Comparing Torque Loss in Standard Implants and Short Implants with Increased Vertical Cantilever Abutments: an In Vitro Study / Comparação da perda de torque em implantes padrão e implantes curtos com pilares cantilever verticais aumentados (in vitro)

Objectives: With regard to the prevalence of abutment screw loosening (SL) and bone height reduction, particularly in the posterior regions of the jaws, as well as the contradictory issue of applying short implants instead of surgeries, along with all preparations associated with longer implants, the present study aimed to compare the amount of torque loss in short implants with increased vertical cantilever abutments and standard ones. Material and Methods: In this experimental study, a total number of 20 implants (MegaGen Implant Co., Ltd, South Korea) with 4.5 mm diameter including 10 short implants (7 mm) and 10 standard ones (10 mm) were utilized. Using a surveyor, fixtures were perpendicularly mounted in 13×34 mm resin for short implants and 19×34 mm resin for standard ones. The abutments of the same height but different cuff heights (2.5 mm for the standard implants and 5.5 mm for the short ones) were then tightened with 30 N.cm, via a digital torque meter. To compensate the settling effect, the abutment screw was re-tightened with 30 N.cm after 10 min. Upon applying 500,000 cycles at 75 N.cm and 1 Hz along the longitudinal axis on each sample, blind reverse torque value (RTV) was measured with a digital torque meter. The data were finally analyzed using Student's t-test. Results:Both groups experienced torque loss, but there was no statistically significant difference between the case and control groups in terms of abutment SL (p = 0451). Conclusion: Short implants seem to be a good mechanical alternative in emergencies with respect to torque loss and abutment SL. (AU)

Objetivos: Considerando a prevalência de afrouxamento de parafuso dos pilares, redução da altura óssea especialmente nas regiões posteriores, a questão contraditória da aplicação de implantes curtos em vez de cirurgias e todos os preparos associados a implantes mais longos, este estudo buscou comparar implantes curtos com pilares cantilever verticais aumentados e implantes padrão na quantidade de perda de torque. Material e métodos: Neste estudo experimental, foram utilizados 20 implantes (Megagen, Coreia do Sul) com diâmetro de 4,5 mm, incluindo 10 implantes curtos (7 mm) e 10 implantes padrão (10 mm). A fixação foi realizada perpendicularmente em uma resina 13 × 34 mm para implantes curtos e uma resina 19 × 34 mm para implantes padrão, usando um topógrafo. Os pilares da mesma altura, mas com diferentes comprimentos de manguito (2,5 mm para os implantes padrão e 5,5 mm para os implantes curtos) foram apertados com 30 N, utilizando um torquímetro digital. Para compensar o efeito de sedimentação, o parafuso do pilar foi reapertado com 30 N após 10 min. Depois de aplicar 500.000 ciclos a 75 N e 1 Hz ao longo do eixo longitudinal em cada amostra, o valor de torque reverso cego foi medido com um medidor de torque digital. Os dados foram analisados pelo teste t de Student. Resultados: Todos os grupos tiveram perda de torque, mas não houve diferença estatisticamente significativa entre os grupos caso e controle em termos de afrouxamento do parafuso do pilar (p = 0451). Conclusão: Os implantes curtos parecem ser uma boa alternativa mecânica em emergências em termos de perda de torque e afrouxamento do parafuso do pilar. (AU)

Effectiveness of Two Desensitizer Materials, Potassium Nitrate and Fluoride Varnish in Relieving Hypersensitivity After Crown Preparation.

