J. Dent. 1992;


20: 27-32

Fabrication times for indirect composite resin restorations P. J. J. M. Plasmans, M. A. van’t Hof* and N. H. J. Creugers Department of Oral Function and Prosthetic Dentistryand *Department Dental Clinical Research, University of Nijmegen, The Netherlands

of Medical Statistics,

TRIKON: Institute


ABSTRACT Fabrication times for indirect posterior composite resin restorations were recorded in a prospective clinical efficacy study. Four operators completed 132 one-visit inlays and onlays utilizing a new indirect posterior composite resin system (KS). The mean time needed for the fabrication of one ICS restoration was 90 min, including the ‘laboratory time’. When two restorations were provided simultaneously, the overall mean fabrication time was 120 min. The fabrication times were significantly influenced by the operator and the number of restorations. In several clinical phases a 40 per cent difference in mean fabrication time could be identified between operators. The extent of the restoration had no influence on mean fabrication time. The results of this study are considered to provide some indication of the cost-effectiveness of ICS restorations. KEY WORDS: J. Dent. 1992;

Posterior composites (indirect) 20: 27-32

(Received 15 August 1990;

reviewed 5 October 1990;

accepted 30 July 1991)

Correspondence should be addressed to: Dr P. J. J. M. Plasmans, University of Nijmegen, Dental School, Department of Oral Function and Prosthetic Dentistn/, Philips van Leydenlaan 25, 6525 EX Nijmegen, The Netherlands.

INTRODUCTION Direct tooth-coloured resin-based alternatives to dental amalgam suffer a number of serious limitations. Restorations of first-generation posterior composite resin materials (posterior composites) frequently failed due to polymerization shrinkage, hydrolitic instability, marginal leakage, postoperative sensitivity, excessive wear and recurrence of caries (Jorgensen et al., 1975; Sdderholm et al., 1984; Jensen and Chan, 1985; Eick and Welch, 1986). Furthermore, technique sensitivity and handling difficulties limited the applications of these materials in posterior teeth (Leinfelder, 1989; Letzel, 1989; Roulet, 1989). Indirect tooth-coloured restorations are not considered to suffer as many difficulties as direct composites. However, the conventional fabrication technique of these indirect restorations is time consuming and expensive compared with the direct method, since at least two treatment sessions and time in the laboratory are required (Burke et al., 1991). Indirect posterior composites were introduced to overcome the limitations of direct posterior composites and to o (1992) Butterworth-Heinemann 0300-5712/92/010027-06


provide simple and quick indirect tooth-coloured restorations. It has been suggested that indirect methods utilizing posterior composites might allow control of the problems related to polymerization shrinkage (leakage, flexing of cusps and postoperative sensitivity) while handling procedures would be easier (Robinson et al., 1987; Shethet al., 1989; Douglas et al., 1989; Watts, 1989). The systems available so far do not necessarily facilitate the restoration of contacts and approximal contour, because important stages in the procedure are performed intra-orally (i.e. Coltene Brilliant DI-500 system, Coltbne, Konstanz, Germany; Kulzer Inlay CS, Kulzer GmbH, Wehrheim, Germany). Another disadvantage is that two treatment sessions are needed (i.e. EOS, Vivadent, Schaan, Liechtenstein; SR-Isosit, Ivoclar AG, Schaan, Liechtenstein; Kulzer Inlay LS, Kulzer GmbH, Wehrheim, Germany). Recently a new experimental system, including some existing commercially available products and some new (not yet commercially available) products, has been developed as a single-visit indirect composite system


J. Dent.



No. 1

(ICS-system, 3M Co., St Paul, MN, USA). To become a successful treatment this experimental ICS system should provide durable restorations of high quality at acceptable cost. These aspects are subject to a efficacy study being performed at the Dental School of Nijmegen. This report deals with one of the efficiency aspects of the ICS restoration, namely the fabrication time, which is considered to be one of the components of cost calculations. The cost of an indirect restoration comprises the dentist’s fee and the costs of materials and dental laboratory work. The dentist’s fee varies from one country to another; in some countries fees are regulated by law, while in others the fees are unregulated. Whatever the system, the costs depend on the time needed to accomplish the clinical procedures of a restoration. Studies on times needed to apply amalgam restorations, posterior composite resin restorations and adhesive bridges indicate that different factors may have an influence on the treatment time, such as tooth type, the operator, the extent of the restoration and the number of restorations (Hendriks et al., 1985; Advokaat, 1985; Creugers and van? Hof, 1987; Plasmans and van’t Hof, 1987; Verzijden et al., 1990). The aim of the present study was to investigate the fabrication times of experimental ICS restorations and to describe factors influencing these times.



