Biomechanical behavior of endocrown restorations with different CAD-CAM materials: A 3D finite element and in vitro analysis

Statement of problemThe performance of endocrowns fabricated with different types of computer-aided design and computer-aided manufacturing (CAD-CAM) materials is unclear.PurposeThe purpose of this finite element analysis (FEA) and in vitro study was to compare and evaluate the stress distribution, failure probability, and fracture resistance of endodontically treated teeth restored with endocrowns from CAD-CAM milling blocks including ceramic, polymer-infiltrated ceramic (PICN), and composite resin.Material and methodsAn endodontically treated first mandibular molar restored with an endocrown was modeled by using a CAD software program and imported into an FEA software program. The model was duplicated and received restorations made from CAD-CAM blocks: Vita Suprinity (VS), IPS e.max CAD (EMX), Vita Enamic (VE), Lava Ultimate (LU), and Grandio blocs (GR). Stress distributions under axial and oblique loading were analyzed. The Weibull function was combined with the FEA results to predict long-term failure probability. The mechanical failure behavior of endocrowns manufactured with these materials was tested by using a universal testing machine. Load-to-failure was recorded, and fractured specimens were subjected to fractography. The data were analyzed by 1-way ANOVA and the post hoc Tukey test (α=.05).ResultsThe models of GR and LU exhibited a more even stress distribution. The Weibull analysis revealed that 5 models performed in a similar manner under normal occlusal forces, while LU and VE models achieved the highest probabilities during clenching. The fracture loads of GR (3808 ±607 N) were significantly higher than those of other materials (P<.05). More favorable failure modes were observed in the GR and VE groups. Fractography showed a greater probability of compression curls and arrest lines in the endocrowns of VE, LU, and GR groups.ConclusionsWhen restoring endodontically treated teeth, endocrown fabricated with composite resin exhibited a more uniform stress distribution and higher fracture resistance. More evidence from long-term clinical studies is needed to verify this effect.     

影响髓腔固位冠边缘密合性及机械强度的材料与牙体预备因素

髓腔固位冠是一种全冠和超嵌体的改良型,兼具粘接固位和髓腔机械固位。边缘密合性和机械强度是口腔修复体最常见的评价标准,笔者就近年来髓腔固位冠边缘密合性和机械强度的国内外研究进行综述。研究结果表明:各类临床常用的修复材料如玻璃陶瓷、氧化锆陶瓷及树脂基陶瓷制作的髓腔固位冠基本都具有临床可接受的边缘密合性;氧化锆是临床常用的陶瓷材料,但有不可再修复的根折风险;与氧化锆陶瓷材料相比,树脂基陶瓷、玻璃陶瓷如二硅酸锂陶瓷制作的髓腔固位冠较少出现不可再修复的缺陷,但其强度不及氧化锆。同时,牙体预备方式如髓腔固位冠类型、髓腔固位深度、髓腔洞形轴壁外展度以及(牙合)面厚度均对髓腔固位冠的机械强度存在影响。釉锆作为一种新型氧化锆材料,与传统氧化锆有相似的弹性模量(210 GPa),但美观性更佳,且与髓腔固位冠一样适合于咬合空间不足的短冠患者。如何进行改良以降低氧化锆制作髓腔固位冠修复失败后的根折风险需要进一步的研究。     

