What's New in Dentistry
Tissue-engineered odontogenesis in dog mandibles
Recently, researchers have reported the generation of toothlike structures from stem cells. This process is accomplished by seeding dissociated tooth bud cells onto biodegradable polymer scaffolds. The regenerated tissue consists of dentin and well-differentiated pulp chambers. These tooth structures are implanted in the omentum of the abdomen in rats. After 25 weeks, enamel tissue is also formed. However, to date, it is not known whether a tissue-engineered tooth would function when grafted into the jaw. A pilot for this type of research has now been accomplished and was recently published in the Journal of Oral and Maxillofacial Surgery (2006;64:283–289). The purpose of this study was to test whether the transplantation of dissociated odontogenic cells could induce the regeneration of tooth tissue in the canine jaw, which has less blood supply than the omentum. Eight male dogs aged 8 to 12 weeks were operated on to obtain unerupted first molars on both sides. The entire tooth bud tissues were minced into small pieces and dissociated with collagenase. Then, single cells from one tooth bud were seeded onto a fiber mesh and incubated for 12 hours. These isolated cell constructs were placed into the empty sockets from which the tooth had been extracted. Then, with time, intraoral radiographic and histologic examinations were used to determine whether the transplanted cells were calcified. After 24 weeks, microradiographic computed tomography showed regenerated hard tissues in the jaw, and histologic staining showed tubular dentin and bone. In the regenerated tissue, dentinal matrix had formed; however, enamel tissue and root formation were not observed. This is one of the first studies to show successful transplantation of tooth-engineered tissue into the jaw of experimental animals. The implanted cells were able to survive and form hard tissues. The authors believe that the next step in the process is to establish which of the cell types involved has the greatest capacity to regenerate tooth structures, because the success rate would increase if those cells could be enriched and transplanted. Someday in the not too distant future, surgeons may be transplanting teeth and not titanium implants into edentulous ridges.
Immediate implants have high success rates
Many long-term studies have shown the high level of predictability for titanium implants placed into edentulous alveolar ridges in humans. The most commonly used protocol allows a 6- to 12-month healing period following tooth extraction so that the implant can be placed into mature bone. However, studies have shown that about 45% of the residual alveolar ridge may be resorbed after tooth extraction, with the majority of the resorption occurring during the first 6 months after extraction. Therefore, immediate implant placement into extraction sockets has been proposed as a method to preserve the bone at the surgical site. In addition, immediate implant placement reduces the number of surgical procedures and the treatment time for the patient. However, the success rates of immediate implants has been questioned. A recent study published in the International Journal of Oral and Maxillofacial Implants (2006;21:71–80), documents the success rates of 1925 consecutively placed immediate implants from 1988 to 2004. This retrospective study involved a posttreatment examination of 891 patients in whom these implants had been placed. In all cases, the treatment required atraumatic tooth extraction, immediate implant placement, and mineralized freeze-dried bone grafting with an absorbable barrier to cover exposed implant threads. Implant failure was documented along with time of failure, age, gender, and reason for implant failure. The results showed that a total of 77 implants were lost in 68 patients. The overall implant survival rate was therefore 96.0%, with a failure rate of 3.7% prerestoration and 0.3% postrestoration. This study showed that machined-surface implants were twice as likely to fail as rough-surface implants. In addition, men were 1.65 times more likely to experience implant failure, and implants placed in sites from which teeth were removed for periodontal reasons were 2.3 times more likely to fail than implants placed in other sites. This study concludes that with a 96% survival rate after 16 years, immediate implant placement following tooth extraction may be considered to be a predictable procedure.
