Assessment of dimensional stability of novel VPES impression material at different time intervals with standard disinfectants.

BACKGROUND: Vinyl polyether silicone (VPES) is a novel impression biomaterial made of a combination of vinyl polysiloxane (VPS) and polyether (PE). Thus, it is significant to assess its properties and behaviour under varied disinfectant test conditions. This study aimed to assess the dimensional stability of novel VPES impression material after immersion in standard disinfectants for different time intervals. METHODS: Elastomeric impression material used -medium body regular set (Monophase) [Exa'lence GC America]. A total of 84 Specimens were fabricated using stainless steel die and ring (ADA specification 19). These samples were distributed into a control group (n=12) and a test group (n=72). The test group was divided into 3 groups, based on the type of disinfectant used - Group-A- 2% Glutaraldehyde, Group-B- 0. 5% Sodium hypochlorite and Group-C- 2% Chlorhexidine each test group was further divided into 2 subgroups (n=12/subgroup) based on time intervals for which each sample was immersed in the disinfectants - subgroup-1- 10 mins and Subgroup 2- 30 mins. After the impression material was set, it was removed from the ring and then it was washed in water for 15 seconds. Control group measurements were made immediately on a stereomicroscope and other samples were immersed in the three disinfection solutions for 10 mins and 30 mins to check the dimensional stability by measuring the distance between the lines generated by the stainless steel die on the samples using a stereomicroscope at x40 magnification. RESULTS: The distance measured in the control group was 4397.2078 µm and 4396.1571 µm; for the test group Group-A- 2% Glutaraldehyde was 4396.4075 µm and 4394.5992 µm; Group-B- 0. 5% Sodium hypochlorite was 4394.5453 µm and 4389.4711 µm Group-C- 2% Chlorhexidine was 4395.2953 µm and 4387.1703 µm respectively for 10 mins and 30 mins. Percentage dimensional change was in the range of 0.02 - 0.25 for all the groups for 10 mins and 30 mins. CONCLUSIONS: 2 % Glutaraldehyde is the most suitable disinfectant for VPES elastomeric impression material in terms of dimensional stability and shows minimum dimensional changes as compared to that of 2% Chlorhexidine and 0.5% Sodium hypochlorite.

Positional accuracy of a single implant analog in additively manufactured casts in biobased model resin.

OBJECTIVES: To evaluate the positional accuracy of implant analogs in biobased model resin by comparing them to that of implant analogs in model resin casts and conventional analogs in dental stone casts. METHODS: Polyvinylsiloxane impressions of a partially edentulous mandibular model with a single implant were made and poured in type IV dental stone. The same model was also digitized with an intraoral scanner and additively manufactured implant casts were fabricated in biobased model resin (FotoDent biobased model) and model resin (FotoDent model 2 beige-opaque) (n = 8). All casts and the model were digitized with a laboratory scanner, and the scan files were imported into a 3-dimensional analysis software (Geomagic Control X). The linear deviations of 2 standardized points on the scan body used during digitization were automatically calculated on x-, y-, and z-axes. Average deviations were used to define precision, and 1-way analysis of variance and Tukey HSD tests were used for statistical analyses (α = 0.05). RESULTS: Biobased model resin led to higher deviations than dental stone (all axes, P ≤ 0.031) and model resin (y-axis, P = 0.015). Biobased model resin resulted in the lowest precision of implant analog position (P ≤ 0.049). The difference in the positional accuracy of implant analogs of model resin and stone casts was nonsignificant (P ≥ 0.196). CONCLUSIONS: Implant analogs in biobased model resin casts mostly had lower positional accuracy, whereas those in model resin and stone casts had similar positional accuracy. Regardless of the material, analogs deviated more towards mesial, while buccal deviations in additively manufactured casts and lingual deviations in stone casts were more prominent.

Digital Evaluation of Trueness and Precision of Modern Impression Materials in Implant- Retained Mandibular Overdentures.

