Elastic deformation of the mandibular jaw revisited-a clinical comparison between digital and conventional impressions using a reference

Objectives

Due to the partly strongly differing results in the literature, the aim of the present study was to investigate a possible deformation of the mandible during mouth opening using an intraoral scanner (IOS) and a conventional impression for comparison with a reference aid.

Materials and methods

Four steel spheres were reversibly luted in the mandibular (n = 50) with a metallic reference aid at maximum mouth opening (MMO). Two digital impressions (Trios3), at MMO and at slightly mouth opening SMO and a conventional impression (Impregum), were taken as the measuring accuracy of the reference structure was already known. Difference between MMO-SMO for digital impressions and deviations between digital and conventional (SMO) were calculated. Furthermore, the angle between the normal vectors of two constructed planes was measured. Statistical analysis was performed with SPSS25.

Results

Deviations for linear distances ranged from −1 ± 3 μm up to 17 ± 78 μm (digital impressions, MMO-SMO), from 19 ± 16 μm up to 132 ± 90 μm (digital impressions, SMO), and from 28 ± 17 μm up to 60 ± 52 μm (conventional impressions, SMO). There were no significant differences for digital impressions (MMO-SMO), and there were significant differences between the conventional and digital impressions at SMO.

Conclusions

Based on the results of the present study, no mandibular deformation could be detected during mouth opening with regard to the digital impressions. The results were rather within the measuring tolerance of the intraoral scanner.

Clinical relevance

Based on the present study, no deformation of the mandibular during mouth opening could be observed at the level previously assumed. Therewith related, dental techniques related to a possible mandibular deformation therefore should be reconsidered.

[Effect of disinfectant with benzethon chloramine and isopropanol as main active ingredients on the accuracy of dental impression]

OBJECTIVE

To assess the effect of disinfectant (Cavicide) with benzethon chloramine and isopropanol as main active ingredients disinfectant on dental impression accuracy.

METHODS

The effect of Cavicide on three impression materials (alginate, polyether and vinylpolysiloxane) were assessed using a standard model. The standard model was digitized by an extraoral scanner (IScan D103i, Imetric). For each kind of impression materials, thirty impressions were taken following the manufactures' instruction in the same conditions. Subsequently, the impressions were randomly divided into three groups, with ten impressions in each group. After the impression taking was completed, the three groups underwent pure water rinse for 1 min (blank control, BC), 2% glutaraldehyde solution immersion disinfection for 30 min (glutaraldehyde, GD), and Cavicide solution spray disinfection for 5 min (Cavicide, CC), respectively. All the impressions were digitized by the extraoral scanner (IScan D103i, Imetric) after disinfection and exported to a dedicated three-dimensional analysis software (Geomagic Qualify 2014, Geomagic, USA). In the software, the digital models of the impressions were trimmed to teeth and then superimposed with the digitized standard model via best-fit alignment. Root mean square (RMS) was used to evaluate the deviations between the impression and the standard model. The deviation in the anterior and posterior regions was evaluated respectively. One-way ANOVA test and the LSD post-hoc test were used to compare the deviations between the three groups (P < 0.05). The color map of each superimposition was saved for visual analysis.

RESULTS

For the polyether and vinylpolysiloxane materials, the difference between the three groups was not statistically significant (P=0.933, P=0.827). For the alginate material, the difference in posterior region between group GD and group BC, as well as group GD and group CC were statistically significant (GD vs. BC, P=0.001; GD vs. CC, P=0.002), while the difference between group BC and group CC was not statistically significant (P=0.854). The visual analysis showed an obvious deviation in the buccal-lingual direction in group GD.

CONCLUSION

Disinfectant (Cavicide) with benzethon chloramine and isopropanol as main active ingredients using spray disinfection has no effect on the accuracy of the alginate, polyether and vinylpolysiloxane impressions.

Comparative Analysis of Marginal Accuracy of Complete Crowns Fabricated by Using Ringless and Metal Ring Investment Systems: An In Vitro Study

AIM

To compare the vertical margin accuracy of lost wax castings produced by the conventional casting technique with all metal (WIRONIUM®) and PFM alloy (WIRON®99) using a metal ring and ringless system.

