Relationship between masticatory function and internal structure of the mandible based on computed tomography findings

INTRODUCTION: The purposes of this study were to investigate bone mineral density as a part of bone construction in human skulls and to examine the relationship between dentofacial morphology and masticatory function by using computed tomography (CT) findings. Changes in bone mineral density in the mandible because of loss of masticatory function were tested in rats by experimentally producing an environment that inhibited mastication by the molars. METHODS: Data for the human study were obtained from 27 modern male Japanese skulls (mean age, 28 years) from the University of Tokyo. Cortical bone thickness (CBT) and CT value (CV) were measured by each CT scan of the first and molars. For the animal study, a metal cap was inserted between the maxillary and mandibular incisors to prevent the molars from biting in 6-week-old male Wistar rats. The rats were killed after 2, 4, or 6 weeks, and bone mineral density was measured in cancellous and cortical bone equivalent to the first molar region by using peripheral quantitative computed tomography. RESULTS: In the human skull study, significant negative correlations were observed between CV in the regions of the buccal side of the second molar and the angle between the Frankfort horizontal and mandibular planes. Significant negative correlations were also observed between the gonial angle and CV in the buccal and basal sides. In the animal study, cancellous bone mineral density began to decline 4 weeks after the start of the experiment in the masticatory hypofunction group compared with the control group. By week 6, cancellous bone density had declined by 11.6% on the buccal side, 16.7% on the lingual side, 12.3% at the bifurcation of the root, and 38.1% at the root apex. Cortical bone density declined by 8% to 12% on the lingual side. CONCLUSIONS: The results support our hypothesis that a functional adaptive response by the mandible to mechanical stress resulting from mastication occurs not only in the muscle insertion area, but also in mandibular alveolar bone in the molar region.     

Impact of <Emphasis Type="Italic">Streptococcus mutans</Emphasis> on the generation of fluorescence from artificially induced enamel and dentin carious lesions in vitro

The purpose of this study was to examine whether Streptococcus mutans is implicated in the generation of fluorescence detected in carious lesions. Enamel surfaces and dentin cavities of extracted human teeth were subjected to artificial caries generation by exposing them either to a culture medium containing S. mutans or to a lactic acid buffer for 2 weeks. Fluorescence from the lesions was detected with confocal laser scanning microscopy or fluorescence microscopy at various excitation wavelengths, and maximum fluorescence radiance was computed using imageanalyzing software. Culture media of S. mutans were also examined for fluorescence generation. The results demonstrated that S. mutans-induced enamel and dentin lesions exhibited increased fluorescence in the red and green spectral regions, with the signal stronger in the red region. In the blue region, however, fluorescence signals in the corresponding area were below the background level. Significantly weaker or virtually no fluorescence was detected in lactic acid-demineralized lesions at all excitation wavelengths. Neither bacterial cells nor culture media generated any fluorescence. These results indicate that, although the presence of S. mutans may be a prerequisite for the emission of fluorescence from carious lesions, some interaction of S. mutans with exposed tooth matrix elements may also be required for the generation or unmasking of fluorophores.     

Development of casting investment preventing blackening of noble metal alloys Part 2. Application of developed investment for type 4 gold alloy

The objective of this study was to evaluate the efficacy of the developed investment for the prevention of blackening of a cast Type 4 gold and to analyze the oxides on its surface in relation to the blackening of the alloy. The experimental investments were prepared using a gypsum-bonded investment in which boron (B) or aluminum (Al) was added as a reducing agent. A Type 4 gold alloy was cast into the mold made of the prepared investment. The effect of the additives was evaluated from the color difference (deltaE*) between the as-cast surface and the polished surface of the cast specimen. B and Al were effective to prevent the blackening of a Type 4 gold alloy and the color of the as-cast surface approached that of the polished surface with increasing B and Al content. The prevention of the blackening of the gold alloy can be achieved by restraining the formation of CuO.     

