Influence of marginal configuration and porcelain addition on the fit of In-Ceram crowns

Advantages and drawbacks of different methods to measure marginal gaps in fixed dental prostheses: A scoping review

OBJECTIVES

This review aimed to compare traditional and digital methods to assess marginal gaps in fixed dental prostheses. Each method's characteristics, advantages, and limitations were identified and discussed, also addressing the knowledge gaps in the current scientific literature.

DATA

Studies comparing currently available techniques for marginal gap examination were investigated. The main techniques analyzed were the Cross-Sectional Method (CSM), Direct View (DV), Silicone Replica Technique (SRT), Dual-Scan Method (DSM), Triple-Scan Method (TSM), Optical Coherence Tomography (OCT), and Micro-Computed Tomography (MCT).

SOURCES

Two experienced independent reviewers screened online databases (MEDLINE via PubMed and Scopus) to identify studies published in English up to March 2024. References from primary studies and the main peer-reviewed scientific journals were manually searched.

STUDY SELECTION

From an initial pool of 8126 articles, the reviewers meticulously selected 25 in vitro studies on objective comparisons between two or more methods for assessing marginal gaps in fixed dental prostheses on natural teeth. Publications that assessed marginal gaps in implant-supported fixed dental prostheses were excluded.

CONCLUSIONS

This study highlights that while traditional methods like CSM and SRT are widely used and validated, they have limitations in comprehensive gap assessment, often neglecting recommended measurement points. The DV technique, focusing solely on external gaps, may be less relevant for modern assessments. Conversely, three-dimensional techniques like TSM, DSM, OCT, and MCT offer a more thorough evaluation of dental restoration fit. Moreover, digital methods such as TSM and DSM have a significant potential for future clinical application.

CLINICAL SIGNIFICANCE

This review examined methods for evaluating marginal gaps in fixed dental prostheses. The review aids dental professionals and researchers in choosing the most suitable technique for clinical in vivo or laboratory assessment of the marginal adaptation of dental restorations. This study also indicates the need for an established and standardized assessment protocol for the marginal fit.

Marginal fit of monolithic versus layered zirconia crowns assessed with 2 marginal gap methods

STATEMENT OF PROBLEM

Zirconia can be used either monolithically or veneered with porcelain. However, whether veneering zirconia affects marginal fit is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the marginal fit of the monolithic and layered zirconia prostheses using 2 different assessment methods.

MATERIAL AND METHODS

An ideal complete crown with a chamfer finish line was prepared on an extracted maxillary central incisor. Two prosthesis designs, a framework and a monolithic design, and 2 marginal fit evaluation methods, the silicone replica and the triple scanning techniques, were used. In the first group, 10 crowns were fabricated with the framework design followed by porcelain veneering, and 10 crowns were fabricated monolithically in the second group. The marginal gap in each group was evaluated with both the silicone replica and triple scan methods. Data were statistically analyzed with a 2-way repeated measures ANOVA (α=.05).

RESULTS

A significant difference was found in the mean marginal gap by design type (P=.003), with the monolithic prostheses having lower mean marginal gaps (31.0 and 84.0 µm). However, both groups showed clinically acceptable marginal fit. No significant difference was found between the assessment methods (P=.092).

CONCLUSIONS

Monolithic zirconia crowns had a better marginal fit than veneered zirconia frameworks. Both the replica and triple scan techniques for marginal gap assessment yielded similar results.

Internal fit evaluation of indirect restorations fabricated from CAD/CAM composite blocks versus ceramic blocks in badly broken teeth using cone beam CT (CBCT): double-blinded randomized clinical trial

Objective

The restoration durability is essentially governed by optimum marginal integrity of an indirect restoration that is obtained and maintained by essential factors. This study aimed to evaluate the internal gap of indirect restorations fabricated from CAD/CAM composite blocks versus ceramic blocks in badly broken teeth using cone beam CT (CBCT) to determine their internal fit accuracy over the cast.

Materials and methods

Fifty-four participants were allocated into two groups: composite blocks or ceramic blocks. The trial participants and assessors were blinded to the material assignment, whereas the operator was not. Cavity preparation was performed followed by cavity optimization and impression taking. The produced master cast was scanned, restoration was designed using Exocad 2019 software and the final restoration was milled. The restoration was doubled-checked on the cast for internal fit using cone beam computed tomography (CBCT), and intraorally for interproximal contact and marginal adaptation before final cementation. CBCT measurements were collected and statistically analyzed. Restoration was cemented with resin cement and was immediately assessed clinically, then after one year and two years of follow-up periods.

Results

Results of an independent t-test revealed Composite blocks samples (0.25mm ± 0.03) to have a significantly better adaptation than ceramic blocks samples (0.29 mm ± 0.04) (p = 0.008).