MATERIALS AND METHODS

A brass die assembly was used to fabricate standardized wax pattern crowns. A total of 100 wax patterns were made with both ringless and metal ring investment systems. Wax patterns were readapted and refined on the master die and divided into two groups, namely, group I and group II with 50 wax patterns in each group. Group I (ringless system) and group II (metal ring system) were further divided into subgroups having a sample size of 25 in each group. Each coping was invested and cast individually. The marginal discrepancy between the metal die and the castings were measured by a stereomicroscope and AutoCAD software 2013. Measurement was made on the facial area of the metal die.

RESULTS

The resultant casts obtained from different casting systems show statistically significant difference found between the marginal discrepancies using metal ring and ringless castings system, and statistically nonsignificant difference was found between the marginal discrepancies using all metal alloy (WIRONIUM®) and PFM alloy (WIRON®99) within the same group.

CONCLUSION

The marginal discrepancy for castings made with ringless casting system was less when compared to metal ring casting system, and there was no difference in marginal discrepancy when compared to all metal alloy (WIRONIUM®) and PFM alloy (WIRON®99) within the same group.

CLINICAL SIGNIFICANCE

Marginal fit is influenced by several factors including type of crown, tooth preparation geometry, dimensional accuracy of impression materials, factors related to dental casting, type of cement, luting pressure, duration of cementation, and use of occlusal vents or die spacers.

Effect of impression holding time and tray removal speed on the dimensional accuracy of impressions for artificial abutment tooth inclined

Oral scanners allow dental impressions to be taken in a short time without the use of an impression material. However, it has been noted that high impression accuracy cannot be obtained in cases where the abutment is inclined or in cases where the span is long. Consequently, in daily clinical practice, impressions are often created using silicone impression material. When taking an impression using silicone impression material, the curing time or the removal time of the impression material are often based on the intuition of the dental staff. This study investigated the effects of impression holding time and impression tray removal speed on the dimensional accuracy of impressions. A specimen with an abutment inclined 30° to the removal direction of an impression was prepared. Four types of silicone rubber impression materials were used. Impressions were taken with two levels of holding time and two levels of removal speed using an autograph. The diameter of stone models was measured at 3, 6, and 9 mm from the baseline of each. The height of the inclined and opposite sides was also measured. Two-way analysis of variance was used to analyze data regarding the assessment of the effects of holding time and tray removal speed. The reproducibility of the impressions was affected by the volume of undercut caused by the inclined abutment. For a large undercut, longer holding times and faster tray removal speeds are recommended to reduce the deformation of silicone rubber impressions.

A Novel Design of a Pick-up-Type Impression Coping

Dental impressions are used to produce a replica of an oral structure for use as a permanent record or in the production of a dental restoration or prosthesis. Accurate impression-taking is an essential procedure in implant dentistry. Traditionally, clinicians have used two different implant impression techniques: transfer and pick-up. The pick-up impression technique is considered to be the more accurate of the two because with this technique the impression copings are maintained within the impression upon removal from the mouth, thus eliminating the potential for error that may occur when manually placing the copings in the impression as in the transfer technique. This design has become increasingly popular and useful for multi-unit impressions. The purpose of this article is to review various pick-up impression copings and propose a new impression coping design for accurate, easy impression-taking without discrepancies.

An Investigation of the Effect of Modifying and Reusing Impression Copings on Transfer of Implant Analog Position and Angulation

AIM

The aim of this research was to determine whether sterilization and reutilization of impression copings had an impact on the accuracy of casts made for multiimplant restorations.

MATERIALS AND METHODS

Four master casts embedded with five implant analogs were fabricated. Polyvinyl siloxane (PVS) impressions of the master cast with copings attached to the analogs were made and poured in dental stone. The impression copings were subjected to cleaning and sterilization. These processes were repeated 30 cycles for each of the two groups of five impression copings: one without modification and one with modification that included air abrasion and PVS adhesive. A coordinate measuring machine (CMM) was used to measure relative angles and distances between the reference analog and analogs. The relative angles and distances measured on the stone casts were compared to the master resin cast to obtain positional and angular displacements.

