Bone physiology of tooth movement, ankylosis, and osseointegration

Tooth movement is a highly conserved physiologic mechanism for continuous adaptation of the dentition. Physiologic drift of teeth is essential for maintaining appropriate stomatognathic function over a lifetime. Orthodontics is a therapeutic exploitation of this physiologic mechanism. The relative position of a tooth is dictated by the equilibrium of forces acting on it. The periodontium is an “organ” of functionally coordinated tissues that responds to continuous loads. The critical adaptive tissue for the expression of tooth movement is the periodontal ligament. Finite element modeling suggests that differential levels of stress in bone and its supporting soft tissue control the tooth movement response. With regard to orthodontics, bone formation is analogous to the orthopedic hypertrophic response, whereas bone resorption corresponds more closely to fatigue failure. Ankylosed teeth and osseointegrated implants can provide good occlusal function and serve as effective orthodontic anchorage. Using fatigue failure mechanics, implants can serve as anchorage to move ankylosed teeth. When healthy teeth are moved into atrophic areas of the alveolar process, substantial amounts of new bone and attached gingiva are produced. Orthodontics is a form of tissue engineering.     

The effects of intrusive loading on axial movements of impeded and unimpeded rat incisors: estimation of eruptive force

Axial movements of impeded and unimpeded rat mandibular incisors were measured following application and removal of intrusive loads of 1, 2, 5, 10 and 20 mN in a stepwise order at intervals of 1h on erupting teeth. The tooth movements were recorded by a displacement detector under artificial respiration with halothane anaesthesia. The loading and unloading procedures brought about the tooth movements in two steps: an initial rapid movement immediately after application or removal of the load and a subsequent slow and gradual movement. The initial rapid intrusive or extrusive tooth movements were significantly greater in the unimpeded than in the impeded teeth at the same load. The forces to stop extrusive tooth movements, estimated from the formula of regression lines showing correlations between the intrusive loads from 0 to 5 mN and tooth movements (microm/30 min), were 4.2 mN in the impeded and 2.9 mN in the unimpeded incisors. We suggest that repeated shortenings of the rat incisor did not cause an increase in the eruptive force and that changes in the resistance of the periodontal ligament predominantly regulate the axial movement of the rat incisor.     

Assessment of tooth mobility using small loads

Abstract. Tooth mobility at loads between 20 p and 80 p was studied in maxillary incisors and canines in eight subjects with moderate periodontal disease. The periodontal conditions of the investigated teeth exhibited clinical criteria of gingival inflammation and a moderate loss of attachment. None of the subjects showed subjective or clinical signs of occlusal disturbances. In all, 35 teeth were investigated over the 12-week period following periodontal hygiene treatment, including oral hygiene instructions and removal of supra- and subgingival plaque and calculus.
During the course of the investigation, a gradual decrease of tooth mobility was observed amounting to a tooth mobility decrease of 65 % (using the corrective formula described by Mühlemann 1960) at 50 p load.
Tooth mobility curves within the 20–80 p loading area were transformed to lines of regression (Persson & Svensson 1980). Analyses of the lines showed significantly lower tooth mobility values 12 weeks after start of treatment.     

A quantitative assessment of the effects of axially directed extrusive loads on displacement of the impeded and unimpeded rabbit mandibular incisor

Extrusive loads of 0.01–1.0 N were applied to the impeded mandibular incisors of 12 rabbits. Tooth position was monitored continuously with a variable capacitance displacement transducer. On suddenly applying an extrusive load, a biphasic displacement of the tooth was recorded. A rapid extrusive phase was followed by a more gradual extrusion. A similar, but intrusive, biphasic recovery response was seen on suddenly removing the load. The group-mean displacements showed that for all phases the responses were force-dependent, though not linearly graded. For a given load, the group-mean displacements during the first phases of the extrusive and recovery cycles did not show significant differences. However, the displacement during the second phase of the extrusive cycle was significantly greater than that of the recovery cycle for a load between 0.2 and 1.0 N. Extrusive loads were also applied to unimpeded teeth. Though no differences between impeded and unimpeded teeth were observed in the biphasic displacement patterns, significantly greater mobility was seen for the unimpeded incisors in all phases. The findings show that biomechanical changes of the periodontal tissues, of importance to studies on tooth eruption, occur in the chronically unimpeded tooth.     

