Dan Lundgren

Continuous versus interrupted continuous orthodontic force related to early tooth movement and root resorption

The aim of the present clinical investigation was to assess the effects of continuous and interrupted continuous forces of the same magnitude (50 cN = 50 g) on orthodontic tooth movement and related adverse tissue reactions, i.e., root resorption. Thirty-two maxillary first premolars in 16 patients, 8 boys and 8 girls (mean age 13.9 years), were moved buccally by means of a fixed orthodontic appliance with a sectional arch. The patients were divided into two groups of 8, for experimental periods of 4 and 7 weeks. The continuous force was checked and reactivated weekly to 50 cN. The interrupted continuous force applied to the contralateral premolars was left uncontrolled for 3 weeks, after which the arch was made passive for 1 week for tissue rest and recovery. Tooth movements were studied on dental casts using a coordinate measuring machine (Validator 100, TESA SA, Renens, Switzerland). Horizontal tooth movement with continuous force was more effective than with interrupted continuous force after 7 weeks. Histological sections of the experimental teeth, however, showed no difference in the amount or severity of root resorption between the two forces. Individual variations in both the magnitude of tooth movement and the amount and severity of root resorption for both of the two force systems were great.

Marginal Bone Level Changes at Dental Implants after 5 Years in Function: A Meta‐Analysis

BACKGROUND It is important that peri-implant bone breakdown caused by, for example, undue load and/or peri-implantitis, is prevented or minimized. Some continuous loss of marginal bone is generally accepted, but the question remains as to what extent it must occur. PURPOSE The purpose of this study was to compile and compare data on peri-implant marginal bone level changes from prospective studies that have registered the peri-implant marginal bone level radiographically at the time of prosthetic loading, and after 5 years of follow-up for implant systems currently available on the market. MATERIALS AND METHODS A literature search was carried out to identify prospective studies on peri-implant marginal bone level changes around dental implants. To be included in a meta-analysis, the implant systems should have been subjected to at least two independent studies. Copycats without documentation were not accepted. RESULTS Forty prospective studies that presented with a 5-year data were identified. Three implant systems met the inclusion criteria of having at least two independent studies; Astra Tech Dental Implant System® (Astra Tech AB, Mölndal, Sweden), Brånemark System (Nobel Biocare AB, Göteborg, Sweden), and Straumann Dental Implant System (Institute Straumann AG, Basel, Switzerland). The pooled mean marginal bone level change amounted to -0.24 mm (95% CI -0.345, -0.135) for the Astra Tech Dental Implant System, 0.75 mm (95% CI -0.802, -0.693) for the Brånemark System, and 0.48 mm (95% CI -0.598, -0.360) for the Straumann Dental Implant System over 5 years, with a statistically significant difference (p < .01) between the systems. CONCLUSIONS The identified implant systems showed an annual bone loss below or much below what hitherto has been set up as a limit for success. A careful documentation of marginal bone level changes should be mandatory for all implant systems before being marketed. It is also time for revision of existing success criteria to refine the basis for clinical quality judgment of implant treatment.

Time-related root resorption after application of acontrolled continuous orthodontic force*

The aim of this investigation was to study root resorption after application of a weekly controlled, continuous orthodontic force of 50 cN (approximately 50 gm). Fifty-six maxillary premolars in 18 boys and 38 girls (mean age 13.8 years) were moved buccally with a fixed orthodontic appliance. The contralateral premolar served as a control. The experimental periods varied from 1 to 7 weeks with eight children in each group. Root resorption was registered after 1 week and occurred in all test teeth but four. The surface extension as well as the depth of the resorption showed a marked increase after 2 weeks. Starting from the third week, eight test teeth exhibited apical root resorption that had reached half way to the pulp, or more. After 7 weeks, the test teeth showed on average more than 20 times larger mean resorbed root contour than the control teeth. Individual variations were considerable regarding both extension and depth of root resorption within each test group and were not correlated to the magnitude of tooth movement achieved. The radiographs failed to reveal any adverse tissue reactions. The great individual variations in root resorption without association to the amount of tooth displacement indicate that so far unknown individual factors are influential in these adverse tissue reactions.

