Periodontal ligament areas and occlusal forces in dentitions restored with cross-arch unilateral posterior two-unit cantilever bridges

This investigation was undertaken in order to analyse to what extent the magnitudes of chewing and biting forces in dentitions restored with cross-arch unilateral posterior two-unit cantilever bridges are correlated to the area of the periodontal tissue supporting the abutments. 12 subjects, whose dentitions were periodontally treated and prosthetically restored, participated in the study. The chewing and biting forces, simultaneously measured in various parts of, as well as over the entire dentition, were correlated to the periodontal ligament areas of the abutments supporting the bridge constructions. A strong positive correlation (r = 0.83; P less than 0.01) was found between the total remaining periodontal ligament area and the mean total chewing force. A positive correlation (r = 0.57; P = 0.05) was also found between the local remaining periodontal ligament area of the posterior end abutment tooth and the local chewing force in that region. No positive correlation was found between the amount of periodontal tissue support and the magnitude of the forces developed during biting with maximal strength in habitual occlusion either totally or locally, although there was a strong tendency (r = 0.54; 0.6 greater than P greater than 0.5) towards decreasing total maximal bite force with decreasing total remaining periodontal ligament area. A strong positive correlation (r = 0.74; P less than 0.01) was found on the end abutment side between the local remaining periodontal ligament area of the end abutment tooth and the local forces in that region during biting with maximal strength over a limited area at a time.(ABSTRACT TRUNCATED AT 250 WORDS)     

Occlusal force pattern during chewing and biting in dentitions restored with fixed bridges of cross-arch extension

The pattern of axially directed occlusal forces, i.e. magnitude, distribution, duration and frequency of occlusal forces perpendicular to the occlusal plane, was studied during chewing, swallowing and biting in twelve subjects whose dentitions were periodontally treated and prosthetically restored with fixed, cross-arch bridges whose periodontal support included bilateral end abutments. The measuring devices consisted of four strain gauge transducers bilaterally mounted into pontics of maxillary bridges to represent the posterior and anterior regions. The forces could thus be studied in various parts of as well as over the entire dentition simultaneously. All subjects exhibited a rhythmic chewing pattern with preference of one side as chewing side. Local chewing and biting forces were always larger in the posterior than in the anterior regions and largest in the posterior region of the preferred chewing side. The total chewing and swallowing forces were about 100 Newtons (N) whereas the total maximal bite force in habitual occlusion amounted to 320 N. On average 37% of the total maximal bite force in habitual occlusion was utilized during chewing (and swallowing). The capacity of the periodontal tissues on the preferred chewing side to withstand transient occlusal forces was utilized to an average of 25% during chewing and swallowing and to an average of 57% during biting with maximal strength in habitual occlusion. The mean duration of that part of the chewing cycle during which the teeth were subjected to occlusal forces was 240 ms. The duration of the occlusal forces during swallowing was about three times longer. It is concluded that the periodontal tissues can withstand transient occlusal forces which are much larger than those generally operating during chewing, swallowing and biting with maximal strength in habitual occlusion. However, when the bite force is concentrated to a limited area of the tooth-arch, its magnitude seems to be limited by feedback mechanisms evoked in the periodontal tissues of that region.     

A standardized programme for studying the occlusal force pattern during chewing and biting in prosthetically restored dentitions

