Influence of abutment angulation on loss of prosthetic abutment torque under mechanical cycling

Statement of problemInternal conical connections provide mechanical stability for the prosthetic abutment and implant connection. However, some clinical situations require the use of angled prosthetic abutments that may increase stress on supportive implants by difference force vectors under cyclic loading.PurposeThe purpose of this in vitro study was to measure the screw loosening values of prosthetic abutments with internal conical connections (indexed and nonindexed) having different angles under mechanical cycling.Material and methodsThirty-six implants (4.0×13 mm, Titamax) with internal conical connections and their respective universal prosthetic abutments (n=36, 3.5×3.3 mm) were divided into indexed and nonindexed groups (n=18) with abutment inclinations of 0 (straight), 17, and 30 degrees. An insertion torque of 15 Ncm was applied according to the manufacturer’s specifications. The specimens underwent fatigue testing of 500 000 cycles at a frequency of 2 Hz with a dynamic compressive load of 120 N at an angle of 30 degrees. The detorque values were measured by using a digital torque meter and tabulated for statistical analyses.ResultsThe specimens with indexed abutments had mean ±standard deviation detorque values of 6.72 ±2.29 Ncm under mechanical cycling, whereas those with nonindexed abutments had values of 8.98 ±1.84 Ncm. In the indexed group, the lowest detorque value was observed for abutments at 30 degrees compared with the straight group (P<.05). As for nonindexed abutments, similar detorque values were observed after increasing the abutment inclination (P>.05).ConclusionsA decrease in detorque values in the indexed abutments related to their inclination was found under mechanical cycling, whereas the prosthetic abutments with 30 degrees of angulation had the lowest values. No decrease was found in the nonindexed abutments.     

Influence of second-order bracket-archwire misalignments on loads generated during third-order archwire rotation in orthodontic treatment

Objective:To investigate the influence of a rotational second-order bracket-archwire misalignment on the loads generated during third-order torque procedures. Specifically, torque in the second- and third-order directions was considered.Materials and Methods:An orthodontic torque simulator (OTS) was used to simulate the third-order torque between Damon Q brackets and 0.019 × 0.025-inch stainless steel archwires. Second-order misalignments were introduced in 0.5° increments from a neutral position, 0.0°, up to 3.0° of misalignment. A sample size of 30 brackets was used for each misalignment. The archwire was then rotated in the OTS from its neutral position up to 30° in 3° increments and then unloaded in the same increments. At each position, all forces and torques were recorded. Repeated-measures analysis of variance was used to determine if the second-order misalignments significantly affected torque values in the second- and third-order directions.Results:From statistical analysis of the experimental data, it was found that the only statistically significant differences in third-order torque between a misaligned state and the neutral position occurred for 2.5° and 3.0° of misalignment, with mean differences of 2.54 Nmm and 2.33 Nmm, respectively. In addition, in pairwise comparisons of second-order torque for each misalignment increment, statistical differences were observed in all comparisons except for 0.0° vs 0.5° and 1.5° vs 2.0°.Conclusion:The introduction of a second-order misalignment during third-order torque simulation resulted in statistically significant differences in both second- and third-order torque response; however, the former is arguably clinically insignificant.     

Effects of third-order torque on frictional force of self-ligating brackets

Objective:To investigate the effects of third-order torque on frictional properties of self-ligating brackets (SLBs).Materials and Methods:Three SLBs (two passive and one active) and three archwires (0.016 × 0.022-inch nickel-titanium, and 0.017 × 0.025-inch and 0.019 × 0.025-inch stainless steel) were used. Static friction was measured by drawing archwires though bracket slots with four torque levels (0°, 10°, 20°, 30°), using a mechanical testing machine (n  =  10). A conventional stainless-steel bracket was used for comparison. Results were subjected to Kruskal-Wallis and Mann-Whitney U-tests. Contact between the bracket and wire was studied using a scanning electron microscope.Results:In most bracket-wire combinations, increasing the torque produced a significant increase in static friction. Most SLB-wire combinations at all torques produced less friction than that from the conventional bracket. Active-type SLB-wire combinations showed higher friction than that from passive-type SLB-wire combinations in most conditions. When increasing the torque, more contact between the wall of a bracket slot and the edge of a wire was observed for all bracket types.Conclusions:Increasing torque when using SLBs causes an increase in friction, since contact between the bracket slot wall and the wire edge becomes greater; the design of brackets influences static friction.     

