Precision of Fit of Two Margin Designs for Metal-Ceramic Crowns

STATEMENT OF PROBLEM: Although metal-ceramic restorations are widely used, there is a lack of information about how the fit is affected by margin designs. PURPOSE: This study measured and compared the precision of fit of metal-ceramic crowns with two margin designs. MATERIAL AND METHODS: Thirty-two extracted human premolar teeth were prepared for complete-coverage restorations with an internally rounded shoulder preparation. Impressions were made from all teeth, and master dies were poured with improved stone type V. MC crowns were fabricated with a porcelain-butt margin on the buccal aspect (n = 32) and a feather-edge metal margin on the lingual aspect (n = 32), which served as a control group. Precision of fit was measured three times at the mid-buccal and mid-lingual margins of each crown with a profilometer. The data were statistically analyzed with the paired t-test (alpha < .05). RESULTS: Mean marginal gap size of porcelain-butt margins was 27.93 microm (+/-15.84) and of feather-edge metal margins 42.43 microm (+/-24.12). The marginal gap size of feather-edge metal margins was statistically significantly greater than that of porcelain-butt margins (p = 0.0045). CONCLUSION: The marginal fit of porcelain-butt margins was significantly better than that of feather-edge metal margins. CLINICAL IMPLICATIONS: Porcelain-butt margins in this study had a better marginal fit than feather-edge metal margins, and thus have given clinicians evidence to prefer the use of porcelain-butt margins.     

3种桩核系统全瓷冠边缘和内部适合性比较的实验研究

目的:研究遮色钴铬合金桩核、氧化锆桩核、纤维桩树脂核三种牙色桩核系统氧化锆全瓷冠修复后冠边缘和内部适合性的差异,为临床桩核全瓷冠修复方法和材料的选择提供参考依据。方法:24颗离体上颌中切牙在釉牙骨质界冠方2.0 mm处截冠,按临床操作程序和方法分别制作遮色钴铬合金桩核、氧化锆桩核、纤维桩树脂核各8个,均加二氧化锆全瓷冠修复。在100倍体视显微镜下,采用间隙印模测量法比较3组冠的边缘和内部间隙大小,应用SPSS 17.0软件对实验数据进行统计分析。结果:遮色钴铬合金桩核组、氧化锆桩核组、纤维桩树脂核组锆瓷冠的边缘间隙测量结果分别为(96.98±3.51)、(62.34±3.22)、(59.00±3.96) μm。内部间隙为(95.71±2.52)、(73.14±2.04)、(68.52±4.08)μm。遮色钴铬合金桩核组的边缘间隙及内部间隙与氧化锆桩核组、纤维桩树脂核组间差异均有统计学意义(P<0.05),氧化锆桩核组与纤维桩树脂核组之间边缘及内部间隙差异均无统计学意义。结论:3种桩核方法上制作的氧化锆全瓷冠边缘适合性均在临床可接受范围内,但采用氧化锆桩核、纤维桩树脂核制得的全瓷冠其边缘适合性更接近美国牙科协会标准,更值得推广应用。     

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.     

CAD/CAM瓷嵌体的适合性研究

应用体视显微镜观测新型的ＣＥＲＥＣⅡ型机制作的瓷嵌体与离体人牙粘接前后的适合性。结果表明：粘接前，洞型与嵌体轴壁间隙，龈壁间隙，Ｈｅ面平均间隙５８．５μｍ；粘接后，平均边缘浮升量，粘接剂厚度在轴壁，龈壁，Ｈｅ面平均厚度８０μｍ。提示：ＣＥＲＥＣⅡ型机制作的瓷嵌体具有良好的适合性，可以满足临床的应用。     

Comparison of the Marginal Fit of Pressable Ceramic to Metal Ceramic Restorations

Purpose: The aim of this in vitro study was to compare the marginal adaptation of a pressed ceramic material, when used with and without a metal substructure, to a traditional feldspathic porcelain‐fused‐to‐metal restoration with a porcelain butt margin. Materials and Methods: A maxillary central incisor typodont tooth was prepared with a 1.5 mm 360° shoulder with rounded internal line angle, and 30 polyether impressions were made. Dies were poured in type IV dental stone, and 30 restorations were fabricated: 10 metal ceramic restorations (MCR) with porcelain butt joints, 10 pressed to metal restorations (PTM), and 10 all‐ceramic restorations (PCR). All restorations were evaluated on their respective dies at 45× magnification using an Olympus SZX‐12, measurements of the marginal openings were made, and ANOVA and Scheffé post hoc tests were used to evaluate the data. Results: The mean marginal opening was 72.2 ± 5.9 μm for MCR, 49.0 ± 5.9 μm for PTM, and 55.8 ± 5.9 μm for PCR. The post hoc tests showed that there was a statistical difference between the marginal adaptation of the PTM and MCR groups (p < 0.05). There was no significant difference in marginal adaptation between the PTM and the PCR groups, or the PCR and the MCR groups. Conclusions: The PTM group demonstrated a smaller mean marginal opening than the MCR group. The mean marginal openings of all three groups were within a clinically acceptable range.     

