A comparative study of marginal fit of copings prepared with various techniques on different implant abutments.

This study evaluated fabrication techniques of recently introduced all-ceramic copings' marginal adaptation on two different implant abutments with different finish lines. Five different copings were prepared (Casted chrome-cobalt metal coping, Zirkonzahn, Cercon, In Ceram Alumina and IPS e.max Press) on two cementable implant abutments with two marginal designs. Ten samples for each coping group were prepared (totally 100 samples). Copings were cemented to implant abutments and marginal gap measurements were done from 24 points with stereomicroscope and the datas were analyzed by the Kruskal-Wallis test before cementation. Cercon copings showed the lowest marginal fit scores and metal copings showed the highest scores. After cementation, all marginal gap values have been increased. All marginal gap values obtained from crown copings can be considered in clinically acceptable limits (<120 µm) except metal copings after cementation on abutment with 135 degrees shoulder group (123 µm).

Evaluation of marginal and internal fit of ceramic and metallic crown copings using x-ray microtomography (micro-CT) technology.

STATEMENT OF PROBLEM: Prosthetic crown fit to the walls of the tooth preparation may vary depending on the material used for crown fabrication. PURPOSE: The purpose of this study was to compare the marginal and internal fit of crown copings fabricated from 3 different materials. MATERIAL AND METHODS: The selected materials were zirconia (ZirkonZahn system, group Y-TZP), lithium disilicate (IPS e.max Press system, group LSZ), and nickel-chromium alloy (lost-wax casting, group NiCr). Five specimens of each material were seated on standard dies. An x-ray microtomography (micro-CT) device was used to obtain volumetric reconstructions of each specimen. Points for fit measurement were located in Adobe Photoshop, and measurements were obtained in the CTAn SkyScan software environment. Marginal fit was measured at 4 points and internal fit at 9 points in each coping. Mean measurements from the 3 groups were compared by analysis of variance (ANOVA) at the 5% significance level, and between-group differences were assessed with the Tukey range test. RESULTS: The nickel-chromium alloy exhibited the best marginal fit overall, comparable with zirconia and significantly different from lithium disilicate. Lithium disilicate exhibited the lowest mean values for internal fit, similar to zirconia and significantly different from the nickel-chrome alloy. CONCLUSIONS: The marginal and internal fit parameters of the 3 tested materials were within clinically acceptable range.

Discrepancies in marginal and internal fits for different metal and alumina infrastructures cemented on implant abutments.

Cemented crowns are increasingly being used on dental implants instead of on screw-retained prostheses because of the reliability of internal Morse taper implant-abutment connections. However, there is a lack of information on the fit of metal ceramic and premachined alumina infrastructures. Therefore, the aim of this study was to evaluate the marginal and internal fits of different metal and alumina infrastructures cemented on universal post abutments. A total of 45 abutments (6 mm in height and 3.3 mm in diameter) were divided into five groups on the basis of their infrastructure material: cobalt-chromium (CoCr), nickel-chromium (NiCr), nickel-chromium-molybdenum-titanium (NiCrMoTi), gold (Au), and premachined alumina. The alumina group showed marginal overextension, and the Au group showed the highest discrepancy in marginal fit among the metal alloys. The CoCr and alumina groups showed the lowest discrepancies in internal fit. In conclusion, the alumina cylinders exhibited the best internal fit, despite their horizontal overextension. Among the metal alloys, CoCr exhibited the best fit at critical regions, such as the cervical and occlusal areas.

An Overview of Preformed Metal Crowns. Part 1: Conventional Technique.

This article details the clinical techniques for conventional preformed metal crown placement. It aims to increase the readers' awareness of the clinical advantages of preformed metal crowns and the indications for their use. The second part will discuss the Hall Technique. CPD/Clinical Relevance: This two-part article aims to guide the reader through the conventional and alternative techniques available for placement of a preformed metal crown whilst providing an update of the evidence for each.

