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PubMed1996

Effect of different cooling rates on fracture toughness and microhardness of a glazed alumina reinforced porcelain.

Dental porcelain has superior esthetics but may be subject to fracture during mastication. Residual compressive stresses on the porcelain surface after cooling enhance resistance of porcelain to crack initiation, as quantified by its fracture toughness (Kc). The effect of different cooling rates on Kc and hardness of a glazed porcelain reinforced with approximately 2% aluminum oxide was examined in 45 porcelain disks that were divided into three groups. After final glaze firing, one group was cooled rapidly, the second was cooled at a medium rate, and the third was cooled slowly. Fracture toughness was determined with a microindentation procedure. The mean Kc recorded for rapidly cooled porcelain (1.74 +/- 0.09 MN/m3/2), for medium-cooled porcelain (1.41 +/- 0.07 MN/m3/2), and for slow-cooled porcelain (1.29 +/- 0.07 MN/m3/2) was statistically different (p < 0.001, analysis of variance and Bonferroni post hoc test). No statistically significant differences in Vickers hardness values were recorded when porcelain was cooled at different rates (530 to 540) (analysis of variance). The faster cooling rate of a glazed alumina reinforced porcelain resulted in greater fracture toughness but had no effect on hardness.

Aluminum Oxide↗
PubMed1997

Surveying removable partial dentures: the importance of guiding planes and path of insertion for stability.

STATEMENT OF PROBLEM: Although removable partial dentures are a favored option for the restoration of many situations that involve partial tooth loss, some patients are not satisfied with a removable partial denture, especially when it is not stable during mastication. A dental surveyor can be used to prevent countless problems related to the production of removable partial dentures. Many professionals working with oral rehabilitation fail to take advantage of the many uses of a surveyor in planning and designing chromium alloy and other metal removable partial denture frameworks. PURPOSE: This article uses an academic approach to describe the criteria used to determine the path and removal of a removable partial denture. A fundamental requirement for understanding the correct use of the dental surveyor is to prevent indiscriminate use of a path of insertion perpendicular to the occlusal plane, and extreme inclinations of the cast in the attempt to create undercuts on some teeth.

Chromium Alloys↗
PubMed1999

Fatigue testing and microscopic evaluation of post and core restorations under artificial crowns.

STATEMENT OF PROBLEM: Coronoradicular reconstruction techniques of pulpless teeth include prefabricated post systems that retain a core material such as silver amalgam, composite, glass ionomer, or modified glass ionomer cement. Mechanical properties of these materials are critical to sustain masticatory forces. PURPOSE: This in vitro study compared the mechanical resistance of 3 core materials (silver amalgam, composite, and silver-reinforced glass ionomer) under masticatory conditions. MATERIAL AND METHODS: Industrially fabricated teeth were used and a total of 75 specimens were divided into 3 groups of 25 specimens. Titanium canal posts were placed, followed by core buildups in amalgam, composite, or glass ionomer. Teeth were prepared for full cast crowns and the crowns were fabricated and cemented with glass ionomer cement. Twenty specimens from each group were placed in a mastication simulator cyclically loading the teeth with a 400 N force for 1.5 million cycles. The 5 remaining specimens were used as controls. Teeth were sectioned and observed macroscopically and microscopically to determine the rate of defects for each material. Observed defects were verified with the Kruskal-Wallis test. The 3 core materials were ranked with the Tukey multiple comparison test. RESULTS: Significant differences of mechanical behavior were found for the 3 materials. At P <.01, silver amalgam was significantly superior to composite and glass ionomer. Composite was significantly superior to glass ionomer. CONCLUSION: Cores fabricated with amalgam had the lowest rate of defects when tested under artificial crowns. Glass ionomer, when used as a core material under artificial crowns, showed the highest rate of defects after an instantaneous load of 400 N for a 1,500,000 repetition cycle.

Biomechanical Phenomena↗
PubMed1999

Toward an understanding of implant occlusion and strain adaptive bone modeling and remodeling.