AIM: The aim of this clinical investigation was to compare the efficacy of fluoride varnish and potassium nitrate on the reduction of hypersensitivity of prepared teeth both pre and post cementation. MATERIALS AND METHODS: In this randomized clinical trial, patients who needed at least three single crowns fixed partial prosthesis were included. Two desensitizing agents including fluoride varnish and potassium nitrate were used in this study and compared to the control group (sterile saline). In each patient, each prepared tooth was randomly assigned to one group. The desensitizing agent was applied on prepared teeth immediately after tooth preparation. The sensitivity of the teeth was measured by means of an air sensitivity test based on the visual analog scale at five different time points: baseline (2 hours after preparation), 7 days after preparation, before cementation, after cementation and one-week post cementation. Data were analyzed by Kruskal-Wallis and Friedman tests with a significant level of 0.05. RESULTS: Overall 300 vital abutment teeth needed full crown coverage in 100 patients were included. Both desensitizers' agents decreased the sensitivity of vital abutment teeth compared to the control group at every time intervals except at baseline (p = 0.089). There was no significant difference between fluoride varnish and potassium nitrate in the reduction of pre-cementation sensitivity while one week after cementation, sensitivity was more relieved by potassium nitrate compared to fluoride varnish (p = 0.023). CONCLUSION: The application of both desensitizers is effective in sensitivity reduction of vital abutment teeth. Potassium nitrate, however, is more eligible one week after cementation compared to fluoride varnish. CLINICAL SIGNIFICANCE: Both potassium nitrate and fluoride varnish are capable of desensitizing prepared tooth for the fixed partial denture.

Investigating the effect of G-Bond and Z-PRIME Plus on the bond strength between prefabricated zirconia posts and the root canal wall in vitro.

Background. The aim of this study was to analyze the effect of G-Bond and Z-PRIME Plus on the bond strength between prefabricated zirconia posts and the root canal wall. Methods. The study was carried out on 21 premolar teeth with similar conditions. The samples were cut at the CEJ. After root canal treatment of the roots, the post space was prepared up to a length of 10mm. The samples were randomly assigned to two groups of 10. G-Bond was used in one group and Z-PRIME Plus in the other to prepare the posts' surfaces. After cementation and mounting the samples in polyester, the post was cut from the apical area into three equal sections. The bond strength of the samples was tested using the push-out test on a universal testing machine. Data wereanalyzed using t-test. Results. The meanpush-out bond strengths in the control,G-Bond and Z-PRIME Plus groups were 14.3, 27.6±11.8 and 27.4±13.4N, respectively. There was no statistically significant difference between the two groups (P<0.9). Both methods of surface treatment increased bond strength. The bond strengths were different in different sections such as coronal, middle and apical in each group. Conclusion. There was no significant differencebetween the G-Bond and Z-PRIME Plus groups and both products in-creased the bond strength of prefabricated zirconia posts.

Adhesion of Streptococcus Mutans to Glass Ionomer, BisCem Cement and Enamel: An in Vitro Study.

OBJECTIVES: Considering the adhesion of some microorganisms such as Streptococcus mutans (S. mutans) to restorative materials and the unrecognized consequences of this phenomenon, and due to the controversies in this regard, it is important to discover the materials to which the lowest adhesion of S. mutans occurs. The objective of this study was to assess the level of adhesion of S. mutans to glass ionomer (GI), BisCem Cement and enamel. MATERIALS AND METHODS: In this in vitro experimental study, 12 specimens including five GI blocks (GC America Inc., Alsip, IL, USA), five BisCem blocks (Bisco Inc., Schaumburg, IL, USA) and two enamel blocks were exposed to a bacterial suspension (1×10(6) mg/mL). After incubation for one hour at 37°C, the swab samples were taken and cultured in blood agar. The S. mutans colonies were counted by unaided vision after 48 hours of incubation. The results were analyzed using ANOVA followed by the Tukey's test. RESULTS: The number of colonies attributed to enamel, GI, and BisCem blocks was 24±2, 24.2±2.7 and 14.8±1.7 colonies/mm(2), respectively. There was no difference between enamel and GI in terms of adhesion of S. mutans (P=0.08 and P>0.001, respectively); however, the difference between these two and BisCem was statistically significant (P= 0.00075 and P<0.001, respectively). CONCLUSION: Within the limitations of this study, BisCem cement is superior to GI for the cementation of indirect restorations.

Smile line and occlusion: An epidemiological study.

