Influence of Platform Switching, Abutment Design and Connection Protocols on the Stability of Peri-Implant Tissues. A Systematic Review.

PURPOSE: To appraise the effect of abutment factors namely platform switching, design and connection protocols on the stability of peri-implant tissues. MATERIALS AND METHODS: An electronic and hand search were conducted. Randomized control trials and controlled prospective studies of at least one-year follow-up, published in the last 12 years, were included. RESULTS: Initial electronic database search generated 3054 studies, while individual journal and hand searching resulted in 232 articles. Sixty-three publications were selected for full text analysis based on inclusion and exclusion criteria. Nineteen articles investigated platform switching. Fourteen studies reported positive influence of platform switching while five studies did not find a significant difference in bone loss compared to platform matched abutments. Two articles reported on concave abutments and found no advantage over conventional abutments. Seven studies investigated "one-abutment-one-time protocol", two found comparable results to multiple abutment disconnections while five studies suggested better soft and hard tissue maintenance. The risk of bias was unclear or high in most studies. CONCLUSION: Platform switched abutments may reduce crestal bone loss during the first year. There is insufficient evidence to suggest better clinical outcomes of concave abutment. There is insufficient evidence to indicate the superiority of 'one abutment-one-time protocol'.

The medial pterygoid muscle: a stabiliser of horizontal jaw movement.

There is limited information of the normal function of the human medial pterygoid muscle (MPt). The aims were to determine whether (i) the MPt is active throughout horizontal jaw movements with the teeth apart and (ii) whether single motor units (SMUs) are active during horizontal and opening-closing jaw movements. Intramuscular electrodes were placed in the right MPt of 18 participants who performed five teeth-apart tasks: (i) postural position, (ii) ipsilateral (i.e. right) jaw movement, (iii) contralateral movement, (iv) protrusive movement and (v) opening-closing movement. Movement tasks were guided by a target and were divided into BEFORE, OUT, HOLDING, RETURN and AFTER phases according to the movement trajectories recorded by a jaw tracking system. Increased EMG activity was consistently found in the OUT, HOLDING and RETURN phases of the contralateral and protrusive movement tasks. An increased RETURN phase activity in the ipsilateral task indicates an important role for the MPt in the contralateral force vector. Of the 14 SMUs active in the opening-closing task, 64% were also active in at least one horizontal task. There were tonically active SMUs at the postural jaw position in 44% of participants. These new data point to an important role for the MPt in the fine control of low forces as required for stabilisation of vertical mandibular position not only to maintain postural position, but also throughout horizontal jaw movements with the teeth apart. These findings provide baseline information for future investigations of the possible role of this muscle in oro-facial pain conditions.

An investigation of risk factors associated with tooth surface loss: a pilot study.

Few prospective studies have investigated risk factors associated with severe tooth surface loss. This case-control study assessed the possible association between medical history, diet, psychological profile and salivary pH and flow [Delongis 1982, Johansson 1993] with the incidence of severe tooth surface loss. A total of 80 subjects (40 cases and 40 age- and gender-matched controls) aged 25-85 years were recruited. Cases were subjects with severe tooth surface loss, and controls with mild tooth surface loss. Conditional logistic regression analysis estimated the odds of severe tooth surface loss to be 15·4 times higher for those with cardiovascular disease and 16 times for gastrointestinal disturbances. Most domains of the psychological profile were associated with elevated risk of severe tooth surface loss, particularly the effects of finance and health. Recreational drug use and prescription medications were also associated with severe tooth surface loss. There was no association between salivary flow and severe tooth surface loss. Although not statistically significant, the pH was slightly lower in the severe tooth surface loss group.

Occlusion on implants - is there a problem?

Oral rehabilitation restores form and function and impacts on general health. Teeth provide a discriminating sense of touch and directional specificity for occlusal perception, management of food with mastication and swallowing, and awareness of its texture and hardness. Peripheral feedback for control of jaw muscles includes the enamel-dentine-pulp complex and mechanoreceptors in the periodontal tissues. The implications of feedback from periodontal and other intra-oral mechanoreceptors as well as changes in central representation are significant for function and adaptation to oral rehabilitation. With implants, in the absence of the periodontium and periodontal mechanoreceptor feedback, fine motor control of mastication is reduced, but patients are still able to function adequately. Further, there is no significant difference in function with full-arch fixed prostheses on teeth in comparison with implants. Predictable implant outcomes depend on bone support. Optimum restoration design appears to be significant for bone remodelling and bone strains around implants with occlusal loading. Finite element analysis data confirmed load concentrations at the coronal bone around the upper section of the implant where bone loss is commonly observed clinically. Load concentration increased with steeper cusp inclination and broader occlusal table and decreased with central fossa loading and narrower occlusal table size. It is recommended that occlusal design should follow a narrow occlusal table, with central fossa loading in intercuspal contact and low cusp inclination to minimise lateral loading in function and parafunction. Acknowledging these features should address potential problems associated with the occlusion in implant therapy.