Alveolar bone loss induced by the orthodontic tooth movement under hypofunctional conditions in rats

PurposeTo examine the effect of occlusal hypofunctional conditions on orthodontic tooth movement and its relation to the structure and quality of alveolar bone using the rat model.Materials and methodsTwelve-week-old male Sprague-Dawley rats were divided into 4 groups of 8 animals each: normal occlusion (N) group, normal occlusion with tooth movement (M) group, occlusal hypofunction (H) group, and occlusal hypofunction with tooth movement (HM) group. In H and HM groups, the anterior bite plate and metal cap were attached to the maxillary and mandibular incisors using a light-curing composite resin to induce the occlusal hypofunctional condition. In M and HM groups, an orthodontic force was applied in a palatal direction to the buccal surface of the maxillary first molar (M1) using a nickel–titanium alloy wire. Micro-CT imaging and histomorphometric analysis using fluorescent bone labeling of the alveolar bone surrounding the M1s were performed in each group.ResultsTooth movement of M1 in HM group, was rather accelerated with enhanced tipping than in M group. Micro-CT analysis revealed significant decrease in bone volume fraction, bone mineral density and trabecular thickness of the interradicular bone in HM group among the experimental groups. The fluorescent labeling lines in the interradicular bone were decreased in number in H and M groups compared with N group. A few discontinuous irregular dotted lines-like labeling was observed in HM group.ConclusionThe occlusal hypofunctional condition accelerates orthodontic tooth movement of the respective teeth, while it results in severe bone loss in the surrounding alveolar bone.     

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目的比较Ⅰ、Ⅱ、Ⅲ类错验及正畸治疗后患者与个别正常验的咬合力差异,为正畸临床诊断和术后稳定性评价提供参考。方法于2006年1月至2008年12月选择来大连大学附属口腔医院正畸科就诊的无正畸治疗史的Ⅰ、Ⅱ、Ⅲ类错铪患者110例及正畸治疗后患者42例,另选择个别正常矜志愿者28名。采用T-ScanⅡ咬合力分析系统,对其[牙合]力总值进行比较分析。结果Ⅰ、Ⅱ、Ⅲ类错[牙合]的验力总值均低于个别正常[牙合]（P〈0．05）;正畸治疗后患者虽获得良好的咬合关系,[牙合]力总值增加,但与个别正常[牙合]比较,差异仍有统计学意义（P〈0．05）。结论正畸治疗可改善咬合关系,增加[牙合]力总值,但与个别正常[牙合]的[牙合]力总值仍有差异,推断牙齿在建立良好的咬合关系后,仍需要一定时间的咬合面磨合、神经肌肉的改建,才能更好地发挥咬合功能。     

Long-term follow-up of maxillary incisors with severe apical root resorption

The purpose of the study was to analyse the mobility of teeth with severe orthodontically induced root resorption, at follow-up several years after active treatment, and to evaluate mobility in relation to root length and alveolar bone support. Seventy-three maxillary incisors were examined in 20 patients, 10-15 years after active treatment in 13 patients (age 24-32 years) and 5-10 years after active treatment in seven patients (age 20-25 years). All had worn fixed or removable retainers; seven still had bonded twistflex retainers. Total root length and intra-alveolar root length were measured on intra-oral radiographs. Tooth mobility was assessed clinically according to Miller's Index (0-4) and the Periotest method. Crestal alveolar bone level, periodontal pocket depth, gingival, and plaque indices, occlusal contacts during occlusion and function, and dental wear were recorded. There was a significant correlation (P < 0.05) between tooth mobility, and total root length and intra-alveolar root length. No correlation was found between tooth mobility and retention with twistflex retainers. None of the variables for assessment of periodontal status, occlusion and function were related to total root length or tooth mobility. It is concluded that there is a risk of tooth mobility in a maxillary incisor that undergoes severe root resorption during orthodontic treatment, if the remaining total root length is < or = 9 mm. The risk is less if the remaining root length is > 9 mm. Follow-up of teeth with severe orthodontically induced root resorption is indicated.     

A computer model of the periodontal ligament space in man

An engineering model of the periodontal ligament fibres was used to calculate length changes in the fibres with: direct occlusal forces on the tooth, occlusal loads on other teeth in the arch and splinting. The fibre elongations appear to influence tooth eruption, the clinical behaviour of splinted and non-splinted teeth, and the establishment of vertical dimension of occlusion and occlusal plane height. The model also provides insight into the controversy surrounding the intermediate plexus of the ligament.     

