Effect of seating force on film thickness of new adhesive luting agents

Comparison of fit and trueness of zirconia crowns fabricated by different combinations of open CAD-CAM systems

PURPOSE

This study aims to clinically compare the fitness and trueness of zirconia crowns fabricated by different combinations of open CAD-CAM systems.

MATERIALS AND METHODS

Total of 40 patients were enrolled in this study, and 9 different zirconia crowns were prepared per patient. Each crown was made through the cross-application of 3 different design software (EZIS VR, 3Shape Dental System, Exocad) with 3 different processing devices (Aegis HM, Trione Z, Motion 2). The marginal gap, absolute marginal discrepancy, internal gap(axial, line angle, occlusal) by a silicone replica technique were measured to compare the fit of the crown. The scanned inner and outer surfaces of the crowns were compared to CAD data using 3D metrology software to evaluate trueness.

RESULTS

There were significant differences in the marginal gap, absolute marginal discrepancy, axial and line angle internal gap among the groups (P < .05) in the comparison of fit. There was no statistically significant difference among the groups in terms of occlusal internal gap. The trueness ranged from 36.19 to 43.78 µm but there was no statistically significant difference within the groups (P > .05).

CONCLUSION

All 9 groups showed clinically acceptable level of marginal gaps ranging from 74.26 to 112.20 µm in terms of fit comparison. In the comparison of trueness, no significant difference within each group was spotted. Within the limitation of this study, open CAD-CAM systems used in this study can be assembled properly to fabricate zirconia crown.

Luting indirect restorations with resin cements versus composite resins: Effects of preheating and ultrasound energy on film thickness

OBJECTIVE

This study aims to evaluate and compare the film thickness obtained with a resin cement and two composite resins, preheated and/or ultrasonically vibrated, as luting agents.

MATERIALS AND METHODS

One hundred and twenty-six (126) pairs of resin discs were randomly assigned to six experimental groups (n = 21) according to luting agent (Variolink Esthetic LC, IPS Empress Direct or Estelite Omega) and cementation technique (preheating at 68°C and/or ultrasonic vibration). Specimens were luted by applying a controlled force. Following sectioning and film thickness measurement through field emission gun scanning electron microscopy, statistical analysis was carried out considering a 5% significance level.

RESULTS

Statistically significant lower film thickness was observed in Variolink Esthetic LC group when compared to all composite resin groups (p < 0.001), except IPS Empress Direct preheated and ultrasonically vibrated group (p = 0.073). IPS Empress Direct with ultrasonic vibration yielded statistically lower film thickness values than Estelite Omega groups, regardless of luting technique (p < 0.05). Ultrasonically vibrated Estelite Omega groups showed statistically lower film thickness values than solely preheated groups (p < 0.05).

CONCLUSIONS

Both Variolink Esthetic LC and IPS Empress Direct preheated and ultrasonically vibrated provided the lowest film thickness. The addition of ultrasonic vibration during cementation proved to be effective in reducing film thickness of both tested composite resins.

CLINICAL SIGNIFICANCE

The cementation technique will have variable results depending on the luting material. Adhesive cementation protocols with composite resins should mainly consider ultrasonic vibration, but also preheating, as strategies for reducing film thickness. The tested resin cement, alongside with IPS Empress Direct composite resin preheated and ultrasonically vibrated, provided the lowest film thickness among the tested materials and techniques.

Wear and marginal quality of aesthetic crowns for primary molars

BACKGROUND

Due to limited aesthetics of stainless-steel crowns, the demand for tooth-coloured crowns has recently risen. Few studies have investigated the marginal integrity and wear behaviour of tooth-coloured primary molar crowns under subcritical load in vitro.

AIM

This in vitro study evaluated the marginal quality and wear of newly introduced resin composite and hybrid ceramic crowns compared with metal and zirconia crowns.

DESIGN

Metal, resin composite, hybrid ceramic (CAD/CAM), and various zirconia crowns were investigated. After thermomechanical loading (2,500 thermocycles/100,000 × 50N), marginal quality of luting gaps and wear of crowns/antagonists were evaluated using replicas under a light or 3D laser scanning microscope. Results were analysed with the Mann-Whitney U test or one-way ANOVA (p < .05).