INTRODUCTION: The purpose of this in vitro study was to evaluate the dimensional accuracy, trueness, and precision of vinyl siloxane ether (VSXE) and polyvinylsiloxane (PVS) impression materials using different impression techniques. MATERIAL AND METHODS: A three-dimensional (3D) printed mandibular model with implants and metal rods served as the reference model. Impressions were taken in custom trays, resulting in four groups: PVS-closed-tray, VSXE-closed-tray, PVS-open-tray, and VSXE-open-tray. The reference model and impressions were scanned and analyzed using 3D analysis software to assess the trueness and precision within each group. RESULTS: There was significant difference in trueness between the groups, with PVS closed tray showing a higher deviation than VSXE-closed-tray and PVS-open-tray. VSXE-open-tray had the lowest deviation, which was statistically significant. In terms of precision, PVS-closed-tray showed the highest deviation, while no significant differences were found among the other groups. CONCLUSIONS: VSXE impression material with an open tray technique consistently demonstrated the highest levels of accuracy and precision. Conversely, PVS impression material with a closed tray technique yielded less favorable results. CLINICAL RELEVANCE: Better understanding of trueness and precision of new impression materials with new impression techniques will increase their clinical effectiveness.

A comparative in vitro analysis of various temporization materials with respect to pulp chamber temperature changes during polymerization.

AIM: (1) To compare the temperature rise in the pulp chamber with different resin materials used for making provisional fixed partial dentures in anterior and posterior region while using Polyvinylsiloxane impression materials as matrix. (2) To identify a superior provisionalization material based on the amount of heat dissipated suitable for anterior and posterior provisional fixed partial denture fabrication. SETTINGS AND DESIGN: Temporary crowns and bridges are integral to Fixed Prosthodontics. It has been observed that conventional fixed prosthesis temporisation materials release heat due to the exothermic polymerisation reaction. When such a provisional material is directly let to set on a vital tooth, the heat transfer causes irreversible changes in the pulp tissue depending of the degree of change. Hence, this study observes amount of heat generation in various materials during temporisation procedure, by simulating similar conditions. MATERIALS AND METHODS: Two Models were fabricated, one simulating missing lateral incisor (Model A) and another simulating missing first molar (Model B). Intact maxillary central incisors and canine for Model A and intact mandibular Second Premolar and Second Molar were selected to act as abutments. These abutment teeth were fitted with the tip of a K-type Thermocouple inside their pulp chambers and these were connected to a digital thermometer. Five temporisation materials were chosen for fabrication of temporary crowns through Direct technique. (1) polymethy methacrylate (Self Cure acrylic), (2) bisacryl composite (Protemp 4), (3) visible light cure urethane dimethacrylate (Revotec LC), (4) barium glass and fumed silica infused methacrylate (Dentsply Integrity) and (5)nano-hybrid composite (VOCO Structur 3). Ten observations were made for each provisional material on each model. During each observation, temperature rise was recorded at 30s interval from the time of application, through the peak and till a decrease in temperature is observed. Polyvinyl siloxane was used as matrix for all except light cure resin, where polypropylene sheet was used. STATISTICAL ANALYSIS USED: Anova test used for statistical. RESULTS: ANOVA test revealed that there was a significant difference in the temperature changes associated with the provisional restorative materials used. Among the five, polymethy methacrylate (self cure resin) showed the maximum rise in temperature, followed by bisacryl composite (Protemp 4), visible light cure urethane dimethacrylate (Revotec LC), barium glass and fumed silica infused methacrylate (Dentsply Integrity) and nano-hybrid composite (VOCO Structur 3). There was no comparable difference between Model A and B but an overall reduction of temperature rise was observed in model B. CONCLUSION: VOCO Structur 3 showed the least temperature rise in the pulp chamber, and overall temperature rise was less for model B which can be attributed to the residual dentin thickness.

[Effect of different kinds of gingival retraction agents on the polymerization inhibition of polyvinyl siloxane impression materials].

