Tissue engineering strategies for the future generation of dental implants.
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Amelogenin↗
Biomedical subjects
Clark M Stanford
Publications and source records attributed to Clark M Stanford.
Prosthetic considerations for implant surgery.
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Dental Abutments↗
In vitro fracture resistance of endodontically treated central incisors with varying ferrule heights and configurations.
STATEMENT OF PROBLEM: The in vitro effectiveness of a uniform circumferential ferrule has been established in the literature; however, the effect of a nonuniform circumferential ferrule height on fracture resistance is unknown. PURPOSE: This in vitro study investigated the resistance to static loading of endodontically treated teeth with uniform and nonuniform ferrule configurations. MATERIAL AND METHODS: Fifty extracted intact maxillary human central incisors were randomly assigned to 1 of 5 groups: CRN, no root canal treatment (RCT), restored with a crown; RCT/CRN, no dowel/core, restored with a crown; 2 FRL, 2-mm ferrule, cast dowel/core and crown; 0.5/2 FRL, nonuniform ferrule (2 mm buccal and lingual, 0.5 mm proximal), cast dowel/core and crown; and 0 FRL, no ferrule, cast dowel/core and crown. The teeth were prepared to standardized specifications and stored for 72 hours in 100% humidity prior to testing. Testing was conducted with a universal testing machine with the application of a static load, and the load (N) at failure was recorded. Statistical analysis was performed with a 1-way analysis of variance and the Tukey Honestly Significant Difference test (alpha=.05). The mode of fracture was noted by visual inspection for all specimens. RESULTS: There was strong evidence of group differences in mean fracture strength ( P <.0001). Following adjustment for all pairwise group comparisons, it was found that the lack of a ferrule resulted in a significantly lower mean fracture strength (0 FRL: 264.93 +/- 78.33 N) relative to all other groups. The presence of a nonuniform (0.5 to 2-mm vertical height) ferrule (0.5/2 FRL: 426.64 +/- 88.33 N) resulted in a significant decrease ( P =.0001) in mean fracture strength when compared with the uniform 2-mm vertical ferrule (2 FRL: 587.23 +/- 110.25 N), the group without RCT (CRN: 583.67 +/- 86.09 N), and the RCT-treated tooth with a crown alone (CRN/RCT: 571.04 +/- 154.86 N). The predominant mode of failure was an oblique fracture extending from the lingual margin to the facial surface just below the insertion of the tooth into the acrylic resin. CONCLUSION: The results demonstrated that central incisors restored with cast dowel/core and crowns with a 2-mm uniform ferrule were more fracture resistant compared to central incisors with nonuniform (0.5 to 2 mm) ferrule heights. Both the 2-mm ferrule and nonuniform ferrule groups were more fracture resistant than the group that lacked a ferrule.
Crowns↗
Application of oral implants to the general dental practice.
BACKGROUND: The use of dental implants has become a management strategy for replacing missing teeth. As new implant surface technologies develop and prosthetic options increase, the field of dental implantology continues to change. General dentists con sidering the use of this treatment modality in their practices should understand the vital role treatment planning plays in achieving predictable outcomes. OVERVIEW: This article reviews specific issues the general dentist typically faces when considering patients for single-tooth, partially-edentulous-arch and full-arch tooth replacement using dental implants. The author analyzes patient-based assessments, as well as diagnostic criteria and steps, to help practitioners predict patient-specific issues that may signal complications. He also discusses approaches for resolving complications. The article emphasizes the importance of careful evaluation in predicting patient-specific issues that can lead to gingival recession and suggests approaches to manage these situations. CONCLUSIONS AND CLINICAL IMPLICATIONS: Dental implants have become an increasingly common treatment option for missing dentition. Because innovations in implant surfaces continue to promote faster bone growth with better predictability, general dentists should be aware of the importance of treatment planning, assessment and teamwork in achieving successful outcomes.
Dental Implantation, Endosseous↗
Alterations of surface hardness with gypsum die hardeners.