Adaptação marginal em copings de dois sistemas cerâmicos livres de metal / Marginal fit in copings of two metal free ceramic systems

Este trabalhou avaliou a adaptação marginal de infraestruturas cerâmicas (copings em alumina) de dois sistemas cerâmicos livres de metal. Foram pesquisados os sistemas In-Ceram e Procera. Os valores de discrepância vertical presentes entre as margens de nove copings de cada sistema cerâmico e a margem de um modelo mestre metálico foram medidos com microscópio eletrônico de varredura em 5 pontos de cada infraestrutura. Esses valores foram medidos em micrômetros (pm). Os resultados foram analisados estatisticamente com o software SPSS (Statistical Package for the Social Sciences 11.0), através do teste t de Student, considerando-se significativos os valores de p<0(05. Os valores médios de discrepância marginal dos dois sistemas, medidos em microscópio eletrônico de varredura, mostraram diferença estatística entre si (p=0,001), sendo observadas desadaptações de 39±11pm (sistemas Procera) e 11 5±56pm (sistema In-Ceram). Conclui-se que os dois sistemas cerâmicos livres de metal avaliados apresentaram adaptação marginal dentro de limites aceitáveis clinicamente.

This work has evaluated the marginal fit of alumina copings of two metal free ceramic systems, namely Procera and In-Ceram systems. The marginal fit values of the margins in nine copings of each ceramic system and in a metal master model were assessed using electron- scanning microcopy in five points of the margin of each coping. Such values were measured in micrometers (pm). The results were analyzed statistically by the SPSS software (p<0.05). The marginal fit mean values for both systems have presented statistical difference (p=0.001), being of 39±11 pm and 115±56pm for the Procera and Inc-Ceram systems, respectively. Both systems have presented marginal fit according to the clinical acceptance.

A comparative study on microgap of premade abutments and abutments cast in base metal alloys.

The study compared the marginal accuracy of premade and cast abutments. Premade titanium, stainless steel, and gold abutments formed the control groups. Plastic abutments were cast in nickel-chromium, cobalt-chromium and grade IV titanium. The abutment/implant interface was analyzed. Analysis of variance and Duncan's multiple range test revealed no significant difference in mean marginal microgap between premade gold and titanium abutments and between premade stainless steel and cast titanium abutments. Statistically significant differences (P < .001) were found among all other groups.

Mercury intrusion porosimetry and assessment of cement-dentin interface of anti-washout-type mineral trioxide aggregate.

INTRODUCTION: One of the disadvantages of mineral trioxide aggregate (MTA) is washout (ie, the tendency of freshly prepared cement paste to disintegrate upon early contact with physiological fluids). A novel MTA (MTA Plus; Prevest Denpro, Jammu City, India) exhibits low washout and superior physical properties when mixed with a gel instead of water. When used as a root-end filler, MTA is in contact with both bone and root dentin. This study aimed to investigate the porosity and interfacial characteristics of the novel MTA mixed with water or antiwashout gel. METHODS: Porosity was evaluated after 1 or 28 days of immersion in Hank's balanced salt solution using mercury intrusion porosimetry. The root dentin to material interface was investigated using a scanning electron microscope and energy-dispersive X-ray spectroscopy complete with line scans and elemental maps. RESULTS: Anti-washout-type MTA Plus was found to have lower initial porosity than MTA Plus mixed with water although this trend was reversed after 28 days of immersion in physiological fluid. Both materials exhibited good marginal adaptation. The diffusion of silicon, calcium, and phosphorus across the cement/dentin interface was observed. CONCLUSIONS: MTA Plus mixed with antiwashout gel was found to have lower initial porosity than MTA Plus mixed with water. Both materials exhibited good marginal adaptation and the diffusion of silicon, calcium, and phosphorous across the cement/dentin interface. Thus, the anti-washout-type MTA can be considered to be a suitable substitute for ordinary MTA in all its indications.

Accuracy of ringless casting and accelerated wax-elimination technique: a comparative in vitro study.

