William L. Kydd

Leakage associated with load fatigue-induced preliminary failure of full crowns placed over three different post and core systems.

Thirty-six maxillary central incisors were endodontically treated and restored with a post and core and cast crown. Three different post and core systems were evaluated. Restored teeth were fatigue-loaded until preliminary failure of the casting occurred as detected by a strain gauge bonded across the lingual margin of the cast crown. After preliminary failure, fatigue loading was continued for 100,000 load cycles with the crown margin exposed to basic fuschin dye. Teeth were then immersed in dye for 24 h, sectioned, and evaluated for leakage. There was no significant difference in the number of load cycles required to cause preliminary failure among the three post and core systems. Leakage occurred in all three groups, with no significant difference between groups. The occurrence of preliminary failure is clinically undetectable, yet it allows leakage between the restoration and tooth that may extend down the prepared post space.

Duration of nocturnal tooth contacts during bruxing

11. Ogus, HD, and Toiler, PA: Common disorders of the temporomandibular joint. Dental Practitioner Handbook No. 26, 1981. Oberg, T, Carlsson, GE, and Fajers, CM: The temporomandibular joint--A morphological study on human autopsy material. Acta Odontol &and 29:349, 1971. Griffin, CJ. Hawthorn R, and Harris, R: Anatomy and histology of the human temporomandibular joint. Monogr Oral Sci 4~1, 1975. Smith, RJ: Mandibular biomechanics and temporomandibular function in primates. Am J Phys Anthropol 49:341, 1978. Boering, G Anatomical and physiological considerations regarding the temporomandibular joint. Int Dent J 29:245, 1979. Kivirikko, KI: Urinary excretion of hydroxyproline in health and disease. Int Rev Connect Tissue Res 5:93, 1970. Bergman, I, and Loxley, R: The determination of hydroxyproline in urine hydroxysates. Clin Chim Acta 27:347, 1970. Prockop, DJ, Kivirikko, KI, Tuderman, L, and Guzman, NA: The biosynthesis of collagen and its disorders. N Engl J Med 30:13, 1979. Munksgaard, EC, Rhodes, M, Mayne, R, and Butler, WT: Collagen synthesis and secretion by rat incisor odontoblasts in organ culture. Eur J Biochem 82:609, 1978. Crouch, E, and Bornstein, P: Collagen synthesis by human amniotic fluid cells in culture: Characterization of procollagen with three identical proalpha 1 (I) chains. Biochemistry 17~5499, 1978 Narayanan, AS, and Page, RC: Biochemical characterisation of collagens synthesised by hbroblasts derived from normal and diseased human gingiva. J Biol Chem 251:5464, 1976. 12.

The effect of cusp form and occlusal surface area on denture base deformation

Abstract A method has been described which will permit separate evaluation of the effect of cusp form and area of the occlusal table on deformation of the denture base. The deformation of the denture base during various test procedures was continuously recorded.

Functional loading of the dentition during mastication

A method is described whereby the electrical activity in the masseter muscles is used as an index of chewing force. By using the kinesiograph, it was possible to determine the interrelationship of the phases of the chewing cycle and to measure the duration of each phase. On the basis of a pilot study of 10 dentate subjects and two complete denture wearers, it appears that, although the magnitude of the applied load is reduced in denture wearers, this is to some extent compensated for by an increase in the time it is applied. The results also suggest that a greater force is applied to the supporting mucoperiosteum when inverted cusp teeth are used in the construction of the dentures.

Marginal leakage of cast gold crowns luted with zinc phosphate cement: an in vivo study.

Marginal gaps of cast restorations are filled with luting agents that are soluble in intraoral fluids. This study investigated the marginal openings in eight extracted teeth with cast crowns that had been intraoral for 20 years or more. These teeth were extracted either because of periodontal disease or to facilitate insertion of a removable partial denture. Initially, the roots of the teeth were sealed with two coats of fingernail polish within 2 mm of the crown-tooth interface. Next, the teeth were immersed in a 0.05% aqueous solution of basic fuchsin die for 24 hours. Finally, each tooth was sectioned at four locations 1 mm apart. At each of these four sections, cement film thickness between tooth and casting, and microleakage were determined. The results of this study showed a mean cement film thickness of 74 microns on the mesial surface and 57 microns on the distal surface. Mean microleakage values were 432 microns on the mesial surface and 274 microns on the distal surface.

The response of the human periodontal ligament to torsional loading—I. Experimental methods

Abstract A test technique is described in which torsional loads are applied to human maxillary central incisors in vivo . The central axis of the incisor is located by a stereoscopic X-ray method and the tooth loading device is adjusted by means of a setting jig so that torque is applied about this central axis. The maximum torque which can be applied is ± 0·05 Nm and the maximum rotation of the tooth is ± 0·02 radian (± 1·2). A servo-control system allows one to apply any desired torque or deflection history. e.g. a creep or stress relaxation test or a cyclic load of any waveform. Initial results obtained with this system are presented and show that the torque vs rotation response is initially linear but becomes highly nonlinear at higher torques. Creep tests and cyclic loading tests indicate that the periodontal ligament is viscoelastic in nature. Periods of cyclic loading separated by rest periods of 1–20 min show that the commonly observed decrease in tissue stiffness during the initial few load cycles is not a permanent effect in this in vivo test. Recovery to the initial stiffness takes place rapidly. e.g. 50 per cent recovery in 5 min at zero load.

Root Surface Measurement Using a Digital Computer

An accurate method is presented for the determination of the area of the periodontal ligament attached to teeth. This method requires the use of digitizing equipment for an accurate determination of tooth cross sections and a digital computer for final manipulation of the area calculations. The procedure is general and is not restricted to single-rooted teeth.

Swallowing and resting forces related to lingual flange thickness in removable partial dentures

Abstract A method of evaluating forces of the tongue in a lateral direction utilizing transducers placed in denture bases of removable partial dentures has been presented. Results suggest that on a daily basis the resting posture of the tongue contributes more lateral force to a lower dental prosthesis than has been recognized. In order to minimize lateral forces of the tongue directed toward dental prostheses, it would seem advisable to make the lingual flanges as thin as possible.

Bone-titanium implant response to mechanical stress

The purpose of this study was to investigate the nature and strength of any bond which may develop between alveolar bone and titanium allow implants. Implants were placed in a previously prepared edentulous region in the mandibles of dogs. The implants were conical in shape with circumferential grooves to provide axial retention. Five months later the implants were rotated. No indication was found of an adhesive bond being broken.

A stereoscopic X-ray procedure for locating the centroidal axis of the root of a maxillary central incisor.

Abstract A stereoscopic X-ray technique for determining the centroidal axis of a maxillary central incisor is described in this paper. This axis is defined by two points, the first being the apex of the root and the second defined as being between two lead foil markers on the labial and lingual surfaces. The X-ray film is located against a flat machined surface which contains two gold inserts defining an x-y coordinate system, from which measurements can be made directly. The determination of the locations of the two required points on the centroidal axis required that three separate radiographs be taken of the specified tooth from three given directions. The stereoscopic X-ray device used for this purpose allows accurate control on the relative positions of the X-ray source, the tooth and the X-ray film. Accuracy was checked by photographing a radio-opaque target and the results of this check indicated a potential error of 0·001 in.