STATEMENT OF PROBLEM: Die stones require abrasion resistance, dimensional stability with time, and high surface wettability material properties. PURPOSE: The purpose of this study was to compare the surface microhardness (Knoop) of 4 contemporary gypsum materials with and without surface die hardener. MATERIAL AND METHODS: Materials used were a Type III stone (Microstone) and 3 die stones (Die-Keen, Silky-Rock, and ResinRock). Die hardener was cyanoacrylate (Permabond 910) or Clear Coat. Specimens of stone were hand mixed with distilled room temperature water and vacuum spatulated according to manufacturer's directions. Five cylinders (15 x 15 mm) per group were poured, using vibration, into phenolic ring molds positioned on top of a glass slide. The face of each specimen was polished with 2400-grit Al2O sandpaper. One face of each of 5 specimens/material was coated with cyanoacrylate; 5 specimens/material were coated with Clear Coat, air thinned and dried; and 5 specimens/material had no treatment (control). Knoop hardness (kg/mm2) readings were made on each face (5 readings/time point) 3, 12, and 24 hours after pouring. An ANOVA procedure with post hoc Tukey tests were performed (alpha=.05). RESULTS: Microhardness did not vary between 3 and 24 hours for any material (P>.05). Microstone had significantly lower surface hardness (P<.0001) than the die stones. Specimens coated with die hardener had lower hardness values (P<.001 in all cases) CONCLUSIONS: The 3 types of die stones evaluated in this study did not differ significantly in surface microhardness. Under these conditions, die hardener coatings reduced the surface hardness of the gypsum material.
Analysis of Variance↗
Functional behaviour of bone around dental implants.
Achieving a long-term stable implant interface is a significant clinical issue when there is insufficient cortical bone stabilisation at implant placement. Clinical outcomes studies suggest that the higher risk implants are those placed in compromised cortical bone (thin, porous, etc.) in anatomical sites with minimal existing trabecular bone (characterised as type IV bone). In establishing and maintaining an implant interface in such an environment, one needs to consider the impact of masticatory forces, the response of bone to these forces and the impact of age on the adaptive capacity of bone. These forces, in turn, have the potential to create localised changes in interfacial stiffness through viscoelastic changes at the interface. Changes in bone as a function of age (e.g. localised hypermineralised osteopetrosis and localised areas of osteopenia) will alter the communication between osteocytes and osteoblasts creating the potential for differences in response of osteoblastic cells in the older population. A key to understanding the biomechanical and functional behaviour of implants in the older population is to control the anticipated modelling and remodelling behaviour through implant design that takes into account how tissues respond to the mechanically active environment.
Aged↗
Influence of surface hardener on gypsum abrasion resistance and water sorption.
STATEMENT OF PROBLEM: Abrasion is a major concern when gypsum products are used for dies, leading to the frequent recommendation that surface hardeners should be used before waxing or scanning. PURPOSE: This study evaluated abrasion resistance and water sorption with 4 commonly used gypsum die materials with and without the application of surface die hardeners. MATERIAL AND METHODS: Three ADA Type IV (Vel-Mix, ResinRock, and Silky-Rock) and 1 Type V die material (Die-Keen) were evaluated for abrasion resistance after application of 2 surface hardeners (Permabond 910 cyanoacrylate and Clear Coat). Thirty specimens of each material were fabricated using an impression of a standard brass die machined with 1-mm high ridges, sloped 45 degrees. Gypsum materials were mixed according to manufacturers' recommendations and allowed to set 1 hour before separating. All replicated dies were allowed to bench set for 14 days before testing. One hour before testing, specimens were arbitrarily assigned to 1 of 3 treatment subgroups (n=10/group): no treatment (control), coated with Permabond 910, or coated with Clear Coat. In the coated groups, die hardener was painted over the grooves and air dried. Abrasion resistance (measured by weight loss) was evaluated using a reciprocal abrasion device in which a stylus applied a 50-g mass perpendicular to the ridges. Mass loss was determined using an analytical balance before and after each test cycle. Five sets of 20 unidirectional passes were made on each specimen. A scanning electron microscope was used to evaluate the surface of specimens in each treatment subgroup. Water sorption was also evaluated using 2 Type IV (Silky-Rock, ResinRock) and 1 Type III (Microstone) gypsum materials. Specimen dies were separated 1 hour after pouring the impression and allowed to bench set 1 week before testing. Five specimens from each material group received a coating of a surface hardener 1 hour before testing. Specimens were placed in distilled water for 15 minutes and differences in mass were determined using an analytical balance before and after each test. A 2-way analysis of variance was completed followed by a Tukey post hoc test (alpha=.05). RESULTS: The 2-way analysis of variance revealed an interaction between product and surface coating (P=.0459). Given this interaction, the 12 combinations determined by surface treatment and material type were considered individually using the Tukey method. Vel-Mix, control (2.62 +/- 2.64 mg) had the most material loss and Vel-Mix, Clear Coat (0.48 +/- 0.29 mg) had the least material loss. Water sorption results indicated an interaction between the gypsum material and the surface treatment (P<.0001). The control groups of Microstone (299.2 +/- 49.6 mg) and Silky-Rock (159.0 +/- 8.5 mg) showed the most water sorption compared with the other treatment groups. CONCLUSIONS: This study demonstrated that a significant improvement in abrasion resistance occurred only with specific gypsum/surface hardener material combinations. Also, water sorption decreased significantly for Microstone and Silky-Rock gypsum materials when a surface hardener was used.