PURPOSE: The purpose of this study was to determine whether the ringless casting and accelerated wax-elimination techniques can be combined to offer a cost-effective, clinically acceptable, and time-saving alternative for fabricating single unit castings in fixed prosthodontics. MATERIALS AND METHODS: Sixty standardized wax copings were fabricated on a type IV stone replica of a stainless steel die. The wax patterns were divided into four groups. The first group was cast using the ringless investment technique and conventional wax-elimination method; the second group was cast using the ringless investment technique and accelerated wax-elimination method; the third group was cast using the conventional metal ring investment technique and conventional wax-elimination method; the fourth group was cast using the metal ring investment technique and accelerated wax-elimination method. The vertical marginal gap was measured at four sites per specimen, using a digital optical microscope at 100× magnification. The results were analyzed using two-way ANOVA to determine statistical significance. RESULTS: The vertical marginal gaps of castings fabricated using the ringless technique (76.98 ± 7.59 µm) were significantly less (p < 0.05) than those castings fabricated using the conventional metal ring technique (138.44 ± 28.59 µm); however, the vertical marginal gaps of the conventional (102.63 ± 36.12 µm) and accelerated wax-elimination (112.79 ± 38.34 µm) castings were not statistically significant (p > 0.05). CONCLUSIONS: The ringless investment technique can produce castings with higher accuracy and can be favorably combined with the accelerated wax-elimination method as a vital alternative to the time-consuming conventional technique of casting restorations in fixed prosthodontics.

Practice-based clinical evaluation of ceramic single crowns after at least five years.

STATEMENT OF PROBLEM: Long-term practice-based clinical evaluations of various contemporary ceramic crown restorations from multiple practitioners are limited. PURPOSE: The aims of this study were to evaluate the clinical performance of ceramic single crowns and to identify factors that influence their clinical performance. MATERIAL AND METHODS: Ceramic single crowns that had been placed at the Mayo Clinic and in function since 2005 were identified and included in the study. The restorations were examined clinically, radiographically, and with photographs. Modified United States Public Health Services criteria were used for the clinical evaluation. The ceramic systems evaluated were bilayer and monolayer. RESULTS: Fifty-nine patients (41 women, 18 men) with 226 single teeth and implants restored with single ceramic crowns were identified. The mean duration from insertion date to study examination date was 6.1 years. Thirteen restorations (6%) were replaced at a mean 3.3 years after insertion date (range, 0.1-6.1 years). Estimated replacement-free survival rates (95% confidence interval [CI]; number of teeth/implants still at risk) at 5 years after insertion date were 95.1% (95% CI, 92.2-98.1; 153) and at 10 years were 92.8% (95% CI, 89.1-96.8; 8). The most common reason for replacement was fracture to the core of posterior layered ceramic crowns. The most commonly used luting agent was resin-modified ionomer cement. Most restorations exhibited clinically acceptable marginal integrity, shade, no caries recurrence, and no periapical pathology. CONCLUSIONS: The clinical performance of ceramic single crowns at 5 and 10 years supports their application in all areas of the mouth. With the majority of fractures to the core occurring early in the lifetime of layered ceramic posterior crowns, consideration of other monolithic ceramic systems for posterior crowns is advised.

Clinically relevant fracture testing of all-ceramic crowns.

OBJECTIVES: Fracture strength measured in vitro indicates that most all-ceramic crowns should be able to withstand mastication forces. Nevertheless, fractures are one of the major clinical problems with all-ceramic restorations. Furthermore, the fracture mode of all-ceramic crowns observed in clinical use differs from that found in conventional fracture strength tests. The aim of the present study was to develop and investigate a method that simulates clinical fracture behavior in vitro. METHODS: 30 crowns with alumina cores were made to fit a cylindrical model with a molar-like preparation design. These crowns were randomly allocated to 3 tests groups (n=10). The crowns in group 1 were cemented to abutment models of epoxy and subsequently fractured by occlusal loading without contact damage. The crowns in group 2 were fractured by cementation with expanding cement. The crowns in group 3 were cemented on an abutment model of epoxy split almost in two and fractured by increasing the diameter of the model in the bucco-lingual direction. The fractured crowns were analyzed by fractographic methods and compared to a reference group of 10 crowns fractured in clinical use. RESULTS: The fracture modes of all the in vitro crowns were similar to clinical fracture modes. The fracture modes in group 1 were most closely matched to the clinical fractures. These crowns also fractured at clinically relevant loads. CONCLUSION: Laboratory tests that induce a distortion of the abutment model during occlusal loading without occlusal contact damage can simulate clinical fractures of all-ceramic crowns.

Effect of proanthocyanidin treatment on the bonding effectiveness of adhesive restorations in pulp chamber.

