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Comparative Study of Composite Resin Placement

Centripetal Buildup Versus Incremental Technique

An in vitro study was performed to evaluate the effect of two different proximal restoration techniques with different matrix systems on the marginal seal and microhardness of Class II composite restorations. Results indicated that the lowest, however, not significantly different, microleakage was achieved in totally bonded deep Class II restorations prepared with margins surrounded by enamel when using transparent matrices and reflective wedges in combination with the centripetal buildup technique. Highest surface hardness of composite resin was related to transparent matrices and reflecting wedges.

Marginal leakage appears to be an inherent shortcoming of all dental restorations.1-5 Various techniques have been advocated to enhance the marginal adaptation and reduce the microleakage of composite restorations. Multilayer techniques, in contrary to bulk packing methods, have decreased marginal gap formations.6,7 The size reduction of the composite material, the diminution of polymerization shrinkage, and the enlargement of the free surface area in relation to the volume are of great importance in this context.8 The three-sided light-curing technique enables initial progress in this direction; it is questionable if other techniques can maintain better results.9 While promising results have been achieved with centripetal buildups, comparative microleakage tests were not conducted.10 An important benefit of this procedure is that a thin proximal layer placed towards the matrix band is cured before adjacent composite increments are applied into the cavity. This can reduce the V/A ratio, where V is the cavity volume and A is the area of the cavity walls. When the whole margin area is first filled with an increment, fewer contraction gaps at the margins can be expected using the centripetal technique versus the incremental technique. Even if such a gap does develop, the next increment is likely to fill this gap.

In addition to methods, various materials (eg, light-curing tips, matrix systems) have also been investigated.11,12 Different experimental designs for microhardness and marginal analysis can be found in current literature.13-15 To investigate marginal leakage of dental restorations, isotope or dye penetration has been used.16,17 Following penetration, one mesiodistal section of the restoration was without a description of the penetration patterns at the buccal or lingual sides of the restoration.18,19 Although several investigations of microleakage have been conducted,  most of the investigations involved Class II cavities in extracted teeth. These specimens were not, however, mounted in contact with adjacent teeth to ensure their movement during separation techniques.17,18

Microhardness analyses in specimens that were irradiated from all sides to obtain polymerization with a high conversion rate in light-curing composite are found in the literature. In most instances, cavities are simulated with standardized metal blocks to obtain flat surfaces for microhardness analysis.13,14,20 Under clinical conditions, however, flat restoration surfaces can only be obtained in exceptional cases. The results, therefore, may not have reflected the leakage and microhardness pattern of Class II cavities, which are larger and more complex under optimized in vivo simulating conditions. Some clinical studies show that a number of hindrances remain in the attempt to develop an optimal method for placing composite restorations that will remain intact in the oral cavity over extended function.4,21,22 Provided the preparation margins are surrounded by enamel, most multilayer placement techniques can achieve adequate results in marginal adaptation of composite materials.16,18,23 Deeper cavities with gingival floors that end in dentin constitute a challenge for the adhesive mechanism.24,25

One purpose of this investigation was to create an experimental design that allows (under simulated in vivo conditions) the examination of different restorative techniques (incremental versus centripetal technique) for the approximal box of Class II cavities. This study also examined the effect of an opaque matrix system versus a transparent matrix/wedge on the marginal seal of composite restorations. In addition, the Vickers hardness of the approximal surfaces of composite restorations was measured under simulated clinical conditions, but in a different experimental arrangement.


Materials and Methods

Specimen Preparation

One hundred sixty unrestored, extracted molar teeth free of caries and fracture lines were randomly divided in two experimental designs: 96 specimen were used for the evaluation of the marginal seal, and 64 teeth were employed for the evaluation of surface microhardness of composite restorations. Once the specimen were cleaned with pumice and water, they were mounted in silicon models in proximal contact with other specimens, which ensured the movement of teeth during separation techniques that simulated clinical conditions. Teeth were divided into two groups according to the following specifications: in the first group, the gingival floor was surrounded by enamel, in the second group by dentin. Each tooth was prepared with two Class II cavities using parallel buccal and lingual walls on the occlusal aspect and in the proximal boxes.

