Gerald J. Re

Shear bond strengths and scanning electron microscope evaluation of three different retentive methods for resin-bonded retainers

T he “Maryland bridge” with resin-bonded retainers has been well described in the literature.‘-‘3 Electrolytically etching the base metal markedly improved the bond strength between the metal and resin.8J0 However, to avoid contamination by saliva and foreign substances on the internal surface of the retainer, etching has been advocated after a try-in appointment.‘0~‘2 Because of the laboratory equipment needed and the sensitivity of the electrolytic technique, dentists have limited control of the quality of the metal etch. Table I. Composite shear bond strengths (megapascals)

Fracture strength of molars containing three surface amalgam restorations

L onservative amalgam preparations have been recommended over the past 25 years.‘-” In general, the more recent textbooks on operative dentistry have also stated that dental tissue should be conserved whenever possible.‘-’ Two studies have determined the axial load required to fracture teeth with varying widths of occlusal preparation.” * Mandibular molars with Class I preparations one-third greater than the intercuspal width were found to be significantly stronger than those with small restorations or no restoration at all.* Previous fracture studies dealt only with the effect of varying the widths of the occlusal preparation in molar teeth and the mesiocclusodistal preparation in premolar teeth.‘, p This article reports the effect of three surface amalgam restorations on the fracture strength of human mandibular molars.

Fracture resistance of lower molars with varying faciocclusolingual amalgam restorations

C lass I carious lesions in lower molars occur frequently. These cavities may involve the facial, occlusal, and lingual developmental grooves of the tooth. Empirically, faciocclusolingual (FOL) amalgam restorations would appear to have a “stapling” effect in resisting fracture of the tooth mesiodistally. Silvestri and Singh’ have even recommended the placement of FOL amalgam restorations as a means of temporary stabilization of lower molars with vertical incomplete mesiodistal fractures. The purpose of this research was to determine whether the FOL amalgam would enhance resistance to fracture of previously sound lower molar teeth by preparing these teeth with varying width and depth FOL preparations and then fracturing the teeth by occlusal loading.

Effect of Mandibular Molar Anatomy on the Buccal Class I Cavity Preparation

In mandibular molars, enamel dramatically increases in thickness at the buccal pit area and progresses occlusally due to an extensive concavity in the buccal dentinal core, In order to comply with the principles of operative dentistry, this anatomic variance dictates that, if the ultimate restoration is to be placed in dentin, the axial wall of a Class I buccal pit preparation should incline medially rather than follow the external contour of the tooth. The occlusal cavosurface angle of the preparation should be obtuse to coincide with enamel rod direction. Retention, when needed, should be placed at the mesio-axial and disto-axial line angles to avoid undermining occlusal intercuspal enamel, especially as the preparation approaches 2 mm occlusal to the buccal pit,

Fracturing Molars with Axial Forces

Extracted human molars were prepared with different sized occlusal cavities and restored with a high-copper amalgam. Loads were applied along the long axis of the teeth, and forces required to fracture the teeth were recorded. More force was required to break samples with the larger restorations than was required to break samples with the smaller restorations.

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In vitro evaluation of the shoulder stop in a self-threading pin

S chaefer and Reisbick’ studied the Link Series selfthreading pin (Whaledent International, New York, N.Y.). This was an improved two-in-one pin with two shear points instead of one. They found no significant differences in seating depths of either the first or second pin after testing Minim (0.024 inch/O.610 mm) and regular size (0.031 inch/O.775 mm) pins. Whaledent improved the Link Series pin technique by developing the Link Plus system with a shoulder stop and a tapered lead tip on each pin. According to the manufacturer, the shoulder stop provides “stress-free shearing in both stages, minimum apical stress at bottom of channel and more consistent and full pin depth placement.” The tapered lead tip permits easy access into the pin channel. Kelsey et a1.2 compared the Link Series and the Link Plus two-in-one pins. They discovered that the pins could be seated completely with the exception of the second pin of the Link Plus system, which required an Auto Klutch (Whaledent International) reduction gear handpiece for complete seating. However, Whaledent stated that Link Plus pins can be installed easily with a conventional latchtype handpiece, but the gear reduction handpiece facilitates channel preparation and pin placement. They also stated that the pin “will shear when seated at the shoulder stop.” They presented a schematic drawing (Whaledent International, printed in U.S.A., Oct. 1982) depicting the shoulder stop as a safeguard even with the dentinal surface. An effective shoulder stop would have to be limited by the dentinal surface to fulfill the third provision, “minimum apical stress at bottom of channel.” The purpose of this study was to determine whether the shoulder stop is effective and whether there is minimum apical stress when the pins are fully seated. The ability of the conventional speed air-driven contraangle handpiece to prepare the channel and place pins was also evaluated.

Rubber dam isolation in a difficult situation

Rubber dam retainers can be modified easily in the dental office to enable the dentist to isolate teeth with difficult restorative problems with the rubber dam. Isolation with the rubber dam enhances visibility and access and gives the dentist the opportunity to render safe, restorative care of high quality to the patient.

Modification of rubber dam clamp increases access to distal surfaces of anchor teeth

T he last tooth in the dental arch frequently requires treatment of dental caries. Using the rubber dam, dentists encounter difficulty in preparing the distoproximal box because the bow of the clamp interferes with the dental handpiece. This problem has been partly ameliorated by the clamp with a long distal extension. However, in some instances, the extension impinges on the anterior border of the mandibular ramus, causes rotation of the clamp, and decreases access to the distoproximal surface. The clamp also has a tendency to tip forward and limit access. The purpose of this study was to determine if access to the distoproxim.al surface of an anchor tooth could be increased by modifying the bow-jaw relationship of current rubber dam clamps.

Matrix band application for the occlusolingual or occlusobuccal amalgam restoration

Abstract This technique provides an expedient method of matrix application for occlusolingual and occlusobuccal amalgam preparations.