Improvement and long-term stability of neuromuscular adaptation in implant-supported overdentures.

OBJECTIVES: In edentulous patients, implant-supported overdentures can improve chewing efficiency and patient satisfaction, and even a positive impact on bone tissue preservation has been observed. The objective of this long-term study was to investigate whether kinesiographic and electromyographic (EMG) parameters would also benefit from implant placement and whether the status achieved would remain consistent over time. MATERIAL AND METHODS: The functional adaptability of the neuromuscular system in edentulous patients has been recorded in four different states of restoration: (1) insufficient old dentures, (2) new complete dentures, (3) implant-supported overdentures, and (4) implant-supported overdentures 10 years in use. In each state of restoration, the neuromuscular adaptation was assessed during masticatory activity on the basis of myodynamic parameters such as vertical opening, frontal extension and closing velocity. EMG parameters, i.e. Musculus masseter and Musculus temporalis activities were recorded simultaneously. RESULTS: The results revealed a general increase in the myodynamic and EMG-parameters. All of them clearly approached the values for normal dentate subjects and maintained this level over a period of 10 years. The significant changes between states 2 and 3 indicate that implant stabilization of dentures is accompanied by an immediate increase of the neuromuscular parameters. CONCLUSIONS: In elderly edentulous patients, the treatment with two interforaminal implants provides evidence of neuromuscular adaptation towards values of healthy dentate. Thus, the known benefits of implant placement such as tissue perseverance and improved function are complemented by improved neuromuscular adaptation.

Different bone loading patterns due to fixation of three-unit and five-unit implant prostheses.

BACKGROUND: It has been considered that implant prostheses ought to display passive fit. The objective of this finite element analysis (FEA) was to simulate the bone loading resulting from the fixation of implant-supported three and five-unit fixed partial dentures (FPDs). METHODS: Based on a patient case, six different FPD-groups were fabricated using either two or three implants for support. Strain gauges on the pontics of the prostheses were used for in vivo measurements. Based on the values obtained, bone loading models were simulated using three-dimensional finite element analysis and the results obtained were represented as von Mises equivalent stress. RESULTS: The mean strain (epsilon) values ranged from 15 micro epsilon to 170 micro epsilon for the three-unit FPDs and from 32 micro epsilon to 302 micro epsilon for the five-unit FPDs. FEA revealed von Mises stresses up to 30 MPa in the cortical area, while in trabecular bone values up to 5 MPa were observed. Static implant loading of similar magnitude can be provoked through 200 N axial load. CONCLUSIONS: Although the in vivo measured strain levels (epsilon) were of higher magnitude for the five-unit prostheses, FEA revealed bone loading of comparable magnitude for both three- and five-unit FPDs. Multi-unit prostheses may demonstrate greater inaccuracies compared with single implant restorations, but due to the absence of moment loading the multi-implant configuration appears to compensate for the higher strain development.

Stress and inflammation as a detrimental combination for peri-implant bone loss.

The causes of peri-implant bone loss continue to be controversial. To determine the impact of biomechanical stress and inflammation, we investigated a total of 80 interforaminal implants in situ for more than 10 years. Two stress groups, with 14 patients each, were established: a low-stress situation with single-standing implants, and an increased-stress situation with splinted implants. To categorize inflammation, we introduced a Composite Inflammation Score using 4 inflammatory parameters. Peri-implant bone loss was calculated from digital panoramic radiographs. To differentiate between the effects of stress and inflammation, we compared bone loss in both stress groups at equivalent levels of inflammation. With greater Composite Inflammation Score values, a clear discrepancy between single-standing and splinted implants was evident (p = 0.117/0.000, regression analysis; p = 0.135/0.000, analysis of variance; p = 0.002, t tests). While stress and inflammation alone may not necessarily be detrimental factors, the presence of stress heightens peri-implant bone loss significantly as inflammation increases.

Zinc gluconate in the treatment of dysgeusia--a randomized clinical trial.

In the treatment of dysgeusia, the use of zinc has been frequently tried, with equivocal results. The aim of the present randomized clinical trial, which involved a sufficiently large sample, was therefore to determine the efficacy of zinc treatment. Fifty patients with idiopathic dysgeusia were carefully selected. Zinc gluconate (140 mg/day; n=26) or placebo (lactose; n=24) was randomly assigned to the patients. The patients on zinc improved in terms of gustatory function (p <0.001) and rated the dysgeusia as being less severe (p <0.05). Similarly, signs of depression in the zinc group were less severe (Beck Depression Inventory, p <0.05; mood scale, p <0.05). With the exception of the salivary calcium level, which was higher in the zinc patients (p <0.05), no other significant group differences were found. In conclusion, zinc appears to improve general gustatory function and, consequently, general mood scores in dysgeusia patients.

