Accuracy of merging scans of definitive fixed prosthodontic impressions to obtain single, accurate digitized master casts.

PURPOSE: Many elastomeric impressions sent to commercial laboratory dental technicians may include marginal defects. To fabricate accurate restorations, digital technology may be used to merge digital files of defective impressions into a single standard tessellation language (STL) file free of errors. This would save clinicians and patients time and may improve clinical care. The purpose of this study was to compare the accuracy of digital master casts reconstructed from merged STL files of defective impressions with the file of the original defect-free preparations. MATERIAL AND METHODS: Ivorine teeth on a dentoform were prepared to receive a posterior fixed dental prosthesis (FDP) with complete coverage preparations. An impression was made in a stock tray using polyvinyl siloxane (PVS) impression material and an extraoral scanner (E3, 3Shape, Denmark) was used to digitize the impression; this was the reference cast. Wax was used to create defects on the buccal and lingual margins of the preparations. Fifteen PVS impressions were made of the FDP preparations with defects in the mesial and distal margins; another set of 15 PVS impressions was made of FDP preparations with defects in the buccal and palatal margins for a total of 30 impressions. All impressions were digitized using the same extraoral scanner (E3, 3Shape, Denmark). Corresponding STL files were paired and merged, and a master cast was created by eliminating the defects using the scanned data. This master cast was compared to the reference cast using reverse engineering software (Geomagic, Morrisville, NC, USA). The results were expressed as average errors and standard deviations in the master casts relative to the reference cast. To account for the presence of positive and negative values in the data set, in terms of errors, the root mean square (RMS) value was calculated for each sample. RESULTS: The mean average error in the sample was -0.4 µm. The average upper limit of 95% confidence interval was +36.5 µm, while the average lower limit of 95% confidence interval was -37.3 µm. The mean RMS of the errors found was 18.9 µm. CONCLUSIONS: The results of this study indicated that merging digitized definitive impressions to correct marginal defects resulted in master casts with a high level of accuracy relative to the reference cast.

Is a Wiggling-Motion Modified Two-Step Impression Technique as Accurate as Conventional Techniques in Restorative Dentistry?

BACKGROUND: The purpose of this study was to evaluate dental impression accuracy of one-step and two-step techniques compared to a modified two-step technique. METHODS: Four impression techniques were compared: (1) a one-step double mix (DM) technique, (2) a cut-out (CO) technique, in which space relief was created using a blade and a laboratory bur, (3) a membrane (ME) technique, in which space relief was created by placing a PVC membrane on top of the putty material during the primary impression, and (4) a wiggling motion (WI) technique, in which PVC membrane was placed and additional wiggling movements were performed during the first 20 s when the primary impression was seated upon the master model (MM). Impressions were poured with type IV stone. Casts were scanned with a laboratory scanner and measurements were made for each cast using three-dimensional analysis software. RESULTS: All groups presented differences compared to MM group, in at least one intra-abutment distance. Groups DM and ME presented the most significant differences, in three and two distances, respectively, whereas CO and WI presented one significant different distance compared to MM. There were no differences between MM and the four techniques for inter-abutment distances. CONCLUSIONS: WI yielded similar results with CO technique. Both performed better than the other groups.

Evaluation of the properties of a new super quick-setting (2 min) polyether impression material.