A recently described method for studying occlusal forces in prosthetically restored dentitions (Lundgren & Laurell, 1984) was applied in a standardized programme to elucidate the occlusal force pattern and the functional capability of a dentition during chewing and biting. The method is based on the use of strain gauge transducers mounted into preformed matrices evenly distributed over the tooth-arch. The programme was tested in a subject prosthetically restored with a fixed bridge of cross-arch design in the upper jaw, and with unsplinted teeth in the lower jaw. It involved chewing of (a) peanuts, (b) roast beef with potato salad, biting with maximal strength in habitual occlusion and biting over one limited contact area at a time. The magnitude of the occlusal forces developed during chewing and swallowing was well below all biting forces. The magnitude of the total force acting over the entire dentition when biting at maximal strength in habitual occlusion did not seem to be limited by reactions from the teeth or the periodontal tissues but, seemingly, by the capability of the jaw-closing muscles themselves. The magnitude of the local bite force over one limited contact area at a time was much smaller than that which the jaw-closing muscles were able to develop. This indicated that feedback mechanisms in the periodontal tissues and/or the temporo-mandibular joints were limiting factors for these forces. The programme will be applied to studies of dentitions supplied with prosthetic constructions of various design and with different distribution of periodontal support.     

Occlusal force pattern during chewing and biting in dentitions restored with fixed bridges of cross-arch extension

The pattern of axially (perpendicular to the occlusal plane) directed occlusal forces developed during light tooth tapping in habitual occlusion, chewing, swallowing and maximal biting was studied in twelve subjects whose dentitions were periodontally treated and prosthetically restored with cross-arch bridges with unilateral posterior two-unit cantilevers. The measuring devices consisted of four strain-gauge transducers uniformly and bilaterally mounted in pontics of maxillary bridges to represent the posterior (end abutment and distal cantilever respectively) and anterior regions. Thus, the forces could be studied locally in various parts of the dentition simultaneously as well as totally over the entire dentition. The results demonstrated that the distal cantilever unit, on average, was subjected to forces about or less than half of those over the contralateral end abutment unit irrespective of the activity studied. Furthermore, the cantilever forces either equalled or were even significantly smaller than those of the anterior regions. All subjects preferred the end abutment side as the chewing side. When the cantilever side was used as the chewing side, which occurred most infrequently, the bolus was usually located in the anterior region. The mean total chewing force (about 50 N) was only about half of that found in a previous study of subjects supplied with cross-arch bridges with bilateral end abutments (Lundgren & Laurell, 1985). Furthermore, on average only 26% of the voluntary muscular capacity was used during chewing, compared with 37% in the 'bilateral end abutment group' referred to. The reasons for the comparably small forces over the distal cantilever unit and the lower muscular utilization during chewing in cross-bridges with unilateral posterior two-unit cantilevers as well as the implications of the findings for the dimension of such bridge constructions are discussed.     

The capacity of reduced periodontal tissues to support fixed bridgework

The total area of periodontal ligament around the abutment teeth in 60 fixed bridges, inserted in patients treated for advanced periodontal disease, was calculated and compared with the total "periodontal ligament area" of the teeth replaced by pontics. The calculations revealed that only in 8% of the bridge restorations did the periodontal ligament area of the abutment teeth equal or exceed that of the replaced teeth. In 57% of the bridge material the periodontal ligament area of the abutments was less than 50% of the anticipated normal ligament area of the pontics. Despite the fact that the periodontal support for the restorations was dramatically reduced, all bridges have functioned properly for 8-11 years and the periodontal tissues around the abutment teeth have not suffered further loss of attachment during the period of maintenance care.     

Occlusal force pattern during mastication in dentitions with mandibular fixed partial dentures supported on osseointegrated implants

The occlusal force pattern during chewing and biting was studied in eight edentulous patients whose dentitions had been restored with mandibular bilateral posterior two-unit cantilever fixed prostheses supported on osseointegrated titanium fixtures and occluding with complete maxillary dentures. The chewing pattern was comparable to that reported for subjects with complete healthy dentitions or with tooth-supported cross-arch fixed partial dentures. However, during chewing and swallowing the voluntary capacity of the jaw-closing muscles was used to a much greater extent. Contrary to reports for cantilevers in tooth-supported cross-arch unilateral posterior two-unit cantilever fixed partial dentures occluding with natural teeth, the posterior cantilever segments in the present fixture-supported cantilever prostheses occluding with complete dentures regularly exhibited the largest local forces. Despite this, material failures of this type of fixed prostheses are rare, as demonstrated in long-term follow-up studies.     