STATEMENT OF PROBLEM: Dental implant failure rates for osseointegration are greater in the highly atro-phic maxilla. Presuming higher failure rates relate to strain-driven adaptation, an enhanced understanding of formative bone response to loading (modeling) and maintenance of an integrated state (remodeling) should improve treatment. PURPOSE: To understand the role of occlusal loading on long-term osseointegration in areas of compromised cancellous bone, a review of the salient features of adaptive bone modeling and remodeling is presented with an emphasis on cancellous bone responses. CONCLUSIONS: The ability for dental implants to maintain a long-term stable interface in the maxilla lies in the ability of trabecular bone to maintain adequate local material (strength) and architectural (connectivity) properties. In this discussion, an emphasis has been placed on understanding how trabecular bone can respond to the mastication-induced loading environment on an implant.

Adaptation, Physiological↗
PubMed1986

A simulation approach to understanding the masticatory process.

An analysis of the reduction of food particle sizes during human mastication is presented in terms of the probability of a particle being broken (selection function) and the distribution of fragment sizes produced when it fails (breakage function). Both selection and breakage functions are defined and a general equation produced. Several feasible behaviours for these two variables that have been suggested in the literature are modelled by computer simulation and the results are compared to published breakdown patterns. The conclusions are that selection and breakage functions probably behave very simply with respect to particle size, and that these behaviours could be deduced from an analysis of food particle size distributions and the rate at which particle sizes are reduced per chew.

Computers↗
PubMed1996

Considerations for modeling.

There has been a great growth in the biophysical knowledge base of the human masticatory system, which increases the chances of success in numerical and experimental modeling of the oral environment. The chief advances in understanding are in the areas of the dentino-enamel complex, the force-movement cycle of the mandible, mastication, comminution and salivary lubrication. These areas are reviewed, and suggested average clinical conditions are offered as a starting point for experiments in laboratory clinical simulation as it relates to the studies in biomaterials and biomechanics in dental research.

Biomechanical Phenomena↗
PubMed2000

Chewing and swallowing as indices of the stimulation to eat during meals in humans: effects revealed by the edogram method and video recordings.

Patterns of chewing and swallowing were recorded during standardized meals in humans. Cocktail size (3 cm2) open sandwiches were served in one of five different flavors. An oscillographic recording of chewing and swallowing showed that chewing activity varied with the palatability and variety of foods. Chewing time was shorter and fewer chews were observed as palatability increased. Swallowing did not change as a function of stimulus flavor. Pause duration between two successive food pieces became shorter as palatability increased. The effects of sensory factors were most evident at the beginning of meals and decreased until the end of meals. A later study which compared eating parameters in sandwich, semi-solid, and traditional French meals (different courses ingested in succession: appetizer, main course, cheese and dessert), as assessed from video recordings, found that different microstructure parameters responded to palatability manipulation in different meal types. Strength of mastication and prandial drinking might be other important parameters to look at in order to understand the motivation to eat and its fluctuations during the meal.

Adolescent↗
PubMed1998

Development of trigeminal mesencephalic and motor nuclei in relation to masseter muscle innervation in mice.

This study evaluated temporospatial changes in the central organization of trigeminal mesencephalic (mesV) and motor (motV) nuclei during their development. Very little is known regarding the timing of formation of these trigeminal nuclei and the role that target tissue interactions may have on their spatial organization. Cells located in motV innervate muscles of mastication while the mesV nucleus contains populations of primary afferent cells that innervate muscle spindles in jaw closing muscles and periodontal mechanoreceptors around the roots of teeth. To label mesV afferents and motV efferents during their development, lipophilic dyes, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) or 4-(4-dihexadecylamino)styryl)-N-methylpyridinium iodide (DiA), were inserted into various jaw muscles, the dorsomedial mesencephalic region or tooth buds of maxillary or mandibular teeth of embryonic or postnatal mouse pups. Parasagittal sections were evaluated under epifluorescence to determine the temporospatial organization of trigeminal nuclei and the timing of outgrowth of their processes to target tissues. Early in development, motV motoneurons were organized in columns or clusters closely associated with groups of motoneuron axon fascicles that innervated a specific muscle. Double labelling of masseter and temporalis muscles showed that the columns containing motoneurons associated with these muscles were interdigitated early in development but later condensed into respective motoneuron pools. In contrast, no spatial organization of mesV afferent cell bodies was observed throughout the developmental sequence examined. The results of this study also demonstrated that motV processes enter into jaw muscle at least 1 day prior to proprioceptive afferents. MesV afferent appearance at the tooth was further delayed by 10 days suggesting different signaling mechanisms for these two targets.

