Early orthodontic treatment: what are the imperatives?

BACKGROUND: Then authors provide a critical review of the issues involved in determining the appropriate timing of orthodontic treatment. Both single- and two-phase treatments are discussed and guidelines are offered to assist in formulating treatment plans. OVERVIEW: In providing orthodontic care for pediatric patients, clinicians often question whether to begin treatment early--during the primary or early-transitional dentition--or wait until all or most of the permanent teeth are present. The authors review the most current literature (from 1991 to 1999), including several recently completed and ongoing randomized clinical trials, to critically evaluate the effectiveness of each approach. PRACTICAL IMPLICATIONS: The controversy surrounding early vs. late orthodontic treatment is often confusing to the dental community. This article reviews both sides of the issue for orthodontic treatment of Class II and III malocclusions, as well as for the management of Class I crowding and problems in the transverse dimension. Early orthodontic treatment is effective and desirable in specific situations. However, the evidence is equally compelling that such an approach is not indicated in many cases for which later, single-phase treatment is more effective. Therefore, clinicians must decide, on a case-by-case basis, when to provide orthodontic treatment. For many patients, delaying treatment until later in their dental and skeletal development may be advisable.

Third molar management: a case for routine removal in adolescent and young adult orthodontic patients.

The role of the orthodontist is to treat patients to optimal function, aesthetics, and long-term stability. The controversy surrounding third molars has focused on the pathologic problems they may cause and the risk/benefits of their removal. Although malocclusion is not considered a disease, it is unreasonable to ignore the orthodontic issues related to third molars, especially in patients who make the investment to achieve an ideal occlusion. Part of a complete orthodontic treatment plan is a recommendation regarding third molars. The plan should include a rationale and recommendation for their removal based on the orthodontic treatment objectives.

Blockade of the initiation of murine odontogenesis in vitro by citral, an inhibitor of endogenous retinoic acid synthesis.

Endogenous retinoids are present in the embryonic mouse mandible and reach a concentration peak immediately before the formation of the dental lamina. Because exogenous retinoids alter the pattern of the dental lamina and the expression of epidermal growth factor mRNA (a transcript necessary for initiation of odontogenesis), the role of retinoic acid in the initiation of odontogenesis was studied here. Citral (3,7-dimethyl-2,6-octadienal), a known inhibitor of retinoic acid synthesis, was used to block the endogenous synthesis of retinoic acid in the mouse embryonic mandible before the formation of the dental lamina (gestational day 9). A 24-h exposure to citral totally blocked tooth formation in 7/10 mandibles. Reductions of endogenous retinoic acid concentrations were confirmed by high-performance liquid chromatography. Tooth formation was restored by simultaneous treatment with all-trans retinoic acid or 9-cis retinoic acid during the citral exposures (first 24 h of culture). Endogenous retinoic acid is necessary for the initiation of odontogenesis.

Orthodontic correction of maxillary flaring using provisional restorations.

An unconventional orthodontic correction can be accomplished by using preexisting provisional restorations, which can be modified for use in active tooth movement or splinted together for orthodontic anchorage. This technique has an advantage over conventional fixed appliance orthodontic therapy because it can accomplish tooth movement concurrently with restorative and periodontal therapy. Consequently, the timing or sequencing of periodontal and restorative treatment is optimal, and the overall treatment is more efficient. The learning objective of this article is to describe the minor tooth movement necessary to achieve the optimum occlusal scheme, crown form, and tooth position for the forces of occlusion to be displaced down the long axis of the periodontally compromised teeth. Once the occlusion, periodontal health, and crown contours for the provisional splinted restoration are acceptable, the final splinted restoration can be similarly fabricated, and it becomes an excellent orthodontic retainer.

Spatial distribution of endogenous retinoids in the murine embryonic mandible.

Retinoids play an important part in pattern formation during embryonic development. Exogenous retinoids alter the pattern of skeletal, neural and odontogenic tissues. Endogenous retinoids have been demonstrated previously in the murine embryonic mandible, reaching a concentration peak during the initiation of odontogenesis. It was now found that endogenous retinoids are present in a concentration gradient in the embryonic mouse mandible at the time of the initiation of the dental lamina. All-trans-retinoic acid was more concentrated in the incisor region and retinol in the molar region. These results, and the fact that exogenous retinoids produce supernumerary incisors and missing molars, suggest that all-trans-retinoic acid may instruct incisor morphology.

Effects of the intermediate retinoid metabolite retinal on the pattern of the dental lamina in vitro.