Prospective 3-year study of cross-arch fixed partial dentures in patients with advanced periodontal disease.

STATEMENT OF PROBLEM: Several choices exist for the treatment of advanced periodontal disease. One is a combined periodontal and prosthetic treatment that includes cross-arch fixed partial dentures (FPDs). However, the outcomes of such therapy have been reported mainly from studies in Scandinavian countries. PURPOSE: The aims of this study were: (1) to longitudinally evaluate, after periodontal and prosthodontic treatment that included cross-arch FPDs, treatment outcomes in Korean patients who suffered from severe periodontitis; and (2) to evaluate the patients' treatment assessments and the FPDs after 3 years. MATERIAL AND METHODS: This survey included 39 Korean patients provided with 50 FPDs. Clinical and radiographic examinations were performed at the time of delivery of the FPDs and at the 3-year follow-up examinations. The prostheses were divided into 3 groups according to design (end abutments, unilateral cantilever, and bilateral cantilevers) and the amount of supporting tissues at the time of insertion. On average, only 26% of the total original periodontal tissue remained at the time of insertion. The FPDs consisted of 11 to 14 units, with a mean of 5 to 7 abutments in the 3 groups. The mean periodontal ligament area of the abutments was 79% of the total ligament area of the replaced teeth. RESULTS: At the 3-year follow-up examination, the FPDs were stable in all patients, who in general displayed good oral hygiene and had healthy periodontal conditions. The change in periodontal ligament area over the 3-year observation period was negligible (1 mm(2) per dental unit) and showed no statistically significant difference in relation to FPD design. Most patients were satisfied with the function of their FPDs with respect to mastication, phonetics, hygiene, esthetics, and chewing comfort. A few patients stated that they were careful with the FPDs and avoided certain foods (for example, raw peanuts and grilled squid) because they felt insecure with the cantilever segments. Most patients reported that they would choose the same treatment again. CONCLUSION: Patients with advanced periodontal disease demonstrated successful outcomes over a 3-year period and reported satisfaction with combined periodontal and restorative treatment that included cross-arch FPDs.     

Influence of occlusion on posterior cantilevers.

The incorporation of posterior two-unit cantilevers in fixed prosthodontics is generally discouraged because of the assumption that large posterior chewing and biting forces might jeopardize the prosthesis and the abutment teeth. This investigation was performed to study (1) the distribution of chewing and closing forces in dentitions with cross-arch bilateral posterior two-unit cantilever fixed partial dentures and (2) the influence of different occlusal arrangements on the magnitude of these forces along the cantilever segments. Six patients were included in the study. Axially directed closing and chewing forces were measured with miniature transducers bilaterally mounted in pontic units anteriorly and in each of the four cantilever units. In ideal occlusion, occlusal forces decreased considerably along the cantilever segments in the distal direction. Infraoccluding the distal cantilever unit by 80 microns had little influence on the magnitude of the initially small local force in this region, whereas an 80 microns high primary occlusal contact considerably increased the local force over the distal cantilever unit. The clinical implications of the results are discussed.     

Functional analysis of fixed bridges on abutment teeth with reduced periodontal support

The present study examines (he function of fixed bridges on abutment teeth with reduced but non-inflamed periodontal tissues. Eighteen patients with advanced periodontal breakdown and indication for oral rehabilitation received periodontal treatment and their dentitions were restored with fixed bridgework. The analysis of function performed 2-5 years after insertion of the reconstructions was made by (1) evaluation of the patients' opinion on chewing ability and function of the masticatory system; (2) clinical examination of the border movements of the mandible, the status of the temporomandivular joints and the chewing muscles, and (3) measurements of the bite force in different areas of the dentition. The results of the study show that the functional capacity of the type of extensive bridgework discussed is good and that the patients–in spite of severe loss of periodontal tissue–achieve bite force values that are almost comparable to those in individuals with natural teeth. Comparison of the function of fixed bridges and that of removable dentures is also discussed.     

