Practice‐based clinical evaluation of metal–ceramic and zirconia molar crowns: 3‐year results

This practice‐based study evaluates the clinical performance of conventionally luted metal–ceramic and zirconia molar crowns fabricated with pronounced anatomical core design and a prolonged cooling period of the veneering porcelain. Fifty‐three patients were treated from 07/2008 until 07/2009 with either metal–ceramic crowns (MCC) (high‐noble alloy + low‐fusing porcelain) or zirconia crowns (Cercon System, DeguDent, Germany). Forty‐nine patients (30 women/19 men) with 100 restorations (metal–ceramic: 48/zirconia: 52, mean observational period: 36·5 ± 6 months) participated in a clinical follow‐up examination and were included in the study. Time‐dependent survival (in situ criteria), success (event‐free restorations) and chipping rates (defects of the veneering ceramics) were calculated according to the Kaplan–Meier method and analysed in relation to the crown fabrication technique, using a Cox regression model (P < 0·05). Three complete failures (metal–ceramic: 1, zirconia: 2) were recorded (survival rate after 3 years: metal–ceramic: 97·6%, zirconia: 95·2%). Of the metal–ceramic restorations, 90·9% remained event‐free (two ceramic fractures, one endodontic treatment), whereas the success rate for the zirconia was 86·8% (two ceramic fractures, one endodontic treatment, one secondary caries). No significant differences in survival (P = 0·53), success (P = 0·49) and ceramic fracture rates (P = 0·57) were detected. The combination of a pronounced anatomical core design and a modified firing of the veneering porcelain for the fabrication of zirconia molar crowns resulted in a 3‐year survival, success and chipping rate comparable to MCC.     

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.     

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 practice‐based clinical evaluation of the survival and success of metal‐ceramic and zirconia molar crowns: 5‐year results

This practice‐based study evaluates the survival and success of conventionally luted metal‐ceramic and zirconia molar crowns fabricated by using a prolonged cooling period for the veneering porcelain. Fifty‐three patients were treated from 07/2008 to 07/2009 with either metal‐ceramic crowns (MCC) or zirconia crowns (ZC). Forty‐five patients (26 female) with 91 restorations (obser‐vational period: 64·0 ± 4·8 months) participated in a clinical follow‐up examination and were included in the study. Estimated cumulative survival (ECSv), success (ECSc) and veneering ceramic success (ECVCSc) were calculated (Kaplan–Meier) and analysed by the crown fabrication technique and the position of the restoration (Cox regression model) (P < 0·05). Five complete failures (MCC: 2, ZC: 3) were recorded (5‐year ECSv: MCC: 97·6%, (95% confidence interval (95%‐CI): [93%; 100%]/ZC: 94·0%, (95%‐CI): [87%; 100%]). Of the MCCs (n = 41), 85·0%, [95%‐CI: (77%; 96%)] remained event‐free, whereas the ECSc for the ZCs (n = 50) was 74·3% (95%‐CI): [61%; 87%]. No significant differences in ECSv (P = 0·51), ECSc (P = 0·43) and ECVCSc (P = 0·36) were detected between the two fabrication techniques. Restorations placed on terminal abutments (n = 44) demonstrated a significantly lower ECVCSc (P = 0·035), (5‐year VCF‐rate: 14·8%) than crowns placed on tooth‐neighboured abutments (n = 47), (5‐year VCF‐rate: 4·3%). In the present study, zirconia molar crowns demonstrated a 5‐year ECSv, ECSc and ECVCSc comparable to MCCs. Irrespective of the fabrication technique, crowns on terminal abutments bear a significantly increased risk for VCFs. Clinical investigations with an increased number of restorations are needed.     

