We would urge that clinicians reject the philosophy that 'it's only the first impression', as poor primary casts do not provide a good basis for customised trays, nor do they earn the clinician the respect of the technician. In consequence, the clinician will experience problems as undersized primary impressions commonly result in the production of inadequate definitive impressions and these may result in support and/or stability problems in the processed denture.Ĭare is required, however, in the lower arch, as a poorly chosen tray and a conventional irreversible hydrocolloid impression material may not give the acceptable result obtained with more viscous materials. Under-sized trays will result in problems for the technician making the customised trays on undersized primary casts ( Fig. This enables the clinician to visualise the width of tray required to record the functional width of the sulcus ie the tray should extend 5 mm beyond the external surface of the residual ridge.īy keeping the posterior aspect of the tray in place and rotating the anterior portion of the tray towards the labial sulcus, the clinician can determine if the tray is of an appropriate length.Ĭare taken at this stage will ensure that over-large trays are avoided – this will reduce patient discomfort and reduce the likelihood of the incorporation of tissue folds at this stage. When assessing the stock trays for size, the clinician is advised to place the distal portion of the tray just distal to the posterior landmarks of the tuberosities in the upper arch, and onto the retromolar pads of the lower. The clinician should examine the edentulous mouth and assess the length and width of the arch to be restored. Trays for primary impressions tend to be selected from a supply of 'stock' trays which are designed to cover a broad range of arch forms and sizes. The importance of recording the form of the floor of the mouth in relation to the mylohyoid muscle and the retromylohyoid fossae cannot be understated. These deficiencies tend to result in an unstable denture. Lower impressions tend to be 'short' of the retromolar pads and do not accurately record the functional forms of the floor of the mouth and the retromylohyoid fossae. 1 Two principal points to mention here are especially relevant. In this chapter, considerable emphasis is placed on impression techniques, as recent studies indicate that flawed impressions account for the majority of denture problems. Reline and rebase techniques (including secondary template impressions). With this philosophical principle established, impression making for complete dentures may be categorised as follows: This implies an active role and not a passive role and the clinician should consider that impressions are made, not taken.
If the impression material is absent over the tissue surface of the tray, a support problem will be introduced to the completed denture.Įnsure that areas that will require relief are marked on the definitive impression using an indelible pencil.įollowing on from the diagnostic and preparatory phases of treatment, the impression visits provide the clinician with the opportunity to confirm the diagnosis of oral conditions and, of equal importance, to determine the likely degree of patient compliance to the treatment.Īccording to the Oxford English Dictionary, an impression is an imprint produced by 'the pressure of one thing upon or into the surface of another'. Use the impression material that works best in your hands. Practise the insertion of the tray to enable a) the patient to be aware of what is required in impression making and b) the clinician to be confident of his technique.Įnsure the technician is aware of the requirements for each tray (eg spacing, handles, lack of perforations, etc). Determine which form of definitive impression is indicated, on the basis of the nature of the supporting tissues/patient's functional requirements. Rationale and practice of definitive techniquesįurther examples of good practice concerning teamworkĬarefully survey the denture-bearing area and select a stock tray of appropriate extension. Rationale and practice of primary impressions
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