Comparison of Overall Fit of Milled and Laser-Sintered CAD/CAM Crown Copings

Evaluation of the influence of connection configuration on the implant-abutment interface vertical misfit of original milled titanium and laser-sintered cobalt-chromium abutments

OBJECTIVES

This study aimed to assess the vertical misfit at the implant-abutment interface in external and internal connections across various implant brands, comparing original milled titanium abutments with laser-sintered cobalt-chromium (Co-Cr) abutments.

MATERIALS AND METHODS

A total of 160 implants from four different brands were utilized, with 80 featuring external connections (EC) and 80 internal connections (IC). Original milled titanium abutments (n = 160) and Co-Cr laser-sintered abutments (n = 160) were randomly attached to each connection type, following the manufacturer's recommended torque. After undergoing thermal cycling, the vertical misfit was measured using a scanning electron microscope. Statistical analyses were performed using the Kruskal-Wallis and Mann-Whitney U tests. The significance level was set at α = 0.05.

RESULTS

The original milled titanium abutments exhibited the lowest misfit values. Significant differences were identified between both abutment types for EC (d = 109.578 μm; p = 0.0001) and IC (d = 44.317 μm; p = 0.002). The EC with laser-sintered abutments demonstrated the highest marginal misfit values, with an average of nearly 30 μm, while a misfit value of 11.382 μm was achieved in the IC. Differences were observed among the brands for milled abutments in both EC and IC. Similarly, variations were also noted for the laser-sintered Co-Cr abutments in EC and IC configurations.

CONCLUSIONS

The vertical misfit of the original milled titanium abutments in all groups was within the clinically acceptable range for IC. The connection type significantly impacted the vertical misfit in laser-sintered Co-Cr abutments. Differences among the implant systems were observed for both connection types and abutment types evaluated.

CLINICAL RELEVANCE

Using original milled titanium abutments, particularly in internal connection systems, can lead to better fit and stability at the implant-abutment interface, potentially reducing the risk of mechanical complications and improving long-term implant success.

An In Vitro Comparison of Marginal Fit of Single-Unit Copings Fabricated Using Computer-Aided Design/Computer-Aided Manufacturing Zirconia, Direct Metal Laser Sintering and Porcelain-Fused-to-Metal

INTRODUCTION

The marginal fit of dental restorations is essential for longevity and effectiveness of fixed prostheses, particularly single-unit crowns. Direct digital scanning offers significant advantages over indirect methods, providing a non-invasive, accurate, and reproducible means to evaluate marginal fit. This study aimed to assess the marginal fit of single-unit copings fabricated using computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia, direct metal laser sintering (DMLS), and porcelain-fused-to-metal (PFM) utilizing direct three-dimensional (3D) scanning.

MATERIALS AND METHODS

The current in vitro investigation involved 60 right mandibular second premolar typodont teeth (Dentmark, Ambala, Haryana, India) designated for single-unit fixed dental prostheses. The specimens were categorized into three groups of 20 specimens each. Direct scanning for all groups was performed using the Helios 500 intraoral scanner (Orikam Healthcare India Pvt. Ltd., Haryana, India). Upon fabrication, all copings were directly scanned using a 3D scanner (Shining 3D EX Pro, California, USA). Marginal discrepancies were assessed using the Exocad software (CAD software, Darmstadt, Germany).

RESULTS

Mean marginal discrepancies of zirconia, DMLS, and PFM copings were evaluated and compared. Zirconia copings had the lowest mean discrepancy of 0.0172 mm whereas DMLS copings had a mean discrepancy of 0.0256 mm. The PFM copings had the highest mean discrepancy of 0.0375 mm. A one-way analysis of variance (ANOVA) indicated a significant difference in the marginal fit (p < 0.05). Post-hoc Tukey test comparisons revealed significant differences between the three groups (p < 0.05).

CONCLUSION

In conclusion, CAD/CAM-fabricated zirconia crowns exhibit superior marginal fit compared to DMLS and PFM copings, owing to precise digital design, milling, and material stability. DMLS copings, although less precise, still outperform PFM crowns, which display significant marginal gaps owing to the limitations of the lost-wax method.

Effect of Fabrication Technique on the Microgap of CAD/CAM Cobalt-Chrome and Zirconia Abutments on a Conical Connection Implant: An In Vitro Study

The aim of this in vitro study was to investigate the microgaps at the implant-abutment interface when zirconia (Zr) and CAD/CAM or cast Co-Cr abutments were used.

