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Accurate impressions provide a foundation for successful implant prosthodontics. This paper is aimed at the general dental practitioner (GDP) who would like to start restoring dental implants and demystifies the terminology, introduces the basic armamentarium and discusses the relative merits of different implant impression techniques. Detailed, step-by-step instructions for making impressions using the closed and open tray techniques are provided and the importance of verification jigs are highlighted. Clinical relevance A successful restoration is dependent upon proper planning and meticulous clinical processes. An understanding of impression techniques is therefore fundamental for the GDP wishing to restore implant-supported prostheses. Objectives The reader should be familiar with different implant components and understand the impression techniques used in implant dentistry.

Introduction The responsibility of ensuring impressions have been cleaned and disinfected before dispatch to the dental laboratory lies solely with the dentist. Uncertainty of impression disinfection risks both the health of the receiving dental technician and potential repeat disinfection of an already disinfected impression with detrimental consequences for its dimensions. Objective To ascertain, from the perspectives of dentists and dental technicians, current impression decontamination and disinfection practices with, in the case of the technicians, an estimate of the relative prevalence of contaminated voids within apparently disinfected impressions. Design Anonymous postal questionnaire. Method Dentist (n = 200) and dental technician (n = 200) potential participants, selected at random from the registers held by the General Dental Council, were invited to complete an anonymous postal questionnaire that sought to establish current practices and perceived effectiveness of impression disinfection. Results Questionnaire return rates of 42.1% and 31.2% were recorded for dentists and dental technicians respectively. A wide range of solutions, at different dilutions of the same product, was used by the dentists to disinfect dental impressions. 37.2% rinsed the impressions with water, and 2.6% always brushed debris away, before disinfection. 24.7% of dentists did not inform the laboratory of disinfection. Irrespective of the disinfection status of the received impressions, 50% of the responding dental technicians disinfected all impressions. 95% of them had received blood-contaminated impressions. 15% had encountered blood-filled voids upon trimming back the peripheries of impressions. 64.7% were confident that the impressions received by them had been disinfected by the dentists. Conclusions Compliance with good practice is less than ideal and education in impression disinfection for both dentists and dental technicians is required to address this.

The presence of displaceable denture-bearing tissues often presents a difficulty when making complete dentures. Unless managed appropriately, such 'flabby ridges' adversely affect the support, retention and stability of complete dentures. Many impression techniques have been proposed to help overcome this difficulty. While these vary in approach, they are similar in their complexity, are often quite time-consuming to perform, and rely on materials not commonly in use in contemporary general dental practice. The purpose of this paper is to describe an impression technique for flabby ridges that makes use of polyvinylsiloxane impression dental materials routinely available in general dental practice.

Objective The reproducibility of clinical records of the occlusion was assessed in three dimensions using mounted casts. Three distinct areas were examined: 1) mandibular positions (intercuspal position (IP) or retruded contact position (RCP)), 2) materials used in recording the occlusion, 3) clinical variation. Design Interocclusal records were made in a random order of three patients: one fixed prosthodontics case, one removable partial denture case and one complete denture case, with two different types of waxes, record rims, two different brands of vinyl polysiloxanes and one irreversible hydrocolloid. Setting Private practice and Karolinska Institute, Huddinge, Sweden, Subjects One general dental practitioner and three voluntary patients. Results Point estimation of variance components indicate that 70-93% of the variation of the positions of the mounted casts are caused by: 1) clinical variation for all three cases and in three directions, 2) the influence of recording materials 0-29%, and 3) mandibular positions (IP/RCP) 0-11%. The ranges of the positions of the mounted casts were lower for the dentate case (0.04-1.39 mm) than for the partially dentate case (0.17-2.65 mm), which in turn was lower than those for the edentulous case (1.42-5.59 mm). Conclusion Clinical variation seems to dominate the variation in positions of mounting casts when making interocclusal records, rather than mandibular position or the recording materials used. Therefore a dentist who makes one single interocclusal record cannot presume that it will reproduce the interocclusal relationship intended, which in the present study was most obvious for the edentulous case. The results showed that impression materials stabilised by a tray did not differ significantly from waxes and record rims concerning the reproducibility. Therefore the stabilised impression materials are an alternative, which also give additional advantages like reduction of appointments as well as superior accuracy.

