Influence of the deflasking delay time on the displacements of maxillary denture teeth

The purpose of this study was to investigate the displacement of teeth occurring in dentures following storage in water at a temperature of 37oC. Ten maxillary dentures were constructed with Classico heat-cured acrylic resin using conventional metal flasks. Metallic reference pins were placed on the incisal border of the central incisors (I), buccal cusp of the first premolars (PM), and mesiobuccal cusp of the second molars (M). The acrylic resin was polymerized twelve hours after final flask closure in a water cycle at 74oC for 9 hours. The flasks were removed from the thermo-curing unit after water cooling and then bench stored for 3 hours. After deflasking and finishing, the dentures were stored in water at a temperature of 37oC for periods of 7, 30, and 90 days. Following deflasking and each storage period tested, the I-I (incisor to incisor), PM-PM (premolar to premolar), and M-M (molar to molar) transverse distances, and LI-LM (left incisor to left molar) and RI-RM (right incisor to right molar) anteroposterior distances were measured with a STM Olympus microscope, with accuracy of 0.0005 mm. Colleted data were submitted to ANOVA and Tukey test (5%). No statistically significant difference was observed in the displacement of teeth in the transverse and anteroposterior distances.     

Influence of Flask Closure and Flask Cooling Methods on Tooth Movement in Maxillary Dentures

PURPOSE: This study investigated the tooth movement of standardized simulated dentures processed by traditional closure or the new Rafael Saide (RS) tension system when cooled in the curing water itself or in curing water followed by bench storage for 3 hours. MATERIALS AND METHODS: Forty stone casts were formed from a mold of an edentulous maxillary arch. The wax denture record bases were made on the casts; the height of the wax rim occlusion was 20 mm in the labial sulcus of the cast and 10 mm in the posterior region. The upper stone cast was mounted on a Mondial 4000 semi-adjustable articulator with wax rim interocclusal references in relation to the lower stone cast teeth. Metallic pins were placed in the incisal border of the maxillary central incisors (I), labial cusp of the first premolars (PM), and mesiolabial cusp of the second molars (M). The incisor-to-incisor (I-I), premolar-to-premolar (PM-PM), and molar-to-molar (M-M) transversal distances and left incisor-to-left molar (LI-LM), and right incisor-to-right molar (RI-RM) anteroposterior distances were measured before and after denture polymerization with an optical microscope with a tolerance of 0.0005 mm. For traditional closure, the dentures were flasked conventionally in standard metallic flasks, which were afterward placed in spring clamps. For the new RS system closure, the flasks were pressed between the metallic plates of the tension system after the final closure. The Clássico heat-polymerizing acrylic resin dough was packed in the flasks under a final packing pressure of 1.250 kg f. Twelve hours after flask closure, the dentures were polymerized in a moist heat-polymerizing cycle for 9 hours at 74 degrees C. The denture was deflasked after cooling in the water of the polymerizing cycle (groups A and C) or in the water of the polymerizing cycle and then bench-stored for 3 hours (groups B and D). Collected data were analyzed with analysis of variance and Tukey's test (p< 0.05). RESULTS: There was no statistically significant difference (p> 0.05) between the conventional and new RS system closure methods for the transversal distances after polymerization in all studied groups. The anteroposterior distances did not change with deflasking after water bath cooling. There were statistically significant differences (p< 0.05) in the anteroposterior distances with deflasking after water bath cooling and then bench storage for 3 hours. CONCLUSION: Tooth movement was similar in dentures processed by traditional closure and by the new RS tension system, with the exception of the anteroposterior distances when the flasks were cooled in their own curing water and bench-stored for 3 hours.     

Dimensional stability of distances between posterior teeth in maxillary complete dentures