OBJECTIVES: Although a new super-quick setting polyether impression material has been commercially recently introduced, its properties have not been yet reported. Thus, it was the aim of this study to assess the dimensional stability, tear strength, and elastic recovery of the new material and to compare it with another commonly used polyether and polyvinyl siloxane. MATERIALS AND METHODS: A new super-quick set polyether, a regular set polyether and a polyvinylsiloxane (PVS) impression material have been used in the study. Dimensional changes were measured using a modified mold as per ISO 4823:2000 after 1 h and 7 days. Tear strength was evaluated by subjecting specimens to tension until failure with a crosshead speed of 250 mm/min. Elastic recovery was measured by deforming specimens using a materials testing machine to a height of 16 mm (20% strain). The change in length (ΔL) was measured afterwards and elastic recovery was calculated in percentages. RESULTS: Dimensional changes of the super quick and regular set polyether were comparable in both the vertical and horizontal dimensions after 24 h and 7 days. All the tested materials showed dimensional change values far below the maximum accepted ISO requirement (1.5%). The super quick setting polyether showed significantly improved tear strength (4.9 N/mm) in comparison to the regular set polyether (3.5 N/mm) and similar to PVS (5.2 N/mm). The elastic recovery of PVS (99.6%) was the highest among all the groups. CONCLUSIONS AND CLINICAL RELEVANCE: The newly available super-fast set polyether offers a great potential for a reduced chair side time and comfort for both, the patient and the dentist. Super quick polyether showed as well improved tear strength, which is considered one of the shortcomings of the regular set polyether. In addition, the new polyether was as accurate as the regular set polyether and with good elastic recovery.

Digital assessment of properties of the three different generations of dental elastomeric impression materials.

BACKGROUND: This study aimed to compare the dimensional accuracy, hydrophilicity and detail reproduction of the hybrid vinylsiloxnether with polyether and polyvinylsiloxane parent elastomers using modified digital techniques and software. This was done in an attempt to aid in solving the conflict between the different studies published by competitive manufacturers using different common manual approaches. METHODS: A polyether, polyvinylsiloxanes and vinyl polyether silicone hybrid elastomeric impression materials were used in the study. Dimensional accuracy was evaluated through taking impressions of a metallic mold with four posts representing a partially edentulous maxillary arch, that were then poured with stone. Accuracy was calculated from the mean of measurements taken between fixed points on the casts using digital single-lens reflex camera to produce high-resolution digital pictures for all the casts with magnification up to 35×. Hydrophilicity was assessed by contact angle measurements using AutoCAD software. The detail reproduction was measured under dry conditions according to ANSI/ADA Standard No. 19 and under wet conditions as per ISO 4823. A metallic mold was used with three V shaped grooves of 20, 50, and 75 µm width. Specimens were prepared and examination was made immediately after setting using digital images at a magnification of 16×. RESULTS: The hybrid impression (0.035 mm) material showed significantly higher dimensional accuracy compared to the polyether (0.051 mm) but was not as accurate as the polyvinyl siloxane impression material (0.024 mm). The contact angles of the hybrid material before and after setting was significantly lower than the parent materials. With regard to the detail reproduction, the three tested materials were able precisely to reproduce the three grooves of the mold under dry conditions. Whereas, under wet conditions, the hybrid material showed higher prevalence of well-defined reproduction of details same as polyether but higher than polyvinylsiloxane that showed prevalence of details with loss of sharpness and continuity. CONCLUSIONS: The digital technique used could be a more reliable and an easier method for assessment of impression materials properties. The hybridization of polyvinyl siloxane and polyether yielded a promising material that combines the good merits of both materials and overcomes some of their drawbacks.

Tear strength and elastic recovery of new generation hybrid elastomeric impression material: A comparative study.

OBJECTIVE: Since there is no material in the market met all the ideal requirements of an impression material, thus in an attempt to find one, hybridization between the two most commonly used impression materials were done. The aim of the hybridization was to obtain a new material combining the good merits of both and eliminate their shortcomings. Thus, this study aimed to assess the impact of hybridization between polyether with addition silicone on tear strength and elastic recovery of the new material and compare such effect with regard to parent materials. RESULTS: A polyether (PE), polyvinyl siloxanse (PVS) and vinyl polyether silicone (VPES) hybrid elastomers were used in the present study. Tear strength was measured one hour after setting time of each material according to the manufacturer and the three materials showed statistically comparable tear strength in N/mm. Elastic recovery was evaluated one minute after the setting time recommended by the manufacturer. The three materials were statistically insignificant from each other, and all met the ISO4823 requirement of having greater than 96.5% recovery.

Effect of Various Retentive Element Materials on Retention of Mandibular Implant-Retained Overdentures.

