Michael E. Razzoog

Precision of fit: The Procera AllCeram crown

STATEMENT OF PROBLEM Strength, color stability, and precision of fit are requirements for all-ceramic restorations. The Procera AllCeram crown system, composed of a densely sintered high-purity alumina core combined with a low fusing surface porcelain, appears to satisfy most of these requirements. However, evaluation of marginal fit has not been reported. PURPOSE This study measured the precision of fit of the Procera AllCeram crown fabricated with Procera CAD/CAM technology for the premolar and molar teeth fit to a die. MATERIAL AND METHODS Five ivorine maxillary first premolars and first molars were prepared for full-coverage crowns. Preparations were standardized with a convergence angle of 10 degrees, chamfer margins of 1.3 to 1.5 mm circumferentially, and occlusal reduction of 2.0 mm. AllCeram crowns were fabricated for the dies, and the fit of the crown to the die was determined by using a standardized procedure with a silicone impression material that served a dual role: (1) as a retrievable luting agent, and (2) to replicate the internal aspects of the crown. Laser videography was used to measure the gap dimension between the crowns and the dies at the marginal opening, the axial wall, the cusp tip, and the occlusal adaptation measurement locations. Mean gap dimensions and standard deviations (SDs) were calculated for marginal opening, internal adaptation, and precision of fit. RESULTS Mean gap dimensions and standard deviations at the marginal opening for the premolar and molar crowns were 56.0 microns SD +/- 21 and 63.0 microns SD +/- 13 microns, respectively. The mean gap dimensions and SDs of the internal adaptation were 69.0 microns SD +/- 17 microns for axial wall, 48.0 microns SD +/- 12 microns for cusp tip, and 36.0 microns SD +/- 7 microns for occlusal adaptation for the premolar crowns; and 49.0 microns SD +/- 3 microns axial wall, 67.0 microns SD +/- 21 microns cusp tip, and 74.0 microns SD +/- 29 microns occlusal adaptation for molar crowns. Precision of fit and SDs for premolar and molar crowns were 52.0 microns SD +/- 19 microns and 63.0 microns SD +/- 20 microns, respectively. Mean marginal openings and precision of fit gap dimensions for the crown groups were not significantly different at the .05 level. However, gap dimensions that defined the internal adaptation at the measurement locations were different (P < or = .05). CONCLUSION Mean gap dimensions for marginal openings, internal adaptation, and precision of fit for the crown groups were below 70 microns. These findings show that the crowns studied can be prescribed with confidence knowing that the precision of fit will consistently be less than 70 microns.

Shear bond strength of a resin cement to densely sintered high-purity alumina with various surface conditions

Procera Sandvik AB is now manufacturing a densely sintered high-purity alumina core for an all-ceramic crown designed for anterior and posterior restorations. Whereas the material holds promise on the basis of in vitro strength tests, the ability to alter the surface and use conventional bonded resin cements has not been reported previously in the literature. Samples of the core were treated by means of one of four methods routinely used for all ceramic restorations, and then a commercially available resin cement was bonded to the surface. A shear bond test of the adhesion showed that the highest shear bond strengths of 11.99 +/- 3.12 MPa were obtained with air abrasion at 80 psi and 50-microm alumina particles.

Critical evaluation of patient responses to dental implant therapy

STATEMENT OF PROBLEM Successful rehabilitation of the edentulous condition requires functional and psychosocial adaptation by the patient. Quality of life is markedly affected by the amount of satisfaction or dissatisfaction with their dental therapy. Patient concerns are primarily related to comfort, function, and esthetics. When these do not meet the patients expectations, anxiety, insecurity, diminished self-esteem, and introversion are typical psychosocial responses. PURPOSE The objectives of the study were to assess the patients subjective feelings about: (a) comfort, (b) function, (c) esthetics, (d) speech, (e) self-image, and (f) overall dental health with their existing complete dentures, and after implant therapy and prosthodontic rehabilitation. MATERIAL AND METHODS Two health-related quality of life (HRQL) questionnaires were developed to evaluate the effectiveness of dental implant therapy; one dealing with their feelings about their conventional complete dentures, and the second dealing with implant therapy. The first questionnaire was administered with supervision before receiving implant treatment. The second questionnaire was administered within 1 year after completion of prosthetic rehabilitation. Twenty-six patients who received implants to support a mandibular prosthesis and a new maxillary denture formed the experimental population. RESULTS Discriminative and evaluative analysis of subjective patient responses provided reliable, accurate, and reproducible results. Assessment of subject feelings before and after implant therapy and prosthodontic rehabilitation demonstrated significant differences when before treatment responses were compared with the responses after therapy. CONCLUSIONS Significant differences for comfort, function, speech, esthetics, self-image, and dental health were demonstrated when conventional complete dentures and dental implant therapy were compared. HRQL data provided scientific evidence of an improved quality of life after dental implant therapy (p < 0.000).