The preparations were cut with a diamond bur in a high-speed handpiece with water coolant. The finishing procedure was performed in a similar fashion. After six preparations, a new bur was used. To ensure as much uniformity among the preparations as possible, a periodontal probe was utilized as a guide: the depth of the gingival floors of the preparations was estimated from 4.5 mm (Group 1) to 7.5 mm (Group 2); the pulpal floor extended 3 mm into dentin; all proximal extensions were estimated at 6 mm for both groups. No bevels were prepared. After the preparations were completed, the teeth were randomly assigned to eight groups of 24 teeth each. The teeth in all groups were restored with a hybrid composite resin using the total-etch technique as recommended by the manufacturer. The combination of composite insertion technique and the matrix system varied with each group. Each layer was subjected to a 40-second exposure to the curing unit. Prior to each use of this curing unit, a curing radiometer was employed to measure light output in the 400 nm to 500 nm wavelength range. The measured light intensity varied from 800 mW / cm2 to 1000 mW / cm2.


Incremental Technique

In the groups EIM, EIT, DIM, and DIT, the composite resin was placed with an incremental technique: the first layer of composite resin was placed on the gingival floor, the second and third layers were placed diagonally, and the last increment was used to complete the filling in the occlusal portion of the cavity. The incremental technique in cavities with a depth of 4.5 mm was performed in the following sequence: 1.5 mm + 2 mm + 1 mm. For cavities with a depth of 7.5 mm, the following sequence was used: 1.5 mm + 2 mm + 2 mm + 2 mm.


Centripetal Technique

In the groups ECM, ECT, DCM, and DCT, the hybrid resin was placed in a centripetal technique: a first layer of resin (1 mm thick) was placed towards the matrix band, and the subsequent increments (2 mm thick) were applied horizontally towards the occlusal area of the cavity (Figure 1). Since the same number of increments was used for buildup (depending on the depth of the cavities), this investigation evaluated the layering technique used.


Opaque Matrix System

In the groups EIM, ECM, DIM, and DCM, a 0.05-mm Tofflemire metal matrix band and a No. 15 in a retainer with wooden wedges were applied to the specimen. Each increment of composite for these specimens was cured only from the occlusal side with visible light for 40 seconds. Following removal of the matrix system, the restorations were cured for 40 seconds from the buccal and occlusal aspects for both techniques.


Transparent Matrix/Wedge System

In the groups EIT, ECT, DIT, and DCT, a precontoured 0.05-mm transparent matrix band in a retainer was applied with reflective wedges. Each increment of composite was cured with visible light for 40 seconds. With the incremental technique, the first layer was cured indirectly through the light wedge; the second and third layers were polymerized from the buccal and oral direction in order to ensure that the shrinkage vectors were directed toward the cavity margins. The last increment was polymerized from the occlusal aspect. With the centripetal technique, the first layer was polymerized from occlusal direction, the second layer through the light wedge, the third and fourth layers from the buccal and occlusal direction as previously described, and last layer from the occlusal aspect. Following the removal of the matrix system, no postcuring was performed for the definitive restoration.

All restorations were finished immediately after placement with fluted carbide burs, soft polishing disks, and silicon polishing under water coolant. Plastic finishing strips were used for the finishing of the interproximal surface. Postcuring was not performed.


Evaluation of Marginal Seal

The specimens were removed from their mounting and thermocycled for 5000 cycles (5¡C to 55¡C) with a dwell time of one minute at each temperature. After thermocycling, two coats of colored fingernail varnish were applied to all specimens, excluding the restoration margins of 1.5 mm.

Microleakage was assessed with 2% methylene blue diffusion for 24 hours at 37¡C. The teeth were then embedded in a self-curing, transparent epoxy resin, longitudinally sectioned with a diamond saw in a buccolingual direction at the approximal box of the restoration, and dye penetration was evaluated by light microscopy at (32 magnitude. The gingival margins of the embedded specimens in transparent resin were marked from the mesiodistal view for the first section. From here, two sections of 500 µm were obtained with a mean loss of 280 µm per section. Microleakage was calculated in percent of the total length of the gingival margins of the cavity.