The effect of age on morphology and eruption of the lower incisors in mature rats

OBJECTIVE: This study investigated the effect of age on tooth and periodontium morphology and on tooth eruption in the lower incisors of 28 female rats, initial age 10 weeks. DESIGN: Morphometric data of the incisors in three young mature rats (weight 199+/-2.4 g) were compared to that of three 18-week-old (weight 260+/-5 g) animals. The rate of eruption was monitored during 12 months in 11 rats with all teeth in occlusion and in 11 rats with one lower incisor kept constantly out of occlusion. RESULTS:: The incisors continued to enlarge after the animals reached maturity with the size of the teeth increasing both longitudinally and circumferentially. Tooth volume increased by 21%, while that of the periodontal ligament was enlarged by only 12%. The rate of impeded eruption declined steadily from a mean value of 542+/-49 microm/day during the first experimental month to a mean value of 443+/-25 microm/day during the concluding month (p<0.05). The eruption rate of the teeth exceeded that of attrition rate by 2.4%. The unimpeded eruption proceeded steadily throughout the experimental year, at a mean rate of 811+/-12. CONCLUSIONS: Apparently in mature rats age has no effect on the genetic potential as expressed by the unimpeded eruption. In the impeded teeth age does affect the phenotypic expression of the eruptive function governed by occlusal forces as well as by the form and size ratio of the tooth and its PDL.     

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提要：牙齿松动是牙周病主要的临床症状之一。如何治疗松动牙、防止牙周炎进行性加重、尽可能地保存牙齿、促进牙周组织的重建再生,是牙周科医生致力于解决的主要问题。经牙周基础治疗、去除危险因素、消除牙周组织炎症并建立平衡牙合后,多数患牙的松动度可不同程度减轻。而松动度较大的患牙经牙周治疗也很难恢复正常,并影响咀嚼功能,产生继发性牙合创伤,使得牙周组织破坏、吸收加剧。对动度较大的松动牙进行固定,消除其创伤,减轻牙合力负担,使之行使正常咬合功能,牙周膜接受功能性刺激,从而促进牙周组织的修复和愈合。因此,松牙固定是牙周治疗的必要措施。牙周炎的松牙固定是将单根或多根患牙与健康牙通过夹板连接成一个稳固的“多根牙”,建立起一个新的咀嚼单位。本文对牙周病的松动牙固定、各类牙周夹板在临床上的使用及夹板固定技术做一介绍。     

Tooth autotransplantation in a free iliac crest graft for prosthetic reconstruction

This report documents successful tooth autotransplantation to a free iliac crest graft in an exemplar case. A 14-year-old male patient was operated thrice with increasing amounts of resection for recurrent odontogenic myxoma. When mandibular continuity resection finally was performed, a free iliac crest block autotransplant was used for reconstruction. Upon metal removal 5 months later, 3 wisdom teeth with two-thirds complete root development were transplanted to the free graft and retained by fixed orthodontic appliances including skeletal anchorage with orthodontic microscrews. Tooth graft taking was awaited for 8 weeks with retention. Following undisturbed healing without occlusal forces, 6 months of orthodontic treatment intentionally extruded the autotransplanted teeth to antagonist contact. The third and most dorsal tooth became mobile after 3 months and was lost. The surviving 2 teeth were fitted by a prosthetic bridge as extrusion into the occlusal plane was not completely successful. This exemplar case shows benefit of tooth autotransplants in selected cases of jaw reconstruction with distal bone autotransplants as alternative to dental titanium implants and suprastructures. Orthodontic microscrews can moreover support tooth movement and positioning as anchorage device in altered anatomy.     