Fixed cantilever splints on teeth with normal and reduced periodontal support

Photoelastic models were used to visualize stresses developed in teeth and supporting bone by cantilever fixed partial dentures where the most distal abutments had either crater or trough osseous defects. The effects of splinting the periodontally involved teeth to one or more additional sound teeth were studied. It was shown that for a cantilever fixed partial denture with either normal periodontal support, or a distal abutment with a moderate degree of mobility and bone loss, the following can be concluded: (1) occlusal forces on a cantilever fixed partial denture were significantly distributed to only the three teeth closest to the loaded cantilever, (2) optimum stress reduction occurred with the splinting of a periodontally compromised tooth to two periodontally sound teeth. Increasing the number of splinted abutments did not result in a proportional reduction of stress in the periodontium, and (3) no significant cross-arch sharing of occlusal loads was seen.     

Failure of dental bridges. IV. Effect of supporting periodontal ligament

summary The relationship between bridge failure and the periodontal ligament area of their abutments was studied in 156 dental bridges constructed for 132 patients. Of the bridges constructed at the College of Dentistry, King Saud University, 26.9% did not meet the published criteria of Ante's Law while 50.0% of those made in general dental practice did not meet the same criteria. However, radiographic evaluation of abutment teeth in 56 failed bridges revealed that there were only two cases with evidence of overloading the abutments.     

Long-term follow-up of cross-arch fixed partial dentures in patients with advanced periodontal destruction Evaluation of the supporting tissues

The aim of the study was to evaluate the periodontal conditions in patients treated more than 10 years ago for advanced periodontal disease and rehabilitated with cross-arch fixed partial dentures (FPDs). Of 50 randomly selected patients, 34 subjects carrying 43 FPDs agreed to participate in a clinical and radiographic follow-up examination. The FPDs were divided into three groups on the basis of prosthesis design (end abutments, unilateral cantilever, and bilateral cantilevers) and amount of supporting tissues at the time of bridge installation. Seventy per cent of the FPDs were found to be unchanged, whereas the rest had been modified due to various complications leading to extraction of one or more of the abutment teeth. Six FPDs (14%) had been partially replaced by FPDs anchored to osseointegrated dental implants. A total of 21 (8%) of the original 274 abutment teeth had been extracted. Longitudinal changes in the amount of periodontal support were minimal over the average of 15 years of follow-up. FPD design or initial amount of supporting tissues was found not to have significant influence on longitudinal changes in periodontal conditions. It was concluded that combined periodontal and prosthodontic treatment of patients with advanced loss of periodontal support may provide a high rate of long-term successful outcome, provided proper adequate periodontal and prosthetic treatment and maintenance care are given.     

Occlusal force pattern in dentitions with mandibular implant-supported fixed cantilever prostheses occluded with complete dentures

Naturally occurring axially directed closing and chewing forces were measured in ten patients with mandibular fixture-supported cross-arch prostheses occluding with maxillary complete dentures. The design of the mandibular constructions was characterized by bilateral posterior two-unit cantilevers. The forces were measured using eight miniature strain gauge transducers mounted in the maxillary denture and evenly distributed over the tooth arch. Forces were thus measured at four occlusal contact points over the fixture segment and over each of the four posterior cantilever units simultaneously, giving a detailed picture of the force distribution. The total forces developed during maximal closing in habitual occlusion and chewing were of the same magnitude as previously reported for patients with tooth-supported cross-arch fixed partial dentures occluding with natural teeth using the same method. Contradictory to previous findings, in dentitions with comparable tooth-supported cantilever constructions occluding with natural teeth, local closing and chewing forces increased bilaterally in the distal direction. On average, 70% of the forces were borne by the cantilevers and 30% by the fixture-supported segment of the prostheses.     

