Effect of interfacial bond quality on the direction of polymerization shrinkage flow in resin composite restorations

Shrinkage in light curing resin composites is assumed to be directed toward the light source. However, the strong bond at the dentin-resin interface achieved by newer generation dentin bonding systems may affect the direction of polymerization shrinkage. In this study, various curing modes of adhesive resin simulating different bond qualities were applied to determine the extent of interfacial gap formation with a scanning electron microscope. We also measured the free surface depression with a profilometer. The direction of polymerization shrinkage was inferred from the ratio of the interfacial gap measurement at the floor to the free surface depression. Various curing modes used in this study include Group 1: light curing of resin composite without the bonding agent as the negative control; Group 2: simultaneous light curing of the bonding agent and resin composite; Group 3: start of the chemical cure of the dual-cured bonding agent before light curing the resin composite; Group 4: curing the light-initiated bonding agent before insertion and light curing of the resin composite. When the bonding agent was light cured prior to inserting the resin composite (Group 4), the free surface depression was the greatest and the interfacial gap smallest among those in all groups. Therefore, if a good bond between dentin and resin composite can be established, the shrinkage flow will be directed toward a center located near the bonded interface rather than toward the incident light, thus reducing detrimental shrinkage stress.     

Anthropometric study of the upper lip and the nose of infants less than a year of age

We divided healthy newborns (aged between 2 weeks and 6 months) into four groups, less than 2 weeks old, 60 +/- 7 days, 120 +/- 7 days, and 180 +/- 7 days, between June 2001 and February 2002, and each group had 40 infants. The lineal distances included 13 items related to the nose, mouth, and lips.The average width of the columella at the midpoint was 3.2, 3.5, 3.7, and 3.8 mm for the 2-week-old group, the 2-month-old group, the 4-month-old group, and the 6-month-old group, respectively. The average height of the columella was 4.7, 4.9, 5.2, and 5.3 mm. The average length between the medial alar bases was 13.7, 14.4, 17.4, and 17.6 mm. The average length from the base to the tip of Cupid's bow was 9.5, 10.0, 10.5, and 10.6 mm. The average length from the columella lateral base to the tip of Cupid's bow was 8.4, 9.9, 10.2, and 10.5 mm. The average length from the columella central base to the center of Cupid's bow was 8.3, 9.5, 9.8, and 9.9 mm. The average width of one limb of Cupid's bow was 2.7, 3.1, 3.4, and 3.5 mm. The average length from the tip of Cupid's bow to the commissure was 13.4, 14.7, 16.4, and 16.9 mm. The average intercommissural distance was 26.8, 30.3, 30.8, and 32.7 mm. The average width of the philtral column at the columella base was 3.1, 3.6, 3.7, and 4.0 mm. The average width of the philtral columns at the mid-portion was 3.7, 4.6, 4.6, and 4.6 mm. The average height of the nasal tip protrusion was 8.7, 11.0, 11.7, and 12.1 mm. The average width of the nose was 20.7, 23.7, 25.3, and 25.9 mm. In conclusion, these data are expected to be useful for patients with a bilateral cleft lip.     

A comparative evaluation of different compensating curves in the lingual and labial techniques using 3D FEM.

Because adults dislike the visibility of orthodontic appliances, the use of the lingual orthodontic technique has increased over time. But few studies compare tooth movement of the lingual technique with that of the labial technique. In this study, human mandibular left teeth were aligned, and a 3-dimensional finite element model was made (consisting of 19382 nodes and 12150 elements). To compare the effect of compensating curves on canine retraction between the lingual and the labial orthodontic techniques, the compensating curve was increased on the.016-in stainless steel labial or lingual archwire, and a 150-g force was applied distally on the canine. The relative direction and the amount of tooth displacement of the finite element model were compared on a schematic displacement graph (magnified 10,000 times), and the compressive stress distributed on the root surface was observed. The pattern of tooth movement (with or without a compensating curve) was different between the labial and the lingual techniques. As the amount of compensating curve increased (0, 2, and 4 mm) in the archwire, the rotation and the distal tipping of the canine was reduced. The antitip and antirotation action of compensating curve on the canine retraction was greater in the labial archwire than in the lingual archwire.     

