- Email: [email protected]
Virtual diagnostics and guided tooth preparation for the minimally invasive rehabilitation of a patient with extensive tooth wear: A validation of a digital workflow
DENTAL TECHNIQUE
Virtual diagnostics and guided tooth preparation for the minimally invasive rehabilitation of a patient with extensive tooth wear: A validation of a digital workflow Hyeonjong Lee, DMD, PhD,a Vincent Fehmer, MDT,b Kung-Rock Kwon, DMD, PhD,c Felix Burkhardt, DDS,d Ahran Pae, DMD, PhD,e and Irena Sailer, Prof Dr Med Dentf Recent developments in digABSTRACT ital technologies in dentistry The recent evolution of digital technologies in dentistry has enabled virtual 3D diagnostic analysis have led to significant of a dentition before treatment, allowing for virtual, minimally invasive treatment planning. In this changes of treatment conreport, an extensively worn dentition was 3D virtual analyzed at an increased vertical dimension of cepts in prosthodontics. occlusion. Virtual waxing (exocad DentalCAD; Exocad) and subsequent analysis of the need for Optical scanning allows digiminimally invasive preparations were performed. Areas of each tooth without adequate clearance for the minimal thickness of a definitive restoration (set at 1.5 mm in the software), including the talization of the initial clinical amount of tooth substance to be removed (GOM Inspect; GOM), were visualized in color. A situation, delivering virtual preparation guide was virtually designed according to this diagnostic plan (3-matic; Materialise) and files of the initial status of the 3D printed (Connex3 Objet260; Stratasys) from resin (VeroMagenta RGD851; Stratasys). The teeth dentition in the standard were minimally prepared using the guide, and the amount of preparation was validated by tessellation language (STL) superimposing the scan of the prepared model on the initial scan and comparing it with the format. The STL files can be diagnostic plan. (J Prosthet Dent 2019;-:---) input into a computer-aided composite resin materials and cemented with adhedesign (CAD) software program and analyzed.1 Digital sive material as an alternative to conventional fixed diagnostics, including digital waxing and trial restoraprostheses.3,4 tions, can then be performed. Subsequently, the type Studies have shown5,6 that conventional preparation and design of the planned restorations can be exported of complete coverage ceramic crowns necessitates anteas digital files and milled or printed by means of rior or posterior tooth reduction ranging between 40% computer-aided manufacturing (CAM) technology to and 70%. In contrast, tooth reduction for ceramic veneers fabricate CAD-CAM trial restorations.2 After tooth on maxillary central incisors ranges between 17% and preparation, the planned restorations can be fabricated 30%.5,6 Extensive tooth preparation can cause hyperwith the CAD-CAM technology. sensitivity and pulpal damage.7-11 For this reason, and Different types of ceramic and composite resin consistent with the development of materials and admaterials have been developed for fabrication, openhesive dentistry, current prosthodontic concepts have ing up new prosthetic treatments. Less-invasive proposed less-invasive restorations before preparing a restorations, such as veneers, onlays, and partialcrown. coverage crowns, can be milled from ceramic or
a
International Scholar, Division of Fixed Prosthodontics and Biomaterials, University Clinic of Dentistry, University of Geneva, Geneva, Switzerland; and Assistant Professor, Department of Prosthodontics, School of Dentistry, Pusan National University, Yangsan, Republic of Korea. b Master Dental Technician, Division of Fixed Prosthodontics and Biomaterials, University Clinic of Dentistry, University of Geneva, Geneva, Switzerland. c Professor, Department of Prosthodontics, School of Dentistry, Kyung Hee University, Seoul, Republic of Korea. d Resident, Division of Fixed Prosthodontics and Biomaterials, University Clinic of Dentistry, University of Geneva, Geneva, Switzerland. e Professor, Department of Prosthodontics, School of Dentistry, Kyung Hee University, Seoul, Republic of Korea. f Professor, Division of Fixed Prosthodontics and Biomaterials, University Clinic of Dentistry, University of Geneva, Geneva, Switzerland.
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Figure 1. Analysis of clearance between maxillary and mandibular dentition after optimal increase of vertical dimension for restorative space. A, Occlusal view. B, Lateral view. C, Cross-sectional rear view at second molar area. D, Virtual diagnostic waxing on maxillary dentition.
Figure 2. Virtual arbitrary relief in pit and fissure areas on maxillary cast for better adaptation of guide.
Figure 3. Construction of 2-mm-thick structure surrounding maxillary model.
