A síndrome de Down (SD) é a anomalia genética mais comum em seres humanos e acomete todas as etnias e níveis socioeconômicos. Esta síndrome também se manifesta na cavidade bucal dos indivíduos, alterando tecidos moles e duros, a constituição salivar e a microbiologia oral. Em relação à cárie dentária, muitos estudos na literatura avaliaram a experiência desta doença nas pessoas com SD, mas os resultados são conflitantes. Enquanto a maioria dos trabalhos reportou uma menor experiência de cárie nas pessoas com a síndrome comparadas a indivíduos não sindrômicos, outros estudos não mostraram diferença. Assim, três estudos foram conduzidos para elucidar algumas controvérsias. O primeiro estudo foi uma revisão sistemática de literatura que teve como objetivo determinar se existem ou não diferenças na experiência de cárie entre pessoas com e sem SD. Foram incluídos 13 artigos para extração dos dados. Entretanto, devido à baixa qualidade metodológica de todos os estudos, concluiu-se que não existe evidência cientifica para suportar a hipótese que pessoas com SD apresentem menor experiência de cárie do que indivíduos não sindrômicos. O segundo estudo teve caráter observacional e transversal e foi conduzido com131 crianças entre 6 e 12 anos de idade (60 com SD e 71 sem SD). Foram verificados os índices de placa (IP), índice de sangramento gengival (ISG), experiência de cárie e quantificação salivar Streptococcus mutans (S. mutans). Questionários que incluíram hábitos de escovação, dieta e renda dos participantes foram realizados. A experiência de cárie foi similar entre os dois grupos. Os IP e ISG foram menores nas crianças com SD e isto foi associado a uma maior supervisão dos pais ou responsáveis durante a escovação. Significativamente mais crianças com SD tiveram altas contagens salivares de S. mutans. O estudo concluiu que crianças com e sem SD da mesma faixa-etária apresentam experiência de cárie similar. Entretanto, crianças com SD frequentemente apresentam maiores contagens salivares de S. mutans do que crianças sem a síndrome. Além disso, crianças com SD que têm escovação supervisionada por pais ou cuidadores apresentam menores índices de placa e sangramento gengival. O terceiro estudo foi observacional laboratorial conduzido com o objetivo de avaliar a diversidade genotípica de S. 5 mutans e a acidogenicidade de diferentes genótipos deste microrganismo em crianças com e sem SD. Dezessete crianças (9 com SD e 8 sem SD) com altas contagens salivares de S. mutans foram selecionadas. Elas foram divididas em dois grupos: livres de cárie e com alta experiência de cárie. Isolados de S. mutans foram obtidos de cada paciente e 99 cepas (50 de SD e 49 sem SD) foram confirmadas utilizando PCR. Por meio de AP-PCR, observaram-se os diferentes perfis genotípicos. A acidogenicidade de uma cepa representativa para cada genótipo obtido foi avaliada. As crianças com SD tiveram uma menor diversidade genotípica de S. mutans do que as crianças sem a síndrome, e os genótipos avaliados das crianças com SD foram significativamente menos acidogênicos do que nas crianças sem síndrome. O estudo concluiu que crianças com SD apresentam genótipos de S. mutans menos acidogênicos quando comparados aos de crianças sem a síndrome. Os resultados dos trabalhos realizados permitem concluir que: não existem evidências científicas que suportem a hipótese que pessoas com SD apresentem menor experiência de cárie do que indivíduos sem a síndrome; pessoas com SD apresentam experiência de cárie similar a pessoas sem a síndrome; existe uma maior frequência de crianças com SD que apresentam altas contagens salivares de S. mutans do que crianças sem a síndrome; crianças com SD que têm escovação supervisionada por pais ou cuidadores apresentam menores índices de placa e sangramento gengival; os genótipos de S. mutans encontrados na cavidade bucal de crianças com SD são menos acidogênicos do que os das crianças sem síndrome. / Down Syndrome (DS) is the most common genetic anomaly in human, affecting all ethnicities and socioeconomic levels. The syndrome has also manifestations in the oral cavity of the subjects, altering soft and hard tissues, salivary constitution and oral microbiology. Regarding dental caries, previous studies have found conflicting results when evaluating the caries experience in DS subjects. While the majority of researchers reported a lower caries experience in DS versus non-DS subjects, other studies did not find difference. In order to elucidate the controversies, three studies were conducted. The first study was a systematic review with the aim of determining if there was difference in the caries experience in DS and non-DS subjects. In total, 13 articles were included for data extraction. However, due to the low methodological quality of all the studies, it was concluded that there was no scientific evidence to support the hypothesis that DS subjects have a