The cantilever fixed partial denture--a literature review.

The cantilever fixed partial denture (FPD) is a restoration with one or more abutments at one end and unsupported at the other end. Forces transmitted through the cantilevered pontics can cause tilting and rotational movements of the abutments. In a cross-arch unilateral cantilever FPD, the distal cantilevered unit is subjected to comparatively less force than the contralateral posterior abutment. The unilateral lack of terminal abutments causes lateral bending forces activate peripheral inhibitory feedback reactions from the periodontal and/or temporomandibular mechanoreceptors. The greatest strain in distal cantilevered FPDs is recorded mesial to the most distal retainer because most fractures occur in this location. To improve the prognosis of the FPD cantilever, the number of abutments should be increased and the number of pontics decreased. The abutment teeth need long roots and acceptable alveolar support. Prepared abutments require adequate length and parallel axial walls. An equilibrated and harmonious occlusion is necessary, as well as exemplary oral hygiene. A cantilevered FPD with adequate periodontal support can replace any tooth in the dental arch, but is especially useful as an alternative to a removable partial denture. The cantilevered FPD requires at least two abutment teeth. The only documented exception permitting a single abutment is the replacement of a maxillary lateral incisor with the canine as an abutment. An alternative to the cantilevered FPD is the osseointegrated implant. As osseointegrated implants become more popular, the need for the tooth-supported cantilevered FPD may decline, but it will remain an alternative treatment modality.     

微种植体压低基牙后双端固定桥修复基牙及支持组织的动力学研究

目的：探讨动态加载时微种植体压低基牙后固定桥力学行为的改变,为临床压低基牙后再进行牙体预备提供理论依据。方法：采用螺旋CT扫描健康人上颌骨、牙及牙周支持组织的二维图像,通过Mimics10.01、Ansys13.0等图像合成、有限元分析软件建立基牙牙槽骨水平吸收10%,上颌后牙分别压低0、0.5、1.0、1.5、2.0 mm后双端固定桥修复的三维有限元分析模型,模拟在1个咀嚼周期0.875 s内连续性施加垂直向、斜向(颊向与舌向)载荷作用,比较压低基牙前、后修复体、牙、牙周膜及硬骨板的应力随时间的变化情况。结果：随着压低量增加,修复体、牙体应力发生一定改变,这一改变与修复体结构、牙体结构有很大关系。牙周膜及硬骨板面积增大,整体应力有所降低。在一个动态载荷周期内,随着时间的积累,牙、修复体、牙周膜、硬骨板的应力均逐渐增大,在斜向载荷作用下,应力达到峰值,卸载终期仍有少量的应力残余。结论：采用微种植体压低基牙后,降低了修复体、牙、牙周膜、硬骨板的应力。在1个咀嚼周期中,基牙及支持组织的应力具有时间依赖性,侧向力对其影响大于垂直向力,且1个咀嚼周期结束时,基牙及支持组织有应力残余。随着基牙压低量的增加,残余应力减少。     

Maximal bite force in patients with reduced periodontal tissue support with and without splinting