One prerequisite for minimally invasive prosthodontic treatment is thorough pretreatment diagnostics to define the treatment goals. To provide the least invasive approach, clinicians should determine the exact area and amount of tooth preparation needed before clinical treatment. To define the preparation needed, pretreatment diagnostics, including diagnostic waxing of the
planned restorations, are essential. The conventional methods of transferring this information to the patient are trial restorations and silicone matrices. Trial restorations reproduce the diagnostic waxing and can be transferred to the existing dentition. They are used to visualize and communicate the treatment outcome to the patient, dentist, and dental laboratory technician.2 Once
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Figure 4. A, Sectional view between both dentitions. B, Sectional view after creating 2-mm-thick outer offset on maxillary cast (cast A) and 1.5-mm-thick offset on mandibular cast (cast B). Orange arrow shows point exposed on guide. C, Subtraction of cast B from cast A. Area within 1.5-mm interocclusal clearance exposed. D, Posterior view of designed guide (blue).
approved, silicone matrices of the waxing can be used to define the tooth preparation.12-20 Limitations of this conventional workflow include the time and effort needed to produce a conventional diagnostic waxing and trial restoration and their associated costs. One further limitation is the predictability of the transfer of this plan to the patient. Silicone matrices may help evaluate the area and amount of tooth preparation needed during the procedure, but the predictability of the procedure is not ensured. Silicone matrices deliver 2D information during the preparation and are limited to 1 or 2 buccolingual or mesiodistal slices. To ensure minimal invasiveness and optimal standardization, a 3D preparation guide is desirable. The 3D information of maxillary and mandibular dentitions obtained by means of optical scans can be used for virtual diagnostics and treatment planning. Furthermore, in clinical situations with reduction of the vertical dimension of occlusion (VDO), a virtual increase of VDO can be performed.21,22 Optimal interocclusal clearances can also be determined in the 3D analysis by following the recommendations for different restorative
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materials. Locations without sufficient clearance are color coded on the 3D image (virtual 3D diagnostics), indicating the amount of tooth substance to be removed based on the 3D virtual diagnostics. To transfer this 3D information predictably to the clinical situation and to ensure least invasive tooth preparation, CAD-CAM preparation guides need to be designed and produced. In this report, restoration of an extensively worn maxillary dentition without the loss of VDO but with space available is presenteddcategory 2 according to the treatment options in the restoration of an extremely worn dentition.23 The VDO was increased to obtain space, but some preparation was still needed on the posterior teeth to achieve the minimal clearance for ceramic restorations. The casts of a previously treated patient were used to evaluate this concept. A 3D diagnosis was performed to determine the needed amount of VDO increase and define the areas with insufficient clearance for the planned reconstructions after a virtual VDO increase. A 3Dprinted guide based on the virtual 3D diagnostics was named K-L (Kwon & Lee) preparation guide, and it was used for the minimally invasive preparations.
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Figure 5. A, Information of location and amount of tooth to be prepared. White region indicates area over 1.5 mm of clearance. Each color on color bar shows each relative clearance within 1.5 mm. B, Designed guide of left side. C, Designed guide of right side.
TECHNIQUE 1. Scan maxillary and mandibular dentitions to obtain STL data by using intraoral digital scans or a laboratory scanner (IScan D104; Imetric) to scan diagnostic casts. 2. Diagnose the optimal increase in VDO, that is, the opening in the incisal area, considering the THE JOURNAL OF PROSTHETIC DENTISTRY
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minimum thickness of restorations in the posterior region and esthetics in the anterior area. Establish this with a 3D virtual analysis software program (GOM Inspect; GOM) (Fig. 1A, B). Fabricate an anterior guide at the established VDO (Pattern resin LS; GC) to make a clinical occlusal registration (Jet bite; Coltène) based on the previous 3D virtual analysis. Align the maxillary and mandibular STL files according to the occlusal registration by applying a best-fit algorithm (GOM Inspect; GOM) (Fig. 1C). Relieve the maxillary cast to virtually fill in pits and grooves on the teeth that might interfere with the adaptation of the guide (3-matic; Materialise) (Fig. 2). Construct a 2-mm-thick structure, resembling an occlusal device, to cover the teeth and surrounding structures of the maxillary model (cast A) (Fig. 3). Define a 1.5-mm occlusal clearance on the mandibular cast (cast B). This clearance is defined by the minimum thickness of the material selected for the definitive restoration (for this restoration, it is lithium disilicate glass-ceramic) (Fig. 4A, B). Virtually subtract cast B from cast A. The areas not fulfilling the space requirements are thereby visualized. Subsequently, design 2 separate preparation guides (first quadrant, second quadrant) to allow for removal of the respective parts from cast A (Figs. 4C, D, 5). Fabricate the preparation guides by using a 3D printer (Connex3 Objet260; Stratasys) and place it on the cast for analysis of the needed preparation (Fig. 6A-C). Perform the guided tooth preparation by removing only the tooth substance extending beyond the guide. Use a football-shaped diamond rotary instrument (no. 250/4250 red, Guided Universal Prep Set; Intensiv) (Fig. 6D).
