Guided bone regeneration of large mandibular defects in a primate model

BACKGROUND: An earlier publication from our laboratory described the use of guided bone regeneration to fill large bone voids in the mandible created through en bloc resection in primates. The present report is an embellishment of this paper and describes bone regeneration experiments in 18 adult male Macaca mulatta monkeys to determine how long membranes must be in position to promote guided bone regeneration. METHODS: Thirty-six lesions were created in the mandibles of 18 monkeys in a standardized mandibular defect of 8 x 19 mm. Reinforced ePTFE membranes were placed in the animals and held in place with mini screws and sutures for anywhere from 1 to 12 months. No material was added to the defect. In addition to clinical studies, digital subtraction radiology and fluorescent labeling with tetracycline and histomorphometry are described. RESULTS: The results indicate that no bone gain was observed in membranes exposed for 1 month or less, but bone gain (approximately well over 90% of defects) was observed at 12 months when membranes were left in situ for 2 to 12 months (P <0.0001). No significant difference in the amount of bone gained at 12 months was observed for membranes left in place for intervals ranging from 2 to 12 months. A significant correlation between the amount of bone gain observed at 3 and 12 months was observed (P <0.0001). CONCLUSIONS: Data therefore suggest that membranes left in situ for 1 month or less result in minimal bone gain compared with membranes left in place from 2 to 12 months. In addition, labeling and stained sections clearly showed that the bone produced after 2 months of membrane placement is mature.     

Time-dependent decrease and seasonal variation of the porosity of recently erupted sound dental enamel in vivo

Recently erupted teeth are more sensitive to dental caries than teeth that have remained free from caries lesions for a few years after eruption. It has been hypothesized that this may be ascribed to differences in enamel porosity. The objective of the present work was to assess the time-dependence of electrical conductance, as an indication of porosity, of occlusal enamel in recently erupted permanent molar teeth. Fifty children aged 5-15 years of age, receiving regular dental care at six-month intervals, participated in the study when their first molar teeth (in 5- to 6-year-olds) or their second molar teeth (in 11- to 15-year-olds) had not been exposed to the oral environment for more than six months. On the first semi-annual check-up after eruption of a first or second molar, baseline diagnostic measurements, i.e., visual inspection and electrical conductance measurements (ECMs), were made at three or four pre-defined sites in the fissures. Subsequently, data collection was repeated every six months for three years. Sites were excluded from ECMs when a caries lesion was observed at a site by visual inspection. After 36 months, there were 257 sites in teeth considered sound upon visual examination. The ECM values of these sound sites showed a clear decrease with time after the first examination. The conductance decreased on average from 0.13 (Momega)(-1) to 0.059 (Momega)(-1). Since the conductance is assumed to be proportional to the porosity of the enamel, the latter decreased by a factor of 2.2 over the 36-month period. The results furthermore indicated a higher conductance for maxillary than for mandibular enamel. Almost all sites in that sample appeared to be in teeth that were observed for the first time during the months September to December. Electrical conductance, and therefore enamel porosity, of the sites showed a periodic variation with season of observation: In the fall, the conductance was higher than in the spring. This implies that a dentist should be more prudent in the fall than in the spring when indicating restorative treatment of an incipient caries lesion.     

Fatigue behavior of the zinc-phosphate cement layer

PURPOSE: Fatigue behavior of luting cement film between model fixed partial dentures (FPD) and their dies was investigated to gain a better understanding of the mechanical properties of zinc-phosphate cement. MATERIALS AND METHODS: Fifty-six brass dies were made, half of them with grooves and half without grooves. A cantilever FPD for each die was cast in Au-Pd-Ag alloy. Four linear strain gauges were attached to the marginal portions of each retainer. The FPDs were cemented to the dies using zinc-phosphate cement. A fatigue test machine was used to cyclically load the specimens with 50 or 100 N for 5.5 x 10(5) cycles (1 Hz) in 37 degrees C water. During the fatigue test, strain measurements were made after every 0.5 x 10(5) load cycles to discover if strain response was altered. After completion of the fatigue test, ultimate tensile strength of each specimen was measured and statistically analyzed by 2-way analysis of variance. RESULTS: With or without grooves, strain responses were the same at every periodic strain measurement throughout the 50-N fatigue test. For the 100-N fatigue test, strain responses for the specimens without grooves were different before and after cyclic testing, but there was no difference for the specimens with grooves. There were no significant differences in tensile strength among the specimens after the fatigue tests. CONCLUSION: No fatigue fracture was observed in zinc-phosphate cement film after repetitive loading. Repetitive loading may improve stress transmission within the zinc-phosphate cement film.     

