Assessment of internal fit and micro leakage of conventionally fabricated ceramometallic restoration versus CAD wax and press veneering (in-vitro study)

Abstract Statement of problem Accuracy of internal fit and microleakage for CAD-CAM systems used in metal coping fabrication and veneered with layering or pressing porcelain in ceramometallic restoration is unclear. Material and methods A master metal die was milled to resemble the right mandibular first molar preparation for coverage with ceramometallic restoration. Master die was duplicated to twenty-four resin specimen dies.They were divided into two groups according to metal coping construction technique using either conventional (C) or CAD (D) wax. Each group was subdivided into two subgroups (n = 6) according to the technique of porcelain veneering (layered or pressed) to fabricate ceramometallic restorations, where subgroup (CL, DL) were conventionally layered by porcelain and (CP, DP) were press veneered. A standardized thickness of metal and porcelain was performed in all specimens as per manufacturer’s instructions for techniques ceramometallic restoration construction. Evaluation of internal fit was done with silicone replica technique using stereomicroscope at ×24 magnification where the thickness of silicon layer was measured at 20 reference points on each specimen. Then specimens were subjected to thermocycling. Sectioned specimens were assessed for microleakage using a stereomicroscope at ×12 magnification along die-cement interface with a five scale score. Results Mean internal gap values of veneering showed a statistically nonsignificant difference between specimens made with layering(L) and pressing(P). Different techniques of wax construction showed a non-significant difference in internal gap values between specimens made with conventional(C) and CAD(D) waxing. However, a significant difference was found in the internal gap at different sites. The highest internal gap was found at the occlusal surface, while the lowest gap was found at the finish line. The highest mean microleakage score was found with CAD wax and press veneering, while the lowest mean microleakage score was found with conventional wax and press veneering. Conclusion Both construction techniques of ceramometallic restoration were considered reliable in restoration production within a clinically acceptable range regarding internal fit and microleakage. There is a strong positive correlation between internal fit and microleakage of ceramometallic restoration constructed.

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Influence of two different cement space settings and three different cement types on the fit of polymer-infiltrated ceramic network material crowns manufactured using a complete digital workflow

Clinical Oral Investigations ◽

10.1007/s00784-019-03053-1 ◽

2019 ◽

Vol 24 (6) ◽

pp. 1929-1938 ◽

Cited By ~ 1

Author(s):

Rinet Dauti ◽

Bledar Lilaj ◽

Patrick Heimel ◽

Andreas Moritz ◽

Andreas Schedle ◽

...

Keyword(s):

Ct Scanning ◽

Adhesive System ◽

Digital Workflow ◽

Mean Values ◽

Relyx Unicem ◽

Significant Difference ◽

Marginal Discrepancy ◽

Materials Used ◽

Internal Fit ◽

Internal Gap

Abstract Objectives The study evaluates the influence of two spacer settings and three resin luting materials on the marginal and internal fit of polymer-infiltrated ceramic network (PICN) material crowns manufactured using a complete digital workflow. Methods Optical impressions of fifty identical dies were performed using the 3M scanner (software version 5.0.2). Twenty crowns were designed using Ceramill Mind (version 3.4.10.1163), from which ten with spacer setting of 50 μm (G1) and ten with 80 μm (G2). Thirty crowns (spacer setting of 50 μm) were divided into three groups corresponding to the resin materials used as follows: RelyX Unicem (RX), Variolink Esthetic (VLE), and Nexus 3 (NX3). All crowns were milled from Vita Enamic blocks. After micro-CT scanning, absolute marginal discrepancy (AMD), internal gap (IG), total cement space volume (TCV), and marginal porosities (VP) were measured. Results Significant difference was detected on the VP between the RX and NX3 group (p = 0.033). The mean values of all parameters were the following: AMD (μm): G1 182.6, G2 253.7, RX 210.8, VLE 195.5, NX3 186.6; IG (μm): G1 215.6, G2 173.1, RX 171.1, VLE 198.6, NX3 203; TCV (mm3): G1 22.9, G2 20.49, RX 17.57, VLE 17.49, NX3 20.59; VP (mm3): G1 0.26, G2 0.34, RX 0.32, VLE 0.46, NX3 0.54. Conclusions Fit of PICN material crowns was not significantly influenced by increasing the spacer settings and cementation with different resin materials. Additionally, RelyX Unicem showed significantly less porosities as compared with Nexus3. Clinical relevance Both 50 μm and 80 μm virtual spacer settings can be suggested for the manufacture of PICN crowns when Ceramill Mind (version 3.4.10.1163) is used. Furthermore, a self-adhesive system can be recommended for the cementation.