After tooth preparation, the result was compared with the initial virtual plan for validation of the concept. The clearance obtained from the guided preparation was evaluated by scanning the cast after the preparation and superimposing the STL file on the file of the plan. The results indicated accurate transfer of the guided preparation plan to the clinical execution (Figs. 7, 8). DISCUSSION With the development of reinforced ceramic materials and adhesive dentistry, minimally invasive partial coverage restorations with increased VDO can be selected in preference to complete coverage crowns to restore an extensively worn dentition. However, sufficient clearance for the restoration in the posterior area may not be possible even with an increase of VDO. Lee et al
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Figure 6. A, Guide fabricated by 3D printer. B, C, Guide placed on cast. D, Preparation using high-speed handpiece.
Turner and Missirlian23 identified 3 distinct categories for the restoration of extensively worn dentitions in relation to VDO and treatment options. An increase of VDO should be determined considering various conditions. In this patient, the increase of VDO was established from the anterior esthetics and optimal posterior material. An area with insufficient clearance can be specified through 3D analysis with the presented method. Subsequently, the preparation guide can be designed and fabricated based on the previous 3D analysis to transfer the virtual plan to the clinical situation. The thickness of the guide in this report was set to 2 mm, considering clinical and mechanical aspects. Determining the VDO increase is an important step in the treatment. Virtual 3D diagnostics of clearance between both dentitions can be made after defining the amount of virtual VDO increase. The tentative amount of increase can be virtually planned with the help of this analysis. However, due to the possible error of a virtual VDO increase, clinical occlusal registration by using an anterior occlusal registration device is also recommended. In 2008, Vailati and Belser18-20 introduced a 3-step technique to rehabilitate extensively worn dentitions. This technique comprised 3 laboratory steps alternated
Lee et al
with 3 clinical steps, allowing for the predictable minimally invasive esthetic and functional rehabilitation of patients with dental erosion. The concept in this report can be integrated into the 3-step technique to virtually plan for complete mouth adhesive restoration of extensively worn dentitions. Conventionally, analysis of the mounted cast is one of the main factors in determining the amount of VDO increase. A tentative amount of VDO increase was performed through visual inspection of the mounted cast in the articulator. With the help of a 3D digital software program, a virtual vertical increase of VDO is now possible.21,22 Precise evaluation of maxillary and mandibular dentitions can be obtained. The K-L preparation guide was virtually designed, CAM fabricated, and used for the minimally invasive tooth preparation for this patient. Once the STL files of both dentitions and the occlusal registration were acquired, the guide could be designed automatically by inserting intended clearance values. As this guide was designed by using a CAD software program, the shape and dimensions of the guide were predictable and clearly defined. The magenta color of the guide helped to easily distinguish the needed amount of tooth reduction (Fig. 9). Virtual 3D occlusal analysis indicated the amount of insufficient clearance and, hence, needed tooth
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Figure 7. Validation between before and after preparation using guide. Differences visualized in colordwhitish color shows the area with >1.5-mm clearance and colored regions show areas and amount of teeth to be prepared to obtain at least 1-mm clearance. A, Right side before preparation. Color shows area that should be prepared. B, Left side before preparation. C, Right side after preparation. D, Left side after preparation.
Figure 8. Cross-sectional view to validate clearance change before and after preparation. A, Section at right second molar. B, Section at left second molar.