Conclusions

Both materials have acceptable internal adaptation with a noticed difference reflected in their clinical performance.

Clinical relevance

Both indirect esthetic CAD/CAM restorations exhibit acceptable internal and marginal adaptation in posterior teeth however, composite blocks have a better adaptation than ceramic blocks.

Trial registration

This trial was registered in clinicaltrials.gov (NCT04784676).

Mechanical behavior of nano-hybrid composite in comparison to lithium disilicate as posterior cement-retained implant-supported crowns restoring different abutments

OBJECTIVE

Resin-based materials are gaining popularity in implant dentistry due to their shock absorption capacity. Therefore, the aim of this study was to evaluate the fracture strength and failure mode of resilient materials for both crowns and abutments and compare them to the most widely used materials in different combinations after subjection to long-term fatigue loading.

METHODS

Forty-eight cement-retained implant-restorations were assembled on titanium implants. Identical custom-made CAD/CAM abutments were milled out of 3 different materials (n = 16); T: titanium, Z: zirconia and P: ceramic-reinforced PEEK. Each group was subdivided, according to the restorative crown material, into two subgroups (n = 8); C: nano-hybrid composite and L: Lithium disilicate. Specimens were subjected to dynamic load of 98 N for 1,200,000 cycles with integrated thermal cycling. The surviving specimens were subjected to quasi-static loading until failure. Shapiro-Wilk test was used to test for normality. One-way ANOVA followed by Tukey's post-hoc test was used to detect statistically significant differences between groups.

RESULTS

All specimens withstood 1,200,000 load cycles. The fracture strength values varied from a minimum of 1639 ± 205 N for group PL to a maximum of 2949 ± 478 N for group ZL.

SIGNIFICANCE

The abutment material influenced the fracture strength and failure mode of the restoration. A combination of zirconia abutments and nano-hybrid composite showed the most favorable mode of failure within the test groups. Therefore, this combination might be recommended as an alternative for restoring single implants in the posterior area.

Scanning electron microscopy assessment of the load-bearing capacity of cad/cam-fabricated molar crowns

Although fiber-reinforced composites are commonly used in dental practice, whether fiber-reinforced crowns and fixed partial dentures can be used as definitive prostheses remains to be determined. This study used scanning electron microscopy to evaluate the load-bearing capacity of non-reinforced and fiber-reinforced composite (FRC) molar crowns prepared by computer-aided design/computer-aided manufacturing (CAD/CAM). The crowns were fabricated from three empirical FRC blocks, one empirical composite block, and one commercial ceramic block. The FRC resin was prepared by mixing BaO silicate particles, E-glass fiber, and dimethacrylate resin. Specimens were divided into five groups (n = 10), differing in the amounts of filler, resin, and fiber. Crowns were statically loaded until fracture. One-way analysis of variance and Tukey's post hoc multiple comparison tests were used for statistical analyses. The groups showed significant differences in load-bearing capacity; empirical bidirectional FRC resin blocks had the highest capacity, while commercial ceramic blocks had the lowest capacity. Molar crowns formed from FRC resin blocks had higher load-bearing capacity compared to non-reinforced composite resin and ceramic blocks. These results show that fiber reinforcement increased the load-bearing capacity of molar crowns.

A Validation Study of the Impression Replica Technique

PURPOSE

To validate the well-known and often-used impression replica technique for measuring fit between a preparation and a crown in vitro.

MATERIALS AND METHODS

The validation consisted of three steps. First, a measuring instrument was validated to elucidate its accuracy. Second, a specimen consisting of male and female counterparts was created and validated by the measuring instrument. Calculations were made for the exact values of three gaps between the male and female. Finally, impression replicas were produced of the specimen gaps and sectioned into four pieces. The replicas were then measured with the use of a light microscope. The values received from measuring the specimen were then compared with the values received from the impression replicas, and the technique was thereby validated.

RESULTS

The impression replica technique overvalued all measured gaps. Depending on location of the three measuring sites, the difference between the specimen and the impression replicas varied from 47 to 130 μm.

CONCLUSION

The impression replica technique overestimates gaps within the range of 2% to 11%. The validation of the replica technique enables the method to be used as a reference when testing other methods for evaluating fit in dentistry.

Evaluation of marginal gap of lithium disilicate glass ceramic crowns with optical coherence tomography

Marginal gap (MG) was the most important factor to evaluate the success of crowns. The study was to assess the MG of lithium disilicate glass ceramic crowns with spectral domain optical coherence tomography (OCT) and stereomicroscopy in vitro, and to provide evidence to measure the MG with OCT. Consistency was observed between OCT and stereomicroscopy to measure the MG after cementation. There was no significant difference between the MG of lithium disilicate glass ceramic crowns using OCT and stereomicroscopy (OCT 59.55  ±  7.22  μm, stereomicroscope 59.48  ±  6.53  μm, P  =  0.736) after cementation. OCT was a noninvasive diagnostic technique to measure the MG of lithium disilicate glass ceramic crowns.

