Microbiology of the pericoronal pouch in mandibular third molar pericoronitis

The microorganisms associated with mandibular third molar pericoronitis were investigated using direct microscopy and anaerobic culture method. The pericoronal pouch was sampled with paper points in A) 8 patients without mandibular third molar pericoronitis and B) 6 patients with mandibular third molar pericoronilis. Under the microscope, the microflora was found to be a complex mixture comprising gram-positive and gram-negative cocci, rods and filaments (including fusiform and curved rods), motile rods and spirochetes. Significantly higher proportions of motile, gram-negative rods were found in group B than in group A. The predominant cultivable microflora of 9 samples: A (4) and B (5) comprised several species of facultative and obligate anaerobic bacteria, namely Peptostreptococcus. Streptococcus, Actinomyces, Eubacterium, Propionibacterium, Veillonella, Porphyromonas, Prevotella, Bacteroides, Fusobacterium, Campylobacter, Staphylococcus, Stomatococcus, Lactobacillus, Neisseria, Capnocytophaga, Haemophilia, Selenomonas and Centipeda species. The microflora in pericoronitis appeared similar to that of diseased periodontal pockets.     

The plunging ranula. Pathogenesis, diagnosis and management

Ranulas are cysts resulting from retention, or extravasation of saliva from the sublingual gland. Two varieties are described: a superficial or oral ranula and a cervical or plunging ranula. The plunging ranula is located below the mylohyoid muscle and may present as a swelling in the upper part of the neck. Four cases are described to illustrate that this condition can be the cause of a neck swelling. Aetiology, differential diagnosis and surgical management are also discussed. Recurrences are mainly due to unfamiliarity with this phenomenon and ignorance of its aetiology. Successful treatment of the plunging ranula consists of excision of the ipsilateral sublingual salivary gland, which is the source of this disorder, and intra-oral evacuation of the pseudocyst of the neck swelling. There is no need for an extensive neck dissection of the cervical extension.     

Finite element analysis of three- and four-unit bridges

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.     

Construction of a maxillary prosthesis with a hollow obturator by the balloon technique and a case report

The authors devised a new method for making a maxillary prosthesis with a hollow obturator, which was named the Balloon Technique. This new technique has a number of advantages over the conventional method in that it not only facilitates the molding of a soft plastic hollow obturator in a single process, but also simplifies the trial fitting of the completed obturator. Furthermore, it makes possible firm adhesion of the hollow obturator and the denture base by the hot-melt method while the denture base resin is cured. Finally, the completed maxillary prosthesis is extremely light.     

Protective efficacy of active and passive immunizations against experimental infection with Bacteroides gingivalis in ligated hamsters

The protective efficacy of immunization against Bacteroides gingivalis infection was examined in hamsters. Whole cells or extracted hemagglutinin of B. gingivalis 381 was injected with incomplete Freund adjuvant into the inguinal regions of hamsters. Two weeks after the rats received a booster injection, cotton threads were tied coronally to the gingival margins of the mandibular first molars, and then a streptomycin-resistant B. gingivalis 381R' strain was inoculated into the rats' oral cavities. The subcutaneous immunizations resulted in slight reductions in the numbers of B. gingivalis on the ligature threads compared with the sham-immunized group. Peroral administration of whole cells of B. gingivalis to hamsters elicited salivary immunoglobulin responses, but no reduction of B. gingivalis 381R' colonization was found in this group. Repeated passive immunizations with rabbit antiserum to B. gingivalis into the oral cavities of the hamsters resulted in a reduction in the number of organisms in the periodontal region.     

A scanning electron microscope study of monkey maturation-stage ameloblasts

The maturation-stage enamel organs of Macaca arctoides and Macaca mulatta were examined in order to determine whether the cells were similar to those of the continuously erupting rat incisor. Tooth buds of the permanent dentition were fixed in formaldehyde-glutaraldehyde and post-fixed in OsO4. The enamel organs were separated from the enamel during dehydration, critical-point-dried, metal-coated, and examined in a scanning electron microscope. The results showed that there were few differences in the morphology of maturation-stage ameloblasts of these primates compared with those of other species reported in the literature. The apical plasma membranes were either smooth- or ruffle-ended, while the later membranes had maze, microvillous, or ridge configurations, also seen in rats, and an additional configuration of interdigitating bulbous extensions. The blood vessels of the papillary layer in monkeys were about 7 micron in diameter, considerably larger than those of the rat.     

