Formation of Diagonal Gaps as Stress-Relieving Sites: Rethinking the Concept of
            Increment Splitting in Direct Occlusal Composite Restorations

The split-increment horizontal placement technique is currently used, along with other restorative techniques, in moderate-to-large occlusal cavities for reducing the shrinkage stress generated during light polymerization. Such stress, if released uncontrolled, may cause damage within the composite, tooth or at the adhesive interface. The term “diagonal cut” was used in our original paper published in 2005 to refer to the action of dividing each composite increment into segments prior to light polymerization and was presented in two-dimensional illustration. Besides, we made no mention in the original paper of the term “diagonal gap” as an outcome of such diagonal cutting. We currently recognize the importance of introducing the “diagonal gap” term and the need for shedding some light on its role to help provide a more comprehensive view of the split-increment technique. The purpose of the current paper is to rethink our increment splitting concept used in direct occlusal composite restorations by introducing the term “diagonal gap” as a stress-relieving vertical site and demonstrating it in a three-dimensional illustration for providing a more comprehensive understanding of the split-increment technique. Conclusion: In the current paper, the term “diagonal gap” is introduced to refer to the vertical gap created by diagonal cutting of the horizontal composite increment, before light curing. This gap enables the segmented composite increment to undergo unrestrained shrinkage, where each segment being free from adhesion at the gap site can deform independently from the other segments. The relief of the polymerization shrinkage stress generated during light curing prevents formation of cracks in enamel and/or composite, and debonding of adhesive interfaces. Keywords: deformation; diagonal gap; incremental; occlusal; polymerization shrinkage; posterior composite; segment; split-increment; stress reduction; stress-relieving site

Download Full-text

The influence of curing times and light curing methods on the polymerization shrinkage stress of a shrinkage-optimized composite with hybrid-type prepolymer fillers

Dental Materials ◽

10.1016/j.dental.2006.06.019 ◽

2007 ◽

Vol 23 (7) ◽

pp. 777-784 ◽

Cited By ~ 32

Author(s):

Anuradha Visvanathan ◽

Nicoleta Ilie ◽

Reinhard Hickel ◽

Karl-Heinz Kunzelmann

Keyword(s):

Shrinkage Stress ◽

Polymerization Shrinkage ◽

Hybrid Type ◽

Curing Methods ◽

Light Curing

Download Full-text

Comparison of Internal Adaptation in Class II Bulk-fill Composite Restorations Using Micro-CT

Operative Dentistry ◽

10.2341/16-023-l ◽

2017 ◽

Vol 42 (2) ◽

pp. 203-214 ◽

Cited By ~ 10

Author(s):

SH Han ◽

SH Park

Keyword(s):

Class Ii ◽

Ct Images ◽

Shrinkage Stress ◽

Micro Ct ◽

Polymerization Shrinkage ◽

Composite Restorations ◽

Group 3 ◽

Internal Adaptation ◽

Group 5 ◽

Group 2

SUMMARY Purpose: This study compared the internal adaptation of bulk-fill composite restorations in class II cavities and explored the relationship between internal adaptation and polymerization shrinkage or stress. Methods and Materials: Standardized mesio-occluso-distal cavities were prepared in 40 extracted human third molars and randomly divided into five groups (n=8). After having been applied by total-etch XP bond (Dentsply Caulk, Milford, DE, USA) and light curing, the teeth were restored with the following resin composites: group 1, Filtek Z350 (3M ESPE, St. Paul, MN, USA); group 2, SDR (Dentsply Caulk, Milford, DE, USA) + Z350; group 3, Venus Bulk Fill (Heraeus Kulzer, Dormagen, Germany) + Z350; group 4, Tetric N-Ceram Bulk Fill (Ivoclar Vivadent, Schaan, Liechtenstein); and group 5, SonicFill (Kerr, West Collins, Orange, CA, USA). After thermo-mechanical load cycling, cross-sectional microcomputerized tomography (micro-CT) images were taken. Internal adaptation was measured as imperfect margin percentage (IM%), which was the percentage of defective margin length relative to whole margin length. On the micro-CT images, IM% was measured at five interfaces. Linear polymerization shrinkage (LS) and polymerization shrinkage stress (PS) were measured on each composite with a custom linometer and universal testing machine. To explore the correlation of IM% and LS or PS, the Pearson correlation test was used. Results: The IM% of the gingival and pulpal cavity floors were inferior to those of the cavity walls. The IM% values of the groups were found to be as follows: group 5 ≤ groups 1 and 4 ≤ group 2 ≤ group 3. The correlation analysis showed that the p value was 0.006 between LS and IM% and 0.003 between PS and IM%, indicating significant correlations (p<0.05). Conclusion: Flowable bulk-fill composites had a higher IM% and polymerization shrinkage stress than did packable bulk-fill and hybrid composites. In class II composite restoration, the gingival floor of the proximal box and pulpal floor of the cavity had higher IM% than did the buccal and lingual walls of the proximal box. LS and PS, which were measured under compliance-allowed conditions, were significantly related to internal adaptation.