Pathologic tooth migration

Pathologic tooth migration (PTM) is a common complication of moderate to severe periodontitis and is often the motivation for patients to seek periodontal therapy. In this review of the literature, available information concerning prevalence, etiology, treatment, and prevention of pathologic tooth migration is summarized. Prevalence of PTM among periodontal patients has been reported to range from 30.03% to 55.8%. A survey of the literature regarding chief complaints of periodontal patients support these high prevalence findings. The etiology of PTM appears to be multifactorial. Periodontal bone loss appears to be a major factor in the etiology of PTM. Many aspects of occlusion can contribute to abnormal migration of teeth, and more than one of those factors may be present in an individual patient. Soft tissue forces of the tongue, cheeks, and lips are known to cause tooth movement and in some situations can cause PTM. Also considered important in the etiology of PTM is pressure produced from inflammatory tissues within periodontal pockets. Because extrusion is a common form of PTM, clinical observations support the theory that eruption forces sometimes play a role in the etiology of PTM. Many oral habits have been associated with PTM which are often difficult for the therapist to detect. Most cases of severe PTM require a team approach to achieve success. Periodontal, orthodontic, and prosthodontic treatment are often required. Many patient variables enter into the selection of treatment for PTM. In early stages of PTM, spontaneous correction of migrated teeth sometimes occurs after periodontal therapy. Light intrusive forces are used successfully to treat extrusion and flaring forms of PTM. Based on the literature reviewed, it appears that many cases of PTM could be prevented through the early diagnosis and treatment of periodontal disease, occlusal contributing factors, gingival enlargement, and oral habits.     

Segmental alveolar distraction for the correction of unilateral open-bite caused by multiple ankylosed teeth: a case report

Ankylosed teeth fail to erupt to meet their counterparts in the opposite jaw. In cases where ankylosis occurs in multiple teeth, the occlusion shows an open bite. This article describes a case of unilateral open bite caused by multiple ankylosed teeth, where treatment involved segmental alveolar bone distraction. A 25-year-old female patient presented with a left-sided unilateral open bite. On the left-hand side, only the lower incisors were not ankylosed. On the right, the maxillary first molar was ankylosed. All these ankylosed teeth were positioned below the occlusal plane. Her mother and brother also had multiple ankylosed teeth, and a familial cause was considered. Orthodontic tooth movement was considered impossible and segmental osteotomy on the left maxillary alveolar bone and downward bone distraction were performed as an alternative. A distractor consisting of orthodontic bands, wires and screws was devised and worn in the left mandibular dentition. Multi-bracket orthodontic appliances were also used for distraction. The amount of vertical movement was 7 mm at the premolar region. Five months after distraction, the multibracket appliance was removed, and fixed and removable retainers were placed. Eight months after distraction, prosthodontic restorations on the occlusal surfaces of the ankylosed teeth were made to obtain the final occlusion. The unilateral open bite was successfully treated and a good occlusion was obtained. The occlusion has shown good long-term stability for more than 3 years.     

Tooth movement and changes in periodontal tissue in response to orthodontic force in rats vary depending on the time of day the force is applied.

The purpose of this study was to investigate whether there are any differences in tooth movement or in the response of periodontal tissue to orthodontic force when the force is applied at different times of the day. One hundred 6-week-old male Wistar rats were divided into one control group without force application and three experimental groups based on the time of day the force was applied to the upper first molars. Animals in the whole-day group received force continuously throughout the experimental period, while animals in the light- and dark-period groups received force only during the light (07:00-19:00) or dark period (19:00-07:00), respectively. Tooth movement was measured using the occlusal view of a precise plaster model with a profile projector. Periodontal tissues were evaluated histologically. The time course of tooth movement varied among the groups. Tooth movement over 21 days in the whole-day and light-period groups was about twice that as in the dark-period group. The formation of new bone on the tension side in the whole-day and light-period groups was more than twice that as in the dark-period group. On the pressure side, more osteoclasts appeared on the alveolar bone in the whole-day and light-period groups than in the dark-period group. The light-period group showed less extensive hyalinization of the periodontal ligament (PDL) than the whole-day group. The area of root resorption on day 21 also varied among the groups. Interference by masticatory forces did not seem to be a principal cause of the decreased tooth movement in the dark-period group. These results indicate that there are considerable variations in tooth movement and in the response of periodontal tissue to orthodontic force when the force is applied at different times of the day in rats. The results suggest that diurnal rhythms in bone metabolism have important implications in orthodontic treatment.     