RESULTS

Marginal quality of the new resin composite and hybrid ceramic crowns performed well in comparison with SSC and zirconia crowns. Adhesive bonding of crowns resulted in superior marginal seal compared with conventional GIC (Mann-Whitney U test, p < .05). Regarding wear, zirconia crowns exhibited significantly worse results than resin composite or hybrid ceramic crowns and SSCs (ANOVA, p < 0.05).

CONCLUSION

The new resin composite and hybrid ceramic crown exhibited good performance in comparison with SSCs and zirconia crowns considering both wear and marginal quality after subcritical loading.

Effects of precementation on minimizing residual cement around the marginal area of dental implants

STATEMENT OF PROBLEM

Residual cement is detrimental to the long-term success of dental implants with a cement-retained restoration. The complete elimination of excess cement remains a challenge.

PURPOSE

The purpose of this in vitro study was to evaluate the effects of precementation technique on minimizing the residual cement and retention of restorations.

MATERIAL AND METHODS

Four custom cobalt-chromium alloy (Co-Cr) abutments were manufactured by computer-aided design and computer-aided manufacturing (CAD-CAM) as precementation abutments with height and radius reductions of 25 μm (A25), 50 μm (A50), 75 μm (A75), and 100 μm (A100). Fifty CAD-CAM-fabricated standard Co-Cr abutments and corresponding crowns were randomly matched and treated as follows: 10 specimens were cemented with the conventional cementation procedure with glass ionomer cement (G0), and 40 were precemented with precementation abutments (n=10) before the definitive cementation with standard abutments (G25, G50, G75, G100). The weight of the cement in the cement space was calculated, and the marginal sealing was evaluated by using a stereoscopic microscope. The effects of precementation with resin cement on minimizing residual cement around the marginal area of dental implants were further evaluated extraorally. The influence of precementation with glass ionomer and resin cement on the retention force was analyzed by using a universal testing machine at a crosshead speed of 0.5 mm/min. One-way ANOVA was used to analyze cement mass and marginal sealing values. Two-way ANOVA was used to compare the retention forces (α=.05).

RESULTS

The cement weight of G50 (7.2 ±0.6 mg) was significantly higher than that of G25 (6.0 ±1.1 mg, P<.05), while no significant differences in cement weights were found among G50, G75, and G100. Consistently, the G50, G75, and G100 had higher marginal sealing values than that of the G25 (P<.01). Extraoral experiments showed that the precementation with A50 reduced subgingival residual cement without affecting retention.

CONCLUSIONS

These in vitro results suggest that precementation with a precisely manufactured precementation abutment minimized the residual cement around implant abutments, and 50 μm could be a preferable precementation space.

Comparison of the fit of cast gold crowns fabricated from the digital and the conventional impression techniques

PURPOSE

The purpose of this study was to compare the fit of cast gold crowns fabricated from the conventional and the digital impression technique.

MATERIALS AND METHODS

Artificial tooth in a master model and abutment teeth in ten patients were restored with cast gold crowns fabricated from the digital and the conventional impression technique. The forty silicone replicas were cut in three sections; each section was evaluated in nine points. The measurement was carried out by using a measuring microscope and I-Soultion. Data from the silicone replica were analyzed and all tests were performed with α-level of 0.05.

RESULTS

1. The average gaps of cast gold crowns fabricated from the digital impression technique were larger than those of the conventional impression technique significantly. 2. In marginal and internal axial gap of cast gold crowns, no statistical differences were found between the two impression techniques. 3. The internal occlusal gaps of cast gold crowns fabricated from the digital impression technique were larger than those of the conventional impression technique significantly.

CONCLUSION

Both prostheses presented clinically acceptable results with comparing the fit. The prostheses fabricated from the digital impression technique showed more gaps, in respect of occlusal surface.

Radiopacity of Composite Luting Cements Using a Digital Technique

PURPOSE

The aim of this in vitro study was to evaluate the radiopacity of 20 common dental composite luting materials using a digital technique.

MATERIALS AND METHODS

A 1-mm-thick specimen of each material with a human tooth slice and aluminium step wedge were tested using digital radiographs under four combinations of exposure and voltage. The radiopacity in pixels was determined using computer software. The equivalent thickness of aluminium for each material was then calculated based on the calibration curve.

