The effects of sterilization on addition silicone impressions in custom and stock metal trays.

Five groups of addition silicone impressions (four made in custom autopolymerizing acrylic resin trays and one in stock metal rim-lock trays) were made of a stainless-steel master die. The first group (control group) was not sterilized. The second group was sterilized in an ethylene oxide gas autoclave, the third group in a steam autoclave, and the fourth and fifth groups by immersion for 12 hours in 2% glutaraldehyde. Casts made from each sterilization group were found to be significantly different from control impressions by multivariate analysis of variance and should not be used to fabricate prostheses.

Bond strength of six dentinal adhesives.

This study compared the shear bond strengths on dentine of five dentine adhesives against Scotchbond 2 as a control. Dentine specimens from 225 extracted human permanent molar teeth were used in a matched-pair design, such that 45 tooth sides were treated along with the matching control for each of the five test materials. Shear bond strength testing was conducted 24 h after the completion of each specimen. Results showed that mean force (MPa) for the materials were: XR Bond, 17.1 +/- 5.1; Scotchbond Multi-Purpose, 15.9 +/- 6.5; Syntac, 13.5 +/- 8.6; All-Bond 2, 6.2 +/- 4.1; Scotchbond 2 (control composite score), 4.9 +/- 3.0; Denthesive, 3.4 +/- 1.7. Matched pair t-test comparisons with Scotchbond 2 control were: XR Bond, P = 0.0005; Scotchbond Multi-Purpose, P = 0.0005; Syntac, P = 0.0005; All-Bond 2, P = 0.0368; Denthesive, P = 0.005. Analysis of variance determined a statistically significant difference (P = 0.05) between the means of the bond strengths, which fell into four groups: Group A, XR Bond and Scotchbond Multi-Purpose; Group B, Syntac; Group C, All-Bond 2 and Scotchbond 2; Group D, Scotchbond 2 and Denthesive. In Group C, there was no significant difference between Scotchbond 2 and All-Bond 2. In Group D there was no significant difference between Scotchbond 2 and Denthesive, however, there was significant difference between All-Bond 2 and Denthesive. It was concluded that XR Bond and Scotchbond Multi-Purpose had significantly better shear bond strength than the other dentine adhesives.

Clinical evaluation of resin-bonded bridges: a retrospective study.

Eighty-five patients with a total of 103 resin-bonded bridges placed by practitioners at the University of Minnesota School of Dentistry between 1982 and 1989 were recalled for a clinical evaluation of their restorations. Tissue condition, patient satisfaction, bridge failures by location and by sex of patient, and average length of service for both successful and failed bridges were recorded. After an average service of 3.25 years, 12.6% of the fixed partial dentures had debonded. Debondings occurred most frequently in the mandibular arch. Failures occurred more frequently in men than in women, and prostheses with more than two retainers had twice the probability for problems.

Improved pontic/tissue relationships using porous coralline hydroxyapatite block.

Porous coralline hydroxyapatite blocks were implanted in the anterior region of several patients to improve the pontic/ridge relationship for a fixed prosthesis, thereby improving esthetic appearance and oral hygiene performance. A beveled incision on the palate was used to displace the flap coronofacially without leaving an area of denuded bone or graft. Flap margins were sutured to the adjacent palatal tissues. At the 2 1/2- and 3-year postgrafting follow-up, the implant area was healthy and ridge contours have been maintained. The permanent fixed partial denture is functional, and radiographic evaluation indicates the continued presence of the porous coralline hydroxyapatite implant. Three-year results have been promising enough to warrant continuing the procedure in patients requiring localized ridge augmentation.

Effects of lubrication on the retention of tapered and parallel cast post and cores.

The effects of lubrication on the retention of parallel-sided and tapered cast post and cores cemented with zinc phosphate-cement (ZnPO4) and glass ionomer cements were investigated. Seventy-two maxillary canine teeth of similar size were selected for direct, parallel-sided post and core castings. The canines were sectioned at the cementoenamel junction and mounted in resin blocks. A post space was prepared to 1.5 mm (d) x 10 mm (I) with a handpiece mounted in a surveyor. The teeth were divided into four groups: ZnPO4 without lubricant, ZnPO4 with lubricant rinsed with water, ZnPO4 with lubricant removed by solvent, and ZnPO4 with solvent alone. The same four groups were made by using glass ionomer cement. Retention was tested with a 4200 series Instron machine by pulling the castings out of the teeth. There were no significant differences in retention among the eight groups of parallel posts at alpha = 0.05. The testing procedure was repeated by using an 11 mm post with 6 degrees of taper. With tapered posts, a statistically significant reduction in retention was found in the lubricated samples when compared to the nonlubricated samples.

Dimensional stability of a polyvinylsiloxane impression material following ethylene oxide and steam autoclave sterilization.

