Effects of a removable partial denture and its rest location on the forces exerted on an abutment tooth in vivo

The 3-dimensional forces exerted on an abutment tooth of a removable partial denture (RPD) were measured in vivo during clenching using a force-measuring device with a piezoelectric transducer. The device was mounted on the mandibular right second premolar of a subject with an edentulous maxilla. The magnitude of the forces was higher and the direction was more posterior without the RPD in place. The direction was most posterior with an RPD with a distal rest only and most anterior with an RPD with a mesial rest only. The 3-dimensional forces exerted on an abutment tooth thus depend on both the presence of a denture and the rest location.     

The effects on function of distal-extension removable partial dentures as determined by occlusal rest position

The mesial rest may be an excellent method of reducing unfavorable occlusal forces acting on the abutment tooth. However, when anatomic conditions and therapeutic necessity require alternatives, the distal rest may be used. The use of the distal rest demands that additional procedures be used to reduce the occlusal trauma to the abutment tooth.     

不同临床设计的ERA附着体义齿修复下颌牙列游离端缺损的三维有限元分析

目的:研究3种不同临床设计ERA附着体义齿修复下颌远中游离端缺损的应力及位移分布.方法:建立ERA附着体义齿修复下颌远中游离端缺损的三维有限元模型,根据临床设计分为基本组、支托组和跨弓组.应用有限元法研究在垂直及45°斜向2种载荷方向100 N的作用下,基牙及基托下黏膜的应力和位移以及基托的位移情况.结果:2种载荷下3组模型均在远中基牙远中邻面肩台出现应力集中,远中基牙预备体咬合面位移最大,支托组基牙位移最大,分别为14.91 μm和63.09μm,其次为基本组(9.38 μm和50.56μm),跨弓组最小(8.85 μm和47.31μnn).结论:在本研究条件下,为远中游离端牙列缺损设计基本的ERA附着体义齿更趋于合理.     

Location of centres of resistance for maxillary anterior teeth measured on human autopsy material.

The location of the centre of resistance (CR) of various consolidated units of maxillary anterior teeth was determined in this study using human autopsy material. The units studied consisted of two central incisors, four incisors, and six anterior teeth. When horizontal forces were applied the CR for the two- and six-tooth units was located approximately 6.5 mm apical to the bracket position. For the four-tooth unit, CR was placed slightly more occlusally, the distance being 5.0 mm. Applying vertical forces CR was located about 13.0 mm posterior to the bracket position for the two- and four-tooth unit. The incorporation of the canines into the incisor segment resulted in a distal shift of CR of 6 mm. CR for the six anterior teeth was, thus, located on a line 3 mm behind the distal surface of the canines. Increasing force levels had little effect on the location of CR for a given unit.     

Finite element contact stress analysis of the RPD abutment tooth and periodontal ligament

OBJECTIVES: The purpose of this study was to determine the influence of the occlusal rest position in removable partial dentures on the displacement of the abutment tooth and the stress distribution in the periodontal ligament (PL). METHODS: We constructed three-dimensional finite element models of the mandibular first and second premolars. A layer of the PL and a mesial or distal occlusal rest were produced on the second premolar as an abutment. A zero displacement was prescribed on the outer surface of the PL and the first premolar. In each simulation, the rest was moved 0.05 mm vertically to the apical direction, with or without restriction of horizontal movements. We simulated the contact phenomena on the abutment surfaces, and calculated the movements of the abutment and stress distributions in the PL. RESULTS: We observed a maximum distal displacement of 42 microm at the buccal cusp of the abutment and a principal compressive stress of 0.35 MPa in the PL when the abutment was vertically loaded by a distal rest that was allowed to move horizontally. However, the displacements and stresses were relatively small, and were all within the physiological limitations of the tissues. The restriction of the horizontal movement of the rests was effective in reducing the horizontal displacements of the abutment, regardless of the rest position. CONCLUSIONS: The single vertical load exerted from either the mesial or distal rest on the abutment was unlikely to cause any mechanical damage to its supporting tissues.     

