The quality of fixed prosthodontic impressions: An assessment of crown and bridge impressions received at commercial laboratories

Conventional Dental Impressions vs. Impressions Reinforced with Rigid Mouthguards

The impression materials utilized today in dental medicine offer a good reproducibility and are easily accepted by patients. However, because they are polymer-based, they have issues regarding their dimensional stability. In this respect, the present work proposes a new type of dental impression, which is reinforced with rigid mouthguards. The aim of the study is to test the performances of such new impressions by comparing them to conventional ones-from this critical point of view, of the dimensional stability. Three types of polymeric materials were considered for both types of impressions: alginate, condensation silicone, and addition silicone. In order to obtain the new type of impressions, a manufacturing technique was developed, comprising the following phases: (i) conventional impressions were made; (ii) a plaster model was duplicated, and 15 rigid mouthguards were obtained; (iii) they were inserted in the impression technique, with each mouthguard positioned on the cast before the high-consistency material was inserted in the tray and the practitioner took the impression; (iv) the mouthguard remained in the tray and the low-viscosity material was inserted over the mouthguard; (v) the impression was positioned on the model, and after the material hardened, the mouthguard-reinforced impression was analyzed. In the evaluation of the dimensional stability, rigorous statistical analysis was essential to discern the performance differences between conventional and mouthguard-reinforced dental impressions. Statistical analyses employed non-parametric Mann-Whitney U tests because of the non-normal distribution of the data. They indicated a statistically significant improvement in the dimensional stability of addition silicone impressions when reinforced with mouthguards (p < 0.05), showcasing superior performance over conventional methods. Conversely, alginate and condensation silicone reinforced impressions did not exhibit the same level of stability improvement, suggesting the need for further optimization of these materials. In conclusion, from the three considered elastomers, addition silicone was found to be the prime candidate for high-precision dental impressions, with the potential to improve their quality from conventional impressions by utilizing the proposed reinforcing technique.

Addition Silicone Impressions in Fixed Prosthodontics: Clinical Standpoints

Addition silicones have revolutionized the field of fixed prosthodontics because of their dimensional stability, sufficient tear strength and excellent detail reproduction. This review study aims to provide a detailed description of the essential variables to be taken into account during the process of making addition silicone impressions in fixed prosthodontics. These variables include the selection of appropriate tray type, size, and fabrication; the use of tray adhesive; gingival displacement techniques; manipulation of the impression material; the choice of the impression material's viscosity; impression techniques; and the proper insertion, removal, disinfection, and pouring of the cast. Additionally, this review aims to help doctors produce high-quality impressions by empowering them to critically assess the impressions to spot mistakes and motivating them to redo impressions that have serious problems before submitting them to the laboratory.

Evaluation of the quality of fixed prosthesis impressions in private laboratories in a sample from Yemen

Background

Fixed prosthodontics require an accurate impression for the teeth and the area to be restored for the laboratory to fabricate the desired restoration without mistakes. This study evaluated the quality of impressions received by private laboratories for the fabrication of fixed prosthesis by describing the frequency of clinically detectable errors and by analyzing association between the various factors involved.

Methods

165 impressions were collected from four dental laboratories. Jaw involved, type of tray, size of tray, number of prepared units, type of impression materials, techniques and viscosity in case of elastomeric impressions and type of prosthesis requested were recorded. Data referring to errors and visible defects including errors in finish line, in preparation area, in silicone impression technique and blood in impression were also documented. Factors affecting errors present were also assessed. Association between dentist gender and experience years and impression errors was assessed. Chi square and Fisher exact tests used to examine the association between categorical variables and outcomes.

Results

The total of error considering not immediately pouring as an error. Alginate was the most impression used. of impressions evaluated (50.9%), 97% were have at least one visible error; 92.1% had errors in finish line, 53.9% had errors in preparation area and (72.8%) of elastomeric impressions were have at least one error in technique. Blood in impression was detected in 52.1% of impressions. Significant association was found between material type and errors in finishing line and preparation area. Significant relationships were found between gender and errors in silicone impression technique (p < 0.05).

Conclusion

Within the limitations of this study, high frequency of detectable errors was found in fixed prosthesis impressions received by private dental laboratories. This high frequency is of serious concern, as this will result in poor fitted fixed prosthesis provided to patients.