PURPOSE: To evaluate the effect of different kinds of gingival retraction agents after directly contacted with polyvinyl siloxane impression materials on polymerization inhibition and the inhibition degree. METHODS: Five kinds of gingival retraction agents (0.1% epinephrine hydrochloride, 0.05% oxymetazoline, 15.5% ferric sulfate, 25% aluminum chloride and 5% aluminum chloride) were chosen, normal saline was as control group, and two kinds of polyvinyl siloxane impression materials (ExpressTM, ImprintTM Ⅱ) were combined into 12 groups. There were 12 specimens in each group and 144 specimens in total. Silicone rubber impression materials were mixed by the same operator using a dispensing gun into the acrylic mold, so that they could directly contact the gingival retraction agents on the densely woven cotton fabrics. The samples were removed when the polymerization time arrived according to the manufactures' recommendations and then placed under a stereomicroscope with a magnification of 10 times to observe whether polymerization inhibition occurred, the degree of inhibition was compared afterwards. SPSS 22.0 software package was used for statistical analysis. RESULTS: The polymerization inhibition of two kinds of silicone rubber impression materials occurred in 15.5% ferric sulfate group and 25% aluminum chloride group, and the inhibition occurrence rate was 100%, the difference was statistically significant (P＜0.05) compared with normal saline group. Inhibition was not found in 0.1% epinephrine hydrochloride group, 0.05% oxymetazoline group and 5% aluminum chloride. The effect of 15.5% ferric sulfate and 25% aluminum chloride on polymerization inhibition degree of ImprintTM Ⅱ was greater than ExpressTM, and the difference was statistically significant(P＜0.05). CONCLUSIONS: When silicone rubber impression material is used during impression procedure, attention should be paid to the effect of the gingival retraction agent containing 15.5% ferric sulfate and 25% aluminum chloride on its polymerization. The gingival retraction agent should be washed before impression to avoid the residue directly contacting the silicone rubber to prevent polymerization.

Dimensional Stability and Retention Strength of Impressions to Custom Impression Trays Fabricated Using Conventional Method and Additive Technology - An In-vitro Study.

BACKGROUND: 3D printing technology is replacing manual fabrication in all fields. 3D-printed impression trays should be assessed as they could replace conventional impression trays in the future. AIM: In-vitro comparison and evaluation of the dimensional stability and retention strength of impressions to custom impression trays fabricated using conventional method and additive technology. MATERIALS AND METHODS: A maxillary edentulous auto-polymerizing acrylic resin model served as the master model. Two moulds were prepared from the master model in order to obtain 12 casts. One cast was scanned for 3D printing digital light processing (DLP) and fused deposition modelling (FDM) 24 impression trays using polylactic acid (PLA). Twelve casts were used to fabricate light cure impression trays. Polyvinyl-siloxane impressions were made on the master model using 36 impression trays and 18 trays each were used to assess dimensional stability and retention strength. RESULTS: In dimensional stability analysis, one sample t-test revealed a statistically significant difference between each group and the master model followed by a one-way ANOVA. There were significant differences, but the difference was less with FDM trays (P < 0.05). In retention strength analysis, one-way Analysis of variance (ANOVA) revealed statistically significant difference between each group and post-hoc test revealed specific difference, the highest with FDM trays (P < 0.05). CONCLUSION: Dimensional changes were observed at 30 minutes and 72 hours. Lesser dimensional changes were observed when impressions were made using FDM trays followed by DLP and light cure trays. The mean retention strength seen in descending order was FDM, followed by DLP and light cure trays. The best retention strength was noticed when impressions were made using FDM trays.

Synthesis of a novel injectable alginate impression material and impression accuracy evaluation.

OBJECTIVES: This work aimed to synthesize a novel injectable alginate impression material and evaluate its accuracy. METHODS: Certain proportions of sodium alginate, trisodium phosphate dodecahydrate, potassium fluorotitanate, diatomaceous earth, and other ingredients were dissolved in water and mixed evenly with a planetary centrifugal mixer to obtain a certain viscosity base paste. Certain proportions of calcium sulfate hemihydrate, magnesium oxide, glycerin, and polyethylene glycol (PEG) 400 were mixed evenly with a planetary centrifugal mixer to obtain the reactor paste with the same viscosity as the base paste. The base and reactor pastes were poured into a two-cylinder cartridge at a 2∶1 volume ratio. A gun device was used to accomplish mixing by compressing materials into a mixing tip. The samples were divided into three groups: injectable alginate impression materials (IA group) as the experimental group, and Jeltrate alginate impression materials (JA group) and Silagum-putty/light addition silicone rubber impression materials (SI group) as the two control groups. RESULTS: Scanning electron microscopy (SEM) showed that the injectable alginate impression materials had a denser structure and fewer bubbles than the commercial alginate impression material. The accuracy of the three kinds of impression materials was evaluated by 3D image superposition. The deviations between the three test group models and the standard model (trueness) were 49.58 µm±1.453 µm (IA group), 54.75 µm±7.264 µm (JA group), and 30.92 µm±1.013 µm (SI group). The deviations of the models within each test group (precision) were 85.79 µm±8.191 µm (IA group), 97.65 µm±11.060 µm (JA group), and 56.51 µm±4.995 µm (SI group). Significant differences in trueness and precision were found among the three kinds of impression materials (P<0.05). CONCLUSIONS: The accuracy of the new injectable alginate impression material was better than that of the traditional powder-type alginate impression material but worse than that of the addition silicone rubber impression materials. The novel injec-table alginate impression material demonstrated good operation performance and impression accuracy, showing broad application prospect.