2种不同粘接水门汀对树脂类冠修复材料和全瓷托槽剪切粘接力的影响

目的 评价两种不同粘接水门汀对树脂类冠修复材料和全瓷托槽剪切粘接力的影响。方法 选用2种水门汀Transbond XT和RelyX Ultimate,将上颌前磨牙全瓷托槽Inspire Ice与4种树脂类冠修复材料粘接。试件冷热循环5 000次后测量断裂载荷（N）,并观察破坏形态。结果 单因素方差分析结果F=4.52（P＜0.001）,显示粘接条件对陶瓷托槽和树脂类冠修复材料的剪切粘接力影响具有统计学意义。其中Lava Ultimate+Transbond XT组和Lava Ultimate+ RelyX Ultimate+托槽喷砂组分别为（325.10±135.54）N和（304.71±35.71）N,较其他组高,Lava Ultimate+ Transbond XT+托槽喷砂组最低,为（118.12±57.58）N。结论 树脂基陶瓷材料Lava Ultimate和全瓷托槽的剪切粘接力较暂时冠修复材料高。全瓷托槽未喷砂时,正畸全瓷托槽粘接水门汀Transbond XT和修复用水门汀RelyX Ultimate的粘接力未见明显区别,喷砂后全瓷托槽失去固位小球,RelyX Ultimate有更高的粘接力。     

Fatigue fracture resistance of titanium and chairside CAD-CAM zirconia implant abutments supporting zirconia crowns: An in vitro comparative and finite element analysis study

Statement of problemZirconia abutments with a titanium base are promising candidates to substitute for titanium abutments based on clinical studies reporting good short-term survival rates. However, information on the long-term performance of zirconia abutments supporting ceramic crowns is scarce.PurposeThis in vitro comparative and finite element analysis study compared the fatigue life performance of ceramic computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic restorations and zirconia abutments fabricated with a chairside workflow connected to a titanium interface versus titanium abutments.Material and methodsTwenty-two internal connection implants were divided into 2 groups, one with a zirconia abutment and monolithic ceramic zirconia crown (ZZ) and the other with a titanium abutment and zirconia crown (TiZ). They were subjected to a fatigue test to determine the fatigue limit and fatigue performance of each group as per International Organization for Standardization (ISO) 14801. Microstructural analysis of the fracture surfaces was conducted by using a scanning electron microscope (SEM). Simulations of the in vitro study were also conducted by means of finite element analysis (FEA) to assess the stress distribution over the different parts of the restoration.ResultsThe fatigue limit was 250 N for the TiZ group and 325 N for the ZZ group. In both groups, the screw was the part most susceptible to fatigue and was where the failure initiated. In the zirconia abutment models, the stress on the screw was reduced.ConclusionsChairside CAD-CAM zirconia abutments with a titanium base supporting zirconia crowns had higher fatigue fracture resistance compared with that of titanium abutments.     

Adhesive restoration of anterior endodontically treated teeth: influence of post length on fracture strength

Objectives

This study aims to evaluate the fracture resistance of endodontically treated anterior teeth restored with crowns made of composite or ceramic and retained without the use of a post (endocrowns) or with posts of 5 mm (short) and 10 mm in length (long).

Material and methods

Forty-eight intact maxillary incisors were selected for the study. After endodontic treatment, the crowns were sectioned 2 mm coronally to the cementoenamel junction provided with a ferrule of 2 mm. The roots were randomly divided into six groups (n?=?8) according to the post length and type of coronary restoration. The crowns were fabricated with the chairside economical restoration of esthetic ceramics system. Group 1 was restored with a 10-mm glass fiber post, composite core, and a full-coverage ceramic crown (LPCer); group 2, with a 5-mm glass fiber post, composite core, and a full-coverage ceramic crown (SPCer); group 3, with a 10-mm glass fiber post, composite core, and a full-coverage composite crown (LPCpr); group 4, with a 5-mm glass fiber post, composite core, and a full-coverage composite crown (SPCpr); and groups 5 (EndoCer) and 6 (EndoCpr) were restored with ceramic and composite endocrowns, respectively. The teeth were then thermomechanically loaded in a chewing machine. After fatigue, the specimens were loaded to fracture. Data were analyzed with ANOVA and chi-square test. Mode of failure was defined as repairable or non-repairable.

Results

Presence of post, post length, and crown material had no significant effect on the fracture resistance. Groups restored with endocrowns presented a higher number of repairable fractures in respect to the other groups.

Conclusions

Presence of a post had no effect on the restorations’ fracture strength.