RESULTS

For impression copings that were not modified, a significant difference was detected for both positional and angular displacements. For impression copings that were modified, a significant change was observed only for positional displacement. The maximum discrepancies measured for positional and angular displacements after 30 cycles of reuse were only 81 μm and 0.46°, respectively, regardless of the modification.

CONCLUSION

Within the limitations of this study, unmodified impression copings that have undergone 30 cycles of cleaning and sterilization appeared to incur more impression inaccuracy than those impression copings that were modified by airborne-particle abrasion and PVS adhesive.

CLINICAL SIGNIFICANCE

Impression copings used in this study can likely be recycled up to 30 times without reducing the accuracy of the impression to a level that may be considered clinically significant.

Impression-Making in 2020: How Long Before Analog Methods Are Obsolete?

Impression-making is a necessary part of providing restorative and rehabilitative dentistry to patients. The use of physical impression trays and materials dates back to at least the 19th century, which included the development of corrective and functional impression techniques.1 This method of acquiring and conveying information remained largely unchanged throughout the 20th century, although the development and subsequent improvement of elastomeric impression materials greatly enhanced the quality and predictability of impression results. Now with the digitization of the dental profession, the introduction and advancement of digital impressions represents the latest step forward in impression-making. This article reviews the current state of physical impression-making and the.

Technique Using a Novel Verification Guide for Complete Seating of Open-Tray Impression Copings

The purpose of impression-taking is to attain the accurate transfer of intraoral information for extraoral use. It is a crucial step in performing a successful dental implant restorative procedure. To accurately replicate the implant position for adaptation of an abutment that will completely engage with the implant, a pick-up impression is taken with an impression coping. Several factors can affect seating of the impression coping, including soft-tissue interference, the size of the impression coping, angulation, proximity or contact with adjacent teeth, damage to the coping, misfit caused by use of other manufacturers' parts, and differences between seating in an external- versus internal-connection implant. This article presents use of a novel verification guide that is intended to ensure complete seating of the impression coping with the implant.

Accuracy of data obtained from impression scans and cast scans using different impression materials

AIM

Despite the expanding implementation of intraoral scanning (IOS) devices, indirect digitization of conventional impressions or casts still represents the primary access to CAD/CAM. The aim of this study was to evaluate the accuracy of data acquired from impression scans and cast scans with respect to impression material and type of cast used.

MATERIALS AND METHODS

A standardized titanium model for a four-unit fixed dental prosthesis (FDP) served as a testing model. Industrial computed tomography (CT) was applied, generating a reference data set. Four different impression materials were utilized (n = 12 per material): 1) Impregum Penta (polyether/group PE); 2) Imprint 4 Penta Super Quick Heavy + Super Quick Light (polyvinyl siloxane (PVS)/group PVS-I); 3) Dimension Penta H Quick + L (PVS/group PVS-D); and 4) Imprint 4 Preliminary Penta Super Quick (PVS/group PVS-P). Data were obtained from three different model situations, ie, impressions (group IMP), unsectioned plaster casts (group UNSEC), and sectioned casts (group SEC). The surfaces were digitized three times each using a laboratory scanner. The resulting test data were superposed with the reference data using a best-fit algorithm to evaluate accuracy. Statistical analysis was conducted using the Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney tests (level of significance: P < 0.050).

RESULTS

Imprint 4 Penta presented the highest overall accuracy, while Imprint 4 Preliminary Penta Super Quick displayed the poorest results. Regarding the model situation (impression scan vs cast scan), impression scans from Impregum Penta and Imprint 4 Penta showed superior results.

CONCLUSION

Impression scans in combination with high-precision impression material results in the most accurate data.

Accuracy of Intra-Oral Scans Compared to Conventional Impression in Vitro

AIM

The purpose of the present study was to assess the accuracy of intra-oral scans and conventional impression measured at various points on a single tooth preparation.

METHODS

Ten conventional silicone impressions, and ten intra oral-scans using eight different digital intra oral digital scanners were taken of a prepared master tooth. The conventional impressions were directly digitised using a laboratory scanner. Each scan/impression was superimposed on a high-accuracy digital model of the prepared master tooth. For each superimposition, the deviation from the prepared master tooth was measured at six points on four two-dimensional cross-sections. Data was analysed using two-way analysis of variance (ANOVA).