lower caries experience than non-DS subjects. The second study was observational and cross-sectional and was performed with 131 children aged between 6-12 (60 with DS and 71 non-DS). The plaque index (PI), gingival bleeding index (GBI), caries experience and salivary Streptococcus mutans (S. mutans) quantification were investigated. Questionnaires that included tooth brushing habits, diet and income of the subjects were performed. Caries experience was similar in both groups. PI and GBI were lower in DS subjects, what was associated with a higher parental/caregiver supervision. Significantly more children with DS had high salivary counts of S. mutans. The study concluded that children with and without DS of the same age range have similar caries experience. However, children with DS often have higher salivary counts of S. mutans than children without the syndrome. In addition, children with DS who have tooth brushing supervised by parents or caregivers have lower PI and GBI. The third study was laboratory observational aimed to evaluate the S. mutans genotypical diversity and the associated acidogenicity in DS and non-DS children. Seventeen children (9 DS and 8 non-DS) with high salivary counts of S. mutans were selected and divided in two groups: caries-free and high caries experience. S. mutans isolates were obtained from each subject and 99 strains (50 in DS and 7 49 in non-DS) were confirmed through PCR. Different genotypical profiles were observed through AP-PCR technique. The acidogenicity of a representative strain from each genotype was analysed. DS children presented a lower S. mutans genotypical diversity than non-DS children. Moreover, the DS genotypes were significantly associated with less acidogenic than non-DS. The study concluded that children with DS present less acidogenic S. mutans genotypes when compared to children without the syndrome. In summary, the results of this studies allow conclude that: DS subjects have a similar caries experience than non-DS subjects; a significant higher frequency of DS children have higher S. mutans salivary counts than children without the syndrome; children with DS who have tooth brushing supervised by parents or caregivers have lower PI and GBI; the genotypes of S. mutans found in the oral cavity of children with DS are less acidogneic than those of children without the syndrome.

Avaliou-se, em crianças, o efeito de bochechos diários com solução placebo composta de água deionizada mentolada (Grupo I); gluconato de clorexidina 0,12% associado ao fluoreto de sódio 0,05% (Grupo II); digluconato de clorexidina 0,2% (Grupo III) e esteviosídeo 0,5% associado ao fluoreto de sódio 0,05% pH 3,4 (Grupo IV), sobre a inibição do acúmulo de placa dentária e sobre o nível de estreptococos mutans salivar. Para a verificação do efeito sobre a placa, empregou-se o índice de LÖE e a contagem microbiana na saliva foi realizada através do CARITEST SM (Herpo – Produtos Dentários LTDA). A amostra constou de 200 crianças de 7 a 11 anos de idade, sendo 50 por grupo, nas quais avaliou-se o acúmulo de placa dentária no início e final do experimento. Dessas crianças, foram selecionadas 20 de cada grupo, ao acaso, para as coletas de saliva que foram executadas em 3 etapas: inicial (antes do primeiro bochecho), 24 horas após o primeiro bochecho e uma semana após o último bochecho. Em todos os grupos, as crianças receberam profilaxia profissional antes do início do experimento e seguiram o regime de bochechos diários, com 5 ml de solução, por 1 minuto, durante 4 semanas. Os resultados mostraram uma inibição do acúmulo de placa de 2,89%; 26,75%; 41,20% e 5,91% para os grupos I, II, III e IV, respectivamente. Em relação às faces dentárias, os grupos II e III, mostraram maiores reduções percentuais para a face vestibular, vindo a seguir a proximal e lingual, sendo que no grupo II, não existiu diferença estatisticamente significante entre todas as faces e para o grupo III, essa diferença foi entre as faces lingual e mesial. Já no grupo IV, esse resultado foi maior para a face lingual, diferindo estatisticamente apenas da face distal. A solução de digluconato de clorexidina 0,2% registrou menor aceitação pelas crianças e, juntamente com a solução de gluconato de clorexidina 0,12% associada ao fluoreto de sódio 0,05%, promoveu pigmentações dentárias suaves e semelhantes. Com relação à contagem de estreptococos mutans, devido as crianças apresentarem no início do experimento baixos valores desses microrganismos, os mesmos assim permaneceram, não existindo diferença estatisticamente significante entre as contagens. Concluiu-se que a solução de gluconato de clorexidina 0,12% associada ao fluoreto de sódio 0,05% e a solução de digluconato de clorexidina 0,2% foram no regime utilizado, as mais efetivas no controle do acúmulo de placa dentária, em crianças. Entretanto, a segunda registrou maior redução percentual e menor