Current overview for chemical disinfection of dental impressions and models based on its criteria of usage: A microbiological study.

Objectives: The aims of this study were to compare the efficacy of two proven chemical disinfectants, glutaraldehyde and povidone iodine on dental impression and models by determining the reduction in the microbial load, and to compare changes in the physical properties of the models after adding the disinfectants. Materials and Methods: Irreversible hydrocolloid upper impressions of 90 patients were made and divided into 3 groups of 30 samples each; Group A--Control group; Impressions were run under clean tap water before pouring the model. Group B--2% Glutaraldehyde sprayed on the impression and left in situ for 10 min before pouring the model. Group C -10 ml of (5%) povidone iodine incorporated into the gypsum before pouring the model. Models from all three groups were subjected to microbiological assessment at three different time intervals, T0--24 h, T1--1 month and T2--3 months of storage by comparing the colony forming units (CFUs) of bacteria and fungi. The compressive strength of 5 models from each group was also analyzed in Newton's/mm2. Results: 2% Glutaraldehyde proved more effective than povidone iodine after 24 h of storage (T1), however at the end of 1 month (T1) and 3 months (T2) the Povidone group showed the maximum disinfection. Both the disinfectants caused a reduction in the compressive strength of the model with the povidone iodine group showing the maximum reduction. Conclusion: Although povidone iodine was the most effective disinfectant after 3 months, it showed a significant reduction in the compressive strength and caused discoloration of the model. 2% Glutaraldehyde proved to be the choice of disinfectant with minimal adverse effects.

Sodium carbonate improves adherence of two-layer alginate for preliminary impressions of complete dentures.

PURPOSE: This in vitro study evaluated the effect of sodium carbonate (Na2CO3) concentration on adhesion between two layers of irreversible hydrocolloid wash impression material. METHODS: The first layer of irreversible hydrocolloid was brushed with three concentrations (0.1, 0.7, or 7.0 wt.%) of Na2CO3. Irreversible hydrocolloid not brushed with Na2CO3 was used as a negative control. Adhesion between the two layers (bond strength and adhesion energy) was then evaluated using a traction test, and the fracture modes were identified. The results of traction test were analyzed with a one-way ANOVA followed by a Tukey post hoc test. Chi-square test was used for analyzed failure mode after testing (α= 0.05). RESULTS: The bond strength (0.034 ±0.005 MPa) and adhesion energy (60.240 ±12.817 J.m⁻ ²) of the 0.7% Na2CO3 group were significantly higher than those of the other groups (P< 0.05). The 0.7% Na2CO3 group displayed only cohesive failure (ײ= 16; P< 0.0001). CLINICAL SIGNIFICANCE: Conditioning the surface of the first layer of irreversible hydrocolloid with 0.7% sodium carbonate improved adhesion between the two layers and may help clinicians improve the quality of the preliminary impressions of removable complete dentures.

Comparison of the Hardness of Novel Experimental Vinyl Poly Siloxane (VPS) Impression Materials with Commercially Available Ones.

PURPOSE: To determine the hardness and Young's moduli of both commercial and experimental vinyl poly siloxane (VPS). METHODS: The purpose of this study was to develop a medium-bodied experimental (Exp-I, II, III, IV, and V) VPS impression materials and to analyse their effects on hardness and Young's modulus and compare them with three commercial VPS materials (Aquasil, Elite, and Extrude) using Shore A hardness tester. Measurements were recorded after 1, 24, 72, and 168 hours of mixing. The results were analysed with one-way ANOVA and post hoc Tukey's test using the SPSS PASW statistical 22 software. RESULTS: Commercial and experimental vinyl polysiloxane exhibited higher Shore A hardness values with time (i.e., 1 hour after mixing, 24 hours after mixing, 72 hours after mixing, and 1 week after mixing). All Comml and Exp VPS demonstrated a significant increase (ANOVA, p < 0.05) in hardness at increasing time points. Generally, all commercial VPS exhibited significantly higher values for Shore A hardness compared to all Exp formulations. For commercial products, Elt M presented significantly highest values at all-time points followed by Aq M then Extr M. Exp-I was significantly harder than all other Exp VPS at all-time points. Young's modulus values were directly related to Shore A hardness; materials with higher Shore A hardness values had higher Young's moduli. CONCLUSION: Continued polymerisation of elastomeric impression materials results in increased hardness over time. Hardness, Young's moduli, and rigidity of the set commercial and experimental VPS materials were within the required limits. Shore A hardness and Young's moduli were directly proportional to each other, and commercial and experimental materials had enough rigidity to contain the stone during pouring.

