Experimental zirconia abutments for implant-supported single-tooth restorations in esthetically demanding regions: 4-year results of a prospective clinical study

PURPOSE: This prospective clinical study evaluated an experimental implant abutment made of densely sintered zirconia with respect to peri-implant hard and soft tissue reaction as well as fracture resistance over time. MATERIALS AND METHODS: Twenty-seven consecutively treated patients with 54 single-tooth implants were included. Zirconia abutment ingots were individually shaped and set on the implants with gold screws. All-ceramic (Empress I) crowns were cemented using a composite cement. At the 1- and 4-year examinations, reconstructions were evaluated for technical problems (fracture of abutment or crown, loosening of abutment screw). Modified Plaque and simplified Gingival Indices were recorded at implants and neighboring teeth, and peri-implant bone levels were radiographically determined. RESULTS: All but 1 of the 27 patients with 53 restorations could be evaluated at 1 year, and 36 restorations in 18 patients were evaluated 4 years after abutment and crown insertion. The median observation period for the reconstructions was 49.2 months. No abutment fractures occurred. Abutment screw loosening was reported for 2 restorations at 8 months and 27 months, respectively. Mean Plaque Index was 0.4 (SD 0.6) at abutments and 0.5 (SD 0.6) at teeth; mean Gingival Index was 0.7 (SD 0.5) at abutments and 0.9 (SD 0.5) at teeth. Mean marginal bone loss measured 1.2 mm (SD 0.5) after 4 years of functional loading. CONCLUSION: Zirconia abutments offered sufficient stability to support implant-supported single-tooth reconstructions in anterior and premolar regions. The soft and hard tissue reaction toward zirconia was favorable.     

Periodontal response to all-ceramic crowns (IPS Empress) in general practice

Abstract:  Objective:  The purpose of this study was to investigate the periodontal response to the presence of all-ceramic crowns (IPS Empress) in general practice patients. Methods:  The convenience sample included 82 IPS Empress crowns placed in 64 patients. These crowns had been in place for an average of 16.27 (SD 9.26) months and ranged from 6.2 to 48.87 months at the time of clinical examination. Periodontal health status (as determined by dental plaque, gingival health status, periodontal pockets) was assessed around all crowned teeth and around matched contralateral teeth by one calibrated examiner. Periodontal indices utilized included the Plaque Index (PI), Gingival Index (GI) and pocket depth (PD) with calibrated probes graduated in millimetres. Plaque, gingival and PD values for crowned teeth were compared with those for control teeth using Wilcoxon signed-rank test for each clinical parameters. Chi-square was used to test the significance of the difference in their distribution between crowns and control teeth. Results:  Statistically, PI (0.35), GI (0.41) and mean PD scores (1.42) of IPS Empress crowned teeth compared less favourably with scores of the control teeth (0.27, 0.23 and 0.86 respectively). Conclusion:  Teeth with IPS Empress crowns had poorer periodontal health and more clinically evident plaque than uncrowned teeth.     

Comparison of Fracture Resistance and Fit Accuracy of Customized Zirconia Abutments with Prefabricated Zirconia Abutments in Internal Hexagonal Implants

Background: Customized zirconia abutments are increasingly applied for the fabrication of esthetic implant restorations aimed at imitating the natural situation. These abutments are individually shaped according to the anatomical needs of the respective implant site. Purpose: This study sought to compare the fracture resistance and fit accuracy of prefabricated and customized zirconia abutments using an internal hexagonal implant system (TSV®, Zimmer, Carlsbad, CA, USA). Materials and Methods: Two zirconia abutment groups were tested: prefabricated zirconia abutments (ZirAce, Acucera, Seoul, Korea) and customized zirconia abutments milled by the Zirkonzahn milling system. Twenty zirconia abutments per group were connected to implants on an acrylic resin base with 30‐Ncm torque. The fracture resistance of zirconia abutments was measured with an angle of 30° at a crosshead speed of 1 mm/min using the universal testing machine (Z020, Zwick, Ulm, Germany). Marginal and internal gaps between implants and zirconia abutments were measured after sectioning the embedded specimens using a digital microhardness tester (MXT70, Matsuzawa, Tokyo, Japan). Results: The customized abutments were significantly stronger (1,430.2 N) than the prefabricated abutments (1,064.1 N). The mean marginal adaptation of customized abutments revealed a microgap that was increased (11.5 µm) over that in prefabricated abutments (4.3 µm). Conclusion: Within the limitations of this study, the customized abutments are significantly stronger than prefabricated abutments, but the fit is less accurate. The strength and fit of both abutments are within clinically acceptable limit.     