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Evaluating the effect of different combination of impression and pouring materials on marginal and internal adaptation of zirconia crowns.

Journal Of Oral Research ◽

10.17126/joralres.2020.083 ◽

2020 ◽

Vol 9 (5) ◽

pp. 414-422

Author(s):

Safoura Ghodsi ◽

◽

Sara Mogharrabi ◽

Samane Jalali ◽

Asadallah Ahmadzadeh ◽

...

Keyword(s):

Finish Line ◽

Significant Difference ◽

Different Types ◽

Cad Cam ◽

Zirconia Crowns ◽

Maxillary Premolars ◽

Internal Adaptation ◽

The Mean ◽

Internal Gap ◽

Exact Relationship

Purpose: Two important factors in dental prosthesis are making an accurate impression and producing a suitable cast which represents the exact relationship between prepared tooth and oral structures. This study, aimed to investigate the effects of different combinations of impression and pouring materials on marginal and internal adaptation of premolar zirconia crowns. Material and Methods: Forty maxillary premolars were prepared considering round shoulder finish line. The impressions were made either by additional (Panasil) or condensation (Speedex) silicon, and poured by two different types of gypsum materials (Siladent or GC gypsum) (N=10). Zirconia crowns were fabricated using a CAD-CAM system. The crowns were cemented, and the samples were cut in bucco-lingual direction. Marginal and internal gaps were measured by stereomicroscope (×25). Results: The mean marginal gaps for Pansil-Siladent, Panasil-GC, Speedex-Siladent, and Speedex-GC were 141 μm, 143 μm, 131 μm, and 137 μm respectively. The internal gaps were 334 μm, 292 μm, 278 μm, and 257 μm respectively. The independent T-Student test showed no significant differences in average marginal or internal gap among various impression and gypsum materials or their interactions (p>0.05). Two-way ANOVA test showed no significant differences in maximum marginal or internal gap among various impression and gypsum materials and their interactions (p>0.05). Conclusion: The present study revealed no statistically significant difference in marginal/internal gap among crowns prepared using different combinations of impression-pouring materials evaluated.

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Tomographic Evaluation of the Internal Adaptation for Recent Calcium Silicate-Based Pulp Capping Materials in Primary Teeth

BioMed Research International ◽

10.1155/2021/5523145 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

A. A. Al Tuwirqi ◽

E. A. El Ashiry ◽

A. Y. Alzahrani ◽

N. Bamashmous ◽

T. A. Bakhsh

Keyword(s):

Primary Teeth ◽

Control Group ◽

Strong Positive Correlation ◽

Micro Ct ◽

Positive Correlation ◽

Pulp Capping ◽

Significant Difference ◽

Internal Adaptation ◽

Group B ◽

Internal Gap

Objectives. To evaluate the internal adaptation of recent pulp capping materials (TheraCal and Biodentine) relative to MTA when used as indirect pulp capping for primary teeth. Materials and Methods. Thirty primary molars were randomly allocated into three groups, group (A) was TheraCal, group (B) was Biodentine, and MTA was the control group (C). A standardized round class-V cavity (1.5 mm diameter and 2 mm depth) was prepared using a milling machine on the buccal surface of each tooth with the pulpal floor located on the dentin. Then, pulp-capping materials were applied. Finally, all teeth were restored by composite restoration. The internal adaptation of the pulp-capping materials to the dentinal surface was investigated by microcomputed tomography (Micro-CT) to determine the internal gap volume, and by optical coherence tomography (OCT) to determine the high-intensity reflection of light from the floor. Results. Based on Micro-CT findings, TheraCal showed significantly higher internal gap volume than both MTA and Biodentine ( p < 0.001 ), while MTA and Biodentine did not show a significant difference in the gap volume. Based on the OCT findings, TheraCal showed a significantly higher intensity of light reflection than both MTA and Biodentine ( p < 0.001 ); however, there was no significant difference between MTA and Biodentine. Pearson’s correlation test showed that there was a strong positive correlation between Micro-CT and OCT ( r = 0.686 , N = 30 , p < 0.001 ). Conclusions. Biodentine and MTA showed a comparable result in terms of their internal adaptation on the dentinal surface of the primary teeth, and both were better than TheraCal. There is a moderate to a strong positive correlation between Micro-CT and OCT in the measurement of internal adaptation of the tested pulp capping materials. OCT can be helpful and beneficial for the clinical setting and allow dentists to screen and evaluate restorations during follow-up.