The influence of the leaf gauge and anterior jig on jaw muscle electromyography and condylar head displacement: a pilot study.

BACKGROUND: A leaf gauge and an anterior jig may be used to assist the recording of a reproducible jaw position for restorative and prosthodontic treatment. This study investigated possible condylar displacement using an opto-electronic jaw-tracking device and a leaf gauge or anterior jig. The effect of a leaf gauge and anterior jig on jaw muscle electromyography was also examined. METHODS: Five healthy adults without symptoms of temporomandibular disorders were selected. Condylar displacement during clenching were recorded simultaneously with electromyographic activity of superior and inferior heads of the lateral pterygoid, anterior and posterior temporalis, masseter, and suprahyoid muscles. Subjects were trained to bite at maximum and half-maximum bite-force using an anterior jig incorporating a force transducer. RESULTS: No consistent condylar displacement was observed in x, y and z axes between different bite-forces although there was a trend towards superior displacement. Comparison of maximum intercuspal clench and maximum clench on a leaf gauge and an anterior jig produced significant decrease in anterior temporalis activity (p < 0.05), whilst an anterior jig with maximum clench significantly decreased posterior temporalis muscle activity. CONCLUSION: Within the limits of this pilot study, no consistent change in condylar position was identified with these appliances.

Fear of pain in orofacial pain patients.

In the present study, we examined whether fear of pain, dental fear, general indices of psychological distress, and self-reported stress levels differed between 40 orofacial pain patients and 40 gender and age matched control general dental patients. We also explored how fear of pain, as measured by the Fear of Pain Questionnaire-III (J Behav Med 21 (1998) 389), relates to established measures of psychological problems in our sample of patients. Finally, we examined whether fear of pain uniquely and significantly predicts dental fear and psychological distress relative to other theoretically-relevant psychological factors. Our results indicate that fear of severe pain and anxiety-related distress, broadly defined, are particularly elevated in orofacial pain patients relative to matched controls. Additionally, fear of pain shares a significant relation with dental fear but not other general psychological symptomology, and uniquely and significantly predicts dental fear relative to other theoretically-relevant variables. Taken together, these data, in conjunction with other recent studies, suggest greater attention be placed on understanding the fear of pain in orofacial pain patients and its relation to dental fear and anxiety.

An association of membrane-damaging toxins from coagulase-negative staphylococci and chronic orofacial muscle pain.

Forty-six patients presenting with chronic orofacial muscle pain and eight age- and sex-matched control subjects were investigated for the carriage prevalence of, and exotoxin production by, coagulase-negative staphylococci (CNS). The eight control subjects were selected from an initial group of 41 subjects on the basis of the absence of musculoskeletal symptoms. There was a significantly higher prevalence and multiple carriage of four or more strains of CNS in patients with chronic muscle pain than in control subjects (23 versus 9 isolates/10 subjects). Two of the 103 CNS isolates from patients with muscle pain and none from the control subjects produced toxic shock syndrome toxin 1 (TSST-1), suggesting that pyrogenic toxins do not significantly contribute to the aetiology of chronic muscle pain. There was a significantly higher prevalence of delta-haemolysin (41 of 114) and 'horse'-haemolysin (56 of 114) production by CNS isolates from patients with chronic muscle pain compared with those from control subjects. None of the control subjects was colonised with CNS that produced significant amount of either delta- or 'horse'-haemolysin, whereas 35 of 44 patients with chronic orofacial muscle pain were colonised with CNS that produced significant amounts of 'horse'-haemolysin, 37 that produced delta-haemolysin and 33 that produced both delta- and horse-haemolysin. This study suggests that membrane-damaging toxins, like delta- and 'horse'-haemolysin, may play a role in the aetiology of chronic orofacial muscle pain.

Electromyographic evidence for functional heterogeneity in the inferior head of the human lateral pterygoid muscle: a preliminary multi-unit study.