A Promising Potential of Brown Algae Sargassum polycystum as Irreversible Hydrocolloid Impression Material.

This study aimed to investigate the potential use of brown algae Sargassum polycystum as irreversible hydrocolloid (alginate) impression material. Potassium alginate extracted from Sargassum polycystum was prepared in three different compositions (14%, 15%, and 16%) and mixed with other standard components to form an alginate impression material. Prior to that, the purity of potassium alginate was quantified with Fourier Transform Infrared Spectroscopy (FTIR) analysis. As a control material, the alginate impression material from a commercially available product was used. All alginate impression materials were then applied to a die stone model. Dimensional accuracy was measured by calculating the mesiodistal width of incisors in the generated dental cast using a digital caliper 0.01 accuracy (five replications). In addition, to evaluate the dimensional stability, the impression results were poured at four different periods (immediately, 5 min, 10 min, and 15 min). An independent t-test was performed to compare the measurement results with p < 0.05 considered significant. Analytical results confirm that the impression material containing 15% potassium alginate gives the best dimensional accuracy similar to control (p > 0.05). Meanwhile, the optimal dimensional stability was produced in the impression material containing 16% potassium alginate. Our study suggested that brown algae Sargassum polycystum has a promising potential to be used as an alginate impression material in clinical application.

Dimensional stability of alginate molds scanned at different storage times / Estabilidade dimensional de moldes de alginato digitalizados em diferentes tempos de armazenamento

ABSTRACT The aim of this study was to evaluate the precision and accuracy of molds made with four commercial brands of alginate scanned at different times using digital model analysis. Eighty molds of a standard Typodont were made using 4 types of alginate (CCC: Cavex Color Change; IA: Identic Alginate; HY5: Hydrogum 5 and JP: Jeltrate Plus). The molds were scanned at four times: immediately (T1), 24h (T2), 72h (T3) and 120h (T4) after molding. Measurements were taken in three dimensions: anteroposterior, transverse and vertical. Significant differences in dimensional changes were noted between the materials over time (p <0.05). Anteroposterior dimensional variation was noted between times, especially for IA and JP. For transverse and vertical variables, a difference was found between the groups, especially at 24 h, 72 h and 120 h. CCC presented significant dimensional shrinkage only at T120 (transverse). IA and JP presented larger dimensional distortions in the vertical measurements. The molding materials used were not dimensionally stable when evaluated after 120 hours of molding. However, such evidence suggests that alginates with longer storage time, such as Cavex Color Change, are more accurate than conventional alginates.

RESUMO O objetivo do presente estudo foi avaliar a precisao e acurácia por meio de análise de modelos digitais de moldes digitalizados obtidos com quatro marcas comerciais de alginato em diferentes tempos. Oitenta moldes de um Typodont padrao foram obtidos utilizando 4 tipos de alginato (CCC: Cavex Color Change; IA: Identic Alginate; HY5: Hydrogum 5 e JP: Jeltrate Plus). Os moldes foram escaneados em quatro tempos: mediatamente (T1), 24h (T2), 72h (T3) e 120h (T4) após a moldagem. As medidas foram feitas em très dimensoes: ântero-posterior, transversal e vertical. Diferenças significativas nas mudanças dimensionais foram observadas entre os materiais ao longo do tempo (p <0,05). Variação dimensional ântero-posterior foi observada entre os tempos, principalmente para IA e JP. Para as variáveis transversal e vertical houve diferenga entre os grupos, principalmente em 24h, 72h e 120h. CCC apresentou contração dimensional significativa apenas em T120 (transversal). IA e JP apresentaram maiores distorções dimensionais na vertical. Os materiais de moldagem utilizados nao foram dimensionalmente estáveis quando avaliados após 120 horas de moldagem. No entanto, tais evidencias sugerem que os alginatos com maior tempo de armazenamento, como Cavex Color Change, sao mais precisos do que os alginatos convencionais.

