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PubMed1991

Dentin surface reproduction with hydrophilic and hydrophobic impression materials.

The detail reproduction of ground moist dentin surfaces with hydrophilic and hydrophobic elastomeric impression materials and the transfer of details onto stone casts produced from such impressions were investigated. Practically no difference was found in the detail-reproducing ability of the six impression materials and that of the dies produced therefrom. The surface roughness data were not related to the degree of hydrophilicity determined as the contact angle between water and impression material in spite of the considerable variation in contact angles of the six materials investigated. The critical surface tension of an experimental low-viscosity vinyl polysiloxane material of typical composition was 22.2 and 22.9 mN/m in the uncured and cured state, respectively. The contact angle between water and this compound was 105 degrees. The critical surface tension of wet dentin is reported to be 45.1 mN/m (Glantz, 1969), which means that the experimental impression paste will spread on wet dentin in spite of the pronounced hydrophobicity of the set product.

Analysis of Variance↗
PubMed1994

Prosthodontic complications related to compromised implant placement.

Successful prosthodontic treatment is dependent on optimal placement of the endosseous implants. This article describes prosthodontic problems associated with nonoptimal implant placement and suggests clinical guidelines to minimize recurrence of these problems.

Clinical Protocols↗
PubMed1988

Dental crowding and its relationship to mesiodistal crown diameters and arch dimensions.

An investigation was carried out to determine the correlation among cumulative mesiodistal crown widths, arch dimensions, and the degree of primary dental arch crowding. Two different ethnic groups were studied--namely, indigenous British and Pakistani immigrant groups--to determine whether similar correlations existed as part of a larger study of ethnic comparisons. Correlation matrix computation and multiple regression analysis were among the tests used. The results showed that in both ethnic groups there were very significant correlations between certain arch dimensions and the degree of crowding. There was no significant correlation between cumulative mesiodistal crown widths and dental crowding when considered in isolation. In combination with the other parameters, however, cumulative mesiodistal crown widths contributed significantly to the overall regression equation. This suggested a complex interrelationship among cumulative mesiodistal crown widths, the various arch dimensions, and primary dental crowding.

Adolescent↗
PubMed1989

Postretention evaluation of stability and relapse--mandibular arches with generalized spacing.

Assessment of cases that had been out of retention a minimum of 10 years and had displayed generalized spacing of anterior teeth before treatment showed consistent reduction of arch length and intercanine width into adult years. Intercanine width constriction typically occurred while arch length decreased in every case, both width and length reduction being progressive with time. Crowding was minimal for the majority of cases; few demonstrated the severe crowding more typical of cases with pretreatment crowding.

Adolescent↗
PubMed1995

Measurement of tooth displacements and mouthpiece forces during brass instrument playing.

In order to assess the actual load on front teeth and tooth supportive tissue during brass instrument playing, a measuring system was developed permitting simultaneous recordings of mouthpiece forces and incisor deflections. By the application of strain gauges, the mouthpiece itself was converted into an extra-oral force transducer, whilst an intra-oral metal appliance similar to a removable partial denture served as the base for strain gauge transducers sensing incisor displacements. The measurements only slightly affected the handling of the instruments under examination (trumpet, french horn, tenor horn, and tuba) and yielded the following average results for three to five players per instrument: peak force values were in the range of 29 N (tuba) to 50 N (trumpet), and the respective peak displacements were 43 microns and 100 microns.

Biomechanical Phenomena↗
PubMed2005

Treatment outcomes in 4 modes of orthodontic practice.

BACKGROUND: This study is a continuation of a previously published report on the outcome of orthodontic treatment provided in offices representing different modes of practice. METHODS: The sample consisted of duplicate pretreatment (T1) and posttreatment (T2) dental casts of 348 patients from traditional private orthodontic practices (5 offices, 134 patients), company-owned practices (5 offices, 107 patients), offices associated with practice-management organizations (2 offices, 60 patients), and general dental practices (2 offices, 47 patients). Methods were used to obtain random, representative samples from each office, starting with lists of patients who were treated consecutively with full fixed orthodontic appliances. The dental casts were measured by 2 independent judges who used the unweighted PAR score. RESULTS: Good interjudge agreement was shown on the initial casts, but the agreement was not as strong on the final casts. CONCLUSIONS: The measurements showed that treatment outcomes were generally satisfactory, although some significant differences between offices and management modes were shown.