OBJECTIVE: To analyze the effect of proanthocyanidin (PA) treatment of the pulp chamber dentin after NaOCl and EDTA irrigation on the microleakage and interfacial morphology of adhesive restorations. STUDY DESIGN: Pulp chambers of 66 extracted permanent molars were exposed. In half of the samples, pulp chamber dentin was bonded with Clearfil S3 after irrigation with normal saline (Group1a); 1% NaOCl and 17% EDTA (Group1b) or 1% NaOCl, 17% EDTA and 30% PA (Group1c) and in other half samples, pulp chamber dentin was bonded with Futurabond NR after irrigation with normal saline (Group 2a); 1% NaOCl and 17% EDTA (Group 2b) or 1% NaOCl, 17% EDTA and 30% PA (Group 2c). After adhesive procedures, Filtek Z 250 restorations were placed in the pulp chambers. Microleakage assessment was done in ten samples from each group and scanning electron microscopic examination was done in one sample from each group. Statistical analysis was done using Mann-Whitney and Kruskal Wallis tests at a significance level of P<0.05. RESULTS: Both the adhesives showed extensive microleakage. NaOCl and EDTA irrigation had no significant effect on the microleakage of both the adhesives. PA treatment of the pulp chamber dentin after NaOCl and EDTA irrigation significantly reduced microleakage in both the adhesives. CONCLUSION: It was concluded that 1 minute application of 30% proanthocyanidin solution in the pulp chamber after NaOCl and EDTA irrigation improved the subsequent bonding of self-etch adhesives to pulp chamber dentin.

Inhibition of enamel mineral loss by fissure sealant: an in situ study.

OBJECTIVES: This study evaluated the effect of fluoride and non-fluoride sealants on hardness decrease (HD) and marginal adaptation (MA) on enamel substrates after cariogenic challenge. METHODS: Occlusal enamel blocks, from human third molars, were randomly divided into six groups (n=12), according to occlusal fissures condition (S - sound; C - caries-like lesion; CF - caries-like lesion+topical fluoride) and sealants (F - FluroShield; H - Helioseal Clear Chroma). Lesion depths were 79.3±33.9 and 61.3±23.9 for C and CF groups, respectively. Sealants were placed on occlusal surface and stored at 100% humidity (37°C; 24h/d). HD was measured by cross-sectional microhardness analysis at the sealant margin distances: -1 (under sealant), 0 (sealant margin), 1, 2 (outer sealant). Sealant MA was observed by polarized light microscopy and scored according to: 0 - failure (no sealant MA or total sealant loss); 1 - success (sealant MA present). MA and HD were analysed by ANOVA-R and mixed model analysis, respectively. RESULTS: For HD (ΔS), F values (6900.5±3686.6) were significantly lower than H values (8534.6±5375.3) regardless of enamel substrates and sealant margin distances. Significant differences were observed among sealant margin distances: -1 (5934.0±3282.6)<0 (8701.5±6175.7)=1 (8473.2±4299.4)=2 (7761.5±4035.1), regardless of sealant and substrate. MA was similar for all groups (p≥0.05). CONCLUSION: MA was not affected by sealant type or substrate condition, whereas enamel HD was favourably impacted by fluoride in the sealant. In addition, sealants were more effective as a physical barrier than as its chemical potency in reducing enamel HD. CLINICAL SIGNIFICANCE: Sealing with a fluoride material is a recommended procedure to prevent caries of occlusal permanent molars in high-caries-risk patients, even though those exhibiting white spot lesions, since the enamel hardness decrease when fluoride sealant was used in vitro.

Improvement to the marginal coping fit of commercially pure titanium cast in phosphate-bonded investment by using a simple pattern coating technique.

