Marginal Adaptation and Fracture Resistance of Lithium Disilicate Laminate Veneers on Teeth with Different Preparation Depths

Marginal Adaptation of Veneers: A Systematic Review

This study aimed to systematically review the literature to evaluate the marginal adaptation of veneers using different fabrication methods, namely, conventional feldspathic porcelain laminate veneers (PLVs), computer-aided design-computer-aided machining (CAD-CAM) veneers, and pressed veneers. A comprehensive literature search was performed using electronic databases (PubMed and Google Scholar) as well as hand searches to identify all relevant studies related to veneers and marginal adaptation. The identified studies were screened for assessing the inclusion and exclusion criteria. The included articles were then subjected to data extraction and analysis. The search resulted in 130 articles, of which six were included in this systematic review. All included articles were assessed for adaptation of margins. Based on the findings of this systematic review, no significant differences were found in the marginal adaptation of CAD-CAM and conventional feldspathic PLVs. The marginal fidelity of ceramic veneers issuing from the various fabrication techniques was clinically acceptable.

Three-dimensional Quantification of Enamel Preservation in Tooth Preparation for Porcelain Laminate Veneers: A Fully Digital Workflow In Vitro Study

OBJECTIVE

This in vitro study aimed to evaluate the preservation of enamel after tooth preparation for porcelain laminate veneers (PLVs) at different preparation depths based on a fully digital workflow.

METHODS AND MATERIALS

Sixty extracted human maxillary anterior teeth, including 20 maxillary central incisors (MCIs), 20 maxillary lateral incisors (MLIs), and 20 maxillary canines (MCs) underwent microcomputed tomography (CT) scanning, and were reconstructed as three-dimensional (3D) enamel and dentin models. Subsequently, the three-dimensional (3D) enamel models were imported into Materialise, where each enamel model underwent seven types of virtual preparation for PLVs at preparation depths at 0.1-mm increments from 0.1-0.3-0.5 mm (D1) to 0.7-0.9-1.1 mm (D7). The enamel surface was depicted by merging the virtual preparation and, respective, dentin models. The enamel area and prepared surface were measured to calculate the percentage of enamel (R%). The data were statistically analyzed using one-way analysis of variance (ANOVA) (α=0.05).

RESULTS

The group-wise mean (standard deviation) R values for the MCIs were as follows: D1-D3: 100.00 (0) each, and D4-D7: 74.70 (2.45), 51.40 (5.12), 24.40 (3.06), and 0.00 (0), respectively. The group-wise mean R values for the MLIs were 100.00 (0), 73.70 (3.40), 53.50 (3.44), 25.20 (3.79), and 0.90 (0.99) for the D1-D5 groups, respectively; and 0.00 (0) each for the D6-D7 groups. The group-wise mean (standard deviations) R values for the MCs were as follows: D1-D3: 100.00 (0) each, and D4-D7: 99.00 (1.34), 77.10 (3.28), 74.20 (3.61), and 52.20 (4.09), respectively. The one-way ANOVA revealed significant differences between the seven groups in the MCIs, MLIs, and MCs (p<0.05).

CONCLUSIONS

Our results recommended preparation depths of up to 0.3-0.5-0.7 mm (MCIs), 0.1-0.3-0.5 mm (MLIs), and 0.4-0.6-0.8 mm (MCs) to facilitate complete intraenamel preparation. Moreover, 50% enamel was preserved at preparation depths of 0.5-0.7-0.9 mm (MCIs), 0.3-0.5-0.7 mm (MLIs), and 0.7-0.9-1.1 mm (MCs).

Questions about the numerical value and quantitative data transfer of tooth preparation-from experience guidance to digital guidance

Tooth preparation is a common operation in dental clinical practice. This procedure is irreversible and invasive from the point of view of tooth preservation. Conditions of the abutment tooth, treatment methods, and restoration materials for target restoration affect tooth preparation. To achieve the goals of tooth tissue preservation, dental pulp protection, and periodontal health, dentistry professionals agreed on the importance of minimizing the amount of tooth reduction. The foundations for realizing this consensus are as follows. First, the available restoration materials with improved comprehensive performance need less target restoration space. Next, teeth can be prepared under a digital guide, and the real-time measurement of restoration space can be verified due to the invention of digital technologies for the analysis of the quantity and shape of the prepared tooth and tooth measurement. Moreover, guiding methods for preparation have been developed from freehand operation under the naked eye based on accumulated personal experience to digital-guidance jointing microscope. These innovations indicate the creation of a prototype of guided prosthodontics that is precise and applies real-time measurement throughout the process of tooth preparation. From the perspective of the evolution of digital, guided, and micro prosthodontics, this article raised seven questions about the numerical value and quantitative data transfer of tooth preparation and evaluated the authenticity of existing numerical requirements from the perspective of the four elements of measurement. Identifying unified measuring methods and developing measuring tools with a precision of hundred or ten microns will be the key to solving the problem about the authenticity of numerical measurement. Furthermore, this paper summarizes the methods of how to control tooth reduction and explains in depth why the currently dominant tooth preparation technology, which is based on empiricism, cannot effectively achieve the goals in digital prosthodontics. Therefore, we strongly call for rebuilding the digital foundation of prosthodontic treatment immediately.

Comparison of marginal and internal fit of pressed lithium disilicate veneers fabricated via a manual waxing technique versus a 3D printed technique

OBJECTIVE

The purpose of this in vitro study was to compare the marginal and internal fit of pressed lithium disilicate veneers fabricated from a 3D printed castable wax resin versus a manual waxing technique.