Adolescent↗
PubMed2006

Palatal displacement of canines and maxillary skeletal width.

INTRODUCTION: The purpose of this study was to determine whether a clinically significant association exists between maxillary skeletal width and palatal canine impaction, also known as palatally displaced canine (PDC). METHODS: Seventy-nine patients with PDC were matched for age, sex, and malocclusion to 79 controls. Maxillary and mandibular skeletal widths and nasal cavity widths were measured on posteroanterior cephalograms; maxillary and mandibular intermolar widths were measured on dental casts; and maxillary interalveolar arch widths at 3 levels (canine, premolar, and first molar) were measured on occlusograms. RESULTS: Only maxillary alveolar arch width at the canine level was significantly different between the 2 groups. However, further analysis showed that the presence of erupted deciduous or permanent canines, rather than their absence in the canine area (whether due to extraction, exfoliation, impaction, or not yet having erupted), was strongly associated with maxillary intercanine alveolar arch width. CONCLUSIONS: The additional finding in this study that the eruptive status of canines significantly affects maxillary alveolar arch width in this area suggests that maxillary intercanine alveolar arch width as measured in this or other studies is not a good predictor of PDC.

Adolescent↗
PubMed2007

Assessing the American Board of Orthodontics objective grading system: digital vs plaster dental casts.

INTRODUCTION: The purposes of this study were to determine whether the American Board of Orthodontics objective grading system (ABO OGS) can be assessed accurately from digital dental casts and whether there are statistical differences between digital and plaster dental casts in scoring the ABO OGS. METHODS: Thirty posttreatment plaster dental casts were selected and scanned by OrthoCAD (Cadent, Carlstadt, NJ) to produce 30 corresponding digital dental casts. The plaster and digital casts were compared by using the criteria of the ABO OGS. Because the data were ordinal, a nonparametic statistical analysis was used. RESULTS: The Wilcoxon test for paired samples showed significant differences between the plaster and digital casts for occlusal contacts, occlusal relationships, and total scores (P <.05). No significant differences were found for alignment, marginal ridges, overjet, and interproximal contacts. Buccolingual inclination was not included in this study because of inability to perform proper measurements with the OrthoCAD program. Mean differences of points deducted ranged from .03 point for marginal ridges to 5.07 points for the total score. The variable with the most points deducted related to occlusal relationships, and the fewest points were deducted for interproximal contacts. CONCLUSIONS: Based on this study, the current OrthoCAD program (version 2.2) was not adequate for scoring all parameters as required by the ABO OGS.

Certification↗
PubMed2004

Factors affecting the accuracy of elastometric impression materials.

OBJECTIVES: The purpose of this study was to evaluate the effects of (1) various impression materials, (2) different storage times and (3) the proportion of inorganic filler on the accuracy and stability of elastometric impression materials. METHODS: The impression materials studied included three alginate impression materials (Algiace Z, CAVEX and Jeltrate), five commercial silicone impression materials (Aquasil, Exaflex regular type, Express, Coltex fine and Rapid liner) and two experimental silicone impression materials designed for this study (KE106A and KE106B). Impressions were made of 10 metal dies that mimicked prepared crowns. After an impression was taken, dental stone was immediately poured into the alginate impressions, while the silicone impressions was poured 30 min later and waited for 1 h for setting. The second and third stone dies were made 1 and 24 h later, respectively. The diameters of the occlusal surfaces of the metal dies and stone casts were determined using photographs of the surfaces taken with a Kodak DC 290 digital camera. The pictures were then measured using a photomicrograph digitized integration system to calculate any discrepancy. Because each impression was used to make three rounds of stone dies, two-factor mixed factorial ANOVA was used to evaluate the effect of materials and storage time on the accuracy of the stone casts. The simple effects analysis, combined with multiple comparisons considering the per family type I error rate, was performed following confirmation that an interaction between the two factors was significant. RESULTS: The results showed that: (1) there was a significant interaction effect between materials and storage times on the accuracy of the impressions. (2) Two addition type silicone materials, Aquasil and Exaflex, had the greatest accuracy and stability. (3) The experimental material KE106A had the least accuracy in the first and second rounds and the alginate impression material CAVEX had the least accuracy in the third round. (4) The stabilities of CAVEX and Jeltrate were the least consistent of the 10 materials and decreased significantly with storage time. (5) When the experimental material had a low proportion of filler (KE106A), there was a significantly greater dimensional discrepancy compared to the same material with a higher proportion of filler (KE106B). CONCLUSIONS: The accuracies varied among the 10 impression materials over three rounds. Of all the materials, the addition type silicone materials, Aquasil and Exaflex, had relatively greater accuracy and stability. The discrepancy of the alginate impression materials increased with storage time. The large loading of filler showed less discrepancy.