RESULTS

Most intra oral scanners had lower accuracy at the preparation margin compared to smooth surfaces. When only conventional impression and the latest intra oral scanners of various manufacturers are considered, the mean discrepancy at the preparation margin was 50μm (SD 16) for conventional impression, 15μm (SD 4) for trios 3, 26μm (SD 4) for LAVA TDS, 29μm (SD 7) for CEREC Omnicam, 30μm (SD 6) for CS 3600 and 64μm (SD 7) for GC aadva. The increased accuracy of trios 3 was statistically significant (p<0.05).

CONCLUSIONS

At the preparation margin, Trios 3 performed significantly better than conventional impression and the other intra oral scanners. LAVA TDS, CEREC Omnicam and CS3600 showed similar accuracy at the margin, yet better than conventional impression and GC Aadva.

[Effect of two manual mixing methods on the accuracy of alginate impression]

PURPOSE

The effect of clockwise mixing method and clockwise combined eight-shaped mixing method on the accuracy of alginate impression was compared.

METHODS

From march to April 2018, 40 dental restoration cases in the Department of Stomatology, Zhoupu Hospital, Pudong District, Shanghai were selected. Two nurses and the same doctor treated 40 patients with single crown porcelain restoration. Two sets of models were taken by two kinds of mixing methods, which were divided into experimental group and control group. Clockwise manual mixing method was used in the control group to take the model, while clockwise combined eight-shaped mixing method was used in the experimental group to take the model. SPSS 24.0 software package was used for Mann-Whitney rank sum test.

RESULTS

The same high-grade technician used a magnifying glass to observe the prepared impression, recorded the shoulder print, the sulcus wing and bubble generation, and comprehensively evaluated the impression quality. A comparison was made between the two groups, Z=-4.634, P<0.001, and the difference was statistically significant. Among them, the ratio of excellent quality of the clockwise combined eight-shaped mixing method (77.5%) was significantly higher than that of the clockwise mixing method (10%), and the proportion of level IV unqualification (2.5%) was significantly lower than that of the clockwise mixing method (27.5%).

CONCLUSIONS

The quality of impression using clockwise combined eight-shaped mixing method is higher than that of the clockwise method, which improves the success rate of the mold and reduces the discomfort caused by repeated impression. Application of this technique is helpful to the promotion of occult knowledge among nurses.

Quantifying Flabby Ridge Tissue Displacement During Impression-Making for Patients With Combination Syndrome

Patients with Combination syndrome present with early bone loss and flabby hyperplastic tissues in the anterior maxilla caused by functional loads exerted by mandibular anterior teeth on maxillary complete dentures. Use of conventional mucocompressive impression techniques captures flabby maxillary anterior ridge tissue in a distorted state, and dentures made from such impressions could displace flabby tissues when loaded and become loose when unloaded. In this study, which examined two patients diagnosed with Combination syndrome, computer-aided design/computer-aided manufacturing (CAD/CAM) technology was used to determine the degrees of displacement when six impression materials were used for making final impressions for complete dentures.

Accuracy and practicality of intraoral scanner in dentistry: A literature review

PURPOSE

The digitization of the dental field has been vigorously promoted in recent years. An impression using an intraoral scanner is considered to significantly change future dental treatment. The purpose of this review is to evaluate accuracy and practicality of various intraoral scanners and verification method of intraoral scanners.

STUDY SELECTION

This review was based on articles searched through the MEDLINE and PubMed databases. The main keywords that were employed during the search were "Oral Scanner, Intraoral Scanners, Desktop Scanner, and Digital Impression".

RESULT

It was reported that illuminance and color temperature affected trueness and precision of intraoral scanners. The repeatability of intraoral scanners indicated the possibility of producing fixed prostheses within the range of being partially edentulous. It is considered difficult to use intraoral scanners in fabricating cross-arch fixed prostheses. However, with intraoral scanners, it may be considered possible to fabricate mouth guards and dentures equivalent to those of desktop scanners. Current intraoral scanner scans are considered more comfortable than traditional impressions that use irreversible hydrocolloid and elastomeric impression materials.

