Inlays and Onlays.pdf

1 Assist. Prof. Dr. Özay ÖNÖRAL COURSE ID Code of Committee: CS-2 Name of Committee: Fixed Prosthetic Restorations Lecturer: Assoc. Prof. Dr. Özay Önöral Topic of the Course: Inlay-Onlay-Endocrown Preparation Techniques Duration of the Course: 50 minutes After completion of this course, th...

1 Assist. Prof. Dr. Özay ÖNÖRAL COURSE ID Code of Committee: CS-2 Name of Committee: Fixed Prosthetic Restorations Lecturer: Assoc. Prof. Dr. Özay Önöral Topic of the Course: Inlay-Onlay-Endocrown Preparation Techniques Duration of the Course: 50 minutes After completion of this course, the student will be able to: Use cavity terminology Define the preparation stages and limits for inlay restoration List the cavity principles for ceramic inlay restorations Evaluate MOD inlay restoration in terms of susceptibility to complications Define the preparation stages and limits for onlay restoration Define the preparation stages and limits for endo-crown restoration. Compare ferrule-formed and unformed endo-crown restorations in terms of clinical success Contemporary Fixed Prosthodontics, 6th Edition. Book by Junhei Fujimoto, Martin F. Land, and Stephen F. Rosenstiel. Published by Elsevier in 2022. Fundamentals of Fixed Prosthodontics, 4th Edition. Book by Herbert T. Shillingburg, David A. Sather, Edwin L. Wilson, Joseph R. Cain, Donald L. Mitchell, Luis J. Blanco, and James C. Kessler. Published by Quintessence in 2012. Learning Objectives of the Course: Suggested References to Review: Near East University, Faculty of Dentistry 2 Assist. Prof. Dr. Özay ÖNÖRAL PREPARATION PRINCIPLES OF INLAYS, ONLAYS, AND ENDOCROWNS INTRODUCTION Inlay and onlay restorations are the minimally-invasive prosthetic approaches, obtained by indirect methods as an alternative to conventional amalgam filing or composite restorations. They are considered within partial crowns. INLAY RESTORATIONS Inlay restorations are indirect restorations that include a part of the clinical crown; isthmus and proximal surfaces of the natural tooth. They are a great alternative to traditional metallic fillings because less of the tooth structure needs to be removed. For the restoration of Class I cavities, the use of inlays is less common as the desired repair can usually be achieved by composite resins. In the restoration of a small carious lesion, an inlay is not very conservative of tooth structure. This is because additional tooth removal is necessary after minimal proximal extension to achieve a cavity preparation without undercuts and to enable access for impression making. This extension may lead to additional display of metal and gingival encroachment, which is undesirable for periodontal health. But for Class-II (only for mesio-occlusal [MO] and disto-occlusal [DO] cavities) and Class-V cavities, inlay restorations are strongly recommended. Because inlays do not encircle the tooth, they rely on the bulk of the buccal and lingual cusps for resistance and retention form. There is concern that high occlusal force will lead to cusp fracture as a result of wedging from the inlay. For Class-II MOD cavity, since the fracture risk of the cups is highest; inlay restoration is not recommended to the clinicians. Near East University, Faculty of Dentistry 3 Assist. Prof. Dr. Özay ÖNÖRAL Preparations for these inlays are meant to provide adequate thickness for the restorative material and a passive insertion pattern with rounded internal angles and well-defined margins. All line and point angles, internal and external, should be rounded to avoid stress concentrations in the restoration and tooth, therefore reducing the potential for fractures. Clinical failures may happen if these undesired stress concentration areas are formed. The most dramatic and common type of this, is the fracture and loss of an entire tubercle. Sometimes the tooth structure can stretch without breaking and the cement layer may break up leading marginal leakage. This creates base for the caries to form. Preparation Principles in Class-II (Proximo-Occlusal) Inlay Restorations While deciding to restore a proximo-occlusal cavity with inlay, the most important factor is the integrity of the proximal surface and the marginal ridge. The principles in inlay preparation are similar to those in conservative dentistry but there are some characteristic properties. These are; parallel walls, single path of insertion, a smooth base and margin bevels. Occlusal Outline 1. Penetrate the central groove just to the depth of the dentin (typically about 1.8 mm) with a small round or tapered carbide bur held in the path of placement of the inlay. In general, this is perpendicular to an Near East University, Faculty of Dentistry 4 Assist. Prof. Dr. Özay ÖNÖRAL imaginary line connecting the buccal and lingual cusps, not necessarily perpendicular to the occlusal plane. For example, on mandibular premolars, it is angled toward the lingual aspect. 