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Figure 9. Clinical application of guide. A, Guide placed on posterior area. B, Minimally invasive preparation performed according to contour of guide.
reduction. It provided visualized information on the location and amount of teeth to be prepared. This 3D diagnostic tool can be used for patient consultation and minimally invasive preparation. In addition, although this technique was introduced for VDO increase in the present patient, it may also be applied in various other clinical situations. If the functions used in this report could be integrated into a commercial dental CAD software program, the presented procedure would be easier to apply in daily practice. SUMMARY The K-L guide based on 3D virtual diagnostics indicates the location and amount of tooth substance to be removed. It can be easily designed and printed using the CAD-CAM technology. REFERENCES 1. Lee H, Kim HS, Noh K, Paek J, Pae A. A simplified method for evaluating the 3-dimensional cement space of dental prostheses by using a digital scanner. J Prosthet Dent 2017;118:584-6. 2. Sancho-Puchades M, Fehmer V, Sailer I. Advanced smile diagnostics using CAD/CAM mock-ups. Int J Esthet Dent 2015;10:374-91. 3. Edelhoff D, Liebermann A, Beuer F, Stimmelmayr M, Guth JF. Minimally invasive treatment options in fixed prosthodontics. Quintessence Int 2016;47: 207-16. 4. Pieger S, Salman A, Bidra AS. Clinical outcomes of lithium disilicate single crowns and partial fixed dental prostheses: a systematic review. J Prosthet Dent 2014;112:22-30. 5. Edelhoff D, Sorensen JA. Tooth structure removal associated with various preparation designs for anterior teeth. J Prosthet Dent 2002;87:503-9. 6. Al-Fouzan AF. Gravimetric analysis of removed tooth structure associated with different preparation designs. Saudi J Dent Res 2016;7:1-6. 7. Foster LV. Failed conventional bridge work from general dental practice: clinical aspects and treatment needs of 142 cases. Br Dent J 1990;168:199-201. 8. Cheung GS, Lai SC, Ng RP. Fate of vital pulps beneath a metal-ceramic crown or a bridge retainer. Int Endod J 2005;38:521-30. 9. Wisithphrom K, Murray PE, About I, Windsor LJ. Interactions between cavity preparation and restoration events and their effects on pulp vitality. Int J Periodontics Restorative Dent 2006;26:596-605.
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10. Saito K, Nakatomi M, Ohshima H. Dynamics of bromodeoxyuridine labelretaining dental pulp cells during pulpal healing after cavity preparation in mice. J Endod 2013;39:1250-5. 11. Schwartz NL, Whitsett LD, Berry TG, Stewart JL. Unserviceable crowns and fixed partial dentures: life-span and causes for loss of serviceability. J Am Dent Assoc 1970;81:1395-401. 12. Yu A, Lee H. A wax guide to measure the amount of occlusal reduction during tooth preparation in fixed prosthodontics. J Prosthet Dent 2010;103: 256-7. 13. Magne P, Belser UC. Novel porcelain laminate preparation approach driven by a diagnostic mock-up. J Esthet Restor Dent 2004;16:7-16. 14. Niu E, Tarrazzi D. Use of a silicone transfer index to prepare parallel guide planes. J Prosthet Dent 2010;104:347-8. 15. Cho SH, Nagy WW. Customized occlusal reduction guide made from a thermoplastic sheet. J Prosthet Dent 2015;114:307-8. 16. Lee JH. Guided tooth preparation for a pediatric zirconia crown. J Am Dent Assoc 2018;149:202-8. 17. Cho SH, Nagy WW. Labial reduction guide for laminate veneer preparation. J Prosthet Dent 2015;114:490-2. 18. Vailati F, Belser UC. Full-mouth adhesive rehabilitation of a severely eroded dentition: the three-step technique. Part 1. Eur J Esthet Dent 2008;3:30-44. 19. Vailati F, Belser UC. Full-mouth adhesive rehabilitation of a severely eroded dentition: the three-step technique. Part 2. Eur J Esthet Dent 2008;3:128-46. 20. Vailati F, Belser UC. Full-mouth adhesive rehabilitation of a severely eroded dentition: the three-step technique. Part 3. Eur J Esthet Dent 2008;3:236-57. 21. Solaberrieta E, Otegi JR, Minguez R, Etxaniz O. Improved digital transfer of the maxillary cast to a virtual articulator. J Prosthet Dent 2014;112:921-4. 22. Alghazzawi TF. Advancements in CAD/CAM technology: Options for practical implementation. J Prosthodont Res 2016;60:72-84. 23. Turner KA, Missirlian DM. Restoration of the extremely worn dentition. J Prosthet Dent 1984;52:467-74. Corresponding author: Dr Irena Sailer Division Prothèse Fixe et Biomateriaux Clinique Universitaire de Medecine Dentaire Université de Genève Michel Servet 1, 1211 Geneva SWITZERLAND Email: [email protected] Acknowledgments The authors would like to express gratitude to the ITI Foundation for providing the ITI scholarship to the first author at the University of Geneva, enabling the present developments. Copyright © 2019 by the Editorial Council for The Journal of Prosthetic Dentistry. https://doi.org/10.1016/j.prosdent.2018.11.023
