The International Journal of Prosthodontics, 02/1996

This study investigated the relationship between abutment total occlusal convergence angle (taper) and the resistance of cemented crowns subjected to dynamic loading. Crown and abutment analogs were placed using zinc-oxide-eugenol, zinc-phosphate, glass-ionomer, or resin composite cement. Total occlusal convergence angles of 2.5, 5, 10, 15, 20, 30, and 40 degrees were tested. Dynmic stresses were applied to the luted components until the bond failed for the components reached 10 6 load cycles. The data were analyzed using the staircase technique. The relationship between convergence and resistance was approximately linear for all the cements tested. Crowns luted with resin composite cement were more resistant to dynamic lateral loding than those placed using glass-ionomer or zinc-phosphate cements. Crowns luted with zinc-oxide-eugenol cement presented the least resistance to cyclic lateral stresses.

This in vivo study evaluated the fracture resistance of bovine teeth with prefabricated carbon fiber posts. Fourteen bovine teeth having similar lengths and dimensions were mounted in an acrylic resin block having a simulated periodontal ligament. The post space was prepared using two calibrated drills that provided an 8.5 mm post length. The prefabricated carbon fiber post was luted with a resin luting agent, and the core was made using the system's autopolymerizing resin core material. A crown was luted to each prepared tooth. Each test specimen was intermittently loaded (250N) at an angulation of 45 degrees to the long axis of the tooth at a frequency of 2 loads per second. Four of the roots had an incomplete longitudinal fracture after loading. The results of this study were compared to a previous study by the authors that had been conducted under similar conditions with prefabricated parallel-sided posts (Para-Post) and tapered, individually cast posts. The failure rates of the two types of posts from the previous study were significantly higher (Logrand test; P.02) than those of the carbon fiber posts.

Interim soft denture liners or conditioners may be valuable therapeutic materials. The life of these liners varies, but it can be extended by the use of a poly(methyl methacrylate) coating material (Monopoly). This study evaluated the ability of Monopoly to prevent water absorption and plasticizer loss from an underlying tissue conditioner (Visco-gel). Disk specimens of Visco-gel coated with Monopoly were immersed in water that was sampled at 24 hours, 1 week, 2 weeks, and 1 month. Uncoated Visco-gel samplea acted as controls. Water absorption was determined gravimetrically at each time interval and decanted water was subjected to separation by reversed phase high performance liquid chromatography for component identification. All samples suffered significant initial weight loss followed by a trend toward weight gain in the uncoated control group, probably because of water absorption. The Monopoly coating appeared to reduce this effect. Plasticizer loss from the tissue conditioner was below quantifiable limits by high-performance liquid chromatography, but methyl methacrylate monomer loss from the Monopoly coating was demonstrated. Some clinical implications are discussed.

Calcium phosphate ceramic coatings with a hydroxyapatite chemistry applied on the surface of dental implants eliminate the need for initial mechanical retention and decrease the time necessary for bonding the implants to the bone. Hydroxyapatite-coated implants retrieved from patients were found to be compatible and to have bonded strongly to the bone, but the coatings showed thinning because of partial or total loss of coating material. This study compared the behavior in bone of newly developed fluorapatite and heat-treated hydroxyapatite coatings, with the clinically used hydroxyapatite coatings used as controls in experimental studies in dogs. The biologic responses to fluorapatite and heat-treated hydroxyapatite coatings were the same as those to hydroxyapatite coatings, and bone condensation around all coatings was histologically evident. However, the coating thickness of the fluorapatite and heat-treated hydroxyapatite coatings remained stable with only minor changes during the observation period of 24 months.