This study aimed to examine the retentive characteristics of each retentive element material and the effects from thermocycling using the two implant-retained mandibular overdenture model. Two stud abutments and three retentive element materials; nylon, polyetheretherketone (PEEK) and polyvinylsiloxane (PVS) were used in this study. Four tested groups, with a total of 40 overdentures, were fabricated, including a Locator® abutment with nylon retention insert (NY), Novaloc® abutment with PEEK retention insert (PK), Locator® abutment with PVS retention insert (RL), and Novaloc® abutment with PVS retention insert (RN). The retentive force (N) was measured before thermocycling, and at 2500, 5000, and 10,000 cycles after thermocycling. Significant changes in the percentage of retention loss were found in the NY and PK groups (p < 0.05) at 6 and 12 months for the RL group (p < 0.05) after artificial aging. The RN group exhibited a constant retentive force (p > 0.05). The tendency of the percentage of retention loss significantly increased for PEEK, nylon, and PVS silicone over time. The results of the present study implied that retentive element materials tend to lose their retentive capability as a result of thermal undulation and water dispersion. Nylon and PEEK, comprising strong polar groups in polymer chains, showed a higher rate of retention loss than polyvinylsiloxane.

Multi-Material 3D Printing of a Customized Sports Mouth Guard: Proof-of-Concept Clinical Case.

A multilayer mouth guard is known to have the best protective performance. However, its manufacturing in a digital workflow may be challenging with regards to virtual design and materialization. The present case demonstrates a pathway to fabricate a multilayer individualized mouth guard in a fully digital workflow, which starts with intraoral scanning. A free-form CAD software was used for the virtual design. Two various CAM techniques were used, including Polyjet 3D printing of rubber-like soft material and silicone printing using Drop-on-Demand technique. For both methods the outer layer was manufactured from more rigid materials to facilitate its protective function; the inner layer was printed from a softer material to aid a better adaptation to mucosa and teeth. Both 3D printed multilayer mouth guards showed a clinically acceptable fit and were met with patient appraisal. Their protective capacities must be evaluated in further clinical studies.

Effect of Implant Angulation and Depth on the Accuracy of Casts Using the Open Tray Splinted Impression Technique.

The purpose of this study was to evaluate the accuracy of open tray dental implant impressions when the implants are placed with varying implant angulations and depths. Four partially edentulous models were fabricated using photopolymer resin, each having different angulation and depth of the implant analogs. A total of 40 open tray elastomeric impressions were made, which were poured in type IV die stone (n = 10). These casts were evaluated and compared for accurate reproduction of the spatial orientation of the implant analogs in the models using digitization in 3 dimensions. The results were analyzed using the independent T test. Statistically significant differences were observed when the casts were compared with their respective master models. These casts had the implant replicas placed deeper within the replicated soft tissue. Making accurate impressions in partially edentulous situations with dental implants placed with varying depth and angulation is critical and clinically demanding. There is a need for future in vivo research to identify methods and materials, exploring digital impression techniques as well, in order to make precise impressions.

Retentive Characteristics of a Polyetheretherketone Post-Core Restoration with Polyvinylsiloxane Attachments.

A new application of a polyetheretherketone (PEEK) post-core restoration combined with polyvinylsiloxane (PVS) attachments was proposed and substantiated. This study aimed to evaluate retentive characteristics of the PEEK post-core restoration with PVS attachment systems. Specimens with PVS attachments were fabricated to evaluate retention force during 10,000 cyclic dislodgements. Additionally, the retention forces of PVS attachments with three different values of Shore hardness were further measured before and after aging treatments. The results of cyclic dislodgement test indicated a strong negative linear relationship between the cyclic times and retention force (p < 0.0001, r = -0.957). Furthermore, the retention forces of the PVS were significantly improved with Shore hardness increased, which was also affected by the aging treatment (F (2, 138) = 10.95, p < 0.0001). Therefore, the PEEK post-core restoration with PVS attachments exhibited the favorable retention force, which could be a promising alternative for dental prostheses.

