The effects of altering vertical dimension onthe masticatory muscles and temporomandibular joint

The effects of increasing occlusal vertical dimension on the deep masseter of rat at different ages

OBJECTIVE

To investigate the influence of increasing the occlusal vertical dimension (iOVD) on the fibre-type distribution and ultrastructure of deep masseter of rat at different ages.

DESIGN

A total of forty-eight male Wistar rats were divided into two groups according to age: 'teenage' group (n=24, 1.5 months) and 'young adult' group (n=24, 8 months). Both the teenage and the young adult rats were then randomly divided into the control group (n=12) and the experimental group (n=12). The occlusal vertical dimensions of the rats in the experimental groups were increased by placing composite resin on all maxillary molars. The fibre-type distribution and ultrastructure of the deep masseter were subsequently observed on day 7 and day 14 after iOVD.

RESULTS

In the teenage experimental group, the proportion of type IIa fibres increased, while the proportion of type IIb and type IIx fibres decreased by day 7 after iOVD (P<0.05). However, no significant fibre phenotype transformation was observed in the young adult experimental group until day 14 after iOVD. In addition, the proportion of type IIa in the teenage experimental group was higher than that of the young adult experimental group on day 7 and 14 (P<0.05). Under the transmission electron microscope, muscle fibre reconstruction and the compensatory increase in the number and volume of mitochondria appeared earlier in the teenage experimental group. The cellular traumatic reaction was less than that in the young adult experimental group.

CONCLUSION

The teenage rat alters masseter muscle structure to a slower phenotype earlier and to a greater degree than that of the young adult rat when increasing the occlusal vertical dimension.

Intramaxillary and intermaxillary absolute anchorage with an endosseous dental implant and rare-earth magnets

This case report describes the management of a partially edentulous adult with a severe deepbite malocclusion and a collapsed buccal segment because of supraeruption of the maxillary second and third molars. The treatment involved placement of an endosseous dental implant to achieve absolute intermaxillary and intramaxillary anchorage. Rare-earth magnets embedded in acrylic bite-blocks were used to intrude the supraerupted maxillary molars on the right side. After use as an anchorage device, the implant was restored and brought into occlusion. Good occlusal and esthetic results were achieved with this cost-effective treatment.