A study of muscle pressure in making functional impression. Horizontal and vertical forces on oral vestibulum of maxilla with full natural dentition

The purpose of this thesis was to establish objectively a technique for muscle training in functional impression of denture space. Ten normal subjects in their twenties were employed. Small transducers were placed in labial and buccal sides of gingival mucosa of the maxilla. The horizontal and vertical muscular forces of the molar, premolar and anterior regions were recorded simultaneously during rest position, during the application of Myomonitor, during pronunciation and during the fourteen types of functional movements relating to muscle training. The data were statistically analyzed and the following results were obtained. 1. The average muscular force during rest position was minimal in all areas measured and could be used as standard for other functional movements. 2. Each type of functional movement had its distinct muscular force in all areas measured and there were significant differences among the areas of measurement and among the directions of measurement. 3. The functional movements that showed maximum muscular force were, in the anterior region, suction of the index finger for both vertical and horizontal directions, in the premolar region, suction of the index finger for horizontal direction and rotation of the cheek for vertical direction, in the molar region, inward rolling of upper lip for both directions. 4. The number of functional movement which showed significant differences in the muscular forces among directions tend to increase as one move from anterior to premolar and to molar region. In this case the horizontal forces became larger than the vertical forces. Also both the horizontal and vertical forces tend to increase as one move anteriorly. 5. The muscular forces obtained from the rotation movement made by the subject were larger than the forces of the rotation movement made by the clinicians in all areas measured. 6. The average muscular force during the application of Myo-monitor was minimal and similar to the force during rest position. 7. There was a large difference among individuals in the muscular forces during pronunciation, and all were below the average force of the fourteen functional movements. 8. From the above results it is suggested that a technique for muscle training be established objectively for the functional impression of maxillary labial and buccal denture space.     

下颌游离端义齿(牙合)支托设计的有限元分析

用三维有限元的方法,对设计了三种(牙合)支托的下颌单侧游离端义齿,分别在人工牙上采用九种不同的加载方法,对近基牙支持组织的应力和位移进行了研究分析,并进行统计学处理.结果远中(牙合)支托引起基牙支持组织的应力和位移值均最大;而近中(牙合)支托和双支托在近远中方向上,基牙牙周组织应力和位移的差异无统计学意义;无论是何种(牙合)支托应力和位移值均随加载点向远中移动过程中而逐渐减小.     

In vitro evaluation of a measurement method to analyze the interdental, mesially directed force

In order to evaluate interdental forces as a benchmark for mesial drift, a measurement technique was tested and evaluated on a human specimen. The measurement technique is based on the principle that a mesially directed horizontal force (F_H) within a complete dental arch has an effect on interdental friction at the points of contact. The dynamic force (F_z), needed to pull out a defined metal strip from the interdental space is equal to the interdental frictional force (F_R). Assuming unmodified approximal surfaces and unchanged tooth mobility in a complete dental arch, relative modifications of the interdental frictional force level provide a way of measuring horizontal force fluctuations. The validity of this measurement technique was measured by applying mesially directed forces of 1 to 5 N to the distal surface of the 2nd molar in a human specimen. The frictional forces measured increased in proportion to the distally applied force. The mesially directed force on the 2nd molar was transmitted in the dental arch anteriorly up to the incisor region and resulted in an increase of frictional forces. The reproducibility of this measurement technique was tested by quantitative analysis of potential measurement errors in the human specimen. The effect on interdental force measurement of the speed at which the metal strip is pulled was evaluated in a range of 50 to 500 mm/min. At the maximum pulling speed of 500 mm/min, a maximum scatter of 8% was recorded. Dependency of the dynamic force on direction of pull was measurable only when the metal strip was angled at more than 15^o. Experimental tests on the human specimen confirmed that the measurement technique presented here is sufficiently valid and reproducible for clinical long-term studies of interdental forces.     

