How to predict the timing of eruption of mandibular second premolars.

OBJECTIVE: To evaluate the relationship between the stages of dental formation and the timing of eruption of mandibular second premolars. MATERIALS AND METHODS: The sample comprised panoramic radiographs of 25 children, 7 to 12 years old, observed by space supervision during development of dentition. The initial radiograph (T1) was taken in the mixed dentition period and the progress radiograph (T2) close to the eruption of mandibular second premolars. The stages of dental formation were determined by the proportion between crown length and total length (CL/TL) as well by the Simpson and Kunos index. Average values between right and left sides (35, 45) were correlated to the time elapsed until dental eruption (T2-T1). Statistical analysis was performed by Pearson correlation analysis. RESULTS: The proportion CL/TL presented higher correlation index with time to eruption than the Simpson and Kunos index. The linear regression equation for prediction of timing of eruption showed high coefficient of determination, low deviation, and good accuracy. According to survival analysis, mean deviation at 95% confidence level was between 3.6 and 6.4 months. There was no difference in contralateral measurements, with high intraclass correlation coefficient for both CL/TL proportion and Simpson and Kunos index. CONCLUSIONS: More advanced stages of dental formation indicate less time until dental eruption. The strong correlation with crown length/total length proportion (CL/TL) provides a linear regression equation for prediction of the timing of eruption of mandibular second premolars.

Cumulative effect of disinfection procedures on microhardness and tridimensional stability of a poly(methyl methacrylate) denture base resin.

Microwave irradiation has been used for disinfection of dentures instead of chemical solutions; yet, its effect on resin properties after repeated procedures still is unclear. This study evaluated the cumulative effect of two disinfection methods on Knoop microhardness and tridimensional stability of a poly(methyl methacrylate) denture base resin. For the microhardness measurement, 24-resin discs received mechanical polishing and were submitted to the following treatments: (1) control (no disinfection), (2) chemical disinfection (immersion in 100ppm chloride solution for 24h), or (3) microwave disinfection (irradiation at 690 W for 6 min). Disinfection procedures were performed twice (T1, T2) with a 7-day interval. Knoop microhardness was recorded after polishing (T0) and after T1 and T2. For the dimensional stability test (measured by the adaptation of the denture bases), 36-maxillary denture bases were obtained from type III dental stone casts duplicated from a metallic master model and submitted to the disinfection treatment. Adaptation of denture bases was measured at baseline (T0) and after T1 and T2 by weighing a vinyl polysiloxane film reproducing the gap between resin base and master model. Data were analyzed by ANOVA GLM for repeated measures and Bonferroni's test, alpha = 0.05. Knoop microhardness was not modified by any disinfection procedure but decreased over time. Denture resin bases submitted to microwave disinfection had gradual increase of distortion over time, while bases immersed in chloride solution did not differ from the control group and remained dimensionally stable from T1 to T2.

Effect of microwave disinfection on denture base adaptation and resin surface roughness.

This study evaluated the effect of disinfection methods [chemical disinfection (immersion in 100 ppm chloride solution) or microwave disinfection (690 W for 6 min)] on the internal adaptation of denture bases and resin surface roughness. For the adaptation test, 18 maxillary denture bases were obtained from stone casts duplicated from a metallic master model and submitted to the following treatments: 1) control (no disinfection), 2) chemical disinfection or 3) microwave disinfection. Disinfection procedures were performed twice (T1, T2) with a 7-day interval between them. Internal adaptation was measured at baseline (T0) and after T1 and T2 by weighing a vinyl polysiloxane film reproducing the gap between the resin base and the master model. For surface roughness measurement, 60 rectangular (5x10x40 mm) resin specimens were either mechanically or chemically polished and then submitted to the disinfection treatments. Surface roughness (Ra) was recorded after polishing (T0) and after T1 and T2. Data were analyzed by ANOVA GLM for repeated measures and Bonferroni correction at 5% significance level. Bases submitted to microwave disinfection had gradual increase of misfit, while bases immersed in chloride solution did not differ from the control group. Surface roughness increased in the mechanical polishing groups with microwave disinfection and decreased in the chemical polishing groups.

Effect of microwave disinfection on denture base adaptation and resin surface roughness

This study evaluated the effect of disinfection methods [chemical disinfection (immersion in 100 ppm chloride solution) or microwave disinfection (690 W for 6 min)] on the internal adaptation of denture bases and resin surface roughness. For the adaptation test, 18 maxillary denture bases were obtained from stone casts duplicated from a metallic master model and submitted to the following treatments: 1) control (no disinfection), 2) chemical disinfection or 3) microwave disinfection. Disinfection procedures were performed twice (T1, T2) with a 7-day interval between them. Internal adaptation was measured at baseline (T0) and after T1 and T2 by weighing a vinyl polysiloxane film reproducing the gap between the resin base and the master model. For surface roughness measurement, 60 rectangular (5x10x40 mm) resin specimens were either mechanically or chemically polished and then submitted to the disinfection treatments. Surface roughness (Ra) was recorded after polishing (T0) and after T1 and T2. Data were analyzed by ANOVA GLM for repeated measures and Bonferroni correction at 5 percent significance level. Bases submitted to microwave disinfection had gradual increase of misfit, while bases immersed in chloride solution did not differ from the control group. Surface roughness increased in the mechanical polishing groups with microwave disinfection and decreased in the chemical polishing groups.