2. The preparation depth shouldn’t be less than 2mm at the level of central fossa for the ceramic inlays, whereas this depth is 1.5mm for composite inlays. 3. The walls of the isthmus will be slightly inclined by the bur used to cut them. There should be pulpal wall but no undercut areas. If undercuts are formed after the preparation, these regions should be restored with Glass Ionomer Liner. 4. Extend the occlusal outline through the central groove with the tapered carbide. The bur should be held in the same path of placement and kept at the same depth—just into dentin. 5. The buccolingual extension should be as conservative as possible to preserve the bulk of the buccal and lingual cusps because an occlusal bevel will widen it later. 6. Resistance to proximal displacement is achieved with a small occlusal dovetail or pinhole. A distinct dovetail extends facially, enhancing resistance and retention. The pulpal floor should be flat, at an even depth of approximately 1.5 mm, and perpendicular to the path of insertion for maximum resistance. The outline should avoid occlusal contacts marked with articulating paper. Proximal Aspect Preparation 7. Extend the outline proximally, undermining the marginal ridge, and stop it at the height of contour of the ridge. 8. Advance the bur cervically (apical direction) to the carious lesion (if any) and then lingually and buccally, taking care to hold it in the precise path of placement. Do not be too conservative with the gingival extension, since this proximal box length is an important factor in the inlay retention. There should be a thin layer of enamel remaining between the side of the bur and the adjacent tooth. This prevents accidental damage. 9. The gingival floor of the box should be flat. A gingival margin trimmer is used to form a V-shaped groove at the junction of the axial wall and the gingival floor of the box. This groove sometimes referred to as the “Minnesota ditch” is placed to enhance resistance to displacement by occlusal forces. The width of the gingival floor of the box should be about 1.0 mm (mesiodistally). 10. The buccoaxial and linguoaxial line angles of the box are accentuated with a no. 169L bur. The same bur is also used to form the facial and lingual walls of the box, and they are smoothed with an enamel chisel. The box walls, not the angles, resist displacement. The opposing buccal and lingual walls contribute significantly to retention, so great care must be taken not to tilt the bur during this step. Those walls should have a minimum degree of divergence of the facial and lingual walls to promote optimum retention and resistance. As taper increases, stress rises and retention decreases. Near East University, Faculty of Dentistry 5 Assist. Prof. Dr. Özay ÖNÖRAL 11. The final extension will be achieved when the facial and lingual flares are placed. Widen the isthmus where it joins the box, rounding any angle in the area where they meet. 12. Flares are flat planes added to the buccal and lingual walls of the box using a flame diamond or an enamel hatchet. The hatchet is reserved for use in those areas where esthetics is an important consideration. The flares provide for the acute angle of gold to meet the finish line on the preparation. Check the flares to make sure that they draw. The buccal flare leans slightly to the buccal; the lingual flare, slightly to the lingual; and both flares, slightly to the center of the tooth. A flare is cut equally at the expense of the wall of the box and of the outer enamel surface of the tooth. As a result, a flare is narrow at its gingival end and much wider at its occlusal end. 13. To start the flare, place the flame diamond in the proximal box and use the small-diameter tip to cut the cavo-surface angle of the box from the gingival floor up. Continue the occlusally directed sweep of the diamond tip without changing the angle or direction of the instrument. The diamond should be cutting only when it is moving in the occlusal direction. If it is moved back and forth, the finish line may be rounded over. 14. The completed inlay will require a minimum of 0.6 mm of proximal clearance to allow an impression to be made, but some of this will be achieved with the proximal flares and gingival bevels. Sharp line angles between the occlusal outline and proximal box are rounded at this time. 15. Identify and remove any caries not eliminated by the proximal box preparation, using an excavator or a round bur in the low-speed handpiece. Beveling 16. The flame diamond is carried across the gingival cavo-surface angle of the box, forming a gingival bevel on the box that is a smooth continuation of the buccal and lingual flares. Avoid creating undercuts where the gingival bevel joins the flares (commonly seen error). Lean the flame diamond against the pulpal axial line angle. The bevel should lay between 30 and 45 degrees to provide an optimum blend of strength and marginal fit. A gingival margin trimmer is unacceptable because it will produce a ragged finish line. 17. Prepare proximal bevels on the buccal and lingual walls with the tapered bur oriented in the path of placement. There should be a smooth transition between the proximal and gingival bevels. 