Influence of stainless steel inserts on the resistance to sliding of esthetic brackets with second-order angulation in the dry and wet states

Stainless steel (SS) inserts have been added to plastic, ceramic, and composite brackets to improve their frictional characteristics while preserving their esthetic appeal. When coupled with SS archwires, the resistances to sliding of esthetic brackets with and without SS inserts were compared with control brackets of SS. The resistances to sliding were measured in both the dry and wet (saliva) states at 32 second-order angles between -12 and + 12 degrees. When clearances existed between the walls of the brackets and the archwires, the resistances to sliding for the esthetic brackets without inserts were between 38 cN in the dry state and 73 cN in the wet state; those of the esthetic brackets with inserts ranged from 42 cN in the dry state to 65 cN in both states. The resistances to sliding of the SS brackets equaled 38 and 52 cN in the dry and wet states, respectively. When clearances no longer existed, the resistances to sliding for the esthetic brackets with and without inserts generally increased with angulation at a rate equal to or greater than that of the SS brackets--except for the polycarbonate (PC) brackets in the dry state. Because PC brackets without inserts elastically deformed, they had lower resistances to sliding when deformation occurred. For the polycrystalline alumina brackets without inserts, the resistances to sliding increased rapidly and nonlinearly as angulation increased above 4.8 degrees. Upon examination, the presence of scratches on the archwires and SS debris on the brackets was observed. The addition of these particular SS inserts did not considerably improve the resistance to sliding over those esthetic brackets without inserts.     

陶瓷托槽与金属弓丝第二序列成角状态下摩擦性能的研究

目的研究陶瓷托槽与金属弓丝在第二序列成角状态下的摩擦力,探讨影响托槽弓丝间摩擦力的因素。方法进行托槽外观形貌的测量与观察,计算托槽与弓丝第二序列成角下的临界角,并设计带可调节罗盘的载物台,用MTS Tytron250微力试验机体外测试三种陶瓷托槽（A、B、C）和一种金属托槽（D）与0.016英寸不锈钢圆丝（SS）在第二序列成角分别为0度、2度、5度、8度时的最大静摩擦力和滑动摩擦力。结果与0.016英寸SS的摩擦力总体表现出B托槽〉C托槽〉A托槽〉D托槽的趋势,在四种成角状态下的最大静摩擦力随角度加大而增大,总体表现为0度到2度的摩擦力增加没有显著性,增大夹角后摩擦力增加量不同托槽间有差异：A托槽与弓丝在2度到5度成角状态下的摩擦力增加没有显著性,而5度到8度的摩擦力有显著增加;B托槽在2度到5度摩擦力有显著增加,而5度到8度摩擦力增加不显著;虽然2度到5度摩擦力增大没有显著性,但8度与0度状态下相比,C托槽与弓丝间的摩擦力有显著增加;D托槽在2度、5度、8度时摩擦力间差异无显著性。结论选用带金属槽沟的陶瓷托槽,增加陶瓷托槽边缘的圆钝程度等能减缓牙齿移动中托槽-弓丝成角引起的滑动阻力增加;使用传统陶瓷托槽要注意充分排齐。     

Influence of implant angulation with different crowns on stress distribution

The aim of this study was to perform a photoelastic analysis of stress distribution on straight and angulated implants with different crowns (screwed and cemented). Three models were made of photoelastic resin PL-2: model 1: external hexagon implant 3.75×10.00 mm at 0 degrees; model 2: external hexagon implant 3.75×10.00 mm at 17 degrees; model 3: external hexagon implant 3.75×10.00 mm at 30 degrees. Axial and oblique (45 degrees) load (100 N) was applied with a universal testing machine. The photoelastic fringes on the models were recorded with a digital camera and visualized in a graphic software for qualitative analysis. The axial loading generated the same pattern of stress distribution. The highest stresses were concentrated between medium and apical thirds. The oblique loading generated a similar pattern of stress distribution in the models with similar implant angulation; the highest stress was located on the cervical region opposite to implant angulation and on the apical third. It was concluded that the higher the implant angulation, the higher the stress value, independent of crown type. The screwed prostheses exhibited the highest stress concentration. The oblique load generated higher stress value and concentration than the axial load.     