个性化全瓷基台在前牙种植修复中的应用

目的探讨个性化全瓷基台在前牙区种植修复的美学效果。 方法临床上收集51例前牙缺失患者（共植入60枚种植体）作为研究对象,根据患者意愿,26例选择个性化金属纯钛基台纳入对照组即：个性化钛基台+全瓷冠修复（30枚）;25例患者选择个性化全瓷基台纳入实验组即：个性化全瓷基台+全瓷冠修复（30枚）。通过两组对照研究,术后1、6、12个月复诊,分别记录红白复合美学指数、牙龈指数及菌斑指数,将数据进行统计学分析。 结果术后1、6个月红白美学指数差异无统计学意义;术后12个月比较：（1）红色美学指数：实验组（30例）高于对照组（28例）,差异有统计学意义（χ²= 6.696,P= 0.020）;（2）白色美学指数：实验组（30例）高于于对照组（29例）,差异有统计学意义（χ²=6.634,P= 0.021）。术后1个月菌斑指数和牙龈指数差异无统计学意义;术后6个月两组比较菌斑指数（t= 3.128,P= 0.003）和牙龈指数（Z=-3.537,P= 0.000）差异均有统计学意义;术后12个月两组比较菌斑指数（t= 3.027,P= 0.004）和牙龈指数（Z=-6.785,P= 0.000）差异均有统计学意义。 结论在前牙种植美容修复中,个性化全瓷基台较钛基台优势明显,值得临床推广。     

Marginal adaptation of all-ceramic crowns on implant abutments

Background: Studies focusing on the marginal accuracy of all‐ceramic crowns on implant abutments are in short supply. Purpose: This study evaluated the marginal accuracy of all‐ceramic crowns on different implant abutments. Materials and Methods: Ninety‐six standardized maxillary central incisor crowns (48 alumina and 48 zirconia) were fabricated for each of the six test groups (n = 16) (Ti1, titanium abutments–alumina crowns; Ti2, titanium abutments–zirconia crowns; Al1, alumina abutments–alumina crowns; Al2, alumina abutments–zirconia crowns; Zr1, zirconia abutments–alumina crowns; Zr2, zirconia abutments–zirconia crowns). The crowns were adhesively luted using a resin luting agent. The marginal gaps were examined on epoxy replicas before and after luting as well as after masticatory simulation at 200× magnification. Results: The geometrical mean (95% confidence limits) marginal gap values before cementation, after cementation, and after masticatory simulation were group Ti1: 39(37–42), 57(53–62), and 49(46–53); group Ti2: 43(40–47), 71(67–76), and 64(59–69); group Al1: 57(54–61), 87(85–90), and 67(65–69); group Al2: 66(63–69), 96(90–101), and 75(72–78); group Zr1: 54(51–57), 79(76–82), and 65(63–67); and group Zr2: 64(60–68), 85(80–91), and 75(70–81). The comparison between non‐cemented and cemented stages in each group demonstrated a significant increase in the marginal gap values after cementation in all groups (p < .001), while the comparison between cemented and aged stages in each group showed a significant decrease in the marginal gap values in groups Al1, Al2, and Zr1 (p < .0001). This reduction was not significant for groups Ti1, Ti2, and Zr2 (p > .05). Conclusion: The marginal accuracy of all tested restorations meets the requirements for clinical acceptance.     