Objective: To evaluate the accuracy of working casts for crown and bridge restorations made from twin mix putty/wash silicone elastomeric impression materials using different types of stock tray. Design: A master cast was made from ivorine teeth in a mandibular model. Three teeth were prepared for full crown restorations to simulate a single unit and a three unit bridge. Impressions were taken using four different types of impression tray and two different viscosities of silicone putty, together with a wash. Full metal crowns were constructed and seated on duplicate master casts and measurements made of the marginal discrepancies. Setting: The work was carried out in a dental technology laboratory in a university department of restorative dentistry in 1995/1996. Results: Metal and rigid plastic impression trays showed the least discrepancy (about 50 microns), the latter slightly greater with the normal putty than the soft one. Impressions taken with flexible plastic trays produced considerable discrepancy with both putties, approximately 210 microns and 180 microns respectively. Conclusions: Metal and rigid plastic stock trays give greater accuracy in the putty/wash silicone twin mix impression technique compared with flexible plastic ones for crown and bridge work. Those using the latter should be aware of their shortcoming in this respect

Aim: To describe and investigate a simple, effective new method for controlled removal of unsightly, malformed surface enamel. Subjects and methods: 22 mottled incisor teeth were chosen from a group of 12 patients, aged 9-15 years. One half of the labial surface of the tooth was covered with a layer of unfilled bis-GMA resin so that it remained unaffected by the procedure. The other half was treated by etching the enamel with 35% phosphoric acid for 30 seconds, washing and drying. The frosted, etched enamel was removed with a composite finishing bur (Jet 7901) running dry in an air turbine, until a shiny enamel surface reappeared. The enamel was then smoothed with a pumice and water slurry in a slow-rotating rubber prophylaxis cup. The bis-GMA resin was peeled off, and an elastomeric impression of the tooth (now with one half of its labial surface treated, and the other untreated) was taken. The treatment of the remainder of the labial aspect was then completed. The thickness of the mid-labial enamel removed was measured directly from the impression by surface imaging, using a confocal microscope. Results: The mean thickness of enamel removed was 164 microns (SD +/− 85 microns). Conclusions: This technique results in equivalent amounts of enamel removal to that claimed for other more complex and time-consuming methods

The object of making an impression in implant dentistry is to accurately relate an analogue of the implant or implant abutment to the other structures in the dental arch. This is affected by use of an impression coping which is attached to the implant or implant abutment. This impression coping is incorporated in an impression - much as a metal framework is 'picked up' in a remount impression for fixed prosthodontics. With implant copings the coping is usually attached to the implant or abutment with screws. The impression material used is usually an elastomeric impression material; the two types most widely used and shown to be the most appropriate are polyether and polyvinyl siloxane impression materials.

This study investigated the effect of a commonly used immersion disinfectant upon three different impression materials and any subsequent effects on the abrasion resistance, hardness and surface detail reproduction of gypsum casts.A laboratory study.Under standardised conditions a total of 120 impressions were made of a ruled test block using irreversible hydrocolloid (Alginoplast), an 'alginate alternative' addition-cure silicone (Position Penta) and a conventional addition-cure silicone (President). The impressions were examined for surface detail reproduction prior to and after disinfection with Perform-ID. The type III casts were evaluated for surface detail reproduction, surface hardness and abrasion resistance.(1) None of the disinfected alginate specimens could reproduce the 50 microm line. (2) Casts produced from the disinfected alginate were significantly less hard than from disinfected Position Penta and President (P0.001). (3) Disinfection significantly affected the abrasion resistance of casts made from Position Penta (P = 0.029). (4) Disinfection did not significantly affect President or its subsequent casts (P0.05).If disinfecting with Perform-ID, the impression should be made with a conventional addition-cured silicone if good surface detail reproduction of the impression material and a hard and abrasion resistant type III gypsum cast are required.

Aim: Various ethical and legal guidelines require dental practitioners to adequately design, prescribe and fabricate good quality prostheses. The purpose of this investigation was to examine the quality of written instructions and choice of impression trays and materials for both fixed and removable prosthodontics in Ireland and the United Kingdom. Materials and methods: A pre-piloted questionnaire was distributed to a number of large commercial laboratories geographically distributed throughout the United Kingdom and Ireland. Information was sought relating to the quality of written instructions and use of impression trays and materials for three forms of ‘dental precision casting’ — cobalt-chromium based removable partial dentures, full veneer porcelain-fused-to-metal crowns, and conventional fixed bridges. Results: Six hundred questionnaires were distributed, and information was received relating to 447 items of prosthodontic treatment (response rate= 75%). Ninety-five per cent of cases were privately funded. Using pre-determined grading criteria, poor or no written instructions were provided in one-half of cases examined. One-half of master impressions were made using a plastic stock tray. The technician felt that material had been appropriately disinfected prior to being sent to the laboratory in only 57% of cases. Conclusion: The written instructions and master impressions examined in this study failed to meet the relevant ethical and legal guidelines in approximately 50% of cases.

