Objectives: There is continuing demand for non-implant prosthodontic treatment and yet there is a paucity of high quality Randomised Controlled Trial (RCT) evidence for best practice. The aim of this research was to provide evidence for best practice in prosthodontic impressions by comparing two impressionmaterials in a double-blind, randomised, crossover, controlled, clinical trial. Methods: Eighty-five patients were recruited, using published eligibility criteria, to the trial at Leeds Dental Institute, UK. Each patient received two sets of dentures; made using either alginate or silicone impressions. Randomisations determined the order of assessment and order of impres- sions. The primary outcome was patient blinded preference for unadjusted dentures. Secondary outcomes were patient preference for the adjusted dentures, rating of comfort, stability and chewing efficiency, experience of each impression, and an OHIP-EDENT questionnaire. Results: Seventy-eight (91.8%) patients completed the primary assessment. 53(67.9%) patients preferred dentures made from silicone impressions while 14(17.9%) preferred alginate impres- sions. 4(5.1%) patients found both dentures equally satisfactory and 7 (9.0%) found both equally unsatisfactory. There was a 50% difference in preference rates (in favour of silicone) (95%CI 32.7– 67.3%, p < 0.0001).
Olin et al.  reported the use of ethylene oxide gas autoclaving of heavy and light bodied addition silicone impression material in custom autopolymerising acrylic resin trays. The results of this study showed that there were significant structural changes (>0.5% change) occurring post-autoclaving suggesting that this is due to the distortion of the trays themselves or their incapability to prevent expansion of the impression material. Another study showed that a polyvinylsiloxane (addition cure silicone) impression material could be autoclaved without any significant dimensional changes using stock metal trays, albeit, it should be viewed cautiously when steril- ised at 132˚C . This was further supported with addition-cured silicone impressions autoclaved at 134˚C pro- ducing less than 0.5% dimensional change . Given that there is now evidence that impressionmaterials can be autoclave-sterilised and that clinical practitioners prefer sterilisation in general, a suitable type of tray and adhesive is now available ; a range of materials needs to be evaluated.
This is to certify that the dissertation titled “ THE INFLUENCE OF PUTTY WASH IMPRESSION TECHNIQUE ON DIMENSIONAL ACCURACY OF 2 COMMERCIALLY AVAILABLE VINYL POLY SILOXANE IMPRESSIONMATERIALS - AN INVITRO STUDY ” is a bonafide record of work carried out under my guidance by Dr. M. KANMANI during the period of 2004-2006. This dissertation is submitted in partial fulfillment for the degree of Master of Dental Surgery awarded by Tamil Nadu Dr. M.G.R. Medical University, Chennai in the branch of Prosthodontics. It has not been submitted partially or fully for the award of any other degree or diploma.
This study was conducted to compare and evaluate the positional accuracy of implants with two different splinting materials using two different elastomeric impressionmaterials. A reference model of the edentulous mandible with four implant replicas in the anterior region was fabricated in heat cure clear acrylic resin and was used as control group in this study (Control-Group R). The impression techniques were divided into two groups, pattern resin as splinting material using VPS and VPES as impression material and BisGMA as splinting material using VPS and VPES as impression material and grouped as Group I(A), II(A) and Group I(B), II(B) respectively. Five impressions of the reference models were made in each group with custom trays using VPS and VPES impression material. The impressions were poured using type IV dental stone and the retrieved master casts were grouped and evaluated for positional accuracy of inter implant relationship using a Coordinate measuring machine. Nine inter implant distances, three each in x, y and z axes and four implant angles in z axis were measured from the reference model and the master casts. The differences in the inter implant distances in x, y and z axes and the implant angular differences in the z-axis, in relation to the reference model were measured for all the casts. The results were tabulated and statistically analysed using one way ANOVA and Post-Hoc test.
