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PubMed2002

Shaping ability of GTTM Rotary Files in simulated resin root canals.

AIM: The aim of this study was to determine the shaping ability of GT Rotary Files in simulated root canals. METHODOLOGY: Forty canals with four different shapes in terms of angle (40 degrees and 60 degrees) and position of curvature (straight section before curve: 8 and 12 mm) were prepared using a crown-down/stepback technique. Pre-operative and post-operative pictures, recorded using an image analysis system, were super-imposed and aberrations recorded. Measurements were carried out at 5 different points: at the canal orifice (0): half-way to the orifice in the straight section (HO); the beginning of the curve (BC); the apex of the curve (AC): the endpoint (EP). RESULTS: Two instrument fractures occurred and 9 instruments were deformed. Overall, eight zips and one ledge were created. There were significant differences (P < 0.001) for the total width of the canals between the various canal shapes at AC, BC and HO. There were significant differences (P < 0.001) for the amount of resin removed from the outer aspect of the curve at AC, BC and HO; and for the amount of resin removed from the inner aspect of the curve at all five measuring points (0, AC and EP (P < 0.05) and HO and BC (P < 0.001)). Mean transportation was towards the inner aspect of the canal in canals with straight sections of 12 mm regardless the curve angle; towards the outer aspect in canals with straight sections of 8 mm and 40 degrees curves at all the five measuring points, and at AC, BC and HO when the curve was 60 degrees. CONCLUSIONS: Under the conditions of this study, GT Rotary Files produced acceptable canal shapes. In narrow and curved canals, the length of the straight section of the canal determines the direction of transportation more than the angle of the curve. In the 60 degrees curves, a high incidence of instrument deformation was found when using the 0.04 tapered instruments.

Dental Alloys↗
PubMed2003

Influence of operator experience on canal preparation time when using the rotary Ni-Ti ProFile system in simulated curved canals.

AIM: The aim of this study was to determine the influence of operator experience on the time needed for canal preparation when using a rotary nickel-titanium (Ni-Ti) system. METHOD: A total of 100 simulated curved canals in resin blocks were used. Four operators prepared a total of 25 canals each. The operators included practitioners with prior experience of the preparation technique, and practitioners with no experience. The working length for each instrument was precisely predetermined. All canals were instrumented with rotary Ni-Ti ProFile Variable Taper Series 29 engine-driven instruments using a high-torque handpiece (Maillefer, Ballaigues, Switzerland). The time taken to prepare each canal was recorded. Significant differences between the operators were analysed using the Student's t-test and the Kruskall-Wallis and Dunn nonparametric tests. RESULTS: Comparison of canal preparation times demonstrated a statistically significant difference between the four operators (P < 0.001). In the inexperienced group, a significant linear regression between canal number and preparation time occurred. CONCLUSION: Time required for canal preparation was inversely related to operator experience.

Analysis of Variance↗
PubMed1999

Assessment of tooth preparation designs for posterior resin-bonded porcelain restorations.

Tooth preparation designs advocated for posterior resin-bonded porcelain restorations were evaluated for clinical application. This study examined the design of tooth preparations from stone dies for individual posterior resin-bonded porcelain onlays and complete porcelain crowns placed in a specialist practice, and compared features that provided retentive and porcelain fracture-resistance with those in the dental literature. Stone dies of tooth preparations for 57 onlay and 46 crown preparations were provided. Measurements were recorded for the tooth preparations with the aid of interocclusal silicone impressions. Proximal boxes, grooves and occlusal steps resulting from removal of amalgam restorations were common. These retentive features were more evident with onlays, and appeared larger on the distal than the mesial surfaces. Internal tooth preparation tapers or convergence angles were frequently greater than 20 degrees, leading to relatively-wide occlusal isthmus widths, especially for onlays. There were wide variations in occlusal surface reductions for the central fossae and supporting cusps. Tapers for tooth preparations were frequently more extensive, and occlusal surface reductions were often less than recommended. The implications of these differences for long-term clinical success should be resolved.

Adult↗
PubMed2000

Biomechanical effects of double or wide implants for single molar replacement in the posterior mandibular region.

Double implants have been thought to have biomechanical advantages for single molar replacement. To evaluate the effectiveness of double implants versus a wide implant, the vertical forces and torque on each implant were calculated by three-dimensional geometric analysis. Buccal load (100N) perpendicular to cuspal inclination (20 degrees) was applied at the occlusal surface of the superstructure. The three kinds of load points (A, B, C) were 1.5, 3.5, and 5.5 mm from the mesial contact point, respectively. Three implants were compared: mesial and distal double implants (phi 3.3 mm), and a wide implant (phi 5 mm). The wide implant showed torque around the long axis (1.8-15.0 N x cm) whereas double implants had no torque. On the other hand, the vertical forces on the mesial double implant were both smaller (60%: loaded at point C) and larger (140%: loaded at point A) than the wide implant. Given the smaller surface area of the mesial double implant, this large force may generate much higher stress in the peri-implant bone. These results suggest that the biomechanical advantage of double implants for single molar replacement is questionable when the occlusal force is loaded at the occlusal surface near the contact point.

