The change in microstructure and hardness in a cast Co-Cr alloy (type A) with a carbon content of 0.45% was studied both when the alloy was aged at temperatures between 600 degree C and 1200 degrees C and when it was isothermically heat-treated at temperatures between 800 degrees C and 1000 degrees C after solubility treatment at 1200 degrees C. Furthermore, studies were undertaken on how aging at 800 degrees C, solubility treatment at 1200 degrees C and isothermal heat treatment at 800 degrees C after solubility treatment at 1200 degrees C affected the mechanical properties. The results showed that both aging and isothermal heat treatment could change both microstructure and hardness. The changes in the mechanical properties by heat-treatment, however, did not improve the usefulness of the alloy in dentistry, principally because the elongation was reduced. The change in microstructure explained the change in hardness and in mechanical properties. It was interesting to note that the properties of a Co-Cr alloy were not affected by heat-treatment at temperatures below 600 degrees C. This means that addition of gold alloys, which are soldered to a base of Co-Cr, can be both homogenised and/or hardened without affecting the properties of the Co-Cr alloy.
EMG activity was recorded from the masseter muscles of 10 naturally dentate subjects during the chewing of hazelnuts, peanuts, Optosil and chewing gum. The frequency of motor pauses (10-50 ms long) in the EMG patterns was found to be related to the textural properties of the test food. It was also found that the frequency varied for different parts of the chewing sequence, being significantly higher initially than in the last part of the chewing sequence. Motor pauses of this length, however, were absent from many of the EMG patterns. It is concluded that these motor pauses are signs of certain events during chewing but are probably not part of any basic reflex necessary for the neurophysiological regulation of chewing.
By varying the amount of acetylen in acetylene-oxygen flames Co-Cr test pieces with a varying carbon content were produced. The hardness, yield point for 0.05 per cent, 0.1 per cent and 0.2 per cent tensile strength and elongation were determined for these test-pieces. The results showed that hardness, yield points and tensile strength increased with increased carbon content, whereas the elongation lessened. The clinical importance of the altered mechanical properties due to increased carbon content in the Co-Cr alloy under study was discussed.
An experimental short term study on the effect of an occlusal interference on the path of closure of the mandible was carried out on 8 persons. The interference consisted of a gold inlay placed unilaterally in one of the mandibular first molars. Clinical and electromyographic studies revealed functional disturbances or pain in all subjects. The masticatory musculature was tender to palpation and showed coordinational disturbances; the TMJ showed tenderness to palpation, clicking and irregular movements and the interfering teeth periodontal tenderness.
The purpose of this investigation was to analyse the long-term effects of activator treatment on the dental arches and arch relationships, the dento-facial skeleton and the function of the masticatory system. A follow-up study was performed on 112 patients treated 10-20 years previously with activators as the sole orthodontic appliance. In connection with activator treatment extractions of permanent teeth were performed on 66 patients while 46 patients were treated without tooth extractions. The investigation consisted of four separate portions (Parts I-IV).
The purpose of the investigation was to examine the creep rate in an amalgam Class V restoration. The stresses in a central bucco-lingual plane of a loaded bicuspid with a Class V restoration were computed with aid of the finite element method. When the stresses were known, the creep rate was calculated. The results showed that the creep rate of a load of 150 N varied between 0.6% and 3.5% per 104 s for amalgams with large differences between their viscoelastic behaviors. A gap between the restoration and the cavity margin will thus occur if a tooth is often heavily loaded.
The aim of present investigation was to compare the antibacterial effect of biochemical root canal cleansing in permanent non-vital upper incisors with immature with those with mature root. The material comprised three groups made up of 34, 46 and 28 teeth in which the mechanical cleansing was accompanied by flushing with sterile saline and sodium hypochlorite solutions giving 0.5 or 5.0% active chloride, respectively. Samples were taken in root canals initially after removal of necrotic tissue and after completed cleansing, transferred to solid and liquid media for aerobically and anaerobically and incubated until growth appeared or up to 10 days. The microorganisms were identified by biochemical tests and gas-chromatographic analysis. The antibacterial effect of mechanical cleansing with sterile saline was very low (9%) and limited to the teeth with mature root. The flushing with sodium hypochlorite increased the antibacterial effect to about 25%. No statistical difference was found in the antibacterial effect between flushing with 0.5 % or 5.0% sodium hypochlorite solutions. The antibacterial effect was, however, irrespective of the sodium hypochlorite concentrations, less good in teeth with immature root at the statistically significant 5% level. It was concluded that mechanical cleansing of root canals in teeth with immature root with the instruments now available is inadequate. This inadequacy cannot be compensated for by use of highly concentrated solution, with dissolving effect on necrotic tissue, for flushing. The use of such substances which also have toxic effect on the tissue should be avoided.