Marginal fit of cemented and screw-retained crowns incorporated on the Straumann (ITI)® Dental Implant System: an in vitro study

Aim: The aim of this study was to assess the marginal fit of crowns on the Straumann (ITI)^® Dental Implant System with special consideration of different casting dental materials. Material and methods: Sixty porcelain‐fused‐to‐metal crowns were fabricated: 18 crowns on standard cone abutments with an impression cylinder, partially prefabricated analogs, no coping and screw‐retained (A); 18 crowns on solid abutments without an impression device, no analogs, no coping and cemented (B); and 18 crowns on solid abutments using an impression transfer cap, an analog with a shoulder, no coping and cemented (C). In each group, six crowns were made on epoxy mastercasts (Bluestar^®), six on synthetic plaster (Moldasynt^®) and six on super hard stone (Fujirock^®). Six additional crowns were fabricated with the transversal screw retention system onto the Octa^® system with impression transfer caps, metal analogs, gold copings and screw‐retained (D). Impregum^® was used as impression material. Crowns of B and C were cemented with KetacCem^®. Crowns of A and D were fixed with an occlusal screw torqued at 15 N cm. Crowns were embedded, cut and polished. Under a light microscope using a magnification of × 100, the distance between the crown margin (CM) and the shoulder (marginal gap, MG) and the distance between the CM and the end of the shoulder (crown length, CL) was measured. Results: MGs were 15.4±13.2 μm (A), 21.2±23.1 μm (B), 11±12.1 μm (C) and 10.4±9.3 μm (D). No statistically significantly differences using either of the casting materials were observed. CLs were ?21.3±24.8 μm (A), 3±28.9 μm (B), 0.5±22 μm (C) and 0.1±15.8 μm (D). Crowns were shorter on synthetic casting materials compared with stone casts (P<0.005). Conclusions: CMs fit precisely with both cemented and screw‐retained versions as well as when using no, partial or full analogs.     

Resonance frequency measurements in vivo and related surface properties of magnesium-incorporated, micropatterned and magnesium-incorporated TiUnite®, Osseotite®, SLA® and TiOblast® implants

Objective: To investigate implant stability using resonance frequency measurements of topographically changed and/or surface chemistry‐modified implants in rabbit bone. Material and methods: Six groups of microstructured, screw‐shaped titanium implants: two oxidized, cation‐incorporated experimental implants [Mg implants and MgMp implants with micropatterned thread flanges (80–150 μm wide and 60–70 μm deep)] and four commercially available clinical implants (TiUnite^®, Osseotite^®, SLA^®, and TiOblast^®) were installed in 10 rabbit tibia for 6 weeks. The surface properties of the implants were characterized in detail using several analytical techniques. Implant stability was measured using a resonance frequency analyzer (Osstell^?). Results: Surface characterization of the implants revealed microstructured, moderately rough implant surfaces varying 0.7–1.4 μm in S_a (mean height deviation), but with clear differences in surface chemistry. After 6 weeks, all implants showed statistically significantly higher increases in implant stability. When compared with one another, MgMp implants showed the most significant mean implant stability quotient (ISQ) value relative to the others (P≤0.016). In terms of increment (ΔISQ) in implant stability, MgMp implants showed a significantly greater value as compared with Osseotite^® (P≤0.005), TiOblast^® (P≤0.005), TiUnite^® (P≤0.005), SLA^® (P≤0.007), and Mg implants (P≤0.012). In addition, transducer direction dependence of resonance frequency analysis (RFA) measurements was observed such that the differences in the mean ISQ values between longitudinal and perpendicular measurements were significant at implant placement (P≤0.004) and after 6 weeks (P≤0). Conclusion: The present study found that implant surface properties influence RFA measurements of implant stability. Surface chemistry‐modified titanium implants showed higher mean ISQ values than did topographically changed implants. In particular, cation (magnesium)‐incorporated micropatterns in MgMp implants may play a primary role in ΔISQ.     

Comparison of ready-to-use EMDOGAIN®-gel and EMDOGAIN® in patients with chronic adult periodontitis

OBJECTIVES: The aim of this multicenter trial was to compare the clinical and radiographical outcome of a ready-to-use Emdogain-gel (test) with the marketed Emdogain (control). METHODS: Subjects with bilateral infrabony defects > or =4 mm deep and > or =2 mm wide according to radiographs were selected. 88 subjects with probing pocket depth (PPD) > or =6 mm > or =1 month after supervised oral hygiene and scaling participated. At baseline plaque index, bleeding on probing, PPD and probing attachment level were recorded and reproducible radiographs for computer-based bone level measurements were taken. In each subject, 1 tooth was randomly treated with the test and 1 tooth with the control gel. Examinations were repeated 8 and 16 months post-operatively. RESULTS: After 16 months, the mean test PPD was 4.1 mm and the mean control PPD 4.2 mm. The mean gain of attachment was 2.7 mm for test and 2.9 mm for the control sites, and the radiographic measurements demonstrated a mean gain of 1 mm for both test and control sites. CONCLUSION: This series of cases demonstrated a statistically significant reduction of pocket depths and gain of attachment and bone after 8 and 16 months with no difference between the 2 preparations.     