To investigate, by questionnaire, the use and selection of materials and techniques for indirect restorations and fixed prosthodontics by dental practitioners in the North West of England and Scotland.A questionnaire was sent to 1,000 general dental practitioners selected at random from dentists in Scotland and the North West of England. Non-responders were sent another questionnaire after a period of 4 weeks had elapsed.A total of 701 usable questionnaires were returned, giving a response rate of 70%. When selecting a material for the core build-up of vital teeth, practitioners used the following materials (%): amalgam (60), dual and light-cured resin composite (54), glass-ionomer cements (47), compomer (29) and resin-modified glass-ionomer cements (24). Where the use of a post was indicated indirect posts of both precious (67) and non-precious (37) alloys were preferred to prefabricated posts by the majority of practitioners for the restoration of root filled teeth. Direct titanium (14) and stainless steel (14) posts were not used extensively. Impression materials used by the practitioners were as follows: addition-cured silicone (70), condensation-cured silicone (20), polyether (9) and polysulphide (2). Traditional glass-ionomer cements (59) were used for the luting of single and multiple porcelain fused to metal units, with zinc phosphate and polycarboxylate cements (33) being the preferred alternatives.The majority of the practitioners surveyed in this study used: amalgam for core build-ups; indirect posts; addition-cured silicone for impressions; and glass-ionomer cements for luting procedures.

Well-fitting indirect restorations can only be made if there are accurate models of the oral tissues available, made from high quality impressions. Waiting for an impression to set may be more stressful for the dentist than the patient. Should the impression need to be repeated there is the embarrassment of having to explain this to the patient, the cost implications of material and time wasted and the aggravation of running late for the next appointment. Yet, if a 'Nelsonian' eye is turned to a defective impression we can only expect a substandard restoration in return.

To determine the quality of impressions for crown and bridge work made in general dental practice.All impressions for crown and bridge work which had been sent to four commercial dental laboratories in the UK were assessed by two examiners, each laboratory being visited on two occasions.290 cases which had been received by the laboratories on the days of the visits were assessed for a number of factors related to quality. There was no selection or rejection--all impressions received were examined.Flexible plastic trays were used for the majority of working impressions for crown and bridge work in general dental practice (72%), many had been re-used (13%), defects in the recording of the prepared teeth were common, and cross infection control was not routine.Quality standards for impressions for crown and bridge work in general dental practice in the UK are a cause for concern if the sample of cases seen in this study is typical.

The potential for cross-infection from microbial contaminated dental impressions has long been recognised. This study set out to investigate impression decontamination procedures currently used in UK dental hospitals (1995) and to see how these may have changed since a previous survey, carried out in 1988. A variety of disinfection solutions and regimes were highlighted both within and between dental hospitals. Several of the disinfecting solutions currently being used have not been specifically tested for efficacy with impression materials. The laboratories were asked to highlight any adverse reactions. Five laboratories reported that some alginates resulted in casts with poor surface properties when immersed in hypochlorite (0.1 and 1%), sodium dichloroisocyanurate, and 2% glutaraldehyde solutions. This paper highlights that there is no universally recognised impression disinfection/sterilisation protocol. It is recommended that all impressions should at least undergo a disinfecting procedure by immersion in 1% sodium hypochlorite for a minimum of 10 minutes.

The following article is intended to question certain procedures designed to prevent cross-infection. It is the first of a series of occasional articles describing new techniques, research, and new products, which it is hoped, may enable dental practitioners to update their knowledge of this rapidly changing subject.

This penultimate part of the centenary series looks at E Matthews' paper on "The alginates in dentistry' and is reviewed by Mike Braden. In the paper, Matthews discussed the need to find a suitable alternative to certain dental materials such as agar agar when the main supplier of this, Japan, entered the Second World War.