The aim of this study was to assess the displacement of posterior teeth in maxillary complete dentures stored in water at 37 degrees C. Twenty acrylic resin-based maxillary complete dentures were constructed with the anterior teeth arranged in normal overlap and the posterior teeth in Angle class I. Metallic pins were placed on the labial cusp of the first premolars (PM), and on the mesiolabial cusp of the second molars (M). The final acrylic resin pressing was made in a metallic flask with aid of the RS tension system, and polymerized in a moist-hot cycle at 74 degrees C for 9 hours. The dentures were deflasked after cooling in their own polymerizing water or after cooling in polymerizing water plus bench storage for 3 hours, and stored in water at 37 degrees C for periods of 7, 30, and 90 days. Following deflasking and after each storage period tested, the PM-PM (premolar to premolar), M-M (molar to molar), LPM-LM (left premolar to left molar), and RPM-RM (right premolar to right molar) distances were measured with an STM Olympus microscope, with an accuracy of 0.0005 mm. Collected data were submitted to ANOVA and Tukey's test (5%). There was no statistically significant difference for the PM-PM, M-M, and LPM-LM distances after all storage periods when the flask cooling methods were considered. With exception of the RPM-RM distance after the 30-days water plus bench storage period, the other distances remained statistically stable.     

Effect of investment material and water immersion time on tooth movement in complete denture

This study verified the effect of the association gypsum or silicone investment support materials and water immersion on the relative tooth movement in complete dentures. Wax record bases with teeth were assigned to 2 groups (n=10): 1--type III dental stone (control), and 2--condensation silicone. Linear distances (mm) between teeth were recorded after deflasking and after water storage for 1 week, 1 month and 3 months. With the exception of the silicone for the pre-molar distance after water storage for 3 months, the association between the type of investment and period of water storage did not alter the distances between teeth.     

Influence of different flask systems on tooth displacement and framework misfit in mandibular fixed implant-supported complete dentures

PurposeTo evaluate the influence of different metallic flask systems for acrylic resin denture processing on tooth displacement and framework misfit of mandibular fixed implant-supported complete dentures.MethodsStandard mandibular implant-supported complete dentures in five implants were waxed and randomly assigned to three groups: G1 – conventional flask, G2 – double flask, and G3 – occlusion flask. Framework misfit in all the implants and the linear distances between teeth (I-I – incisor-to-incisor; P-P – premolar-to-premolar; M-M – molar-to-molar; RI-RM – right-incisor-to-right-molar; and LI-LM – left-incisor-to-left-molar) were measured before and after denture processing using an optical microscope. Dentures were processed by hot water curing cycle (9 h/74 °C). Collected data were analyzed by paired Student's t-test and one-way ANOVA (α = 0.05).ResultsAll the measured distances presented changes in tooth displacement after denture processing. However, the M-M distance for G1 (p = 0.003) and the P-P (p = 0.042) and LI-LM (p = 0.044) distances for G3 showed statistically significant differences. Differences between the flask systems were not statistically significant. Statistically significant differences in the framework misfit due to denture processing were found for all the implants and groups, with the exception of right median implant for G2 and right distal implant for G3. A comparison of the flask systems found statistically significant differences in which G1 presented an increase in the misfit values and G2 and G3 a decrease.ConclusionsDifferent flask systems did not cause significant changes in tooth displacement. Frameworks misfit values were influenced by the different flask systems. The conventional flask presented an increase in the framework misfit, while the experimental flasks showed a decrease.     

Maxillary arch dimensions in Saudi and Egyptian population sample

Observations relating to maxillary arch dimensions were obtained from 243 randomly selected subjects. The group consisted of 146 Saudi subjects with an average age of 24 years and 97 Egyptian subjects with an average age of 27 years. The measurement distances from canine to canine (C-C), molar to molar (M-M), molar to canine (M-C), and molar to incisor (M-I) were based on Mack4 criteria. There was a highly significant difference by sex for Saudi and Egyptian samples, and the mean value of C-C, M-M, and M-I intercusp distances was significantly higher for Egyptians than for the Saudi sample. No significant difference was found in the M-C measurement. The results of this study demonstrate the median location of maxillary arch dimensions of Saudi and Egyptian groups combined as a sample Middle Eastern population when compared with Nigerian and British samples. Furthermore, this work can be used as a basis for future studies by anthropologists in all countries of the Middle East to define the possible changes that occur in the maxillary arch dimensions and the expected changes in the future.     

The influence of storage on dimensional changes in maxillary acrylic denture bases and the effect on tooth displacement

This study investigated the influence of both room temperature storage and water storage on tooth displacement in complete dentures. Thirty maxillary dentures were manufactured and processed using 3 different curing cycles; long, short conventional and microwaved. Distances between fixed points on teeth were measured and the dentures stored at room temperature for 24 weeks. After storage, the distances were measured again and the dentures then stored in water at 37 degrees C for 24 weeks, when the distances were re-evaluated. Anteroposterior distances demonstrated contraction in all acrylic resins. Incisor-incisor (air = -8.5% and water = -7.0%) and molar-molar (room = -1.8% and water = -1.1%) distance changes were greater in the Onda-Cryl resin (p < 0.05), whereas the premolar-premolar (room = -2.2% and water = -1.7%) distance was higher in the QC-20 resin (p < 0.05).     

