Biological factors contributing to failures of osseointegrated oral implants. (II). Etiopathogenesis

The aim of the present review is to evaluate the English language literature regarding factors associated with the loss of oral implants. An evidence-based format in conjunction, when possible, with a meta-analytic approach is used. The review identifies the following factors to be associated with biological failures of oral implants: medical status of the patient, smoking, bone quality, bone grafting, irradiation therapy, parafunctions, operator experience, degree of surgical trauma, bacterial contamination, lack of preoperative antibiotics, immediate loading, nonsubmerged procedure, number of implants supporting a prosthesis, implant surface characteristics and design. Excessive surgical trauma together with an impaired healing ability, premature loading and infection are likely to be the most common causes of early implant losses. Whereas progressive chronic marginal infection (peri-implantitis) and overload in conjunction with the host characteristics are the major etiological agents causing late failures. Furthermore, it appears that implant surface properties (roughness and type of coating) may influence the failure pattern. Various surface properties may therefore be indicated for different anatomical and host conditions. Finally, the histopathology of implant losses is described and discussed in relation to the clinical findings.

Bruxism is mainly regulated centrally, not peripherally

Bruxism is a controversial phenomenon. Both its definition and the diagnostic procedure contribute to the fact that the literature about the aetiology of this disorder is difficult to interpret. There is, however, consensus about the multifactorial nature of the aetiology. Besides peripheral (morphological) factors, central (pathophysiological and psychological) factors can be distinguished. In the past, morphological factors, like occlusal discrepancies and the anatomy of the bony structures of the orofacial region, have been considered the main causative factors for bruxism. Nowadays, these factors play only a small role, if any. Recent focus is more on the pathophysiological factors. For example, bruxism has been suggested to be part of a sleep arousal response. In addition, bruxism appears to be modulated by various neurotransmitters in the central nervous system. More specifically, disturbances in the central dopaminergic system have been linked to bruxism. Further, factors like smoking, alcohol, drugs, diseases and trauma may be involved in the bruxism aetiology. Psychological factors like stress and personality are frequently mentioned in relation to bruxism as well. However, research to these factors comes to equivocal results and needs further attention. Taken all evidence together, bruxism appears to be mainly regulated centrally, not peripherally.

Possible role of tensile stress in the etiology of cervical erosive lesions of teeth

A tensile stress hypothesis for the etiology of idiopathic cervical erosions of human teeth is presented. It is proposed that when occlusion is not ideal, lateral forces cause the teeth to bend. The tensile stresses created during bending disrupt the chemical bonds of the crystalline structures of enamel and dentin. Small molecules may enter between the crystals and prevent the reestablishment of the chemical bonds. As a result, the disrupted tooth structure is more susceptible to loss through dissolution and abrasion and results in the development of the typically wedge-shaped lesions. Patients with lesions typical of hundreds examined by the authors were presented to illustrate the concept. The possible consequences of the proposed hypothesis were discussed. The hypothetical conclusions made in this article will be tested by experimentation.

A multiple logistic regression analysis of the risk and relative odds of temporomandibular disorders as a function of common occlusal features

A multiple logistic regression analysis was used to compute the odds ratios for 11 common occlusal features for asymptomatic controls (n = 147) vs. five temporomandibular disorder groups: Disc Displacement with Reduction (n = 81), Disc Displacement without Reduction (n = 48), Osteoarthrosis with Disc Displacement History (n = 75), Primary Osteoarthrosis (n = 85), and Myalgia Only (n = 124). Features that did not contribute included: retruded contact position (RCP) to intercuspal position (ICP) occlusal slides < or = 2 mm, slide asymmetry, unilateral RCP contacts, deep overbite, minimal overjet, dental midline discrepancies, < or = 4 missing teeth, and maxillo-mandibular first molar relationship or cross-arch asymmetry. Groupings of a minimum of two to at most five occlusal variables contributed to the TMD patient groups. Significant increases in risk occurred selectively with anterior open bite (p < 0.01), unilateral maxillary lingual crossbite (p < 0.05 to p < 0.01), overjets > 6-7 mm (p < 0.05 to p < 0.01), > or > 5-6 missing posterior teeth (p < 0.05 to p < 0.01), and RCP-ICP slides > 2 mm (p < 0.05 to p < 0.01). While the contribution of occlusion to the disease groups was not zero, most of the variation in each disease population was not explained by occlusal parameters. Thus, occlusion cannot be considered the unique or dominant factor in defining TMD populations. Certain features such as anterior open bite in osteoarthrosis patients were considered to be a consequence of rather than etiological factors for the disorder.