Implant-tissue interface of endosseous dental implants in dogs. Validity of clinical evaluation methods

Plaque and gingival bleeding were scored and probing, radiography, and histologic methods were used to evaluate clinical methods for estimating alterations of supporting structures at functioning endosseous dental implants. Twelve implant abutment posts in three Labrador retriever dogs were assessed. The observation period was 3 months of submerged healing followed by 6 months in function.In the presence of daily gingival cleaning, both plaque and gingival bleeding scores were reduced on implant abutments. No correlation was found between gingival scores and the degree of bone resorption.The correlation between probing and radiographic measurements was studied by comparing 136 parallel measurements. The average difference was 0.4 mm. Discrepancies were observed when evaluating bone loss that reached the shoulder area. Better accordance was obtained when moderate (2 to 4 mm) or extensive (6 to 8 mm) resorption was assessed.Histologic evaluation indicated alternating regions of implant-bone contact and fibrous encapsulation. Progressive infiltrates were observed in the permucosal area, sometimes extending into the deeper parts of the supporting bone.A combination of probing and radiographic measurements seems to give the most reliable information about the level of bone support and is recommended to be included in routine control of implant abutments.     

The use of six selected teeth in population measures of periodontal status

Selected teeth have been used to represent the entire dentition in many epidemiological and clinical investigations. The present study sought to assess the relationship between the six selected teeth described by Ramfjord and the entire dentition for the Plaque Index, Gingival Index, Calculus Index and Loss of Attachment. The computations were performed on measurements obtained in investigations of the natural history of periodontal disease in Norway and Sri Lanka. A consistently strong correlation was observed between the tooth subset and whole mouth for all indices in both populations. This relationship persisted even though single members or pairs of the subset of teeth were removed from the calculations. Some bias, however, was observed with all indices. Plaque and gingival indices obtained from the six teeth underestimated whole mouth scores in the low range (less than 1.0) and overestimated scores in the high range (greater than 2.0). Use of the tooth subset for calculus and loss of attachment consistently overestimated scores for the entire dentition.     

Immediate placement and provisionalization of maxillary anterior single implants: 1-year prospective study

PURPOSE: This 1-year prospective study evaluated the implant success rate, peri-implant tissue response, and esthetic outcome of immediately placed and provisionalized maxillary anterior single implants. MATERIALS AND METHODS: Thirty-five patients (8 men, 27 women) with a mean age of 36.5 years (range 18 to 65) were included in this study. Thirty-five threaded, hydroxyapatite-coated implants were placed and provisionalized immediately after each failing tooth had been removed. The definitive restoration was placed 6 months later. The patients were evaluated clinically and radiographically at implant placement and at 3, 6, and 12 months after implant placement. RESULTS: At 12 months, all implants remained osseointegrated. The mean marginal bone change from the time of implant placement to 12 months was -0.26 +/- 0.40 mm mesially and -0.22 +/- 0.28 mm distally. No significant differences in the Plaque Index scores were noted at different time intervals. The mean midfacial gingival level and mesial and distal papilla level changes from pretreatment to 12 months were -0.55 +/- 0.53 mm, -0.53 +/- 0.39 mm, and -0.39 +/- 0.40 mm, respectively. All patients were very satisfied with the esthetic outcome and none had noticed any changes at the gingival level. DISCUSSION: Although marginal bone and gingival level changes were statistically significant from pretreatment to 12 months of follow-up, they were well within clinical expectations. CONCLUSION: The results of this study suggest that favorable implant success rates, peri-implant tissue responses, and esthetic outcomes can be achieved with immediately placed and provisionalized maxillary anterior single implants.     

Cement thickness at implant‐supported single‐tooth Lava assemblies: a scanning electron microscopic investigation