CONCLUSION

Since the intraoral scanner is an evolving device, further improvement in accuracy is expected in the future. In addition, verification of the accuracy of intraoral scanners must be conducted accordingly.

Comparison of Dimensional Accuracy of Stone Models Fabricated by Three Different Impression Techniques Using Two Brands of Polyvinyl Siloxane Impression Materials

AIM

The aim of this study is to check the dimensional precision of stone models made by two different brands of polyvinyl siloxane impression materials using the monophase, one-step, and two-step putty/light-body impression techniques.

MATERIALS AND METHODS

A metal model, having two crown preparations, was fabricated. With each technique, 40 impressions were made using two types of polyvinyl siloxane impression materials (Aquasil and Virtual). A total of 240 impressions were made with both the polyvinyl siloxane impression materials. Monophase impressions were made with a medium body using an acrylic custom tray. By simultaneous usage of putty and light-body, one-step impressions were made with a perforated metal stock tray. For two-step impressions, a 25-40 microns thick cellophane sheet spacer was used. The stone casts were obtained from the impressions of the stainless steel model. Three different dimensions (height, diameter, and inter-abutment distance) on these resultant stone casts were compared with the standard die. The accuracy of two different brands of impression materials was also compared. The results were then statistically analyzed.

RESULTS

The resultant casts obtained from the different impression techniques had significantly larger dimensions in height and diameter, but smaller dimensions were observed for the inter-abutment distance. Larger deviation in resultant casts was observed in the monophase than one-step impression technique and the least deviation was observed in the two-step impression technique.

CONCLUSION

The two-step impression technique produced the most accurate results in terms of the resultant casts. Out of the two different brands, Aquasil produced more fare results.

CLINICAL SIGNIFICANCE

Adequate marginal adaptation, proper fit and least distortion of the castings, and the final prosthesis can be achieved by using the adequate impression technique and impression material.

A comparison of patient experience, chair-side time, accuracy of dental arch measurements and costs of acquisition of dental models

OBJECTIVE

To compare patient experience, chairside time, dental arch distances, and costs of dental models derived from intraoral scans and alginate impressions in pre-orthodontic children and young adolescents.

MATERIALS AND METHODS

Fifty-nine children and young adolescents (9-15 years, mean: 12.70 years) had an intraoral scan and an alginate impression prior to orthodontic treatment. During the procedures, chairside time was registered in minutes and patient experience was assessed by a Visual Analogue Scale questionnaire. Four maxillary dental arch distances were measured on digital models, on plaster casts, and directly in the mouth (intraoral). The cost of each procedure was presented graphically. Differences between the two procedures were tested by paired t-test and general linear model.

RESULTS

Patient experience was statistically better during intraoral scan compared with alginate impression regarding comfort, gag reflex, breathing, smell/sound, taste/vibration, and all statements concerning anxiety (P < .05). No significant difference in chairside time between the two procedures was found. No statistically significant differences in dental arch distances between digital models and plaster casts were found, but dental arch distances measured intraorally differed significantly from both digital models and plaster casts (P < .05). Cost calculation showed that the digital procedure was 10.7 times more expensive than the conventional procedure initially and, that after 3.6 years, the two procedures were equal in cost.

CONCLUSIONS

Children preferred intraoral scan rather than alginate impression. Chairside time was equal for the two procedures as were the measurements of maxillary dental arch distances. The two procedures were equal in cost at 3.6 years.

Linear Dimensional Changes of Five Interocclusal Recording Materials When Immersed in Two Disinfectants for Different Time Intervals

AIM

In this study, we intend to compare the linear dimensional changes of interocclusal recording media by immersing them in disinfectant solutions at different time intervals.

MATERIALS AND METHODS

Five interocclusal recording materials were used for this study and were grouped according to material types, namely wax, zinc oxide eugenol impression paste, polyether, polyvinyl siloxane, and bisacryl bite registration material. Each material was manipulated and injected into a stainless steel die. The materials were divided into 5 groups with 5 subgroups of 10 samples with a total of 250 samples. The samples were subjected to immersion in 2% glutaraldehyde and 0.5% sodium hypochlorite each for 30 and 60 minutes. Linear dimensional changes of the samples were tested by measuring the distance between points A and B at different time intervals by means of a stereomicroscope and compared with the control group.