Clinical relevance

Although this in vitro study has some limitations in respect to its clinical relevance, the restoration of largely destroyed anterior teeth with the use of an endocrown or a short glass fiber post might have advantages over a large glass fiber post.     

Mechanical behavior of endocrowns fabricated with different CAD-CAM ceramic systems

Statement of problemThe mechanical behavior of ceramic endocrowns is unclear.PurposeThe purpose of this in vitro and 3-dimensional finite element analysis (3D-FEA) study was to evaluate the mechanical behavior of endodontically treated teeth restored with ceramic endocrowns made by using different computer-aided design and computer-aided manufacturing (CAD-CAM) systems.Material and methodsSixty mandibular human molars were endodontically treated, prepared for endocrowns, and divided into 4 groups (n=15) according to the following various ceramic systems: leucite-based glass-ceramic (LC group), lithium disilicate-based glass-ceramic (LD group), glass-ceramic based on zirconia-reinforced lithium silicate (LSZ group), and monolithic zirconia (ZR group). After adhesive bonding, the specimens were subjected to thermomechanical loading and then to fracture resistance testing in a universal testing machine. The failure mode of the specimens was qualitatively evaluated. Three-dimensional FEA was performed to evaluate the stress distribution in each group. Data were analyzed by using a 1-way ANOVA and the Tukey HSD test (α=.05).ResultsStatistically significant differences among the groups were observed (P<.05). The outcomes of the LC, LD, and LSZ groups were similar (1178 N, 1935 N, and 1859 N) but different from those of the ZR group (6333 N). The LC and LD groups had a higher ratio of restorable failures, while LSZ and ZR had more nonrestorable failures. Fractographic analysis indicated a regular failure pattern in the ZR group and irregular failure patterns in the other groups. Three-dimensional FEA revealed similar values and stress pattern distributions among the groups.ConclusionsThe mechanical performance of monolithic zirconia was better than that of the other ceramic endocrowns considered in this research; however, monolithic zirconia presented a higher rate of catastrophic tooth structure failure.     

Failure loads of heat-pressed versus milled lithium disilicate endocrowns

Objectives

This study aimed to compare the failure load of heat-pressed versus milled lithium disilicate endocrowns.

Materials and methods

Twenty extracted mandibular molars were sectioned 1.5 mm above the CEJ. Root canal treatment and endocrown preparation were done for all teeth. Samples were then divided into two groups: heat-pressed glass ceramic endocrowns (HP group) (n?=?10) and milled endocrowns (CAD group) (n?=?10). Cementation was done using self-adhesive resin cement, and a compressive load was applied on the occlusal surface of the specimens until failure occurred.

Results

The mean failure loads were significantly higher in the HP group (2546.5?±?339 N) compared to the CAD group (1759.9?±?114.2) (p?<?0.05), and majority of failures were due to fracture of the restoration.

Conclusions

Failure loads of heat-pressed lithium disilicate endocrown are superior to milled endocrown.

Clinical relevance

Molars restored with lithium disilicate endocrowns have higher failure loads than the maximum human bite force regardless of the fabrication method. Although heat-pressed endocrowns have superior failure loads to milled ones, both are indicated for restoring endodontically treated molar teeth.

     

Fracture strength of monolithic all-ceramic crowns made of high translucent yttrium oxide-stabilized zirconium dioxide compared to porcelain-veneered crowns and lithium disilicate crowns