This patient-centred study has been designed to ad- dress a key question in the construction of complete dentures, whether impression material has an impact on subsequent comfort and function of the constructed denture and whether that denture can be adjusted to the satisfaction of the patients. A crossover design has been used to eliminate many of the potentially confounding variables found in denture construction; patients are gi- ven 2 sets of dentures and act as their own control. This requires attention to the detail of the duplication techni- ques for the dentures  to ensure the dentures are similar in all aspects apart from the impression material used at the secondary impression stage. In doing this, any preferences expressed can be reliably attributed to the impression material and not any other aspect of the denture construction. Additionally, a habituation period has been included in this study to guard against the po- tential for bias seen in other crossover studies  that patients may prefer the denture they try in the second study period, a bias that has been attributed to the fact that the new dentures can feel very different to the patients existing dentures and the first study period is spent habituating to the new feel of the dentures [9,17]. This study has been blinded to patients, dentists and dental nurses by marking the dentures only with coloured acrylic dots and by ensuring that all adjustment of den- tures is managed by a dentist not involved in their con- struction/fitting. The primary outcome has been chosen to cover both patient-centred considerations (patient preference for denture impression material, previously shown to be a sensitive and effective tool [23,24]) and health-economic considerations (cost-benefits associated with each of the denture impressionmaterials).
On the other hand, polyvinylsiloxane are accurate impressionmaterials with excellent dimensional stability, good detail reproduction, high tear strength, adequate working time, and high recovery from deformation. Although meeting many of the criteria for an ideal impression material, polyvinylsiloxanes intrinsically are hydrophobic in nature, which can result in voids at the margin of the tooth preparation in the impression and bubbles in gypsum casts. However, VPS materials are recently being labeled as hydrophilic due to the addition of extrinsic surfactants 7-9 .
For registration or production of forms and rela- tions of the teeth and related oral tissues, impres- sion materials can be used; indeed, as a critical step in processing and fitting of a dental prosthesis, an impression must be taken [1,2]. Several types of im- pression materials are produced. These include sili- cones, polyether, polysulfide and alginate which are available for crowns and fixed partial denture im- pressions. Silicone impressionmaterials are consid- ered to be suitable impressionmaterials to be used for fixed prostheses . Also, it has been reported that silicone has the ability to resist deformation procedures and save its dimensional stability during disinfection procedure . Among silicone impres- sion materials, one type, called polyvinyl siloxane (PVS), is reported to have precise detail reproduc- tion, dimensional accuracy and stability, low creep, a relatively short setting time, moderate to high tear resistance, and elastic recovery from undercuts .
Digital screw torque checker has been used in various studies to evaluate the reverse torque values to determine the screw loosening of abutments/prosthesis. The device has the capacity to measure and store the readings. It has an accuracy level of 0.05 N.cm, which helps to detect small change in torque values and has an inbuilt memory to store up to 100 readings. A similar torque measuring device was used to assess the torque values to rotate the open tray copings in one report. 16 This instrument can be successfully adopted to analyse the rotational resistance offered by different impressionmaterials for open tray impressions. In view of the above, there is a need to identify the best combination of open tray impression coping design and impression material to overcome the problem of rotation of unsplinted impression copings within the impression material.
The Federation Dentaire Internationale (FDI) requires as a standard precaution that all patients’ impressions should be rinsed under running water to remove saliva and visible blood. Then, they should be placed and sealed in a proper container and labeled as disinfected or not disinfected before being sent to the dental laboratory . Also, the American Dental Association (ADA), the Centre for Disease Control (CDC) and Prevention with the Australian Dental Association, have all listed a similar standard procedure for the disinfection of dental impressions [11-13]. Nevertheless, care should be taken that the disinfection procedure does not have adverse effect on the dimensional stability or surface details of the dental impression. This is important because the various types of impressionmaterials available have features such as: accuracy, elastic recovery, dimensional stability, flexibility, a long shelf-life, tolerable taste to patients and relatively affordable . Thus, the choice of disinfectant depends on the type of impression material chosen since the composition, concentration of the disinfectant and the exposure time would greatly affect the compatibility of these disinfectants with the specific impressionmaterials [15-18].
Numerous holes were created on the upper and lateral faces of the tray for retention of the impression material, creation of way out and reduction of internal pressures of impression material. Moreover, to obtain better adhesion, all impression trays were covered with a thin layer of adhesive material. Impressionmaterials used in this study included Speedex and Irasil condensa- tion silicones which are enormously used in Iran’s den- tal offices because of their low price, availability and ease of access. The engaged impression technique was space-including technique; the proper and necessary space for the wash material was 1.5 mm, which was provided by a metal spacer, as previously described. Since there is enough space for wash material and it protects the putty material against the stress exerted, the least dimensional changes are present in this technique.
hypochlorite solution (Milton 1%), for 10 min, and a further 10 impressions for 15 min. The other 5 impressions of each material were used as a control group without immersion in disinfectant solutions. Results: Neither polyether nor polysulfide impressions showed any statistically significant difference (ANOVA) from their control measurements after being soaked in the two disinfectant solutions. However, when the alginate impressions were disinfected by sodium hypochlorite for 15 minutes, a significant distortion (~0,122 mm) occurred, compared with control group. Conclusion: Within the limits of this study it can be concluded that the immersion practices for disinfection did not influence the quality of impressions obtained, except when sodium hypochlorite was used as disinfectant and immersion time was 15 minutes. UNITERMS: dimensional stability; disinfection; impressionmaterials.
