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Posterior composite restorations are common. It is important for the dental practitioner to understand the science behind these restorations and learn techniques to effectively and efficiently complete them, providing patients with a better outcome and improving the overall practice.
Despite methods and materials that were common in the past, when patients come into a dental practice today, they rarely ask for tooth repair by use of amalgam. Most individuals are now more concerned with the "black," metallic appearance of amalgam material. Today's dentists use many different composites when restoring posterior teeth. According to a survey by the American Dental Association, composite-resin restorations now outnumber amalgam restorations in the United States. In fact, a significant number of US dentists do not ever use amalgam.1 Therefore, to perform at the highest level, it is important to have a clear understanding of composite-resin restorations.
For large preparations, dentists currently depend on composite restorations. Reasons include the following:
1. The use of amalgam has declined greatly. In today's society, with an immense focus on appearance, patients are looking for options that are more esthetically pleasing than amalgam. Additionally, composite materials have been greatly improved, allowing them to be used in larger restorations, including multi-surface restorations. According to research compiled from the Dental Registry and DNA Depository project, composites slightly outperformed amalgams over a period of 5 years.2
2. Annual failure rates of composites are low. Today's scientific literature, backed by supporting evidence, demonstrates that composite restorations have low annual failure rates, similar to amalgam restorations,2 although some research has shown amalgam to have greater longevity.3 Even in Class I and Class II restorations, 90% of composite resins had failure rates of just 1% to 3%.4 Demarco and colleagues' review of 15 years of manuscripts on posterior composite restorations found at least a 5-year follow-up period on these clinical cases.
It is common today to use composite resin for restorations, for several reasons. Four of those reasons were explained in a 2006 article by Deliperi et al,5 as follows:
1. Continuous development
Resin-composite materials are constantly evolving to offer better physical properties and esthetics. Additionally, they are generally easier for dentists to use, including the ease of use of the adhesive side.
2. Patient demand
As previously mentioned, much emphasis today is placed on appearance. Patients have come to expect results that look as natural and as tooth-like as possible, which is more esthetically pleasing and less noticeable.
3. Patient (and dentist) desire to save any remaining sound tooth structure
Sound tooth structure allows more bonding to enamel, which will protect more of the tooth because less of the dentin is removed. It is important to respect the biologic components of the tooth.
Cost remains an influential factor. Composite resin necessitates less chair time for the dentist, which equates to lower cost for the patient when compared with any other indirect procedure.
Failure of Composites
Despite advances in materials and techniques, restorations may fail. According to an article by Spencer et al, replacement of failed restorations consumes 60% of the average dentist's practice time. In 2006, results from clinical studies suggested that of the 173.2 million composite and amalgam restorations that were placed in the United States, more than 50% were replacements for failed restorations. One of the most common reasons that restorations failed was recurrent decay at the site of the composite-tooth interface, which has continued to be the main reason for replacement of composite restorations.6
The dentist must take certain factors into consideration when performing restorations, such as the shrinkage of materials when polymerized. The composite and the tooth should blend in well, and the interface between the composite and the tooth should be fairly invisible. The most important aspect is the occlusal anatomy. Function must always come first. Restoring teeth to a shape and anatomy that allows them to function well in the patient's mouth is the main goal.
It is important to maintain a conservative mentality, preserving as much of the tooth structure as possible when removing an old restoration or preparing a tooth due to a new lesion. Removal of sound tooth structure and performing any extension for prevention are older techniques that are not necessary to employ today. Limiting the preparation to removal of infected (soft) dentin and existing restorative materials is all that is needed before placing a bonded restoration.
According to a review by Arandi, the presence of a peripheral enamel margin reduced the degradation rate in resin-dentin interfaces for most materials. It provides better protection for the pulpal complex; if it is less than or equal to 0.5 mm, a liner will be needed.7 If the clinician is working with secondary decay or a previously performed restoration that is fractured or is very deep, some considerations will be necessary to manage the deep dentin. A material that is capable of sealing the dentin will be needed because when performing acid etch, prime, and bond, the clinician does not want to have any resin globules going through the dentin tubules (cytotoxic effect) and ultimately affecting the vitality of the tooth.
Another important aspect of restoring teeth is the occlusal analysis. Occlusion must always be considered when performing restorative dentistry. Occlusion will affect not only the teeth that remain, but also the tooth that is being restored.
Factors to be considered:
Centric relation: Condyles fully seated in the glenoid fossa.
Checking occlusion: Preoperative occlusal analysis must be completed before restoration removal.
The clinician will not always need to perform an adjustment, but when restoring a tooth that has signs of instability, such as fracture lines or excessive wear, it makes sense to see whether the patient may benefit from a mild occlusal adjustment.
During the restoration procedure, overall, it is important to consider the following:
1. Field isolation. There are many important reasons why the clinician will want to maintain a clean surface and tooth field without any contamination of the area, whether from putting the tongue back or otherwise.
2. Moisture control. Moisture control is important not only after cleaning the tooth but during the procedure itself to prevent contamination. It is one of the reasons why Class II restorations have a higher failure rate: generally, they will fail in proximal boxes, likely due to lack of moisture control.