Objective. The aim of the study was to provide data on the fracture strength of monolithic high translucent Y-TZP crowns and porcelain-veneered high translucent Y-TZP crown cores and to compare that data with the fracture strength of porcelain-veneered Y-TZP crown cores and monolithic lithium disilicate glass-ceramic crowns. Materials and methods. Sixty standardized crowns divided into six groups (n = 10) were fabricated: monolithic high translucent Y-TZP crowns, brand A, monolithic high translucent Y-TZP crowns, brand B, veneered high translucent Y-TZP crown cores, brand A, veneered high translucent Y-TZP crown cores, brand B, heat-pressed monolithic lithium disilicate crowns and veneered Y-TZP crown cores. All crowns were thermocycled, cemented onto dies, cyclically pre-loaded and finally loaded to fracture. Results. The monolithic Y-TZP groups showed significantly higher fracture strength (2795 N and 3038 N) compared to all other groups. The fracture strength in the veneered Y-TZP group (2229 N) was significantly higher than the monolithic lithium disilicate group (1856 N) and the veneered high translucent Y-TZP groups (1480 N and 1808 N). Conclusions. The fracture strength of monolithic high translucent Y-TZP crowns is considerably higher than that of porcelain-veneered Y-TZP crown cores, porcelain-veneered high translucent Y-TZP crown cores and monolithic lithium disilicate crowns. The fracture strength of a crown made of monolithic high translucent Y-TZP is, with a large safety margin, sufficient for clinical use for the majority of patients. Porcelain-veneered Y-TZP crown cores show higher fracture resistance than monolithic lithium disilicate crowns.     

The Effect of Crown Lengthening on the Outcome of Endodontically Treated Posterior Teeth: 10-year Survival Analysis

IntroductionThe purpose of this study was to investigate the effect of a crown lengthening (CL) procedure and the crown-root ratio after CL on the long-term survival of endodontically treated teeth (ETT).MethodsPermanent posterior teeth with opposing dentition that had received adequate nonsurgical root canal treatment (NSRCT) and a full-coverage crown between January 1, 2006, and January 1, 2016 were included in this retrospective study. The data collected included dates of the NSRCT, time of extraction if extracted, age, sex, location, the crown-root ratio after CL, and the presence of a lesion. All included ETT were divided into 2 groups:

• 1.the CL group, CL was indicated and performed after NSRCT before crown placement and
• 2.the control group: ETT with adequate ferrule after NSRCT. Data were analyzed using the Kaplan-Cox regression model (α = 0.05).

Results5-year survival rates of ETT in the control and CL groups were 88.6% and 82.2%, respectively (P > .05). The 10-year survival rates of ETT in the control and CL groups were 74.5% and 51%, respectively (P < .05). ETT that received the CL procedure after NSRCT were almost 2.3 times more likely to get extracted compared with ETT that did not need the CL procedure at the 10-year follow-up (hazard ratio = 2.29, P < .05). Also, ETT with an inadequate crown-root ratio (1:1) after CL showed the lowest survival rate (40%) compared with ETT with an adequate crown-root ratio (<1:1).ConclusionsA crown-root ratio of 1:1 after osseous CL may affect the long-term survival of ETT. Despite the promising survival rate of ETT with an adequate crown-root ratio after CL, the long-term survival of NSRCT with an inadequate crown-root ratio (1:1) should be considered in the treatment planning phase. Also, it is worth mentioning that the results of the present study should be evaluated in future prospective studies.     