STATEMENT OF PROBLEM: Coatings of zirconite, Y(2)O(3) or ZrO(2) on wax patterns before investing in phosphate-bonded investments have been recommended to reduce the reaction layer in titanium castings, but they are not easily obtainable. Spinel-based investments are relatively stable with molten titanium and could be used as coatings to improve the quality of castings made with those investments. PURPOSE: The purpose of this study was to evaluate the effect of pattern coating with a commercial spinel-based investment before investing in 1 of 3 phosphate-bonded inves tments on the marginal coping fit and surface roughness of commercially pure titanium castings. MATERIAL AND METHODS: Ten square acrylic resin patterns (12 × 12 × 2 mm) per group were invested in the phosphate-bonded investments Rematitan Plus (RP), Rema Exakt (RE), and Castorit Super C (CA) with or without a coating of the spinel-based investment, Rematitan Ultra (RU). After casting, the specimens were cleaned and the surface roughness was measured with a profilometer. Copings for dental implants with conical abutment were invested, eliminated, and cast as previously described. The copings were cleaned and misfit was measured with a profile projector (n=10). For both tests, the difference between the mean value of RU only and each value of the phosphate-bonded investment was calculated, and the data were analyzed by 2-way ANOVA and Tukey's HSD test (α=.05). In addition, the investment roughness was measured in bar specimens (30 × 10 × 10 mm), and the data (n=10) were analyzed by 1-way ANOVA and Tukey's HSD post hoc test (α=.05). RESULTS: Two-way ANOVA for casting surface roughness was significant because of the investment, the coating technique, and the interaction between variables. One-way ANOVA was performed to prove the interaction term, and Tukey's post hoc test showed that RP with coating had the lowest mean, while RP had the highest. CA with coating was not different from RP with coating or CA without coating. RE with coating was similar to CA, while RE was different from all groups. For coping marginal fit, the 2-way ANOVA was significant for the investment, the coating technique, and the interaction between variables. The interaction was analyzed by1-way ANOVA and Tukey's HSD test that showed no significant difference among the coated groups, which had better marginal fit than the groups without coating. Among the groups without coating, CA had significant lower marginal misfit than RP, while RE was not different from CA and RP. For the investment surface roughness, the 1-way ANOVA was significant. CA and RU were smoother than RE and RP (P<.001). CONCLUSIONS: The coating technique improved the quality of castings fabricated with phosphate-bonded investments.

Influence of CAD/CAM systems and cement selection on marginal discrepancy of zirconia-based ceramic crowns.

PURPOSE: To analyze the effect of ceramic manufacturing technique and luting cement selection on the marginal adaptation of zirconium oxide-based all-ceramic crowns. METHODS: An extracted mandibular first premolar was prepared for a complete coverage restoration and subsequently duplicated 40 times in a liquid crystal polymer (LCP). All-ceramic crowns (n = 10) were fabricated on LCP models using the following systems: glass-infiltrated zirconia-toughened alumina (In-Ceram Zirconia) and yttrium cation-doped tetragonal zirconia polycrystals (In-Ceram YZ, Cercon, and Procera Zirconia). The restorations (n = 5) were cemented on their respective dies with glass-ionomer cement (Ketac Cem Aplicap) and resin cement (Panavia 21). The absolute marginal discrepancy of the crowns was measured before and after cementation by scanning electronic microscopy at 160 points along the circumferential margin. The data were analyzed using one-way ANOVA for repeated measures and for independent samples, Scheffé's multiple range post hoc test, and Student's t-test (alpha = 0.05). RESULTS: There were statistical differences in the mean marginal openings among the four all-ceramic systems before and after luting (P < 0.0001). The Procera restorations had the lowest pre- and post-cementation values (P < 0.0001). A significant increase in the marginal gap size caused by luting media occurred in all tested groups (P < 0.0001). Resin cement resulted in larger marginal discrepancies than glass-ionomer cement (P < 0.0001).

Internal fit of two all-ceramic systems and metal-ceramic crowns.

OBJECTIVES: The aim of this study was to investigate the internal fit (IF) of glass-infiltrated alumina (ICA--In-Ceram Alumina), yttria-stabilized tetragonal zirconia polycrystals (Y-TZP--IPS e.max ZirCAD), and metal-ceramic (MC--Ni-Cr alloy) crowns. MATERIAL AND METHODS: Sixty standardized resin-tooth replicas of a maxillary first molar were produced for crown placement and divided into 3 groups (n=20 each) according to the core material used (metal, ICA or Y-TZP). The IF of the crowns was measured using the replica technique, which employs a light body polyvinyl siloxane impression material to simulate the cement layer thickness. The data were analyzed according to the surfaces obtained for the occlusal space (OS), axial space (AS) and total mean (TM) using two-way ANOVA with Tukey's multiple comparison test (p<0.05). RESULTS: No differences among the different areas were detected in the MC group. For the Y-TZP and ICA groups, AS was statistically lower than both OS and TM. No differences in AS were observed among the groups. However, OS and TM showed significantly higher values for ICA and Y-TZP groups than MC group. Comparisons of ICA and Y-TZP revealed that OS was significantly lower for Y-TZP group, whereas no differences were observed for TM. CONCLUSIONS: The total mean achieved by all groups was within the range of clinical acceptability. However, the metal-ceramic group demonstrated significantly lower values than the all-ceramic groups, especially in OS.

