RELEVANCE OF POSTERIOR COMPOSITES TO ESTHETIC DENTISTRY

Lect.4 Esthetic and Operative Dentistry Dr. Ameer H, AL-Ameedee
Posterior composite
RELEVANCE OF POSTERIOR COMPOSITES TO ESTHETIC DENTISTRY:
When esthetic dentistry began its evolution, the posterior teeth were considered unimportant. As patient expectations have increased, more focus has been placed on the esthetic contribution of posterior teeth (Figure 1). With the mechanics of mandibular function, as humans speak, laugh, and exhibit the behaviors considered human, the incisal edges of the lower anterior teeth and the occlusal surfaces of the posterior teeth are critical (Figure 2).













Interestingly, habits such as pursing of lips and raising the hand to cover the mouth are the same regardless of whether patients dislike the appearance of their anterior or their posterior teeth, the modern anterior cavity preparation that has little or no mechanical undercuts and long infinity edge margins bears little resemblance to the silicate and gold foil preparations that anterior composite has replaced.
Filler Level of the Various Classes
The most important material characteristic in a composite is the filler level by volume because that level will control or minimize the shrinkage, determine the strength and durability, and establish the handling and optical properties of the material. Generally, the higher the filler level, the higher the strength and the lower the shrinkage. Hybrids have the highest-volume filler fraction, followed by microfills and nanofills, which have comparable values. Percentage values in the high 70s are possible with some of the hybrid materials, whereas the microfills and nanofills generally have percentage values in the high 60s. The macrofills were not widely distributed, but they achieved around 65% in volume percent, so they were not as highly packed as a hybrid. They were able to achieve fairly good strength because of the large particles, but not the dense packing. Macrofills
did not finish well because the particle sizes
were so large, making them difficult to polish.
Once the material was in place and subjected
to wear or loss of the matrix material, particles
protruded and gave the restoration a rough
texture. There is no need for mechanical
undercutting to attain long-term retention of
the restoration. This means the dimensions of
the preparation for posterior composites can be
minimized both at the occlusal isthmus and in
the width and depth of the gingival box. Clinical
experience teaches that smaller posterior com
posite resin preparations exhibit restorative longevity far better than larger-sized traditional preparations.

APPLICATION OF SPECIFIC COMPOSITES
Composites can consist of specialized compositions to best meet the requirements of their application. Changes can be made in shrinkage characteristics, curing method, optical properties, and handling characteristics. Filler level is often varied to change viscosity and handling characteristics. One material may be thin, whereas another one may be very heavy or very thick depending on the use. A good example is a flowable composite, which contains lower filler levels so that it has more of a flowing character and a lower viscosity. Very highly filled composites will have stiff handling characteristics, with better ability to be sculpted and shaped(Figure 1).
SENSITIVITY:
Post-operative sensitivity, with amalgam, for example, sensitivity commonly occurs immediately after placement and lasts for a week to 10 days. During the first several days after restoration a definite gap of several microns exists between the walls of the preparation and the amalgam restoration, thereby allowing the transfer of fluids. The sensitivity associated with posterior composites can last considerably longer and demonstrate appreciably greater intensity. The mechanism of sensitivity undoubtedly is somewhat complex. Regardless of the cause, the pain can be directly related to the odontoblast itself. Whatever creates a negative pressure on the odontoblastic process creates a pain response. Sensitivity often can be avoided or eliminated by proper use of a dentin bonding agent. The agent either seals the surface of the dentinal tubules or actually penetrates the individual tubules and isolates the odontoblastic process from the external environment. This can be accomplished by proper use of a dentin bonding agent or a dentin desensitizing agent.
Strength-Resistance Compromises
1- Flowable composite: Because it has a less filler, has lower strength (Figure 2). It contains more resin so it will also have higher shrinkage values. As a result, this is not a good restorative material for stress-bearing conditions. It is used today more as a base and liner because of its flow characteristics, which allow it to adapt to tooth surfaces quite well.
2- packable composite: These materials use very high filler levels and larger filler particles to give the material a very high viscosity (Figure 2-20). they can be handled somewhat like an amalgam and are condensable. These materials were designed to overcome one frustrating feature of placing posterior composite restorations, which is maintaining good proximal contact. It is impossible to force composite into a preparation and actually expand the space between the teeth with the material. The material is passive, so the dentist must establish adequate tooth separation before placing the restoration.

Fluoride-Releasing Composites: The last class of materials consists
of fluoride-releasing composites (Figure 3).
1- Compomers: One of the limitations of a composite is the
hydrophobic or “water-disliking” quality of the matrix materials.
Because these matrix materials do not absorb much water, it is
hard to dissolve fluoride out of the composite. Most fluoride-releasing
composites release a very low amount of fluoride when compared
with glass-ionomers. Glass-ionomers have a much different

polysalt matrix that can absorb water much more readily, providing a better
exchange of the fluoride ions from within the glass-ionomer. The glass-ionomer
also has a higher level of porosity than the typical composite material, making
it more efficient at releasing and reabsorbing fluoride. It is very questionable
whether the fluoride release from composite materials is great enough to be of
any therapeutic benefit.

3- Beautiful II: Second-generation of giomer, which has the power to release
Fluoride. Its fillers are composed of glass particles, S-PRG fillers (surface
pre-reacted glass), and discrete nano-fillers. The PRG fillers are built in by
acid-base reactions between Fluoride containing glass and Polyacrylic acid
in the presence of water to form wet Siliceous hydrogel, and the PRG technology
can be divided into a complete reaction type (FPRG) and
surface reaction type (SPRG); in FPRG (Full pre-reacted glass), the complete
glass filler reacts with polyacid, while in SPRG only the surface of the glass filler
reacts while the glass core remains intact (Figure 3, 4).


THE FIVE Cs:
1-Cracks and Fractures
The original hope was that because composite restorations are adhesive, the composite would be able to repair or splint the tooth together after the cavity preparation has weakened the tooth. Crack initiation must be carefully evaluated and managed during cavity preparation and placement of composite and finishing. This addresses both crack initiation in the tooth and crack initiation or propagation in the composite material.
2- The C-Factor
The guide to the management of polymerization shrinkage in various cavity preparations. C-factor stands for configuration factor and expresses the ratio of internal walls versus external surfaces. A second way to describe C-factor is internal surface area versus external surface area. C-factor is a fundamental flaw in traditional cavity preparations because the parallel walls for resistance and retention work against the dentist during polymerization shrinkage (Figure 10-3).[[[[[[[[[page-271