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Virtual diagnostics and guided tooth preparation for the minimally invasive rehabilitation of a patient with extensive tooth wear: A validation of a digital workflow Hyeonjong Lee, DMD, PhD,a Vincent Fehmer, MDT,b Kung-Rock Kwon, DMD, PhD,c Felix Burkhardt, DDS,d Ahran Pae, DMD, PhD,e and Irena Sailer, Prof Dr Med Dentf Recent developments in digABSTRACT ital technologies in dentistry The recent evolution of digital technologies in dentistry has enabled virtual 3D diagnostic analysis have led to significant of a dentition before treatment, allowing for virtual, minimally invasive treatment planning. In this changes of treatment conreport, an extensively worn dentition was 3D virtual analyzed at an increased vertical dimension of cepts in prosthodontics. occlusion. Virtual waxing (exocad DentalCAD; Exocad) and subsequent analysis of the need for Optical scanning allows digiminimally invasive preparations were performed. Areas of each tooth without adequate clearance for the minimal thickness of a definitive restoration (set at 1.5 mm in the software), including the talization of the initial clinical amount of tooth substance to be removed (GOM Inspect; GOM), were visualized in color. A situation, delivering virtual preparation guide was virtually designed according to this diagnostic plan (3-matic; Materialise) and files of the initial status of the 3D printed (Connex3 Objet260; Stratasys) from resin (VeroMagenta RGD851; Stratasys). The teeth dentition in the standard were minimally prepared using the guide, and the amount of preparation was validated by tessellation language (STL) superimposing the scan of the prepared model on the initial scan and comparing it with the format. The STL files can be diagnostic plan. (J Prosthet Dent 2019;-:---) input into a computer-aided composite resin materials and cemented with adhedesign (CAD) software program and analyzed.1 Digital sive material as an alternative to conventional fixed diagnostics, including digital waxing and trial restoraprostheses.3,4 tions, can then be performed. Subsequently, the type Studies have shown5,6 that conventional preparation and design of the planned restorations can be exported of complete coverage ceramic crowns necessitates anteas digital files and milled or printed by means of rior or posterior tooth reduction ranging between 40% computer-aided manufacturing (CAM) technology to and 70%. In contrast, tooth reduction for ceramic veneers fabricate CAD-CAM trial restorations.2 After tooth on maxillary central incisors ranges between 17% and preparation, the planned restorations can be fabricated 30%.5,6 Extensive tooth preparation can cause hyperwith the CAD-CAM technology. sensitivity and pulpal damage.7-11 For this reason, and Different types of ceramic and composite resin consistent with the development of materials and admaterials have been developed for fabrication, openhesive dentistry, current prosthodontic concepts have ing up new prosthetic treatments. Less-invasive proposed less-invasive restorations before preparing a restorations, such as veneers, onlays, and partialcrown. coverage crowns, can be milled from ceramic or
a
International Scholar, Division of Fixed Prosthodontics and Biomaterials, University Clinic of Dentistry, University of Geneva, Geneva, Switzerland; and Assistant Professor, Department of Prosthodontics, School of Dentistry, Pusan National University, Yangsan, Republic of Korea. b Master Dental Technician, Division of Fixed Prosthodontics and Biomaterials, University Clinic of Dentistry, University of Geneva, Geneva, Switzerland. c Professor, Department of Prosthodontics, School of Dentistry, Kyung Hee University, Seoul, Republic of Korea. d Resident, Division of Fixed Prosthodontics and Biomaterials, University Clinic of Dentistry, University of Geneva, Geneva, Switzerland. e Professor, Department of Prosthodontics, School of Dentistry, Kyung Hee University, Seoul, Republic of Korea. f Professor, Division of Fixed Prosthodontics and Biomaterials, University Clinic of Dentistry, University of Geneva, Geneva, Switzerland.
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Figure 1. Analysis of clearance between maxillary and mandibular dentition after optimal increase of vertical dimension for restorative space. A, Occlusal view. B, Lateral view. C, Cross-sectional rear view at second molar area. D, Virtual diagnostic waxing on maxillary dentition.
Figure 2. Virtual arbitrary relief in pit and fissure areas on maxillary cast for better adaptation of guide.
Figure 3. Construction of 2-mm-thick structure surrounding maxillary model.