Alginates↗
PubMed2006

Resistance to fracture of two all-ceramic crown materials following endodontic access.

STATEMENT OF PROBLEM: There is currently no protocol for managing endodontic access openings for all-ceramic crowns. A direct restorative material is generally used to repair the access opening, rendering a repaired crown as the definitive restoration. This endodontic procedure, however, may weaken the restoration or initiate microcracks that may propagate, resulting in premature failure of the restoration. PURPOSE: The purpose of this in vitro study was to evaluate how an endodontic access opening prepared through an all-ceramic crown altered the structural integrity of the ceramic, and the effect of a repair of this access on the load to failure of an all-ceramic crown. MATERIAL AND METHODS: Twenty-four alumina (Procera) and 24 zirconia (Procera) crowns were fabricated and cemented (Rely X Luting Plus Cement) onto duplicate epoxy resin dies. Twelve crowns of each were accessed to simulate root canal treatment therapy. Surface defects of all accessed specimens were evaluated with an environmental scanning electron microscope. The specimens were repaired with a porcelain repair system (standard adhesive resin/composite resin protocol) and were loaded to failure in a universal testing machine. Observations made visually and microscopically noted veneer delamination from the core, core fracture, shear within the veneer porcelain, or a combination thereof. A Kruskal-Wallis test was used to determine if a significant difference (alpha=.05) in load to failure existed between the 4 groups, and a Mann-Whitney test with a Bonferroni correction (P<.0125) was used for multiple comparisons. A Weibull analysis was also used to estimate the Weibull modulus and characteristic failure for each group. RESULTS: All specimens exhibited edge chipping around the access openings. Some displayed larger chips within the veneering porcelain, and 4 zirconia crowns showed radial crack formation. There was a significant difference in load to failure among all groups with the exception of the alumina intact and repaired specimens (P=.695). The alumina crowns generally showed fracture of the coping with the veneering porcelain still bonded to the core, whereas the zirconia copings tended not to fracture but experienced veneering porcelain delamination. CONCLUSION: Endodontic access through all-ceramic crowns resulted in a significant loss of strength in the zirconia specimens but not in the alumina specimens.

Aluminum Oxide↗
PubMed2006

Cyclic loading of implant-supported prostheses: comparison of gaps at the prosthetic-abutment interface when cycled abutments are replaced with as-manufactured abutments.

STATEMENT OF PROBLEM: Implant-supported prostheses are mechanically connected to implants. When this connection is a screw joint, it is likely that the fit will be imperfect. Previous studies demonstrate that deformation can occur at the interface between the prosthesis and implant following cyclic loading. This deformation alters the fit of components. If implant connection components, abutments, were to be reoriented or replaced, it is likely that deformed surfaces would no longer approximate each other. Likewise, it is possible that the deformation may deleteriously alter the fit to replacement components. PURPOSE: This study evaluated the changes in prosthesis-implant abutment fit when gold cylinders that have been cyclically loaded are mated to as-manufactured abutments. MATERIAL AND METHODS: Fifteen implant-supported frameworks were fabricated using conventional casting techniques and were cyclically loaded under 3 different loading conditions: anterior region, unilaterally on posterior cantilever, and bilaterally on posterior cantilever. A cyclical load of 200 N was applied to each framework for 200,000 cycles. The abutments and frameworks were returned to the definitive casts for measurements. Linear measurements (microm) of the gap between the prosthetic cylinder and the implant-supported abutment at 4 predetermined reference points were made. The cycled abutments were replaced with as-manufactured abutments, and the gaps were measured at the same reference points. The Mann-Whitney rank-sum test was applied to the 2 sets of data to determine whether significant changes in fit were observed following component replacement (alpha = .05). RESULTS: Although minor changes in component fit were seen, the data failed to show that gaps at the prosthetic-abutment interface of cycled abutments were significantly different from those of as-manufactured abutments. CONCLUSIONS: Within the limitations of this study, differences in the fit between the implant-supported prosthesis and the abutments were not significantly different when abutments worn through loading were replaced with new as-manufactured abutments.