Student attitudes towards computer‐aided testing

Introduction: Computer‐aided learning (CAL) is a viable alternative to traditional teaching methods. While CAL is used for teaching only, computer‐aided testing (CAT) can be applied as a computer‐based examination method. The aim of the present study was to evaluate students’ attitude towards CAT as compared to written multiple choice tests. Materials and methods: Forty‐one undergraduate dental students underwent a mock examination consisting of 15 written multiple choice questions and 15 questions delivered using the interactive MobiTed^® system. A questionnaire based on an eight‐item seven‐point Likert scale was used to evaluate the students’ attitude towards CAT. The students’ performance in both tests was analysed using paired t‐tests. Correlations between test performance and questionnaire were expressed by Pearson correlation coefficients. Results: Despite study‐design‐related differences, students’ test performance between written multiple choice and MobiTed^® was comparable. No correlations between test results and questionnaire could be set up. Students rated MobiTed^® to be equivalent to written multiple choice and had no difficulties with the CAT set up. The pre‐defined sequence of questions with each question being shown only once was considered to be a major disadvantage of the CAT system. Complex questions should be displayed longer compared to short questions. Discussion: Computer‐aided testing appeared to be equivalent to written multiple choice tests not only in terms of student performance but also to their perception. This is consistent with previous studies. Conclusions: Interactive multiple choice tests may provide an alternative to written tests, but should allow examinees to have control over the sequence, as well as the length of time the questions are displayed.     

In vitro chipping behaviour of all‐ceramic crowns with a zirconia framework and feldspathic veneering: comparison of CAD/CAM‐produced veneer with manually layered veneer

The purpose of this in vitro study was to assess the breaking load of zirconia‐based crowns veneered with either CAD/CAM‐produced or manually layered feldspathic ceramic. Thirty‐two identical zirconia frameworks (Sirona inCoris ZI, mono L F1), 0·6 mm thick with an anatomically shaped occlusal area, were constructed (Sirona inLab 3.80). Sixteen of the crowns were then veneered by the use of CAD/CAM‐fabricated feldspathic ceramic (CEREC Bloc, Sirona) and 16 by the use of hand‐layered ceramic. The CAD/CAM‐manufactured veneer was attached to the frameworks by the use of Panavia 2.0 (Kuraray). Half of the specimens were loaded until failure without artificial ageing; the other half of the specimens underwent thermal cycling and cyclic loading (1·2 million chewing cycles, force magnitude F_max = 108 N) before the assessment of the ultimate load. To investigate the new technique further, finite element (FE) computations were conducted on the basis of the original geometry. Statistical assessment was made by the use of non‐parametric tests. Initial breaking load was significantly higher in the hand‐layered group than in the CAD/CAM group (mean: 1165·86 N versus 395·45 N). During chewing simulation, however, 87·5% (7/8) of the crowns in the hand‐layered group failed, whereas no crown in the CAD/CAM group failed. The CAD/CAM‐produced veneer was significantly less sensitive to ageing than the hand‐layered veneer.     

Randomized,Controlled Clinical Trial of Bilayer Ceramic and Metal‐Ceramic Crown Performance

Purpose : Analyzing the clinical performance of restorative materials is important, as there is an expectation that these materials and procedures will restore teeth and do no harm. The objective of this research study was to characterize the clinical performance of metal‐ceramic crowns, core ceramic crowns, and core ceramic/veneer ceramic crowns based on 11 clinical criteria. Materials and Methods : An IRB‐approved, randomized, controlled clinical trial was conducted as a single‐blind pilot study. The following three types of full crowns were fabricated: (1) metal‐ceramic crown (MC) made from a Pd‐Au‐Ag‐Sn‐In alloy (Argedent 62) and a glass‐ceramic veneer (IPS d.SIGN veneer); (2) non‐veneered (glazed) lithium disilicate glass‐ceramic crown (LDC) (IPS e.max Press core and e.max Ceram Glaze); and (3) veneered lithia disilicate glass‐ceramic crown (LDC/V) with glass‐ceramic veneer (IPS Empress 2 core and IPS Eris). Single‐unit crowns were randomly assigned. Patients were recalled for each of 3 years and were evaluated by two calibrated clinicians. Thirty‐six crowns were placed in 31 patients. A total of 12 crowns of each of the three crown types were studied. Eleven criteria were evaluated: tissue health, marginal integrity, secondary caries, proximal contact, anatomic contour, occlusion, surface texture, cracks/chips (fractures), color match, tooth sensitivity, and wear (of crowns and opposing enamel). Numerical rankings ranged from 1 to 4, with 4 being excellent, and 1 indicating a need for immediate replacement. Statistical analysis of the numerical rankings was performed using a Fisher's exact test. Results : There was no statistically significant difference between performance of the core ceramic crowns and the two veneered crowns at year 1 and year 2 (p > 0.05). All crowns were rated either as excellent or good for each of the clinical criteria; however, between years 2 and 3, gradual roughening of the occlusal surface occurred in some of the ceramic‐ceramic crowns, possibly caused by dissolution and wear of the glaze. Statistically significant differences in surface texture (p= 0.0013) and crown wear (p= 0.0078) were found at year 3 between the metal‐ceramic crowns and the lithium‐disilicate‐based crowns. Conclusion : Based on the 11 criteria, the clinical performance of ceramic‐ceramic crowns was comparable to that of the metal‐ceramic crowns after 2 years; however, gradual roughening occurred between years 2 and 3, which resulted in differences in surface texture and wear.     