RESULTS

Bisacryl showed the least linear dimensional change when immersed in both the solutions.

CONCLUSION

Bisacryl (Luxabite) presented no linear dimensional change at both time intervals as opposed to the other materials, hence, it is most accurate.

Effect of Multiple Use of Impression Copings and Scanbodies on Implant Cast Accuracy

PURPOSE

There are currently no clear guidelines on the reuse of metal implant impression copings and scanbodies in implant dentistry. Manufacturers generally recommend single use, which has cost and ecological implications. The objectives of this study were to examine the effect of multiple use of implant impression copings and scanbodies on the accuracy of partially dentate implant casts.

MATERIALS AND METHODS

Ten direct polyether impressions were made of a partially dentate mandibular acrylic resin master model fitted with two internal connection implants (Straumann RC bone level) in the positions of right first premolar and molar, to produce 10 dental stone casts. A single set of impression copings was utilized for the 10 impressions. The sample casts and the master model were digitized using a laboratory scanner. Ten digital scans were then performed on an implant stone cast with two bone-level internal connection implant analogs using one set of scanbodies to produce scans 1 to 10. Measurements were made on all the digitized casts using computer software and discrepancies calculated in the x-, y-, and z-axes, and in the overall three-dimensional position (R). Data were statistically analyzed using paired t tests (α = .05), and P values were adjusted using Holm-Bonferroni sequential correction.

RESULTS

The outcomes were mixed, in that no significant differences were found between the casts or scans produced by reusing impression copings (P > .05) and scanbodies (P > .005), respectively, in all dimensions, for most repetition cycles; however, significant differences were noted in the y-axis for cast 6, and in 2 relation to R, for casts 2, 4 (P < .05), and 8 (P < .005), and the scanbody reuse elicited significant differences in 3D(R) with scan 2 alone (P < .005).

CONCLUSION

Reuse of impression copings and scanbodies up to 10 times did not seem to consistently affect the accuracy of partially dentate multi-implant dental casts and digital models.

The influence of impression coping splinting on the accuracy of the open-tray technique

The objective of this study was to examine the effect of splinting of the impression copings on the accuracy of the cast when the open-tray technique is used. An epoxy master cast with 3 implants was fabricated. The first 2 implants were parallel to each other and perpendicular to the horizontal plane (implants A and B), and the third implant (implant C) had a 25-degree inclination. A passively fitting metal framework that was fabricated over this master cast was used to measure accuracy of fit. Ten casts were fabricated from this epoxy resin master cast with the use of polyether material and the open-tray technique. For the first 5 casts, the impression copings were splinted with dental floss and autopolymerizing acrylic resin; in the next 5 casts, the impression copings were not splinted. The metal framework in the master cast was fixed in the new specimens, and the microgap between this prosthesis and the implant analogs was evaluated. The specimens were observed under an optical microscope, and microgap measurements were made on photographs taken at a standardized magnification of 40×. The inclined implant C had the smallest mean microgap among the 3 implants, but the differences were not statistically significant. Microgaps for all 3 implants were smaller when they were splinted, but the difference from the mean of the nonsplinted counterpart was statistically significant only for the inclined implant. The results suggest that there is no clinical advantage in splinting the impression copings for parallel implants. On the other hand, when the implants are not parallel, splinting of the impression copings can result in greater accuracy of the fabricated cast.

Effect of Astringent Products on Accuracy of Polyether Impressions and Plaster Casts

PURPOSE

To investigate whether hemostatic agents have any detrimental effects on polyether impressions and plaster casts after a clinically viable cleaning protocol.

MATERIALS AND METHODS

A total of 60 human molar teeth were manually standardized, prepared, and subdivided into five groups (G): G0 (control/no contamination); G1 (ViscoStat Clear); G2 (ViscoStat); G3 (Astringedent); and G4 (Astringedent X). Each tooth was contaminated with a hemostatic agent for 3 minutes and cleaned with a 30-second air/water spray. Before and after contamination, an impression was taken and a plaster cast was poured. The impressions and plaster casts of all teeth were scanned using a light scanner. Data were matched using a three-dimensional analysis software that displayed color-coded maps. Means of the maximum positive/negative values and of the mean deviations in each group were calculated and compared. All color-coded maps were interpreted descriptively using the program's color scale, and all impressions and plaster casts were microscopically evaluated.