Objectives: The fit of implant‐supported single‐tooth Lava zirconia assemblies was investigated in this study. The implant–abutment interface, the interface between the metallic and the zirconia portion of the abutment and the interface between Lava abutments and copings were evaluated. The adaptation of titanium abutments to implants and Lava copings was investigated as a control. Material and methods: Twenty implants were randomly assigned and connected to Lava abutments (group 1) or titanium abutments (group 2). All specimens were subjected to scanning electron microscopy (SEM) analysis of the fixture/abutment fit. Afterwards, specimens were luted to Lava copings and subjected to a SEM evaluation of the marginal external adaptation of the abutments with the copings. Finally, the samples were embedded in resin, sectioned and subjected to SEM analysis of the following interfaces; group 1: titanium/zirconia interface (between the constitutive components of the Lava abutment) and the zirconia/zirconia interface (between the Lava abutment and the coping); group 2: the titanium/zirconia interface (between the titanium abutment and the Lava coping). Non‐parametric analysis of variance and a post hoc test were used for statistical analysis. Results: Significant differences emerged in the cement thickness between titanium and zirconia components of the Lava abutments as compared with the thickness measured at the interface between Lava copings and the abutments investigated. No differences were found in cement thickness between Lava copings and the two different abutments. Conclusions: When Lava abutments are used, the most critical cement thickness is the internal interface between its titanium and zirconia components. Lava coping adaptation for both Lava and titanium abutments is within the clinical acceptable range. To cite this article:
Apicella D, Veltri M, Chieffi N, Balleri P, Ferrari M. Cement thickness at implant‐supported single‐tooth Lava assemblies: a scanning electron microscopic investigation.
Clin. Oral Impl. Res. 21 , 2010; 747–750.
doi: 10.1111/j.1600‐0501.2009.01882.x     

Zirconia for teeth and implants: a case series

This case series reports on the use of nonsilica-based high-strength full ceramics for different prosthetic indications. Fifty-two consecutive patients received tooth- or implant-supported zirconia reconstructions during a 2-year period. The observation period for reexamination was 12 to 30 months. The most frequent indications were single crowns and short-span fixed partial dentures. A few implant superstructures were screw-retained, whereas all remaining restorations were cemented on natural teeth or zirconia implant abutments. Clinical examination included biologic (probing depths, bleeding on probing) and esthetic (Papilla Index) parameters, as well as technical complications. No implant was lost or caused any problems, but two teeth were lost after horizontal fracture. Overall, the periodontal parameters were favorable. Fractures of frameworks or implant abutments were not observed. Abutment-screw loosening occurred once for one premolar single crown. Furthermore, five implant crowns in the posterior region exhibited chipping of the porcelain veneering material. With regard to esthetics, no reconstructions were considered unacceptable, but three crowns were remade shortly after delivery. In this short-term study, it was observed that biologic, esthetic, and mechanical properties of zirconia were favorable, and the material could be used in various prosthetic indications on teeth or implants.     

The periodontal response to cantilevered resin-bonded bridgework

This study investigated 84 cantilevered resin-bonded bridges (CRBB) in 60 patients. These CRBB (single retainer, single pontic) had been in place for an average of 43.6 months. Periodontal health was assessed on abutment teeth and contralateral control teeth. Periodontal indices utilized were Plaque Index (PI), Gingival Index (GI), Bleeding Index (BI), Pocket Depth (PD) and mobility. The marginal adaptation, the gingival extension of the retainers and the presence or absence of caries around each retainer margin were also assessed. Information about the history of debonding was collected and a success rate of 93% was reported. PI, GI and mean PD compared statistically significantly, less favourably, with scores of the control teeth. Marginal adaptation of the retainers was of a high standard and caries did not appear to be a problem.     

Marginal integrity of direct and indirect castings for implant abutments

PURPOSE: Current implant systems with screw-retained abutments permit direct laboratory fabrication of castings. Computer aided drafting systems further enhance the fabrication of computer-milled abutments (CMAs) and castings. The purpose of this study was to compare marginal accuracy, as measured by gap size, of castings made directly on CMAs with those made indirectly on epoxy and stone dies. MATERIALS AND METHODS: Castings were made directly for 10 CMAs. Marginal gap measurements were made with the castings seated on the abutments (group A). Castings were also made indirectly on stone and epoxy dies obtained from impressions of the abutments. Marginal gap measurements were made with these indirectly made castings seated on their CMAs (groups B and E). In addition, the directly made castings were transferred between CMAs and marginal gap measurements made (group D). Marginal gap measurements of the groups were compared with analysis of variance (ANOVA) and pair-wise comparisons (Scheffé test). RESULTS: Groups A and D had marginal gaps of less than 100 microm. These marginal gaps were significantly smaller (P < .05) than the gaps of groups B and E, made on dies, which were approximately 200 to 500 microm. DISCUSSION AND CONCLUSIONS: With CMAs, it is possible to make an exact duplicate of the abutment. This permits the laboratory to make castings on duplicate abutments with greater precision than can be obtained using the indirect technique. Direct fabrication of castings resulted in smaller marginal gaps, which in turn allows a better marginal seal and improved retention of castings.     