Fracture strength of CAD/CAM composite and composite-ceramic occlusal veneers

PurposeTo determine the effect of material type and restoration thickness on the fracture strength of posterior occlusal veneers made from computer-milled composite (Paradigm MZ100) and composite-ceramic (Lava Ultimate) materials.Methods60 maxillary molars were prepared and restored with CAD/CAM occlusal veneer restorations fabricated from either Paradigm MZ100 or Lava Ultimate blocks at minimal occlusal thicknesses of 0.3, 0.6, and 1.0 mm. Restorations were adhesively bonded and subjected to vertical compressive loading. The maximum force at fracture and mode of failure were recorded. 2-Way ANOVA was used to identify any statistically significant relationships between fracture strength and material type or thickness. Spearman's rank correlation coefficient was used to analyze mode of failure with regard to fracture strength.ResultsThe average maximum loads (N) at fracture for the Paradigm MZ100 groups were 1620 ± 433, 1830 ± 501, and 2027 ± 704 for the material thicknesses of 0.3, 0.6, and 1.0 mm, respectively. The Lava Ultimate groups fractured at slightly higher loads (N) of 2078 ± 605, 2141 ± 473, and 2115 ± 462 at the respective 0.3, 0.6, and 1.0 mm thickness.Statistical analyses revealed that, while no significant difference existed among the various restoration thicknesses in terms of fracture strength (P > 0.05), the material type was found to be influential (P = 0.04). The maximum load at fracture (N) for Lava Ultimate averaged over all thicknesses (2111 ± 500) was significantly higher than that of the Paradigm MZ100 (1826 ± 564). No correlation between mode of failure and fracture strength was found.ConclusionsUnder the conditions of this study, the maximal loads at fracture for these “non-ceramic” occlusal veneer restorations were found to be higher than human masticatory forces. Occlusal veneers made from the two materials tested are likely to survive occlusal forces regardless of restoration thickness, with those fabricated from the composite-ceramic hybrid material being more likely to survive heavier loads.     

Fracture behaviour of zirconia ceramic cantilever fixed dental prostheses in vitro

Objective. Evaluation of the fracture resistance of all-ceramic cantilever fixed dental prostheses (FDPs) manufactured from zirconia frameworks and veneered with a press ceramic. Material and Methods. Two mandibular premolars were prepared either with a box inlay cavity or with a full crown chamfer preparation and then duplicated. 40-three-unit cantilever FDPs replacing one premolar, with a group size of eight for each design, were manufactured. In group i-i the cantilever FDPs were retained by two inlays, in group i-c by an inlay–crown combination, and in group c-c by two crowns. The frameworks in groups i-c-R and c-c-R were reinforced by an additional shoulder on the oral side of the zirconia frameworks. All FDPs were subjected to thermal cycling (TC) and 600,000 cycles of mechanical loading (ML) with 50 N. The load to fracture was measured and fracture sites were evaluated. Results. The mean fracture values ranged from 172 N to 792 N. Fracture-strength values were significantly lower for the i-i retained FDPs than for the i-c and c-c combinations. There was no significant effect of the reinforcing shoulder in groups i-c-R and c-c-R. For FDPs with a crown on the terminal tooth, fractures were usually within the distal wall of the distal crown. Conclusions. Inlay–inlay retained cantilever FDPs cannot withstand the mastication forces expected. Fracture load values for inlay–crown and crown–crown-retained FDPs encourage further clinical investigation. The mode of fracture indicates that reinforcement of the distal crown wall might enhance fracture resistance.     

Survival and success of endocrowns: A systematic review and meta-analysis

Statement of problemEndocrowns are a monoblock type of restoration that use the pulp chamber and remaining coronal tooth structure as a means of retention. However, data on their long-term survival and success rates as compared with conventional crowns are lacking.PurposeThe purpose of this systematic review and meta-analysis was to collate published work on endocrowns to assist clinicians in making decisions on when and whether they are an appropriate restorative option with a predictable outcome for extensively damaged endodontically treated teeth.Material and methodsDatabases such as PubMed (MEDLINE), Scopus, EMBASE, Cochrane library, and Google Scholar were searched up to June 2019 for clinical and in vitro studies on endocrown survival and success rates. For the meta-analysis, endocrown and conventional crown survival and success rates were compared, and the pooled effects were presented as relative risks and 95% confidence intervals using a random effects model.ResultsTen studies fulfilled the inclusion criteria (3 clinical and 7 in vitro) and were included in the systematic review. The meta-analysis of the clinical studies showed an estimated overall 5-year survival rate of 91.4% for endocrowns and 98.3% for conventional crowns. The estimated overall 5-year success rates were 77.7% for endocrowns and 94% for conventional crowns. There were no significant differences in overall survival or success estimates between the assessed restorations (P>.05).ConclusionsAdditional well-designed clinical studies with long-term assessment are needed; however, endocrowns appear to be a promising conservative restorative option with acceptable long-term survival for endodontically treated posterior teeth in selected patients.     