One prerequisite for minimally invasive prosthodontic treatment is thorough pretreatment diagnostics to define the treatment goals. To provide the least invasive approach, clinicians should determine the exact area and amount of tooth preparation needed before clinical treatment. To define the preparation needed, pretreatment diagnostics, including diagnostic waxing of the
planned restorations, are essential. The conventional methods of transferring this information to the patient are trial restorations and silicone matrices. Trial restorations reproduce the diagnostic waxing and can be transferred to the existing dentition. They are used to visualize and communicate the treatment outcome to the patient, dentist, and dental laboratory technician.2 Once
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Figure 4. A, Sectional view between both dentitions. B, Sectional view after creating 2-mm-thick outer offset on maxillary cast (cast A) and 1.5-mm-thick offset on mandibular cast (cast B). Orange arrow shows point exposed on guide. C, Subtraction of cast B from cast A. Area within 1.5-mm interocclusal clearance exposed. D, Posterior view of designed guide (blue).
approved, silicone matrices of the waxing can be used to define the tooth preparation.12-20 Limitations of this conventional workflow include the time and effort needed to produce a conventional diagnostic waxing and trial restoration and their associated costs. One further limitation is the predictability of the transfer of this plan to the patient. Silicone matrices may help evaluate the area and amount of tooth preparation needed during the procedure, but the predictability of the procedure is not ensured. Silicone matrices deliver 2D information during the preparation and are limited to 1 or 2 buccolingual or mesiodistal slices. To ensure minimal invasiveness and optimal standardization, a 3D preparation guide is desirable. The 3D information of maxillary and mandibular dentitions obtained by means of optical scans can be used for virtual diagnostics and treatment planning. Furthermore, in clinical situations with reduction of the vertical dimension of occlusion (VDO), a virtual increase of VDO can be performed.21,22 Optimal interocclusal clearances can also be determined in the 3D analysis by following the recommendations for different restorative
Lee et al
materials. Locations without sufficient clearance are color coded on the 3D image (virtual 3D diagnostics), indicating the amount of tooth substance to be removed based on the 3D virtual diagnostics. To transfer this 3D information predictably to the clinical situation and to ensure least invasive tooth preparation, CAD-CAM preparation guides need to be designed and produced. In this report, restoration of an extensively worn maxillary dentition without the loss of VDO but with space available is presenteddcategory 2 according to the treatment options in the restoration of an extremely worn dentition.23 The VDO was increased to obtain space, but some preparation was still needed on the posterior teeth to achieve the minimal clearance for ceramic restorations. The casts of a previously treated patient were used to evaluate this concept. A 3D diagnosis was performed to determine the needed amount of VDO increase and define the areas with insufficient clearance for the planned reconstructions after a virtual VDO increase. A 3Dprinted guide based on the virtual 3D diagnostics was named K-L (Kwon & Lee) preparation guide, and it was used for the minimally invasive preparations.
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Figure 5. A, Information of location and amount of tooth to be prepared. White region indicates area over 1.5 mm of clearance. Each color on color bar shows each relative clearance within 1.5 mm. B, Designed guide of left side. C, Designed guide of right side.
TECHNIQUE 1. Scan maxillary and mandibular dentitions to obtain STL data by using intraoral digital scans or a laboratory scanner (IScan D104; Imetric) to scan diagnostic casts. 2. Diagnose the optimal increase in VDO, that is, the opening in the incisal area, considering the THE JOURNAL OF PROSTHETIC DENTISTRY
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Issue
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minimum thickness of restorations in the posterior region and esthetics in the anterior area. Establish this with a 3D virtual analysis software program (GOM Inspect; GOM) (Fig. 1A, B). Fabricate an anterior guide at the established VDO (Pattern resin LS; GC) to make a clinical occlusal registration (Jet bite; Coltène) based on the previous 3D virtual analysis. Align the maxillary and mandibular STL files according to the occlusal registration by applying a best-fit algorithm (GOM Inspect; GOM) (Fig. 1C). Relieve the maxillary cast to virtually fill in pits and grooves on the teeth that might interfere with the adaptation of the guide (3-matic; Materialise) (Fig. 2). Construct a 2-mm-thick structure, resembling an occlusal device, to cover the teeth and surrounding structures of the maxillary model (cast A) (Fig. 3). Define a 1.5-mm occlusal clearance on the mandibular cast (cast B). This clearance is defined by the minimum thickness of the material selected for the definitive restoration (for this restoration, it is lithium disilicate glass-ceramic) (Fig. 4A, B). Virtually subtract cast B from cast A. The areas not fulfilling the space requirements are thereby visualized. Subsequently, design 2 separate preparation guides (first quadrant, second quadrant) to allow for removal of the respective parts from cast A (Figs. 4C, D, 5). Fabricate the preparation guides by using a 3D printer (Connex3 Objet260; Stratasys) and place it on the cast for analysis of the needed preparation (Fig. 6A-C). Perform the guided tooth preparation by removing only the tooth substance extending beyond the guide. Use a football-shaped diamond rotary instrument (no. 250/4250 red, Guided Universal Prep Set; Intensiv) (Fig. 6D).