The effects of crown venting or pre‐cementing of CAD/CAM‐constructed all‐ceramic crowns luted on YTZ implants on marginal cement excess

Objectives

The purpose of this study was to analyze the cement excess produced when cementing CAD/CAM‐fabricated lithium disilicate (L) or zirconium dioxide (Z) crowns using adhesive cement (A) or resin‐modified glass ionomer cement (B). Three different cementation techniques were applied: palatal venting (PV), pre‐cementation with custom analogs (CA), and conventional standard procedure (SP).

Materials and Methods

Seventy‐two crowns (36 each material) were assigned to 12 experimental groups depending on the restoration material (L, Z), type of cement (A, B), and cementation technique (PV, CA, SP). Weight measurements were taken during cementation, and the amounts of excess cement, cement retained in crown, and relative excess cement were calculated and statistically analyzed.

Results

A significant direct relation between the amounts of cement applied and excess cement was observed in groups CA and SP. Vented crowns showed least amounts of marginal excess cement (0.8 ± 0.3 μl) followed by CA (4.2 ± 1.1 μl) and SP (8.8 ± 2.5 μl; p < .001). In CA, 32.1% less excess cement (95%CI: 28.4, 35.7) was produced than in the SP group (p < .001), but 27.4% more than in the PV group (95%CI: 23.8,31.0; p < .001). Overall, slightly smaller amounts of adhesive cement (A) than of glass ionomer cement (B) were retained in crowns.

Conclusions

Using crown venting was the most effective measure to reduce the amount of marginal excess cement, followed using a pre‐cementation device. To keep the marginal excess cement of one‐piece zirconia implants to a minimum, both techniques should be considered for clinical application.     

Effect of Crystallization Firing on Marginal Gap of CAD/CAM Fabricated Lithium Disilicate Crowns

Purpose

To evaluate the marginal gaps of CAD/CAM (CEREC 3) produced crowns made from leucite‐reinforced glass‐ceramic (IPS Empress CAD) blocks (LG), and lithium‐disilicate (IPS e.max CAD) blocks before (LD‐B), and after (LD‐A) crystallization firing.

Materials and Methods

A human molar tooth (#19) was mounted with adjacent teeth on a typodont and prepared for a full‐coverage ceramic crown. The typodont was assembled in the mannequin head to simulate clinical conditions. After tooth preparation 15 individual optical impressions were taken by the same operator using titanium dioxide powder and a CEREC 3 camera per manufacturer's instructions. One operator designed and machined the crowns in leucite‐reinforced glass‐ceramic blocks (n = 5) and lithium‐disilicate blocks (n = 10) using the CEREC 3 system. The crowns were rigidly seated on the prepared tooth, and marginal gaps (μm) were measured with an optical microscope (500×) at 12 points, 3 on each of the M, B, D, and L surfaces of the leucite‐reinforced glass‐ceramic crowns and the lithium‐disilicate crowns before and after crystallization firing. Results were analyzed by two‐way ANOVA followed by a Tukey's post hoc multiple comparison test (α = 0.05).

Results

The overall mean marginal gaps (μm) for the crowns evaluated were: LG = 49.2 ± 5.5, LD‐B = 42.9 ± 12.2, and LD‐A = 57.2 ± 16.0. The marginal gaps for LG and LD‐B were not significantly different, but both were significantly less than for LD‐A.

