ABSTRACT
A two-dimensional finite element model of a mandibular quadrant was used to examine differences in magnitude of the principal stresses from the placement of three- and four-unit bridges. The area of interest spanned the first premolar to the second molar. Loading conditions were (i) vertical and distributed and (ii) 30 degrees to the vertical and concentrated. The principal stresses were calculated and compared for: (i) the first molar removed with the remaining bone either cancellous or cancellous surrounded by a cortical shell; (ii) as in (i) but with the second premolar and first molar removed; (iii) a three-unit bridge spanning the second premolar to the second molar; and (iv) a four-unit bridge spanning the first premolar to the second molar. Each tooth was supported by periodontal ligaments, cortical and cancellous bone with each assigned the appropriate physical constants. Removal of the first molar resulted in considerable variation of the stresses especially when the cortical shell was replaced by cancellous bone. Because of the lower modulus of cancellous bone and its lower load-bearing capabilities the stresses were three to ten times lower and more uniform within the cancellous bone. Generally, the addition of a bridge resulted in lower and better distributed sigma min stresses. The bridge also resulted in higher tensile stresses distal to the abutment teeth which theoretically could result in bone deposition. No significant differences in magnitude were observed between the three- and four-unit bridge. From a stress standpoint the bridges resulted in more uniform stress distribution around the abutments and an increase in the tensile stress distal to the abutments. Such findings support the placement of a fixed bridge to maintain bone in an edentulous area.
Subject(s)
Dental Abutments , Dental Stress Analysis , Denture Design , Denture, Partial , Alveolar Process/physiology , Bicuspid/physiology , Elasticity , Humans , Mandible/physiology , Molar/physiology , Periodontium/physiology , Poisson Distribution , Pressure , Tensile StrengthABSTRACT
A two-dimensional finite element model of a mandibular quadrant was used to examine the stresses and displacements resulting from a 100 N load placed as follows: (i) distributed on the second molar, (ii) concentrated at 30 degrees to the vertical on the second molar, and (iii) distributed on the second premolar and second molar. Each tooth was supported by periodontal ligaments, cortical and cancellous bone. The modulus and Poisson's ratios for each material were selected from accepted values. The principal stresses were determined throughout the model, with special emphasis being placed for elements in the immediate vicinity of the teeth mentioned above. It was found that for the case where the load was uniformly distributed on the second molar the stresses sigma min were mostly compressive (-) in nature while sigma max were mostly tensile (+). In the case where the load was concentrated and at 30 degrees to the vertical, the magnitude of the stresses were three to five times greater and the pattern less uniform than those resulting from the distributed load. The concentrated load at 30 degrees to the vertical resulted in higher bending stresses than the distributed load and hence higher sigma max stresses.
Subject(s)
Mandible/physiology , Models, Biological , Bicuspid/physiology , Dental Stress Analysis , Humans , Mandible/anatomy & histology , Molar/physiology , Periodontal Ligament/physiology , Stress, Mechanical , Tooth Root/physiologyABSTRACT
A dimethyl siloxane triacetoxy terminated silane, Type A adhesive, was modified with the base component of a medium grade polydimethyl siloxane with vinyl groups, MDX 4-4210, to produce a more pliable maxillofacial prosthesis. Force-displacement curves of various ratios of Type A adhesive/MDX 4-4210 were determined and compared with force-displacement curves obtained from human subjects. Within the force range of 0.4 to 1.2 N, the force-displacement slopes obtained on human subjects compared favourably with some of the Type A adhesive/MDX 4-4210 test specimens. The force-displacement slopes for the elastomers and humans were not in agreement for forces below 0.4 N.
Subject(s)
Biocompatible Materials , Dimethylpolysiloxanes , Facial Muscles/physiology , Maxillofacial Prosthesis , Silicone Elastomers , Silicones , Siloxanes , Skin Physiological Phenomena , Cheek/physiology , Ear, External/physiology , Elasticity , Forehead , Humans , Stress, MechanicalABSTRACT
Two-dimensional photoelastic models were used to determine the optimum design and loading conditions for a three-unit castable ceramic fixed partial denture. Findings relating to design and material variables can be summarized as follows. 1. Higher modulus cements impart more rigidity to the fixed partial denture design and result in lower stresses. 2. A short connector results in higher stress than a long connector; however, the length of the connector should not exceed one half the mesial-to-distal length of the pontic. 3. An intermediate thickness of cement results in the best stress distribution. 4. The male connector is best attached to the bulkier abutment. 5. Occlusal cement eccentricity is less desirable than cervical eccentricity. 6. The most undesirable loading site is directly above the connector.
Subject(s)
Dental Stress Analysis/methods , Denture Design , Denture Precision Attachment , Denture, Partial, Fixed , Dental Stress Analysis/instrumentation , Humans , Models, BiologicalABSTRACT
A dimethyl siloxane-triacetoxy terminated silane, Type A adhesive, can be modified with the base component of a medium grade polydimethyl siloxane with vinyl groups, MDX 4-4210, to produce more pliable maxillofacial prostheses. The mechanical properties of samples with various Type A adhesive/MDX 4-4210 ratios were determined. Addition of the MDX 4-4210 base decreased the hardness, modulus, and ultimate tensile strength, while the percentage elongation increased. The initial tear strength was relatively constant for the various ratios except for the 50/50 mix, where a 50% decrease was observed. The ability to obtain different mechanical properties by using various ratios of Type A adhesive and MDX 4-4210 could result in the production of maxillofacial prostheses which will more closely stimulate the properties of facial tissues.
Subject(s)
Dimethylpolysiloxanes , Materials Testing , Maxillofacial Prosthesis , Silanes , Silicon , Silicone Elastomers , Silicones , Siloxanes , Adhesiveness , Adhesives , Biomechanical Phenomena , Hardness Tests , Prosthesis Design , Surface Properties , Tensile StrengthSubject(s)
Dental Stress Analysis , Denture Design , Denture, Partial, Removable , Elasticity , Stress, MechanicalABSTRACT
An idealized axisymmetric finite element model of a second premolar restored with a post and core was used to study the distribution and magnitude of stresses as a function of the following parameters: the diameter of the post, the length and the shape of the post, and finally the interface characteristics between post and cement. Emphasis was directed toward the cement layer interposed between the post and the tooth. Bonding between the post and the cement appeared to be the most important parameter to achieve optimal mechanical behavior of the tooth-prosthesis combination.
Subject(s)
Crowns , Dental Stress Analysis , Post and Core Technique , Tooth/physiology , Dental Bonding , Dental Cements , Denture Design , Humans , Models, Biological , Surface Properties , Tooth Root/physiologySubject(s)
Dental Impression Materials , Rubber , Polyethylene Glycols , Silicone Elastomers , SulfidesSubject(s)
Dental Amalgam , Dental Stress Analysis , In Vitro Techniques , Pressure , Stress, Mechanical , Tensile StrengthABSTRACT
The (1) tooth-supported, (2) ridge-supported, and (3) tooth- and ridge-supported variations of the disjunct removable partial denture were studied. When testing loads were applied to three sites, bilaterally and unilaterally, it was found that the stresses were highest when the removable partial framework was tooth-support. No significant difference was recorded between the ridge-supported partial denture and the tooth- and ridge-supported partial framework. Further refinement of the pinsleeve mechanism may be necessary to effect better control over the distributions of the stresses.