Dental implants as strategic supplementary abutments for implant-tooth-supported telescopic crown-retained maxillary dentures: a retrospective follow-up study for up to 9 years

PURPOSE: The aim of this retrospective study was to present the results of implants and natural teeth used as combined abutments to support maxillary telescopic prostheses. MATERIALS AND METHODS: Between 1997 and 2004, 22 patients with residual maxillary teeth underwent prosthodontic rehabilitation with supplementary implant placement of implant-tooth-supported telescopic prostheses. A total of 60 supplementary implants (mean: 2.9 implants; SD: 1.6; range: 1 to 5 per patient) were placed in strategic position and connected with 48 natural abutment teeth (mean: 2.2 teeth; SD: 0.9; range: 1 to 4 per patient) using telescopic crowns. The follow-up registration included implant and natural tooth survival rates and peri-implant and periodontal parameters, along with prosthodontic maintenance. Natural tooth abutments were additionally followed to compare their periodontal parameters at baseline to the follow-up examination. RESULTS: After a mean of 38 months (12 to 108 months) no implants or natural tooth abutments were lost (survival rate: 100%). There was no fracture, endodontic treatment, loss, or intrusion of natural teeth used for telescopic abutments. Implant abutments showed high stability and excellent periimplant soft tissue conditions. Natural tooth abutments used for double crowns also showed uneventful progress. A low rate of prosthodontic maintenance was seen, with implant screw abutment loosening as the most severe complication (3 of 60 implants; 5%). CONCLUSIONS: On the basis of this retrospective clinical review, the following conclusions were drawn: (1) successful function over a prolonged period and a minor complication rate of implant-tooth-supported telescopic maxillary dentures may be anticipated, and (2) the great variety of treatment modalities offered by tooth-implant support for telescopic prostheses appears to be useful as a treatment option for the maxilla in elderly patients.     

Fit of implant frameworks: an in vitro comparison between two fabrication techniques

STATEMENT OF PROBLEM: It has been suggested that a precise fit between the implant and the framework cylinder is necessary to ensure a satisfactory long-term clinical outcome. PURPOSE: The purpose of this study was to compare the precision of fit between implant abutments and framework cylinders in frameworks fabricated by the Procera system and those fabricated from cast gold-alloy. MATERIAL AND METHODS: A total of 19 frameworks, 14 made with the Procera system (type 1) and 5 made of a cast gold-alloy (type 2), were fabricated. A total of 95 implants, 70 type 1 and 25 type 2 frameworks, were evaluated. Three replicas of the space between the implant abutments and the framework cylinders of the master cast were made for each test specimen. The replicas were cut with a scalpel in 2 axial directions: buccal-lingual and right-left. For the purpose of measurement, a microscope with a precision of +/- 0.5 microm was used at original magnification x30. The Student t test was used to determine whether there were significant differences between the framework designs. RESULTS: The buccal-lingual measurements for the type 1 and type 2 frameworks showed mean values of 28.1 microm (SD 9.8) and 42.0 microm (SD 1.8) on the buccal side, respectively, and 25.6 microm (SD 11.2) and 51.6 microm (SD 10.9) on the lingual side, respectively. For the right-left view, the mean measurements were 26.6 microm (SD 8.4) and 49.2 microm (SD 11.4) on the right side, respectively, and 27.4 microm (SD 8.5) and 44.4 microm (SD 6.5) on the left side, respectively. The total mean value for type 1 frameworks was 26.9 microm (SD 9.3); that for type 2 frameworks was 46.8 microm (SD 8.8). CONCLUSION: Within the limitations of this experiment, it was demonstrated that the fit of frameworks made with the Procera system was significantly better than that of the frameworks made with cast gold-alloy (P<.01).     

