary The aim of this study is to review all the published literature investigating the accuracy of fit of zirconia fixed partial dentures (FPD). A comprehensive electronic search was performed through PubMed (MEDLINE) using Boolean operators to combine the following key words: ‘zirconia,’‘margin,’‘FPD,’‘internal,’‘fit,’‘gap,’‘fitting surface,’‘bridge’ and ‘fixed prosthesis.’ The search was limited to articles written in English, published up to January 2010. In addition, a manual search was also conducted through articles and reference lists retrieved from the electronic search and peer‐reviewed journals. A total of 115 articles were retrieved and only 15 met the specified inclusion criteria for the review. Twelve of these articles were in vitro and three of them were in vivo. The selected articles had assessed marginal and/or internal fit of zirconia FPDs against the effect of various parameters that were computer‐aided design and computer‐aided manufacturing (CAD/CAM) and CAM systems, post‐sintered and pre‐sintered milling, framework configuration, span length, veneer application and ageing. Conclusions: CAD/CAM, post‐sintered milling, straight configuration and shorter span frameworks provided superior results than CAM, pre‐sintered milling, curved configuration and longer span frameworks. Veneering zirconia frameworks caused deterioration in fit, while ageing of zirconia had no implications on the fit. Further studies are needed to determine the clinical significance of the differences in the accuracy reported in this review.     

Wear of 3D printed and CAD/CAM milled interim resin materials after chewing simulation

PURPOSEThe purpose of this in vitro study was to investigate the wear resistance and surface roughness of three interim resin materials, which were subjected to chewing simulation.MATERIALS AND METHODSThree interim resin materials were evaluated: (1) three-dimensional (3D) printed (digital light processing type), (2) computer-aided design and computer-aided manufacturing (CAD/CAM) milled, and (3) conventional polymethyl methacrylate interim resin materials. A total of 48 substrate specimens were prepared. The specimens were divided into two subgroups and subjected to 30,000 or 60,000 cycles of chewing simulation (n = 8). The wear volume loss and surface roughness of the materials were compared. Statistical analysis was performed using one-way analysis of variance and Tukey''s post-hoc test (α=.05).RESULTSThe mean ± standard deviation values of wear volume loss (in mm³) against the metal abrader after 60,000 cycles were 0.10 ± 0.01 for the 3D printed resin, 0.21 ± 0.02 for the milled resin, and 0.44 ± 0.01 for the conventional resin. Statistically significant differences among volume losses were found in the order of 3D printed, milled, and conventional interim materials (P<.001). After 60,000 cycles of simulated chewing, the mean surface roughness (Ra; μm) values for 3D printed, milled, and conventional materials were 0.59 ± 0.06, 1.27 ± 0.49, and 1.64 ± 0.44, respectively. A significant difference was found in the Ra value between 3D printed and conventional materials (P=.01).CONCLUSIONThe interim restorative materials for additive and subtractive manufacturing digital technologies exhibited less wear volume loss than the conventional interim resin. The 3D printed interim restorative material showed a smoother surface than the conventional interim material after simulated chewing.     

Effects of tributylborane-activated adhesive and two silane agents on bonding computer-aided design and manufacturing (CAD/CAM) resin composite

The present study was conducted to evaluate the effects of an experimental adhesive agent [methyl methacrylate-tributylborane liquid (MT)] and two adhesive agents containing silane on the bonding between a resin composite block of a computer-aided design and manufacturing (CAD/CAM) system and a light-curing resin composite veneering material. The surfaces of CAD/CAM resin composite specimens were ground with silicon-carbide paper, treated with phosphoric acid, and then primed with either one of the two silane agents [Scotchbond Universal Adhesive (SC) and GC Ceramic Primer II (GC)], no adhesive control (Cont), or one of three combinations (MT/SC, MT/GC, and MT/Cont). A light-curing resin composite was veneered on the primed CAD/CAM resin composite surface. The veneered specimens were subjected to thermocycling between 4 and 60 °C for 10,000 cycles, and the shear bond strengths were determined. All data were analyzed using analysis of variance and a post hoc Tukey–Kramer HSD test (α = 0.05, n = 8). MT/SC (38.7 MPa) exhibited the highest mean bond strengths, followed by MT/GC (30.4 MPa), SC (27.9 MPa), and MT/Cont (25.7 MPa), while Cont (12.9 MPa) and GC (12.3 MPa) resulted in the lowest bond strengths. The use of MT in conjunction with a silane agent significantly improved the bond strength. Surface treatment with appropriate adhesive agents was confirmed as a prerequisite for veneering CAD/CAM resin composite restorations.     

