Custom Milled Zirconia Implant: A Case Series

Introduction

The modern implantology is concerned more with restoring the form and function of patients. In view of achieving this objective, many implant systems were developed in the past decades. The implants systems have evolved over past years mainly in their shape, surface modification and abutment designs. In recent times, emphasis has increased on restoring the esthetics along with masticatory efficiency.¹ To fulfil the criteria of lifelike or natural looking replacement, tooth colour implant materials like zirconia were introduced, further to mimic the natural tooth contour and shape of missing teeth. Recent advances advocate the use of root form or tooth shaped implants. With the advent of implantology, the restorative prosthetic planning turned towards a new direction in modern dentistry.²

Implant dentistry is persistently progressing towards easier clinical steps with minimal complications. Immediate implants are implants inserted immediately after surgical extraction of the teeth to get replaced.³ The immediate implant placement is indicated to decrease treatment time and for avoidance of any surgical arbitration which results in overall cost reduction and ultimately the patient acceptance for such treatments. Root-Analogue Implants (RAI) was first described by Hodosh et al., back in 1969.⁴

Titanium still remains the “gold standard” for dental implants.⁵ Due to increased esthetic concern among people, tooth like materials such as zirconia have gained more popularity. The advantages of zirconia includes its tooth like colour, comparatively less corrosiveness, biocompatibility and high wear resistance. In the last couple of years, the application of programmed techniques in dentistry has become increasingly extensive with the establishment of cone beam computerized tomography (CBCT) and advances such as Computeraided design/computer-aided manufacturing (CAD/ CAM) and direct laser metal sintering (DLMS). DLMS is the application of a high-power laser beam which is directed on a metal powder bed and organised to blend the metal particles according to a CAD file, further producing a thin metal layer of choice.6 Subsequent addition of metal layers gives shape to a desired 3 Dimensional form with minimal post processing requirements. DLMS along with CAD models can fabricate dental implants of different sizes and shapes. A CBCT scan of a tooth can be prepared and transformed into a Root Analogue Implant in order to gain and accurately duplicate the root before extracting the tooth. This permits for immediate placement of dental implant and abstaining the need for surgical intervention.⁷

This clinical case series depicts unique approach in fabrication of custom milled root analogue dental implants, using zirconia material. Zirconia was selected for its high acceptance for esthetics, comparatively high strength and more importantly for its biocompatible nature which prevents the discoloration of gingival tissues occasionally associated with the titanium implants, making zirconia implants a liable alternative to titanium implants.

Case Description

Case Report 1

A 29 year old male patient presented with grossly destructed right maxillary central incisor (Figure 1). Radiograph revealed adequate bone width and bone height (Figure 2). Patient consent was taken and tooth was traumatically extracted. Extraction socket was preserved and extracted root stump was built with resin material and further scanned for milling procedure (Figure 3). Copy milling was done using extraction tooth on one side and zirconia material on other. Zirconia implant was fabricated and sintered (Figure 4). The zirconia implant was inserted while tapping same as endopore implant (Figure 5). 

Post-operative radiograph was taken to assess the implant length and orientation. Temporization was done for a period of three months. After three months, zirconia crown was fabricated and cemented (Figure 6). Conventional post & core was designed and fabricated for right maxillary lateral incisor and zirconia post & core was fabricated for tooth number 9 (Universal Tooth Numbering System). Zirconia crowns were fabricated and cemented for both. Healthy marginal gingiva was present around the zirconia implant, and no postoperative complications were reported. One year follow up presented with a stable implant, with no periimplant tissues along with same marginal bone level as assessed with radiographs and soft-tissue parameters such as absence of bleeding on probing. Excellent esthetic results were achieved and there were no signs of periodontitis or bone resorption.

Case Report 2

A 23-year old female patient presented with a missing mandibular left first molar due to decay (Figure 7). Mandibular left second molar showed a carious lesion which was close to pulp; so indirect pulp capping with restoration was placed and for the missing teeth replacement, implant restoration was advised.

After explaining all the options available in implant materials, patient was keen on getting a metal free replacement; the obvious choice being zirconia because of its tooth colour nature, biocompatibility and strength compared to titanium. For evaluating the quantity and quality of bone, Orthopantamogram (OPG) and Cone beam computed tomogram (CBCT) were advised, which revealed adequate bone quantity and quality for placement of implant.

Single piece zirconia implant was planned and as per the bone analysis, size of 4.1x12 mm was selected. For the implant to be milled, an endopore implant of the determined size was selected, abutment was attached to the implant and the assembly was scanned and copy milled using zirconia block. Custom milled zirconia implant was then placed following all the drilling protocols of endopore implant. Initially crestal incision was given, flap was raised after which pilot drill was used to make the osteotomy hole and the drilling protocol was followed and flaps were sutured around the custom fabricated abutment (Figure 8).

Temporary crown was fabricated on the abutment, which was kept out of function. After the surgery, antibiotics and analgesics were prescribed for five days and patient was instructed not to bite on the surgical site for few days and was advised soft diet. Follow up showed healthy gingiva with no bleeding and minimum post-operative pain and swelling (Figure 9). After four months, all ceramic zirconia crown was cemented in place (Figure 10). At two year follow up, the implant was stable and periimplant tissue was healthy and not much marginal bone loss was noted on radiographs.

Discussion

Hodosh et al., in 1969 pioneered need of replacing missing teeth with custom made Root Analogue Implant (RAI) and encountered failure because there was no osseointegration reported for Poly methyl methacrylate (PMMA) custom made root analogue implant.⁸ Animal studies with root-identical titanium implants yielded extremely favourable results with clear evidence of osseointegration.

During the past three decades, many different materials and shapes were proposed for dental implants. The accepted norm about implants is that it should be made up of stable and biocompatible materials, which form a healthy tissue covering around the implant enabling intact interfacial bond. Recent animal studies have proven efficiency of zirconia implants, and further research involving the human trials will be an essential pathway for the success and acceptance of zirconia implants.⁹

Considering the shortcomings of commercially pure titanium, zirconia implants are considered as excellent endosseous implants. Based on recent studies, the osseointegration of zirconia was similar to that of titanium implant. Surface modifications and microstructural alterations will potentially reinforce the initial bone healing and resistance to removal torque, but the limited data about commercially available implants is restricting the clinicians in considering zirconia as a probable replacement for titanium implants.¹⁰ This case series surely can contribute to the clinical research demonstrating that placement of modified yet significant, custom milled and root-analogue implants can yield excellent esthetic results compared to titanium implants. 

Conclusion

In conclusion, this case series demonstrated satisfactory osseointegration and healthy tissue biocompatibility of zirconia implants and more importantly satisfactory patient acceptance. This might be applied to submerged and non-submerged healing and can prompt further investigations with longer healing periods and large number of implants. The matter related to the immediate loading of dental implant using the conventional implants is the incompatibility with the extraction socket and this can be overcome with root analogue implants