Impression material accuracy for palatal orthodontic miniscrews.

PURPOSE: This study investigates the accuracy of abutment transfer with current impression materials and provides a concise overview, including other relevant factors, in order to enable clinicians to make an informed decision about the optimal impression for this treatment procedure. METHODS: In all, 96 impressions of a cadaver head with two orthodontic miniscrews in place were taken with four common impression materials by two observers and using two methods of application. After pouring with a standard type IV stone and abutment transfer, all models and the upper jaw (which had been separated from the head) were scanned in a standard model scanner (Zirkonzahn® [Zirkohnzahn GmbH, Gais, Italy] S600 ARTI) and evaluated using a computer-aided design (CAD) program (GOM-Inspect [Gesellschaft für optische Messtechnik m.b.H., Braunschweig, Germany]). The deviations were measured at six points per screw and statistically evaluated with SPSS® (IBM, Chicago, IL, USA). RESULTS: Optimal values were obtained with biphasic polyvinylsiloxane, while monophasic polyvinylsiloxane, alginate and polyether also resulted in acceptable accuracy. Observer experience showed no effect and the method of application had only a minor effect on accuracy. CONCLUSIONS: Within the limitations of this study, it seems that all impression materials are suitable for miniscrew abutment transfer, provided that methods of intraoral adaptation of the orthodontic appliance can be employed. If higher accuracy is needed or for clinicians with less experienced, a biphasic polyvinylsiloxane impression with the putty-wash technique should be used as this combination reduces setting time. The most cost-effective version, alginate, can be used if the consequences of greater deviations can be handled. Caution is advised with polyether if undercuts are present.

Modified Tray with Mesh Design for the Management of Flabby Ridge: A Case Report.

Flabby ridge is an excessive movable fibrous tissue, usually affecting the maxillary and mandibular edentulous ridges. It is a typical finding frequently observed in the maxillary anterior region. It usually occurs when natural teeth oppose an edentulous ridge or in long-term denture wearers. The management of flabby ridges includes surgical intervention, implant-retained prostheses, and conventional dentures fabricated using the modified impression technique. This case report depicts a modified technique with the utilization of an aluminum mesh double tray and polyvinylsiloxane impression material for the management of a flabby ridge in the maxillary arch.

Effect of Time and Method of Drying on Bond Strength of Tray Adhesives with Vinyl Polysiloxanes.

AIM: To establish an effective combination of drying time and drying method of the tray adhesive so that maximum bond strength can be achieved between impression tray and impression material. MATERIALS AND METHODS: Cylindrical specimens of auto-polymerizing resin and addition silicone impression material were made. A total of 150 specimens were tested. They were divided into two groups Dentsply and GC. Each group was further divided into five subgroups: • Drying with compressed air for half the time as recommended by the manufacturer • Drying with air blower for half the time as recommended by the manufacturer • Open air drying as recommended by the manufacturer • Open air drying for 15 minutes • Open air drying for 1 hour The samples were tested for tensile bond strength using the universal testing machine. The results were subjected to statistical analysis. RESULT: Open air drying as recommended by the manufacturer was better than drying with a blower or compressed air. There was no significant difference between open-air drying for 5 minutes and open-air drying for 15 minutes or 1 hour. CONCLUSION: Open air drying as recommended by the manufacturer, i.e. 5min, showed good bond strength and drying for more than 5mins does not significantly increase bond strength. CLINICAL SIGNIFICANCE: Tray adhesive should not be dried with compressed air or air blower. Tray adhesive should be applied and kept to dry according to the manufacturer's recommended time.

Retentive characteristics of individual and prefabricated polyvinylsiloxane overdenture attachments: alternative treatment options for geriatric patients.

