SUMMARY
Objectives
The aim of this in vitro study is to evaluate the marginal and internal fit of zirconia core crowns manufactured following different digital and traditional workflows.
Methods
A 6° taper shoulder prepared abutment tooth was used to produce 20 zirconia core crowns using four different scanning techniques: scanned directly with the extraoral lab scanner, scanned with intraoral scanner, dental impressions using individual dental tray and polyether, dental casts from a polyether impressions. Marginal and internal fits were evaluated with digital photography and the silicone replica method.
Results
Medium marginal gaps were 76,00 μm ± 28.9 for extraoral lab scanner, 80.50 μm ± 36,2 for intraoral scanner, 88.10 μm ± 34,8 for dental impression scan and 112,4 μm ± 37,2 for dental cast scan. Medium internal gaps were 23.20 μm ± 10,3 for extraoral lab scanner, 16.20 μm ± 8.3 for intraoral scanner, 27.20 μm ± 16.7 for dental impression scan and 30.20 μm ± 12.7 for dental cast scan.
Conclusion
Internal gap were extensively lower than 70 μm described in literature. Marginal fit was higher than ideal values for all the techniques but within the limit of clinical success. Intraoral scanners obtained the best results for internal gap.
Keywords: dental impression materials, CAD/CAM, intraoral scanner, marginal fit
Introduction
The planning of a prosthetic rehabilitation is surely influenced by several factors, such as clinical preferences for the materials and preparation, treatment costs, aesthetics and patients chief compliant. The accuracy of the restoration, its mechanical stability and marginal adaptation but also a strict domestic and professional oral hygiene protocol represents the keys to success in the long-term clinical evaluation and patient satisfaction.
Inaccurate margins cause plaque accumulation increasing the risk of biological damage on periodontium (1) while an increased internal gap affect negatively mechanical retention and can cause ceramic fractures (2).
Recent advancements in computer-aided design and computer-aided manufacturing (CAD-CAM) technology for dental restorations allow the use of different materials, improving aesthetics, fit and efficiency of CAD-CAM rehabilitations (3–7). For these reasons digital workflow is already a reality in various clinical practises and dental laboratories.
Marginal adaptation and internal fit have been examined in various in vitro and clinical studies (8–10), showing a wide range of results. Unfortunately all these results are poorly comparable because of the numerous differences in the measurement protocols. In a recent systematic review, Authors concluded that there is a lack of univocal consensus in literature and current state of research does not allow for a proper comparison of the various systems suggesting further investigations (11).
The objective of this in vitro study is to evaluate and compare the marginal and internal fit of zirconia copings manufactured following different digital and traditional workflows (12).
Materials and methods
An upper first molar extracted for severe periodontitis was selected for this study. After the tooth has been cleaned and polished, an anti-reflection coating was applied to achieve an optimal accuracy of the 3D scan. From the digital 3D copy of the tooth a digital shoulder preparation with an ideal axial wall taper of 6° was designed (Figure 1). The project was sent to the milling machine (Roland DWX-50, ROLAND 60 DG Mid Europe Srl, Italy) to obtain a zirconia replica of the abutment tooth. Zirconia (NexxZr, Sagemax Europe S.r.l.) was selected as the ideal material for the master cast for its high stability and resistance. The zirconia abutment tooth was finally sintered.
Figure 1.
Digital shoulder preparation with an ideal axial wall taper of 6°.
The abutment tooth was used to produce zirconia copings using four different scanning techniques:
the abutment tooth was scanned directly with the extraoral lab scanner (Dental wings Serie 7) (DE). This ideal situation cannot be repeated clinically and is used as reference for the other three
the abutment tooth was scanned with intraoral scanner (MHT scanner, 3D progress) (DI)
dental impressions of the abutment tooth were taken using individual resin dental tray and a high viscosity polyether (impregum, 3M ESPE). Dental impressions were directly scanned with extraoral lab scanner (TI)
dental casts were prepared with dental stone (Elite stone type IV, Zhermack) from polyether dental impressions and finally scanned with extraoral lab scanner (TC).
Every workflow was repeated five times for a total of 20 different zirconia copings.