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Does Resin Cement Type and Cement Preheating Influence the Marginal and Internal Fit of Lithium Disilicate Single Crowns?

Materials ◽

10.3390/ma15020424 ◽

2022 ◽

Vol 15 (2) ◽

pp. 424

Author(s):

Nourhan Samy ◽

Walid Al-Zordk ◽

Ahmed Elsherbini ◽

Mutlu Özcan ◽

Amal Abdelsamad Sakrana

Keyword(s):

Lithium Disilicate ◽

Resin Cement ◽

The Other ◽

Cement Type ◽

Finish Line ◽

Marginal Fit ◽

Single Crown ◽

Significant Difference ◽

Internal Fit ◽

Single Crowns

This paper assesses the effect of cement type and cement preheating on the marginal and internal fit of lithium disilicate single crown. Methods: 40 maxillary premolars were selected, restored with lithium disilicate single crowns. Teeth were randomly assigned into four groups (n = 10) based on cement type (Panavia SA or LinkForce) and preheating temperature (25 °C or 54 °C). After fabrication of the restoration, cements were incubated at 25 °C or 54 °C for 24 h, and each crown was cemented to its corresponding tooth. After 24 h, all specimens were thermally aged to (10,000 thermal cycles between 5 °C and 55 °C), then load cycled for 240,000 cycles. Each specimen was then sectioned in bucco-palatal direction and inspected under a stereomicroscope at x45 magnification for marginal and internal fit evaluation. The data were statistically analyzed (significance at p ≤ 0.05 level). Results: At the mid-buccal finish line, mid-buccal wall, palatal cusp, mid-palatal wall, mid-palatal finish line, and palatal margin measuring points, there was a significant difference (p ≤ 0.05) between the lithium disilicate group cemented with Panavia SA at 25 °C and the group cemented with LinkForce at 25 °C, while there was no significant difference (p > 0.05) at the other points. At all measuring points, except at the palatal cusp tip (p = 0.948) and palatal margin (p = 0.103), there was a statistically significant difference (p ≤ 0.05) between the lithium disilicate group cemented with Panavia SA at 54 °C and the group cemented with LinkForce at 54 °C. Regardless of cement preheating, statistically significant differences were found in the buccal cusp tip, central groove, palatal cusp tip, and mid-palatal wall (p ≤ 0.05) in the lithium disilicate group cemented with Panavia SA at 25 °C and 54 °C, as well as the mid-palatal chamfer finish line and palatal margin in the LinkForce group cemented with Panavia SA at 25 °C and 54 °C. At the other measurement points, however, there was no significant difference (p > 0.05). Conclusions: The type of resin cement affects the internal and marginal fit of lithium disilicate crowns. At most measuring points, the cement preheating does not improve the internal and marginal fit of all lithium disilicate crowns.

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Determination of vertical dimension of occlusion by using the phonetic vowel "O" and "E"

Vojnosanitetski pregled ◽

10.2298/vsp1502123i ◽

2015 ◽

Vol 72 (2) ◽

pp. 123-131 ◽

Cited By ~ 6

Author(s):

Marko Igic ◽

Nebojsa Krunic ◽

Ljiljana Aleksov ◽

Milena Kostic ◽

Aleksandra Igic ◽

...