OBJECTIVES: Stud attachments are often too adhesive and too susceptible to damage for use in geriatric patients, especially when implants are angulated. This study aimed to evaluate alternative anchoring systems comprising individual and prefabricated polyvinylsiloxane (PVS) attachments. MATERIALS AND METHODS: A total of 182 specimens with individual PVS (IPVS) attachments (Shore hardness [SH] 25, SH50, SH65], prefabricated PVS (PPVS) attachments (SM green, yellow, and red), and Locator attachments (LR blue) were fabricated (n = 7 per group). Retention force was measured using the following parameters: insertion/removal (100, 200, 500, 1000, and 5000 cycles), thermal undulation (10,000 cycles at 5-55 °C; one implant per specimen), implant angulation (0°, 5°, and 10° convergence and divergence; two implants per specimen), and artificial saliva. RESULTS: Insertion/removal and thermal undulation caused no changes in retention force in SM green and IPVS subgroups; conversely, LR blue, SM red, and SM yellow attachments exhibited significant decreases in retention force of up to 66% (all P ≤ 0.001). Implant angulation produced relevant changes in retention force only in LR blue attachments. Artificial saliva caused a general decrease in retention force. CONCLUSIONS: Retention force of low-retentive PVS attachments proved to be comparatively immune to dislocation and thermal undulation, as well as to implant angulation up to 10°. CLINICAL RELEVANCE: Low-retentive PVS attachments could be a treatment option if reduced denture retention is required and/or if angulated implants are in place. Clinical studies are necessary to evaluate the materials' durability under oral conditions.

Management of the flabby ridge using a modified window technique and polyvinylsiloxane impression material.

Flabby ridge is a common clinical finding affecting the alveolar ridges of the mandibular or maxillary arches. The anterior region of maxilla is the most affected area in edentulous patients. Dentures on flabby ridges have compromised stability, support, and retention unless adequate measures for its management are employed. Methods applied for flabby ridge management, include surgical removal and augmentation, special impression techniques, balanced distribution of occlusal loads and implant therapy. Special impressions often involve window technique for static impression of flabby area, which present multiple challenges. The purpose of this technique report is to present a modified window technique for the impression of anterior maxillary flabby tissues for improved and controlled application of polyvinylsiloxane impression material that are routinely available in dental practice.

Trends in Selection, Usage, and Techniques of Interocclusal Record Materials among Private Dental Practitioners: A Survey.

BACKGROUND: Majority of general dental practitioners provide fixed dental prosthesis in India. The aim of this study was to gather information on selection, usage, and materials and methods employed in interocclusal records and their communication with the dental laboratory for restorative procedures practised by dentists in Indore district to evaluate and to improve the quality of current practice. AIM AND OBJECTIVES: The purpose of this cross-sectional study was to understand and to evaluate dental practitioner's knowledge on interocclusal recording materials, its usage, their clinical implications, and their correlation with the laboratory in restorative procedures practiced by the dental practitioners in Indore district. MATERIALS AND METHODS: A questionnaire comprising 11 questions were framed and circulated among general dental practitioners except prosthodontists, and the results were statistically analyzed. RESULTS: Most of the practitioner's preferred wax (54.6%) as an interocclusal recording material over polyvinylsiloxane and polyether. Most of the dentists preferred full arch interocclusal record (27.8%). About 51.5% clinicians trimmed the interocclusal record before sending to the laboratory. CONCLUSION: From this survey, it has been concluded that the practitioner's attitude toward the use of interocclusal record materials is found to be deviated from well-acknowledged prosthodontic quality guidelines.

A modified shark-fin test simulating the single-step/double-mix technique: A comparison of three groups of elastomers.

The shark-fin test was modified to convey the clinical application of a single-step/double-mix technique assessing the behavior of two viscosities applied at one point in time. A medium and light body polyether (PE), a medium and light body polyvinylsiloxane (PVS), and a medium as well as heavy and light body vinyl polyether silicone (PVXE) impression material were analyzed solely, and in a layered mixture of 1:1 and 3:1 at working times of 50, 80, and 120 s. The fin heights were measured with a digital ruler. The wettability was measured 50 and 80 s after mixing by drop shape analysis. The results showed a synergistic effect of the medium and light body PE. This was not observed in PVXE and PVS. Interestingly, PVXE showed an antagonistic flow behavior in 3:1 mixture with medium body. PVXE was more hydrophilic than PE and PVS. Future rheological studies should clarify the detected flow effects.

