Luc Dermaut

Apical root resorption of upper incisors caused by intrusive tooth movement: A radiographic study

The purpose of the study was to investigate whether root resorption of the upper incisors occurs during intrusion of maxillary incisors. It examines the possibility of a relationship between the amount of root shortening and duration of the intrusive force. The ratio of root length before and after intrusion was compared in 20 patients. In 66 incisors with an intrusion period of 29 weeks, an intrusion of 3.6 mm was performed. The control group consisted of 15 patients who underwent no orthodontic treatment. Consequently, 58 incisors had no intrusion. The follow-up time between 2 measurements was +/- 28 weeks. The findings clearly showed root shortening after intrusion. A mean resorption of 18% of the original root length was found. In comparison, none of the control patients showed root shortening. No correlation has been found between the amount of resorption and the amount and duration of intrusion. In combination with the apical deflection of the root, the nasal floor was occasionally a limiting factor for intrusion and this may have caused root resorption.

Soft-tissue profile preference

The relative influence on profile preference of the anteroposterior maxillomandibular relation, the lower facial height, and the form of the dorsum of the nose is a source of interesting controversy. In order to obtain more information on this subject, twenty-seven shadow profile photographs were artificially constructed to represent the main characteristics of the nine profile types proposed by Sassouni combined with three different kinds of nose dorsum. Each series of nine profiles was ranked according to the personal esthetic preference of 249 adults (mean age, 23 years). One group of test persons (40 females and 91 males) had no orthodontic background, while another group (49 females and 69 males) had received some orthodontic teaching. Chi-square tests of significance showed no significant difference between male and female participants in esthetic preference for the sex of a profile. Also, the difference in orthodontic knowledge had no significant effect on esthetic preference. Nose dorsum changes induced significant differences only in Class II normal profiles; convex noses were less appreciated. Calculation of average preference values revealed that Class I normal profile types were clearly the favored ones, followed by Class I deep profiles. Open profile types, on the contrary, were obviously the least appreciated. This sequence indicates that, in profile evaluations, vertical profile characteristics could be more important than anteroposterior features and that a lengthening of the soft-tissue profile is not desirable in most cases. Seven weeks after the first ranking of male profiles, 193 persons were retested. The rank correlation values according to Kendall showed that one out of four persons ranked profiles significantly different in the retest.

Location of the centers of resistance for anterior teeth during retraction using the laser reflection technique

The location of the centers of resistance for various symmetric units of the anterior maxillary dentition for a lingually directed force was studied in two dry human skulls. The units investigated were composed of two incisors, four incisors, and six anterior teeth. In addition, the effect of change in force magnitude on the location of the centers of resistance of these units was investigated. The laser reflection technique was used to study both the direction and magnitude of the initial displacement of the consolidated teeth under loading. The results indicated that the center of resistance shifted apically with the incorporation of a greater number of teeth into an anterior segment. With a unit of six anterior teeth, the apical shift of the center of resistance was the greatest. Increasing force levels had little effect on the location of the center of resistance of a given unit. This phenomenon was observed in both the skulls tested, suggesting that general trends may exist in the displacement characteristics of the dentition when subject to controlled force systems.

Experimental determination of the center of resistance of the upper first molar in a macerated, dry human skull submitted to horizontal headgear traction

Laser speckle interferometry, recently developed for noninvasive measurement of small displacements (microns), was used to study the movement of maxillary molars submitted to extraoral traction. Using an antenna-headgear at different horizontal levels, loadings of 700 gm were applied perpendicular to the long axes of these teeth. Bodily movement was observed when the traction line passed slightly occlusal to the trifurcation of the roots. Therefore, the center of resistance of the upper molar was experimentally localized at this level. Laser speckle interferometry proved to be a promising technique for dental research.

Comparison in shear bond strength of orthodontic brackets between five bonding systems related to different etching times: an in vitro study.

New adhesives are continuously being marketed. The adhesive-bracket bond is still the weakest point in orthodontic bonding. A new device for the measurement of shear bond strength values (SBS) of orthodontic brackets is presented in this article. With this device, five commercial products were evaluated for their SBS: Lee Bond (LB), Concise (C), Super C (SC), Achieve-no-mix (ANM), and Panavia Ex (PE). After applying Begg brackets of laminated minimesh on lower human incisors, the specimens were thermocycled. The products investigated produced high bond strengths. The products tested showed shear bond strengths that were significantly lower than those stained with PE. The application of PE yielded the highest shear values. Nevertheless, some characteristics of this product might be clinically somewhat inconvenient. There was no significant difference in shear bond strength between 15 and 60 seconds enamel etching before bond application.

A CLINICAL TRIAL COMPARING THE FAILURE RATES OF TWO ORTHODONTIC BONDING SYSTEMS

A clinical trial was carried out to compare the failure rates of a visible light-cured fluoride-releasing material with a chemically cured adhesive. Fifty patients were used for the trial and 762 brackets were bonded in a split-mouth experimental design. Bracket failures were reported over the full period of orthodontic treatment. Statistical data analysis was carried out by means of chi 2 tests. The results of this study indicate that brackets, bonded with a chemically cured material (Lee Insta-bond, Lee Pharmaceuticals, EI Monte, Calif.), showed significantly fewer failures than brackets bonded with the light-cured material (Orthon, Orthon Dental Inc., Victoria, Canada). When the site of bond failure was evaluated in an overall manner, there were significantly more lower than upper, and more posterior than anterior bond failures.