RESULTS

All tested materials except one had higher radiopacity than dentin (p > α; α  =  0.01), and 80% of the materials had radiopacity above enamel value (p > α; α  =  0.01). Moreover, 40% of tested materials had radiopacity of three times above the minimal International Organization for Standardization (ISO) values for composite luting cements. At all exposure values, the highest radiopacity was for Solocem and Multilink groups of materials, at three to six times above dentin radiopacity. Only Variolink Veneer showed radiopacity below dentin and enamel.

CONCLUSIONS

Composite luting materials should have radiopacity above ISO values or greater than the dentin or enamel equivalent. The highest radiopacity values were for the Solocem and Multilink family composite luting cements. Clinicians should choose materials with high radiopacity values, and manufacturers should be aware of the radiopacity values when introducing materials on the market.

Evaluation of marginal fit and internal adaptation of zirconia copings fabricated by two CAD - CAM systems: An in vitro study

Statement of Problem:

Three main factors which determine the success of an All-ceramic restoration are esthetic value, resistance to fracture and third being the marginal fit. Marginal fit and internal adaptation are crucial factors in increasing the longevity of the restoration. Newer and economical CAD CAM systems have been introduced claiming better marginal fit and adaptation of All ceramic crowns. CAD CAM systems involves scanning of the die or the tooth preparation and milling of the restoration, which may have variations among the systems available.

Aim of the Study:

Our study intended to check the marginal fit and internal adaptation of commonly used CAD CAM systems namely CERAMILL and CEREC -In Lab MC XL.

Materials and Methods:

Two groups of typodont teeth (n = 10) were prepared using a standardized protocol to receive All ceramic copings. 10 samples of Group A were used for fabrication of copings using CERAMILL system and 10 samples of Group B were used for fabrication of copings using CEREC -In Lab MC XL system. They were then luted with glass ionomer cement under mild finger pressure. Samples were embedded in resin and sliced longitudinally. They were then viewed under stereomicroscope and readings were measured along 15 points using ImageScope software. The P value was set at 0.05 at 95% confidence interval with 80% power. The data were checked for normality and unpaired t-test was used to evaluate the results of the two groups.

Results:

The overall internal adaptation was 61.5 ± 5.2 μm for CERAMILL and 56.9 ± 5.7 μm for CEREC -In Lab MC XL (P < 0.05). The marginal fit for CERAMILL was 83 μm and for CEREC -In Lab MC XL was 68 μm (P < 0.05).

Conclusion:

The marginal adaptation of CEREC -In Lab MC XL (68 μm) was found to be superior to CERAMILL (83 μm) (P < 0.05). Both the CEREC -In Lab MC XL and CERAMILL copings demonstrated internal adaptation and marginal fit within acceptable discrepancy range. When corroborating both the internal adaptation and marginal fit, CEREC -In Lab MC XL was found to be better than CERAMILL.

Radiopacity evaluation of contemporary luting cements by digitization of images

Objective. The aim of this study was to evaluate the radiopacity of two conventional cements (Zinc Cement and Ketac Cem Easymix), one resin-modified glass ionomer cement (RelyX Luting 2) and six resin cements (Multilink, Bistite II DC, RelyX ARC, Fill Magic Dual Cement, Enforce and Panavia F) by digitization of images. Methods. Five disc-shaped specimens (10 × 1.0 mm) were made for each material, according to ISO 4049. After setting of the cements, radiographs were made using occlusal films and a graduated aluminum stepwedge varying from 1.0 to 16 mm in thickness. The radiographs were digitized, and the radiopacity of the cements was compared with the aluminum stepwedge using the software VIXWIN-2000. Data (mmAl) were submitted to one-way ANOVA and Tukey's test (α = 0.05). Results. The Zinc Cement was the most radiopaque material tested (P < 0.05). The resin cements presented higher radiopacity (P < 0.05) than the conventional (Ketac Cem Easymix) or resin-modified glass ionomer (RelyX Luting 2) cements, except for the Fill Magic Dual Cement and Enforce. The Multilink presented the highest radiopacity (P < 0.05) among the resin cements. Conclusion. The glass ionomer-based cements (Ketac Cem Easymix and RelyX Luting 2) and the resin cements (Fill Magic Dual Cement and Enforce) showed lower radiopacity values than the minimum recommended by the ISO standard.