After tooth preparation, the result was compared with the initial virtual plan for validation of the concept. The clearance obtained from the guided preparation was evaluated by scanning the cast after the preparation and superimposing the STL file on the file of the plan. The results indicated accurate transfer of the guided preparation plan to the clinical execution (Figs. 7, 8). DISCUSSION With the development of reinforced ceramic materials and adhesive dentistry, minimally invasive partial coverage restorations with increased VDO can be selected in preference to complete coverage crowns to restore an extensively worn dentition. However, sufficient clearance for the restoration in the posterior area may not be possible even with an increase of VDO. Lee et al
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Figure 6. A, Guide fabricated by 3D printer. B, C, Guide placed on cast. D, Preparation using high-speed handpiece.
Turner and Missirlian23 identified 3 distinct categories for the restoration of extensively worn dentitions in relation to VDO and treatment options. An increase of VDO should be determined considering various conditions. In this patient, the increase of VDO was established from the anterior esthetics and optimal posterior material. An area with insufficient clearance can be specified through 3D analysis with the presented method. Subsequently, the preparation guide can be designed and fabricated based on the previous 3D analysis to transfer the virtual plan to the clinical situation. The thickness of the guide in this report was set to 2 mm, considering clinical and mechanical aspects. Determining the VDO increase is an important step in the treatment. Virtual 3D diagnostics of clearance between both dentitions can be made after defining the amount of virtual VDO increase. The tentative amount of increase can be virtually planned with the help of this analysis. However, due to the possible error of a virtual VDO increase, clinical occlusal registration by using an anterior occlusal registration device is also recommended. In 2008, Vailati and Belser18-20 introduced a 3-step technique to rehabilitate extensively worn dentitions. This technique comprised 3 laboratory steps alternated
Lee et al
with 3 clinical steps, allowing for the predictable minimally invasive esthetic and functional rehabilitation of patients with dental erosion. The concept in this report can be integrated into the 3-step technique to virtually plan for complete mouth adhesive restoration of extensively worn dentitions. Conventionally, analysis of the mounted cast is one of the main factors in determining the amount of VDO increase. A tentative amount of VDO increase was performed through visual inspection of the mounted cast in the articulator. With the help of a 3D digital software program, a virtual vertical increase of VDO is now possible.21,22 Precise evaluation of maxillary and mandibular dentitions can be obtained. The K-L preparation guide was virtually designed, CAM fabricated, and used for the minimally invasive tooth preparation for this patient. Once the STL files of both dentitions and the occlusal registration were acquired, the guide could be designed automatically by inserting intended clearance values. As this guide was designed by using a CAD software program, the shape and dimensions of the guide were predictable and clearly defined. The magenta color of the guide helped to easily distinguish the needed amount of tooth reduction (Fig. 9). Virtual 3D occlusal analysis indicated the amount of insufficient clearance and, hence, needed tooth
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Figure 7. Validation between before and after preparation using guide. Differences visualized in colordwhitish color shows the area with >1.5-mm clearance and colored regions show areas and amount of teeth to be prepared to obtain at least 1-mm clearance. A, Right side before preparation. Color shows area that should be prepared. B, Left side before preparation. C, Right side after preparation. D, Left side after preparation.
Figure 8. Cross-sectional view to validate clearance change before and after preparation. A, Section at right second molar. B, Section at left second molar.
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Figure 9. Clinical application of guide. A, Guide placed on posterior area. B, Minimally invasive preparation performed according to contour of guide.