The ICS system The system is based on P-50 resin bonded ceramic (3M Co., St. Paul, MN, USA), an 87.5 per cent w/w filled small particle composite resin. This material has been shown to perform satisfactorily as a direct posterior composite resin (Mazer and Leinfelder, 1988; Willems et al., 1989). Other products of the system which are available commercially are Vitrebond glass-ionomer, and Scotchbond 2 primer and resin. New experimental products are: an epoxy resin die material; a hot-melt stone model material; and a dualcure composite luting cement (all materials: 3M Co., St Paul, MN, USA).

Patients Patients were recruited by staff members of the restorative departments of the Dental School and a group of general practitioners. The inclusion criteria for patients and teeth were: -

At least one upper premolar or first permanent molar for which a tooth-coloured restoration was desired. Teeth in occlusal function following restoration. Teeth vital and not showing severe periodontal disease, nor radiographically compromised apices or predictable pulp exposure.


Patient healthy, willing to sign an informed consent and to return at regular intervals for evaluation.

There were 48 patients in the study; 21 were men and 27 were women. Their mean age was 37 years (range 2265).

The operators After a training course and successful completion of four inlays by each operator the trial was started. Four dentists were involved in providing the indirect composite resin restorations. These general practitioners, who had between 4 and 7 years postgraduate experience, attended the Dental School to participate in this project. The operators had no previous experience with the system investigated. However, they all had clinical experience with direct posterior composite resin restorations. The clinical procedures were carried out with the help of a dental assistant following the steps of an agreed protocol (Table I). The chairside laboratory procedures were carried out by the operators on the basis of a rotational scheme, so that the time needed for the laboratory phase was independent of the clinical phases.

The restorations A total of 132 restorations were made in upper premolars and upper first permanent molars. In six cases three restorations in one quadrant were made in one session. These restorations (n = 18) were excluded from the statistical analysis due to the small group size. The reasons for fabricating the ICS restorations (several reasons could be scored simultaneously) were: aesthetics (98 per cent), caries (27 per cent), defective previous restoration (20 per cent), bulk fracture of the previous restoration (6 per cent), and cusp fracture of the remaining tooth structure (4 per cent). In 99 per cent of the cases the ICS restoration replaced an existing amalgam restoration. In 80 per cent of the cases the restoration was an inlay and in 20 per cent it was an onlay.

Data collection

and analysis

Eight different fabrication phases were distinguished: six phases in which the patient is actually treated, referred to as ‘clinical phases’, and two ‘chairside laboratory phases’, in which the restoration is constructed. The times needed were recorded for each phase in minutes. When more ICS restorations were made in the same quadrant in one session, the times were recorded per phase and not for each restoration. Within the context of the experimental design, the following factors were analysed: operator, extent of the restoration, and number of restorations. A balancing program was used for treatment allocation to distribute the tooth variable over the operators correctly (Table II). Also the effect of operators’ experience was analysed by describing the restorations made in the first


Table 1. Recommended


for ICS restorations

Clinical phase I Cavity preparation Prepare a conservative inlay preparation with rounded line angles and a GSA of 90” A minimal thickness of 2 mm for the composite resin is necessary Pulp protection/bonding Cover all dentine with light-cured glass ionomer liner Apply etching gel on the remaining enamel margins Cover the glass ionomer and etched enamel with lightcured Scotchbond 2 Clean the Scotchbond 2 layer with a cotton pellet and alcohol to remove the air-inhibited layer Impression Take the impression with a vinyl polysiloxane impression material using standard techniques Laboratory phase Model making Place the clean impression in a hot oven at about 120°C for 5 min Box the bench cooled impression and separate the preparation(s) with metal strips Pour the epoxy resin directly with attached mixing tip in the prepared teeth and adjacent teeth Cover the epoxy and fill the impression with hot melt stone Place a strip of tape in the holt melt stone with the irregular side down Immerse the impression in cold water for 3 min Remove the cast and score the cast adjacent to the preparations and break to expose the preparation. Trim the die if necessary Modelling/finishing Cover the prepared tooth with an uniform thin layer of primer and air-dry for a minute Mix equal amounts of the die release and apply in thin layer and wait about 2 min Place and shape the composite resin restoration and light cure each area extensively Refine the anatomy and marginal fit by finishing the restoration on the die Remove the restoration and post-cure it at 120°C for 5 min Clinical phase II Fitting/adapting Check the fit and occlusion on the original tooth and adjust if necessary Wash the cavity preparation with water and swab with alcohol Place Scotchprep primer on the entire cavity preparation. Dry very thoroughly. Clean the composite resin restoration also with Scotchprep Cementation Bond the inlay into place using Dual Cure Luting Cement Remove excess and cure each area for 30 s Finishing/polishing Finish and polish the restoration and margins Apply fluoride