Blood flow and human periodontal status

The purpose of this study was to evaluate the microcirculation in subjects with moderate gingivitis, periodontitis, and healthy gingiva. Sixty adult volunteers with clinically healthy gingiva, moderate gingivitis, and periodontitis (20 subjects each) participated in this study. The ages of the research samples ranged from 20 to 35 years. Gingival health was evaluated by using the qualitative plaque index, gingival index, gingival bleeding index, tooth mobility, probing pocket depth, clinical attachment level, and laser Doppler flowmetry (LDF) on six maxillary anterior teeth. LDF data were recorded at the facial aspect of free gingivae, interdental gingivae, attached gingivae, and alveolar mucosae on six maxillary anterior teeth, utilizing an acrylic stent to stabilize the probe. This technique was then modified to circumvent contamination by saliva and gingival exudate. When results were compared at similar sites in each patient within a trial group, there were significant differences in blood flow measurements at all the sites examined between moderate gingivitis and periodontitis when compared with measurements in healthy human gingiva. However, blood flow measurements within the same group showed significant differences at every site, at P < 0.01. Received: December 17, 2001 / Accepted: January 23, 2002     

Tensile and shear bond strength of resin-reinforced glass ionomer cement to glazed porcelain

The purpose of this study was to measure the tensile and shear bond strength of resin-reinforced glass ionomer cement (RGIC) to glazed porcelain, to evaluate the durability of RGIC by thermal cycling, and to examine the RGIC remaining on the surface of the porcelain after the bond strength test to evaluate bonding conditions. Three adhesives were used in this study: Concise (CO) as a chemically cured composite resin, Fuji ORTHO (FO) as a chemically cured RGIC, and Fuji ORTHO LC (FOLC) as a light-cured RGIC. Tensile and shear bond strengths were measured 24 hours after bonding orthodontic brackets and also after thermal cycling. Tensile bond strength after 24 hours was 6.6 +/- 3.2 MPa in CO, 7.3 +/- 1.4 MPa in FO, and 8.6 +/- 1.9 MPa in FOLC, and the strength significantly decreased after the thermal cycling test. Shear bond strength after 24 hours was 32.5 +/- 8.9 MPa in CO, 23.3 +/- 6.8 MPa in FO, and 24.7 +/- 6.5 MPa in FOLC, and in contrast to tensile bond strength, no decreases in the strength were detected after the thermal cycling test. CO showed significantly higher shear bond strength than did FO and FOLC. When using the shear bond strength test and CO, destruction of porcelain surfaces frequently occurred after 24 hours and was observed in every specimen after the thermal cycling. RGIC was found to be an advantageous alternative to resin adhesive for bracket bonding to porcelain and to enamel.     

A study on kinetic frictional properties in Begg/KB orthodontic appliances at posterior sites

In Begg and KB techniques, the kinetic frictional force generated between their characteristic orthodontic appliances at posterior sites and the orthodontic wire affects the efficiency of tooth movement. We compared the kinetic frictional force between the recent orthodontic appliances for posterior sites: the by-pass loop-KB buccal tube system (loop-KB tube system) and the conventional by-pass clamp-round buccal tube system (clamp-round tube system), and elucidated the frictional properties of the loop-KB tube system. We used 016"/018" round wires (016/018 round) and 022" × 016" ribbon wire (022 ribbon) with anchorage bend/curve applied. The results obtained were as follows:

Sternocleidomastoid myocutaneous flap for intraoral reconstruction after resection of oral squamous cell carcinoma.

PURPOSE: The sternocleidomastoid (SCM) myocutaneous flap remains an important tool in head and neck reconstruction. This article retrospectively reviews 40 consecutive SCM myocutaneous flaps used for the reconstruction after resection of oral squamous cell carcinoma with respect to reliability and complications. PATIENTS: From 1987 to 1997, 40 patients underwent SCM myocutaneous flap reconstruction of the oral cavity. The age and gender of the patients, site of primary tumor TNM stage, type of associated operation, and clinical course were analyzed. RESULTS: In 8 cases, partial epithelial loss over the skin paddle occurred with survival of the muscle and at least some of the dermis. Unilateral supraomohyoid neck dissection (SND) was performed in 11 cases, and unilateral functional neck dissection, which preserves SCM and/or internal jugular vein and/or accessory nerve, in 16 cases. Pathologically positive nodes were recognized in 14 of these 27 neck dissection cases; in 11 of these 14 cases, the neck lesion was controlled. CONCLUSION: The SCM myocutaneous flap appears to be simple to use and useful for reconstruction of the defect after resection of oral carcinoma, and the indications for this flap will be extended in accordance with the recent increases in the number of supraomohyoid and functional neck dissection cases.     