Acoustic properties of fracture of dental restorative materials and endocrown restorations under quasi-static loading

Objectives(1) To investigate the properties of acoustic emission (AE) signals from fracture of dental materials and endocrown restorations during quasi-static compression using the continuous wavelet transform analysis. (2) To determine by the parameters of AE signals in which structural element of tooth-endocrown system the fracture starts.MethodsFive restorative materials (zirconium dioxide (Prettau zirconia), ceramics (IPS e.max Press), metal ceramics (GC Initial MC+Nicrallium N2 BCS), composite resin (Nano Q), luting cement (Relyx™ U200)) were manufactured into discs, 13 mm diameter, 5 mm thick, which were divided into 5 groups (Group B, C, D, E, F, respectively) and included into Type 1. Twenty-five extracted human molars were divided into 5 groups and included into Type 2: Group A (control, no restoration); BE (tooth restored by zirconium dioxide endocrowns); CE (restored by ceramic endocrowns); DE (restored by metal ceramic endocrowns); EE (restored by composite resin endocrowns). An increasing load was applied to the center of the samples with a hard steel ball until a fracture occurred. The loading rate was 0.12 mm/min. Two-channel AE detection system was used to record the AE activity during testing. The parameters including the peak frequency, bandwidth, duration time and energy of AE signals were analyzed.ResultsThe restorative materials (Type 1) differ from each other by acoustic properties such as the peak frequency main bands and energy of AE signals. The detected AE signals correspond to the different fracture types. The dominant fracture mechanism of Group C, E and F specimens was the macrocracking (brittle fracture), and of Group D specimens was the microcracking, which alternated with the plastic deformation and macrocracking. For the number of events corresponding to the brittle fracture, statistically significant differences (p < 0.05) were found between all group pairs. AE signals were not released during compression test of the zirconium dioxide samples, thus the fracture was not detected.All the AE signals detected during compression test of the different endocrown systems (Type 2) had two peak frequency bands. The fracture of Groups A, BE, CE and DE samples characterized by alternating the micro- and macrocracking with plastic deformation, and the brittle fracture was the dominant fracture mechanism. The restorations of Group EE fractured without plastic deformation. For the number of events corresponding to the brittle fracture, statistically insignificant differences (p > 0.05) were found between Groups A vs CE and A vs EE, and statistically significant differences (p < 0.05) were found between Groups A vs BE and A vs DE.SignificanceThe initiation of fracture in the restorations with endocrowns made from different materials begins with the tooth damage. The metal ceramic endocrown restoration showed the highest fracture resistance, what is especially important for clinical use.     

Use of an occlusal splint and intraoperative imaging with an intraoral approach in the management of mandibular subcondylar fractures

IntroductionTo evaluate the feasibility of safely managing subcondylar fractures using an original surgical procedure combining an intraoral approach, the use of a custom-made occlusal overlay splint, and intraoperative imaging.Materials and methodsCondylar fragment was freed from surrounding soft tissues, was laterally exposed to the ramus, and a miniplate was fixed in place for osteosynthesis. An overlay splint maintaining the dental occlusion was used to facilitate reduction and stabilization during fixation. Intraoperative monitoring by cone-beam computed tomography (CBCT) was performed before completing the fixation.ResultsBetween November 2018 and June 2019, 10 patients were treated using this procedure. The median length of the proximal condylar fragment was 29 mm (range 24–39 min). Five patients had an associated mandibular fracture. The median duration of the condylar fracture surgery was 54.5 min (range 38–79 min). All patients had satisfactory reduction and osteosynthesis with no complications.ConclusionIt is feasible to safely manage subcondylar fractures with this surgical procedure that could facilitate open reduction using intraoral approaches. Occlusal splints maintain downward pressure on the rami bilaterally and symmetrically, helping to anatomically reposition condylar process fractures. Intraoperative imaging is used to monitor this step.     