Internal fit of two all-ceramic systems and metal-ceramic crowns

OBJECTIVES: The aim of this study was to investigate the internal fit (IF) of glass-infiltrated alumina (ICA - In-Ceram Alumina), yttria-stabilized tetragonal zirconia polycrystals (Y-TZP - IPS e.max ZirCAD), and metal-ceramic (MC - Ni-Cr alloy) crowns. MATERIAL AND METHODS: Sixty standardized resin-tooth replicas of a maxillary first molar were produced for crown placement and divided into 3 groups (n=20 each) according to the core material used (metal, ICA or Y-TZP). The IF of the crowns was measured using the replica technique, which employs a light body polyvinyl siloxane impression material to simulate the cement layer thickness. The data were analyzed according to the surfaces obtained for the occlusal space (OS), axial space (AS) and total mean (TM) using two-way ANOVA with Tukey ’s multiple comparison test (p<0.05). RESULTS: No differences among the different areas were detected in the MC group. For the Y-TZP and ICA groups, AS was statistically lower than both OS and TM. No differences in AS were observed among the groups. However, OS and TM showed significantly higher values for ICA and Y-TZP groups than MC group. Comparisons of ICA and Y-TZP revealed that OS was significantly lower for Y-TZP group, whereas no differences were observed for TM. CONCLUSIONS: The total mean achieved by all groups was within the range of clinical acceptability. However, the metal-ceramic group demonstrated significantly lower values than the all-ceramic groups, especially in OS.

The effect of different fabrication steps on the marginal adaptation of two types of glass-infiltrated ceramic crown copings fabricated by CAD/CAM technology.

PURPOSE: Marginal adaptation is an important factor affecting the longevity of all-ceramic restorations, although the effects of different fabrication steps on marginal adaptation at various stages of fabrication are not fully understood. The purpose of this study was to assess with an in vitro model whether In-Ceram alumina (IA) or In-Ceram zirconia (IZ) copings produced by the CAD/CAM method would be clinically acceptable, and to evaluate the effect of each fabrication step (post-milling, post-trimming, and post-glass infiltration) on the marginal discrepancy of the coping. MATERIALS AND METHODS: A melamine tooth was prepared, duplicated, poured with inlay wax, and then cast with metal to fabricate a master die. An InLab 3D system was used to scan the master die and to design and mill the copings. Thirty IA and IZ copings each were developed with thicknesses of 0.6 mm and a 30-µm thick computer luting space. Epoxy resin replicas of the master die were fabricated, and the vertical and horizontal marginal discrepancies were measured using a Micro-Vu optical microscope at three stages of the fabrication (post-milling, post-trimming, post-infiltration). One-way ANOVA was used to analyze the data between the three stages of fabrication for each marginal discrepancy, and a t-test was used to compare vertical and horizontal marginal discrepancies (after glass infiltration) between IZ and IA copings RESULTS: There were no significant differences (p > 0.05) in the vertical marginal discrepancies (µm) between IA (36 ± 14) and IZ (40 ± 14) copings after glass infiltration. ANOVA (comparing three stages within horizontal marginal discrepancy for IZ copings) showed that post-milling (40 ± 26) > post-trimming (23 ± 11) = post-infiltration (19 ± 13). ANOVA (comparing three stages within vertical marginal discrepancy for IZ copings) showed that post-milling (53 ± 12) = post-trimming (47 ± 13) > post-infiltration (36 ± 14). ANOVA (comparing three stages within horizontal marginal discrepancy for IA copings) showed that post-milling (52 ± 28) > post-trimming (30 ± 16) > post-infiltration (30 ± 16). ANOVA (comparing three stages within vertical marginal discrepancy for IA copings) showed that post-milling (54 ± 13) = post-trimming (56 ± 26) > post-infiltration (40 ± 14). CONCLUSION: There was no significant difference in the marginal adaptation of both material copings. After the trimming process, the glass infiltration firing cycle improved the vertical marginal discrepancy for both IZ and IA copings. Clinical implications. IA and IZ copings fabricated by CAD/CAM technology have an acceptable marginal fit as documented in the literature, and the glass infiltration process improves the marginal fit after machining.