Effects of a doubled orthodontic force magnitude on tooth movement and root resorptions. An inter-individual study in adolescents

The aim of this clinical and histological study was to compare the effects of two controlled, continuous forces of 50 cN (approximately 50 g) and 100 cN (approximately 100 g) on tooth movement and root resorptions. The patients, consisting of 32 individuals, 14 boys and 18 girls (mean age 13.1 years), were divided into four groups of eight individuals. The experimental periods were 4 and 7 weeks. In this investigation, designed as an inter-individual study, only the maxillary first premolar on the right side was utilized. The test tooth was buccally moved by means of a fixed orthodontic appliance. A continuous, weekly controlled force of 50 cN was applied to 16 premolars and a force of 100 cN to the remaining 16 test teeth. The force declined on average 22 per cent during the first week when 50 cN was applied and 27 per cent when 100 cN was applied. Tooth movements were studied on dental casts using a coordinate measuring machine. After 4 and 7 weeks, the tooth movements ranged between 0.5 and 3.4 mm (4 weeks) and 2.7 and 7.1 mm (7 weeks) for 50 cN and between 1.0 and 2.9 mm (4 weeks) and 2.2 and 8.3 mm (7 weeks) for 100 cN, with no significant difference when the force magnitude was doubled. Root resorptions were registered in histological sections in all experimental teeth, more frequently after application of 50 cN compared with 100 cN after 7 weeks. However, the severity of root resorption (extension and depth of resorbed root contour and size of root area on histological sections) did not differ significantly when the applied force was doubled to 100 cN. Great individual variations were noted regarding both the magnitude of tooth movement and amount of root resorption.

Repair of orthodontically induced root resorption in adolescents.

The aim of this investigation was to study the reparative potential of orthodontically induced root resorption. Sixty-four maxillary right and left first premolars in 32 patients (15 boys and 17 girls, mean age 13.7 years) were moved buccally with fixed orthodontic appliances and a continuous force of 50 cN (approximately 50 g), activated weekly for 6 weeks. The patients were divided into 4 groups of 8. Retention periods varied from 1 week to 8 weeks. Histological preparations showed that root resorption affected all the test teeth. The percentage of resorptive areas that had begun to repair ranged from 28% after 1 week of retention to 75% after 8 weeks. The healing cementum was almost exclusively of the cellular type. Partial repair, with the resorption cavity walls only partially covered with cementum, was the most frequent type of repair during the first 4 weeks of retention (17% to 31%). Functional repair, with the total surface of the resorption cavity walls covered with varying thicknesses of cementum, dominated after 5, 6, 7 and 8 weeks of retention (33% to 40%). There were no large differences in the healing potential in the cervical, middle, and apical thirds of the root. After 8 weeks, three out of four resorptive areas showed some degree of repair. Individual variations in healing potential were large.

Guided bone regeneration of cranial defects, using biodegradable barriers: an experimental pilot study in the rabbit

The aim of this study was to test if a biodegradable barrier could be used to achieve proper bone healing of full-thickness trephine skull defects, applying the biological principle of guided tissue regeneration (GTR). Two New Zealand white rabbits were used. In each animal, 2 circular through-and-through bone defects with a diameter of 8 mm were created in the midline of the frontal and parietal bones of the calvarium. One defect was covered with the mucoperiosteal flaps without placement of an intervening membrane barrier (control). One test defect (test 1) was covered by a biodegradable, non-porous polylactic acid membrane on the outer (supra-calvarial) side of the defect, and 2 test defects (tests 2 and 3) were covered by similar membranes on both the outer and the inner aspects of the defects, prior to flap closure. 6 weeks postsurgically, the animals were sacrificed and the defect areas including surrounding tissues were harvested for histological preparation. The control defect was essentially occupied by supra-calvarial soft tissue, located in direct contact with the dural tissue. In the test cavities, there was a continuous bridge of regenerated bone extending from one edge of the defect to the other, although in test 1 not attaining the same thickness as the bone bordering the defect. In the 2 other test defects, the regenerated bone had reached a thickness almost corresponding to that of the surrounding bone. The bone regeneration was achieved without recourse to adjunctive bone graft materials.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term prognosis of extensive polyunit cantilevered fixed partial dentures