Accuracy evaluation of 3D printed interim prosthesis fabrication using a CBCT scanning based digital model.

OBJECTIVES: This study aimed to evaluate the marginal and internal gaps in 3D-printed interim crowns made from digital models of cone-beam computed tomography (CBCT) conversion data. MATERIALS AND METHODS: Sixteen polyvinylsiloxane impressions were taken from patients for single crown restorations and were scanned using CBCT. The scanning data were converted to positive Standard Triangulation Language (STL) files using custom-developed software. The fabricated stone models were scanned with an intraoral optical scanner (IOS) to compare the surface accuracy with the STL data obtained by CBCT. The converted STL files were utilized to fabricate interim crowns with a photopolymer using a digital light-processing 3D printer. The replica method was used to analyze the accuracy. The marginal and internal gaps in the replica specimen of each interim crown were measured with a digital microscope. The Friedman test and Mann-Whitney U test (Wilcoxon-signed rank test) were conducted to compare the measurements of the marginal and internal gaps with a 95% level of confidence. RESULTS: The root-mean-square values of the CBCT and IOS ranged from 41.00 to 126.60 µm, and the mean was 60.12 µm. The mean values of the marginal, internal, and total gaps were 132.96 (±139.23) µm, 137.86 (±103.09) µm, and 135.68 (±120.30) µm, respectively. There were no statistically significant differences in the marginal or internal gaps between the mesiodistal and buccolingual surfaces, but the marginal area (132.96 µm) and occlusal area (255.88 µm) had significant mean differences. CONCLUSION: The marginal gap of the fabricated interim crowns based on CBCT STL data was within the acceptable range of clinical success. Through ongoing developments of high-resolution CBCT and the digital model conversion technique, CBCT might be an alternative method to acquire digital models for interim crown fabrication.

Importance of disinfection time and procedure with different alginate impression products to reduce dimensional instability.

AIMS: The aim of this study was to determine the best approach to reduce the unfavorable change in the three different dimensions of impressions using disinfection durations of 15 and 30 min; three different disinfection procedures; and alginate impression products as research factors. MATERIALS AND METHODS: CA37, impressional, and cream alginate impressions were used; distortion in the AB, AC, and BC dimensions of impressions using disinfection durations of 15 and 30 min was studied; and no disinfection (ND), conventional disinfection (CD), and sonicator-activated disinfection (SAD) procedures were measured. RESULTS: Regarding AB dimension, the impressional has best performance when CD was applied for both 15 and 30 min. When SAD was applied for 15 min, impressional and cream alginates provide best performance. When CD was applied for 15 min, CA37 and impressional alginates provide best performance. Although ND-applied CA37 alginate after 30 min provides best performance, because of many outlier values, its implication may not be considered as meaningful. Regarding AC dimension, cream alginate has best performance when CD was applied for 15 min. The AC distances in all the alginates are considerably different from the base model after 30 min. Regarding BC dimension, only the CA37 alginate has the best performance when ND was applied for 15 min. All the alginates are considerably different from that of the base model after 30 min. CONCLUSION: Preference of 15-min disinfection can provide favorable results to obtain all impressions with minimally distorted dimensions. CD is an adequate procedure. The studied SAD needs to be developed further. All alginates are comparably successful to obtain impressions with desired distortion degrees.

Effect of contemporary retraction agents and cleaning with hydrogen peroxide on the polymerization of elastomeric impression materials.

The aim of the study is to investigate the polymerization inhibition of elastomeric impression materials vinylpoly siloxane (VPS) and polyether (PE) when used in combination with retraction materials with and without subsequent cleaning with hydrogen peroxide (H2O2). Methods: Seven stainless steel specimens were fabricated. Four hundred and twenty impressions were made with three different elastomeric materials (140 each) as follows: group 1: VPS-Panasil; group 2: VPS-Express; group 3: PE-Monophase. Each material group was further subdivided into seven subgroups, based on use of no retraction material (control), three different retraction materials [Retraction capsule (RC3M), Dryz, Expasyl], and two cleaning techniques (water and H2O2). All subgroups included 20 impressions, which were made by a single operator using an automix gun. Evaluations were made using a visual scale by three calibrated examiners blindly and independently. Subjective categorization of the impressions were made as inhibited and uninhibited. Data were analyzed using Fisher's exact test and significance was set at p < 0.05. Results: Inhibited impressions were lower than uninhibited impressions among VPS materials (Panasil and Express); Panasil and Express showed comparable (p > 0.05) impression retardation. PE showed significantly higher inhibition compared to VPS materials (p < 0.05). Expasyl showed significantly higher polymerization inhibition than other retraction materials (p < 0.05). The use of H2O2 for cleaning showed significant reduction in polymerization inhibition than cleaning with water for Expasyl (p < 0.05). Conclusion: Overall contemporary retraction materials showed low potential for polymerization inhibition of elastomeric impression materials. Expasyl should be cleaned with H2O2 prior to impression making. However, Dryz and RC3M can show accurate impressions with water cleaning alone.