A time-dependent healing function for immediate loaded implants.

Current interest in immediate dental implant loading has grown due to a number of clinical advantages this treatment modality offers. To obtain a deeper insight into the changing mechanical properties during the healing phase, results from removal torque tests are used in a biomechanical model. The ultimate removal torques, which depend on healing time, are described by a time-dependent healing function. The bone behavior is modeled using an elastic law with damage. The evolution of damage is represented with an incremental equation with an initial damage value and two material parameters. The nonlinear relationship between the torque and the angle of rotation up to the ultimate torque can be calculated. By changing the elastic parameter in the elastic damage law, the remodeling process can be characterized. In a further step, the elastic parameters and the limits for shear stress from the biomechanical model for the removal torque will be used in an FE analysis in order to obtain information on the axial loading limits of a dental implant at different healing times.

Overdenture attachment selection and the loading of implant and denture-bearing area. Part 1: In vivo verification of stereolithographic model.

Preliminary to a study investigating the force transfer from osseointegrated dental implants to the surrounding bone via various types of overdenture attachment, a stereolithographic model (SL-model) was constructed and compared to an in vivo situation in order to confirm the validity of the modeling technique for the planned measurements of implant strain and denture-bearing area loading. The SL-model was generated using the patient's computer tomographic data and duplicated in a material of known elastic properties. The model was fitted with sensors to measure strains in the peri-implant bone and loading forces within the posterior mandibular bone, i.e. the denture-bearing area of the mandible. Special telescopic copings were constructed to measure implant strain in this model as well as in vivo. Using these copings under identical overdenture loading conditions, the strains measured at the implants in vivo and in vitro were the same and never exceeded a tolerance of two standard deviations or a mean difference of -8.5% of the in vitro value. This indicates that the model was reliable for the measurement of implant strain. Denture-bearing area loading within the alveolar ridge cannot be measured in vivo. Instead, a method of extrapolating in vivo denture-bearing area loading figures from implant strain readings was developed and tested (better than 90% accuracy). These in vivo extrapolated figures were then compared to in vitro readings under otherwise identical loading conditions. The result indicated that the SL-model is reliable for measurements of denture-bearing area loading with an error of 10 to 20%.

Overdenture attachment selection and the loading of implant and denture-bearing area. Part 2: A methodical study using five types of attachment.

In general, an implant is loaded via axial and horizontal forces. Besides this, moment loading can also occur. The aim of this study was to investigate how different prosthetic connectors with overdentures develop force transfer to implant and bone as well as to the denture-bearing alveolar ridge. Five connectors were investigated on a stereolithographic model fabricated according to a real patient situation. The model was fitted with strain gauges on the "bone" distal and medial to the implants and with vertical force transducers in the alveolar "bone" under the denture-bearing area. The parallel-sided rigid telescopic connector developed the highest moment loading of the implant (P<0.001), which would suggest restraint in the use of this connector. The bar construction also showed somewhat high moments but these may have been at least partly exaggerated by the individual patient situation. Loading results through the non-rigid telescopic copings, single spherical attachments and magnet overdentures demonstrated a low level of implant moment loading which would in part result from horizontal forces caused by denture forward shift during force application. The denture-bearing area loading was different with all attachments (P<0.001) and was related to the rigidity of the connector and reached the highest values with the non-rigid telescopic coping. The clinical implications of the various findings are discussed.

Oral mucosal blood flow in patients with burning mouth syndrome.

The pathophysiology of burning mouth syndrome (BMS) is largely unknown. Thus, the aim was to study oral mucosal blood flow in BMS-patients using laser Doppler flowmetry (LDF). Thirteen BMS patients (11 female, two male; mean age+/-SD 64.3+/-7.9 years, mean disease duration 18.9+/-6.2 months) and 13 healthy non-smoking controls matched for age and gender (11 female, two male; mean age 64.7+/-8.1 years) were investigated. Using the LDF technique mucosal blood flow (mBF) was measured at the hard palate, the tip of the tongue, on the midline of the oral vestibule, and on the lip. Measurements were made at rest and over 2 min following dry ice application of 10 s duration using a pencil shaped apparatus. In addition, blood pressure (BP), heart rate (HR), peripheral cutaneous blood flow, and transcutaneous pCO(2) were continuously recorded. Mucosal blood flow (mBF) increased at all measurement sites in response to dry ice application (P<0.001) with peak flow at 0.5--1.5 min after stimulation onset. During the following 1.5--2 min, blood flow decreased at all sites with a tendency to return to baseline towards the end of the observation period. Except for BP and peripheral blood flow, all of the cardiovascular changes exhibited significant changes during the observation period; no differences between groups were detected. When compared to healthy controls BMS patients generally exhibited larger changes in mBF. These changes were significant for recordings made on the hard palate (F[1,24]=13.9, P<0.001). Dry ice stimulation appears to be an effective, non-invasive and reasonably tolerable means to investigate mucosal blood flow at different mucosal sites. In general, vasoreactivity in BMS patients was higher than in healthy controls. BMS patients exhibited a higher response on the hard palate compared to controls. These changes in oral blood flow appear to be specifically related to BMS symptoms indicating a disturbed vasoreactivity.