aceitação com relação ao sabor da solução. / In children, the effect of mouthwashing was observed placebos solution made of mentholated deionized water (Group I), chlorhexidine gluconate 0.12% mixed sodium fluoride 0.05% (Group II), chlorhexidine digluconate 0.2% (Group III) and estevioside 0.5% mixed with sodium fluoride 0.05% ph 3.4 (Group IV), over the dental plaque accumulation and over the level of the salivary streptococcus mutans. In order to verify the effect on the plaque, the LÖE index was used and the saliva microbial count was taken through the CARITEST SM (Herpo – Produtos Dentários LTDA). The sample consisted of 200 children between 7 and 11 years old, 50 per group. The accumulation of the dental plaque was evaluated at the beginning and at the end of the experiment. Twenty of these children were randomly selected from each group, in order to collect the saliva. This was done in 3 phases: initial (before the first mouthwashing), 24 hours after the first washing and a week after the last washing. In all groups, the children received professional profilaxy before the experiment and followed the routine of daily mouthwashing with 5ml of solution per minute, for 4 weeks. The results show an inhibition on the plaque accumulation of 2.81%; 26.75%; 41.2% and 5.91% for the Groups I, II, III and IV respectively. In relation to the Abstract 167 dental faces, Groups II and III, show greater percentage reduction to the vestibular face, followed by the proximal and lingual, whereas, in Group II, there was no statistically significant difference between them and Group III. This difference occurred between the lingual and mesial faces. As to Group IV, this result was greater on the lingual face, and statistically different only on the distal face. The chlorhexidine digluconate 0.2% solution showed smaller acceptance by the children, and with the chlorhexidine gluconate 0.12% solution mixed with the sodium fluoride 0.05%, it created smooth and similar dental pigmentation. In relation to the streptococcus mutans count, since the children showed low numbers of these microorganisms at the beginning of the experiment, they remained the same, producing no statistically significant difference between the counts. Therefore, it was concluded that the chlorhexidine gluconate 0.12% mixed with the sodium fluoride 0.05% and the chlorhexidine digluconate 0.2% solution were more affective in the control of the accumulation of the dental plaque in the method used. However, the second method showed a greater percentual reduction and a smaller acceptance related to the solution flavor.

Orientador: Marlise Inêz Klein / Resumo: A cárie dentária é um problema de saúde pública mundial causada por uma interação entre dieta rica em açúcar e microrganismos em biofilmes dentais. Abordagens para controlar esses microrganismos em biofilmes são necessárias. Portanto, o objetivo foi avaliar potencial antimicrobiano (cultura planctônica) e antibiofilme de doze extratos de Casearia Sylvestris (0,50 mg/mL) de diferentes biomas brasileiros (Mata Atlântica, Cerrado, Caatinga, Pampa e Pantanal) e variedades (sylvestris, lingua e intermediária) contra duas espécies encontradas em biofilmes cariogênicos (Streptococcus mutans e Candida albicans). A caracterização química dos extratos brutos foi feita via cromatografia. A atividade antimicrobiana foi determinada pela população microbiana (UFC/mL) enquanto a atividade antibiofilme pela população microbiana (UFC/mL) e biomassa dos biofilmes tratados. Para os extratos ativos para S. mutans, foi avaliado o efeito na formação inicial da matriz de glucanos (atividade de GtfB), o desprendimento após a adesão desta bactéria à película salivar e à matriz inicial de glucanos e citotoxicicidade via ensaio MTT. Também foi avaliado o potencial antimicrobiano contra S. mutans de três frações (metanol, acetato de etila e hexano; 0,25 mg/mL) oriundas dos doze extratos. Três extratos do bioma Mata Atlântica e variedade sylvestris reduziram em >50% (ou >3 logs) as contagens de células viáveis de S. mutans (vs. veículo; p <0,0001), enquanto dois extratos, pertencentes ao mesmo bioma e va... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Dental caries is a worldwide public health problem caused by an interaction between a diet rich in sugar and microorganisms in dental biofilms. Approaches to control these microorganisms in biofilms are necessary. Therefore, the objective of this study was to evaluate the antimicrobial (planktonic) and antibiofilm potential of twelve Casearia sylvestris extracts (0.50 mg/mL) from different Brazilian biomes (Atlantic Forest, Cerrado, Caatinga, Pampa and Pantanal) and variety (sylvestris, lingua and intermediate) against two species found in cariogenic biofilms (Streptococcus mutans and Candida albicans). The chemical characterization of crude extracts was done via chromatography. The antimicrobial activity was