Subgingival restorations with resin ionomer: a periodontal alternative

The successful use and placement of subgingival resin-ionomer restorations in both anterior root and molar furcation defects are demonstrated in this article. Sustained tissue health and minimal probing depths at the surgical site demonstrate clinical success. These case reports illustrate the continued success of alternative treatment procedures for restoring subgingival mechanical root or periodontal lesions.     

Clinicopathologic study of odontogenic keratocysts in Singapore and Malaysia

This was a retrospective study of odontogenic keratocysts in people from the Singapore-Malaysian region. The purpose of this study was to present the clinicopathologic features of odontogenic keratocysts in the Oriental population and to compare these data with those from other reported studies. Biopsy records from 1981 to 1992 of 61 cases of odontogenic keratocysts from patients in Malaysia and Singapore showed that 42.6% of patients were female and 57.4% of patients were male. Among patients with cysts, 75.4% were Chinese, 6.6% were Malays, 9.8% were Indians and 8.2% were other ethnic groups. The mean age of these patients was 26.98 +/- 15.38 years with a peak incidence occurring in the second to fourth decades. The location of the lesions was more often in the mandible (65.5%) than the maxilla (31.0%). There was a marked predilection for lesions to occur in the posterior mandible. Histologically, 90.2% of the cysts were lined with a para-keratinized stratified squamous epithelium while only 3.3% of the cysts were lined with orthokeratinized stratified squamous epithelium. Mixed para-keratinized and orthokeratinized epithelial linings were observed in 4 cases (6.5%). The cyst linings were mainly uninflamed (95.1%). Inflammation of the cyst wall was found in 42 cases (68.8%). Twelve (19.7%) cases contained keratin in the lumen. A satellite cyst was observed in only 6 cases (9.8%). In conclusion, most clinical and histological features seen in this study were similar to those found for Caucasians. The only clinical feature that was different was the peak age incidence, that ranged from the second to fourth decades, with an absence of a second peak. Odontogenic keratocysts presenting at the site of the dentigerous cyst were observed in 7 cases (11.5%).     

Syndromes 22. Rieger's syndrome

Rieger syndrome is a rare autosomal-dominant disorder characterized by defects of the anterior chamber of the eye, failure of the periumbilical skin to involute, and developmental malformations of the dentition. Recognition of the dental anomalies may result in the early diagnosis of this syndrome and prevent progressive visual loss.     

In vivo degradation of bleaching gel used in whitening teeth

BACKGROUND: The purpose of the study described here was to determine the in vivo degradation rate of 10 percent carbamide peroxide, or CP, gel in bleaching trays. The degradation rate indicates the remaining concentration of the active agent on the facial surfaces at various intervals. METHODS: The researchers fabricated bleaching trays with 0.5-millimeter reservoirs and loaded them with a 10 percent CP whitening gel. The tray was seated in place in 15 patients for six different intervals that ranged from 15 seconds to 10 hours. When the tray was removed, three samples were collected from each patient: the gel remaining in the tray; the adherent gel scraped from the teeth; and a "grab" sample from the reservoir of tooth no. 8. The researchers analyzed these samples for CP according to the method specified by the U.S. Pharmacopeial Convention. RESULTS: The percentage of CP recovered decreased as the intervals increased: 87 percent at 15 seconds, 10 percent at 10 hours. Log of tray, teeth and grab samples, respectively, at 15 seconds were 0.94, 0.98 and 0.96 and at 10 hours were -0.13, -0.38 and 0.11. The first-hour degradation rate for tray, teeth and grab samples, respectively, was 2.0 times, 3.6 times and one time the rate during the next nine hours. The within-subject repeatability of the samples was excellent. CONCLUSIONS: The degradation rate of CP during the bleaching process is biexponential. In the tray and teeth samples, the degradation rate was accelerated during the first hour. Further research is needed to determine the cause of this acceleration. CLINICAL IMPLICATIONS: The active agent in CP bleaching gel is available in bleaching trays for more than 10 hours. After two hours, more than 50 percent of the active agent is available, and 10 percent is available after 10 hours.     