Vertical misfit of laser-sintered and vacuum-cast implant-supported crown copings luted with definitive and temporary luting agents

OBJECTIVES

This study aimed to evaluate the vertical discrepancy of implant-supported crown structures constructed with vacuum-casting and Direct Metal Laser Sintering (DMLS) technologies, and luted with different cement types.

STUDY DESIGN

Crown copings were fabricated using: (1) direct metal laser sintered Co-Cr (LS); (2) vacuum-cast Co-Cr (CC); and (3) vacuum-cast Ti (CT). Frameworks were luted onto machined implant abutments under constant seating pressure. Each alloy group was randomly divided into 5 subgroups (n = 10 each) according to the cement system utilized: Subgroup 1 (KC) used resin-modified glass-ionomer Ketac Cem Plus; Subgroup 2 (PF) used Panavia F 2.0 dual-cure resin cement; Subgroup 3 (RXU) used RelyX Unicem 2 Automix self-adhesive dual-cure resin cement; Subgroup 4 (PIC) used acrylic/urethane-based temporary Premier Implant Cement; and Subgroup 5 (DT) used acrylic/urethane-based temporary DentoTemp cement. Vertical misfit was measured by scanning electron microscopy (SEM). Two-way ANOVA and Student-Newman-Keuls tests were run to investigate the effect of alloy/fabrication technique, and cement type on vertical misfit. The statistical significance was set at α = 0.05.

RESULTS

The alloy/manufacturing technique and the luting cement affected the vertical discrepancy (p < 0.001). For each cement type, LS samples exhibited the best fit (p < 0.01) whereas CC and CT frames were statistically similar. Within each alloy group, PF and RXU provided comparably greater discrepancies than KC, PIC, and DT, which showed no differences.

CONCLUSIONS

Laser sintering may be an alternative to vacuum-casting of base metals to obtain passive-fitting implant-supported crown copings. The best marginal adaptation corresponded to laser sintered structures luted with glass-ionomer KC, or temporary PIC or DT cements. The highest discrepancies were recorded for Co-Cr and Ti cast frameworks bonded with PF or RXU resinous agents. All groups were within the clinically acceptable misfit range.

Fracture strength of direct versus indirect laminates with and without fiber application at the cementation interface

OBJECTIVES

This study compared the fracture strength of direct and indirect resin composite laminate veneers and evaluated the effect of a bidirectional E-glass woven fiber application at different locations at the cementation interface.

METHODS

Standard preparations on canines (N=50, 10 per group) were made using a depth cutting bur (0.7mm depth) designed for laminate veneer restorations. Forty indirect laminates using a highly filled polymeric material (Estenia) and 10 direct laminates (Quadrant Anterior Shine) were prepared according to the manufacturer's instructions. Bidirectional E-glass woven-fiber sheet (0.06mm) (Everstick) was applied at different locations at the cementation interface. The control group received no fibers. The specimens were stored in water at 37 degrees C for 1 month prior to fracture testing performed in a universal testing machine where the load was applied from the incisal direction at 137 degrees (1mm/min).

RESULTS

No significant differences were found between the five groups (P>0.01) (one-way ANOVA). While indirect laminate veneers showed mean fracture strength of 247+/-47N, direct laminate veneers revealed 239+/-104N. The use of E-glass fibers at the cementation interface at different locations did not increase the fracture strength significantly (286-313N) (P>0.01). Failure analysis showed mainly cohesive fracture of the veneer restoration (20/50) and adhesive failure between the cementation interface and the laminate with fiber exposure (19/50) covering more than half of the restorations.

SIGNIFICANCE

Direct and indirect resin composite laminate veneers showed comparable mean fracture strengths. The use of E-glass woven-fiber sheet at the cementation interface did not increase the fracture strength of the polymeric laminate veneers.

Microleakage of various cementing agents for full cast crowns

OBJECTIVES

To evaluate microleakage and marginal gaps in full cast crown restorations bonded with six different types of cementing agents.