OBJECTIVE: Functional heterogeneity, i.e. regional or selective activation of subpopulations of fibres within a muscle, has been described in some jaw and limb muscles. Each head of the lateral pterygoid muscle may also be functionally heterogeneous. The aims of this investigation were to develop a technique to test this hypothesis, and to use this technique to determine whether there is any multi-unit electromyographic (EMG) evidence for functional heterogeneity within the inferior head of the lateral pterygoid (IHLP). METHODS: In 3 human subjects without craniomandibular disorders, recordings were made of condylar movement and multi-unit EMG activity from two sites in the IHLP during repeated trials of a contralateral (n = 21) and a protrusive (n = 26) jaw movement. The recording sites within IHLP were approached extraorally (labelled IHLP-extra) and were verified by computer tomography (CT); the other (IHLP-intra) were from sites in IHLP approached intraorally. RESULTS: In each subject, the time of occurrence of the peak filtered signal from IHLP-extra was significantly different (P<0.05) from IHLP-intra for all protrusion trials but not for contralateral trials. CONCLUSIONS: The data suggest a task-dependent change in motor unit recruitment order within IHLP and that IHLP is functionally heterogeneous.

Regional nerve block of the temporomandibular joint capsule: a technique for clinical research and differential diagnosis.

In previous studies in which regional anesthesia of the temporomandibular joint capsule was used to examine the role of the joint in mandibular movement and distinguish it from muscle control, the anesthetic techniques used have not been satisfactorily described. The accuracy of the injection technique described in this paper was determined by dissection and radiogrphic examination of fixed and fresh specimens. Using this technique, trial patient studies were made using an anesthetic solution to which a radiopaque medium was added. Radiographic examination of the patients affirmed the location of the injected material, while clinical assessment determined its functional effectiveness. Using the described technique, anesthetic solution was accurately and reproducibly introduced posteriorly and laterally to the temporomandibular joint to achieve anesthesia of the joint.

Latency and inhibition of human masticatory muscles following stimuli.

Latency-inhibition behavior was always produced in contracting anterior temporal muscles following the application of various stimuli to the teeth and jaws of 31 subjects. Statistically significant differences in duration were generally observed with different procedures. In half of the subjects, the first one or two closures in a sequence of repetitive tapping evoked a longer period of inhibition than subsequent closures. No reflex or latency-inhibition behavior could be produced in contracting digastric muscles. Comparisons of means for individual subjects did not follow the pattern suggested by comparisons of total sample means in almost half of the subjects.

Functional heterogeneity in the superior head of the human lateral pterygoid.

The activity of the superior head of the human lateral pterygoid muscle (SHLP) is controversial. Given the non-parallel alignment of some SHLP fibers, the SHLP may be capable of differential activation. The aims were to clarify SHLP activity patterns in relation to location within SHLP. In 18 subjects, SHLP single motor units were intramuscularly recorded at computer-tomography-verified sites during horizontal (e.g., protrusion) and vertical (e.g., opening) jaw tasks (recorded by a jaw-tracking device) and at resting postural jaw position. None of 92 units was active at the resting postural position. Medially located units (21) showed activity during contralateral movement, protrusion, and opening; 5 were also active on jaw closing. There was a significant association between unit location and the number of units active during vertical tasks (i.e., jaw closing and clenching). Analysis of the data suggests differential activation within SHLP and raises the possibility of functional heterogeneity within SHLP.

Analysis of human mandibular mechanics based on screw theory and in vivo data.

In this paper the mechanics of human mandibular function is described in terms of the associated screws. The two distinct, yet related features of jaw mechanics, involving the motion itself as well as the forces, are both functions of the anatomical constraints, namely the contact areas that exist within the temporomandibular joint, and the forces of the muscles and tendons that allow motion to occur. The relationships that exist between these two aspects of jaw-motion are identified in this paper showing that muscle forces can be uniquely represented in terms of the action screw. This new approach to analyzing the mechanics of jaw-motion also incorporates the previously studied motion screw or helical axis. A consistent dynamic model is formulated where the action screw is used to represent the action of the closing muscle forces while the moment arms of the muscle forces are determined about the motion screw representing mandibular kinematics. The action screw formulation is verified using in vivo motion data and MR image information for a single asymptomatic subject. The results confirm the feasibility of the method and its application in dental research. A general increase in the mechanical advantage of most muscles, in the distance between action and motion screws as well as in the expended energy towards the end of the jaw-closing phase was observed. Asymmetries in the distribution of muscle force magnitudes appeared to influence the resultant force and moment of the action screw but had little effect on its spatial location. The method presented is intended to facilitate understanding of mandibular function and dysfunction.