Histological evaluation of peri-implant bone at implants subjected to occlusal overload or plaque accumulation

Breakdown of bone around oral implants following occlusal overload or plaque accumulation was evaluated in monkeys. 5 screw-type implants of pure titanium (Astra Tech) were inserted in the mandible of 4 monkeys (Macaca Fascicularis). 6 months after insertion of the implants a fixed partial prosthesis was mounted on the 2 implants in 1 of the lateral segments. The prosthesis was in supra-occlusal contact with an antagonizing splint and caused a lateral directed excessive occlusal load (overload). Implants retaining the prosthesis were brushed 1 x week and subgingival cleaning was performed 1 x month. The remaining implants were never cleaned and, additionally, a cotton cord was placed around the abutments of these implants to promote plaque accumulation. 6 out of 8 implants with occlusal overload became loose. 2 of these were lost, whereas the remaining 4 were retained in the jaws. After 18 months of occlusal load or plaque accumulation, the monkeys were sacrificed. Tissue blocks with the implants were infiltrated and embedded in acrylic resin. Approximately 50 microns thick sections of the implants and surrounding tissues were made. All implants with plaque accumulation were osseointegrated, but exhibited an average histologic marginal bone loss of 2.4 mm (range: 0.8-4.0 mm). Of the 6 implants with occlusal overload available for histologic analysis, 2 implants in 1 monkey had lost osseointegration completely and 2 other implants were osseointegrated in the apical part only, whereas the remaining 2 were still osseointegrated but exhibited a bone loss of 1.8-1.9 mm.

Variation in tooth wear in young adults over a two-year period

STATEMENT OF PROBLEM

Although all the processes of loss of hard tissue are important, attrition on the occlusal surfaces commands our attention.

PURPOSE OF STUDY

The enamel wear rate of 18 young adults over 2 consecutive years was measured independently by volume loss and mean depth loss. Any significant differences in tooth wear resulting from gender and a clinical diagnosis of bruxism were identified.

MATERIAL AND METHODS

A strict protocol for dental impressions provided epoxy models, which were digitized with a null point contact stylus. AnSur software provided a complete morphologic description of changes in the wear facets.

RESULTS

The mean loss for all teeth measured was 0.04 mm3 by volume and 10.7 microns by depth for the first year.

CONCLUSIONS

These numbers were approximately doubled at 2 years of cumulative wear.

A prospective investigation over two decades on signs and symptoms of temporomandibular disorders and associated variables. A final summary

The aim of this summary of a longitudinal investigation on temporomandibular disorders (TMD) was to present the prevalence figures of signs and symptoms of TMD and certain other examined variables, and the correlations between these variables, over a 20-year period. Originally, 402 randomly selected 7-, 11-, and 15-year-olds were examined clinically and by means of a questionnaire. The same examination procedure was repeated three times: after 4-5 years and after 10 and 20 years, respectively. Signs and symptoms of TMD were mainly mild, but common already in childhood. They increased up to young adulthood, after which they leveled out. Progression to severe pain and dysfunction was rare, and spontaneous recovery from more pronounced symptoms was also rare. Significant correlations between reported bruxism and TMD symptoms were found, and a baseline report of tooth-grinding was a predictor of TMD treatment during the 20 years covered by the investigation. Occlusal factors were only weakly associated with TMD signs and symptoms. However, a lateral forced bite between the retruded contact position (RCP) and the intercuspal contact position (ICP) and a unilateral crossbite deserve further consideration as possible local risk factors for development of TMD. In conclusion, a substantial fluctuation of TMD signs and symptoms was observed in this sample of Swedish subjects followed for 20 years from childhood to adult. The demand for TMD treatment was low at all examinations, while the estimated treatment need was larger. One-third of subjects who had some kind of orthodontic treatment did not run a higher risk of developing TMD later in life.

Physiologic dimensions of the periodontium significant to the restorative dentist

When treating patients, the objectives of restorative therapy must be clear. The first and most basic objective is preservation of the teeth. The attainment of this objective would be far less complex if it could be considered independent of restoration of function, comfort and esthetics, but such is not the case. The latter objectives usually require sophisticated restorative dentistry and often include restorations with intracrevicular margins. Although it is widely accepted that the best restorative margin is one that is placed coronal to marginal tissue, most restorations have margins in the gingival crevice, and permanent tissue damage is common. In attempting to reach his objective, the restorative dentist must remember the fundamental precept of the health professions, which is: Do no harm. Daily observation of the three physiologic dimensions permits the therapist to restore teeth with minimal injury to the periodontium.