Keyword(s):

Cognitive Functions ◽

Complete Denture ◽

Reference Points ◽

Vertical Dimension ◽

Entire Sample ◽

Average Value ◽

Significant Difference ◽

The Relationship

Background/Aim. The vertical dimension of occlusion is a very important parameter for proper reconstruction of the relationship between the jaws. The literature describes many methods for its finding, from the simple, easily applicable clinically, to quite complicated, with the use of one or more devices for determination. The aim of this study was to examine the possibility of determining the vertical dimension of occlusion using the vocals ?O? and ?E? with the control of values o btained by applying cognitive functions. Methods. This investigation was performed with the two groups of patients. The first group consisted of 50 females and 50 males, aged 18 to 30 years. In this group the distance between the reference points (on top of the nose and chin) was measured in the position of the mandible in the vertical dimension of occlusion, the vertical dimension at rest and the pronunciation of the words ?OLO? and ?ELE?. Checking the correctness of the particular value for the word ?OLO? was also performed by the phonetic method with the application of cognitive exercises when the patients counted from 89 to 80. The obtained difference in the average values i n determining the vertical dimension of occlusion and the ?OLO? and ?ELE? in the first group was used as the reference for determining the vertical dimension of occlusion in the second group of patients. The second group comprised of 31 edentulous persons (14 females and 17 males), aged from 54 to 85 years who had been made a complete denture. Results. The average value obtained for the vertical dimension of rest for the entire sample was 2.16 mm, for the word ?OLO? for the entire sample was 5.51 mm and for the word ?ELE? for the entire sample was 7.47 mm. There was no statistically significant difference between the genders for the value of the vertical dimension at rest, ?ELE? and ?OLO?. There was a statistically significant difference between the values f or the vertical dimension at rest, ?OLO? and ?ELE? for both genders. There was a statistically significant correlation between the value for the vertical dimension at rest, ?OLO? and ?ELE?, for both groups of subjects. Conclusion. Determining the vertical dimension of occlusion requires 5.5 mm subtraction from the position of the mandible in pronunciation of the word ?OLO? or 7.5 mm in pronunciation of the word ?ELE?.

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Marginal and Internal Fit of Ceramic Prostheses Fabricated from Different Chairside CAD/CAM Systems: An In Vitro Study

Applied Sciences ◽

10.3390/app11020857 ◽

2021 ◽

Vol 11 (2) ◽

pp. 857

Author(s):

Keunbada Son ◽

Kyu-Bok Lee

Keyword(s):

Computer Aided Design ◽

In Vitro Study ◽

Vitro Study ◽

Marginal Gap ◽

Significant Difference ◽

Cad Cam ◽

Ceramic Crowns ◽

Internal Fit ◽

Cam Systems

The purpose of this in vitro study was to evaluate marginal and internal fits of ceramic crowns fabricated with chairside computer-aided design and manufacturing (CAD/CAM) systems. An experimental model based on ISO 12836:2015 was digitally scanned with different intraoral scanners (Omnicam (CEREC), EZIS PO (DDS), and CS3500 (Carestream)). Ceramic crowns were fabricated using the CAD/CAM process recommended by each system (CEREC, EZIS, and Carestream systems; N = 15). The 3-dimensional (3D) marginal and internal fit of each ceramic crown was measured using a 3D inspection software (Geomagic control X). Differences among the systems and various measurements were evaluated using the Kruskal–Wallis test. Statistically significant differences were validated using pairwise comparisons (α = 0.05). Occlusal gaps in the CEREC, EZIS, and Carestream groups were 113.0, 161.3, and 438.2 µm, respectively (p < 0.001). The axial gaps were 83.4, 78.0, and 107.9 µm, respectively. The marginal gaps were 77.8, 99.3, and 60.6 µm, respectively, and the whole gaps were 85.9, 107.3, and 214.0 µm, respectively. Significant differences were observed with the EZIS system compared with the other two systems in terms of the marginal gap sizes. The CEREC system showed no significant differences among the four measured regions. However, the EZIS and Carestream systems did show a statistically significant difference (p < 0.05). All three systems were judged to be capable of fabricating clinically acceptable prostheses, because the marginal gap, which is the most important factor in the marginal fit of prostheses, was recorded to be below 100 µm in all three systems.

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Comparison of hematological parameters and perinatal outcomes between COVID-19 pregnancies and healthy pregnancy cohort

Journal of Perinatal Medicine ◽

10.1515/jpm-2020-0403 ◽

2020 ◽

Vol 0 (0) ◽

Author(s):

Esin Merve Erol Koç ◽

Rahime Bedir Fındık ◽

Hatice Akkaya ◽

Işılay Karadağ ◽

Eda Özden Tokalıoğlu ◽

...