Retinoids have important roles in pattern formation during embryonic development and might act as endogenous morphogens. They are necessary for normal odontogenesis and excess retinol alters the pattern of odontogenesis producing supernumerary buds of the dental lamina in the diastema region of the mouse mandible. Because the metabolism of retinoids in the developing mandible is unknown, the effects of retinal (an intermediate metabolite in the local conversion of retinol to retinoic acid) on the patterning of odontogenesis were examined. Retinal produces supernumerary buds and enhanced epithelial proliferation in day-9 mandibles in vitro. The endogenous levels of retinal in the mandible at the time of initiation of odontogenesis were also measured by high-performance liquid chromatography. Retinal was detected only at day 10 and not at later stages of development. Local metabolism of this intermediate retinoid may be a rate-determining step in the production of active retinoid metabolites that may control the pattern of the dentition, which is established at the time of the appearance of the dental lamina at embryonic day 12.

Temporal distribution of endogenous retinoids in the embryonic mouse mandible.

Retinoids play an important part in embryonic pattern formation. They are necessary for normal differentiation of odontogenic tissues and, in excess, disrupt the pattern of tooth formation. Excess retinoids produce supernumerary buds of the dental lamina in the diastema region of the mouse embryonic mandible where teeth do not normally form. This effect is coincident with an increase in epithelial proliferation and an alteration in epidermal growth factor mRNA expression (a gene product necessary for tooth formation). It was found by high-performance liquid chromatography that endogenous retinoids are present in the developing murine mandible and that concentrations of some retinoids reach a peak at the time of the initiation of odontogenesis (dental lamina formation).

Stability of reconstituted methohexital sodium.

The purpose of this study was to determine the stability of reconstituted solutions of methohexital sodium over a 6-week period. Stability of methohexital was examined using reversed-phase high-performance liquid chromatography. The results indicate that reconstituted methohexital is extremely stable for up to 6 weeks when stored at 4 degrees C. When stored at room temperature, reconstituted solutions of methohexital contained increasing levels of degradation products and showed a corresponding decrease in methohexital over a 6-week period. However, the rate of degradation of the drug was slow, with less than 10% of the methohexital undergoing breakdown. In addition, tests for microbial contamination of the solutions stored at room temperature and under refrigeration were negative for up to 6 weeks. This study demonstrates that methohexital, when stored under refrigeration for up to 6 weeks, is virtually chemically identical to a freshly reconstituted solution of the drug. When stored at room temperature, there is some degradation of the drug, but it is not known whether the small amount of degradation is clinically significant. This study emphasizes the importance of obtaining scientific data to support changes in guidelines related to handling and storage of drugs.

Assay of ornithine decarboxylase activity by reversed-phase high-performance liquid chromatography.

Ornithine decarboxylase (L-ornithine carboxylase; EC 4.1.1.17; ODCase) is a key enzyme in the biosynthesis of polyamines. It catalyzes the decarboxylation of L-ornithine to putrescine. The high-performance liquid chromatographic (HPLC) method described here for determining ODCase activity combines the sensitivity of radiochemical detection with the separative capacity of HPLC without the necessity of generating a pre-column derivative. In this study, [1,2-3H]putrescine was separated from L-[2,3-3H]ornithine using reversed-phase HPLC eluted isocratically. This method was used to study ODCase from both prokaryotic and mammalian sources. With the ODCase from Escherichia coli we found the reaction rates to be linear for 5 min with an apparent Michaelis constant (KM) of 20 mM. After 1 h this activity had produced approximately four-fold more product at pH 5.0 than at pH 7.3. In contrast, the initial rate of ODCase from submandibular glands was linear for 60 min. Also, the rate of putrescine synthesis was ten-fold higher in the embryonic gland than in the adult which was 8-80 times lower than that of E. coli.

Distribution of taste and general sensory nerve endings in fungiform papillae of the hamster.

Sensory endings of chorda tympani and lingual (trigeminal) nerve fibers were identified by selective denervation and localized within specific regions of fungiform pipillae in the hamster. The chorda tympani was resected from the middle ear and the peripheral fibers were allowed to degenerate for 1, 3, or 8 days prior to perfusion-fixation and electron-microscopic examination of the anterior tongue. Taste buds were virtually devoid of intact nerves by 3 days following chorda tympani denervation. Remnants of the fibers were restricted to taste buds. Lingual fibers, on the other hand, persist in normal numbers after chorda tympani resection and populate perigemmal areas of connective tissue and extragemmal areas located apically in the squamous, nontaste epithelium surrounding the taste bud. This study provides evidence of a segregation of chorda tympani fibers in the taste bud and lingual nerve fibers in the apical fungiform papilla. The lingual nerve-epithelial arrangement and superficial location, near the least cornified area of the tongue, may be well suited for relatively sensitive somatosensation, possibly mechanoreception. Thus, the apical fungiform papilla appears to be a site where both taste and tactile oral stimuli interact with receptors.