Cuspal movement and microleakage in premolar teeth restored with a packable composite cured in bulk or in increments

Abstract

Introduction. The aim of this study was to investigate the effect of two novel curing systems (a plasma arc light, and a ‘turbo-boosted’ conventional curing light) on cuspal movement and gingival microleakage of ‘packable’ resin-based composite (RBC) restorations placed in extracted maxillary premolar teeth.

Materials and methods. Forty sound extracted upper premolar teeth were subjected to standardised preparation of a large mesio-occlusal-distal cavity before restoration with a RBC. Four curing regimens were used. Either the RBC was placed in bulk and light-cured in one increment using (a) the plasma arc light; (b) the ‘turbo-boosted’ curing light, or the RBC was placed in eight increments using (c) the plasma arc light; (d) the ‘turbo-boosted’ curing light. A deflection measuring gauge allowed a measurement of cuspal deflection at each stage of polymerisation. Restored teeth were thermocycled before immersion in a 0.2% basic fuchsin dye for 24 h. After sagittal sectioning of the restored teeth in a mesio-distal plane, the sectioned restorations were examined to assess cervical microleakage.

Results. Cuspal deflection measurements were significantly increased when the ‘turbo-boosted’ halogen curing light was compared with the plasma arc light. Total mean cuspal deflection measurements obtained with incremental cure were significantly increased compared with bulk cure for both light sources. Gingival microleakage for bulk restored teeth was significantly increased compared with teeth restored incrementally. Incremental restoration with the plasma arc light had significantly increased gingival microleakage compared with the ‘turbo-boosted’ halogen curing light.

Conclusions. The packable composite tested could not be cured adequately to a depth of 5 mm with the plasma arc light within the specified irradiation time. Under the test conditions of the current investigation, bulk curing only appeared to be practical with the high intensity halogen light (40 s activation). Incremental build-up and polymerisation optimised marginal seal for the high intensity halogen light but led to greater cuspal deflection.

Introduction

Tooth-coloured restorations, mainly, direct-placement, resin-based composite (RBC), are increasingly being used for restoration of posterior teeth, often as replacements for failed or unaesthetic restorations in dental amalgam. Currently available formulations of these materials are now recommended for a wide variety of clinical situations, and a meta-analysis, published in 1994, has demonstrated promising clinical performance.¹ It is likely that currently available resin composite materials, which have been developed since the publication of the meta-analysis, may perform similarly, or even better.

Placement of RBC materials have been described as ‘technique sensitive’ as a result of the need for attention to detail during placement and bonding to tooth substance, not withstanding the difficulties experienced by clinicians in achieving adequate contact points.² In this respect, a number of manufacturers have introduced so-called ‘packable’ materials, some with claims of increased depth of cure when compared with ‘traditional’ RBC materials. It has been suggested that steps must be taken during polymerisation to nullify the potential problems of polymerisation contraction, from which all RBC materials suffer inherently.³ This may cause the movement of cusps (and pain to the patient) or gingival microleakage if the bond at the restoration margin fails. If this occurs, patients may experience sensitivity relating to fluid movement at the dentine/restoration interface in the presence of patent dentinal tubules. Furthermore, inadequate polymerisation of composite at the base of a class II restoration may lead to secondary caries. Gingival microleakage and subsequent cavomarginal discoloration may erroneously be diagnosed as secondary caries. Gingival microleakage has been cited as an important causes of failure in restorative dentistry.⁴ It is therefore essential that an adequate seal is obtained.

Currently available RBC materials are cured in increments by visible light. As each increment may be up to 2 mm in depth, accordingly, in a large restoration, multiple incremental cures of 30–40 s may be required.⁴ This is time-consuming in the surgery and therefore expensive to the patient.⁴ There are two potential methods of reducing this potentially expensive surgery time.

• A number of manufacturers have introduced plasma-arc curing lights, or ‘boosted’ versions of high intensity halogen lights. These lights are considered to possess much higher light intensity than conventional systems, with manufacturers claiming that curing may be completed in deeper increments with a consequent reduction in curing times.

• Several manufacturers have produced materials which are claimed to be amenable to curing in incremental depths of 5 mm.⁵

If the claims of shorter curing times with plasma-arc lights are correct, it may be possible to substantially reduce curing times, although the long term clinical effectiveness of restorations cured with these lights has not yet been established. There have been doubts raised, from the results of tests of physical characteristics of some materials, of the effectiveness of the cure obtained using plasma lights6., 7., 8. and this requires further investigation. Furthermore, the effect of the reduced curing times on cuspal movement and microleakage, has not previously been investigated.

It is therefore the aim of this project to investigate the effect of two novel curing systems (the plasma arc light, and a ‘turbo-boosted’ conventional curing light) on cuspal movement and microleakage of restorations placed in extracted maxillary premolar teeth.