METHODS

Sixty non-carious human premolars and molars were prepared in a standardized manner for full cast crown restorations. The mesial and distal margins were located in dentin, while the vestibular and palatal/lingual margins were located in enamel. Crowns were made from a high-gold alloy using a standardized technique. The specimens were randomized to six groups of cementing agents: one zinc-phosphate cement (Harvard cement), one conventional glass-ionomer cement (Fuji I), one resin-modified glass-ionomer cement (Fuji Plus), two standard resin cements (RelyX ARC, Panavia F), and one self-adhesive universal resin cement (RelyX Unicem). After 4 weeks of storage in distilled water at 37 degrees C, the specimens were subjected to 5000 thermocycles ranging from 5 to 55 degrees C. Then, they were placed in a silver nitrate solution, embedded in resin blocks, and vertically cut in buccolingual and mesiodistal direction. Subsequently, the objects were evaluated for microleakage and marginal gap using a high-resolution digital microscope camera.

RESULTS

A number of inter-group differences were statistically significant. RelyX Unicem showed the smallest degree of microleakage both in enamel and in dentin. Panavia F und RelyX Unicem were associated with significantly larger marginal gaps than all other cementing agents. No association was observed between microleakage and marginal gap other than a weak direct correlation when using Harvard cement on enamel.

SIGNIFICANCE

The cementing agents investigated revealed different sealing abilities. These differences were not associated with specific types of materials.

Vertical marginal discrepancy of ceramic copings with different ceramic materials, finish lines, and luting agents: an in vitro evaluation

STATEMENT OF PROBLEM

Prosthetic restorations that fit poorly may affect periodontal health and occlusion. Studies that have evaluated the accuracy of fit of ceramic restorations before and after cementation assessed primarily intracoronal restorations.

PURPOSE

This in vitro study evaluated the effect of different finish lines, ceramic manufacturing techniques, and luting agents on the vertical discrepancy of ceramic copings.

MATERIAL AND METHODS

Two stainless steel molars were prepared for complete crowns with 2 different finish lines (heavy chamfer and rounded shoulder); each molar was duplicated to fabricate 90 copings. A total of 180 copings generated 18 groups (n=10 for each finish line-coping material-luting agent combination). Luting agents tested included zinc phosphate, resin-modified glass ionomer (Fuji Plus), and resin composite cements (Panavia F). A metal frame was developed on which to screw the stainless steel model and a ceramic coping; the distance (microm) between 2 predetermined points was measured before and after cementation by a profile projector under a torquing force. A 4-way ANOVA with repeated measurements was performed to assess the influence of each factor in the vertical marginal discrepancy: 3 between-coping factors (finish line-coping material-luting agent) and 1 within-coping factor (before and after cementation) (alpha=.05).

RESULTS

Procera copings presented the lowest mean values ( P <.05) of vertical marginal discrepancy before and after cementation (25/44 microm) when compared to Empress 2 (68/110 microm) and InCeram Alumina copings (57/117 microm), regardless of any combinations among all finish lines and luting agents tested.

CONCLUSION

Considering each factor separately, the ceramic manufacturing technique appeared to be the most important factor tested for the definitive vertical discrepancy of all-ceramic copings, with lower mean values for Procera copings.

Crowns and other extra-coronal restorations: try-in and cementation of crowns

Having successfully negotiated the planning, preparation, impression and prescription of your crown, the cementation stage represents the culmination of all your efforts. This stage is not difficult, but a successful outcome needs as much care as the preceding stages. Once a restoration is cemented there is no scope for modification or repeat You have to get it right first time. Decemented crowns often have thick layers of residual cement suggesting problems with either initial seating or cement handling. When the fate of restorations costing hundreds of pounds depends on correct proportioning of cements and the quality of the mix, the value of a well-trained and experienced dental nurse is easy to see. Both dentist and nurse need a working knowledge of the materials they are handling.

Effect of tooth surface roughness on marginal seating and retention of complete metal crowns

STATEMENT OF PROBLEM

Retention and marginal adaptation factors have major influence on the failure of cemented complete veneer crowns.

PURPOSE

This study investigated the effect of axial surface roughness on the marginal seating and retention of silver-palladium crowns luted with zinc phosphate, glass ionomer, and resin cements.