Dimensional stability of alginate molds scanned at different storage times.

The aim of this study was to evaluate the precision and accuracy of molds made with four commercial brands of alginate scanned at different times using digital model analysis. Eighty molds of a standard Typodont were made using 4 types of alginate (CCC: Cavex Color Change; IA: Identic Alginate; HY5: Hydrogum 5 and JP: Jeltrate Plus). The molds were scanned at four times: immediately (T1), 24h (T2), 72h (T3) and 120h (T4) after molding. Measurements were taken in three dimensions: anteroposterior, transverse and vertical. Significant differences in dimensional changes were noted between the materials over time (p <0.05). Anteroposterior dimensional variation was noted between times, especially for IA and JP. For transverse and vertical variables, a difference was found between the groups, especially at 24 h, 72 h and 120 h. CCC presented significant dimensional shrinkage only at T120 (transverse). IA and JP presented larger dimensional distortions in the vertical measurements. The molding materials used were not dimensionally stable when evaluated after 120 hours of molding. However, such evidence suggests that alginates with longer storage time, such as Cavex Color Change, are more accurate than conventional alginates.

O objetivo do presente estudo foi avaliar a precisão e acurácia por meio de análise de modelos digitais de moldes digitalizados obtidos com quatro marcas comerciais de alginato em diferentes tempos. Oitenta moldes de um Typodont padrão foram obtidos utilizando 4 tipos de alginato (CCC: Cavex Color Change; IA: Identic Alginate; HY5: Hydrogum 5 e JP: Jeltrate Plus). Os moldes foram escaneados em quatro tempos: imediatamente (T1), 24h (T2), 72h (T3) e 120h (T4) após a moldagem. As medidas foram feitas em três dimensões: ântero-posterior, transversal e vertical. Diferenças significativas nas mudanças dimensionais foram observadas entre os materiais ao longo do tempo (p <0,05). Variação dimensional ântero-posterior foi observada entre os tempos, principalmente para IA e JP. Para as variáveis transversal e vertical houve diferença entre os grupos, principalmente em 24h, 72h e 120h. CCC apresentou contração dimensional significativa apenas em T120 (transversal). IA e JP apresentaram maiores distorções dimensionais na vertical. Os materiais de moldagem utilizados não foram dimensionalmente estáveis quando avaliados após 120 horas de moldagem. No entanto, tais evidências sugerem que os alginatos com maior tempo de armazenamento, como Cavex Color Change, são mais precisos do que os alginatos convencionais.

Influence of time, temperature and humidity on the accuracy of alginate impressions.

BACKGROUND: The goal of the current in vitro study was to assess the dimensional accuracy of dental impressions when stored at different times, temperature and humidity. METHODS: Impressions were poured to an aluminium triangular die and three teeth placed at the three corners of the die. A total of 130 impressions were made, in which 10 were poured immediately following manufacturers' instructions and the remaining 120 specimens were divided into two groups on the basis of relative humidity during storage. Group-1: 100%, Group-2: 50% relative humidity. Impression was poured with type IV gypsum. The below points were chosen to determine the length between in each of the specimens using the traveling microscope with 10x magnifications after 24 hours of model recovery for calculating the effect of changes in storage conditions- relative humidity, temperature and delay in pouring the impressions, on dimensional accuracy. RESULTS: Analysis of the results revealed that the casts achieved by pouring alginate impressions without delay were most accurate than the delay pouring. With the increase in temperature and time, the distance between the points increased and the casts obtained were bigger. CONCLUSION: Irreversible hydrocolloids should be poured immediately for optimum dimensional stability.