Absorption↗
Effects of implant microtopography on osteoblast cell attachment.
PURPOSE: The overall aim of this project was to study osteoblast cell attachment on titanium surfaces with varying surface roughness. MATERIALS AND METHODS: Commercially pure titanium surfaces were prepared by polishing through 600-grit sandpaper, sandblasting, or sandblasting followed by acid etching to produce surfaces of varying roughness, as determined by scanning electron microscopy and atomic force microscopy. In vitro cell attachment of MC3T3-E1 osteoblasts was performed on the prepared surfaces in both serum-containing and serum-free media conditions. RESULTS: Cell attachment was directly related to the average surface roughness, with the highest levels of cell attachment observed on sandblasted and sandblasted-acidetched surfaces. Similar patterns of cell attachment were observed when serum-free conditions were employed. CONCLUSIONS: Combined surface analytical and cell/molecular biological techniques are powerful tools to broaden our understanding of biological events occurring at the implant-tissue interface. Data acquired from these in vitro techniques provide a translational application to in vivo clinical models leading to the next generation of dental implants.
3T3 Cells↗
How do tissues respond and adapt to stresses around a prosthesis? A primer on finite element stress analysis for orthopaedic surgeons.
Joint implant design clearly affects long-term outcome. While many implant designs have been empirically-based, finite element analysis has the potential to identify beneficial and deleterious features prior to clinical trials. Finite element analysis is a powerful analytic tool allowing computation of the stress and strain distribution throughout an implant construct. Whether it is useful depends upon many assumptions and details of the model. Since ultimate failure is related to biological factors in addition to mechanical, and since the mechanical causes of failure are related to load history, rather than a few loading conditions, chief among them is whether the stresses or strains under limited loading conditions relate to outcome. Newer approaches can minimize this and the many other model limitations. If the surgeon is to critically and properly interpret the results in scientific articles and sales literature, he or she must have a fundamental understanding of finite element analysis. We outline here the major capabilities of finite element analysis, as well as the assumptions and limitations.
Arthroplasty, Replacement↗
Bone quantity and quality: are they relevant predictors of implant outcomes?
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Alveolar Ridge Augmentation↗
Abrasion resistance of a resin-impregnated type IV gypsum in comparison to conventional products.