The aim of this retrospective study was to elucidate the long-term prognoses of extensive fixed partial dentures including unilateral or bilateral polyunit cantilevers in patients with healthy but reduced periodontal support. Following periodontal therapy 36 cross-arch fixed partial dentures with two or more cantilever units unilaterally or bilaterally were fitted in 34 patients. In the prosthodontic design, special attention was given to the retention to long parallel preparations, to the dimensions of the framework, and to the occlusal design. After completion of therapy, the patients were enrolled in a regular maintenance care program and followed up for a period of 5 to 12 years. During this follow-up period one abutment tooth was fractured in one patient. One fixed partial denture with extremely reduced periodontal support was lost as a result of complete periodontal breakdown from occlusal trauma. For 33 fixed partial dentures, neither periodontal nor technical complications occurred.

Membrane-guided bone regeneration: Segmental radius defects studied in the rabbit

We tested the principle of guided tissue regeneration (GTR) for healing segmental long-bone defects. 7 mm (3 animals) or 10 mm (5 animals) long segmental defects were created in the diaphyses of both radii in 8 rabbits. The defect on one side was covered with a barrier membrane of expanded polytetrafluoroethylene membrane shaped as a tube, while the contralateral side with no membrane served as the control. Healing was followed with radiographs obtained repeatedly during a 13- (n 3) or 27- (n 5) week period. Thereafter, the animals were killed and ground sections of the defect sites were prepared for histologic examination. Radiographically, the control sites showed some early subperiosteal callus formation and nonunion of the defects after 6 weeks. The bone ends were rounded off and sealed with cortical bone. No major changes were noted after 6 weeks. At the test sites, subperiosteal bone formation at the bone ends was first observed radiographically at 2 weeks. At 9 weeks, a thin cortical bone bridged the defect along the inner surface of the membrane. Histologically, an interrupted line of thin, cortical bone was observed along the inner surface of the barrier membrane. Fatty bone marrow occupied the central and largest volume of the defect. We conclude that it seems possible to use the principle of GTR to accomplish bone union of segmental long-bone defects.

Guided jaw-bone regeneration using an experimental rabbit model

The aims of this study were to evaluate the space-maintaining capacity of two biocompatible barrier materials and to assess the effect of barrier occlusiveness on the amount of regenerated bone. Defects were prepared in the edentulous area on both sides of the maxillas in 22 rabbits. The rabbits were divided into three groups. Gore-Tex augmentation material (GTAM) (ePTFE)-barriers were placed to cover the experimental defects and compared with totally occlusive or perforated titanium foils and uncovered control defects respectively. After four weeks of healing, histological analyses and morphometrical measurements demonstrated that the amount of regenerated bone tissue was about the same underneath the collapsed GTAM-barriers as in the controls. The highest degree of regeneration was obtained in defects underneath the titanium foils, particularly if they were perforated, whether or not they were covered by GTAM-barriers. It was concluded that the space-maintaining properties of a barrier may be at least as important as barrier occlusiveness when regenerating bone defects.

Occlusal force pattern during mastication in dentitions with mandibular fixed partial dentures supported on osseointegrated implants

The occlusal force pattern during chewing and biting was studied in eight edentulous patients whose dentitions had been restored with mandibular bilateral posterior two-unit cantilever fixed prostheses supported on osseointegrated titanium fixtures and occluding with complete maxillary dentures. The chewing pattern was comparable to that reported for subjects with complete healthy dentitions or with tooth-supported cross-arch fixed partial dentures. However, during chewing and swallowing the voluntary capacity of the jaw-closing muscles was used to a much greater extent. Contrary to reports for cantilevers in tooth-supported cross-arch unilateral posterior two-unit cantilever fixed partial dentures occluding with natural teeth, the posterior cantilever segments in the present fixture-supported cantilever prostheses occluding with complete dentures regularly exhibited the largest local forces. Despite this, material failures of this type of fixed prostheses are rare, as demonstrated in long-term follow-up studies.