Effects of image and education on the precision of the measurement method for evaluating prosthesis misfit

STATEMENT OF PROBLEM

Various methods for measuring prosthesis misfit have been suggested. Although the cross-sectional images between the crown and abutment are used to evaluate the misfit, the effects of the image and the observer's knowledge on the precision of measurement are unknown.

PURPOSE

The purpose of this in vitro study was to investigate the effects of the image and of education on the precision of prosthesis misfit measurement methods using inter- and intraobserver variability analyses.

MATERIAL AND METHODS

The cross-sectional images in the margin were obtained using the computer-aided replica technique (CART), silicone replica technique (RT), and sectioning technique (ST). Twenty-five observers measured the absolute marginal discrepancy values in the images obtained from each group 4 times at an interval of 2 weeks; the observers went through different education sessions regarding the selection of the measurement points. The precision of measurement was determined and compared using the likelihood-ratio test statistic (α=.05) and the intraclass correlation coefficient with the linear mixed-effects model.

RESULTS

The CART group exhibited the smallest deviations in the measurement variations, followed by the ST and RT groups (P<.001). Additional education on misfit measurements generally decreased the deviation values in all the groups, but without any significant differences.

CONCLUSIONS

The cross-sectional image obtained from the measurement methods and education on the evaluation method affected the precision of the prosthesis misfit measurement. Digital methods might be a useful tool to significantly enhance the precision of the measurements.

The effect of veneering on the marginal fit of CAD/CAM-generated, copy-milled, and cast metal copings

OBJECTIVE

This in vitro study investigated the marginal fit of metal and zirconia copings before and after veneering on dies with shoulder/chamfer (s/c) finish lines.

MATERIALS AND METHODS

Using CAD/CAM, ten (n = 10) each s/c zirconia (NZ) copings and ten (n = 10) each s/c metal (MM) copings were generated. As controls, ten (n = 10) each s/c zirconia copings were copy-milled (ZZ) and ten (n = 10) each s/c metal copings were cast (CC). The vertical marginal discrepancy of the copings was measured at 20 predefined spots of the circular shoulder and chamfer finish lines in microns (μm) before and after a first and a second veneering firing using a stereomicroscope at ×40 magnification. Data were statistically analyzed, and the comparisons of CAD/CAM-milled (NZ, MM), copy-milled (ZZ), and cast (CC) copings before and after veneering were made at a significance level of p < 0.05.

RESULTS

Gap width at s/c finish lines of ZZ was (91 ± 11/100 ± 28) and increased significantly (109 ± 21/141 ± 18) after the first firing (ZZ1). NZ showed significantly smaller gaps than ZZ (36 ± 6/46 ± 12) and (NZ1) after the first firing (61 ± 16/71 ± 29). Gap widths of CC groups (36 ± 8/25 ± 4) were not significantly different from NZ but were significantly lower after the (CC1) first veneering firing (40 ± 8/42 ± 7). MM copings showed gap values similar to NZ. Second firings did not significantly increase gaps in all groups except ZZ2 of chamfer finish line.

CONCLUSION

Veneering increased the marginal gap width of copings.

CLINICAL RELEVANCE

Within the limits of this in vitro study, aesthetic ceramic veneering of CAD/CAM-generated copings caused a statistically significant but tolerable loss of marginal fit precision.

Comparison of the fit accuracy of zirconia-based prostheses generated by two CAD/CAM systems

PURPOSE

The purposes of this study are to evaluate the internal and marginal adaptation of two widely used CAD/CAM systems and to study the effect of porcelain press veneering process on the prosthesis adaptation.

MATERIALS AND METHODS

Molar of a lower jaw typodont resin model was prepared by adjusting a 1.0 mm circumferential chamfer, an occlusal reduction of 2.0 mm, and a 5° convergence angle and was duplicated as an abrasion-resistant master die. The monolithic crowns and copings were fabricated with two different CAD/CAM system-Ceramil and Zirkonzahn systems. Two kinds of non-destructive analysis methods are used in this study. First, weight technique was used to determine the overall fitting accuracy. And, to evaluate internal and marginal fit of specific part, replica technique procedures were performed.

RESULTS

The silicone weight for the cement space of monolithic crowns and copings manufactured with Ceramil system was significantly higher than that from Zirkonzahn system. This gap might cause the differences in the silicone weight because the prostheses were manufactured according to the recommendation of each system. Marginal discrepancies of copings made with Ceramil system were between 106 and 117 µm and those from Zirkonzahn system were between 111 and 115 µm. Marginal discrepancies of copings made with Ceramil system were between 101 and 131 µm and those from Zirkonzahn system were between 116 and 131 µm.

