Periodontal ligament areas and occlusal forces in dentitions restored with cross-arch bilateral end abutment bridges

The aim of the present investigation was to find out to what extent the magnitudes of chewing and biting forces in dentitions restored with cross-arch bilateral end abutment bridges are correlated to the areas of the periodontal ligament supporting the abutment teeth. 12 subjects whose dentitions had been periodontally treated and prosthetically restored participated in the study. The chewing and biting forces were measured in various parts of as well as over the entire dentition simultaneously using 4 strain gauge transducers bilaterally placed in pontics of the posterior (first molar/second premolar) and anterior regions. Based on calculations of the periodontal ligament areas, a new periodontal support index, PSIL, is introduced. This index expresses the relation between the total remaining periodontal ligament area supporting the bridge abutments and total maximal periodontal ligament area if all teeth were preserved as abutments. It is compared with the index of Ante, PSIA, which expresses the relation between the total remaining periodontal ligament area of all abutments and the total maximal periodontal ligament area of all replaced teeth. Within the present group of subjects, PSIL varied from 10 to 44% and PSIA from 17 to 118%. Based on the results of the correlation analyses, it is suggested that in dentitions restored with cross-arch bilateral end abutment bridges, the magnitude of the chewing forces is positively correlated to the areas of the periodontal ligament supporting the bridge abutments, whereas the periodontal ligament areas have no influence on the comparatively larger biting forces. The relevance of the 2 periodontal support indices and the clinical implications of the results of the study are discussed.     

Distribution of occlusal forces along unilateral posterior two-unit cantilever segments in cross-arch fixed partial dentures

Axially directed occlusal forces over unilateral posterior two-unit cantilever segments of cross-arch fixed partial dentures were measured during natural functioning by using built-in transducers, one in each cantilever unit. The mean local maximal occluding and maximal chewing forces were significantly larger over the first (124 N and 64 N) than over the second (21 N and 29 N) cantilever unit. The average intraindividual ratio between the forces over the first and second cantilever unit amounted to 12:1 for maximal occlusion and 3:1 for maximal chewing. Despite the smaller mean total maximal chewing (92 N) than mean total maximal occluding cantilever force (145 N), the resulting axially directed mean bending moments in the joint between the distal abutment crown and the cantilever segment did not differ significantly. This is explained by the larger mean maximal chewing (29 N) than mean maximal occluding (21 N) force over the second cantilever unit. This demonstrated that not only the magnitude of occluding and chewing forces over cantilever segments but also their distribution along the cantilevers is of importance for the magnitude of functional stress created in cantilever fixed prosthesis.     

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.     

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.     

About gravity and occlusal forces in the jaws: Review

Mechanical forces resulting from gravitation seem to be essential for structural adaptation and remodeling of skeletal bones. These forces have the capability of delivering powerfully distorting stimuli to skeletal bones in a very short time, several times a day, in a uniform direction. Facial and jaw bones are not subjected to gravity impact forces. These bones need a mechanism of “compensation” for this deficiency. The goal is achieved by a unique mechanism that substitutes for gravity impact forces - the mechanism of occlusal load transmission to the bone via the periodontal apparatus space. In cases of early loss of teeth and loss of periodontal ligament this mechanism will be missing resulting in premature bone aging.     

Location of main occluding areas and masticatory ability in patients with reduced occlusal support

Background:  The purpose of this study was to investigate the differences in location of the main occluding area with reduction of occlusal support and to evaluate the subsequent impairment in masticatory ability.
Methods:  One hundred and two patients were recruited according to the Eichner's index, which is based on the number of occlusal support zones. Each subject was instructed to clench a piece of temporary stopping in the particular occluding area that was preferably used during mastication. The main occluding area was judged by locating the tooth on which the temporary stopping rested. Subjective masticatory ability was self-assessed by means of a questionnaire.
Results:  Group classification depending upon the location of the main occluding area was significantly associated with the category of the Eichner's index. The level of masticatory ability was significantly associated with the category of the Eichner's index. Moreover, masticatory ability was significantly more impaired in subjects with main occluding areas at the premolar regions compared to those at the molar regions.
Conclusions:  The location of the main occluding area may differ under the influence of the remaining natural teeth. The location of the main occluding area and the masticatory ability are likely to be closely related.     

Effect of experimentally induced occlusal trauma on substance p expression in human dental pulp and periodontal ligament

Introduction

The purpose of this study was to quantify the effect of occlusal trauma experimentally induced with occlusal interferences on substance P (SP) expression in healthy human dental pulp and periodontal ligament.