Conclusions

The type of ceramic material did not affect the marginal gap of CAD/CAM crowns. The crystallization firing process required for lithium‐disilicate crowns resulted in a significant increase in marginal gap size, likely due to shrinkage of the ceramic during the crystallization process. Clinical Relevance: The marginal gap of CAD/CAM‐fabricated lithium disilicate crowns increases following crystallization firing. The marginal gap still remains within clinically acceptable parameters.     

计算机辅助设计与制造树脂暂时冠与自凝树脂、Luxatemp暂时冠的边缘密合度比较

目的 比较自凝树脂、Luxatemp与计算机辅助设计与制造（CAD/CAM）树脂暂时冠修复体的边缘密合度差异。方法 按全冠牙体制备标准预备牙体30个,取模并灌注石膏模型后,分别制作自凝树脂、Luxatemp与CAD/ CAM树脂暂时冠各30个,将其就位于石膏模型上。通过体式显微镜,对利用硅橡胶复制技术得到的暂时冠与石膏模型间的边缘间隙宽度代型进行测量,计算各组30个样本边缘间隙的平均值。采用SPSS 19.0软件包对实验数据进行单因素方差分析。结果 自凝树脂、Luxatemp与CAD/CAM树脂暂时冠边缘间隙平均值分别为（179.06±33.24）、（88.83±9.56）和（43.61±7.27） μm。CAD/CAM树脂暂时冠边缘间隙显著小于自凝树脂和Luxatemp暂时冠（P< 0.05）,自凝树脂暂时冠边缘间隙显著大于Luxatemp与CAD/CAM树脂暂时冠（P<0.05）。结论 CAD/CAM树脂暂时冠边缘密合度显著优于自凝树脂和Luxatemp暂时冠, CAD/CAM具有较高的临床应用价值。     

Effect of silane pretreatment on the immediate bonding of universal adhesives to computer‐aided design/computer‐aided manufacturing lithium disilicate glass ceramics

The aim of this study was to investigate the effect of silane pretreatment on the universal adhesive bonding between lithium disilicate glass ceramic and composite resin. IPS e.max ceramic blocks etched with hydrofluoric acid were randomly assigned to one of eight groups treated with one of four universal adhesives (two silane‐free adhesives and two silane‐containing adhesives), each with or without silane pretreatment. Bonded specimens were stored in water for 24 h. The shear bond strength (SBS) of the ceramic‐resin interface was measured to evaluate bond strength, and the debonded interface after the SBS test was analysed using field‐emission scanning electron microscopy to determine failure mode. Light microscopy was performed to analyse microleakage and marginal sealing ability. Silane pretreatment significantly and positively influenced SBS and marginal sealing ability. For all the universal adhesive groups, SBS increased and the percentage of microleakage decreased after the pretreatment. Without the pretreatment, SBS and the percentage of microleakage were not significantly different between the silane‐containing universal adhesive groups and the silane‐free groups. Cohesive failure was the main fracture pattern. The results suggest that additional silane pretreatment can effectively improve the bonding strength and marginal sealing of adhesives to lithium disilicate glass ceramics. The bonding performance of silane‐containing universal adhesives without pretreatment is similar to that of silane‐free adhesives.     

Surface modification with alumina blasting and H2SO4–HCl etching for bonding two resin‐composite veneers to titanium

The purpose of this study was to investigate the effect of an experimental surface treatment with alumina blasting and acid etching on the bond strengths between each of two resin composites and commercially pure titanium. The titanium surface was blasted with alumina and then etched with 45wt% H₂SO₄ and 15wt% HCl (H₂SO₄–HCl). A light‐ and heat‐curing resin composite (Estenia) and a light‐curing resin composite (Ceramage) were used with adjunctive metal primers. Veneered specimens were subjected to thermal cycling between 4 and 60°C for 50,000 cycles, and the shear bond strengths were determined. The highest bond strengths were obtained for Blasting/H₂SO₄‐HCl/Estenia (30.2 ± 4.5 MPa) and Blasting/Etching/Ceramage (26.0 ± 4.5 MPa), the values of which were not statistically different, followed by Blasting/No etching/Estenia (20.4 ± 2.4 MPa) and Blasting/No etching/Ceramage (0.8 ± 0.3 MPa). Scanning electron microscopy observations revealed that alumina blasting and H₂SO₄–HCl etching creates a number of micro‐ and nanoscale cavities on the titanium surface, which contribute to adhesive bonding.     