Biomechanical Phenomena↗
PubMed2004

A novel approach to evaluating the reproducibility of a replication technique for the manufacture of electroconductive replicas for use in quantitative clinical dental wear studies.

The assessment of the progression of tooth surface loss has until recently been limited to either the application of subjective ranking scales or visual comparison of sequential study casts. The development of quantitative measuring techniques offers the potential of greater accuracy and sensitivity. As direct intra-oral measurement is problematical such approaches often utilize impressions of the teeth, recorded at different epochs, to construct replicas for mapping and comparison. This in vitro investigation sought to determine the reproducibility of such an approach taking into account the total process chain. Two inlay cavities (one large, one small) were prepared in the palatal aspect of a plastic maxillary central incisor and restored with two flush fitting inlays. A series of impressions of this tooth were recorded, using a special tray and an addition cured light bodied silicone impression material (President, Coltene, Switzerland), with (a) both inlays in (b) both inlays out (c) large inlay out and small inlay in (d) large inlay in and small inlay out - a total of 16 impressions. Electroconductive replicas were fabricated from these and mapped using a computer controlled probe. Each series simulated wear of the tooth. A surface matching and difference detection algorithm was then used to compare each series of replicas and calculate the proportion of the surface undergoing simulated wear by a direct comparison of (a) matched to (b) or, indirectly as the summation of the results of matches of (a) with (c) and (a) with (d). The mean proportion of the surface with wear calculated directly was 26.6% (s.d.=0.6) and indirectly 26.1% (s.d. = 0.5). A one-way anova revealed no significant difference (P > 0.05). It is concluded that determining wear by this method is highly reproducible.

Algorithms↗
PubMed2002

Prediction of arch perimeter changes due to orthodontic treatment.

A borderline orthodontic case with mild to moderate space deficiency can be treated without extractions. Expansion can be used to relieve space deficiency. The prediction of arch perimeter change for a given amount of expansion is helpful in planning the treatment of a patient who needs expansion, and it can facilitate nonextraction orthodontic treatment. To date, different amounts of arch perimeter change have been proposed for the same amount of expansion. A computer program is explained in this study, and examples of its uses are given. By entering 4 parameters of a dental arch into the computer program before and after an orthodontic procedure, one can simply calculate the total and the anterior arch perimeters and see the differences between them numerically and graphically. The program can save, print, change, and delete the calculated data for each patient. For clinicians who do not choose to use the computer program, 2 regression formulas are also presented to calculate the anterior and the total dental arch perimeters. The perimeters of 23 pairs of well-aligned dental arches were measured to check the accuracy of the computer program and the formulas. Paired t tests did not show statistically significant differences between the actual, the computer-derived, and the formula-derived perimeters of the dental arches at 95% confidence level.

Computer Graphics↗
PubMed2000

Accuracy of casts generated from dual-arch impressions.

STATEMENT OF PROBLEM: Dual-arch trays are often used to make simultaneous impressions of a prepared tooth and the opposing teeth. Many dentists are concerned with the accuracy of the casts generated from this type of impression. PURPOSE: The purpose of this investigation was to compare the accuracy of stone casts of a prepared tooth generated using 2 types of dual-arch impression tray/impression material combinations. MATERIAL AND METHODS: The maxillary left first molar on a dentoform mounted on an articulator was prepared for a full-coverage gold crown. Ten impressions were made with either a plastic (P) or metal (M) tray and a polyether (PE) or vinyl polysiloxane (VPS) impression material. Each impression was cast in improved dental stone, and the buccolingual dimension of the die was measured at the midpoint of the buccal and lingual gingival margins. The prepared tooth (T) served as the control. The data were analyzed using a 2-factor analysis of variance (ANOVA) alpha=.05. RESULTS: The P/VPS combination (10.673 mm) produced the largest die, followed by P/PE (10.602), T (10.508), M/PE (10.484), and M/VPS (10.472). The 2-factor ANOVA showed a significant difference between the tray types but not between the impression materials. CONCLUSION: The metal trays produced dies smaller than the tooth, and the plastic trays produced dies that were larger.

Dental Impression Materials↗
PubMed2001

Modification of a Super-Sep bottle for paint-on application of a separating medium used in flasking dentures.

