Fixed Restorations. Irena Sailer
to extensive cantilever units, causing widening of the periodontal ligament of tooth 45 and increased mobility of the restoration. The problem disappeared after redesigning the restoration with a smaller cantilever unit that only had occlusal contact in MIP and without contact in lateral movements.
Temporomandibular disorders
The diagnosis of temporomandibular disorder (TMD) is based largely on history and physical examination findings. The symptoms of TMD are often associated with jaw movement (eg, opening and closing the mouth, chewing) and pain in the pre-auricular, masseter, or temporalis regions. Another source of orofacial pain should be suspected if the pain is not affected by jaw movement. Adventitious sounds of the jaw such as clicking or crepitus may occur with TMD, but do also occur in asymptomatic patients. The most common presenting signs and symptoms of TMD were facial pain, ear discomfort, headache, and jaw discomfort or dysfunction. Chronic TMD is defined by pain of more than 3 months’ duration.
Clinical examination that may support the diagnosis of TMD should be performed and registered. Such examinations are: abnormal or deviation in the mandibular movement; decreased range of motion measured in millimeters or by applying the three-finger rule; tenderness of masticatory, neck or shoulder muscles; pain with dynamic loading. A clicking, crepitus, or locking of the temporomandibular joint (TMJ) may accompany joint dysfunction. A single click during opening of the mouth may be associated with an anterior disc displacement. A second click during closure of the mouth results in recapture of the displaced disc; this condition is referred to as disc displacement with reduction. When disc displacement progresses and the patient is unable to fully open the mouth (ie, the disc is blocking translation of the condyle), this condition is referred to as closed lock. Crepitus is related to articular surface disruption, which often occurs in patients with osteoarthritis.
Design
Designing the occlusal scheme is a crucial Part of the treatment plan. The decision whether or not to apply a unilateral balanced occlusion (group function) or a mutually protected occlusion (canine guidance) depends on the initial occlusal situation of the natural dentition, the presence or absence of TMD, the position and extension of the planned restoration, the planned restoration material, and if the restoration is tooth- or implant-supported. There are some principal differences between tooth- and implant-supported restorations. The proprioception of an implant is 8.8 times lower than that of a tooth45,46. Hence, almost nine times more load must be applied to an implant until the patient feels the load. Teeth under occlusal load move approximately 50 µm downwards within the alveola supported by the periodontal ligament. If the same load is applied to an osseointegrated implant it does not move due to the ankylosis. Due to this, some clinicians have fabricated implant-supported restorations in slight infraocclusion. This might make sense if a partially dentate patient is restored with occluding implant-supported restorations in both jaws. However, if an implant-supported restoration that articulates with natural teeth is made in infraocclusion, the antagonist teeth will tend to extrude into contact and the implant-supported restoration will end up in contact.
In designing the occlusal scheme, the following steps have to be taken:
■ During the occlusal analysis, it has to be registered whether the natural dentition is in unilateral balanced occlusion (group function) or in mutually protected occlusion (canine guidance). The basic principle is that a patient who has been functioning well without any signs of TMD in unilateral, balanced, or mutually protected occlusion should be restored utilizing the same occlusal scheme as present in the natural dentition.
■ During the occlusal analysis, it must be evaluated whether MIP and CO are in the same position or whether there is a slide between the two positions (MIP ≠ CO). If MIP and CO are not in the same position, the premature contacts have to be located and a decision has to be made whether occlusal adjustment should be initiated to reduce or eliminate the premature contacts creating MIP = CO, or whether the restoration should be made long-centric, allowing for a certain freedom in the occlusion.
■ To evaluate the dental arch and decide whether additional treatment steps such as orthodontic treatment are needed for better position of abutment teeth, to correct malpositioned teeth or crowding (Fig 1-2-17).
Fig 1-2-17a to 1-2-17c Patient with a mediastema and an old ceramic crown in position 11. The teeth were orthodontically aligned for even distribution of the diastemas before redoing the crown on tooth 21 and placing two ceramic veneers on teeth 12 and 22.
■ If unilateral balanced occlusion (group function) is planned for multiple-unit restorations, care should the taken to have at least two occlusal contacts simultaneously on the restoration on the working side in lateral movements.
■ If mutually protected occlusion (canine guidance) is planned, steep latero-protrusion facets on the canines causing resistance on the working side in lateral movements should be avoided (Fig 1-2-18).
Fig 1-2-18 If canine guidance is planned, steep latero-protrusion facets on restored canines should be avoided.
■ Avoid making balancing mediotrusion contacts in the new restoration.
■ Avoid having posterior contacts in the new restoration during protrusion.
■ To avoid losing the occlusal relationship when full-arch restorations are made, it usually makes sense to restore the occlusion in segments. That is, first restore the posterior area to gain a stable occlusion and then as a second step the anterior area. If the primary goal of treatment is to change the length, shape, and position of the anterior teeth, comprehensive pretreatment diagnostics are crucial to determine the prospective incisal/occlusal plane prior to the restoration of the posterior segments. In conclusion, the basic principle is not to restore everything simultaneously, but to first stabilize the posterior support before restoring the anterior segments.
Vertical dimension of occlusion
Recent minimally invasive treatment concepts include an increase of the vertical dimension of occlusion (VDO) in order to gain interocclusal space for the restorations.
There are several indications for raising the VDO:
■ Restoring missing tooth substance by patients with significant attrition or erosion.
■ For esthetic reasons, that is to increase the anterior intraocclusal space to be able to increase the length of anterior teeth.
■ To eliminate traumatic deep bite.
■ To increase the vertical dimension of the lower face.
■ In selected cases with TMD after thorough diagnosis with occlusal stents and provisional restorations.
Different approaches have been proposed for raising the VDO. As it is usually not recommended to do both maxilla and mandible simultaneously for patients that need extensive restorations in both jaws, the first decision to make is with which jaw to begin. If the VDO has to be increased in both jaws, it is highly recommended to begin with the maxilla in order to harmonize the esthetically relevant occlusal and incisal maxillary planes with the smile line and the bi-pupillary line. The mandibular occlusal plane is then adapted accordingly.
In selected situations only minor augmentation of the VDO may be needed. In these cases, the decision has to be made in which jaw the VDO shall be augmented. The crucial parameter for this choice again is the relationship of the maxillary occlusal/incisal plane and the smile and bi-pupillary lines, and the dental situation.
Finally, if the plan is to restore both jaws extensively it is recommended to finish one jaw, having the final restorations articulating