Animals↗
PubMed1998

Development of fusimotor innervation correlates with group Ia afferents but is independent of neurotrophin-3.

Fusimotor neurons, group Ia afferents and muscle spindles are absent in mutant mice lacking the gene for neurotrophin-3 (NT3). To partition the effect of Ia afferent or spindle absence from that of NT3 deprivation on fusimotor neuron development, we examined the fusimotor system in a mutant mouse (NesPIXpNT3) that lacks Ia afferents and spindles, but has normal or elevated tissue levels of NT3 during embryogenesis. Fusimotor fibers were absent in lumbar ventral spinal roots, and limb muscles were devoid of Ia afferents and spindles in adult NesPIXpNT3 mice. In contrast, no deficiency in motoneuron numbers was observed in the trigeminal nucleus which contains cell bodies of motor axons innervating muscles of mastication. Spindles and Ia afferents were also present in the masticatory muscles. Thus, the development and/or survival of fusimotor neurons correlates with the presence of Ia afferents and/or spindles, and not with the amount of NT3 in the spinal cord or muscle.

Animals↗
PubMed1997

Third molar surgery--a preliminary report on aspects affecting quality of life in the early postoperative period.

The issue of quality of life has largely been neglected within oral surgical practice. A questionnaire was designed to assess the effect of third molar surgery on a number of measures of health care outcome within the first postoperative week, that appeared not to have been previously addressed. These included level of physical discomfort, oral and vocal function, patients' perception of their appearance and social interaction. Patients were asked to complete the questionnaire one day following surgery and again 7 days after surgery. For each question they recorded the answer best describing how they felt, on a 4-point scale. Twenty-nine paired returns were received, for which the results for day 1 and day 7 were summated and compared. A two sample t-test revealed a small but significant improvement in the patients' perception of their quality of life over that time period. When a subset of 11 questions relating to physical wellbeing were analysed using the Wilcoxon Signed Rank Test, a significant improvement in only two of the 11 parameters (ability to masticate and perception of appearance) was found. These results show that within the first postoperative week some patients can experience a deterioration in their quality of life, that extends beyond the traditionally recognized side effects and which shows little improvement in the first postoperative week. It has been stated that patients have a right to know if their lifestyles are to be compromised by the effects of their treatment. We suggest that consideration be given to including reference at the preoperative assessment to some of these outcomes.

Eating↗
PubMed2003

Experimentally induced unilateral tooth loss: expression of type II collagen in temporomandibular joint cartilage.

PURPOSE: We sought to examine possible changes in pattern and concentration of type II collagen in the condylar cartilage and articular disc of the temporomandibular joint (TMJ) in response to unilateral extraction of mandibular teeth in a rabbit model as a means of elucidating the effects of unilateral mastication on the TMJ. METHODS: A total of 12 experimental rabbits were killed either 3 or 6 weeks after the extractions, and 3 additional rabbits without extractions were used as controls. TMJ blocks from both sides of each of the 15 animals were examined for type II collagen via an immunoperoxidase procedure. RESULTS: Anti-type II collagen antibody (Ab) binding was detected mainly in the hypertrophic chondroblast layer of the condylar cartilage of normal rabbits. At 3 weeks after unilateral extraction of teeth, anti-type II collagen Ab binding to the territorial matrix of the hypertrophic chondroblast layer of the condylar cartilage and to the disc was stronger than normal. The increase in Ab binding appeared more dramatic on the nonfunctional side than on the functional side of TMJ. Variations from the normal pattern of anti-type II collagen Ab binding in terms of distribution through the extracellular matrix and fibrillar appearance were also observed. CONCLUSION: The findings suggest that the condylar cartilage and disc adapt to the imbalance induced by unilateral extraction of teeth through chondrocyte repair responses involving collagen II expression that appear to differ between the functional and nonfunctional sides of the TMJ.

