Centripetal layered build-up of a posterior direct composite resin

To achieve better marginal adaptation to the gingival floor and long-term aesthetic of posterior composite restoration, Dr Christopher Ho presents a novel technique which replaces the lost tooth structure by layering from the periphery towards the centre of the cavity.

There has been the emergence of nano-hybrid composite resins that enable dentists to provide strong, life-like aesthetic restorations. They promise better polish, the longevity of lustre, better handling and high strength.

All composite resins when polymerised shrink from 1.6-5% which can lead to marginal openings, internal debonding, cuspal flexure and microfracture. This polymerisation shrinkage can further lead to microleakage and marginal staining, caries, post-operative sensitivity, and pulpal problems.

The nanohybrid-filled composites, such as Harmonise, contain much smaller filler particles of 0.02 microns compared to 0.4-1 microns with the hybrids. With the smaller particle size, there is a subsequent higher filler loading, which enables considerably less shrinkage and also allows better polish and gloss retention.

In considering the restoration of teeth, layering of composite resin is carried out to:

  • Minimise polymerisation stresses,
  • Increase polymerisation depth,
  • Achieve good anatomic contour, and
  • Obtain the best aesthetic result.

Implementation of different incremental layering techniques is used to achieve the best aesthetic result but also to minimise the stresses that are encountered with a direct composite restoration.

There are many different layering techniques used for posterior teeth from the horizontal and vertical build-up to oblique layering and successive cusp build-up techniques.

No clear advantage for any technique has been evidenced from the literature, but a thorough understanding of composite shrinkage and how to combat the stresses induced to a tooth are the responsibility of every clinician that places direct resin restorations.

Restorative sequence

Shade Selection (Fig. 1): Selection should be made at the start of the appointment and before rubber dam placement to prevent incorrect matching due to dehydration and the subsequent increase in value.

Rubber dam placement (Fig. 2):  After the administration of local anaesthesia, the teeth were isolated with a rubber dam to achieve adequate isolation. This allows protection from contaminants like blood, saliva and crevicular fluid.

Preparation (Fig. 3): Removal of amalgam and caries were done using a rotary instrument, which included carious dentin and residual amalgam staining. The preparation only involved affected tooth structure, and the adhesive preparation allowed maximum preservation of tooth structure.

Etching (Fig. 4): The “Selective Etch” technique was used with 37% phosphoric acid on enamel only. The tooth was then washed thoroughly with water spray. Optibond Versa (Kerr) was applied with a disposable applicator for 20 seconds. This was done with a scrubbing motion and left the dentin glossy, demonstrating good resin impregnation. The bond was light cured.

Internal adaptation (Fig. 5): A layer of flowable composite resin was used as the first increment. Due to its lower viscosity, it is self-adapting and enables an intimate contact with the dentin. This was first placed at the gingival margin and cured followed by another very thin layer at the pulpal floor. Flowable composite resin has also been discussed to have a stress-absorbing property with it having a high modulus of elasticity, which allows it to bend and stretch more, and absorb stress from polymerisation shrinkage.

Incremental layering (Fig. 6): Layering the restoration reduces polymerisation shrinkage and enhances the aesthetics of the restoration allowing a natural layering of the restoration.

Building the proximal contact: A sectional matrix was used with a Lucidwedge (Hawe-Neos). The proximal contact was then built up with Harmonise composite to simulate the enamel in this area. This cavity form has become a simple Class I restoration.

Building the artificial dentin (Fig. 7): The artificial dentin layer was built up with an incremental technique. Each layer was built up in diagonal increments of less than 2mm. Opposing walls were not contacted by the same increment to minimise wall-to-wall shrinkage and cuspal deflection. The shade used was an A3 body shade of composite. This layer of artificial dentin was stopped short of where the anatomic layer of enamel begins and was approximately 1mm short of the final anatomic contour.

Building the artificial enamel layer (Fig. 8): It has been stated by Muia that the colour of a tooth comes from the dentin with the enamel acting like a fibreoptic rod transmitting the light. Therefore, the final enamel layer was translucent. Any warming effects like yellow tints or opacities like white spots can be added before this final layer of translucent goes on. These tints are built up internally giving them a real depth to them. A layer of enamel composite was built up and the surface was invaginated with an instrument while still soft. This layer is contoured with its associated fissures and cusps and light cured.

Addition of occlusal staining (Fig. 9): This can be achieved with a number 10 endodontic file or a probe with some brown or ochre tint (Kerr Kolor Plus). The tint was run into the fissures and the excess was removed with a disposable micro brush. This final layer was cured.

Finishing and polishing (Fig. 10): This was performed to reproduce the shape, contour and lustre of the natural dentition. Initial contouring was done with multi-fluted finishing burs and finishing discs for the proximal contours. All areas of the restoration were polished and checked for occlusal interferences. Polishing was carried out with rubber silicone points and the Optishine (Hawe-Neos), which maintained the surface texture and anatomy.

Published in Dental Asia July/August 2022 issue.

About the author

Dr Christopher Ho is a specialist prosthodontist who completed postgraduate studies in Masters of Clinical Dentistry in Prosthodontics from the University of London, and a Doctorate in Clinical Dentistry in Prosthodontics from the University of Sydney. He is a fellow of the Pierre Fauchard Academy, American College of Dentists, and a special field member of the Royal Australasian College of Dental Surgeons in Prosthodontics. He is the head of the School of Postgraduate Dentistry, Australasian College of Dental Practitioners, and a visiting lecturer for the postgraduate oral implant diploma and prosthodontic programmes at the University of Sydney, and Kings College London, UK.