Additive manufacturing of lithium disilicate glass-ceramic by vat polymerization for dental appliances

ObjectivesThe objectives of this study were to evaluate the mechanical properties of lithium disilicate components produced by additive manufacturing (AM) and to assess the effect of build orientation on the resistance to fracture.MethodsOversized bars were printed with a glass-filled photoactive resin using a digital light processing technique. After sintering and post-processing, flexure and chevron notch fracture toughness bars were obtained in three principal orientations (0°, 45°, and 90°) with respect to the build direction. Mechanical properties were obtained according to the relevant ASTM standards. The hardness, indentation fracture resistance, and elastic modulus were measured for each orientation, and a Weibull analysis was conducted with the flexure responses. Fractography of the fracture surfaces was performed to identify the failure origins.ResultsThe 0° orientation exhibited characteristic strength, Weibull modulus, and elastic modulus of 313 MPa, 4.42, and 168 ± 3 GPa, respectively, which are comparable to lithium disilicate materials from traditional processes. However, build orientation contributed significantly to the flexure strength, elastic modulus, and Weibull modulus; the characteristic strengths for the 45° and 90° build orientations were 86 MPa and 177 MPa, respectively. The primary contribution to the orientation dependence was the number of residual build layer-related flaws from incomplete union between printed layers. Of note, hardness and the fracture toughness were not dependent on build orientation.SignificanceAM of lithium disilicate materials can achieve the mechanical properties of materials produced by traditionally processing. Thus, while further process development is warranted, the outlook for dentistry is promising.     

Comparison of fracture-load values of cantilevered FDPs

Abstract

Objective. Evaluation of the effect of different framework designs and of fatigue on the fracture-load values of cantilevered fixed dental prostheses (FDPs). The load values were compared with those for lithium disilicate ceramic and metal–ceramic FDPs. Materials and methods. Fifty cantilevered FDPs were manufactured using a zirconia framework veneered with a feldspathic ceramic. Ten FDPs were made from a lithium disilicate ceramic and 10 were designed as metal–ceramic FDPs. All FDPs were anchored by two premolar crowns to replace a missing premolar. Twenty of the 50 zirconia FDPs were regarded as the control groups; these were divided into two groups—with and without fatigue. The other 30 zirconia FDPs were divided into three test groups with different framework designs. The load to fracture was measured and fracture sites were identified. The Kruskal–Wallis test and the Mann–Whitney U-test were used for statistical analysis. Results. Most of the all-ceramic FDPs fractured within the distal wall of the terminal crown abutment. The mean fracture-load ranged between 346–493 N for the FDPs with the 0.7 mm framework. Mean values for the three zirconia test groups ranged from 529–590 N. Reinforcement of the framework resulted in significantly higher fracture-loads than for the control group. Values for lithium disilicate restorations were significantly lower than those for the test groups and the values for the metal–ceramic group were significantly higher than those for the test groups. Conclusion. Although reinforcement of the distal crown core might enhance the fracture resistance of all-ceramic cantilever FPDs, they cannot yet be unreservedly recommended for clinical use.     

Improving fatigue damage resistance of alumina through surface grading

Porcelain-veneered alumina crown restorations often fail from bulk fracture resulting from radial cracks that initiate at the cementation surface with repeated flexure of the stiffer crown layers on the soft dentin support. We hypothesized that bulk fracture may be substantially mitigated by grading the elastic modulus at the crown surfaces. In this study, we fabricated graded structures by infiltrating glass into dense alumina plates, resulting in a diminished modulus at the surface layers. The plates were then bonded to polycarbonate substrates and subjected to fatigue loading in water. Tests were terminated when fracture occurred at the cementation tensile surface or at the fatigue endurance limit (1 million cycles). Infiltrated specimens showed a significant increase in fatigue fracture loads over non-infiltrated controls. Our results indicate that controlled elastic gradients at the surface could be highly beneficial in the design of fracture-resistant alumina crowns.     