Effect of processing method on the dimensional accuracy and water sorption of acrylic resin dentures

STATEMENT OF PROBLEM: Acrylic resin complete dentures exhibit certain unavoidable dimensional changes. Processing shrinkage and expansion due to water uptake are 2 important aspects influencing dimensional accuracy. PURPOSE: This study investigated linear dimensional changes and water sorption of dentures processed by dry and wet heat with different rates of cooling. METHODS: Fine crosses marked on tinfoil inserts were placed at the incisive papilla and tuberosity regions of edentulous maxillary casts and incorporated into the dentures during polymerization by 3 processing techniques. A traveling microscope was used to measure the distances between the reference points to determine dimensional changes. Water uptake and content were determined by the mass changes of the dentures with an electronic balance. Data of linear dimensional change and water sorption were analyzed by multivariate analysis of variance and analysis of variance, respectively. Bonferroni simultaneous confidence intervals (95%) were applied for multiple comparison. RESULTS: Dry heat-processed and water bath-processed acrylic resin dentures did not exhibit significant differences in shrinkage (0.42% to 0.58%) at water saturation. Amounts of water sorption of dentures processed by dry and wet heat (0.50 and 0.48 mass%, respectively) were not significantly different, and their associated expansion did not entirely compensate for the processing shrinkage. The initial water content of dry heat-processed dentures (1.77 mass%) was unexpectedly slightly higher than that of wet heat-processed dentures (1.68 mass%). The rate at which the dentures cooled did not affect their initial water content and subsequent water uptake. CONCLUSIONS: Water uptake of dry and wet heat-processed acrylic resin dentures after deflasking was in both cases low, and the dentures did not reveal significant differences in shrinkage at water saturation. Air oven-processed and water bath-processed acrylic resin dentures show similar dimensional shrinkage at water saturation.     

Functional impression and bite registration: a single session procedure for the construction of complete dentures

The closed-mouth technique for the construction of complete dentures provides in the first session both impressions and a rough idea of the jaw relation in habitual intercuspation. The aim of this study was to apply this methodological advantage to the open-mouth technique and to assess whether the arbitrary moulding of tooth position-analogue plastic rims on functional impression trays facilitates a subsequent preliminary bite registration. Therefore, 104 complete dentures, manufactured by students during their final exams, were surveyed at 22 different test points using the Gutowski–Meyding gauge. Furthermore, the position of the front teeth, the lip support and the vertical dimension were assessed clinically. The results were as follows Upper complete denture vertical distance: middle of ridge – incisal edge of central incisor: 13 ± 3 mm (5–21) vertical distance: middle of ridge – tip of cusp of first molar: 9 ± 2 mm (2–16) sagittal distance: middle of ridge – incisal edge of central incisor 7 ± 2 mm (3–14) Lower complete denture vertical distance: middle of ridge – incisal edge of central incisor: 12 ± 3 mm (7–19) vertical distance: middle of ridge – tip of cusp of first molar: 13 ± 3 mm (5–20) sagittal distance: middle of ridge – incisal edge of central incisor: 3 ± 2 mm (0–6) Complete dentures in maximum intercuspation vertical distance upper to lower ridge region central incisor 20 ± 4 mm (12–33) vertical distance upper to lower ridge region first molar 21 ± 4 mm (9–34) Because of the interindividual variance the arbitrary moulding of the tooth position-analogue plastic rims seems not ideal. However, a functional and aesthetically pleasing existing denture should be surveyed to pre-shape functional impression trays. Such individualized trays proved clinically a valuable tool for functional impressions and an immediate preliminary bite registration.     

A comparative study between three ethnic groups to derive some standards for maxillary arch dimensions

A sample of 91 adult Philippinos, 45 males and 46 females, were selected for maxillary arch measurements. The intercanine width (C-C), intermolar width (M-M), molar incisor (M-I) and molar canine (M-C) length were measured. The measurements were compared to previous studies of maxillary arch dimensions for adult male and female Egyptians and Saudi Arabians. The results showed wider (M-M) measurements for the Egyptians than for the Philippinos, who also showed wider (C-C) arch dimensions than the Saudi Arabians.     