MATERIAL AND METHODS

Coarse and fine diamond stones were used to create various surface roughnesses of premolars. A milling machine was used to control the height and angle of the axial walls of tooth preparations. Ten cast metal crowns in 6 subgroups were luted with 3 cements (Phosphacap, Fuji Cap I, and Panavia 21). Marginal seating was recorded with a Digimatic indicator. Retention was determined by measuring the tensile force required to remove a metal crown with a Lloyd testing machine.

RESULTS

Two-way analysis of variance revealed statistically significant differences (P <.001) in retention for both luting cements and surface roughness. No significant difference was recorded for marginal seating relative to roughness (P =.860) and interaction effects (P =.204). Tukey-HSD tests revealed substantial differences in retention among Phosphacap, Fuji Cap I, and Panavia 21 cements. Significant differences were not confirmed in marginal seating between Fuji Cap I and Phosphacap cements with coarse diamonds, and Phosphacap and Panavia 21 cements with fine diamonds.

CONCLUSIONS

The best retention for complete metal crown was demonstrated for tooth preparations ground with coarse diamonds and cemented with Panavia 21 cement. Differences in axial surface roughness had no effect on the marginal seating of the complete metal crowns.

Dental luting agents: A review of the current literature

STATEMENT OF PROBLEM

The practice of fixed prosthodontic has changed dramatically with the introduction of innovative techniques and materials. Adhesive resin systems are examples of these changes that have led to the popularity of bonded ceramics and resin-retained fixed partial dentures. Today's dentist has the choice of a water-based luting agent (zinc phosphate, zinc polycarboxylate, glass ionomer, or reinforced zinc oxide-eugenol) or a resin system with or without an adhesive. Recent formulations of glass ionomer luting agents include resin components (resin-modified glass ionomers), which are increasingly popular in clinical practice.

PURPOSE

This review summarizes the research on these systems with the goal of providing information that will help the reader choose the most suitable material.

MATERIAL

The scientific studies have been evaluated in relation to the following categories: (1) biocompatibility, (2) caries or plaque inhibition, (3) microleakage, (4) strength and other mechanical properties, (5) solubility, (6) water sorption, (7) adhesion, (8) setting stresses, (9) wear resistance, (10) color stability, (11) radiopacity, (12) film thickness or viscosity, and (13) working and setting times. In addition, guidelines on luting-agent manipulation are related to available literature and include: (1) temporary cement removal, (2) smear layer removal, (3) powder/liquid ratio, (4) mixing temperature and speed, (5) seating force and vibration, and (6) moisture control. Tables of available products and their properties are also presented together with current recommendations by the authors with a rationale.

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 < or = .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 microns; 2) metal frameworks, 6.21 +/- 1.34 microns; 3) metal-ceramic crowns, 11.06 +/- 3.21 microns; and 4) zinc-phosphate cemented crowns, 31.47 +/- 6.65 microns. 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 microns).

Marginal discrepancy of ceramic crowns with redesigned implant components

A previous study indicated a mean marginal discrepancy of 169 microns (SD = 23) for cemented CeraOne ceramic crowns. Since then, the components have been redesigned by the manufacturer. This study assessed the marginal discrepancy of the new components by use of a video camera and stereomicroscope connected to a computer. Fifteen samples each of (a) ceramic caps (control), (b) ceramic caps fired once in a porcelain oven (c) ceramic crowns, and (d) cemented (zinc phosphate) ceramic crowns were examined. The results indicated that the mean marginal discrepancies were: caps 20.4 microns (SD = 10.8), fired caps 18.3 microns (SD = 9.3), crowns 28.1 microns (SD = 9.7), and cemented crowns 65.9 microns (SD = 15.8). Statistical analysis (ANOVA) revealed significant differences between these mean marginal discrepancies (p < 0.0001). A Scheffe F-test revealed no statistically significant difference between the means for caps, fired caps, and crowns, whereas cemented crowns had significantly greater mean marginal discrepancies compared with all uncemented retainers (p < 0.0001). The mean marginal discrepancy of the redesigned CeraOne ceramic system (cemented crowns) was reduced by more than 100 microns compared with the original design.