STATEMENT OF PROBLEM: Limited abrasion resistance is one of the disadvantages of gypsum materials. One means to improve these properties may be the addition of various polymers to reinforce surface and subsurface wear resistance. PURPOSE: The purpose of this study was to evaluate the abrasion resistance of 3 types of gypsum materials with a novel abrasion wear device. MATERIAL AND METHODS: A standard test specimen (50 x 50 x 8 mm) with repeating 1 mm, 45 degrees -angle vertical ridges was used as the test surface. Three types of gypsum materials were evaluated: a type III stone, a conventional type IV stone, and a resin-impregnated type IV stone. Specimens of each material (n = 30) were poured in a vinyl polysiloxane impression of the standard test specimen with the use of an acrylic resin custom tray. Each gypsum product was mixed according to the manufacturer's instructions, poured, and separated 1 hour later. Specimens were trimmed and allowed to bench set for 24 hours (n = 15) or 7 days (n = 15). Abrasion was evaluated with the use of a reciprocal moving stage positioned below a weighted stylus. The stylus was loaded with 3 different weights (15, 50, and 75 g), and the individual gypsum specimens were moved reciprocally for 10 passes. Before and after each set of passes, the specimen was measured on an analytical balance to determine material loss. Three-way ANOVA and Scheffe's multiple comparisons test were used to analyze the data (P<.05). RESULTS: Type III gypsum at 24 hours exhibited significantly greater material loss than type IV stones at both 7 days and 24 hours (P<.001). Type III gypsum specimens exhibited significantly greater material loss at 24 hours than at 7 days (P<.001). There was no significant difference in the abrasion resistance of type IV specimens at 24 hours and 7 days. CONCLUSION: Within the limitations of this study, no significant differences in abrasion resistance were found between specimens fabricated with resin-impregnated and conventional type IV stones, although the former exhibited the least material loss.
Acrylic Resins↗
Relative translucency of six all-ceramic systems. Part I: core materials.
STATEMENT OF PROBLEM: All-ceramic restorations have been advocated for superior esthetics. Various materials have been used to improve ceramic core strength, but it is unclear whether they affect the opacity of all-ceramic systems. PURPOSE: This study compared the translucency of 6 all-ceramic system core materials at clinically appropriate thicknesses. MATERIALS AND METHODS: Disc specimens 13 mm in diameter and 0.49 +/- 0.01 mm in thickness were fabricated from the following materials (n = 5 per group): IPS Empress dentin, IPS Empress 2 dentin, In-Ceram Alumina core, In-Ceram Spinell core, In-Ceram Zirconia core, and Procera AllCeram core. Empress and Empress 2 dentin specimens also were fabricated and tested at a thickness of 0.77 +/- 0.02 mm (the manufacturer's recommended core thickness is 0.8 mm). A high-noble metal-ceramic alloy (Porc. 52 SF) served as the control, and Vitadur Alpha opaque dentin was used as a standard. Sample reflectance (ratio of the intensity of reflected light to that of the incident light) was measured with an integrating sphere attached to a spectrophotometer across the visible spectrum (380 to 700 nm); 0-degree illumination and diffuse viewing geometry were used. Contrast ratios were calculated from the luminous reflectance (Y) of the specimens with a black (Yb) and a white (Yw) backing to give Yb/Yw with CIE illuminant D65 and a 2-degree observer function (0.0 = transparent, 1.0 = opaque). One-way analysis of variance and Tukey's multiple-comparison test were used to analyze the data (P<.05). RESULTS: Contrast ratios in order of most translucent to most opaque were as follows: Vitadur Alpha 0.60 +/- 0.03, Empress (0.5 mm) 0.64 +/- 0.01, In-Ceram Spinell 0.67 +/- 0.02, Empress 2 (0.5 mm) 0.68 +/- 0.02, Empress (0.8 mm) 0.72 +/- 0.01, Procera 0.72 +/- 0.01, Empress 2 (0.8 mm) 0.74 +/- 0.01, In-Ceram Alumina 0.87 +/- 0.01, In-Ceram Zirconia 1.00 +/- 0.01, and 52 SF alloy 1.00 +/- 0.00. CONCLUSION: Within the limitations of this study, there was a range of ceramic core translucency at clinically relevant core thicknesses. In order of decreasing translucency, the ranges were Vitadur Alpha dentin (standard) > In-Ceram Spinell > Empress, Procera, Empress 2 > In-Ceram Alumina > In-Ceram Zirconia, 52 SF alloy.
Aluminum Oxide↗
Relative translucency of six all-ceramic systems. Part II: core and veneer materials.