Various dimensional measuring techniques are used in clinical and academic dentistry for dental stone models and scanned models. Manual measurements are performed with a Vernier caliper or needlepoint calipers, and they are the standard method to evaluate the accuracy of den tal models. Manual measurements have some advantages, such as the ease of application, low cost and immediate ap plicability. Alternatively, 3dimensional computer dental models, scanned with an optical or laser beam, are con sidered appropriate in clinical applications. In this study, the dimensional changes of different impressionmaterials were evaluated with digital radiography, which differs from the methods described in the current literature. Digital ra diography is considered to be more economical than the 3dimensional computer application and more reliable than the manual methods. 8,9
Alginates, like irreversible hydrocolloids, are very sensitive to the mixing ratio between powder and water. Manufactur- ers add suitable spoons for powder and measuring cups for water, but it is possible to use these accessories imprecisely, i.e., due to a problem with the meniscus of water or because of using powder which has been packed or settled in the con- tainer, particularly after storage over a long period of time. In such conditions, the obtained mixing ratio may differ from the recommended one, resulting in as much as 15% excess or shortage of water. Obviously, different mixing proportions between powder and water may change the setting charac- teristics and the viscosity of alginate impressionmaterials. 15
Background: The accuracy of the final prosthesis is affected by the final im- pression technique and master cast production. The aim of the present study was to evaluate the effect of the functional impression technique with various impressionmaterials on the surface characteristic of dental stone casts and their clinical effect on the retention of complete dentures. Method: Specimens of three impressionmaterials/stone casts were fabricated. The specimens of the impressionmaterials/stone casts were divided into three equal groups (I, II, and III). The impressionmaterials used were as follows: tissue conditioner group (I), zinc oxide (ZEO) (group II) and poly (vinyl siloxane) (PVS) (group III). Cylindrical split aluminium moulds were designed to receive the impres- sion materials and the stone mixture. The surface roughness of the stone cast specimens of the three groups (I, II, and III) was measured with a surface pro- filometer and analyzed by a scanning electron microscope. A clinical study in- cluded five severely resorbed mandibular edentulous alveolar ridges and edentulous maxillary arches. Each subject received three heat-cured acrylic resin dentures, fabricated using the functional impression technique. The three dentures were identical except for the different impressionmaterials used from Groups I, II and III. The retentive force of each denture for each subject was measured. Result: The results of this study revealed that the mean value of surface roughness of the stone cast surface of group I was higher than group II and group III. A statistically significant difference was observed in surface roughness and the retentive dislodging force between the three studied groups. Although using a tissue conditioner as a functional impression ma- terial led to a high level of surface roughness and good retention, it could not How to cite this paper: Alammari, M.R.
Background and Aim: Disinfection of dental impressionmaterials can alter their dimensional stability, which in turn can affect the accuracy of dental casts. This study aimed to determine the effect of three disinfectants on the dimensional changes of irreversible hydrocolloid impressionmaterials and addition silicones. Materials and Methods: In this in vitro experimental study, forty alginate and 40 addition silicone impressions were made using special trays. The impressions were disinfected by the spraying method for 10 minutes except for the control group. Then, they were poured with type IV dental stone. The prepared casts were main- tained for 24 hours in a similar condition. Next, the dimensions and the external distance between two dies were measured at three time intervals using a digital caliper with 0.01 mm accuracy, and the average values were recorded. The yielded measurements were compared with each other and with metal models. One-way ANOVA and one sample t-test (α=0.05) were used for data analysis.