Dental Abutments↗
PubMed2003

A clinical study comparing the three-dimensional accuracy of a working die generated from two dual-arch trays and a complete-arch custom tray.

STATEMENT OF PROBLEM: Dual-arch trays are often used by the dentists to make crown impressions of opposing quadrants simultaneously. Metal and plastic trays are available, but little is known about the accuracy of the impressions and resultant working dies. PURPOSE: The purpose of this study was to conduct a clinical trial to compare the accuracy of gypsum working dies made from impressions with metal dual-arch, plastic dual-arch, and complete-arch custom trays. MATERIAL AND METHODS: Eight patients requiring a posterior single tooth implant restoration were selected on the basis of inclusion and exclusion criteria. A customized abutment was measured in 3 dimensions (buccolingual, mesiodistal, and occlusogingival) by use of a measuring microscope. Three polyvinyl siloxane impressions were made of the abutment with a complete-arch custom tray, a plastic, and a metal dual-arch tray. Each impression was poured with type IV improved dental die stone. The diameter (buccolingual and mesiodistal), from gingivoaxial to gingivoaxial point angle, and height (occlusogingival), gingivoaxial to occlusoaxial point angle of the abutment standard was determined by measuring each dimension several times to obtain a mean. These 3 mean values served as the controls and were compared with the same measurements of the gypsum dies generated by the 3 different impression techniques. The patient was asked to rank the 3 impressions in order of overall comfort. A multivariate repeated measures single factor ANOVA was used in the statistical analysis (alpha=.05). When main effects were significant, a pairwise comparison of mean values was conducted with Bonferonni adjustment for multiple comparisons. RESULTS: There were no significant differences in die accuracy among the 3 trays for the mesiodistal (3.507 mm) and occlusogingival (3.584 mm) dimensions of the implant abutment. Dies were smaller than the standard for these 2 dimensions and larger in the buccolingual dimension. There was a significant difference in accuracy between the metal and plastic dual-arch trays. The dies produced from the metal dual-arch tray were 20 microm larger than the abutment standard compared with 3 microm larger for the plastic tray. The occlusogingival dimension of the working dies was 30 to 40 microm shorter than the implant abutment. Seven of the 8 patients ranked the plastic dual-arch impression as the most comfortable and the complete-arch custom tray as the least comfortable. CONCLUSIONS: Within the limitations of this study, the dimensions of working dies from a custom tray impression did not differ significantly from those created with dual arch trays. However, working dies from a plastic dual-arch tray were more accurate buccolingually than those from metal dual-arch trays.

Crowns↗
PubMed2003

Calcium hypochlorite as a disinfecting additive for dental stone.