A method is presented for reinforcing dental composite restorative materials by incorporation of a polymer impregnated porous inorganic component. A method for producing such an inorganic component in the form of a three-dimensional glass fiber network is described. The structure of the network is demonstrated with the aid of scanning electron microscopy.
Fluorine gradients were analysed in sound facial enamel of 58 pairs of homologous contralateral premolar teeth. A macroscopic stepwise acid etching technique was used to determine the F-concentration to the depths of 40-200 microns. Usually three successive enamel layers (10, 10, and 20 microns) from enamel surface and inwards were removed. Eight pairs of teeth (control group) which had not been subjected to any form of fluoride treatment in the study, were used to assess the difference between teeth extracted at three-week-interval. The F-gradients were almost identical, with only small differences between the teeth. F-concentrations usually decreased from about 900 ppm within the first 10 microns to about 200 ppm at a depth of 40-50 microns. In ten experimental groups (5 pairs of teeth in each group) the F-uptake was studied after various forms of topical application. Contralateral teeth served as control teeth. The highest F-uptake was observed when a fluoride varnish, Duraphat (5% NaF) was applied three times at one weeks' interval. The F-concentrations were about 2000, 900 and 550 ppm, respectively, in the first, second and third enamel layer. The increase in F-concentration in the first enamel layers analysed was significant, but not in the deepest. When testing the effect of paintings procedures with 2% NaF (pH = 7 and 5); 8% SnF2; 5% Na2PO3F; 2% APF-gel (Flura-Gel) in a similar way, a moderate F-uptake was found (100-450 ppm). The uptake of F was limited to the first 10 microns of the enamel. Only 2% NaF (pH = 5) And the APF-gel gave a significant F-uptake within the first layer. Daily mouthwashing procedures during 21 days resulted in insignificant uptake of F when 0.025% and 0.05% NaF solutions were used. Not even rinsing with 0.025% NaF solution for more than 100 days and rinsing with 0.2% NaF solution once a week for three weeks resulted in any significant uptake. The results showed that the F-uptake in vivo from conventional topical application is small and limited to the first few microns of the enamel surface. However, by prolonging the exposure of the enamel surfaces to fluorides in varnishes with high F-concentrations it appears possible to highly raise the F-concentration of the enamel surface and in deeper layers.
An individualized technique for radiography of the temporomandibular joint utilizing oblique lateral transcranial projection is described. The patient is fixed in a cephalostat and the central ray directed through the horizontal long axis of the condyle. The information yielded when applying the individualized technique has been compared with that yielded from a standard technique and tomography. The plane of sectioning for tomography was oriented perpendicular to the horizontal long axis of the condyle. The material comprised radiographs from 30 joints. The condyle to fossa relation was studied as well as the occurence of structural changes. Neither the individualized technique nor the standardized technique gave an accurate picture of the condyle to fossa relation when compared to tomography. However, the individualized technique tended to give the same result as tomography more often. Tomography revealed the greatest number of structural changes (66) followed by individualized technique (47) and standard technique (19). Most changes were noted exclusively in one projection. A combination of individualized technique and tomography revealed more changes than a combination of tomography and standard technique.
A standardized surgical procedure in rats is described which allowed a histometric registration of the repair of cementum, periondontal ligaments and bone, and which eliminated the possibility of interference of pocket epithelium during the healing process. Using an extraoral incision, the lateral surface of the mandible was exposed, and a cavity was cut through the vestibular bone plate, the periodontal ligaments and into the root surface, using a specially designed handpiece and bur. This procedure was performed in 20 male Wistar rats, 9 weeks old. The observation period was 12 weeks. The systematic error, precision and interanimal variation were examined for histometric registrations of the repair of cementum, periodontal ligaments and bone. The precision of the histometric procedures was in this study found to be 5% or less for most of the different structures measured, and the estimated combined systematic errors probably less than 5% for cementum repair. The coefficient of variation in cementum repair among different rats was 24%. This variance has two components, the combined influence of systematic errors and precision of histologic and histometric procedures and the other the biological variance due to inter-animal differences. The precision and systematic errors probably do not account for more than one third of this variance, the remaining two thirds being inter-animal differences. These differences could not be completely controlled in this study in spite of the use of a controlled genetic strain of rats bred in litters of the same size under SPF conditions.