Keyword(s):

Complete Blood Count ◽

Perinatal Outcomes ◽

Control Group ◽

Strong Positive Correlation ◽

Monocyte Count ◽

Distribution Width ◽

Neutrophil Lymphocyte Ratio ◽

Lymphocyte Ratio ◽

Significant Difference ◽

Adverse Perinatal Outcomes

AbstractObjectivesTo evaluate the relationship between Coronavirus Disease 2019 (COVID-19) in pregnancy and adverse perinatal outcomes. The secondary aim is to analyze the diagnostic value of hematologic parameters in COVID-19 complicated pregnancies.MethodsThe current study is conducted in a high volume tertiary obstetrics center burdened by COVID-19 pandemics, in Turkey. In this cohort study, perinatal outcomes and complete blood count indices performed at the time of admission of 39 pregnancies (Study group) complicated by COVID-19 were compared with 69 uncomplicated pregnancies (Control group).ResultsThere was no significant difference between the obstetric and neonatal outcomes of pregnancies with COVID-19 compared to data of healthy pregnancies, except the increased C-section rate (p=0.026). Monocyte count, red cell distribution width (RDW), neutrophil/lymphocyte ratio (NLR), and monocyte/lymphocyte ratio (MLR) were significantly increased (p<0.0001, p=0.009, p=0.043, p<0.0001, respectively) whereas the MPV and plateletcrit were significantly decreased (p=0.001, p=0.008) in pregnants with COVID-19. ROC analysis revealed that the optimal cut-off value for MLR was 0.354 which indicated 96.7% specificity and 59.5% sensitivity in diagnosis of pregnant women with COVID-19. A strong positive correlation was found between the MLR and the presence of cough symptom (r=41.4, p=<0.0001).ConclusionsThe study revealed that, pregnancies complicated by COVID-19 is not related with adverse perinatal outcomes. MLR may serve as a supportive diagnostic parameter together with the Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) in assessment of COVID-19 in pregnant cohort.

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Marginal and internal fit and intaglio surface trueness of interim crowns fabricated from tooth preparation of four finish line locations

Scientific Reports ◽

10.1038/s41598-021-93455-7 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Keunbada Son ◽

Young-Tak Son ◽

Ji-Min Lee ◽

Kyu-Bok Lee

Keyword(s):

Three Dimensional ◽

Clinical Situation ◽

Intraoral Scanner ◽

Replica Technique ◽

Finish Line ◽

Marginal Fit ◽

Tooth Preparation ◽

The Right ◽

Internal Fit ◽

Marginal Region

AbstractThis study evaluated the marginal and internal fit and intaglio surface trueness of interim crowns fabricated from tooth preparation scanned at four finish line locations. The right maxillary first molar tooth preparation model was fabricated using a ceramic material and placed in four finish line locations (supragingival, equigingival, subgingival, and subgingival with a cord). Intraoral scanning was performed. Crowns were designed based on the scanned area. Interim crowns were fabricated using a stereolithography three-dimensional (3D) printer (N = 16 per location). Marginal and internal fit were evaluated with a silicone replica technique. Intaglio surface trueness was evaluated using a 3D inspection software. One-way analysis of variance and Tukey HSD test were performed for comparisons (α = 0.05). The marginal and internal fit showed significant differences according to locations (P < 0.05); the marginal fit showed the best results in the supragingival finish line (P < 0.05). Intaglio surface trueness was significantly different in the marginal region, with the highest value in the subgingival location (P < 0.05). Crowns fabricated on the subgingival finish line caused inaccurate marginal fit due to poor fabrication reproducibility of the marginal region. The use of an intraoral scanner should be decided on the clinical situation and needs.

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Impact of Resin Composite Viscosity and Fill-technique on Internal Gap in Class I Restorations: An OCT Evaluation

Operative Dentistry ◽

10.2341/20-144b-l ◽

2021 ◽

Author(s):

KR Kantovitz ◽

LL Cabral ◽

NR Carlos ◽

AZ de Freitas ◽

DC Peruzzo ◽

...