RESULTS

Values of mean deviations throughout all matched scans showed maximum values ranging from -30.1 to +17.5 μm. None of the groups showed significantly different deviation values or patterns when compared to each other. Impressions showed a thin, discontinuous coating for G2, G3, and G4; no changes were found for plaster casts.

CONCLUSION

Presented deviations showed the same values and distribution patterns within all groups. A cleaning protocol of 30 seconds of air/water spray is sufficient to remove hemostatic agents, preventing effects to polyether impressions and plaster casts. However, ferric sulfate-containing hemostatic agents left discontinuous coatings on impression surfaces.

Influence of Edentulous Tray Modification on the Pressure Distribution of the Impression: An In Vitro Study

PURPOSE

To clarify the relationship between the pressure generated during impressions (impression pressure) and the presssure beneath the corresponding denture base (functional pressure) and to examine the influence of tray modifications.

MATERIALS AND METHODS

Impression and functional pressures were measured on models with the same appearance but different bone morphologies for comparison. Pressures with modified trays with additional relief and escape holes were also measured for comparison.

RESULTS

The correlation between impression pressure and functional pressure was high, and both could be changed by tray modifications.

CONCLUSION

The distribution of impression pressure will be recreated beneath the denture base, and modifications of trays can control the pressure distribution.

[Establishment and preliminary clinical evaluation of edentulous custom trays designed and fabricated by chair-side CAD and 3D printing systems]

OBJECTIVE

To design and fabricate edentulous custom trays by chair-side computer-aided design and 3-dimensional printing (CAD/3DP) system of independent research and development and to evaluate their clinical effects based on prosthodontists'satisfaction using the visual analogue scale (VAS).

METHODS

Fifteen edentulous patients were randomly recruited by three prosthodontists who passed the unified operating process training. The custom trays for each patient were fabricated using both chair-side CAD/3DP system of independent development and manually conventional method, and the final impressions were made by silicone impression materials (light body). The prosthodontist's satisfaction was surveyed by the three prosthodontists via the questionnaire based on visual analogue scales.

RESULTS

In the degree of the prosthodontist's satisfaction of final impressions, the average satisfactions of "try in" (the overall size, shape, convenience, etc.) on the 3DP custom tray made by independent development chair-side system and the manually conventional method were 9.18±0.19 and 8.23±0.22, respectively. The average satisfactions of the border line position (border extensions, frenal notch)were 8.91±0.40 and 7.96±0.23, respectively. The average satisfactions of the stability in border molding were 8.80±0.83 and 8.01±0.81, respectively. The average satisfactions of the quality of final impression (completeness, thickness of impression material, exposure of custom tray, shape of border) were 8.94±0.68 and 7.99±0.42, respectively. The average satisfactions of the difficulty of high quality impression (times of repetition, efficiency) were 9.20±0.37 and 7.88±0.22, respectively. The average satisfactions of the overall satisfaction were 9.11±0.49 and 7.95±0.15, respectively. There was significant difference in the satisfaction of "try in", border line position, stability in border molding, quality of final impression, difficulty of high quality impression, and overall satisfaction between the 3DP custom tray made by chair-side system of independent development and the manually conventional method (P<0.05).

CONCLUSION

In the degree of the prosthodontist's satisfaction of final impression, the 3DP custom tray made by chair-side system of independent development is higher than that of the conventional custom tray, and it meets the clinical requirements and can be popularized in clinical application.

[Establishment and preliminary clinical evaluation of edentulous custom trays designed and fabricated by chair-side CAD and 3D printing systems]

OBJECTIVE

To design and fabricate edentulous custom trays by chair-side computer-aided design and 3-dimensional printing (CAD/3DP) system of independent research and development and to evaluate their clinical effects based on prosthodontists'satisfaction using the visual analogue scale (VAS).

