Case Report

By Prof. Khamis Hassan
Corresponding Author Prof. Khamis Hassan
Restorative Dental Sciences Department, College of Dentistry, King Saud University, POB 60169 - Saudi Arabia 11545
Submitting Author Prof. Khamis A Hassan

Posterior Composites, Polymerization Shrinkage, Stress Reduction, C-Factor, Split-Increment, Horizontal, Placement Technique

Hassan K. Polymerization Shrinkage Stress Reduction in Direct Occlusal Composite Restoration Placed Using Split-increment Horizontal Technique - Case Report. WebmedCentral DENTISTRY 2010;1(9):WMC00626
doi: 10.9754/journal.wmc.2010.00626
Submitted on: 14 Sep 2010 08:54:29 PM GMT
Published on: 14 Sep 2010 10:35:56 PM GMT


Several incremental placement techniques have been introduced in an effort to reduce polymerization shrinkage stress associated with light curing of composite resins.In the horizontal technique, placement of each composite increment connects the cavity floor with the four surrounding walls and produces, upon light curing, the highest and the most unfavorable C-factor ratio of 5.Concern has been expressed when individual increments are placed to sinultaneously contact opposing cavity walls before light-curing as the resulting polymerization shrinkage stress may cause the cusps to deform by bending toward each other.This stress may cause postoperative sensitivity and can be detrimental to the tooth and the marginal integrity over time.
In the presented split-increment horizontal technique, each horizontal increment was split into four triangular-shaped portions before curing, where each portion bonds only to one cavity wall and part of the floor.Then, one diagonal cut was completely filled with dentin shade composite and light-cured, followed by filling and curing of one half of the second diagonal cut at a time.This increment splitting would reduce the C-factor ratio from 5 to 0.5 and permit the shrinkage stress to be relieved by flow of the free composite surface at the diagonal cuts and not at the bonded interfaces, thus minimizing the adverse effects of the generated polymerization shrinkage stresses.


There has been an increase in the use of composite resin for restoring posterior teeth in the past few years.  It is well-known that all composite resins shrink during polymerization, and shrinkage presents several challenges during placement and light-curing. Upon resin curing, polymerization shrinkage stresses are generated which may initiate adhesive failure at the composite-tooth interface leading to gap formation between composite resin and cavity walls.  Oral fluids containing bacteria may fill this gap and cause microleakage and secondary caries.  Cohesive failure may also occur in the form of microcracks of composite resin. In addition, coronal deformation may result from transfer of these shrinkage stresses to the tooth causing postoperative sensitivity and propagation of existing enamel microcracks.
The magnitude of these stresses depends on several factors including resin modulus of elasticity, rate of polymerization and restorative techniques as well as cavity configuration (C-factor).  The C-factor is the ratio between bonded and unbonded surfaces where the higher the ratio, the higher is the polymerization stress.
Class I occlusal cavity preparations have the highest C-factor as they have only one free, unbonded surface which is able to deform as polymerization shrinkage occurs, causing the highest and most unfavorable stresses at the cavity walls and margins.
Practitioners and researchers are aware of the adverse effects of the shrinkage stresses.  Several efforts have been made to decrease these stresses and were directed toward improving composite resin formulation, curing methods and restorative placement techniques.
Incremental placement techniques are widely recognized as a major factor in the reduction of shrinkage stresses. These techniques include the horizontal occluso-gingival layering, the wedge-shaped oblique layering, the successive cusp buildup technique,  and the split-increment horizontal placement technique.
Clinicians realize that placing an “esthetic” high quality posterior composite resin restoration is demanding and technique-sensitive.  In the present technique the clinicians need to sculpt only the last dentin increment and the enamel increment overlying it as well, while in the cusp successive buildup technique, the clinicians are required to place and sculpt several wedge-shaped oblique increments for building up each cusp separately.  This would require considerably more of the chair-side time than that needed to place a similar restoration using the split-increment technique. The increased time would require an increased fee charged to the patient.
This paper reports a clinical case that presents a step-by-step demonstration of Class I occlusal composite resin restoration placed using the split-increment horizontal placement technique.  In this technique, each composite horizontal increment is split into four portions before curing.  Each portion of the split-increment contacts only two cavity surfaces, not opposing each other, during light curing.

Case Report(s)

A 35-year old male patient presented with a defective large Class I occlusal amalgam restoration in tooth No. 37 (lower left second molar).  The selected shade was A1.  After anesthesia of the involved quadrant and rubber dam application, amalgam was removed and cavity was refined using standardized operative procedures.
Single Bond 2 adhesive system (3M ESPE, St Paul, MN, USA) was applied to the entire cavity following the manufacturer’s directions.  The first  2 mm increment (A2 dentin shade) of Filtek Supreme Plus nanofilled composite resin (3M ESPE, St Paul, MN, USA) was placed horizontally and adapted to the cavity floor.  Before light curing, this increment was diagonally split into four portions, Figure 1, using a blunt hand instrument in push stroke.  Then, the increment was light-cured for 40 seconds from occlusal direction using Elipar Highlight curing light unit (ESPE America, Inc., Norristown, PA, USA).
One diagonal cut was completely filled with the same chroma dentin shade composite, Figure 2, followed by light curing for 20 seconds from occlusal direction.  The second diagonal cut was then filled with the same chroma dentin shade composite, Figure 3, and light-cured in the same manner.
The second increment of dentin shade composite (A1), which is one chroma less than the previous one, was placed horizontally to cover the first light-cured increment, Figure 4.  This increment matching the selected shade was extended to the DEJ.  Similar treatment of this increment was performed as described for the previous one, except that top 1/5 of the central area of the two diagonal cuts was left unfilled with composite.  This area was used for internal characterization with brown Chroma Zone Color Stain (Kurary, New York, NY, USA).
Following the internal characterization, the enamel shade composite increment (A1), matching the selected shade was placed horizontally to replace the lost enamel and extended from DEJ to contact the preparation cavosurface margin.  This increment was shaped to establish the occlusal morphology, then split into four portions and light-cured for 20 seconds each from buccal, lingual and occlusal directions, Figure 5.
The final increment of highly translucent shade composite (YT) was placed to cover the enamel shade composite split-increment, without touching the cavosurface margin and light-cured for 40 seconds from the occlusal direction. This increment was not split.
Occlusal contouring of composite resin was performed using composite modeling instruments with silicon tips.  Finishing was completed with Astropol small flame rubber polisher (Ivoclar, Amherst, NY, USA).  Figure 6 shows the finished restoration.


The split-increment horizontal technique introduced for placement of direct posterior composite resin in moderate-large occlusal Class I cavities offers several advantages.  It would result in minimizing the detrimental effects of polymerization shrinkage stresses at the cavity walls and adhesive interface by the reducing the C-factor ratio from 5.0 to 0.5.  Comared to the successive cusp build-up technique, the split-increment technique would make placement of composite resin in Class I occlusal cavities easier and faster and would encourage the less-experienced general practitioners to satisfy the esthetic dental needs of their patients by providing high-quality posterior composite restorations.


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Source(s) of Funding

This is a non-funded article

Competing Interests

There is no competing interests


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