Modifying a Super-Sep bottle by adding a brush to the lid for paint-on use allows for the precise application of the separating medium used when flasking dentures. Super-Sep offers many advantages over other commonly used separating mediums: It is virtually dimensionless, allowing for better accuracy; it dries quickly and functions best on moist stone; and it can be poured against immediately. The latter fact means less time is needed before the subsequent layers of stone can be applied when denture flasking.

Calcium Sulfate↗
PubMed2002

Accuracy of 3 conceptually different die systems used for implant casts.

STATEMENT OF PROBLEM: Given that meticulous implant prosthodontic procedures are recommended to obtain the best possible intraoral fit, the die systems used for multi-implant casts warrant further investigation. PURPOSE. The purpose of this in vitro study was to compare the accuracy of implant casts fabricated from 3 conceptually different die systems at the solid, sectioned, and repeated stages. MATERIAL AND METHODS: Thirty direct transfer implant impressions were made of the master cast with a polyether impression material. Ten experimental implant casts were fabricated for each of the 3 different die systems tested: double-pour (Pindex), plastic base (DVA), and die tray (KO Tray). The solid experimental casts were sectioned and then removed from the die system 30 times. Linear distances between steel balls placed on each abutment replica were measured with a traveling microscope to determine the accuracy of the experimental casts at different stages. Data were analyzed with repeated-measures analysis of variance (alpha=.05) and the post hoc Ryan-Einot-Gabriel-Welsch multiple-range test (REGWQ). RESULTS: Repeated-measures analysis of variance revealed a significant interaction between the die systems and different stages (P=.0432). REGWQ showed the die tray system to be significantly more accurate at the solid than at the sectioned and repeated stages. The die tray system was significantly less accurate than the double-pour and plastic base systems at the sectioned stage. CONCLUSION: Within the limitations of this study, the use of a double-pour or plastic base die system is recommended when sectioned dies are needed for a multi-implant-retained prosthesis.

Acrylic Resins↗
PubMed1994

Light maxillary expansion forces with the magnetic expansion device. A preliminary investigation.

An active maxillary magnetic expansion device (MED) was developed to be used clinically. The aim was to show the effects of light and continuous forces producing less traumatic stimulation of maxillary sutural growth than a conventional rapid maxillary expansion device. In this study, two different types of appliances were used on six patients between 7 years 4 months and 16 years 2 months: the first type was bonded, the other one used bands. For better appreciation, four implants were placed on each patient: two apically between central and lateral incisors, and two between second premolars and molars. A standardized radiographic technique was used to take occlusal radiographs, and postero-anterior and lateral headplates. The results varied according to the age and the appliance used. The skeletal effect with the banded MED was between 16 and 77 per cent, and for the bonded MED 0 and 25 per cent in comparison to the overall expansion. It seems that 250-500 g of continuous magnetic forces can produce dental and skeletal movements in a light force expansion concept, but further studies with larger samples are needed to make firm conclusions.

Activator Appliances↗
PubMed1996

A method of measuring the apical base.

The maxillary and mandibular apical base areas were measured, using a gnathograph, on the study casts of 156 adults and children representing Class II division 1, Class II division 2 and Class III malocclusions. There were significant differences between the groups at each age. The maxillary apical base areas tended to be smaller for the adults than for the children in all three occlusal classes. By contrast, the mandibular apical base areas tended to be larger for the adults than for the children, except in Class II division 1 malocclusion. Following a logarithmic transformation to stabilize the variance, regression lines were fitted to relate the size of the maxillary and mandibular apical bases to one another, for the malocclusion groups within each age group. The method gives additional information regarding the degree of apical base discrepancy in a given case, but more work is required before it can be used as a diagnostic tool.

Adolescent↗
PubMed1999

Primary alveolar cleft bone grafting in unilateral cleft lip and palate: arch dimensions at age 8.

The purpose of this investigation is to determine whether primary alveolar cleft bone grafting in infants with unilateral cleft lip and palate (N = 17) leads to less favorable dental arch dimensions at age 8 when compared with other 8-year-old patients with unilateral cleft lip and palate who received no alveolar bone grafting procedures (N = 49). Dental casts were obtained for the primary grafted group, and arch lengths and widths were digitally recorded with a reflex microscope. These arch dimensions were then compared with the reported data for a nongrafted group and a noncleft group of 8-year-old children. The major findings were: 1) that the dental arches of both cleft groups generally demonstrated a significant diminution in length and width (P < 0.05) compared with the noncleft groups, and 2) that the patients who underwent primary alveolar cleft bone grafting showed no statistically significant difference for any arch dimension (P < 0.05) when compared with the nongrafted group lacking this additional surgical procedure.

Alveolar Process↗
PubMed2001

Shortening of mandibular linear distance with multivector distraction.