Relationship of Margin Design for Fiber‐Reinforced Composite Crowns to Compressive Fracture Resistance

Purpose: Fiber‐reinforced composite restorations provide excellent esthetics; however, little is known regarding the influence of margin design on marginal fit and fracture resistance for this type of crown. This study evaluated the effect of variations in tooth‐preparation design on the marginal fit and compressive fracture resistance of fiber‐reinforced composite crowns. Materials and Methods: Three metal dies with a total convergence of 5° and different margin designs (0.5‐mm light chamfer, 1.0‐mm deep chamfer, and 1.0‐mm shoulder) were prepared. Sixty standardized crowns (FibreKor) were made on duplicated base metal alloy dies (n = 20 for each margin design). Marginal fit was stereoscopically evaluated by measuring the distances between each of the four pairs of indentations on the crowns and on the dies. The specimens were then subjected to a compressive fracture‐loading test using a universal testing machine. The data were analyzed with one‐way analysis of variance (ANOVA) followed by Ryan‐Einot‐Gabriel‐Welsch multiple‐range test (α= 0.05). Results: Analysis of marginal fit and fracture resistance disclosed a statistically significant difference for tooth‐preparation design (p < 0.001). The marginal adaptation of preparations with the 0.5‐mm light chamfer (66.2 μm) and 1.0‐mm deep chamfer (69.7 μm) was significantly better than preparations with a shoulder finish line (92.8 μm) (p < 0.001). The fracture strength of the preparations with the 0.5‐mm light chamfer (15.8 MPa) and 1.0‐mm deep chamfer (15.1 MPa) was significantly greater than those of the preparations with the 1.0‐mm shoulder (13.7 MPa) (p < 0.001). Conclusions: Marginal fit of fiber‐reinforced crowns was adversely affected by tooth‐preparation design. The marginal gaps were greater for the shoulder margin specimens than in the light or deep chamfer margin specimens; however, the fracture strength of the chamfer margin specimens was greater than that of the shoulder margin specimens.     

Comparison of two bone substitute biomaterials consisting of a mixture of fibrin sealant (Tisseel®) and MBCP™ (TricOs®) with an autograft in sinus lift surgery in sheep

Objectives: The aim of this study was to assess the efficacy and safety of macroporous biphasic calcium phosphate (MBCP^?)/fibrin grafts (TricOs^®)/(Tisseel^®) for sinus lift augmentation in sheep. Autologous bone grafts were used as a positive control, and dental implants were placed to assess the efficiency of the composite. Materials and methods: A total of 12 adult sheep (24 maxillary sinuses) were randomized to receive sinus lift augmentation with MBCP^?/fibrin grafts obtained by either simultaneous or sequential addition of thrombin and fibrinogen to MBCP^?, or autologous bone grafts. Six months post‐sinus lift surgery, dental implants were placed. At 6 months post‐sinus lift and 3 months after dental implant placement, the characteristics of newly formed bone and dental implant stability were assessed. The methods used were radiography, scanning electron microscopy, light microscopy, micro‐CT analysis, radio frequency analysis (RFA), and image analysis. Results: There were no clinical adverse events in the post‐operative period. New bone formation was similar for MBCP^?/fibrin grafts and autografts at 21–20% and 20%, respectively, at 6 months, and at 34–35% and 35%, respectively, at 9 months. Implantability of dental implants was better at the time of placement with MBCP^?/fibrin grafts than autografts at 81–88% and 69%, respectively. Three months after placement, RFA showed better implantability with MBCP^?/fibrin grafts than with autografts at 75–82% and 71%, respectively. The bone contact measurements were around 50% for the three groups, without significant differences. Conclusions: This study shows that following sinus lift augmentation in sheep, MBCP^?/fibrin grafts support new bone formation that is comparable to autografts, while providing better support for the dental implants.     

Orofacial and gastrointestinal hyperplasia and neoplasia in smad4+/− and elf+/−/smad4+/− mutant mice

Background:  Smad4 is vital to the roles of Smads 2 and 3 in transforming growth factor-beta (TGF)-β signal transduction, and inactivated Smad4 is common to human gastrointestinal cancers. The embryonic liver fodrin (ELF) is a β-spectrin that facilitates the nuclear translocation of activated Smad4.
Methods:  Smad4 ^+/− mice, known to develop gastrointestinal cancer, were crossbred with elf ^+/− mice. The smad4 ^+/− and smad4 ^+/−/ elf ^+/− offspring were autopsied as abnormalities developed.
Results:  In addition to polyps and adenocarcinomas of the stomach and duodenum, the smad4 ^+/− mice developed squamous cell carcinomas of the skin, oral mucosa and forestomach, benign neoplasms of connective tissue and lacrimal gland, and a lymphoma. The smad4 ^+/−/ elf ^+/− mice developed extensive hyperplasia and neoplasia of the gastric mucosa.
Conclusion:  These findings indicate that investigating interactions among smad4 , elf , and other genes involved in TGF-β signaling should be useful in further delineating the processes of neoplasia in a wide variety of tissues.