De Araujo et al 11 assessed the effect of bulk of the material and undercuts on the dimensional accuracy of impressionmaterials. He found out that a greater distortion was caused with increase in thickness of the impression material from 1 to 4 mm. As the thickness of the material increased, dimensional accuracy decreased and so the material should be uniform all over the surface. All impressionmaterials were mixed according to the manufacturer’s directions by using, where required, clean dispensing automix gun. No attempts were made to dispense by weight. Each specimen was made from a separate mix. The catalyst and base components from the manufacturer were supplied in a self mixing apparatus consisting of two cylinders of impression mater, a static mixing nozzle and a ratchet extrusion device. This material was mixed in the manner specified by the manufacturer. The cartridge was bled in conformity with manufacturer’s advice to make certain appropriate dispensing ratios. The material was weighed down into a fine-tipped impression syringe and applied to the ruled areas of the stainless steel block. The impression material was pressed in advance of the syringe tip. This technique gives way the smallest number of voids as made known in the pilot study.
2007) An ideal impression material should have perfect dimensional stability such that the impression would retain its original accuracy indefinitely. (Shaba et al., 2007) Most acceptable limits for accuracy are from 0.1% to 0.27%. Other researchers claim that a value of 50 μm is the maximum acceptable discrepancy between a master cast and a poured impression made from the master model. (Brett et al., 1995) The common factors that cause dimensional changes in alginate impressions are setting contraction, thermal contraction and release of internal stresses on cooling from the body temperature to room temperature. (Marker, 1996; Mc Cabe and Angus Walls, 1998) These changes can be due to inherent properties of syneresis, imbibitions and evaporation. (Kenneth J. Anusavice, 2003; Marker, 1996) The setting reaction of alginate causes replacement of monovalent ions by divalent ions result in cross-linking of the alginate chains that continues to increase after the material has set and this contributes to dimensional changes after withdrawl from the oral cavity. The dimensional stability is directly related to storage period of the alginate impression and it changes with increasing storage time. So it is highly recommended to pour the cast immediately or 10 to 15 minutes to the maximum of 30 minutes of storage after taking impression with alginate to avoid dimensional changes. So to overcome the dimensional inaccuracy, various companies have started marketing improvised or extended storage alginates, which they claim to be near equivalent to elastomers in accuracy and can bepoured after long time. (Toros Alcan et al., 2009) The limited scientific investigations evaluating the dimensional stability of extended-storage alginates, support manufacturers’ claims of acceptable results even after 100 hours of storage period. Thus this in-vitro study was conducted to determine the dimensional accuracy of the casts obtained from three types of alginate impressionmaterials poured after three different storage periods. The objective of this study were to determine the influence of storage period on the dimensional changes of alginate impressions.
Kakatkar VR (2013) 42 A questionnaire survey was carried out to know which materials used by private practitioners to make impressions and what techniques being followed. The questionnaire was send to Goa, dental practitioners. The dental surgeons were from Pune, Mumbai, Goa, Satasa, Nashik, Indore, Jodhipur, Nanded, Aurangabad, Sangli, Kolhapur. From the survey it was concluded that a satisfactory impression technique can be suggested. A primary impression in alginate or impression compound can be made. A final impression in a tray material or cold cure custom tray with border moulding using low fusing compound and final impression using ZOE paste or light body elastomers could be recorded. Use of elastomers to carry out border moulding required les time and was convenient. But properties of oftened green stick and putty elastomers to achieve peripheral seal needs to be investigated.
The American Dental Association (ADA, 1985) and many other professional organizations proposed guidelines to limit cross-contamination during dental clinical procedures such as impression disinfection. However, unfortunately, adequate data regarding infection control and sterility of impressionmaterials received by the dentist from the manufacturer are not readily available. Further study in this area is war- ranted because of the increasing number of subjects
To reduce the risk of prosthetic complications when restoring implants, passive fit of the framework is reccommonded. With inreasing misfit of the framework, the external preload is magnified when prosthetic screws are torqued to specifications and static stresses raise the risk of prosthetic complications. Weet et al discribed various methods of improving the framework fit. Among these, the use of a dimensionally accurate impressionmaterials was reported to be the most critical factor, perticularly when it is not possible to achieve fit of the frame work by a sectioning and soldering procedures. The use of plaster as an index material for implant impression has been describe for partially edentulous patients. For such techniques, an initial impression is necessary to make a custom tray. This technique uses a stock impression tray that allows for a 1-appointment impression procedure. Although this procedure can be used for completely or partially edentulous patients, the situation presented is for a completely edentulous mandible.