Get a taste for the sandwich technique

Sillas Duarte highlights the benefits of the sandwich impression technique for minimally invasive bonded porcelain veneers

Introduction

Restoring aesthetically discoloured, malformed, poorly restored, or broken-down teeth represents a challenge in routine dental practice.รต, 2 Indirect porcelain veneers are the ideal restoration for intrinsically stained teeth.3

However, porcelain veneers can be affected by the colour of the prepared abutment teeth.4 Minimal preparation, associated with sub-opaquing of the abutment teeth, enables progressive lightening of highly stained teeth to create a natural shade depth in porcelain veneer procedures.2, 5, 6

The clinical success of minimally invasive preparations for porcelain veneers depends on the use of a high precision impression material/technique and skilled dental technicians. Polyvinyl siloxane (PVS) impression materials have demonstrated the ability to copy the finest details required for highly demanding restorations.7 The impression technique also plays an important role in the aesthetic rehabilitation procedure.

The technique of choice for porcelain veneers is a one-step/double-mix impression using polyvinyl siloxane materials associated with a ‘double-cord’ gingival displacement.8

The following clinical report describes an example of aesthetic rehabilitation of anterior teeth using porcelain veneers together with the one-step/double-mix impression technique.

Clinical case

A 22-year-old patient with good oral health had a discoloured greyish central incisor (21) and a colour defective composite restoration on the other central incisor (11) (Fig 1). The patient was seeking improvement of the anterior aesthetics and closure of the small diastema between the two central incisors.

Bonded porcelain veneers were suggested to correct the shape and discolouration of the teeth, as well as to convey a pleasant aesthetic appearance. An alginate impression was taken and poured in type IV synthetic die to analyse the interocclusal relationship. A diagnostic wax-up was used to establish the correct contour of the central incisors.9

A silicone matrix was made from the diagnostic wax-up and used as guide for the tooth preparation.10 The patient was not anaesthetised to control the depth of preparation. Tooth 11 received a minimal preparation of 0.3 mm thickness, leaving the preparation entirely in the enamel. For tooth 21, a preparation depth of 0.5 mm was performed over the entire facial surface. The difference in preparation depth for each tooth was used to compensate for the grey discolouration of tooth 21.

After preparation, each tooth was acid-etched with 37 per cent phosphoric acid gel for 15 seconds, washed and air-dried. A total-etch dentine adhesive (TECO SilvR Dose, DMG, Hamburg, Germany) was applied to tooth 21, and light cured for 20 seconds. Next, an A1 opaque composite shade was applied to the gingival third to mask the grey discolouration. The prepared teeth were then polished with rubber points and prepared for impression-taking. A double-cord technique was used for deflection of the soft tissues. The large retraction cord was left in place for five minutes before taking the impression (Fig 2). An appropriately sized disposable impression tray was selected.

Minimally invasive preparations require a precise impression material and technique; otherwise, detailed areas would not be accurately duplicated. Thus, selection of a hydrophilic material such as PVS is imperative for meticulous reproduction of the preparations.7 In addition, the sandwich technique should be used because of the high accuracy and quality obtained with the final impression.8, 11

Mechanical automixing of the impression materials is highly recommended, in order to obtain an optimised consistency. Automixing of PVS materials has been shown to reduce or eliminate voids, prevent the risk of contamination, and improve the PVS’s physical properties when compared to those of spatula-mixed materials.12 An automix unit for impression materials (MixStar-eMotion, DMG) was loaded with Honigum-MixStar Putty (DMG) and a preconfigured programme selected, as per the manufacturer’s instructions.

The impression tray was carefully and homogeneously filled with Honigum-MixStar Putty (Fig 3). Note, each side of the tray was completely filled before extending it into the other areas. Subsequently, Honigum-Light was automixed using a hand gun and extruded directly over the Honigum-MixStar Putty in the tray (Fig 4). The Honigum-Light must be applied not only in the preparation areas, but also to the total extension of the arch. This procedure facilitates correct occlusal equilibration of the stone casts. In the meantime, the retraction cord was removed and Honigum-Light was applied simultaneously to the preparations (Fig 5). The loaded tray was positioned in the mouth.

After the material was completely set, the impression was removed and examined (Fig 6). All the details of the minimal preparations were visible (Fig 7). A close-up view of the impression revealed a fine and detailed reproduction of the preparations’ finishing lines. In addition, the PVS’s high accuracy was observed in a cross-sectioned view of the impression (Fig 8). Note the penetration of Honigum-Light within the gingival sulcus. Provisional restorations were fabricated for the prepared teeth and the patient was dismissed.

The impression was poured with a type IV synthetic die (Fig_9). Two porcelain veneers were produced for teeth 11 and 21 with 0.3 mm and 0.5 mm thickness, respectively (Fig 10).

At the next visit, the provisional restorations were removed and a porcelain veneer try-in performed. Try-in shaded glycerin pastes were used because of the high translucency of the porcelain veneers. A translucent shade was selected for tooth 11 and an A3 opaque composite was selected for tooth 21 to mask the discolouration. After the patient’s and clinician’s final approval, the porcelain veneers were bonded to the teeth, resulting in a highly successful final aesthetic outcome (Fig 11).

The Honigum impression material range is distributed in the UK and Ireland by DMG Dental Products (UK) Ltd. To find out more, call 01656 789 401, email info@dmg-dental.co.uk or visit www.dmg-dental.com

About the author

Sillas Duarte Jr, DDS, MS, PhD, is an associate professor at the Department of Comprehensive Care within the Case School of Dental Medicine, Case Western Reserve University, Cleveland, Ohio.

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Published: 7 September, 2011 at 16:23