It was noted that when a multivector distractor is used, there is shortening of the linear distraction distance when the gonial angle is reduced and the transverse distance is increased. The purpose of this study was to measure the distance change at the mandibular corticotomy site when the gonial angle is reduced or the transverse distance is increased. The Synthes multivector distractor was used in this experiment. After initial linear distraction, the distractor was activated by angular and transverse adjustments to achieve an angular, a transverse, and a combined angular and transverse reorientation. The length of the pin from the distractor to the tip of pin was evaluated at 15, 20, and 25 mm. With the pins place at 180 degrees , the distractor arm length was evaluated at 30, 35, 40, 45 and 50 mm apart, respectively. The distance change between the ends of the pins was measured by means of a caliper. For angular activation, one turn shortened the linear distraction distance at the pin end by 1.5 to 2.2 mm. For transverse activation, one turn shortened the linear distraction distance by 1.1 to 2 mm. For combined angular and transverse activation, one turn of angular activation plus one turn of transverse activation shortened the linear distraction distance by 2.2 to 3.2 mm. For angular activation, increasing the pin length did not alter the distance between the pin ends for any of the specific activations. Increase in the distractor arm length in angular reduction resulted in significant increase in the shortening. For transverse increase, alteration in the distractor arm length resulted in the same shortening. Increase in the pin length resulted in increased shortening at the pin ends. When the transverse and angular activation were combined, the shortening was 80% of the combined measurements. The distance between the pin ends will reflect the distance between the bone segment at that site. It will be different at the outer cortex of the bone. These measurements will be valuable in planning the extent of additional linear distraction needed, when the angle is reduced or transverse distance is increased with the use of a multivector distractor. Alteration in the distractor arm length and pin length has a significant effect on the extent of shortening.

Biomechanical Phenomena↗
PubMed2003

Placement of mineral trioxide aggregate using two different techniques.

The purpose of this study was to determine if the adaptation of mineral trioxide aggregate (MTA) would differ when placed into simulated root canals of varying length when using two different placement and condensation methods. Hand condensation was compared to ultrasonic condensation. Eighty polyethylene tubes were divided into four groups of 20 tubes each. The tubes in the four groups were prepared to receive 3-, 5-, 7-, and 10-mm lengths of MTA respectively. Each group of 20 tubes was subdivided; 10 samples of each length had MTA placed and condensed by the hand method and the other 10 by the ultrasonic method. After condensation the samples were evaluated with a light microscope and radiographs for the degree of adaptation of the MTA to the tube walls and for the presence of voids within the MTA material itself. The results demonstrated an 80% agreement for findings between the light microscopy and radiographic evaluation. Hand condensation resulted in better adaptation to the tube walls and less voids than the ultrasonic method. There was no significant difference in the results for any of the four lengths of MTA placed by the hand method (p > 0.9). At this time hand condensation should be considered the preferred method for placement of MTA.

Aluminum Compounds↗
PubMed2004

Evaluation of transfer impressions for osseointegrated implants at various angulations.

The accuracy of impressions that transfer the relationship of the implant to the metal framework of the prosthesis continues to be a problem. This study was designed to evaluate the accuracy of the transfer process under variable conditions with regard to implant analog angulations, impression materials, and techniques. Replicas (n = 60) of a metal matrix (control) containing four implants at 90 degrees , 80 degrees , 75 degrees , and 65 degrees in relation to the horizontal surface were obtained by using three impression techniques: T1-indirect technique with conical copings in closed trays; T2-direct technique with square copings in open trays; and T3-square copings splinted with autopolymerizing acrylic resin; and four elastomers: "P"-polysulfide; "I"-polyether; "A"-addition silicone; and "Z"-condensation silicone. The values of the implant analog angulations were assessed by a profilometer to the nearest 0.017 degrees , then submitted to analysis of variance for comparisons at significance of 5% (P < .05). For implant analog at 90 degrees , the material "A" associated with T2 and material "Z" with T3 behaved differently (P < .05) from all groups. At 80 degrees , all materials behaved differently (P < .01) with T1. At 75 degrees , when T1 was associated, materials "P" and "A" showed similar behavior, as well as materials "I" and "Z"; however, "P" and "A" were different from "I" and "Z" (P < .01). When T3 was associated, all experimental groups behaved differently among them (P < .01). At 65 degrees , the materials "P" and "Z" behaved differently (P < .01) from the control group with T1, T2, and T3; the materials "I" and "A" behaved differently from the control group (P < .01) when T1 and T2, respectively, were associated. The more perpendicular the implant analog angulation is in relation to the horizontal surface, the more accurate the impression. The best materials were material "I" and "A" and the most satisfactory technique was technique 3.

Dental Casting Technique↗