Short and long-latency responses in human masseter muscle evoked by chin taps.

Ten healthy subjects received downward, backward and upward chin taps with standardized force and direction. Taps in all three directions elicited short (M1) and long (M2 and M3)-latency excitatory EMG responses in the masseter muscle. M1 (mean latency 8.9 ms, amplitude 150 microV) occurred more frequently and with shorter latency during clenching than during relaxation or opening. Downward taps were more efficient in evoking jaw-jerks (25 per cent) than upward (14 per cent) and backward ones (16 per cent). M2 was a weak biphasic deflection occurring during the silent period (mean latency 42 ms, amplitude 87 microV) and M3 was an EMG burst following the silent period (mean latency 69.3 ms, amplitude 169 microV). No long-latency evoked responses were obtained from the relaxed masseter. Thus, muscle stretch increases M1 response frequency but is not a necessary prerequisite. The hypothesis that vibratory transmission plays an important role was confirmed. Voluntary activation of the stimulated muscle (clenching) increases M1-response frequency and shortens response latency.

Reflex responses to taps in various directions from the human digastric muscle.

Reflex responses to standardized solenoid chin taps were studied on 21 subjects with electromyographic (EMG) recordings from two jaw muscle antagonists, the masseter and the digastric. Taps were delivered downward and upward as parallel as possible to the masseter fibre direction and also backwards at right angles to these directions. Taps were delivered during isometric masseter and digastric activity as well as during relaxed postural position. Reflex excitation of the digastric muscle with a latency of 25-35 ms was recorded during all three situations after taps in all three directions. When this response was superimposed on ongoing digastric isometric activity after downward and upward taps, it was followed by a period of inhibition (mean duration 31 ms) and directly followed by a second EMG burst (mean latencies 73 and 75 ms, respectively). Responses were significantly (p less than 0.001) more often obtained during digastric background activity than during postural position and clench. Upward and downward taps were equally efficient in evoking the responses, significantly (p less than 0.001) more so than backward taps. The concurrent recordings of the masseter EMG imply the possibility of a reciprocal interplay between the two antagonists. The results accord with reports of the capability of the digastric muscle to produce reflex responses despite lack of anatomically-defined muscle spindles.

Electromyographic recordings of human jaw-jerk reflex characteristics evoked under standardized conditions.

A device for imparting reproducible chin taps was employed to evoke monosynaptic jaw-closing reflexes in subjects without (group A) and with (group B) overt muscle-joint pain dysfunction. Latency, duration and amplitude values obtained were consistent within an individual at constant tap force at a single-recording session but varied among subjects. Latency differences between sides were greater in subjects exhibiting mild to moderate dysfunction (group B) than in group A, but there were not corresponding differences in duration and amplitude. Stimuli were delivered in 5 subjects whilst the jaw was firmly held at postural jaw position with the aid of acrylic resin indices secured with adhesive to the maxillary and mandibular teeth. Recordable reflex responses were evoked in the masseter muscles of one subject only, indicating that vibration alone was not an adequate stimulus consistently to evoke a jaw-closing reflex at postural jaw position. Spindle stretch is needed, unless postural motoneurone excitability is at a sufficiently high level. Reproducible jaw-closing reflexes were evoked following standardized stimuli; subtle variations in motoneurone excitability, such as reflected by differences in jaw-jerk latency between sides, may then become apparent.

Placement and verification of recording electrodes in the superior head of the human lateral pterygoid muscle.

Previous studies in man have relied only on electromyographic (EMG) activity patterns and anatomical landmarks to confirm electrode placement in the superior head of the lateral pterygoid. Computed tomography (CT) was used here to determine whether indwelling fine wires could be visualized in that muscle head in man and thus provide evidence for correct placement before EMG. Two imaging sessions were conducted in six individuals. First, a series of contiguous axial CT slices was obtained to calculate the trajectory of insertion of fine wire electrodes into the superior head. For each individual, the trajectories for the location of the fine wires in the approximate mediolateral and anteroposterior centre of the superior head were different. Further axial CT slices were taken after electrode insertion; in each case, these slices clearly showed the wire ends located within the muscle. It was concluded that fine wires in the lateral pterygoid can be imaged by CT. Furthermore, imaging is necessary to accommodate interindividual anatomical variations and to confirm the position of the electrodes within the muscle.