即刻种植和早期种植对前牙美学区种植体周围软组织的影响分析

目的:分析即刻种植和早期种植对前牙美学区种植体周边软组织的影响。方法:随机抽取我院于2015年8月至2019年8月期间收治的60例单颗前牙缺失患者,其中有30例患者于拔牙后行即刻种植(观察组),30例拔牙后行早期植入(对照组),均予以Astra Tech种植体及种植体植入半年后给予氧化锆全瓷修复,并在半年后复查,对比分析两组患者的红色美学评分(PES)等。结果:两组患者对比PES总分和各节点PES评分无明显差异(P>0.05)而在各节点PES评分中,牙龈生物型和牙槽骨缺损、远中龈乳头,缺失牙位和牙龈高度及缺牙原因和近、远中龈高度存在显著相关性。结论:即刻种植和早期种植对前牙美学区种植体周边软组织之间的影响差异不明显,对前牙美学区种植体修复时软组织美学产生的主要影响包括缺失牙位、牙龈生物型及缺牙原因。     

Marginal and internal fit of Cerec 3 CAD/CAM all-ceramic crowns

PURPOSE: The purpose of this study was to examine the effects of the occlusal convergence angle of the abutment and the computer's luting space setting on the marginal and internal fit of Cerec 3 computer-aided design/manufacturing (CAD/CAM) all-ceramic crowns. MATERIALS AND METHODS: Mandibular second premolar all-ceramic crowns were fabricated for nine different conditions using Cerec 3: all combinations of abutments with three different total occlusal convergence angles (4, 8, and 12 degrees) with three different luting space settings (10, 30, and 50 microm). The completed crowns were seated on the abutments, and the marginal gaps were measured. The internal gaps between the crowns and abutments were also measured, using test-fit silicone paste. RESULTS: When the luting space was set to 10 microm, the marginal gaps of the crowns were greater than when it was set to 30 or 50 microm. When the luting space was set to 30 or 50 microm, the marginal gaps ranged from 53 to 67 microm and were not affected by the occlusal convergence angle of the abutment. The internal gaps were within a range of 116 to 162 microm and tended to decrease as the occlusal convergence angle of the abutment decreased. CONCLUSION: When the luting space was set to 30 microm, crowns with a good fit could be fabricated on the Cerec 3 system, regardless of the occlusal convergence angle of the abutment.     

Effects of bur abrasive particle size and abutment composition on preparation of ceramic implant abutments

STATEMENT OF PROBLEM: Amid increasing use of preparable ceramic implant abutments, there is a lack of quantitative data to show which abrasive particle size of diamond bur yields the fastest reduction and provides the smoothest surface. PURPOSE: The research aim was to determine the effects of diamond bur abrasive particle size and abutment material composition on preparation efficiency, prepared surface roughness, and surface deterioration of diamond burs. MATERIAL AND METHODS: Fifteen alumina (Cera Base) and 15 zirconia (ZiReal) implant abutments were each machined using a high-speed hand piece with a diamond bur having 1 of 3 abrasive particle sizes (150, 100, or 30 microm) (n=5). Control abutments (n=5) were analyzed without machining. Abutments were weighed before starting and between machining cycles. Three profilometry measurements (root mean square surface roughness) were made for each abutment. Scanning electron micrographs were made of each bur. Lost abrasive particles were then counted on each micrograph through a randomly placed template. Two-way analysis of variance (alpha=0.05) was used to test for significant effects. RESULTS: Bur abrasive particle size and ceramic type had a significant interactive effect on the amount of material removed (P<.001). Super coarse (150 microm) burs yielded the roughest surfaces for each abutment material (P<.001), and prepared alumina surfaces were rougher than zirconia surfaces (P<.001). Super coarse burs showed the highest proportion of lost particles (P<.001). Abutment composition did not significantly affect bur wear. CONCLUSION: Super coarse burs yielded the most efficient material removal for alumina abutments. All abrasive particle sizes removed a similar amount of material from zirconia abutments. Fine-grained alumina abutments experienced greater material removal and rougher prepared surfaces compared with zirconia abutments. Material was removed by an intergranular fracture mechanism for alumina abutments, in contrast to transgranular fracture for zirconia abutments.     