Is the Buccolingual Crown Diameter for Transverse Malocclusions?

OBJECTIVE: We investigated whether there is a correlation between the buccolingual crown diameter and cusp tip distance and if that can be considered a factor influencing the formation of a transversal malocclusion. MATERIALS AND METHODS: The buccolingual crown diameters and cusp tip distances of all premolars and first molars of 102 normal dentitions and 123 dentitions with a transverse malocclusion were measured and examined for significant differences. We also investigated whether there were differences in size between the genders and between left and right sides. RESULTS: General differences in buccolingual crown diameters ranged from 0.3 mm to 0.6 mm, and in cusp tip distance from 0.4 mm to 0.7 mm. Buccolingual crown width was generally greater in boys than girls, whereas we observed no statistically significant difference in cusp tip distances. Comparison of left and right sides revealed no significant difference. We were able to statistically prove the correlation between buccolingual tooth diameter and cusp tip distance. CONCLUSIONS: The results suggest that larger teeth with a greater cusp tip distance offer a more favorable prerequisite for the appearance of regular transversal occlusal relations than those with a smaller distance. The buccolingual crown width and its corresponding cusp tip distance seem important for initial contact with the antagonists, and may be regarded as a factor that determines whether or not a crossbite develops.     

Caries prevalence in Turner's syndrome (45,X females)

Dental caries prevelance in permanent teeth (DFS) was studied in 50 patients with Turner's syndrome (45,X females) and 41 normal first-degree female relatives. Caries prevalence was lower in 45,X women than in controls, and this difference was more pronounced in the incisor region than in pre-molar and molar teeth.     

Effect of denture thickness on tooth movement during processing of complete dentures

In this investigation the effect of denture thickness on tooth movement during processing of complete dentures was studied. A maxillary cast from a patient was duplicated to obtain 10 identical casts. Base plates were constructed on five casts using 1·25 mm thick wax. Base plates were constructed on the other five casts using 2·5 mm thick wax. Teeth were placed on the ridge of each cast and a TMS pin was placed vertically, upright, in each tooth. The dentures were invested, cured, decasted, finished and polished. Each denture was radiographed immediately before processing, after deflasking, on removal from the cast and after finishing and polishing using a standard technique. The radiographs were digitized using an Eikonix image digitizer. The results showed that there were significant variations in tooth movement between thick and thin denture bases. Also an increase in the molar‐to‐molar distance was found in both the thin and thick dentures but the magnitude of tooth movement was more in thick dentures.     

微波凝固型塑料制作的全口义齿精度变化

目的：了解微波凝固型塑料制作的全口义齿精度变化。方法：应用三维座标测定仪对微波凝固型塑料及热凝塑料制作的全口义齿进行精度测量并比较。结果：塑料凝固后即时变化显示微波凝固型塑料比热凝塑料收缩率大,至３或４ 周呈现时间性变化。结论：微波凝固型塑料在凝固后３ 或４ 周存在时间性变化。     

Functional mobility measurement of removable partial dentures using newly-developed analyzing system in six degrees of freedom--effect of cusp inclination of molar artificial teeth on denture displacement in function]

A measuring system to record three-dimensional displacement of removable partial dentures (RPDs) in six degrees of freedom has been developed. The system employed three pairs of photodiode and LED that were set up in a triangle. This system was capable of recording the in vivo RPD displacement with a recording sensitivity of 0.1 mm. In vivo displacement of upper RPDs with unilateral distal extension saddle was investigated using this measuring system to determine the effect of artificial cusp inclination of molar teeth on denture mobility. Two groups of different artificial dentition were switched to be attached to each of three experimental RPDs. The artificial teeth with cusp inclinations were calibrated to contact with opposing natural dentition during lateral grinding of the mandible, while the other artificial teeth were prepared to disclude with the mandibular teeth (flat-cusp group). Displacement range and average position of a reference point at the first molar of the RPDs during mastication were measured and analyzed as a function of the cusp inclination and the test food. As a result, the average displacement of the RPDs toward the edentulous ridge was smaller in the cusp group than that in the flat-cusp group, while the range of horizontal displacement in the buccal-palatal direction was greater in the former group than the latter. The denture wearers demonstrated typical grinding strokes at the end of the closing phase of the mandiblar movements when they chewed a peanut, which was attributed to a wide range of horizontal displacement of the dentures.     