determined by the viable microbial population (CFU/mL) and the antibiofilm activity by the viable microbial population (CFU/mL) and biomass of the biofilms treated. For the extracts active for S. mutans, the effect on the initial formation of the glucan matrix (GtfB activity), the release after adhesion of this bacterium to the salivary film and the initial matrix of glucans and cytotoxicity via the MTT assay was evaluated. In addition, the antimicrobial potential against S. mutans of three fractions (methanol, ethyl acetate and hexane, 0.25 mg/mL) from the twelve extracts was also evaluated. Three extracts of the Atlantic Forest biome and sylvestris variety reduced the counts of viable S. mutans cells (vs. vehicle, p <0.0001) by >50% (or >3 logs), while two extracts bel... (Complete abstract click electronic access below) / Mestre

Dental caries is the most common bacterial disease of humans and occurs when oral bacteria produce acids, following their fermentation of dietary carbohydrates. This acid can then cause a localised demineralisation of the tooth surface. A group of seven species of bacteria, collectively known as the mutans streptococci, have been predominantly implicated in the onset of dental caries. In particular, Streptococcus mutans and Streptococcus sobrinus have been shown to be the main aetiological agents of this disease in humans. Most attempts to control the microbial component of caries target these bacteria. The past 50 years has provided considerable information about the pathogenesis of dental caries, the likely route and time of transmission of cariogenic bacteria to susceptible hosts and possible ways of either treating or controlling the onset of this disease. In regards to the latter, many techniques (such as the use of tooth brushes, mouth washes, dental floss and tooth paste) for the control of plaque build-up exist and the examples listed are generally part of a daily routine. However, these techniques need to be applied regularly, and as such only highly-motivated individuals generally experience improved oral health. Therefore, the search for more effective less labour-intensive approaches continues. One area of research is into the potential application of small ribosomally-synthesised antimicrobial peptides, known as bacteriocins. Bacteriocins generally inhibit closely-related species that occupy the same ecological niche. Their relatively-specific targeting, plus the fact that many are remarkably heat and chemically-stable molecules, makes them excellent candidates for possible anti-caries applications. Numerous bacteriocins produced by the lactic acid bacteria have now been identified. Most can be broadly categorised into one of four main classes, of which Class I, the lantibiotics and Class II, the small (<10 kDa) non-modified peptides, contain the most examples. Many screens for anti-mutans streptococcal (MS) bacteriocins have been carried out and it appears that the best source of anti-MS bacteriocins are the mutans streptococci themselves. Research in this laboratory has identified examples of anti-mutans streptococcal bacteriocins produced by both mutans streptococci and non-mutans streptococci. The present study investigated the anti-MS inhibitors produced by two streptococcal strains, S. mutans N and Streptococcus sanguis K11. During the course of this study a third strain, S. mutans UA159, was also studied for its bacteriocinogenic properties. Although S. sanguis K11 produces anti-mutans streptococcal inhibitory activity, this appears only effective against Streptococcus rattus. In addition however, the inhibitory activity of this strain is also directed against all tested strains of Streptococcus agalactiae and ca. 50% of Streptococcus pyogenes. In the present study a 5069 Da novel inhibitory agent (sanguicin K11) was characterised and shown responsible for this unusual inhibitory spectrum. Through reverse genetics the sanK11 locus was identified and shown to encode a Class II type bacteriocin, the first shown to be produced by S. sanguis. Following screens of additional S. sanguis, sanK11 was shown to be present only in strains producing the same type of inhibitory pattern (P-type) as strain K11. The cysteine residues at positions 7 and 38 of the sanguicin K11 propeptide were shown to form a disulphide bridge essential for sanguicin K11 inhibitory activity. S. mutans N and eight other S. mutans strains have been found to have what appears to be the same inhibitory spectrum, which includes members of the mutans streptococci and several other oral streptococcal species. One strain (UA140) of the eight has previously been shown to produce the lantibiotic mutacin I and the non-lantibiotic mutacin IV. S. mutans N was known to produce the non-lantibiotic mutacin N. The current study set out to investigate how two strains, apparently producing completely different bacteriocins could have the