Electromyographic activity of the human lateral pterygoid muscle during contralateral and protrusive jaw movements.

Understanding of the normal function of the lateral pterygoid muscle is limited. The principal aim here was to determine whether there is a progressive increase in lateral pterygoid activity as the mandibular condyle moves downwards and forwards as would be expected if the muscle is concerned with the precise horizontal positioning of the mandible. In eight humans, recordings were made of the activity of the superior (SHLP) and inferior (IHLP) heads of the lateral pterygoid and the masseter, anterior temporal, posterior temporal and digastric muscles, together with the movement of the palpated lateral condylar pole (JAWS-3D tracking system) during trials of a contralateral and a protrusive jaw movement. Recording sites in SHLP and, in one participant, IHLP were verified by computed tomography. In each participant there was a progressive increase in the rectified and smoothed SHLP and IHLP activity in association with condylar movement during the contralateral and protrusive jaw movement. Further, irregularities in condylar movement, which reflected variations in the rate at which the jaw was moved, were correlated in time with prominent bursts of SHLP and IHLP activity. In all participants there was a consistently high correlation coefficient between the rectified and smoothed SHLP and IHLP activity and condylar displacement during the contralateral or protrusive jaw movements. For example, the mean (+/-SD) correlation between anterior condylar translation during contralateral excursion and SHLP activity was 0.91+/-0.09, and for IHLP 0.96+/-0.02. For the masseter, anterior temporal, posterior temporal and digastric muscles, mean r-values were, respectively, 0.10+/-0.77; -0.14+/-0.72; 0.24+/-0.78; 0.54+/-0.47. When treated as a group the correlation coefficients for SHLP and IHLP were statistically significantly different from the correlation coefficients for the other muscles treated as a group (ANOVA; p < 0.002 for correlation with anterior translation). These observations support the notion that the lateral pterygoid provides the principal driving force for moving the jaw forwards or laterally in protrusive or lateral excursive condylar movements. Further, the data suggest that the muscle plays a part in the fine control of jaw movements.

Management of craniomandibular disorders. Part II: Clinical assessment of patients with craniocervical dysfunction.

Comprehensive evaluation of mandibular function requires a broader assessment of the head, neck, and jaws than is normally performed. Examining only the teeth and periodontium will fail to assess problems in muscles and joints, which should be considered in the management plan. Recognition of function-related symptoms is important in the prediction of treatment outcomes. Stress-induced muscle tension and traumatic oral habits may be linked with reported symptoms of headache, earache, and temporomandibular joint problems, and the significance of these symptoms should be assessed through detailed clinical examination.

Management of craniomandibular disorders. Part 1: A craniocervical dysfunction index.

A craniocervical dysfunction index has been developed (based on the Helkimo Dysfunction Index) to comprehensively assess craniocervical dysfunction and to objectively monitor the management of patients who present with these clinical problems. The close functional interrelationship of temporomandibular joints, jaw muscles, and cervical joints and muscles is reviewed, and a mechanism is proposed to explain dysfunctional relationships between these structures. This is the first of three papers stemming from a clinical study that investigated craniomandibular disorders and assessed the effect of routine dental management on craniomandibular and craniocervical dysfunction.

Assessment of pain (distribution and onset), Symptoms, SCL-90-R Inventory responses, and the association with infectious events in patients with chronic orofacial pain.

A visual analog pain scale and scalar responses to 13 pain/symptom indicator Symptom Checklist-90-Revised (SCL-90-R) questions were used to assess symptom prevalence and pain severity in 43 chronic orofacial muscle pain patients and 40 control subjects. The orofacial muscle pain group reported pain in an axial skeletal distribution; neurocognitive, gastrogenitourinary, and musculoskeletal symptoms; infectious events at or preceding onset; similar symptoms in sexual partners; and low prevalence of trauma. Sudden onset was reported by 30.2% of pain patients. Strong associations were found between chronic orofacial muscle pain and (1) onset-related infectious-like events (67.4%); (2) a higher prevalence of history of respiratory and gastrogenitourinary infectious events; and (3) high prevalences of similar pain symptoms in long-term sexual partners. The SCL-90-R somatization scores (> 62) had a higher prevalence in the chronic pain group. No prevalence differences or associations with pain/symptom indicators were found for depression or anxiety dimension scores. These data suggest that patients with recurrent systemic infectious events have a higher prevalence of reporting of chronic orofacial muscle pain compared with control subjects, and these infectious events are associated with the onset of chronic orofacial muscle pain in 67% of patients.