A standardized surgical periodontal injury was performed in 67 male Wistar rats 9 weeks of age. An osteotomy was made with a burr through the vestibular bone plate and the periodontal ligaments and into the superficial part of the root surface of the mandibular first molar. The rats were sacrificed with observation periods ranging from 1 day to 2 years postoperatively. A histometric registration was made of the repair of alveolar bone, periodontal ligaments and cementum. Bone repair was found after 7 days and included a bony alkalosis. On the period from 7 to 14 days after surgery this ankylosis was removed by resorption process. Argyrophilic reticulin fibers were present 3 to 5 days after surgery. Precollagen fibers were found after 4 days, whereas mature collagen fibers inserting in new formed cementum, was seen after 14 days. The number of collagen fibers increased substantially until 28 days after surgery. Initial cementum repair was found after 14 days and increased substantially with increasing observation periods tending to reach the thickness of the contralateral control tooth. Based on these findings a new concept of healing of the surgically injured periodontium in rats is presented. According to this the healing occurs in three successive phases. 1. Bone repair with formation of an ankylosis. 2. Repair of the periodontal ligament including removal of the established ankylosis. 3. Repair of Cementum.
The purpose of the investigation was clinically, microbiologically and radiologically to assess the effect of calcium hydroxide as a temporary root-filling inserted in the same sitting as root canal debridement in non-vital permanent incisors with mature and immature root, infected or uninfected root canal and with or without radiologically demonstrated periapical bone changes. The material consisted of 141 teeth divided in 3 groups in which mechanical cleansing was accompanied by flushing with sterile saline and sodium hypochlorite solutions giving 0.5% or 5.0% active chlorine, respectively. Microbiological samples were taken from root canals after extirpation of necrotic pulp tissue, after completed cleansing of the root canal and 3 and 6 month after treatment. Results of treatment were evaluated from the radiographs taken before treatment and at the 3 and 6 month follow-ups. Complication, pain and an abscess, occurred in 2 cases, 2 and 5 days, respectively, after treatment. No statistical correlation between occurrence of samples that gave growth, taken from the root canals at 3 (8%) or 6-month control (9%) and 1) bacteriological status of the root canal prior to filling with calcium hydroxide, 2) the development of the root or 3) periapical healing at 3 or 6 month follow-up could be ascertained. Periapical bone healing at the end of 6-months observation period was noted in 61 teeth (46%), regression of periapical bone lesions in 64 (49%) and no periapical healing in 6 (5%). The only difference in healing pattern, statistically significant on 0.1% level, was found in the group of teeth flushed with 5.0% sodium hypochlorite. At 3 month control they showed percentually less cases with regression and more cases with no healing of periapical bone lesions than the teeth in the other two groups. It was concluded that treatment in one sitting can be done routinely, irrespective of the initial status, in all those cases where no other treatment is possible. If the periodontium or the periapical bone are injured during cleansing procedures or if necrotic rests are not pressed out through the apical foramen, no complications after treatment need to be feared.
The relative resistance of the oral mucosa to carcinogenic influences was studied in connection with altered fatty acid composition of the oral epithelium in the rat. The water-soluble carcinogen 4-nitrochinoline N-oxide was used. The lipid changes were induced either through essential fatty acid (EFA) deficiency or through carbon tetrachloride-induced liver cirrhosis. Although the strongest initial reaction in the oral mucosa was seen in the EFA-deficient rats, a result considered to be due to increased permeability of the epithelium to the carcinogen, oral carcinoma did not develop earlier in the EFA-deficient group than in normal controls. The liver cirrhotic group developed clinical signs of carcinoma earliest (5.4 months) whereas in EFA-deficient and normal rats carcinoma appeared after an average of 6.0 and 6.5 months, respectively. However, as a previous study (Lekholm 1976) has shown that the fatty acid changes were less pronounced in cirrhotic than in EFA-deficient rats, it would appear that there is no clear correlation between the extent of lipid distrubance and reduced resistance of the oral epithelium to the induction of carcinoma.