reduction. It provided visualized information on the location and amount of teeth to be prepared. This 3D diagnostic tool can be used for patient consultation and minimally invasive preparation. In addition, although this technique was introduced for VDO increase in the present patient, it may also be applied in various other clinical situations. If the functions used in this report could be integrated into a commercial dental CAD software program, the presented procedure would be easier to apply in daily practice. SUMMARY The K-L guide based on 3D virtual diagnostics indicates the location and amount of tooth substance to be removed. It can be easily designed and printed using the CAD-CAM technology. REFERENCES 1. Lee H, Kim HS, Noh K, Paek J, Pae A. A simplified method for evaluating the 3-dimensional cement space of dental prostheses by using a digital scanner. J Prosthet Dent 2017;118:584-6. 2. Sancho-Puchades M, Fehmer V, Sailer I. Advanced smile diagnostics using CAD/CAM mock-ups. Int J Esthet Dent 2015;10:374-91. 3. Edelhoff D, Liebermann A, Beuer F, Stimmelmayr M, Guth JF. Minimally invasive treatment options in fixed prosthodontics. Quintessence Int 2016;47: 207-16. 4. Pieger S, Salman A, Bidra AS. Clinical outcomes of lithium disilicate single crowns and partial fixed dental prostheses: a systematic review. J Prosthet Dent 2014;112:22-30. 5. Edelhoff D, Sorensen JA. Tooth structure removal associated with various preparation designs for anterior teeth. J Prosthet Dent 2002;87:503-9. 6. Al-Fouzan AF. Gravimetric analysis of removed tooth structure associated with different preparation designs. Saudi J Dent Res 2016;7:1-6. 7. Foster LV. Failed conventional bridge work from general dental practice: clinical aspects and treatment needs of 142 cases. Br Dent J 1990;168:199-201. 8. Cheung GS, Lai SC, Ng RP. Fate of vital pulps beneath a metal-ceramic crown or a bridge retainer. Int Endod J 2005;38:521-30. 9. Wisithphrom K, Murray PE, About I, Windsor LJ. Interactions between cavity preparation and restoration events and their effects on pulp vitality. Int J Periodontics Restorative Dent 2006;26:596-605.
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10. Saito K, Nakatomi M, Ohshima H. Dynamics of bromodeoxyuridine labelretaining dental pulp cells during pulpal healing after cavity preparation in mice. J Endod 2013;39:1250-5. 11. Schwartz NL, Whitsett LD, Berry TG, Stewart JL. Unserviceable crowns and fixed partial dentures: life-span and causes for loss of serviceability. J Am Dent Assoc 1970;81:1395-401. 12. Yu A, Lee H. A wax guide to measure the amount of occlusal reduction during tooth preparation in fixed prosthodontics. J Prosthet Dent 2010;103: 256-7. 13. Magne P, Belser UC. Novel porcelain laminate preparation approach driven by a diagnostic mock-up. J Esthet Restor Dent 2004;16:7-16. 14. Niu E, Tarrazzi D. Use of a silicone transfer index to prepare parallel guide planes. J Prosthet Dent 2010;104:347-8. 15. Cho SH, Nagy WW. Customized occlusal reduction guide made from a thermoplastic sheet. J Prosthet Dent 2015;114:307-8. 16. Lee JH. Guided tooth preparation for a pediatric zirconia crown. J Am Dent Assoc 2018;149:202-8. 17. Cho SH, Nagy WW. Labial reduction guide for laminate veneer preparation. J Prosthet Dent 2015;114:490-2. 18. Vailati F, Belser UC. Full-mouth adhesive rehabilitation of a severely eroded dentition: the three-step technique. Part 1. Eur J Esthet Dent 2008;3:30-44. 19. Vailati F, Belser UC. Full-mouth adhesive rehabilitation of a severely eroded dentition: the three-step technique. Part 2. Eur J Esthet Dent 2008;3:128-46. 20. Vailati F, Belser UC. Full-mouth adhesive rehabilitation of a severely eroded dentition: the three-step technique. Part 3. Eur J Esthet Dent 2008;3:236-57. 21. Solaberrieta E, Otegi JR, Minguez R, Etxaniz O. Improved digital transfer of the maxillary cast to a virtual articulator. J Prosthet Dent 2014;112:921-4. 22. Alghazzawi TF. Advancements in CAD/CAM technology: Options for practical implementation. J Prosthodont Res 2016;60:72-84. 23. Turner KA, Missirlian DM. Restoration of the extremely worn dentition. J Prosthet Dent 1984;52:467-74. Corresponding author: Dr Irena Sailer Division Prothèse Fixe et Biomateriaux Clinique Universitaire de Medecine Dentaire Université de Genève Michel Servet 1, 1211 Geneva SWITZERLAND Email: [email protected] Acknowledgments The authors would like to express gratitude to the ITI Foundation for providing the ITI scholarship to the first author at the University of Geneva, enabling the present developments. Copyright © 2019 by the Editorial Council for The Journal of Prosthetic Dentistry. https://doi.org/10.1016/j.prosdent.2018.11.023
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