CONCLUSION

Marginal discrepancy was relatively lower in Ceramil system and internal gap was smaller in Zirkonzahn system. There were significant differences in the internal gap of monolithic crown and coping among the 2 CAD/CAM systems. Marginal discrepancy produced from the 2 CAD/CAM systems were within a reported clinically acceptable range of marginal discrepancy.

Marginal and internal fit of metal copings fabricated with rapid prototyping and conventional waxing

STATEMENT OF PROBLEM

Given the limitations of conventional waxing, computer-aided design and computer-aided manufacturing (CAD-CAM) technologies have been developed as alternative methods of making patterns.

PURPOSE

The purpose of this in vitro study was to compare the marginal and internal fit of metal copings derived from wax patterns fabricated by rapid prototyping (RP) to those created by the conventional handmade technique.

MATERIAL AND METHODS

Twenty-four standardized brass dies were milled and divided into 2 groups (n=12) according to the wax pattern fabrication method. The CAD-RP group was assigned to the experimental group, and the conventional group to the control group. The cross-sectional technique was used to assess the marginal and internal discrepancies at 15 points on the master die by using a digital microscope. An independent t test was used for statistical analysis (α=.01).

RESULTS

The CAD-RP group had a total mean (±SD) for absolute marginal discrepancy of 117.1 (±11.5) μm and a mean marginal discrepancy of 89.8 (±8.3) μm. The conventional group had an absolute marginal discrepancy 88.1 (±10.7) μm and a mean marginal discrepancy of 69.5 (±15.6) μm. The overall mean (±SD) of the total internal discrepancy, separately calculated as the axial internal discrepancy and occlusal internal discrepancy, was 95.9 (±8.0) μm for the CAD-RP group and 76.9 (±10.2) μm for the conventional group. The independent t test results showed significant differences between the 2 groups. The CAD-RP group had larger discrepancies at all measured areas than the conventional group, which was statistically significant (P<.01).

CONCLUSIONS

Within the limitations of this in vitro study, the conventional method of wax pattern fabrication produced copings with better marginal and internal fit than the CAD-RP method. However, the marginal and internal fit for both groups were within clinically acceptable ranges.

Fabrication of all-ceramic crowns by a new method

A new method of all-ceramic production using alumina coping has been developed. The present study investigates the influence of secondary firing (glass infiltration firing) conditions. Samples of porcelain build-up without secondary firing were also assessed. The suitability of coping that included secondary firing was found to be affected by the rate of temperature increase during the secondary firing. However, cracking developed in the fired porcelain if porcelain was built up onto secondarily-fired coping. In contrast, cracking did not occur with coping that was not secondarily fired. The bending strength after porcelain build-up was 70 MPa or higher, suggesting the possibility of clinical applications as an anterior crown. These findings establish that this is method of producing all-ceramic crowns that allows for low-cost manufacture in a short period of about 1 h.

Influence of preparation depths on the fracture load of customized zirconia abutments with titanium insert

PURPOSE

This study evaluated the fracture load of customized zirconia abutments with titanium insert according to preparation depths, with or without 5-year artificial aging.

MATERIALS AND METHODS

Thirty-six identical lithium disilicate crowns (IPS e.max press) were fabricated to replace a maxillary right central incisor and cemented to the customized zirconia abutment with titanium insert on a 4.5×10 mm titanium fixture. Abutments were fabricated with 3 preparation depths (0.5 mm, 0.7 mm, and 0.9 mm). Half of the samples were then processed using thermocycling (temperature: 5-55℃, dwelling time: 120s) and chewing simulation (1,200,000 cycles, 49 N load). All specimens were classified into 6 groups depending on the preparation depth and artificial aging (non-artificial aging groups: N5, N7, N9; artificial aging groups: A5, A7, A9). Static load was applied at 135 degrees to the implant axis in a universal testing machine. Statistical analyses of the results were performed using 1-way ANOVA, 2-way ANOVA, independent t-test and multiple linear regression.

RESULTS

The fracture loads were 539.28 ± 63.11 N (N5), 406.56 ± 28.94 N (N7), 366.66 ± 30.19 N (N9), 392.61 ± 50.57 N (A5), 317.94 ± 30.05 N (A7), and 292.74 ± 37.15 N (A9). The fracture load of group N5 was significantly higher than those of group N7 and N9 (P<.017). Consequently, the fracture load of group A5 was also significantly higher than those of group A7 and A9 (P<.05). After artificial aging, the fracture load was significantly decreased in all groups with various preparation depths (P<.05).

CONCLUSION

The fracture load of a single anterior implant restored with lithium disilicate crown on zirconia abutment with titanium insert differed depending on the preparation depths. After 5-year artificial aging, the fracture loads of all preparation groups decreased significantly.