Evaluation of Surface Hardness

Sixteen teeth of each group were embedded in resin and sectioned on the approximal sides to receive a parallel plane area. This flat surface was necessary to facilitate Vickers hardness tests. Afterwards, different cavities with already described sizes were prepared into the specimens. A strip of the matrix band used (transparent or metal) was glued to the resin blocks without forming marginal gaps between the prepared cavities and the matrix band. Restorations were applied, as previously described, and all curing procedures were performed from the occlusal surface of the cavity. After curing, the matrix band was removed, no postcuring technique was used, and the Vickers hardness of the planed approximal composite surfaces was measured with microhardness meter at a load of 0.3 kg for 30 seconds. The Vickers hardness was measured on the approximal composite surface 24 hours following resin placement. Six measurements were made at predetermined, regularly distributed sites in the cervical area of the approximal surface. The values were evaluated by light microscopy at (200 magnitude. Hardness was calculated by dividing the applied load by the surface area of the indentation.


Statistical Analysis

The mean values and standard deviations were calculated for each group. Data were analyzed with nonparametric statistics; the Kruskal-Wallis Multiple-Comparison Z-Value Test - including the Bonferroni Correction  - were used with alpha = 0.05 for statistical analysis of the results.

(Continued from page 1 )


Evaluation of Marginal Seal

The results of the dye penetration of the various groups of composite restorations were recorded (Table 1). Marginal microleakage or its absence was observed in each group evaluated in this study. Each restoration demonstrated marginal microleakage on the gingival wall. Highest values were found in the groups DCM (92.42%) and DIT (89.31%), which were significantly different from the groups EIT (59.4%), ECM (54.26%), and ECT (52.37%). Since buccolingual sections were obtained in order to encompass the entirety of the cervical shoulder in the buccolingual direction, the method of sectioning may have influenced the results obtained. An occasional high standard deviation was observed as a result of the either perfect seal or high values of penetration that were obtained in this evaluation.


Evaluation of Surface Hardness

The results of the microhardness measurements were listed (Table 2). For all groups investigated, there was a strong correlation between increased microhardness and the use of transparent matrices. When transparent matrices were used, no statistically significant correlation was found between the use of the incremental technique versus centripetal technique or of the location of the cavity preparation. For the group DCM (opaque matrix system in combination with the centripetal technique in deep cavities), a significant decrease in microhardness values was noted compared with all seven possible groups.



As a composite resin material undergoes polymerization shrinkage, the force of this shrinkage may exceed the bond strength of the material to tooth structure.26 Shrinkage-free resins that would permit the placement of perfectly adapted and sealed restorations are not yet available. Factors allowing the optimization of the marginal adaptation of composite resin restorations can be found in the composite resin material, cavity preparation, and placement technique. A multistep insertion technique, in combination with transparent matrices and reflective wedges, has been designed to enhance the marginal quality of Class II composite restorations.8 In addition, the marginal adaptation can be significantly improved by the use of a buildup base material that reduces the size of the composite restoration, thus increasing the free surface-to-volume ratio.27,28 Based on these facts, and in combination with various parameters previously described, a comparison was made between the centripetal and incremental techniques. It was found that the centripetal technique showed better marginal adaptation in cavities prepared in enamel than did the common incremental technique. Several authors have indicated that one of the most important principles for incremental placement is to reduce the V/A ratio by applying the first increment to only one cavity wall.29 Other reports have indicated that the application of composite in oblique layers resulted in fewer contraction gaps at the margins.30,31 There has been disagreement concerning the relative merits of apical oblique versus coronal oblique incremental patterns, although differences between these are of less significance than the need for incremental rather than single-bulk technique.32

In the present study, it was found that neither the technique nor the matrix band material had statistical significant influence in the marginal microleakage. Only the preparation depth influenced the results. Eakle and Ito reported that significantly less leakage occurred under gingival margins when the proximal box ended on enamel than when it terminated on cementum.19 The same behavior was found in this study, where the highest microleakage value in the enamel-surrounded groups 75.83% penetration (EIM), as opposed to the highest value of 92.42% (DCM) in deeper cavities. Numerous researchers noted that neither of the one-bulk incremental placement techniques was able to produce consistently leak-free margins, even on etched enamel.17,19

Through the use of the centripetal technique, the V/A ratio could be reduced. This differed from the incremental technique, where the complete apical area of the cavity was filled with the first layer of composite resin material. In the incremental technique, this first layer had less contact with the lateral walls than did the resin in the first layer of the centripetal buildup technique. Alternatively, the first layer of the centripetal technique had no contact to the pulpoaxial walls and thus had less tendency to contract toward this wall and away from the cervical floor during polymerization. In the proximal box, the polymerization shrinkage tended to pull this first horizontal increment away from the cervical margin. The second layer of the incremental technique, which was a diagonal layer, was not able to cover the first portion in the cervical area, which did occur with the second layer of the centripetal buildup technique.