seven treatment sessions (in most cases ten ICS restorations) as ‘inexperienced’ while the other restorations were referred to as ‘experienced’. The influence of the operator on the time of the

et al.:


Table II. Distribution operator



for composite


Tooth variables 1





Operator 2 3




Tooth number 16-26 15-25 14-24

4 15 15

4 13 16

3 20 11

1 16 14

12 64 56


26 4 4

27 26 5 7 111

24 6

103 22 7

Total number of ICS






B, buccal; L, lingual.

chairside laboratory phase was not analysed because all the operators participated in the fabrication of individual restorations in this phase. The influence of tooth type was not analysed due to the small number of ICS restorations in molars. Analysis of variance (ANOVA) was used to study the influence of the factors described on fabrication times. As a skewed distribution of the fabrication times was obtained a logtransformation was used to produce a normal distribution. Effects were expressed as percentages rather than times (Plasmans and van’t Hof, 1987).

RESULTS The overall mean fabrication time, overall median fabrication time and the median fabrication time for one restoration and for two restorations are shown in Table ZZZ (II = 114). A median fabrication time of 93 min was found if one restoration per session was made. If two restorations were completed in the same session the median fabrication time was 125 min. Chairside laboratory phases took 37 min for one and 46 min for two restorations. The analysis of variance indicated that for most fabrication phases the number of restorations and the operator were significant variables (P < 0.05). The extent of the restoration had no significant influence on any of the fabrication phases (Table IV). Table V presents the percentages increase in time per fabrication phase if two restorations were completed in one session, as well as the percentage differences between the median times per phase for different operators. For example, operator 3 needed 31 per cent less time for cavity preparation than the average. ANOVA showed that experience only had a significant influence on the fitting/adapting clinical phase (43 per cent faster) and in consequence on the complete clinical phase II (14 per cent faster). Experience had no significant effect on the total fabrication time.

DISCUSSION The mean time needed to complete all clinical and chairside laboratory procedures in the fabrication of one


J. Dent.


20: No. 1

Table 111.Mean and median fabrication times (min) according to (sub)phase and number of restorations per quadrant (n = 1 14)


Mean 1 or 2 Median 7 or 2 restorations restorations


Median 2 restorations

Clinical phase I Cavity preparation Pulp protection/ bonding Impression

28.7 11.7 9.8

27.0 10.1 9.0

21.9 7.5 7.4

31.3 12.5 10.3





Chairside laboratory phase Model making Modelling/finishing





24.1 19.6

22.0 18.4

20.7 15.0

22.9 21.2

Clinical phase II Fitting/adapting Cementation Finishing/polishing

41.8 13.9 8.9 18.9

39.5 11.4 8.4 16.9

33.0 9.3 6.9 14.5

44.9 13.3 9.7 18.8

Clinical phase I + II Overall






1 10.3



Table IV. Significance level of ANOVA for number of restorations per session, operator and extent of restoration for the treatment phases (n = 1 14) Number of restorations


Extent of restoration

Clinical phase I Cavity preparation Pulp protection/ bonding Impression

xxx xxx xxx

xxx xxx xx

n.s. ns. n.s.




Laboratory phase Model making Modelling/ finishing

xx n.s. xxx

1;; (I)

n.s. n.s. n.s.

Clinical phase II Fitting/adapting Cementation Finishing/ polishing

xxx x xxx X

xxx xxx n.s. n.s.

n.s. n.s. n.s. n.s.

Clinical phase I and II








Treatment phase

Median I restoration

(I), not tested. The time of the laboratory phase is independent of the operator. n.s., not significant, P > 0.05. x, 0.01 < P < 0.05. xx,0.001

Fabrication times for indirect composite resin restorations.

Fabrication times for indirect posterior composite resin restorations were recorded in a prospective clinical efficacy study. Four operators completed...
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