METHODS

Sixty-four conical connection implants and their abutments were divided into four groups (Co-Cr (milled, laser-sintered and castable) and Zirconia (milled)). After chewing simulation (300,000 cycles, under 200 N loads at 2 Hz at a 30° angle) and thermocycling (10,000 cycles, 5 to 50 °C, dwelling time 55 s), the implant-abutment microgap was measured 14 times at each of the four anatomical aspects on each specimen by using a scanning electron microscope (SEM). Kruskal-Wallis and pair-wise comparison were used to analyze the data (α = 0.05).

RESULTS

The SEM analysis revealed smaller microgaps with Co-Cr milled abutments (0.69-8.39 μm) followed by Zr abutments (0.12-6.57 μm), Co-Cr sintered (7.31-25.7 μm) and cast Co-Cr (1.68-85.97 μm). Statistically significant differences were found between milled and cast Co-Cr, milled and laser-sintered Co-Cr, and between Zr and cast and laser-sintered Co-Cr (p < 0.05).

CONCLUSIONS

The material and the abutment fabrication technique affected the implant-abutment microgap magnitude. The Zr and the milled Co-Cr presented smaller microgaps. Although the CAD/CAM abutments presented the most favorable values, all tested groups had microgaps within a range of 10 to 150 μm.

A Scoping Review on the Accuracy of Fit of Removable Partial Dentures in a Developing Digital Context

PURPOSE

The aim of this paper is to evaluate studies on the quality of fit of alloy removable-partial-dentures (RPDs) produced by computer-aided design/computer-aided manufacturing (CAD/CAM) and rapid prototyping (RP) technology. This paper offers a comprehensive scoping review of various methods of assessing the quality of fit of RPDs in the context of a developing digital approach to manufacturing and assessment.

METHODOLOGY/APPROACH

A search was made using MEDLINE/PubMed, Scopus, and Science Direct to identify the studies of the accuracy of fit of RPDs.

FINDINGS

Optical and physical examination of dentures "in situ" on the model or in the patient's oral cavity were the most commonly used methods for the assessment of fit of RPDs. Eighteen of the included studies assessed the internal fit between RPDs and oral tissues or models using either polyvinyl silicone materials as filler, calipers, photographs, and microscopes or a combination of these. Two studies used visual assessment. Most studies reported that the fit of RPDs ranged from satisfactory to excellent. However, many of these assessments seemed somewhat subjective and flawed with regard to assessing indentations of the framework into a model or distortion. Two papers used a new method of computer-based superimposition which included a color map of discrepancies to assess the fit of the machine-produced RPDs offering possibilities to quantify the assessment of fit, perhaps leading to a more objective assessment. Despite the limited number of clinical trials, the available evidence was thought to reinforce the claim that the fit of RPDs fabricated digitally was acceptable.

CONCLUSION

The recent introduction of color maps to compare the differences between the fitting surface and the model is promising. However, a new method for displaying discrepancies shown by color maps is introduced, which could lead to a more quantitative assessment.

Dental Student Perspectives of a Comprehensive-Based Teaching Methodology: A Confidence, Effectiveness, and Challenge Report

Background/Objectives. The holistic methodology in education has been widely appreciated and implicated in dental schools in the last decade. Our department of conservative dentistry decided to reform the educational model of teaching from a traditional requirement-based model to a hybrid model incorporating comprehensive care treatment. The aim of our study was to assess students' confidence and perspectives regarding the benefits of a comprehensive model of teaching. Materials and Methods. A questionnaire was distributed at the end of the academic year 2018-2019 and designed to investigate students' opinions on the benefits of the new model of teaching, as well as difficulties encountered and possible shortcomings. In addition, self-perceived confidence level was assessed for the purpose of comparing confidence during supervised tasks versus confidence during comprehensive patient care. Results. Complete responses were gathered from 127 students out of 202, giving a response rate of 63%. The majority of students believed that the comprehensive model of teaching allowed them to better address patients' needs, gave higher satisfaction, positively influenced self-confidence, permitted greater exposure to clinical techniques, and enhanced reasoning and analytical skills. However, their confidence was still lower in comprehensive patient management when compared to supervised tasks. Conclusion. Our students showed an appreciation of the comprehensive care model. Self-learning and didactic skills were enhanced. It would, therefore, be beneficial to adapt this methodology to earlier years and other disciplines to enhance the effectiveness of education and achievement of learning outcomes.