Methods

Twenty-eight human dental pulp and periodontal ligament samples were obtained from healthy premolars in which extraction was indicated for orthodontic reasons. Before extraction, occlusal trauma was induced with experimental occlusal interferences in half of these premolars by placing a resin block over their occlusal surface and submitting patients to chew gum for 30 minutes. The remaining healthy premolars were extracted without occlusal trauma and served as a control group. All dental pulp and periodontal ligament samples were processed, and SP was measured by radioimmunoassay.

Results

There was 45% and 120% greater SP expression in dental pulp and periodontal ligament, respectively, of teeth with experimentally induced occlusal trauma. Paired t test showed statistically significant differences for both human dental pulp and periodontal ligament (P = .02 and P < .001, respectively) of teeth submitted to occlusal trauma when compared with control group values.

Conclusions

SP expression in human dental pulp and periodontal ligament increases when teeth are submitted to occlusal trauma experimentally induced with occlusal interferences.     

Influence of number and distribution of occlusal cantilever contacts on closing and chewing forces in dentitions with implant-supported fixed prostheses occluding with complete dentures

Axially directed closing and chewing forces were measured in patients with mandibular fixture-supported cross-arch bilateral posterior two-unit cantilever fixed prostheses occluding with maxillary complete dentures. Eight miniature strain-gauge transducers mounted in the maxillary denture enabled registration of local and total forces over the entire prosthetic restoration simultaneously. In "basic occlusion," with simultaneous occlusal contacts on all occluding units, closing and chewing forces were distally increasing. Infraoccluding the first cantilever unit bilaterally approximately 100 microns resulted in decreased total closing and chewing forces over the cantilever segments, but did not influence the leverage at the cantilever joint distal to the distal retainers. Infraoccluding the second cantilever units approximately 100 microns caused a pronounced reduction of both the total closing and chewing forces over the entire prosthetic restoration as well as over the cantilever segments, and also resulted in a marked (50%) decrease in the leverage at the cantilever joints. Causes of the force and leverage reductions and some clinical considerations are discussed.     

Correlation between occlusal contact and root resorption in teeth with periodontal disease

Crespo Vázquez E, Crespo Abelleira A, Suárez Quintanilla JM, Rodriguez Cobos MA. Correlation between occlusal contact and root resorption in teeth with periodontal disease. J Periodont Res 2011; 46: 82–88. © 2010 John Wiley & Sons A/S Background and Objective: The present study was designed to investigate the influence of occlusal forces on radicular resorption in teeth with periodontal disease. The occlusal forces are a cause in the aggravation of the periodontal disease and therefore influences in the increase the extension and the depth of the radicular resorption. Material and Methods: We quantified radicular resorption, its extension across the radicular surface and its depth, in 88 teeth with periodontal disease with and without occlusal contact, pertaining to patients between 43 and 91 years of age. A histological method was used to obtain 6‐μm‐thick sections. The sections were observed under an Olympus BX40 optical microscope and processed by an image analysis program. Measurements of length and area were used to calculate the percentages of surface and volume of cement reabsorbed. Results: In both groups presenting periodontal pathology (groups 2 and 3) the percentages of the surface and volume of reabsorbed cement were greater in those teeth with antagonist contact. The greatest percentages of radicular resorption were observed in teeth of group 3 showing antagonism. Conclusion: The severity of periodontal disease increases the extension and the depth of the radicular resorption, and the presence of antagonist forces aggravates the resorption.     

Alteration of bFGF expression with growth and age in rat molar periodontal ligament

Objective:To test the hypothesis that immunohistochemical changes in expression of basic fibroblast growth factor in the periodontal ligament do not change with age.Materials and Methods:Thirty male Wistar-ST rats were divided into growing groups (5, 9, and 15 weeks of age) and aging groups (6, 12, and 18 months of age). Serial sagittal sections (5 µm thick) were cut parallel at the distobuccal roots of the maxillary first molar. Paraffin-embedded tissue sections were stained with hematoxylin and eosin and rabbit polyclonal antibodies to basic fibroblast growth factor.Results:The number and the area of basic fibroblast growth factor–immunoreactive cells in the periodontal ligament of the maxillary first molar decreased with age. The number of basic fibroblast growth factor–immunoreactive cells was much greater in the root furcation area, which experiences the greatest effect of occlusal force. Regardless of age, the production of basic fibroblast growth factor in the periodontal ligament may occur subject to functional demand.Conclusions:The hypothesis is rejected. The expression of basic fibroblast growth factor in the periodontal ligament decreased with age.     