An in vitro investigation of the wear of enamel on porcelain and gold in saliva

This study compared enamel wear against low-fusing porcelain (Procera All-Ceramic) with the wear against feldspathic porcelain (Ceramco) and gold alloy (Olympia). Human enamel abraders were polished to a 3 microns variance on silicon carbide paper. Five enamel abraders were abraded against five disks that were fabricated from (1) gold alloy polished to 1 micron variance, (2) autoglazed feldspathic porcelain, and (3) autoglazed low-fusing porcelain. The enamel sample was tested in human saliva in a wear machine with a constant load of 1 pound during 10,000 rotational cycles. The amount of wear was determined with a stereomicroscope at magnification x64. Significant differences in mean enamel wear were found when abraded against Olympia gold (9 microns), Procera All-Ceramic (60 microns), and Ceramco feldspathic porcelain (230 microns). Significant differences in restorative material wear were found between Olympia gold (0.32 microns) and the porcelain materials, Procera All-Ceramic (4.3 microns) and Ceramco feldspathic porcelain (3.7 microns).

Microbial colonization of dental implants in partially edentulous subjects

This study assessed the colonization of Brånemark dental implants by periodontopathic bacteria in four partially edentulous patients with a total of 10 implants. Marginal and subgingival plaque on the implants was sampled 14 days and 28 days after second-stage surgery and compared with plaque from three teeth closest to the implant sites sampled before second-stage surgery (baseline) and at 14 and 28 days. Slot immunoblot assay was used to determine the presence or absence of bacterial antigen to six different periodontopathic microorganisms. In general, colonization of marginal implant plaque occurred within 14 days, whereas subgingival colonization took longer and occurred within 28 days. It appears that Brånemark dental implants placed in partially edentulous patients may be colonized by disease-associated bacteria within 14 days of second-stage surgery.

Color stability of long-term soft denture liners.

The use of resilient denture liners in complete denture construction has become increasingly popular for providing comfort for denture wearers. The primary disadvantage of these materials is that the physical and mechanical properties change rapidly with time in a service environment. The purpose of this study is to evaluate the color stability of five commercially available soft denture liners as a function of accelerated aging. Color measurements were made before aging with a colorimeter and data processor. The samples were then weathered for 100 hours in an accelerated aging chamber in the presence of a xenon ultraviolet visible-light source, an intermittent water spray at 110 degrees F, and 90% humidity. After aging, color measurements were made again and color differences (delta E) were calculated. Results were statistically tested with analysis of variance and Scheffé intervals were calculated at 0.96. It was concluded that accelerated aging can be used to evaluate color stability of soft denture liners.

Effect of preload torque on the ultimate tensile strength of implant prosthetic retaining screws

The preload concept proposes that an optimal torque exists to which implant prosthetic retaining screws should be tightened. According to this theory, the preload prevents separation of implant components, thus protecting the screw from fracture. Recent research suggests that most implant-retained prostheses in function today were placed using improper preloads. The purpose of this investigation was to determine whether or not improper preloading of prosthetic implant-retaining screws would adversely affect their ultimate tensile strength. Fifteen Nobelpharma-slotted gold screws from one lot were tightened to 6, 10, and 15 N/cm with a torque gauge and ultimate tensile strength values determined. The procedure was duplicated using 15 Nobelpharma gold screws from another lot tightened to 0, 10, and 20 N/cm. Within each of the test groups, there was no significant difference in the ultimate tensile strength among the three preload torques. However, a paired t test (P = 0.005) determined that there was a significant difference between the two lots with respect to the ultimate tensile strength of the screws preloaded to 10 N/cm. Altering the preload torque applied to Nobelpharma gold-retaining screws does not affect their ultimate tensile strength. The ultimate tensile strength of the screws from the two lots differed, suggesting an unannounced change in component specifications. (Implant Dent 1994;3:17–21)