Evaluation and comparison of resistance to compression of various interocclusal recording media: an in vitro study.

BACKGROUND: This in vitro study was conducted to compare the compression resistance of various interocclusal recording materials when subjected to a compressive load. MATERIALS AND METHODS: Each interocclusal recording material was manipulated according to the manufacturer instruction and placed into a metallic cylinder. A total of 20 specimens for each interocclusal recording material were made. A total 100 specimens were fabricated. Each specimen was placed in the Universal Testing Machine exerting pressure on it, and a force of 100 g/cm(2) was exerted on each sample. 30 s later the reading of the Universal Testing Machine was recorded using a vertical traveling micrometer microscope with an accuracy of ± 0.001 mm. This value was marked as reading "A." 60 s after the application of the first force (100 g/cm(2)), a second force of 1000 g/cm(2) was applied gradually during an interval of 10 s. 30 s later the reading of the Universal Testing Machine exerting pressure on the specimen was recorded again. This value was marked as reading "B." The difference between readings "A" and "B" recorded the compression to resistance of each material. Comparisons within the groups and between the groups were done by using one-way ANOVA and Tukey's HSD test. RESULT: There was significant variation between all interocclusal bite registration materials. According to the mean valve of each interocclusal bite registration material, Polyvinylsiloxane Bite Registration Material have better resistance to compression followed by Polyether interocclusal bite registration material, Aluwax Bite, and Impression Wax, Modeling Wax and at last Zinc Oxide Eugenol Impression Paste. CONCLUSION: Polyvinylsiloxane interocclusal registration material had the greatest resistance to compression. The least resistance to compression was noticed with zinc oxide-eugenol paste.

Effects of sulfur-based hemostatic agents and gingival retraction cords handled with latex gloves on the polymerization of polyvinyl siloxane impression materials

OBJECTIVES: This study investigated the possible interactions between three addition silicone materials (Express®, Aquasil Ultra® and Adsil®), three hemostatic agents (ferric sulfate, StatGel FS®; aluminum sulfate, GelCord®; and aluminum chloride, Hemostop®) and gingival retraction cords previously handled with latex gloves to determine whether direct contact with medicaments or indirect contamination by latex in conditions similar to those found in clinical practice inhibit or affect the setting of the impression materials. MATERIAL AND METHODS: A portable device for the simultaneous test of several specimens was specifically developed for this study. Polymerization inhibition was analyzed by examination of the impressions and the molded surface. Ten trials were performed for each addition silicone material used in the study, at a total of 240 study samples. RESULTS: All the samples tested (N=240) were nonreactive regardless of the type of combination used. CONCLUSIONS: Aluminum sulfate, ferric sulfate and aluminum chloride hemostatic solutions did not show any inhibitory potential on the addition silicone samples under study, and there were no changes in polymerization as a result of contact between addition silicone and retraction cords handled with latex gloves.

Drying time of tray adhesive for adequate tensile bond strength between polyvinylsiloxane impression and tray resin material.

