Presentation on theme: "MISCH: CHAPTER 12. Presented by:Dr.mehrak Amjadi Supervised by: Dr. Mansour Rismanchian And Dr.saied Nosouhian Dental of implantology Dental implants."— Presentation transcript:
MISCH: CHAPTER 12
Presented by:Dr.mehrak Amjadi Supervised by: Dr. Mansour Rismanchian And Dr.saied Nosouhian Dental of implantology Dental implants research center Isfahan university of mediacal science PREIMPLANT PROSTHODONTICS
OVERAL EVALUATION, SPECIFIC CRITERIA, AND PRETREATMENT PROSTHESIS Mehrak Amjadi
1) MAXILLARY ANT. TEETH POSITION The labial position of the max ant teeth is first determined with the lip in repose. overall support of the maxillary lip and its relationship to the nose and presence or absence of a philtrum in the midline
MAXILLARY ANT. TEETH POSITION The vertical position of the max ant teeth : canine tip is located 1 mm level with the lip in repose, regardless of age or sex of the patient. The centrals are 1 to 2 mm longer than canine. If the patient is wearing a maxillary complete denture,the maxillary anterior tooth position is often incorrect
2) EXISTING OCCLUSAL VERTICAL DIMENSION OVD: the distance between 2 points (one in max and the other directly below in the mandible) when the occluding members are in contact. OVD requires clinical evaluation not diagnostic casts. OVD is not a precise dimension, because a range of dimensions is possible without clinical symptoms. withou OVD often decreases over time without clinical consequence in the dentate or edentulous patients.
OVD Any change in OVD affects the CHS. Any change in OVD modifies the horizontal dimensional relationship of the maxilla to the mandible. change in OVD will modify anterior guidance, range of function, and esthetics. The most important effect of OVD on tooth / impalnt = effect on the biomechanics of anterior guidance. The more closed OVD the farther the mandible rotates the more CL III the chin appears.
OVD In a Class II, division 2 patient, the more closed the OVO, the steeper the anterior guidance and the greater the vertical overlap of the anterior teeth. Anterior guidance is necessary to maintain incisal guidance during mandibular excursions to decrease the risk of posterior interferences. These conditions will increase the forces to the anterior teeth.
OVD completely edentulous patients restored with fixed implant prosthodontics Opening OVD + decreasing the incisal guidance increase force on posterior implants during mandibular excrusion. Change in OVD may affect the sibilant sounds by altering the horizontal position of the mandible.
OVD Situations that altering OVD is mandatory: 1. Esthetic α incisal edge position, facial measurements, occlusal plane. 2. Function α canine position, incisal guidance, angle of load to teeth or implants. 3. Structural needs of the dentition α dimensions of teeth for restoration while maintaining a biologic width.
Methods for evaluating OVD OBJECTIVE METHODS: use facial dimensions SUBJECTIVE METHODS: rely on esthetics, resting arch position, and closet speaking space. OVD = RESTING POSITION – FWS (3 mm) The amount of FWS depends on factors like head posture, emotional state, presence or absence of teeth, parafunction, and the time of recording. The physiologic rest position should not be primary method to evaluate OVD. The speaking method (making S sound) also should not be used as the only method to establish OVD.
Experienced clinicians often use subjective method to assess OVD. The objective method is usually the method of choice to evaluate existing OVD or establish a different OVD during prosthetic reconstruction. THE GOLDEN RATIO: the length and width of a golden rectangle as 1 to
Radiographic methods to determine an objective OVD are also documented in the literature. Tracings on a cephalometric radiograph is suggested when gross jaw excess or deficiency is noted. Esthetics are influenced by OVD, because of the relationship to the maxillomandibular positions. The smaller the OVD, the more Class 1IIthe jaw relationship becomes; the greater the OVO, the more Class II the relationship becomes.
The maxillary anterior tooth position is determined first and is most important for the esthetic criteria of reconstruction. complete maxillary denture opposing a partially edentulous mandible may result in COMBINATION (KELLY) SYNDROM: Max incisor denture positions up and rotates back Lower natural ant teeth overerupt Occlusal plane tilted apically in ant and coronally in post Enlarged tuberosities Maxillary palatal hyperplasia Highly mobile tissue in the premaxilla.
COMBINATION (KELLY) SYNDROM: The proper maxillary incisal edge position and OVD are especially critical for these patients, because of the incidence of mandibular incisor extrusion beyond the maxillary occlusal plane. To position the maxillary incisors properly, the mandibular anterior teeth must be repositioned at the proper incisal plane.Endodontic therapy and crown lengthening procedures usually precede the restorations on the lower arch to obtain a retentive and esthetic restoration.
3) MANDIBULAR INCISOR EDGE POSITION mandibular incisor edge should contact the lingual aspect of maxillary anterior natural teeth at the desired OVD position. A vertical overlap of 3 to 5 mm is acceptable. INCISAL GUIDANCE: influence of contacting surfaces of the mandibular and maxillary anterior teeth on mandibular movements. tooth separation CHRISTENSENS PHENOMENON: IG is responsible for the amount of post tooth separation during mandibular excursions and to do so it should be steeper than condylar disc assembly.
IG IG is evaluated on the mounted diagnostic casts. A steep IG 1)avoid post interferences during mandibular excursions, 2) greater forces on anterior crowns
4,5) EXISTING OCCLUSAL PLANES The position of occlusal planes relates to the curve of spee and wilson ( the radius of a 4 inch sphere). Ideally, the maxillary posterior occlusal plane should be parallel to the Camper's plane. Odontoplasty, endodontic therapy, or crowns are indicated to remedy tipping or extrusions of adjacent or opposing natural teeth.