18. The inlay preparation is finished by placing a bevel on the occlusal isthmus with a flame diamond. If a shallow bevel is used in this location, the result will be a thin flash of metal that will probably extend into areas of occlusal contact. A hollow ground bevel or chamfer is normally preferred and can be conveniently placed with a round bur or stone. The bevel on the isthmus begins at the junction of the occlusal one-third and the gingival two-thirds of the isthmus walls, and should extend outward at an angle of 15 to 20 degrees. Near East University, Faculty of Dentistry 6 Assist. Prof. Dr. Özay ÖNÖRAL 19. The bevel must be minimal, because compressive stress increases as the inclination of the bevel increases. The bevel is likely to produce a finish-able casting. Blend the occlusal bevel into the proximal flares to produce a smooth, continuous finish line. Use a flame carbide bur to go over the flares and the bevels. The flame bur produces the most consistent bevel, and carbide finishing burs will produce the smoothest finish lines. A torpedo diamond can be used to create the bevel. 20. As a final step, smooth the preparation where necessary, paying particular attention to the margin. Preparation Principles in Class-V Inlay Restorations Class V inlays can be used on posterior teeth with large buccal or gingival lesions. The retention of such inlays can be increased with the use of pins in the mesial and distal. Such restorations shouldn’t be used in lesions where marginal sealing cannot be achieved well and with very large caries. It is a suitable restoration method for cavities or cervical abrasions located on the vestibule surface and extending down towards the gingiva. Application of a rubber-dam or gingival retraction during preparation makes it easier to work. The preparation borders are determined by a fissure bur that tapers towards the tip. The occlusal wall is positioned at the height of the crown contour if the caries or previous restoration width does not require more. Near East University, Faculty of Dentistry 7 Assist. Prof. Dr. Özay ÖNÖRAL The walls are prepared slightly-angled and meet the enamel with a right angle at the edge of the cavity. Pin slots are opened 2mm in depth in places that will not damage the pulp and in the parts where there is sufficient tooth tissue, with a 0.6 mm bur. A narrow bevel is made at an angle of 45° on the cavity walls. Significant Features for Ceramic Inlay Restorations Preparation design is influenced by the selected restorative material (weaker materials requiring additional bulk), the fabrication method, and the ability to bond the restoration. Clinicians must further consider aesthetics, fracture resistance, and edge-strength capabilities of the selected restorative material. Ceramics are brittle. Though significant progress has been made in the development of new and improved materials, the inherent brittleness remains a limiting factor that can be minimized through proper preparation design. Preparation guidelines for ceramic inlays differ from those for cast gold. Retention form is not as critical due to the bonded nature of the restoration, and bevels are contraindicated. Cavo-surface angles of 90° are preferred, and the preparation must have smooth-flowing margins to facilitate the fabrication of the restoration. Rounded internal line angles and the butt-joint cavo-surface margins facilitate many aspects of conventional laboratory or chair-side inlay fabrication. The bulk of ceramic must be established in areas of potential contact from adjacent and opposing teeth, and good visual access to all prepared surfaces facilitates optical capture and subsequent fabrication. Undercuts should be avoided. A minimum cervico-occlusal axial wall convergence of 10°–12° is consistent with general recommendations for cast-inlay preparations, although the adhesive nature of the bond may permit deviation from that specific angle of occlusal divergence. Box walls should diverge in an occlusal direction by approximately 10° or more, which will facilitate optical capture and reduce the risk of excessive binding during seating for initial evaluation. Often, it is not necessary to remove all undercuts once the desired outline form has been established, as it may be possible to simply block those out on die systems in the dental laboratory. There appears to be a reasonable consensus about minimally required dimensions for all ceramic posterior inlay preparations. Generally, a minimum of 1.5–2 mm of pulpal floor depth, 1–1.5 mm of axial reduction, and 2 mm of isthmus width define minimally adequate preparation dimensions. Such