Marginal fit was evaluated with digital photography (Figure 2). Three pictures for each zirconia copings were taken using a SLR digital camera (Canon EOS 350d, 60mm macro lens and ring flash) (13). The camera was positioned on a tripod and the abutment tooth was placed on a support which could only rotate every 60°. All the pictures were imported and analysed using an image processing program (ImageJ, opensource).
Figure 2.
Marginal fit evaluated with the image processing program (ImageJ, opensource).
Internal fit was evaluated using the silicone replica method for the evaluation of marginal fit of cast crown described in 2008 by Laurent et al. (14). The impressions were taken with a low viscosity polyether (Permadyne Light Body, 3M ESPE).
Measurements were performed at five points (occlusal, vestibular, palatal, distal and mesial) for each silicone replica. These five points were marked on the abutment tooth and then reported on the silicone replica to measure always the same points. Measurements were performed using a thickness gauge (Figure 3).
Figure 3.
Measurement of internal fit was evaluated using the silicone replica method and a thickness gauge.
Statistical analysis
All the values were reported as individual data on the statistic software (SPSS, IBM). Median and standard deviation were calculated. Statistical analysis was performed using non-parametric Kruskal-Wallis test and Wilcoxon-Mann-Whitney test setting comparing groups results for both marginal and internal fit using data obtained for extraoral lab scanner (DE) as references. The value p<0.05 was considered as the limit of statistical significance.
Results
In this study 20 zirconia copings obtained from four different scanning techniques of an ideal abutment tooth were evaluated.
Regarding marginal fit data are shown in Table 1. Medium marginal gaps were 76,00 μm ± 28.9 for extraoral lab scanner (DE), 80.50 μm ± 36,2 for intraoral scanner (DI), 88.10 μm ± 34,8 for dental impression scan (TI) and 112,4 μm ± 37,2 for dental cast scan (TC). A statistical significant difference was found for both dental cast (p= 0.005) and dental impression (p=0.024) but not for digital intraoral scanner (p>0.05). Regarding internal fit data are shown in Table 2.
Table 1.
Marginal gap values for the three positions. Values are expressed in micrometre.
| DE | DI | TI | TC | |
|---|---|---|---|---|
| Position 1 | ||||
| DX | 52 | 130 | 73 | 61 |
| 49 | 25 | 127 | 181 | |
| 77 | 57 | 98 | 101 | |
| 81 | 15 | 102 | 163 | |
| 60 | 75 | 115 | 146 | |
| SX | 93 | 141 | 34 | 180 |
| 120 | 50 | 137 | 96 | |
| 30 | 78 | 102 | 160 | |
| 117 | 124 | 56 | 112 | |
| 119 | 29 | 126 | 119 | |
| Position 2 | ||||
| DX | 48 | 66 | 52 | 53 |
| 63 | 24 | 30 | 38 | |
| 19 | 86 | 39 | 170 | |
| 35 | 54 | 34 | 75 | |
| 85 | 83 | 52 | 128 | |
| SX | 49 | 82 | 90 | 147 |
| 83 | 90 | 85 | 74 | |
| 89 | 98 | 123 | 125 | |
| 73 | 126 | 84 | 113 | |
| 58 | 123 | 113 | 78 | |
| Position 3 | ||||
| DX | 67 | 80 | 46 | 68 |
| 106 | 101 | 53 | 116 | |
| 54 | 18 | 108 | 83 | |
| 53 | 61 | 103 | 135 | |
| 96 | 89 | 78 | 98 | |
| SX | 112 | 106 | 128 | 118 |
| 126 | 86 | 83 | 114 | |
| 65 | 124 | 159 | 99 | |
| 103 | 64 | 113 | 113 | |
| 98 | 130 | 100 | 108 | |
| mean | 76,0 | 80,5 | 88,1 | 112,4 |
| DS | 28,9 | 36,2 | 34,8 | 37,2 |
Table 2.