The effect of tooth size discrepancy on occlusion: An experimental study

The purposes of this experimental study are the following: (1) to compare the anterior and overall tooth size ratios reported by Bolton to values reported in epidemiologic studies, (2) to assess the accuracy of tooth size discrepancy measurements, (3) to investigate to what extent generalized tooth size discrepancy affects occlusion, (4) to investigate the effect of leveling the curve of Spee, and (5) to evaluate the effect of extraction therapy of 4 premolars on occlusion. For the first part of the study, Boltons mean anterior and overall tooth size ratio (as well as the extraction values) were compared with calculations derived from 4 publications reporting mean mesiodistal tooth width by using the t test (P </=.05). The second part of the study was carried out on a setup made from 1 dental cast of a male patient judged to have an ideal occlusion at the end of a nonextraction treatment. Our data reveal (1) no significant difference between the overall tooth size ratios of the Bolton values compared to 4 studies, but the anterior ratios were significantly different, (2) high reproducibility (99%) of tooth size discrepancy measurements, (3) that severe tooth size discrepancy affects the occlusion only a little, (4) that an excessive (6 mm) curve of Spee creates the poorest setup result, and (5) that extraction therapy only slightly affected the final occlusion. The effect of generalized tooth size discrepancy appears to be limited.

The center of resistance of anterior teeth during intrusion using the laser reflection technique and holographic interferometry

The aim of this investigation was to define the location of the center of resistance of various consolidated units of the maxillary anterior dentition using a dry human skull when subject to intrusive forces. The laser reflection technique and the holographic interferometric technique were employed to measure the displacement of the dentition to the applied forces. The units studied consisted of two central incisors, four incisors, and six anterior teeth. The incorporation of the lateral incisors into the upper incisor segment resulted in a small distal shift of the center of resistance (+/- 2 mm). However, when the canines were included into this unit, the center of resistance shifted distally by a significantly larger amount (+/- 7 mm). Increasing the magnitude of intrusive forces applied to the various units appeared to have no effect on the location of the center of resistance.

The Critical Apical Diameter to Obtain Regeneration of the Pulp Tissue after Tooth Transplantation, Replantation, or Regenerative Endodontic Treatment

INTRODUCTION Regeneration of pulp-like tissue in the pulp chamber after tooth transplantation, replantation, or in regenerative endodontic treatment is only possible if the apical foramen is open. According to the literature, the success of regeneration decreases considerably if the foramen is smaller than 1 mm when measured on radiographs. The aim of this study was to study histologically the relation between the width of the apical foramen and regeneration of tissue in the pulp chamber after autotransplantation. METHODS Fifteen single-rooted mature teeth of 3 adult beagle dogs were used. All experimental teeth were extracted and underwent apicoectomy. The teeth were photographed from the apical side, and the width of the foramen was calculated. The foramen width ranged from 0.24-1.09 mm. All teeth were replanted in infraocclusion. The observation period was 90 days after transplantation. RESULTS The 10 teeth with the smallest apical diameter, ranging between 0.24 and 0.53 mm, showed vital tissue in at least one third of the pulp chamber. The 6 most successful teeth showing vital tissue in the entire pulp chamber had an apical diameter between 0.32 and 0.65 mm, and 80% of the experimental teeth with a diameter varying between 1.09 and 0.31 mm showed vital tissue in at least one third of the pulp chamber 90 days after transplantation. CONCLUSIONS The size of the apical foramen seems not to be the all decisive factor for successful revascularization and ingrowth of new tissue after transplantation. The minimum width of the apical foramen has not been determined, but a size smaller than 1 mm does not prevent revascularization and ingrowth of vital tissue. In this animal study an apical foramen of 0.32 mm did not prevent ingrowth of new tissue in two-thirds of the pulp chamber 90 days after transplantation.

Histologic analysis of pulpal revascularization of autotransplanted immature teeth after removal of the original pulp tissue

The survival rate of replanted and autotransplanted teeth is mainly affected by the reaction of the pulp. Pulpal necrosis can cause periapical inflammation and inflammatory root resorption. The purpose of this study is to learn more about the pulpal changes in autotransplanted immature teeth whose pulp tissue was removed before transplantation. The experimental material consisted of 16 single-rooted teeth with open apices, from a beagle dog (3 months of age). At day 0, 4 teeth were extracted, the pulpal tissues were removed, and the teeth were then transplanted to their contralateral side. The same procedure was carried out on days 9, 16, and 23, each time for 4 single-rooted teeth. Longitudinal paraffin sections were made for histologic investigation. The results showed that, after 7 days, 2 of the 4 teeth had an ingrowth of new tissue over one fourth of their length. After 14 days, all 4 teeth had ingrowth (> or =one fourth of the pulp chamber). At the 21-day observation, more than half of the pulp chambers of all teeth were filled, and, after 30 days, there was total ingrowth in 3 of the 4 teeth. This new tissue consisted of well-organized and well-vascularized connective tissue.