Download Full-text

Influence of the Compliance and Layering Method on the Wall Deflection of Simulated Cavities in Bulk-fill Composite Restoration

Operative Dentistry ◽

10.2341/15-260-l ◽

2016 ◽

Vol 41 (6) ◽

pp. e183-e194 ◽

Cited By ~ 18

Author(s):

Y-J Kim ◽

R Kim ◽

JL Ferracane ◽

I-B Lee

Keyword(s):

Wall Thickness ◽

Mold Wall ◽

Flexural Modulus ◽

The Other ◽

Shrinkage Stress ◽

Linear Variable Differential Transformer ◽

Polymerization Shrinkage ◽

Wall Deflection ◽

Composite Restorations ◽

Composite Restoration

SUMMARY The aim of this study was to investigate the effects of the layering method and compliance on the wall deflection of simulated cavities in bulk-fill and conventional composite restorations and to examine the relationships between the wall deflection and the polymerization shrinkage, flexural modulus, and polymerization shrinkage stress of composites. Six light-cured composites were used in this study. Two of these were conventional methacrylate-based composites (Filtek Z250 and Filtek Z350 XT Flowable [Z350F]), whereas four were bulk-fill composites (SonicFill, Tetric N-Ceram Bulk-Fill, SureFil SDR Flow [SDR], and Filtek Bulk-Fill). One hundred eighty aluminum molds simulating a mesio-occluso-distal cavity (6 W×8 L×4 D mm) were prepared and classified into three groups with mold wall thicknesses of 1, 2, and 3 mm. Each group was further subdivided according to the composite layering method (bulk or incremental layering). Linear variable differential transformer probes were used to measure the mold wall deflection of each composite (n=5) over a period of 2000 seconds (33.3 minutes). The polymerization shrinkage, flexural modulus, and polymerization shrinkage stress of the six composites were also measured. All groups with bulk filling exhibited significantly higher deflection compared with groups with incremental layering. The deflection decreased as mold wall thickness increased. The highest and lowest polymerization shrinkage stresses were recorded for Z350F (5.07 MPa) and SDR (1.70 MPa), respectively. The correlation between polymerization shrinkage and the mold wall deflection decreased with increasing wall thickness. On the other hand, the correlation between flexural modulus and the mold wall deflection increased with increasing wall thickness. For all groups, wall deflection correlated strongly with polymerization shrinkage stress.

Download Full-text

Light induced polymerization of resin composite restorative materials

Medicinski pregled ◽

10.2298/mpns0412556b ◽

2004 ◽

Vol 57 (11-12) ◽

pp. 556-560

Author(s):

Larisa Blazic ◽

Dubravka Markovic ◽

Milanko Djuric

Keyword(s):

Stress Reduction ◽

Resin Composite ◽

Dental Materials ◽

Adhesive Bond ◽

Adhesive System ◽

Filler Loading ◽

Polymerization Reaction ◽

Shrinkage Stress ◽

Polymerization Shrinkage ◽

Dental Resins

Introduction Dimensional stability of polymer-based dental materials is compromised by polymerization reaction of the monomer. The conversion into a polymer is accompanied by a closer packing of molecules, which leads to volume reduction called curing contraction or polymerization shrinkage. Curing contraction may break the adhesion between the adhesive system and hard tooth tissues forming micrographs which may result in marginal deterioration, recurrent caries and pulp injury. Polymerization shrinkage of resin-based restorative dental materials Polymerization of the organic phase (monomer molecules) of resin-based dental materials causes shrinkage. The space occupied by filler particles is not associated with polymerization shrinkage. However, high filler loading within certain limits, can contribute to a lesser curing contraction. Polymerization shrinkage stress and stress reduction possibilities Polymerization shrinkage stress of polymer-based dental resins can be controlled in various ways. The adhesive bond in tooth-restoration interface guides the contraction forces to cavity walls. If leakage occurs, complications like secondary caries and pulpal irritation may jeopardize the longevity of a restoration. Stress relieve can be obtained by modifications of the monomer and photoinitiator, or by specially designed tooth preparation and application of bases and liners of low modulus of elasticity. The polymerization contraction can be compensated by water absorption due to oral cavity surrounding. The newest approach to stress relief is based on modulation of polymerization initiation. Conclusion This work deals with polymerization contraction and how to achieve leak-proof restoration. Restorative techniques that may reduce the negative effect of polymerization shrinkage stress need further research in order to confirm up-to-date findings.