BACKGROUND: Chewing and biting forces are supposed to be limited by sensory input from periodontal mechanoreceptors. This is why the threshold level of those receptors should be lower in teeth with reduced periodontal tissue support. The purposes of the present study were to evaluate the influence of reduced periodontal tissue support on maximal bite force in natural dentitions and to study the effect of splinting on maximal bite force. METHODS: In 10 patients with reduced periodontal tissue support (test), as well as in 10 periodontally healthy subjects (control), maximal bite force was measured. The remaining periodontal ligament area in the test group was calculated from x-rays. Bite force was assessed at 4 mm mouth opening in the premolar region without and following splinting of the posterior teeth and transduced using a strain-gauge (full-bridge circuit). Maximal bite force measured with and without splinting was compared between test and control subjects, and within each group. RESULTS: In test subjects, the mean periodontal ligament area was 48.5% (SD = 10.1) across first premolars and 50.0% (SD = 12.2) across posterior teeth (control: 100%). In test subjects, the mean maximal bite force without splinting was 357 N (SD = 70), and in control subjects, 378 N (SD = 66; P > 0.05). After splinting, the bite force in test subjects was 509 N (SD = 75), and in control subjects, 534 N (SD = 49; P > 0.05). Bite force before and after splinting was P < 0.05 within each group. CONCLUSIONS: Reduced periodontal tissue support does not seem to limit bite force with maximal strength in natural dentitions as measured by a device that opens the bite by 4 mm. Furthermore, maximal biting forces at 4 mm mouth opening are increased when molar teeth are included in a posterior splint.     

下颌固定桥基牙牙槽骨单侧吸收对基牙应力分布的影响

目的:研究双端固定桥基牙牙槽骨单侧吸收对基牙应力分布的影响。方法:采用螺旋CT扫描获取健康人下颌骨、牙齿、牙周支持组织的二维图像,通过图像合成软件建立三维数字模型,并应用三维有限元分析软件生成下颌后牙三单位固定桥的三维有限元分析模型。在相同垂直和水平载荷情况下,分析基牙牙槽骨单侧吸收时固定桥各基牙的应力分布。结果:当前磨牙端基牙牙槽骨单侧吸收达25%、磨牙端基牙牙槽骨无吸收时,前磨牙端基牙开始出现应力集中;当磨牙端基牙牙槽骨单侧吸收达35%、前磨牙端基牙牙槽骨无吸收时,磨牙端基牙开始出现应力集中。结论:下颌后牙双端固定桥基牙应力分布与基牙牙槽骨吸收形式密切相关,但二者之间不是线性关系而是存在临界区,基牙牙槽骨单侧吸收的程度对基牙应力分布的影响弱于多侧吸收。     

Effects of overdentures upon remaining oral structures.

This study provided the following guidelines in the selection of specific designs for overdenture abutments: 1. The Dolder bar, which exhibits more cross-arch involvement than the Zest anchor, will share the occlusal load across the arch, between the abutments and the supporting structures. 2. The posterior edentulous regions will receive some physiologic stimulation with the Dolder bar, for it shares more stress here than the Zest anchor. 3. The forces on the Dolder bar produce stress directed more apically than that from the Zest anchor. Since this force is better tolerated, use of the Dolder bar may be indicated for a short-rooted tooth with less supporting bone. 4. The greater stress concentrated around the abutment teeth by the Zest anchor makes use of this design in a tooth that is periodontally sound and has a long root structure well imbedded in supporting bone seem logical.     

Restoration of periodontally compromised dentitions using cross-arch bridges. Principles of perio-prosthetic patient management

Severe periodontal disease often leads to tooth loss, necessitating prosthetic rehabilitation to restore function and aesthetics. The concept of perio-prosthetic treatment using extensive bridges of cross-arch design was introduced approximately 30 years ago. Long term follow-up studies have shown that teeth with reduced periodontal support can be used as abutments for extensive fixed prostheses, provided periodontal disease has been treated successfully, and an effective recall programme has been instituted to prevent periodontal disease recurrence. Low complication rates have been reported with these extensive constructions.     

铰链式冠外附着体义齿对支持组织应力分布的影响

目的 探讨铰链式冠外附着体的临床适用范围方法：采用有限元应力分析法，分析不同基牙数目时．该附着体义齿支持组织的应力分布情况。结果：基牙和人工牙在正中咬合时，基牙数目对支持组织的应力分布无明显影响．且基牙和牙槽嵴顶黏膜的应力分布均匀。结论：用该附着体修复第二磨牙末端游离缺损时，可采用单基牙。该附着体适用于基牙条件稍差，而牙槽嵴黏膜条件较好的患者：