Fatigue resistance of simplified CAD–CAM restorations: Foundation material and ceramic thickness effects on the fatigue behavior of partially- and fully-stabilized zirconia

ObjectiveTo evaluate the fatigue failure load, number of cycles until failure and survival probability of partially (PSZ) and fully-stabilized (FSZ) polycrystalline zirconia disc shaped specimens with different thicknesses adhesively cemented onto foundations with distinct elastic moduli.MethodsDisc-shaped specimens (n = 15, Ø = 10 mm; thickness = 1.0 and 0.7 mm) of CAD/CAM PSZ and FSZ blocks were adhesively cemented onto discs with different foundations (Ø = 10 mm; thickness = 2.0 mm) made from epoxy resin, composite resin or Ni–Cr metallic alloy. The cemented assemblies were subjected to fatigue testing using a step-stress approach (600?2800 N; step-size of 100 N; 10,000 cycles per step; 20 Hz) and the data was submitted to specific statistical tests (α = 0.05). Fractography and finite element (FEA) analyzes were also performed.ResultsPSZ and FSZ presented higher fatigue failure load, number of cycles until failure and survival probabilities when cemented onto metallic alloy. All PSZ specimens survived the fatigue test when cemented onto Ni–Cr alloy (100% probability of survival at 2800 N; 230,000 cycles). Regardless of the foundation type, PSZ had better fatigue behavior than FSZ. For thickness, thinner PSZ restorations underperformed when bonded to softer foundations, while FSZ groups and groups bonded to metallic foundations had no statistical difference.SignificanceThe foundation material strongly influences the fatigue performance of PSZ and FSZ restorations, which presented mechanical behavior improvements when bonded to a metallic foundation. PSZ restorations showed better fatigue behavior than FSZ, while the ceramic thickness only influenced PSZ restorations bonded to softer foundations.     

The influence of indirect bonded restorations on clinical prognosis of endodontically treated teeth: A systematic review and meta-analysis

ObjectiveThe loss of the dental coronal portion following carious lesions or fractures leads to endodontic treatment with subsequent restoration to ensure correct anatomy and function. Recently, partial adhesive restorations have been widely proposed to increase the survival rate of endodontically treated teeth. The primary purpose of this review is to assess the failure rate of indirect partial adhesive restorations on endodontically treated teeth (ETT), considering the follow-up period.MethodsThe indications reported in the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) were used to draft the present review. The study was constructed on PICO questions: population (patients who need indirect adhesive restorative treatment on endodontically treated teeth with onlay and overlay), intervention (onlay and overlay), control (patients with onlay and overlay on endodontically treated teeth) and outcome (failure rate and types of failure for onlay and overlay). The asked scientific question was: what are the failure rate and types of failure for adhesive indirect partial restorations on ETT?ResultsThe overall failure rate that emerges is 0.087 with a ratio of 121/1254, I² 80 % p-value< 0.001. Moreover, by meta-regression with covariates the follow-up period reports a coefficient of 0.013 with a P-value< 0.001. In conclusion, the indirect partial restorations on endodontically treated teeth displayed overall acceptable outcomes in terms of success from 2 to 4 years after their placement with only 4.32 % of failure. Failures increase after 7 years up to 12–30 years with failure rates of approximatively 10.65 % and 20.94 %. The analysis of the included articles reporting the causes of restorations failures showed that 15.51 % of cases were related to the loss of dental element.SignificanceBesides the survival rates of indirect adhesive restorations on endodontically treated posterior teeth, it was highlighted that the majority of failures appeared restorable. Thus, partial restorations seemed able to prevent the ETT tooth loss.     

Translational research on clinically failed zirconia implants

Objectives

To provide fractographic analysis of clinically fractured zirconia implants recovered with their cemented crown. To calculate bending moments, corresponding stress and crack onset location on the implant’s fracture surface using a mathematical model integrating spatial coordinates of the crown-implant part and occlusal loading obtained from 2D and 3D images.