Study on frictional characteristics of KB horizontal brackets. A comparative study of kinetic frictional forces to be caused between various kinds of brackets and wires

KB horizontal brackets were designed to tip no more than 6 degrees at the maximum. This tipping amount is based on the idea of reducing friction between a wire and brackets to allow the effective tooth movement of the Begg technique even with horizontally long brackets, and does not originate in the concept of carrying out tipping movement. Thereon, experimental measurements by use of Rheometer were conducted to review for comparison of the kinetic frictional forces caused between various wires and the following four types of brackets; KB horizontal brackets, Tip edge brackets, Straight edge brackets and Begg brackets. 1. In case of utilizing ribbon arch wires and rectangular wires, no significant difference was acknowledged among Tip edge, KB horizontal and Straight edge brackets. 2. There proved to be a reduction in the kinetic frictional forces by incorporating tip into the edgewise slots, when using smaller dimensions of the wires which call for the effective tooth movement, however, Begg brackets (in conjunction with Ordinary T-pins and/or Safety T-pins) showed the small value which is far less than that of the three kinds of brackets.     

Finite element analysis of deflections in major connectors for maxillary RPDs

PURPOSE: The effect of major connector design on deflection in maxillary removable partial denture (RPD) frameworks under simulated occlusal loading was analyzed by means of three-dimensional finite element models. MATERIALS AND METHODS: Thirteen maxillary major connectors were produced for a Kennedy Class II case. Eleven frameworks consisted of posterior palatal straps with different anteroposterior widths at the midline. Anteroposterior and horseshoe bars were also constructed for comparison. In each framework, the occlusal rest on the abutment adjacent to the edentulous ridge was fixed in a vertical direction, and the rest on the contralateral side was fixed in all directions. A biting force of 20 N was vertically distributed simultaneously on each of the three missing posterior teeth locations. RESULTS: For the posterior palatal straps, the maximum vertical displacement at the saddle and the buccal displacement at both the saddle and the rest adjacent to the saddle decreased as their connector width increased from 6 to 29 mm, whereas maximum distal displacements were insensitive to the connector width. The posterior straps with anteroposterior widths of more than 18 mm revealed comparable rigidity to the anteroposterior bar. The horseshoe bar and the posterior straps with smaller widths demonstrated greater displacements than the other frameworks. CONCLUSION: The rigid connectors proved to be the most effective in transmitting applied occlusal forces to the contralateral side of the framework.     

RPI卡环的改良设计

描述了改良ＲＰＩ卡环的设计,并与传统的ＰＲＩ卡环相比较,改良ＲＰＩ卡固位尖端只需进入基牙颊面最远的较小倒凹则可获得听固位,而且更美观,同时也符合远中游离鞍基围绕近中Ｈｅ支托转下沉中,Ｉ杆固位尖端与基牙脱离接触原则。因此发言奶卡环可小或避免伟给基牙持力,量种适用远中淳离端可摘局部义齿的新型止环设计。     

Influence of ridge inclination and implant localization on the association of mandibular Kennedy class I removable partial denture

The aim of this study was to evaluate the tendency of displacement of the supporting structures of the distal extension removable partial denture (DERPD) associated to the implant with different inclinations of alveolar ridge and implant localizations through a two-dimensional finite-element method. Sixteen mandibular models were fabricated, presenting horizontal, distally descending, distally ascending, or descending-ascending ridges. All models presented the left canine and were rehabilitated with conventional DERPD or implant-retained prosthesis with the ERA system. The models were obtained by the AutoCAD software and transferred to the finite-element software ANSYS 9.0 for analysis. A force of 50 N was applied on the cusp tips of the teeth, with 5 points of loading of 10 N. The results were visualized by displacement maps. For all ridge inclinations, the assembly of the DERPD with distal plate retained by an anterior implant exhibited the lowest requisition of the supporting structures. The highest tendency of displacement occurred in the model with distally ascending ridge with incisal rest. It was concluded that the association of the implant decreased the displacement of the DERPD, and the anterior positioning of the implant associated to the DERPD with the distal plate preserved the supporting structures for all ridges.     