Is there any difference between the British and Japanese de?nitions of the mandibular cortical index (MCI) on panoramic radiographs? A pilot study

Objectives To assess the reproducibility of the mandibular cortical index (MCI) on panoramic radiographs among British and Japanese observers, and to investigate the difference between the British and Japanese observers in the definition of MCI.Methods Three observers, a Japanese oral radiologist, a British oral radiologist, and a British prosthodontist, classified the inferior cortex of the mandible on a set of 100 duplicated films of randomly selected panoramic radiographs twice, 2 weeks apart, using the MCI. The kappa index for intra- and interobserver agreement was calculated for the three observers.Results The kappa index for intraobserver agreement was moderate (0.56) to perfect (0.86) for the three observers. Interobserver agreement between the Japanese and the British oral radiologists was moderate at the first reading (kappa, 0.59) and substantial at the second (0.61). Interobserver agreement between the prosthodontist on the one hand and each of the oral radiologists on the other was fair (0.35, 0.38) at the first reading, but moderate (0.43, 0.60) at the second reading. The prosthodontist tended to overestimate the MCI compared with either of the oral radiologists.Conclusion Our results suggest that the definition of MCI used by Japanese observers is basically similar to that used by British observers, although some improvements in the definition of MCI would be necessary for clinical dental practice.     

Longitudinal study of patients with TMJ dysfunction by tomographic examination: Condylar position and clinical sign

For patients with TMJ dysfunction, operators often change the condylar position by various methods. The aim of this study is to investigate how much the changes with time of condylar positions are related to the changes of clinical signs. The subjects were 584 joints of 127 patients with TMJ dysfunction to whom the serial lateral TMJ tomography was performed more than twice. In the most of cases where the condylar position had moved downward, inter-incisal distance had increased and TMJ noise had ameliorated. Furthermore, in many cases where the condylar position had moved forward, the amelioration of the TMJ pain was observed. It was considered that those ameliorations occurred because the positional relationship between the condylar head and the articular disk or posterior attachment had been improved.     

Formation of acellular cementum-like layers, with and without extrinsic fiber insertion, along inert bone surfaces of aging c-Src gene knockout mice

To investigate the long-term effects of c-src deficiency on skeletal and dental tissues, we examined the lower jaws and long bones of c-src gene knockout (c-src KO) mice by histological and histochemical methods. Numerous multinucleated osteoclasts were distributed throughout the mandible in 5-wk-old c-src KO mice, but by 14 wk they had almost completely disappeared from the alveolar bone, leaving tartrate-resistant acid phosphatase (TRAP)-positive layers along the bone surface. Deposition of osteopontin-positive mineralized tissue, reminiscent of acellular afibrillar cementum (AAC), was confirmed along the TRAP-positive bone surface at 14 wk. The layer progressively thickened up to 21 months. A comparable mineralized layer was noted along the trabeculae of long bones as thickened cement lines. In the periostin-rich areas of jaw bones, but not in the long bones, portions of AAC-like mineralized layers were often replaced with and/or covered by acellular extrinsic fiber cementum (AEFC)-like tissue. These data suggest that the deposition of AAC-like mineralized tissue is a general phenomenon that may occur along inert or slowly remodeling bone surfaces under conditions characterized by reduced bone-resorbing activity, whereas the induction of AEFC-like tissue seems to be associated with the expression of certain molecules that are particularly abundant in the microenvironment of the periodontal ligament.