Effect Of Lignocaine Addition On The Properties Of Irreversible Hydrocolloid Impression Material.

BACKGROUND: Irreversible hydrocolloid impression materials have been a staple in dentistry and useful for the fabrication of dental prosthesis. Gagging is most commonly experienced during maxillary impression making, which may affect the clinical management of the patient. Different techniques have been described to alleviate this problem. One of them is mixing lignocaine local anesthetic solution in irreversible hydrocolloid impression material before making the impression. The objective of this study was to evaluate the effect of lignocaine addition in irreversible hydrocolloid impression on the properties of irreversible hydrocolloid impression materials. METHODS: Irreversible hydrocolloid was mixed with water (Control group) or water and adrenalin (Lidocaine hydrochloride) (Experimental group). Compressive strength, tear strength and setting time were measured according to ISO1567 and ANSI/ADA specifications 18. The structural analysis of both groups was also evaluated by Fourier Transform Infrared Spectroscopy (FTIR). RESULTS: In the experimental group, insignificant decrease was observed in compressive and tear strength of irreversible hydrocolloid (p>0.05). There was significant (p<0.05) increase in setting time of irreversible hydrocolloid impression material. FTIR analysis indicated no change in chemistry of irreversible hydrocolloid before and after setting. CONCLUSIONS: Addition of lignocaine in irreversible hydrocolloid impression material may result in control of gag reflex without affecting its mechanical and chemical properties.

Effect of mucostatic and selective pressure impression techniques on residual ridge resorption in individuals with different bone mineral densities: A prospective clinical pilot study.

STATEMENT OF PROBLEM: Although different impression techniques have been advocated for complete denture prosthodontics, objective studies that predict their effect on alveolar bone resorption are lacking. PURPOSE: The purpose of this prospective clinical pilot study was to objectively evaluate the effect of complete dentures fabricated by different impression techniques on mandibular residual ridge resorption in individuals with different bone mineral density. MATERIAL AND METHODS: Ninety-six participants with edentulism, selected according to inclusion criteria, underwent bone mineral density assessment and were divided into normal, osteopenic, and osteoporotic groups. Half of the participants in each group were provided with dentures fabricated by selective pressure impression technique (subgroup SIT), and the other half were provided with dentures fabricated by mucostatic impression technique (subgroup MIT). Computed tomographic scans of the mandible were made at denture delivery and 1 year after prosthesis use to assess alveolar bone height and width difference at marked locations at and after denture delivery. The data obtained were analyzed with the Student t test (α=.05). RESULTS: Significantly less reduction in mandibular ridge height and width was found in the MIT versus the SIT subgroups in both osteopenic and osteoporotic participants (P<.05). No significant subgroup difference was found for normal bone mineral density group, although resorption increased in height and width for the SIT subgroup. CONCLUSIONS: Mandibular residual ridge resorption was reduced for dentures fabricated using the mucostatic impression technique compared with the selective pressure impression technique in individuals with diminished bone density.

Accuracy of Three Digitization Methods for the Dental Arch with Various Tooth Preparation Designs: An In Vitro Study.

PURPOSE: To evaluate the accuracy of three digitization methods for the maxillary dental arch. MATERIALS AND METHODS: A maxillary typodont with various tooth preparation designs was used as the reference model. The scanned data were classified into direct scanning (DS), cast scanning (CS), and impression scanning (IS) groups according to the techniques applied for digitization (n = 10/group). An intraoral scanner was used for the DS group. Impressions obtained with polyether impression material were scanned with a tabletop scanner for the IS group. For the CS group, the definitive casts fabricated from the obtained impressions were scanned with the same tabletop scanner. The accuracy (trueness and precision) of the produced virtual dental casts was evaluated with specialized software. The full-arch and individual abutment deviations were measured with regard to root mean square error (RMSE) values. Data were analyzed with statistical software with an α = 0 . 05 . RESULTS: The RMSE values for both trueness and precision were lowest in the IS group, followed by the CS and DS groups, with statistically significant differences among the groups (p < 0.05). The trueness of individual abutments was significantly higher in the IS group than in the DS group. In addition, the trueness of individual abutments was affected by the location of the abutments in the DS group, whereas it did not differ between individual abutments in the CS and IS groups. CONCLUSIONS: These findings suggest that the IS method is an accurate digitization technique for the creation of a virtual dental cast.