STATEMENT OF PROBLEM: Dental casts come into direct contact with impression materials and other items that are contaminated by saliva and blood from a patient's mouth, leaving the casts susceptible to cross-contamination. Topical methods of disinfecting casts are difficult to control, while immersion methods are potentially destructive. Thus, an additional method to control cross-contamination between patients and laboratory personnel is needed. PURPOSE: This study was undertaken in an attempt to develop a dental stone with disinfecting properties and adequate compressive and tensile strengths. MATERIAL AND METHODS: Calcium hypochlorite [Ca(OCl)(2)] in aqueous solution in concentrations from 0 to 1.5% was tested as a disinfecting additive to type V dental stone. The compressive and tensile strength properties of the modified stone were measured (MPa) using a universal testing machine at a consistency similar to unmodified stone. Strength data were analyzed by 1-way ANOVA and post hoc Tukey-Kramer procedure (alpha < or =.05). To measure the disinfecting ability, the effect on Bacillis subtilis bacteriophage phi29 was tested in triplicate to find the minimum concentration at which no phage was detected. Additionally, 3 impressions were disinfected with CaviCide, and 3 impressions rinsed in water served as controls. RESULTS: In general, the effect of adding the disinfectant to the stone was a decrease in strength. Exceptions were the dry compressive strength, for which there was a significant increase in strength (P=.048) at 0.5%, and the wet compressive and wet tensile strength, which showed no significant difference between the 1.5% and the control. When Ca(OCl)(2) was added at the concentration 0.5% (2765 ppm available chlorine), the gypsum had acceptable mechanical properties; dry compressive strength was 78.86 +/- 4.12 MPa, and dry tensile strength was 10.64 +/- 1.27 MPa, compared to control values of 67.85 +/- 6.28 and 13.41 +/- 1.24 MPa, respectively. At concentrations of 0.3% and higher (36 1650 ppm of available chlorine), calcium hypochlorite was able to completely inactivate phi29. CONCLUSION: It is possible to prepare a type V dental stone that contains a disinfectant, has adequate mechanical properties, and will reduce numbers of residual microorganisms. For example, stone mixed with water containing 0.5% Ca(OCl)(2) meets these criteria.

Analysis of Variance↗
PubMed1991

The accuracy of polyvinyl siloxane impressions made with standard and reinforced stock trays.

A laboratory investigation was done to assess the influence of proprietary stock trays on the accuracy of impressions recorded with heavy light-body (HL) and putty light-body (PL) wash impression techniques. Two brands of trays were tested and the same trays were reinforced with acrylic resin. Individual die accuracy and overall distortion of the resultant casts were assessed. PL impressions in both stock trays gave undersized buccolingual dimensions at the preparation finishing lines whereas reinforcing the trays reduced this distortion. Significant inaccuracy at the second molar was found for all trays when PL impressions were made. These distortions would have resulted in clinically unacceptable dies. HL impressions, regardless of tray type, produced highly accurate dies at this critical site. Resultant overall cast distortion was reduced, but not eliminated, by using reinforced trays with either PL or HL techniques.

Acrylic Resins↗
PubMed1995

Reliability of antagonistic arch impression in dental prostheses: clinical evaluation of different preimpression preparation procedures.

This study compared the influence of different methods of preimpression preparation on the quality of occlusal reproduction in irreversible hydrocolloid impressions. A total of 30 impressions of the lower dental arch of a patient were made with five different preimpression preparation procedures. Stone casts were made and analyzed. Critical comparison showed that the preimpression preparation influenced the quality of the occlusal surface of the cast. Fingerpainting the occlusal surface with fluid hydrocolloid before positioning the loaded impression tray, associated with use of a saliva ejector, reduced the incidence of macroscopic defects on the occlusal surface of the impressions.

Adult↗
PubMed1995

A comparison of three wetting agents used to facilitate the pouring of dies.

This study compared the effect of a clinical surfactant and one of three laboratory surfactants used before pouring dies from elastomeric impression materials. A total of 154 impressions were recorded. Hydrosystem surfactant was used before the recording of 78 of these impressions. A total of 154 dies were poured with Wax-mate, Tensilab, or Hydrosystem surfactants and examined for surface voids by an examiner who was unaware which wetting agent was used. Six dies were grossly defective and discarded. When the Hydrosystem surfactant had not been used during impression recording there was no significant difference between Hydrosystem (mean 10.2 +/- 8.8 voids, n 25), Wax-mate (mean 13.1 +/- 14.4 voids, n 25), and Tensilab (mean 14.9 +/- 11.6 voids, n 21) surfactants when the dies were poured. When Hydrosystem surfactant was used during impression recording, there was no significant difference between the number of voids on dies produced with Hydrosystem (mean 3.8 +/- 3.9 voids, n 26), Wax-mate (3.9 +/- 3.3 voids, n 25), or Tensilab (3.7 +/- 4.9 voids, n 26) surfactants. However, each of the groups in which Hydrosystem surfactant was used before impression recording resulted in dies with significantly fewer voids than when it had not been used, independent of the surface wetting agent used in the pouring of dies (p < 0.05). To reduce the number of voids in laboratory dies, this in vitro study suggested that a topical surfactant should be used before an impression is recorded.

Analysis of Variance↗