Posterior restoration rotational torque associated with cuspal incline angulation: A proof of concept.

STATEMENT OF PROBLEM: Off-axis, external forces with a moment arm on posterior restorations have not been investigated in experimental studies. PURPOSE: The purpose of this proof-of-concept study was to determine the interaction between occlusal force directed toward cuspal incline angulations with variations in base width and preparation vertical heights. Torque forces on a single crown restoration in simulated premolar and molar tooth forms were calculated for 3 different rotational axes. MATERIAL AND METHODS: Trigonometric calculations were made to determine the amount of torque generated in a simulated-crown restoration in premolar and molar tooth forms. Restorations with different cuspal incline angulations were loaded with an off-axis force of 200 N. This force was applied to 5 different cuspal incline angulations in both tooth forms at varying preparation heights. Right triangles were used to enable trigonometric computations of the resulting moment arms that accompanied the 3 rotational axes. RESULTS: The total torque values were calculated with a range from 7.5 to 372.8 Ncm. The highest levels of torque were generated in the 5-mm-high molar tooth form with a rotational axis located within the root form, perpendicular to the 45-degree cuspal incline. In general, large moment arms were generated with steep cuspal incline angulations and mid-root axis locations; the lowest torque values in all cuspal incline angulations were found in the rotational axis locations at the crown finish line. The torque values at the rotational axis finish line location were found to be greatest in the largest vertical tooth form height category (5 mm) in both tooth model sizes. CONCLUSIONS: The crown restoration cuspal incline angulations, vertical preparation heights, base widths, and rotational axis locations all played a role in the torque force levels generated, probably influencing restoration stability.

FEA evaluation of the resistance form of a premolar crown.

PURPOSE: The purpose of this study was to evaluate the influence of buccal and lingual wall convergence angles on the ability of the preparation to resist rotational displacement. MATERIALS AND METHODS: An intact premolar digitized by micro-CT yielded a 3D reproduction of a human tooth. Simulated crown preparations with known buccolingual axial wall convergence angles (4°, 8°, 12°, 16°, 20°, 24°, 28° 32°), sloped-shoulder marginal area, and occlusal reduction were created and restored with a ceramic crown. The tooth restoration was loaded with a 200 N force at 45° to the incline of the buccal cusp. The responses of the restored tooth with luting agents were analyzed using the 3D finite element method. RESULTS: This study demonstrated that a convergence angle of the preparation above 12° produced a decrease of the resistance of the crown to rotational effects. The study also showed that the use of luting agents that provide bonding between the restoration and dentine improved the rotational resistance of the crown on preparations with large convergence angles. CONCLUSIONS: Use of buccolingual convergence angles greater than 12° reduced the resistance form of the preparation. Luting agents capable of delivering strong bonding between the crown and the preparation improved the resistance in highly tapered preparations.

Rotational Restoration Resistance and Future Possibilities for Digital Impression Technology: Literature Review and Survey Data.

Digital impression procedures increasingly have been utilized to capture final impressions of fixed prosthodontic preparations in the natural tooth and single-implant restorations as well as for fixed partial dentures in both conditions. The literature related to restoration resistance to rotational displacement has been reviewed. Many digital camera systems have "open architecture" with the generation of generic standard tessellation language (STL) files. These STL files can be analyzed by software to determine preparation attribute-compliance with evidence-based standards. This literature review presents an overview of the knowledge base and survey data of US certified dental technicians (CDTs) and Canadian registered dental technicians (RDTs). The technician data reveal opinions about the level of clinician compliance with standards from the literature and possible future developments for additional applications of this emerging technology.

Axial wall angulation for rotational resistance in a theoretical-maxillary premolar model.