HSP70在大鼠牙移动过程中的表达及其生物学意义

目的:研究大鼠磨牙移动过程中诱导型热休克蛋白70(HSP70)在牙周组织中的动态表达特点,推测其在牙周组织改建中的生物学意义。方法:建立大鼠牙移动的动物模型,采用免疫组织化学方法观察大鼠磨牙移动1、3、5、7、14d内诱导型HSP70在牙周组织中的动态表达及定位情况。结果:HSP70的表达在牙周膜受力早期呈强阳性,随后表达逐渐减弱,至14d为弱阳性;同一时期牙周膜的张力侧和压力侧诱导型HSP70的表达存在差异。结论:HSP70在大鼠磨牙受外力移动过程中呈现由强到弱的动态变化及区域性变化,这可能与牙周组织损伤的应激保护和改建过程中蛋白合成的需要有关。     

Segmental alveolar distraction for the correction of unilateral open-bite caused by multiple ankylosed teeth: A case report

Abstract

Ankylosed teeth fail to erupt to meet their counterparts in the opposite jaw. In cases where ankylosis occurs in multiple teeth, the occlusion shows an open bite. This article describes a case of unilateral open bite caused by multiple ankylosed teeth, where treatment involved segmental alveolar bone distraction. A 25-year-old female patient presented with a left-sided unilateral open bite. On the left-hand side, only the lower incisors were not ankylosed. On the right, the maxillary first molar was ankylosed. All these ankylosed teeth were positioned below the occlusal plane. Her mother and brother also had multiple ankylosed teeth, and a familial cause was considered. Orthodontic tooth movement was considered impossible and segmental osteotomy on the left maxillary alveolar bone and downward bone distraction were performed as an alternative. A distractor consisting of orthodontic bands, wires and screws was devised and worn in the left mandibular dentition. Multi-bracket orthodontic appliances were also used for distraction. The amount of vertical movement was 7 mm at the premolar region. Five months after distraction, the multibracket appliance was removed, and fixed and removable retainers were placed. Eight months after distraction, prosthodontic restorations on the occlusal surfaces of the ankylosed teeth were made to obtain the final occlusion. The unilateral open bite was successfully treated and a good occlusion was obtained. The occlusion has shown good long-term stability for more than 3 years.     

Short-term extrusion of isolated teeth of adult monkeys (Macaca fascicularis)

By means of a variable capacitance device, the occlusal movements of 12 fully-developed teeth were recorded in 6 adult monkeys. Sustained extrusion was seen, with rhythmic pulsations due to the heart beat and to breathing. Extrusion varied from 10 to 138 μm over periods of 40–360 min, and became progressively slower with time. Because of the protracted nature of the extrusion, it is probable that these tooth movements were caused by forces generated in the periodontal ligament resulting from biochemical changes in the periodontium rather than by vascular alterations, and occurred as a result of the removal of intrusive loads from the opposing teeth.     

An interdisciplinary treatment to manage pathologic tooth migration: a clinical report

Pathologic tooth migration (PTM) is a common symptom of periodontal disease and a motivation for the patient to seek dental therapy. The primary factors causing PTM are periodontitis and occlusal trauma. Comprehensive treatment for managing a moderate degree of PTM, including periodontal, orthodontic and prosthodontic treatment is described. Increasing the occlusal vertical dimension (OVD) with provisional restorations was attempted to create space for retracting maxillary flared teeth. Retraction and intrusion of maxillary flared incisors were achieved by a sectional orthodontic appliance. Splinted crowns from maxillary right lateral incisor to left lateral incisor were fabricated and connected to posterior prostheses by means of attachments to prevent relapse and to provide long-term stability.     

下颌骨牵引成骨区即刻牙移动的实验研究

目的：研究下颌骨牵引成骨后在新骨区即刻牙移动时牙周组织的改建行为及牙移动规律。方法：选择4只牙列完整的Beagle犬,其中2只犬建立双侧下颌骨牵引成骨动物模型,牵引完成后,即刻以30g力远中移动下颌第三前磨牙进入牵引成骨区;另外2只犬拔除双侧下颌第四前磨牙后3个月,以30g力远中移动下颌第三前磨牙。实验中,每周加力1次拍摄X线片,并记录牙移动速率。牙移动8周后,观察实验牙及其牙周组织特点。测量数据采用SPSS12.0软件包进行t检验。结果：实验牙借助自制的持续加力装置移动进入牵引成骨区,实验牙未产生倾斜,牙无明显松动,牙根未见明显吸收。实验组牙移动速度显著快于对照组,P〈0.01。组组织学观察发现,牙槽骨和牙周膜未出现不可逆性损伤。结论：牵引成骨区的新生骨质中,牙可以快速而平稳地移动。