Though previous experiments with fat-soluble carcinogens have demonstrated a protective effect of the saliva against chemically induced oral cancer it is not known if this also holds true for water-soluble carcinogenic agents. In vitro experiments indicate that the water-soluble 4NQO (4-nitrochinoline N-oxide) easily penetrates a layer of saliva similar with that normally present on the oral mucous membranes. It is possible that this quality, on intraoral applications of 4NQO, could eliminate the protective barrier of saliva. The protective effect of the saliva was examined in the present investigation. Xerostomia was induced in 15 rats and 4NQO was applied to the palate 3 times a week. After 4.7 months, on an average, palatal cancer appeared in all rats. In comparable investigations the result was 7 months with rats treated in an identical manner except for their salivary secretion remaining intact. This time difference represents approximately 33% of the time necessary for the development of oral cancer in normal rats by means of 4NQO. It was concluded, that a protective effect of the saliva exists whether the oral mucous membranes are attacked by water--or fat-soluble carcinogens.
A calcium hydroxide-containing cement (Reocap) was tested with regard to its suitability as a pulp capping agent. The pulp of 34 monkey teeth was exposed and Reocap was applied to the pulp wound and the cavity floor, after which the cavities were filled with amalgam. The observation periods were 8 days (10 teeth) and 80 days (24 teeth). After 8 days a necrotic area was seen in the pulp subjacent to the pulp capping agent and the surrounding tissue was inflamed to varying degree. After 80 days hard tissue formation was observed at the exposure site in 21 teeth. The hard tissue enclosed areas of necrotic and/or vital tissue and a complete bridge had not formed. In 7 teeth the pulp was necrotic whereas 3 teeth presented a pulp free of inflammation. In the remaining teeth the pulp showed a chronic inflammatory reaction. As judged by these results, Reocap does not appear to be as well suited as a pulp capping agent as pure calcium hydroxide.
The influence of different acetylene-oxygen flames on the carbon content of a dental cobalt-chromium alloy, type A, was studied under standardised casting conditions. The alloy was cast, both immediately after the formation of the Bull's eye and after prolonging the melting time. Further, the effect of re-casting, varying the amount of alloy casted and using different sections of the same acetylene-oxygen flame when melting was studied. The results showed on the one hand that the chemical character of the section of flame used and not the gasmixture as such determined the carbon content of the casting, and on the other that the acetylene-oxygen flames can increase but not decrease the carbon content in the casting. Increase of the carbon content of a cobalt-chromium alloy causes a considerable change in its microstructure.
In a specially designed casting and gas measuring equipment the melting process used in dentistry for Co-Cr alloys using the acetylene-oxygen flame as heating source were investigated. The influence of different gas mixtures in the flame and different crucible temperatures on: 1. The temperature increase in the alloy. 2. The melting time of the alloy. 3. The temperature in the alloy when all the metal has melted and forms the spherical shape--the Bull's eye stage. 4. The melting time when different amounts of alloy were used in the melt. 5. The temperature increase and melting time when flux are used. 6. Different distances between the torch and the alloy. were studied. The results showed that the melting process is mainly governed by the heating effect and the chemical character of the parts of the flame used and also on the initial temperature of the crucible.
The local clinical and histological reactions resulting from the use of a tissue adhesive, isobutylcyanoacrylate, were studied in the oral cavity of dogs. In each of 4 animals, 6 pairs of parallel incisions were made in the buccal mucosa. One incision in each pair was closed with adhesive material while the other incision was sutured with silk. The wounds were studied clinically and histologically at intervals ranging from 2 to 21 days. Clinically there were differences in the healing between gland glued and sutured incisions during the first 11 days. After 11 days the healing reactions were approximately the same in both groups. Histologically, the adhesive caused a delayed and disturbed healing of both the epithelium and connective tissue compared with that observed when sutures were used. As a result of this investigation, isobutylcyanoacrylate is not recommended for use instead of conventional and modern suturing materials when closing intraoral wounds.