Symposium on semiprecision attachments in removable partial dentures. Laboratory procedures

The fabrication of semiprecision rest systems will differ depending on whether a prefabricated rest system or milled-in rest system is indicated. In a prefabricated rest seat, a die-related model must be used and the rest seats must be waxed into the wax pattern. A means of fabricating both locking and nonlocking rests has been described. The instruments and tools necessary for the milled-in rest seat have been illustrated. The need for a stress-releasing attachment for distal-extension removable partial dentures is satisfied by the Thompson dowel rest. In fabricating the Thompson dowel rest prosthesis, both vertical parallelism and horizontal parallelism are essential for rotation. The use of a parallelometer and the parallel rule insures precise positioning of the Thompson dowel rest, which in turn, will enable the distal extension partial to rotate.     

Photoelastic analysis of the influence of residual ridge inclination in conjugated class I mandibular prostheses with different attachment systems

Abstract

Objectives: The aim of this study was to evaluate the stress distribution in mandibular free-end removable partial dentures (RPD) associated with FPD in the abutment teeth considering different inclinations of the residual ridge: (1) horizontal and (2) distal descending ridges and two designs of free-end RPD with different attachment systems were tested: (1) clasp and (2) system ERA. Methods. Axial loads (100 N) were applied on the teeth of the RPD. The images were recorded and the stress distribution was evaluated through photoelastic fringes. Results. In general, the distal descending ridge presented more photoelastic fringes in the region of the roots of the abutment teeth while the horizontal ridge exhibited higher compression in the base of the prosthesis. In the horizontal ridge, the denture with clasp presented more favourable stress distribution than the denture with the system ERA. In the distal descending ridge, the denture with the system ERA relieved the region of the abutment teeth and overloaded the residual ridge. Conclusion: The horizontal ridge presented more favourable performance; the dentures with clasp exhibited better performance for both ridges evaluated; the denture with the system ERA presented better results in the distal descending ridge.     

无托槽隐形矫治拔牙病例的后牙不同轴倾度对牙齿三维力学影响

目的 研究无托槽隐形矫治技术拔除双侧上颌第一前磨牙病例整体内收前牙，后牙不同轴倾度时，各个牙齿的瞬时受力情况。方法 设置4组后牙不同轴倾度的上颌牙列，T1组后牙为正常牙合轴倾度，T2组后牙在T1组基础上后倾5°,T3组后牙在T1组基础上前倾5°,T4组后牙在T1组基础上前倾10°。拔除双侧第一前磨牙，整体内收前牙0.25 mm,在矫治器六轴力传感器测试平台上测量4组牙列中各个牙齿在三维方向的瞬时力。每组牙列设计12副隐形矫治器。结果 与T1组相比，T2组切牙伸长力减小，尖牙远中向力增加，后牙近中向力减小，磨牙颊向和伸长力增大，差异均有统计学意义(P<0.05)。与T1组相比，T3和T4组切牙舌向力和伸长力增大，尖牙远中向力增大，后牙近中向力也增大，磨牙颊向和伸长力增大，差异均有统计学意义(P<0.05)。结论 后牙后倾时利于前牙转矩的表达，有助于保护后牙支抗，但增加了磨牙的颊向力和伸长力。后牙前倾时，前牙更容易出现转矩丢失，覆牙合加深的现象。后牙越前倾，覆牙合越容易加深，后牙支抗容易丢失。     

A photoelastic study of rests on solitary abutments for distal-extension removable partial dentures

With a distal-extension removable partial denture, maximum use of existing oral structures can aid in the total support of the prosthesis and reduce the force on the solitary abutment. Four rests with relieved and unrelieved guide plates were evaluated for optimum stress distribution around the root of a solitary premolar abutment. These rests were the mesial, the distal, the mesial and distal, and the continuous rest. The findings demonstrated that The continuous rest had the most favorable stress concentration. All other rest designs demonstrated more lateral stress than the continuous rest. Relieved guide plates demonstrated 58% less maximum shear stress in the apical portion than unrelieved guide plates.     