Histological comparison of healing extraction sockets implanted with bioactive glass or demineralized freeze-dried bone allograft: a pilot study

BACKGROUND: Various materials have been used immediately following tooth extraction to fill and/or cover the socket in an attempt to limit or prevent ridge resorption. The purpose of the present pilot study was to establish a reliable model to investigate the effect of various bone graft and bone replacement materials on extraction socket healing. This study also compared healing extraction sockets 6 to 8 months postimplantation of a bioactive glass (BG) or demineralized freeze-dried bone allograft (DFDBA) to an unfilled socket control (C). METHODS: Following tooth extraction, a total of 30 sockets in 19 patients were randomly divided into 3 treatment groups: 10 sockets received BG, 10 sockets DFDBA, and 10 sockets served as unfilled controls. Primary coverage was achieved by flap advancement over each socket. Six to 8 months postextraction at time of implant placement, histological cores of the treatment sites were obtained. These cores were processed, undecalcified sections prepared and stained with Stevenel blue/van Gieson's picric fuchsin, and histomorphometrically analyzed. Vital bone, connective tissue and marrow, and residual graft particles were reported as a percentage of the total core. RESULTS: A model system was described in humans and used to evaluate the healing response in the 3 treatment groups. Results concluded that mean vital bone present was 59.5% for BG-, 34.7% for DFDBA-, and 32.4% for C-treated sites. These differences were not statistically significant. However, the residual implant material was significantly higher in DFDBA-treated (13.5%) versus BG-treated sockets (5.5%). CONCLUSIONS: Although the differences in percent vital bone were not statistically significant among the 3 treatment groups in this pilot study, BG material was observed to act as an osteoconductive material which had a positive effect on socket healing at 6 to 8 months postextraction. Further research following implant placement in treated and control sockets is warranted to determine if bone implant contact is improved in BG-filled versus unfilled sockets.     

Thickness of posterior palatal masticatory mucosa: the use of computerized tomography

BACKGROUND: Periodontal plastic surgery is used to fulfill the esthetic and functional demands of patients. The palatal masticatory mucosa is the main donor site for connective tissue, and the thickness of the graft tissue obtained is an important factor for the success of this technique. The aim of this study was to measure the thickness of masticatory mucosa in the posterior palatal area using computerized tomography (CT). METHODS: The thickness measurements were performed on the images of 100 adult subjects who underwent CT on the maxilla for implant surgery. Twenty-four standard measurement points were defined in the hard palate according to the gingival margin and the middle palatal suture. The radiographic measurements were used after calibration. The data were analyzed to determine the differences in the mucosal thickness according to gender, age, tooth position, and depth of the palatal vault. RESULTS: The overall mean thickness of the palatal masticatory mucosa was 3.83 +/- 0.58 mm (range: 2.29 to 6.25 mm). Females had significantly thinner mean masticatory mucosa (3.66 +/- 0.52 mm) than males (3.95 +/- 0.60 mm) (P <0.0001). The thickness of the palatal masticatory mucosa increased with age. The mean thickness according to tooth site was 3.46 mm (maxillary canine), 3.66 mm (first premolar), 3.81 mm (second premolar), 3.13 mm (first molar), 3.31 mm (the base of the interproximal papilla of the first and second molars), and 3.39 mm (second molar). There was an overall increase in the thickness of the palatal masticatory mucosa as the distance from the gingival margin to the middle palatine suture increased, with the exception of the Ca-d (a point at 12 mm from the gingival margin of the canine) region. There was no significant difference in the thickness of the palatal masticatory mucosa between the groups with high or low palatal vaults. CONCLUSIONS: The palatal masticatory mucosa thickness increased from the canine to premolar region but decreased at the first molar region and increased again in the second molar region, with the thinnest area at the first molar region and the thickest at the second premolar region. The canine to premolar region seems to be the most appropriate donor site that contains a uniformly thick mucosa. CT can be considered an alternative method for the measurement of palatal soft tissue thickness.     

A Rationale For Not Connecting Implants to Natural Teeth

When restoring partially edentulous arches with implants, there are some practitioners who believe it is occasionally beneficial to connect implants to natural teeth. This connection is performed to gain shared support from the natural tooth and implant, prevent rotation of the restoration, or sometimes merely to retain the natural tooth. A discussion and review of the literature concerning this connection is presented, and a patient treatment is shown to illustrate potential complications.