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The osteopetrotic op/op rats suffered from a complete failure of tooth eruption in association with a reduced bone resorption. An unresorbed occlusal bone overlaid the germs which remained embedded in bone. The process of prefunctional eruption in limited growing teeth depends on the resorption of the alveolar bone covering the germs. The aim of this study was to investigate the effects of hematopoïetic grafts in newborn op/op rats on the process of prefunctional eruption. Fifteen op/op treated rats were used for radiographic, microradiographic and histologic examinations. After transfusion of bone marrow cells, we observed the restoration of bone resorption and a delayed eruption of the molars. The incisors never erupted. They developed odontome-like tumors near their apices. These results confirm the dependence of tooth eruption on bone resorption.

Thirty-one healthy patients whose third molars needed to be removed were randomly placed into two groups. Before sedation the control group (n = 16) received normal saline solution and the experimental group (n = 15) received 125 mg of methylprednisolone intravenously. Swelling was measured by photographic and face-bow techniques, trismus was determined by measuring maximal interincisal opening, and pain was evaluated by asking the patients to report the number of pain pills they used and assess th severity of their pain daily. The swelling and pain, but not the trismus, that developed after third molar removal were significantly reduced by a single dose of methylprednisolone.

The effect of age on dental tissues was studied on histologic sections of totally impacted teeth obtained from patients between 11 and 76 years of age. Impacted teeth were used in order to obviate the influence of the environmental effects prevalent in the oral cavity. The presence of concentric denticles and diffuse calcifications was determined, and the width of secondary dentin, predentin, and cementum was measured. The width of predentin and cementum increased linearly with age, whereas the aging process of secondary dentin formation and diffuse calcifications followed a different pattern. The incidence of concentric denticles was identical for all age groups.

Transmigration of impacted mandibular cuspid is a rare finding. A cuspid is classified as "transmigrated" when more than half of its length has passed the mid-line. 13 cases of transmigration of impacted mandibular cuspids are presented, 3 of which occurred in pairs, raising the total number of teeth to 16. Radiographs showed positions ranging from a vertical impaction, to a cuspid having crossed the mid-line completely, reaching the first molar area of the opposite side.

In an attempt to make a dynamic study of the isoelectric point and the chargeability of human dental enamel, an electrochemical approach was utilized. Zeta potential of three kinds of the enamel was measured by a streaming potential method. As a result, these isoelectric points could be decided.

Erupted and impacted teeth from young (12 to 24 years of age) and older persons (over 50 years of age) were bonded by a standard technique using etching times of 0, 15, 30, and 60 seconds. Two subgroups of teeth were soaked for 7 days and compared with those in the remainder of the group. Test specimens were loaded in shear to bond failure by means of a testing machine with a 200- kg load cell and a crosshead speed of 5 mm/minute. Results indicated insignificant bond-strength differences between young-impacted and young-erupted teeth for any given etching time. Very small bond-strength differences were found for various etching times (15, 30, and 60 seconds). A significant difference was found between 24-hour soak and 7-day soak for the etching times of 30 and 60 seconds only.

In 79 of 124 children with bilaterally located widened follicles around non-erupted canines one of the maxillary canines was chosen by lot for surgical exposure of the tooth crown. In seven cases both maxillary canines were exposed. The remaining 38 children were radiographically controlled at certain time intervals as were the 86 cases where surgery was performed. The follicles removed from 52 cases were histologically examined. The result showed that surgical exposure did not enhance the eruption of the tooth. The histological examination showed that the histologic appearance of the extirpated follicle did not correspond to the radiographically verified width of the pericoronal space. The specimens were composed of a loosely arranged fibrous connective tissue with an epithelial lining occurring in 77% of the cases. The epithelial lining consisted of reduced enamel epithelium and showed in none of the cases squamous metaplasia or keratinization. Nor was there any clinical or histologic sign of a neoplastic or cystic change of the follicle.

The present study supports previous findings that root resorption takes place simultaneously with and after the elimination of hyalinized tissue. The cementoid layer and the more mature periodontal collagen fibers adjacent to cementum are possible barriers preventing root resorption. The microenvironment around hyalinized tissue is favorable for the introduction of hard-tissue resorbing cells. The findings show that the elimination of hyalinized tissue leads to the removal of the cementoid and the mature collagen thus leaving a raw cemental surface without a barrier. It is therefore hypothesized that such an area is readily attacked by odontoclasts. Once resorption lacunae are established, the cementum is resorbed from the rear as an undermining process. By continued orthodontic force application the resorption process will proceed even after all hyalinized tissue is eliminated. If the orthodontic force is discontinued or falls under a certain level, the resorption lacunae are repaired.

Surgical exposure may be an integral part of orthodontic treatment of impacted teeth. In some cases the surgical procedure alone results in eruption and alignment of such teeth. The nature of the mechanism that starts concomitantly with the removal of covering tissues is not known. The aim of this investigation was to study factors associated with eruption as well as the eruption route of impacted and unerupted teeth following surgical exposure. The material consisted of 542 impacted teeth in 389 patients. The findings given strong support to the hypothesis that forces within surrounding tissues act upon the exposed crown in such a way as to direct it toward the area where the tissues were removed.

A longitudinal study, using three views simultaneously, was conducted on twenty North American black males to investigate mandibular third molar eruption. Each subject had two third molars present. Forty third molars were studied. Lateral, posteroanterior, and oblique (45 degrees left and right) cephalograms, along with plaster casts, were used. The following observations on the third molars were made; the age at which they can be identified; angulation of the occlusal surface; eruptive path, including the vertical, anteroposterior, and buccolingual positions; and the age of delineation between being unerupted or impacted, including factors related thereto. The Fisher's exact test from the SPSS package and the central tendency were the statistical instruments used to aid in interpreting the data. In some persons the crypt of the developing third molar was seen as early as 7.5 years and the occlusal surface was identified as early as age 8 years, with a mean of 9.75 years. Third molars usually form in the ramus with the distal cusp above the occlusal plane, the occlusal surface of the molar has a great cant facing anteriorly, the tooth descends below the occlusal plane, and appears to upright around 14 to 16 years of age. The impaction of the mandibular third molar is a complex multifactorial mechanism. The wide buccal location of mandibular third molars and the inadequate anteroposterior space between the distal surface of the second molar and the anterior surface of the ramus are important factors in third molar impaction. This study does not support the concept of early prediction of third molar impaction and enucleation of the asymptomatic developing third molars. If possible, the final decision for extraction of asymptomatic mandibular third molars that appear to be impacted should be delayed until after the age of 16 years.