Biomechanical effects of maxillary protraction on the craniofacial complex

The deformational effects on the human skull resulting from maxillary protraction were examined by means of strain gauges and displacement transducers. A maxillary protraction appliance was used that included a reverse headgear attached to the maxillary first molars. The protraction forces that were applied to this appliance were parallel to the occlusal plane at the following locations: the height of the maxillary arch, 5 mm above the palatal plane, and 10 mm above the Frankfort horizontal plane. The results indicated that protraction forces at the level of the maxillary arch produced an anterior rotation and forward movement of the maxilla, protraction forces 10 mm above the Frankfort horizontal plane produced a posterior rotation of the maxilla with a forward movement of nasion, and protraction forces 5 mm above the palatal plane produced a combination of parallel forward movement and a very slight anterior rotation of the maxilla. Moreover, constriction of the anterior part of the palate occurred in all cases.     

On the part played by the socket in tooth support

Transducers of movement were used to detect the direction and amount of displacement of the alveolar margins of fifteen teeth in two adult monkeys. Controlled horizontal and intrusive thrusts were applied manually. Bone displacement started in response to forces appreciably less than 100 g and occurred in a linear manner with forces up to 1 kg. Horizontal forces of more than about 50 g tended to cause the labial and lingual alveolar plates to be displaced in the same direction as the applied force. The distance the bone was displaced and subsequently recoiled was less than the displacement and recoil of the root in the linear phase of movement. This implies increasing tissue compression on the side to which the tooth was moved and decreasing pressure in the membrane on the other side with elastic deformation of the socket. Intrusive force caused dilatation of the socket. The conclusion is reached that force to a tooth cause compression and tension in the periodontal membrane.     

Clinical evaluation of abutment teeth of removable partial denture by means of the Periotest method

Prosthodontics should be one of the means of establishing conditions for the maintenance of periodontal health. The forces applied to the abutment teeth and their effects are very important considerations in the design and construction of the removable partial dentures. This 6-month follow-up clinical study evaluated the degree of mobility of abutment teeth of distal extension and tooth supported removable partial dentures by using Periotest. Two types of clasp design were selected for evaluation. In cases with unilateral and bilateral distal-extension, a clasp design including a T clasp of Roach retentive arm, a rigid reciprocal arm and a mesial rest were used. For the abutments of tooth-supported removable partial dentures, a second clasp design with a cast circumferential buccal retentive arm, a rigid reciprocal clasp arm and a rest adjacent to the edentulous ridges was selected. A total of 68 abutment teeth was analysed. Periotest values were made at the time of denture placement (control) and at 1, 3 and 6 months after the denture placement. The statistical analysis was performed using Friedman test. All analysis was performed at a 0.05 level of significance. The results revelled that no significant changes in tooth mobility were observed during the 6-months follow-up (P > 0.05). In conclusion, our findings suggest that adequate oral hygiene instructions, careful prosthetic treatment planning and regular recall appointments play an important role in preventing changes in abutment tooth mobility caused by removable partial denture placement.     

Mobility of premolars under load in partially edentulous dentition

The mobility of the upper and lower premolars under load was investigated in relation to the interproximal contact and occlusal facets. The mobility was measured on ten subjects with the molars missing in the bucco-lingual and mesio-distal direction, using a non-contact sensor system, when a 500 gram load was applied in the horizontal direction, during hard biting in intercuspation and biting of foods. The ratio of the tooth movement in the bucco-lingual direction to the mesio-distal direction was larger in the upper premolars than in the lower ones. As the total mobility increased, the tooth movement was larger on the buccal side than on the lingual side of the upper jaw, on the lingual side than on the buccal side of the lower jaw, and on the mesial side than on the distal side of both jaws. The direction of the movement did not coincide with the direction of the load, due to the horizontal rotation. When biting, the first premolars showed a mesial movement and the second premolars showed a more distal movement than the first premolars. A correlation between the direction of the tooth movement during hard biting and that of the facets was observed.