Fatigue analysis of computer‐aided design/computer‐aided manufacturing resin‐based composite vs. lithium disilicate glass‐ceramic

Resin‐based composite molar crowns made by computer‐aided design/computer‐aided manufacturing (CAD/CAM) systems have been proposed as an inexpensive alternative to metal‐ceramic or all‐ceramic crowns. However, there is a lack of scientific information regarding fatigue resistance. This study aimed to analyze the fatigue behavior of CAD/CAM resin‐based composite compared with lithium disilicate glass‐ceramic. One‐hundred and sixty bar‐shaped specimens were fabricated using resin‐based composite blocks [Lava Ultimate (LU); 3M/ESPE] and lithium disilicate glass‐ceramic [IPS e.max press (EMP); Ivoclar/Vivadent]. The specimens were divided into four groups: no treatment (NT); thermal cycling (TC); mechanical cycling (MC); and thermal cycling followed by mechanical cycling (TCMC). Thermal cycling was performed by alternate immersion in water baths of 5°C and 55°C for 5 × 10⁴ cycles. Mechanical cycling was performed in a three‐point bending test, with a maximum load of 40 N, for 1.2 × 10⁶ cycles. In addition, LU and EMP molar crowns were fabricated and subjected to fatigue treatments followed by load‐to‐failure testing. The flexural strength of LU was not severely reduced by the fatigue treatments. The fatigue treatments did not significantly affect the fracture resistance of LU molar crowns. The results demonstrate the potential of clinical application of CAD/CAM‐generated resin‐based composite molar crowns in terms of fatigue resistance.     

A preliminary evaluation of the structural integrity and fracture mode of minimally prepared resin bonded CAD/CAM crowns

Purpose

This study was a preliminary evaluation of two minimal preparation designs proposed for ceramic and composite resin bonded CAD/CAM crowns. It compared the structural integrity and fracture mode of teeth restored with traditionally and minimally prepared resin bonded CAD/CAM crowns fabricated from the same material hypothesizing that teeth restored with minimal resin bonded crowns would demonstrate the same fracture strength to teeth restored with traditional resin bonded crowns.

Materials and methods

Forty intact maxillary molar teeth were used and divided in four groups. Two groups were prepared according to a traditional crown preparation design and two groups were prepared according to minimal preparation designs. A resin composite (Paradigm MZ100, 3M ESPE) and a leucite glass–ceramic (ProCAD, Ivoclar Vivadent) were used for the fabrication of the crowns using CEREC Scan. Crowns of ceramic were cemented using Variolink II (Ivoclar Vivadent) and crowns of composite with Rely X Unicem Aplicap™ (3M ESPE) and loaded until fracture. Load data was analysed using ANOVA comparing crowns of the same restorative material. The mode of fracture was also recorded and analysed (Kruskal–Wallis).

Results

For the composite system the mean fracture load and SD was 1682 N (±315) for the traditional and 1751 N (±338) for the minimal crowns. For the ceramic system the mean fracture load and SD was 1512 N (±373) for the traditional and 1837 (±356) for the minimal crowns. No statistically significant difference was found between the two designs for each system. Nonparametric analysis (Kruskal–Wallis) of the fracture mode showed no statistical significant difference between designs for either material (p > .05).

Conclusion

Within the limitations of this experimental design, it was found that minimally prepared resin bonded CEREC crowns demonstrated equal fracture resistance and mode of fracture to that of crowns bonded to traditionally prepared teeth.     

计算机辅助设计和制作全解剖形态氧化锆冠修复后牙牙体缺损的临床效果

目的探讨计算机辅助设计和制作系统制作全解剖形态氧化锆冠（全锆冠）修复后牙牙体缺损的即刻修复质量和短期疗效。方法选取36例后牙牙体缺损患者,使用计算机辅助设计和制作系统,制作40颗全锆冠,修复后即刻及1年采用改良的美国牙科协会评价标准对修复体进行评价,对患者进行满意度调查。结果 40例修复体1次戴牙成功率达100%,戴牙后1年患者满意率为100%。结论全解剖形态氧化锆冠短期疗效确切,可以作为后牙牙体缺损的有效修复方案。     

Effect of tooth brushing simulation on the surface properties of various resin-matrix computer-aided design/computer-aided manufacturing ceramics

Purpose

The purpose was to investigate the alterations in surface properties of different resin-matrix CAD/CAM ceramics following tooth brushing simulation (TBS) and compare them with a direct resin composite and a glass ceramic CAD/CAM material.

Materials and methods

Four resin-based CAD/CAM restoratives (Brilliant Crios—BR, Lava™ Ultimate—LV, Grandio Blocs—GR and Shofu Block HC—SH), a leucite-reinforced glass ceramic (IPS Empress® CAD—EC) and a resin composite (Filtek™ Z250—FZ) for direct restorations were tested. In particular, surface loss, hardness, roughness and morphology were investigated utilizing confocal microscopy, scanning electron microscopy and nanoindentation tester. TBS was conducted for 4 × 15 min on the surface of the samples and then the changes in their surface properties were evaluated.