The influence of trauma from occlusion on reduced but healthy periodontal tissues in dogs

The experiments were performed in five dogs fed a soft diet which allowed dental plaque accumulation. Experimental periodontal breakdown was introduced on Day 0. After 180 days trauma from occlusion was produced in 4P and P4 i.e. the mandibular fourth premolars, in the manner described by Svanberg & Lindhe (1973). On day 280 the periodontal pockets around 4P and P4 were eliminated. A notch was prepared in the root at the level of the bottom of the surgically eradicated pocket. In addition, the occlusal trauma in the 4P region was deleted. From Day 280 to Day 370 the teeth of the animals were brushed twice a day. The animals were then sacrificed, radiographs of the premolar regions were taken, and tissue sections comprising 3P4P1M (and P3P4M1) were produced and subjected to microscopic analysis. The results indicate that jiggling type occlusal trauma and tooth hypermobility are not factors which detrimentally affect healing following periodontal surgery.

A Positive Correlation Between Occlusal Trauma and Peri-implant Bone Loss: Literature Support

The relationship between occlusal overload and peri-implant bone loss remains a controversial topic in implant dentistry. A causal relationship between the incidence of marginal bone loss next to an implant and occlusal overload implies a treatment plan and occlusal scheme would benefit from a force management approach. A MEDLINE-assisted and hand search of peer-reviewed English literature and relative textbooks were used for a selective review of articles addressing biomechanical stress and bone loss in cellular biomechanics, engineering principles, mechanical properties of bone, animal studies, clinical reports, bone physiology, and implant design biomechanics. These papers demonstrate occlusal overload on implants may increase the incidence of marginal bone loss.

Effect of longstanding jiggling on experimental marginal periodontitis in the beagle dog

The aim of the present experiment was to study the effect of a prolonged period of jiggling force application on the rate of progression of ligature-induced, plaque-associated marginal periodontitis in the beagle dog. The experiment was performed on eight dogs fed a diet which permitted dental plaque accumulation. On Day 0 a phase of periodontal tissue breakdown was initiated around the mandibular fourth premolars (4P; P4) by the placing of plaque retention ligatures around the neck of the teeth. The ligatures were exchanged once a month throughout the entire study. On Day 60 trauma from occlusion of the jiggling type was produced in the P4 region and maintained for 300 days. The animals were sacrificed on Day 360. Following sacrifice tissue sections comprising 1M, 4P, 3P and P3, P4, M1 were produced and subjected to microscopic analysis. The experiment revealed that in the dog jiggling forces applied to teeth which ae also subjected to ligature-induced and plaque-associated marginal periodontitis, may enhance the rate of destruction of the periodontium.

Impact of implant overloading on the peri-implant bone in inflamed and non-inflamed peri-implant mucosa

OBJECTIVE

To assess the impact of overloading on peri-implant bone level and the bone-to-implant contact (BIC) in the presence of healthy or inflamed peri-implant tissues.

MATERIALS AND METHODS

Four screw-shaped machined implants were placed bilaterally in the mandible of four beagle dogs and left submerged for 3 months. Prosthetic abutments were connected either in supra-occlusal contact with the opposite teeth (overloaded) or in infra-occlusal position (unloaded). In each dog, cotton floss ligatures were placed unilaterally around abutments to promote plaque accumulation; the contralateral side was brushed three times a week. There were four experimental sites, two implants in each: loaded uninflamed (LU), loaded inflamed (LI), unloaded uninflamed (UU), and unloaded inflamed (UI). Clinical and radiographic parameters were recorded at baseline and every 3 months throughout the observation period. At 12 months, the dogs were sacrificed and histomorphometric analysis was performed.

RESULTS

Implants with ligature-induced peri-implantitis presented high inflammatory indices throughout the observation period. Clinical parameters did not change from baseline for both LU and UU. Loading significantly increased the percentage of BIC (BIC%) (P<0.05) and slightly increased crestal bone resorption, but not apical to the implant neck. Both LI and UI groups showed significant peri-implant bone loss (P<0.01), mostly horizontal on the buccal aspect and angular on the lingual aspect, which exposed implant threads. Loading significantly (P<0.05) increased implant thread exposure due to buccal and lingual vertical bone resorption.

CONCLUSIONS

In the presence of uninflamed peri-implant mucosa, overloading of implants in the dog model increased BIC% and slightly reduced marginal bone level. However, resorption did not progress beyond the implant neck. Overloading aggravated the plaque-induced bone resorption when peri-implant inflammation was present.

The infrabony pocket and its relationship to trauma from occlusion and subgingival plaque

