Effects of long-term occlusal hypofunction and its recovery on the morphogenesis of molar roots and the periodontium in rats

Abstract

Objectives: To investigate the effects of long-term, artificially created, hypofunctional occlusion and its recovery on the morphology of rat molar roots. Material and Methods: Eighteen 5-week-old Wistar-strain male rats were randomly divided according to their periodontal conditions into normal, hypofunctional, and recovery groups (n 5 6 in each). In the experimental hypofunctional and recovery groups, a bite-raising appliance was set to produce hypofunction at the molar region. All groups were analyzed at 16 weeks of age using three-dimensional micro-computed tomography. Root length, width, and area as well as the thickness and the area of the periodontal ligament (PDL) space of the maxillary first molar were calculated. Results: Roots were longer and narrower in the hypofunctional group than in the control group. The mesial root in particular showed a dramatic change. Root area also decreased significantly in the hypofunctional group compared to the other groups. Moreover, the PDL thickness and area decreased significantly in the hypofunctional group compared to the control group, but increased in the recovery group compared to the hypofunctional group. Conclusions: These findings suggest that root size and PDL structure may be reduced due to disuse atrophy resulting from a defect in occlusal function, but may be recovered following a gain of occlusal stimuli. (Angle Orthod. 2013;83:597-604.)

Restoration of a vertical alveolar bone defect by orthodontic relocation of a mesially impacted mandibular first molar

“…Advancing age, especially over 30 years, has been associated with the failure of orthodontic eruption of impacted teeth. 10,11,35,36 Histologically, teeth that are nonfunctional for a prolonged time such as impacted teeth undergo pathologic changes: eg, disuse atrophy of the periodontal ligament 37,38 and replacement resorption 39 that prevents orthodontic tooth movement. Therefore, the prognosis of an impacted tooth in a patient older than 30 years is considered poor.…”

Prevention of root resorption in hypofunctional teeth by occlusal function recovery

“…We developed an experimental hypofunctional model in the molar region using a bite-raising appliance. 7,8 This method makes it possible to stimulate a hypofunctional condition in the molar region and to return to normal occlusion after removal of the appliance by the result of soft X-ray images at 16 weeks of age. All of the animals also exhibited normal growth without any significant differences among the experimental groups from 16 weeks to 19 weeks, with the exception of the temporary body weight loss by the attachment of the appliance of bite plate and QH, respectively.…”

“…Two experimental groups, hypofunctional and recovery, were established. In the hypofunctional group, an appliance consisting of a metal cap made of band material (3M Unitek Co, Tokyo, Japan) and an anterior bite plate made of new ST lock base (Dentsply-Sankin, Tokyo, Japan) were bonded with composite resin (Clearfil Majesty LV, Kuraray Co Ltd, Kurashiki, Japan) on the maxillary and mandibular incisors, respectively 7,8 ( Figure 1A). In the hypofunctional group, the appliances were used for 11 weeks.…”

“…5,6 Moreover, it is assumed that the root and PDL structures may be less developed because of disuse atrophy resulting from defective occlusal function, and that these structures may recover after occlusal stimuli is regained. 7 However, it still remains unclear whether or not root resorption of hypofunctional teeth is more prominent during experimental tooth movement and can be prevented by the recovery of occlusal stimuli. It is also unclear if root resorption during orthodontic tooth movement is associated with the expressions of receptor activator of nuclear factorkB ligand (RANKL), macrophage-colony stimulating factor (M-CSF), and interleukin (IL)-8.…”

Bone changes around the maxillary posterior teeth opposing the implants in mandible: a clinical study

“…Bone is constantly remodeling itself in response to occlusal stimuli and other factors. 8,9 When the teeth are extracted, the antagonist teeth are in a nonfunction or hypofunction state for several months. This situation is especially related to implant restoration, because of 3 to 6 months waiting for osseointegration of implants.…”