Effect of axial wall modification on the retention of cement-retained, implant-supported crowns.

STATEMENT OF PROBLEM: Compromised angulation of implants may result in abutment preparation that is less than ideal. Compromised abutment preparation may affect the retention of implant-retained crowns. PURPOSE: The purpose of this study was to investigate the effect of 5 implant abutment designs on the retention of cement-retained crowns by varying the number and position of the axial walls. MATERIAL AND METHODS: Five prefabricated abutments were attached to an implant analog and embedded in an acrylic resin block. The first abutment was left intact without modification. Axial walls were partially removed from the remaining abutments to produce abutments with 3 walls, 2 adjacent walls, 2 opposing walls, and 1 wall. Five crowns were made for each group. The screw access channel for the first abutment was completely filled with composite resin and the rest were partially filled. The retentive surface area of each abutment was calculated. Crowns were cemented with zinc phosphate cement. Tensile force was applied to separate the castings from the abutments. Peak load to dislodgment was recorded. A 1-way ANOVA was used to test for a significant difference followed by the Tukey Honestly Significant Difference test (α=.05). RESULTS: The abutment with 2 opposing axial walls had significantly higher retention than that of all other groups (F=149.9, df =24, P<.001). The abutment with 3 walls exhibited the second highest retention and was significantly greater than abutments with 2 adjacent walls, 1, and 4 walls. Abutments with 2 adjacent walls and 1 wall were not significantly different from each other. The unmodified abutment with 4 walls exhibited the lowest retention despite having a large retentive surface area. CONCLUSIONS: The retention of cemented crowns on implant abutments is influenced by the number and position of axial walls.

X-ray microtomographic evaluation of the influence of two preparation types on marginal fit of CAD/CAM alumina copings: a pilot study.

This study evaluated the influence of two preparation types on the marginal fit of computer-aided design/computer-assisted manufacture (CAD/CAM) alumina copings. Two subgroups of four alumina copings each were fabricated using alumina master dies with either a chamfer or 90-degree shoulder preparation. Copings were scanned with an x-ray microtomographic scanner, and marginal fit was evaluated. The preparation types presented no statistically significant differences regarding marginal gap (P = .410) and absolute marginal discrepancy (P = .229). No correlation was found between marginal fit of CAD/CAM alumina copings and preparation type. Marginal fit could be considered within the limits of clinical acceptance.

Clinical evaluation of 209 all-ceramic single crowns cemented on natural and implant-supported abutments with different luting agents: a 6-year retrospective study.

BACKGROUND: The Procera AllCeram™ system (Nobel Biocare AB, Göteborg, Sweden) is a valid alternative to metal-ceramic restorations. However, limited long-term data of its use for single crowns on natural and implant-supported abutments are available. PURPOSE: The present study aimed at evaluating the clinical performances of Procera AllCeram single crowns in both anterior and posterior regions of the oral cavity either on natural tooth or implant abutments over a period of 6 years. MATERIALS AND METHODS: Two hundred nine single crowns were fabricated and used in 112 patients. Zinc phosphate and resin luting agents were used to cement the restorations. The crowns were evaluated according to the California Dental Association's quality assessment system. RESULTS: Three crowns were lost at follow-up. Of the 206 restorations, which completed the 6-year follow-up, 9 crowns were affected by mechanical complications and 7 crowns failed. All surviving crowns were ranked as either excellent or acceptable. Cumulative survival and success rates of 95.2 and 90.9%, respectively, were recorded. CONCLUSIONS: Within the limitations of the present study, Procera AllCeram crowns proved to be a reliable clinical option to restore both anterior and posterior missing teeth either on natural or implant abutments. The resin cement used in the present study performed better than the zinc phosphate luting agent.