isthmus width minimizes fracture risk by stresses resulting from occlusal forces. Insufficient material thickness will result in fracture. Without adequate reduction, isthmus width, and smooth 90° cavo-surface margins, the ceramic material will not be able to withstand the significant loads to which it is subjected posteriorly. The minimum dimensions cited above are suggested for commonly used ceramics, such as leucite-reinforced porcelain or lithium disilicates. If monolithic materials such as zirconium are used, these dimensions can likely be Near East University, Faculty of Dentistry 8 Assist. Prof. Dr. Özay ÖNÖRAL reduced, at least theoretically, and margin design altered due to the inherently greater material strength. Preparation guideline is given in the following table. INTERNAL FORM EXTERNAL FORM 1.5 to 2 mm of pulpal depth 90-degree cavo-surface margins Rounded internal line angles 2 mm of isthmus width 10 to 12 degrees of axial wall convergence 2 mm of occlusal reduction for cuspal coverage Greater than or equal to 10 degrees of divergence Smooth flowing margins on buccal and lingual walls 1 to 1.5 mm of axial wall reduction Depending on the amount of residual tooth structure after caries removal, it may be desirable to use a base material under ceramic inlays. Composite resin has adequate strength and rigidity to serve as a base material, whereas glass ionomer, with its lower modulus of elasticity, is too flexible, which may increase the risk of inlay fracture. ONLAY RESTORATIONS Onlays are indirect restorations that include isthmus, proximal surfaces (mesial, distal or both), and at least one cusp. An onlay is a more conservative option than full crown. Here are such indications: (1) Broken teeth with intact buccal or lingual cusps; (2) MOD restorations with wide isthmuses; (3) Endodontically treated posterior teeth with sound buccal and lingual tooth structure; (4) To correct the occlusal plane of a tooth. However, for the cases with high caries rate or for the teeth with short clinical crown height, onlay is contraindicated. Preparation Principles in Onlay Restorations Near East University, Faculty of Dentistry 9 Assist. Prof. Dr. Özay ÖNÖRAL 1. Prepare the occlusal outline with a tapered carbide bur just beyond the enamel-dentin junction (approximately 1.8 mm deep) and extend it through the central groove, incorporating any deep buccal or lingual grooves. Existing restorations are removed as part of this step (see Fig. A). 2. Extend the outline both mesially and distally to the height of contour of the marginal ridge. After being done with preparations, the isthmus of the onlay seems shallower than that of inlay as the occlusal aspect has been reduced. 3. As with an inlay, the boxes with an MOD onlay are prepared by advancing the bur gingivally and then buccally and lingually, always holding it in the precise path of placement of the preparation. If a thin section of proximal enamel remains as the bur advances, damage to the adjacent tooth will be prevented (see Fig. B). 4. Correct gingival, buccal, and lingual extension of the preparation normally depends on the contact area with the adjacent tooth. A minimum clearance of 0.6 mm is needed for impression making. 5. Sometimes existing restorations or caries necessitate that a box be extended beyond optimal. However, if a box requires extension beyond the transitional line angle, the preparation will have little resistance form, and an alternative restoration such as a complete crown should be considered. 6. Preparing the boxes is a key step when an onlay is fabricated (see Fig. C and D). The tapered bur should be held precisely in the planned path of placement throughout. Tilting, often caused by trying to advance the bur too quickly, is commonly done and is difficult to correct. Near East University, Faculty of Dentistry 10 Assist. Prof. Dr. Özay ÖNÖRAL 7. Round sharp line angles between the occlusal outline and proximal boxes. 8. Remove any remaining caries by using an excavator or a round bur in the low-speed handpiece. 9. Place a cement base to restore the excavated tissue. Good judgment is needed to ensure that adequate sound dentin is present on the axial walls to provide retention and resistance. 10. Place depth orientation grooves on the functional cusps. To give additional clearance at the cusp tip, the bur must be oriented more horizontally than the intended restoration cusp. The grooves should be 1.3 mm deep, allowing 0.2 mm for smoothing (see Fig. E). 11. Place 0.8 mm grooves on the nonfunctional cusps. On nonfunctional cusps, the bur is oriented parallel to the cuspal inclines. As with all depth grooves, it is assumed that the tooth is in good occlusal relation before preparation. If it is not, a vacuum-formed matrix made from the diagnostic waxing procedure is recommended as a guide. 12. Connect the grooves to form the occlusal reduction, maintaining the general contour of the original anatomy. 