Animals↗
PubMed1993

Masticatory function in patients with mandibular prognathism before and after orthognathic surgery.

Masticatory function was analyzed in 54 patients with mandibular prognathism before or after orthognathic treatment and in 40 adults with normal occlusion. Masticatory efficiency was evaluated spectrophotometrically by measuring the amount of adenosine triphosphate eluted from masticated adenosine triphosphate granules. Occlusal contact was evaluated by calculating the number and area of occlusal contacts from the illuminated images of a silicone record of the occlusion that was stored in the image analysis system with the aid of a charge-coupled device camera. The mean masticatory efficiency of the preoperative group was approximately half that of the control group. The value for the postoperative group was slightly higher than that for the preoperative group, but there was no statistical difference between the two groups. Likewise, the number and area of occlusal contacts in the preoperative group were also approximately half or less as compared with those of the control group, and they did not show significant changes postoperatively. Statistically, there were correlations between the masticatory efficiency and the number and area of occlusal contacts. The results indicate that although the occlusal relationship of the upper and lower teeth were greatly improved by orthognathic treatment, the postoperative occlusion is not tight enough and may need further adjustment at the end of the treatment.

Adenosine Triphosphate↗
PubMed1996

Mandibular excursions and maximum bite forces in patients with temporomandibular joint disorders.

PURPOSE: This study evaluated mandibular motion and bite force in patients with temporomandibular joint disorders after joint surgery. PATIENTS AND METHODS: Maximum voluntary mandibular motion, maximum excursion during mastication, and maximum bite force were examined in 25 female patients before temporomandibular joint surgery. Their pretreatment performance was compared with that at 6 weeks, 6 months, and 1 year after surgery, and with performance of 26 normal female volunteers. RESULTS: Before surgery, all of the patients' movements and bite forces were smaller than those of controls. One year after surgery, maximum interincisal opening increased significantly, but lateral excursion and protrusion remained unchanged. Maximum bite forces increased significantly and nearly reached control levels. CONCLUSIONS: Patients with severe restriction in temporomandibular joint function exhibit general improvements in some mandibular movements and in maximum bite force after surgical treatment.

Adolescent↗
PubMed1997

Rigid fixation and strain patterns in the pig zygomatic arch and suture.

PURPOSE: In orthognathic surgery, rigid fixation is routinely used to hold together bone fragments that may experience heavy force from attached masticatory muscles. Internal fixation plates are assumed to hold bony parts rigidly, but the mobility at such sites subjected to normal masticatory function has not been measured. The purpose of this study was to investigate in vivo the degree to which a linear plate immobilizes separated bones, specifically sutures. MATERIALS AND METHODS: Three female miniature pigs (Sus scrofa) had 1.3-mm Synthes titanium plates placed across the suture in the zygomatic arch. Foil strain gauges were used to record load deformation in the zygomatic and squamosal (temporal) bones and across the vertical and horizontal parts of the suture. Strain was recorded in vivo during mastication and in anesthetized pigs with electrical stimulation of masticatory muscles. RESULTS: Strain at the suture was not reduced from normal levels. The plate induced increases in strain within the bones, but the changes were slight. CONCLUSION: The results indicate that linear "rigid fixation" does not immobilize sutures.

Animals↗
PubMed1998

Arthroscopic management of temporomandibular joint disc perforations and associated advanced chondromalacia by discoplasty and abrasion arthroplasty: a supplemental report.