Objectives: The aim of this study was to determine the influence of short base lengths and supplemental grooves on surface area and rotational resistance in a simulated-maxillary premolar. Materials and Methods: Trigonometric calculations were done to determine the total surface area with and without supplemental grooves. Additional computations were done to determine the maximum wall angle needed to resist rotation displacement in a premolar-sized model. Wall heights of 3.0, 4.0, and 5.0 mm were used in the surface area and rotational axis computations. The rotational axis was located on the lingual restoration margin to produce a buccal-to-lingual rotational displacement. Results: Total surface area decreased with increasing four-wall taper levels from 2° to 18° and decreasing preparation heights from 5 to 3 mm. Significant surface area improvements were found with the supplemental use of mesial and distal axial grooves compared with the same condition without grooves in all taper levels and preparation height categories. Resistance to rotational displacement was determined to occur at only at very low levels of opposing wall taper angles. The use of supplemental grooves on mesial and distal axial walls significantly improved both total surface area and rotational resistance. Conclusions: The vertical wall taper angles, preparation heights, and supplemental grooves play a role in resistance form and restoration stability.

Correction: Effects of collagen matrix and bioreactor cultivation on cartilage regeneration of a full-thickness critical-size knee joint cartilage defects with subchondral bone damage in a rabbit model.

[This corrects the article DOI: 10.1371/journal.pone.0196779.].

Effects of collagen matrix and bioreactor cultivation on cartilage regeneration of a full-thickness critical-size knee joint cartilage defects with subchondral bone damage in a rabbit model.

Cartilage has limited self-repair ability. The purpose of this study was to investigate the effects of different species of collagen-engineered neocartilage for the treatment of critical-size defects in the articular joint in a rabbit model. Type II and I collagen obtained from rabbits and rats was mixed to form a scaffold. The type II/I collagen scaffold was then mixed with rabbit chondrocytes to biofabricate neocartilage constructs using a rotating cell culture system [three-dimensional (3D)-bioreactor]. The rabbit chondrocytes were mixed with rabbit collagen scaffold and rat collagen scaffold to form neoRBT (neo-rabbit cartilage) and neoRAT (neo-rat cartilage) constructs, respectively. The neocartilage matrix constructs were implanted into surgically created defects in rabbit knee chondyles, and histological examinations were performed after 2 and 3 months. Cartilage-like lacunae formation surrounding the chondrocytes was noted in the cell cultures. After 3 months, both the neoRBT and neoRAT groups showed cartilage-like repair tissue covering the 5-mm circular, 4-mm-deep defects that were created in the rabbit condyle and filled with neocartilage plugs. Reparative chondrocytes were aligned as apparent clusters in both the neoRAT and neoRBT groups. Both neoRBT and neoRAT cartilage repair demonstrated integration with healthy adjacent tissue; however, more integration was obtained using the neoRAT cartilage. Our data indicate that different species of type II/I collagen matrix and 3D bioreactor cultivation can facilitate cartilage engineering in vitro for the repair of critical-size defect.

Axial-wall inclination angle and vertical height interactions in molar full crown preparations.

OBJECTIVE: This study has been designed to evaluate the interaction of axial wall heights with inclination angles in full crown tooth preparations. The interaction of these parameters was related to the resulting preparation surface area. MATERIALS AND METHODS: A right regular pyramid was used to simulate a single mandibular molar preparation with known convergence angles and vertical heights. Various combinations of these two variables allowed the calculation of surface areas with a formula for the area of a pyramid and right triangles through trigonometric manipulations. The pyramidal model system had a 9-mm square base with vertical heights from 3- to 5-mm and single-side inclination angles from 2 to 25 degrees. The occlusal surface was a flat, square or rectangular surface and was included in the total area. RESULTS: A percentage of surface area lost or gained served as the dependent variables. The significance levels were set at 10.0% or greater magnitude of loss/gain in a surface area compared to the ideal 2 degree-level. Significant area loss was demonstrated in all alpha-level comparisons. The largest change was found in the 5-mm height grouping compared to the 3-mm height grouping, -36.6% difference between groups at the 2 degree-level. CONCLUSIONS: Axial single-side inclination angles greater than 10 degrees in 3- and 4-mm height-molars are detrimental to maximum surface area in full crown restorations. The 5-mm axial wall height with < or = 10 degree single wall has been shown to maximize the luting agent surface area between restoration and tooth structure.