BACKGROUND: The purpose of the present study was to discuss some new concepts of the desirable characteristics of smile tooth display. Due to the increasing application of cosmetic dental treatments, there is an increasing need for better understanding of the esthetic principles. MATERIALS AND METHODS: In the present descriptive study, with 212 participants, included were patients with no history of orthodontic treatment, loss or prosthetic replacement of anterior teeth, extracted teeth, lips with asymmetry or a history of trauma. Chi-square test was used to determine possible significances in the relation of smile line to Angle occlusion class, overbite and overjet and arch form. A P level of <0.05 was set as to be significant. RESULTS: Chi-square test indicated that there was a significant difference between the smile design and overbite, overjet and gender but no statistically significant association was found between the smile design and crossbite, molar Angle classification and arch form. CONCLUSION: Within the limitations of such studies, it might be concluded that there is a significant and important relation between some occlusal parameters and smile design, which must be considered.

In vitro evaluation of the effect of different diameters of quartz fiber posts on fracture resistance of dental roots / Avaliação in vitro do efeito de diferentes diâmetros de pinos de fibras de quartzo na resistência à fratura de raízes dentais

OBJECTIVES: One of the controversial factors in fracture resistance of endodontically treated teeth that are reconstructed with fiber posts is the diameter of these posts. The aim of this study is to evaluate the effect of three different sizes of quartz fiber post (#0.5- #2 - #3) on fracture resistance of dental root. MATERIAL AND METHOD: In this in vitro study, 30 mandibular premolars were selected, sectioned from CEJ, endodontically treated and randomly assigned to three groups (n=10). Post spaces were prepared and quartz fiber posts) D.T. Light-Post™ (with three different sizes (#0.5-#2 - #3) were seated respectively in three groups. All posts were cemented with Panavia F 2.0 dual cure resin bonding and cement. Composite resin cores were built up using a preformed polyester matrix. Specimens were embedded in acrylic resin blocks with a layer of elastic polyether Impergum around roots as PDL. A compressive load at a crosshead speed of 1mm/min was applied axially to the central fossa of each specimen using a Universal Testing Machine, until the occurrence of root fracture. Data were analyzed using one-way analysis of variance. RESULTS: There was no significant statistical difference in fracture resistance among three groups (P>0.05). Mean fracture load was 1010±250.95 N for group A with post #0.5 and 934.4± 295.18 N for group B with post #2 and ±1001301.42 N forgroup C with post #3. CONCLUSIONS: According to the findings, larger sizes of fiber posts do not decrease the fracture resistance of the root structure. Larger diameters have higher fracture resistance and furthermore by increasing the bonding area between post and root canal wall and core material, they can improve the unity within root structure and provide more stability for core material. Unlikelarger sizes of metal posts, fiber posts with larger diameters adhere to the root structure more efficiently. As a result, they will not reduce the fracture resistance of root...

OBJETIVOS: Fator controverso na resistência à fratura de dentes endodonticamente tratados, reconstruídos com pinos de fibra, é o diâmetro destes pinos. O objetivo deste estudo é avaliar o efeito de três diferentes tamanhos de pinos de fibras de quartzo (#0,5 – #2 - #3) na resistência à fratura de raízes dentárias. MATERIAL E MÉTODO: Neste estudo in vitro, 30 pré-molares mandibulares foram selecionados, seccionados, tratados endodonticamente e designados aleatoriamente em três grupos (n=10). Condutos foram preparados e pinos de fibras de quartzo (D.T. Light – Post TM) com três diferentes tamanhos (#0.5- #2 - #3) foram fixados, respectivamente em três grupos. Todos os pinos foram cimentados com cimento Panavia F 2.0. Pinos de resina foram construídos usando uma matriz pré-formada de poliéster. Os corpos de prova foram embebidos em blocos de resina acrílica com uma camada de ImpregumTM ao redor das raízes. Cargas compressivas na razão de 1 mm/min foram aplicadas axialmente na fossa central de cada corpo de prova, usando uma máquina universal de testes até a ocorrência de fratura radicular. Os dados foram submetidos à análise de variância. RESULTADOS: Não houve diferenças estatisticamente significantes na resistência à fratura entre os três grupos (P>0,05). A carga média de fratura foi 1010+-250.95 N para o grupo C, com o pino # 3. CONCLUSÕES: De acordo com os achados, tamanhos maiores de pinos de fibra não diminuem a resistência da estrutura radicular. Maiores diâmetros têm mais resistência à fratura e, além disso, pelo incremento da área de cimentação entre o pino e a parede da raiz, podem melhorar a união dentro da estrutura radicular e proporcionar mais estabilidade para o material de núcleo. Ao contrário de pinos metálicos de maior tamanho, os pinos de fibra de maior diâmetro aderem à estrutura radicular com mais eficiência. Como resultado, não reduzirão a resistência à fraturada raiz. Assim sendo, quando restaurarem-se dentes endodonticamente...