Internal fit values for the four different zirconia core caps in occlusal, buccal, palatal, mesial and distal position. Values are expressed in micrometre.
| O | B | P | M | D | |
|---|---|---|---|---|---|
| 1 | 20 | 10 | 30 | 5 | 30 |
| 2 | 30 | 20 | 40 | 5 | 20 |
| 3 | 30 | 15 | 40 | 5 | 30 |
| 4 | 20 | 15 | 25 | 10 | 20 |
| 5 | 20 | 10 | 30 | 5 | 20 |
| Mean | 23,2 | ||||
| DS | 10,3 | ||||
| DI | |||||
| 1 | 40 | 20 | 20 | 15 | 20 |
| 2 | 30 | 10 | 10 | 15 | 10 |
| 3 | 20 | 5 | 10 | 15 | 10 |
| 4 | 20 | 5 | 30 | 10 | 20 |
| 5 | 20 | 10 | 20 | 10 | 10 |
| Mean | 16,2 | ||||
| DS | 8,3 | ||||
| TI | |||||
| 1 | 60 | 20 | 50 | 50 | 30 |
| 2 | 30 | 10 | 20 | 20 | 40 |
| 3 | 40 | 10 | 10 | 10 | 50 |
| 4 | 40 | 15 | 10 | 15 | 40 |
| 5 | 50 | 10 | 10 | 10 | 30 |
| Mean | 27,2 | ||||
| DS | 16,7 | ||||
| TC | |||||
| 1 | 30 | 40 | 50 | 60 | 60 |
| 2 | 30 | 40 | 20 | 15 | 25 |
| 3 | 30 | 20 | 30 | 15 | 30 |
| 4 | 30 | 20 | 30 | 40 | 30 |
| 5 | 20 | 10 | 30 | 20 | 30 |
| Mean | 30,2 | ||||
| DS | 12,7 | ||||
Medium internal gaps were 23.20 μm ± 10,3 for extraoral lab scanner (DE), 16.20 μm ± 8.3 for intraoral scanner (DI), 27.20 μm ± 16.7 for dental impression scan (TI) and 30.20 μm ± 12.7 for dental cast scan (TC). A statistical significant difference was found for both dental cast (p= 0.007) and dental impression (p=0.028) but not for digital intraoral scanner (p>0.05) that even obtain a better performance than extraoral lab scanner.
Discussions
In the last few years, advancements in CAD-CAM technologies and digital intraoral scanners allowed a complete digital workflow for prosthetic rehabilitations in order to eliminate the impression taking phase and all traditional dental casts. Several studies evaluated the accuracy of intraoral scanners comparing their performance to traditional impressions, highlighting many limits in intraoral conditions particularly for subgingival margins and particular areas such as retromolar region. There is a lack of univocal consensus in literature regarding which workflow is more accurate: some Authors show better results for traditional workflow (15), while others show comparable (16, 17) or even better for digital workflow (18). Marginal and internal fits are objective factors for the clinical success of our rehabilitations. Marginal accuracy is important to reduce plaque accumulation and secondary cavities (19–21). Authors suggested the goal of 25–40 μm for marginal fit while nowadays 75–160 μm are considered clinically successful (22). Internal fit is necessary to avoid crowns fracture and mechanical dislocation. Tuntiprawon et al. (23) set a 70 μm cutoff for internal gap beyond which crown fracture occurs even for physiological bite force.
The aim of this in vivo study was to compare both marginal and internal fit of zirconia copings obtained from four different impression techniques. The first technique, scanning the abutment tooth with an extraoral lab scanner, is obviously not achievable clinically and was used as reference for the following three: intraoral scanner, scan of a polyether impression and scan of a type IV dental stone cast obtained by a traditional impression.
Marginal fit was evaluated with a specific software of image processing. Statistical significant differences were found for both traditional protocols. The most inaccurate procedure results the scan of dental cast surely affected by dimensional alterations of both impression material and dental stone. Intraoral scanner showed comparable result to extraoral reference scanner confirming previous researches (15, 16, 24–26). It must be kept in mind that results for intraoral scanners can be affected positively in in vitro studies due to ideal condition that are impossible to achieve clinically. For these reasons Authors expect a worsening of intraoral results in real clinical situation.