Clinical fit of four‐unit zirconia posterior fixed dental prostheses

The objective of this clinical study was to assess the internal and marginal accuracy of computer‐aided design/computer‐aided manufacturing (CAD/CAM)‐generated four‐unit all‐ceramic posterior fixed dental prostheses (FDPs). The data were compared with the results of three‐unit metal‐ceramic and all‐ceramic FDPs that were obtained in a previous study. Twenty‐four patients were provided with all‐ceramic posterior four‐unit FDPs made from semisintered blank zirconia material. Prior to definitive insertion the accuracy was evaluated using a replica technique with a light body silicone that was stabilized with a heavy body material. The replica samples were examined using microscopy. The median marginal gap of the 24 four‐unit FDPs was 77 μm. The median gap widths were 87 μm at the midaxial wall, 167 μm at the axio‐occlusal transition of the abutments, and 170 μm at centro‐occlusal location. Although the marginal accuracy of the four‐unit FDPs differed significantly from that of the three‐unit metal‐ceramic FDPs (median 54 μm), the values obtained were clinically satisfactory and showed that semisintered zirconia blanks could be used for the fabrication of four‐unit FDPs.     

An In Vivo Evaluation of Fit of Zirconium‐Oxide Based Ceramic Single Crowns,Generated with Two CAD/CAM Systems,in Comparison to Metal Ceramic Single Crowns

Purpose: The purpose of this study was to assess in vivo the marginal fit of single crowns produced using two CAD/CAM all‐ceramic systems, in comparison to more traditional metal ceramic crowns. Materials and Methods: Thirty vital, caries‐free, and previously untreated teeth were chosen in five patients who needed extraction for implant placement and therefore were included in this study. In the control group (C), 10 regular metal ceramic crowns with porcelain occlusal surfaces were fabricated. In the other two groups (Z and E), CAD/CAM technology was used for the fabrication of 20 zirconium‐oxide‐based ceramic single crowns with two systems. All zirconia crowns were cemented with glass‐ionomer cement, always following the manufacturer's instructions. The same dentist carried out all clinical phases. The teeth were extracted 1 month later. Marginal gaps along vertical planes were measured for each crown, using a total of four landmarks for each tooth by means of a microscope at a magnification of 50×. On completion of microscopic evaluation, representative specimens from each group were prepared for ESEM evaluation. Mean and standard deviations of the four landmarks (mesial, distal, buccal, palatal) at each single crown were calculated for each group. Multivariate analysis of variance (MANOVA) was performed to determine whether the four landmarks, taken into consideration together, differed between groups. Two‐way ANOVA was performed to study in detail, for each landmark, how the three systems used to produce the FPDs affected the gap measurements. Differences were considered to be significant at p < 0.05. Results: MANOVA revealed no quantitative differences of the four landmarks, when taken into consideration together, between the three groups (p < 0.0001). Two‐way ANOVA, performed at each landmark, revealed no quantitative differences between the three groups (p < 0.0001 for each landmark). Conclusions: Within the limitations of this study, it was concluded that the two zirconium‐oxide‐based ceramic CAD/CAM systems demonstrated a similar and acceptable marginal fit when compared to more traditional metal ceramic crowns.     

Fracture resistance of zirconia‐based all‐ceramic crowns after bur adjustment

Intra‐oral grinding is often required to optimize occlusion of all‐ceramic restorations. The effect of burs of different grit size on the fracture resistance of veneered zirconia crowns was investigated in this study. Forty‐eight standardized zirconia copings were produced. The ceramic veneer was designed with a positive ellipsoidal defect on the palatal aspect of the crowns. To simulate adjustment of dental restorations by burs, this palatal defect was removed by use of three different diamond‐coated burs with grit sizes 46, 107, or 151 μm (fine, medium, or coarse, respectively). Each different grit size of bur was used to grind 16 crowns. All crowns were then polished and surface roughness was measured. Half of the specimens underwent thermomechanical aging (10,000 thermocycles between 6.5°C and 60°C) and 1.2 million cycles of chewing simulation (F = 108 N). A linear regression model was computed to test the effect of aging and grinding grit size at a level of significance of α = 0.05. Fracture loads increased with decreasing grit size. Grit size and aging had a significant effect on the fracture resistance of the crowns. Use of fine and coarse burs for intra‐oral adjustments resulted in different fracture resistance of veneered zirconia crowns. Coarse burs should be avoided in the final stage of grinding before polishing.     

