The buccinator during mastication: A functional and anatomical evaluation in minipigs.

OBJECTIVE: The buccinator muscle forms the lateral wall of the oral cavity. It is presumed to aid mastication by maintaining bolus position. Such a function would involve thickening the cheek, possibly compressing the alveolar bone and contributing to malocclusions. However, neither buccinator deformation nor its effect on pressure has been demonstrated. Our objective was to evaluate buccinator EMG during feeding, its changes in length and thickness, and the pressure exerted on its alveolar attachment, using miniature pigs as an animal model. METHODS: EMG of the buccinator and other oral muscles was recorded with fine-wire electrodes. Anteroposterior length and mediolateral thickness of the buccinator were evaluated with implanted sonomicrometry crystals, and pressure was measured by flat transducers placed beneath the mandibular origin of the buccinator. Recordings were made during feeding and muscle stimulation. Tissues were collected postmortem for histology. RESULTS: During mastication, buccinator EMG showed regular peaks that preceded those of the jaw closers. Pattern differences clearly distinguished working and balancing sides. The buccinator shortened and thickened when it contracted. Positive pressures were observed at the mandibular attachment of the buccinator, increasing when the muscle was active. Histological evaluation showed a complex interweaving of fibres closely associated with salivary tissue. CONCLUSIONS: Buccinator contraction does thicken the cheek, and during mastication this activity takes place just as the closing stroke begins. In addition to controlling the bolus, there may be an effect on salivation. Despite the fact that the muscle pulls on its attachment, the local mechanical environment at the alveolar bone is one of positive pressure.

Fatigue analysis in the masseters and temporalis muscles in patients with temporomandibular disorder during short period of mastication.

The purpose of this experiment was to look for signals of muscle fatigue in volunteers with Temporomandibular Disorders (TMD) during short period of mastication. Twenty female volunteers selected by Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) participated, 10 with myogenic TMD (experimental) and 10 clinically normal (control). The Masseter and Temporalis muscles were evaluated electromyographically with active differential surface electrodes. The masticatory activity was recorded for 15 seconds and the signals were normalized by 4 seconds of teeth clenching. Three complete masticatory cycles were taken to calculating the median frequency (MF) and electromyographic amplitude (RMS). The data were submitted to statistics analysis and non-parametric tests. The results showed that RMS and median frequency did not change during the mastication period analyzed, indicating the absence of muscle fatigue, for the Masseter and Temporalis muscles in both groups (p> 0.05). These results confirm the absence of signals of muscle fatigue in masticatory muscles during short period of mastication even in individuals with TMD, possibly due to increased of blood flow, consequence of dynamic muscle contraction and the individual characteristics of muscle fiber composition and recruitment.

Fatigue analysis in the masseters and temporalis muscles in patients with temporomandibular disorder during short period of mastication

The purpose of this experiment was to look for signals of muscle fatigue in volunteers with Temporomandibular Disorders (TMD) during short period of mastication. Twenty female volunteers selected by Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) participated, 10 with myogenic TMD (experimental) and 10 clinically normal (control). The Masseter and Temporalis muscles were evaluated electromyographically with active differential surface electrodes. The masticatory activity was recorded for 15 seconds and the signals were normalized by 4 seconds of teeth clenching. Three complete masticatory cycles were taken to calculating the median frequency (MF) and electromyographic amplitude (RMS). The data were submitted to statistics analysis and non-parametric tests. The results showed that RMS and median frequency did not change during the mastication period analyzed, indicating the absence of muscle fatigue, for the Masseter and Temporalis muscles in both groups (p>0.05). These results confirm the absence of signals of muscle fatigue in masticatory muscles during short period of mastication even in individuals with TMD, possibly due to increased of blood flow, consequence of dynamic muscle contraction and the individual characteristics of muscle fiber composition and recruitment.

A proposta deste experimento foi procurar sinais de fadiga muscular em voluntarios com disfuncao temporomandibular (DTM) durante curto periodo de mastigacao. Vinte voluntarios do sexo feminino foram selecionados pelo Criterio de Diagnostico de Pesquisa para desordem tempomandibular, 10 com DTM miogenica (experimental) e 10 clinicamente normais (controle). Os musculos Masseter e Temporal foram avaliados eletromiograficamente com eletrodos diferenciais de superficie ativos. A atividade mastigatoria foi registrada por 15 segundos e os sinais foram normalizados por 4 segundos de apertamento dental. A frequencia mediana (FM) e da amplitude eletrmoigrafica (RMS) dos sinais eletromiograficos foram obtidos em 3 diferentes intervalos de tempo. Os valores da FM e RMS foram submetidos a analise estatistica descritiva e a testes nao parametricos. Os resultados demonstraram que o RMS e a FM nao mudaram durante o periodo de mastigacao, indicando ausencia de fatiga muscular para o musculo Masseter e Temporal, em ambos os grupos (p>0.05). Estes resultados confirmam a ausencia de sinais de fatiga muscular durante curto periodo de mastigacao, mesmo em individuos com DTM, possivelmente devido ao aumento do fluxo sanguineo em consequencia da dinamica de contracao muscular e das caracteristicas individuais da composicao das fibras musculares e do recrutamento.