Internal gap was evaluated using the silicone replica technique validated by Laurent in 2008 (14). All the values that we obtained were extensively lower than 70 μm described in literature suggesting that both digital and traditional workflow are sufficiently precise. A particular interesting finding was that intraoral scanner showed even better results than the extraoral scanner. Obviously these results are not affected by saliva, crevicular fluid, teeth position and oral conformation but anyway highlight the high quality of recent intraoral scanners.
In conclusion marginal fit was higher that ideal values for all the techniques but comparable with other studies in literature and within the limit of clinical success. Intraoral scanner obtained the best results for internal gap but further clinical in vivo research are needed to confirm these results.
Footnotes
Disclosure
Funding: none.
Competing interests: none.
Ethical approval: not required.
Patient permission: not required.
References
- 1.Amiri-Jezeh M, Rateitschak E, Weiger R, Walter C. The impact of the margin of restorations on periodontal health-a review. Schweizer Monatsschrift für Zahnmedizin. 2006;116(6):606–13. [PubMed] [Google Scholar]
- 2.Nakamura T, Sugano T, Usami H, et al. Fitting accuracy and fracture resistance of crowns using a hybrid zirconia frame made of both porous and dense zirconia. Dent Mater J. 2015;34(2):257–62. doi: 10.4012/dmj.2014-145. [DOI] [PubMed] [Google Scholar]
- 3.Dogan DO, Gorler O, Mutaf B, Ozcan M, Eyuboglu GB, Ulgey M. Fracture Resistance of Molar Crowns Fabricated with Monolithic All-Ceramic CAD/CAM Materials Cemented on Titanium Abutments: An In Vitro Study. J Prosthodont. 2015 doi: 10.1111/jopr.12393. [DOI] [PubMed] [Google Scholar]
- 4.Lee K-H, Yeo I-S, Wu BM, et al. Effects of Computer-Aided Manufacturing Technology on Precision of Clinical Metal-Free Restorations. Biomed Res Int. 2015;2015:619027. doi: 10.1155/2015/619027. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.Gargari M, Lorè B, Ceruso FM. Esthetic and function rehabilitation of severely worn dentition with prosthetic-restorative approach and VDO increase. Case report. ORAL and Implantology. 2014 Apr;7(2):40–45. [PMC free article] [PubMed] [Google Scholar]
- 6.Spinelli D, Ottria L, De Vico G, Bollero R, Barlattani A, Jr, Bollero P. Full rehabilitation with nobel clinician® and procera implant bridge®: Case report. ORAL and Implantology. 2013 Apr;6(2):25–36. [PMC free article] [PubMed] [Google Scholar]
- 7.Gargari M, Prete V, Pujia A, Ceruso FM. Full-arch maxillary rehabilitation fixed on 6 implants. ORAL and Implantology. 2013;6(1):1–4. [PMC free article] [PubMed] [Google Scholar]
- 8.Fathi HM, Al-Masoody AH, El-Ghezawi N, Johnson A. The Accuracy of Fit of Crowns Made From Wax Patterns Produced Conventionally (Hand Formed) and Via CAD/CAM Technology. Eur J Prosthodont Restor Dent. 2016;24(1):10–7. [PubMed] [Google Scholar]
- 9.Rajan BN, Jayaraman S, Kandhasamy B, Rajakumaran I. Evaluation of marginal fit and internal adaptation of zirconia copings fabricated by two CAD - CAM systems: An in vitro study. J Indian Prosthodont Soc. 2015;15(2):173–8. doi: 10.4103/0972-4052.159970. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Kocaağaoğlu H, Kılınç HI, Albayrak H. Effect of digital impressions and production protocols on the adaptation of zirconia copings. J Prosthet Dent. 2016 doi: 10.1016/j.prosdent.2016.06.004. [DOI] [PubMed] [Google Scholar]