The precision of fit at the implant prosthodontic interface

STATEMENT OF PROBLEM Percussion, visual observation, and conventional periapical radiographs are the methods most frequently used clinically to evaluate the accuracy of implant component assemblies, whereas methods to measure the precision of fit are limited. PURPOSE In this study the Periotest instrument was used to evaluate the stability of the interfaces between the implant and the abutment, along with the abutment and the gold cylinder under a series of assembly conditions. The hypothesis tested is that a more negative Periotest value (PTV) would indicate an accurate fit and a more positive value PTV would correlate with an inaccurate fit. MATERIAL AND METHODS To investigate this hypothesis in vitro, two bovine ribs were used as patient simulation models. Each model contained three self-tapping Brånemark implants placed approximately 7 to 10 mm apart and arranged in a reasonable curvature. A series of component assembly conditions were created as accurate and inaccurate with thickness gauges of 25.4 microns, 50.8 microns, and 101.6 microns. RESULTS The mean Periotest values and SDs for accurately assembled abutments and gold cylinders were -6.0 +/- 0.32 and -3.4 +/- 0.68, respectively. Periotest value data of the assembly conditions were statistically analyzed with multiple regression analysis. The misfit in the implant to abutment interface resulted in a more negative Periotest value trend (r = 0.54) with increases in gauge thickness. However, the same magnitudes of misfit at the abutment to gold cylinder interface produced a more positive Periotest value trend (r = 0.72). CONCLUSION The PTV trends were consistent with increased stability at the abutment to implant interface from the increasing magnitude of misfit created with the thickness gauges. In contrast, the measurement trends observed for the abutment to gold cylinder interface were consistent with decreased stability with each increase in gauge thickness inserted at the interface.

Silane to enhance the bond between polymethyl methacrylate and titanium

The machined surface of wrought titanium frameworks used in implant-supported, fixed prostheses does not bond well with acrylic resin. Surface pretreatment has been suggested to enhance the retention of polymethyl methacrylate to machined titanium surfaces. This study evaluated a new bonding material (Rocatec) to determine its effect on the bond strength between titanium and polymethyl methacrylate. Twenty rod-shaped specimens of grade 2 titanium (7.6 x 0.3 cm in diameter) were divided into two groups of 10 samples. Group A received no pretreatment and group B was pretreated with 110 microns alumina air abrasive and the Rocatec material. Heat-cured denture base resin was processed around each titanium sample in a cylindrical shape approximately 0.9 x 1.5 cm. A Shell-Nielsen shear test was performed with a universal testing machine at a crosshead speed of 0.5 mm/minute to determine the bond strength in megapascals (MPa). Group B specimens (23.8 +/- 1.78 MPa) had a shear strength 68% greater than group A (16.1 +/- 1.61 MPa) (p 0.0001). The results of this study indicated that surface pretreatment of grade 2 titanium with 110 microns alumina air abrasive plus Rocatec bonding material significantly enhances the shear bond strength to PMMA.

Translucency of shaded zirconia core material

STATEMENT OF PROBLEM With the development of various zirconia core shades, questions arise regarding the effect of the shaded zirconia on the translucency of ceramic crowns. PURPOSE The purpose of this study was to investigate the translucency of the 3 Procera Zirconia shaded core materials. The hypothesis was that differences exist in the translucency of various shaded zirconia cores. MATERIAL AND METHODS Disk-shaped (0.6 ± 0.01 × 12 mm) zirconia core (Procera Zirconia) specimens (n=90) were fabricated by the manufacturer using a CAD/CAM process. The disks were fabricated in 3 groups according to shade (light, medium, intense) (n=30). A spectrophotometer was used to measure contrast ratio (CR) which is indicative of translucency. One-way ANOVA was conducted to determine significant differences among the shades (α=.05). RESULTS A significant difference in translucency between the light and intense shades (P=.030) and the medium and intense shades (P<.001) was observed. There was no significant difference between the light and medium shades (P=.15). CONCLUSIONS Shaded zirconia is partially translucent. In addition, significant differences in translucency measurements were identified between specific shades.