A proper curve of Spee and curve of Wilson are also indicated for proper esthetics and are reproduced in the compensating curves for complete denture fabrication. An occlusal plane analyzer may be used on diagnostic casts to evaluate pretreatment conditions and assist in intraoral occlusal plane correction.
The natural dentition opposing a partially edentulous ridge also must be carefully examined and often needs modification before surgical placement of the implants. The implant drills and implant body insertion often require a posterior CHS of more than 8 mm from the ideal occlusal plane. Enameloplasty of the stamp cusps of the opposing teeth is often indicated to redirect occlusal forces over the long axis of the implant body.
The existing tooth and arch relationships do not need to be perfect before implant treatment. The correct tooth positions should be first determined, so even if the total treatment time is extended over several years, at least each segment will aim toward a consistent goal.
1. Lip line 2. Maxillomandibular arch relationship 3. Existing occlusion 4. CHS 5. TMJ status 6. Existing of hopeless teeth 7. Existing prosthesis 8. Arch form 9. Natural teeth adjacent to implant site. 10. Soft tissue evaluation of the edentulous site.
LIP LINE General rule: 1 -2 mm of max ant teeth should display with the lip at rest. But it is better to position the prosthetic teeth in most likely location for the patients natural teeth. The average upper lip is 20 to 22 mm for women and 22 to 26 for men. The canine position at the corner of the lip is not affected by the lip bow effect. Thus, it is more consistent position and usually corresponds to the length of the resting lip position from the 30 to 60 years of age in both male and female.
The low lip line displays no interdental papilla or gingiva above the teeth during smiling. The high lip demonstrates all of the interdental papilla and more than 2 mm of tissue above the cervices of the teeth. The selection of FP2 or FP3 is often based solely on the evaluation of the high lip line. An FP2 (in low lip line patients) is easier to fabricate because of fewer porcelain bake cycles.
In patients with a high lip line who are missing all their ant teeth, the prosthetic teeth can be made longer (up to 12 mm) instead of the average 10 mm to reduce gingival display. The height of the maxillary ant teeth is determined by: 1. Establishing incisal edge by the lip in repose. 2. The high smile line determines the height of the tooth (9-12 mm) 3. The width of the anterior teeth is determined by the height/width ratios.
Mandibular lip line Although the maxillary high lip line is evaluated during smiling, the mandibular low lip line is evaluated during speech. In pronunciation of sibilants or S some patients may expose the entire ant mand teeth. An FP3 may be indicated in a patient with low mandibular lip position.
MAXILLOMANDIBULAR ARCH RELATIONSHIP Teeth ext bone loss placing implant in lingual position facially overcontoured restoration cantilever. To counteract cantilever effect increased implant number, size, design, and change prosthesis to RP4, and spilinting implants.
MAXILLOMANDIBULAR ARCH RELATIONSHIP palatal resorption of the maxilla with the anterior rotation of the mandible Class III relationship- >> Class III mandibular mechanics do not apply (no anterior excursions during mastication or parafunction). can contribute significant lateral forces on the maxillary restoration-> additional splinted / implants are suggested in the maxilla with the widest A-P distance available.
EXISTING OCCLUSION MI : complete intercuspatin of opposing teeth independent of condylar position. CO : occlusion of opposing teeth when mandible is in CR. The more teeth replaced or restored, the more likely the patient restored to CR occlusion. One tooth replacement MI position.
CROWN HEIGHT SPACE CHS= distance between bone level and occlusal or incisal plane. IDEAL CHS for FP1 implant mm. Angled force, high CHS, angled implant placement force magnifier. A 12 degree force o implant increases the force by 20%
Excessive CHS The biomechanics of CHS are related to lever mechanics. CHS is a vertical cantilever and therefore is also a force magnifier. When the direction of a force is in the long axis of the implant, the stresses to the bone are not magnified in relation to the CHS
Excessive CHS CHS is excessive when more than 15 mm = vertical cantilever. In the case of removable prostheses with mobility and soft tissue support, two prosthetic levers of height : 1. the height of the attachment system to the crest of the bone. The greater the height distance, the greater the forces applied to the bar, screws, and implants 2. the distance from the attachment to the occlusal plane. This distance represents the increase in prosthetic forces applied to the attachment.
Excessive CHS In crown heights of more than 15 mm : no cantilever should be considered unless all other force factors are minimal. The occlusal contact intensity should be reduced Occlusal contacts in CR occlusion may even be eliminated on the most posterior aspect of a cantilever.
Treatment plan for Excessive CHS: Shorten cantilever length Minimize buccal and lingual offset loads. Increase diameter and number of implants. Improve implant design Fabricate removable restoration or hybrid pr. Splint implants together
Reduced CHS Reduced CHS causes: material failure increased material flexibility Reduction of retention It is better to use metal in occluding surfaces in these cases. minimum restoration space required: 3i< noble< biohorizon< astra< lifecore< straumann.
Reduced CHS Less than 3 mm of abutment height indicates a screw retained crown, 3 to 4 mm requires a screw retained or resin-cemented restoration, and greater than 4 mm of abutment height allows the operator's preference. When a screw is used to retain the crown the strength of occlusal porcelain is reduced by 40%. The most common method of retention for a fixed prosthesis is cement retention. The most common method of bar retention is screw retention. in ideal to excessive CHS situations, the cemented bar should be considered.
Reduced CHS Reduced CHS causes: material failure increased material flexibility Reduction of retention It is better to use metal in occluding surfaces in these cases. When a screw is used to retain the crown the strength of occlusal porcelain is reduced by 40%. minimum restoration space required: 3i< noble< biohorizon< frialit< astra< lifecore< straumann.