Download Full-text

Influence of composite resin volume and C-factor on the polymerization shrinkage stress

Brazilian Dental Science ◽

10.14295/bds.2016.v19i2.1257 ◽

2016 ◽

Vol 19 (2) ◽

pp. 72 ◽

Cited By ~ 3

Author(s):

Rafael Francisco Lia Mondelli ◽

Marilia Mattar de Amoêdo Campos Velo ◽

Rafael Simões Gonçalves ◽

Bhenya Ottoni Tostes ◽

Sergio Kiyoshi Ishikiriama ◽

...

Keyword(s):

Composite Resin ◽

In Vitro Study ◽

Composite Resins ◽

Steel Plates ◽

Shrinkage Stress ◽

Lower Stress ◽

Polymerization Shrinkage ◽

Light Curing ◽

Clinical Problems

Objective: Composite polymerization shrinkage stress is an inherent process of chemical and light composite resin activation. Consequently, this fact has been associated to potential clinical problems. The aim of the present in vitro study was to evaluate the volume and C-factor influence on chemical and lightcuring composite resin polymerization shrinkage stress, using a non-rigid method that thereby provides lower stress values, causing a minimal deflection in load cell. Materials and Methods: The contraction forces of the Z-250 and Concise composite resins during polymerization were recorded in an UTM in two experiments. In the first experiment, the Z-250 composite was inserted beetwen two rectangular steel plates (6.0 x 2.0 mm), varyng the resin volumes and C-factors, in a single increment, polymerized for 20 s and the forces generated were recorded for 120 s. In the second experiment, a pair of rectangular steel plates (3x2mm) and two square steel plates (2x2mm), with varied heights (2; 3 mm, respectively), were used to determine the C-factor (0.6; 0.3) influence. Results: The polymerized Z-250 results showed that the volume variations, independent of the C-factor, had a direct influence on the shrinkage stress, different from the Concise, which was influenced by the C-factor. Conclusion: The present study showed that a higher volume of composite resins determines an increase in the shrinkage stress of light-curing composites.KeywordsC-factor. Composite resin. Polymerization. Shrinkage stress.

Download Full-text

Effect of light-curing units and activation mode on polymerization shrinkage and shrinkage stress of composite resins

Journal of Applied Oral Science ◽

10.1590/s1678-77572008000100008 ◽

2008 ◽

Vol 16 (1) ◽

pp. 35-42 ◽

Cited By ~ 18

Author(s):

Lawrence Gonzaga Lopes ◽

Eduardo Batista Franco ◽

José Carlos Pereira ◽

Rafael Francisco Lia Mondelli

Keyword(s):

Composite Resins ◽

Shrinkage Stress ◽

Polymerization Shrinkage ◽

Light Curing ◽

Effect Of Light

Download Full-text

A Review of Polymerization Shrinkage Stress: Current Techniques for Posterior Direct Resin Restorations

The Journal of Contemporary Dental Practice ◽

10.5005/jcdp-7-4-79 ◽

2006 ◽

Vol 7 (4) ◽

pp. 79-88 ◽

Cited By ~ 50

Author(s):

Luca Giachetti ◽

Daniele Scaminaci Russo ◽

Claudia Bambi ◽

Romano Grandini

Keyword(s):

Composite Resins ◽

Polymerization Process ◽

Shrinkage Stress ◽

Polymerization Shrinkage ◽

Light Curing ◽

Composite Resin Restorations ◽

Negative Characteristic ◽

Posterior Restorations ◽

Resin Restorations

Abstract In general excellent results cannot be guaranteed when using resin-based composites for posterior restorations. This is due to polymerization shrinkage which can still be regarded as the primary negative characteristic of composite resins. A review of available literature regarding the polymerization process, its flaws, and suggested strategies to avoid shrinkage stress was conducted. Several factors responsible for the polymerization process may negatively affect the integrity of the tooth-restoration complex. There is no straightforward way of handlling adhesive restorative materials that can guarantee the reliability of a restoration. At present, the practitioner has to coexist with the problem of polymerization shrinkage and destructive shrinkage stress. However, evolving improvements associated with resin-based composite materials, dental adhesives, filling, and light curing techniques have improved the predictability of such restorations. This critical review paper is meant to be a useful contribution to the recognition and understanding of problems related to polymerization shrinkage and to provide clinicians with the opportunity to improve the quality of composite resin restorations. Citation Giachetti L, Scaminaci Russo D, Bambi C, Grandini R. A Review of Polymerization Shrinkage Stress: Current Techniques for Posterior Direct Resin Restorations. J Contemp Dent Pract 2006 September;(7)4:079-088.

Download Full-text