银杏叶提取物对脂多糖作用下人牙周膜细胞增殖及分泌细胞因子的影响

目的 观察银杏叶提取物(Ginkgo biloba extract,GBE)对脂多糖(lipopolysaccharide,LPS)作用下人牙周膜细胞(periodental ligament cell,PDLC)增殖及分泌白细胞介素(interleukin,IL)6、IL-1β及肿瘤坏死因子α(tumor necrosis factor-α,TNF-α)的影响,为GBE在牙周病防治中的应用提供依据.方法 选取2010年5至7月在遵义医学院附属口腔医院口腔颌面外科门诊因正畸拔除的10例11 ～15岁患者的20颗前磨牙,采用改良组织块培养法体外原代培养人PDLC,实验共分5组:①阴性对照组,含10 ml/L胎牛血清的达尔伯克改良伊格尔培养基(Dulbecco's modified Eagle's medium,DMEM)培养液;②LPS组,含10 ml/L胎牛血清的DMEM培养液+100 mg/L LPS;③LPS+0.1 g/L GBE组,含10 ml/L胎牛血清的DMEM培养液+100 mg/L LPS+0.1g/L GBE;④LPS+0.01 g/L GBE组,含10 ml/L胎牛血清的DMEM培养液+100 mg/L LPS +0.01 g/L GBE;⑤LPS+地塞米松组,含10 ml/L胎牛血清的DMEM培养液+100 mg/L LPS+2 mg/L地塞米松.甲基噻唑基四唑(methyl thiazolyl tetrazolium,MTT)法测定GBE对LPS作用下人PDLC活性的影响,酶联免疫吸附测定法测定各组IL-6、IL-1β及TNF-α的含量,对所得结果分别进行单因素方差分析,采用LSD-t检验进行组间两两比较,检验水准为双侧α=0.05.结果 实验12、24、48及72 h,LPS+0.1 g/L GBE组的吸光度值(分别为0.30±0.03、0.33±0.02、0.34 ±0.02及0.35 ±0.02)均显著高于LPS组(分别为0.20±0.03、0.20±0.02、0.22±0.04及0.24±0.02)(P＜0.05),PDLC IL-6、IL-1 β及TNF-α的分泌量均显著低于LPS组(P＜0.05);实验12、24、48及72 h,LPS+0.01 g/L GBE组吸光度值(分别为0.27±0.05、0.31 ±0.03、0.33±0.03及0.32 ±0.01)均显著高于LPS组(P＜0.05),PDLC IL-6、IL-1β及TNF-α的分泌量均显著低于LPS组(P＜0.05).结论 GBE对LPS作用下的人PDLC有保护作用.     

Two-year follow-up of changes in bite force and occlusal contact area after intraoral vertical ramus osteotomy with and without Le Fort I osteotomy

This study was performed to examine the longitudinal changes in bite force and occlusal contact area after mandibular setback surgery via intraoral vertical ramus osteotomy (IVRO). Patients with mandibular prognathism who underwent IVRO (surgical group: 39 men and 39 women) were compared with subjects with class I skeletal and dental relationships (control group; 32 men and 35 women). The surgical group was divided into two subgroups: 1-jaw surgery (n = 30) and 2-jaw surgery (n = 48). Bite force and contact area were measured in maximum intercuspation with the Dental Prescale System before treatment, within 1 month before surgery, and at 1, 3, 6, 9, 12, and 24 months postsurgery. A linear mixed model was used to investigate the time-dependent changes and associated factors. Bite force and contact area decreased during presurgical orthodontic treatment, were minimal at 1 month postsurgery, and increased gradually thereafter. The 1-jaw and 2-jaw subgroups showed no significant differences in bite force. The time-dependent changes in bite force were significantly different according to the contact area (P < 0.05). The results of this study suggest that bite force and occlusal contact area gradually increase throughout the postsurgical evaluation period. Increasing the occlusal contact area may be essential for improving bite force after surgery.     

Location of main occluding areas and masticatory ability in patients with implant-supported prostheses

Background: The purpose of this study was to locate the main occluding area when the reduced posterior occlusal support was treated with an implant‐supported prosthesis and to evaluate the subsequent improvement in the masticatory ability as compared with removable partial dentures. Methods: Twenty‐six patients with implant prostheses and 24 patients with removable partial dentures were recruited for this study. All patients had partially lost their posterior occlusal support. The first molar region in any quadrant was always included in the prosthetic region. Each subject was instructed to clench a piece of temporary stopping as a test food on the occluding area that was preferably used during mastication. The main occluding area was judged by locating the tooth on which the temporary stopping rested during clenching. Subjective masticatory ability was self‐assessed by means of a questionnaire. Results: The main occluding area of the subjects in the implant group was located more posterior compared with the removable partial denture group. The level of masticatory ability in the implant group was the same as that in the control group. Conclusions:  The location of the main occluding area and the masticatory ability of the subjects with implants were equivalent to those with healthy natural dentition.