Comparison of Digital and Conventional Impression Methods by Preclinical Students: Efficiency and Future Expectations

Aims and Objectives:

The purpose of this study is to compare digital and conventional impression methods by preclinical students in terms of time and ease and to evaluate their preferences and future expectations.

Materials and Methods:

Twenty volunteered, 2^nd year preclinical students (11 females and 9 males) participated in this study. Students took digital and conventional impressions of the left lower first molar which was made full ceramic crown preparation and opposite full arch from a typodont model (Frasaco, Frasaco GmbH, Tettnang, Germany). They used intraoral scanner (CEREC Omnicam, Sirona Dental GmbH, Bensheim, Germany) for digital impression and also used additional type (Express XT Penta H, 3M ESPE, Seefeld, Germany) and condensation type (Zetaplus, Zhermack SpA, Badia Polesine, Italy) silicones for conventional impression. Their taking impression time was measured. Before taking impression and after taking impression, two kinds of questionnaires were conducted to students about their preference, ease of impression methods, and their future expectations. Statistical analysis was performed by IBM SPSS 23 and Excel 2010 version. Differences between conventional and digital impression in terms of time were analyzed by student’s-t paired test and effect of gender was analyzed by students’s-t independent test.

Results:

There were statistically significant differences between digital and conventional impression methods in terms of taking impression and total impression time (P < 0.001). But there wasn’t any statistically significant difference between two methods in terms of preparation time. About 85% of students preferred the digital impression method and also 85% of students found that the digital impression method was easy. 95% of students expected to find intraoral scanner in the clinic where working first time.

Conclusions:

As a result of this study, it has been seen that the students preferred the digital impression method to the conventional impression method and found that the digital impression method was easier.

Laboratory Technician Assessment of the Quality of Single-Unit Crown Preparations and Impressions as Predictors of the Clinical Acceptability of Crowns as Determined by the Treating Dentist: Findings from the National Dental Practice-Based Research Network

PURPOSE

In-laboratory assessment by laboratory technicians may offer insight to increase clinical success of dental crowns, and research in this area is lacking.

MATERIALS AND METHODS

Dentists in the National Dental Practice-Based Research Network enrolled patients in a study about single-unit crowns; laboratory technicians evaluated the quality of tooth preparations and impressions. The primary outcome for each crown was clinical acceptability (CAC), as judged by the treating dentist. A secondary outcome was "Goodness of Fit (GOF)," a composite score of several aspects of clinical fit, also judged by the study dentist. A mixed-effects logistic regression was used to analyze associations between laboratory technician ratings and the CAC and GOF.

RESULTS

Dentists (n = 205) evaluated 3731 crowns. Technicians ranked the marginal detail of impressions as good or excellent in 92% of cases; other aspects of the impression were ranked good or excellent 88% of the time. Regarding tooth preparation, about 90% of preparations were considered adequate (neither excessive nor inadequate reduction). Factors associated with higher CAC were more preparation taper, and use of optical imaging. Factors associated with better GOF were higher impression quality, greater occlusal reduction, more preparation taper, and optical imaging.

CONCLUSIONS

Overall quality of preparations and impressions was very high, as evaluated by laboratory technicians. Several clinical parameters were associated with higher CAC and GOF. Clinicians who struggle with crown remakes might consider less conservative tooth preparation, as well as using digital impression technology.

The segmental impression technique: A straightforward solution to a difficult problem

Trying to capture all the details of multiple teeth preparation in one impression is challenging. Techniques have been suggested to extend the working time of an impression material. This article describes a segmental impression technique to accurately capture all the preparation margins while allowing additional impression-making time.

Clinical acceptance of single-unit crowns and its association with impression and tissue displacement techniques: Findings from the National Dental Practice-Based Research Network

STATEMENT OF PROBLEM

The definitive impression for a single-unit crown involves many material and technique factors that may affect the success of the crown.

PURPOSE

The purpose of this prospective cohort study was to determine whether impression technique (tray selection), impression material, or tissue displacement technique are associated with the clinical acceptability of the crown (CAC).