Effect of dynamic loading methods on cement film thickness in vitro

PURPOSE

Reduced cement flm thicknesses can improve crown seating and decrease marginal discrepancies. Improved marginal adaptation has the potential to reduce plaque accumulation, periodontal disease, and cement dissolution. Studies have indicated that dynamic seating methods can reduce seating discrepancies associated with zinc phosphate and resin cements. However, other types of cements and other dynamic techniques have not yet been studied or compared, nor has the mechanism for improved seating been fully explained. Therefore, the purpose of this study was to investigate the effect of a variety of loading methods on the film thicknesses of current types of crown and fixed partial denture cements compressed between glass plates.

MATERIALS AND METHODS

This study investigated the effect of three dynamic loading methods on film thickness of six representative fixed prosthodontic cements. These included zinc phosphate, resin-modified glass ionomer, encapsulated glass ionomer, adhesive composite resin, composite resin, and polycarboxylate. The method was derived from American Dental Association specifications for cement film thickness. In control groups, the cements were placed between two glass glass plates and statically loaded with a 15-kg weight. The test groups were initially similarly loaded, and then for 30 seconds further subjected to simulated repeated patient opening and closing, vibrations from an electromallet, or an ultrasonic device.

RESULTS

Mean film thicknesses ranged from 7.4 micrometers for polycarboxylate / ultrasound up to 40.3 micrometers for composite resin / static. Two-way analysis of variance revealed that the effects of material type and cementation method and their interaction all significantly affected film thickness (P < .0001). Multiple range analysis showed that dynamic methods were generally superior to static loading and that the ultrasonic method was the best overall.

CONCLUSIONS

The different dynamic loading methods all significantly decreased cement film thicknesses between glass plates. The ultrasonic method was the most effective. The type of cement used also influenced film thickness. Composite resins were more affected than other materials.

In vivo marginal adaptation of cast crowns luted with different cements

Large marginal crown discrepancies are deleterious. Although previous studies have examined casting seating in vitro, few have evaluated the effects of different luting cements on in vivo seating. Hence this in vivo study compared marginal discrepancies created by different cements on cast crowns. Tooth preparations were completed according to acceptable procedures on previously intact human molars that were severely periodontally compromised and scheduled for extraction. Castings were made by conventional techniques. The castings were randomly assigned to the following luting agents: zinc phosphate cement, resin-modified glass-ionomer cement, and the same resin-modified glass-ionomer cement with a dentinal bonding agent. After 6 months the teeth were carefully extracted, embedded, and sectioned, and vertical and horizontal discrepancies were measured. Analysis of variance revealed that all cements resulted in similar discrepancies. Vertical discrepancies were considerably greater than horizontal discrepancies, and the distributions of marginal discrepancies were skewed towards upper ranges.

Luting cement-metal surface physicochemical interactions on film thickness

Low film thickness is critical to the clinical success of cemented castings. This study investigated the effect of luting agent-metal physico-chemical surface interactions on film thicknesses of representative luting agents. Control group luting agents were placed between two glass plates, as described by American Dental Association specifications 8, 61, and 66, and test group luting agents were positioned between glass and metal plates. The materials selected were zinc phosphate cement, polycarboxylate cement, glass ionomer cement, glass ionomer-composite resin hybrid cement and a resinous cement, with a type III gold alloy, a noble metal ceramic alloy, and a base metal ceramic alloy. A two-way analysis of variance and follow-up tests were done. The effects of the type of metal surface, type of cement, and their statistical interaction significantly affected film thickness (p < 0.0001). The type of cement had a greater affect on film thickness than the type of metal. A glass ionomer cement produced lower overall film thicknesses than other cement types, and a noble metal ceramic alloy created lower overall film thicknesses than other types of metal. American Dental Association specifications for cement film thickness did not accurately reflect normal cement use.

Influence of marginal opening on microleakage of cemented artificial crowns

This study investigated the relationship between marginal opening and microleakage. Standardized preparations were made on intact human premolars, and copings were cast in a base metal alloy by use of conventional techniques. The castings were randomly assigned to the following luting agent groups: zinc phosphate cement, polycarboxylate cement, glass ionomer cement, phosphate ester composite resin, and a composite resin with a NPG-GMA dentinal bonding agent and were cemented in a standardized manner. The marginal openings between teeth and castings were measured, and microleakage was determined at the same points. Within the confines of the in vitro model used, no significant correlation between marginal opening and microleakage was established for either pooled data or individual luting agent groups.