Influence of third molar space on angulation and dental arch crowding

The influence of the third molars on mandibular incisor crowding has been extensively studied but remains controversial. The purpose of this study was to ascertain whether, in Mongolian subjects, the lower third molar can affect anterior crowding and/or the inclination of teeth in the lower lateral segments. Panoramic radiographs, 45° oblique cephalograms, and dental casts were taken from Mongolian subjects (age range 18.3–24.1 years, mean 21.0 years) exhibiting impaction of all four third molars and an Angle Class I molar relationship. The Ganss ratio was calculated using panoramic radiographs, whereas the gonial angle and angulation of lower canines, premolars and molars were measured using 45° oblique cephalograms. Little’s index of irregularity was calculated using dental casts. Significant relationships between the angulation of the third and second molars and between the first molars and second premolars were found. Conversely, there was no significant correlation between the angulation of third molars, first premolars and canines. The Ganss ratio calculations showed that the lower first and second molars and the second premolars inclined mesially if there was insufficient space for the lower third molars. However, there was no significant correlation between Little’s index of irregularity and third molar angulation. Furthermore, although the third molar influences the lateral segments, no obvious relationship between the third molar and anterior crowding was observed. Therefore, the angulation of the third molar appears not to cause anterior crowding.     

槽沟尺寸对转矩控制影响的实验研究

目的研究在同一牙弓中牙齿存在相互作用的条件下,2种槽沟尺寸的托槽在转矩控制方面是否有差异。方法通过Typodont水浴实验,模拟临床矫治过程,测量结束弓丝为0.431 8 mm×0.635 0 mm不锈钢方丝时,使用0.558 8 mm×0.711 2 mm托槽和0.457 2 mm×0.635 0 mm托槽时上颌5┼5共10颗牙齿的唇舌向倾斜度。实验重复10次。通过计算机编程进行计算,将唇舌向倾斜度转换为上颌5┼5的转矩余隙角ψ。对2种槽沟尺寸托槽的ψ的绝对值进行配对t检验。结果2种槽沟尺寸的托槽在转矩控制方面的差异具有统计学意义,当结束弓丝为0.431 8 mm×0.635 0 mm不锈钢方丝时,0.558 8 mm×0.711 2 mm和0.457 2 mm×0.635 0 mm托槽转矩余隙角ψ的绝对值分别为6.140°±3.758°和2.608°±1.479°,2种托槽间转矩余隙角ψ的绝对值的均值相差3.532°,0.457 2 mm×0.635 0 mm托槽的转矩余隙角较小。在2种槽沟尺寸托槽的作用下,上颌左右尖牙ψ的绝对值分别为2.560°±2.605°、4.230°±2.817°、1.260°±0.747°和2.070°±0.663°,尖牙较其他牙位ψ的绝对值的差值要小。结论2种槽沟尺寸的托槽在转矩控制方面存在差异,弓丝尺寸相同时,0.457 2 mm×0.635 0 mm托槽可以更好地控制牙齿的转矩。槽沟尺寸对转矩控制的影响小于以往研究的理论计算值和材料学实验结果,可能是由于同一牙弓牙齿间的相互影响所致。     

Comparison of resistance to sliding between different self-ligating brackets with second-order angulation in the dry and saliva states.