Inlay‐retained cantilever fixed dental prostheses to substitute a single premolar: impact of zirconia framework design after dynamic loading

The purpose of this in‐vitro study was to evaluate the influence of the framework design on the durability of inlay‐retained cantilever fixed dental prostheses (IR‐FDPs), made from zirconia ceramic, after artificial ageing. Forty‐eight caries‐free human premolars were prepared as abutments for all‐ceramic cantilevered IR‐FDPs using six framework designs: occlusal–distal (OD) inlay, OD inlay with an oral retainer wing, OD inlay with two retainer wings, mesial–occlusal–distal (MOD) inlay, MOD inlay with an oral retainer ring, and veneer partial coping with a distal box (VB). Zirconia IR‐FDPs were fabricated via computer‐aided design/computer‐aided manufacturing (CAD/CAM) technology. The bonding surfaces were air‐abraded (50 μm alumina/0.1 MPa), and the frameworks were bonded with adhesive resin cement. Specimens were stored for 150 d in a 37°C water bath during which they were thermocycled between 5 and 55°C for 37,500 cycles; thereafter, they were exposed to 600,000 cycles of dynamic loading with a 5‐kg load in a chewing simulator. All surviving specimens were loaded onto the pontic and tested until failure using a universal testing machine. The mean failure load of the groups ranged from 260.8 to 746.7 N. Statistical analysis showed that both MOD groups exhibited significantly higher failure loads compared with the other groups (i.e. the three OD groups and the VB group) and that there was no significant difference in the failure load among the OD groups and the VB group. In conclusion, zirconia IR‐FDPs with a modified design exhibited promising failure modes.     

Success,clinical performance and patient satisfaction of direct fibre‐reinforced composite fixed partial dentures – a two‐year clinical study

To evaluate the success, clinical performance and patient satisfaction of directly placed fibre‐reinforced composite (FRC) fixed partial dentures (FPDs) in 2 years. One hundred sixty‐seven FRC FPDs (120 subjects) were directly fabricated to restore a single missing tooth by six Advanced Education in General Dentistry (AEGD) residents. The FRC FPDs recipients were rando‐mised into two groups according to the fibre materials (pre‐impregnated glass or polyethylene). Clinical performance was evaluated at baseline (2 weeks), 6, 12 and 24 months by two calibrated evaluators for prosthesis adaptation, colour match, marginal discoloration, surface roughness, caries and post‐operative sensitivity using modified United State Public Health Service (USPHS) criteria. Prosthesis appearance, colour, chewing ability and overall satisfaction were evaluated by patients using a visual analogue scale (VAS). Kaplan–Meier estimation was used to estimate the prosthesis success. Ninety‐four patients with 137 FRC FPDs returned (21·67% attrition rate for study subjects, 17·94% for FRC FPDs). Seventeen FRC FPDs failed, due to one‐end (n = 4) or two‐ends (n = 4) debonding or pontic fracture (n = 9). The cumu‐lative 2‐year success rate was 84·32% and survival rate was 92·7%; there were no statistically significant differences between the groups according to different missing tooth location, retention type or fibre materials (P > 0·05). Patient satisfaction regarding prosthesis appearance, col‐our, chewing ability and overall satisfaction was rated high on the VAS (mean >80 mm) for all criteria at all time points. The FRC FPDs (restoring single tooth) fabricated by AEGD residents achieved acceptable success and survival rates in a 2‐year follow‐up.     