Polyvinlsiloxane impressions were made from a stainless steel master die machined to stimulate five full veneer crown preparations symmetrically placed in an arch form. Three groups of 10 impressions each were made. Treatment groups were sterilized using an ethylene oxide gas and a conventional steam autoclave. Casts were poured and intrapreparation, height, and diameter measurements were made using a stereomicroscope, a digital electronic caliper, and a 1-inch travel dial indicator. Analysis of dimensional changes for the two groups showed that casts made from impressions sterilized by ethylene oxide are acceptable for use in the construction of fixed or removable prostheses. Casts made from impressions sterilized in a steam autoclave can be used for the fabrication of diagnostic casts and some transitional prostheses, but not for routine construction of crowns or fixed partial dentures.

Effect of prolonged ultrasonic instrumentation on the retention of cemented cast crowns.

Occasionally the need arises to remove restorations that have been cemented. Several ultrasonic tips have been developed to aid in removing cemented restorations. Earlier studies of the effects of ultrasonic vibration reveal detrimental effects on amalgam surface and marginal integrity and, at short instrumentation periods (2.5 minutes) in vitro, no significant effect on the retention of cemented cast crowns. Twenty identically machined metal dies had nonprecious crowns waxed, cast, and fitted. Each casting was cemented twice with glass ionomer and zinc phosphate cement. Each cement was tested for the effects of vibration on retention. The cements were mixed according to manufacturer's specifications, placed under 5 kg load, then placed in 37 degrees C water and contained in a humidor. Retention was tested with a 4202 Instron machine to determine the forces needed to overcome retention. Retention ranged from a high of 125.36 kg for glass ionomer without vibration to a low of 19.11 kg for zinc phosphate vibrated for 12 minutes. The use of vibration is considered an advantageous adjunct to other cast restoration removal devices.

Bond strength of a light-cured and two auto-cured glass ionomer liners.

Ninety-nine extracted human molar teeth were used in this study comparing the shear bond strengths on dentine of one light-cured and two auto-cured polyalkenoate (glass ionomer) cements. Bond strength can be influenced by differences in tooth structure. A balanced-incomplete block design (Hull and Nie, 1981) was used to reduce variation attributable to such differences. Cements were applied to paired dentine surfaces in combinations such that 66 tooth sides were treated with each material. A light-cured dentinal adhesive and composite resin restorative material were then placed and shear bond strength testing was conducted exactly 24 h after the completion of each specimen. Mean forces (MPa) for the three materials were compared using an appropriate analysis of variance model (balanced-incomplete-blocks) The shear bond strengths (MPa) of the light-cured liner (Espe, Seefeld/Oberbay, FRG) was 4.71 +/- 1.16. Vitrabond showed the greatest variance of all three materials tested, however this material's average bond strength was greater than the maximum achieved for the other materials. Student-Newman-Keuls comparison of means showed that all cements differed significantly from each other (alpha = 0.05). It is concluded that the light-cured glass ionomer liner exhibited significantly better shear bond strength performance than the two auto-cured glass ionomers tested.

Retentive strength of six temporary dental cements.

The retentive strength of three zinc oxide-eugenol cements and three noneugenol-containing zinc oxide cements and the effect of the addition of petrolatum on retention were tested. The addition of petrolatum was found to affect retention of the cements significantly. Retention strengths varied from 1.6 kg to 40.0 kg. Of the Class 1, Type 2, systems tested, noneugenol cements had higher retentive values than did the eugenol-containing cements.

Technical note: fluoride pre-treatment effects on microleakage of a resin bonding agent.

This pilot study reports the effect of fluoride pre-treatment of dentin and enamel on microleakage of a resin bonding agent. Pairs of circular class V cavities involving 50% enamel and 50% cementum were cut in 12 extracted third molars. Each tooth contained a control and a treatment cavity (matched-pair design). A stannous fluoride solution (0.717% SnF2, Gel-Kam, Scherer Laboratories, Dallas, TX) was applied to the entire treatment preparation of each tooth. A dentin resin bonding system (Scotchbond 2 with Scotchprep, a dentin primer, 3M Dental Products Div., St. Paul, MN) was applied per manufacturer's instructions. Silux resin (3M) was placed over the resin bonding agent, light-cured, and finished. The teeth were subjected to 500 temperature cycles between 5 and 55 degrees C. A silver nitrate staining technique was used for evaluation of microleakage. The mean leakage for the control was 2235 +/- 1146 microns, and 2105 +/- 1052 microns for the fluoride treatment sites. It is concluded, from this pilot study with small sample size, that pre-treatment with fluoride of dentin and enamel prior to the placement of a resin bonding agent produced no significant change in microleakage (Student's t test for paired samples, p = 0.6492).

Current prosthodontic practice: a dental laboratory survey.

A survey was distributed to dental laboratory owners at the 1988 annual meeting of the Minnesota Dental Laboratory Association. Current laboratory practice in infection control, the use of nonprecious alloys, the amount of time devoted to complete removable prosthodontics, and complete denture laboratory techniques were surveyed. Responses indicate a moderate level of awareness and compliance with infection control techniques recommended by the American Dental Association, a declining demand for removable prosthodontic services, a high percentage of use of nonprecious alloys, and a very high rate of porcelain occlusion requested by dental practitioners. Comparisons with other laboratory surveys and the implications of these results for undergraduate education in prosthodontics are discussed.