Resistance to sliding was investigated for 3 self-ligating brackets having passive slides and 3 self-ligating brackets having active clips. Four of these products are currently marketed, and 2 are of historic interest. For all cases, an 0.018 x 0.025-in stainless steel archwire was drawn through each bracket at a rate of 10 mm/min over a distance of 2.5 mm. For each bracket, the resistances to sliding were measured at 14 second-order angulations, which ranged from -9 degrees to +9 degrees. Both the dry and the wet (human saliva) states were evaluated at 34 degrees C. From dimensional measurements, the critical contact angles for binding were determined for all products and ranged from 3 degrees to 5 degrees. Below each characteristic critical angle, brackets with passive slides exhibited negligible friction; brackets with active clips exhibited frictional forces as great as 50 cN (50 g). Above each critical angle, all brackets had elastic binding forces that increased at similar rates as angulation increased and were independent of bracket design. Generally speaking, at second-order angulations that exceeded the critical angle, brackets with active clips that had a low critical angle had more resistance to sliding than did brackets with active clips that had a higher critical angle. Brackets with passive slides that had a high critical angle exhibited the lowest resistance to sliding, but could do so at a cost of some loss of control. Nonetheless, self-ligating brackets represent a compromise between friction and control; ie, self-ligating brackets produce frictional forces that are more reproducible than do conventionally ligated stainless steel brackets but without the potential control problems associated with Begg-style brackets.     

Effect of archwire size and material on the resistance to sliding of self-ligating brackets with second-order angulation in the dry state.

When paired with a particular self-ligating bracket design, the material and the geometric characteristics of an archwire influence its resistance to sliding. Four designs of self-ligating brackets (1 with a slide, 3 with clips) were coupled with 5 types of archwires: 14-mil round austenitic nickel-titanium, 16 x 22-mil rectangular austenitic nickel-titanium, 19 x 25-mil rectangular austenitic nickel-titanium, 19 x 25-mil rectangular martensitic nickel-titanium, and 19 x 25-mil rectangular stainless steel. The resistance to sliding (RS) of each archwire-bracket couple was measured at second-order angles between -9 degrees and 9 degrees. Interbracket distances of 8 and 18 mm between the test bracket and the adjacent brackets mimicked closure of a premolar extraction. When clearance exists, the RS is negligible for self-ligating brackets with slides coupled to any size of wire as well as for those with clips when coupled to wires that do not contact the clip. Once the wire attains a certain size and contacts the clip, the RS depends on the archwire size, the bracket design, and the materials of the couple. When coupled with the 16 x 22-mil wire, the brackets with clips applied normal forces ranging from a low of 5.6 centi-Newtons (cN) (1 cN = 1 g) to a high of 230 cN. When clearance disappears, the RS increased proportionally with the second-order angle. The 19 x 25-mil stainless steel wires, which were the most stiff, increased at rates between 75 and 84 cN/degree; the 14-mil austenitic nickel-titanium wires, which were the least stiff, increased at rates from 2.6 to 5.4 cN/degree. The treatment objectives for a particular patient at a specific stage should determine the appropriate archwire-bracket combination.     

Resistance to sliding of orthodontic brackets with bumps in the slot floors and walls: effects of second-order angulation.

OBJECTIVE: Two stainless steel (SS) bracket designs with two bumps across the slot floors and rounded slot walls and one polycrystalline alumina (PCA) bracket design with one bump along the slot floor were compared to conventional SS and PCA brackets. METHODS: For each design, the resistances to sliding of four archwire-bracket couples, two in the dry state and two in the wet (saliva) state, were measured at 32 second-order angles between -12 and +12 degrees. RESULTS: When clearances existed, the kinetic coefficients of friction of the SS brackets ranged from 0.13 to 0.15 in the dry state and from 0.17 to 0.18 in the wet state. For the PCA brackets, the kinetic coefficients of friction were 0.18 for both designs in the dry state and were 0.18 for the brackets with bumps and 0.24 for the brackets without bumps in the wet state. SIGNIFICANCE: Overall, the bumps and rounded slot walls did not reduce classical friction. When the brackets with rounded slots were modeled, the critical contact angles for binding were larger than the values based on the apparent dimensions, but were less than those based on the true dimensions. When clearances did not exist, the rates of binding were greater for the SS brackets with bumps and rounded walls than for the conventional brackets. The rates of binding increased because the rounded walls forced the archwires into complex shapes. Both PCA bracket designs had similar rates of binding; but unlike the conventional design, the brackets with the bumps did not permanently deform the archwires at large angles.     