Stimulation by low concentrations of fluoride of the proliferation and alkaline phosphatase activity of human dental pulp cells in vitro

Fluoride has been used for decades, either systemically or topically, to prevent dental caries. The purpose of this study was to clarify the effects of low concentrations of fluoride on proliferation, differentiation and extracellular-matrix synthesis in normal human dental pulp cells (DP-1 and DP-2) in vitro. The effects were compared with those on a human osteoblastic osteosarcoma cell line, TE-85. Fluoride at micromolar concentrations significantly and dose-dependently stimulated [3H]thymidine incorporation into DNA in DP-1, DP-2 and TE-85 cells, with optimal effects around 50 microM, by 127 +/- 7%, 124 +/- 0.6% and 152 +/- 13.4%, respectively. To assess the potential influence of fluoride on cell differentiation, the effects of mitogenic concentrations on alkaline phosphatase activity were measured. Fluoride significantly increased the enzyme's activity in DP-1 and TE-85 by 177 +/- 12% and 144 +/- 12.3%. To evaluate the effect on extracellular-matrix synthesis, the synthesis of type I collagen was indirectly determined by an assay of procollagen type I c-peptide production. Fluoride significantly increased that production by 150 +/- 8.7% in TE-85, but not in either DP-1 or DP-2. These observations suggest that fluoride, if used at low concentrations, could be a useful therapeutic agent where increased regeneration of dentine is desired, such as after pulp amputation, by stimulating the proliferation and differentiation of the dental pulp cells.     

Analysis of surgical referral patterns for endosseous dental implants

Endosseous implants have traditionally been surgically placed by oral and maxillofacial surgeons, periodontists, and general practitioners. The purpose of this study was to examine surgical referral patterns for patients receiving implants in the treatment of partial edentulism. The records of 542 patients who received 1,313 implants between 1993 and 1997 were analyzed. Data relative to anatomic area, patient demographics, type of implant system, and any complication encountered were collected. Surgical cohorts were compared using Wilcoxon's rank-sum or chi-square tests, and complication rates were estimated using survival analysis methods. Results indicate no significant difference (P > .05) between cohorts with regard to placement of implants in the anatomic locations of the anterior mandible, anterior maxilla, posterior mandible, and posterior maxilla. Patient demographic information was not statistically different, with the exception of mean patient age, where oral and maxillofacial surgeons have been younger patients (P < .0001). Relatively few complications were seen, with no significant difference in complications rates between cohorts (P > .05). The type of implant system used showed no significant difference with respect to anatomic location or complication occurrence (P > .05). This study indicates that implant surgical referral patterns were similar in this setting between periodontal and oral and maxillofacial surgeons, with the only difference being a tendency to refer younger patients to the oral surgeons.     

Perception of middorsum palatal stops from the speech of three children with repaired cleft palate.

OBJECTIVE: The purpose of this study was to examine listeners' perception of the middorsum palatal stop, a compensatory articulation used by individuals with repaired cleft palates. DESIGN: This study tested whether listeners could discriminate middorsum palatal stops from matched alveolar (/t/) and velar (/k/) stops using a two-button "change/no-change" procedure. It also explored how listeners identified the palatal stop by rating each sound on a scale of one to eight. PARTICIPANTS: Twenty listeners, 10 untrained and 10 trained in general phonetics (graduate students in speech-language pathology), participated in discrimination and identification tasks during a 1-hour session in the Speech Perception Laboratory at the University of Buffalo. MEASURES: Discrimination was measured using d-prime, a score based on listeners' hits, correct rejections, misses, and false alarms to the changes/no changes in the stimuli. Identification was measured by the mean rating score for each class of stops. RESULTS: Listeners discriminated middorsum palatal stops from alveolar and velar stops, but their ratings for the middorsum palatal stops did not differ from those for the regular stop consonants. The two groups differing in phonetic training did not perform differently. CONCLUSIONS: Listeners can discriminate middorsum palatal stops from other stop articulations, but they did not identify them differently from alveolar and velar stop consonants. The results suggest that considerable training listening to middorsum palatal stops is necessary for listeners to be able to reliably identify them.