Marginal Adaptation of Cerec 3 CAD/CAM Composite Crowns Using Two Different Finish Line Preparation Designs

PURPOSE: The purpose of this study was to compare marginal discrepancies of Cerec 3 CAD/CAM composite crowns, fabricated on human prepared teeth with two different finish line designs, chamfer and shoulder. MATERIALS AND METHODS: Sixteen human molar teeth were used to prepare full crowns. Eight teeth were prepared with a 1-mm-wide chamfer finish line and the other eight with a 1.2- to 1.5-mm circumferential shoulder. Cerec 3 crowns were fabricated from optical impressions using Paradigm MZ100 composite polymer. Marginal adaptation was evaluated in two ways: (1) using modified United States Public Health Service (USPHS) criteria to evaluate eight preselected sites on each crown margin, and (2) using scanning electron microscopy (SEM) to measure marginal gaps on all four axial walls with 15 measurements on each wall (60 measurements per crown). An evaluation of the number of acceptable crowns, determined by having all measured sites per tooth with margin gap size less than 100 microm, as a function of finish line design was also conducted. RESULTS: In both chamfer and shoulder groups, there were only two crowns (out of eight) with clinically acceptable ratings for all eight measurement sites according to USPHS criteria. Fisher's chi-square analysis showed that there was no statistically significant difference in marginal adaptability as a function of finish line design ( p>0.05). With SEM imaging, overall mean marginal gaps for the chamfer group were 65.9+/-38.7 microm (range 35.0 to 130.0 microm), and for the shoulder group were 46.0+/-9.2 microm (range 26.3 to 55.6 microm); this difference was not found to be statistically significant ( p>0.05). While crown assessment based on mean marginal discrepancy measurements indicated that both the chamfer and shoulder groups were considered clinically acceptable (<100 microm); crown acceptability based on all measurement sites being less than 100 mum indicated that in the chamfer and shoulder groups there were four and three acceptable crowns out of eight, respectively. The Fisher's chi-square test indicated no statistically significant difference between the groups ( p>0.05). An agreement rate of 81.2% was calculated between the two evaluation methods, modified USPHS criteria and SEM measurements. CONCLUSIONS: Based on mean marginal discrepancy measurements, the typical marginal assessment technique, Cerec 3 Paradigm MZ100 crown restorations appear to have acceptable marginal adaptability (mean discrepancies <100 microm). Thus, the evidence from this investigation would suggest that the finish line preparation design had no effect on marginal adaptation for Cerec 3 composite crowns.     

Marginal Discrepancy of All-Ceramic Crowns Cemented on Implant Abutments

Purpose The purpose of this investigation was to determine the mean marginal discrepancy of all-ceramic crowns cemented on implant abutments. Materials and Methods Five Brånemark CeraOne abutments were connected to implant fixtures embedded in acrylic resin blocks. The marginal discrepancy was measured using a video camera connected to a digitizing board at four locations on each abutment for five samples in each of the following groups: all-ceramic caps (caps), all-ceramic crowns (crowns), and all-ceramic crowns cemented with zinc phosphate cement (cemented crowns). Results The mean marginal discrepancies were as follows: caps, 99.0 μm (SD, 16); crowns, 117.8 μm (SD, 20); and cemented crowns, 168.8 μm (SD, 23). Statistically significant differences were found between all three groups at the 99% level of confidence. In addition there were two significant differences between abutments. Conclusions Subgingival marginal discrepancies of the magnitude measured in this study have been shown to cause periodontal problems. It is probable that the marginal discrepancy of CeraOne restorations, as tested, can be improved. Efforts should be made to enhance the marginal accuracy of these restorations.