The effect of various veneering techniques on the marginal fit of zirconia copings

PURPOSE

This study aimed to evaluate the fit of zirconia ceramics before and after veneering, using 3 different veneering processes (layering, press-over, and CAD-on techniques).

MATERIALS AND METHODS

Thirty standardized zirconia CAD/CAM frameworks were constructed and divided into three groups of 10 each. The first group was veneered using the traditional layering technique. Press-over and CAD-on techniques were used to veneer second and third groups. The marginal gap of specimens was measured before and after veneering process at 18 sites on the master die using a digital microscope. Paired t-test was used to evaluate mean marginal gap changes. One-way ANOVA and post hoc tests were also employed for comparison among 3 groups (α=.05).

RESULTS

Marginal gap of 3 groups was increased after porcelain veneering. The mean marginal gap values after veneering in the layering group (63.06 µm) was higher than press-over (50.64 µm) and CAD-on (51.50 µm) veneered groups (P<.001).

CONCLUSION

Three veneering methods altered the marginal fit of zirconia copings. Conventional layering technique increased the marginal gap of zirconia framework more than pressing and CAD-on techniques. All ceramic crowns made through three different veneering methods revealed clinically acceptable marginal fit.

Accuracy of ceramic restorations made with two CAD/CAM systems

STATEMENT OF PROBLEM

Different types of CAD/CAM systems are currently available, but information regarding which system produces the best marginal fit is lacking.

PURPOSE

The purpose of this study was to evaluate the effect of 2 different CAD/CAM systems (Cerec inLab, Kavo Everest) on the marginal fit of 2 types of zirconia-based and lithium disilicate crowns.

MATERIAL AND METHODS

Forty zirconia-based and lithium disilicate crowns, 20 each, were fabricated with the Cerec inLab and Everest CAD/CAM systems on a specially designed stainless steel die to ensure the standardization of specimen shape and dimensions. The vertical marginal fit for all tested crowns was evaluated by using a digital microscope at ×100 magnification, and the data were tabulated and statistically analyzed with 2-way ANOVA, followed by the Tukey honestly significant difference (HSD) test with a confidence level of .05 to determine the mean differences.

RESULTS

The results showed that the CAD/CAM technique, ceramic type, and their interaction had a statistically significant effect on the mean marginal fit of both ceramic types tested.

CONCLUSIONS

Better marginal fit values were exhibited by the Everest CAD/CAM technique for both ceramic types tested.

Considerations for ceramic inlays in posterior teeth: a review

This review of ceramic inlays in posterior teeth includes a review of the history of ceramic restorations, followed by common indications and contraindications for their use. A discussion on the potential for tooth wear is followed by a review of recommended preparation design considerations, fabrication methods, and material choices. Despite the improved materials available for fabrication of porcelain inlays, fracture remains a primary mode of inlay failure. Therefore, a brief discussion on strengthening methods for ceramics is included. The review concludes with a section on luting considerations, and offers the clinician specific recommendations for luting procedures. In conclusion, inlay success rates and longevity, as reported in the literature, are summarized.

Influence of zirconia abutment preparation on the fracture strength of single implant lithium disilicate crowns after chewing simulation

OBJECTIVE

The use of all-ceramic crowns over zirconia abutments is a well-established esthetic treatment option in implant dentistry; however, the effect of the mechanical processing due to abutment preparation has not been investigated under functional loading. The purpose of the study was to evaluate the influence of the zirconia abutment preparation depth and preparation mode on the fracture strength and fracture mode of lithium disilicate crowns after chewing simulation.

MATERIAL AND METHODS

Seventy single implant-supported lithium disilicate glass-ceramic crowns (IPS e.max Press, Ivoclar Vivadent) were adhesively cemented (Multilink Automix, Ivoclar Vivadent) onto zirconia abutments (ZirDesign, Astra Tech) using implants with a diameter of 4.5 mm and a length of 15.0 mm (Osseospeed, Astra Tech). Study design concerned the replacement of a maxillary central incisor (11.0 mm in height and 8.0 mm in width). Subgroups (n = 7) were subjected to dynamic loading (C) up to 1.2 × 10(6) loading cycles at 135° with 98N in a thermomechanical chewing simulator (Kausimulator, Willytech); followed by quasi-static loading at a cross-head speed of 0.5 mm/min until fracture in a universal testing machine (Z010/TN2S, Zwick). Additional subgroups were also subjected to quasi-static loading (S) at 135°. Lithium disilicate implant crowns were divided into five study groups (n = 14) according to the abutment preparation depth [A (control): 0.5 mm, B: 0.7 mm, C: 0.9 mm, and preparation mode [(No label): milling by the manufacturer, (P): copy-milling by the Celay System (Mikrona)].