The role of trauma from occlusion and subgingival plaque in the pathogenesis of the infrabony pocket as observed in the radiograph was studied in 48 teeth which had to be extracted because of advanced periodontal disease. Prior to extraction the teeth were examined with regard to the degree of mobility and the direction of the horizontal components of the masticatory forces. Following extraction, the teeth were stained and examined under the stereomicroscope. When the tooth is adequately stained, the subgingival plaque and the remaining attachment fibers can be distinguished easily from the area of the junctional epithelium. The observations which were made on the extracted teeth were then correlated with what could be seen in the radiograph. The following major observations were made: In the depth of the infrabony pocket there was a close congruence between the front of the subgingival plaque and the borderline of the remaining attachment fibers, the distance varying between 0.2 and 2.0 mm. There was also a close relationship between the front of the subgingival plaque and the alveolar crest adjacent to the tooth as well as between the surface of the subgingival plaque and the opposite vertical wall of the infrabony pocket, the distances ranging between 1 and 3 mm. The horizontal forces were mainly or exclusively oriented bucco-lingually, whereas the infrabony pockets were located mesially or distally, i.e. parallel to the direction of the force and not at a right angle to it as observed in experimental studies. The mobility of the teeth adjacent to which infrabony pockets developed was normal in 42% of the cases, slightly increased in 31%, and only in 11% of the cases was it excessively increased. In 19 cases the infrabony pocket was located on one of the roots of lower molars which were removed by hemisection. In eight of the 12 cases, which were observed for periods from 1 to 10 years, the remaining root functioned well without further development of angular bone defects or infrabony pockets. All of them became markedly firmer as a consequence of successful periodontal treatment. Three of the four remaining roots were extracted because of periapical problems. There was no evidence to indicate that trauma from occlusion had been involved in the pathogenesis of the infrabony pockets.

Role of posterior transverse interarch discrepancy in Class II, Division 1 malocclusion during the mixed dentition phase

Posterior transverse interarch discrepancy (PTID), measured as the difference between the maxillary and mandibular intermolar widths, was investigated in a sample of 60 Class II, Division 1 subjects during the mixed dentition phase. Two main groups were detected: Class II group 1 (30 subjects) with PTID and Class II group 2 (30 subjects) without PTID. A sample of 30 Class I subjects in the mixed dentition phase was used as a control group. In Class II group 1, PTID was found to be due to a significantly narrower maxillary arch. The craniofacial skeletal features of both Class II groups and of the Class I group were assessed. The Class II group with PTID showed mandibular retrusion associated with a posteriorly displaced mandible of normal size (functional mandibular retrusion). The Class II group without PTID had mandibular retrusion due to a micrognathic mandible (anatomic mandibular retrusion). The relevance of these findings for treatment planning in Class II, Division 1 malocclusion in the mixed dentition was stressed.

Alveolar ridge resorption and mandibular atrophy. A review of the role of local and systemic factors

Loss of alveolar bone from the edentulous jaws is a serious and common clinical problem, especially among the elderly. The retention and stability of dentures are reduced, but little is known about the pathogenesis of this bone loss. The existing data suggest that either local factors, for instance occlusal trauma, or systemic factors such as postmenopausal osteoporosis, contribute to edentulous alveolar bone resorption. This paper reviews the evidence for the aetiology of residual ridge resorption following tooth extraction.

The dependence of mandibular dysfunction in children on functional and morphologic malocclusion

The influence of dental status, occlusal interference, occlusal anomalies, and general background variables on bruxism and subjective symptoms and clinical signs of mandibular dysfunction has been studied in children. Three samples of children, aged 7, 11, and 15 years, were included. The interrelations were analyzed by rank-correlation and stepwise multiple regression. In the rank-correlation analyses, dental wear and age were significantly correlated to all of the dysfunction variables. Bruxism (reported by the subjects) was not found to be significantly correlated to any of the independent variables in the regression analysis. Subjective symptoms of dysfunction could be explained to a small extent by the independent variables, of which dental wear and sucking habits were found to be the most important. Recurrent headache was, to a certain extent, dependent upon age and sex. TMJ clicking was positively correlated with dental wear and unilateral contact in the retruded contact position but was most influenced by age and sex; TMJ clicking increased with age and was more common in girls than in boys. The clinical dysfunction index of Helkimo and tenderness of the masticatory muscles on palpation were explainable, although to a minor degree, by the influence of a combination of age, occlusal interference, motor activity, and psychological factors. Functional malocclusion (occlusal interference) is more important than morphologic malocclusion in explaining the existence of mandibular dysfunction. Nevertheless, morphologic malocclusion such as Class II and Class III occlusion, frontal open-bite, and cross-bite, when associated with functional malocclusion, may create a predisposition to mandibular dysfunction. The study confirms the multifactorial etiology of mandibular dysfunction.

Fatigue root fracture: a spontaneous root fracture in non-endodontically treated teeth

A series of 46 cases of root fracture with four different patterns occurring in 51 non-endodontically treated teeth were studied. All of the patients had chewing habits which induced a unique root fracture. The results of this study suggest an additional cause of root fracture that has not been described previously. Here, the new term 'fatigue root fracture' is used to describe a fracture that results from an excessive, repetitive, heavy masticatory stress applied to a tooth. The majority (80%) of cases of this kind of fracture are vertical and occur mainly (96%) in persons over the age of 40. In addition, all the teeth affected were posterior teeth, and the majority (51%) were mandibular first molars.