Results

After TBS, all the experimental groups exhibited surface loss to different extent. FZ and BR presented the highest surface loss, while EC and GR the lowest (p < 0.05). Regarding surface roughness, all the tested materials exhibited increase after TBS (p < 0.05), except LV (p = 0.099). EC presented the lowest Sa values, while FZ and BR the highest (p < 0.05). Changes in surface morphology were in compliance with the results of surface roughness and also surface hardness was correlated with surface loss.

Conclusions

The tested resin-matrix CAD/CAM ceramic restorative materials showed a competent behavior against abrasive forces applied during TBS. Surface loss and roughness changes were material dependent and superior compared to a resin composite for direct restorations, while in comparison with a leucite-reinforced glass ceramic exhibited inferior properties.

Clinical significance

Tooth brushing affected differently the surface of the tested restorative materials. However, the abrasive wear that was induced was negligible. Clinical studies are necessary to ascertain if there is clinical significance of these surface alterations that may demand repair of such restorations.     

Stain susceptibility of composite and ceramic CAD/CAM blocks versus direct resin composites with different resinous matrices

To evaluate the stain susceptibility of CAD/CAM blocks and direct composite after long term exposure to various staining agents. 40 disk-shaped samples were fabricated from each of nine materials; six CAD/CAM (Vitablocs Mark II, Paradigm MZ100, Experimental Vita Hybrid Ceramic, Vita Enamic, Experimental Kerr and Lava Ultimate) and three direct composites (Filtek Supreme, Venus Diamond and Filtek Silorane). Samples were randomly divided into five groups (n = 8) according to different staining solutions (distilled water, tea, red wine, coffee and artificial saliva). Initial L*a*b* values were assessed using a calibrated digital spectrophotometer. Specimens were immersed in staining solutions and stored in an incubator at 37 °C for 120 days. L*a*b* values were assessed again and color change (?E) was calculated as difference between recorded L*a*b* values. ANOVA, and Duncan test were used to identify differences between groups (α = 0.05). Significant differences in ?E values were detected between materials (p = 0.000). Among all staining solutions, the highest ?E value was observed with red wine. The new CAD/CAM blocks (Vita Enamic, Vita Hybrid Ceramic and Lava Ultimate) showed the highest resistance to staining compared to the MZ100 composite resin blocks. Filtek Silorane, a direct composite, showed high stain resistance values compared to CAD/CAM materials and other direct composites. Ceramic and composite CAD/CAM blocks had lower staining susceptibility than methacrylate based direct composite. Staining susceptibility of the new resin based CAD/CAM materials Vita Enamic and Lava Ultimate was comparable to feldspathic ceramic blocks (Vitablocs Mark II). Filtek Silorane showed promising results that were comparable to some CAD/CAM blocks.     

Microstructure,topography, surface roughness,fractal dimension,internal and marginal adaptation of pressed and milled lithium-disilicate monolithic restorations

PurposeTo characterize the effect of two processing techniques (pressing and CAD/CAM — Computer Aided Design/Computer Aided Machining) of lithium-disilicate (LD) based crowns on the microstructure, topography, roughness, fractal dimension, internal and marginal adaptation.MethodsOne-hundred identical preparations for monolithic crowns were made with dentin analogue material (G10 epoxy resin). One of the preparations was scanned and a monolithic crown in lithium-disilicate was planned in the CAD system. Fifty crowns were milled in a wax pattern and subjected to pressing (IPS e.max Press), while 50 crowns were machined at CAD/CAM (IPS e.max CAD) and posteriorly crystallized. Internal and marginal adaptation were assessed via replica technique at four manufacturing moments (Milled wax pattern; LD^PRESS; Milled LD^CAD; Crystallized LD^CAD) and considering 5 regions (margin, cervico-axial angle, axial wall, axial-occlusal angle and occlusal wall). Complementary analysis considering microstructure and topography, roughness and fractal dimension were performed in Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM).ResultsThe processing technique resulted in different ceramic microstructure, topography, roughness and fractal dimension, whereas CAD/CAM lead to smoother, more homogeneous but more complex topography features (higher fractal dimension) in comparison to the pressing technique (P < 0.05). Regarding marginal and internal fit, LD^PRESS crowns showed to be more adapted at the margin, while LD^CAD were more adapted at the occluso-axial angle; other regions were not statistically different (α = 0.05).ConclusionsCAD/CAM and the pressing techniques for manufacturing LD crowns lead to completely different ceramic surface characteristics and affect crown adaptation at the margin and at occluso-axial angle.