Dimensional change in dentures processed in silicone and stone moulds

Anecdotal evidence suggests that many dental laboratories are surrounding the teeth and gingival margins of the wax patterns for complete dentures with silicone laboratory putty prior to investing in dental stone or plaster to facilitate deflasking and polishing. This project investigates differences in dimension during processing when putty is used. Two groups of ten standardised dentures, one group with silicone, one group without were processed. Cross arch measurements were made before and after processing using an eight hour curing cycle followed by slow cooling. No statistically significant difference in change in dimension was observed between the two groups, indicating that this is an acceptable method.     

A fundamental study on the influence of posterior artificial tooth forms on denture movements during mastication

The form of posterior artificial tooth is an essential factor related to denture stability during mastication and to masticatory ability. Generally, cusp teeth are selected out of consideration for balance during eccentric occlusion. From another viewpoint, cuspless teeth are selected to ensure stability and to prevent the occurrence of lateral vectors caused by the inclination of the occlusal facet. It has been reported, however, that the counterbalance phenomenon occurring between occlusal facets decreases the lateral vector. Moreover, cusp teeth are useful in increasing the possibility of establishing bilateral balance. Guidelines for selecting posterior artificial teeth in the production of functional dentures are diverse and cannot be said to have been firmly established yet. This model experiment, which employed complete lower dentures, was designed to provide basic information for discussing the influence of occlusal facets of cusp teeth on denture movements during mastication and to arrive at some clinical suggestions for selecting posterior artificial teeth. Artificial teeth with cusp angles of 0 degrees, 10 degrees, 20 degrees, and 30 degrees were made by adjusting setting conditions on a condylar type articulator. Four kinds of experimental dentures were made and used in measuring horizontal movements of lower dentures during the crushing of experimental food. Final phase of chewing stroke was taken into consideration in establishing two types of loading direction. One type was at 70 degrees (DL 70 degrees) to the occlusal plane on the frontal plane and from the outer side (the working side). The other type was 90 degrees (DL 90 degrees) to the occlusal plane. Maximum load was 15kg and the denture displacement was analyzed at 2kg, 4kg, 8kg and 15kg. Experimental foods were smoked cuttlefish (sectile food), raisins (food flattened under pressure), and peanuts (crushable food). Analyses were made of experimental denture movement patterns and denture displacement amounts. Results 1. Experimental denture movement patterns differed according to the nature of the experimental food. The pattern in the case of smoked cuttlefish was mainly of the C type; that is, primarily motion first to the balancing side and then to the working side. The pattern for raisins was mainly of the S type; that is, primarily motion first to the working side, then to the balancing side, and then to the working side again. Several patterns appeared in the case of peanuts.(ABSTRACT TRUNCATED AT 400 WORDS)     

Relationship between retention forces and stress at the distal border in maxillary complete dentures: Measurement of retention forces and finite-element analysis in individual participants

Statement of problem

Although the retention force of maxillary complete dentures has been measured in numerous studies with different devices, the biomechanical mechanism associated with the generation of this retention force cannot be determined.

Surface enamel fluoride concentrations of different types of human teeth in a high- and near-optimal-fluoride area

The surface enamel (approximately 4 micron) fluoride concentrations of different tooth types (11, 21, 22, 23, 24) were determined in 12-13-year-old children who were life-long residents in a naturally high (3.70 ppm) and in a near optimal (0.62 ppm) fluoride area. Enamel biopsies were taken by means of an acid-etch procedure, and the fluoride levels were measured with an adapted fluoride-ion-selective electrode. The enamel fluoride concentrations were related to the fluoride levels of the drinking water, and it appeared that the enamel fluoride concentrations of the different tooth types (except for the pre-molars) were associated with the length of the pre-eruptive period. In general, for both areas, the mean enamel fluoride concentrations increased from the central incisor to the lateral incisor and were found to be the highest in the canine, while the mean fluoride content of the first pre-molar nearly equaled that of the central incisor. No statistically significant differences (p greater than 0.05) were found between the enamel fluoride concentrations of the different tooth types or the etching depths, from different sexes.