A series of 10 incrementally larter, machined ASTM Grade 23 titanium non-segmented (UCLA type)abutments was loaded off axis with 133 N and cycled at 1150 verticle strokes per minute and 28 counterclockwise rotations per minute to determine screw joint stability. Abutment internal hexagonals ranged from 0.1065 to 0.1110 inches. External hexagonal mean flat-to-flat width was 2.684 mm. Rotational misfit between internal and external hexagonals ranged from 1.94 degrees for the smallest abutment to 14.87 degrees for the largest. Scew joint failure ranged from 134,000 to 9.3 million cycles. The tightest matrix/patrix hexagonal screw joint failed at a mean of 6.7 million cycles. This study indicated that there was a direct correlation between hexagonal misfit and screw joint loosening. The greater the hexagonal misfit, the greater the probability of screw loosening. A rotational misfit of under 2 degrees provided the most stable and predictable screw joint.

This study evaluated posterior resin-bonded prostheses using inlays as retainers. Thirty-nine patients missing at least one premolar or first molar received 51 resin bonded fixed partial dentures with high noble alloy inlay retainers and a metal ceramic pontic. Resin luting material bonding to the framework was secured by the Silicoating method (24 fixed partial dentures), lost sugar method (13 fixed partial dentures), or tin plating (14 fixed partial dentures). Clinical examinations were performed 1 week, 1 month, 6 months, 1 year, 2 years and 5 years after cementation. None of the fixed partial dentures with silicoating or sugar crystal impressions lost retention, whereas two of the tin-plated fixed partial dentures required replacement. Resin-bonded inlay-retained prostheses appear to be a faborable alternative to other type of fixed partial dentures.

Adhesion failure of resilient lining materials to poly(methyl methacrylate) denture base material is a problem that is encountered clinically. This study compared the shear bond strength of some of the commercially available resilient lining materials to various denture base resins. Significant differences were observed in the shear strengths between the selected resilient liners and the denture base materials. Coe Super Soft specimens failed principally cohesively. Molloplast-B specimens always failed cohesively and Novus specimens always failed adhesively. Therefore, it was apparent that the bond strengths of Molloplast-B and Coe Super Soft specimens exceeded the cohesive strength. The bond strength of Novus was dependent on the denture base material and was greatest with Lucitone 199 and TS 1195.

This study was conducted to examine prevalence of craniomandibular disorders in young adults compared with that in older subjects. In addition, the relationship between various oral conditions and this dysfunction was studied. No difference was found in the incidence of craniomandibular disorders between the groups. Classification according to the Helkimo index showed significant difference in complaints of craniomandibular disorders symptoms between the groups. Most of the older patients did not complain of mild disorders. The results suggest that conditions such as the number of teeth, presence or absence of dentures, and the type of denture worn are not important factors in the pathogenesis of craniomandibular disorders.

This study compared lingualized occlusion and completely balanced occlusion using a simulation device. Sixteen pressure transducers were placed in the simulated residual ridge area supporting the test dentures. Lingualized occlusion was found to transfer stresses from the occluding denture.

The working times of five poly(vinyl siloxane) impression materials were estimated by evaluating the dimensional accuracy of stone dies of impressions of a standard model made at successive time intervals. The stainless steel standard model was represented by two abutments having known distances between landmarks in three dimensions. Three dimensions in the x-, y-, and z-axes of the stone dies were measured with a traveling microscope. A time interval was rejected as being within the working time if the percentage change of the resultant dies, in any dimension, was statistically different from those measured from stone dies from previous time intervals. The absolute dimensions of those dies from the rejected time interval also must have exceeded all those from previous time intervals. Results showed that the working times estimated that this method generally were about 30 seconds longer than those recommended by the manufacturers.

In this study, soft tissue discoloration including the marginal gingiva, gingival papilla, and attached gingiva were evaluated in subjects with artificial crowns and compared to the soft tissue of natural teeth using a spectrophotometer. Gingivae around artificial crowns had a lower value (L*) and chroma (C*ab) than the gingivae surrounding natural teeth. Hue (HAB) shifts toward red-purple were frequently noted. There was generally a more noticeable color difference (E*ab) in the marginal gingiva and gingival papilla of teeth with crowns than was found in the attached tissue.