RESULTS

All specimens survived dynamic loading and mean fracture strengths (N) after quasi-static loading were as follows: Group SA: 384 ± 84; Group CA: 403 ± 67; Group SB: 294 ± 95; Group CB: 374 ± 75; Group SC: 332 ± 52; Group CC: 373 ± 105; Group SPB: 332 ± 80; Group CPB: 499 ± 91; Group SPC: 380 ± 101; and Group CPC: 358 ± 54.

CONCLUSIONS

Statistical analysis using multiple linear regression showed that both the preparation depth and mode had no influence on the fracture strength of the implant crowns (P > 0.05); however, fracture strength increased statistically significantly after 5 years chewing simulation (P = 0.01).

A comparison of marginal fit of glass infiltrated alumina copings fabricated using two different techniques and the effect of firing cycles over them

PURPOSE

This study evaluated marginal fit of glass infiltrated alumina cores fabricated using two techniques and their marginal stability after firing cycles of veneering porcelain.

MATERIALS AND METHODS

Fifteen standardized all-ceramic crowns were fabricated on a metal die using each technique: slip cast technique of VITA In-Ceram sprint Alumina (Group A as control) and plastic foil matrix technique of Turkom-Cera fused alumina core system (Group B). Copings were compared between groups and within groups at coping stage and after firing each layer of veneering porcelain. A device was used to standardize seating of copings on the metal die and positioning of the specimens under the microscope after each stage of fabrication. The specimens were not cemented and marginal gap was measured using an image analyzing software (Imagepro Express) on the photographs captured under an optical microscope. Two tailed unpaired 't test' was used to compare marginal gaps in two groups and one way ANOVA was used to analyze marginal distortion within each group at 95% confidence interval.

RESULTS

The marginal gap was smaller at the coping stage in group B (60 + 30 µm) than group A (81 + 21 µm) with statistical significance. After firing of veneering porcelain the difference was insignificant. At the final stage, both groups exhibited lower mean marginal gaps than at the initial coping stage with the difference of 11.75 µm for group A and 11.94 µm for group B, but it was statistically insignificant due to high value of standard deviation.

CONCLUSION

Within the limitations of this study, it was concluded that both techniques produced copings with comparable and acceptable marginal fit and marginal stability on firing veneering porcelain.

Marginal, Internal Fit and Microleakage of Zirconia Infrastructures: An In-Vitro Study

Fitting accuracy and microleakage dominate prognostic covariates for the long-term durability of crown restorations. The fitting accuracy and microleakage potential of zirconia infrastructures might be influenced by manufacturing technology.

Influence of porcelain veneering on the marginal fit of Digident and Lava CAD/CAM zirconia ceramic crowns

PURPOSE

Marginal fit is a very important factor considering the restoration's long-term success. However, adding porcelain to copings can cause distortion and lead to an inadequate fit which exposes more luting material to the oral environment and causes secondary caries. The purpose of this study was to compare the marginal fit of 2 different all-ceramic crown systems before and after porcelain veneering. This study was also intended to verify the marginal fit of crowns originated from green machining of partially sintered blocks of zirconia (Lava CAD/CAM system) and that of crowns obtained through machining of fully sintered blocks of zirconia (Digident CAD/CAM system).

MATERIALS AND METHODS

20 crowns were made per each system and the marginal fit was evaluated through a light microscope with image processing (Accura 2000) at 50 points that were randomly selected. Each crown was measured twice: the first measurement was done after obtaining a 0.5 mm coping and the second measurement was done after porcelain veneering. The means and standard deviations were calculated and statistical inferences among the 2 groups were made using independent t-test and within the same group through paired t-test.

RESULTS

The means and standard deviations of the marginal fit were 61.52 ± 2.88 µm for the Digident CAD/CAM zirconia ceramic crowns before porcelain veneering and 83.15 ± 3.51 µm after porcelain veneering. Lava CAD/CAM zirconia ceramic crowns showed means and standard deviations of 62.22 ± 1.78 µm before porcelain veneering and 82.03 ± 1.85 µm after porcelain veneering. Both groups showed significant differences when analyzing the marginal gaps before and after porcelain veneering within each group. However, no significant differences were found when comparing the marginal gaps of each group before porcelain veneering and after porcelain veneering as well.

CONCLUSION

The 2 all-ceramic crown systems showed marginal gaps that were within a reported clinically acceptable range of marginal discrepancy.

