James B. Summitt

Annual review of selected dental literature: Report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

This review was conducted to assist the busy dentist in keeping abreast of the latest scientific information regarding the clinical practice of dentistry. Each of the authors, who are considered experts in their disciplines, was asked to peruse the scientific literature in their discipline published in 2016 and review the articles for important information that may affect treatment decisions. Comments on experimental methodology, statistical evaluation, and the overall validity of conclusions are included with many of the reviews. The reviews are not meant to stand alone but are intended to inform the interested reader about what has been discovered in the past year. The readers are then invited to go to the source, if they want more detail.

The resistance to tensile, compression, and torsional forces provided by four post systems.

This study measured the force required to displace four different endodontic posts (an experimental, Para-Post, Flexi-Post, and V Lock) when tensile, torsion, or compressive forces were applied. Extracted mandibular premolars were decoronated at the cementoenamel junction, the roots were divided into groups of similar size, and the pulpal tissue was removed. The canals were enlarged, cleaned, and filled with gutta percha. Post preparations were made, and the posts were cut and cemented into the post spaces with resin cement. The roots were notched with a separating disc and lowered into a metal tube filled with acrylic resin. Two Minim pins were placed into the coronal dentin paralleling the post. Composite resin cores were made around the coronal 4 mm of the posts and the two pins for 10 specimens from each group. The specimens were placed into a standardized fixture and a load applied until failure. The tensile load required to pull the experimental post and resin was significantly less than the load required to remove the threaded posts. Flexi-Posts provided the greatest resistance to torsion and tensile loading. The compressive load required to fracture the core over the V-Lock post was significantly greater than the other post systems.

Fracture resistance of amalgam coronal-radicular restorations

The effect of pulp chamber depth and extension into the root canal space on fracture resistance was examined on endodontically treated teeth with coronal-radicular amalgam restorations. Six groups of 10 mandibular molars were mounted in acrylic resin, and crowns were ground apically until the wall height of the pulp chamber was 2, 4, or 6 mm. Three millimeters of gutta-percha was removed from the three canals of one-half the teeth and amalgam was condensed into the canal space to a height 7.5 mm above the cementoenamel junction (CEJ). The remaining teeth had amalgam condensed from the floor of the chamber to 7.5 mm above the CEJ. The amalgam restorations were loaded with an Instron instrument (Instron Corp., Canton, Mass.) until failure. Amalgam extension into the root canal space contributed minimally to the fracture resistance of the amalgam coronal-radicular restoration with four or more millimeters of chamber wall. If less than 4 mm of chamber wall height remained, however, the fracture load was substantially increased. Amalgam extension into the root canal space should be confined to teeth with limited remaining pulp chambers.

Conservative cavity preparations

When a caries lesion is detected, non-surgical means of treatment (fluorides, antimicrobials, and patient education) should be used unless it is a frank caries lesion. In that case, the lesion should be treated restoratively, but the patient should also be educated and treated to reduce caries risk. When the frank caries lesion is relatively small, the restorative treatment should simply involve removal of carious dentin and overlying unsupported enamel and placement of the restorative material. Of course, for weakened areas of the tooth, more extensive restorations may be indicated.

Effect of a resin lining and rebonding on the marginal leakage of amalgam restorations

This in vitro study compared microleakage in Class V amalgam restorations with three different lining agents and with no lining agent, with and without resin rebonding of the margins. Eight groups of ten molars were divided into four pairs of groups. Class V preparations were cut in the facial surfaces of each molar so that the occlusal margin was in enamel and the gingival margin in dentine. The preparations in one pair of groups received no lining agent; the preparations in the remaining three pairs of groups were lined with one of the following: Copalite, Universal Bond 3 (UB3) Primer and Adhesive, or UB3 Primer only. The enamel walls of the preparations receiving the UB3 Primer and Adhesive were etched prior to applying the lining material. Amalgam was hand condensed into each preparation. In one of each pair of groups, the margins of restorations were treated with 37% phosphoric acid gel, rinsed and dried, and UB3 Adhesive was applied over amalgam and tooth margins and polymerized (rebonded). Specimens were thermocycled, stained and sectioned. Microleakage was graded using a stereomicroscope. Mean microleakage scores for occlusal and gingival margins were calculated and analysed. At enamel margins, non-rebonded Copalite and all rebonded specimens showed less microleakage than the other non-rebonded groups. The group lined with UB3 Primer only and rebonded showed significantly less (P < 0.01) microleakage at enamel margins than all the other groups except the group lined with Copalite and rebonded. At cementum/dentine margins, restorations lined with UB3 Primer and rebonded showed significantly less microleakage than the other groups.