PURPOSE: This article describes the results of treating temporomandibular joint (TMJ) articular disc perforation and advanced chondromalacia arthroscopically by the use of discoplasty and abrasion arthroplasty. PATIENTS AND METHODS: Forty-four joints were treated in 25 patients (23 females and 2 males). Twenty-nine disc perforations were present, 24 joints had grade III chondromalacia (fibrillated cartilage), and 14 joints had grade IV chondromalacia (exposed bone). Surgical procedures included 14 abrasion arthroplasties and 24 motorized shavings or holmium laser vaporizations. Holmium laser discoplasty with mobilization was used in 29 joints. Patients were followed-up for an average of 40.8 months (11 to 74 months). RESULTS: Preoperative pain on the visual analog scale (VAS) (1 to 10 cm) ranged from 5 to 10 cm, with an average of 7.4 cm. Postoperatively, nine patients had no pain and 16 patients had an average VAS of 2.7 cm (range, 1 to 5 cm). Preoperatively, 30 joints had clicking, and 14 joints had crepitation. Postoperatively, 25 joints had no noise, 12 joints had slight intermittent clicking, and seven joints had crepitation. The preoperative range of motion averaged 29.7 mm. Postoperatively, the range of motion averaged 37.7 mm (range, 33 to 42 mm). All patients could masticate a regular diet except hard food after an average of 40.8 months (11 to 74 months). CONCLUSIONS: These findings seem to justify the arthroscopic surgical procedures of discoplasty for disc perforations, motorized shaving, or holmium laser vaporization of grade III chondromalacia, and abrasion arthroplasty for bone exposure. The results also question the need for discectomy in the treatment of disc perforation.

Adult↗
PubMed1998

Correlation between inclination of occlusal plane and masticatory movement.

OBJECTIVES: The purpose of this study was to investigate the relationship between the inclination of the occlusal plane and masticatory movement. METHODS: Masticatory movements of 41 young adults were measured using the three-dimensional Mandibular Movement Analyzing System. The inclination of the occlusal plane was measured in the sagittal plane using a three-dimensional digitizer. RESULTS: In the sagittal plane, the masticatory closing path and the occlusal plane were consistent in maintaining a perpendicular relation with each other regardless of the inter-individual variation of the inclination of the occlusal plane. Subjects with an anteriorly inclined occlusal plane showed a vertical closing path, and subjects with a posteriorly inclined occlusal plane showed a flat closing path in the frontal plane. These characteristics were explained by the variation of the timing on the balancing-side condylar return correlated with the inclination of the occlusal plane. CONCLUSIONS: There is a significant correlation between the inclination of the occlusal plane and the direction of the closing path during mastication.

Adult↗
PubMed1978

Reconstruction of the horizontal rami of the mandible following avulsion in childhood.

A 7-year-old boy was involved in a road traffic accident in October 1971, and apparently had been dragged along face downwards with resultant avulsion of the entire horizontal mandibular rami, and most of the mandibular alveolar soft tissue and teeth. Repair by metal implants was attempted but these proved unsatisfactory, and soft tissue replacement for the missing alveolus was carried out by flap raised from arm. Rib grafting was carried out on three occasions at almost yearly intervals, but each time, probably owing to vascular insufficiency, non-union (or more correctly non-replacement) occurred in the left canine region. To "import" a new blood supply, and free some of the scar tissue, a compound muscle/bone/skin flap bearing the clavicle and sternomastoid muscle was transposed to the mandibular bed. This form of grafting was used extensively in World War I to repair facial gunshot wounds, and the transposed blood supply enabled success in the pre-antibiotic period. Bony union is now satisfactory 5 years after injuries and dentures have been recently fitted; speech is normal, the child's facial contours acceptable, and mastication has been satisfactory during this period.

Bone Transplantation↗
PubMed1979

Temporomandibular joint meniscectomy--effects on joint structure and masticatory function in macaca fascicularis.

The postoperative effects of unilateral temporomandibular joint meniscectomy on joint structure and masticatory function were evaluated in four mature Macaca fascicularis and compared with one control. Mandibular movement during mastication was monitored objectively with an optoelectronic tracking system within four months and again within twelve months postmeniscectomy in each animal. Temporomandibular joint structure was documented radiographically and histologically. Results showed that degenerative joint disease was produced in the postsurgical joint, and that the morphological changes were location-dependent. Fibrous ankylosis was observed histologically in three animals. The contralateral joints were not affected morphologically, except for bony resorption of the articular eminence noted microscopically in one animal. Radiographically, however, the joint appeared normal. Variable alterations in masticatory patterns were observed following unilateral meniscectomy. While there appeared to be an association between temporomandibular joint structure and masticatory function, radiographic and microscopic observation of morphological alterations in the joint did not result in predictable functional limitations in chewing pattern.

Animals↗