MATERIALS AND METHODS

A typodont model central incisor was prepared for a porcelain veneer. Following stone model fabrication from a polyvinyl siloxane impression, the model was digitized using a laboratory scanner. Group 1 veneers were designed digitally and 3D printed with a castable wax resin, then pressed. Group 2 veneers were fabricated using a manual wax and press approach. Veneers from both groups were bonded to printed dies. Following measurements of marginal adaptation under a stereo microscope, the dies were sectioned and measurements were made for internal adaption. Statistical analysis included a Kolmogorov test and a Mann-Whitney U test.

RESULTS

Average marginal gap (μm) for Group 1 was 40.37 ± 11.75 and 50.63 ± 16.99 for Group 2 (p = 0.51). Average internal gap (μm) for Group 1 was 61.21 ± 18.20 and 68.03 ± 14.07 for Group 2 (p = 0.178).

CONCLUSION

There was no difference in marginal fit or internal fit between pressed lithium disilicate veneers fabricated with a 3D printed castable resin and those fabricated with a manual waxing technique. The use of digital technologies and 3D printing provide significant advantages in the fabrication of pressed glass ceramic veneers, with marginal and internal adaptation comparable to manual wax and press techniques.

Minimal invasive microscopic tooth preparation in esthetic restoration: a specialist consensus

By removing a part of the structure, the tooth preparation provides restorative space, bonding surface, and finish line for various restorations on abutment. Preparation technique plays critical role in achieving the optimal result of tooth preparation. With successful application of microscope in endodontics for >30 years, there is a full expectation of microscopic dentistry. However, as relatively little progress has been made in the application of microscopic dentistry in prosthodontics, the following assumptions have been proposed: Is it suitable to choose the tooth preparation technique under the naked eye in the microscopic vision? Is there a more accurate preparation technology intended for the microscope? To obtain long-term stable therapeutic effects, is it much easier to achieve maximum tooth preservation and retinal protection and maintain periodontal tissue and oral function health under microscopic vision? Whether the microscopic prosthodontics is a gimmick or a breakthrough in obtaining an ideal tooth preparation should be resolved in microscopic tooth preparation. This article attempts to illustrate the concept, core elements, and indications of microscopic minimally invasive tooth preparation, physiological basis of dental pulp, periodontium and functions involved in tool preparation, position ergonomics and visual basis for dentists, comparison of tooth preparation by naked eyes and a microscope, and comparison of different designs of microscopic minimally invasive tooth preparation techniques. Furthermore, a clinical protocol for microscopic minimally invasive tooth preparation based on target restorative space guide plate has been put forward and new insights on the quantity and shape of microscopic minimally invasive tooth preparation has been provided.

[Minimal invasive microscopic tooth preparation based on endodontic, periodontal and functional health]

Tooth preparation is the primary and core operation technique for dental esthetic restoration treatment, due to its effect of providing restoration space, bonding interfaces and marginal lines for dental rehabilitation after tooth tissue reduction. The concept of microscopic minimal invasive dentistry put forward the issue of conducting high-quality tooth preparation, conserve tooth-structure, protect vital pulp and periodontal tissue simultaneously. This study reviewed the concepts, physiology background, design and minimal invasive microscopic tooth preparation, and in the meantime, individualized strategies and the two core elements of tooth preparation (quantity and shape) are listed.

A comparison of the marginal and internal fit of porcelain laminate veneers fabricated by pressing and CAD-CAM milling and cemented with 2 different resin cements

STATEMENT OF PROBLEM

The marginal and internal adaptations of porcelain laminate veneers (PLVs) are key elements in their long-term success. However, the marginal and internal fit obtained with a pressable material compared with computer-aided design and computer-aided manufacturing (CAD-CAM) needs further investigation as does the choice of cement used.

PURPOSE

The purpose of this in vitro study was to evaluate the marginal and internal fit of PLVs fabricated using pressing and CAD-CAM milling and cemented using 2 types of composite resin cement.

MATERIAL AND METHODS

Twenty PLVs were fabricated from VITA PM9 pressable material, and 20 veneers were milled using VITA Blocs Mark II. Veneers were cemented to composite resin dies using either RelyX Veneer cement or Variolink-N cement. Specimens were embedded in clear resin and sectioned incisogingivally and mesiodistally. Marginal discrepancy at the incisal and cervical positions and the internal gap at 6 different locations were evaluated by using a scanning electron microscope. Two-way ANOVA followed by Tukey multiple comparisons were used to examine difference among groups (α=.05).

RESULTS

The cement and fabrication methods did not show any significant effect for absolute marginal gap (AMG) at the incisal edge, AMG at the cervical margin or marginal gap at the incisal edge. However, both had a significant effect on marginal gap at the cervical margin (P=.038 for the fabrication method and P=.050 for the cement used). Also, both cement and fabrication methods had a significant effect on internal gap average (P<.001). The lowest gap values were reported for veneers fabricated from VITA PM9 by using the press technique and cemented with RelyX Veneer cement. When the position of gap measurements was taken into consideration, it was the only significant factor (P<.001 for the effect of position on AMG and P<.001 for the effect of position on marginal gap). Gaps at the cervical position were significantly lower than gaps at the incisal position.

CONCLUSIONS

Smaller marginal and internal discrepancies were recorded for PLVs fabricated by using the pressing technique and cemented using RelyX Veneer cement compared with milled veneers and Variolink-N cement. Larger discrepancies were present incisally than cervically.