Effects of ligation type and method on the resistance to sliding of novel orthodontic brackets with second-order angulation in the dry and wet states

Rectangular stainless steel (SS) archwires were coupled with four SS bracket designs: Mini Diamond Twin, which was a conventional twin bracket; VersaT, which had bumps along the slot floor and rounded slot walls; Shoulder, which had bosses outside the tie-wings to lift the ligation off the archwire; and Synergy, which had bosses between the outer and inner tie-wings, bumps along the slot floor, and rounded slot walls. For all designs, the values of resistance to sliding (RS) were measured at five normal forces and 32 second-order angulations in the dry and wet (saliva) states. RS values at these same angles and states were also measured for the following: Mini Diamond Twin brackets ligated with rings and SS ligature wires; VersaT brackets ligated with rings; Shoulder brackets ligated with rings in a figure-8 and a figure-O around the tie-wings; and Synergy brackets ligated with rings around the outer tie-wings and around the inner tie-wings. In both states, the coefficients of friction were similar for the Mini Diamond Twin, VersaT, and Synergy brackets; the values for the Shoulder brackets were slightly greater than for the other three designs. In the passive configuration, the features of the Shoulder and Synergy brackets reduced RS when the rings were not in contact with the archwires. In the active configuration, the binding behavioral patterns of the brackets were not influenced by ligation methods. Thus, these different ligation types and methods only affected the classical frictional component of RS in the passive configuration.     

Biting efficiency in relation to incisal angulation

Previous studies suggest the orientation of the incisor teeth to the path of jaw movement pronouncedly affects their efficiency of action. To test this hypothesis, upper and lower incisal portions of a study model with ideal Asian occlusion were mounted on a mechanical tester and impressed into rectangular blocks made of 15.3% w/w starch gels or Cheddar cheese. At varying angulations of attack between the long axis of the teeth (defining the orientation of the tooth crown) and force direction, the teeth were driven into the blocks for 4-6mm until fractures had grown in the foods. Both the angle of attack and the work divided by fractured area produced in the food, termed 'work to fracture', were measured. The food type (cheese or gel), incisal type (upper or lower pair) and angle of inclination were significant effects on the works to fracture. The minimal work was for angles slightly proclined to the vertical, although only angles of proclination >40 degrees were significantly higher than all other angles. Retroclination or large angles of proclination made little difference to the work done, but produced markedly off-axis cracks. It is suggested that human incisors act most efficiently at small gapes and that orthodontic corrections will thus offer definite functional benefits.     

Influence of X-ray beam angulation upon the radiographic image of proximal carious lesions

Abstract Twenty-two extracted human molars and premolars with a total of34 initial proximal carious lesions were radiographed in 16 different views varying the horizontal angulation of the X-ray beam in steps of 2.5° The radiographs were read simultaneously by three observers. Clinical and radiographic diagnoses were compared. When utilizing all 16 views the concordance was 95%. All proximal surfaces were scored using four scoring classes. Surfaces without radiolucencies were scored 0, and carious surfaces were scored according to the extent of the radiolucencies. Nine sound and 12 carious surfaces were assigned identical scores in all 16 views, while 22 (65%) of the carious surfaces were assigned two, three or four different scores. Deviations from a direction of the X-ray beam tangential to the proximal surface eliciting a radiographic image belonging to a different score were measured. In 71% of the cases a deviation of 7.5° or less elicited a different score. Projectional circumstances should be taken into consideration in interpreting proximal radiolucencies.     

Resistance to sliding of self-ligating brackets versus conventional stainless steel twin brackets with second-order angulation in the dry and wet (saliva) states.

The frictional properties of conventional stainless steel brackets that were coupled with rectangular stainless steel archwires and ligated with stainless steel ligature wires and the frictional properties of closed self-ligating brackets coupled with the same archwires were compared in terms of second-order angulation. The slides of these self-ligating brackets passively restrained the archwires within the slots. As a control, the frictional properties of the opened self-ligating brackets, which were ligated with stainless steel ligature wires, were measured. The resistance to sliding of the conventional brackets and the opened self-ligating brackets were measured at ligation forces ranging from 200 to 600 cN and at angles from -9 degrees to 9 degrees. The resistances to sliding of the closed self-ligating brackets were measured at the same angles, but no external ligation forces were applied. In the passive configuration, the conventional brackets exhibited similar frictional resistance as the opened self-ligating brackets, whereas the closed self-ligating brackets exhibited no friction. In the active configuration, all brackets exhibited increased resistance to sliding as the angulation increased. At all angles, the resistances to sliding of the closed self-ligating brackets were lower than those of the conventional brackets because of the absence of a ligation force when the slide restrained the archwire.     