Oral mucosal blood flow following dry ice stimulation in humans.

The aim of the current pilot study was to establish a procedure that would allow the investigation of microcirculatory changes in the oral cavity. The authors studied the effects of painful stimulation using dry ice (CO2). To investigate potential regional differences in the change of blood flow, recordings were made for the tongue and at the mucosa of the hard palate, lip, and oral vestibule. The authors investigated 26 patients divided into groups of younger subjects (10 men, 3 women; age range 21-31 y) and older patients (2 men, 11 women; age range 54-74 y). Mucosal blood flow (mBF) was obtained at the hard palate, at the tip of the tongue, on the midline of the oral vestibule, and at the lip. Measurements were made during rest and for 2 minutes after application of dry ice for a 10-second duration, using a pencil-shaped apparatus. Blood pressure, heart rate, cutaneous blood flow, transcutaneous partial pressure of carbon dioxiode (PCO2) and partial pressure of oxygen (PO2) were recorded. Mucosal blood flow increased at all sites in response to application of dry ice (p <0.001), with peak flow at 0.5 minute to 1.5 minutes after onset of stimulation. During the 1.5 minutes to 2 minutes, blood flow decreased at all measurement sites with a tendency to return to baseline. Heart rate, blood pressure, pCO2, PO2, and cutaneous blood flow did not show significant changes. Overall, responses in older patients showed more variance when compared with younger patients. Stimulation by dry ice appears to be an effective, noninvasive, and tolerable means to investigate mucosal blood flow at different mucosal sites. Preliminary data indicate different levels of responsiveness to painful cold stimulation at different sites on the oral and perioral mucosa; particularly, mucosal blood flow response at the tongue was least pronounced. Therefore, assessment of stimulated mucosal blood flow appears to be a promising tool to investigate the pathophysiology of a number of neurologic symptoms, eg, the burning mouth syndrome.

Clinical outcomes of three Parkinson's disease patients treated with mandibular implant overdentures.

Parkinson's disease (PD) often affects the oro-pharyngeal musculature, leading to problems with speaking, chewing and swallowing. The inevitable reduction in food and fluid intake contributes to the further deterioration of neurological symptoms. Parkinson's disease patients have great difficulties in adjusting to the use of complete dentures. It is the purpose of this report to evaluate the benefit of using dental implants combined with overdentures to improve chewing and predigestion capacity in severely handicapped PD patients. Three edentulous PD patients (2 male, 1 female; mean age 75.7 years; mean PD duration 4.3 years; PD severity grade III according to Hoehn and Yahr; mean edentulousness 19.3 years) complaining of poor chewing ability were included in this evaluation. One-stage dental implants were placed in the interforaminal region of the mandible. After completion of healing, new overdentures were fabricated. Custom-made non-rigid (resilient) telescopic attachments were used for retention of the overdentures on the implants. Follow-up examinations of the 3 patients were made between 28 and 42 months after the completion of treatment, and peri-implant tissue conditions as well as the patients' self-assessed satisfaction level were recorded. A modified gastrointestinal symptoms questionnaire, Hoehn and Yahr Scale and body weight measurements were used to monitor gastrointestinal impairment and PD severity. The peri-implant parameters indicated healthy soft tissue conditions and all Periotest values were in the negative range. The patients judged their chewing abilities to be greatly improved. Since placing the implants, PD severity had deteriorated to grade IV (Hoehn and Yahr scale) in 2 patients and was stable in 1 patient. The body weight had improved slightly in all patients (mean 2.2 kg). On the gastrointestinal scale, all patients had improved from a mean score of 8.7 to 5.7. Non-rigid telescopic attachments for overdenture stabilization are particularly suitable for PD patients as they are easy to handle and to clean. The patients reported remarkable improvement in their chewing ability, an assessment which would seem to be supported by the improved gastro-intestinal index. The regimen described appears to be a useful adjunctive treatment in edentulous Parkinson's disease patients and may be considered for patients with diseases similarly affecting motor skills.