A comparison of the efficacy of potassium nitrate and Gluma desensitizer in the reduction of hypersensitivity in teeth with full-crown preparations.

AIM: The aim of this clinical investigation was to compare the efficacy of Gluma Desensitizer and potassium nitrate desensitizing agents on the reduction of hypersensitivity of teeth prepared for full coverage crowns. METHODS AND MATERIALS: This study included 75 vital teeth in 25 patients in need of fixed prosthesis treatment. After completing routine examinations, hypersensitivity of the teeth was measured using an air sensitivity test. The measurement of sensitivity was using a Visual Analog Scale (VAS) before preparation, after preparation, before using desensitizers, after using desensitizers, and before cementation. Each tooth was randomly put into one of the three groups of 25 teeth according to the desensitizing agent used (potassium nitrate, Gluma, and the control). In each patient potassium nitrate was used on one of the abutments and Gluma was used on the other abutment and on the third abutment (the control) no substance was used. RESULTS: Both desensitizers decreased dentinal hypersensitivity in vital teeth prepared for full-coverage crowns, but potassium nitrate was more effective when applied before cementation. In 88% of the teeth to which Gluma was applied a vascular pain (with pulse) was present. CONCLUSION: The results of this investigation suggest the application of potassium nitrate to dentin in full crown preparations prior to cementation reduces post-operative sensitivity. CLINICAL SIGNIFICANCE: Clinical experiments show the preparation of vital teeth for full coverage crowns can cause sharp, transient pain as a result of dentinal hypersensitivity in the majority of cases. Several different substances and methods have been suggested for reducing such hypersensitivity including costly laser treatments. However, the findings of this study indicate the use of desensitizer substances such as potassium nitrate can reduce tooth hypersensitivity efficiently with less expense.

Evaluating the effect of a sloping shoulder and a shoulder bevel on the marginal integrity of porcelain-fused-to-metal (PFM) veneer crowns.

AIM: A porcelain-fused-to-metal (PFM) veneer crown restoration is considered successful when biological, mechanical, and esthetical concerns are satisfied. Restorations with poor marginal integrity may contribute to the cause of severe caries and periodontal defects. The most important factor in achieving successful marginal integrity is preparation design. Although a sloping shoulder preparation offers biologic and esthetic advantages over a shoulder bevel, a comparison of the marginal integrity of these two designs is less clear and is the main focus of this study. METHODS AND MATERIALS: This study was based on the analysis of 40 PFM veneer specimens fabricated on 20 stone dies. Each die had a beveled shoulder on one side of the preparation and a sloping shoulder design on the other. All specimens were selected and managed in an identical manner throughout the entire experimental process. All specimens were fabricated on stone dies made from a standard stainless steel die with the two shoulder designs in the preparation. Marginal integrity of the PFM veneers was evaluated using a scanning electron microscope to measure the gap between the restoration and tooth margin. The data were analyzed using the Student t-test at a significance level of p>0.05. RESULTS: An average amount of gap (+/- SD) for the test groups were as follows: shoulder bevel, 40.78+/-18.4 microns; sloping shoulder, 52.8+/-27.4 microns (p>0.05). All the data were within acceptable clinical range and no significant difference between two preparation designs were observed. CONCLUSIONS: Within the limitations of this study the marginal integrity of both preparation designs were found to be similar. Since the sloping shoulder design offers biological and esthetical advantages over the shoulder bevel, its use is indicated for anterior restorations.