In deep cavities, the dentin adhesive material was unable to inhibit dye penetration. Lui et al determined that the worst marginal adaptation of restorations was found in the cervical area and attributed to the effect of polymerization shrinkage, inadequate adaptation of noncondensable resin, difficulty of placement at the proximal box, and shrinkage toward the light source.23 In the present study, this behavior was only registered in groups EIM, ECM, and DCM. It is, however, surprising that all cavities in the Lui study were filled with different techniques and in different depths yet always with metal matrices and wooden wedges. Wooden wedges, when properly used, enhance the adaptation to the cavity walls and provide firm contact areas and anatomical proximal contours.33 Scherer et al registered that restorations made with transparent matrices and reflective wedges exhibited less microleakage than those delivered with opaque matrices and wooden wedges.25 Furthermore, Lutz et al proved that the concept of directing the polymerization shrinkage vectors toward the margins of a cavity by using light-reflective wedges with reflective cores was efficient.28

In another study,12 it was shown that the worst marginal qualities were obtained in cavities filled with composite in a one-step technique and with opaque wedges and matrices (62.2% excellent margins) in contrast to composite fillings with transparent matrices and laterally reflecting wedges (79.4% excellent margins). The values were not significantly different. In that study, however, the cavities were placed in a one-bulk technique and opaque matrices were only cured from the occlusal direction. No postcuring was performed following the replacement of the opaque matrices and wooden wedges. In the present study, only the restorations delivered with metal matrix bands were postcured. For this purpose, postcuring was performed for 40 seconds from the buccal and occlusal aspects. The additional use of reflective wedges in the proximal area during the postcuring period was not investigated in this study, as the authors believed that a postcuring situation with reflective wedges in the proximal area would not accurately reflect the differences in the aforementioned techniques.

A statistically significant increase in microhardness was obtained in all groups treated with transparent matrices and reflective wedges. This could be attributed to the higher degree of conversion and crosslinking of the resin.13,34 There is also a correlation between the curing light intensity and the depth of cure.

von Beetzen et al investigated the microhardness of composite restorations and determined that the Herculite composite material, also used in this study, was characterized by Vickers values ranging from 44 HV to 59.8 HV, depending on the polymerization technique.13 In the experimental set-up of their investigation, standardized Class II cavities in brass blocks were filled with composite in 2.5-mm increments, which were then cured for 60 seconds from the occlusal aspect of the cavity. Plastic matrix bands were used and, after the increments had been cured from the occlusal aspects, no postcuring was done - as in the present study. Although higher values (59.8 HV) were obtained when using a transparent cone for the polymerization,13 comparable values were also achieved for the restorations using both metal matrices (42.65 HV for group EIM) and transparent matrices (64.48 HV for group EIT) in the current investigation. This is due to the 1.5-mm increments in this study, the preparation of extracted teeth rather than metal blocks, and the use of an additional curing unit. Questions were raised, however, regarding the examination of surface hardness conducting different polymerization procedures, as in evaluation of the marginal seal. In the experimental design of microhardness analysis, the different matrix bands were glued to the flat surface of the specimen. Although securing and utilization of different wedges was not conducted in this investigation, it would be interesting, to do this in further investigations. A postcuring polymerization technique, which could have improved the results, was also rejected.



The authors concluded that none of the insertion techniques and matrix bands used in this study were able to prevent extensive microleakage at the cervical margins of Class II composite restorations. The marginal integrity of composite resins placed in cavities ending in enamel and restored with the centripetal technique and transparent matrices was exceptional (though not significantly different) to those filled in the incremental technique in combination with either reflective or wooden wedges.

Cavities prepared with their marginal aspects in dentin showed no significant differences in their microleakage behavior either in dependence of the matrix band material nor of the placement technique. In deep cavities, best (although not statistically significant) results were obtained when the centripetal technique was used in combination of transparent matrices. The preparation depth significantly influenced the results, with less leakage observed in margins located within the enamel. The results also determined that the highest mean hardness values for composite resin restorations were achieved using transparent matrices.


*Assistant Professor, Department of Operative Dentistry, Johann Wolfgang Goethe University, Frankfurt am Main, Germany.


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