Long‐Term Follow‐Up of CeraOne™ Single‐Implant Restorations: An 18‐Year Follow‐Up Study Based on a Prospective Patient Cohort

Background: Knowledge on long‐term clinical performance of more than 5 years on the single‐implant CeraOne? (Nobel Biocare AB, Gothenburg, Sweden) concept is limited. Purpose: The aim of this study is to report the long‐term clinical performance of the first CeraOne single‐implant restorations, installed 17 to 19 years ago. Materials and Methods: The group comprised 57 patients provided with 65 CeraOne single‐tooth restorations. Sixty‐two all‐ceramic and three metal‐ceramic crowns were cemented between 1989 and 1991. Patients were followed up clinically and with intraoral radiographs at placement, after 1, 5, and between 17 and 19 years after placement. Results: Data were available for altogether 48 patients, followed up on an average time of 18 years. Excluding deceased patients (n = 2) and failed implant patients (n = 2), only five patients were lost to follow‐up (8.8%). Two implants failed, resulting in an 18‐year implant cumulative success rate (CSR) of 96.8%, and altogether eight original single‐crown restorations were replaced (CSR 83.8%). The most common reason for crown replacement was infra‐position of the implant crown (n = 3). Many of the remaining original crowns showed various signs of implant crown infraposition at the termination of the study. In general, the soft tissue at the restorations was assessed to be healthy and comparable with the gingiva at the adjacent natural teeth. Bone levels were on an average stable with only few patients exhibiting bone loss of more than 2 mm during 18 years in function. Conclusion: This long‐term follow‐up study of single‐implant restorations shows encouraging results with few implant failures and minimal bone loss over an 18‐year period. Original single‐crown restorations were replaced more frequently, because of, for example, implant crown infraposition and veneer fractures. The CeraOne concept proved to be a highly predictable and safe prosthodontic treatment.     

Marginal Adaptation of Implant-Supported Metal-Ceramic Crowns Fabricated With Gold Cylinders

Purpose The purpose of this investigation was to determine the mean marginal discrepancy of metal-ceramic crowns fabricated with gold cylinders and cemented on implant abutments. These discrepancies were then compared with those measured previously for implant-supported ceramic crowns. Materials and Methods Fifteen Nobel BioCare CeraOne abutments were connected to implant fixtures embedded in acrylic resin blocks. Marginal discrepancies were determined for gold cylinders, gold cylinders plus ceramic alloy (metal frameworks), completed metal-ceramic crowns, and cemented metal-ceramic crowns using a stereomicroscope equipped with a video camera linked to a computer. A Hotelling's T² test (p .05) was used to evaluate potential differences in mean marginal discrepancies among groups. Results The mean marginal discrepancies were: 1) gold cylinders, 7.56 ± 2.73 μm; 2) metal frameworks, 6.21 ± 1.34 μm; 3) metal-ceramic crowns, 11.06 ± 3.21 μm; and 4) zinc-phosphate cemented crowns, 31.47 ± 6.65 μm. No significant difference between gold cylinders and metal frameworks was found. Mean marginal discrepancies for metal-ceramic crowns were significantly greater than discrepancies for cast gold cylinders. Cemented-crown mean marginal discrepancy was significantly greater than all other means. Conclusions Cemented metal-ceramic crowns fabricated using proprietary gold cylinders exhibited well-fitting margins (31.47 μm).     

Internal fit of three‐unit fixed dental prostheses produced by computer‐aided design/computer‐aided manufacturing and the lost‐wax metal casting technique assessed using the triple‐scan protocol

Suboptimal adaptation of fixed dental prostheses (FDPs) can lead to technical and biological complications. It is unclear if the computer‐aided design/computer‐aided manufacturing (CAD/CAM) technique improves adaptation of FDPs compared with FDPs made using the lost‐wax and metal casting technique. Three‐unit FDPs were manufactured by CAD/CAM based on digital impression of a typodont model. The FDPs were made from one of five materials: pre‐sintered zirconium dioxide; hot isostatic pressed zirconium dioxide; lithium disilicate glass‐ceramic; milled cobalt‐chromium; and laser‐sintered cobalt‐chromium. The FDPs made using the lost‐wax and metal casting technique were used as reference. The fit of the FDPs was analysed using the triple‐scan method. The fit was evaluated for both single abutments and three‐unit FDPs. The average cement space varied between 50 μm and 300 μm. Insignificant differences in internal fit were observed between the CAD/CAM‐manufactured FDPs, and none of the FPDs had cement spaces that were statistically significantly different from those of the reference FDP. For all FDPs, the cement space at a marginal band 0.5–1.0 mm from the preparation margin was less than 100 μm. The milled cobalt‐chromium FDP had the closest fit. The cement space of FDPs produced using the CAD/CAM technique was similar to that of FDPs produced using the conventional lost‐wax and metal casting technique.