same inhibitory spectrum. Reverse genetics identified the mutacin N structural gene (mutN) and mutagenesis studies showed that this bacteriocin was responsible only for the inhibitory activity against mutans streptococci. Further sequencing around the mutN locus identified a second bacteriocin-like locus (mutO) adjacent to mutN. mutO was also identified to have anti-mutans streptococcal inhibitory activity and because of the close proximity of mutO and mutN and given the homology they share with other known two-peptide bacteriocins it seemed probable that mutacins O and N are components of a new member of this special class of bacteriocins (Class IIb, the two peptide bacteriocins) in which the optimal inhibitory activity is dependent on the co-operative activity of the two peptides. Further investigations of strain N examined the expression of mutacins O and N. During a search for a suitable heterologous non-mutacinogenic S. mutans strain to act as an expression host, the genome reference strain, S. mutans UA159 was given consideration. However, contrary to previous reports, this strain was found to exhibit bacteriocin-like inhibitory activity. During a follow-up investigation, strain UA159 was found to inhibit 84 strains representing 11 different species of bacteria, but no inhibition of mutans streptococci was detected. The locus (nlmAB) encoding the two-peptide bacteriocin mutacin IV was identified within the UA159 genome. Using genetic dissection of nlmA and nlmB, the contribution of each peptide was examined and it was found that only the NlmA* propeptide appears to be active, raising doubts as to whether mutacin IV is a bona fide two-peptide bacteriocin. Deletion of the entire nlmAB locus created a mutant strain that exhibited a loss of inhibitory activity against the same 64 strains as was found for the nlmA mutant. A BLASTP search for the consensus leader sequence that precedes the propeptide of Class II bacteriocins, identified ORFs encoding 9 more putative bacteriocin-like peptides. Further genetic dissection identified the SMU.1914c locus as being responsible for the inhibitory activity against a further 15 strains not already sensitive to mutacin IV. SMU.1914c was renamed mutacin V. However, it appears that another as yet unidentified mutacin(s) is also produced by strain UA159 given that three indicator strains still remained sensitive to a double mutant [UA[Delta](1914/NlmAB)] in which both the mutacin IV and putative mutacin V loci were inactivated. Export of Class II bacteriocins has been found to occur by either a SEC-dependent system or via a dedicated peptide ATP Binding Cassette (ABC) transporter. Three potential ABC transporter ORFs were identified in S. mutans UA159. Two (comA and cslA) had the characteristic accessory factor ORF (comB and cslB respectively) located adjacent to the main ABC transporter ORF, while the third ORF763 appeared to lack this. Mutagenesis of each of these five ORFS was carried out and confirmed cslAB to be the ABC transporter involved in the export of the competence stimulating factor, while the function of ORF763 could not be established in this study. Mutagenesis of either comA or comB resulted in a complete cessation of bacteriocin production by the respective mutant strains. Historically, comA and comB is the nomenclature used for loci encoding the exporter of the competence inducing factors in streptococci. In light of this new information, comA and comB were renamed nlmT and nlmE respectively, to account for the newly defined role of this ABC transporter. The present study investigated four bacteriocins two of which (sanguicin K11 and mutacin ON) appear to have some potential for application to anti-caries control, and the others (mutacins IV and V) being shown to be produced by the genome reference strain (UA159). All three mutacins were shown to be exported from their respective producer cells by the NlmTE ABC transporter, while sanguicin K11 is predicted to be exported by a peptide ABC transporter located adjacent to sanK11. Bacteriocins may yet provide a novel alternative for the treatment and control of dental caries. In their favour is that fact that they have relatively narrow defined inhibitory spectra and thus are unlikely to produce widespread changes to plaque ecosystems. Potential uses include as topical agents where bacteriocin preparations could be incorporated into dentrifices such as toothpastes or mouthwashes. Alternatively, streptococci producing anti-mutans streptococcal bacteriocins could be implanted into the oral cavity in strain replacement therapy strategies. There are pros and cons to each technique and the most effective anti-caries control appears more likely to result from "cocktail therapy" where bacteriocins are combined with a number of other anti-mutans streptococcal agents to achieve long-lasting protection against mutans streptococcus proliferation.