- 11.Contrepois M, Soenen A, Bartala M, Laviole O. Marginal adaptation of ceramic crowns: A systematic review. J Prosthet Dent. 2012;110(6):447–454.e10. doi: 10.1016/j.prosdent.2013.08.003. [DOI] [PubMed] [Google Scholar]
- 12.Gargari M, Ottria L, Morelli V, Benli M, Ceruso FM. Conservative zirconia-ceramic bridge in front teeth. Case report. ORAL and Implantology. 2015 Oct;7( 4):93–98. [Google Scholar]
- 13.Casaglia A, De Dominicis P, Arcuri L, Gargari M, Ottria L. Dental photography today. Part 1: Basic concepts. ORAL and Implantology. 2016;8(4):122–129. doi: 10.11138/orl/2015.8.4.122. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Laurent M, Scheer P, Dejou J, Laborde G. Clinical evaluation of the marginal fit of cast crowns – validation of the silicone replica method. J Oral Rehabil. 2008:116–22. doi: 10.1111/j.1365-2842.2003.01203.x. [DOI] [PubMed] [Google Scholar]
- 15.Mehl A, Ender A, Mörmann W, Attin T. Accuracy testing of a new intraoral 3D camera. Int J Comput Dent. 2009;12(1):11–28. [PubMed] [Google Scholar]
- 16.Ender A, Mehl A. Accuracy of complete-arch dental impressions: a new method of measuring trueness and precision. J Prosthet Dent. 2013;109(2):121–8. doi: 10.1016/S0022-3913(13)60028-1. [DOI] [PubMed] [Google Scholar]
- 17.Di Fiore A, Meneghello R, Savio G, Sivolella S, Katsoulis J, Stellini E. In Vitro Implant Impression Accuracy Using a New Photopolymerizing SDR Splinting Material. Clin Implant Dent Relat Res. 2015;17( Suppl 2):e721–9. doi: 10.1111/cid.12321. [DOI] [PubMed] [Google Scholar]
- 18.Syrek A, Reich G, Ranftl D, Klein C, Cerny B, Brodesser J. Clinical evaluation of all-ceramic crowns fabricated from intraoral digital impressions based on the principle of active wavefront sampling. J Dent. 2010;38(7):553–9. doi: 10.1016/j.jdent.2010.03.015. [DOI] [PubMed] [Google Scholar]
- 19.Lang NP, Kiel RA, Anderhalden K. Clinical and microbiological effects of subgingival restorations with overhanging or clinically perfect margins. J Clin Periodontol. 1983;10(6):563–78. doi: 10.1111/j.1600-051x.1983.tb01295.x. [DOI] [PubMed] [Google Scholar]
- 20.Knoernschild KL, Campbell SD. Periodontal tissue responses after insertion of artificial crowns and fixed partial dentures. J Prosthet Dent. 2000;84(5):492–8. doi: 10.1067/mpr.2000.110262. [DOI] [PubMed] [Google Scholar]
- 21.Tao J, Yoda M, Kimura K, Okuno O. Fit of metal ceramic crowns cast in Au-1.6 wt% Ti alloy for different abutment finish line curvature. Dent Mater. 2006;22( 5):397–404. doi: 10.1016/j.dental.2005.04.025. [DOI] [PubMed] [Google Scholar]
- 22.Nawafleh NA, Mack F, Evans J, Mackay J, Hatamleh MM. Accuracy and reliability of methods to measure marginal adaptation of crowns and FDPs: a literature review. J Prosthodont. 2013;22(5):419–28. doi: 10.1111/jopr.12006. [DOI] [PubMed] [Google Scholar]
- 23.Tuntiprawon M, Wilson PR. The effect of cement thickness on the fracture strength of all-ceramic crowns. Aust Dent J. 1995;40(1):17–21. doi: 10.1111/j.1834-7819.1995.tb05607.x. [DOI] [PubMed] [Google Scholar]
- 24.Beuer F, Schweiger J, Edelhoff D. Digital dentistry: an overview of recent developments for CAD/CAM generated restorations. Br Dent J. 2008;204(9):505–11. doi: 10.1038/sj.bdj.2008.350. [DOI] [PubMed] [Google Scholar]
- 25.Fasbinder DJ. Digital dentistry: innovation for restorative treatment. Compend Contin Educ Dent. 2010:2–11. quiz 12. [PubMed] [Google Scholar]
- 26.Luthardt RG, Loos R, Quaas S. Accuracy of intraoral data acquisition in comparison to the conventional impression. Int J Comput Dent. 2005;8(4):283–94. [PubMed] [Google Scholar]