Este estudo avaliou o efeito de métodos de desinfecção [desinfecção química (imersão em solução clorada 100 ppm) ou desinfecção por microondas (690 W por 6 min)] na adaptação interna de bases de próteses totais e na rugosidade superficial da resina. Para o teste de adaptação, 18 bases superiores foram duplicadas a partir de um modelo-mestre metálico e submetidas aos seguintes tratamentos: 1) controle (sem desinfecção), 2) desinfecção química ou 3) desinfecção por microondas. Os procedimentos de desinfecção foram realizados duas vezes (T1, T2) com intervalo de 7 dias. A adaptação interna foi medida no baseline (T0), após T1 e T2 por pesagem de um filme de silicona de adição que reproduzia o espaço entre base de resina e modelo-mestre. Para a rugosidade superficial, 60 espécimes retangulares (5x10x40 mm) receberam polimento mecânico ou químico e foram submetidos aos tratamentos de desinfecção. A rugosidade superficial (Ra) foi registrada após o polimento (T0) e após T1 e T2. Os dados foram analisados por ANOVA GLM para medições repetidas e teste de Bonferroni com nível de significância de 5 por cento. As bases submetidas à desinfecção por microondas tiveram aumento gradual de desadaptação, enquanto que as bases imersas em solução clorada não diferiram do grupo controle. A rugosidade superficial aumentou nos grupos de polimento mecânico e desinfecção por microondas e diminuiu nos grupos de polimento químico.

Reliability of a digital image method for measuring medial mandibular flexure in dentate subjects

A deflexão mandibular medial (MMF) é uma deformação funcional que ocorre com a aproximação das hemi-mandíbulas em abertura e protrusão, podendo afetar próteses convencionais e implanto-suportadas em arco. OBJETIVOS: Este trabalho avaliou a confiabilidade intra- e inter-examinador de um método de imagem digital para aferição linear da MMF. MATERIAL E MÉTODOS: Foram selecionados sete voluntários adultos dentados, obtendo-se registros oclusais inferiores de silicona de adição em repouso, abertura e protrusão máximas. Os registros foram escaneados juntamente com um paquímetro Mitutoyo com abertura de 10mm num aumento de 200%. A imagem foi processada no programa Adobe Photoshop obtendo-se pontos de referência intermolares, e as medições lineares foram feitas no programa ImageTool (UTHSCSA) calibrado com a medida padrão do paquímetro. Foram feitas medições em triplicata da medida da distância intermolar para cada imagem. A MMF foi calculada subtraindo-se a distância intermolar em abertura da distância em repouso/ protrusão. Os dados foram analisados por coeficientes de correlação intraclasse (ICC) para estimar a confiabilidade intra- e inter-examinadores. RESULTADOS: Os valores de MMF variaram de -0,21 a 0,44mm. Os ICCs intra-examinador foram 0,982 e 0,993, e o ICC inter-examinador foi 0,696. CONCLUSAO: Os resultados demonstram excelente confiabilidade intra-examinador e boa confiabilidade inter-examinador deste método de imagem digital para aferição de MMF em adultos dentados.

Rugosidade superficial de resina acrílica submetida a diferentes métodos de polimento / Superface roughness of acrylic submitted polishing methods

Este trabalho avaliou a rugosidade superficial de uma resina acrílica ativada termicamente polimerizada por técnica convencional e por microondas, submetida a polimento mecânico ou polimento químico. Amostras de resina acrílica (Veracril) foram confeccionadas (5x10x40 mm) e divididas em seis grupos (n=10/grupo): Polimerização convencional sem polimento (CS); Polimerização convencional, polimento mecânico (CM); Polimerização convencional, polimento químico (CQ); Polimerização por microondas, sem polimento (MS); Polimerização por microondas, polimento mecânico (MM); e Polimerização por microondas, polimento químico (MQ). A rugosidade superficial média Ra foi avaliada com rugosímetro Mitutoyo SJ-201. As médias (DP) de Ra (ìM) obtidos foram: CS = 0,24 (0,02) B; CM = 0,15(0,07) a; CQ = 0,25 (0,05) b; MS = 0,23 (0,02) b; MM = 0,14 (0,01) a; MQ = 0,28 (0,03) b. Médias seguidas por letras distintas foram estatisticamente diferentes entre si (ANOVA e Teste de Tukey, alfa=0,05). Não houve influência do tipo de polimerização na rugosidade superficial. Os grupos com polimento mecânico apresentaram os menores valores de rugosidade em comparação com outros grupos do polimento químico e sem polimento. O polimento químico não foi eficaz em proporcionar uma superfície mais lisa

Reliability of a digital image method for measuring medial mandibular flexure in dentate subjects.

UNLABELLED: Medial mandibular flexure (MMF) is the functional approximation of hemi-mandibles in jaw opening and protrusion, which may affect conventional or implant-supported arch prostheses. OBJECTIVE: This study evaluated the intra- and inter-rater reliability of a digital image method for linear measurement of MMF in dentate subjects. MATERIAL AND METHODS: Mandibular occlusal impressions in vinyl polysiloxane during rest and maximum opening were obtained from seven adult volunteers. Each impression and the Mitutoyo digital calipers with a 10mm opening were scanned at a 200% magnification. The images were processed using Adobe Photoshop software to get reference points on contralateral first molars. Linear intermolar measurements were taken using the Image Tool software (UTHSCSA), which was calibrated with the standard opening of the digital calipers. Intermolar distance was measured in triplicate for each image by two independent examiners. MMF was calculated by subtracting the intermolar distance in maximum opening (or protrusion) from the distance in rest position. Data were analyzed by intraclass correlation (ICC) tests for estimating intra- and inter-rater reliability. RESULTS: MMF values ranged from -0.21 to 0.44mm. Intra-rater ICCs were 0.982 and 0.993, and inter-rater ICC was 0.696. CONCLUSION: The present results show excellent intra-rater and good inter-rater reliability of this digital image method for measuring MMF in dentate subjects.