PknB is a putative transmembrane eukaryotic-type serine/threonine protein kinase (STPK) in the cariogenic bacterium Streptococcus mutans that affects biofilm formation, genetic competence and acid tolerance. PknB contains extracellular penicillin-binding and serine/threonine kinase associated (PASTA) domains predicted to bind the D-alanyl-D-alanine (D-ala-D-ala) dipeptide of unlinked peptidoglycan. D-ala-D-ala elicits responses dependent and independent of the presence of pknB. Biofilm-derived cells of a pknB-deficient mutant (PKNB) exhibited concentration-dependent growth enhancement with D-ala-D-ala, which was not a nutrient response as addition of L-alanine or D-alanine did not give the same results. A total of 77 genes were differentially expressed in PKNB, including 7 with putative functions in fatty acid biosynthesis. PKNB was more sensitive to cell wall- and membrane-targeting antibiotics compared to wild-type. Based on these results, PknB in S. mutans appears to play an important role in cell wall biosynthesis, response to membrane stress and/or regulation of cell membrane composition.

PknB is a putative transmembrane eukaryotic-type serine/threonine protein kinase (STPK) in the cariogenic bacterium Streptococcus mutans that affects biofilm formation, genetic competence and acid tolerance. PknB contains extracellular penicillin-binding and serine/threonine kinase associated (PASTA) domains predicted to bind the D-alanyl-D-alanine (D-ala-D-ala) dipeptide of unlinked peptidoglycan. D-ala-D-ala elicits responses dependent and independent of the presence of pknB. Biofilm-derived cells of a pknB-deficient mutant (PKNB) exhibited concentration-dependent growth enhancement with D-ala-D-ala, which was not a nutrient response as addition of L-alanine or D-alanine did not give the same results. A total of 77 genes were differentially expressed in PKNB, including 7 with putative functions in fatty acid biosynthesis. PKNB was more sensitive to cell wall- and membrane-targeting antibiotics compared to wild-type. Based on these results, PknB in S. mutans appears to play an important role in cell wall biosynthesis, response to membrane stress and/or regulation of cell membrane composition.

No description available.

Chromosomal toxin-antitoxin (TA) modules have been proposed to function as regulators of cell growth in response to environmental perturbations. The objective of this study was to characterize the MazEF TA system of the human pathogen Streptococcus mutans. Our data showed that the mazEF genes form a bicistronic operon. MazF toxin had a toxic effect on cells and this effect can be neutralized by coexpression of its cognate antitoxin MazE. Furthermore, we demonstrated that MazE and MazF proteins interact with each other in vivo, confirming the nature of this TA as a type II addiction system. We also demonstrated that MazF is a toxic nuclease arresting cell growth through the mechanism of RNA cleavage and that MazE inhibits the RNase activity of MazF by forming a protein complex. Our results suggest that the MazEF TA might represent a cell growth modulator facilitating the persistence of S. mutans in the oral cavity.

Chromosomal toxin-antitoxin (TA) modules have been proposed to function as regulators of cell growth in response to environmental perturbations. The objective of this study was to characterize the MazEF TA system of the human pathogen Streptococcus mutans. Our data showed that the mazEF genes form a bicistronic operon. MazF toxin had a toxic effect on cells and this effect can be neutralized by coexpression of its cognate antitoxin MazE. Furthermore, we demonstrated that MazE and MazF proteins interact with each other in vivo, confirming the nature of this TA as a type II addiction system. We also demonstrated that MazF is a toxic nuclease arresting cell growth through the mechanism of RNA cleavage and that MazE inhibits the RNase activity of MazF by forming a protein complex. Our results suggest that the MazEF TA might represent a cell growth modulator facilitating the persistence of S. mutans in the oral cavity.

Thesis (doctoral)--Göteborg University, 1994. / Added t.p. with thesis statement inserted. Includes bibliographical references.