Relationship between the inclination of the coronoid process of the mandible and the electromyographic activity of the temporal muscle in skeletal Class I and II individuals.

The aim of this study was to verify the relationship between the inclination of the coronoid process of the mandible, and electromyographic activity of the anterior part of the temporal muscle in skeletal Class I and II individuals. Forty-seven volunteers (mean age 24.5 +/- 3.9 years) were subdivided into two groups, according to angle ANB: Class I (n = 25) and II (n = 22). Two radiographic examinations were performed; one lateral cephalogram to measure angle ANB, and one frontal cephalogram to measure the inclination of the coronoid process. Electromyographic (EMG) examination of the anterior part of the subjects' temporal muscles was performed. Statistical analysis of the data showed that Class II individuals presented lower electromyographic activity of the anterior part of the temporal muscle. Based on the results obtained, it was concluded that the skeletal classes analyzed had no influence on the inclination of the coronoid process. The inclination of the coronoid process was not influenced by the electromyographic activity of the anterior part of the temporal muscle in Class I and II individuals; however, the lower electromyographic activity of the anterior part of the temporal muscle could be influenced by the skeletal class in Class II individuals.

Comportamento muscular durante diferentes práticas odontológicas / Muscular behaviour during differents dental practices

As Lesões por Esforços Repetitivos (LER) e Distúrbios Osteomusculares Relacionados ao Trabalho (DORT), são a segunda causa de afastamento do trabalho no Brasil. Aproximadamente 60% dos cirurgiões-dentistas apresentam algum tipo de dor músculo-esquelética no ambiente de trabalho. O pescoço, costas, ombros e membros superiores se apresentam como os sítios de dor mais freqüentes, devido às exigências da alta precisão, posição estática e sustentada, limitado espaço de movimentação e pela contração isométrica criada pelo movimento executado. O presente estudo teve como objetivo investigar o comportamento eletromiográfico e o ponto de fadiga referida dos músculos deltóide (porção medial) e trapézio (porções descendente e transversa)bilateralmente. Foram avaliadas quarenta voluntárias, estudantes de Odontologia com média de idade de 21 anos, na posição de trabalho, divididas por especialidades clínicas em quatro grupos: 1 - periodontia, 2 - cirurgia, 3 - clínica geral e 4 - não cirurgiões-dentistas. Os músculos mais ativos foram as porções transversas dos trapézios, em seguida deltóides e porções descendentes dos trapézios e os mais fatigáveis foram os deltóides, em seqüência os trapézios, porções transversas e descendentes. Os músculos do antímero direito apresentaram-se mais ativos que os do esquerdo. O grupo 3 apresentou maior atividade eletromiográfica enquanto que o grupo 1 mostrou ser menos ativo. O grupo 4 apresentou ser mais vulnerável à fadiga muscular enquanto que o grupo 2 mostrou ser mais resistente. Concluímos que o trabalho odontológico executado por longos períodos diários leva os músculos da cintura escapular e cervicais à fadiga e dores musculares, independente da especialidade clínica realizada.

Biological assessment of porous-implant hydroxyapatite combined with periosteal grafting in maxillary defects.

PURPOSE: To investigate the use of porous hydroxyapatite (HA) combined with periosteal graft to repair an induced maxillary bone defect. MATERIALS AND METHODS: A defect was produced in the premaxillary bone of rats. Four groups were used: 1) those treated with the mucoperiosteal graft from the premaxilla; 2) those treated with HA combined with mucoperiosteal graft from the premaxilla; 3) those treated with HA combined with periosteal graft from the femur; and 4) those treated with periosteal graft from the femur. RESULTS: The radiographic aspects from all groups showed no signs of bone formation after 2 weeks. After 16 weeks, there was evidence of points of radiolucency inside the HA implants. Cell proliferation occurred from the periosteum covering the defect. Bone tissue grew from the defect margin to inside the defect in all cases. Mature bone was seen around the HA implants after 8 and 16 weeks. CONCLUSION: The periosteal graft provides satisfactory support to the HA implant, allowing the growth of new bone.