UNLABELLED: STATEMENT OF PROBLEM All-ceramic core materials with various strengthening compositions have a range of translucencies. It is unknown whether translucency differs when all-ceramic materials are fabricated similarly to the clinical restoration with a veneered core material. PURPOSE: This study compared the translucency of 6 all-ceramic materials veneered and glazed at clinically appropriate thicknesses. MATERIALS AND METHODS: Core specimens (n = 5 per group) of Empress dentin, Empress 2 dentin, In-Ceram Alumina, In-Ceram Spinell, In-Ceram Zirconia, and Procera AllCeram were fabricated as described in Part I of this study and veneered with their corresponding dentin porcelain to a final thickness of 1.47 +/- 0.01 mm. These specimens were compared with veneered Vitadur Alpha opaque dentin (as a standard), a clear glass disc (positive control), and a high-noble metal-ceramic alloy (Porc. 52 SF) veneered with Vitadur Omega dentin (negative control). Specimen reflectance was measured with an integrating sphere attached to a spectrophotometer across the visible spectrum (380 to 700 nm); 0-degree illumination and diffuse viewing geometry were used. Measurements were repeated after a glazing cycle. Contrast ratios were calculated from the luminous reflectance (Y) of the specimens with a black (Yb) and a white backing (Yw) to give Yb/Yw with CIE illuminant D65 and a 2-degree observer function (0.0 = transparent, 1.0 = opaque). One-way analysis of variance and Tukey's multiple-comparison test were used to analyze the data (P<.05). RESULTS: Significant differences in contrast ratios were found among the ceramic systems tested when they were veneered (P<.0001) and after the glazing cycle (P<.0001). Significant changes in contrast ratios (P<.0001) also were identified when the veneered specimens were glazed. CONCLUSION: Within the limitations of this study, a range of translucency was identified in the veneered all-ceramic systems tested. Such variability may affect their ability to match natural teeth. The glazing cycle resulted in decreased opacity for all test materials except the completely opaque In-Ceram Zirconia and metal-ceramic specimens.
Aluminum Oxide↗
Achieving and maintaining predictable implant esthetics through the maintenance of bone around dental implants.
The position of gingival soft tissues depends on the position and health of the underlying alveolar bone. Implant designs are evolving to maintain bone at predictable positions on the implant body through the development of stable and simplified prosthetic choices in abutment designs. The positioning of the restorative abutment deep inside the implant allows the abutment-implant joint to remain stable for a prolonged service life. With this stability, the titanium abutment allows the connective tissue and junctional epithelial seal ("biological width") to form and remain on the side of the abutment, rather than the side of the implant. Abutment joint stability plus well-defined implant surface topographies allow predictable implant rehabilitation in challenging situations. With the use of a mechanically and biologically stable joint interface, the prosthetic flexibility of a two-piece modular-style implant system allows the greatest flexibility for application in routine surgical and restorative implant dentistry.
Adult↗
Effects of fluoride-modified titanium surfaces on osteoblast proliferation and gene expression.
PURPOSE: The objective of this study was to test the hypothesis that fluoride-modified titanium surfaces would enhance osteoblast differentiation. Osteoblast growth on a moderately rough etched fluoride-modified titanium surface (alteration in cellular differentiation) was compared to osteoblast growth on the same surface grit-blasted with titanium dioxide. The potential role of nanometer-level alterations on cell shape and subsequent differentiation was then compared. MATERIALS AND METHODS: Human embryonic palatal mesenchymal (HEPM) cultures were incubated on the respective surfaces for 1, 3, and 7 days, followed by analysis for cell proliferation, alkaline phosphatase (ALP) -specific activity, and mRNA steady-state expression for bone-related genes (ALP, type I collagen, osteocalcin, bone sialoprotein [BSP] II, Cbfa1, and osterix) by real-time polymerase chain reaction (PCR). RESULTS: The different surfaces did not alter the mRNA expression for ALP, type I collagen, osterix, osteocalcin, or BSP II. However, Cbfa1 expression on the fluoride-modified titanium surface was significantly higher (P < .001) at 1 week. The number of cells on this surface was 20% lower than the number of cells on the surface TiO2-blasted with 25-microm particles but not significantly different from the number of cells on the surface TiO2-blasted with 125-microm particles. Cells grown on all the titanium surfaces expressed similar levels of ALP activity. CONCLUSIONS: The results indicated that a fluoride-modified surface topography, in synergy with surface roughness, may have a greater influence on the level of expression of Cbfa1 (a key regulator for osteogenesis) than the unmodified titanium surfaces studied.
Acid Etching, Dental↗