Keyword(s):

Repeated Measures ◽

Resin Composite ◽

Oral Care ◽

High Viscosity ◽

Class I ◽

Low Viscosity ◽

Significant Difference ◽

Before And After ◽

Internal Adaptation ◽

Internal Gap

SUMMARY The aim of this in vitro study was to quantitatively evaluate the internal gap of resin composites of high-and low-viscosity used in single- and incremental-fill techniques in Class I cavities exposed to thermal cycling (TC) using optical coherence tomography (OCT). Cavities of 4-mm depth and 3-mm diameter were prepared in 36 third molars randomly distributed into four groups, according to viscosity of restorative resin-based composite (high or low viscosity, all from 3M Oral Care) and technique application (bulk or incremental fill) used (n=9): RC, high-viscosity, incremental-fill, resin-based composite (Filtek Z350 XT Universal Restorative); BF, high-viscosity, bulk-fill, resin-based composite (Filtek One Bulk Fill); LRC, low-viscosity, incremental-fill, resin-based composite (Filtek Z350 XT Flowable Universal Restorative); and LBF, low-viscosity, bulk-fill, resin-based composite (Filtek Flowable Restorative). Single Bond Universal Adhesive system (3M Oral Care) was used in all the experimental groups. The incremental-fill technique was used for RC and LRC groups (2-mm increments), and a single-layer technique was used for BF and LBF groups, as recommended by the manufacturer. The internal adaptation of the resin at all dentin walls was evaluated before and after TC (5000 cycles between 5°C and 55°C) using OCT images. Five images of each restored tooth were obtained. Images were analyzed using ImageJ software that measured the entire length of the gaps at the dentin–restoration interface. The length of gaps (μm) was analyzed using two-way repeated measures ANOVA and the Tukey tests (α=0.05). There was a significant interaction between material types and TC (p=0.006), and a significant difference among all material types (p<0.0001), before and after TC (p<0.0001). Increased internal gaps at the dentin–restoration interface were noticed after TC for all groups. RC presented the lowest value of internal gap before and after TC, while LBF showed the highest values of internal gap after TC. In conclusion, TC negatively affected the integrity of internal gap, whereas high-viscosity, incremental-fill, resin-based composite presented better performance in terms of internal adaptation than low-viscosity, bulk-fill materials in Class I cavities.

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Analysis of Symptom Development in Relation to Quantity of Rice stripe virus in Rice (Oryza sativa) to Simplify Evaluation of Resistance

Phytopathology ◽

10.1094/phyto-07-18-0277-r ◽

2019 ◽

Vol 109 (4) ◽

pp. 701-707 ◽

Cited By ~ 2

Author(s):

Mitsuru Okuda ◽

Takuya Shiba ◽

Masahiro Hirae ◽

Akira Masunaka ◽

Minoru Takeshita

Keyword(s):

Oryza Sativa ◽

Quantitative Polymerase Chain Reaction ◽

Relative Concentration ◽

Elongation Factor ◽

Experimental System ◽

Rice Stripe Virus ◽

Strong Positive Correlation ◽

Significant Difference ◽

Grade Scale ◽

New Formula

Rice stripe virus (RSV) is one of the most devastating pathogens of rice (Oryza sativa) in rice-growing regions of East Asia. We analyzed the increase in RSV accumulation in infected rice plants over time and evaluated the association between disease severity and RSV accumulation with the aim of establishing an experimental system for accurate and efficient evaluation of RSV resistance in rice. As an index of RSV accumulation in plants, relative concentration of RNA corresponding to the coat protein gene region was measured using reverse-transcription quantitative polymerase chain reaction. Actin and elongation factor 1a were used as the host reference genes. RSV concentrations tended to increase with time from 7 to 28 days after inoculation, and a strong positive correlation was observed between the log RSV concentrations in the midsections of the uppermost leaves and in the stems at the first leaf sheath position. We analyzed RSV concentrations at these two locations 21 days after inoculation with RSV and assessed severity of disease symptoms based on a commonly used scale (Washio’s six-grade scale) rated as A (most severe), B, Bt, C, Cr, or D (mild symptoms). RSV concentrations at both locations were high in plants graded A, B, or Bt, with no significant difference in concentration of RSV among the three grades, but concentrations were significantly higher in the three grades compared with that in the plants in grade D. RSV concentrations were highly variable among plants in grades C and Cr. On the basis of these data, we propose a new formula to estimate the range of disease severities with greater ease and practical value. The values calculated by the new formula corresponded well to those based on Washio’s six-grade scale.

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