13. Prepare a 1.0-mm functional cusp ledge with the cylindrical carbide bur (see Fig. F). This gives the restoration bulk in a high-stress area, preventing deformation during function. The ledge should be placed about 1 mm apical to the opposing centric contacts. It extends into the proximal boxes but should not be positioned too far apically; otherwise, the resistance form from the boxes will be lost. 14. There are 2 acceptable occlusal finish lines for the functional cusp of an MOD onlay: an occlusal shoulder or a heavy chamfer. Both configurations provide an acute edge of metal at the cavo-surface angle, with a nearby bulk of metal for strength. The shoulder with a bevel is easier to prepare properly and should be used by the novice. 15. Round any sharp line angles, particularly at the junction of the ledge and occlusal surface. 16. Check for adequate occlusal reduction by having the patient close into soft wax and measuring with a thickness gauge. 17. Establish a smooth, continuous bevel on all margins. The 0.5-0.7 mm gingival bevel is placed, as for an inlay, with the thin carbide or diamond held at 45 degrees to the path of placement, or approximately parallel to the adjacent tooth contour. This will blend smoothly with the buccal and lingual bevels, which have been prepared with the bur held in the path of placement. 18. Occlusal finishing bevels 0.5 to 0.7 mm are placed at the buccal and lingual occlusal finish lines with a flame diamond followed by a no. 170L carbide bur. The buccal bevel is perpendicular to path of insertion where esthetics are important, and forms a heavier contra-bevel where they are not. Bevel the functional cusps. Where additional bulk at the margin is needed, a chamfer should be substituted for the straight bevel. This can be placed with a round-tipped diamond. For the upper teeth, on the palatal slope of the palatal cusp and for the lower teeth, on the buccal slope of the buccal cusp, a wide bevel is Near East University, Faculty of Dentistry 11 Assist. Prof. Dr. Özay ÖNÖRAL made in order to provide sufficient space for metal thickness. Functional cusp beveling is made only for metal onlays. There is no need to bevel on ceramic or composite onlays. 19. Complete the preparation by rechecking the occlusal clearance in all excursions and assessing for smoothness (see Fig. G and H). Endo-crown Restorations These restorations do not differ from onlays and therefore, can be categorized under onlay restorations. The distinctive feature of endo-crown restoration is that it has to be applied on endodontically-treated natural teeth. The endo-crown is suitable for all molars, particularly those with clinically low crowns, calcified root canals or very slender roots. The endo-crown is contraindicated if adhesion cannot be assured, if the pulpal chamber is less than 3 mm deep or if the cervical margin is less than 2 mm wide for most of its circumference. The butt joint, or cervical sidewalk, is the base of the restoration — with a band of peripheral enamel that optimizes bonding. Unlike chamfer or shoulder preparation techniques, crimping is prohibited. The goal is to achieve a wide, even, stable surface that resists the compressive stresses that are most common on molars. The prepared surface is parallel to the occlusal plane to ensure stress resistance along the major axis of the tooth. Ferrule-containing endo-crown preparations revealed significantly superior failure loads than regular endo-crown restorations. Moreover, less occurrences of disastrous failure were detected with Endo-crown preparations containing 1 mm of preparation ferrule design. Near East University, Faculty of Dentistry 12 Assist. Prof. Dr. Özay ÖNÖRAL The pulpal chamber cavity ensures retention and stability. Its shape — trapezoidal in mandibular molars and triangular in maxillary molars — enhances the restoration’s stability. There is no need for additional preparation. The saddle form of the pulpal floor enhances stability. This anatomy, along with the adhesive qualities of the bonding material, makes it unnecessary to attempt further use of post involving root canals. Actually, the root canals do not require any specific shape; therefore, they are not weakened by the drilling and they will not be subject to the stresses associated with the use of post. The compressive stresses are reduced, being distributed over the cervical butt joint and the walls of the pulp chamber. NUMBER OF APPOINTMENTS IN INLAY AND ONLAY INDIRECT RESTORATIONS They require 2 appointments; during the first visit, damaged or decayed area is removed and the tooth is prepared in accordance with the principles of inlay or onlay. An impression (conventionally or digitally) is taken and sent to the laboratory for fabrication. During the second visit, the restoration is bonded to the tooth with the aid of resin cements. Near East University, Faculty of Dentistry