Effects of delayed polishing on gap formation of cervical restorations

This study evaluated the effect of polishing after one-day storage in water on the gap formation around a Class V restoration completely bordered by enamel (coronal cavity) using one resin-modified glass ionomer, one compomer and one conventional glass ionomer as a control. The study also examined gap formation of these materials in two different cervical restorations-a cervical cavity incisally bordered by enamel and cervically bordered by dentin and a root surface cavity completely bordered by dentin. When the specimens of the two types of glass-ionomer material were polished immediately after the setting procedure, 100-120 gaps around the coronal restorative cavity were observed. In contrast, only 10-20 gaps were observed when the specimens were polished after one-day storage. Significant differences in the two glass-ionomer restorative materials were observed between immediate polishing and polishing after one-day storage. The compomer not show this pattern. Restorations placed in enamel/dentin and all-dentin gave results similar to those in all-enamel.     

Effect of serotonin (5-HT) on trigeminal rhythmic activities generated in in vitro brainstem block preparations

We used rat isolated brainstem block preparations to analyze the functional roles of serotonin receptors in the generation of trigeminal rhythmic activities. We previously reported that trigeminal rhythmic activities could be induced by some pharmacological applications in an isolated brainstem preparation with a rostral boundary at the border between the inferior and superior colliculus, and a caudal border at the level of the rostral facial nucleus. However, the same stimulation did not induce trigeminal rhythmic activities in a whole brainstem block preparation with the same rostral boundary and a caudal border at the obex level. In the present study, both the 5-HT(1A) phthalimido-butyl-piperazine, and the 5-HT(2C) agonist, 1-2,5-dimethoxy-4-iodophenyl-2-aminopropane, combined with N-methyl-D,L-aspartate and bicuculline, elicited trigeminal rhythmic activities in a whole brainstem block preparation. Our results suggest that serotonin has both facilitation and inhibition effects on the generation of trigeminal rhythmic activities in an isolated brainstem block preparation in vitro.     

Upper removable appliance or Jones Jig for distalizing first molars? A randomized clinical trial

Aim – To compare the effectiveness of two intra‐oral methods of distalizing upper first permanent molars: an upper removable appliance (URA) and a Jones Jig. Sample – Twelve patients were randomly allocated to URA treatment and 11 patients to a Jones Jig. Methods – Upper study models were collected at the start of treatment and after 6 months of appliance wear. The amount of distal movement, tipping and rotation of the upper first permanent molars and mesial movement of the upper first permanent premolars was measured using a reflex metrograph. Results – There were no statistically significant differences between the two treatment methods for any of the outcome measures (P < 0.05). Distal movement obtained by both appliances was approximately 1 mm. Conclusions – The amount of distal movement obtained with both appliances was small and no differences were shown in the amount of molar tooth movement. It is suggested that there is no advantage in using the Jones Jig as a non‐compliance appliance.     

The effect of disc thickness and trauma on disc surface friction in the porcine temporomandibular joint

The pathomechanics of osteoarthritis in the human temporomandibular joint (TMJ) are unknown. Compromised lubrication is a potential factor, but, lubrication within even the normal TMJ is not understood completely. Weeping lubrication is a concept that may be applicable to the TMJ. A characteristic of weeping lubrication is a slow increase in friction during static loading. The rate of increase in friction is related to the rate of lateral movement of synovial fluid away from the loading area. The TMJ disc is expected to be the main source of TMJ lubrication. This study tested two variables, disc thickness and magnitude of trauma to the disc, as factors that can affect the rate of flow of synovial fluid and thus alter lubrication of the disc surfaces. To test these variables, TMJ disc surface friction was measured before and after an impulse load. Before the impulse load, all discs demonstrated a gradual increase in friction during light static loading. The rate of increase in friction was inversely related to the disc thickness (R(2)=0.75). After an impulse load of known magnitude and peak force, disc surface friction was higher. The magnitude of this surface friction was correlated with the magnitude of the impulsive blow (R(2)=0.89) and the area of surface damage (R(2)=0.85). Disc thickness was a significant factor in determining the minimal impulse needed to produce higher surface friction (R(2)=0.99). These results confirm that disc thickness and trauma to the disc affect surface friction in the TMJ, and therefore may be important factors in compromised lubrication and the development of osteoarthritis.