Phenotypic changes in proliferation, differentiation, and migration of chondrocytes: 3D in vitro models for joint wound healing.

We aim to establish a 3D model of cartilage wound healing, and explore the involvement of chondrocytes in its repair. To characterize chondrocyte involvement in wound healing, an in vitro 3D model composed of chondrocyte mixing with either type II/I collagen or type I collagen matrix was established. The "defects" measuring 5 mm in diameter were made on each collagen matrix-chondrocyte construct to mimic in vivo cartilage defects. The effects of basic fibroblast growth factor (bFGF) on chondrocytes migration and differentiation were studied. The migration and Glucosaminoglycan (GAG) synthesis of chondrocytes in the defect areas were observed by microscopy after Alcian-blue staining. In the presence of bFGF, GAG expression increased significantly when chondrocytes were cultured in type II/I collagen matrix compared to type I collagen matrix. However, mild GAG accumulation was also found when cells were cultured in either type I or type II/I collagens without bFGF. In a 3D model of cartilage wound healing, bFGF promote chondrocyte proliferation, migration and differentiation in the presence of type II/I collagen matrix, and showed potential to regulate wound healing. These wound healing models may provide feasible methods to explore various drugs prior to human trials.

Surface area improvement with grooves and boxes in mandibular molar crown preparations.

STATEMENT OF PROBLEM: Axial-wall inclination has been shown to affect the stability of a cemented restoration in function, resulting in early restoration failure. PURPOSE: The purpose of this study was to evaluate surface area improvement with the use of supplemental grooves in tooth preparations for complete crowns. MATERIAL AND METHODS: The surface area preparation improvement in combinations of unfavorable/marginal height and axial-wall inclinations was quantified. A right regular pyramid was used to simulate a single mandibular molar tooth preparation with known axial-wall inclinations and vertical heights. Various combinations of these 2 variables allowed the calculation of surface areas with a formula for the area of a pyramid, cones, and right triangles through geometric/trigonometric manipulations. The pyramidal model system had a 9-mm square base with marginal and unfavorable vertical heights, 3 or 4 mm, and axial-wall inclination angles from 2 to 25 degrees. Conical-shaped grooves of varying lengths and widths, depending on height and axial-wall inclinations, were introduced with a tapered fissure bur. The percentage of surface area gained or lost through the supplementation with tapered grooves and boxes served as the dependent variables, alpha-factors (1) through (5). RESULTS: Significant area gains were demonstrated in all alpha-level comparisons. The greatest change was found in the 4-mm height grouping, as a positive 35.2% gain in the 25-degree level with 4 grooves. CONCLUSIONS: Axial-wall groove and box supplementation were shown to improve the surface areas of simulated mandibular molar preparations with unfavorable axial-wall inclination and vertical height levels.

Effect of margin location on crown preparation resistance form.

STATEMENT OF THE PROBLEM: The location of preparation margins may compromise the fixed prosthodontic restoration's resistance form. Purpose This study evaluated changes of opposite wall margin position on rotational resistance form compared to the equal-height margin configuration. MATERIAL AND METHODS: The trigonometric computation of the minimal resistance form preparation taper, alpha1 , was determined using a previously described formula. The alpha1-values for different tooth sizes with variation of base widths (range 4 to 10 mm) and vertical wall heights (range 4 to 9 mm) were calculated. The alpha1-values represent resistance form with both opposing wall margins at the same vertical height position. The alpha2-values were calculated with additional formulas to address uneven margin heights. Calculated alpha2-values of 10 degrees or less were considered clinically significant due to the known level of difficulty for the clinician. RESULTS: As a general trend, the alpha2-values were reduced compared to the alpha1-values with shortening opposing vertical wall heights in all tooth-size categories. Clinically significant changes in the resistance form taper were shown in all tooth size categories except the smallest 4-mm tooth base size. CONCLUSION: Fixed prosthodontic restoration resistance form is negatively affected by uneven vertical margin placement. This phenomenon reduces the resistance form of the restoration compared to equal-height margin placement.