Influence of torque control motors and the operator's proficiency on ProTaper failures

OBJECTIVE: The purpose of this study was to evaluate the influence of 2 electric torque control motors and operator experience with a specific nickel-titanium rotary instrumentation technique on the incidence of deformation and separation of instruments. STUDY DESIGN: ProTaper (PT) nickel-titanium rotary instruments were used at 300 rpm. In the first part of the study, electric high torque control (group 1) and low torque control (group 2) motors were compared. In the second part of the study, 3 operators with varying experience (groups 3, 4, and 5) were also compared. Twenty sets of PT instruments and 100 canals of extracted human molars were used in each group. Each set of PT instruments was used in up to 5 canals and sterilized before each case. For irrigation, 2.5% NaOCl was used. The number of deformed and separated instruments among the groups (within each part of the study) was statistically analyzed for significance with pair-wise comparisons by using the Fisher exact test (alpha =.05). RESULTS: In part 1, instrument deformation and separation did not occur in groups 1 and 2. In part 2, 25 and 12 instruments were deformed and separated, respectively, with the least experienced operator. Instrument deformation and separation did not occur with the most experienced operator. The Fisher exact test revealed a significant difference between groups 3 and 4 with respect to instrument deformation (P =.0296). In addition, the Fisher exact test revealed that the incidence of instrument deformation was statistically different between groups 3 and 5 (P <.0001) and groups 4 and 5 (P =.0018). The incidence of instrument separation was significantly higher in group 5 than in groups 3 and 4 (P =.001). CONCLUSIONS: Preclinical training in the use of the PT technique at 300 rpm is crucial to prevent instrument separation and reduce the incidence of instrument deformation. The use of an electric high torque control motor is safe with the experienced operator.     

Influence of rotational speed, torque and operator's proficiency on ProFile failures

AIM: The purpose of this study was to evaluate the influence of rotational speed, torque, and operator experience with a specific Ni-Ti rotary instrumentation technique on the incidence of locking, deformation and separation of instruments. METHODOLOGY: ProFile Ni-Ti rotary instruments (PRI) sizes 40-15 with a 6% taper were used in a crown-down technique. In one group of canals (n = 300) speeds of 150, 250 and 350 rpm (subgroups 1, 2 and 3) were used. Each one of the subgroups included 100 canals. In a second group (n = 300) torque was set at 20, 30 and 55 Ncm (subgroups 4, 5 and 6). In the third group (n = 300) three operators with varying experience (subgroups 7, 8 and 9) were also compared. Each subgroup included the use of 10 sets of PRI and 100 canals of extracted human molars. Each set of PRI was used in up to 10 canals and then sterilized before each case. NaOCl 2.5% was used as an irrigant. The number of locked, deformed, and separated instruments for the different groups, and within each part of the study was analysed statistically for significance with chi-squared tests. RESULTS: In group 1 only one instrument was deformed in the 150-rpm group and no instruments separated or locked. In the 250-rpm group instrument separation did not occur, however, a high incidence of locking, deformation and separation was noted in the 350-rpm group. In general, instrument sizes 30-15 locked, deformed and separated. Chi-squared statistics showed a significant difference between the 150 and 350 rpm groups but no difference between the 150 and 250 rpm groups with regard to instrument separation. Overall, there was a trend toward a higher incidence of instrument deformation and separation in smaller instruments. Locking and separation occurred during the final passage of the instruments, in the last (tenth) canal in each subgroup. In the second group, neither separation nor deformation and locking occurred during the use of the ProFile instruments, at 150 rpm, and at the different torque values. In the third group, chi-squared analysis demonstrated that significantly more instruments separated with the least experienced operator. Instrument locking, deformation, and separation did not occur with the most experienced operator. CONCLUSIONS: Preclinical training in the use of the PRI technique with crown-down at 150 rpm were crucial in avoiding instrument separation and reducing the incidence of instrument locking and deformation.