3. Avoid contamination. During the procedure, the clinician should make sure not to contaminate the bonded surface. Contamination can occur with something as minor as a cheek touching the area of the field.
4. Protect patients. It is imperative to protect the patient from chemicals and foreign objects (ie, anything that may fall into his or her mouth).
Tools can be used to attach a light piece for illumination. This helps to provide the aspects of field isolation and seals the back of the throat to protect against contamination. However, it does not control crevicular fluid because it is suctioning fluid from the patient's mouth. If the clinician has a Class II with deep proximal margins and crevicular fluid, it will not help to avoid contamination in the area. Ways to help avoid contamination include use of a rubber dam.
The rubber dam (Figure 1) is often the best option for the above four considerations because it addresses all of them, including good moisture control in the proximal boxes. If the case has a deep box, the clinician can always place a chord into that gingival sulcus. The rubber dam is placed and correctly inverted into the gingival margins in one or both boxes.
The rubber dam provides absolute isolation. It will retract the lips and tongue and will allow complete control of crevicular fluid in Class II restorations.
Four Ways to Bond Remaining Tooth Structures
Both the rubber dam and the floss ligature technique allow access to the enamel and the area to be etched before placing the universal adhesive and using it in a self-etch mode before placing it on the dentin.
To begin the restorative aspects of the procedure, the first consideration is to plan how to bond the remaining tooth structure. Bonding can be done in four different ways.
1. Three-Step Technique
The three-step technique is considered the gold standard for full mouth rehabilitation; it continues to yield the best results.8 The steps for this method are:
1. acid etch the enamel
1. acid etch the enamel
2. self-etch only on dentin
a. can use two separate products:
one that comes in one bottle or
one that comes in two bottles.
Many studies have shown that the extra coat of the adhesive is productive to having the ideal thickness, proper layering, and better bonding capabilities.8 The clinician will want to ensure to acid etch the enamel first. If there is enough remaining dentin thickness, it may be incorporated into the bonding before using total etch. Then the clinician can use prime and bond or universal adhesive, whichever is used in the practice. Although universal adhesives work well, the clinician does not need to eliminate phosphoric acid etching from enamel and selective etching before applying the self-etching mode onto the dentin.
2. Floss Ligature Technique
When using a rubber dam for a patient who has deep boxes, if the clinician finds that the depth is so great that it requires elevation of the margin, a technique that allows inversion of the rubber dam will be desired. This is the floss ligature technique. This technique provides the clinician with complete access to the tooth and the surrounding area that must be accessed. The floss ligature technique allows the clinician to access very thin enamel on both mesial and distal aspects of the preparation as well as the buccal and lingual.
3. The Split Tofflemire Technique
By using a Tofflemire band (Figure 2) and cutting the active portion in half with scissors, the clinician will remove 50% of the band. After cutting the band down, it is sliced in half, used without a wedge, and placed around the tooth to elevate the margin. This is done to bring the gingival margin into better occlusion so that it can achieve good contact, creating a margin that is more easily reached.
After the first layer of the composite is cured, a second Tofflemire band is used. Because the clinician now has the cured composite used to elevate the margin, the clinician can use a wedge and not have the shape of the embrasure indented, nicked, or altered. If the clinician needed to place the wedge on the first increment of the composite, it would lead to a flat and wide embrasure area following the anatomy or shape of the wedge itself.
First, the gingival floor should be raised without a wedge by cutting 50% of the band, performing a light-cure, and using a second band. This will allow the clinician to wedge and use the composite and tooth structure present on the distal portion to put on pressure, separate the tooth, and compensate for the thickness of the band, now reestablishing contact.
4. The Customized Matrix Technique
The customized matrix technique may accelerate the process for some restorations.
Bulk-fill materials for restorations have many advantages, including less clinical time, which helps when performing quadrant dentistry. During rubber dam isolation, the dam needs to be inverted into the gingival sulcus to keep the enamel margins clean and dry, and the area can remain free of contaminants. Then the clinician can acid etch, prime and bond, and deliver the composite resin through the sonic tip system. After it is delivered, it flows noticeably well around the tooth. After waiting 5 to 10 seconds to be better able to handle it, the clinician then removes the excess and attempts to get into the small grooves of the tooth, developing a dental occlusal anatomy. It is esthetic to have the more natural appearance of the layering technique while also using bulk-fill restorations. They make the process faster and are appropriate for quadrant dentistry as well.
It is important to consider whether the patient will experience any difficulties if his or her layers are too thick or beyond 4 mm. According to a 2016 study, the use of a 4-mm incremental technique with a flowable bulk-fill resin composite showed slightly better, although not statistically significant, durability when compared with 2 mm.9 Therefore, the clinician should be cautious when restoring teeth with bulk-fill composite materials of more than 4 mm in depth.
In conclusion, there are many reasons why composite-resin restorations are now favored over amalgam, including improved physical and handling properties, polishability, and more esthetic material. In recent years they have experienced significant improvement of their physical properties and esthetic superiority. Additionally, the concept of minimally invasive and adhesive dentistry has been made possible by the chemical advantages of composite materials when compared with amalgam.
About the Author
Mario F. Romero, DDS
Assistant Professor, Department of Restorative Sciences, Augusta University, Augusta, Georgia
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