MATERIAL AND METHODS

Dentists in the National Dental Practice-Based Research Network documented details of the preparation, impression, and delivery of 3730 consecutive single-unit crowns. Mixed-effects logistic regression analyses were performed to evaluate associations between impression techniques and materials and the CAC and to assess associations between the presence of a subgingival margin with the displacement technique and the outcome variables CAC and number of impressions required.

RESULTS

Of the 3730 crowns, 3589 (96.2%) were deemed clinically acceptable. A significant difference in the CAC was found with different impression techniques (P<.001) and different impression materials (P<.001). The percentage of the CAC for digital scans was 99.5%, 95.8% for dual-arch trays, 95.2% for quadrant trays, and 94.0% for complete-arch impression trays. Although no statistically significant difference was found in the CAC produced with dual-arch trays without both mesial and distal contacts, crowns fabricated under these conditions were less likely to achieve excellent occlusion. The percentage of the CAC for digital scans was 99.5%, 97.0% for polyether impressions, 95.5% for polyvinyl siloxane impressions, and 90.5% for other impression materials. Accounting for the location of the margin, the use of a dual-cord displacement technique was significantly associated with lower rates of requiring more than 1 impression (P=.015, odds ratio=1.43).

CONCLUSIONS

Dual-arch trays produced clinically acceptable crowns; however, if the prepared tooth was unbounded, the occlusal fit was more likely to have been compromised. Digital scans produced a slightly higher rate of CAC than conventional impression materials. The use of a dual-cord technique was associated with a decreased need to remake impressions when the margins were subgingival.

A clinical comparison of digital and conventional impression techniques regarding finish line locations and impression time

OBJECTIVE

This study compared digital and conventional impression techniques regarding impression time, frequency of adjustments, and adaptation of cobalt-chromium (Co-Cr) copings with supragingival and subgingival finish lines.

MATERIALS AND METHODS

Thirty premolars prepared for single-unit metal-ceramic restorations with supragingival and subgingival finish lines (n = 15). Conventional impression and digital scan of prepared teeth were made. Using computer aided design/computer aided manufacturing (CAD/CAM) system the copings were produced by a milling machine from Co-Cr blocks and internal and marginal discrepancies were measured using silicone replica technique. Data were analyzed using repeated measures ANOVA and Mann-Whitney test (alpha = .05).

RESULTS

The impression technique had a significant effect on the magnitude of gap (P < .001). The internal and marginal gaps in the digital technique (49.43 μ and 60.07 μ, respectively) were significantly lower than the values in the conventional method (91.88 μ and 96.96 μ, respectively-P < .001). Finish line positions had no significant effect on the fit and marginal gap of copings (P = .54 and .243, respectively). The mean impression time (19':27″ in conventional technique and 10':31″ in digital technique) was significantly shorter (P < .001) and the mean frequency of adjustments (2.2 times for conventional and 1.3 times for digital technique) was significantly lower in the digital technique (P < .001). The gingival biotype (thick or thin) had no significant effect on marginal and internal fit (P = .052 and .319, respectively).

CONCLUSION

The digital technique was superior in terms of fit, impression time, and frequency of adjustments. Finish line positions had no significant effect on the fit of copings.

CLINICAL SIGNIFICANCE

Using intraoral scanner promotes the fits of restorations in supragingival and subgingival finish lines.

Aplicabilidade clínica dos avanços da tecnologia CAD-CAM em Odontologia

O avanço tecnológico tem se mostrado um grande aliado em diversas áreas, assim como na odontologia. O surgimento da tecnológica CAD/CAM (Computer Aided Design/Computer Aided Manufacturing) na década de 1950 trouxe outra realidade para a prática clínica diária. Previamente todo o processo laboratorial de trabalhos protéticos era demorado e puramente físico, atualmente a fabricação das peças protéticas demanda um menor tempo devido a utilização do meio digital, o que consequentemente diminui as consultas aos Cirurgiões-Dentistas. A adição de ferramentas digitais no planejamento e na execução dos tratamentos odontológicos alterou completamente o workflow, fazendo com que a busca para um aperfeiçoamento seja constante visando sempre o melhor atendimento e qualidade dos tratamentos realizados. Dessa forma este trabalho tem o objetivo de realizar uma revisão crítica da literatura sobre a aplicabilidade clínica da tecnologia CAD-CAM em Odontologia.