METHODS

Fifteen edentulous patients were randomly recruited by three prosthodontists who passed the unified operating process training. The custom trays for each patient were fabricated using both chair-side CAD/3DP system of independent development and manually conventional method, and the final impressions were made by silicone impression materials (light body). The prosthodontist's satisfaction was surveyed by the three prosthodontists via the questionnaire based on visual analogue scales.

RESULTS

In the degree of the prosthodontist's satisfaction of final impressions, the average satisfactions of "try in" (the overall size, shape, convenience, etc.) on the 3DP custom tray made by independent development chair-side system and the manually conventional method were 9.18±0.19 and 8.23±0.22, respectively. The average satisfactions of the border line position (border extensions, frenal notch)were 8.91±0.40 and 7.96±0.23, respectively. The average satisfactions of the stability in border molding were 8.80±0.83 and 8.01±0.81, respectively. The average satisfactions of the quality of final impression (completeness, thickness of impression material, exposure of custom tray, shape of border) were 8.94±0.68 and 7.99±0.42, respectively. The average satisfactions of the difficulty of high quality impression (times of repetition, efficiency) were 9.20±0.37 and 7.88±0.22, respectively. The average satisfactions of the overall satisfaction were 9.11±0.49 and 7.95±0.15, respectively. There was significant difference in the satisfaction of "try in", border line position, stability in border molding, quality of final impression, difficulty of high quality impression, and overall satisfaction between the 3DP custom tray made by chair-side system of independent development and the manually conventional method (P<0.05).

CONCLUSION

In the degree of the prosthodontist's satisfaction of final impression, the 3DP custom tray made by chair-side system of independent development is higher than that of the conventional custom tray, and it meets the clinical requirements and can be popularized in clinical application.

Performance of a repair service set for the retrieval of fractured abutment screws: a pilot in vitro study

PURPOSE

To report the success of a repair service set for the retrieval of fractured screws and to compare three clinical assessments to an in vitro assessment to verify the completeness of removal of the fractured screws.

MATERIALS AND METHODS

Twelve clinicians were asked to remove fractured implant abutment screws from prepared specimens by means of a repair service set. The completeness of the removal of any abutment screw material was measured by the fit of an impression post, a dental surgery microscope, and the use of an elastomeric impression material.

RESULTS

After the participants attempted to remove the fractured screw with the repair service set, 100%, 83.3%, 66.7%, and 75% of the fractured screws were considered successful in the impression post, dental surgery microscope, silicone replica, and stereomicroscope assessments, respectively.

CONCLUSION

The retrieval of fractured screws succeeded in 75% of the cases. The silicone replica technique and the dental surgery microscope had similar diagnostic values to the stereoscopic microscope assessment.

The Fit Accuracy of Removable Partial Denture Metal Frameworks Using Conventional and 3D Printed Techniques: An In Vitro Study

AIM

To evaluate the accuracy of removable partial denture (RPD) metal frameworks fabricated by the conventional lost-wax (CLW) technique and those made by the selective laser melting (SLM).

MATERIALS AND METHODS

A dentoform of a mandibular Kennedy class III, modification 1 dental arch were surveyed, and rest seats were prepared on the abutment teeth. The dentoform was then duplicated into a metal die which was used as a reference model. Thirty RPD metal frameworks were fabricated by two techniques; fifteen for each technique. Polyvinyl siloxane (PVS) impression material was painted on the intaglio surface of the rests of each framework which is then seated on the reference die. PVS specimens that represent the gap under the rest were measured in four zones: buccal, lingual, marginal and central by a single examiner using a digital microscope at 50x in micrometers.

RESULTS

Comparison between the two techniques for each abutment tooth revealed that the CLW technique had better fit in one tooth, while the SLM technique showed a better fit in two teeth. Regarding the edentulous span length within the SLM technique, the long edentulous span had a significantly better fit. When comparing the four measured rest zones, it was found that in the CLW technique group, the marginal zone had the highest fit accuracy while the lingual zone showed the lowest fit accuracy. In the SLM group, the central zone had the best fit and the buccal zone had the worst fit.

CONCLUSION

RPD frameworks fabricated using the SLM technique showed better fit accuracy than those made by the CLW technique, however, the difference was not statistically significant.

CLINICAL SIGNIFICANCE

SLM is a promising technique for the fabrication of RPD frameworks in routine clinical practice.