Chlorhexidine chip valuable for patients with chronic periodontitis
Chronic periodontitis is an infectious disease resulting in inflammation within the supporting tissues of the teeth, because of the colonization of periodontopathic microorganisms in the gingival sulcus. The main therapeutic approaches for periodontal diseases include mechanical scaling and root planing to remove bacterial deposits from tooth surfaces. In addition, antibiotics and other chemotherapeutic agents are usually prescribed for patients who do not respond to conventional mechanical therapy. Adjunctive use of systemic antimicrobials has also been useful in treating recurrent periodontal pockets. However, these antimicrobials have side effects when used systemically, so local administration to specific periodontal pockets is more desirable. Therefore, antimicrobial chips of chlorhexidine have been developed to be placed in reticent periodontal pockets in order to combat the periodontal pathogens. A recent study published in the Journal of Periodontology (2006;77:437–443) aimed to determine the effect of chlorhexidine chips on the levels of prostaglandin-2, which is a strong mediator of the inflammatory process. This was a randomized single-blind study carried out in parallel design on a sample of subjects with chronic periodontitis. The test group received scaling and root planing plus a chlorhexidine chip placed in the sulcus. The control group received only scaling and root planing. The subjects were evaluated sequentially over a 6-month period. The results of this study showed that the reduction in mean probing depths was greater in the experimental group than in the control group. In addition, the levels of prostaglandin-2 showed greater reduction in the group with the chlorhexidine chip than in the control group. Based upon the findings of this study, the chlorhexidine chip reduced prostaglandin-2 levels in the crevicular fluid and had a positive effect on clinical parameters when used as adjunctive therapy along with scaling and root planing in patients with chronic periodontitis.
Age and gender are powerful predictors for periodontal attachment loss
Periodontal diseases affect a relatively high percentage of the adult population and are the most frequent cause of tooth extraction for people over 40 years of age. In order to combat periodontal disease, it would be helpful to know which people are at higher risk, and to identify risk determinants for severe clinical attachment loss in a large sample of subjects. A study published in the Journal of Periodontology (2006;77:479–489), reported on the findings of a large cross-sectional survey of over 2000 subjects aged 35 to 64 years with at least six teeth. Each of the subjects had a complete full-mouth periodontal examination of four sites per tooth. The periodontal status of each subject was assessed by criteria based on the severity and extent of clinical attachment loss. The survey showed that 19.7% of the subjects had clinical attachment loss of greater than 5 mm. Older individuals had a 1.8 times higher risk of chronic periodontal disease than younger subjects. In addition, males were 1.7 times more likely than females to have clinical attachment loss. Subjects with greater body mass index had a 1.2 odds ratio for higher risk for periodontal disease. Finally, the number of missing teeth had a 1.1 odds ratio and the gingival bleeding index showed a 1.7 odds ratio for greater clinical attachment loss. In conclusion, this large cross-sectional study showed that age and gender are powerful independent predictors of clinical attachment loss, as is the gingival bleeding index. To a lesser extent, the number of missing teeth and body mass were also good predictive variables. Therefore, the patient profile for severe clinical attachment loss is an older overweight male with missing teeth and a higher gingival bleeding index.
High carbonated soft drink consumption leads to increased dental caries in primary teeth
It has been reported that contemporary fluid consumption patterns of children are now more diverse than in past years, because carbonated soft drinks and fruit juices have replaced much of the previous consumption of water and milk among children. The implications of these changes in fluid consumption have not been well studied, especially the association between carbonated soft drink consumption and dental caries. A study published in the Journal of Dental Research (2006;85: 262–266) evaluated fluid consumption patterns among children aged 2 to 10 years in order to assess the association between high consumption of carbonated soft drinks and dental caries in the primary dentition among children in the United States. This analysis used fluid intake data from a 24-hour recall interview in the NHANES III study carried out from 1988 to 1994 on nearly 6000 children. Based upon analysis of the extensive data from this study, carbonated soft drinks comprised 8.5% of total fluid consumption among children aged 2 to 10 years. Milk and juice each comprised less than 20%, whereas plain water constituted about 32% of total fluid consumption. There were significant associations between fluid consumption patterns and sociodemographic factors. High carbonated soft drink consumption and high water intake appeared to be more characteristic of older children, aged 6 to 10 years. Boys showed slightly higher carbonated soft drink consumption than girls. African American children showed higher water consumption and lower milk consumption than children from other race/ethnic groups. White children showed a higher tendency toward high carbonated soft drink consumption than children from other race/ethnic groups. The children in the high carbonated soft drink consumption cluster showed a higher tendency toward caries experience than those children in the high milk and high water clusters. Children with a high milk consumption pattern had a tendency toward the lowest caries experience. The authors conclude that high consumption of carbonated soft drinks by young children is a risk indicator for dental caries in the primary dentition and should be discouraged.