Influence of the veneering process on the marginal fit of zirconia fixed dental prostheses

Distortions in the marginal region during manufacture are detrimental to the long-term success of fixed dental prostheses (FDPs). The aim of the present in vitro study was to evaluate changes in marginal fit because of the veneering process of four-unit FDPs made from different zirconia materials. Two groups of FDPs with 10 specimens each were machined from white body zirconia blanks (VITA In-Ceram YZ Cubes, KaVo Everest ZS-Blanks) by means of computer-aided design/computer-aided manufacturing systems and subsequently sintered to their final density. The marginal and internal gaps of the frameworks were determined using a replica technique. Afterwards, frameworks were veneered with the recommended ceramics (VITA VM9, GC Initial Zr), and fitting accuracy was evaluated again. Statistical analyses were performed by Student's t-test with the level of significance chosen at 0.05. With one framework/veneering system (Everest ZS-Blanks/Initial Zr), both marginal gap (P = 0.019) and internal gap (P = 0.001) at the premolar retainer were significantly affected by the veneering process. The resulting distortions were directed towards the lumina of the retainers and the mean values of the measured gaps decreased by about 23.8 mum (marginal gap) and 27.3 mum (internal gap). For the other system (In-Ceram YZ Cubes/VM9), no distortions because of the veneering were found. The veneering of zirconia restorations may lead to significant changes in the marginal fit, while the combination of core and veneering material used influences the resulting distortions.

Influence of Cervical Finish Line Type on the Marginal Adaptation of Zirconia Ceramic Crowns

Cervical finish line type has an influence on the marginal adaptation of Y-TZP restorations. Both shoulder and mini-chamfer exhibited the least marginal opening values for zirconia crowns and can be recommended for clinical applications.

Properties and cyclic fatigue of glass infiltrated tape cast alumina cores produced using a water-based solvent

OBJECTIVE

The purpose of this study was to investigate the properties of tape cast alumina composite produced using a water-based solvent and its possible clinical use as an all ceramic crown system in a fixed partial denture. Durability of the system will be measured by fatigue test to simulate the masticating conditions of the oral cavity.

METHODS

The optimal weight ratio of water-based alumina tape was determined by tensile strength, shrinkage ratio and durability. The coefficient of thermal expansion, fracture toughness, biaxial flexural strength and flexural strength after fatigue test of a composite produced from alumina tape at optimal weight ratios were determined and compared to In-Ceram alumina core (control).

RESULTS

The weight ratio of alumina/(alumina+binder+plasticizer) of 0.84 and binder/(binder+plasticizer) of 0.5 was observed to be the optimal composition for achieving excellent composite properties. Coefficient of thermal expansion of the sintered alumina tape was observed to be 7.3x10(-6)/degrees C, and this value was increased to 7.5x10(-6)/degrees C after infiltrating the sintered tape with glass. The fracture toughness and biaxial flexural strength of glass infiltrated alumina tape was observed to be 4.6 MPa m(1/2) and 498 MPa, respectively. After cyclic loading for 10(2)-10(6) cycles, no significant change in the biaxial flexural strength was observed between the glass infiltrated alumina core and the In-Ceram alumina core (p>0.05).

SIGNIFICANCE

The observed properties provide evidence that the water-based tape cast alumina-glass composite is suitable for clinical use as an all ceramic crown system in a fixed partial denture.

Influence of margin design on the fit of high-precious alloy restorations in patients

OBJECTIVE

It was the objective of this study, to analyze the influence of the marginal design on the marginal accuracy of a casting in a clinical setup in patients.

METHODS

Ninety volunteer patients' teeth-which were intended for extraction due to medical reasons-were prepared prior to extraction. Three different types of finishing line-chamfer, 135 degrees shoulder and 90 degrees shoulder-were employed. Two each c-silicone and pvs impressions were taken of each tooth using either a two-stage or a one-stage putty-wash technique. After preparation and impression taking the teeth were extracted. Gypsum casts were poured from the impressions and high precious alloy castings fabricated on the dies and marginal discrepancies were determined on the extracted teeth.

RESULTS

The median value of marginal discrepancies was lower than 150 microm for all groups. The difference between the three different preparation types was significant (H-test, p<0.05). The lowest median values were obtained for the chamfer preparations, while the 90 degrees shoulders always produced the highest median values. Preparations at gingva level exhibited more accurate marginal fit than subgingival preparations. No significant differences could be observed between the pvs and c-silicone materials or the one-step and two-step putty-wash techniques.

CONCLUSIONS

The marginal designs of the preparations had much less influence on the marginal fit of high precious alloy castings than expected. There is considerable reason to assume that technical but clinical parameters influence the quality of fixed prosthodontics much more than has been believed in the past.

Influence of firing cycles on the margin distortion of 3 all-ceramic crown systems

STATEMENT OF PROBLEM

Although all-ceramic restorations are widely used, there is a lack of information about how the fit is affected by fabrication procedures. The adequacy of the fit of all-ceramic restorations has been questioned.

PURPOSE

This study examined the effect of porcelain and glaze firing cycles on the fit of 3 types of all-ceramic crowns.