STATEMENT OF PROBLEM: Use of custom tray and tray adhesive is clinically recommended for elastomeric impression material. However there is not clear mention of drying time of tray adhesive in achieving appropriate bonding strength of tray material and impression material. PURPOSE: This study is to investigate an appropriate drying time of tray adhesives by evaluating tensile bonding strength between two types of polyvinylsiloxane impression materials and resin tray, according to various drying time intervals of tray adhesives, and with different manufacturing company combination of impression material and tray adhesive. MATERIAL AND METHODS: Adhesives used in this study were Silfix (Dentsply Caulk, Milford, Del, USA) and VPS Tray Adhesive (3M ESPE, Seefeld, Germany) and impression materials were Aquasil Ultra (monophase regular set, Dentsply Caulk, Milford, Del, USA) and Imprint II Garant (regular body, 3M ESPE, Seefeld, Germany). They were used combinations from the same manufacture and exchanged combinations of the two. The drying time was designed to air dry, 5 minutes, 10 minutes, 15 minutes, 20 minutes, and 25 minutes. Total 240 of test specimens were prepared by auto-polymerizing tray material (Instant Tray Mix, Lang, Wheeling, Il, USA) with 10 specimens in each group. The specimens were placed in the Universal Testing machine (Instron, model 3366, Instron Corp, University avenue, Nowood, MA, USA) to perform the tensile test (cross head speed 5 mm/min). The statistically efficient drying time was evaluated through ANOVA and Scheffe test. All the tests were performed at 95% confidence level. RESULTS: The results revealed that at least 10 minutes is needed for Silfix-Aquasil, and 15 minutes for VPS Tray Adhesive-Imprint II, to attain an appropriate tensile bonding strength. VPS Tray Adhesive-Imprint II had a superior tensile bonding strength when compared to Silfix-Aquasil over 15 minutes. Silfix-Aquasil had a superior bonding strength to VPS Tray Adhesive-Aquasil, and VPS Tray Adhesive-Imprint II had a superior tensile bonding strength to Silfix-Imprint II at all drying periods. CONCLUSION: Significant increase in tensile bonding strength with Silfix-Aquasil and VPS Tray adhesive-Imprint II combination until 10 and 15 minutes respectively. Tray adhesive-impression material combination from the same company presented higher tensile bonding strength at all drying time intervals than when using tray adhesive-impression material of different manufactures.

Drying time of tray adhesive for adequate tensile bond strength between polyvinylsiloxane impression and tray resin material

STATEMENT OF PROBLEM: Use of custom tray and tray adhesive is clinically recommended for elastomeric impression material. However there is not clear mention of drying time of tray adhesive in achieving appropriate bonding strength of tray material and impression material. PURPOSE: This study is to investigate an appropriate drying time of tray adhesives by evaluating tensile bonding strength between two types of polyvinylsiloxane impression materials and resin tray, according to various drying time intervals of tray adhesives, and with different manufacturing company combination of impression material and tray adhesive. MATERIAL AND METHODS: Adhesives used in this study were Silfix (Dentsply Caulk, Milford, Del, USA) and VPS Tray Adhesive (3M ESPE, Seefeld, Germany) and impression materials were Aquasil Ultra (monophase regular set, Dentsply Caulk, Milford, Del, USA) and Imprint II Garant (regular body, 3M ESPE, Seefeld, Germany). They were used combinations from the same manufacture and exchanged combinations of the two. The drying time was designed to air dry, 5 minutes, 10 minutes, 15 minutes, 20 minutes, and 25 minutes. Total 240 of test specimens were prepared by auto-polymerizing tray material (Instant Tray Mix, Lang, Wheeling, Il, USA) with 10 specimens in each group. The specimens were placed in the Universal Testing machine (Instron, model 3366, Instron Corp, University avenue, Nowood, MA, USA) to perform the tensile test (cross head speed 5 mm/min). The statistically efficient drying time was evaluated through ANOVA and Scheffe test. All the tests were performed at 95% confidence level. RESULTS: The results revealed that at least 10 minutes is needed for Silfix-Aquasil, and 15 minutes for VPS Tray Adhesive-Imprint II, to attain an appropriate tensile bonding strength. VPS Tray Adhesive-Imprint II had a superior tensile bonding strength when compared to Silfix-Aquasil over 15 minutes. Silfix-Aquasil had a superior bonding strength to VPS Tray Adhesive-Aquasil, and VPS Tray Adhesive-Imprint II had a superior tensile bonding strength to Silfix-Imprint II at all drying periods. CONCLUSION: Significant increase in tensile bonding strength with Silfix-Aquasil and VPS Tray adhesive-Imprint II combination until 10 and 15 minutes respectively. Tray adhesive-impression material combination from the same company presented higher tensile bonding strength at all drying time intervals than when using tray adhesive-impression material of different manufactures.