MATERIAL AND METHODS

Ten standardized all-ceramic crowns were fabricated on a metal die from each of 3 systems: conventional In-Ceram, copy-milled In-Ceram, and copy-milled feldspathic crowns. Copings of the conventional and copy-milled In-Ceram crowns and nonglazed copy-milled feldspathic crowns served as the control. A device was used to apply a uniform load on specimens during measurement and to reposition the specimens on the measurement device after each manufacturing process. The specimens were not cemented and were measured on the metal die using a profile projector. Measurements were recorded at 18 points selected along horizontal and vertical planes. The crown systems were compared by use of the Student t test and 1-way analysis of variance (ANOVA). Data of measurements repeated at identical locations were analyzed with a multivariate repeated-measures ANOVA. The Bonferroni post hoc test was used for multiple comparisons (alpha=.05).

RESULTS

The conventional In-Ceram (57 +/- 24 microm) and copy-milled In-Ceram (57 +/- 32 microm) crowns demonstrated nearly identical marginal discrepancy values, followed by the copy-milled feldspathic crowns with a mean of 17 +/- 12 microm in the vertical plane. The copy-milled In-Ceram crowns had a mean horizontal discrepancy value of -12 +/- 4 microm, followed by the copy-milled feldspathic crowns with a mean of -4 +/- 5 microm and the conventional In-Ceram crowns with a mean of -6 +/- 4 microm. Statistical analyses demonstrated no significant differences in the marginal discrepancy values among the 3 all-ceramic crown systems, except for the horizontal discrepancy values between the conventional and copy-milled In-Ceram crowns after the porcelain firing cycle. Results indicated that the addition of porcelain to the copings caused a significant change ( P <.05) in the marginal fit of the crowns, except for the fit in the horizontal plane of the conventional In-Ceram crowns. However, no significant changes occurred in the fit of the 3 all-ceramic crowns after the glaze firing cycle. There were significant differences in the marginal discrepancy values among the measurement locations ( P <.05), and the discrepancy value at each location was independent of the mean of the entire crown.

CONCLUSIONS

Within the limitations of this study, it was concluded that the 3 all-ceramic crown systems demonstrated a comparable and acceptable marginal fit. The porcelain firing cycle affected the marginal fit of the all-ceramic crowns. However, the glaze firing cycle had no significant effect on fit. The conventional and copy-milled In-Ceram crowns demonstrated medial deformations at the labial and palatal surfaces that might result in occlusal displacement of the crown.

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.

In vitro marginal fit of three all-ceramic crown systems

STATEMENT OF PROBLEM

Studies on marginal discrepancies of single restorations using various systems and materials have resulted in statistical inferences that are ambiguous because of small sample sizes and limited numbers of measurements per specimen.

PURPOSE

The purpose of this study was to compare the marginal adaptation of single anterior restorations made using different systems.

MATERIAL AND METHODS

The in vitro marginal discrepancies of 3 different all-ceramic crown systems (Celay In-Ceram, conventional In-Ceram, and IPS Empress 2 layering technique), and a control group of metal ceramic restorations were evaluated and compared by measuring the gap dimension between the crowns and the prepared tooth at the marginal opening. The crowns were made for 1 extracted maxillary central incisor prepared with a 1-mm shoulder margin and 6-degree tapered walls by milling. Thirty crowns per system were fabricated. Crown measurements were recorded with an optical microscope, with an accuracy of +/-0.1 microm, at 50 points spaced approximately 400 microm along the circumferential margin. The criterion of 120 microm was used as the maximum clinically acceptable marginal gap. Mean gap dimensions and standard deviations were calculated for marginal opening. The data were analyzed with a 1-way analysis of variance (alpha=.05).

RESULTS

Mean gap dimensions and standard deviations at the marginal opening for the incisor crowns were 87 +/- 34 microm for control, 83 +/- 33 microm for Celay In-Ceram, 112 +/- 55 microm for conventional In-Ceram, and 46 +/- 16 microm for the IPS Empress 2 layering technique. Significant differences were found among the crown groups (P<.05). Compared with the control group, the IPS Empress 2 group had significantly smaller marginal discrepancies (P<.05), and the conventional In-Ceram group exhibited significantly greater marginal discrepancies (P<.05). There was no significant difference between the Celay In-Ceram and the control group.

CONCLUSION

Within the limitations of this study, the marginal discrepancies were all within the clinically acceptable standard set at 120 microm. However, the IPS Empress 2 system showed the smallest and most homogeneous gap dimension, whereas the conventional In-Ceram system presented the largest and more variable gap dimension compared with the metal ceramic (control) restoration.

Crowns and extra-coronal restorations: materials selection

Materials selection is the second in the series on crowns and other extra-coronal restorations. Some of us are less than inspired by dental materials science. Nevertheless, many of the things that concern us clinically with crowns and their alternatives are based on material properties. We worry about the strength of the restoration, how well it fits and its aesthetics. We also worry about wear, occlusal control and biocompatibility. Not least of our concerns are dental laboratory charges, which inevitably have to be passed on to the patient.